Carmen S. Dence

Brain glucose uptake, oxygen metabolism, and blood flow in humans were measured with positron emission tomography, and a resting-state molar ratio of oxygen to glucose consumption of 4.1:1 was obtained. Physiological neural activity, however, increased glucose uptake and blood flow much more (51 and 50 percent, respectively) than oxygen consumption (5 percent) and produced a molar ratio for the increases of 0.4:1. Transient increases in neural activity cause a tissue uptake of glucose in excess of that consumed by oxidative metabolism, acutely consume much less energy than previously believed, and regulate local blood flow for purposes other than oxidative metabolism.

Amyloid-beta(42) (Abeta(42)) appears central to Alzheimer's disease (AD) pathogenesis and is a major component of amyloid plaques. Mean cerebrospinal fluid (CSF) Abeta(42) is decreased in dementia of the Alzheimer's type. This decrease may reflect plaques acting as an Abeta(42) "sink," hindering transport of soluble Abeta(42) between brain and CSF. We investigated this hypothesis.We compared the in vivo brain amyloid load (via positron emission tomography imaging of the amyloid-binding agent, Pittsburgh Compound-B [PIB]) with CSF Abeta(42) and other measures (via enzyme-linked immunosorbent assay) in clinically characterized research subjects.Subjects fell into two nonoverlapping groups: those with positive PIB binding had the lowest CSF Abeta(42) level, and those with negative PIB binding had the highest CSF Abeta(42) level. No relation was observed between PIB binding and CSF Abeta(40), tau, phospho-tau(181), plasma Abeta(40), or plasma Abeta(42). Importantly, PIB binding and CSF Abeta(42) did not consistently correspond with clinical diagnosis; three cognitively normal subjects were PIB-positive with low CSF Abeta(42), suggesting the presence of amyloid in the absence of cognitive impairment (ie, preclinical AD).These observations suggest that brain amyloid deposition results in low CSF Abeta(42), and that amyloid imaging and CSF Abeta(42) may potentially serve as antecedent biomarkers of (preclinical) AD.

Beta-amyloid (Abeta) plaques are the hallmark of Alzheimer disease (AD). A PET imaging tracer that binds to Abeta plaques in vivo, N-methyl-[(11)C]2-(4'-methylaminophenyl)-6-hydroxybenzothiazole (or [(11)C]PIB for "Pittsburgh Compound-B"), has significantly higher binding in subjects diagnosed with dementia of the Alzheimer type (DAT) compared to nondemented controls. The authors used this imaging technique to investigate whether abnormal binding occurs in clinically normal individuals, prior to the development of cognitive changes.Forty-one nondemented subjects (age range 20 to 86 years) and 10 patients with DAT (age range 66 to 86 years) underwent [(11)C]PIB PET scanning. Regions of interest were drawn on the MRI over the cerebellar, prefrontal, lateral temporal, occipital, gyrus rectus, precuneus, and striatal cortex. Binding potential values (BPs), proportional to the density of [(11)C]PIB-Abeta binding sites, were calculated using the Logan graphical analysis and the cerebellar cortex for a reference tissue.Patients with DAT had elevated BP values vs nondemented subjects (p < 0.0001). Four of the 41 nondemented subjects had elevated cortical BP values and their BP values as a group were not significantly different from the DAT subjects' BP values. Two of these four nondemented subjects had [(11)C]PIB uptake, both visually and quantitatively, that was indistinguishable from the DAT subjects.Elevated [(11)C]PIB binding in nondemented subjects suggests that [(11)C]PIB amyloid imaging may be sensitive for detection of a preclinical Alzheimer disease state. Longitudinal studies will be required to determine the association of elevated [(11)C]PIB binding and risk of developing dementia of the Alzheimer type.

Background— Obesity is a risk factor for impaired cardiac performance, particularly in women. Animal studies suggest that alterations in myocardial fatty acid metabolism and efficiency in obesity can cause decreased cardiac performance. In the present study, we tested the hypothesis that myocardial fatty acid metabolism and efficiency are abnormal in obese women. Methods and Results— We studied 31 young women (body mass index [BMI] 19 to 52 kg/m 2 ); 19 were obese (BMI &gt;30 kg/m 2 ). Myocardial oxygen consumption (MV̇ o 2 ) and fatty acid uptake (MFAUp), utilization (MFAU), and oxidation (MFAO) were quantified by positron emission tomography. Cardiac work was measured by echocardiography, and efficiency was calculated as work/MV̇ o 2 . BMI correlated with MV̇ o 2 ( r =0.58, P =0.0006), MFAUp ( r =0.42, P &lt;0.05), and efficiency ( r =−0.40, P &lt;0.05). Insulin resistance, quantified by the glucose area under the curve (AUC) during an oral glucose tolerance test, correlated with MFAUp ( r =0.55, P &lt;0.005), MFAU ( r =0.62, P &lt;0.001), and MFAO ( r =0.58, P &lt;0.005). A multivariate, stepwise regression analysis showed that BMI was the only independent predictor of MV̇ o 2 and efficiency ( P =0.0005 and P &lt;0.05, respectively). Glucose AUC was the only independent predictor of MFAUp, MFAU, and MFAO ( P &lt;0.05, &lt;0.005, and &lt;0.005, respectively). Conclusions— In young women, obesity is a significant predictor of increased MV̇ o 2 and decreased efficiency, and insulin resistance is a robust predictor of MFAUp, MFAU, and MFAO. This increase in fatty acid metabolism and decrease in efficiency is concordant with observations made in experimental models of obesity. These metabolic changes may play a role in the pathogenesis of decreased cardiac performance in obese women.

The purpose of this study was to determine if myocardial fatty acid utilization (MFAU) and myocardial fatty acid oxidation (MFAO) are increased in diabetic patients. Experimental models of diabetes mellitus demonstrate that MFAU and MFAO are increased, and that this dependence on myocardial fatty acid metabolism may be detrimental to cardiac function. Whether similar metabolic changes occur in humans with diabetes mellitus is unclear. Eleven healthy non-diabetic control patients (5 women, ages 25 ± 5 years) and 11 otherwise healthy patients with type 1 diabetes mellitus (T1DM) (8 women, ages 36 ± 10 years, HbA1c 8.4 ± 1.9%) underwent positron emission tomography for the determination of myocardial blood flow (MBF); myocardial oxygen consumption (MVo2); myocardial glucose utilization (MGU); and MFAU, MFAO, and %MFAO. Plasma lactate, insulin, and MBF levels were similar between the two groups. However, plasma glucose (5.71 ± 0.98 μmol/ml vs. 5.28 ± 0.65 μmol/ml, p = 0.04), free fatty acid levels (0.60 ± 0.24 μmol/ml vs. 0.19 ± 0.07 μmol/ml, p < 0.0001), and MVo2(6.64 ± 2.21 vs. 4.51 ± 1.39 μmol/g/min, p = 0.007) levels were higher in the T1DM subjects. Furthermore, compared with control patients, T1DM subjects exhibited higher MFAU (213 ± 135 nmol/g/min vs. 57 ± 28 nmol/g/min, p = 0.0004), MFAO (206 ± 131 nmol/g/min s. 50 ± 26 nmol/g/min, p = 0.0002), and %MFAO (94 ± 6% vs. 81 ± 19%, respectively, p = 0.04). In contrast, MGU was lower in T1DM subjects than in controls (207 ± 108 nmol/g/min vs. 403 ± 191 nmol/g/min, p = 0.0008). Humans with diabetes mellitus exhibit increased MFAU and MFAO and reduced MGU consistent with observations obtained in experimental models of diabetes.

We sought to determine the gender-specific effects of obesity on myocardial metabolism, work, and efficiency. Myocardial metabolism abnormalities may contribute to the development of obesity-related heart failure. Increased myocardial oxygen consumption (MVO2) and fatty acid (FA) metabolism and decreased efficiency occur with obesity in women. It is unknown whether similar changes occur with obesity in men. We quantified cardiac work, efficiency, myocardial blood flow (MBF), MVO2, glucose, and FA metabolism with echocardiography and positron emission tomography in nonobese and obese men and women (N = 86). There were significant differences between the obese (n = 35) and nonobese (n = 51) subjects in age, body composition, plasma lipids, and insulin resistance in addition to differences between the men (n = 30) and women (n = 56) in body composition and plasma lipids. Female gender independently predicted increased cardiac work (p < 0.001). Female gender also related to lower efficiency (p < 0.05). Obesity and female gender independently predicted greater MBF (p < 0.01, p < 0.0005, respectively) and MVO2 (p < 0.0005, p < 0.0001). Myocardial glucose uptake was not different among the 4 subject groups, but obesity and gender interacted in predicting glucose uptake (p < 0.05). Lower myocardial glucose utilization was independently predicted by female gender (p < 0.05), and it independently predicted lower myocardial glucose utilization/plasma insulin (p < 0.05). Obesity and gender significantly interacted in the determination of glucose utilization/plasma insulin (p = 0.01). There were no differences in FA uptake among the 4 groups, and although increasing obesity correlated with greater myocardial FA utilization and oxidation; female gender (p < 0.005, p < 0.01) and plasma triglycerides (p < 0.05, p < 0.005) were their independent predictors. Women's and men's myocardial metabolic responses to obesity are not exactly the same. Obesity and gender modulate MBF and MVO2, are related to myocardial substrate metabolism, and sometimes interact in its prediction. Gender modifies efficiency. Gender-related differences in myocardial metabolism may affect the development of/adaptation to obesity-related cardiac disease.

Results of studies in experimental animals have shown that, with age, myocardial fatty acid metabolism decreases, and glucose metabolism increases. Whether similar changes occur in humans is unknown.Seventeen healthy younger normal volunteers (six males, 26 +/- 5 years) and 19 healthy older volunteers (nine males, 67 +/- 5 years) underwent positron emission tomography (PET) under resting conditions in the fasted state. Myocardial blood flow (MBF), myocardial oxygen consumption (MVO(2)), myocardial fatty acid utilization (MFAU) and oxidation (MFAO), and myocardial glucose utilization (MGU) were quantified by PET with (15)O-water, (11)C-acetate, (11)C-palmitate, and(11)C-glucose, respectively.Although MBF was similar between the groups, MVO(2) was higher in the older subjects (5.6 +/- 1.6 micromol/g/min) compared with younger subjects (4.6 +/- 1.0 micromol/g/min, p < 0.04). Rates of MFAU and MFAO (corrected for MVO(2)) were significantly lower in older subjects than in younger subjects (MFAU/MVO(2): 35 +/- 10 vs. 51 +/- 20 nmol free fatty acids (FFA)/nmol O(2) x 10(-3), p < 0.005, and MFAO/MVO(2): 33 +/- 10 vs. 48 +/- 18 nmol FFA/nmol O(2) x 10(-3), p < 0.004). In contrast, the rates of MGU corrected for MVO(2) did not differ between the groups.With aging, humans exhibit a decline in MFAU and MFAO. Although absolute rates of MGU do not increase, by virtue of the decline in MFAU there is likely an increase in relative contribution of MGU to substrate metabolism. The clinical significance of this metabolic switch awaits further study.

A novel strategy based on metal-free "click" chemistry was developed for the copper-64 radiolabeling of the core in shell-cross-linked nanoparticles (SCK-NPs). Compared with Cu(I)-catalyzed click chemistry, this metal-free strategy provides the following advantages for Cu-64 labeling of the core of SCK-NPs: (1) elimination of copper exchange between nonradioactive Cu in the catalyst and DOTA-chelated Cu-64; (2) elimination of the internal click reactions between the azide and acetylene groups in the same NPs; and (3) increased efficiency of the click reaction because water-soluble Cu(I) does not need to reach the hydrophobic core of the NPs. When 50 mCi Cu-64 was used for the radiolabeling, the specific activity of the radiolabeled product was 975 Ci/μmol at the end of synthesis, which represents the attachment of ca. 500 Cu-64 atoms per SCK-NP, giving in essence a 500-fold amplification of specific activity of the NP over that of the Cu-64 chelate. To the best of our knowledge, this is the highest specific activity obtained for Cu-64-labeled nanoparticles.

This first-in-human study was designed to evaluate the safety and dosimetry of the progesterone analog 21-(18)F-fluoro-16α,17α-[(R)-(1'-α-furylmethylidene)dioxy]-19-norpregn-4-ene-3,20-dione ((18)F-FFNP), as well the feasibility of imaging tumor progesterone receptors (PRs) by PET in breast cancer.Women with breast cancer underwent PET with (18)F-FFNP. Tumor (18)F-FFNP uptake was assessed semiquantitatively by determining maximum standardized uptake value and tumor-to-normal breast (T/N) activity ratio and by Logan graphical analysis. The PET results were correlated with estrogen receptor (ER) and PR status, assessed by in vitro assays of the tumor tissue. The biodistribution of (18)F-FFNP was measured in patients by whole-body PET, and human dosimetry was estimated.Twenty patients with 22 primary breast cancers (16 PR-positive [PR+] and 6 PR-negative [PR-]) were evaluated. Tumor maximum standardized uptake value was not significantly different in PR+ and PR- cancers (mean ± SD, 2.5 ± 0.9 vs. 2.0 ± 1.3, P = 0.386), but the T/N ratio was significantly greater in the PR+ cancers (2.6 ± 0.9 vs. 1.5 ± 0.3, P = 0.001). In addition, there was a significant correlation between distribution volume ratio and T/N ratio (r = 0.89; P = 0.001) but not between distribution volume ratio and either PR status or standardized uptake value, likely because of small sample size. On the basis of whole-body PET data in 12 patients, the gallbladder appeared to be the dose-limiting organ, with an average radiation dose of 0.113 mGy/MBq. The whole-body dose was 0.015 mGy/MBq, and the effective dose was 0.020 mSv/MBq. No adverse effects of (18)F-FFNP were encountered.(18)F-FFNP PET is a safe, noninvasive means for evaluating tumor PRs in vivo in patients with breast cancer. The relatively small absorbed doses to normal organs allow for the safe injection of up to 440 MBq of (18)F-FFNP.

Patients with type 2 diabetes (T2DM), particularly women, are at risk for heart failure. Myocardial substrate metabolism derangements contribute to cardiac dysfunction in diabetic animal models. The purpose of this study was to determine the effects of diabetes and sex on myocardial metabolism and diastolic function in humans, separate from those of obesity. Thirty‐six diabetic subjects (22 women) and 36 nondiabetic, BMI‐matched subjects (21 women) underwent positron emission tomography (myocardial metabolism) and echocardiography (structure, function). Myocardial blood flow and oxygen consumption (MVO 2 ) were higher in women than men ( P = 0.003 and &lt;0.0001, respectively). Plasma fatty acid (FA) levels were higher in diabetics (vs. obese, P &lt; 0.003) and sex and diabetes status interacted in its prediction ( P = 0.03). Myocardial FA utilization, oxidation, and esterification were higher and percent FA oxidation lower in diabetics (vs. obese, P = 0.0004, P = 0.007, P = 0.002, P = 0.02). FA utilization and esterification were higher and percent FA oxidation lower in women (vs. men, P = 0.03, P = 0.01, P = 0.03). Diabetes and sex did not affect myocardial glucose utilization, but myocardial glucose uptake/plasma insulin was lower in the diabetics ( P = 0.04). Left ventricular relaxation was lower in diabetics ( P &lt; 0.0001) and in men ( P = 0.001), and diabetes and sex interacted in its prediction ( P = 0.03). Sex, T2DM, or their interaction affect myocardial blood flow, MVO 2 , FA metabolism, and relaxation separate from obesity's effects. Sexually dimorphic myocardial metabolic and relaxation responses to diabetes may play a role in the known cardiovascular differences between men and women with diabetes.

Recent antecedent hypoglycemia has been found to shift glycemic thresholds for autonomic (including adrenomedullary epinephrine), symptomatic, and other responses to subsequent hypoglycemia to lower plasma glucose concentrations. This change in threshold is the basis of the clinical syndromes of hypoglycemia unawareness and, in part, defective glucose counterregulation and the unifying concept of hypoglycemia-associated autonomic failure in type 1 diabetes. We tested in healthy young adults the hypothesis that recent antecedent hypoglycemia increases blood-to-brain glucose transport, a plausible mechanism of this phenomenon. Eight subjects were studied after euglycemia, and nine were studied after ∼24 h of interprandial hypoglycemia (∼55 mg/dl, ∼3.0 mmol/l). The latter were shown to have reduced plasma epinephrine (P = 0.009), neurogenic symptoms (P = 0.009), and other responses to subsequent hypoglycemia. Global bihemispheric blood-to-brain glucose transport and cerebral glucose metabolism were calculated from rate constants derived from blood and brain time-activity curves—the latter determined by positron emission tomography (PET)—after intravenous injection of [1-11C]glucose at clamped plasma glucose concentrations of 65 mg/dl (3.6 mmol/l). For these calculations, a model was used that includes a fourth rate constant to account for egress of [11C] metabolites. Cerebral blood flow was measured with intravenous [15O]water using PET. After euglycemia and after hypoglycemia, rates of blood-to-brain glucose transport (24.6 ± 2.3 and 22.4 ± 2.4 μmol · 100 g−1 · min−1, respectively), cerebral glucose metabolism (16.8 ± 0.9 and 15.9 ± 0.9 μmol · 100 g−1 · min−1, respectively) and cerebral blood flow (56.8 ± 3.9 and 53.3 ± 4.4 ml · 100 g−1 · min−1, respectively) were virtually identical. These data do not support the hypothesis that recent antecedent hypoglycemia increases blood-to-brain glucose transport during subsequent hypoglycemia. They do not exclude regional increments in blood-to-brain glucose transport. Alternatively, the fundamental alteration might lie beyond the blood-brain barrier.

Copper(II)-diacetyl-bis(N4-methylthiosemicarbazone), or Cu-ATSM, a hypoxia imaging agent, has been shown to be predictive of response to traditional cancer therapies in patients with a wide range of tumors. It is known that the environment of the tumor results in a myriad of physiological consequences, including hypoxia, alterations in metabolism and proliferation. In an effort to better characterize the relationships between Cu-ATSM and other prominent radiopharmaceuticals, this current study was undertaken to compare the regional distribution of 64Cu-ATSM with [18F]fluoromisonidazole (18F-FMISO), [18F]fluoro-2-deoxy-d-glucose (18F-FDG) and [18F]fluorothymidine (18F-FLT) in 9L tumors. Taking advantage of the different half-life of 18F (t1/2=110 min) in comparison to 64Cu (t1/2=12.7 h), we undertook a dual-tracer autoradiography study in 9L tumors. Four groups were examined: (a) 18F-FMISO, 2 h postinjection (p.i.) and 64Cu-ATSM, 10 min p.i.; (b) 18F-FMISO, 2 h p.i. and 64Cu-ATSM, 24 h p.i.; (c) 18F-FDG, 1 h p.i. and 64Cu-ATSM, 10 min p.i.; and (d) 18F-FLT, 1 h p.i. and 64Cu-ATSM, 10 min p.i. Small-animal PET imaging was performed in 9L tumor-bearing rats with imaging on concurrent days comparing 64Cu-ATSM with 18F-FMISO and 18F-FLT. It was shown that the regional distribution of 18F-FMISO and 64Cu-ATSM showed an excellent correlation when the 64Cu-ATSM had been allowed to distribute for either 10 min (R2=.84) or 24 h (R2=.86). The regional comparisons between 64Cu-ATSM (10 min) and 18F-FDG (1 h) resulted in a very poor correlation (R2=.08) between the regional uptake of the two agents. The comparison between 18F-FLT and 64Cu-ATSM showed a strong relationship (R2=.83) between the two tracers. The small-animal PET images for the distribution comparisons between 64Cu-ATSM and 18F-FMISO and 18F-FLT were in agreement with the data generated from the autoradiography studies. The data show that it is important to remember that a number of different metabolic situations can exist when considering the relationship between regions of high glucose uptake, proliferation and hypoxia.

Estrogen receptor-a (ERa) and progesterone receptor (PR) are expressed in most human breast cancers and are important predictive factors for directing therapy.Because of de novo and acquired resistance to endocrine therapy, there remains a need to identify which ERa-positive (ERa 1 )/PR-positive (PR 1 ) tumors are most likely to respond.The purpose of this study was to use estrogen-and progestin-based radiopharmaceuticals to image ERa and PR in mouse mammary tumors at baseline and after hormonal therapy and to determine whether changes in these imaging biomarkers can serve as an early predictive indicator of therapeutic response.Methods: Mammary adenocarcinomas that spontaneously develop in aged female mice deficient in signal transducer and activator of transcription-1 (STAT1) were used.Imaging of ERa and PR in primary tumor-bearing mice and mice implanted with mammary cell lines (SSM1, SSM2, and SSM3) derived from primary STAT1-deficient (STAT1 2/2 ) tumors was performed.Hormonal treatments consisted of estradiol, an ER agonist; letrozole, an aromatase inhibitor; and fulvestrant, a pure ER antagonist.Small-animal PET/CT was performed using 18 F-fluoroestradiol ( 18 F-FES) for ER, 18 F-fluoro furanyl norprogesterone ( 18 F-FFNP) for PR, and 18 F-FDG for glucose uptake.Tracer uptake in the tumor was quantified and compared with receptor concentration determined by in vitro assays of resected tumors.Results: Primary STAT1 2/2 mammary tumors and implanted SSM2 and SSM3 tumors showed high 18 F-FES and 18 F-FFNP uptake and were confirmed to be ERa 1 /PR 1 .Classic estrogen-induced regulation of the progesterone receptor gene was demonstrated by increased 18 F-FFNP uptake of estradiol-treated SSM3 tumors.Treatment with fulvestrant decreased 18 F-FFNP, 18 F-FES, and 18 F-FDG uptake and inhibited growth of SSM3 tumors but decreased only 18 F-FES uptake in SSM2 tumors, with no effect on growth, despite both tumors being ERa 1 / PR 1 .Decreased 18 F-FFNP uptake by SSM3 tumors occurred early after initiation of treatment, before measurable tumor growth inhibition.Conclusion: Using small-animal PET, a profile was identified that distinguished fulvestrant-sensitive from ful-vestrant-resistant ERa 1 /PR 1 tumors before changes in tumor size.This work demonstrates that imaging baseline tumoral 18 F-FES uptake and initial changes in 18 F-FFNP uptake in a noninvasive manner is a potentially useful strategy to identify responders and nonresponders to endocrine therapy at an early stage.

Estrogen receptor β (ERβ), a less active ER subtype that appears to have a restraining effect on the more active ERα, could be a factor that determines the level of estrogen action in certain estrogen target tissues. ERβ is found in breast cancer, and its levels relative to ERα decline with disease progression. Thus, the independent quantification of ERα and ERβ levels in breast cancer by imaging might be predictive of responses to different hormone therapies. To develop an imaging agent for ERβ, we synthesized a fluoroethyl analogue of DPN (2,3-bis(4-hydroxyphenyl)propanonitrile), a known ERβ-selective ligand. This analogue, FEDPN (5-fluoro-(2R*,3S*)-2,3-bis(4-hydroxyphenyl)pentanenitrile), has an 8.3-fold absolute affinity preference for ERβ. [18F]Fluoride-labeled FEDPN was prepared from a toluenesulfonate precursor, which provided [18F]FEDPN with a specific activity greater than 3100 Ci/mmol after HPLC purification. Biodistribution studies in immature female rats using estradiol as a blocking agent revealed specific uptake of [18F]FEDPN in the uterus and ovaries. Experiments using ERα- and ERβ-knockout mice demonstrated the expected ERα-subtype dependence in the tissue uptake of the known 16α-[18F]fluoro-17β-estradiol ([18F]FES), which has a 6.3-fold preference for ERα. The tissue uptake of [18F]FEDPN in the ER knockout mice showed some evidence of mediation by ERβ, but the levels of specific uptake of this agent were relatively modest. Based on our results, imaging of ERα can be done effectively with [18F]FES, but imaging of ERβ will likely require agents with more optimized ERβ binding affinity and selectivity than [18F]FEDNP.

Underlying cellular hypoxia, which may be difficult to detect, has been postulated to be a major cause of morbidity and mortality in sepsis. We employed the novel hypoxic marker [18F]fluoromisonidazole to determine whether cellular hypoxia was present in a peritonitis model of sepsis in the rat. A second group of septic and control rats had organ blood flow measurements determined by the radiolabeled microsphere technique to relate possible ischemia to decreased organ perfusion. No evidence of cellular hypoxia was detected in skeletal muscle, brain, liver, heart, or diaphragm in the septic rats. Ligation of the femoral artery caused a greater reduction in flow (55% decrease vs. 20% decrease, P less than 0.05) and an increased retention of [18F]fluoromisonidazole in skeletal muscle of the septic rats. We conclude that sepsis does not invariably result in systemic, i.e., multiorgan, cellular hypoxia and that underlying cellular hypoxia is not the major pathophysiological abnormality in sepsis. The greater reduction in muscle blood flow and the increased retention of [18F]fluoromisonidazole in the ischemic muscle of septic rats implies that they may be more vulnerable to hypoxia.

Both physiologic and pathophysiologic conditions affect the myocardium's substrate use and, consequently, its structure, function, and adaptability. The effect of sex on myocardial oxygen, glucose, and fatty acid metabolism in humans is unknown.We studied 25 young subjects (13 women and 12 men) using positron emission tomography, quantifying myocardial blood flow, myocardial oxygen consumption (MVO2), and glucose and fatty acid extraction and metabolism. MVO2 was higher in women than in men (5.74 +/- 1.08 micromol x g(-1) x min(-1) vs 4.26 +/- 0.69 micromol x g(-1) x min(-1), P < .005). Myocardial glucose extraction fraction and utilization were lower in women than in men (0.025 +/- 0.019 vs 0.062 +/- 0.028 [P < .001] and 133 +/- 96 nmol x g(-1) x min(-1) vs 287 +/- 164 nmol x g(-1) x min(-1) [P < .01], respectively). There were no sex differences in myocardial blood flow, fatty acid metabolism, or plasma glucose, fatty acid, or insulin levels. Female sex was an independent predictor of increased MVO2 (P = .01) and decreased myocardial glucose extraction fraction and utilization (P < .005 and P < .05, respectively). Insulin sensitivity was an independent predictor of increased myocardial glucose extraction fraction and utilization (P < .01 and P = .01, respectively).Further studies are necessary to elucidate the mechanisms responsible for sex-associated differences in myocardial metabolism. However, the presence of such differences may provide a partial explanation for the observed sex-related differences in the prevalence and manifestation of a variety of cardiac disorders.

Syntheses of [18F]haloperidol and [18F]spiroperidol in both no-carrier-added and carrier-added forms have been accomplished. The no-carrier-added [18F]butyrophenone neuroleptics were prepared in low (<2%) yield by acid decomposition of aryl piperidine triazenes. Carrier-added 18F-neuroleptics were prepared in better (5–17%) yields by 18F-for-19F nucleophilic aromatic substitution. The preparation of all synthetic precursors, and procedures for radiolabeling are fully described.

Few data regarding early developmental changes in cerebral (blood-to-brain) glucose transport (CTXglc) and CMRglc are available for humans. We measured CBF, CTXglc, and CMRglc with positron emission tomography at 4 to 7 days of life in six preterm human infants whose estimated gestational age was 25 to 34 weeks. The Michaelis-Menten constants Kt and Tmax were estimated from CTXglc and the calculated cerebral capillary plasma glucose concentration. Mean CMRglc was 8.8 mumol 100 g-1 min-1. The CMRglc did not correlate with plasma glucose concentration (r = .315, P = .543), whereas CTXglc showed a significant correlation with plasma glucose concentration (r = .836, P = .038). Estimation of the Michaelis-Menten constants from the best fit to the measured data produced values of Kt = 6.0 mumol mL-1 and Tmax = 32.6 mumol 100 g-1 min-1. These values for Kt in the developing human brain are similar to those that have been reported for the mature brain of adolescent and adult humans and adult nonhuman primates, indicating the affinity of the glucose transport protein for D-glucose is similar. However, Tmax is approximately one third to one half of the comparable values for mature brain, indicating a reduced number of available luminal transporters.

To test the hypothesis that blood-to-brain glucose transport is reduced in poorly controlled type 1 diabetes, we studied seven patients with a mean (+/- SD) HbA1c level of 10.1 +/- 1.2% and nine nondiabetic subjects during hyperinsulinemic, mildly hypoglycemic (approximately 3.6 mmol/l, approximately 65 mg/dl) glucose clamps. Blood-to-brain glucose transport and cerebral glucose metabolism were calculated from rate constants derived from blood and brain time-activity curves--the latter determined by positron emission tomography (PET)--after intravenous injection of [1-(11)C]glucose using a model that includes a fourth rate constant to account for regional egress of 11C metabolites. Cerebral blood flow and cerebral blood volume were determined with intravenous H2(15)O and inhaled C(15)O, respectively, also by PET. At plateau plasma glucose concentrations of 3.6 +/- 0.0 and 3.7 +/- 0.1 mmol/l, rates of blood-to-brain glucose transport were similar in the two groups (23.7 +/- 2.2 and 21.6 +/- 2.9 micromol x 100 g(-1) x min(-1), P = 0.569, in the control subjects and the patients, respectively). There were also no differences in the rates of cerebral glucose metabolism (16.8 +/- 0.8 and 16.3 +/- 1.2 micromol x 100 g(-1) x min(-1), P = 0.693, respectively). Plasma epinephrine (1,380 +/- 340 vs. 450 +/- 170 pmol/l, P = 0.0440) and glucagon (26 +/- 5 vs. 12 +/- 1 pmol/l, P = 0.0300) responses to mild hypoglycemia were reduced in the patients with type 1 diabetes. We conclude that neither blood-to-brain glucose transport nor cerebral glucose metabolism is measurably reduced in people with poorly controlled type 1 diabetes.

Four conformationally flexible benzamide analogs having a high affinity and outstanding selectivity for sigma(2) versus sigma(1) receptors were synthesized and radiolabeled with carbon-11 by reaction with [(11)C]methyl iodide. The four (11)C-labeled radiotracers were evaluated for their potential to image the proliferative status of breast tumors with positron emission tomography (PET). In vivo studies in female BALB/C mice bearing EMT-6 breast tumors showed that one radiotracer, (2-methoxy-(11)C)-N-(4-(3,4-dihydro-6,7-dimethoxy-isoquinolin-2(1H)-yl)butyl)-5-methylbenzamide ([(11)C]2), had a high tumor uptake and suitable tumor/background ratio for imaging purposes. Blocking studies were consistent with the labeling of sigma(2) receptors in vivo. A study comparing the in vivo properties of [(11)C]2 and (18)F-3'-fluoro-3'-deoxy-L-thymidine ([(18)F]FLT) indicated that [(11)C]2 had either similar (lung, fat) or better (blood, muscle) tumor/organ ratios than [(18)F]FLT in the tissues that are important for breast tumor imaging. Consequently, [(11)C]2 is a potential radiotracer for imaging the proliferative status of breast tumors in vivo with PET.

PET with (11)C-acetate ((11)C-ACE) has a high sensitivity for detection of prostate cancer and several other cancers that are poorly detected with (18)F-FDG. However, the short half-life (20.4 min) of (11)C limits the general availability of (11)C-ACE. (18)F-Fluoroacetate ((18)F-FAC) is an analog of acetate with a longer radioactive half-life ((18)F = 110 min). This study was undertaken to assess the potential usefulness of (18)F-FAC as a prostate tumor imaging agent.We developed an efficient radiosynthesis for (18)F-FAC, which has already been adapted to a commercial synthesizer. Biodistribution studies of (18)F-FAC were compared with (11)C-ACE in normal Sprague-Dawley male rats and CWR22 tumor-bearing nu/nu mice. We also performed a small-animal PET study of (18)F-FAC in CWR22 tumor-bearing nu/nu mice and a whole-body PET study in a baboon to examine defluorination.We obtained (18)F-FAC in a radiochemical yield of 55% +/- 5% (mean +/- SD) in approximately 35 min and with a radiochemical purity of >99%. Rat biodistribution showed extensive defluorination, which was not observed in the baboon PET, as indicated by the standardized uptake values (SUVs) (SUVs of iliac bones and femurs were 0.26 and 0.3 at 1 h and 0.22 and 0.4 at 2 h, respectively). CWR22 tumor-bearing nu/nu mice showed tumor uptake (mean +/- SD) of 0.78 +/- 0.06 %ID/g (injected dose per gram of tissue) for (11)C-ACE versus 4.01 +/- 0.32 %ID/g for (18)F-FAC. For most organs-except blood, muscle, and fat-the tumor-to-organ ratios at 30 min after injection were higher with (18)F-FAC, whereas the tumor-to-heart and tumor-to-prostate ratios were similar.All of these data indicate that (18)F-FAC may be a useful alternative to (11)C-ACE tracer for the detection of prostate tumors by PET.

The level of progesterone receptors (PRs) in breast tumors can be used to guide the selection of endocrine therapies for breast cancer patients. To this end, we have prepared a fluorine-18 labeled analogue of Tanaproget, a nonsteroidal progestin with very high PR binding affinity and low affinity for androgen and glucocorticoid receptors, and have studied its tissue distribution in estrogen-primed rats to evaluate its potential for imaging PR levels by positron emission tomography. 4-[18F]Fluoropropyl-Tanaproget ([18F]9, FPTP) was prepared in three steps, within 140 min at an overall decay-corrected yield of 5% and effective specific activity of >550 Ci/mmol. In biodistribution studies, [18F]9 uptake was high in target tissues at both 1 and 3 h (uterus, 4.55 and 5.26%ID/g; ovary, 2.32 and 2.20%ID/g, respectively) and was cleanly blocked by coinjection of excess unlabeled compound. Uterus to blood and muscle activity ratios were 9.2 and 5.2 at 1 h and 32 and 26 at 3 h, respectively. The biodistribution of [18F]9 compares favorably to that of previously prepared F-18 labeled steroidal progestins, FENP and FFNP. Its high target tissue uptake efficiency and selectivity, and prolonged retention, suggest that it has excellent promise as a PET imaging agent for PR-positive breast tumors.

Because studies in animal models of type-2 diabetes mellitus (DM) show that excessive myocardial fatty acid (FA) metabolism (at the expense of glucose metabolism) cause cardiac dysfunction, we hypothesized that women with DM would have more FA and less glucose myocardial metabolism than normal or even obese (OB) women. Women who were lean volunteers (NV) (N = 14; age 35 ± 17 years, body mass index 23 ± 1 kg/m2), OB (N = 28;31 ± 6 years, BMI 39 ± 7 kg/m2), and DM (n = 22; 54 ± 11 years, BMI 38 ± 5 kg/m2) were studied. Cardiac positron emission tomography was performed for the determination of myocardial blood flow, oxygen consumption, FA and glucose metabolism. Cardiac work was measured by echocardiography and efficiency by the ratio of work to myocardial oxygen consumption. Fractional glucose uptake was comparable between NV and OB but lower in DM (P < .05 versus NV). Myocardial FA utilization and oxidation were both higher in DM compared with NV and OB (P < .0001). Myocardial FA utilization and oxidation had positive correlations with HOMA (R = 0.35, P = .005 and R = 0.40, P = .001, respectively) whereas fractional glucose uptake exhibited an inverse correlation (R = −.31, P = .01). Cardiac work and efficiency were similar among the three groups. In women, the presence of OB and DM compared with OB alone is associated with a greater reliance on myocardial FA metabolism at the expense of glucose metabolism. These perturbations in myocardial metabolism are not associated in a decline left ventricular efficiency or function suggesting that the metabolic perturbations may precede an eventual decline left ventricular function as is seen in animal models of DM.

Fluorine‐18‐labeled steroid receptor tracers, 16 α ‐[ 18 F]fluoroestradiol (FES), [ 18 F]fluoro furanyl norprogesterone (FFNP), and 16 β ‐[ 18 F]fluoro‐5 α ‐dihydrotestosterone (FDHT), are important imaging tools for studies of breast and prostate cancers using positron emission tomography (PET). The automated production of these ligands with high specific activity (SA) as radiopharmaceuticals requires modification and optimization of the currently reported methods. [ 18 F]FES with high SA was synthesized in over 60% radiochemical yield (RCY) at the end of synthesis (EOS) using a small amount of precursor (1) (as low as 0.3 mg) and 1 M H 2 SO 4 for deprotection of the intermediate (2). [ 18 F]FFNP was synthesized in up to 77% RCY at EOS using the triflate precursor (4) at room temperature or in 25% RCY using the mesylate precursor (6) at 65°C. Both methods are highly reproducible and afford high SA. [ 18 F]FDHT was synthesized by radiofluoride incorporation at room temperature, reduction with NaBH 4 , and deprotection with HCl/acetone, giving [ 18 F]FDHT in up to 75% yield (RCY). All of these methods can be easily translated to automated production. The information provided here will aid in the development of automated production of these steroid receptor tracers with high or improved yields, optimal SA, and ease of processing for research and clinical use. Copyright © 2014 John Wiley &amp; Sons, Ltd.

Type 2 diabetes, obesity, and sex difference affect myocardial glucose uptake and utilization. However, their effect on the intramyocellular fate of glucose in humans has been unknown. How the heart uses glucose is important, because it affects energy production and oxygen efficiency, which in turn affect heart function and adaptability. We hypothesized that type 2 diabetes, sex difference, and obesity affect myocardial glucose oxidation, glycolysis, and glycogen production. In a first-in-human study, we measured intramyocardiocellular glucose metabolism from time-activity curves generated from previously obtained positron emission tomography scans of 110 subjects in 3 groups: nonobese, obese, and diabetes. Group and sex difference interacted in the prediction of all glucose uptake, utilization, and metabolism rates. Group independently predicted fractional glucose uptake and its components: glycolysis, glycogen deposition, and glucose oxidation rates. Sex difference predicted glycolysis rates. However, there were fewer differences in glucose metabolism between diabetic patients and others when plasma glucose levels were included in the modeling. The potentially detrimental effects of obesity and diabetes on myocardial glucose metabolism are more pronounced in men than women. This sex difference dimorphism needs to be taken into account in the design, trials, and application of metabolic modulator therapy. Slightly higher plasma glucose levels improve depressed glucose oxidation and glycogen deposition rates in diabetic patients.

Abstract Purpose: To investigate whether longitudinal functional PET imaging of mammary tumors using the radiopharmaceuticals [18F]FDG (to measure glucose uptake), [18F]FES [to measure estrogen receptor (ER) levels], or [18F]FFNP [to measure progesterone receptor (PgR) levels] is predictive of response to estrogen-deprivation therapy. Experimental Design: [18F]FDG, [18F]FES, and [18F]FFNP uptake in endocrine-sensitive and -resistant mammary tumors was quantified serially by PET before ovariectomy or estrogen withdrawal in mice, and on days 3 and 4 after estrogen-deprivation therapy. Specificity of [18F]FFNP uptake in ERα+ mammary tumors was determined by competition assay using unlabeled ligands for PgR or glucocorticoid receptor (GR). PgR expression was also assayed by immunohistochemistry (IHC). Results: The levels of [18F]FES and [18F]FDG tumor uptake remained unchanged in endocrine-sensitive tumors after estrogen-deprivation therapy compared with those at pretreatment. In contrast, estrogen-deprivation therapy led to a reduction in PgR expression and [18F]FFNP uptake in endocrine-sensitive tumors, but not in endocrine-resistant tumors, as early as 3 days after treatment; the changes in PgR levels were confirmed by IHC. Unlabeled PgR ligand R5020 but not GR ligand dexamethasone blocked [18F]FFNP tumor uptake, indicating that [18F]FFNP bound specifically to PgR. Therefore, a reduction in FFNP tumor to muscle ratio in mammary tumors predicts sensitivity to estrogen-deprivation therapy. Conclusions: Monitoring the acute changes in ERα activity by measuring [18F]FFNP uptake in mammary tumors predicts tumor response to estrogen-deprivation therapy. Longitudinal noninvasive PET imaging using [18F]FFNP is a robust and effective approach to predict tumor responsiveness to endocrine treatment. Clin Cancer Res; 21(5); 1063–70. ©2014 AACR.

In animal models of heart failure (HF), myocardial metabolism shifts from high-energy fatty acid (FA) metabolism toward glucose. However, FA (vs glucose) metabolism generates more ATP/mole; thus, FA metabolism may be especially advantageous in HF. Sex modulates myocardial blood flow (MBF) and substrate metabolism in normal humans. Whether sex affects MBF and metabolism in patients with HF is unknown.We studied 19 well-matched men and women with nonischemic HF (EF ≤ 35%). MBF and myocardial substrate metabolism were quantified using positron emission tomography. Women had higher MBF (mL/g/minute), FA uptake (mL/g/minute), and FA utilization (nmol/g/minute) (P < 0.005, P < 0.005, P < 0.05, respectively) and trended toward having higher FA oxidation than men (P = 0.09). These findings were independent of age, obesity, and insulin resistance. There were no sex-related differences in fasting myocardial glucose uptake or metabolism. Higher MBF was related to improved event-free survival (HR 0.31, P = 0.02).In nonischemic HF, women have higher MBF and FA uptake and metabolism than men, irrespective of age, obesity, or insulin resistance. Moreover, higher MBF portends a better prognosis. These sex-related differences should be taken into account in the development and targeting of novel agents aimed at modulating MBF and metabolism in HF.

Poly(ADP-ribose) polymerase-1 (PARP-1) is an abundant nuclear enzyme of eukaryotic cells that has been implicated in response to DNA injury. PARP-1 detects single-strand DNA breaks induced by a variety of genotoxic insults. A hyperactivation of PARP-1 is believed to play a critical role in tissues undergoing cellular death by necrosis. Therefore, a radiotracer that could image PARP-1 levels with PET could provide a useful tool in measuring necrosis in a variety of pathological conditions. The phenanthridinone derivative, 2-(dimethylamino)-N-(5,6-dihydro-6-oxophenanthridin-2-yl)acetamide (PJ34), has a high affinity for PARP-1 (IC50=20 nM) and is a suitable lead compound for PET radiotracer development. The synthesis of [11C]PJ34 was accomplished by base-catalyzed reaction of the corresponding des-methyl precursor, N-(5,6-dihydro-6-oxophenanthridin-2-yl)-2-(methylamino)acetamide with [11C]methyl iodide in DMF. The radiolabeling yield was 60% and the specific activity was ∼2000 mCi/μmol (decay corrected to E.O.B.). The total radiosynthesis time was approximately 50 min. Preliminary in vivo biodistribution studies in a rodent model of diabetes indicate that [11C]PJ34 displays a high uptake in tissues where PARP-1 is hyperactivated. These data indicate that [11C]PJ34 may be a useful radiotracer for imaging tissues undergoing cellular death via necrosis.

Androgen receptors (AR) are overexpressed in most primary and metastatic prostate cancers. To develop a nonsteroidal AR-mediated imaging agent, we synthesized and radiolabeled several analogs of the potent antiandrogen bicalutamide: [18F]bicalutamide, 4-[76Br]bromobicalutamide, and [76Br]bromo-thiobicalutamide. Two of these analogs, 4-[76Br]bromobicalutamide and [76Br]bromo-thiobicalutamide, were found to have a substantially increased affinity for the androgen receptor (AR) compared to that of bicalutamide. The synthesis of [18F]bicalutamide utilized a pseudocarrier approach to effect addition of a carbanion generated from tracer-level amounts of a radiolabeled precursor to an unlabeled carbonyl precursor. 4-[76Br]Bromobicalutamide and [76Br]bromo-thiobicalutamide were labeled through electrophilic bromination of a tributylstannane precursor. The former could be prepared in high specific activity, and its tissue distribution was tested in vivo. Androgen target tissue uptake was evident in castrated adult male rats; however, in DES-treated, AR-positive, tumor-bearing male mice, tumor uptake was low.

Abstract Carbon‐11‐labeled palmitic acid is produced routinely at Washington University School of Medicine for studies ofmyocardial metabolism. To accomodate the needs of 8–15 preparations per week and the large amounts of radioactivity (&gt;20 mCi/study) required, a remotely‐controlled system for the preparation of [1‐ 11 C]palmitic acid has been constructed. The system is small (0.04 m 3 ), completely portable and contained totally within a small lead‐shielded hood. Large quantities of C‐11 palmitic acid (up to 675 mCi) have been prepared, with minimum radiation exposure to the operator. This system has been in full operation for two years, and has been used for more than 200 syntheses with a failure rate of less than 5%.

We have synthesized and characterized four new fluorinated halobenzamides as sigma receptor ligands for use with positron emission tomography (PET). All the compounds were found to have high sigma-1 affinities (Ki = 0.38-0.98 nM), and the 4-fluoro-substituted benzamides were found to be more potent sigma-2 ligands (Ki = 3.77-4.02 nM) than their corresponding 2-fluoro analogs (Ki = 20.3-22.8 nM). The [18F] radiochemical syntheses of two of the analogs gave overall yields between 3-10% (EOS), radiochemical purities > 99%, and specific activities between 800-1200 Ci/mmol (29.6-44.4 TBq/mmol). Rat biodistribution and blocking experiments were performed with 2-[18F](N-fluorobenzylpiperidin-4yl)-4-iodobenzamide, the analog with the best Ki value for sigma-1 sites (0.38 nM). Results of these experiments demonstrate specific uptake of the compound in tissues believed to contain sigma receptors, such as lungs, kidneys, heart, brain, and spleen and indicate its potential as a candidate for use in PET imaging of tissues containing these receptors.

Previous studies have demonstrated that the positron-emitting fluorine-18 (18F)-labeled fluoromisonidazole is a specific tracer of myocardial hypoxia. Its fractional extraction Is enhanced in ischemic or hypoxic myocardium but returns to baseline levels on reperfusion and recovery of normal function. Thus, this agent might be useful in delineating acutely hypoxic but potentially salvageable myocardium. Accordingly, to delineate the relation between the myocardial extraction of 18F-fluoromisonidazole after intravenous administration and the time of antecedent ischemia in vivo, uptake of tracer was measured with positron emission tomography and direct postmortem tissue analysis in 14 dogs in which tracer was administered within 3 h of coronary occlusion (a time associated with marked potential for salvage on reperfusion); in 4 dogs after 6 h of coronary occlusion (a time associated with minimal salvage of myocardium on reperfusion); and in 8 dogs after > 24 h of coronary occlusion (to delineate uptake in tissue that is irreversibly damaged). The residual fraction (that is, the amount of tracer extracted and retained in a region) in ischemic myocardium in the dogs in which 18F-fluoromisonidazole was administered within 3 h after occlusion averaged (± standard deviation) 23 ± 18%, which was higher than the residual fraction in myocardium subjected to ischemia for either 6 or > 24 h before tracer administration (12 ± 7% and 5 ± 2%, respectively, p < 0.01 for both). Retention of tracer in remote normal myocardium averaged 2 ± 1%. Because marked enhancement of extraction of 18F-fluoromisonidazole occurred in myocardium only early after the ischemic insult, this agent may hold promise for the noninvasive identification of Jeopardized but salvageable myocardium. In addition, it should be useful in enhancing the understanding of the basic role of myocardial hypoxia in cardiac disease and its response to treatment.

Two fluorine-18-labeled reagents, methyl 3-[18F]fluoro-5-nitrobenzimidate and 4-[18F]fluorophenacyl bromide, have been prepared for covalent attachment of fluorine-18 to proteins. Both reagents can be prepared in moderate yields (30-50%, EOB) in synthesis times of 50-70 min. Reaction of these reagents with proteins (human serum albumin, human fibrinogen, and human immunoglobulin A) is pH independent, protein concentration dependent, and takes 5-60 min at mild pH (8.0) and temperature (25-37 degrees C), in yields up to 95% (corrected). The 18F-labeled proteins are purified by size exclusion chromatography.

9-(4-[18F] Fluoro-3-hydroxymethylbutyl) guanine ([18F] FHBG), an imaging agent for gene therapy using PET, was prepared in a one-pot, two-step synthesis. Microwave (MW) mediated nucleophilic fluorination of N2, monomethoxytrityl-9-[4-(tosyl)-3-monomethoxytrityl-methylbutyl] guanine using no-carrier-added [18F] fluoride, followed by deprotection with hydrochloric acid and HPLC purification, gave [18F] FHBG. The radiochemical yield (decay corrected) was 12+/-5% (n = 35), the synthesis time was 55-60 min, and the radiochemical purity was >99%. The compound was used for lung imaging and was injected into Sprague-Dawley rats previously infected with the herpes simplex virus type 1 thymidine kinase (HSV1-tk) reporter gene. MicroPET imaging showed accumulation confined to the lungs.

Four different approaches towards the synthesis of [18F]FMISO have been studied. The first approach was based on the reaction of epoxide 4 and [18F]fluoride. Both specific activity and radiochemical yield (<1%) for [18F]FMISO were low. Two new approaches, starting with compounds 8 and 9, have failed to give [18F]FMISO. The fourth approach, based on the reaction of [18F]epifluorohydrin 10, prepared from Tosylate 13 and [18F]KF/Kryptofix 222, has provided a reliable, no-carrier added synthesis of [18F]FMISO. The product was obtained in a radiochemical yield of 7–12% at end-of-synthesis (based on [18F]fluoride) with a specific activity of >400 Ci/mmol and a synthesis time of 1.5 h. Preliminary PET studies suggest that [18F]FMISO may be a promising tracer for delineation of ischemic but viable myocardium.

Lactate is a key myocardial energy source.Lactate metabolism is altered in a variety of conditions, such as exercise and diabetes mellitus.However, to our knowledge, noninvasive quantitative measurements of myocardial lactate metabolism have never been performed because of the lack of an adequate radiotracer.In this study we tested L-3-11 C-lactate ( 11 C-lactate) as such a tracer.Methods: Twenty-three dogs were studied under a wide range of metabolic interventions. 11C-Lactate and 13 C-lactate were injected as boluses and PET data were acquired for 1 h.Concomitant arterial and coronary sinus (ART/CS) blood samples were collected to identify 13 C-lactate metabolites and to measure fractional myocardial extraction/production of 11 C metabolite fractions ( 11 C acidic: 11 CO 2 and 11 C-lactate; 11 C basic: 11 C-labeled amino acids; and 11 C neutral: 11 C-glucose).Lactate metabolism was quantified using 2 PET approaches: monoexponential clearance analysis (oxidation only) and kinetic modeling of PET 11 C-myocardial curves.Results: Arterial 11 C acidic, neutral, and basic metabolites were identified as primarily 11 C-labeled lactate 1 pyruvate, glucose, and alanine, respectively.Despite a significant contribution of 11 C-glucose (23%-45%) and 11 C-alanine (,11%) to total arterial 11 C activity, both were minimally extracted (1)/produced(2) by the heart (1.7% 6 1.0% and 20.12% 6 0.84%, respectively).Whereas extraction of 11 C-lactate correlated nonlinearly with that of unlabeled lactate extraction (r 5 0.86, P , 0.0001), 11 CO 2 production correlated linearly with extraction of unlabeled lactate (r 5 0.89, P , 0.0001, slope 5 1.20 6 0.13).In studies with physiologic free fatty acids (FFA) (415 6 216 nmol/mL), 11 C-lactate was highly extracted (32% 6 12%) and oxidized (26% 6 14%), and PET monoexponential clearance and kinetic modeling analyses resulted in accurate estimates of lactate oxidation and metabolism.In contrast, supraphysiologic levels of plasma FFA (4,111 6 1,709 nmol/mL) led to poor PET estimates of lactate metabolism due to negligible lactate oxidation (1% 6 2%) and complete backdiffusion of unmetabolized 11 C-lactate into the vasculature (28% 6 22%).Conclusion: Under conditions of net lactate extraction, L-3-11 Clactate faithfully traces myocardial metabolism of exogenous lactate.Furthermore, in physiologic substrate environments, noninvasive measurements of lactate metabolism are feasible with PET using myocardial clearance analysis (oxidation) or compartmental modeling.Thus, L-3-11 C-lactate should prove quite useful in widening our understanding of the role that lactate oxidation plays in the heart and other tissues and organs.

The aim of this study was to investigate whether compartmental modeling of 1-11 C-glucose PET kinetics can be used for noninvasive measurements of myocardial glucose metabolism beyond its initial extraction.Methods: 1-11 C-Glucose and U-13 Cglucose were injected simultaneously into 22 mongrel dogs under a wide range of metabolic states; this was followed by 1 h of PET data acquisition.Heart tissue samples were analyzed for 13 C-glycogen content (nmol/g).Arterial and coronary sinus blood samples (ART/CS) were analyzed for glucose (mmol/mL), 11 C-glucose, 11 CO 2 , and 11 C-total acidic metabolites ( 11 Clactate [LA] 1 11 CO 2 ) (counts/min/mL) and were used to calculate myocardial fractions of (a) glucose and 1-11 C-glucose extractions, EF(GLU) and EF( 11C-GLU); (b) 11 C-GLU and 11 C-LA oxidation, OF( 11 C-GLU) and OF( 11 C-LA); (c) 11 C-glycolsysis, GCF( 11 C-GLU); and (d) 11 C-glycogen content, GNF( 11 C-GLU).On the basis of these measurements, a compartmental model (M) that accounts for the contribution of exogenous 11 C-LA to myocardial 11 C activity was implemented to measure M-EF(GLU), M-GCF(GLU), M-OF(GLU), M-GNF(GLU), and the fraction of myocardial glucose stored as glycogen M-GNF(GLU)/M-EF(GLU)).Results: ART/CS data showed the following: (a) A strong correlation was found between EF( 11 C-GLU) and EF(GLU) (r 5 0.92, P , 0.0001; slope 5 0.95, P 5 not significantly different from 1).(b) In interventions with high glucose extraction and oxidation, the contribution of OF( 11 C-GLU) to total oxidation was higher than that of OF( 11 C-LA) (P , 0.01).In contrast, in interventions in which glucose uptake and oxidation were inhibited, OF( 11 C-LA) was higher than OF( 11 C-GLU) (P , 0.05).(c) A strong correlation was found between GNF( 11 C-GLU)/EF(GLU) and direct measurements of fractional 13 C-glycogen content, (r 5 0.96, P , 0.0001).Modelderived PET measurements of M-EF(GLU), M-GCF(GLU), and M-OF(GLU) strongly correlated with EF(GLU) (slope 5 0.92, r 5 0.95, P , 0.0001), GCF( 11 C-GLU) (slope 5 0.79, r 5 0.97, P , 0.0001), and OF( 11 C-GLU) (slope 5 0.70, r 5 0.96, P , 0.0001), respectively.M-GNF(GLU)/M-EF(GLU) strongly correlated with fractional 13 C-content (r 5 0.92, P , 0.0001).Conclusion: Under nonischemic conditions, it is feasible to measure myocardial glu-cose metabolism noninvasively beyond its initial extraction with PET using 1-11 C-glucose and a compartmental modeling approach that takes into account uptake and oxidation of secondarily labeled exogenous 11 C-lactate.

In humans, under resting conditions there is an age-related decrease in myocardial fatty acid utilization (MFAU) and oxidation (MFAO) and a relative increase in myocardial glucose utilization (MGU). The impact of age on an individual's myocardial metabolic response to catecholamines is not well defined. Sixteen younger (mean age, 26 +/- 5 yr) and 14 older (mean age, 69 +/- 4 yr) volunteers underwent positron emission tomography to measure myocardial blood flow, myocardial oxygen consumption (M.VO2), MFAU, MFAO, and MGU both under resting conditions and during dobutamine infusion. In response to dobutamine administration, the rate-pressure product, myocardial blood flow, and M.VO2 measurements increased by similar amounts in both groups. No age-related differences were noted in the responses of plasma insulin, glucose, fatty acid, or lactate levels to dobutamine. With dobutamine infusion, MFAU and MFAO increased by a similar extent in both younger and older volunteers (age/dobutamine interactions, P = 0.62 and 0.75, respectively). In contrast, MGU increased with dobutamine administration in the younger (from 149 +/- 71 to 209 +/- 78 nmol.g(-1).min(-1); P = 0.04) but not in the older (from 235 +/- 147 to 176 +/- 84 nmol.g(-1).min(-1); P = 0.23; age/dobutamine interaction, P = 0.03) group. With dobutamine infusion, hearts in both younger and older volunteers responded by increasing their MFAU and MFAO values. Whereas younger hearts also responded with an increase in MGU, older hearts did not. Although the clinical significance of these findings awaits further study, these results may partially explain the impaired contractile reserve and the increased incidence of cardiovascular disease in older individuals.

Using existing robotic hardware and software programs developed for the synthesis of several positron-emitting radiopharmaceuticals for PET imaging [Brodack et al. (1988) Appl. Radiat. Isot. 39, 689], the additional automated synthesis of 2-deoxy-2-[18F]fluoro-D-glucose (2-[18F]FDG) has been incorporated into our Zymate Laboratory Automation System. The robotic synthesis of 2-[18F]FDG took less than one week to implement, including the organization of software subroutines and construction of an additional heating station. The end of synthesis yield (12-17%) and radiochemical purity (96-99%) for the robotic preparation of 2-[18F]FDG is similar to that of the manual synthesis. This automated method uses anhydrous tetrabutylammonium [18F]fluoride as the reactive fluoride source in the labeling step. The procedure is a modification of the synthesis reported by Hamacher et al. [Hamacher et al. (1986) J. Nucl. Med. 27, 235].

We evaluated positron emission tomographic imaging of pulmonary transgene expression, using an enhanced mutant herpes simplex virus-1 thymidine kinase as the reporter gene, in the lungs of normal rats. Sixteen rats were studied 3 days after an intratracheal administration of 5 x 10(9) to 1 x 10(11) viral particles of a replication-incompetent adenovirus containing a fusion gene of the mutant kinase and green fluorescent protein. Three rats infected with adenovirus containing no insert (null vector) served as control subjects. Images were obtained 1 hour after an intravenous injection of 9-(4-[18F]-fluoro-3-hydroxymethylbutyl)guanine, an imaging substrate for the viral kinase. After euthanasia, tissue radioactivity was determined in a gamma counter, and thymidine kinase activity and green fluorescent protein levels were measured in lung tissue samples. Imaging and gamma counting radioactivity measurements were strongly and linearly correlated (r2 = 0.96, p < 0.001). Imaging detected thymidine kinase expression above background (null vector) in 15 of 16 rats, even at low viral doses that produced little to no measurable green fluorescent protein expression. Lung 9-(4-[18F]-fluoro-3-hydroxymethylbutyl)guanine uptake (as assessed by imaging) correlated with in vitro assays of both kinase activity (r(2) = 0.48, p < 0.001) and fluorescent protein (r(2) = 0.46, p < 0.001). We conclude that positron emission tomographic imaging is a sensitive and quantitative method for detecting pulmonary reporter gene expression noninvasively.

3'-Deoxy-3'-(18)F-fluorothymidine ((18)F-FLT) has been recently described as a radiopharmaceutical for measuring cellular proliferation using PET imaging. Evaluation of tumor proliferative activity by PET using (18)F-FLT could be a procedure to assess the viability of tumor, such as histologic grade, clinical stage, and prognosis as well as the early effects of cancer therapy. This study was undertaken to determine whether (18)F-FLT is useful in the detection of prostate cancer as well as monitoring therapeutic effects in a human tumor model.The androgen-dependent human prostate tumor, CWR22, was implanted into athymic mice. This well-established model of prostate cancer was used in all studies. To determine the optimal imaging times for (18)F-FLT, a biodistribution was performed in CWR22 mice. (18)F-FLT (740 kBq [20 micro Ci]) was administered via the tail vein and uptake was determined in selected tissues at 5 min, 20 min, and 1, 2, and 4 h after injection (n = 5, each time point). Androgen ablation studies were conducted in the CWR22 model with either diethylstilbestrol (DES) or surgical castration. Animals received DES every 2 d for 3 wk. The effectiveness of therapy was monitored using (18)F-FLT microPET as baseline, during treatment, and after treatment. Tracer accumulation in the tumor was then analyzed by comparing tumor-to-muscle ratios derived from reconstructed microPET data.At 2 h after injection, the (18)F-FLT uptake in tumor was 0.69 +/- 0.14 percentage injected dose per gram of tissue, showing the highest activity of all organs measured. The microPET study with dynamic imaging showed that (18)F-FLT uptake in blood reached its plateau within 1 min and was rapidly cleared, whereas (18)F-FLT uptake in tumor reached its plateau in 30 min and remained up to 60 min. microPET using (18)F-FLT successfully imaged the implanted CWR22 tumor in the mice at both 1 and 2 h after injection. There was a marked reduction of (18)F-FLT uptake in tumor after castration or DES treatment; however, there were no differences in (18)F-FLT uptake in the tumor in the control group. These changes of (18)F-FLT uptake in tumor parallel the changes of actual tumor measurement.These results indicate that (18)F-FLT is a useful tracer for detection of prostate cancer in an animal model. (18)F-FLT has the potential for monitoring the therapeutic effect of androgen ablation therapy in prostate cancer.

An increasing number and variety of studies on rodent models are being conducted using small-animal positron emission tomography scanners. We aimed to determine if animal handling techniques could be developed to perform routine animal imaging in a timely and efficient manner and with minimal effect on animal physiology. These techniques need to be reproducible in the same animal while maintaining hemodynamic and physiological stability. The necessary techniques include (a) the use of inhalant anesthesia, (b) arterial and venous cannulation for multiple tracer administrations and blood sampling, (c) development of small-volume analytic columns and techniques and (d) measurement of the physiological environment during the imaging session. We provide an example of a cardiac imaging study using four radiotracers (15O-water, 1-[11C]-acetate, 1-[11C]-palmitate and 1-[11C]-glucose) injected into normal rats. Plasma substrates, CO2 production and total metabolites were measured. The animals remained anesthetized over the entire imaging session, and their physiological state was maintained. The intrastudy stability of the physiological measurements and substrate levels and interstudy reproducibility of the measurements are reported.

Peroxisome proliferator-activated receptor-gamma (PPARgamma) is an important regulator of lipid metabolism; it controls the differentiation of preadipocytes and is also found at high levels in small metastatic tumors. In this report, we describe the radiochemical synthesis and evaluation of two (18)F-labeled analogs of the potent and selective PPARgamma agonist farglitazar.The isomeric aromatic fluorine-substituted target compounds [(2S)-(2-benzoylphenylamino)-3-(4-(2-[2-(4-[(18)F]fluorophenyl)-5-methyloxazol-4-yl]ethoxy)-phenyl)propionic acid ([(18)F]-1) and (2S)-[2-(4-fluorobenzoyl)phenylamino]-3-(4-[2-(5-methyl-2-phenyloxazol-4-yl)ethoxy]-phenyl)propionic acid ([(18)F]-2)] were prepared in fluorine-18-labeled form, respectively, by radiofluorination of an iodonium salt precursor or by Ullmann-type condensation with 2-iodo-4'-[(18)F]fluorobenzophenone after nucleophilic aromatic substitution with [(18)F]fluoride ion. Each compound was obtained in high specific activity and good radiochemical yield.(18)F-1 and (18)F-2 have high and selective PPARgamma binding affinities comparable to that of the parent molecule farglitazar, and they were found to have good metabolic stability. Tissue biodistribution studies of (18)F-1 and (18)F-2 were conducted, but PPARgamma-mediated uptake of both agents was minimal.This study completes our first look at an important class of PPARgamma ligands as potential positron emission tomography (PET) imaging agents for breast cancer and vascular disease. Although (18)F-1 and (18)F-2 have high affinities for PPARgamma and good metabolic stability, their poor target-tissue distribution properties, which likely reflect their high lipophilicity combined with the low titer of PPARgamma in target tissues, indicate that they have limited potential as PPARgamma PET imaging agents.

The goal of this study was to test whether myocardial triglyceride (TG) turnover including oxidation of TG-derived fatty acids (FA) could be assessed with PET and (11)C-palmitate.A total of 26 dogs were studied fasted (FAST), during Intralipid infusion (IL), during a hyperinsulinemic-euglycemic clamp without (HIEG), or with Intralipid infusion (HIEG + IL). (11)C-palmitate was injected, and 45 minutes were allowed for labeling of myocardial TG pool. 3D PET data were then acquired for 60 minutes, with first 15 minutes at baseline followed by 45 minutes during cardiac work stimulated with constant infusion of either phenylephrine (FAST, n = 6; IL, n = 6; HIEG + IL, n = 6) or dobutamine (FAST, n = 4; HIEG, n = 4). Myocardial (11)C washout during adrenergic stimulation (AS) was fitted to a mono-exponential function (Km(PET)). To determine the source of this (11)C clearance, Km(PET) was compared to direct coronary sinus-arterial measurements of total (11)C activity, (11)C-palmitate, and (11)CO(2). Before AS, PET curves in all groups were flat indicating absence of net clearance of (11)C activity from heart. In both FAST groups, AS resulted in negligible net (11)C activity and (11)CO(2) production higher than net (11)C-palmitate uptake. AS with phenylephrine resulted in net myocardial uptake of total (11)C activity and (11)C-palmitate in IL and HIEG + IL, and (11)CO(2) production lower than (11)C-palmitate uptake. In contrast, AS with dobutamine in HIEG resulted in net clearance of all (11)C metabolites (total (11)C activity, (11)C-palmitate and (11)CO(2)) with (11)CO(2) contributing 66% to endogenous FA oxidation. The AS resulted in significant Km(PET) in all the groups, except HIEG + IL. However, positive correlation between Km(PET) and (11)CO(2) was observed only in HIEG (R (2) = 0.83, P = .09).This is the first study to demonstrate that using PET and pre-labeling of intracardiac TG pool with (11)C-palmitate, noninvasive assessment of myocardial TG use is feasible under metabolic conditions that favor endogenous TG use such as increased metabolic demand (beta-adrenergic stimulation of cardiac work) with limited availability of exogenous substrate (HIEG).

Our objective was to determine, in the hearts of women with type 1 diabetes mellitus (T1DM), whether the fate of extracted glucose is altered and, if so, what the impact of dobutamine is on myocardial substrate metabolism. In experimental models of T1DM, myocardial glycolysis and glucose oxidation are reduced with the impairment becoming more pronounced with dobutamine. Whether similar changes occur in humans with T1DM is unclear.Myocardial perfusion, oxygen consumption, and glucose and fatty acid metabolism were measured with positron emission tomography in 19 women, 7 normal volunteers (NVs) and 12 with T1DM. The NVs and 6 T1DM (DM1) patients were studied under baseline metabolic conditions and 6 T1DM patients were studied during hyperinsulinemic-euglycemic clamp (DM1-C), both at rest and during dobutamine. At rest, myocardial glucose uptake, glycolysis, glycogen storage, and oxidation were reduced by similar levels in DM1 patients compared with NVs (P < .05). During dobutamine, although myocardial glucose uptake was not different from DM1 patients at rest, fractional glycolysis was lower compared with NVs or DM1-C patients and reflected a lower glucose oxidation rate (P < .001). Measurements of myocardial glucose metabolism at rest and during dobutamine were comparable between NVs and DM1-C patients. During dobutamine, myocardial fatty acid uptake and oxidation increased in all 3 groups.In women with T1DM, (1) myocardial glucose metabolism is impaired downstream from initial uptake, (2) these abnormalities become more pronounced with dobutamine and are paralleled by an increase in myocardial fatty acid metabolism, and (3) insulin restores glucose metabolism to levels observed in normal control subjects.

Click labeling using 2-[¹⁸F]fluoroethyl azide has been proven to be promising methods of radiolabeling small molecules and peptides, some of which are undergoing clinical evaluations. However, the previously reported method afforded low yield, poor purities and under desirable reproducibility.A vacuum distillation method was used to isolate 2-[¹⁸F]fluoroethyl azide, and the solvent effect of acetonitrile and dimethylformamide (DMF) on the click labeling using Cu(I) from copper sulfate/sodium ascorbate was studied. The labeling conditions were optimized to radiosynthesize a hydroxysuccinimide ester (N-hydroxysuccinimide, or NHS).2-[¹⁸F]fluoroethyl azide was isolated by the vacuum distillation method with >80% yield within 10min in a "pure" and click-ready form. It was found that the amount of DMF was critical for maintaining high levels of Cu(I) from copper sulfate/sodium ascorbate in order to rapidly complete the click labeling reaction. The addition of bathophenanthrolinedisulfonic acid disodium salt to the mixture of copper sulfate/sodium ascorbate also greatly improved the click labeling efficiency. Through exploiting these optimizations, a base-labile NHS ester was rapidly radiosynthesized in 90% isolated yield with good chemical and radiochemical purities.We have developed a general method to click-label small molecules efficiently using [¹⁸F]2 for research and clinical use. This NHS ester can be used for conjugation chemistry to label antibodies, peptides and small molecules as positron emission tomography tracers.

The phenylpiperazine ring which could not be obtained by reacting aniline derivatives with bis(2-bromoethyl)-N-(ethoxycarbonyl)amine (1a) in a wide spectrum of solvents and temperatures was synthesized rapidly on solid support in high yield. By this approach the potent serotonin agonist TFMPP (2) was synthesized in 40 min, in 80% yield. The time scale of this reaction and the simplicity of the work-up match the requirements for short lived neurological radiopharmaceutical production.

We have synthesized six androgens labeled with 18F as potential imaging agents for prostatic cancer. These include 16 beta-fluorine-substituted testosterone, dihydrotestosterone and mibolerone, 16 alpha- and 16 beta-fluorine substituted 7 alpha-methyl-19-nortestosterone, and 20-fluoro-R1881 (metribolone). All of the radiochemical preparations proceeded in satisfactory yield, giving material with adequately high effective specific activity for the in vivo studies. In the tissue distribution studies in diethylstilbestrol-treated male rats, high selective uptake by the prostate was observed that ranged from 0.39% to 1.21% injected dose (ID)/g at 1 hr and 0.20 to 0.47 at 4 hr, with prostate-to-blood and prostate-to-muscle ratios ranging from 3.28 to 9.45, respectively, at 1 hr and 4.06 to 35.0, respectively, at 4 hr. Those compounds that are likely to be metabolized rapidly showed lower prostate uptake but higher uptake selectivity at 4 hr; at earlier times, uptake selectivities were more comparable. Compounds with a 16 beta-fluorine substituent showed extensive metabolic defluorination, resulting in ca. 50% of the dose being deposited in bone at 4 hr. This is consistent with a 16 alpha-hydroxylation process that may proceed rapidly with these compounds, but would be retarded by a 17 alpha-methylation, blocked by inversion of stereochemistry at C-16, and would not affect fluorine at the C-20 position. These fluoroandrogens, together with 20-fluoromibolerone described previously, are the first positron-emitting androgens to show high affinity and selective uptake by androgen target tissues in vivo, and they may be useful as in vivo prostate imaging agents in man.

Fluoromisonidazole, a member of a class of compounds referred to as "hypoxic sensitizers," accumulates in hypoxic, viable tumor cells. We hypothesized that it might therefore accumulate also in ischemic, but non-necrotic myocardium potentially salvageable by interventional therapy. To evaluate the myocardial kinetics of [18F]fluoromisonidazole (FM), 20 isolated perfused rabbit hearts were used to characterize the uptake and binding of tracer under control conditions (n = 6), or with ischemia (flow 10% of control, n = 5), hypoxia without low flow (control flow rates with hypoxic medium, n = 5), or with reperfusion (n = 4). Myocardial retention of tracer detected externally with gamma scintillation probes after 20 min of constant [18F]FM infusion followed by 20 min of washout with nonradioactive buffer was 41 +/- 7% and 46 +/- 8% of peak activity in hearts subjected to ischemia or hypoxia, respectively, and significantly higher than in hearts subjected to either control perfusion or to ischemia followed by reperfusion (18 +/- 6 and 16 +/- 5% of peak activity, respectively, p less than 0.01). The biologic half-time of retained tracer was 40 hr in all hearts indicating essentially irreversible binding. Based on these findings, we measured uptake of [18F]FM using positron emission tomography in five dogs subjected to acute coronary occlusion. Five to thirteen millicuries of tracer were injected within 3 hr of occlusion. Within 30 min after administration of tracer, 18F accumulation in ischemic myocardium was greater than that observed in normal myocardium. The results indicate that [18F]FM accumulates in ischemic myocardium in relation to diminished tissue oxygen content and not simply because of diminished flow. Thus, this class of compounds may be potentially useful to help identify hypoxic myocardium.

15-(4-(2-[¹⁸F]fluoroethoxy)phenyl)pentadecanoic acid ([¹⁸F]7) was synthesized as a PET probe for assessing myocardial fatty acid metabolism. The radiosynthesis of [¹⁸F]7 was accomplished using a two-step reaction, starting with the corresponding tosylate ester, methyl 15-(4-(2-(tosyloxy)ethoxy)phenyl)pentadecanoate (5), and gave the radiolabeled fatty acid, [¹⁸F]7 in a radiolabeling yield of 55-60% and a specific activity of >2000 Ci/mmol (decay corrected to EOB). The biological evaluation of [¹⁸F]7 in rats displayed high uptake in heart (1.94%ID/g at 5 min), which was higher than the uptake (%ID/g) in blood, lung, muscle, pancreas, and brain. MicroPET studies of [¹⁸F]7 in Sprague-Dawley rats demonstrated excellent images of the myocardium when compared with [¹¹C]palmitate images in the same animal. Moreover, the tracer kinetics of [¹⁸F]7 paralleled those seen with [¹¹C]palmitate, with an early peak followed by biphasic washout. When compared to [¹¹C]palmitate, [¹⁸F]7 exhibited a slower early clearance (0.17 ± 0.01 vs 0.30 ± 0.02, P < 0.0001) and a significantly higher late clearance (0.0030 ± 0.0005 vs 0.0006 ± 0.00013, P < 0.01). These initial studies suggest that [¹⁸F]7 could be a potentially useful clinical PET tracer to assess abnormal myocardial fatty acid metabolism.

Independent measurement of the levels of both the estrogen receptors, ERα and ERβ, in breast cancer could improve prediction of benefit from endocrine therapies. While ERα levels can be measured by positron emission tomography (PET) using 16α-[(18)F]fluoroestradiol (FES), no effective agent for imaging ERβ by PET has yet been reported.We have prepared the fluorine-18 labeled form of 8β-(2-fluoroethyl)estradiol (8BFEE(2)), an analog of an ERβ-selective steroidal estrogen, 8β-vinylestradiol; efficient incorporation of fluorine-18 was achieved, but required very vigorous conditions. We have examined the biodistribution of this compound, as well as of Br-041, an analog of a known non-steroidal ERβ-selective ligand (ERB-041), labeled with bromine-76. Studies were done in immature female rodents, with various pharmacological and endocrine perturbations to assess ERβ selectivity of uptake.Little evidence of ERβ-mediated uptake was observed with either [(18)F]8BFEE(2) or [(76)Br]Br-041. Attempts to increase the ERβ content of target tissues were not effective and failed to improve biodistribution selectivity.Because on an absolute basis level, ERβ levels are low in all target tissues, these studies have highlighted the need to develop improved in vivo models for evaluating ERβ-selective radiopharmaceuticals for use in PET imaging. Genetically engineered breast cancer cells that are being developed to express either ERα or ERβ in a regulated manner, grown as xenografts in immune-compromised mice, could prove useful for future studies to develop ER subtype-selective radiopharmaceuticals.

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTSynthesis and Tissue Biodistribution of [.omega.-11C]Palmitic Acid. A Novel Pet Imaging Agent for Cardiac Fatty acid MetabolismBrad O. Buckman, Henry F. VanBrocklin, Carmen S. Dence, Steven R. Bergmann, Michael J. Welch, and John A. KatzenellenbogenCite this: J. Med. Chem. 1994, 37, 15, 2481–2485Publication Date (Print):July 22, 1994Publication History Published online1 May 2002Published inissue 22 July 1994https://doi.org/10.1021/jm00041a028RIGHTS & PERMISSIONSArticle Views224Altmetric-Citations23LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (1 MB) Get e-Alerts Get e-Alerts

The ligands currently used for PET studies of the dopamine receptor are fluorine-18-labeled spiperone (FSp) and carbon-11 or fluorine-18-labeled N-methyl-spiperone. All three of these ligands have drawbacks in either their chemical preparation or their biological behavior. We have previously prepared a series of N-fluoroalkyl-spiperone derivatives which are simple to prepare in high radiochemical yield. N-[18F]fluoropropyl-spiperone (3-F-Pr-Sp) and N-[18F]fluoroethyl-spiperone (2-F-Et-Sp) were the most promising ligands. In vitro competitive binding studies showed affinities for the dopamine receptor of 3-F-Pr-Sp > FSp > 2-F-Et-Sp. Brain extraction studies in a primate model showed that FSp, 2-F-Et-Sp, and 3-F-Pr-Sp were not completely extracted by the brain. High bone uptake and kidney clearance was observed with 3-F-Pr-Sp, while 2-F-Et-Sp cleared through the intestine in rats. This is in contrast to FSp where clearance is through the kidney. Studies to evaluate the extraction of metabolites in the brain were carried out by administering large doses (10 mCi) of FSp, 2-F-Et-Sp and 3-F-Pr-Sp to rats and reinjecting the metabolites in blood into other rats. These experiments showed that < 0.02% of the metabolites from FSp and 3-F-Pr-Sp entered the brain, while 0.5% of the metabolites from 2-F-Et-Sp entered the brain. The majority of the activity present in the cerebellum after the administration of 2-F-Et-Sp is metabolites; therefore 2-F-Et-Sp is unsuitable for PET imaging studies. PET imaging studies in baboons and in one normal human volunteer with 3-F-Pr-Sp showed a high striatum-to-cerbellum ratio, showing that 3-F-Pr-Sp can replace ligands currently in use to study dopamine receptors.

This feasibility study was undertaken to determine whether kinetic modeling in conjunction with small-animal PET could noninvasively quantify alterations in myocardial perfusion and substrate metabolism in rats.All small-animal PET was performed on either of 2 tomographs. Myocardial blood flow and substrate metabolism were measured in 10 male Zucker diabetic fatty rats (ZDF, fa/fa) and 10 lean littermates (Lean, Fa/+) using (15)O-water, 1-(11)C-glucose, 1-(11)C-acetate, and 1-(11)C-palmitate. Animals were 12.0 +/- 1.4-wk old.Consistent with a type 2 diabetic phenotype, the ZDF animals showed higher plasma hemoglobin A(1c), insulin, glucose, and free fatty acid (FFA) levels than their lean controls. Myocardial glucose uptake (mL/g/min) was not significantly different between the 2 groups. However, higher glucose plasma levels in the ZDF rats resulted in higher myocardial glucose utilization (nmol/g/min) (Lean, 629 +/- 785, vs. ZDF, 1,737 +/- 1,406; P = 0.06). Similarly, myocardial FFA uptake (mL/g/min) was not significantly different between the 2 groups, (Lean, 0.51 +/- 28, vs. ZDF, 0.72 +/- 0.19; P = not significant) However, due to higher FFA plasma levels, utilization and oxidation (nmol/g/min) were significantly higher in the ZDF group (Lean, 519 +/- 462, vs. ZDF, 1,623 +/- 712, P < .001; and Lean, 453 +/- 478, vs. ZDF, 1,636 +/- 730, P < .01).Noninvasive measurements of myocardial substrate metabolism in ZDF rats using small-animal PET are consistent with the expected early metabolic abnormalities that occur in this well-characterized model of type 2 diabetes mellitus. Thus, small-animal PET demonstrates significant promise in providing a means to link the myocardial metabolic abnormalities that occur in rat of disease with the human condition.

In this study, we compared the accuracy of the rate of myocardial glucose use (rMGU) measured using PET and 1-(11)C-glucose with the rate measured using PET and the more conventional tracer (18)F-FDG.PET measurements of myocardial tracer uptake (K, in mL/g/min) and rMGU (in nmol/g/min) were obtained with 1-(11)C-glucose and (18)F-FDG in 21 dogs using kinetic modeling and the Patlak graphical method, respectively. Eighteen dogs were studied during hyperinsulinemic-euglycemic clamp performed either at rest or combined with phenylephrine, dobutamine, intralipid infusion, or intralipid infusion and dobutamine. Three dogs were studied during intralipid infusion alone under resting conditions. Arterial-coronary sinus sampling was performed to measure the K of both tracers (n = 14) and rMGU by the Fick method (n = 21).PET-derived values for K from either 1-(11)C-glucose or (18)F-FDG correlated closely with directly measured tracer K values (glucose: y = 0.98x + 0.01, r = 0.79, P < 0.001; (18)F-FDG: y = 0.74x + 0.03, r = 0.77, P < 0.001). In contrast, correlation with K values of unlabeled glucose measured directly was better for 1-(11)C-glucose (y = 0.92x + 0.02, r = 0.96, P < 0.0001) than for (18)F-FDG (y = 0.66x + 0.05, r = 0.72, P < 0.01) (P < 0.001 for comparison of correlation coefficients). As a consequence, PET-derived values for rMGU correlated more closely with Fick-derived measurements of unlabeled glucose using 1-(11)C-glucose (y = 0.82x + 168, r = 0.97, P < 0.0001) than with (18)F-FDG (y = 0.81x + 278, r = 0.79, P < 0.001) (P < 0.001 for comparison of correlation coefficients).Over a wide range of conditions, PET-derived measurements of rMGU are obtained more accurately with 1-(11)C-glucose than with (18)F-FDG.

Abstract Attempts to measure blood‐to‐brain glucose transport and cerebral glucose metabolism with 11 C‐glucose have been hampered by methods that require jugular venous sampling or do not adequately account for the efflux of labeled metabolites from the brain. We performed eight positron emission tomography studies with 1‐ 11 C‐d‐glucose in macaques at arterial plasma glucose concentrations of 8.43 to 1.51 μmol ml −1 (152–27 mg dl −1 ) using a model that includes a fourth rate constant to account for regional egrees of all 11 C‐metabolites. Values for blood‐to‐brain glucose influx, cerebral glucose metabolism, and brain free glucose concentration agreed closely with values obtained in mammals by other investigators. Values for net extraction fraction corresponded closely to simultaneously measured arteriovenous values. We demonstrated that utilization of a model that includes a fourth rate constant to account for regional egress of all 11 C‐metabolites with positron emission tomography and 1‐ 11 C‐d‐glucose provides accurate measurements of blood‐to‐brain glucose transport and cerebral glucose metabolism in vivo without need for jugular venous sampling, even under conditions of severe hypoglycemia.

An improved synthesis of 1-[11C]D-glucose is described. The major improvement is achieved when a 0.033 M borate buffer at pH 8.1 is used to effect the condensation of d-arabinose with NH4(11)CN. Subsequent reduction of the 1-[11C]D-aldonitriles gives the epimeric sugars 1-[11C]D-glucose and 1-[11C]D-mannose in a ratio of 1.8 +/- 0.57 as the major products. The decay corrected radiochemical yield is about 30% for the mixture of sugars. The overall synthesis, starting with the production of NH4(11)CN, is conducted in a dedicated remote system. The remote gantry was easy to build with commercially available valves and glassware, and has been practically trouble-free after more than 2 years of use. Improved purification and quality control of the final product uses ion chromatography and a more efficient resin, and is also described. A preliminary PET study on a macaque has been conducted using 1-[11C]D-glucose obtained with this new improved synthesis.

A modified synthesis of [18F]fluoromisonidazole is reported which makes use of microwave heating to reduce the synthesis time to ca 70 min from EOB. A remote system for column purification, concentration and delivery to an HPLC syringe, which reduces the total absorbed dose to the operator, is also described.

Although monoclonal antibodies have been radiolabeled with many different radionuclides, the application of positron emission tomography (PET) to the imaging of radiolabeled antibodies has been limited to the investigation of a small number of long-lived radionuclides. In this study, we labeled F(ab')2 fragments of a mouse monoclonal antibody (BB5-G1) specific for a human parathyroid surface antigen with the positron emitting radionuclides, gallium-68 and fluorine-18. The biodistribution of the fragments was evaluated in a nude mice model and the results were compared to those obtained with fragments labeled with iodine-125 and indium-111 using conventional labeling techniques. All labeled fragments bound to human parathyroid tissue implanted in nude mice, with parathyroid-to-muscle ratios reaching as high as 10:1, 4 h after administration. A major difference was observed in the uptake and clearance of the various labeled fragments through the kidney. The halogen activity cleared, but the metal radioactivity was retained in the kidney. The results indicate that the fluorine-18 or gallium-68 labeled fragment may be useful for parathyroid imaging with positron emission tomography.

This chapter elaborates the imaging of myocardium enzymatic pathways with carbon-11 radiotracers. Under normal conditions, the heart utilizes a variety of metabolic pathways, such as the oxidation of carbohydrates, fatty acids, lactate, and pyruvate, to meet the high-energy demands of contraction and maintenance of cellular function. Carbon-11 is produced by the 14N(p, α) 11C reaction using a gas target system of 0.5% oxygen in nitrogen with typical bombardments of 20 –40 min at 40 μA beam power. The product obtained from the target is [11C]CO2, which is then trapped under vacuum in a specially designed stainless steel coil cooled to −196° with liquid nitrogen. It is found that as blood contains radiolabeled metabolites in addition to 1-[11C]palmitate, the PET-derived 11C blood activity must be corrected for the presence of 11CO2 in order to derive the true input function. It is found that data analyses require minimum manual data entry and, on average, are completed within 2 h from the time the myocardial positron emission tomography (PET) images are reconstructed, making these types of complex studies feasible to implement in a clinical PET environment.

A simple, rapid and fully automated preparation of sodium [18F]fluoroacetate has been developed by taking advantage of the similarities between the reaction pathways of [18F]fluoroacetate and [18F]-2-fluoro-deoxyglucose (FDG). The automated synthesis of sodium [18F]fluoroacetate was achieved with a commercial [18F]FDG synthesizer, the TRACERlab MXFDG. The method produced the desired compound in a short synthesis time (32 min) and with a high and reproducible radiochemical yield (50.2±4.8%, decay corrected). The radiochemical purity of sodium [18F]fluoroacetate was greater than 99%.

Androgen receptor (AR), which is overexpressed in most prostate cancers, is the target of androgen ablation and antiandrogen therapies: it is also the target for the receptor-mediated imaging of AR-positive prostate cancer using radiolabeled ligands. Previous AR imaging agents were based on a steroidal core labeled with fluorine. To develop a novel class of nonsteroidal imaging agents, with binding and pharmacological characteristics that are more similar to those of clinically used AR antagonists, we synthesized N-(3-fluoro-4-nitronaphthyl)-cis-5-norbornene-endo-2,3-dicarboxylic imide (3-F-NNDI), an analog of recently reported AR antagonist ligands.3-F-NNDI was synthesized in six steps starting with 1-nitronaphthalene, with fluorine incorporation as the final step. The labeling of 3-F-NNDI with fluorine-18 was achieved through a novel, extremely mild, S(N)Ar displacement reaction of an o-nitro-activated arene trimethylammonium salt, and 3-[(18)F]F-NNDI was prepared in high specific activity.3-F-NNDI was found to have an AR-binding affinity similar to that of its parent compound. In vitro assays demonstrated high stability of the labeled compound under physiological conditions in buffer and in the blood. Androgen target tissue uptake in diethylstilbestrol-pretreated male rats, however, was minimal, probably because of extensive metabolic defluorination the radiolabeled ligand.This study is part of our first look at a novel class of nonsteroidal AR antagonists as positron emission tomography (PET) imaging agents that are alternatives to steroidal AR agonist-based imaging agents. Although 3-[(18)F]F-NNDI has significant affinity for AR, it showed limited promise as a PET imaging agent because of its poor target tissue distribution properties.

C4-[18F]Fluorocyclofenil ([18F]FCF, 6) and C3-[18F]fluoroethylcyclofenil ([18F]FECF, 9), two high-affinity nonsteroidal estrogens, were prepared and investigated as potential agents for imaging estrogen receptors (ERs) in breast tumors. Both of these compounds could be prepared conveniently from alkyl methanesulfonate precursors (5,8) by fluoride displacement reactions, and they were obtained in high radiochemical purity and radiochemical yields, with effective specific activities sufficient for in vivo biodistribution studies. While the biodistribution of [18F]FCF (6) in immature female rats showed no selective target tissue uptake, the biodistribution of [18F]FECF (9) showed selective uptake by the uterus, but this uptake could not be blocked by excess estradiol. The poor in vivo biodistribution of these otherwise high-affinity ligands arouses curiosity, and together with recent results on the biodistribution of other nonsteroidal ligands suggests that factors other than receptor binding affinity are important for in vivo imaging of estrogen target tissues and ER-positive breast tumors.

Electrostatic interactions facilitate conjugation reactions of cationic poly(amido)amine (PAMAM) dendrimers with anionic NHS reagents.

We have prepared two estrogens labeled with carbon-11, 17α-[11C]methylestradiol and 11β-ethyl-17α-[11C]methylestradiol, at a specific activity of 300–1000 Ci/mmol (11.1–37 TBq/mmol), and we have determined their in vivo biodistribution in immature female rats. Both compounds accumulated selectively in two target tissues, the uterus and ovaries, reaching levels of 3.5–4.9 % ID/g at 20 min and 4.6–6.6 %ID/g at 40 min; uterus-to-blood ratios reached 12–23. Uterine uptake showed a saturation dependence with the amount of injected mass, and was displaced by unlabeled estradiol, indicating that this uptake was receptor mediated. These results suggest that these compounds may be useful in estrogen receptor-based imaging of breast tumors.

Journal of Labelled Compounds and RadiopharmaceuticalsVolume 26, Issue 1-12 p. 391-392 Symposium Abstract Microwave-facilitated synthesis of [18F]-spiperone D.-R. Hwang, D.-R. Hwang Edward Mallinckrodt Institute of Radiology, Washington University School of Medicine, St. Louis, MO 63110Search for more papers by this authorS.M. Moerlein, S.M. Moerlein Edward Mallinckrodt Institute of Radiology, Washington University School of Medicine, St. Louis, MO 63110Search for more papers by this authorC.S. Dence, C.S. Dence Edward Mallinckrodt Institute of Radiology, Washington University School of Medicine, St. Louis, MO 63110Search for more papers by this authorM.J. Welch, M.J. Welch Edward Mallinckrodt Institute of Radiology, Washington University School of Medicine, St. Louis, MO 63110Search for more papers by this author D.-R. Hwang, D.-R. Hwang Edward Mallinckrodt Institute of Radiology, Washington University School of Medicine, St. Louis, MO 63110Search for more papers by this authorS.M. Moerlein, S.M. Moerlein Edward Mallinckrodt Institute of Radiology, Washington University School of Medicine, St. Louis, MO 63110Search for more papers by this authorC.S. Dence, C.S. Dence Edward Mallinckrodt Institute of Radiology, Washington University School of Medicine, St. Louis, MO 63110Search for more papers by this authorM.J. Welch, M.J. Welch Edward Mallinckrodt Institute of Radiology, Washington University School of Medicine, St. Louis, MO 63110Search for more papers by this author First published: January 1989 https://doi.org/10.1002/jlcr.25802601167Citations: 17AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article.Citing Literature Volume26, Issue1-12January 1989Pages 391-392 RelatedInformation

The synthesis of ω-[11C], ω-1-[11C] and ω-3-[11C] palmitic acid employing a cross-coupling reaction between a functionalized copper-zinc reagent with [11C]MeI, [1-11C]EtI and [1-11C]BuI is described. A tert-butyl-protected ω-iodo fatty acid precursor tBuO2C-(CH2)n-I (n = 11, 13, 14) was converted into the corresponding dialkylzinc reagent [tBuO2C-(CH2)n]2Zn which reacts with Me2CuI(MgCl)2 to give a highly reactive copper reagent [tBuO2C-(CH2)n]2CuI(MgCl)2 Me2Zn as the labeling precursor. The cross-coupling reaction with [11C]MeI, [1-11C]EtI and [1-11C]BuI provided the protected palmitic acid, specifically labeled with carbon-11 in several positions. The corresponding carbon-13 labeled compounds were synthesized to verify the labeling position. In a typical synthesis with [1-11C]EtI starting with 250 mCi of [11C]CO2, 14 mCi (6% decay-corrected based on [11C]CO2) of ω-1-[11C]palmitic acid was obtained within 30 minutes after EOB in 88% radiochemical purity prior to purification by HPLC. The general feature of this approach allows the convenient synthesis of palmitic acid specifically labeled in the ω, ω-1 or ω-3 positions by using several [11C]-labeled alkyl iodides ([11C]MeI, [1-11C]EtI or [1-11C]BuI) in the same cross-coupling protocol. Copyright © 2000 John Wiley & Sons, Ltd.

A new procedure for labeling alkylbenzenes with no-carrier-added (nca) [18F]fluoride is reported. This will allow the use of [18F]-for-nitro aromatic nucleophilic displacement reaction for labeling aromatic compounds with no activating groups on the benzene ring. The new procedure involves (A) the [18F]-for-nitro displacement reaction on nitrophenones, and (B) the reduction of [18F]fluorophenones with triethylsilane and trifluoroacetic acid to alkylfluorobenzenes. The desired 18F-labeled alkylbenzenes were prepared in a synthesis time of 1 h with a radiochemical yield of 20% at end-of-synthesis. The procedure has been successfully applied to the synthesis of 18F-labeled alkylating agents, such as 4-[18F]fluorophenethyl bromide, 4, and 4-[18F]fluorophenbutyl chloride, 5. Using the reaction of piperidine and 4 as a model, the potential use of phenethylbromide 4 for labeling biologically important amines was examined. Initial results indicated that the desired alkylated piperidine was formed in low yields (<5%) due to the conversion of halide 4 to [18F]fluorostyrene (>85%) under basic conditions. The new procedure provides an easy method of labeling alkylbenzenes with fluorine-18.

Abstract A highly efficient radiosynthesis of p-[ 18 F ] fluorophenacy bromide has been developed employing a polymer supported bromination of p-[ 18 F ] fluoroacetophenone .

No carrier-added 1-[11C]putrescine has been prepared using a simple two-step procedure. Radiochemical yields of 1-2% at end-of-synthesis were obtained in a synthesis time of 50-60 min. The in vivo uptake of no carrier-added 1-[11C]putrescine into rat prostate was determined and compared to the uptake of no carrier-added material containing varying amounts of non-radioactive putrescine. The in vivo results indicate that the mechanism of uptake into the prostate is saturable.

Sex hormone-binding globulin (SHBG) is believed to play a key role in steroidal radiopharmaceutical delivery to target tissues in humans.To better understand the action of SHBG, we have synthesized and tested in vivo 2 novel 18 F-labeled androgens: 7a-18 F-fluoromethyl-dihydrotestosterone (7a-18 F-FM-DHT) and 7a-18 F-fluoromethyl-nortestosterone (7a-18 F-FM-norT).Both 7a-18 F-FM-DHT and 7a-18 F-FM-norT have high affinity for the androgen receptor (AR); however, 7a-18 F-FM-DHT has a high affinity for SHBG, whereas 7a-18 F-FM-norT has a relatively low affinity.Methods: We developed an efficient radiochemical synthesis for both 7a-18 F-FM-DHT and 7a-18 F-FM-norT, producing them in good radiochemical yield and high specific activity.Biodistribution studies of both compounds were done on diethylstilbestrol-pretreated and DHT-blocked Sprague-Dawley male rats.Metabolism studies were done to determine the amount of intact ligand in the prostate.Results: We obtained 7a-18 F-FM-DHT and 7a-18 F-FM-norT in radiochemical yields of about 30% and radiochemical purities of greater than 99%.Rat biodistribution studies showed selective AR-mediated uptake in the prostate for both compounds.Both compounds showed relatively little defluorination, but the norT analog was more metabolically stable than the DHT analog.Conclusion: These studies show that 7a-18 F-FM-DHT and 7a-18 F-FM-norT have potential for use in human clinical imaging trials to evaluate more definitively the role of SHBG in radiotracer delivery of steroidal systems to target tissues.

3578 Background: Survivin, an inhibitor of an apoptosis protein, widely overexpressed in cancer is associated with poor clinical outcome. We performed the first worldwide human microdosing imaging PK study of an ASO with LY2181308, a specific, second generation antisense inhibitor of Survivin using carbon-11 radiolabelled LY2181308 ([ 11 C]LY2181308). Methods: LY2181308 was administered at the recommended phase II dose (750 mg over 3 hours IV daily x 3, then once weekly). [ 11 C]LY2181308 was manufactured to GMP standard by random [ 11 C]methylation with [ 11 C]methyl iodide of LY2181308 using a GE Tracerlab FXc molecule. [ 11 C]LY2181308-PET scans were performed at baseline and during treatment infusion. [ 11 C]LY2181308 uptake in normal tissue and tumour was quantified. Results: Three pts (2 female Caucasian/1 male Asian) were scanned after administering [ 11 C]LY2181308 which delivered (135–376 μg) of LY2181308. Despite its large size (6778 amu), [ 11 C]LY2181308 rapidly distributed to tissues, with maximal uptake in kidney followed by liver, spleen, vertebral body, tumour, spinal cord, lung, and muscle at baseline. Although renal uptake was high, urinary elimination (bladder activity) was low suggesting renal trapping of [ 11 C]LY2181308 at baseline. For a normalised injected dose of 1 mg, mean (range) tumour concentrations of 31 (4–41) ng/ml were observed at baseline, consistent with that predicted from the preclinical PK/PD model. In a pt with mesothelioma who also had a second [ 11 C]LY2181308-PET scan during LY2181308 treatment infusion, there was about 2-fold increase in [ 11 C]LY2181308 tumour uptake, in contrast to markedly reduced uptake in kidneys, liver, and spleen and similar aortic (circulatory) [ 11 C]LY2181308 levels. In this patient, tumour [ 18 F]FDG- PET uptake at 28 days was reduced by up to 40% after treatment, suggesting drug activity. Conclusions: [ 11 C]LY2181308 pharmacokinetics suggest biologically active human tumour drug concentrations can be attained. LY2181308 therapy saturated normal tissue kinetics and increased tumour uptake of [ 11 C]LY2181308. Data uniquely obtained from fully regulated microdosing studies may rationalise and hasten drug development. [Table: see text]

Two 18F-labeled analogues of dexetimides, 2-[18F]fluorodexetimide (2-FDEX) and 4-[18F]fluorodexetimide (4-FDEX), were prepared and evaluated in vivo as possible agents for the study of the muscarinic acetylcholine receptor (mAChR) with PET. Two synthetic approaches, a 2-step reductive alkylation procedure and a 4-step alkylation approach, were investigated. The alkylation approach with higher overall radiochemical yields was used to prepare 2- and 4-FDEX for biodistribution studies. The overall synthesis time for both compounds was 2.5 h and the overall radiochemical yield at end-of-synthesis was 12%. The specific activity was found to be greater than 600 mCi/mumol. Biodistribution studies of 2-FDEX in rats produced striatum-to-cerebellum and cortex-to-cerebellum ratios of 8.6 +/- 1.1 and 8.4 +/- 1.0 at 1 h after injection, and 12.1 +/- 2.1 and 10.7 +/- 2.2 at 3 h, respectively. Substantial radioactivity detected in bone indicated the in vivo defluorination of 2-FDEX. The striatum-to-cerebellum ratio for 4-FDEX was slightly lower at 1 h (5.9 +/- 0.9) but equally high at 3 h (12.3 +/- 2.0) when compared to 2-FDEX, and there was little bone uptake. The uptake of both 2-FDEX and 4-FDEX into mAChR rich brain regions (e.g. striatum, cortex) was blocked by a dose of dexetimide (5 mg/kg). Our results suggest 4-FDEX is a potential PET agent for study mAChR in vivo.

The labeled serotonin agonist 3-[18F]fluoro-N-(alpha,alpha,alpha-trifluoro-m-tolyl)piperazine (18FTFMPP) was prepared rapidly using the labeling procedure for trifluorotoluenes, [18F]fluoro-for-nitro exchange, followed by an alumina-supported bis-alkylation. After normal-phase HPLC purification, the labeled product was obtained in 20-32% (n = 20) decay-corrected radiochemical yield with a radiochemical purity > 98% and a specific activity of 100 GBq/mumol. The synthesis time including purification was 3 h. The receptor binding affinity of FTFMPP to rat brain membranes was found to be similar to that of the nonfluorinated parent compound (TFMPP). Although TFMPP has been proposed by others as an agent for the imaging of serotonin receptors, only minimal receptor-mediated uptake was observed.

Reports have implicated neuronal nitric oxide synthetase (nNOS) in the pathological effects of neurodegenerative diseases. S-Methyl-L-thiocitrulline (MTICU), a potent and selective nNOS inhibitor (Ki = 1.2 nM), was chosen as our initial target molecule for positron emitter labeling as a potential nNOS tracer. We report the synthesis, biological evaluation and primate brain images of S-[11C]methyl-L-thiocitrulline ([I11C]MTICU).The two-step synthesis of [11C]MTICU consisted of the S-alkylation of alpha-N-Boc-L-thiocitrulline t-butyl ester with [11C]Mel followed by TFA hydrolysis and HPLC purification. The final product was obtained within 50 min (yield = 9.1%-12.5%, based on [11C]Mel S.A. = 27-680 Ci/mmol at end of synthesis). The lipophilicity of [11C]MTICU was determined by octanol/water partition coefficient (LogP). Blood stability of this tracer in vitro and in vivo was measured by HPLC analysis. Biodistribution using female Sprague-Dawley rats was performed, including examination of uptake in cerebellum and olfactory bulb (high nNOS) as well as cortex and brain stem (low nNOS). Carbon-11-MTICU was administered to a female baboon and brain images were obtained using a Siemens ECAT EXACT scanner for determination of brain regional uptake and blood-brain barrier permeability.At 30 min postinjection, [11C]MTICU remained 64% intact in vivo and 95% intact in vitro. Lipophilicity estimation gave Log p = 1.08 +/- 0.08 (n = 6). The brain (0.11% ID/g)-to-blood (0.20% ID/g) ratio was 1:2 at 30 min postinjection. Uptake in the cerebellum was 20% higher than in either the cortex or the brain stem (p < 0.05). Blockage using 1 mg/kg MTICU reduced uptake in the cerebellum and the cortex by 22%, but did not affect the brain stem. PET imaging showed that [11C]MTICU brain uptake, corrected for blood volume, was stable from 10 min to 1 hr at approximately 0.4% ID/organ. PET images of a baboon brain showed increased uptake in the region of the olfactory bulb compared to uniform biodistribution in the rest of the brain.The [11C]MTICU is a tracer that is potentially useful in determining nNOS levels in vivo.

The purpose of the present study was to assess the accuracy of rates of myocardial fatty acid esterification (MFAE) obtained using positron emission tomography (PET). Sixteen dogs were studied after an overnight fast (FAST), during a euglycemic hyperinsulinemic clamp (CLAMP), or during infusion of intralipid (IL) or IL plus dobutamine (IL/DOB). MFAE was quantified using [1-11C]palmitate and PET and compared to the rate of triglyceride (TG) synthesis measured using [1-13C]palmitate and tissue sampling. Plasma free fatty acid (FFA) concentration varied ~20-fold across groups, with this variation in FFA availability accompanied by a ~20-fold range in TG synthesis. MFAE varied ~12-fold across groups, and was significantly correlated with TG synthesis (R = 0.80, P < .001). MFAE, however, was 3- to 4-fold higher than TG synthesis in FAST, CLAMP, and IL, but only ~50% higher when cardiac work was increased in IL/DOB, suggesting that MFAE reflects, in part, the incorporation of label into amino acids via TCA cycle exchange reactions. Changes in MFAE parallel changes in TG synthesis, at least in the basal state. Although the data need to be interpreted cautiously, such measurements should be useful for quantifying acute changes in FFA storage by the heart in various pathophysiological states.

Research and discovery of novel radiopharmaceuticals and targets thereof generally involves initial studies in cell cultures, followed by animal studies, both of which present several inherent limitations. The objective of this work was to develop a tissue bioreactor (TBR) enabling modulation of the microenvironment and to integrate the TBR with a small-animal PET scanner to facilitate imaging biomarker research and discovery and validation of radiopharmaceuticals.The TBR chamber is a custom-blown, water-jacketed, glass vessel enclosed in a circulating perfusion bath powered by a peristaltic pump, which is integrated within the field of view of the PET scanner. The chamber is in series with a gas exchanger and a vessel for degassing the system during filling. Dissolved oxygen/temperature probes and septa for injection or sampling are located at the inlet and outlet of the cell chamber. A pH probe is located at the chamber outlet. Effluent is collected in the fraction collector as mixed-cup samples. In addition, both medium and tissue chamber can be sampled to investigate tissue and secretory products through multiscale analysis. As a proof of concept, we studied the effects of lipids on glucose uptake using HepG2 cells. To that end, we varied the nutrient substrate environment over a period of approximately 27 d, before and after the addition of lipids, and studied the effects of pioglitazone, a peroxisome proliferator-activated receptor γ agonist, on lipid and glucose uptake. In parallel, the TBR was imaged by PET in conjunction with (11)C-palmitate in the presence and absence of lipids to characterize (11)C-palmitate uptake.The O2 consumption, glucose consumption, lactate production, and free fatty acid consumption and production rates were consistent in demonstrating the effects of lipids on glucose uptake. Pioglitazone exhibited improved glucose uptake within 3 d of treatment. Semiquantitative analysis suggested that lipids induced greater (11)C-palmitate uptake.The integrated TBR offers a platform to monitor and modulate the tissue microenvironment, thus facilitating tissue-specific imaging and therapeutic biomarkers of disease, identification of molecular diagnostic markers, and validation of radiopharmaceuticals in both rodent and human cell lines.

We have developed a technique for the rapid conversion of the nitrogen-13 induced in a graphite target into nitrogen oxides. This was accomplished by heating the graphite target in a stream of pure oxygen at 800 °C. Less than 20% of the radioactivity was found in the form of [13N]nitrogen. The rest of the radioactivity was efficiently trapped in a solid-phase medium that consisted of an aqueous solution of 5% NaOH dispersed in silica gel. The radioactivity from this solid-phase medium was eluted with water (94% recovery) and found to be in the form of 13NO2− (99%). This was subsequently converted to [13N]ammonia with Raney-nickel, either by a conventional liquid-phase reduction with an overall conversion efficiency to ammonia of 45%, or by an incorporation of the Raney-nickel into the solid-phase medium. The latter system resulted in an overall conversion efficiency to ammonia of 37 ± 9%, with a radiochemical purity of nearly 100% and a synthesis time under 17 min.

Using positron emission tomography (PET) and nitric oxide radiolabeled with nitrogen-13 (half-life 9.97 min) we probed the distribution and kinetics of inhaled nitric oxide in anesthetized dogs. The washout of this gas after inhalation was much slower than that observed for [13N]nitrogen gas, demonstrating its uptake by lung tissue. The small fraction of radioactivity found in the plasma was determined to be in the form of [13N]nitrate. The administered gas contained < 1 ppm of nonradioactive nitric oxide, which is believed to be below the physiologic threshold for vasorelaxation.

Abstract A remote system has been constructed for the preparation of 11 C‐glucose via photosynthesis. The system is totally contained in a shielded hood, with all manipulations done from the outside. This system is capable of routine delivery of 25–50 mCi of 11 C‐glucose which has a radiochemical purity &gt;95% and is sterile and pyrogen free. The design, construction and operation of this system are fully described.

Our objective was to determine, in the hearts of women with type 1 diabetes mellitus (T1DM), whether the fate of extracted glucose is altered and, if so, what the impact of dobutamine is on myocardial substrate metabolism. In experimental models of T1DM, myocardial glycolysis and glucose oxidation are reduced with the impairment becoming more pronounced with dobutamine. Whether similar changes occur in humans with T1DM is unclear. Myocardial perfusion, oxygen consumption, and glucose and fatty acid metabolism were measured with positron emission tomography in 19 women, 7 normal volunteers (NVs) and 12 with T1DM. The NVs and 6 T1DM (DM1) patients were studied under baseline metabolic conditions and 6 T1DM patients were studied during hyperinsulinemic-euglycemic clamp (DM1-C), both at rest and during dobutamine. At rest, myocardial glucose uptake, glycolysis, glycogen storage, and oxidation were reduced by similar levels in DM1 patients compared with NVs (P < .05). During dobutamine, although myocardial glucose uptake was not different from DM1 patients at rest, fractional glycolysis was lower compared with NVs or DM1-C patients and reflected a lower glucose oxidation rate (P < .001). Measurements of myocardial glucose metabolism at rest and during dobutamine were comparable between NVs and DM1-C patients. During dobutamine, myocardial fatty acid uptake and oxidation increased in all 3 groups. In women with T1DM, (1) myocardial glucose metabolism is impaired downstream from initial uptake, (2) these abnormalities become more pronounced with dobutamine and are paralleled by an increase in myocardial fatty acid metabolism, and (3) insulin restores glucose metabolism to levels observed in normal control subjects.

Abstract The use of SEP-PAKR C18 cartridges for the isolation and purification of radiopharmaceuticals, labeled with the 20.4 minute half-life radionuclide carbon-11, is reported. Synthesis and SEP-PAK preparative chrotmatographic purification of [1-11C]palmitic acid, [11C-methyl]benzyl methyl ether, [1-11C]butan-1-ol, and [1-11C]pyruvic acid are described. The use of SEP-PAK C18 cartridges has allowed development of rapid and remote methods for handling of high amounts (> 100 mCi) of radioactive products.

The recent development of low energy accelerators for positron emission tomography has necessitated the development of new targets for 13N production. 12C(d,n)13N reaction yields in graphite at low deuteron beam energies (0.8-3.2 MeV) are presented and a new technique for the in situ extraction of 13N activity from solid graphite and subsequent conversion to [13N] ammonia is described. The target is windowless and is reusable for multiple isotope production runs. This technique utilizes radio frequency induction heating to rapidly heat the graphite to combustion temperatures in an O2 gas stream. The conversion of activity induced in the target to [13N] ammonia in under 10 min with an overall decay-corrected efficiency of 45% is reported.

1. Analysis of nine parts of the rat nephron from glomerulus to papilla showed a wide variety of metabolic responses to high loads of fructose among the different segments. 2. There were dramatic increases in fructose-1-P and glucose-6-P in the proximal straight tubule, with lesser changes in the proximal convoluted tubule and none elsewhere. 3. Fructokinase was also confined to the proximal tubule with highest activity in the straight segment. 4. Fructose-1-P aldolase was highest in the proximal convoluted tubule. Fructose bisphosphate aldolase peaked in the distal straight tubule. 5. Glycerol-1-P increased strikingly in the proximal tubule but the peak effect was in the convoluted segment. 6. Highest concentrations of ATP were found in the distal convoluted tubule and did not change with loads of fructose whereas, ATP fell 80% in the proximal straight tubule and somewhat less in the convoluted portion.

In this study we demonstrated that significant egress of FDG from myocardium occurs within the first hour after tracer injection leading to nonlinear Patlak plots. There are also significant amounts of acidic FDG metabolites present in the blood. However, the impact of these metabolites on the estimates of myocardial glucose utilization (MGU) is negligible. Although further studies will be required to elucidate the reason for the egress of tracer from myocardium, not accounting for it will result in erroneous estimates of MGU.

Residualizing labels for proteins are designed to remain entrapped within cells following uptake and degradation of the carrier protein. In the present work we report the synthesis of a novel residualizing label, N-lactitol-S-([18F]fluorophenacyl)-cysteamine ([18F]LCSH, and its use for quantifying the accumulation of low density lipoprotein in tissues in vivo by positron emission tomography (PET). The retention of degradation products in tissues from lipoprotein or from other rapidly catabolized protein pharmaceuticals tagged with [18F]LCSH reduces leakage of tracer into the plasma compartment. Thus, residualizing labels provide a valuable tool for enhancing signal-to-noise ratios, even during the relatively short interval of PET studies.

A general introduction to the problems associated with the use of C-11 and F-18 as radiotracers in the production of diagnostic compounds in a clinical setting is presented. The systematic development of a useful radiopharmaceutical, 11C-palmitic acid, is discussed in detail, from the production of the radionuclide to the final delivery of the product for clinical and animal studies. Steps in the procedure in which technical and chemical problems might arise are emphasized.

1167 Objectives To shorten F-18 incorporation times and simplify purifications of radiopharmaceuticals, a highly carboxyphilic di-t-butyl-phenylsilyl chloride system (1) was employed to load unprotected small molecules or peptides onto a resin, enabling their labeling and release in one step (Figure 1). Methods Compound 1-NHS ester reacted with the amine in 17-α-ethynylestradiol derivative (EE2) within 10-20 min at room temperature to give compound 2, without reaction with the phenol or alcohol (Route 1). The silyl chloride in compound 2 was unaffected during silica chromatography and could be quantitatively loaded onto an acidic (H) resin. A copper-free click strategy was adopted to load the unprotected RGD peptide onto the resin (Route 2). DBCO (dibenzocyclooctyne)-COOH was reacted with compound 1 to form the silyl ester, which was subsequently coupled with 0.8 eq. RGD peptide to give compound 3, quantitatively. Finally, compound 3 was loaded onto an azide-functionalized resin with high efficiency using a copper-free click reaction. Results To reduce activity loss due to decay, target water 18F-H2[18O]O was used directly for radiolabeling. After screening a few solvents, a 5:1 ratio of DMSO to F-18 water was found to give good F-18 incorporation into the silyl group, resulting in selective and efficient release of F-18 labeled EE2 and RGD peptide from the resin in very high radiochemical yield. Suprisingly, no F-18 activity remained on the resin. The released F-18 labeled compounds were purified by filtration and monitored by HPLC, and specific activities in the range of 1800-2500 Ci/mmol were routinely obtained. Conclusions This resin-supported F-18 labeling approach, coupled with the direct use of F-18 in target water, could simplify and shorten the whole F-18 labeling process, while maintaining high specific activity. Research Support DOE (DE-SC0005434 and DE-FG02-08ER64671)

1162 Objectives Most conventional approaches to label phenols with F-18 involve nucleophilic substitution on electron-deficient precursors followed by conversion to phenols, a sequence often inefficient and time consuming. Our objective was to fill this methodological gap in F-18 radiochemisty by developing a series of unusual synthetic transformations to label phenols (and other electron-rich aromatic systems) with F-18 at high specific activity, rapidly, reliably, and conveniently. Methods We conceived of a diazo compound as a precursor from which it should be possible to prepare F-18 labeled phenols through halofluorination of the diazo group followed by elimination. Diazoketone 1, derived from the corresponding cyclohexenone, was treated with 1,3-dibromo-5,5-dimethylhydantoin (DBDMH) in the presence of an appropriate fluoride source to give α-fluoro-α-bromoketone 2. HBr elimination afforded the desired ortho-fluorophenol 3 in a moderate yield. Results Despite the success of this unique ortho-fluorophenol synthesis using cold fluoride, adaptation to F-18 labeling has proved to be challenging, even beyond typical tracer-level reactivity problems. In fact, even the addition of decayed target water to an otherwise successful protocol for F-19 labeling, suppressed product formation. Current work is focused on two possible interferences, residual water and metal ions (possibly from target foil) which reduce fluoride nucleophilicity or form carbenoids from the diazo group, respectively. By removing water by additional drying with t-BuOH and adding a chelator to capture metal contaminants, we have observed formation of fluorophenol 3, even when target water is used. Conclusions This halo-fluorination/elimination procedure enabled rapid preparation of o-fluorophenol rapidly and regioselectively. The interferences in target water were successfully removed by extensive drying and addition of chelator. Research Support DOE (DE-SC0005434 and DE-FG02-08ER64671)

569 Objectives Shell Crosslinked Knedel-like nanoparticles (SCK-NPs) have controllable size, shape, flexibility, and functionality, and offer unique opportunities for achieving very high specific activity and effective molecular targeting activity required for the detection and quantification of low abundance biological targets using nuclear imaging. The goal of this project is to [18F]-radiolabel SCK-NPs with high specific activity by a two-step reaction using copper-free click chemistry. Methods A dibenzylcyclooctyne (DBCO) derivative for copper-free click chemistry was labeled with F-18 via a two-step procedure using DBCO-amine, available commercially, and [18F]F(CH2CH2O)3Ts, prepared from the di-tosyl precursor under typical labeling conditions. The copper-free click chemistry was carried out in aqueous DMSO solution using HPLC purified [18F]-DBCO compound and SCK-NPs having the core functionalized with azide groups. The [18F]-labeled SCK-NPs were purified by passage over a Zeba® desalting column, and were analyzed by radio-FPLC and TLC. Results [18F]-labeled DBCO analogue was made in 80% yield (TLC). [18F]-SCK-NPs was confirmed by FPLC. Unlike copper(I)-catalyzed click reactions, which require the simultaneous presence of azide, alkyne and copper (I) in the lipophilic core of SCK-NPs, the copper-free reaction of [18F]-DBCO and SCK-NPs is advantageous not only because it is a two-component reaction but because in aqueous solution the very lipophilic [18F]-DBCO is driven into the hydrophobic core of the SCK-NP. Preliminary results showed up to 60% of F-18 activity becomes attached to the nanoparticles by the click reaction, with little activity due to non-covalent sequestration of [18F]-DBCO in the core. Conclusions SCK-NPs have been successfully radiolabeled in the core with F-18 using a copper-free click reaction. Optimization of this labeling is in progress to achieve high specific activity in large scale reactions. Research Support DOE # ER64671

460 Objectives Fluorine-18 16α-fluoroestradiol (FES) is a valuable tool to study the status of estrogen receptor (ER) in primary and metastatic breast cancers using positron emission tomography (PET). The FES synthesis has been improved by using 3-O-methoxymethyl-16, 17-O-sulfuryl-16-epiestriol as precursor for clinical use. For small animal studies, the effective specific activity (ESA) is critical because a high dose of FES with low ESA may saturate the ER and block the uptake. So far for this method, no ESA has been published, and variable radiochemical yields and specific activity have been reported. Our goal was to optimize the labeling process to achieve optimal ESA for FES. Methods The synthesis of [18F]FES was carried out under typical labeling conditions (K222, K2CO3) using as low as 0.3 mg of precursor in acetonitrile at 110 oC for 7 min, followed by acid hydrolysis using 100 µL 1 M H2SO4 and 400 µL acetonitrile at 110 oC for 10 min. [18F]FES was purified by a reversed phase HPLC system. SA and ESA were measured by HPLC and by using a receptor binding assay, respectively. Results Starting with 50 mCi [18F]fluoride (untreated), up to 70% (isolated, decay corrected) of [18F]FES was obtained within 90 min using only 0.3 mg substrate . The yield was highly reproducible when 1 M H2SO4 instead of 1 N HCl was used for the hydrolysis. H2SO4 also avoided the potential formation of chloro-analogue of FES. The HPLC parameters were chosen to avoid no major mass peaks eluting around FES. The ESA measured was up to 10,000 mCi/µmol, which matches the SA by HPLC. Administering high dose (300 µCi/dose) of FES to a 20 g tumor bearing mouse did not reduce the target uptake of the tracer. Conclusions We synthesized [18F]FES with optimal yields and ESA by using a minimal amount of substrate, H2SO4 hydrolysis and a careful HPLC purification. These improvements can be easily adapted to an automatic synthesizer. Research Support NIH U01CA141541-0