Sex affects myocardial blood flow and fatty acid substrate metabolism in humans with nonischemic heart failure.

BACKGROUND: 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. METHODS AND RESULTS: 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). CONCLUSIONS: 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.

Type 2 diabetes, obesity, and sex difference affect the fate of glucose in the human heart.

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.

Longitudinal noninvasive imaging of progesterone receptor as a predictive biomarker of tumor responsiveness to estrogen deprivation therapy.

PURPOSE: To investigate whether longitudinal functional PET imaging of mammary tumors using the radiopharmaceuticals [(18)F]FDG (to measure glucose uptake), [(18)F]FES [to measure estrogen receptor (ER) levels], or [(18)F]FFNP [to measure progesterone receptor (PgR) levels] is predictive of response to estrogen-deprivation therapy. EXPERIMENTAL DESIGN: [(18)F]FDG, [(18)F]FES, and [(18)F]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 [(18)F]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 [(18)F]FES and [(18)F]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 [(18)F]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 [(18)F]FFNP tumor uptake, indicating that [(18)F]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 [(18)F]FFNP uptake in mammary tumors predicts tumor response to estrogen-deprivation therapy. Longitudinal noninvasive PET imaging using [(18)F]FFNP is a robust and effective approach to predict tumor responsiveness to endocrine treatment.

Utilizing electrostatic interactions to facilitate F-18 radiolabeling of poly(amido)amine (PAMAM) dendrimers.

The development of methods for the facile conjugation and radiolabeling of poly(amido)amine (PAMAM) dendrimers would be of great benefit in evaluating biomedical applications of these intriguing molecularly defined polymers. Two anionic N-hydroxysuccinimide (NHS) esters (7 and 10) were developed and radiolabeled with fluorine-18 using Cu(I)-catalyzed click reactions. The radiolabeling of a primary amine-terminated PAMAM generation-6 (G6) dendrimer with [(18)F]7 or [(18)F]10 was complete in water or methanol within 5 min at room temperature. This highly efficient conjugation reaction benefits from a high, localized concentration of these NHS esters on the surface of PAMAM dendrimers, due to the electrostatic attraction between the anionic NHS esters and the positively-charged PAMAM dendrimers. The large medium effect (pH, salt, solvent) observed for these conjugation reactions is consistent with this mechanism. This novel strategy of utilizing electrostatic interactions provides a novel, facile, and efficient method for the conjugation and radiolabeling of PAMAM dendrimers that also has potential for radiolabeling other appropriate nanoparticles.

Optimization of the preparation of fluorine-18-labeled steroid receptor ligands 16alpha-[18F]fluoroestradiol (FES), [18F]fluoro furanyl norprogesterone (FFNP), and 16beta-[18F]fluoro-5alpha-dihydrotestosterone (FDHT) as radiopharmaceuticals.

Fluorine-18-labeled steroid receptor tracers, 16α-[(18)F]fluoroestradiol (FES), [(18)F]fluoro furanyl norprogesterone (FFNP), and 16ß-[(18)F]fluoro-5α-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 H2SO4 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 NaBH4 , 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.

A PET-compatible tissue bioreactor for research, discovery, and validation of imaging biomarkers and radiopharmaceuticals: system design and proof-of-concept studies.

UNLABELLED: 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. METHODS: 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. RESULTS: 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. CONCLUSION: 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.

Synthesis and biological evaluation of two agents for imaging estrogen receptor ß by positron emission tomography: challenges in PET imaging of a low abundance target.

INTRODUCTION: Independent measurement of the levels of both the estrogen receptors, ERα and ERß, 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 ERß by PET has yet been reported. METHODS: We have prepared the fluorine-18 labeled form of 8ß-(2-fluoroethyl)estradiol (8BFEE(2)), an analog of an ERß-selective steroidal estrogen, 8ß-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 ERß-selective ligand (ERB-041), labeled with bromine-76. Studies were done in immature female rodents, with various pharmacological and endocrine perturbations to assess ERß selectivity of uptake. RESULTS: Little evidence of ERß-mediated uptake was observed with either [(18)F]8BFEE(2) or [(76)Br]Br-041. Attempts to increase the ERß content of target tissues were not effective and failed to improve biodistribution selectivity. CONCLUSIONS: Because on an absolute basis level, ERß levels are low in all target tissues, these studies have highlighted the need to develop improved in vivo models for evaluating ERß-selective radiopharmaceuticals for use in PET imaging. Genetically engineered breast cancer cells that are being developed to express either ERα or ERß in a regulated manner, grown as xenografts in immune-compromised mice, could prove useful for future studies to develop ER subtype-selective radiopharmaceuticals.

Highly efficient click labeling using 2-[¹8F]fluoroethyl azide and synthesis of an ¹8FN-hydroxysuccinimide ester as conjugation agent.

INTRODUCTION: 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. METHODS: 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). RESULTS: 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. CONCLUSIONS: 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.

Small-animal PET of steroid hormone receptors predicts tumor response to endocrine therapy using a preclinical model of breast cancer.

UNLABELLED: Estrogen receptor-α (ERα) 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 ERα-positive (ERα(+))/PR-positive (PR(+)) tumors are most likely to respond. The purpose of this study was to use estrogen- and progestin-based radiopharmaceuticals to image ERα 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 ERα and PR in primary tumor-bearing mice and mice implanted with mammary cell lines (SSM1, SSM2, and SSM3) derived from primary STAT1-deficient (STAT1(-/-)) 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(-/-) mammary tumors and implanted SSM2 and SSM3 tumors showed high (18)F-FES and (18)F-FFNP uptake and were confirmed to be ERα(+)/PR(+). 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 ERα(+)/PR(+). 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 fulvestrant-resistant ERα(+)/PR(+) 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.

64Cu Core-labeled nanoparticles with high specific activity via metal-free click chemistry.

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.

Assessment of progesterone receptors in breast carcinoma by PET with 21-18F-fluoro-16α,17α-[(R)-(1'-α-furylmethylidene)dioxy]-19-norpregn-4-ene-3,20-dione.

UNLABELLED: 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. METHODS: 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. RESULTS: 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. CONCLUSION: (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.

Sex and type 2 diabetes: obesity-independent effects on left ventricular substrate metabolism and relaxation in humans.

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 <0.0001, respectively). Plasma fatty acid (FA) levels were higher in diabetics (vs. obese, P < 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 < 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.

Potentiation of abnormalities in myocardial metabolism with the development of diabetes in women with obesity and insulin resistance.

BACKGROUND: 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. RESEARCH DESIGN AND METHODS: Women who were lean volunteers (NV) (N = 14; age 35 ± 17 years, body mass index 23 ± 1 kg/m(2)), 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. RESULTS: 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. CONCLUSIONS: 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.

Early response assessment in prostate carcinoma by ¹8F-fluorothymidine following anticancer therapy with docetaxel using preclinical tumour models.

PURPOSE: The aim of the study was to assess the potential usefulness of 3-deoxy-3-(18)F-fluorothymidine (FLT) as a radiopharmaceutical for imaging the early therapeutic effects of docetaxel (DTX) on tumour proliferation in hormone-refractory prostate cancer (HRPC). METHODS: Cells of the androgen-independent human prostate tumour cell line, 22Rv1, were implanted in athymic male mice. Approximately 3 weeks after cell implantation, the mice were treated with DTX or vehicle. Before and after the treatment, the mice were imaged with a microPET-Focus-F120 scanner (Concorde Microsystems, Knoxville, TN, USA) using FLT and (18)F-fluorodeoxyglucose (FDG). Tracer accumulations in the tumours were then analysed and compared with the proliferation activity and apoptotic index of the tumours. In a separate cell study, 22Rv1 cells were treated with DTX, then incubated with FLT or FDG and examined for their tracer uptake. RESULTS: The microPET imaging showed a significant decrease of FLT uptake in tumours after administration of DTX, while the changes of FDG uptake were minimal. Immunohistochemical analysis of the tumours revealed that the changes of FLT uptake were well correlated with those of proliferation activity but not with the apoptotic index. In vitro studies demonstrated that the significant decrease of FLT uptake in the cells after incubation with DTX correlated with the % S-phase cell fraction, while there were only minimal changes in the prostate-specific antigen concentration of the cell medium and FDG uptake in the cells. CONCLUSION: These results indicate that FLT is a promising tracer for monitoring the early effects of anticancer therapy with DTX in patients with HRPC.

Synthesis and evaluation of 15-(4-(2-[¹8F]Fluoroethoxy)phenyl)pentadecanoic acid: a potential PET tracer for studying myocardial fatty acid metabolism.

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.

Development of [F-18]fluorine-substituted Tanaproget as a progesterone receptor imaging agent for positron emission tomography.

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-[(18)F]Fluoropropyl-Tanaproget ([(18)F]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, [(18)F]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 [(18)F]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.

Radiochemical synthesis, rodent biodistribution and tumor uptake, and dosimetry calculations of [¹¹C] methylated LY2181308.

PURPOSE: The aim of the study was to develop a rapid and reproducible method to label LY2181308, an antisense oligonucleotide to Survivin, with carbon-11 in order to study its in vivo biodistribution and tumor uptake in rodents and its human dosimetry based on baboon data. METHODS: Randomly [¹¹C] methylated LY2181308 was produced with [¹¹C] methyl iodide. The biodistribution was performed in female Sprague-Dawley (SD) rats and EMT-6 tumor-bearing mice in the presence of nonradioactive LY2181308. Human dosimetry calculations were based on baboon PET studies. RESULTS: In SD rats, the kidney and liver were the organs with the most accumulation of radioactivity. Tumor uptake in mice was also relatively high after 5 min and remained constant for up to 1 h. Baboon dosimetry suggested that up to 42 mCi of radioactivity could be administered to human with a dose-limiting organ being the kidneys with a radiation dose of 32 µGy/MBq (0.118 rad/mCi). CONCLUSIONS: [¹¹C] methylated LY2181308 to rodents and baboons showed its biodistribution, tumor uptake, and human dosimetry evaluation. These results should facilitate the understanding of the pharmacokinetics of LY2181308 prior to use as a potential new therapeutic agent in oncology as well as to warrant more in vivo validations as a potentially useful tumor-imaging agent.

Measurement of myocardial fatty acid esterification using [1-11C]palmitate and PET: comparison with direct measurements of myocardial triglyceride synthesis.

BACKGROUND: 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). METHODS AND RESULTS: 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-(11)C]palmitate and PET and compared to the rate of triglyceride (TG) synthesis measured using [1-(13)C]palmitate and tissue sampling. Plasma free fatty acid (FFA) concentration varied approximately 20-fold across groups, with this variation in FFA availability accompanied by a approximately 20-fold range in TG synthesis. MFAE varied approximately 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 approximately 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. CONCLUSIONS: 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.

Assessment of myocardial triglyceride oxidation with PET and 11C-palmitate.

BACKGROUND: 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. METHODS AND RESULTS: 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). CONCLUSIONS: 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).

Fluorine-18 labeling and biodistribution studies on peroxisome proliferator-activated receptor-gamma ligands: potential positron emission tomography imaging agents.

INTRODUCTION: 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. MATERIALS AND METHODS: 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. RESULTS AND DISCUSSION: (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. CONCLUSION: 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.