Organ-specific dietary fatty acid uptake in humans using positron emission tomography coupled to computed tomography.

A noninvasive method to determine postprandial fatty acid tissue partition may elucidate the link between excess dietary fat and type 2 diabetes. We hypothesized that the positron-emitting fatty acid analog 14(R,S)-[(18)F]fluoro-6-thia-heptadecanoic acid ((18)FTHA) administered orally during a meal would be incorporated into chylomicron triglycerides, allowing determination of interorgan dietary fatty acid uptake. We administered (18)FTHA orally at the beginning of a standard liquid meal ingested in nine healthy men. There was no significant (18)FTHA uptake in the portal vein and the liver during the 1st hour. Whole body PET/CT acquisition revealed early appearance of (18)FTHA in the distal thoracic duct, reaching a peak at time 240 min. (18)FTHA mean standard uptake value increased progressively in the liver, heart, quadriceps, and subcutaneous and visceral adipose tissues between time 60 and 240 min. Most circulating (18)F activity between time 0 and 360 min was recovered into chylomicron triglycerides. Using Triton WR-1339 treatment in rats that received (18)FTHA by gavage, we confirmed that >90% of this tracer reached the circulation as triglycerides. This novel noninvasive method to determine tissue dietary fatty acid distribution in humans should prove useful in the study of the mechanisms leading to lipotoxicity.

Abnormal in vivo myocardial energy substrate uptake in diet-induced type 2 diabetic cardiomyopathy in rats.

The purpose of this study was to determine in vivo myocardial energy metabolism and function in a nutritional model of type 2 diabetes. Wistar rats rendered insulin-resistant and mildly hyperglycemic, hyperinsulinemic, and hypertriglyceridemic with a high-fructose/high-fat diet over a 6-wk period with injection of a small dose of streptozotocin (HFHFS) and control rats were studied using micro-PET (microPET) without or with a euglycemic hyperinsulinemic clamp. During glucose clamp, myocardial metabolic rate of glucose measured with [(18)F]fluorodeoxyglucose ([(18)F]FDG) was reduced by approximately 81% (P < 0.05), whereas myocardial plasma nonesterified fatty acid (NEFA) uptake as determined by [(18)F]fluorothia-6-heptadecanoic acid ([(18)F]FTHA) was not significantly changed in HFHFS vs. control rats. Myocardial oxidative metabolism as assessed by [(11)C]acetate and myocardial perfusion index as assessed by [(13)N]ammonia were similar in both groups, whereas left ventricular ejection fraction as assessed by microPET was reduced by 26% in HFHFS rats (P < 0.05). Without glucose clamp, NEFA uptake was approximately 40% lower in HFHFS rats (P < 0.05). However, myocardial uptake of [(18)F]FTHA administered by gastric gavage was significantly higher in HFHFS rats (P < 0.05). These abnormalities were associated with reduced Glut4 mRNA expression and increased Cd36 mRNA expression and mitochondrial carnitine palmitoyltransferase 1 activity (P < 0.05). HFHFS rats display type 2 diabetes complicated by left ventricular contractile dysfunction with profound reduction in myocardial glucose utilization, activation of fatty acid metabolic pathways, and preserved myocardial oxidative metabolism, suggesting reduced myocardial metabolic efficiency. In this model, increased myocardial fatty acid exposure likely occurs from circulating triglyceride, but not from circulating plasma NEFA.

Mechanism of reduced myocardial glucose utilization during acute hypertriglyceridemia in rats.

PURPOSE: The purpose of the research is to study the effect of acute inhibition of intravascular lipolysis on myocardial substrate selection during hypertriglyceridemia using in vivo radiotracer analysis and positron emission tomography. PROCEDURES: We induced acute hypertriglyceridemia in vivo using an intravenous infusion of Intralipid 20% (IL) without and with acute inhibition of fatty acid delivery from circulating triglycerides with injection of Triton WR-1339 (TRI) during a euglycemic-hyperinsulinemic clamp in Wistar rats. We determined the effect of TRI on myocardial uptake of circulating triglycerides and free fatty acids using intravenous injection of [(3)H]-triolein and [(14)C]-bromopalmitate, respectively. Myocardial blood flow, oxidative metabolism, and metabolic rate of glucose (MMRG) were determined using micro-positron emission tomography (microPET) with [(13)N]-ammonia, [(11)C]-acetate, and 2-deoxy-2-[F-18]fluoro-D: -glucose (FDG). RESULTS: TRI reduced myocardial incorporation of [(3)H]-triolein but not [(14)C]-bromopalmitate showing that it selectively reduces myocardial fatty acid delivery from circulating triglycerides but not from free fatty acids. IL reduced myocardial blood flow and MMRG by 37% and 56%, respectively, but did not affect myocardial oxidative metabolism. TRI did not abolish the effect of IL on myocardial blood flow and MMRG. CONCLUSIONS: Hypertriglyceridemia acutely reduces myocardial blood flow and MMRG in rats, but this effect is not explained by increased myocardial fatty acid delivery through intravascular triglyceride lipolysis.

Intratumoral 18F-FLT infusion in metabolic targeted radiotherapy.

BACKGROUND: The goal of targeted radiotherapy (TRT) is to administer radionuclides to tumor cells, while limiting radiation exposure to normal tissues. 3'-Deoxy-3'-[18F]-fluorothymidine (18F-FLT) is able to target tumor cells and emits a positron with energy appropriate for local (~ 1 mm range) radiotherapy. In the present work, we investigated the potential of TRT with a local administration of 18F-FLT alone or in combination with 5-fluorouracil (5FU), which acts as a chemotherapeutic agent and radiosensitizer. Treatment efficiency of 18F-FLT combined or not with 5FU was evaluated by intratumoral (i.t.) infusion into subcutaneous HCT116 colorectal tumors implanted in nu/nu mice. The tumor uptake and kinetics of 18F-FLT were determined and compared to 2-deoxy-2-[18F]-fluoro-D-glucose (18F-FDG) by dynamic positron emission tomography (PET) imaging following i.t. injection. The therapeutic responses of 18F-FLT alone and with 5FU were evaluated and compared with 18F-FDG and external beam radiotherapy (EBRT). The level of prostaglandin E2 (PGE2) biosynthesis was measured by liquid chromatography/tandem mass spectrometry (LC/MS/MS) in order to determine the level of inflammation to healthy tissues surrounding the tumor, after i.t. injection of 18F-FLT, and compared to EBRT. RESULTS: We found that i.t. administration of 18F-FLT offers (1) the highest tumor-to-muscle uptake ratio not only in the injected tumor, but also in distant tumors, suggesting potential for concurrent metastases treatment and (2) a sixfold gain in radiotherapeutic efficacy in the primary tumor relative to EBRT, which can be further enhanced with concurrent i.t. administration of the radiosensitizer 5FU. While EBRT stimulated PGE2 production in peritumoral tissues, no significant increase of PGE2 was measured in this area following i.t. administration of 18F-FLT. CONCLUSION: Considering the biochemical stability of 18F-FLT and the physical properties of localized 18F, this study shows that TRT via intratumoral infusion of 18F-FLT and 5FU could provide a new effective treatment option for solid tumors. Using this approach in a colorectal tumor model, the tumor and its metastases could be efficiently irradiated locally with much lower doses absorbed by healthy tissues than with i.t. administration of 18F-FDG or conventional EBRT.

[11C] acetoacetate utilization by breast and prostate tumors: a PET and biodistribution study in mice.

PURPOSE: A significant positive correlation has been observed between ketone body availability and their uptake by tumor cells. Our objective was to evaluate [11C]acetoacetate as a potential tracer of ketone body utilization by breast and prostate tumors and to compare it with [11C]acetate. METHODS: Biodistribution studies were performed with [11C]acetoacetate and [11C]acetate in mice bearing breast or prostate tumors. The percentage of the injected dose accumulated per gram of tissue was determined. These results were complemented by dynamic positron emission tomography (PET) imaging of the radiotracer uptake and dosimetry calculations. RESULTS: [11C]Acetoacetate uptake was optimal between 5 and 30 min, with maximal uptake of 2.72, 2.42, 2.54, and 2.19% injected dose (%ID)/g for MC7-L1, MC4-L2, PC3, and LN-CaP tumors respectively. Tumor retention for [11C]acetoacetate tended to be higher than [11C]acetate, but this did not reach statistical significance. [11C]Acetate uptake was reached within 15 min with optimal uptake of 1.25, 2.30, and 0.96%ID/g for MC7-L1, MC4-L2, and PC-3 tumors, respectively. CONCLUSIONS: We observed a moderate uptake of [11C]acetoacetate in breast and prostate tumors with low background activity due to rapid elimination of this tracer. Further studies are warranted to determine if this tracer can detect slow-growing breast and prostate cancers in the clinical setting.

Improved Estrogen Receptor Assessment by PET Using the Novel Radiotracer 18F-4FMFES in Estrogen Receptor-Positive Breast Cancer Patients: An Ongoing Phase II Clinical Trial.

After encouraging preclinical and human dosimetry results for the novel estrogen receptor (ER) PET radiotracer 4-fluoro-11ß-methoxy-16α-18F-fluoroestradiol (18F-4FMFES), a phase II clinical trial was initiated to compare the PET imaging diagnostic potential of 18F-4FMFES with that of 16α-18F-fluoroestradiol (18F-FES) in ER-positive (ER+) breast cancer patients. Methods: Patients diagnosed with ER+ breast cancer (n = 31) were recruited for this study, including 6 who underwent mastectomy or axillary node dissection. For each patient, 18F-FES and 18F-4FMFES PET/CT scans were done sequentially (within a week) and in random order. One hour after injection of either radiotracer, a head-to-thigh static scan with a 2-min acquisition per bed position was obtained. Blood samples were taken at different times after injection to assess each tracer metabolism by reverse-phase thin-layer chromatography. The SUVmean of nonspecific tissues and the SUVmax of the tumor were evaluated for each detected lesion, and tumor-to-nonspecific organ ratios were calculated. Results: Blood metabolite analysis 60 min after injection of the tracer showed a 2.5-fold increase in metabolic stability of 18F-4FMFES over 18F-FES. Although for most foci 18F-4FMFES PET had an SUVmax similar to that of 18F-FES PET, tumor contrast improved substantially in all cases. Lower uptake was consistently observed in nonspecific tissues for 18F-4FMFES, notably a 4-fold decrease in blood-pool activity as compared with 18F-FES. Consequently, image quality was considerably improved using 18F-4FMFES, with lower overall background activity. As a result, 18F-4FMFES successfully identified 9 more lesions than 18F-FES. Conclusion: This phase II study with ER+ breast cancer patients showed that 18F-4FMFES PET achieves a lower nonspecific signal and better tumor contrast than 18F-FES PET, resulting in improved diagnostic confidence and lower false-negative diagnoses.

Automated synthesis of 11C-acetoacetic acid, a key alternate brain fuel to glucose.

An automated, one-pot radio-synthesis module for the routine preparation of 1-[(11)C]acetoacetic acid has been developed. The enolate anion of acetone was reacted with [(11)C]CO(2) in tetrahydrofuran (THF), followed by hydrolysis and purification by ion-exchange chromatography. The total synthesis time was 18 min and radiochemical yield was 34% after decay correction. HPLC analysis showed < or =3% impurities while residual THF (< or =200 ppm) and ethanol (< or =500 ppm) were well under the tolerable limits for human studies.

Assessment of the novel estrogen receptor PET tracer 4-fluoro-11ß-methoxy-16α-[(18)F]fluoroestradiol (4FMFES) by PET imaging in a breast cancer murine model.

PURPOSE: The aim of this study was to compare the in vivo stability, uptake, and positron emission tomography (PET) imaging performance of a novel estrogen receptor PET tracer, 4-fluoro-11ß-methoxy-16α-[(18)F]fluoroestradiol (4FMFES), with 16α-[(18)F]fluoroestradiol (FES). PROCEDURES: MC7-L1 and MC4-L2 (ER+) cell lines and their ERα-knockdown variants (ERαKD) were implanted subcutaneously in Balb/c mice. After 21 days, mice were imaged using either FES or 4FMFES. One hour post-injection, static images were acquired for 30 min and the tumor %ID/g uptake values were derived. Biodistribution data were also obtained 1 h following the injection of either FES or 4FMFES. Blood samples were taken at different times and analyzed on thin-layer chromatography to quantify the presence of radiometabolites for each radiotracer. To assess specific targeting to the estrogen receptors, mice bearing only ER+ tumors were treated with the competitive ER inhibitor fulvestrant 48 h prior to imaging with 4FMFES. RESULTS: Metabolic stability was found to be similar for both tracers in mice. Both FES and 4FMFES differentiated ER+ tumors from ERαKD tumors in biodistribution and PET imaging studies. 4FMFES achieved a significantly higher %ID/g uptake in ER+ tumors and MC4-L2 ERαKD tumors than FES in the PET imaging studies. Also, tumor-to-background ratio was higher in ER+ tumors using 4FMFES compared to FES. Dissection data showed a significantly higher %ID/g in all tested cell lines and ER-rich tissues using 4FMFES versus FES. Fulvestrant-treated mice had either low or undetectable tumor uptake. CONCLUSION: In a tumor-bearing mouse model, 4FMFES achieves better specific tumor uptake and better contrast than FES, making it a promising candidate for ER imaging.

[18F]-fluoroestradiol quantitative PET imaging to differentiate ER+ and ERα-knockdown breast tumors in mice.

INTRODUCTION: The purpose of this study was to develop a noninvasive model in tumor-bearing mice to investigate the use of 16α-[(18)F]fluoro-17ß-estradiol (FES) positron emission tomography (PET) imaging as a tool to discriminate between tumors having different estrogen receptor (ER) α status. METHODS: MC7-L1 and MC4-L2 murine mammary adenocarcinoma cell lines (ER+) received a small hairpin RNA targeting the ERα gene by lentiviral infection. In vitro assessment of ERα levels of the new cell lines (MC7-L1 and MC4-L2 ERα-knockdown; ERαKD), compared to the parental cell lines, was performed by immunoblotting (-75% ERα protein) and binding assays (-50% estrogen binding). These cell lines were implanted subcutaneously in Balb/c mice and allowed to grow up to a volume of at least 20 mm(3). FES and [(18)F]fluorodeoxyglucose (FDG) PET images were acquired to measure FES and FDG uptake in the various tumors. RESULTS: FES uptake as assessed by PET imaging was 1.06±0.21 percent injected dose per gram of tissue (%ID/g) for MC7-L1 tumors and 0.47±0.08 %ID/g for MC7-L1 ERαKD tumors. MC4-L2 tumors had a FES uptake of 1.03±0.30 %ID/g, whereas its ERαKD equivalent was 0.51±0.19 %ID/g. Each ERαKD tumor had a significantly lower %ID/g value, by ~50%, than its ER+ counterpart. Biodistribution studies confirmed these findings and gave %ID/g values that were not significantly different from PET imaging data. FDG PET showed no significant uptake difference between the ER+ and ERαKD tumors, indicating that the metabolic phenotype of the ERαKD cell lines was not altered. CONCLUSION: FES PET imaging was able to reliably differentiate between tumors having differences in their ERα expression in vivo, in a mouse model. Quantitative data obtained by FES PET were in concordance with biodistribution studies and in vitro assays. It is concluded that FES PET imaging can likely be used to monitor subtle ER status changes during the course of hormone therapy.

Normal postprandial nonesterified fatty acid uptake in muscles despite increased circulating fatty acids in type 2 diabetes.

OBJECTIVE: Postprandial plasma nonesterified fatty acid (NEFA) appearance is increased in type 2 diabetes. Our objective was to determine whether skeletal muscle uptake of plasma NEFA is abnormal during the postprandial state in type 2 diabetes. RESEARCH DESIGN AND METHODS: Thigh muscle blood flow and oxidative metabolism indexes and NEFA uptake were determined using positron emission tomography coupled with computed tomography (PET/CT) with [(11)C]acetate and 14(R,S)-[(18)F]fluoro-6-thia-heptadecanoic acid ((18)FTHA) in seven healthy control subjects (CON) and seven subjects with type 2 diabetes during continuous oral intake of a liquid meal to achieve steady postprandial NEFA levels with insulin infusion to maintain similar plasma glucose levels in both groups. RESULTS: In the postprandial state, plasma NEFA level was higher in type 2 diabetic subjects versus CON (P < 0.01), whereas plasma glucose was at the same level in both groups. Muscle NEFA fractional extraction and blood flow index levels were 56% (P < 0.05) and 24% (P = 0.27) lower in type 2 diabetes, respectively. However, muscle NEFA uptake was similar to that of CON (quadriceps femoris [QF] 1.47 ± 0.23 vs. 1.37 ± 0.24 nmol·g(-1)·min(-1), P = 0.77; biceps femoris [BF] 1.54 ± 0.26 vs. 1.46 ± 0.28 nmol·g(-1)·min(-1), P = 0.85). Muscle oxidative metabolism was similar in both groups. Muscle NEFA fractional extraction and blood flow index were strongly and positively correlated (r = 0.79, P < 0.005). CONCLUSIONS: Postprandial muscle NEFA uptake is normal despite elevated systemic NEFA levels and acute normalization of plasma glucose in type 2 diabetes. Lower postprandial muscle blood flow with resulting reduction in muscle NEFA fractional extraction may explain this phenomenon.

Ultrafast studies of the excited-state dynamics of copper and nickel phthalocyanine tetrasulfonates: potential sensitizers for the two-photon photodynamic therapy of tumors.

In order to evaluate the potential of copper and nickel phthalocyanine tetrasulfonates as sensitizers for two-photon photodynamic therapy, we conducted kinetic femtosecond measurements of transient absorption and bleaching of their excited state dynamics in aqueous solution. Samples were pumped with 620 nm and 310 nm laser light, which allowed us to study relaxation processes from both the first and second singlet (or doublet for the copper phthalocyanine) excited states. A second excitation from the first excited triplet state, approximately 685 and 105 ps after the first excitation for copper and nickel phthalocyanine tetrasulfonate respectively, was the most efficient way to bring the molecules to an upper triplet state. Presumably this highest triplet state can inflict molecular damage on adjacent biomolecules int eh absence of oxygen, resulting in the desired cytotoxic cellular response. Transient absorption spectra at different fixed delays indicate that optimum efficiency would require that the second photon has a wavelength of approximately 750 nm.