Purpose

Quantitative in vivo [¹⁸F]-(2S,4R)4-fluoroglutamine ([¹⁸F]4-FGln or more simply [¹⁸F]FGln) metabolic kinetic parameters are compared with activity levels of glutamine metabolism in different types of hepatocellular carcinoma (HCC).

Methods

For this study, we used two transgenic mouse models of HCC induced by protooncogenes, MYC, and MET. Biochemical data have shown that tumors induced by MYC have increased levels of glutamine metabolism compared to those induced by MET. One-hour dynamic [¹⁸F]FGln PET data were acquired and reconstructed for fasted MYC mice (n = 11 tumors from 7 animals), fasted MET mice (n = 8 tumors from 6 animals), fasted FVBN controls (n = 8 normal liver regions from 6 animals), nonfasted MYC mice (n = 16 tumors from 6 animals), and nonfasted FVBN controls (n = 8 normal liver regions from 3 animals). The influx rate constants (K ₁) using the one-tissue compartment model were derived for each tumor with the left ventricular blood pool input function.

Results

Influx rate constants were significantly higher for MYC tumors (K ₁ = 0.374 ± 0.133) than for MET tumors (K ₁ = 0.141 ± 0.058) under fasting conditions (P = 0.0002). Rate constants were also significantly lower for MET tumors (K ₁ = 0.141 ± 0.135) than normal livers (K ₁ = 0.332 ± 0.179) under fasting conditions (P = 0.0123). Fasting conditions tested for MYC tumors and normal livers did not result in any significant difference with P values > 0.005.

Conclusion

Higher influx rate constants corresponded to elevated levels of glutamine metabolism as determined by biochemical assays. The data showed that there is a distinctive difference in glutamine metabolism between MYC and MET tumors. Our study has demonstrated the potential of [¹⁸F]FGln PET imaging as a tool to assess glutamine metabolism in HCC tumors in vivo with a caution that it may not be able to clearly distinguish HCC tumors from normal liver tissue.

Unlabelled

Myocardial metabolic and perfusion imaging is a vital tool for understanding the physiologic consequences of heart failure. We used PET imaging to examine the longitudinal kinetics of (18)F-FDG and 14(R,S)-(18)F-fluoro-6-thia-heptadecanoic acid ((18)F-FTHA) as analogs of glucose and fatty acid (FA) to quantify metabolic substrate shifts with the spontaneously hypertensive rat (SHR) as a model of left ventricular hypertrophy (LVH) and failure. Myocardial perfusion and left ventricular function were also investigated using a newly developed radiotracer (18)F-fluorodihydrorotenol ((18)F-FDHROL).

Methods

Longitudinal dynamic electrocardiogram-gated small-animal PET/CT studies were performed with 8 SHR and 8 normotensive Wistar-Kyoto (WKY) rats over their life cycle. We determined the myocardial influx rate constant for (18)F-FDG and (18)F-FTHA (Ki(FDG) and Ki(FTHA), respectively) and the wash-in rate constant for (18)F-FDHROL (K1(FDHROL)). (18)F-FDHROL data were also used to quantify left ventricular ejection fraction (LVEF) and end-diastolic volume (EDV). Blood samples were drawn to independently measure plasma concentrations of glucose, insulin, and free fatty acids (FFAs).

Results

Ki(FDG) and Ki(FTHA) were higher in SHRs than WKY rats (P < 3 × 10(-8) and 0.005, respectively) independent of age. A decrease in Ki(FDG) with age was evident when models were combined (P = 0.034). The SHR exhibited higher K1(FDHROL) (P < 5 × 10(-6)) than the control, with no age-dependent trends in either model (P = 0.058). Glucose plasma concentrations were lower in SHRs than controls (P < 6 × 10(-12)), with an age-dependent rise for WKY rats (P < 2 × 10(-5)). Insulin plasma concentrations were higher in SHRs than controls (P < 3 × 10(-3)), with an age-dependent decrease when models were combined (P = 0.046). FFA levels were similar between models (P = 0.374), but an increase with age was evident only in SHR (P < 7 × 10(-6)).

Conclusion

The SHR exhibited alterations in myocardial substrate use at 8 mo characterized by increased glucose and FA utilizations. At 20 mo, the SHR had LVH characterized by decreased LVEF and increased EDV, while simultaneously sustaining higher glucose and similar FA utilizations (compared with WKY rats), which indicates maladaptation of energy substrates in the failing heart. Elevated K1(FDHROL) in the SHR may reflect elevated oxygen consumption and decreased capillary density in the hypertrophied heart. From our findings, metabolic changes appear to precede mechanical changes of LVH progression in the SHR model.

Unlabelled

Myocardial metabolic and perfusion imaging is a vital tool for understanding the physiologic consequences of heart failure. We used PET imaging to examine the longitudinal kinetics of (18)F-FDG and 14(R,S)-(18)F-fluoro-6-thia-heptadecanoic acid ((18)F-FTHA) as analogs of glucose and fatty acid (FA) to quantify metabolic substrate shifts with the spontaneously hypertensive rat (SHR) as a model of left ventricular hypertrophy (LVH) and failure. Myocardial perfusion and left ventricular function were also investigated using a newly developed radiotracer (18)F-fluorodihydrorotenol ((18)F-FDHROL).

Methods

Longitudinal dynamic electrocardiogram-gated small-animal PET/CT studies were performed with 8 SHR and 8 normotensive Wistar-Kyoto (WKY) rats over their life cycle. We determined the myocardial influx rate constant for (18)F-FDG and (18)F-FTHA (Ki(FDG) and Ki(FTHA), respectively) and the wash-in rate constant for (18)F-FDHROL (K1(FDHROL)). (18)F-FDHROL data were also used to quantify left ventricular ejection fraction (LVEF) and end-diastolic volume (EDV). Blood samples were drawn to independently measure plasma concentrations of glucose, insulin, and free fatty acids (FFAs).

Results

Ki(FDG) and Ki(FTHA) were higher in SHRs than WKY rats (P < 3 × 10(-8) and 0.005, respectively) independent of age. A decrease in Ki(FDG) with age was evident when models were combined (P = 0.034). The SHR exhibited higher K1(FDHROL) (P < 5 × 10(-6)) than the control, with no age-dependent trends in either model (P = 0.058). Glucose plasma concentrations were lower in SHRs than controls (P < 6 × 10(-12)), with an age-dependent rise for WKY rats (P < 2 × 10(-5)). Insulin plasma concentrations were higher in SHRs than controls (P < 3 × 10(-3)), with an age-dependent decrease when models were combined (P = 0.046). FFA levels were similar between models (P = 0.374), but an increase with age was evident only in SHR (P < 7 × 10(-6)).

Conclusion

The SHR exhibited alterations in myocardial substrate use at 8 mo characterized by increased glucose and FA utilizations. At 20 mo, the SHR had LVH characterized by decreased LVEF and increased EDV, while simultaneously sustaining higher glucose and similar FA utilizations (compared with WKY rats), which indicates maladaptation of energy substrates in the failing heart. Elevated K1(FDHROL) in the SHR may reflect elevated oxygen consumption and decreased capillary density in the hypertrophied heart. From our findings, metabolic changes appear to precede mechanical changes of LVH progression in the SHR model.

The increased proteolytic activity of membrane-bound and secreted proteases on the surface of cancer cells and in the transformed stroma is a common characteristic of aggressive metastatic prostate cancer. We describe here the development of an active site-specific probe for detecting a secreted peritumoral protease expressed by cancer cells and the surrounding tumor microenvironment. Using a human fragment antigen-binding phage display library, we identified a human antibody termed U33 that selectively inhibited the active form of the protease urokinase plasminogen activator (uPA, PLAU). In the full-length immunoglobulin form, U33 IgG labeled with near-infrared fluorophores or radionuclides allowed us to noninvasively detect active uPA in prostate cancer xenograft models using optical and single-photon emission computed tomography imaging modalities. U33 IgG labeled with (111)In had a remarkable tumor uptake of 43.2% injected dose per gram (%ID/g) 72 hours after tail vein injection of the radiolabeled probe in subcutaneous xenografts. In addition, U33 was able to image active uPA in small soft-tissue and osseous metastatic lesions using a cardiac dissemination prostate cancer model that recapitulated metastatic human cancer. The favorable imaging properties were the direct result of U33 IgG internalization through an uPA receptor-mediated mechanism in which U33 mimicked the function of the endogenous inhibitor of uPA to gain entry into the cancer cell. Overall, our imaging probe targets a prostate cancer-associated protease, through a unique mechanism, allowing for the noninvasive preclinical imaging of prostate cancer lesions.

Components of the plasminogen activation system, which are overexpressed in aggressive breast cancer subtypes, offer appealing targets for development of new diagnostics and therapeutics. By comparing gene expression data in patient populations and cultured cell lines, we identified elevated levels of the urokinase plasminogen activation receptor (uPAR, PLAUR) in highly aggressive breast cancer subtypes and cell lines. Recombinant human anti-uPAR antagonistic antibodies exhibited potent binding in vitro to the surface of cancer cells expressing uPAR. In vivo these antibodies detected uPAR expression in triple negative breast cancer (TNBC) tumor xenografts using near infrared imaging and (111)In single-photon emission computed tomography. Antibody-based uPAR imaging probes accurately detected small disseminated lesions in a tumor metastasis model, complementing the current clinical imaging standard (18)F-fluorodeoxyglucose at detecting non-glucose-avid metastatic lesions. A monotherapy study using the antagonistic antibodies resulted in a significant decrease in tumor growth in a TNBC xenograft model. In addition, a radioimmunotherapy study, using the anti-uPAR antibodies conjugated to the therapeutic radioisotope (177)Lu, found that they were effective at reducing tumor burden in vivo. Taken together, our results offer a preclinical proof of concept for uPAR targeting as a strategy for breast cancer diagnosis and therapy using this novel human antibody technology.

Using longitudinal micro positron emission tomography (microPET)/computed tomography (CT) studies, we quantified changes in myocardial metabolism and perfusion in spontaneously hypertensive rats (SHRs), a model of left ventricular hypertrophy (LVH). Fatty acid and glucose metabolism were quantified in the hearts of SHRs and Wistar-Kyoto (WKY) normotensive rats using long-chain fatty acid analog ¹⁸F-fluoro-6-thia heptadecanoic acid (¹⁸F-FTHA) and glucose analog ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG) under normal or fasting conditions. We also used ¹⁸F-fluorodihydrorotenol (¹⁸F-FDHROL) to investigate perfusion in their hearts without fasting. Rats were imaged at 4 or 5 times over their life cycle. Compartment modeling was used to estimate the rate constants for the radiotracers. Blood samples were obtained and analyzed for glucose and free fatty acid concentrations. SHRs demonstrated no significant difference in ¹⁸F-FDHROL wash-in rate constant ( P = .1) and distribution volume ( P = .1), significantly higher ¹⁸F-FDG myocardial influx rate constant ( P = 4×10^-8), and significantly lower ¹⁸F-FTHA myocardial influx rate constant ( P = .007) than WKYs during the 2009-2010 study without fasting. SHRs demonstrated a significantly higher ¹⁸F-FDHROL wash-in rate constant ( P = 5×10^-6) and distribution volume ( P = 3×10^-8), significantly higher ¹⁸F-FDG myocardial influx rate constant ( P = 3×10^-8), and a higher trend of ¹⁸F-FTHA myocardial influx rate constant (not significant, P = .1) than WKYs during the 2011-2012 study with fasting. Changes in glucose plasma concentrations were generally negatively correlated with corresponding radiotracer influx rate constant changes. The study indicates a switch from preferred fatty acid metabolism to increased glucose metabolism with hypertrophy. Increased perfusion during the 2011-2012 study may be indicative of increased aerobic metabolism in the SHR model of LVH.