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The present study describes the analysis of amino acid transporters ASCT1, ASCT2, LAT1, and xc− in breast cancer under normoxic and hypoxic conditions. [18F]FDOPA-PET and [18F]FSPG-PET were used as imaging biomarkers to probe l-type amino acid transporter (LAT1) and cystine-glutamate antiporter (xc−) in breast cancer models. LAT1 and xc− transporters were studied under normoxic and hypoxic conditions with radiotracers [18F]FDOPA and [18F]FSPG in estrogen receptor–positive (ER+) MCF7 and triple-negative MDA-MB231 cells and in human mammary epithelial MCF10A control cells. Protein expression was analyzed using Western blot and immunohistochemistry. ASCT1 protein expression levels were comparable in all three cell lines, while noticeable ASCT2 expression levels were only found in MCF10A control cells. Higher LAT1 protein expression was detected in ER+ MCF7 cells. High xc− protein expression levels were detected in MDA-MB231 cells. Uptake of [18F]FDOPA through LAT1 was significantly higher in MCF7 versus MDA-MB231 cells, while the uptake of [18F]FSPG through xc− resulted in the opposite confirming expression and functional differences for both amino acid transporters in different breast cancer models. Hypoxia significantly increased [18F]FDOPA uptake in MCF7 cells and [18F]FSPG uptake in MDA-MB231 cells. In vivo PET imaging revealed substantially higher tumor uptake of [18F]FDOPA in MCF7 tumors as well as [18F]FSPG uptake in MDA-MB231 tumors confirming differences detected in vitro. ER+ breast cancer cells express higher levels of amino acid transporter LAT1, whereas triple-negative breast cancer cells express more xc−. Cellular uptake and PET imaging experiments with [18F]FDOPA and [18F]FSPG confirmed functional LAT1 and xc− expression profiles. There was initial evidence that hypoxia regulates the function of both amino acid transporters in breast cancer. The results further indicated that [18F]FDOPA and [18F]FSPG are suitable radiotracer to distinguish between ER+ and triple-negative breast cancer types.

Elevated proliferation rates in cancer can be visualized with positron emission tomography (PET) using 3′-deoxy-3′-l-[18F]fluorothymidine ([18F]FLT). This study investigates whether [18F]FLT transp...

Radiolabeled peptides play a central role in nuclear medicine as radiotheranostics for targeted imaging and therapy of cancer. We have recently proposed the use of metabolically stabilized GRPR antagonist BBN2 for radiolabeling withDOTA-Ava-BBN2 was radiolabeled with radiometalsRadiopeptides [Comparison ofThe favorable PET imaging performance of [

The present study describes the analysis of amino acid transporters ASCT1, ASCT2, LAT1, and xLAT1 and xASCT1 protein expression levels were comparable in all three cell lines, while noticeable ASCT2 expression levels were only found in MCF10A control cells. Higher LAT1 protein expression was detected in ER+ MCF7 cells. High xER+ breast cancer cells express higher levels of amino acid transporter LAT1, whereas triple-negative breast cancer cells express more x

Elevated growth in breast cancer (BC) activates hypoxia-inducible factor (HIF1α) and downstream, facilitative glucose transporter 1 (GLUT1), which can be visualized with 2-deoxy-2-[18F]fluoro-d-glucose ([18F]FDG). GLUT5 (fructose) and GLUT2 (glucose/fructose) might provide alternative targets for BC imaging as to why effects of hypoxia on GLUT1/2/5 levels and function were examined in human BC models. GLUT1/2/5 and HIF1α mRNA was analyzed in BC patient biopsies. In MCF10A, MCF7, and MDA-MB231 cells, [18F]FDG, 6-deoxy-6-[18F]fluoro-d-fructose (6-[18F]FDF) and [18F]-fluoroazomycin arabinoside were used in radiotracer experiments, whereas GLUT1/2/5 mRNA was analyzed with real-time PCR and protein levels determined via Western blot/immunohistochemistry. Positron emission tomography imaging was performed in MCF7 and MDA-MB231 tumor-bearing mice. Glucose/fructose/cytochalasin B reduced cellular 6-[18F]FDF uptake by 50%, indicating functional involvement of GLUT2. With GLUT5 staining lower than GLUT1, 6-[18F]FDF revealed lower uptake than [18F]FDG [standardized uptake value (SUV)6-[18F]FDF, 120 min 0.77 ± 0.06 vs. SUV[18F]FDG, 120 min 1.08 ± 0.07] in MDA-MB231 tumors and was blocked by 20% with cytochalasin B after 10 min. Whereas correspondence between 6-[18F]FDF uptake and GLUT5 protein was low, high GLUT2 levels were detected in all cell lines and tumor models. Besides GLUT1, GLUT5 seems to be regulated under hypoxia on the molecular and functional level. Additionally, results strongly support a functional involvement of GLUT2 in fructose metabolism, possibly by compensating for the weaker expression and function of GLUT5 in BC.-Hamann, I., Krys, D., Glubrecht, D., Bouvet, V., Marshall, A., Vos, L., Mackey, J. R., Wuest, M., Wuest, F. Expression and function of hexose transporters GLUT1, GLUT2, and GLUT5 in breast cancer-effects of hypoxia.

Use of [18F]FDG-positron emission tomography (PET) in clinical breast cancer (BC) imaging is limited mainly by insufficient expression levels of facilitative glucose transporter (GLUT)1 in up to 50% of all patients. Fructose-specific facilitative hexose transporter GLUT5 represents an alternative biomarker for PET imaging of hexose metabolism in BC. The goal of the present study was to compare the uptake characteristics of selected hexose-based PET radiotracers in murine BC model EMT6. Uptake of 1-deoxy-1-[18F]fluoro-d-fructose (1-[18F]FDF), 6-deoxy-6-[18F]fluoro-d-fructose (6-[18F]FDF), 1-deoxy-1-[18F]fluoro-2,5-anhydro-mannitol (1-[18F]FDAM), 2-deoxy-2-[18F]fluoro-d-glucose (2-[18F]FDG), and 6-deoxy-6-[18F]fluoro-d-glucose (6-[18F]FDG) was studied in EMT6 cells, tumors, and muscle and correlated to GLUT1 and GLUT5 expression levels. Fructose-derivative 6-[18F]FDF revealed greater tumor uptake than did structural analog 1-[18F]FDF, whereas 1-[18F]FDAM with locked anomeric configuration showed similar low tumor uptake to that of 1-[18F]FDF. Glucose-derivative 6-[18F]FDG reached maximum tumor uptake at 20 minutes, with no further accumulation over time. Uptake of 2-[18F]FDG was greatest and continuously increasing owing to metabolic trapping through phosphorylation by hexokinase II. In EMT6 tumors, GLUT5 mRNA expression was 20,000-fold lower compared with GLUT1. Whereas the latter was much greater in tumor than in muscle tissue (GLUT1 50:1), the opposite was found for GLUT5 mRNA expression (GLUT5 1:6). GLUT5 protein levels were higher in tumor versus muscle tissue as determined by Western blot and immunohistochemistry. Our data suggest that tumor uptake of fructose metabolism-targeting radiotracers 1-[18F]FDF, 6-[18F]FDF, and 1-[18F]FDAM does not correlate with GLUT5 mRNA levels but is linked to GLUT5 protein levels. In conclusion, our results highlight the importance of detailed biochemical studies on GLUT protein expression levels in combination with PET imaging studies for functional characterization of GLUTs in BC.