Tumor Localization of 16β-18F-Fluoro-5α-Dihydrotestosterone Versus 18F-FDG in Patients with Progressive, Metastatic Prostate Cancer

This trial was an initial assessment of the feasibility, in vivo targeting, and biokinetics of 16β- 1 8 F-fluoro-5α-dihydrotestosterone ( 1 8 F-FDHTI PET in patients with metastatic prostate cancer to assess androgen receptor expression. Methods: Seven patients with progressive clinically metastatic prostate cancer underwent 1 8 F-FDG and 1 8 F-FDHT PET scans in addition to conventional imaging methods. Three patients had their studies repeated 1 mo later, 2 while on testosterone therapy, and the third after treatment with 17-allylamino-17-demethoxygeldanamycin (17-RAG). High-pressure liquid radiochromatography was used to separate 1 8 F-FDHT from radiolabeled metabolites. Lesion-by-lesion comparisons between the 1 8 F-FDHT, 1 8 F-FDG, and conventional imaging methods were performed. Results: Metabolism of 1 8 F-FDHT was rapid, with 80% conversion within 10 min to radiolabeled metabolites that circulated bound to plasma proteins. Tumor uptake was rapid and tumor retention was prolonged. Fifty-nine lesions were identified by conventional imaging methods. 1 8 F-FDG PET was positive in 57 of 59 lesions (97%), with an average lesion maximum standardized uptake value (SUV m a x ) = 5.22. 1 8 F-FDHT PET was positive in 46 of 59 lesions (78%), with the average positive lesion SUV m a x = 5.28. Treatment with testosterone resulted in diminished 1 8 F-FDHT uptake at the tumor site. Conclusion: 1 8 F-FDHT localizes to tumor sites in patients with progressive clinically metastatic prostate cancer and may be a promising agent to analyze antigen receptors and their impact on the clinical management of prostate cancer.