In vivo biodistribution of an androgen receptor avid PET imaging agent 7-alpha-fluoro-17 alpha-methyl-5-alpha-dihydrotestosterone ([(18)F]FMDHT) in rats pretreated with cetrorelix, a GnRH antagonist.

Purpose: For this study, we have assessed the in vivo distribution and androgen receptor (AR) seeking properties of an F-18-labeled androgen [(18)F]FMDHT in rats castrated with a GnRH antagonist.

Materials And Methods: The radiochemical synthesis of [(18)F]FMDHT was performed using a previously published method. The radiochemical synthesis provided the desired product in good radiochemical yields and radiochemical purity. In vivo biodistribution studies were performed in chemically castrated rats. The animals were castrated using cetrorelix, a GnRH antagonist. To assess the specificity of [(18)F]FMDHT towards ARs, a separate group of animals was pretreated with a large dose of androgen before the [(18)F]FMDHT injection.

Results: The in vivo biodistribution results show selective uptake of [(18)F]FMDHT in the prostate that ranged from 0.46 + 0.10 %ID/g at 1 h to 0.59 + 0.16 %ID/g at 3 h with prostate to muscle ratio ranging from 8.06 + 2.46 at 1 h to 18.81 + 4.90 at 3 h.

Conclusions: These in vivo distribution studies document a high selectivity and specificity of [(18)F]FMDHT towards AR rich tissues and suggests that [(18)F]FMDHT may be a useful in vivo PET imaging ligand.