Synthesis and biological evaluation of [¹⁸F]bicalutamide, 4-[⁷⁶Br]bromobicalutamide, and 4-[⁷⁶Br]bromo- thiobicalutamide as non-steroidal androgens for prostate cancer imaging

Androgen receptors (AR) are overexpressed in most primary and metastatic prostate cancers. To develop a nonsteroidal AR-mediated imaging agent, we synthesized and radiolabeled several analogs of the potent antiandrogen bicalutamide: [¹⁸F]bicalutamide, 4-[⁷⁶Br] bromobicalutamide, and [⁷⁶Br]bromo-thiobicalutamide. Two of these analogs, 4-[⁷⁶Br]bromobicalutamide and [⁷⁶Br]bromo- thiobicalutamide, were found to have a substantially increased affinity for the androgen receptor (AR) compared to that of bicalutamide. The synthesis of [ ¹⁸F]bicalutamide utilized a pseudocarrier approach to effect addition of a carbanion generated from tracer-level amounts of a radiolabeled precursor to an unlabeled carbonyl precursor. 4-[⁷⁶Br]Bromobicalutamide and [⁷⁶Br]bromo-thiobicalutamide were labeled through electrophilic bromination of a tributylstannane precursor. The former could be prepared in high specific activity, and its tissue distribution was tested in vivo. Androgen target tissue uptake was evident in castrated adult male rats; however, in DES-treated, AR-positive, tumor-bearing male mice, tumor uptake was low.