Synthesis of C-6 fluoroandrogens: Evaluation of ligands for tumor receptor imaging

Article abstract of DOI:10.1016/0039-128X(95)00009-F

Seven androgens, substituted with fluorine at C-6, were prepared as potential imaging agents for androgen receptor-positive prostate tumors and were evaluated in vitro in terms of their lipophilicity and their relative binding affinities (RBA, relative to R1881 = 100) for the androgen receptor and for sex steroid binding protein.Introduction of a fluorine atom into the C-6 position of an androgen generally decreases binding affinity to the androgen receptor, except in the two cases: 6α-fluoro-19-nor-testosterone RBA = 41.6 versus 30.6 for the unsubstituted steroid) and 6α-fluorotestosterone (RBA = 8.9 versus 6.6).Receptor binding of the C-6 fluoro-androgens is also stereospecific, showing higher binding affinities for the α-epimers compared to the corresponding β-epimers (4:1 - 15:1).Binding affinity to sex steroid binding protein is the lowest with 19-nor-testosterone, which is also the least lipophilic androgen studied.Based on the binding properties of compounds in this series, 6α-fluoro-19-nor-testosterone appears to have the most promise as a tumor imaging agent. - Keywords: C-6-fluoroandrogens; fluorine substitution; relative binding affinity; 6α- and 6β-epimers; log P_o/w; prostate tumors