Synthesis and evaluation of fluorine-18 labeled androgens as imaging agents for prostatic tumors

In vivo imaging of prostatic carcinoma has been an attractive goal for many researchers. With the positron emission tomography technique., fluorine-18 labeled androgens will be good candidates for in vivo imaging of prostatic tumors. The authors have prepared nine fluorine substituted androgens and found that six of them have quite high relative binding affinity (RBA, R1881=100) to androgen receptors, 16β-F-DHT (RBA=42.7), 16β-F-T (RBA=2.1), 16β-F-Mib (RBA=26.4), 16β-F-MNT (RBA=38.6), 20-F-Mib (RBA=53.2) and 20-F-R1881 (RBA=13.2), suitable to merit their preparation in fluorine-18 labeled form for in vivo studies. One of them, 20-F-Mib, has been labeled and has showed good uptake in vivo; the prostate to blood and the prostate to muscle (non-target) ratios are both ca. 12 at 4h after injection. This is the first fluorine-18 labeled androgen that shows highly selective uptake by prostate tissue of males rats. A study of structure-activity relationships has also been attempted and is discussed