Synthesis and Preliminary Bioevaluation of 99m Tc(CO) 3 -17α-Triazolylandrost-4-Ene-3-One Derivative Prepared via Click Chemistry Route

Abstract

Azolyl steroids are known to manifest antiprostate cancer and antiandrogenic activities. These azolyl steroids have been shown to express affinity toward androgen receptors (ARs) overexpressed on LNCaP (human prostate adenocarcinoma) cell line. Hence, suitably derivatized azolyl steroids can be envisaged as potential vectors for targeting overexpression of ARs in prostate cancer. In the present study, testosterone has been derivatized to 17α-azidoandrost-4-ene-3-one using microwave-mediated azidation of the mesylate. Subsequently, a facile one-pot Cu(I)-catalyzed Click reaction was carried out to synthesize ^99mTc(CO)₃-labeled 17α-triazolylandrost-4-ene-3-one, which was characterized by HPLC. The chemical characterization of ^99mTc(CO)₃-17α-triazolylandrost-4-ene-3-one was carried out by preparing its corresponding rhenium complex using [NEt₄]₂[Re(CO)₃Br₃] precursor. The radiolabeled complex could be prepared in >95% radiochemical yield as determined by HPLC. In vitro studies of ^99mTc(CO)₃-17α-triazolylandrost-4-ene-3-one complex in LNCaP cell lines overexpressing ARs showed binding of 4.95%±1.2%, with inhibition of 8%±0.9%. In vivo biodistribution studies in male Wistar rats have shown uptake in the prostate to the extent of 0.48%±0.19% injected dose/g at 1 hpi and retention therein till 3 hpi. The present study demonstrates a novel and facile one-pot reaction for preparation of ^99mTc-labeled 17α-triazolylandrost-4-ene-3-one complex using Click chemistry. The corresponding Re-analog has been prepared for purpose of comparative characterization with the ^99mTc-labeled complex. The radiosynthetic strategy described in this article can be further extended toward preparation of radiolabeled complexes of other triazolyl steroidal derivatives.