Aromatase inhibition in JAr choriocarcinoma cells by 7 alpha-arylaliphatic androgens

The JAr choriocarcinoma cell cultures have demonstrated high levels of aromatase activity and have been useful for assaying a wide variety of aromatase inhibitors for aromatase inhibition in intact cells. Recently, several 7 alpha-arylaliphatic androgens have shown effective inhibition of human placental microsomal aromatase in vitro, with apparent K-i values ranging from 10 to 20 nM. A series of 7 alpha-arylaliphatic androst-4-ene-3,17-dione compounds demonstrated potent competitive inhibition, and 7 alpha-arylaliphatic androsta-1,4-diene-3,17-diones were enzyme-activated irreversible inhibitors. Both series of these potent inhibitors were investigated for the ability to inhibit aromatase activity in JAr cells by measuring the conversion of [1 beta-H-3]-androstenedione to (H2O)-H-3 and unlabelled estrone. JAr cell cultures were incubated for 2 h at 37 degrees C with the aromatase inhibitors at concentrations of 10 pM to 10 mu M, the percentage of enzyme inhibition was determined, and IC50 values for inhibitors were calculated. Both series of synthetic compounds demonstrated good to excellent aromatase inhibition, and the most effective inhibitors in both series were those compounds with a phenylpropyl substituent at the 7 alpha-position of the steroid nucleus. The 7 alpha-arylaliphatic androst-4-ene-3,17-diones exhibited inhibition of JAr aromatase activity with IC50 values from 300 to 434 nM. More potent aromatase inhibition was observed with the 7 alpha-arylaliphatic androsta-1,4-diene-3,17-diones, which exhibited IC50 values from 64 to 232 nM. Enhanced efficacy of steroidal enzyme-activated irreversible inhibitors compared to competitive inhibitors was observed in these studies and is consistent with previous reports. These results suggest that JAr choriocarcinoma cells with high levels of aromatase activity may be useful in differentiating steroidal aromatase inhibitors exhibiting different mechanisms of enzyme inhibition. In summary, the 7 alpha-phenylpropyl androsta-1,4-diene-3,17-dione analogs, which are enzyme-activated irreversible inhibitors, demonstrated the most effective inhibition of aromatase activity present in the JAr cell cultures among the various 7 alpha-arylaliphatic androgens. (C) 1997 Elsevier Science Ltd.