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

Abstract 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 7α-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 7α-arylaliphatic androst-4-ene-3,17-dione compounds demonstrated potent competitive inhibition, and 7α-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 [1β- 3 H]-androstenedione to 3 H 2 O and unlabelled estrone. JAr cell cultures were incubated for 2 h at 37°C with the aromatase inhibitors at concentrations to 10 pM to 10 μM, the percentage of enzyme inhibition was determined, and IC 50 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 7α-position of the steroid nucleus. The 7α-arylaliphatic androst-4-ene-3,17-diones exhibited inhibition of JAr aromatase activity with IC 50 values from 300 to 434 nM. More potent aromatase inhibition was observed with the 7α-arylaliphatic androsta-1,4-diene-3,17-diones, which exhibited IC 50 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 7α-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 7α-arylaliphatic androgens.