Interaction between tris(4-chlorophenyl)methanol and the human androgen receptor in vitro

The interaction between tris(4-chlorophenyl)methanol (TCPM), an environmental contaminant of uncertain origin, and the human androgen receptor was examined in vitro using a previously characterized human androgen receptor reporter gene assay in which PC-3 LUC(AR+) cells respond to 5alpha-dihydrotestosterone (DHT) with enhanced luciferase activity. In two preliminary studies, TCPM (1 microM) had no effect on androgen receptor activation in the absence of DHT (50 pM), but DHT-mediated activation of the androgen receptor was decreased more than 90% by TCPM at 1 microM. This was not due to an effect of TCPM on cell viability since, with TCPM concentrations of 0.1 and 1.0 microM, cell viability was 111 and 102%, respectively, but at 10 microM TCPM, cell viability was reduced to 60% compared with controls. For kinetic studies of the effects of TCPM on androgen receptor activation, DHT was added at 0, 5, 25, 50, 75, 100, 250 and 500 pM and the TCPM concentrations used were 0, 1, 10, 100, 300 and 1000 nM. This range incorporated the levels of TCPM in human adipose tissue, where concentrations up to 55 nM (20 ng/g lipid) have been measured. TCPM increased the value of the K(m(app)) of the androgen receptor for DHT 4-6-fold with little or no effect on the V(max(app)). Slope and intercept replots revealed that TCPM inhibited the DHT-mediated activation of the androgen receptor in a competitive manner with K(i(app)) values of 0.26, 0.26 and 0.20 microM compared with respective K(m(app)) values of 9.8, 3.1 and 3.9 pM. Thus, TCPM is a competitive antagonist of human androgen receptor activation and the value of the K(i(app)) indicates that TCPM would be approximately 10-50 times more potent as an inhibitor than the previously identified androgen receptor antagonists p,p'-DDE and vinclozilin and also, the K(i(app)) values (200-260 nM) are very close to the concentration of TCPM found in the adipose tissue of some humans (55 nM).