Mechanisms of cell growth inhibition and cell cycle arrest in human colonic adenocarcinoma cells by dehydroepiandrosterone: role of isoprenoid biosynthesis.

We have previously demonstrated that the chemopreventive agent dehydroepiandrosterone (DHEA) inhibits the isoprenylation of cellular proteins by depletion of endogenous mevalonate. We now report that treatment of HT-29 SF human colonic adenocarcinoma cells with DHEA at concentrations ranging from 12.5 to 200 microM for up to 72 h inhibited growth and arrested cells in the G1 phase of the cell cycle in a time- and dose-dependent manner. Exposure to 25 or 50 microM DHEA also transiently delayed cells in G2M phase after 48 h. Addition of mevalonic acid partially overcame both the growth and cell cycle effects of 25 microM DHEA in the initial 48 h. During prolonged exposure (72 h), the addition of mevalonic acid as well as cholesterol was required to reconstitute cell cycle progression. This suggests that the depletion of endogenous mevalonate and other isoprenoids is involved in DHEA-mediated growth inhibition and cell cycle arrest.