Cells were cultured in IMEM with 10% charcoal-stripped serum medium (CSSM) without phenol red and with 600 µg/ml of G418 for 4 days before plating. Cells (100, 000) were seeded in 100 mm dishes and, 24 hrs later, were exposed for 3 days to the specific treatment. (A), antiproliferative effect of increasing concentrations of letrozole in the presence of 25 nM of androstenedione (AD) on MCF-7/Ac1 cell growth (left) and cell cycle distribution (right). Cell growth is expressed as the percentage of the cells compared with the control cells (25 nM AD treated cells, 575,000 cells at day 3). Columns, mean of two to three experiments, each in triplicates; bars, S.D. *, P<0.05, when compared to cells only treated with 25 nM AD; n.s, not significant. CSSM, untreated cells cultured in charcoal-stripped serum medium without phenol red and with 600 µg/ml of G418. (B), antiproliferative effect of increasing concentrations of anastrozole in the presence of 25 nM of androstenedione (AD) on MCF-7/Ac1 cell growth (left) and cell cycle distribution (right). (C), antiproliferative effect of increasing concentrations of exemestane in the presence of 25 nM of androstenedione (AD) on MCF-7/Ac1 cell growth (left) and cell cycle distribution (right).