Antiproliferative effects of RAD001, 4-OH tamoxifen, and letrozole in endocrine sensitive and resistant breast cancer cell lines. Cells were treated with a standard concentration of androstenedione (10 nM) and doubling concentrations of RAD001 ± letrozole (100 nM) or 4OH-tamoxifen (10 nM). After 6 days of treatment, cell numbers were analyzed by using a Coulter counter. (A, B) MCF7-AROM1. (C, D) BT474-AROM3. (E) LTED cells treated with doubling concentrations of RAD001 in the absence of exogenous E2. (F) LTED cells treated with a standard concentration of E2 (0.01 nM) and doubling concentrations of RAD001 ± 4-OH tamoxifen (10 nM). Data are expressed as fold-change relative to DCC-FBS to show the increase in proliferation in response to androstenedione. Data shown are representative of three independent experiments. Error bars represent ± SEM.