(A) Following 3 days of pretreatment with BEPP or vehicle, MCF7 and MDA-MB-231 cells were treated with 1 or 5 μM 4-OH tamoxifen for an additional 7 days and analyzed at predetermined time points by CellTiter-Glo®. (B) MCF7 cells exhibited decreased proliferation following treatment with 1μM (left) or 5μM (right) 4-OH tamoxifen after pre-treatment with BEPP (green) when compared to cells pre-treated with vehicle before 4-OH tamoxifen (red), or cells treated with vehicle (black) or BEPP (blue) alone throughout. At day 10, overall survival (C) was decreased in BEPP pretreated cells and Annexin V expression levels (D) were increased in BEPP pretreated cells when compared to the other three groups. (E) MDA-MB-231 cells exhibited no significant differences in proliferation following treatment with 1μM (left) or 5μM (right) 4-OH tamoxifen after pre-treatment with BEPP (green), pre-treated with vehicle before 4-OH tamoxifen (red), or cells treated with vehicle (black) or BEPP (blue) alone throughout. At day 10, overall survival (F) and Annexin V expression (G) were not significantly altered in BEPP pretreated cells when compared to the other three groups. *** p<0.001 **p<0.01 *p<0.05 n.s-not significant