BOLD-100 inhibited growth of breast cancer cells. Estrogen receptor positive (ER+) breast cancer cells [MCF7, MCF7(2) and MDA-MB-175] and estrogen receptor negative (ER−) breast cancer cells (MDA-MB-231 and MDA-MB-468) were treated with indicated concentrations of BOLD-100 for 72 h and compared to time = 0 (at the onset of treatment). (A) MCF7(2), (B) MCF7, (C) MDA-MB-175, (D) MDA-MB-231 and (E) MDA-MB-468 cells were significantly (* p < 0.05) inhibited by 100 μM BOLD-100. Time-course (24, 48 and 72 h) with 0, 10 or 100 μM BOLD-100 showed significant (* p < 0.04) inhibition of (F) MCF7(2), (G) MDA-MB-175, (H) MDA-MB-231 and (I) MDA-MB-468 cells with 100 μM compared with 0 μM BOLD-100 at 72 h. ANOVA, p < 0.01; * p < 0.05 for conditions in indicated cells compared with control.