Mechanistic insights into EB171 anticancer activity in MCF7 and MDA-MB-231 breast cancer cells showing differential...

Breast cancer remains one of the leading causes of cancer-related mortality in women worldwide, with estrogen receptor α (ERα) signaling playing a key role in hormone-dependent tumors. Here, we investigated the molecular basis of the anticancer activity of EB171, an amide derivative of betulonic acid, in breast cancer cell lines differing in ERα status (MCF7 and MDA-MB-231). EB171 preferentially reduced viability and proliferation of ERα-positive MCF7 cells, while showing markedly weaker activity in ERα-negative MDA-MB-231 cells, indicating a context-dependent mechanism of action. Mechanistically, EB171 induced replication stress and DNA double-strand breaks, accompanied by activation of cell cycle checkpoints, cyclin suppression, and p21Waf1/Cip1 upregulation. These effects were associated with mitochondrial dysfunction and activation of predominantly intrinsic apoptotic signaling. Importantly, EB171 reduced ERα protein levels in MCF7 cells without significantly affecting ESR1 mRNA expression. This suggests regulation of ERα at a post-transcriptional level, although the underlying mechanism remains to be determined. Notably, the parent compound betulonic acid exerted weaker effects, highlighting the importance of structural modification. Collectively, these findings support further investigation of EB171 as a promising anticancer compound and of the potential contribution of ERα signaling to its biological activity.