The HDAC Inhibitor RM-3-22 Suppresses Triple-Negative Breast Cancer by Uncoupling Autophagy to Drive FSP1-Dependent Ferroptosis.

Triple negative breast cancer (TNBC) remains one of the difficult subtypes to treat since it holds aggressiveness, a high recurrence rate, and is devoid of targeted therapy options. Taking these challenges into view, we developed RM-3-22, a hydroxamic acid-based histone deacetylase (HDAC) inhibitor, as a new therapeutic entity, particularly to target TNBC. Various experiments were performed using TNBC cell lines and a xenograft mouse model. Results revealed that RM-3-22 exhibited greater cytotoxicity than SAHA, an FDA-approved inhibitor with IC50 values of 6.49, 7.3, and 3.89 μM against MDA-MB-231, BT-549, and 4T1 Cells, respectively. RM-3-22 exhibited a strong anti-metastatic profile, as evidenced by impaired migratory capabilities of TNBC cells and significant disruption of the architecture of TNBC cell 3D spheroids. Furthermore, RM-3-22 suppressed TNBC progression by targeting autophagy and ferroptosis, as evidenced by reduced p62 and FSP1 expression and increased LC3B and ACSL4 expression. Our research explored the key axis where induction of autophagy is required for RM-3-22-mediated FSP1-dependent ferroptosis in the TNBC model. Surprisingly, as far as we know, this study is the first to show that HDAC inhibitors could induce autophagy-dependent ferroptosis as a cell death mechanism to halt TNBC progression. These results were further validated by the effective reduction in tumour growth in the xenograft mouse model. Collectively, RM-3-22 could be a promising alternative inhibitor for TNBC by targeting the autophagy-ferroptosis mechanism(s).