RRx-001 sensitizes triple-negative breast cancer cells to oxaliplatin through apoptosis, cell cycle arrest, and immune modulation.

Triple-negative breast cancer is considered a highly aggressive type of breast cancer, for which there are few therapeutic options, and a very high level of resistance to chemotherapy. This research study has explored the synergistic anticancer effects of RRx-001 in combination with oxaliplatin on MDA-MB-231 cells. Cytotoxic effects were assessed using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. Mechanistic studies were also conducted, including reactive oxygen species analysis, cell cycle analysis, colony formation assays, apoptosis assays, migration assays, and measurement of programmed death-ligand 1 expression by Western blotting. The results showed that RRx-001 was more effective than oxaliplatin after 24 hours (IC50: 9.878 μM vs 202.2 μM). When RRx-001 was added to oxaliplatin, it produced a marked increase in cytotoxicity such that the effective IC50 value for oxaliplatin was reduced by ∼10-fold. Moreover, the combination of RRx-001 + oxaliplatin resulted in increased generation of reactive oxygen species, caused S-phase arrest, reduced clonogenic survival, and increased apoptosis, as indicated by elevated levels of cleaved poly(ADP-ribose) polymerase-1. Further, RRx-001 diminished oxaliplatin's induction of programmed death-ligand 1 and significantly reduced cell migration. Collectively, these results demonstrate that RRx-001 has the ability to increase the efficacy of oxaliplatin through a number of synergistic mechanisms, and therefore may serve as a viable dose-sparing therapeutic option for patients with triple-negative breast cancer. SIGNIFICANCE STATEMENT: This study reports the discovery of RRx-001, a novel small molecule that enhances the activity of oxaliplatin. The use of this chemotherapy is diminished by the rapid emergence of resistance in tumor cells; this results in continued migration capability within tumor cells. RRx-001 addresses all oxaliplatin resistance mechanisms, and therefore may serve as an adjuvant therapeutic option for patients with triple-negative breast cancer.