RRx-001 Accelerates Low Dose Oxaliplatin-Induced Cytotoxicity in Triple-Negative Breast Cancer Cells via Synergistic Antitumor Mechanisms

Abstract

Background: Triple-negative breast cancer (TNBC) represents an aggressive subtype that has few therapeutic options for targeting and is highly resistant to chemotherapy. The compound RRx-001 is a dinitroazetidine compound with both immune-modulating and epigenetic properties, whereas oxaliplatin elicits immunogenic cell death. Objective: To evaluate the synergistic cytotoxic effects of RRx-001 combined with oxaliplatin in MDA-MB-231 TNBC cells. Methods: Viability assays using the MTT assay were performed. The IC50 concentrations were derived from dose response curves. The drug interaction analysis was completed utilizing the Chou-Talalay method, along with CompuSyn software to calculate the combination index (CI) and dose reduction index (DRI). The intracellular reactive oxygen species (ROS) levels were assayed by performing a fluorometric assay with DCFH-DA. Results: RRx-001 exhibited greater cytotoxicity (IC50=9.878 µM) than did oxaliplatin (IC50=202.2 µM). When the two drugs were used, the combination resulted in a significant decrease in the IC50 value for oxaliplatin (to 9.705 µM, ≈20.9-fold reduction). A strong synergy was seen (CI=0.0227 at Fa=0.05) with significant reductions in the doses required for each drug. Additionally, a combination of these two drugs significantly increases amounts of ROS compared to either drug alone. Conclusions: RRx-001 has been shown to significantly enhance the cytotoxicity of oxaliplatin through synergistic and ROS-mediated pathways, suggesting that it may represent a viable option for a dose-sparing combinatorial therapeutic approach to treat TNBC.