Synergistic Enhancement of Apo2L/TRAIL and DR4-Induced Apoptosis by Arsenic Trioxide in Triple-Negative Breast Cancer Cells: A Comparison to Conventional Chemotherapy.

Triple-negative breast cancer (TNBC) is an aggressive subtype lacking hormonal and HER2 receptors, making it highly resistant to treatment. Apo2L/TRAIL, a tumor necrosis factor-related ligand, induces apoptosis in cancer cells via the death receptor DR4. However, TNBC often develops resistance to TRAIL-mediated apoptosis, limiting its therapeutic potential. This study investigates whether arsenic trioxide (ATO) can overcome TRAIL resistance by modulating the Apo2L/TRAIL pathway and enhancing the effects of carboplatin (CP) and cyclophosphamide (CY). TNBC cell lines BT-20 and MDA-MB-231 were treated with ATO, CP, CY, and their combinations. Cell viability was measured using the MTT assay, while real-time PCR and Western blot analysis assessed Apo2L/TRAIL and DR4 expression. Statistical analysis was performed using ANOVA with Dunnett's post hoc test. ATO induced dose-dependent cytotoxicity in TNBC cells, which was significantly enhanced in combination treatments. The highest reductions in cell viability were observed with 3 µM ATO plus 5000 µM CP or 500 µM CY (p < 0.0001). ATO markedly upregulated Apo2L/TRAIL and DR4 at both mRNA and protein levels, with the most pronounced effects seen in ATO-CY combinations. These findings indicate that ATO sensitizes TNBC cells to TRAIL-mediated apoptosis by upregulating DR4 and Apo2L/TRAIL, while also exhibiting strong synergistic cytotoxicity with CP and CY. This highlights ATO's potential as an adjuvant therapy to improve TNBC treatment efficacy and overcome chemoresistance, warranting further clinical exploration.