BH3 mimetic and dual PI3K/mTOR inhibitor attenuates gemcitabine resistance in triple-negative breast cancer.

Triple-Negative Breast Cancer can develop resistance to gemcitabine and overcoming this resistance is critical for effective treatment. In cancer cells, anti-apoptotic Bcl-2 family proteins are often upregulated, disrupting apoptosis. ABT-737 binds to Bcl-2 and Bcl-xL to promote apoptosis but not Mcl-1 protein. NVP-BEZ235, a PI3K-mTOR dual inhibitor, reduces cell proliferation, increases sensitivity to chemotherapeutic agents and overcomes resistance. This study demonstrates the synergistic effects of ABT-737 and NVP-BEZ235 in overcoming gemcitabine resistance Triple-Negative Breast Cancer (MDA-MB-231GEMR) cell line. MDA-MB-231GEMR cell line was established with continuous treatment of gemcitabine and the resistance factor of MDA-MB-231GEMR cell line were confirmed via proliferation and qPCR analysis. Cytotoxicity of ABT-737, NVP-BEZ235 and combination on MDA-MB-231GEMR was assessed using Resazurin cell viability assay, resulting in a combination index value of 0.794. The effective doses were 5µM ABT-737 and 0.1µM NVP-BEZ235 for MDA-MB-231GEMR cell line at 72 h. The combination treatment reduced migration and colony formation abilities in MDA-MB-231GEMR and MDA-MB-231 cell lines. Co-treatment of both drugs induced cell cycle arrest at Sub-G0 phase in MDA-MB-231GEMR cell lines. Gene expression analysis demonstrated a significant increase in Mcl-1 expression and a reduction in Bcl-2 gene. Furthermore, hENT1 gene expression levels was also upregulated, indicating a potential reversal of resistance. Western blot analysis shows Bcl-2 protein expression levels decreased compared to control group. In silico analysis using GEPIA revealed a relation between hENT1 with Mcl-1 and Bcl2. These findings reveal ABT-737 and NVP-BEZ235 attenuate MDA-MB-231GEMR cell line and show potential implication on reversing resistance in TNBC for further studies.