Combination of chemotherapy and c-MET inhibitors has synergistic effects in c-MET overexpressing pancreatic cancer cells

Pancreatic ductal adenocarcinoma (PDAC) remains as one of the most lethal malignancies. c-MET is an important oncogenic kinase involved in PDAC progression. We determined the anticancer effect of c-MET inhibitors, crizotinib and cabozantinib, combined with chemotherapeutic agents, doxorubicin, oxaliplatin and gemcitabine, against different PDAC and a lung adenocarcinoma cell line expressing different levels of c-MET. MTT assay was performed to assess cell growth inhibition. Synergistic combinations were evaluated in spheroid cultures, while apoptosis was determined through Hoechst33258 staining. The effect of drug combinations on cell cycle and apoptosis induction was examined by RNase/PI flow cytometric assay. We also evaluated reactive oxygen species (ROS) levels using 2′,7′-dichlorofluorescein-diacetate (DCFH-DA) assay to explore the possible mechanisms contributing to synergism. Combination of crizotinib or cabozantinib with doxorubicin exhibited synergistic effects in c-MET overexpressing cells. Conversely, combinations of c-MET inhibitors with other agents were additive or even antagonistic. Combination index (CI) values calculated with Calcusyn software were 0.631–0.730 for crizotinib and 0.542–0.746 for cabozantinib co-administered with doxorubicin. These synergistic combinations showed significant spheroid growth inhibition and apoptosis induction in Suit-2, c-MET dependent PDAC cells. These combinations also significantly increased the number of cells in both apoptotic sub-G1 phase and the G2/M phase compared to single-drug treatment. Increased ROS production seemed to be a possible mechanism underlying synergism. In conclusion, c-MET inhibitors synergize with DNA damaging agent, doxorubicin, in cancer cells with c-MET overexpression, indicating that these combination therapies may be a promising cancer therapeutic strategy.