The Synthetic Capsaicin‐analog Arvanil sensitizes Cisplatin‐Resistant Human Lung Cancer Cells to the pro‐apoptotic activity of Irinotecan

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Cisplatin-based combination therapy is the standard of care for the treatment of human lung cancer. Initially, cisplatin shows excellent therapeutic response but the tumor inevitably relapses (within a year) and this relapsed tumor is resistant to cisplatin. A few human lung cancers do not respond to cisplatin-based first-line chemotherapy. These patients are said to have platinum-refractory lung tumors. Patients with platinum resistant or refractory disease have very limited options, as the only standard chemotherapy with an FDA-approved drug, irinotecan has an objective response rate of approximately 3% and little or no survival benefit. Therefore, agents which improve the therapeutic response (of human lung cancers) towards irinotecan may be useful for the treatment of cisplatin-resistant human lung cancer. The nutritional compound capsaicin sensitized cisplatin-resistant H69-CPR human small cell lung cancer (SCLC) cells towards irinotecan-induced apoptosis. Arvanil is a synthetic capsaicin-analog which displays enhanced growth-suppressive activity in human SCLC. The present study aims to investigate the combinatorial apoptotic activity of arvanil and irinotecan in cisplatin-resistant lung cancer. Caspase-3 activity assays reveal that the combination of irinotecan and arvanil displayed greater apoptotic activity in H69-CPR human cisplatin-resistant SCLC cells than the drugs used alone. These experiments were repeated in a second cisplatin-resistant lung cancer cell line PC9-CDDP and similar results were obtained. Chou-Talalay isobologram analysis showed the interaction between irinotecan and arvanil is synergistic in H69-CPR and PC9-CDDP cells. The combination of arvanil/irinotecan showed a greater synergistic pro-apoptotic activity than the combination of capsaicin/irinotecan. in H69-CPR and PC9-CDDP cells. The pro-apoptotic activity of arvanil/irinotecan was mediated elevation of intracellular calcium and required the calpain pathway. Taken together, our findings pave the way for the discovery of novel combination therapies for the therapy of cisplatin-resistant human lung cancer.