Anticancer Effects of Antihypertensive L-Type Calcium Channel Blockers on Chemoresistant Lung Cancer Cells via Autophagy and Apoptosis

Purpose: Hypertension and cancer are frequently found comorbidity occurring in same individual. This study was intended to evaluate the anticancer effects of commonly used antihypertensive medications and chemotherapy on chemoresistant lung cancer cells. Methods: Calcium channel blockers (CCBs), including Verapamil, Diltiazem, and Nifedipine, either alone or combined with docetaxel (DOC) or vincristine (VCR) were used to treat A549 lung adenocarcinoma chemoresistant sublines. Cell viability was determined by MTT assay, and colony formation assay was used to demonstrate the long-term effect of CCBs on proliferation of the sublines. Apoptosis was evaluated by Annexin V assay and autophagy intensity was quantitated from acidic vesicular organelle formation. Pan-caspase inhibitor, shATG5 interference and chloroquine were applied to study the roles of Verapamil on apoptosis and autophagy, with related proteins verified by Western blot analysis. Results: Results show that 10 mu M of Verapamil and Diltiazem, but not Nifedipine, differentially induce autophagy in DOC-resistant or VCR-resistant A549 cells, respectively. When CCBs are combined with DOC or VCR to treat the sublines, 10 mu M of Verapamil induces autophagy more significantly than Diltiazem and Nifedipine, respectively, in DOC-resistant (54.91 +/- 0.76, 18.03 +/- 0.69, 7.05 +/- 0.30) or VCR-resistant A549 (32.41 +/- 1.04, 21.51 +/- 0.63, 7.14 +/- 0.24) cells. Inhibition of apoptosis by pan-caspase inhibitor partly reduced cell death indicates association of caspase-dependent cell death but with persistence of autophagy. Inhibition of autophagy by interfering ATG5 expression reduced c-PARP level and apoptotic cells suggest a pro-death role of autophagy. Chloroquine treatment enhanced autophagosome accumulation and cell death but with reduced c-PARP level suggests that mechanism of caspase-independent cell death also contributes to Verapamil/chemotherapy-induced anticancer effects. Conclusion: Verapamil combined with DOC or VCR induces chemoresistant lung cancer cells to death through autophagy burst and apoptosis more strongly than Diltiazem and Nifedipine. Administering Verapamil or Diltiazem individually with chemotherapy, but not Nifedipine, can be considered in lung cancer patients with hypertension.