Effect of Paris saponin I on radiosensitivity in a gefitinib-resistant lung adenocarcinoma cell line

Previous studies have observed that Paris saponin I (PSI) exerts a wide range of pharmacological activities, including cytotoxic activity against a number of malignancies, such as non-small cell lung cancers. The present study aimed to investigate the radiosensitization of PSI treatment on a gefitinib-resistant lung adenocarcinoma cell line, PC-9-ZD, and its possible mechanism. A 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-tetrazolium bromide assay was used to determine the growth inhibition effect of PSI. A clonogenic assay was performed to determine the radiosensitizing effect of PSI treatment on the PC-9-ZD cell line. A single-hit multi-target model was used to plot survival curves and calculate sensitizing enhancement ratios. The cell cycle was analyzed by flow cytometry and cell apoptosis was analyzed with fluorescein-isothiocyanate-Annexin V/propidium iodide and Hoechst staining. The expression levels of the proteins were detected by western blotting. There was a significant reduction observed in the proliferation of the PC-9-ZD cell lines that were treated with PSI. PSI enhanced the radiosensitivity of the PC-9-ZD cells with a sensitization enhancement ratio of 1.77. Furthermore, PSI induced G2/M arrest and apoptosis of the irradiated PC-9-ZD cells. Notably, B-cell lymphoma 2 (Bcl-2) was downregulated, and caspase-3, Bcl-2-like protein 4 (Bax) and cyclin-dependent kinase inhibitor 1 (P21(waf1/cip1)) were upregulated by the PSI treatment. The present study showed that PSI treatment exhibited potent radiosensitivity against gefitinib-resistant PC-9-ZD cells in vitro. This radiosensitivity was associated with cell cycle arrest at the G2/M phase, and apoptosis via an increase in caspase-3, Bax and P21(waf1/cip1) as well as a decrease in Bcl-2 production.