Although many attempts have been made to improve the efficacy of radiotherapy to treat cancer, radiation resistance is still an obstacle in lung cancer treatment. Oridonin is a natural compound with promising antitumor efficacy that can trigger cancer cell death; however, its direct cellular targets, efficacy as a radiosensitizer, and underlying mechanisms of activity remain unclear. Herein, we report that oridonin exhibits additive cytotoxic and antitumor activity with radiation using the H460 non-small cell lung cancer cell lines. We assessed the effect of oridonin by proliferation, clonogenic, reactive oxygen species (ROS) production, DNA damage, and apoptosis assays. In vitro, oridonin enhanced the radiation-induced inhibition of cell growth and clonogenic survival. Oridonin also facilitated radiation-induced ROS production and DNA damage and enhanced apoptotic cell death. In vivo, the combination of oridonin and radiation effectively inhibited H460 xenograft tumor growth, with higher caspase-3 activation and H2A histone family member X (H2AX) phosphorylation compared with that of radiation alone. Our findings suggest that oridonin possesses a novel mechanism to enhance radiation therapeutic responses by increasing DNA damage and apoptosis. In conclusion, oridonin may be a novel small molecule to improve radiotherapy in non-small cell lung cancer.
Keywords: ROS; apoptosis; oridonin; radiation; sensitization.