Triptolide enhances radiosensitivity of lung cancer cells via G2/M arrest and autophage

Abstract

Background: Triptolide is a diterpenoid triepoxide derived from the Chinese herb Tripterygium wilfordii that has been used as a natural medicine in East Asia for hundreds of years. The radiosensitizing effect of triptolide has scarcely been investigated. Thus we explored the effect and underlying molecular mechanisms in combined triptolide and radiotherapy using lung cancer cells.

Materials and Methods: Colony formation assays were conducted to test the radiosensitizing effect of triptolide in lung cancer cell lines (A549 and H460). To determine how triptolide enhances the radiosensitivity, we investigated the immunofluorescence cytometric analysis of apoptosis, western blot analysis for pro-apoptotic signaling pathways, cell cycle analysis, and change in autophage after treatment with fixed dose of triptolide and/or irradiation.

Results: Combined triptolide and irradiation significantly decreased the surviving fractions than irradiation alone in both cell lines with sensitizing enhancement ratio of 1.56 and 1.51, respectively. Annexin V staining showed that the combination treatment increased apoptosis. The PARP and caspase-3 cleavage, and cytochrome C, bax, and bcl-2 expressions were also more prominent in combination treatment. In addition, cell cycle analysis showed increased G2/M cell cycle arrest in triptolide combination. LC3B overexpression was also observed suggesting autophage may be involved in the cell death in triptolide and irradiation combination.

Conclusion: Triptolide enhanced radiosensitivity of lung cancer cells via apoptosis, cell cycle arrest, and autophage. Our data suggest that triptolide may be a candidate radiosensitizer for the treatment of lung cancer.