Semen podocarpi extract enhances radiosensitivity in nasopharyngeal carcinoma cells via Raf/MEK/ERK signaling pathway

Abstract

Objective: To investigate the chemical components of Semen podocarpi extract (SPE) and its effect on nasopharyngeal carcinoma cells and CNE-2R cells.

Methods: Chemical components in SPE were identified by UPLC-MS/MS. CCK-8 and cell cloning experiments were applied to evaluate the effects of SPE on the proliferation of CNE-2R cells, and a single-hit multitarget model was used to calculate the radiobiological parameters. Cell apoptosis and cell cycle were analyzed by flow cytometry, and the levels of genes and proteins of the Raf/MEK/ERK pathway were determined by RT-PCR and Western blotting.

Results: A total of 37 compounds from SPE were identified, and SPE with or without irradiation inhibited the proliferation of CNE-2R cells. SPE also promoted apoptosis, arrested cells in the G₂/M phase, and presented radiosensitizing effects. Compared with irradiation alone, the effects of SPE+irradiation on apoptosis and cell cycle distribution were not significantly different. In addition, SPE had no significant effect on MEK gene expression. SPE significantly increased the gene expression of C-Raf and significantly reduced the protein expression of C-Raf, as well as the gene and protein expression of ERK1 and ERK2. The protein levels of C-Raf, ERK1, and ERK2 were also significantly lower in cells treated with SPE+irradiation than in cells treated with irradiation alone.

Conclusions: The effects of SPE on inhibiting cell proliferation and promoting apoptosis are likely associated with cell cycle arrest and Raf/MEK/ERK pathway regulation, and the mechanism underlying radiosensitization by SPE may involve downregulating the protein expression of C-Raf, ERK1, and ERK2.

Keywords

Podocarpus macrophyllus / Nasopharyngeal carcinoma / Radiosensitization / Chemical composition / Inumakilactone / Podocarpus flavone