Mechanism of radiosensitization effect of berberine on human nasopharyngeal carcinoma in hypoxia

Objective To investigate the radiosensitiation effect of berberine on human nasopharyngeal carcinoma （ NPC） in hypoxia condition and explore the underlying mechanisms. Methods MTT assay, clonogenic assay and flow cytometry were performed to analyze cell proliferation, colony formation and apoptosis, respectively. Male nude mice inoculated subcutaneously with CNE-2 cells were used to examine the radiosensitization effect of berberine in vivo. The expressions of HIF-1α and VEGF were assessed by Western blot. Results Berberine efficiently inhibited the proliferation of CNE-2 cells in time-dependent and dose-dependent fashions with an IC50 of （ 14.9 ± 2.2 ） μmol/L. Clonogenic survival assay showed that berberine （ 5 μmol/L ） sensitized CNE-2 cells to ionizing radiation in hypoxia and its SERD0 was 1.27. Under hypoxic condition, berberine alone （5, 15 μmol/L） could induce apoptosis （t=5.01, 9.02,P〈0.05） and it further promoted 8 Gy radiation-induced apoptosis （t =5.31, 9.91,P 〈0.05）. Moreover, berberine significantly delayed the tumor growth in the combination group （berberine ＋irradiation） compared with the mice received irradiation alone or PBS （t =2.96, 14.52, P 〈0.05）. Immunobloting assay showed that berberine inhibited the upregulation of HIF-1α and VEGF induced by hypoxia in CNE-2 cells. Conclusion Berberine confers radiosensitivity on hypoxic NPC in vitro and in vivo, which is probably associated with the downregulation of HIF-1α and VEGF expressions. Key words: Berberine; Nasopharyngeal carcinoma; Hypoxia; Radiosensitivity; Hypoxia induced factor