A low dose of AZD8055 enhances radiosensitivity of nasopharyngeal carcinoma cells by activating autophagy and apoptosis.

Activation of the PI3K/mTOR pathways is significantly correlated with a poor prognosis in nasopharyngeal carcinoma (NPC). Inhibition of these pathways was reported to be effective in restoring radiosensitivity. In this study, the activity of the novel ATP-competitive, orally bioavailable mTOR inhibitor AZD8055 was found to inhibit the phosphorylated mTOR and NPC cells proliferation. The IC50 doses in CNE1 and CNE2 cell lines were 60 and 100 nanomolar, respectively. AZD8055 significantly enhanced the inhibitions of cell growth and colony formation induced by irradiation (P < 0.05 for all). AZD8055 at the IC50 doses prolonged G2/M arrest (P < 0.05) and promoted the apoptosis (P < 0.01) induced by irradiation and autophagy in NPC cells. Blocking autophagy weaken the cell growth inhibition and decreased apoptosis induced by AZD8055 combined with irradiation. Treatment with AZD8055 at 5, 10 and 20 mg/kg/d significantly enhanced NPC cell radiosensitivity in vivo and significantly induced apoptosis and autophagy in tumor tissues, Neither 5 nor 20 mg/kg/d AZD8055 induced significantly pro-apoptosis bax expressions in mouse livers and kidneys. 5 mg/kg/d produced good radiosensitivity but had little impact on body weight. We concluded that AZD8055 was a promising candidate radiosensitizer for NPC.