Knockdown of Annexin VII Enhances Nasopharyngeal Carcinoma Cell Radiosensitivity in Vivo and in Vitro.

BACKGROUND: Radioresistance leads to treatment failure in patients with nasopharyngeal carcinoma (NPC). Thus, enhancing the radiosensitivity of NPC cells would likely increase the effectiveness of radiotherapy. Annexin VII (Annexin A7, ANXA7) might be a tumor promoter in NPC but its functions in radiosensitivity remain unclear. METHODS: NPC cell lines CNE2-shANXA7 and CNE2-pLKO.1 were generated and CNE2-shANXA7 nude mice xenograft tumor models were established. The main effects and molecular mechanisms of ANXA7 knockdown in NPC radiosensitivity were studied in vitro and in vivo by analyzing cell viability, clonogenicity, apoptosis, cell cycle distribution, tumor radioresponse and immunohistochemistry assay. RESULTS: ANXA7 knockdown revealed potentially enhanced NPC cell radiosensitivity via apoptosis and increased the cell number at the G2/M phase. In the xenograft model, NPC cells with ANXA7 knockdown were dramatically sensitive to irradiation and tumor growth was significantly suppressed. Compared to CNE2-pLKO.1 xenografts, CNE2-shANXA7 showed more gamma H2AX foci and less phospho-DNA PKcs. CONCLUSIONS: ANXA7 knockdown increased the radiosensitivity of NPC by enhancing apoptosis, modulating the cell cycle distribution into more radiosensitive phases, promoting DNA damage, and inhibiting repair. We showed that decreased ANXA7 levels enhanced radiosensitivity and provided insights into the therapeutic targets for NPC radiotherapy.