Abstract:ObjectiveTo investigate the mechanism of synergistic repression and sensibilization of radix arnebiae naphthoquinone derivative ［3,11bis (2hydroxyethansulfanyl)6isohexenyl naphthazarin, SYUNZ4］ combined with radiotherapy on human nasopharyngeal carcinoma (NPC) cell lines.MethodsHuman NPC welldifferentiated squamous cell carcinoma cell line CNE1 and poorly differentiated squamous cell carcinoma cell line CNE2 were randomly divided into four groups: blank control group, SYUNZ4 group, radiotherapy group, combination of SYUNZ4 with radiotherapy group. The radiation dose was 4Gy and cell lines of the combined group were cultured with the maximal nontoxic dose of SYUNZ4 right after finishing radiotherapy. After that, apoptosis induction and effect on cell cycle distribution were studied by flow cytometry.ResultsThe proliferations of CNE1 and CNE2 were significantly inhibited by SYUNZ4 in a concentrationdependent manner. Compared with the blank control group, the cell proliferations were remarkably inhibited in both the radiotherapy group and the combined group (both P<0.05), the proportion of G2/M cells was increased significantly（P<0.05) in the radiotherapy group and that of S and G2/M cells was increased significantly in the combined group (P<0.05). Compared with the radiotherapy group, cell proliferations of CNE1 and CNE2 were more significantly inhibited by combined intervention（both P<0.01）. Compared with the control group, radiation exposure led to a significant increase in apoptosis (P<0.05). Moreover, the apoptotic rates of CNE1 and CNE2 cells in the combined group were significantly increased compared with the radiotherapy group (P<0.05).ConclusionSYUNZ4 combined with radiotherapy can significantly inhibit the proliferation of human NPC cells, which results in cell cycle arrest and apoptosis induction.