ABSTRACT
Objective To investigate the effect of EGCG on the radiosensitivity of human nasopharyngeal carcinoma CNE-1 cells.Methods CNE-1 cells were divided into four groups:control,EGCG treatment,UVC or X-ray exposure,and EGCG combined with UVC or X-rays.After treatment with different concentrations of EGCG for 24,48 and 72 h and UVC or X-rays,cell growth was determined with MTT assay,cell survival was measured with clonogenic assay,cell cycle was deteeted with flow cytometry,cell apoptosis was detected by the annexin V-FITC cell apoptosis kit,and protein expression was assayed by Westem blot.Results EGCG inhibited cell growth in a dose-and time-dependent manner(r =0.817and 0.364).Compared with UVC or X-ray irradiation alone,the radiosensitivity of CNE-1 cells was enhanced by 2 h pre-treatment of 50 μmol/L EGCG,which disrupted S phase arrest caused by UVC( t =18.68,P ＜ 0.05 ) and increased the population of S and G2/M arrest caused by X-rays ( t =7.11 and 6.99,P ＜0.05 ).UVC could cause a significant increase of sub-G1 population( t =6.67,P ＜ 0.05 ) and Annexin V-FITC assay indicated apoptosis was further elevated by EGCG ( t =10.28,P ＜ 0.05 ).However,no significant induction of apoptosis was observed in the cells either irradiated with X-rays alone or combinationly treated with EGCG and X-rays.The combination treatment of EGCG and UVC significantly increased the expression of Bax and Caspase-3 proteins,but failed to affect Bcl-2 protein expression.Conclusions EGCG enhances the growth inhibition of CNE-1 cells caused by UVC or X-rays,which is relevant to apoptosis induction or cell cycle arrest.
ABSTRACT
Objective To explore the influence of honokiol on growth,cell cycle and radiosensitivity in nasopharyngeal carcinoma cells,CNE-1 and CNE-2.Methods MTT assay and clonogenic assay were used to detect cell growth and survival respectively.Flow cytometry was employed to analyze cell cycle progression.Annexin V-FITC kit was used to detect cell apoptosis.Western blot assay was applied to examine protein expression.Results Honokiol signficantly inhibited proliferation of CNE-1 and CNE-2 cells in a dose and time dependent manner,the IC50 value was 2.84 and 2.68 μmol/L(24 h)and 2.50 and 2.20 μmol/L (48 h),respectively.After being treated with 2.5 μmol/L honokiol for 24 h,the ratios of early apoptosis,late apoptosis and necrosis were 24.53％,23.05％ and 7.13％ in CNE-1 cells compared with the control group(t =-41.17,-8.18,-6.08,P ＜0.05).The expression levels of pro-apoptotic proteins Caspase-3 and Bax were significantly increased to 2.31 and 1.89 times (t =-15.92,-17.15,P ＜ 0.05),4.43 and 1.85 times (t =-29.39,-13.47,P ＜ 0.05).Simultaneously the expression level of anti-apoptotic protein Bcl-2 was reduced by 2.22 and 2.74 times(t =26.94,66.14,P ＜ 0.05) as compared with controls after being treated with 4 and 3 μmol/L honokiol.Additionally,honokiol at lower doses signicantly enhanced the senstivity of CNE-1 and CNE-2 cells to X-ray irradiation.The SER was 1.41 and 1.88 in CNE-1 and CNE-2 cells.3 Gy irradiation of X-rays increased the proportion at G2/M state in both cell lines (t =-14.96,-19.26,P ＜ 0.05).Honokiol reduced the G2/M cell cycle arrest induced by irradiation significantly (t =7.65,4.98,P ＜ 0.05).Simultaneously,cyclin B1 protein expression obviously elevated (t =-33.07,-73.49,P ＜ 0.05).Conclusions Honokiol is a potent inhibitor of nasopharyngeal carcinoma cell growth by inducing cell apoptosis and necrosis and works as a radiosensitizer by disrupting G2/M cell cycle checkpoint.