Apoptosis of human colorectal cancer cell line SW480 induced by zinc phthalocyanine-mediated photodynamic therapy

Abstract

Objective To investigate the influence of light dose and concentration of zinc phthalocyanine on the proliferation and apoptosis in vitro of SW480 cells.Methods Four different light doses with six different concentrations of photosensitizer were used to kill SW480 cells,respectively.Cell counting kit-8 (CCK-8) assay was used to test the changes in the proliferation of SW480 cells cultured with different concentrations of zinc phthalocyanine and different light doses in vitro.Cell-cycle kinetics and apoptosis were analyzed by flow cytometry (FCM).The expression of bax and bcl-2 proteins was detected for photodynamic therapy (PDT) by using immunocytochemistry.Results Growth inhibition rate of four different light doses with six different concentrations of photosensitizer was (0.99 ±0.02) ％,(1.00 ±0.02) ％,(1.01 ±0.05)％,(1.01 ±0.01)％,(1.04 ±0.03)％,(1.08 ±0.05)％; (0.54 ±0.05)％,(0.65 ±0.07)％,(0.70 ±0.04)％,(0.76 ± 0.09)％,(0.86 ±0.02)％,(0.91 ±0.04)％; (0.28 ±0.01)％,(0.45 ±0.05)％,(0.60 ±0.02)％,(0.81±0.04)％,(0.91 ±0.07)％,(0.92 ±0.06)％ and (0.18 ±0.01)％,(0.35 ±0.09)％,(0.43 ±0.03)％,(0.75 ±0.04)％,(0.87 ±0.05) ％,(0.92 ± 0.05) ％,respectively.The proliferation of SW480 cells was obviously suppressed by zinc phthalocyanine-mediated photodynamic therapy in a concentration and light dose-dependent manner.Under the conditions of light dose constant 5 J/cm2,and 10 min,the cells were arrested in G2/M phase and apoptosis was induced.When SW480 cells were treated with zinc phthalocyanine at the concentration of 0.000,0.125,0.250,0.500,1.000,and 2.000 mg/L,the apoptosis rate of SW480 cells was (0.17±0.09)％,(0.19±0.08)％,(3.25±0.29)％,(7.38±1.01)％,(14.97 ±1.03)％ and (18.25 ± 1.23)％ respectively.After SW480 cells were treated with 0,2.0 mg/L zinc phthalocyanine respectively,there was no significant difference in the positive expression rate of bax oncoprotein among all groups (P ＞ 0.05).The positive expression rate of bcl-2 protein was significantly decreased after PDT treatment for 6 h (P ＜0.01).After PDT treatment fro 6 h,the bax/bcl-2 ratio in the experimental group was significantly increased with the time prolongation of zinc phthalocyanine-mediated photodynamic therapy (P ＜ 0.01).Conclusion Zinc phthalocyanine-mediated photodynamic therapy can significantly inhibit the proliferation and induces G2/M arrest in human colon cancer cell line SW480,which may be associated with the regulation of bax/bcl-2. Key words: Colonic neoplasms ; Zinc phthalocyanine ; Photodynamic therapy ; Bax