Abstract: Objective To investigate the effects of over-expression E2F1 gene on multi-drug resistance of human colon cancer Oxaliplatin-resistant cell line HCT116/L. Methods HCT116/L cells were divided into 3 groups（HCT116/L+E2F1 group，HCT116/L+NC group and HCT116/L group）. HCT116/L+E2F1 group cells were infected with an over-expression E2F1 recombinated lentiviral vector，HCT116/L+NC group cells were infected with an empty lentiviral vector，and HCT116/L group with no treatment . The expression levels of E2F1 protein was detected by Western blot analysis. The sensitivities to chemotherapeutic drugs（Adriamycin，5-FU，and Cisplatium） were assessed using MTT. The pump-out accumulation rate of Adriamycin and the apoptosis of cells were detected using flow cytometry. The migration of cells was dected by cell scratch test. Western blot was used to detect the expression level of resistance-related gene MDR1. Results The expression level of E2F1 in HCT116/L+E2F1 group was higher than that in HCT116/L+NC group and HCT116/L group（P＜0.05）. The IC50 of Adriamycin，5-FU，and Cisplatium of HCT116/L cells in HCT116/L+E2F1 group were（1.61±0.21） μg/mL，（5.22±0.12） μg/mL and （3.52±0.15） μg/mL，respectively，which were significantly higher than that in HCT116/L+NC group［（0.61±0.11） μg/mL，（3.93±0.54） μg/mL，（2.31±0.45） μg/mL] and HCT116/L group［（0.69±0.13） μg/mL，（4.19±0.51） μg/mL，（2.51±0.42） μg/mL］. The pump rate of Adriamycin was （22.51±0.12）% in HCT116/L+E2F1 group，while HCT116/L group was （8.45±0.11）% and HCT116/L+NC group was（10.92±0.09）%，and the differences were statistically significant（P＜0.05）. The apoptosis rate of HCT116/L+E2F1 group was （6.42±0.52）%，which was significantly lower than that of HCT116/L+NC group （12.81±0.69）% and HCT116/L group （11.45±0.31）%. HCT116/L+E2F1 group could enhance cell migration ability （P<0.05） and arrested cells in S phase. The expression of MDR1 protein in the HCT116/L+E2F1 group was 0.41±0.08，which was significantly higher than 0.19±0.08 in the HCT116/L+NC group and 0.15±0.07 in the HCT116/L group. Conclusions Over-expression of E2F1 gene can reduce the sensitivity of human colon cancer oxaliplatin-resistant HCT116/L to chemotherapeutic drugs and up-regulate the expression of MDR1 gene，which reduce the accumulation of chemotherapeutic drugs in HCT116/L cells，then enhance the multi-drug resistance of HCT116/L cells.

Key words: Colorectal cancer, E2F1, Multi-drug resistance, Adriamycin, 5-FU, Cisplatium, MDR1