Abstract:  Abstract　Objective: To study the synergistic effect of mDRA-6 and vitamin E succinate (VES) on Raji and K562 leukemic cells and its possible mechanism. Methods: Methyl thiazolyl tetrazolium ( MTT ) assay was used to detect the growth inhibition of VES and mDRA-6 on leukemic Raji and K562 cells. AnnexinV-FITC/PI double staining was carried to analyze the apoptosis of Raji and K562 cells. Flow cytometry was performed to determine death receptor 5 ( DR5 ) expression on cell surface. An immunoblot assay was used to determine the DR5 total protein expression in leukemic cells. Results: The MTT assay showed that the specific cytotoxicity of mDRA-6 against Raji and K562 cells at 10 mg/L for 12 h, reached 21.98% and 5.23%, respectively. At 12 h after the 10 µg/mL mDRA-6 treatment, the death rates of the Raji and K562 cells were 21.98% and 5.23%, respectively. When mDRA-6 with VES at 5, 10, and 20 µmol/L were used to treat the Raji and K562 cells, the death rates of the Raji cells increased to 24.67% ( P > 0.05 ), 35.65% ( P < 0.01 ), and 40.22% ( P < 0.01 ), respectively, and those of the K562 cells increased to 6.00% ( P > 0.05 ), 7.89% ( P < 0.01 ), and 8.67% ( P < 0.01 ), respectively. Annexin V/PI double staining was used to detect the solitary effect of 2 µg/mL mDRA-6 on the Raji and K562 cells at 12 h after the treatment. The apoptotic rates of the Raji and K562 cells were 20.79% and 7.74%, respectively. At 12 h after treatment with 2 µg/mL mDRA-6 and 10 µmol/L VES, the apoptotic rates of the Raji and K562 cells reached 43.18% and 16.99%, respectively. The natural expression of DR5 on the surface of the Raji and K562 cells reached 42.35% and 14.92%, respectively. At 12 h after the effect of 10 µmol/L VES on Raji and K562 cells, the DR5 expression levels at the cell membrane increased to 70.08% and 16.38%, respectively. The immunoblot assay showed that different VES concentrations could increase DR5 protein expression on Raji and K562 cells. Conclusion: VES enhances the apoptotic effects of DR5 monoclonal antibodies on Raji and K562 cells. The possible mechanism is that VES increases DR5 expression on the cell membranes of Raji and K652 cells and DR5 protein expression in the cells.