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AIM: To investigate the reversal effect of LY980503,a benflumetol derivative, on multidrug resistance in vincristine (VCR) -resistant human gastric carcinoma cell line SGC7901/VCR.METHODS: Cells of a human gastric cancer cell line,SGC7901, and its VCR-resistant variant, SGC7901/VCR,were cultivated with LY980503 and/or doxorubicin (DOX).The cytotoxicity of drugs in vitro was assayed by MTT method. Based on the flow cytometric technology, the uptake of DOX was detected in these cells by measuring DOX -associated mean fluorescence intensity (MFI).RESULTS: SGC7901/VCR cells were 23.5 times more resistant to DOX in comparison with SGC7901 cells.LY980503 at the concentrations of 2.0 μmol/L -10 μmol/L had no obvious cytotoxicity to SGC7901 and SGC7901/VCR cells. After simultaneous treatment with LY980503 at the concentrations of 2.0, 4.0 and 10 μmol/L, the ICs0 of DOX to SGC7901/VCR cells decreased from 1.6± 0.12 μmol/L to 0.55 ± 0.024, 0.25 ± 0.032 and 0.11± 0.015 μmol/L, respectively, thus, increasing the DOX sensitivity by 2.9-fold (P ＜ 0. 05), 6.4-fold (P ＜ 0. 01)and 14.5-fold (P ＜ 0. 01), respectively. In the uptake study of DOX, simultaneous incubation of SGC7901/VCR cells with LY980503 significantly increased the DOX -associated MFI in SGC7901/VCR cells. No such results were found in parental SGC7901 cells.CONCLUSION: LY980503 at non-cytotoxic concentrations can effectively circumvent resistance of SGC7901/VCR cells to DOX by increasing intracellular DOX accumulation.