To explore the effect of gambogic acid on the reversal of multi-drug resistance and the expressions of the poly multi-drug resistance protein 1 (MDR1) and P-glycopmtein (P-gp) in SW480/L-OHP cells.

Oxaliplatin resistant SW480/L-OHP cells were established by gradually increasing the concentration of L-OHP and intermittent treatment with high-dose concentration on parental cells (SW480). Methyl thiazolyl tetrazollum (MTT) method was used to detect the reversal index (RI) of SW480/L-OHP cells and the reversal effect of gambogic acid. The cell cycle, apoptosis of cells were determined by flow cytometry assay. Expression of MDR1 mRNA was detected by RT-PCR. Expressions of P-gp proteins were detected by Western blot. All experimental data were dealt with by SPSS13.0 software.

The inhibitory effect of gambogic acid on both SW480 and SW480/L-OHP was detected in a dose-dependent manner. Low-cytotoxic dose of gambogic acid could obviously decrease the IC₅₀ value of SW480/L-OHP cells to Oxaliplatin (P < 0.05). The reversing fold was 3.72. Low-cytotoxic dose of gambogic acid could increase the apoptotic rate evidently and remarkably reduce the expression of MDR1 mRNA and decrease the P-gp expression in SW480/L-OHP cells.

Gambogic acid could partially reverse the multi-drug resistance to Oxaliplatin in SW480/L-OHP cells, which is related to the increased accumulation of intracellular Oxaliplatin, the inhibition of MDR1 gene expression and the decreased expression of P-gp.