RAD001 can reverse drug resistance of SGC7901/DDP cells.

To investigate the role of RAD001 in the reversing of drug resistance of SGC7901/DDP, we cultured SGC7901/DDP cells with different groups of drugs (RAD001, cisplatin (DDP) alone, or the combination of RAD001 and DDP); after that, we detected the drug sensitivity, cell apoptosis, and levels of P-gp, MRP1, and survivin in the cells of SGC7901/DDP by MTT (3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphe-nyltetrazolium bromide) assay, flow cytometry, immunohistochemical analysis, and Western blot analysis. There was no significant difference between DDP 2.5-mg/L group and negative control group. When the cells were pretreated with RAD001 2.5, 5 nmol/L, the proliferation of SGC7901/DDP cells was inhibited by DDP 2.5 mg/L significantly, compared to negative control group, DDP 2.5-mg/L group, and RAD001 2.5, 5-nmol/L group, respectively (P < 0.05); there were significant differences between combination groups (P < 0.05). DDP 2.5 mg/L and RAD001 2.5 nmol/L did not induce apoptosis of SGC7901/DDP cells alone (P > 0.05). When SGC7901/DDP cells were pretreated with RAD001 2.5 nmol/L, DDP 2.5 mg/L increased the apoptosis rate significantly compared to groups of control and DDP 2.5 mg/L alone (P < 0.05). Immunohistochemical staining (Table 5, Fig. 2) and Western blot analysis (Fig. 3) indicated that when SGC7901/DDP cells were pretreated with RAD001 2.5 nmol/L, the expression of P-gp, MRP1, and survivin decreased by different degrees. Our results have confirmed that RAD001 in combination with DDP could overcome chemoresistance of SGC7901/DDP cells by decreasing the levels of P-gp, MRP1, and survivin through the mTOR pathway.