[The mechanism of resistance to 2', 2'-difluorodeoxycytidine (gemcitabine) in a pancreatic cancer cell line].

OBJECTIVE: To study the mechanism of resistance and its reversal to 2', 2'-difluorodeoxycytidine (gemcitabine) in a pancreatic cancer cell line SW1990. METHODS: Immunohistochemistry and RT-PCR techniques were used to investigate the mechanism of drug resistance. Salvicine (SAL) was used to reverse the drug resistance in a gemcitabine-resistant pancreatic cancer cell line (SW1990-GEM). RT-PCR, flow cytometry and MTT assay were employed to evaluate the effect of reversing drug resistance by salvicine. RESULTS: SW1990-GEM cells showed weak expression of P-glycoprotein (P-gp) revealed by immunohistochemistry, while its parental SW1990 cells were negative. Both cell lines did not express multidrug-resistance-related protein (MRP). As compared to the parental SW1990 cells, the mRNA expression of deoxycytidine kinase (dCK) was decreased while that of ribonucleotide reductase (RR) and mdr-1 was increased. With a concentration of 4 nmol/L, at one hr and 24 hr after SAL treatment, there was no change in mdr-1 mRNA expression, and the IC(50) of gemcitabine was 121.36 micromol/L and 121.64 micromol/L, respectively. However, when the concentration of SAL was increased to 30, 60, and 90 nmol/L, there was a dose-dependent down-regulation of mdr-1 mRNA expression in SW1990-GEM cells. The accumulation of rhodamine 123 was concomitantly increased, and the IC(50) of gemcitabine was correspondingly decreased. CONCLUSION: The resistance to gemcitabine of a pancreatic cancer cell line is due to decreased expression of dCK and increased expression of RR and mdr-1. Salvicine, only in toxic concentrations, can reverse the drug resistance by down-regulating mdr-1 gene and P-gp expression.