Expression of P-glycoprotein and multidrug resistance-associated protein is associated with multidrug resistance in gastric cancer.

This study evaluated the sensitivities of gastric cancer cells to various chemotherapy drugs, and investigated the relationship between the expression of P-glycoprotein (P-gp) and multidrug resistance-associated protein (MRP) and multidrug resistance. Drug sensitivities were determined using a methyl-tetrazolium assay: expression levels of P-gp and MRP were measured using immunohistochemistry. On purification culture, gastric cancer cells were found to be most sensitive to cisplatin, mitomycin and adriamycin, moderately sensitive to etoposide and 5-fluorouracil, and less sensitive to homocamptothecin and methotrexate, with sensitivities of 76.7%, 70.0%, 66.7%, 60.0%, 56.7%, 43.3% and 30.0%, respectively. Positive expression for P-gp and MRP in gastric cancer tissues was 41.7% and 29.2%, respectively; co-expression of P-gp and MRP in cancer tissue was 23%. The drug-resistant groups had higher positive expression of P-gp and MRP compared with the drug-sensitive groups. In conclusion, expression of P-gp and MRP seems to be associated with multidrug resistance in gastric cancer.