Elevated expression of P-glycoprotein in kidney and urinary bladder cancers.

A monoclonal antibody, MRK16, recognizing specifically an epitope of P-glycoprotein (P-GP), a highly active efflux transporter of chemotherapeutic agents, was used to determine the degree of expression of P-GP in the normal human kidney and urinary bladder, and in kidney and urinary bladder cancers. P-glycoprotein was localized in the microvilli of the epithelial cells of the proximal renal tubules by immunoelectron microscopy, and detected immunohistochemically in 6 of 20 untreated kidney cancers and 11 of 31 untreated urinary bladder cancers. Some of the cancerous tissues were further examined with regard to P-GP expression by immunoprecipitation. In urinary bladder cancers, the degree of P-GP expression seemed to be somewhat correlated with tumor grading. These results indicate that our method to detect the degree of expression of P-GP by MRK16 may be applicable for the diagnosis of clinical multidrug resistant urinary cancers.