Expression of multidrug resistance-associated protein 2 (MRP2) in normal human tissues and carcinomas using tissue microarrays

Aims: Using tissue microarrays, this study analysed the expression of the multidrug resistance protein, MRP2, by immunohistochemistry with two different MRP2 antibodies. This is the first study to address the expression of MRP2 in various common human neoplasms. Methods and results: Immunohistochemistry was performed on zinc formalin-fixed tissue to evaluate normal tissues and carcinomas using two antibodies against MRP2 (EAG5, a polyclonal antibody, and M2-lll-6, a monoclonal antibody). Immunostaining was localized in neoplastic cells mainly on the cell membrane with M2-lll-6 and cell membrane and cytoplasm with EAG5. In normal tissues MRP2 was expressed in liver, gastrointestinal tract, and kidney tubular epithelial cells with both antibodies. MRP2 was seen in nine of 22 renal cell carcinomas, eight of 13 gastric carcinomas, 25 of 49 breast carcinomas, 14 of 32 lung carcinomas, 39 of 50 colon carcinomas, and 16 of 17 ovarian carcinomas. There was < 10% variability between the two antibodies. MRP2 expression was highest in moderate to poorly differentiated tumours from colon, lung, gastric, and ovarian carcinomas and in grade 2 and 3 breast and renal carcinomas. Conclusion: The expression of MRP2 in many solid human tumours indicates that inherent drug resistance may play an important role as a biomarker for predictive chemotherapy treatment.