Detection of recombinant P-glycoprotein in multidrug resistant cultured cells

The MDR1 multidrug resistance gene encodes a high molecular weight membrane-spanning cell surface protein, P-glycoprotein, that confers multidrug resistance by pumping various cytotoxic drugs, including vinblastine, doxorubicin or paclitaxel, out of cells. Overexpression of P-glycoprotein in human tumors has been recognized as a major obstacle for successful chemotherapy of cancer. Thus, P-glycoprotein represents an important drug target for pharmacological chemosensitizers. Initially, cell culture models to study the multidrug resistance phenotype were established by selecting drug-sensitive cells in step-wise increasing, sublethal concentrations of chemotherapy agents. P-glycoprotein was found to be overexpressed in many of these models. Multidrug resistant cells can also be generated by transfection of cultured cells with the MDR1 gene, followed by selection with cytotoxic drug at a concentration that kills all untransfected host cells. Transfectants expressing wild-type or mutant recombinant P-glycoprotein have significantly contributed to our understanding of the structure of P-glycoprotein and its molecular and cellular functions. Additionally, the MDR1 gene has also been used as a selectable marker for the transfer and coexpression of non-selectable genes. This article details means for detection of P-glycoprotein in DNA-transfected or retrovirally transduced, cultured cells. Different experimental approaches are described that make use of specific antibodies for detection of P-glycoprotein. Strategies to visualize P-glycoprotein include metabolic labeling using 35S-methionine, labeling with a radioactive photoaffinity analog, and non-radioactive immunostaining after Western blotting.