The mdr1 gene, responsible for multidrug-resistance, codes for P-glycoprotein.

The development of simultaneous resistance to multiple drugs in cultured cells occurs after selection for resistance to single agents. This multidrug-resistance phenotype is thought to mimic multidrug-resistance in human tumors treated with chemotherapy. Both the expression of a membrane protein, termed P170 or P-glycoprotein, and the expression of a cloned DNA fragment, termed mdr1, have been shown independently to be associated with multidrug-resistance in cultured cells. In this work, we show that human KB carcinoma cells which express the mdr1 gene also express P-glycoprotein, and that cDNAs encoding P-glycoprotein cross-hybridize with mdr1 cDNAs. Thus, the mdr1 gene codes for P-glycoprotein.