What is MDR?

There are several reasons why drugs may not reach therapeutic levels within cancer cells. One of the most frequent problems is the amplification of a gene commonly known as MDR1 for multiple drug resistance. Another common name for this same protein is the P-glycoprotein. This gene encodes a large transmembrane protein that has the ability to a) stop certain drugs from entering a cell and b) eject drugs from the cell once they have entered. This combination of capabilities makes the MDR protein very effective at reducing intracellular concentrations of a variety of chemotherapy agents. While the normal function of this protein has nothing to do with chemotherapy drugs, it is quite often the reason for chemotherapy drug failure.