Mechanism drug examples efficient repair to damaged dna alkylating agents decreased uptake by cell methotrexate, doxorubicin increased drug efflux p-glycoprotein epipodophyllotoxin, vinca alkaloids, anthracyclines decreased intracellular activation 6-mercaptopurine, 5-fluorouracil increased intracellular breakdown cytosine arabinoside bypass biochemical pathways methotrexate, 6-mercaptopurine, asparaginase gene amplification or over- production of blocked enzyme methotrexate, nitrosoureas resistance to cytotoxic agents.
