ATP-binding cassette transporter (with specific examples: P-glycoprotein [ABCB1], Breast cancer resistance protein [ABCG2], Multidrug resistance-associated protein 1 [ABCC1]) (ABC transporter (ABCB1, ABCG2, ABCC1))

ABC transporters are a superfamily of membrane proteins that actively transport a wide variety of endogenous and exogenous substrates, including chemotherapeutic agents, across cellular membranes using the energy of ATP hydrolysis. In cancer, overexpression of certain ABC transporters—most notably ABCB1, ABCG2, and ABCC1—confers multidrug resistance by effluxing drugs like doxorubicin from tumor cells, thereby reducing intracellular drug concentrations and efficacy. Inhibiting these transporters can restore drug sensitivity in model systems, but clinical success has been limited due to overlapping substrate specificity, redundancy among family members, and physiologic roles in normal tissues. ABC transporter expression levels are investigated as biomarkers for chemoresistance and predictors of patient response in oncology

Other names

P-glycoprotein (P-gp)MDR1 (for ABCB1)BCRP (for ABCG2)MRP1 (for ABCC1)multidrug resistance proteinATP-binding cassette subfamily

Drugs targeting ABC transporters typically act as *substrates* (exported from cells, leading to resistance); *inhibitors* (block efflux to restore cytotoxic drug intracellular levels); *modulators* (alter transporter expression or function)