Genetic Polymorphisms of ATP-Binding Cassette Transporters ABCB1 and ABCC2 and their Impact on Drug Disposition

The ATP-binding cassette (ABC) transporter superfamily comprises membrane proteins that translocate a variety of substrates across extra- and intra-cellular membranes, and act as efflux proteins. ABC transporters are characterised by the presence of genetic polymorphisms mainly represented by single nucleotide polymorphisms (SNPs), some of which having an impact on their activity. Besides physiological substances, drugs are also substrates of some ABC transporters, mainly ABCB1, ABCC1, ABCC2, ABCC3 and ABCG2. Identifying the impact of these polymorphisms on the pharmacokinetics (PK) of these drugs may have important clinical implications, certainly for those characterised by a narrow therapeutic index and significant inter- and intra-patient PK variability. This review focuses specifically on ABCB1 and ABCC2 and critically analyses important publications dealing with the influence of ABCB1 and/or ABCC2 polymorphisms on drug disposition in humans. For different reasons discussed in this paper, the effect of ABCB1 and/or ABCC2 polymorphisms on drug concentrations in blood is not always easy to interpret and to correlate with pharmacological effects. In contrast, intracellular or target tissue drug concentrations appear more directly influenced by these polymorphisms, as illustrated with intralymphocyte concentrations for immunosupressants and antiretrovirals or with cerebrospinal fluid (CSF) concentrations for antiepileptics and antidepressants. Further research on intracellular and/or target tissue drug concentrations are still needed to better characterise the PK-PG (pharmacogenetics) relationship involving ABC transporters.