The biological and clinical role of drug transporters at the intestinal barrier.

Nowadays, over one fourth of all anticancer drugs are developed as oral formulations and this percentage is expected to increase substantially. Oral administration of drugs is patient convenient and practical and is preferred for many reasons. To enable oral drug therapy adequate oral bioavailability must be achieved. One of the factors that have proven to be important in explaining the often variable and low oral bioavailability of many orally applied anticancer drugs is the presence of ATP-binding Cassette drug transporters (ABC transporters) and solute carrier (SLC) transporters. During the past two decades, significant progress has been made in understanding the pharmacological and physiological role of ABC drug efflux and SLC uptake transporters in the disposition of a broad range of drugs, toxins, endogenous compounds and their metabolites. We focus on the expression of ABC and SLC drug transporters at the intestinal barrier and the impact of these transporters on the absorption and disposition of a wide range of orally administered drugs. Furthermore, preclinical and clinical examples of modulation of the activity of intestinal transporters to increase the systemic exposure of orally administered drugs will be reviewed. Screening of test drugs, nutrients and other molecules for ABC and SLC transporter substrates or inhibitors is a useful way to predict their intestinal absorption. Recognition of the importance of intestinal transporters could guide the design and development of oral drugs.