ABCG2, also known as breast cancer resistance protein (BCRP), is an ATP-binding cassette (ABC) transporter that has been shown to confer resistance to several drugs, including mitoxantrone and topotecan. Gleevec (imatinib mesylate) has recently been identified as a substrate for ABCG2. The expression of ABCG2 in the human jejunum has been shown to be higher than expression MDR1, which encodes for P-glycoprotein. Therefore, it is plausible that the oral bioavailability of Gleevec could be dependent on the extent of transport. A single nucleotide polymorphism (C421A) has been identified in ABCG2 and has been shown in vitro to result in functional inactivation of this transporter protein. In this study, the relationship between the genotypes of ABCG2 and the pharmacokinetics or side effects will be retrospectively explored in patients with cancer who had been previously enrolled on clinical trials of Gleevec.
