The ABCG2 multidrug transporter

ABCG2 is an ATP-binding cassette (ABC) half-transporter localized to the cell membrane and important in normal physiology, in normal tissue protection including in the maternal-fetal barrier and the blood brain barrier, and potentially in multidrug resistance. Dimerization is required for function. Polymorphic variants have been described that impair trafficking to the cell surface, and one, Q141K, has been associated with a higher incidence of gout in individuals who are carriers. Working in concert with ABCB1 (P-glycoprotein), ABCG2 is expressed at high levels in the vascular endothelium of the brain and pumps xenobiotics and chemotherapeutics back into the bloodstream. ABCG2 expression is also found at high levels in some cancer types including pancreatic and liver cancers. Whether its expression in these tumor types contributes to drug resistance via drug efflux and reduction in drug accumulation is a question that remains unanswered. Studies of drug accumulation, such as through imaging solid tumors in patients, are needed to answer this question.