BCRP/ABCG2 inhibitors: a patent review (2009-present)

Introduction: BCRP/ABCG2 is a polyspecific ATP binding cassette transporter involved in multidrug resistance of tumors. Compared with P-glycoprotein/ABCB1 only a few inhibitors are known.Areas covered: Identification of ABCG2 inhibitors in compound libraries and efforts made to develop new ABCG2 inhibitors are discussed in the review. Additionally, development of new test systems for testing ABCG2 activity and medical applications of ABCG2 inhibitors and activators are reviewed.Expert opinion: ABCG2 is highly expressed in side-population cells, which possess stem cell properties and are resistant to chemotherapy and radiotherapy. These cells are thought to lead to a relapse after chemotherapy. Therefore, inhibition of ABCG2 could have an additional benefit besides counteracting multidrug resistance. Among the new chemical entities, the bivalent flavonoids seem promising, as selective and broad spectrum inhibitors were found within this class of compounds. However, the available pharmacological data are rather preliminary.