Abstract
Background Crenolanib (crenolanib besylate, 4-piperidinamine, 1-[2-[5-[(3-methyl-3-oxetanyl)methoxy]-1H-benzimidazol-1-yl]-8-quinolinyl]-, monobenzenesulfonate) is a potent and specific type I inhibitor of fms-like tyrosine kinase 3 (FLT3) that targets the active kinase conformation and is effective against FLT3 with internal tandem duplication (ITD) with point mutations induced by, and conferring resistance to, type II FLT3 inhibitors in acute myeloid leukemia (AML) cells. Crenolanib is also an inhibitor of platelet-derived growth factor receptor alpha and beta and is in clinical trials in both gastrointestinal stromal tumors and gliomas. Methods We tested crenolanib interactions with the multidrug resistance-associated ATP-binding cassette proteins ABCB1 (P-glycoprotein), ABCG2 (breast cancer resistance protein) and ABCC1 (multidrug resistance-associated protein 1), which are expressed on AML cells and other cancer cells and are important components of the blood-brain barrier. Results We found that crenolanib is a substrate of ABCB1, as evidenced by approximate five-fold resistance of ABCB1-overexpressing cells to crenolanib, reversal of this resistance by the ABCB1-specific inhibitor PSC-833 and stimulation of ABCB1 ATPase activity by crenolanib. In contrast, crenolanib was not a substrate of ABCG2 or ABCC1. Additionally, it did not inhibit substrate transport by ABCB1, ABCG2 or ABCC1, at pharmacologically relevant concentrations. Finally, incubation of the FLT3-ITD AML cell lines MV4-11 and MOLM-14 with crenolanib at a pharmacologically relevant concentration of 500 nM did not induce upregulation of ABCB1 cell surface expression. Conclusions Thus ABCB1 expression confers resistance to crenolanib and likely limits crenolanib penetration of the central nervous system, but crenolanib at therapeutic concentrations should not alter cellular exposure to ABC protein substrate chemotherapy drugs.