title: Inhibition of ABCG2-mediated transport by protein kinase inhibitors with a bisindolylmaleimide or indolocarbazole structure.
abstract: ABCG2 is a transporter with potential importance in cancer drug resistance, drug oral absorption, and stem cell biology. In an effort to identify novel inhibitors of ABCG2, we examined the ability of commercially available bisindolylmaleimides (BIM) and indolocarbazole protein kinase inhibitors (PKI) to inhibit ABCG2, given the previous demonstration that the indolocarbazole PKI UCN-01 interacted with the transporter. At a concentration of 10 micromol/L, all of the compounds tested increased intracellular fluorescence of the ABCG2-specific substrate pheophorbide a in ABCG2-transfected HEK-293 cells by 1.3- to 6-fold as measured by flow cytometry; the ABCG2-specific inhibitor fumitremorgin C increased intracellular fluorescence by 6.6-fold. In 4-day cytotoxicity assays, wild-type ABCG2-transfected cells were not more than 2-fold resistant to any of the compounds, suggesting that the PKIs are not significantly transported by ABCG2. BIMs I, II, III, IV, and V, K252c, and arcyriaflavin A were also able to inhibit [(125)I]iodoarylazidoprazosin labeling of ABCG2 by 65% to 80% at 20 micromol/L, compared with a 50% to 70% reduction by 20 micromol/L fumitremorgin C. K252c and arcyriaflavin A were the most potent compounds, with IC(50) values for inhibition of [(125)I]iodoarylazidoprazosin labeling of 0.37 and 0.23 micromol/L, respectively. K252c and arcyriaflavin A did not have any effect on the ATPase activity of ABCG2. Four minimally toxic compounds--BIM IV, BIM V, arcyriaflavin A, and K252c-reduced the relative resistance of ABCG2-transfected cells to SN-38 in cytotoxicity assays. We find that indolocarbazole and BIM PKIs directly interact with the ABCG2 protein and may thus increase oral bioavailability of ABCG2 substrates.
authors.affiliation: Medical Oncology Branch and Laboratory of Cell Biology, Center for Cancer Research, NIH, Bethesda, Maryland, USA. robeyr@mail.nih.gov
authors.forename: Robert W
authors.initials: RW
authors.lastname: Robey
authors.forename: Suneet
authors.initials: S
authors.lastname: Shukla
authors.forename: Kenneth
authors.initials: K
authors.lastname: Steadman
authors.forename: Tomasz
authors.initials: T
authors.lastname: Obrzut
authors.forename: Elizabeth M
authors.initials: EM
authors.lastname: Finley
authors.forename: Suresh V
authors.initials: SV
authors.lastname: Ambudkar
authors.forename: Susan E
authors.initials: SE
authors.lastname: Bates
mesh_terms: D000070997:ATP Binding Cassette Transporter, Subfamily G, Member 2; D018528:ATP-Binding Cassette Transporters / Q000037:antagonists & inhibitors* / Q000378:metabolism; D001692:Biological Transport; D002227:Carbazoles / Q000737:chemistry*; D002460:Cell Line; D006801:Humans; D007211:Indoles / Q000737:chemistry*; D008301:Maleimides / Q000737:chemistry*; D015394:Molecular Structure; D009363:Neoplasm Proteins / Q000037:antagonists & inhibitors* / Q000378:metabolism; D047428:Protein Kinase Inhibitors / Q000737:chemistry / Q000494:pharmacology*
chemical_list: C116614:ABCG2 protein, human; D000070997:ATP Binding Cassette Transporter, Subfamily G, Member 2; D018528:ATP-Binding Cassette Transporters; D002227:Carbazoles; D007211:Indoles; D008301:Maleimides; D009363:Neoplasm Proteins; D047428:Protein Kinase Inhibitors; C088060:bisindolylmaleimide