title: Structural determinants of imidazoacridinones facilitating antitumor activity are crucial for substrate recognition by ABCG2.
abstract: Symadex is the lead acridine compound of a novel class of imidazoacridinones (IAs) currently undergoing phase II clinical trials for the treatment of various cancers. Recently, we have shown that Symadex is extruded by ABCG2-overexpressing lung cancer A549/K1.5 cells, thereby resulting in a marked resistance to certain IAs. To identify the IA residues essential for substrate recognition by ABCG2, we here explored the ability of ABCG2 to extrude and confer resistance to a series of 23 IAs differing at defined residue(s) surrounding their common 10-azaanthracene structure. Taking advantage of the inherent fluorescent properties of IAs, ABCG2-dependent efflux and drug resistance were determined in A549/K1.5 cells using flow cytometry in the presence or absence of fumitremorgin C, a specific ABCG2 transport inhibitor. We find that a hydroxyl group at one of the R1, R2, or R3 positions in the proximal IA ring was essential for ABCG2-mediated efflux and consequent IA resistance. Moreover, elongation of the common distal aliphatic side chain attenuated ABCG2-dependent efflux, thereby resulting in the retention of parental cell sensitivity. Hence, the current study offers novel molecular insight into the structural determinants that facilitate ABCG2-mediated drug efflux and consequent drug resistance using a unique platform of fluorescent IAs. Moreover, these results establish that the IA determinants mediating cytotoxicity are precisely those that facilitate ABCG2-dependent drug efflux and IA resistance. The possible clinical implications for the future design of novel acridines that overcome ABCG2-dependent multidrug resistance are discussed.
authors.affiliation: The Fred Wyszkowski Cancer Research Laboratory, Department of Biology, Technion-Israel Institute of Technology, Haifa 32000, Israel.
authors.forename: Eran E
authors.initials: EE
authors.lastname: Bram
authors.forename: Yamit
authors.initials: Y
authors.lastname: Adar
authors.forename: Nufar
authors.initials: N
authors.lastname: Mesika
authors.forename: Michal
authors.initials: M
authors.lastname: Sabisz
authors.forename: Andrzej
authors.initials: A
authors.lastname: Skladanowski
authors.forename: Yehuda G
authors.initials: YG
authors.lastname: Assaraf
mesh_terms: D000070997:ATP Binding Cassette Transporter, Subfamily G, Member 2; D018528:ATP-Binding Cassette Transporters / Q000502:physiology*; D000166:Acridines / Q000737:chemistry / Q000494:pharmacology*; D000609:Aminoacridines / Q000494:pharmacology*; D000970:Antineoplastic Agents / Q000494:pharmacology*; D045744:Cell Line, Tumor; D018432:Drug Resistance, Multiple; D019008:Drug Resistance, Neoplasm; D006801:Humans; D009363:Neoplasm Proteins / Q000502:physiology*; D013329:Structure-Activity Relationship
chemical_list: C116614:ABCG2 protein, human; D000070997:ATP Binding Cassette Transporter, Subfamily G, Member 2; D018528:ATP-Binding Cassette Transporters; D000166:Acridines; D000609:Aminoacridines; D000970:Antineoplastic Agents; D009363:Neoplasm Proteins; C098965:C 1311