title: Effects of drug efflux proteins and topoisomerase I mutations on the camptothecin analogue gimatecan.
abstract: Clinically relevant resistance to the currently approved camptothecins, irinotecan and topotecan, is poorly understood but may involve increased expression of ATP-dependent drug transporters such as ABCG2 (breast cancer resistant protein, BCRP). Gimatecan (ST1481) is a lipophilic 7-substituted camptothecin derivative that exhibits potent anti-tumor activity in a variety of preclinical cancer models and is under investigation in the clinic. Previous studies reported that gimatecan cytotoxicity was not affected by expression of ABCG2. To confirm and extend this finding, we assessed the cytotoxicity of gimatecan in pairs of isogenic cell lines consisting of transfectants expressing either ABCG2 (including wild-type, R482T, or R482G mutants), ABCB1 (P-glycoprotein), ABCC1 (MRP1), ABCC2 (MRP2), or ABCC4 (MRP4). Expression of wild-type or mutant ABCG2 in human cell lines conferred resistance to topotecan but not to gimatecan. Similarly, intracellular accumulation of gimatecan was unaffected by expression of wild-type ABCG2. Furthermore, expression of P-glycoprotein or MRP2 did not alter gimatecan cytotoxicity. Whereas expression of MRP1 had a minor effect on gimatecan cytotoxicity, expression of ABCC4 was found to significantly reduce the anti-proliferative effects of this drug. Cells containing resistance-conferring mutations in topoisomerase I were also resistant to gimatecan. These results suggest that gimatecan may be more effective than irinotecan or topotecan in cancers that express ABCG2, but not in cancers that express high levels of ABCC4 or contain certain topoisomerase I (TOP1) mutations.
authors.affiliation: Department of Pharmacology, Robert Wood Johnson Medical School, University of Medicine and Dentistry of New Jersey, New Brunswick, NJ, USA.
authors.forename: Murugesan K
authors.initials: MK
authors.lastname: Gounder
authors.forename: Ahamed S
authors.initials: AS
authors.lastname: Nazar
authors.forename: Ahamed
authors.initials: A
authors.lastname: Saleem
authors.forename: Pooja
authors.initials: P
authors.lastname: Pungaliya
authors.forename: Diptee
authors.initials: D
authors.lastname: Kulkarni
authors.forename: Richard
authors.initials: R
authors.lastname: Versace
authors.forename: Eric H
authors.initials: EH
authors.lastname: Rubin
mesh_terms: D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology*; D002166:Camptothecin / Q000031:analogs & derivatives* / Q000494:pharmacology; D002460:Cell Line; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D004264:DNA Topoisomerases, Type I / Q000235:genetics / Q000378:metabolism; D004285:Dogs; D019008:Drug Resistance, Neoplasm; D015870:Gene Expression; D006801:Humans; D000077146:Irinotecan; D000089762:Multidrug Resistance-Associated Protein 2; D027425:ATP-Binding Cassette, Sub-Family C Proteins / Q000235:genetics / Q000378:metabolism*; D009154:Mutation; D019772:Topotecan / Q000494:pharmacology; D014162:Transfection
chemical_list: D000970:Antineoplastic Agents; D002166:Camptothecin; D004264:DNA Topoisomerases, Type I; D000077146:Irinotecan; D000089762:Multidrug Resistance-Associated Protein 2; D027425:ATP-Binding Cassette, Sub-Family C Proteins; D019772:Topotecan; C000715087:ABCC2 protein, human; C433984:ST 1481