title: Reversal of MDR1-associated resistance to topotecan by PAK-200S, a new dihydropyridine analogue, in human cancer cell lines.
abstract: Recent data suggest that expression of the membrane P170-glycoprotein (P-gp) may confer resistance to the topoisomerase-I-interactive agent topotecan. The present study describes the cellular effects of a new dihydropyridine analogue, PAK-200S, on P-gp-mediated resistance to topotecan in human breast and ovarian tumour cells. PAK-200S at a non-cytotoxic concentration of 2.0 microM completely reversed resistance to topotecan in P-gp-expressing MCF-7/adr (breast) and A2780/Dx5 (ovarian) tumour cells, respectively, with no effects on parental cells. Cellular pharmacokinetic studies by reversed-phase high-performance liquid chromatography analysis showed significantly lower cellular drug concentrations of the pharmacologically active closed-ring lactone of topotecan in multidrug-resistant cells than in parental cells. PAK-200S was effective in restoring the cellular lactone concentrations of topotecan in resistant MCF-7/adr cells to levels comparable to those obtained in parental cells. Furthermore, exposure of MCF-7/adr cells to topotecan in the presence of PAK-200S significantly increased the induction of protein-linked DNA breaks. PAK-200S did not alter nuclear topoisomerase I-mediated ex vivo pBR322 DNA plasmid unwinding activity and topoisomerase-I protein expression. These results suggest that reversal of P-gp-mediated resistance to topotecan by PAK-200S was related to the restoration of cellular drug concentrations of the active lactone form of topotecan rather than a direct effect on topoisomerase-I function.
authors.affiliation: Department of Internal Medicine (Cancer Research), West German Cancer Center, University of Essen Medical School, Germany.
authors.forename: U
authors.initials: U
authors.lastname: Vanhoefer
authors.forename: M R
authors.initials: MR
authors.lastname: Müller
authors.forename: R A
authors.initials: RA
authors.lastname: Hilger
authors.forename: B
authors.initials: B
authors.lastname: Lindtner
authors.forename: U
authors.initials: U
authors.lastname: Klaassen
authors.forename: N
authors.initials: N
authors.lastname: Schleucher
authors.forename: Y M
authors.initials: YM
authors.lastname: Rustum
authors.forename: S
authors.initials: S
authors.lastname: Seeber
authors.forename: A
authors.initials: A
authors.lastname: Harstrick
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000235:genetics*; D000970:Antineoplastic Agents / Q000493:pharmacokinetics / Q000494:pharmacology*; D015153:Blotting, Western; D004264:DNA Topoisomerases, Type I / Q000378:metabolism; D004250:DNA Topoisomerases, Type II / Q000378:metabolism; D004095:Dihydropyridines / Q000494:pharmacology*; D019008:Drug Resistance, Neoplasm / Q000235:genetics; D004354:Drug Screening Assays, Antitumor; D004357:Drug Synergism; D006801:Humans; D009369:Neoplasms / Q000201:enzymology / Q000235:genetics / Q000473:pathology*; D010641:Phenotype; D019772:Topotecan / Q000493:pharmacokinetics / Q000494:pharmacology*; D014407:Tumor Cells, Cultured
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000970:Antineoplastic Agents; D004095:Dihydropyridines; C075404:PAK 200; D019772:Topotecan; D004264:DNA Topoisomerases, Type I; D004250:DNA Topoisomerases, Type II