title: Circumvention of confluence-dependent resistance in a human multi-drug-resistant colon-cancer cell line.
abstract: Colorectal adenocarcinomas are inherently resistant to anthracyclines and other topoisomerase-II inhibitors. Resistance to doxorubicin of colon cancer cells (Caco2) depends on 2 main mechanisms. The first is typical multi-drug resistance, characterized by the mdr1 gene and its product the P170 membrane glycoprotein. P170 effluxes anthracyclines out of cancer cells and is antagonized in vitro by verapamil. The second mechanism, which develops when cell-culture density increases, we have designated confluence-dependent resistance. Confluence-dependent resistance depends on the reduced topoisomerase II content of the G0/G1-phase cells which accumulate in the confluent population. We show here that short treatments of confluent Caco2 cells with slightly toxic concentrations of DNA-damaging agents (cisplatin, melphalan or mitomycin C) produced a transient accumulation of cells in S- and G2/M-phases of the cell cycle. Concomitantly with the increase in the S-phase population, the topoisomerase II cellular level and the sensitivity of cells to doxorubicin were greatly enhanced. Overcoming confluence-dependent resistance through S-phase accumulation and inhibition of multi-drug resistance by verapamil were fully additive, and a nearly complete reversal of confluent Caco2 cells' resistance to doxorubicin was obtained when both strategies were combined.
authors.affiliation: CJF INSERM 94/08, Faculty of Medicine, Dijon, France.
authors.forename: C
authors.initials: C
authors.lastname: Garrido
authors.forename: B
authors.initials: B
authors.lastname: Chauffert
authors.forename: D
authors.initials: D
authors.lastname: Pinard
authors.forename: F
authors.initials: F
authors.lastname: Tibaut
authors.forename: P
authors.initials: P
authors.lastname: Genne
authors.forename: M
authors.initials: M
authors.lastname: Assem
authors.forename: M T
authors.initials: MT
authors.lastname: Dimanche-Boitrel
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000037:antagonists & inhibitors / Q000096:biosynthesis*; D000230:Adenocarcinoma / Q000188:drug therapy* / Q000378:metabolism* / Q000473:pathology; D000970:Antineoplastic Agents / Q000494:pharmacology*; D002453:Cell Cycle; D002945:Cisplatin / Q000494:pharmacology; D003110:Colonic Neoplasms / Q000188:drug therapy* / Q000378:metabolism* / Q000473:pathology; D004250:DNA Topoisomerases, Type II / Q000096:biosynthesis; D004317:Doxorubicin / Q000494:pharmacology; D018432:Drug Resistance, Multiple; D004354:Drug Screening Assays, Antitumor; D006801:Humans; D008558:Melphalan / Q000494:pharmacology; D008937:Mitomycins / Q000494:pharmacology; D059005:Topoisomerase II Inhibitors; D014407:Tumor Cells, Cultured
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000970:Antineoplastic Agents; D008937:Mitomycins; D059005:Topoisomerase II Inhibitors; D004317:Doxorubicin; D004250:DNA Topoisomerases, Type II; D002945:Cisplatin; D008558:Melphalan