title: Emergence of different mechanisms of resistance in the evolution of multidrug resistance in murine erythroleukemia cell lines.
abstract: We examined the genetic and biochemical bases for drug resistance and the order of appearance of different mechanisms underlying the increasingly more resistant murine erythroleukemia cell lines established in Adriamycin (ADR). In the first-step low-level resistant cell line PC4-A5 (able to grow in 5 ng/mL ADR), there was a 2-fold reduction in topoisomerase IIalpha and topoisomerase IIbeta mRNA levels, as well as topoisomerase IIalpha protein and activity levels as compared with the parental cell line. The topoisomerase IIalpha activity levels remained reduced as the cells became increasingly more resistant. In contrast, the topoisomerase II mRNA and protein levels returned to approximately the parental levels in resistant cells growing in higher drug concentrations (40-160 ng/mL). Parental cells expressed the multidrug resistance protein (MRP), but beginning with PC4-A5 MRP expression decreased and remained reduced in increasingly resistant cell lines. At high levels of ADR resistance, the cells expressed the mdr3 gene concomitant with the appearance of vincristine resistance and energy-dependent daunomycin and vincristine efflux. Glutathione levels, internal pH, and expression of the major vault protein (MVP) remained unchanged in all cell lines. Fluorescence microscopy revealed no alterations in daunomycin distribution or vesicle numbers between the parental and resistant cell lines. Different resistance mechanisms emerge sequentially as cells become more resistant to ADR; the mechanisms are retained during the development of multidrug resistance (MDR). In intermediate-level MDR cell lines (PC4-A10 and PC4-A20), resistance involves an as yet undetermined mechanism(s).
authors.affiliation: Center for Adaptation Genetics and Drug Resistance, and the Department of Molecular Biology and Microbiology, Tufts University School of Medicine, Boston, MA 02111, U.S.A.
authors.forename: D E
authors.initials: DE
authors.lastname: Modrak
authors.forename: M P
authors.initials: MP
authors.lastname: Draper
authors.forename: S B
authors.initials: SB
authors.lastname: Levy
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000235:genetics; D018528:ATP-Binding Cassette Transporters / Q000235:genetics; D000818:Animals; D004250:DNA Topoisomerases, Type II / Q000378:metabolism; D003630:Daunorubicin / Q000378:metabolism; D018432:Drug Resistance, Multiple; D019008:Drug Resistance, Neoplasm; D005047:Etoposide / Q000378:metabolism; D005978:Glutathione / Q000032:analysis; D006863:Hydrogen-Ion Concentration; D004915:Leukemia, Erythroblastic, Acute / Q000188:drug therapy / Q000378:metabolism / Q000473:pathology; D051379:Mice; D027425:ATP-Binding Cassette, Sub-Family C Proteins; D014407:Tumor Cells, Cultured
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D018528:ATP-Binding Cassette Transporters; D004250:DNA Topoisomerases, Type II; D003630:Daunorubicin; D005047:Etoposide; D005978:Glutathione; D027425:ATP-Binding Cassette, Sub-Family C Proteins