title: Resistance to microtubule-targeted cytotoxins in a K562 leukemia cell variant associated with altered tubulin expression and polymerization.
abstract: A vinblastine resistant cell line, KCVB2, was established by co-selecting the parental erythroleukemic cell line K562 with step-wise increased concentrations of vinblastine (Velban) in the presence of the cyclosporin D analogue PSC 833 (2 microM), a potent modulator of the multidrug resistance phenotype. KCVB2 cells are 8-fold resistant to the selecting agent, vinblastine, but also exhibit significant resistance to other vinca alkaloids, including 14-fold resistance to vinorelbine, as well as 6-fold cross-resistance to paclitaxel. Doubling time and morphology were similar to the parental K562 cells. Rt-PCR analysis revealed no alterations in the expression of the mdr1 and MRP genes. Intracellular vinblastine accumulation was unchanged. Disruption of the mitotic spindles and multiple mitotic asters occurred in both cell lines but required higher concentrations of vinblastine in KCVB2 cells than in K562 cells. Significant differences were observed in the tubulin content of KCVB2 cells: reduction of total tubulin content, increased polymerized fraction of total tubulin, and overexpression of class III beta-tubulin which is expressed at very low levels in the parental K562 cells. K562 cells transfected with murine class III beta-tubulin did not display the resistance pattern observed in KCVB2 cells. Revertants of KCVB2 manifested reversion to parental drug sensitivity, an increase in total tubulin level, and a decrease in polymerized tubulin. In conclusion, the KCVB2 cell line displays a novel mechanism of resistance to both depolymerizing and stabilizing microtubule-targeted cytotoxins which does not involve altered cellular drug accumulation, but corresponds to alterations in the total tubulin content and polymerization status, and may involve an effect on microtubule dynamics.
authors.affiliation: Department of Medicine, Divisions of Oncology and Clinical Pharmacology, Stanford University Medical Center, CA 94305, USA.
authors.forename: Charles
authors.initials: C
authors.lastname: Dumontet
authors.forename: Jean-Pierre
authors.initials: JP
authors.lastname: Jaffrezou
authors.forename: Etsuko
authors.initials: E
authors.lastname: Tsuchiya
authors.forename: George E
authors.initials: GE
authors.lastname: Duran
authors.forename: Kevin Gang
authors.initials: KG
authors.lastname: Chen
authors.forename: W Brent
authors.initials: WB
authors.lastname: Derry
authors.forename: Leslie
authors.initials: L
authors.lastname: Wilson
authors.forename: Mary Ann
authors.initials: MA
authors.lastname: Jordan
authors.forename: Branimir I
authors.initials: BI
authors.lastname: Sikic
mesh_terms: D000972:Antineoplastic Agents, Phytogenic / Q000493:pharmacokinetics / Q000494:pharmacology*; D045744:Cell Line, Tumor / Q000187:drug effects / Q000378:metabolism; D002467:Cell Nucleus / Q000187:drug effects; D049109:Cell Proliferation / Q000187:drug effects; D003524:Cyclosporins / Q000187:drug effects / Q000378:metabolism; D019008:Drug Resistance, Neoplasm / Q000502:physiology*; D019450:Genes, MDR; D006801:Humans; D007938:Leukemia / Q000188:drug therapy* / Q000378:metabolism; D008870:Microtubules / Q000187:drug effects* / Q000235:genetics; D008938:Mitosis / Q000187:drug effects; D020133:Reverse Transcriptase Polymerase Chain Reaction; D020539:Sequence Analysis, Protein; D008941:Spindle Apparatus / Q000187:drug effects; D014162:Transfection / Q000379:methods; D014404:Tubulin / Q000032:analysis / Q000187:drug effects* / Q000235:genetics; D014747:Vinblastine / Q000493:pharmacokinetics / Q000494:pharmacology*
chemical_list: D000972:Antineoplastic Agents, Phytogenic; D003524:Cyclosporins; D014404:Tubulin; D014747:Vinblastine; C070272:valspodar