title: Chemoprotection of hematopoietic cells by a mutant P-glycoprotein resistant to a potent chemosensitizer of multidrug-resistant cancers.
abstract: Cancers are frequently chemoresistant because of overexpression of P-glycoprotein. Two different approaches to improve cancer treatment are currently being investigated in clinical trials: inhibition of P-glycoprotein function by reversing agents, and alleviation of leukocytopenia by MDR1 gene transfer to normal bone marrow of patients. We report here that retroviral vectors encoding a mutant P-glycoprotein (MDR1-F983A) protect hematopoietic cells from anticancer drugs even in the presence of trans-(E)-flupentixol, an inhibitor of P-glycoprotein. Transfer of either mutant or wild-type MDR1 to K562 erythroleukemia cells or primary murine bone marrow resulted in reduced accumulation of daunomycin and vinblastine because of increased drug efflux.trans-(E)-Flupentixol at concentrations up to 10 microM failed to reverse drug efflux mediated by the product of the mutant MDR1 while wild-type P-glycoprotein was inhibited. In the presence of 2 microM trans-(E)-flupentixol chemoresistance to daunomycin was circumvented only in K562 cells transduced with wild-type, but not with mutant, MDR1. Moreover, drug resistance of KB-8-5 epidermoid cancer cells, which express the wild-type MDR1 gene at levels comparable to clinical specimens from multidrug-resistant cancers, was fully overcome in the presence of trans-(E)-flupentixol. Vectors expressing mutant P-glycoprotein may help improve chemotherapy by allowing safe dose intensification under conditions in which multidrug-resistant cancers are rendered drug sensitive by reversing agents.
authors.affiliation: Laboratory of Cell Biology, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA.
authors.forename: P
authors.initials: P
authors.lastname: Hafkemeyer
authors.forename: T
authors.initials: T
authors.lastname: Licht
authors.forename: I
authors.initials: I
authors.lastname: Pastan
authors.forename: M M
authors.initials: MM
authors.lastname: Gottesman
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000235:genetics*; D000818:Animals; D000970:Antineoplastic Agents / Q000009:adverse effects*; D001854:Bone Marrow Cells / Q000187:drug effects*; D003630:Daunorubicin / Q000009:adverse effects; D019008:Drug Resistance, Neoplasm; D005475:Flupenthixol / Q000494:pharmacology*; D018014:Gene Transfer Techniques; D005822:Genetic Vectors; D006801:Humans; D020014:K562 Cells; D051379:Mice; D009154:Mutation; D012190:Retroviridae / Q000235:genetics; D014750:Vincristine / Q000009:adverse effects
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000970:Antineoplastic Agents; D014750:Vincristine; D005475:Flupenthixol; D003630:Daunorubicin