title: Calmodulin inhibitor trifluoperazine in combination with doxorubicin induces the selection of tumour cells with the multidrug resistant phenotype.
abstract: Trifluoperazine (TFP) is effective in modulating DNA damage/repair in doxorubicin (DOX) treated cells. In the present study we have characterised the resistance phenotype of parental sensitive L1210 mouse leukaemia cells (L1210/S) adapted to grow in the presence of 0.017 microns DOX+5 microM TFP (L1210/DT). Although with prolonged exposure, 0.017 microM DOX alone produced < 35% cell kill in L1210/S cells, similar cytotoxicity was achieved at 0.43 microM DOX in L1210/S cells selected in the presence of 0.017 microM DOX+5 microM TFP. L1210/DT cells were > 30-fold resistant to DOX following a 3 h drug exposure in a soft agar colony assay. In contrast, DOX sensitivity in cells adapted to grow in 5 microM TFP alone was comparable to L1210/S cells. Resistance to other inhibitors of topoisomerase II in L1210/DT cells was > 30-fold to etoposide and > 6-fold to amsacrine. The levels of the 170 kDa and 180 kDa isoforms of topoisomerase II in an immunoblot were comparable between the L1210/S and L1210/DT cells. Cross resistance to vincristine in the L1210/DT cells was accompanied by the overexpression of plasma membrane P-glycoprotein. Although a 1.5-2-fold decrease in accumulation of etoposide and DOX was observed in the L1210/DT cells, drug levels for equivalent DNA damage in the alkaline elution assay were > 5-fold higher in the L1210/DT versus L1210/S cells. No abrogation in the modulating effects of TFP on DOX, VP-16 or amsacrine induced cytotoxicity was apparent in the L1210/DT cells. Results suggest that: (a) TFP in combination with low concentrations DOX can induce the selection of cells with the multidrug resistant phenotype; and (b) characteristics of cells selected for resistance to DOX or DOX plus TFP are comparable.
authors.affiliation: Department of Cancer Biology, Cleveland Clinic Foundation, Ohio 44195.
authors.forename: N
authors.initials: N
authors.lastname: Kamath
authors.forename: D
authors.initials: D
authors.lastname: Grabowski
authors.forename: J
authors.initials: J
authors.lastname: Ford
authors.forename: R
authors.initials: R
authors.lastname: Ganapathi
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000818:Animals; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000494:pharmacology*; D002147:Calmodulin / Q000037:antagonists & inhibitors; D002352:Carrier Proteins / Q000378:metabolism; D002455:Cell Division / Q000187:drug effects; D004249:DNA Damage; D004250:DNA Topoisomerases, Type II / Q000378:metabolism; D004273:DNA, Neoplasm / Q000187:drug effects; D004317:Doxorubicin / Q000008:administration & dosage / Q000493:pharmacokinetics; D004351:Drug Resistance / Q000235:genetics; D004354:Drug Screening Assays, Antitumor; D005047:Etoposide / Q000493:pharmacokinetics; D007939:Leukemia L1210 / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology; D008562:Membrane Glycoproteins / Q000378:metabolism; D051379:Mice; D010641:Phenotype; D014268:Trifluoperazine / Q000008:administration & dosage; D014407:Tumor Cells, Cultured / Q000187:drug effects
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D002147:Calmodulin; D002352:Carrier Proteins; D004273:DNA, Neoplasm; D008562:Membrane Glycoproteins; D014268:Trifluoperazine; D005047:Etoposide; D004317:Doxorubicin; D004250:DNA Topoisomerases, Type II