title: Characterization of actinomycin-D-resistant CHO cell lines exhibiting a multidrug-resistance phenotype and amplified DNA sequences.
abstract: Actinomycin D (DACT)-resistant sublines of the Chinese hamster ovary cell line CHO-K1 were selected in vitro. Sublines were derived which expressed 5.2-fold (CHO 15DACT) and 35.8-fold (CHO 100DACT) resistance to DACT. The CHO 100DACT subline displayed marked cross-resistance to bleomycin, adriamycin, daunomycin, vinblastine, vincristine, VP 16 and VM 26. No cross-resistance was found to cisplatin or methotrexate. The resistant cells exhibited enhanced (collateral) sensitivity to prednisolone. Combination of prednisolone with vincristine resulted in a pronounced synergistic effect on sensitive cells, whereas in resistant cells the combined effect of both drugs was merely additive. Resistant cells, viably stained with the DNA-specific dye Hoechst 33342, exhibited decreased fluorescence intensities compared to parental cells. In contrast to sensitive cells the resistant sublines did not accumulate the mitochondria-specific dye rhodamine 123. Co-incubation with verapamil, however, effectively enhanced accumulation of the dye. The potential diagnostic value of these fluorescent compounds as marker dyes for the multidrug-resistance phenotype is discussed. Non-toxic doses of verapamil almost completely reversed the resistance to various drugs in CHO 100DACT cells. Specific DNA sequences were amplified in resistant cells, and the increase in resistance was paralleled by a concomitant increase in the copy number of these sequences, suggesting that the corresponding gene may be functionally linked to the multidrug-resistance phenotype.
mesh_terms: D000818:Animals; D002460:Cell Line / Q000187:drug effects; D006224:Cricetinae; D003412:Cricetulus; D004247:DNA / Q000032:analysis; D003609:Dactinomycin / Q000494:pharmacology*; D005260:Female; D005784:Gene Amplification / Q000187:drug effects*; D010053:Ovary; D010641:Phenotype; D011239:Prednisolone / Q000494:pharmacology; D013194:Staining and Labeling; D014750:Vincristine / Q000494:pharmacology
chemical_list: D003609:Dactinomycin; D014750:Vincristine; D004247:DNA; D011239:Prednisolone