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Chinese hamster ovary cells resistant to okadaic acid express a multidrug resistant phenotype
1Department of Neurochemistry and Molecular Biology, Tohoku University, Sendai, Japan.
Abstract:
Two Chinese hamster ovary cell clones resistant to okadaic acid (OA) were isolated. The OA-resistance was associated with resistance to colchicine, Vinca alkaloids and inhibitors of DNA topoisomerase (topo) II. Drug accumulation assays showed that the intracellular levels of OA, vinblastine and vincristine, but not the topo II inhibitor etoposide, were significantly lowered in the OA-resistant mutants than in the parental cells. These results, together with the finding of an increased level of P-glycoprotein (P-gp) in the mutant cells, indicate that the resistances to OA, Vinca alkaloids and colchicine are due to a P-gp-mediated mechanism. Resistance to topo II inhibitors, however, was associated with reduced activity of topo II. Thus, at least two events, overexpression of P-gp and reduction of topo II activity, occurred in a single OA-resistant cell line, contributing to expression of the MDR phenotype.
Insights
Okadaic acid-resistant Chinese hamster ovary cells exhibit multidrug resistance (MDR). This resistance stems from both P-glycoprotein (P-gp) overexpression and reduced topoisomerase II (topo II) activity, impacting drug accumulation and enzyme function.
Area of Science:
- Cell Biology
- Biochemistry
- Pharmacology
Background:
- Okadaic acid (OA) is a potent protein phosphatase inhibitor.
- Multidrug resistance (MDR) is a complex phenomenon often involving drug efflux pumps and altered drug metabolism.
- Chinese hamster ovary (CHO) cells are a widely used model system in toxicology and drug resistance studies.
Purpose of the Study:
- To investigate the mechanisms underlying okadaic acid (OA) resistance in Chinese hamster ovary (CHO) cells.
- To determine the involvement of P-glycoprotein (P-gp) and DNA topoisomerase II (topo II) in OA resistance.
- To characterize the multidrug resistance (MDR) phenotype in OA-resistant cell lines.
Main Methods:
- Isolation and characterization of OA-resistant CHO cell clones.
- Drug accumulation assays to measure intracellular drug levels.
- Assessment of P-glycoprotein (P-gp) expression.
- Measurement of DNA topoisomerase II (topo II) activity.
Main Results:
- OA-resistant CHO cell clones displayed cross-resistance to colchicine, Vinca alkaloids, and some DNA topoisomerase II (topo II) inhibitors.
- Reduced intracellular accumulation of OA, vinblastine, and vincristine was observed in resistant mutants.
- Increased P-glycoprotein (P-gp) levels correlated with resistance to OA, Vinca alkaloids, and colchicine.
- Resistance to topo II inhibitors was linked to decreased topo II activity, independent of P-gp.
Conclusions:
- The study identified a dual mechanism for multidrug resistance (MDR) in OA-resistant CHO cells.
- P-glycoprotein (P-gp) overexpression mediates resistance to OA, Vinca alkaloids, and colchicine.
- Reduced DNA topoisomerase II (topo II) activity contributes to resistance against topo II inhibitors.
- The findings highlight the complexity of MDR development, involving both drug efflux and altered enzyme function.