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Anomalous expression of P-glycoprotein in highly drug-resistant human KB cells
E D Dolci1, R Abramson, Y Xuan
1Department of Pharmacology, University of Vermont, College of Medicine, Burlington 05405.
Abstract:
KB-A1 and KB-A10 are 2 multi-drug-resistant cell lines which are 100- and 1,000-fold resistant to Adriamycin, respectively. We have examined the expression of P-glycoprotein at the molecular and cellular levels in these human carcinoma cells. Both MDR cell lines, when compared to the parental KB-3-1, show characteristic increases in mdr 1 gene copy number, an increase in mdr 1 mRNA expression, a corresponding increase in transcription rate and a consequent over-expression of P-glycoprotein. However, the more highly resistant KB-A10 cells have a lower gene copy number, express less mdr 1 mRNA and contain less P-glycoprotein than the A1 cell line. To determine whether higher levels of cellular resistance were attributable to enhanced efficacy of P-glycoprotein or to other cellular regulatory mechanisms, we examined other major cellular properties known to be associated with the mdr phenotype. Both the KB-A1 and KB-A10 lines exhibit similar increases in protein kinase C activity as compared to the drug-sensitive parent. In addition, neither glutathione-S-transferase nor topoisomerase II activities account for enhanced resistance of the KB-A10 cells. The above observations are contrary to the premise that the level of drug resistance is necessarily proportional to expression of P-glycoprotein or to other common factors thought to participate in drug insensitivity; consequently, new mechanisms of resistance must be in operation in these cells.
Insights
Multi-drug resistance (MDR) in human carcinoma cells involves more than just P-glycoprotein. Even with lower P-glycoprotein levels, KB-A10 cells show high Adriamycin resistance, suggesting novel resistance mechanisms.
Area of Science:
- Molecular Biology
- Cell Biology
- Cancer Research
Background:
- Multi-drug resistance (MDR) is a significant challenge in cancer chemotherapy.
- P-glycoprotein (P-gp) is a key efflux pump implicated in MDR.
- Understanding MDR mechanisms is crucial for developing effective cancer treatments.
Purpose of the Study:
- To investigate the molecular mechanisms of Adriamycin resistance in human carcinoma cell lines KB-A1 and KB-A10.
- To compare the expression and function of P-glycoprotein in drug-sensitive and resistant cell lines.
- To explore alternative cellular mechanisms contributing to MDR beyond P-gp.
Main Methods:
- Analysis of mdr1 gene copy number, mRNA expression, and P-glycoprotein levels.
- Assessment of protein kinase C activity.
- Measurement of glutathione-S-transferase and topoisomerase II activities.
Main Results:
- Both KB-A1 and KB-A10 cell lines exhibited increased mdr1 gene copy number, mRNA, and P-gp expression compared to the parental KB-3-1 cells.
- Surprisingly, the highly resistant KB-A10 cells showed lower P-gp levels than the less resistant KB-A1 cells.
- Similar increases in protein kinase C activity were observed in both MDR lines, while glutathione-S-transferase and topoisomerase II activities did not explain the enhanced resistance.
Conclusions:
- The level of drug resistance is not always directly proportional to P-glycoprotein expression or other known MDR factors.
- Novel cellular regulatory mechanisms likely contribute to the high-level drug resistance observed in KB-A10 cells.
- Further research is needed to elucidate these alternative pathways involved in multidrug resistance.