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Multidrug resistance phenotype associated with selection of an aminopterin resistant dog kidney cell line
M S Turker1, K Z Duffin, A C Smith
1Department of Pathology, University of Kentucky College of Medicine, Lexington 40536.
Abstract:
A determination of the mechanisms of drug resistance in tumour cells is important for developing strategies to combat such resistance in persons receiving chemotherapy. This report describes a combined cellular, biochemical, and molecular analysis of a dog kidney cell line selected for resistance to increasing levels of the hydrophilic antifolate, aminopterin. Three distinct drug resistance phenotypes were observed in cells exhibiting high levels of aminopterin resistance. Two of these phenotypes were decreased aminopterin accumulation and increased levels of dihydrofolate reductase specific activity. The third drug resistance phenotype was noted initially as cross resistance to a variety of hydrophobic drugs indicating multidrug resistance. Biochemical assays demonstrated reduced accumulation of the hydrophobic fluorescent drug daunorubicin and of 3H-colchicine in the aminopterin resistant cells. These results were then correlated with increased levels of the multidrug resistance (mdr) gene product, P-glycoprotein, and mdr mRNA levels in the aminopterin resistant cells. However, experiments designed to prove a role for expression of the mdr gene in providing a degree of aminopterin resistance were unsuccessful. It is concluded that aminopterin selection in these dog kidney cells resulted in expression of at least three distinct drug resistance phenotypes and that one of these phenotypes, multidrug resistance, represented a secondary response to the aminopterin selection.
Insights
Drug resistance in tumor cells is critical for chemotherapy. This study found that aminopterin resistance in dog kidney cells led to decreased drug accumulation, increased enzyme activity, and multidrug resistance, with the latter being a secondary response.
Area of Science:
- Cell Biology
- Pharmacology
- Molecular Biology
Background:
- Understanding drug resistance mechanisms is vital for improving chemotherapy.
- Antifolate drugs like aminopterin are used in cancer treatment.
- Tumor cells can develop resistance to chemotherapy, reducing treatment efficacy.
Purpose of the Study:
- To investigate the mechanisms of drug resistance in a dog kidney cell line selected for resistance to aminopterin.
- To characterize the distinct phenotypes associated with aminopterin resistance.
- To explore the potential role of multidrug resistance in aminopterin resistance.
Main Methods:
- Combined cellular, biochemical, and molecular analysis.
- Selection of a dog kidney cell line for resistance to increasing levels of aminopterin.
- Assays for drug accumulation, enzyme activity (dihydrofolate reductase), and expression of multidrug resistance (mdr) genes and proteins.
Main Results:
- Three distinct drug resistance phenotypes were identified: decreased aminopterin accumulation, increased dihydrofolate reductase activity, and multidrug resistance.
- Aminopterin-resistant cells showed reduced accumulation of hydrophobic drugs like daunorubicin and colchicine.
- Increased levels of P-glycoprotein and mdr mRNA were observed in resistant cells, indicating multidrug resistance.
- Expression of the mdr gene did not appear to confer aminopterin resistance.
Conclusions:
- Aminopterin selection in dog kidney cells induces multiple drug resistance phenotypes.
- Multidrug resistance emerged as a secondary response to aminopterin selection.
- These findings contribute to understanding complex drug resistance mechanisms in cancer therapy.