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Doxorubicin resistance in P388 leukemia--evidence for reduced drug influx
A Ramu1, H B Pollard, L M Rosario
1Department of Radiation and Clinical Oncology, Hadassah University Hospital, Jerusalem, Israel.
Abstract:
Multi-drug resistance (MDR) in cancer cells is associated with reduced drug accumulation. Although intensively studied, the mechanism of this process remains ill-defined. We have now developed a new, rapid and quantitative method of measuring uptake of doxorubicin by these cells, in which the fluorescence of accumulated drug is rapidly quenched by DNA in the cell nucleus. Pre-treatment of cells with deoxyribonuclease eliminates DNA from non-viable, permeable cells, and this obviates the spurious fluorescence quenching that made previous application of this technique useless. Our data strongly suggest that the drug passively diffuses into cells. The rate of this diffusion into drug-resistant cells is considerably lower than that found in drug-sensitive cells. The ratio of the rates of drug entry in these cell types could fully account for the differences between the cell lines in doxorubicin growth-inhibitory activity. In these experiments no evidence for the previously proposed active efflux mechanism was found in either cell line.
Insights
This study reveals that multi-drug resistance (MDR) in cancer cells stems from reduced doxorubicin uptake due to passive diffusion, not active efflux. A new method quantifies this drug entry, explaining resistance mechanisms.
Area of Science:
- Biochemistry
- Molecular Biology
- Cancer Research
Background:
- Multi-drug resistance (MDR) in cancer is a major challenge, often linked to decreased drug accumulation.
- The precise mechanisms underlying reduced drug uptake in MDR cancer cells remain incompletely understood.
Purpose of the Study:
- To develop and validate a novel, rapid, and quantitative method for measuring doxorubicin uptake in cancer cells.
- To elucidate the mechanism of doxorubicin accumulation and its role in MDR.
Main Methods:
- A new technique was developed to measure doxorubicin uptake by quantifying its fluorescence, which is quenched by nuclear DNA.
- Deoxyribonuclease pre-treatment was employed to eliminate DNA in permeable cells, preventing artifactual fluorescence quenching.
- Drug uptake rates were compared between drug-sensitive and drug-resistant cancer cell lines.
Main Results:
- The developed method accurately quantifies intracellular doxorubicin.
- Data strongly indicate that doxorubicin enters cells via passive diffusion.
- The rate of doxorubicin diffusion into drug-resistant cells is significantly lower than into drug-sensitive cells.
- The observed differences in diffusion rates fully explain the varying growth-inhibitory effects of doxorubicin between cell lines.
- No evidence supporting an active efflux mechanism was found.
Conclusions:
- Reduced doxorubicin uptake in MDR cancer cells is primarily due to decreased passive diffusion, not active efflux.
- The novel method provides a reliable tool for studying drug transport mechanisms in cancer.
- Understanding these transport dynamics is crucial for overcoming MDR and improving chemotherapy efficacy.