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Decreased resistance to N,N-dimethylated anthracyclines in multidrug-resistant Friend erythroleukemia cells
A Schaefer1, J Westendorf, K Lingelbach
1Department of Toxicology, University of Hamburg Medical School, Germany.
Abstract:
Doxorubicin-resistant Friend erythroleukemia cells, line F4-6 ADM2R, were selected by exposure of wild-type F4-6 cells to doxorubicin concentrations of up to 1 microgram/ml. In these cells, increased expression of multidrug resistance (MDR) genes was demonstrated by Northern blot analysis. The growth-inhibitory effect of doxorubicin, daunorubicin, N,N-dimethyldoxorubicin, N,N-dimethyldaunorubicin, morpholinodoxorubicin, and pyrromycin was comparatively investigated in resistant and wild-type cells. The doxorubicin-resistant F4-6 cells showed approx. 200-fold resistance to doxorubicin and about 100-fold resistance to daunorubicin with respect to the drug-sensitive counterpart. A dramatic decrease in resistance was observed for the N,N-dimethylated derivatives of doxorubicin and daunorubicin as well as for the N,N-dimethylated natural anthracycline pyrromycin and for morpholinodoxorubicin. Uptake studies using [14C]-daunorubicin and [14C]-N,N-dimethyldaunorubicin in resistant F4-6 cells showed a decreased accumulation of daunorubicin but no significant reduction in N,N-dimethyldaunorubicin accumulation as compared with the wild-type cells. Treatment with verapamil led to increased intracellular levels of daunorubicin in resistant cells, whereas an excess of N,N-dimethyldaunorubicin did not have this effect. Thus, the decreased resistance of the doxorubicin-resistant F4-6 cells to the N-alkylated anthracyclines may at least in part be due to a reduced affinity of these compounds for the efflux pump. The results indicate that the dimethylation of the amino group of the anthracycline sugar moiety and its incorporation within a morpholinyl ring may overcome MDR by similar mechanisms.
Insights
Modified anthracyclines, like N,N-dimethylated versions, show reduced resistance in doxorubicin-resistant cancer cells. This suggests dimethylation may overcome multidrug resistance (MDR) by altering efflux pump affinity.
Area of Science:
- Biochemistry
- Pharmacology
- Cancer Biology
Background:
- Multidrug resistance (MDR) is a major challenge in cancer chemotherapy, limiting the efficacy of drugs like doxorubicin.
- Friend erythroleukemia cells (F4-6 ADM2R) were developed to exhibit resistance to doxorubicin, showing increased multidrug resistance gene expression.
Purpose of the Study:
- To investigate the comparative efficacy of various anthracycline derivatives against doxorubicin-resistant cancer cells.
- To elucidate the mechanisms underlying reduced resistance to modified anthracyclines in resistant cell lines.
Main Methods:
- Selection of doxorubicin-resistant Friend erythroleukemia cells (F4-6 ADM2R).
- Northern blot analysis to confirm increased multidrug resistance gene expression.
- Comparative growth inhibition assays with doxorubicin and its derivatives (daunorubicin, N,N-dimethyldoxorubicin, N,N-dimethyldaunorubicin, morpholinodoxorubicin, pyrromycin).
- Cellular uptake studies using radiolabeled daunorubicin and N,N-dimethyldaunorubicin.
- Verapamil treatment to assess the role of efflux pumps.
Main Results:
- Doxorubicin-resistant cells exhibited ~200-fold resistance to doxorubicin and ~100-fold to daunorubicin.
- Significantly reduced resistance was observed for N,N-dimethylated anthracyclines and morpholinodoxorubicin.
- Uptake studies revealed decreased daunorubicin accumulation but normal N,N-dimethyldaunorubicin accumulation in resistant cells.
- Verapamil increased intracellular daunorubicin, but not N,N-dimethyldaunorubicin, in resistant cells.
Conclusions:
- The N,N-dimethylation of the anthracycline sugar moiety and incorporation into a morpholinyl ring can overcome multidrug resistance (MDR).
- Reduced affinity for the drug efflux pump is a likely mechanism for the decreased resistance to N-alkylated anthracyclines.
- These modifications offer potential strategies to circumvent MDR in cancer treatment.