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The efflux of anthracyclines in multidrug-resistant cell lines
H M Coley1, P R Twentyman, P Workman
1MRC Clinical Oncology and Radiotherapeutics Unit, Cambridge, U.K.
Abstract:
In order to address the association of enhanced drug efflux with the multidrug-resistant (MDR) phenotype, we have studied the cellular pharmacokinetics of anthracyclines in the P-glycoprotein (Pgp)-positive MDR cell lines H69/LX4 (human small cell lung cancer) and EMT6/AR1.0 (mouse mammary tumour). Both doxorubicin (DOX) and daunorubicin (DNR) were accumulated to a lesser extent and effluxed at a higher rate by MDR cells than by their drug-sensitive counterparts. In contrast, the 9-alkyl substituted compound, aclacinomycin A (ACL), was accumulated and effluxed from parent and MDR cells at an identical rate. In experiments designed to examine energy-dependent efflux, DOX and DNR were shown to be efficiently effluxed against the concentration gradient in the presence of glucose. However, in the same experiments the analogues ACL and Ro 31-3294 (9-alkyl and morpholinyl substituted), which have previously been shown to retain activity against MDR cell lines, were accumulated and effluxed at identical rates in parent and MDR EMT6 cells. Hence, 9-alkyl and morpholinyl substituted compounds appear to behave less favourably as substrates for energy-driven drug efflux by Pgp-positive MDR cells than do DOX or DNR. Resistance modifiers verapamil and cyclosporin A appeared to abolish energy-dependent efflux for DOX and DNR in both the EMT6 and H69 MDR lines whereas they had no effect on the cellular efflux of ACL. The altered cellular pharmacology in MDR cell lines may provide a rational basis for the use of modified anthracycline analogues (e.g. 9-alkyl and morpholinyl (substituted) and resistance of modifying agent in the treatment of tumours expressing a Pgp-mediated phenotype.
Insights
Modified anthracyclines show reduced efflux in multidrug-resistant (MDR) cells. These P-glycoprotein (Pgp)-positive MDR cells exhibit altered cellular pharmacokinetics, suggesting potential for novel cancer therapies.
Area of Science:
- Pharmacology
- Cancer Biology
- Drug Resistance
Background:
- Multidrug resistance (MDR) is a major challenge in cancer chemotherapy.
- Enhanced drug efflux mediated by P-glycoprotein (Pgp) contributes to the MDR phenotype.
- Anthracyclines like doxorubicin (DOX) and daunorubicin (DNR) are substrates for Pgp-mediated efflux.
Purpose of the Study:
- To investigate the cellular pharmacokinetics of anthracyclines in Pgp-positive MDR cell lines.
- To compare the efflux of standard anthracyclines with modified analogues.
- To evaluate the potential of modified anthracyclines in overcoming Pgp-mediated drug resistance.
Main Methods:
- Cellular accumulation and efflux studies of DOX, DNR, and modified anthracyclines (aclacinomycin A, Ro 31-3294) in sensitive and MDR cell lines (H69/LX4, EMT6/AR1.0).
- Experiments assessing energy-dependent efflux in the presence of glucose.
- Evaluation of resistance modifiers (verapamil, cyclosporin A) on drug efflux.
Main Results:
- MDR cells accumulated less DOX and DNR and effluxed them at a higher rate compared to sensitive cells.
- Modified anthracyclines (aclacinomycin A, Ro 31-3294) showed similar accumulation and efflux rates in both sensitive and MDR cells.
- Energy-dependent efflux of DOX and DNR was inhibited by resistance modifiers, while efflux of modified anthracyclines was unaffected.
- Modified compounds are less favorable substrates for Pgp-mediated energy-driven efflux.
Conclusions:
- 9-alkyl and morpholinyl substituted anthracyclines are less efficiently effluxed by Pgp-positive MDR cells.
- Modified anthracyclines demonstrate altered cellular pharmacology compared to standard anthracyclines.
- These findings support the use of modified anthracyclines and resistance modifiers for treating Pgp-mediated MDR tumors.