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Subcellular distribution of epothilones in human tumor cells
R B Lichtner1, A Rotgeri, T Bunte
1Research Laboratories of Schering AG, Müllerstrasse 178, 13342 Berlin, Germany. Rosemarie.Lichtner@metagen.de
Abstract:
Epothilones are a new class of natural and potent antineoplastic agents that stabilize microtubules. Although 12,13-epoxide derivatives are potent antiproliferative agents, the activities of the corresponding 12,13-olefin analogs are significantly decreased. These data were confirmed for two new analogs, 6-propyl-EpoB (pEB) and 6-propyl-EpoD (pED), in comparison with the natural compounds EpoB/EpoD, by using human A431, MCF7, and MDR1-overexpressing NCI/Adr cells. By using tritiated pEB/pED, compound uptake, release, and nuclear accumulation were investigated in A431 and NCI/Adr cells. In these cells, epothilones can principally be recognized and exported by Verapamil-sensitive efflux pumps, which are not identical to MDR1. The degree of export depends on the structure, olefin vs. epoxide-analog, and also on the intracellular drug concentration. The accumulation of pED used at 3.5 or 70 nM, respectively, was increased in the presence of 10 microM Verapamil in both cell lines 2- to 8-fold. In contrast, the intracellular levels of pEB were affected by Verapamil only at 3.5 nM pEB in NCI/Adr (2-fold) and not in A431 cells. In addition, strong nuclear accumulation was observed for pEB (40-50%) but not paclitaxel or pED (5-15%) in both cell lines. Our study suggests that differences in growth inhibitory efficacy between epoxide and olefin analogs may be based on different mechanisms of drug accumulation and subcellular distribution.
Insights
Epothilone analogs, 6-propyl-EpoB (pEB) and 6-propyl-EpoD (pED), show varied cellular uptake and nuclear accumulation. Verapamil-sensitive efflux pumps influence epothilone export, impacting their anticancer efficacy.
Area of Science:
- Pharmacology
- Cell Biology
- Medicinal Chemistry
Background:
- Epothilones are potent antineoplastic agents that stabilize microtubules.
- 12,13-epoxide derivatives exhibit strong antiproliferative activity, while 12,13-olefin analogs show reduced efficacy.
Purpose of the Study:
- To investigate the cellular uptake, release, and nuclear accumulation of epothilone analogs.
- To compare the mechanisms of action between epoxide and olefin epothilone analogs.
- To explore the role of efflux pumps in epothilone transport and efficacy.
Main Methods:
- Utilized tritiated 6-propyl-EpoB (pEB) and 6-propyl-EpoD (pED) for uptake and release studies.
- Employed human cancer cell lines (A431, MCF7, NCI/Adr) including MDR1-overexpressing cells.
- Assessed the effect of Verapamil on intracellular drug accumulation and distribution.
Main Results:
- Epothilones are exported by Verapamil-sensitive efflux pumps, distinct from MDR1.
- The degree of export is dependent on analog structure (olefin vs. epoxide) and intracellular concentration.
- pED accumulation increased 2- to 8-fold with Verapamil; pEB accumulation was less affected.
- pEB showed strong nuclear accumulation (40-50%), unlike pED and paclitaxel (5-15%).
Conclusions:
- Differences in growth inhibitory efficacy between epoxide and olefin epothilones correlate with distinct drug accumulation and subcellular distribution patterns.
- Verapamil-sensitive efflux pumps play a significant role in limiting intracellular epothilone concentrations.
- Structural variations significantly influence epothilone interaction with efflux pumps and nuclear targeting.
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