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Effects of the lipophilic anticancer drug teniposide (VM-26) on membrane transport
S E Wright1, L H Hines, J C White
1Department of Biochemistry, Bowman Gray School of Medicine, Wake Forest University, Winston-Salem, NC 27103.
Abstract:
The epipodophyllotoxin glucopyranosides have previously been shown to interact with membrane lipids and to alter the activity of several lipid-embedded membrane proteins. To determine if these agents are acting as general membrane perturbants, we have further examined their effects on membrane processes in Ehrlich ascites tumor cells. [3H]VM-26 and [3H]VP-16 were taken up rapidly and concentrated within the cells in proportion to their lipophilicity. Neither agent was found to have any significant effect on the influx of L-[3H]leucine or alpha-[3H]aminoisobutyric acid. Likewise, these drugs had no significant effects on the hexose transporter. The nucleoside transporter, which is structurally and functionally similar to the hexose transporter, was dramatically affected, however. VM-26 was a non-competitive inhibitor of equilibrium-exchange influx of cytosine arabinoside in Ehrlich cells with a Ki of 15 microM. Equilibrium-exchange influx increased with temperature in control cells (Q10 = 2) but not in VM-26-treated cells; thus, VM-26 was a more potent inhibitor at higher temperatures. VM-26 also significantly reduced zero-trans influx in Ehrlich, P388, L5178Y, and ML-1 cells, and these effects were immediate in onset. VM-26 inhibited high-affinity binding of the nucleoside transport inhibitor nitrobenzylmercaptopurine riboside (NBMPR), but VM-26 enhanced non-specific NBMPR binding to Ehrlich cells. The apparent specificity of the epipodophyllotoxins for the nucleoside transporter is discussed.
Insights
Epipodophyllotoxin glucopyranosides, like VM-26, do not broadly disrupt cell membranes. Instead, these compounds specifically inhibit nucleoside transporters, impacting cancer cell processes.
Area of Science:
- Biochemistry
- Cell Biology
- Pharmacology
Background:
- Epipodophyllotoxin glucopyranosides interact with membrane lipids and affect lipid-embedded proteins.
- Previous studies suggest these agents may act as general membrane perturbants.
- Ehrlich ascites tumor cells are utilized to investigate cellular membrane processes.
Purpose of the Study:
- To determine if epipodophyllotoxin glucopyranosides act as general membrane perturbants.
- To investigate the specific effects of VM-26 and VP-16 on membrane transport in tumor cells.
Main Methods:
- Uptake and cellular concentration of [3H]VM-26 and [3H]VP-16 were measured.
- Effects on the influx of amino acids (L-[3H]leucine, alpha-[3H]aminoisobutyric acid) and hexose transport were assessed.
- Inhibition of nucleoside transporter activity, including equilibrium-exchange and zero-trans influx of cytosine arabinoside, was analyzed.
- Effects on nitrobenzylmercaptopurine riboside (NBMPR) binding were evaluated.
Main Results:
- VM-26 and VP-16 were rapidly taken up and concentrated within cells based on lipophilicity.
- Neither agent significantly affected amino acid or hexose transport.
- VM-26 acted as a non-competitive inhibitor of nucleoside transporter influx (Ki = 15 microM) and reduced its activity at higher temperatures.
- VM-26 inhibited both high-affinity and non-specific binding of NBMPR to Ehrlich cells.
Conclusions:
- Epipodophyllotoxin glucopyranosides, specifically VM-26, do not appear to be general membrane perturbants.
- These agents exhibit specificity towards the nucleoside transporter.
- The findings highlight the targeted action of epipodophyllotoxins on nucleoside transport mechanisms.