Inhibition of Glucosylceramide Synthase Does Not Reverse Drug Resistance in Cancer Cells

Edward Norris-Cervetto,Raymond A Dwek,Terry D Butters,Richard Callaghan,Frances M Platt

doi:10.1074/jbc.m404466200

Abstract

The multidrug-resistant cancer cell lines NCI/AdR(RES) and MES-SA/DX-5 have higher glycolipid levels and higher P-glycoprotein expression than the chemosensitive cell lines MCF7-wt and MES-SA. Inhibiting glycolipid biosynthesis by blocking glucosylceramide synthase has been proposed to reverse drug resistance in MDR cells by causing an increased accumulation of proapoptotic ceramide during treatment of cells with cytotoxic drugs. We treated both multidrug-resistant cell lines with the glucosylceramide synthase inhibitors PDMP (d-threo-1-phenyl-2-decanoylamino-3-morpholino-1-propanol), C9DGJ (N-nonyl-deoxygalactonojirimycin) or C4DGJ (N-butyl-deoxygalactonojirimycin). PDMP achieved a significant reversal of drug resistance in agreement with previous reports. However, the N-alkylated iminosugars C9DGJ and C4DGJ, which are more selective glucosylceramide synthase inhibitors than PDMP, failed to cause any reversal of drug resistance despite depleting glycolipids to the same extent as PDMP. Our results suggest that (a) inhibition of glucosylceramide synthase does not reverse multidrug resistance and (b) the chemosensitization achieved by PDMP cannot be caused by inhibition of glucosylceramide synthase alone.

Highlights

A major limitation in chemotherapy for cancer is multidrug resistance (MDR),1 an innate or acquired phenotype, which allows cancer cells to resist a broad spectrum of chemotherapeutic drugs
Our results suggest that (a) inhibition of glucosylceramide synthase does not reverse multidrug resistance and (b) the chemosensitization achieved by PDMP cannot be caused by inhibition of glucosylceramide synthase alone
Manipulation of glycolipid levels in some MDR cancer cells was able to reverse drug resistance [5,6,7,8,9,10,11,12]. This led to the hypothesis that elevated glucosylceramide synthase (GCS, EC 2.4.1.80) activity is a novel form of multidrug resistance and that inhibition of GCS is a promising therapeutic strategy for combating multidrug resistance

Summary

Introduction

A major limitation in chemotherapy for cancer is multidrug resistance (MDR), an innate or acquired phenotype, which allows cancer cells to resist a broad spectrum of chemotherapeutic drugs. Manipulation of glycolipid levels in some MDR cancer cells was able to reverse drug resistance [5,6,7,8,9,10,11,12]. This led to the hypothesis that elevated glucosylceramide synthase (GCS, EC 2.4.1.80) activity is a novel form of multidrug resistance and that inhibition of GCS is a promising therapeutic strategy for combating multidrug resistance. N-Alkylated iminosugars [29] were chosen because they are well tolerated and appear to have fewer side effects in cells than PDMP and its derivatives [25, 26] N-alkyldeoxygalactonojirimycin (N-alkyl-DGJ) compounds were selected because they are even more selective for GCS than N-alkyl-deoxynojirimycin (N-alkyl-DNJ) compounds which inhibit ␣-glucosidases I and II, albeit with much lower potency [30, 31]

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Results

Conclusion