Vineet Gupta

A role for ceramide in driving cancer cell resistance to doxorubicin

Advanced cancers acquire resistance to chemotherapy, and this results in treatment failure. The cellular mechanisms of chemotherapy resistance are not well understood. Here, for the first time, we show that ceramide contributes to cellular resistance to doxorubicin through up‐regulating the gene expression of glucosylceramide synthase (GCS). Ceramide, a cellular lipid messenger, modulates doxorubicin‐induced cell death. GCS catalyzes ceramide glycosylation, converting ceramide to glucosylceramide; this process hastens ceramide clearance and limits ceramide‐induced apoptosis. In the present study, we evaluated the role of the GCS gene in doxorubicin resistance using several paired wild‐type and drug‐resistant (doxorubicin‐selected) cancer cell lines, including breast, ovary, cervical, and colon. GCS was overexpressed in all drug‐resistant counterparts, and suppressing GCS overexpression using antisense oligonucleotide restored doxorubicin sensitivity. Characterizing the effect mechanism showed that doxorubicin exposure increased ceramide levels, enhanced GCS expression, and imparted cellular resistance. Exogenous C6‐ceramide and sphingomyelinase treatments mimicked the influence of doxorubicin on GCS, activating the GCS promoter and upregulating GCS gene expression. Fumonisin B1, an inhibitor of ceramide synthesis, significantly suppressed doxorubicin‐up‐regulated GCS expression. Promoter truncation, point mutation, gel‐shift, and protein‐DNA ELISA analysis showed that transcription factor Sp1 was essential for ceramide‐induced GCS up‐regulation. These data indicate that ceramide‐governed GCS gene expression drives cellular resistance to doxorubicin.—Liu, Y.‐Y., Yu, J. Y., Yin, D., Patwardhan, G. A., Gupta, V., Hirabayashi, Y., Holleran, W. M., Giuliano, A. E., Jazwinski, S. M., Gouaze‐Andersson, V., Consoli, D. P., Cabot, M. C. A role for ceramide in driving cancer cell resistance to doxorubicin. FASEB J. 22, 2541–2551 (2008)

Ceramide Glycosylation by Glucosylceramide Synthase Selectively Maintains the Properties of Breast Cancer Stem Cells

Background: Glucosylceramide synthase catalyzes ceramide glycosylation that regulates the synthesis of glycosphingolipids. Results: Increased globo-series glycosphingolipids in breast cancer stem cells activate c-Src signaling and β-catenin-mediated transcription up-regulating stem cell factors. Conclusion: Ceramide glycosylation maintains the stemness of cancer stem cells. Significance: Glycosphingolipids in cell membrane actively participate in maintaining cancer stem cells. Cancer stem cells are distinguished from normal adult stem cells by their stemness without tissue homeostasis control. Glycosphingolipids (GSLs), particularly globo-series GSLs, are important markers of undifferentiated embryonic stem cells, but little is known about whether or not ceramide glycosylation, which controls glycosphingolipid synthesis, plays a role in modulating stem cells. Here, we report that ceramide glycosylation catalyzed by glucosylceramide synthase, which is enhanced in breast cancer stem cells (BCSCs) but not in normal mammary epithelial stem cells, maintains tumorous pluripotency of BCSCs. Enhanced ceramide glycosylation and globotriosylceramide (Gb3) correlate well with the numbers of BCSCs in breast cancer cell lines. In BCSCs sorted with CD44+/ESA+/CD24− markers, Gb3 activates c-Src/β-catenin signaling and up-regulates the expression of FGF-2, CD44, and Oct-4 enriching tumorigenesis. Conversely, silencing glucosylceramide synthase expression disrupts Gb3 synthesis and selectively kills BCSCs through deactivation of c-Src/β-catenin signaling. These findings highlight the unexploited role of ceramide glycosylation in selectively maintaining the tumorous pluripotency of cancer stem cells. It speculates that disruption of ceramide glycosylation or globo-series GSL is a useful approach to specifically target BCSCs specifically.

A new mixed-backbone oligonucleotide against glucosylceramide synthase sensitizes multidrug-resistant tumors to apoptosis.

Enhanced ceramide glycosylation catalyzed by glucosylceramide synthase (GCS) limits therapeutic efficiencies of antineoplastic agents including doxorubicin in drug-resistant cancer cells. Aimed to determine the role of GCS in tumor response to chemotherapy, a new mixed-backbone oligonucleotide (MBO-asGCS) with higher stability and efficiency has been generated to silence human GCS gene. MBO-asGCS was taken up efficiently in both drug-sensitive and drug-resistant cells, but it selectively suppressed GCS overexpression, and sensitized drug-resistant cells. MBO-asGCS increased doxorubicin sensitivity by 83-fold in human NCI/ADR-RES, and 43-fold in murine EMT6/AR1 breast cancer cells, respectively. In tumor-bearing mice, MBO-asGCS treatment dramatically inhibited the growth of multidrug-resistant NCI/ADR-RE tumors, decreasing tumor volume to 37%, as compared with scrambled control. Furthermore, MBO-asGCS sensitized multidrug-resistant tumors to chemotherapy, increasing doxorubicin efficiency greater than 2-fold. The sensitization effects of MBO-asGCS relied on the decreases of gene expression and enzyme activity of GCS, and on the increases of C18-ceramide and of caspase-executed apoptosis. MBO-asGCS was accumulation in tumor xenografts was greater in other tissues, excepting liver and kidneys; but MBO-asGCS did not exert significant toxic effects on liver and kidneys. This study, for the first time in vivo, has demonstrated that GCS is a promising therapeutic target for cancer drug resistance, and MBO-asGCS has the potential to be developed as an antineoplastic agent.

Direct assessment of P-glycoprotein efflux to determine tumor response to chemotherapy.

Multidrug resistance is a major impediment to the success of cancer chemotherapy. The overproduced P-glycoprotein that extrudes anticancer drugs from cells, is the most common mechanism detected in multidrug-resistant cancers. Direct measurement of cellular efflux of tumors in vivo, rather than estimation of MDR1 mRNA and P-glycoprotein levels in samples stored or embedded, can functionally characterize the mechanism of drug resistance and determine the choice of anticancer drugs for cancer patients. Herewith, we introduce a new approach to directly determine P-glycoprotein efflux of tumors. Employing Flutax-2 (Oregon green-488 paclitaxel) and fluorescence spectrophotometry, this method has successfully measured cellular transportability including efflux and accumulation in diverse cancer cell lines, tumors and other tissues with high reproducibility. With this method, we have quantitatively determined cellular efflux that is correlated with P-glycoprotein levels and the reversal effects of agents in cell lines of breast, ovarian, cervical and colon cancers, and in tumor-bearing mice. It has sensitively detected these alterations of P-glycoprotein efflux in approximately 5mg tumor or other tissues with high confidence. This direct and quick functional assessment has a potential to determine drug resistance in different types of cancers after surgical resection. Further validation of this method in clinic settings for the diagnosis of drug resistance purpose is needed.

‘Doxorubicin and MBO-asGCS Oligonucleotide Loaded Lipid Nanoparticles Overcome Multidrug Resistance in Adriamycin Resistant Ovarian Cancer Cells (NCI/ADR-RES)

The objective of this study was to increase the potency of doxorubicin against adriamycin-resistant NCI/ADR-RES cells by concurrent treatment with doxorubicin and MBO-asGCS loaded solid-lipid nanoparticles (SLN). Loading doxorubicin as ion-pair complex with deoxytaurocholate into cationic and neutral SLN was investigated. Fast release and poor entrapment were observed in cationic nanoparticles, which were corrected by entrapping the complex in neutral polyoxyethylene (20) stearyl ether (Brij(®) 78)/VitE-TPGS nanoparticles. Slow doxorubicin release confirmed the influence of charge and electrolytes on the dissociation of ion-pair complexes. To evaluate antitumor activity, NCI/ADR-RES cells were treated with separate SLN: one loaded with doxorubicin and another carrying MBO-asGCS oligonucleotide. The viability of cells treated with 5 μM doxorubicin was reduced to 17.2% whereas viability was reduced to 2.5% for cells treated with both 5 μM doxorubicin SLN and 100 nM MBO-asGCS SLN. This suggested enhanced apoptosis due to sensitization and effective intracellular delivery of MBO-asGCS and doxorubicin by SLN.

Direct quantitative determination of ceramide glycosylation in vivo: a new approach to evaluate cellular enzyme activity of glucosylceramide synthase

Glucosylceramide synthase (GCS or GlcT-1), converting ceramide to glucosylceramide, is a key enzyme for the synthesis of glycosphingolipids. Due to its diverse roles in physiology and diseases, GCS may be a disease marker and drug target. Current assays for enzymes including GCS are based on reactions conducted in a test tube using enzyme preparations. Measurement of enzyme activity in laboratory-made conditions cannot directly evaluate the role of GCS in cells. Here, we introduce a new approach to determine GCS cellular activity using fluorescent NBD C6-ceramide in vivo. Cellular GCS transfers UDP-glucose to NBD C6-ceramide and produces NBD C6-glucosylceramide. C6-glucosylceramide is then separated from C6-ceramide by thin-layer chromatography and both are then quantitated by spectrophotometer. This cell-based method is able to quantitate glucosylceramide in pmol range, produced by approximately 50,000 cells or 1.0 mg tissue. This method has been used successfully to evaluate the degrees of GCS enzyme in cells and in tumors subjected to gene manipulation and chemical inhibition. These data indicate that this cell-based fluorescent method is direct, reproducible, and simple for assessing ceramide glycosylation. It is applicable to validate GCS activity in drug-resistant cancers and in other disorders.

The opposite effects of doxorubicin on bone marrow stem cells versus breast cancer stem cells depend on glucosylceramide synthase.

Myelosuppression and drug resistance are common adverse effects in cancer patients with chemotherapy, and those severely limit the therapeutic efficacy and lead treatment failure. It is unclear by which cellular mechanism anticancer drugs suppress bone marrow, while drug-resistant tumors survive. We report that due to the difference of glucosylceramide synthase (GCS), catalyzing ceramide glycosylation, doxorubicin (Dox) eliminates bone marrow stem cells (BMSCs) and expands breast cancer stem cells (BCSCs). It was found that Dox decreased the numbers of BMSCs (ABCG2(+)) and the sphere formation in a dose-dependent fashion in isolated bone marrow cells. In tumor-bearing mice, Dox treatments (5mg/kg, 6 days) decreased the numbers of BMSCs and white blood cells; conversely, those treatments increased the numbers of BCSCs (CD24(-)/CD44(+)/ESA(+)) more than threefold in the same mice. Furthermore, therapeutic-dose of Dox (1mg/kg/week, 42 days) decreased the numbers of BMSCs while it increased BCSCs in vivo. Breast cancer cells, rather than bone marrow cells, highly expressed GCS, which was induced by Dox and correlated with BCSC pluripotency. These results indicate that Dox may have opposite effects, suppressing BMSCs versus expanding BCSCs, and GCS is one determinant of the differentiated responsiveness of bone marrow and cancer cells.

Evaluation of Anticancer Agents Using Flow Cytometry Analysis of Cancer Stem Cells

Flow cytometry can sensitively detect and efficiently sort cells based on fluorescent signals integrated into cellular markers of proteins or DNA. It has been broadly applied to assess cell division, apoptosis and to isolate cells including stem cells. As the seeds for tumorigenesis and metastasis, cancer stem cells (CSCs) are often more resistant to cytotoxins and anticancer agents than other heterogeneous cells in tumors. Analyzing CSCs under treatments is an effective way to evaluate new therapeutic agents for cancers. We introduce a method using flow cytometry to assess breast CSCs (CD44(+)/CD24(-)/(low)) in human MCF-7/Dox breast cancer cells, after the treatment of mixed-backbone oligonucleotide against glucosylceramide synthase. Flow cytometry analysis of CSCs is a reliable, effective, and easy-handling approach to screen agents targeting CSCs.

Abstract 4282: The role of glycosphingolipids in the formation of cancer stem cells and drug resistance

Tumorigenesis and malignant progression of cancers rely on a small subset of cells known as cancer stem cells (CSCs). In addition to forming primary tumors, metastasis and relapse, CSCs always display resistance to cytotoxins and this resistant feature protects CSCs during the course of chemotherapy. Glucosylceramide synthase (GCS) is a limited enzyme catalyzing the first glycosylation in glycosphingolipids synthesis. Glycosphingolipids are likely to play an essential role in maintaining the stemness of stem cells, since that deletion of GCS induces apoptosis of embryonic stem cell and stops embryo development in GCS knockout mice. The stage-specific embryonic antigens (SSEA-3, SSEA-4) are glycosphingolipids and serve as common pluripotent markers for human embryonic stem cells. In the present study, we have found that GCS modulates the formation and maintenance of breast cancer stem cells. GCS overexpression was interrelated to the increase of breast cancer stem cells (BCSCs) and drug resistance in human breast cancer MCF-7 cell lines after doxorubicin induction. In MCF-7/Dox (doxorubicin-resistant) cells, GCS protein was increased by 39-fold accompanied with enhanced enzyme activity, as compared to wild-type MCF-7 cell. Analyzed by using flow cytometry and immunostaining, the BCSCs with CD44 + /CD24-/ESA + phenotype were increased by 5-fold, and 3-fold in MCF-7/Dox and NCI-ADR/RES cell lines, as compared to MCF-7 cell lines, respectively. In BCSCs, GCS enzyme activity was 2-fold greater than other populations sorted from MCF-7/Dox. Silencing GCS by using mixed-backbone oligonucleotide (MBO-asGCS) significantly decreased the numbers of BCSCs in MCF-7/Dox cells. We observed tumorigenesis of NCI/ADR-RE/GCS (GCS overexpressed) and NCI/ADR-RE/asGCS (GCS silenced) in athymic nude mice. Aggressive tumors were found in all mice inoculated with NCI/ADR-RES and NCI/ADR-RE/GCS cells that were BCSC-enriched; however, no tumor or metastasis was observed in mice injected with NCI-ADR/asGCS cells. Furthermore, MBO-asGCS treatment (1 mg/kg) significantly decreased the numbers of BCSCs isolated from tumors of NCI-ADR/RES, as compared with control groups. Furthermore, BCSCs after MBO-asGCS treatment were more sensitive to doxorubicin. These results, for the first time, demonstrate that glycosphingolipid is involved in the regulation of cancer stem cell formation. Silencing GCS eliminates BCSCs, that can reverses drug resistance as well as prevent tumor relapse. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4282.

Abstract 2569: Disruption of ceramide glycosylation restores p53-dependent apoptosis in p53 mutant drug-resistant cancer cells: Alternative splicing determines the feature of p53 activity

Proceedings: AACR 101st Annual Meeting 2010‐‐ Apr 17‐21, 2010; Washington, DC Mutation of tumor suppressor p53 is frequently detected in many different types of cancers. p53 mutants acts as oncogenic proteins preventing programmed cell death and promoting cancer progression. Restoration of p53 that is to increase the expression of wild-type p53 and to eliminate mutant expression can substantially increase the efficacy of chemotherapy and stop malignant progression. However, incomplete understanding the molecular mechanism underlying p53 gene regulation limits the success in p53 restoration. We, for the first time, report that disruption of ceramide glycosylation restores p53 dependent-apoptosis in p53 mutant drug-resistant cancer cells. A lose of 21 base-pair in the mRNA of exon-5 can result in the accumulation of mutant p53 and cells insensitiveness to induced-apoptosis in human NCI/ADR-RE ovarian cancer cells. We found that treatment of mixed-backbone oligonucleotide against human glucosylceramide synthase (MBO-asGCS) increased the levels of wild-type p53 mRNA (containing the 21 bp in exon-5) and protein of wild-type p53 in dose-dependent manner (50-200 nM). In response to doxorubicin-induced DNA damage, phosphorylated p53 (Ser15 in the exon-5) was significantly increased, that in turn increased the protein levels of p21 and Bax, and apoptosis (52% vs. 3%) after MBO-asGCS treatment compared to control in NCI/ADR-RE cells. Silencing of GCS using MBO-asGCS (1 mg/kg) restored wild-type p53 expression and substantially sensitizes NCI/ADR-RE tumors to doxorubicin-induced apoptosis in vivo (10 mice per group), as compared to MBO-scramble control or other treatments. In contrast, introduction of GCS gene in NCI-ADR-RE cells reduces wild-type p53 expression and p53-depedent apoptosis. Further mechanic studies indicated that increased ceramide after GCS silencing modulates the function of SRp30a (ASF/SF2) regulating alternative pre-mRNA splicing. Increasing endogenous ceramide by inhibition of its glycosylation using PDMP or enhanced its production using sphingomylinase promoted wild-type p53 expression at the levels of mRNA, protein and phosphorylation; decreasing ceramide by inhibition of ceramide synthesis using fumonisin (FB1) repressed wild-type p53 expression. Present study indicates that cancer cells marked with mutant p53 phenotype are capable of expressing functional p53; ceramide glycosylation is one molecular mechanism that shifts expression to wild-type form of p53 at alternative splicing of post-transcription processing. MBO-asGCS, a specific agent silencing GCS restores p53-dependent apoptosis in cancer cells. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 2569.