Lack of ceramide generation and altered sphingolipid composition are associated with drug resistance in human ovarian carcinoma cells

Serum and Plasma Sphingolipids as Biomarkers of Anthracycline-Induced Cardiotoxicity

Although effective as a chemotherapy, the utility of Doxorubicin (Dox) is hampered by cardiotoxicity. Despite this, the ability to predict and guide monitoring of patients receiving Dox or other anthracyclines is hampered by a lack of effective biomarkers to identify susceptible patients, and to detect early signs of subclinical cardiotoxicity. Based on their well-established roles in the response to Dox and other chemotherapies, we performed a retrospective analysis of serum and plasma sphingolipids (SLs) from patients undergoing anthracycline-containing therapy, correlating with cardiac parameters assessed by echocardiography. Results showed there were substantial changes in both plasma and serum SL species during therapy including ceramide (Cer), deoxydihydroCer, and dihydrosphingosine with reversion towards baseline following treatment. Linear mixed-effects model analysis revealed that at baseline, a number of SLs correlated with adverse cardiac outcomes with serum sphingosine-1-phosphate (S1P) and dihydroS1P, and plasma Cer performing comparably to the prognostic value of pro-NT-BNP, an established biomarker of cardiotoxicity. Intriguingly, while pro-NT-BNP had no predictive value at mid- and post-therapy timepoints, serum S1P and dhS1P and plasma Cer levels showed correlation with adverse outcomes, particularly at the post-therapy timepoint. Finally, analysis of plasma and serum C16:C24- Cer ratios - previously reported as predictive of adverse cardiac outcomes - showed no correlation in the context of anthracycline treatment. Taken together, this pilot study provides supporting evidence that plasma and serum SLs may have benefit as both prognostic and diagnostic biomarkers for patients undergoing anthracycline-containing therapy. This suggests that diagnostic SL measurements - recently implemented for metabolic-associated cardiac disorders - could have wider utility.

The Role of Sphingolipid Metabolism in Pregnancy-Associated Breast Cancer After Chemotherapy

BACKGROUND

The aim of our study was to determine the role of sphingolipids, which control proliferation and apoptosis, in the placenta of pregnant women with pregnancy-associated breast cancer (PABC) after chemotherapy compared with healthy patients.

METHODS

We analyzed (by the PCR method) the gene expression of key sphingolipid metabolism enzymes (sphingomyelinases (SMPD1 and SMPD3), acid ceramidase (ASAH1), ceramide synthases (CERS 1-6), sphingosine kinase1 (SPHK1), sphingosine-1-phosphate lyase 1 (SGPL1), and sphingosine-1-phosphate receptors (S1PR1, S1PR2, and S1PR3)) and the content of subspecies of ceramides, sphingosine, and sphingosine-1-phosphate in seven patients with PABC after chemotherapy and eight healthy pregnant women as a control group.

RESULTS

We found a significant increase in the expression of genes of acid ceramidase (ASAH1), sphingosine-1-phosphate lyase 1 (SGPL1), sphingosine kinase (SPHK1), and ceramide synthases (CERS 1-3, 5, 6) in the samples of patients with PABC during their treatment with cytostatic chemotherapy. The increase in the expression of the enzymes' genes was not accompanied by changes in the content of the studied sphingolipids. Such significant changes in the expression of genes controlling the level of CER, sphingosine, and S1P may indicate their ability to initiate the metabolism of pro-apoptotic and anti-apoptotic sphingolipids in the placenta of pregnant women with cancer undergoing chemotherapy in order to maintain levels typical of the placenta of healthy women.

CONCLUSIONS

Our results may indicate the promising mechanism of placenta protection during chemotherapy for pregnant women with breast cancer and, consequently, of the newborn. This protective effect of the placenta and especially for the newborn has been discovered for the first time and requires more careful study.

Screening by Q Exactive liquid chromatography/tandem mass spectrometry identified Choline, 25-hydroxyvitamin D2, and SM(d18:0/16:1(9Z) (OH)) as biomarkers for high-grade serous ovarian cancer

High-grade serous ovarian cancer (HGSOC) has a high death rate and poor prognosis. The main causes of poor prognosis are asymptomatic early disease, no effective screening method at present, and advanced disease. Changes in cellular metabolism are characteristic of cancer, and plasma metabolome analysis can be used to identify biomarkers. In this study, we used Q Exactive liquid chromatography tandem mass spectrometry (LC-MS/MS, QE) to compare the differentiation between plasma samples (22 HGSOC samples and 22 normal samples). In total, we detected 124 metabolites, and an orthogonal partial least-squares-discriminant analysis (OPLS-DA) model was useful to distinguish HGSOC patients from healthy controls. Choline, 25-hydroxyvitamin D2, and sphingomyelin (d18:0/16:1(9Z) (OH))/SM(d18:0/16:1(9Z) (OH)) showed significantly differential plasma levels in HGSOC patients under the conditions of variable importance in projection (VIP) > 1, p < 0.05 using Student's t-test, and fold change (FC)  ≥ 1.5 or ≤ 0.667. Metabolic pathway analysis can provide valuable information to enhance the understanding of the underlying pathophysiology of HGSOC. In conclusion, the Q Exactive LC/MS/MS method validation-based plasma metabolomics approach may have potential as a convenient screening method for HGSOC and may be a method to monitor tumor recurrence in patients with HGSOC after surgery SIGNIFICANCE: High-grade serous ovarian cancer (HGSOC) has a high death rate and poor prognosis. The main causes of poor prognosis are asymptomatic early disease, no effective screening method at present, and advanced disease. Changes in cellular metabolism are characteristic of cancer, and plasma metabolome analysis can be used to identify biomarkers. In this study, we used Q Exactive liquid chromatography tandem mass spectrometry (LC-MS/MS, QE) to compare the differentiation between plasma samples (20 HGSOC samples and 20 normal samples). In total, we detected 124 metabolites, and an orthogonal partial least-squares-discriminant analysis (OPLS-DA) model was useful to distinguish HGSOC patients from healthy controls. Choline, 25-hydroxyvitamin D2, and sphingomyelin (d18:0/16:1(9Z) (OH))/SM(d18:0/16:1(9Z) (OH)) showed significantly differential plasma levels in HGSOC patients under the conditions of variable importance in projection (VIP) > 1, p < 0.05 using Student's t-test, and fold change (FC) ≥ 1.5 or ≤ 0.667. Metabolic pathway analysis can provide valuable information to enhance the understanding of the underlying pathophysiology of HGSOC. In conclusion, the Q Exactive LC/MS/MS method validation-based plasma metabolomics approach may have potential as a convenient screening method for HGSOC and may be a method to monitor tumor recurrence in patients with HGSOC after surgery.

The Role of Sphingolipids Metabolism in Cancer Drug Resistance

Drug resistance continues to be one of the major challenges to cure cancer. As research in this field evolves, it has been proposed that numerous bioactive molecules might be involved in the resistance of cancer cells to certain chemotherapeutics. One well-known group of lipids that play a major role in drug resistance are the sphingolipids. Sphingolipids are essential components of the lipid raft domains of the plasma membrane and this structural function is important for apoptosis and/or cell proliferation. Dysregulation of sphingolipids, including ceramide, sphingomyelin or sphingosine 1-phosphate, has been linked to drug resistance in different types of cancer, including breast, melanoma or colon cancer. Sphingolipid metabolism is complex, involving several lipid catabolism with the participation of key enzymes such as glucosylceramide synthase (GCS) and sphingosine kinase 1 (SPHK1). With an overview of the latest available data on this topic and its implications in cancer therapy, this review focuses on the main enzymes implicated in sphingolipids metabolism and their intermediate metabolites involved in cancer drug resistance.

Circulating Lysophosphatidylcholines, Phosphatidylcholines, Ceramides, and Sphingomyelins and Ovarian Cancer Risk: A 23-Year Prospective Study

BACKGROUND

Experimental evidence supports a role of lipid dysregulation in ovarian cancer progression. We estimated associations with ovarian cancer risk for circulating levels of four lipid groups, previously hypothesized to be associated with ovarian cancer, measured 3-23 years before diagnosis.

METHODS

Analyses were conducted among cases (N = 252) and matched controls (N = 252) from the Nurses' Health Studies. We used logistic regression adjusting for risk factors to investigate associations of lysophosphatidylcholines (LPCs), phosphatidylcholines (PCs), ceramides (CERs), and sphingomyelins (SMs) with ovarian cancer risk overall and by histotype. A modified Bonferroni approach (0.05/4 = 0.0125, four lipid groups) and the permutation-based Westfall and Young approach were used to account for testing multiple correlated hypotheses. Odds ratios (ORs; 10th-90th percentile), and 95% confidence intervals of ovarian cancer risk were estimated. All statistical tests were two-sided.

RESULTS

SM sum was statistically significantly associated with ovarian cancer risk (OR = 1.97, 95% CI = 1.16 to 3.32; P = .01/permutation-adjusted P = .20). C16:0 SM, C18:0 SM, and C16:0 CERs were suggestively associated with risk (OR = 1.95-2.10; P = .004-.01; permutation-adjusted P = .08-.21). SM sum, C16:0 SM, and C16:0 CER had stronger odds ratios among postmenopausal women (OR = 2.16-3.22). Odds ratios were similar for serous/poorly differentiated and endometrioid/clear cell tumors, although C18:1 LPC and LPC to PC ratio were suggestively inversely associated, whereas C18:0 SM was suggestively positively associated with risk of endometrioid/clear cell tumors. No individual metabolites were associated with risk when using the permutation-based approach.

CONCLUSIONS

Elevated levels of circulating SMs 3-23 years before diagnosis were associated with increased risk of ovarian cancer, regardless of histotype, with stronger associations among postmenopausal women. Further studies are required to validate and understand the role of lipid dysregulation in ovarian carcinogenesis.

Chemotherapeutic Agents-Induced Ceramide-Rich Platforms (CRPs) in Endothelial Cells and Their Modulation

The prevailing mechanism of action of chemotherapeutic drugs has been challenged by the role of ceramide, a second messenger, shown to induce apoptosis, differentiation, growth arrest, senescence, and autophagy in different cells (Chabner BA, Roberts TG Jr, Nat Rev Cancer 5:65-72, 2005; Jacobi J et al, Cell Signal 29:52-61, 2017; Rotolo J et al, J Clin Invest 122:1786-1790, 2012; Truman JP et al, PLoS One 5:e12310, 2010). Certain chemotherapeutic drugs activate the acid sphingomyelinase (ASMase)/ceramide pathway, generating ceramide in the tumor endothelium and this microvascular dysfunction is crucial for the tumor response. Ceramide has fusigenic properties and as such, when generated within the plasma membrane, initiates the oligomerization of ceramide-and cholesterol-rich domains in the outer leaflet of the plasma membrane, leading to the formation of ceramide-rich microdomains/platforms (CRP) (Jacobi J et al, Cell Signal 29:52-61, 2017; Truman JP et al, PLoS One 5:e12310, 2010; van Hell AJ et al, Cell Signal 34:86-91, 2017; Hajj C, Haimovitz-Friedman A, Handb Exp Pharmacol 216:115-130, 2013) known as "signaling platform." This chapter will discuss the generation, detection, and quantitation of CRP and their possible modulation in endothelial cells, in vitro and in vivo in response to certain chemotherapeutic drugs.

A role for ceramide glycosylation in resistance to oxaliplatin in colorectal cancer

There is growing evidence to support a role for the ceramide-metabolizing enzyme, glucosylceramide synthase (GCS), in resistance to a variety of chemotherapeutic agents. Whether GCS contributes to oxaliplatin resistance in colorectal cancer (CRC) has not yet been determined. We have addressed this potentially important clinical issue by examining GCS function in two panels of oxaliplatin-resistant, isogenic CRC cell lines. Compared to parental cell lines, oxaliplatin-resistant cells have increased expression of GCS protein associated with increased levels of the pro-survival ceramide metabolite, glucosylceramide (GlcCer). Inhibition of GCS expression by RNAi-mediated gene knockdown resulted in a reduction in cellular GlcCer levels, with restored sensitivity to oxaliplatin. Furthermore, oxaliplatin-resistant CRC cells displayed lower ceramide levels both basally and after treatment with oxaliplatin, compared to parental cells. GlcCer, formed by GCS-mediated ceramide glycosylation, is the precursor to a complex array of glycosphingolipids. Differences in cellular levels and species of gangliosides, a family of glycosphingolipids, were also seen between parental and oxaliplatin-resistant CRC cells. Increased Akt activation was also observed in oxaliplatin-resistant CRC cell lines, together with increased expression of the anti-apoptotic protein survivin. Finally, this study shows that GCS protein levels are greatly increased in human CRC specimens, compared to matched, normal colonic mucosa, and that high levels of UGCG gene expression are significantly associated with decreased disease-free survival in colorectal cancer patients. These findings uncover an important cellular role for GCS in oxaliplatin chemosensitivity and may provide a novel cellular target for augmenting chemotherapeutic drug effectiveness in CRC.

The Transfer of Sphingomyelinase Contributes to Drug Resistance in Multiple Myeloma

Multiple myeloma (MM) is well-known for the development of drug resistance, leading to relapse. Therefore, finding novel treatment strategies remains necessary. By performing a lipidomics assay on MM patient plasma, we aimed to identify new targets. We observed a dysregulation in the sphingolipid metabolism, with the upregulation of several ceramides and downregulation of sphingomyelin. This imbalance suggests an increase in sphingomyelinase, the enzyme responsible for hydrolyzing sphingomyelin into ceramide. We confirmed the upregulation of acid sphingomyelinase (ASM) in primary MM cells. Furthermore, we observed an increase in ASM expression in MM cell lines treated with melphalan or bortezomib, as well as in their exosomes. Exosomes high in ASM content were able to transfer the drug-resistant phenotype to chemosensitive cells, hereby suggesting a tumor-protective role for ASM. Finally, inhibition of ASM by amitriptyline improved drug sensitivity in MM cell lines and primary MM cells. In summary, this study is the first to analyze differences in plasma lipid composition of MM patients and match the observed differences to an upregulation of ASM. Moreover, we demonstrate that amitriptyline is able to inhibit ASM and increase sensitivity to anti-myeloma drugs. This study, therefore, provides a rational to include ASM-targeting-drugs in combination strategies in myeloma patients.

Sphingolipid metabolism and drug resistance in ovarian cancer

Despite progress in understanding molecular aberrations that contribute to the development and progression of ovarian cancer, virtually all patients succumb to drug resistant disease at relapse. Emerging data implicate bioactive sphingolipids and regulation of sphingolipid metabolism as components of response to chemotherapy or development of resistance. Increases in cytosolic ceramide induce apoptosis in response to therapy with multiple classes of chemotherapeutic agents. Aberrations in sphingolipid metabolism that accelerate the catabolism of ceramide or that prevent the production and accumulation of ceramide contribute to resistance to standard of care platinum- and taxane-based agents. The aim of this review is to highlight current literature and research investigating the influence of the sphingolipids and enzymes that comprise the sphingosine-1-phosphate pathway on the progression of ovarian cancer. The focus of the review is on the utility of sphingolipid-centric therapeutics as a mechanism to circumvent drug resistance in this tumor type.

FTY720 enhances the anti-tumor activity of carboplatin and tamoxifen in a patient-derived xenograft model of ovarian cancer

Ovarian cancer is the fifth leading cause of cancer-related deaths among women in the United States. Although most patients respond to frontline therapy, virtually all patients relapse with chemoresistant disease. This study addresses the hypothesis that carboplatin or tamoxifen + FTY720, a sphingosine analogue, will minimize or circumvent drug-resistance in ovarian cancer cells and tumor models. In vitro data demonstrate that FTY720 sensitized two drug-resistant (A2780. cp20, HeyA8. MDR) and two high-grade serous ovarian cancer cell lines (COV362, CAOV3) to carboplatin, a standard of care for patients with ovarian cancer, and to the selective estrogen receptor modulator tamoxifen. FTY720 + tamoxifen was synergistic in vitro, and combinations of FTY720 + carboplatin or + tamoxifen were more effective than each single agent in a patient-derived xenograft model of ovarian carcinoma. FTY720 + tamoxifen arrested tumor growth. FTY720 + carboplatin induced tumor regressions, with tumor volumes reduced by ∼86% compared to initial tumor volumes. Anti-tumor efficacy was concomitant with increases in intracellular proapoptotic lipid ceramide. The data suggest that FTY720 + tamoxifen or carboplatin may be effective in treating ovarian tumors.

LC-MS based sphingolipidomic study on A549 human lung adenocarcinoma cell line and its taxol-resistant strain

BACKGROUND

Resistance to chemotherapy drugs (e.g. taxol) has been a major obstacle in successful cancer treatment. In A549 human lung adenocarcinoma, acquired resistance to the first-line chemotherapy taxol has been a critical problem in clinics. Sphingolipid (SPL) controls various aspects of cell growth, survival, adhesion, and motility in cancer, and has been gradually regarded as a key factor in drug resistance. To better understand the taxol-resistant mechanism, a comprehensive sphingolipidomic approach was carried out to investigate the sphingolipid metabolism in taxol-resistant strain of A549 cell (A549T).

METHODS

A549 and A549T cells were extracted according to the procedure with optimal condition for SPLs. Sphingolipidomic analysis was carried out by using an UHPLC coupled with quadrupole time-of-flight (Q-TOF) MS system for qualitative profiling and an UHPLC coupled with triple quadrupole (QQQ) MS system for quantitative analysis. The differentially expressed sphingolipids between taxol-sensitive and -resistant cells were explored by using multivariate analysis.

RESULTS

Based on accurate mass and characteristic fragment ions, 114 SPLs, including 4 new species, were clearly identified. Under the multiple reaction monitoring (MRM) mode of QQQ MS, 75 SPLs were further quantified in both A549 and A549T. Multivariate analysis explored that the levels of 57 sphingolipids significantly altered in A549T comparing to those of A549 (p < 0.001 and VIP > 1), including 35 sphingomyelins (SMs), 14 ceramides (Cers), 3 hexosylceramides (HexCers), 4 lactosylceramides (LacCers) and 1 sphingosine. A significant decrease of SM and Cer levels and overall increase of HexCer and LacCer represent the major SPL metabolic characteristic in A549T.

CONCLUSIONS

This study investigated sphingolipid profiles in human lung adenocarcinoma cell lines, which is the most comprehensive sphingolipidomic analysis of A549 and A549T. To some extent, the mechanism of taxol-resistance could be attributed to the aberrant sphingolipid metabolism, "inhibition of the de novo synthesis pathway" and "activation of glycosphingolipid pathway" may play the dominant role for taxol-resistance in A549T. This study provides insights into the strategy for clinical diagnosis and treatment of taxol resistant lung cancer.

Essential role for acid sphingomyelinase-inhibited autophagy in melanoma response to cisplatin

The sphingolipid metabolising enzyme Acid Sphingomyelinase (A-SMase) has been recently shown to inhibit melanoma progression and correlate inversely to tumour grade. In this study we have investigated the role of A-SMase in the chemo-resistance to anticancer treatmentusing mice with melanoma allografts and melanoma cells differing in terms of expression/activity of A-SMase. Since autophagy is emerging as a key mechanism in tumour growth and chemo-resistance, we have also investigated whether an action of A-SMase in autophagy can explain its role. Melanoma sensitivity to chemotherapeutic agent cisplatin in terms of cell viability/apoptosis, tumour growth, and animal survival depended directly on the A-SMase levels in tumoural cells. A-SMase action was due to inhibition of autophagy through activation of Akt/mammalian target of rapamycin (mTOR) pathway. Treatment of melanoma-bearing mice with the autophagy inhibitor chloroquine restored sensitivity to cisplatin of tumours expressing low levels of A-SMase while no additive effects were observed in tumours characterised by sustained A-SMase levels. The fact that A-SMase in melanomas affects mTOR-regulated autophagy and plays a central role in cisplatin efficacy encourages pre-clinical testing on the modulation of A-SMase levels/activity as possible novel anti-neoplastic strategy.

Acid ceramidase and its inhibitors: a de novo drug target and a new class of drugs for killing glioblastoma cancer stem cells with high efficiency

Glioblastoma remains the most common, malignant primary cancer of the central nervous system with a low life expectancy and an overall survival of less than 1.5 years. The treatment options are limited and there is no cure. Moreover, almost all patients develop recurrent tumors, which typically are more aggressive. Therapeutically resistant glioblastoma or glioblastoma stem-like cells (GSCs) are hypothesized to cause this inevitable recurrence. Identifying prognostic biomarkers of glioblastoma will potentially advance knowledge about glioblastoma tumorigenesis and enable discovery of more effective therapies. Proteomic analysis of more than 600 glioblastoma-specific proteins revealed, for the first time, that expression of acid ceramidase (ASAH1) is associated with poor glioblastoma survival. CD133+ GSCs express significantly higher ASAH1 compared to CD133- GSCs and serum-cultured glioblastoma cell lines, such as U87MG. These findings implicate ASAH1 as a plausible independent prognostic marker, providing a target for a therapy tailored toward GSCs. We further demonstrate that ASAH1 inhibition increases cellular ceramide level and induces apoptosis. Strikingly, U87MG cells, and three different patient-derived glioblastoma stem-like cancer cell lines were efficiently killed, through apoptosis, by three different known ASAH1 inhibitors with IC50's ranging from 11–104 μM. In comparison, the standard glioblastoma chemotherapy agent, temozolomide, had minimal GSC-targeted effects at comparable or even higher concentrations (IC50 > 750 μM against GSCs). ASAH1 is identified as a de novo glioblastoma drug target, and ASAH1 inhibitors, such as carmofur, are shown to be highly effective and to specifically target glioblastoma GSCs. Carmofur is an ASAH1 inhibitor that crosses the blood-brain barrier, a major bottleneck in glioblastoma treatment. It has been approved in Japan since 1981 for colorectal cancer therapy. Therefore, it is poised for repurposing and translation to glioblastoma clinical trials.

Enhanced Acid Sphingomyelinase Activity Drives Immune Evasion and Tumor Growth in Non-Small Cell Lung Carcinoma

The lipid hydrolase enzyme acid sphingomyelinase (ASM) is required for the conversion of the lipid cell membrane component sphingomyelin into ceramide. In cancer cells, ASM-mediated ceramide production is important for apoptosis, cell proliferation, and immune modulation, highlighting ASM as a potential multimodal therapeutic target. In this study, we demonstrate elevated ASM activity in the lung tumor environment and blood serum of patients with non-small cell lung cancer (NSCLC). RNAi-mediated attenuation of SMPD1 in human NSCLC cells rendered them resistant to serum starvation-induced apoptosis. In a murine model of lung adenocarcinoma, ASM deficiency reduced tumor development in a manner associated with significant enhancement of Th1-mediated and cytotoxic T-cell-mediated antitumor immunity. Our findings indicate that targeting ASM in NSCLC can act by tumor cell-intrinsic and -extrinsic mechanisms to suppress tumor cell growth, most notably by enabling an effective antitumor immune response by the host. Cancer Res; 77(21); 5963-76. ©2017 AACR.

Bladder cancer cell growth and motility implicate cannabinoid 2 receptor-mediated modifications of sphingolipids metabolism

The inhibitory effects demonstrated by activation of cannabinoid receptors (CB) on cancer proliferation and migration may also play critical roles in controlling bladder cancer (BC). CB expression on human normal and BC specimens was tested by immunohistochemistry. Human BC cells RT4 and RT112 were challenged with CB agonists and assessed for proliferation, apoptosis, and motility. Cellular sphingolipids (SL) constitution and metabolism were evaluated after metabolic labelling. CB1-2 were detected in BC specimens, but only CB2 was more expressed in the tumour. Both cell lines expressed similar CB2. Exposure to CB2 agonists inhibited BC growth, down-modulated Akt, induced caspase 3-activation and modified SL metabolism. Baseline SL analysis in cell lines showed differences linked to unique migratory behaviours and cytoskeletal re-arrangements. CB2 activation changed the SL composition of more aggressive RT112 cells by reducing (p < 0.01) Gb3 ganglioside (−50 ± 3%) and sphingosine 1-phosphate (S1P, −40 ± 4%), which ended up to reduction in cell motility (−46 ± 5%) with inhibition of p-SRC. CB2-selective antagonists, gene silencing and an inhibitor of SL biosynthesis partially prevented CB2 agonist-induced effects on cell viability and motility. CB2 activation led to ceramide-mediated BC cell apoptosis independently of SL constitutive composition, which instead was modulated by CB2 agonists to reduce cell motility.

Targeting acid sphingomyelinase with anti-angiogenic chemotherapy

Despite great promise, combining anti-angiogenic and conventional anti-cancer drugs has produced limited therapeutic benefit in clinical trials, presumably because mechanisms of anti-angiogenic tissue response remain only partially understood. Here we define a new paradigm, in which anti-angiogenic drugs can be used to chemosensitize tumors by targeting the endothelial acid sphingomyelinase (ASMase) signal transduction pathway. We demonstrate that paclitaxel and etoposide, but not cisplatin, confer ASMase-mediated endothelial injury within minutes. This rapid reaction is required for human HCT-116 colon cancer xenograft complete response and growth delay. Whereas VEGF inhibits ASMase, anti-VEGFR2 antibodies de-repress ASMase, enhancing endothelial apoptosis and drug-induced tumor response in asmase+/+, but not in asmase-/-, hosts. Such chemosensitization occurs only if the anti-angiogenic drug is delivered 1-2h before chemotherapy, but at no other time prior to or post chemotherapy. Our studies suggest that precisely-timed administration of anti-angiogenic drugs in combination with ASMase-targeting anti-cancer drugs is likely to optimize anti-tumor effects of systemic chemotherapy. This strategy warrants evaluation in future clinical trials.

LC-MS Based Sphingolipidomic Study on A2780 Human Ovarian Cancer Cell Line and its Taxol-resistant Strain

Drug resistance elicited by cancer cells continue to cause huge problems world-wide, for example, tens of thousands of patients are suffering from taxol-resistant human ovarian cancer. However, its biochemical mechanisms remain unclear. Sphingolipid metabolic dysregulation has been increasingly regarded as one of the drug-resistant mechanisms for various cancers, which in turn provides potential targets for overcoming the resistance. In the current study, a well-established LC-MS based sphingolipidomic approach was applied to investigate the sphingolipid metabolism of A2780 and taxol-resistant A2780 (A2780T) human ovarian cancer cell lines. 102 sphingolipids (SPLs) were identified based on accurate mass and characteristic fragment ions, among which 12 species have not been reported previously. 89 were further quantitatively analyzed by using multiple reaction monitoring technique. Multivariate analysis revealed that the levels of 52 sphingolipids significantly altered in A2780T cells comparing to those of A2780 cells. These alterations revealed an overall increase of sphingomyelin levels and significant decrease of ceramides, hexosylceramides and lactosylceramides, which concomitantly indicated a deviated SPL metabolism in A2780T. This is the most comprehensive sphingolipidomic analysis of A2780 and A2780T, which investigated significantly changed sphingolipid profile in taxol-resistant cancer cells. The aberrant sphingolipid metabolism in A2780T could be one of the mechanisms of taxol-resistance.

The human ovarian cancer cell line CABA I: A peculiar genetic evolution

The objective of this study was to study the human ovarian cancer cell line CABA I by means of short tandem repeats (STR) profiling and cytogenetic analysis in order to prevent future misidentification or cross-contamination and verify its stability during in vitro cultivation. To this end, cells at passages 18 and 38 were analyzed using cytogenetic techniques in order to verify possible chromosomal aberrations and the karyotypic evolution of this cell line; GTG-banding and FISH were also performed. For STR analysis, DNA was extracted using the automated extractor MagNA pure and analyzed by means of PowerPlex 16 HS. STR profiles were analyzed by GeneMapper 3.2.1 software. Whereas comparative cytogenetic analysis of CABA I cells at passage 18 and 38 has demonstrated considerable genetic instability, we found that STR profiles were essentially unaltered in both analyzed passages, suggesting that the STR profile is reliable and could be used for the regular authentication of CABA I over time. It should be emphasized, however, that of the 16 loci generally used in human STR profiles, only 3 were properly detectable in CABA I. The data highlight that the CABA I cell line demonstrates an anomalous STR profile that does not fully adjust the criteria currently used for the identification of human cells; in spite of this, it remains stable during the in vitro maintainance. Moreover, the genetic instability of the CABA I cell line overlaps with those observed in vivo in tumor cells, making it a suitable candidate to analyze, in vitro, the peculiar genetic evolution of ovarian cancer cells.

The emerging role of acid sphingomyelinase in autophagy

Autophagy, the main intracellular process of cytoplasmic material degradation, is involved in cell survival and death. Autophagy is regulated at various levels and novel modulators of its function are being continuously identified. An intriguing recent observation is that among these modulators is the sphingolipid metabolising enzyme, Acid Sphingomyelinase (A-SMase), already known to play a fundamental role in apoptotic cell death participating in several pathophysiological conditions. In this review we analyse and discuss the relationship between autophagy and A-SMase describing how A-SMase may regulate it and defining, for the first time, the existence of an A-SMase-autophagy axis. The imbalance of this axis plays a role in cancer, nervous system, cardiovascular, and hepatic disorders.

Modulation of Acid Sphingomyelinase in Melanoma Reprogrammes the Tumour Immune Microenvironment

The inflammatory microenvironment induces tumours to acquire an aggressive and immunosuppressive behaviour. Since acid sphingomyelinase (A-SMase) downregulation in melanoma was shown to determine a malignant phenotype, we aimed here to elucidate the role of A-SMase in the regulation of tumour immunogenic microenvironment using in vivo melanoma models in which A-SMase was either downregulated or maintained at constitutively high levels. We found high levels of inflammatory factors in low A-SMase expressing tumours, which also displayed an immunosuppressive/protumoural microenvironment: high levels of myeloid-derived suppressor cells (MDSCs) and regulatory T lymphocytes (Tregs), as well as low levels of dendritic cells (DCs). In contrast, the restoration of A-SMase in melanoma cells not only reduced tumour growth and immunosuppression, but also induced a high recruitment at tumour site of effector immune cells with an antitumoural function. Indeed, we observed a poor homing of MDSCs and Tregs and the increased recruitment of CD8⁺ and CD4⁺ T lymphocytes as well as the infiltration of DCs and CD8⁺/CD44^high T lymphocytes. This study demonstrates that change of A-SMase expression in cancer cells is sufficient per se to tune in vivo melanoma growth and that A-SMase levels modulate immune cells at tumour site. This may be taken into consideration in the setting of therapeutic strategies.

Sphingolipids: key regulators of apoptosis and pivotal players in cancer drug resistance

Drug resistance elicited by cancer cells still constitutes a huge problem that frequently impairs the efficacy of both conventional and novel molecular therapies. Chemotherapy usually acts to induce apoptosis in cancer cells; therefore, the investigation of apoptosis control and of the mechanisms used by cancer cells to evade apoptosis could be translated in an improvement of therapies. Among many tools acquired by cancer cells to this end, the de-regulated synthesis and metabolism of sphingolipids have been well documented. Sphingolipids are known to play many structural and signalling roles in cells, as they are involved in the control of growth, survival, adhesion, and motility. In particular, in order to increase survival, cancer cells: (a) counteract the accumulation of ceramide that is endowed with pro-apoptotic potential and is induced by many drugs; (b) increase the synthesis of sphingosine-1-phosphate and glucosylceramide that are pro-survivals signals; (c) modify the synthesis and the metabolism of complex glycosphingolipids, particularly increasing the levels of modified species of gangliosides such as 9-O acetylated GD3 (αNeu5Ac(2-8)αNeu5Ac(2-3)βGal(1-4)βGlc(1-1)Cer) or N-glycolyl GM3 (αNeu5Ac (2-3)βGal(1-4)βGlc(1-1)Cer) and de-N-acetyl GM3 (NeuNH(2)βGal(1-4)βGlc(1-1)Cer) endowed with anti-apoptotic roles and of globoside Gb3 related to a higher expression of the multidrug resistance gene MDR1. In light of this evidence, the employment of chemical or genetic approaches specifically targeting sphingolipid dysregulations appears a promising tool for the improvement of current chemotherapy efficacy.

Evolving concepts in cancer therapy through targeting sphingolipid metabolism

Traditional methods of cancer treatment are limited in their efficacy due to both inherent and acquired factors. Many different studies have shown that the generation of ceramide in response to cytotoxic therapy is generally an important step leading to cell death. Cancer cells employ different methods to both limit ceramide generation and to remove ceramide in order to become resistant to treatment. Furthermore, sphingosine kinase activity, which phosphorylates sphingosine the product of ceramide hydrolysis, has been linked to multidrug resistance, and can act as a strong survival factor. This review will examine several of the most frequently used cancer therapies and their effect on both ceramide generation and the mechanisms employed to remove it. The development and use of inhibitors of sphingosine kinase will be focused upon as an example of how targeting sphingolipid metabolism may provide an effective means to improve treatment response rates and reduce associated treatment toxicity. This article is part of a Special Issue entitled Tools to study lipid functions.

Glioma cell death induced by irradiation or alkylating agent chemotherapy is independent of the intrinsic ceramide pathway

BACKGROUND/AIMS

Resistance to genotoxic therapy is a characteristic feature of glioma cells. Acid sphingomyelinase (ASM) hydrolyzes sphingomyelin to ceramide and glucosylceramide synthase (GCS) catalyzes ceramide metabolism. Increased ceramide levels have been suggested to enhance chemotherapy-induced death of cancer cells.

METHODS

Microarray and clinical data for ASM and GCS in astrocytomas WHO grade II-IV were acquired from the Rembrandt database. Moreover, the glioblastoma database of the Cancer Genome Atlas network (TCGA) was used for survival data of glioblastoma patients. For in vitro studies, increases in ceramide levels were achieved either by ASM overexpression or by the GCS inhibitor DL-threo-1-phenyl-2-palmitoylamino-3-morpholino-1-propanol (PPMP) in human glioma cell lines. Combinations of alkylating chemotherapy or irradiation and ASM overexpression, PPMP or exogenous ceramide were applied in parental cells. The anti-glioma effects were investigated by assessing proliferation, metabolic activity, viability and clonogenicity. Finally, viability and clonogenicity were assessed in temozolomide (TMZ)-resistant cells upon treatment with PPMP, exogenous ceramide, alkylating chemotherapy, irradiation or their combinations.

RESULTS

Interrogations from the Rembrandt and TCGA database showed a better survival of glioblastoma patients with low expression of ASM or GCS. ASM overexpression or PPMP treatment alone led to ceramide accumulation but did not enhance the anti-glioma activity of alkylating chemotherapy or irradiation. PPMP or exogenous ceramide induced acute cytotoxicity in glioblastoma cells. Combined treatments with chemotherapy or irradiation led to additive, but not synergistic effects. Finally, no synergy was found when TMZ-resistant cells were treated with exogenous ceramide or PPMP alone or in combination with TMZ or irradiation.

CONCLUSION

Modulation of intrinsic glioma cell ceramide levels by ASM overexpression or GCS inhibition does not enhance the anti-glioma activity of alkylating chemotherapy or irradiation.

Sphingolipids in cancer

The bioactive sphingolipids including, ceramide, sphingosine, and sphingosine-1-phosphate (S1P) have important roles in several types of signaling and regulation of many cellular processes including cell proliferation, apoptosis, senescence, angiogenesis, and transformation. Recent accumulating evidence suggests that ceramide- and S1P-mediated pathways have been implicated in cancer development, progression, and chemotherapy. Ceramide mediates numerous cell-stress responses, such as induction of apoptosis and cell senescence, whereas S1P plays pivotal roles in cell survival, migration, and inflammation. These sphingolipids with opposing roles can be interconverted within cells, suggesting that the balance between them is related to cell fate. Importantly, these sphingolipids are metabolically related through actions of enzymes including ceramidases, ceramide synthases, sphingosine kinases, and S1P phosphatases thereby forming a network of metabolically interrelated bioactive lipid mediators whose importance in normal cellular function and diseases is gaining appreciation. In this review, we summarize involvement of sphingolipids and their related enzymes in pathogenesis and therapy of cancer and discuss future directions of sphingolipid field in cancer research.

The roles of glycosphingolipids in the proliferation and neural differentiation of mouse embryonic stem cells

Glycosphingolipids including gangliosides play important regulatory roles in cell proliferation and differentiation. UDP-glucose:ceramide glucosyltransferase (Ugcg) catalyze the initial step in glycosphingolipids biosynthesis pathway. In this study, Ugcg expression was reduced to approximately 80% by short hairpin RNAs (shRNAs) to evaluate the roles of glycosphingolipids in proliferation and neural differentiation of mouse embryonic stem cells (mESCs). HPTLC/immunofluorescence analyses of shRNA- transfected mESCs revealed that treatment with Ugcg-shRNA decreased expression of major gangliosides, GM3 and GD3. Furthermore, MTT and Western blot/immunofluorescence analyses demonstrated that inhibition of the Ugcg expression in mESCs resulted in decrease of cell proliferation (P<0.05) and decrease of activation of the ERK1/2 (P<0.05), respectively. To further investigate the role of glycosphingolipids in neural differentiation, the embryoid bodies formed from Ugcg-shRNA transfected mESCs were differentiated into neural cells by treatment with retinoic acid. We found that inhibition of Ugcg expression did not affect embryoid body (EB) differentiation, as judged by morphological comparison and expression of early neural precursor cell marker, nestin, in differentiated EBs. However, RT-PCR/immunofluorescence analyses showed that expression of microtubule-associated protein 2 (MAP-2) for neurons and glial fibrillary acidic protein (GFAP) for glial cells was decreased in neural cells differentiated from the shRNA-transfected mESCs. These results suggest that glycosphingolipids are involved in the proliferation of mESCs through ERK1/2 activation, and that glycosphingolipids play roles in differentiation of neural precursor cells derived from mESCs.

The unexpected role of acid sphingomyelinase in cell death and the pathophysiology of common diseases

Acid sphingomyelinase (ASM; E.C. 3.1.4.12) is best known for its involvement in the lysosomal storage disorder Niemann-Pick disease (NPD). Through studies that began by investigating this rare disease, recent findings have uncovered the important role of this enzyme in the initiation of ceramide-mediated signal transduction. This unique function involves translocation of the enzyme from intracellular compartments to the outer leaflet of the cell membrane, where hydrolysis of sphingomyelin into ceramide initiates membrane reorganization and facilitates the formation and coalescence of lipid microdomains. These microdomains are sites of protein-protein interactions that lead to downstream signaling, and perturbation of microdomain formation influences the pathophysiology of many common diseases. The initial observations implicating ASM in this process have come from studies using cells from patients with NPD or from ASM knockout (ASMKO) mice, where the genetic deficiency of this enzymatic activity has been shown to protect these cells and animals from stress-induced and developmental apoptosis. This review will discuss the complex biology of this enzyme in the context of these new findings and its recently reported importance in common human diseases, including cancer, sepsis, cardiovascular, pulmonary, liver, and neurological diseases as well as the potential for using ASM (or ASM inhibitors) as therapeutic agents.

Remodeling of cellular cytoskeleton by the acid sphingomyelinase/ceramide pathway

The chemotherapeutic agent cisplatin is widely used in treatment of solid tumors. In breast cancer cells, cisplatin produces early and marked changes in cell morphology and the actin cytoskeleton. These changes manifest as loss of lamellipodia/filopodia and appearance of membrane ruffles. Furthermore, cisplatin induces dephosphorylation of the actin-binding protein ezrin, and its relocation from membrane protrusions to the cytosol. Because cisplatin activates acid sphingomyelinase (ASMase), we investigate here the role of the ASMase/ceramide (Cer) pathway in mediating these morphological changes. We find that cisplatin induces a transient elevation in ASMase activity and its redistribution to the plasma membrane. This translocation is blocked upon overexpression of a dominant-negative (DN) ASMase^S508A mutant and by a DN PKCδ. Importantly; knockdown of ASMase protects MCF-7 cells from cisplatin-induced cytoskeletal changes including ezrin dephosphorylation. Reciprocally, exogenous delivery of D-e-C₁₆-Cer, but not dihydro-C₁₆-Cer, recapitulates the morphotropic effects of cisplatin. Collectively, these results highlight a novel tumor suppressor property for Cer and a function for ASMase in cisplatin-induced cytoskeletal remodeling.

Nitric oxide boosts chemoimmunotherapy via inhibition of acid sphingomyelinase in a mouse model of melanoma

Cisplatin is one of the most effective anticancer drugs, but its severe toxic effects, including depletion of immune-competent cells, limit its efficacy. We combined the systemic treatment with cisplatin with intratumor delivery of dendritic cells (DC) previously treated ex vivo with a pulse of nitric oxide (NO) released by the NO donors (z)-1-[2-(2-aminoethyl)-N-(2-ammonioethyl)amino]-diazen-1-ium-1,2-diolate or isosorbide dinitrate. We found that this chemoimmunotherapy, tested in the B16 mouse model of melanoma, was significantly more efficacious than cisplatin alone, leading to tumor regression and animal survival at low doses of cisplatin that alone had no effect. Tumor cure was not observed when combining cisplatin with DCs not exposed to NO donors, indicating the key role of the pretreatment with NO. We investigated the mechanisms responsible for the synergic effect of NO-treated DCs and cisplatin and found that NO-treated DCs were protected both in vitro and in vivo from cisplatin-induced cytotoxicity. Cisplatin triggered DC apoptosis through increased expression and activation of acid sphingomyelinase; pretreatment of DCs with NO donors prevented such activation and inhibited activation of the downstream proapoptotic events, including generation of ceramide, activation of caspases 3 and 9, and mitochondrial depolarization. The effects of NO were mediated through generation of its physiologic messenger, cyclic GMP. We conclude that NO and NO generating drugs represent promising tools to increase the efficacy of chemoimmunotherapies in vivo, promoting the survival and increasing the function of injected cells by targeting a key pathway in cisplatin-induced cytotoxicity.

Recent advances on the molecular mechanisms involved in the drug resistance of cancer cells and novel targeting therapies

This review summarizes the recent knowledge obtained on the molecular mechanisms involved in the intrinsic and acquired resistance of cancer cells to current cancer therapies. We describe the cascades that are often altered in cancer cells during cancer progression that may contribute in a crucial manner to drug resistance and disease relapse. The emphasis is on the implication of ATP-binding cassette (ABC) multidrug efflux transporters in drug disposition and antiapoptotic factors, including epidermal growth factor receptor cascades and deregulated enzymes in ceramide metabolic pathways. The altered expression and activity of these signaling elements may have a critical role in the resistance of cancer cells to cytotoxic effects induced by diverse chemotherapeutic drugs and cancer recurrence. Of therapeutic interest, new strategies for reversing the multidrug resistance and developing more effective clinical treatments against the highly aggressive, metastatic, and recurrent cancers, based on the molecular targeting of the cancer progenitor cells and their further differentiated progeny, are also described.

Ceramide: From Embryos to Tumors

Ceramides are ubiquitous lipids that have important functions integral to apoptotic signaling. Several therapeutic agents currently exist that induce ceramide-dependent apoptosis in cancerous cells, and a number of enzymes involved in ceramide metabolism are beginning to be recognized as potential targets for cancer therapy. Recent research shows that evasion of ceramide-dependent apoptosis is essential at the earliest stages of embryonic development and is an important mechanism of multidrug resistance. Although ceramide-based strategies for treating cancer are promising, current data about ceramide-resistant tumors require further understanding of the role of ceramide in apoptosis.

A CERTain role for ceramide in taxane-induced cell death

An unexpected benefit of functional genomic screens is that at times they answer questions that they were not designed to ask. A siRNA screen reported by Swanton et al. in this issue of Cancer Cell reveals that silencing of spindle assembly checkpoint genes facilitates mitotic slippage, resulting in escape from taxane-induced cell death, aneuploidy, and chromosomal instability, hallmarks of taxane resistance. Unexpectedly, the screen disclosed that the sphingolipid ceramide is a key regulator of the taxane-mediated spindle assembly checkpoint and taxane-induced cell death. Ceramide metabolism thus serves as a legitimate target for modulation of taxane effect on tumors.

Characteristic expression of globotriaosyl ceramide in human ovarian carcinoma-derived cells with anticancer drug resistance

The transporter protein genes and lipids in human ovarian carcinoma-derived KF28 cells with anticancer-drug-sensitive properties were compared with those in resistant cells, taxol-resistant KF28TX, cisplatin-resistant KFr13, and taxol- and cisplatin-resistant KFr13TX, to identify the molecules required for anticancer-drug resistance. In accordance with previous reports, taxol and cisplatin resistance was closely correlated with expression of the multidrug resistance 1 and bile acid export pump, and multidrug resistance-associated protein 2 genes, respectively. In addition, we found a distinct difference in glycosphingolipids between the sensitive and resistant cells. Although GlcCer was the major glycolipid (83.0%) in sensitive cells, GalCer, LacCer and, particularly, Gb(3)Cer were characteristically increased in all resistant cells, irrespective of whether the resistance was to taxol or cisplatin, and comprised 65-84% of total glycosphingolipids. GM3, which was present at 0.04 microg/mg dry weight in the sensitive cells, showed a twofold increase in the taxol-resistant cells, but was absent in the cisplatin-resistant cells. The altered glycolipid composition was proven to be due to enhanced or suppressed expression of the respective sugar transferase genes. In addition, the ceramide moiety of ceramide monohexoside in the sensitive cells constituted 83% of non-hydroxy fatty acids, but that in the resistant cells comprised 67-74% of alpha-hydroxy fatty acids. Thus, cells containing Gb(3)Cer with alpha-hydroxy fatty acids were found to survive selectively in the presence of taxol and cisplatin, and modification of the glycolipid structure was revealed to occur in association with anticancer-drug resistance.

Pharmacological inhibition or small interfering RNA targeting acid ceramidase sensitizes hepatoma cells to chemotherapy and reduces tumor growth in vivo

Ceramidases (CDases) play a key role in cancer therapy through enhanced conversion of ceramide into sphingosine 1-phosphate (S1P), but their involvement in hepatocarcinogenesis is unknown. Here, we report that daunorubicin (DNR) activated acid CDase post-transcriptionally in established human (HepG2 cells) or mouse (Hepa1c1c7) hepatoma cell lines as well as in primary cells from murine liver tumors, but not in cultured mouse hepatocytes. Acid CDase silencing by small interfering RNA (siRNA) or pharmacological inhibition with N-oleoylethanolamine (NOE) enhanced the ceramide to S1P balance compared to DNR alone, sensitizing hepatoma cells (HepG2, Hep-3B, SK-Hep and Hepa1c1c7) to DNR-induced cell death. DNR plus NOE or acid CDase siRNA-induced cell death was preceded by ultrastructural changes in mitochondria, stimulation of reactive oxygen species generation, release of Smac/DIABLO and cytochrome c and caspase-3 activation. In addition, in vivo siRNA treatment targeting acid CDase reduced tumor growth in liver tumor xenografts of HepG2 cells and enhanced DNR therapy. Thus, acid CDase promotes hepatocarcinogenesis and its antagonism may be a promising strategy in the treatment of liver cancer.