Ceramide synthase 6 modulates TRAIL sensitivity and nuclear translocation of active caspase-3 in colon cancer cells. Oncogene. 2009;28:1132-1141. [PMID: 19137010 DOI: 10.1038/onc.2008.468]

Sphingosine Kinase 2 Regulates Aryl Hydrocarbon Receptor Nuclear Translocation and Target Gene Activation

Sphingolipids play vital roles in metabolism and regulation. Previously, the aryl hydrocarbon receptor (AHR), a ligand-activated transcription factor, was reported to directly regulate ceramide synthesis genes by binding to their promoters. Herein, sphingosine kinase 2 (SPHK2), responsible for producing sphingosine-1-phosphate (S1P), was found to interact with AHR through LXXLL motifs, influencing AHR nuclear localization. Through mutagenesis and co-transfection studies, AHR activation and subsequent nuclear translocation was hindered by SPHK2 LXXLL mutants or SPHK2 lacking a nuclear localization signal (NLS). Similarly, an NLS-deficient AHR mutant impaired SPHK2 nuclear translocation. Silencing SPHK2 reduced AHR expression and its target gene CYP1A1, while SPHK2 overexpression enhanced AHR activity. SPHK2 was found enriched on the CYP1A1 promoter, underscoring its role in AHR target gene activation. Additionally, S1P rapidly increased AHR expression at both the mRNA and protein levels and promoted AHR recruitment to the CYP1A1 promoter. Using mouse models, AHR deficiency compromised SPHK2 nuclear translocation, illustrating a critical interaction where SPHK2 facilitates AHR nuclear localization and supports a positive feedback loop between AHR and sphingolipid enzyme activity in the nucleus. These findings highlight a novel function of SPHK2 in regulating AHR activity and gene expression.

Enzymes of sphingolipid metabolism as transducers of metabolic inputs

Sphingolipids (SLs) constitute a discrete subdomain of metabolism, and they display both structural and signaling functions. Accumulating evidence also points to intimate connections between intermediary metabolism and SL metabolism. Given that many SLs exhibit bioactive properties (i.e. transduce signals), these raise the possibility that an important function of SLs is to relay information on metabolic changes into specific cell responses. This could occur at various levels. Some metabolites are incorporated into SLs, whereas others may initiate regulatory or signaling events that, in turn, modulate SL metabolism. In this review, we elaborate on the former as it represents a poorly appreciated aspect of SL metabolism, and we develop the hypothesis that the SL network is highly sensitive to several specific metabolic changes, focusing on amino acids (serine and alanine), various fatty acids, choline (and ethanolamine), and glucose.

Ceramides are fuel gauges on the drive to cardiometabolic disease

Ceramides are signals of fatty acid excess that accumulate when a cell's energetic needs have been met and its nutrient storage has reached capacity. As these sphingolipids accrue, they alter the metabolism and survival of cells throughout the body including in the heart, liver, blood vessels, skeletal muscle, brain, and kidney. These ceramide actions elicit the tissue dysfunction that underlies cardiometabolic diseases such as diabetes, coronary artery disease, metabolic-associated steatohepatitis, and heart failure. Here, we review the biosynthesis and degradation pathways that maintain ceramide levels in normal physiology and discuss how the loss of ceramide homeostasis drives cardiometabolic pathologies. We highlight signaling nodes that sense small changes in ceramides and in turn reprogram cellular metabolism and stimulate apoptosis. Finally, we evaluate the emerging therapeutic utility of these unique lipids as biomarkers that forecast disease risk and as targets of ceramide-lowering interventions that ameliorate disease.

How ceramides affect the development of colon cancer: from normal colon to carcinoma

The integrity of the colon and the development of colon cancer depend on the sphingolipid balance in colon epithelial cells. In this review, we summarize the current knowledge on how ceramides and their complex derivatives influence normal colon development and colon cancer development. Ceramides, glucosylceramides and sphingomyelin are essential membrane components and, due to their biophysical properties, can influence the activation of membrane proteins, affecting protein-protein interactions and downstream signalling pathways. Here, we review the cellular mechanisms known to be affected by ceramides and their effects on colon development. We also describe which ceramides are deregulated during colorectal carcinogenesis, the molecular mechanisms involved in ceramide deregulation and how this affects carcinogenesis. Finally, we review new methods that are now state of the art for studying lipid-protein interactions in the physiological environment.

The role of BCL2L13 in glioblastoma: turning a need into a target

Glioblastoma (GBM) is the most common aggressive central nervous system cancer. GBM has a high mortality rate, with a median survival time of 12-15 months after diagnosis. A poor prognosis and a shorter life expectancy may result from resistance to standard treatments such as radiation and chemotherapy. Temozolomide has been the mainstay treatment for GBM, but unfortunately, there are high rates of resistance with GBM bypassing apoptosis. A proposed mechanism for bypassing apoptosis is decreased ceramide levels, and previous research has shown that within GBM cells, B cell lymphoma 2-like 13 (BCL2L13) can inhibit ceramide synthase. This review aims to discuss the causes of resistance in GBM cells, followed by a brief description of BCL2L13 and an explanation of its mechanism of action. Further, lipids, specifically ceramide, will be discussed concerning cancer and GBM cells, focusing on ceramide synthase and its role in developing GBM. By gathering all current information on BCL2L13 and ceramide synthase, this review seeks to enable an understanding of these pieces of GBM in the hope of finding an effective treatment for this disease.

Therapeutic Potential for Sphingolipids in Inflammatory Bowel Disease and Colorectal Cancer

Inflammatory bowel disease (IBD), characterized by chronic inflammation in the intestinal tract, increases the risk for the development of colorectal cancer (CRC). Sphingolipids, which have been implicated in IBD and CRC, are a class of bioactive lipids that regulate cell signaling, differentiation, apoptosis, inflammation, and survival. The balance between ceramide (Cer), the central sphingolipid involved in apoptosis and differentiation, and sphingosine-1-phosphate (S1P), a potent signaling molecule involved in proliferation and inflammation, is vital for the maintenance of normal cellular function. Altered sphingolipid metabolism has been implicated in IBD and CRC, with many studies highlighting the importance of S1P in inflammatory signaling and pro-survival pathways. A myriad of sphingolipid analogues, inhibitors, and modulators have been developed to target the sphingolipid metabolic pathway. In this review, the efficacy and therapeutic potential for modulation of sphingolipid metabolism in IBD and CRC will be discussed.

Fanning the Flames of Endoplasmic Reticulum (ER) Stress: Can Sphingolipid Metabolism Be Targeted to Enhance ER Stress-Associated Immunogenic Cell Death in Cancer?

The three arms of the unfolded protein response (UPR) surveil the luminal environment of the endoplasmic reticulum (ER) and transmit information through the lipid bilayer to the cytoplasm to alert the cell of stress conditions within the ER lumen. That same lipid bilayer is the site of de novo synthesis of phospholipids and sphingolipids. Thus, it is no surprise that lipids are modulated by and are modulators of ER stress. Given that sphingolipids have both prosurvival and proapoptotic effects, they also exert opposing effects on life/death decisions in the face of prolonged ER stress detected by the UPR. In this review, we will focus on several recent studies that demonstrate how sphingolipids affect each arm of the UPR. We will also discuss the role of sphingolipids in the process of immunogenic cell death downstream of the protein kinase RNA-like endoplasmic reticulum kinase (PERK)/eukaryotic initiating factor 2α (eIF2α) arm of the UPR. Furthermore, we will discuss strategies to target the sphingolipid metabolic pathway that could potentially act synergistically with agents that induce ER stress as novel anticancer treatments. SIGNIFICANCE STATEMENT: This review provides the readers with a brief discussion of the sphingolipid metabolic pathway and the unfolded protein response. The primary focus of the review is the mechanism(s) by which sphingolipids modulate the endoplasmic reticulum (ER) stress response pathways and the critical role of sphingolipids in the process of immunogenic cell death associated with the ER stress response.

Ceramides and ceramide synthases in cancer: Focus on apoptosis and autophagy

Different studies corroborate a role for ceramide synthases and their downstream products, ceramides, in modulation of apoptosis and autophagy in the context of cancer. These mechanisms of regulation, however, appear to be context dependent in terms of ceramides' fatty acid chain length, subcellular localization, and the presence or absence of their downstream targets. Our current understanding of the role of ceramide synthases and ceramides in regulation of apoptosis and autophagy could be harnessed to pioneer the development of new treatments to activate or inhibit a single type of ceramide synthase, thereby regulating the apoptosis induction or cross talk of apoptosis and autophagy in cancer cells. Moreover, the apoptotic function of ceramide suggests that ceramide analogues can pave the way for the development of novel cancer treatments. Therefore, in the current review paper we discuss the impact of ceramide synthases and ceramides in regulation of apoptosis and autophagy in context of different types of cancers. We also briefly introduce the latest information on ceramide synthase inhibitors, their application in diseases including cancer therapy, and discuss approaches for drug discovery in the field of ceramide synthase inhibitors. We finally discussed strategies for developing strategies to use lipids and ceramides analysis in biological fluids for developing early biomarkers for cancer.

Mass Spectrometry Detects Sphingolipid Metabolites for Discovery of New Strategy for Cancer Therapy from the Aspect of Programmed Cell Death

Sphingolipids, a type of bioactive lipid, play crucial roles within cells, serving as integral components of membranes and exhibiting strong signaling properties that have potential therapeutic implications in anti-cancer treatments. However, due to the diverse group of lipids and intricate mechanisms, sphingolipids still face challenges in enhancing the efficacy of different therapy approaches. In recent decades, mass spectrometry has made significant advancements in uncovering sphingolipid biomarkers and elucidating their impact on cancer development, progression, and resistance. Primary sphingolipids, such as ceramide and sphingosine-1-phosphate, exhibit contrasting roles in regulating cancer cell death and survival. The evasion of cell death is a characteristic hallmark of cancer cells, leading to treatment failure and a poor prognosis. The escape initiates with long-established apoptosis and extends to other programmed cell death (PCD) forms when patients experience chemotherapy, radiotherapy, and/or immunotherapy. Gradually, supportive evidence has uncovered the fundamental molecular mechanisms underlying various forms of PCD leading to the development of innovative molecular, genetic, and pharmacological tools that specifically target sphingolipid signaling nodes. In this study, we provide a comprehensive overview of the sphingolipid biomarkers revealed through mass spectrometry in recent decades, as well as an in-depth analysis of the six main forms of PCD (apoptosis, autophagy, pyroptosis, necroptosis, ferroptosis, and cuproptosis) in aspects of tumorigenesis, metastasis, and tumor response to treatments. We review the corresponding small-molecule compounds associated with these processes and their potential implications in cancer therapy.

Sphingolipid Metabolism in Tumor Cells

Sphingolipids are a diverse family of complex lipids typically composed of a sphingoid base bound to a fatty acid via amide bond. The metabolism of sphingolipids has long remained out of focus of biochemical studies. Recently, it has been attracting an increasing interest of researchers because of different and often multidirectional effects demonstrated by sphingolipids with a similar chemical structure. Sphingosine, ceramides (N-acylsphingosines), and their phosphorylated derivatives (sphingosine-1-phosphate and ceramide-1-phosphates) act as signaling molecules. Ceramides induce apoptosis and regulate stability of cell membranes and cell response to stress. Ceramides and sphingoid bases slow down anabolic and accelerate catabolic reactions, thus suppressing cell proliferation. On the contrary, their phosphorylated derivatives (ceramide-1-phosphate and sphingosine-1-phosphate) stimulate cell proliferation. Involvement of sphingolipids in the regulation of apoptosis and cell proliferation makes them critically important in tumor progression. Sphingolipid metabolism enzymes and sphingolipid receptors can be potential targets for antitumor therapy. This review describes the main pathways of sphingolipid metabolism in human cells, with special emphasis on the properties of this metabolism in tumor cells.

The Effect of Silencing the Genes Responsible for the Level of Sphingosine-1-phosphate on the Apoptosis of Colon Cancer Cells

Sphingosine-1-phosphate (S1P) and ceramides (Cer) are engaged in key events of signal transduction, but their involvement in the pathogenesis of colorectal cancer is not conclusive. The aim of our study was to investigate how the modulation of sphingolipid metabolism through the silencing of the genes involved in the formation (SPHK1) and degradation (SGPL1) of sphingosine-1-phosphate would affect the sphingolipid profile and apoptosis of HCT-116 human colorectal cancer cells. Silencing of SPHK1 expression decreased S1P content in HCT-116 cells, which was accompanied by an elevation in sphingosine, C18:0-Cer, and C18:1-Cer, increase in the expression and activation of Caspase-3 and -9, and augmentation of apoptosis. Interestingly, silencing of SGLP1 expression increased cellular content of both the S1P and Cer (C16:0-; C18:0-; C18:1-; C20:0-; and C22:0-Cer), yet inhibited activation of Caspase-3 and upregulated protein expression of Cathepsin-D. The above findings suggest that modulation of the S1P level and S1P/Cer ratio regulates both cellular apoptosis and CRC metastasis through Cathepsin-D modulation. The cellular ratio of S1P/Cer seems to be a crucial component of the above mechanism.

Ceramide Synthase 1 Inhibits Brain Metastasis of Non-Small Cell Lung Cancer by Interacting with USP14 and Downregulating the PI3K/AKT/mTOR Signaling Pathway

Brain metastasis (BM) is common in patients with non-small cell lung cancer (NSCLC) and is associated with a poor prognosis. Ceramide synthase 1 (CERS1) participates in malignancy development, but its potential role in NSCLC BM remains unclear. This study aimed to explore the physiological effects and molecular mechanism of CERS1 in NSCLC BM. CERS1 expression was evaluated in NSCLC tissues and cell lines, and its physiological roles were subsequently explored in vivo and in vitro. Mass spectrometry and co-immunoprecipitation were performed to explore CERS1-interacting proteins. The associated signaling pathways of CERS1 in NSCLC BM were further investigated using bioinformatics analysis and molecular biotechnology. We demonstrated that CERS1 was significantly downregulated in NSCLC cell lines and BM tissues, and its upregulation was associated with better prognoses. In vitro, CERS1 overexpression inhibited cell migration, invasion, and the ability to penetrate the blood-brain barrier. Moreover, CERS1 interacted with ubiquitin-specific protease 14 (USP14) and inhibited BM progression by downregulating the PI3K/AKT/mTOR signaling pathway. Further, CERS1 expression substantially suppressed BM tumor formation in vivo. This study demonstrated that CERS1 plays a suppressor role in NSCLC BM by interacting with USP14 and downregulating the PI3K/AKT/mTOR signaling pathway, thereby serving as a novel therapeutic target for NSCLC BM.

Molecular species profiles of plasma ceramides in different clinical types of X-linked adrenoleukodystrophy

X-linked adrenoleukodystrophy (X-ALD) is a genetic disorder associated with peroxisomal dysfunction. Patients with this rare disease accumulate very long-chain fatty acids (VLCFAs) in their bodies because of impairment of peroxisomal VLCFA ?-oxidation. Several clinical types of X-ALD, ranging from mild (axonopathy in the spinal cord) to severe (cerebral demyelination), are known. However, the molecular basis for this phenotypic variability remains largely unknown. In this study, we determined plasma ceramide (CER) profile using liquid chromatography-tandem mass spectrometry. We characterized the molecular species profile of CER in the plasma of patients with mild (adrenomyeloneuropathy;AMN) and severe (cerebral) X-ALD. Eleven X-ALD patients (five cerebral, five AMN, and one carrier) and 10 healthy volunteers participated in this study. Elevation of C26:0 CER was found to be a common feature regardless of the clinical types. The level of C26:1 CER was significantly higher in AMN but not in cerebral type, than that in healthy controls. The C26:1 CER level in the cerebral type was significantly lower than that in the AMN type. These results suggest that a high level of C26:0 CER, along with a control level of C26:1 CER, is a characteristic feature of the cerebral type X-ALD. J. Med. Invest. 70 : 403-410, August, 2023.

A genome-wide CRISPR screen implicates plasma membrane asymmetry in exogenous C6-ceramide toxicity

The bioactive sphingolipid ceramide impacts diverse cellular processes (e.g. apoptosis and cell proliferation) through its effects on membrane dynamics and intracellular signaling pathways. The dysregulation of ceramide metabolism has been implicated in cancer evasion of apoptosis and targeting ceramide metabolism has potential therapeutic benefits as a strategy to kill cancer cells and slow tumor growth. However, the mechanisms of cancer cell resistance to ceramide-mediated cell death are vastly intertwined and incompletely understood. To shed light on this mystery, we performed a genome-wide CRISPR-Cas9 screen to systematically identify regulators of cancer resistance to the soluble short chain ceramide, C6 ceramide (C6-Cer). Our results reveal a complex landscape of genetic modifiers of C6-Cer toxicity, including genes associated with ceramide and sphingolipid metabolism, vesicular trafficking, and membrane biology. Furthermore, we find that loss of the phospholipid flippase subunit TMEM30A impairs the plasma membrane trafficking of its binding partner, the P4-type ATPase ATP11B, and depletion of TMEM30A or ATP11B disrupts plasma membrane asymmetry and promotes resistance to C6-Cer toxicity. Together, our findings provide a resource of genetic modifiers of C6-Cer toxicity and reveal an unexpected role of plasma membrane asymmetry in C6-Cer induced cell death.

Ceramide Synthase 6 Mediates Triple-Negative Breast Cancer Response to Chemotherapy Through RhoA- and EGFR-Mediated Signaling Pathways

PURPOSE

Limited treatment options and lack of treatment sensitivity biomarkers make the clinical management of triple-negative breast cancer (TNBC) challenging. Ceramide synthase 6 (CERS6) generates ceramides, which are key intermediates in sphingolipid biosynthesis and play important roles in cancer progression and resistance.

METHODS

CERS6 was analyzed to determine its potential as a treatment sensitivity biomarker. CERS6 levels were determined in patients with breast cancer, and the roles and downstream signaling of CERS6 were analyzed using cellular and biochemical assays.

RESULTS

Analysis of CERS6 expression in 195 patients with TNBC and their clinical response to chemotherapy revealed that individuals with CERS6 overexpression experienced significantly inferior responses to chemotherapy than those without CERS6 overexpression. Functional analysis demonstrated that although CERS6 overexpression did not affect TNBC cell growth and migration, it conferred chemoresistance. CERS6 inhibition significantly reduced growth, migration, and survival by suppressing the RhoA- and EGFR-mediated signaling pathways. Compared to control cells, CERS6-depleted cells were consistently less viable at different concentrations of chemotherapeutic agents.

CONCLUSION

Our study is the first to demonstrate that CERS6 may serve as a treatment sensitivity biomarker in patients with TNBC in response to chemotherapy. In addition, our findings suggested that CERS6 may be a therapeutic target for TNBC treatment.

Serum Metabolomics Profiling Reveals Metabolic Alterations Prior to a Diagnosis with Non-Small Cell Lung Cancer among Chinese Community Residents: A Prospective Nested Case-Control Study

The present high mortality of lung cancer in China stems mainly from the lack of feasible, non-invasive and early disease detection biomarkers. Serum metabolomics profiling to reveal metabolic alterations could expedite the disease detection process and suggest those patients who are harboring disease. Using a nested case-control design, we applied ultra-high-performance liquid chromatography/mass spectrometry (LC-MS)-based serum metabolomics to reveal the metabolomic alterations and to indicate the presence of non-small cell lung cancer (NSCLC) using serum samples collected prior to disease diagnoses. The studied serum samples were collected from 41 patients before a NSCLC diagnosis (within 3.0 y) and 38 matched the cancer-free controls from the prospective Shanghai Suburban Adult Cohort. The NSCLC patients markedly presented cellular metabolism alterations in serum samples collected prior to their disease diagnoses compared with the cancer-free controls. In total, we identified 18 significantly expressed metabolites whose relative abundance showed either an upward or a downward trend, with most of them being lipid and lipid-like molecules, organic acids, and nitrogen compounds. Choline metabolism in cancer, sphingolipid, and glycerophospholipid metabolism emerged as the significant metabolic disturbance of NSCLC. The metabolites involved in these biological processes may be the distinctive features associated with NSCLC prior to a diagnosis.

Exercise Promotes Pro-Apoptotic Ceramide Signaling in a Mouse Melanoma Model

Simple Summary

Exercise has been shown to improve the efficacy of chemotherapy against several tumor models using mice through modulating tumor vascular perfusion, immune function, circulating growth factors, hypoxia, and metabolism in tumor cells and their surrounding microenvironment. However, little is known about the effect of exercise on tumor-cell-intrinsic death mechanisms, such as apoptosis. Ceramide is a bioactive lipid that can promote cell death. The strategy of increasing intracellular ceramide has potential as an anticancer treatment for melanoma with dysregulated ceramide metabolism, but there is not yet a clinically relevant method to do so. We found that moderate aerobic exercise increases pro-apoptotic ceramide in melanoma in mice, and activates p53 signaling, promoting tumor cell apoptosis. This finding suggests that exercise may be most effective as an adjuvant therapy to sensitize cancer cells to anticancer treatments in tumors that exhibit downregulated ceramide generation to evade cell death.

Abstract

Ceramides are essential sphingolipids that mediate cell death and survival. Low ceramide content in melanoma is one mechanism of drug resistance. Thus, increasing the ceramide content in tumor cells is likely to increase their sensitivity to cytotoxic therapy. Aerobic exercise has been shown to modulate ceramide metabolism in healthy tissue, but the relationship between exercise and ceramide in tumors has not been evaluated. Here, we demonstrate that aerobic exercise causes tumor cell apoptosis and accumulation of pro-apoptotic ceramides in B16F10 but not BP melanoma models using mice. B16F10 tumor-bearing mice were treated with two weeks of moderate treadmill exercise, or were control, unexercised mice. A reverse-phase protein array was used to identify canonical p53 apoptotic signaling as a key pathway upregulated by exercise, and we demonstrate increased apoptosis in tumors from exercised mice. Consistent with this finding, pro-apoptotic C16-ceramide, and the ceramide generating enzyme ceramide synthase 6 (CerS6), were higher in B16F10 tumors from exercised mice, while pro-survival sphingosine kinase 1 (Sphk1) was lower. These data suggest that exercise contributes to B16F10 tumor cell death, possibly by modulating ceramide metabolism toward a pro-apoptotic ceramide/sphingosine-1-phosphate balance. However, these results are not consistent in BP tumors, demonstrating that exercise can have different effects on tumors of different patient or mouse origin with the same diagnosis. This work indicates that exercise might be most effective as a therapeutic adjuvant with therapies that kill tumor cells in a ceramide-dependent manner.

Lipidomic profiling of exosomes from colorectal cancer cells and patients reveals potential biomarkers

Strong evidence suggests that differences in the molecular composition of lipids in exosomes depend on the cell type and has an influence on cancer initiation and progression. Here, we analyzed by liquid chromatography–mass spectrometry (LC‐MS) the lipidomic signature of exosomes derived from the human cell lines normal colon mucosa (NCM460D), and colorectal cancer (CRC) nonmetastatic (HCT116) and metastatic (SW620), and exosomes isolated from the plasma of nonmetastatic and metastatic CRC patients and healthy donors. Analysis of this exhaustive lipid study highlighted changes in some molecular species that were found in the cell lines and confirmed in the patients. For example, exosomes from primary cancer patients and nonmetastatic cells compared with healthy donors and control cells displayed a common marked increase in phosphatidylcholine (PC) 34 : 1, phosphatidylethanolamine (PE) 36 : 2, sphingomyelin (SM) d18 : 1/16 : 0, hexosylceramide (HexCer) d18 : 1/24 : 0 and HexCer d18 : 1/24 : 1. Interestingly, these same lipids species were decreased in the metastatic cell line and patients. Further, levels of PE 34 : 2, PE 36 : 2, and phosphorylated PE p16 : 0/20 : 4 were also significantly decreased in metastatic conditions when compared to the nonmetastatic counterparts. The only molecule species found markedly increased in metastatic conditions (in both patients and cells) when compared to controls was ceramide (Cer) d18 : 1/24 : 1. These decreases in lipid species in the extracellular vesicles might reflect function‐associated changes in the metastatic cell membrane. Although these potential biomarkers need to be validated in a larger cohort, they provide new insight toward the use of clusters of lipid biomarkers rather than a single molecule for the diagnosis of different stages of CRC.

Ceramide signaling in the gut

Sphingolipids are essential lipid components in the intestinal epithelial cells (IEC) along the intestinal tract. They play crucial roles in maintaining barrier integrity, regulating nutrient absorption, and acting as signaling molecules to regulate regeneration and differentiation of intestinal mucosa (Kurek et al., 2012). Ceramide is the central sphingolipid species and the precursor of all complex sphingolipids and other downstream simple intermediates like sphingosine (SPH), ceramide-1-phosphate (C-1-P), and sphingosine-1-phosphate (S-1-P). It is also a critical signaling molecule regulating numerous physiologic and pathologic processes. This review will summarize the metabolism of ceramides in the gut and their regulation in inflammatory bowel diseases and colorectal cancer.

Comprehensive analysis of LASS6 expression and prognostic value in ovarian cancer

BACKGROUND

Ceramide plays an important role in the occurrence and development of tumor. The synthesis of ceramide needs the participation of LASS. Current studies have shown that different LASS family members play different functions in tumors, especially LASS6, has been proved to play a key role in breast cancer, gastric cancer, melanoma and so on, but the research on ovarian cancer is very limited.

METHODS

Bioinformatics web resources, including Oncomine, UALCAN, Kaplan-Meier Plotter and TIMER were used to analyze the expression profile, prognostic value and immune infiltration of LASS6. The related genes of LASS6 in ovarian cancer were mined by Regulome Explorer and LinkedOmics database, and cluster analysis was done by DAVID. The PPI network involving LASS6 was constructed by STRING database. Finally, the correlation between 10 genes and LASS6 was analyzed by GEPIA database, and their prognostic value in ovarian cancer was analyzed by Kaplan-Meier plotter.

RESULTS

The expression of LASS6 was up-regulated in ovarian cancer, which was related to the progression and poor prognosis of ovarian cancer. Through GO/KEGG cluster analysis, we also found that LASS6 may affect calcium ion channel and its transport pathways. The analysis of regulatory network involved in LASS6 showed that the high mRNAs of 7 key genes were associated with poor prognosis of OS in patients with ovarian cancer, among which DEGS1 was the most significant.

CONCLUSIONS

LASS6 may play an important role in the regulation of calcium pathway and become a new therapeutic target and potential prognostic marker in ovarian cancer.

Cannabinoids and Endocannabinoid System Changes in Intestinal Inflammation and Colorectal Cancer

Despite the multiple preventive measures and treatment options, colorectal cancer holds a significant place in the world's disease and mortality rates. The development of novel therapy is in critical need, and based on recent experimental data, cannabinoids could become excellent candidates. This review covered known experimental studies regarding the effects of cannabinoids on intestinal inflammation and colorectal cancer. In our opinion, because colorectal cancer is a heterogeneous disease with different genomic landscapes, the choice of cannabinoids for tumor prevention and treatment depends on the type of the disease, its etiology, driver mutations, and the expression levels of cannabinoid receptors. In this review, we describe the molecular changes of the endocannabinoid system in the pathologies of the large intestine, focusing on inflammation and cancer.

Regulation of Death Receptor Signaling by S-Palmitoylation and Detergent-Resistant Membrane Micro Domains-Greasing the Gears of Extrinsic Cell Death Induction, Survival, and Inflammation

Death-receptor-mediated signaling results in either cell death or survival. Such opposite signaling cascades emanate from receptor-associated signaling complexes, which are often formed in different subcellular locations. The proteins involved are frequently post-translationally modified (PTM) by ubiquitination, phosphorylation, or glycosylation to allow proper spatio-temporal regulation/recruitment of these signaling complexes in a defined cellular compartment. During the last couple of years, increasing attention has been paid to the reversible cysteine-centered PTM S-palmitoylation. This PTM regulates the hydrophobicity of soluble and membrane proteins and modulates protein:protein interaction and their interaction with distinct membrane micro-domains (i.e., lipid rafts). We conclude with which functional and mechanistic roles for S-palmitoylation as well as different forms of membrane micro-domains in death-receptor-mediated signal transduction were unraveled in the last two decades.

The Role of Ceramide Metabolism and Signaling in the Regulation of Mitophagy and Cancer Therapy

Simple Summary

Sphingolipids are membrane-associated lipids that are involved in signal transduction pathways regulating cell death, growth, and migration. In cancer cells, sphingolipids regulate pathways relevant to cancer therapy, such as invasion, metastasis, apoptosis, and lethal mitophagy. Notable sphingolipids include ceramide, a sphingolipid that induces death and lethal mitophagy, and sphingosine-1 phosphate, a sphingolipid that induces survival and chemotherapeutic resistance. These sphingolipids participate in regulating the process of mitophagy, where cells encapsulate damaged mitochondria in double-membrane vesicles (called autophagosomes) for degradation. Lethal mitophagy is an anti-tumorigenic mechanism mediated by ceramide, where cells degrade many mitochondria until the cancer cell dies in an apoptosis-independent manner.

Abstract

Sphingolipids are bioactive lipids responsible for regulating diverse cellular functions such as proliferation, migration, senescence, and death. These lipids are characterized by a long-chain sphingosine backbone amide-linked to a fatty acyl chain with variable length. The length of the fatty acyl chain is determined by specific ceramide synthases, and this fatty acyl length also determines the sphingolipid’s specialized functions within the cell. One function in particular, the regulation of the selective autophagy of mitochondria, or mitophagy, is closely regulated by ceramide, a key regulatory sphingolipid. Mitophagy alterations have important implications for cancer cell proliferation, response to chemotherapeutics, and mitophagy-mediated cell death. This review will focus on the alterations of ceramide synthases in cancer and sphingolipid regulation of lethal mitophagy, concerning cancer therapy.

Ceramide Synthase 6 Maximizes p53 Function to Prevent Progeny Formation from Polyploid Giant Cancer Cells

Simple Summary

One mechanism that contributes to cancer recurrence is the ability of some malignant cells to temporarily halt cell division and accumulate multiple nuclei that are later released as progeny, which resume cell division. The release of progeny occurs via primitive cleavage and is highly dependent on the sphingolipid enzyme acid ceramidase but the role of sphingolipid metabolism in this process remains to be elucidated. This study highlights differences in sphingolipid metabolism between non-polyploid and polyploid cancer cells and shows that ceramide synthase 6, which preferentially generates C₁₆-ceramide maximizes the ability of the tumor suppressor p53 to inhibit progeny formation in polyploid cancer cells. These results offer an explanation as to why non-cancerous polyploid cells, which express wildtype p53, do not generate progeny and suggest that cancer cells with deregulated p53 function pose a higher risk of evading therapy especially if enzymes that generate C₁₆-ceramide are also dysregulated.

Abstract

Polyploid giant cancer cells (PGCC) constitute a transiently senescent subpopulation of cancer cells that arises in response to stress. PGCC are capable of generating progeny via a primitive, cleavage-like cell division that is dependent on the sphingolipid enzyme acid ceramidase (ASAH1). The goal of this study was to understand differences in sphingolipid metabolism between non-polyploid and polyploid cancer cells to gain an understanding of the ASAH1-dependence in the PGCC population. Steady-state and flux analysis of sphingolipids did not support our initial hypothesis that the ASAH1 product sphingosine is rapidly converted into the pro-survival lipid sphingosine-1-phosphate. Instead, our results suggest that ASAH1 activity is important for preventing the accumulation of long chain ceramides such as C₁₆-ceramide. We therefore determined how modulation of C₁₆-ceramide, either through CerS6 or p53, a known PGCC suppressor and enhancer of CerS6-derived C₁₆-ceramide, affected PGCC progeny formation. Co-expression of the CerS6 and p53 abrogated the ability of PGCC to form offspring, suggesting that the two genes form a positive feedback loop. CerS6 enhanced the effect of p53 by significantly increasing protein half-life. Our results support the idea that sphingolipid metabolism is of functional importance in PGCC and that targeting this signaling pathway has potential for clinical intervention.

Sphingolipids as critical players in retinal physiology and pathology

Sphingolipids have emerged as bioactive lipids involved in the regulation of many physiological and pathological processes. In the retina, they have been established to participate in numerous processes, such as neuronal survival and death, proliferation and migration of neuronal and vascular cells, inflammation, and neovascularization. Dysregulation of sphingolipids is therefore crucial in the onset and progression of retinal diseases. This review examines the involvement of sphingolipids in retinal physiology and diseases. Ceramide (Cer) has emerged as a common mediator of inflammation and death of neuronal and retinal pigment epithelium cells in animal models of retinopathies such as glaucoma, age-related macular degeneration (AMD), and retinitis pigmentosa. Sphingosine-1-phosphate (S1P) has opposite roles, preventing photoreceptor and ganglion cell degeneration but also promoting inflammation, fibrosis, and neovascularization in AMD, glaucoma, and pro-fibrotic disorders. Alterations in Cer, S1P, and ceramide 1-phosphate may also contribute to uveitis. Notably, use of inhibitors that either prevent Cer increase or modulate S1P signaling, such as Myriocin, desipramine, and Fingolimod (FTY720), preserves neuronal viability and retinal function. These findings underscore the relevance of alterations in the sphingolipid metabolic network in the etiology of multiple retinopathies and highlight the potential of modulating their metabolism for the design of novel therapeutic approaches.

Asah2 Represses the p53-Hmox1 Axis to Protect Myeloid-Derived Suppressor Cells from Ferroptosis

Myeloid-derived suppressor cells (MDSCs) are immune suppressive cells that massively accumulate under pathological conditions to suppress T cell immune response. Dysregulated cell death contributes to MDSC accumulation, but the molecular mechanism underlying this cell death dysregulation is not fully understood. In this study, we report that neutral ceramidase (N-acylsphingosine amidohydrolase [ASAH2]) is highly expressed in tumor-infiltrating MDSCs in colon carcinoma and acts as an MDSC survival factor. To target ASAH2, we performed molecular docking based on human ASAH2 protein structure. Enzymatic inhibition analysis of identified hits determined NC06 as an ASAH2 inhibitor. Chemical and nuclear magnetic resonance analysis determined NC06 as 7-chloro-2-(3-chloroanilino)pyrano[3,4-e][1,3]oxazine-4,5-dione. NC06 inhibits ceramidase activity with an IC₅₀ of 10.16-25.91 μM for human ASAH2 and 18.6-30.2 μM for mouse Asah2 proteins. NC06 induces MDSC death in a dose-dependent manner, and inhibition of ferroptosis decreased NC06-induced MDSC death. NC06 increases glutathione synthesis and decreases lipid reactive oxygen species to suppress ferroptosis in MDSCs. Gene expression profiling identified the p53 pathway as the Asah2 target in MDSCs. Inhibition of Asah2 increased p53 protein stability to upregulate Hmox1 expression to suppress lipid reactive oxygen species production to suppress ferroptosis in MDSCs. NC06 therapy increases MDSC death and reduces MDSC accumulation in tumor-bearing mice, resulting in increased activation of tumor-infiltrating CTLs and suppression of tumor growth in vivo. Our data indicate that ASAH2 protects MDSCs from ferroptosis through destabilizing p53 protein to suppress the p53 pathway in MDSCs in the tumor microenvironment. Targeting ASAH2 with NC06 to induce MDSC ferroptosis is potentially an effective therapy to suppress MDSC accumulation in cancer immunotherapy.

Lipid composition of the cancer cell membrane

Cancer cell possesses numerous adaptations to resist the immune system response and chemotherapy. One of the most significant properties of the neoplastic cells is the altered lipid metabolism, and consequently, the abnormal cell membrane composition. Like in the case of phosphatidylcholine, these changes result in the modulation of certain enzymes and accumulation of energetic material, which could be used for a higher proliferation rate. The changes are so prominent, that some lipids, such as phosphatidylserines, could even be considered as the cancer biomarkers. Additionally, some changes of biophysical properties of cell membranes lead to the higher resistance to chemotherapy, and finally to the disturbances in signalling pathways. Namely, the increased levels of certain lipids, like for instance phosphatidylserine, lead to the attenuation of the immune system response. Also, changes in lipid saturation prevent the cells from demanding conditions of the microenvironment. Particularly interesting is the significance of cell membrane cholesterol content in the modulation of metastasis. This review paper discusses the roles of each lipid type in cancer physiology. The review combined theoretical data with clinical studies to show novel therapeutic options concerning the modulation of cell membranes in oncology.

The role of ceramides in metabolic disorders: when size and localization matters

Ceramide accumulation is a hallmark in the manifestation of numerous obesity-related diseases, such as type 2 diabetes mellitus and atherosclerosis. Until the early 2000s, ceramides were viewed as a homogenous class of sphingolipids. However, it has now become clear that ceramides exert fundamentally different effects depending on the specific fatty acyl chain lengths, which are integrated into ceramides by a group of enzymes known as dihydroceramide synthases. In addition, alterations in ceramide synthesis, trafficking and metabolism in specific cellular compartments exert distinct consequences on metabolic homeostasis. Here, we examine the emerging concept of how the intracellular localization of ceramides with distinct acyl chain lengths can regulate glucose metabolism, thus emphasizing their potential as targets in the development of novel and specific therapies for obesity and obesity-associated diseases.

On the role of sphingolipids in cell survival and death

Sphingolipids, universal components of biological membranes of all eukaryotic organisms, from yeasts to mammals, in addition of playing a structural role, also play an important part of signal transduction pathways. They participate or, also, ignite several fundamental subcellular signaling processes but, more in general, they directly contribute to key biological activities such as cell motility, growth, senescence, differentiation as well as cell fate, i.e., survival or death. The sphingolipid metabolic pathway displays an intricate network of reactions that result in the formation of multiple sphingolipids, including ceramide, and sphingosine-1-phosphate. Different sphingolipids, that have key roles in determining cell fate, can induce opposite effects: as a general rule, sphingosine-1-phosphate promotes cell survival and differentiation, whereas ceramide is known to induce apoptosis. Furthermore, together with cholesterol, sphingolipids also represent the basic lipid component of lipid rafts, cholesterol- and sphingolipid-enriched membrane microdomains directly involved in cell death and survival processes. In this review, we briefly describe the characteristics of sphingolipids and lipid membrane microdomains. In particular, we will consider the involvement of various sphingolipids per se and of lipid rafts in apoptotic pathway, both intrinsic and extrinsic, in nonapoptotic cell death, in autophagy, and in cell differentiation. In addition, their roles in the most common physiological and pathological contexts either as pathogenetic elements or as biomarkers of diseases will be considered. We would also hint how the manipulation of sphingolipid metabolism could represent a potential therapeutic target to be investigated and functionally validated especially for those diseases for which therapeutic options are limited or ineffective.

Sphingolipid Metabolism and Signaling in Skeletal Muscle: From Physiology to Physiopathology

Sphingolipids represent one of the major classes of eukaryotic lipids. They play an essential structural role, especially in cell membranes where they also possess signaling properties and are capable of modulating multiple cell functions, such as apoptosis, cell proliferation, differentiation, and inflammation. Many sphingolipid derivatives, such as ceramide, sphingosine-1-phosphate, and ganglioside, have been shown to play many crucial roles in muscle under physiological and pathological conditions. This review will summarize our knowledge of sphingolipids and their effects on muscle fate, highlighting the role of this class of lipids in modulating muscle cell differentiation, regeneration, aging, response to insulin, and contraction. We show that modulating sphingolipid metabolism may be a novel and interesting way for preventing and/or treating several muscle-related diseases.

Mechanisms of Ceramide-Dependent Cancer Cell Death

Mechanistic details for the roles of sphingolipids and their downstream targets in the regulation of tumor growth, response to chemo/radiotherapy, and metastasis have been investigated in recent studies using innovative molecular, genetic and pharmacologic tools in various cancer models. Induction of ceramide generation in response to cellular stress by chemotherapy, radiation, or exogenous ceramide analog drugs mediates cell death via apoptosis, necroptosis, or mitophagy. In this chapter, distinct functions and mechanisms of action of endogenous ceramides with different fatty acyl chain lengths in the regulation of cancer cell death versus survival will be discussed. In addition, importance of ceramide subcellular localization, trafficking, and lipid-protein binding between ceramide and various target proteins in cancer cells will be reviewed. Moreover, clinical trials from structure-function-based studies to restore antiproliferative ceramide signaling by activating ceramide synthesis will also be analyzed. Future studies are important to understand the mechanistic involvement of ceramide-mediated cell death in anticancer therapy, including immunotherapy.

Inflammatory role of extracellular sphingolipids in Cystic Fibrosis

Ceramide is emerging as one of the players of inflammation in lung diseases. However, data on its inflammatory role in Cystic Fibrosis (CF) as part of the extracellular machinery driven by lung mesenchymal stem cells (MSCs)-derived extracellular vesicles (EVs) are missing. We obtained an in vitro model of CF-MSC by treating control human lung MSCs with a specific CFTR inhibitor. We characterized EVs populations derived from MSCs (ctr EVs) and CF-MSCs (CF-EVs) and analyzed their sphingolipid profile by LC-MS/MS. To evaluate their immunomodulatory function, we treated an in vitro human model of CF, with both EVs populations. Our data show that the two EVs populations differ for the average size, amount, and rate of uptake. CF-EVs display higher ceramide and dihydroceramide accumulation as compared to control EVs, suggesting the involvement of the de novo biosynthesis pathway in the parental CF-MSCs. Higher sphingomyelinase activity in CF-MSCs, driven by inflammation-induced ceramide accumulation, sustains the exocytosis of vesicles that export new formed pro-inflammatory ceramide. Our results suggest that CFTR dysfunction associates with an enhanced sphingolipid metabolism leading to the release of EVs that export the excess of pro-inflammatory Cer to the recipient cells, thus contributing to maintain the unresolved inflammatory status of CF.

Sphingolipidomics Investigation of the Temporal Dynamics after Ischemic Brain Injury

Sphingolipids (SPLs) have been proposed as potential therapeutic targets for strokes, but no reports have ever profiled the changes of the entire range of SPLs after a stroke. This study applied sphingolipidomic methods to investigate the temporal and individual changes in the sphingolipidome including the effect of atorvastatin after ischemic brain injury. We conducted sphingolipidomic profiling of mouse brain tissue by liquid chromatography-electrospray ionization tandem mass spectrometry at 3 h and 24 h after 1 h of middle cerebral artery occlusion (MCAO), and SPL levels were compared with those of the Sham control group. At 3 h post-MCAO, ceramides (Cers) exhibited an increase in levels of long-chain Cers but a decrease in very-long-chain Cers. Moreover, sphingosine, the precursor of sphingosine-1-phosphate (S1P), decreased and S1P increased at 3 h after MCAO. In contrast to 3 h, both long-chain and very-long-chain Cers showed an increased trend at 24 h post-MCAO. Most important, the administration of atorvastatin improved the neurological function of the mice and significantly reversed the SPL changes resulting from the ischemic injury. Furthermore, we used plasma samples from nonstroke control and stroke patients at time points of 72 h after a stroke, and found a similar trend of Cers as in the MCAO model. This study successfully elucidated the overall effect of ischemic injury on SPL metabolism with and without atorvastatin treatment. The network of SPL components that change upon ischemic damage may provide novel therapeutic targets for ischemic stroke.

The role of ceramide in regulating endoplasmic reticulum function

Sphingolipids (SLs) are an important class of membrane lipids containing a long chain sphingoid base backbone. SL synthesis is compartmentalized between two major cell organelles, the endoplasmic reticulum (ER) and the Golgi apparatus. The initial steps of sphingolipid synthesis take place in the ER, where the simplest SL, ceramide, is synthesized. Although ceramide is a critical membrane component, an imbalance of ceramide levels can have significant deleterious effects on cell properties leading to events such as apoptosis. For this reason and others, ER ceramide levels must be tightly regulated. Here, we describe the biological and biophysical properties of ceramide and discuss how this might impact the ER membrane. This article is part of a special issue entitled: ER Platforms for Membrane Lipid Dynamics.

Approaches for probing and evaluating mammalian sphingolipid metabolism

Sphingolipid metabolism plays a critical role in regulating processes that control cellular fate. This dynamic pathway can generate and degrade the central players: ceramide, sphingosine and sphingosine-1-phosphate in almost any membrane in the cell, adding an unexpected level of complexity in deciphering signaling events. While in vitro assays have been developed for most enzymes in SL metabolism, these assays are setup for optimal activity conditions and can fail to take into account regulatory components such as compartmentalization, substrate limitations, and binding partners that can affect cellular enzymatic activity. Therefore, many in-cell assays have been developed to derive results that are authentic to the cellular situation which may give context to alteration in SL mass. This review will discuss approaches for utilizing probes for mammalian in-cell assays to interrogate most enzymatic steps central to SL metabolism. The use of inhibitors in conjunction with these probes can verify the specificity of cellular assays as well as provide valuable insight into flux in the SL network. The use of inhibitors specific to each of the central sphingolipid enzymes are also discussed to assist researchers in further interrogation of these pathways.

Expression of the SNAI2 transcriptional repressor is regulated by C16-ceramide

Ceramide synthase 6 (CerS6) is an enzyme that preferentially generates pro-apoptotic C₁₆-ceramide in the sphingolipid metabolic pathway. Reduced expression of CerS6 has been associated with apoptosis resistance and recent studies point to a role for CerS6 in epithelial mesenchymal transition (EMT). Because cells that undergo EMT are also more resistant to apoptosis, we hypothesized that reduced expression of CerS6 could induce changes that are associated with EMT. We found that shRNA-mediated knockdown of CerS6 increases expression of the EMT transcription factor SNAI2 but not SNAI1 or TWIST. Treatment with C₆-ceramide nanoliposomes (CNL) resulted in a preferential increase in C₁₆-ceramide and suppressed SNAI2 transcriptional activation and protein expression. The increase in C₁₆-ceramide following CNL treatment was dependent on CerS activity and occurred even when CerS6 shRNA was expressed. shRNA against CerS5, which like CerS6 preferentially generates C₁₆-ceramide, also decreased transcriptional activation of SNAI2, suggesting a role for C₁₆-ceramide rather than a specific enzyme in the regulation of this transcription factor. While loss of CerS6 has been associated with apoptosis resistance, we found that cells lacking this protein are more susceptible to the effects CNL. In summary, our study identifies SNAI2 as a novel target whose expression can be influenced by C₁₆-ceramide levels. The potential of CNL to suppress SNAI2 expression has important clinical implications, since elevated expression of this transcription factor has been associated with an aggressive phenotype or poor outcomes in several types of solid tumors.

Ceramide synthase-6 confers resistance to chemotherapy by binding to CD95/Fas in T-cell acute lymphoblastic leukemia

Ceramide synthases (CERS) produce ceramides which are key intermediators in the biosynthesis of complex sphingolipids and play an important role in cell proliferation, differentiation, apoptosis and senescence. CERS6 is an isoform of ceramide synthases known to generate ceramides with C16 acyl chain (C₁₆-Cer). CERS6 and C₁₆-Cer levels were significantly higher in acute lymphoblastic leukemia (ALL) cells in comparison to peripheral blood mononuclear cells and T lymphocytes derived from healthy human volunteers. We investigated the role of CERS6 in chemo-resistance in T-ALL cell lines. Stable knockdown of CERS6 in CCRF-CEM and MOLT-4 cells resulted in increased sensitivity to ABT-737, a pan-BCL-2 inhibitor, while CCRF-CEM cells with exogenous CERS6 expression showed resistance to ABT-737 relative to the vector control. The cytotoxic activity of ABT-737 in CERS6 knockdown cells was significantly reduced by the addition of a caspase-8 inhibitor Z-IETD, suggesting that CERS6 alters the cytotoxicity via extrinsic pathway of apoptosis. By co-immunoprecipitation of CERS6 in CCRF-CEM cells, we identified CD95/Fas, a mediator of extrinsic apoptotic pathway, as a novel CERS6 binding partner. In Fas pull-down samples, FADD (Fas-associated protein with death domain) was detected at higher levels in cells with CERS6 knockdown compared with control cells when treated with ABT-737, and this was reversed by the overexpression of CERS6, demonstrating that CERS6 interferes with Fas–FADD DISC assembly. CERS6 may serve as a biomarker in determining the effectiveness of anticancer agents acting via the extrinsic pathway in T-ALL.

Chemosensitivity of human colon cancer cells is influenced by a p53-dependent enhancement of ceramide synthase 5 and induction of autophagy

Resistance against chemotherapy is a life-threatening complication in colon cancer therapy. To increase response rate, new additional targets that contribute to chemoresistance are still needed to be explored. Ceramides, which belong to the group of sphingolipids, are well-known regulators of cell death and survival, respectively. Here, we show that in human wild-type (^wt) p53 HCT-116 colon cancer cells treatment with oxaliplatin or 5-fluorouracil (5-FU) leads to a strong increase in ceramide synthase 5 (CerS5) expression and C_16:0-ceramide levels, which was not shown in HCT-116 lacking p53 expression (HCT-116 p53^-/-). The increase in CerS5 expression occurs by stabilizing CerS5 mRNA at the 3'-UTR. By contrast, in the p53-deficient cells CerS2 expression and CerS2-related C_24:0- and C_24:1-ceramide levels were elevated which is possibly related to enhanced polyadenylation of the CerS2 transcript in these cells. Stable knockdown of CerS5 expression using CerS5-targeting shRNA led to an increased sensitivity of HCT-116 p53^wt cells, but not of p53^-/- cells, to oxaliplatin and 5-FU. Enhanced sensitivity was accompanied by an inhibition of autophagy and inhibition of mitochondrial respiration in these cells. However, knockdown of CerS2 had no significant effects on chemosensitivity of both cell lines. In conclusion, in p53^wt colon cancer cells chemosensitivity against oxaliplatin or 5-FU could be enhanced by downregulation of CerS5 expression leading to reduced autophagy and mitochondrial respiration.

Targeting sphingolipid metabolism as an approach for combination therapies in haematological malignancies

Conventional chemotherapy-based drug combinations have, until recently, been the backbone of most therapeutic strategies for cancer. In a time of emerging rationale drug development, targeted therapies are beginning to be added to traditional chemotherapeutics to synergistically enhance clinical responses. Of note, the importance of pro-apoptotic ceramide in mediating the anti-cancer effects of these therapies is becoming more apparent. Furthermore, reduced cellular ceramide in favour of pro-survival sphingolipids correlates with tumorigenesis and most importantly, drug resistance. Thus, agents that manipulate sphingolipid metabolism have been explored as potential anti-cancer agents and have recently demonstrated exciting potential to augment the efficacy of anti-cancer therapeutics. This review examines the biology underpinning these observations and the potential use of sphingolipid manipulating agents in the context of existing and emerging therapies for haematological malignancies.

• Efficacy of many chemotherapeutics and targeted therapies is dictated by cellular ceramide levels.

• Oncogene activation skews sphingolipid metabolism to favour the production of pro-survival sphingolipids.

• Inhibitors of enzymes involved in ceramide metabolism exhibit promise in the relapsed-refractory setting.

• Anti-cancer activity of sphingosine kinase inhibitors provides several options for new drug combinations.

Open Questions

• What other clinically utilised drugs rely on increases in ceramide levels for their efficacy and can they be effectively partnered with other ceramide inducing agents?

• How does ceramide modulate the Bcl-2 family proteins, Mcl-1 and Bcl-2?

• Are sphingolipid enzyme inhibitors best suited in the frontline or relapsed-refractory setting?

Interdiction of Sphingolipid Metabolism Revisited: Focus on Prostate Cancer

Sphingolipid metabolism is known to play a role in cell death, survival, and therapy resistance in cancer. Sphingolipids, particularly dihydroceramide and ceramide, are associated with antiproliferative or cell death responses, respectively, and are central to effective cancer therapy. Within the last decade, strides have been made in elucidating many intricacies of sphingolipid metabolism. New information has emerged on the mechanisms by which sphingolipid metabolism is dysregulated during malignancy and how cancer cells survive and/or escape therapeutic interventions. This chapter focuses on three main themes: (1) sphingolipid enzymes that are dysregulated in cancer, particularly in prostate cancer; (2) inhibitors of sphingolipid metabolism that antagonize prosurvival responses; and (3) sphingolipid-driven escape mechanisms that allow cancer cells to evade therapies. We explore clinical and preclinical approaches to interdict sphingolipid metabolism and provide a rationale for combining strategies to drive the generation of antiproliferative ceramides with prevention of ceramide clearance.

Molecular Markers of Therapy-Resistant Glioblastoma and Potential Strategy to Combat Resistance

Glioblastoma (GBM) is the most common primary malignant tumor of the central nervous system. With its overall dismal prognosis (the median survival is 14 months), GBMs demonstrate a resounding resilience against all current treatment modalities. The absence of a major progress in the treatment of GBM maybe a result of our poor understanding of both GBM tumor biology and the mechanisms underlying the acquirement of treatment resistance in recurrent GBMs. A comprehensive understanding of these markers is mandatory for the development of treatments against therapy-resistant GBMs. This review also provides an overview of a novel marker called acid ceramidase and its implication in the development of radioresistant GBMs. Multiple signaling pathways were found altered in radioresistant GBMs. Given these global alterations of multiple signaling pathways found in radioresistant GBMs, an effective treatment for radioresistant GBMs may require a cocktail containing multiple agents targeting multiple cancer-inducing pathways in order to have a chance to make a substantial impact on improving the overall GBM survival.