Ceramide Nanoliposomes as a MLKL-Dependent, Necroptosis-Inducing, Chemotherapeutic Reagent in Ovarian Cancer

Intricate interplay between cell metabolism and necroptosis regulation in metabolic dysfunction-associated steatotic liver disease: A narrative review

Metabolic dysfunction-associated steatotic liver disease (MASLD), formerly known as non-alcoholic fatty liver disease (NAFLD), encompasses a progressive spectrum of liver conditions, ranging from steatosis to metabolic dysfunction-associated steatohepatitis, characterised by hepatocellular death and inflammation, potentially progressing to cirrhosis and/or liver cancer. In both experimental and human MASLD, necroptosis-a regulated immunogenic necrotic cell death pathway-is triggered, yet its exact role in disease pathogenesis remains unclear. Noteworthy, necroptosis-related signalling pathways are emerging as key players in metabolic reprogramming, including lipid and mitochondrial metabolism. Additionally, metabolic dysregulation is a well-established contributor to MASLD development and progression. This review explores the intricate interplay between cell metabolism and necroptosis regulation and its impact on MASLD pathogenesis. Understanding these cellular events may offer new insights into the complexity of MASLD pathophysiology, potentially uncovering therapeutic opportunities and unforeseen metabolic consequences of targeting necroptosis.

Sphingolipid metabolism and regulated cell death in malignant melanoma

Malignant melanoma (MM) is a highly invasive and therapeutically resistant skin malignancy, posing a significant clinical challenge in its treatment. Programmed cell death plays a crucial role in the occurrence and progression of MM. Sphingolipids (SP), as a class of bioactive lipids, may be associated with many kinds of diseases. SPs regulate various forms of programmed cell death in tumors, including apoptosis, necroptosis, ferroptosis, and more. This review will delve into the mechanisms by which different types of SPs modulate various forms of programmed cell death in MM, such as their regulation of cell membrane permeability and signaling pathways, and how they influence the survival and death fate of MM cells. An in-depth exploration of the role of SPs in programmed cell death in MM aids in unraveling the molecular mechanisms of melanoma development and holds significant importance in developing novel therapeutic strategies.

Lipotoxicity: The missing link between diabetes and periodontitis?

Lipotoxicity refers to the accumulation of lipids in tissues other than adipose tissue (body fat). It is one of the major pathophysiological mechanisms responsible for the progression of diabetes complications such as non-alcoholic fatty liver disease and diabetic nephropathy. Accumulating evidence indicates that lipotoxicity also contributes significantly to the toxic effects of diabetes on periodontitis. Therefore, we reviewed the current in vivo, in vitro, and clinical evidence of the detrimental effects of lipotoxicity on periodontitis, focusing on its molecular mechanisms, especially oxidative and endoplasmic reticulum stress, inflammation, ceramides, adipokines, and programmed cell death pathways. By elucidating potential therapeutic strategies targeting lipotoxicity and describing their associated mechanisms and clinical outcomes, including metformin, statins, liraglutide, adiponectin, and omega-3 PUFA, this review seeks to provide a more comprehensive and effective treatment framework against diabetes-associated periodontitis. Furthermore, the challenges and future research directions are proposed, aiming to contribute to a more profound understanding of the impact of lipotoxicity on periodontitis.

The lipid basis of cell death and autophagy

ABBREVIATIONS

ACSL: acyl-CoA synthetase long chain family; DISC: death-inducing signaling complex; DAMPs: danger/damage-associated molecular patterns; Dtgn: dispersed trans-Golgi network; FAR1: fatty acyl-CoA reductase 1; GPX4: glutathione peroxidase 4; LPCAT3: lysophosphatidylcholine acyltransferase 3; LPS: lipopolysaccharide; MUFAs: monounsaturated fatty acids; MOMP: mitochondrial outer membrane permeabilization; MLKL, mixed lineage kinase domain like pseudokinase; oxPAPC: oxidized 1-palmitoyl-2-arachidonoyl-sn-glycero-3-phosphocholine; OxPCs: oxidized phosphatidylcholines; PUFAs: polyunsaturated fatty acids; POR: cytochrome p450 oxidoreductase; PUFAs: polyunsaturated fatty acids; RCD: regulated cell death; RIPK1: receptor interacting serine/threonine kinase 1; SPHK1: sphingosine kinase 1; SOAT1: sterol O-acyltransferase 1; SCP2: sterol carrier protein 2; SFAs: saturated fatty acids; SLC47A1: solute carrier family 47 member 1; SCD: stearoyl-CoA desaturase; VLCFA: very long chain fatty acids.

Pronecroptotic Therapy Using Ceramide Nanoliposomes Is Effective for Triple-Negative Breast Cancer Cells

Regulated necrosis, termed necroptosis, represents a potential therapeutic target for refractory cancer. Ceramide nanoliposomes (CNLs), considered potential chemotherapeutic agents, induce necroptosis by targeting the activating protein mixed lineage kinase domain-like protein (MLKL). In the present study, we examined the potential of pronecroptotic therapy using CNLs for refractory triple-negative breast cancer (TNBC), for which there is a lack of definite and effective therapeutic targets among the various immunohistological subtypes of breast cancer. MLKL mRNA expression in tumor tissues was significantly higher in TNBC patients than in those with non-TNBC subtypes. Similarly, among the 50 breast cancer cell lines examined, MLKL expression was higher in TNBC-classified cell lines. TNBC cell lines were more susceptible to the therapeutic effects of CNLs than the non-TNBC subtypes of breast cancer cell lines. In TNBC-classified MDA-MB-231 cells, the knockdown of MLKL suppressed cell death induced by CNLs or the active substance short-chain C6-ceramide. Accordingly, TNBC cells were prone to CNL-evoked necroptotic cell death. These results will contribute to the development of CNL-based pronecroptotic therapy for TNBC.

Acid Ceramidase Inhibitor LCL-805 Antagonizes Akt Signaling and Promotes Iron-Dependent Cell Death in Acute Myeloid Leukemia

Acute myeloid leukemia (AML) is an aggressive hematologic malignancy requiring urgent treatment advancements. Ceramide is a cell-death-promoting signaling lipid that plays a central role in therapy-induced cell death. We previously determined that acid ceramidase (AC), a ceramide-depleting enzyme, is overexpressed in AML and promotes leukemic survival and drug resistance. The ceramidase inhibitor B-13 and next-generation lysosomal-localizing derivatives termed dimethylglycine (DMG)-B-13 prodrugs have been developed but remain untested in AML. Here, we report the in vitro anti-leukemic efficacy and mechanism of DMG-B-13 prodrug LCL-805 across AML cell lines and primary patient samples. LCL-805 inhibited AC enzymatic activity, increased total ceramides, and reduced sphingosine levels. A median EC50 value of 11.7 μM was achieved for LCL-805 in cell viability assays across 32 human AML cell lines. As a single agent tested across a panel of 71 primary AML patient samples, a median EC50 value of 15.8 μM was achieved. Exogenous ceramide supplementation with C6-ceramide nanoliposomes, which is entering phase I/II clinical trial for relapsed/refractory AML, significantly enhanced LCL-805 killing. Mechanistically, LCL-805 antagonized Akt signaling and led to iron-dependent cell death distinct from canonical ferroptosis. These findings elucidated key factors involved in LCL-805 cytotoxicity and demonstrated the potency of combining AC inhibition with exogenous ceramide.

Solid tumor treatment via augmentation of bioactive C6 ceramide levels with thermally ablative focused ultrasound

Sparse scan partial thermal ablation (TA) with focused ultrasound (FUS) may be deployed to treat solid tumors and increase delivery of systemically administered therapeutics. Furthermore, C6-ceramide-loaded nanoliposomes (CNLs), which rely upon the enhanced-permeation and retention (EPR) effect for delivery, have shown promise for treating solid tumors and are being tested in clinical trials. Here, our objective was to determine whether CNLs synergize with TA in the control of 4T1 breast tumors. CNL monotherapy of 4T1 tumors yielded significant intratumoral bioactive C6 accumulation by the EPR effect, but tumor growth was not controlled. TA increased bioactive C6 accumulation by ~ 12.5-fold over the EPR effect. In addition, TA + CNL caused shifts in long-chain to very-long-chain ceramide ratios (i.e., C16/24 and C18/C24) that could potentially contribute to tumor control. Nonetheless, these changes in intratumoral ceramide levels were still insufficient to confer tumor growth control beyond that achieved when combining with TA with control "ghost" nanoliposomes (GNL). While this lack of synergy could be due to increased "pro-tumor" sphingosine-1-phosphate (S1P) levels, this is unlikely because S1P levels exhibited only a moderate and statistically insignificant increase with TA + CNL. In vitro studies showed that 4T1 cells are highly resistant to C6, offering the most likely explanation for the inability of TA to synergize with CNL. Thus, while our results show that sparse scan TA is a powerful approach for markedly enhancing CNL delivery and generating "anti-tumor" shifts in long-chain to very-long-chain ceramide ratios, resistance of the tumor to C6 can still be a rate-limiting factor for some solid tumor types.

Acid Ceramidase Inhibitor LCL-805 Antagonizes Akt Signaling and Promotes Iron-Dependent Cell Death in Acute Myeloid Leukemia

Acute myeloid leukemia (AML) is an aggressive hematologic malignancy requiring urgent treatment advancements. Ceramide is a cell death-promoting signaling lipid that plays a central role in therapy-induced cell death. Acid ceramidase (AC), a ceramide-depleting enzyme, is overexpressed in AML and promotes leukemic survival and drug resistance. The ceramidase inhibitor B-13 and next-generation lysosomal-localizing derivatives termed dimethylglycine (DMG)-B-13 prodrugs have been developed but remain untested in AML. Here, we report the in vitro anti-leukemic efficacy and mechanism of DMG-B-13 prodrug, LCL-805, across AML cell lines and primary patient samples. LCL-805 inhibited AC enzymatic activity, increased total ceramides, and reduced sphingosine levels. A median EC50 value of 11.7 μM was achieved for LCL-805 in cell viability assays across 32 human AML cell lines. As a single agent tested across a panel of 71 primary AML patient samples, a median EC50 value of 15.8 μM was achieved. Exogenous ceramide supplementation with C6-ceramide nanoliposomes, which is entering phase I/II clinical trial for relapsed/refractory AML, significantly enhanced LCL-805 killing. Mechanistically, LCL-805 antagonized Akt signaling and led to iron-dependent cell death distinct from canonical ferroptosis. These findings elucidated key factors involved in LCL-805 cytotoxicity and demonstrated the potency of combining AC inhibition with exogenous ceramide.

Ceramides and their roles in programmed cell death

Programmed cell death plays a crucial role in maintaining the homeostasis and integrity of multicellular organisms, and its dysregulation contributes to the pathogenesis of many diseases. Programmed cell death is regulated by a range of macromolecules and low-molecular messengers, including ceramides. Endogenous ceramides have different functions, that are influenced by their localization and the presence of their target molecules. This article provides an overview of the current understanding of ceramides and their impact on various types of programmed cell death, including apoptosis, anoikis, macroautophagy and mitophagy, and necroptosis. Moreover, it highlights the emergence of dihydroceramides as a new class of bioactive sphingolipids and their downstream targets as well as their future roles in cancer cell growth, drug resistance and tumor metastasis.

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.

Engineered Lipidic Nanomaterials Inspired by Sphingomyelin Metabolism for Cancer Therapy

Sphingomyelin (SM) and its metabolites are crucial regulators of tumor cell growth, differentiation, senescence, and programmed cell death. With the rise in lipid-based nanomaterials, engineered lipidic nanomaterials inspired by SM metabolism, corresponding lipid targeting, and signaling activation have made fascinating advances in cancer therapeutic processes. In this review, we first described the specific pathways of SM metabolism and the roles of their associated bioactive molecules in mediating cell survival or death. We next summarized the advantages and specific applications of SM metabolism-based lipidic nanomaterials in specific cancer therapies. Finally, we discussed the challenges and perspectives of this emerging and promising SM metabolism-based nanomaterials research area.

Solid Tumor Treatment via Augmentation of Bioactive C6 Ceramide Levels with Thermally Ablative Focused Ultrasound

Sparse scan partial thermal ablation (TA) with focused ultrasound (FUS) may be deployed to treat solid tumors and increase delivery of systemically administered therapeutics. Further, C6-ceramide-loaded nanoliposomes (CNLs), which rely upon the enhanced permeation and retention (EPR) effect for delivery, have shown promise for treating solid tumors and are being tested in clinical trials. Here, our objective was to determine whether CNLs synergize with TA in the control of 4T1 breast tumors. CNL-monotherapy of 4T1 tumors yielded significant intratumoral bioactive C6 accumulation by the EPR effect, but tumor growth was not controlled. TA increased bioactive C6 accumulation by ∼12.5-fold over the EPR effect. In addition, TA+CNL caused shifts in long-chain to very-long-chain ceramide ratios (i.e., C16/24 and C18/C24) that could potentially contribute to tumor control. Nonetheless, these changes in intratumoral ceramide levels were still insufficient to confer tumor growth control beyond that achieved when combining with TA with control "ghost" nanoliposomes (GNL). While this lack of synergy could be due to increased "pro-tumor" sphingosine-1-phosphate (S1P) levels, this is unlikely because S1P levels exhibited only a moderate and statistically insignificant increase with TA+CNL. In vitro studies showed that 4T1 cells are highly resistant to C6, offering the most likely explanation for the inability of TA to synergize with CNL. Thus, while our results show that sparse scan TA is a powerful approach for markedly enhancing CNL delivery and generating "anti-tumor" shifts in long-chain to very-long-chain ceramide ratios, resistance of the tumor to C6 can still be a rate-limiting factor for some solid tumor types.

Inhibition of Ceramide Synthesis Attenuates Chronic Ethanol Induced Cardiotoxicity by Restoring Lysosomal Function and Reducing Necroptosis

AIMS

Chronic alcohol misuse could cause alcoholic cardiomyopathy (ACM), and the specific mechanisms remained largely unknown. In this study, we aimed to explore the effects of endogenous ceramides on chronic ethanol-induced myocardial injury or cell loss (e.g. necroptosis).

METHODS

We established chronic alcohol intoxication models in vivo (male C57BL/6 mice) and in vitro (H9c2 cardiomyoblasts). The ceramide profiles were analyzed in mice myocardium and cultured cardiomyocytes. Further research on the role of ceramides and underlying signaling pathways was carried out in H9c2 cells.

RESULTS AND CONCLUSIONS

The ceramide profiles analysis revealed increased long and very long-chain ceramides in alcoholic myocardium and ethanol-treated cardiomyocytes. Next, we proved that endogenous ceramide inhibition could reduce necroptosis and alleviate cardiomyocytes injury as suggested by decreased levels of p-RIPK1, p-RIPK3 and p-MLKL proteins and cardiac injury factors expression. Furthermore, we found that lysosomal dysfunction also contributed to alcohol-induced cardiac damage and inhibiting ceramide biosynthesis could repaired this to some extent. Cells studies with exogenous C6 ceramide confirmed the pleotropic roles of ceramide in myocardial damage by causing both necroptosis and lysosomal dysfunction. Finally, our data suggested that lysosomal dysfunction could sensitize cardiomyocytes to induction of necroptosis due to the restriction on degradation of RIPK1/RIPK3 proteins. In conclusion, chronic ethanol treatment boosted myocardial ceramide synthesis in animal hearts and cultured cardiomyocytes. Moreover, ceramides exerted crucial roles in the intrinsic signaling pathways of alcohol-induced cardiotoxicity. Targeting ceramide biosynthesis to simultaneously attenuate necroptosis and lysosomal dysfunction might be a novel strategy for preventing alcoholic cardiotoxicity.

Dietary nitrate improves jaw bone remodelling in zoledronate-treated mice

Bisphosphonate-related osteonecrosis of the jaw (BRONJ) is a serious complication that occurs in patients with osteoporosis or metastatic bone cancer treated with bisphosphonate. There is still no effective treatment and prevention strategy for BRONJ. Inorganic nitrate, which is abundant in green vegetables, has been reported to be protective in multiple diseases. To investigate the effects of dietary nitrate on BRONJ-like lesions in mice, we utilized a well-established mouse BRONJ model, in which tooth extraction was performed. Specifically, 4 mM sodium nitrate was administered in advance through drinking water to assess the short- and long-term effects on BRONJ. Zoledronate injection could induce severe healing inhibition of the tooth extraction socket, while addition of pretreating dietary nitrate could alleviate the inhibition by reducing monocyte necrosis and inflammatory cytokines production. Mechanistically, nitrate intake increased plasma nitric oxide levels, which attenuated necroptosis of monocytes by downregulating lipid and lipid-like molecule metabolism via a RIPK3 dependent pathway. Our findings revealed that dietary nitrate could inhibit monocyte necroptosis in BRONJ, regulate the bone immune microenvironment and promote bone remodelling after injury. This study contributes to the understanding of the immunopathogenesis of zoledronate and supports the feasibility of dietary nitrate for the clinical prevention of BRONJ.

Ceramide Nanoliposomes as Potential Therapeutic Reagents for Asthma

Ceramides are an emerging class of anti-inflammatory lipids, and nanoscale ceramide-delivery systems are potential therapeutic strategies for inflammatory diseases. This study investigated the therapeutic effects of ceramide nanoliposomes (CNL) on type 2 inflammation-based asthma, induced by repeated ovalbumin (OVA) challenges. Asthmatic mice intratracheally treated with ceramide-free liposomes (Ghost) displayed typical airway remodeling including mucosal accumulation and subepithelial fibrosis, whereas, in CNL-treated mice, the degree of airway remodeling was significantly decreased. Compared to the Ghost group, CNL treatment unexpectedly failed to significantly influence formation of type 2 cytokines, including IL-5 and IL-13, known to facilitate pathogenic production of airway mucus predominantly comprising MUC5AC mucin. Interestingly, CNL treatment suppressed OVA-evoked hyperplasia of MUC5AC-generating goblet cells in the airways. This suggests that CNL suppressed goblet cell hyperplasia and airway mucosal accumulation independently of type 2 cytokine formation. Mechanistically, CNL treatment suppressed cell growth and EGF-induced activation of Akt, but not ERK1/2, in a human lung epithelial cell culture system recapitulating airway goblet cell hyperplasia. Taken together, CNL is suggested to have therapeutic effects on airway remodeling in allergic asthma by targeting goblet cell hyperplasia. These findings raise the potential of ceramide-based therapies for airway diseases, such as asthma.

Omics approaches to better understand the molecular mechanism of necroptosis and their translational implications

Necroptosis is a type of programed cell death characterized by an inflammatory phenotype due to extensive membrane permeabilization and rupture. Initiation of necroptosis involves activation of tumor necrosis factor receptors by tumor necrosis factor alpha (TNFα) followed by coordinated activities of receptor-interacting protein kinases and mixed lineage kinase-like protein (MLKL). Subsequently, MLKL undergoes phosphorylation and translocates to the plasma membrane, leading to permeabilization. Such permeabilization results in the release of various cytokines and causes extensive inflammatory activity at the organismal level. This inflammatory activity is one of the major differences between apoptosis and necroptosis and links necroptosis to several human pathologies that exhibit inflammation, in addition to the ultimate cell death phenotype. Given the crosstalk between the activation of cell death pathway and inflammatory activity, approaches that provide insights on the regulation of transcripts, proteins and their processing at the global level have substantially improved our understanding of necroptosis and its involvement in different disease states. In this review, we highlight recent omic studies probing the transcriptome, proteome and lipidome which elucidate potential new mechanisms and signaling pathways during necroptosis and the necroptosis-associated inflammatory activity observed in various diseases. We specifically focus on studies investigating the transcriptome and intracellular and released proteome that contribute to inflammatory nature of necroptotic cells. We also highlight different lipids that have been implicated in necroptosis and lipidomic studies identifying lipid players in necroptosis. Finally, we review studies which suggest certain necroptosis-related genes as potential prognosis markers for different cancers and discuss their translational implications.

RIPK1 and RIPK3 are positive prognosticators for cervical cancer patients and C2 ceramide can inhibit tumor cell proliferation in vitro

Introduction

The enzymes Receptor-interacting serine/threonine-protein kinase 1 (RIPK1) und 3 (RIPK3) as well as the protein Mixed lineage kinase domain like pseudokinase (pMLKL) play a role in the signaling cascade of necroptosis. This is a form of programmed cell death which is caspase-independent. High-risk human papilloma virus infection can inhibit necroptosis. Thereby, a persistent infection and consequently the development of cervical cancer can be triggered. Aim of this study was the analysis of the expression of RIPK1, RIPK3 and pMLKL in cervical cancer tissue and the evaluation of its prognostic value on overall survival, progression-free survival and additional clinical parameters.

Methods

The expression of RIPK1, RIPK3, and pMLKL in cervical cancer tissue microarrays of n = 250 patients was analyzed immunohistochemically. Further, the effect of C2 ceramide on several cervical cancer cell lines (CaSki, HeLa, SiHa) was examined. C2 ceramide is a biologically active short-chain ceramide that induces necroptosis in human luteal granulosa cells.

Results

Significantly longer overall survival and progression-free survival rates could be detected in cervical cancer patients expressing nuclear RIPK1 or RIPK3 alone or simultaneously (RIPK1 and RIPK3). Cell viability and proliferation was reduced through C2 ceramide stimulation of cervical cancer cells. Simultaneous stimulation of C2 ceramide and the pan-caspase inhibitor Z-VAD-fmk, or the RIPK1-inhibitor necrostatin-1, partly reversed the negative effect of C2 ceramide on cell viability. This observation could imply that caspase-dependent and -independent forms of cell death, including necroptosis, can occur. AnnexinV-FITC apoptosis staining induced a significant increase in apoptotic cells in CaSki and SiHa cells. The stimulation of CaSki cells with C2 ceramide led to a significant percentual increase in necrotic/intermediate (dying) cells after stimulation with C2 ceramide. In addition, after stimulation with C2 ceramide, CaSki and HeLa cells live cell imaging showed morphological changes which are common for necroptosis.

Discussion

In conclusion, RIPK1 and RIPK3 are independent positive predictors for overall survival and progression-free survival in cervical cancer patients. C2 ceramide can reduce cell viability and proliferation in cervical cancer cells by inducing most likely both apoptosis and necroptosis.

A comprehensive pan-cancer analysis of necroptosis molecules in four gynecologic cancers

Background

In recent years, it has been proved that necroptosis plays an important role in the occurrence, development, invasion, metastasis and drug resistance of malignant tumors. Hence, further evaluation and targeting of necroptosis may be of clinical benefit for gynecologic cancers (GCs).

Methods

To compare consistency and difference, we explored the expression pattern and prognostic value of necroptosis-related genes (NRGs) in pan-GC analysis through Linear regression and Empirical Bayesian, Univariate Cox analysis, and public databases from TCGA and Genotype-Tissue Expression (GTEx), including CESC, OV, UCEC, and UCS. We explored the copy number variation (CNV), methylation level and enrichment pathways of NRGs in the four GCs. Based on LASSO Cox regression analysis or principal component analysis, we established the prognostic NRG-signature or necroptosis-score for the four GCs. In addition, we predicted and compared functional pathways, tumor mutational burden (TMB), somatic mutation features, immunity status, immunotherapy, chemotherapeutic drug sensitivity of the NRG-signature based on NRGs. We also examined the expression level of several NRGs in OV samples that we collected using Quantitative Real-time PCR.

Results

We confirmed the presence of NRGs in expression, prognosis, CNV, and methylation for four GCs, thus comparing the consistency and difference among the four GCs. The prognosis and independent prognostic value of the risk signatures based on NRGs were determined. Through the results of subclass mapping, we found that GC patients with lower risk score may be more sensitive to PDL1 response and more sensitive to immune checkpoint blockade therapy. Drug susceptibility analysis showed that, 51, 45, 64, and 29 drugs with differences between risk groups were yielded in CESC, OV, UCEC, and UCS respectively. For OV, the expression differences of several NRGs in the tissues we collected were similar to that in TCGA.

Conclusion

Our comprehensive analysis of NRGs and NRG-signature demonstrated their similarity and difference, as well as their potential roles in prognosis and could guide therapeutic strategies, thus improving the outcome of GC patients.

Necroptosis pathways in tumorigenesis

Necroptosis is a caspase-independent form of programmed cell death executed by the receptor interacting protein kinase 1 (RIPK1)-RIPK3-mixed lineage kinase domain-like protein (MLKL) signaling cascade, deregulation of which can cause various human diseases including cancer. Escape from programmed cell death is a hallmark of cancer, leading to uncontrolled growth and drug resistance. Therefore, it is crucial to further understand whether necroptosis plays a key role in therapeutic resistance. In this review, we summarize the recent findings of the link between necroptosis and cancer, and discuss that targeting necroptosis is a new strategy to overcome apoptosis resistance in tumor therapy.

Necroptosis: A Pathogenic Negotiator in Human Diseases

Over the past few decades, mechanisms of programmed cell death have attracted the scientific community because they are involved in diverse human diseases. Initially, apoptosis was considered as a crucial mechanistic pathway for programmed cell death; recently, an alternative regulated mode of cell death was identified, mimicking the features of both apoptosis and necrosis. Several lines of evidence have revealed that dysregulation of necroptosis leads to pathological diseases such as cancer, cardiovascular, lung, renal, hepatic, neurodegenerative, and inflammatory diseases. Regulated forms of necrosis are executed by death receptor ligands through the activation of receptor-interacting protein kinase (RIPK)-1/3 and mixed-lineage kinase domain-like (MLKL), resulting in the formation of a necrosome complex. Many papers based on genetic and pharmacological studies have shown that RIPKs and MLKL are the key regulatory effectors during the progression of multiple pathological diseases. This review focused on illuminating the mechanisms underlying necroptosis, the functions of necroptosis-associated proteins, and their influences on disease progression. We also discuss numerous natural and chemical compounds and novel targeted therapies that elicit beneficial roles of necroptotic cell death in malignant cells to bypass apoptosis and drug resistance and to provide suggestions for further research in this field.

Zearalenone Induces MLKL-Dependent Necroptosis in Goat Endometrial Stromal Cells via the Calcium Overload/ROS Pathway

Zearalenone (ZEA) is a fungal mycotoxin known to exert strong reproductive toxicity in animals. As a newly identified type of programmed cell death, necroptosis is regulated by receptor-interacting protein kinase 1 (RIPK1), receptor-interacting protein kinase 3 (RIPK3), and mixed-lineage kinase domain-like pseudokinase (MLKL). However, the role and mechanism of necroptosis in ZEA toxicity remain unclear. In this study, we confirmed the involvement of necroptosis in ZEA-induced cell death in goat endometrial stromal cells (gESCs). The release of lactate dehydrogenase (LDH) and the production of PI-positive cells markedly increased. At the same time, the expression of RIPK1 and RIPK3 mRNAs and P-RIPK3 and P-MLKL proteins were significantly upregulated in ZEA-treated gESCs. Importantly, the MLKL inhibitor necrosulfonamide (NSA) dramatically attenuated gESCs necroptosis and powerfully blocked ZEA-induced reactive oxygen species (ROS) generation and mitochondrial dysfunction. The reactive oxygen species (ROS) scavengers and N-acetylcysteine (NAC) inhibited ZEA-induced cell death. In addition, the inhibition of MLKL alleviated the intracellular Ca²⁺ overload caused by ZEA. The calcium chelator BAPTA-AM markedly suppressed ROS production and mitochondrial damage, thus inhibiting ZEA-induced necroptosis. Therefore, our results revealed the mechanism by which ZEA triggers gESCs necroptosis, which may provide a new therapeutic strategy for ZEA poisoning.

Ferroptosis, necroptosis, and pyroptosis in the occurrence and development of ovarian cancer

Ovarian cancer (OC) is one of the most common malignancies that causes death in women and is a heterogeneous disease with complex molecular and genetic changes. Because of the relatively high recurrence rate of OC, it is crucial to understand the associated mechanisms of drug resistance and to discover potential target for rational targeted therapy. Cell death is a genetically determined process. Active and orderly cell death is prevalent during the development of living organisms and plays a critical role in regulating life homeostasis. Ferroptosis, a novel type of cell death discovered in recent years, is distinct from apoptosis and necrosis and is mainly caused by the imbalance between the production and degradation of intracellular lipid reactive oxygen species triggered by increased iron content. Necroptosis is a regulated non-cysteine protease–dependent programmed cell necrosis, morphologically exhibiting the same features as necrosis and occurring via a unique mechanism of programmed cell death different from the apoptotic signaling pathway. Pyroptosis is a form of programmed cell death that is characterized by the formation of membrane pores and subsequent cell lysis as well as release of pro-inflammatory cell contents mediated by the abscisin family. Studies have shown that ferroptosis, necroptosis, and pyroptosis are involved in the development and progression of a variety of diseases, including tumors. In this review, we summarized the recent advances in ferroptosis, necroptosis, and pyroptosis in the occurrence, development, and therapeutic potential of OC.

Targeting necroptosis as an alternative strategy in tumor treatment: From drugs to nanoparticles

Over last decades, most antitumor therapeutic strategies have focused on apoptosis, however, apoptosis resistance and immunological silence usually led to treatment failure. In this sense, triggering other programmed cell death such as necroptosis may achieve a better therapeutic efficacy and has gained widespread attentions in tumor therapy. Studies in this field have identified several types of necroptosis modulators and highlighted the therapeutic potential of necroptotic cell death in cancer. Nanoparticles further provide possibilities to improve therapeutic outcomes as an efficient drug delivery system, facilitating tumor targeting and controlled cargo release. Furthermore, some nanoparticles themselves can trigger/promote programmed necrosis through hyperthermia, ultrasound and autophagy blockage. These investigations have entered necroptosis for consideration as a promising strategy for tumor therapy, though numerous challenges remain and clinical applications are still distant. In this review, we would briefly introduce molecular mechanism and characteristics of necroptosis, and then summarize recent progress of programmed necrosis and their inducers in tumor therapy. Furthermore, the antitumor strategies that take advantages of nanoparticles to induce necroptosis are also discussed.

Non-apoptotic cell death in ovarian cancer: Treatment, resistance and prognosis

Ovarian cancer is mostly diagnosed at an advanced stage due to the absence of effective screening methods and specific symptoms. Repeated chemotherapy resistance and recurrence before PARPi are used as maintenance therapies, lead to low survival rates and poor prognosis. Apoptotic cell death plays a crucial role in ovarian cancer, which is proved by current researches. With the ongoing development of targeted therapy, non-apoptotic cell death has shown substantial potential in tumor prevention and treatment, including autophagy, ferroptosis, necroptosis, immunogenic cell death, pyroptosis, alkaliptosis, and other modes of cell death. We systematically reviewed the research progress on the role of non-apoptotic cell death in the onset, development, and outcome of ovarian cancer. This review provides a more theoretical basis for exploring therapeutic targets, reversing drug resistance in refractory ovarian cancer, and establishing risk prediction models that help realize the clinical transformation of vital drugs.

Targeting Sphingolipid Metabolism as a Therapeutic Strategy in Cancer Treatment

Sphingolipids are bioactive molecules that have key roles in regulating tumor cell death and survival through, in part, the functional roles of ceramide accumulation and sphingosine-1-phosphate (S1P) production, respectively. Mechanistic studies using cell lines, mouse models, or human tumors have revealed crucial roles of sphingolipid metabolic signaling in regulating tumor progression in response to anticancer therapy. Specifically, studies to understand ceramide and S1P production pathways with their downstream targets have provided novel therapeutic strategies for cancer treatment. In this review, we present recent evidence of the critical roles of sphingolipids and their metabolic enzymes in regulating tumor progression via mechanisms involving cell death or survival. The roles of S1P in enabling tumor growth/metastasis and conferring cancer resistance to existing therapeutics are also highlighted. Additionally, using the publicly available transcriptomic database, we assess the prognostic values of key sphingolipid enzymes on the overall survival of patients with different malignancies and present studies that highlight their clinical implications for anticancer treatment.

Targeting Sphingolipids for Cancer Therapy

Sphingolipids are an extensive class of lipids with different functions in the cell, ranging from proliferation to cell death. Sphingolipids are modified in multiple cancers and are responsible for tumor proliferation, progression, and metastasis. Several inhibitors or activators of sphingolipid signaling, such as fenretinide, safingol, ABC294640, ceramide nanoliposomes (CNLs), SKI-II, α-galactosylceramide, fingolimod, and sonepcizumab, have been described. The objective of this review was to analyze the results from preclinical and clinical trials of these drugs for the treatment of cancer. Sphingolipid-targeting drugs have been tested alone or in combination with chemotherapy, exhibiting antitumor activity alone and in synergism with chemotherapy in vitro and in vivo. As a consequence of treatments, the most frequent mechanism of cell death is apoptosis, followed by autophagy. Aslthough all these drugs have produced good results in preclinical studies of multiple cancers, the outcomes of clinical trials have not been similar. The most effective drugs are fenretinide and α-galactosylceramide (α-GalCer). In contrast, minor adverse effects restricted to a few subjects and hepatic toxicity have been observed in clinical trials of ABC294640 and safingol, respectively. In the case of CNLs, SKI-II, fingolimod and sonepcizumab there are some limitations and absence of enough clinical studies to demonstrate a benefit. The effectiveness or lack of a major therapeutic effect of sphingolipid modulation by some drugs as a cancer therapy and other aspects related to their mechanism of action are discussed in this review.

Role of ceramide/sphingomyelin (SM) balance regulated through "SM cycle" in cancer

Sphingomyelin synthase (SMS), which comprises of two isozymes, SMS1 and SMS2, is the only enzyme that generates sphingomyelin (SM) by transferring phosphocholine of phosphatidylcholine to ceramide in mammals. Conversely, ceramide is generated from SM hydrolysis via sphingomyelinases (SMases), ceramide de novo synthesis, and the salvage pathway. The biosynthetic pathway for SM and ceramide content by SMS and SMase, respectively, is called "SM cycle." SM forms a SM-rich microdomain on the cell membrane to regulate signal transduction, such as proliferation/survival, migration, and inflammation. On the other hand, ceramide acts as a lipid mediator by forming a ceramide-rich platform on the membrane, and ceramide exhibits physiological actions such as cell death, cell cycle arrest, and autophagy induction. Therefore, the regulation of ceramide/SM balance by SMS and SMase is responsible for diverse cell functions not only in physiological cells but also in cancer cells. This review outlines the implications of ceramide/SM balance through "SM cycle" in cancer progression and prevention. In addition, the possible involvement of "SM cycle" is introduced in anti-cancer tumor immunity, which has become a hot topic to innovate a more effective and safer way to conquer cancer in recent years.

Sphingolipids as multifaceted mediators in ovarian cancer

Ovarian cancer is the most lethal gynaecological malignancy. It is commonly diagnosed at advanced stage when it has metastasised to the abdominal cavity and treatment becomes very challenging. While current standard therapy involving debulking surgery and platinum + taxane-based chemotherapy is associated with high response rates initially, the large majority of patients relapse and ultimately succumb to chemotherapy-resistant disease. In order to improve survival novel strategies for early detection and therapeutics against treatment-refractory disease are urgently needed. A promising new target against ovarian cancer is the sphingolipid pathway which is commonly hijacked in cancer to support cell proliferation and survival and has been shown to promote chemoresistance and metastasis in a wide range of malignant neoplasms. In particular, the sphingosine kinase 1-sphingosine 1-phosphate receptor 1 axis has been shown to be altered in ovarian cancer in multiple ways and therefore represents an attractive therapeutic target. Here we review the roles of sphingolipids in ovarian cancer progression, metastasis and chemoresistance, highlighting novel strategies to target this pathway that represent potential avenues to improve patient survival.

Ceramide synthase 2-C24:1 -ceramide axis limits the metastatic potential of ovarian cancer cells

Regulation of sphingolipid metabolism plays a role in cellular homeostasis, and dysregulation of these pathways is involved in cancer progression. Previously, our reports identified ceramide as an anti-metastatic lipid. In the present study, we investigated the biochemical alterations in ceramide-centered metabolism of sphingolipids that were associated with metastatic potential. We established metastasis-prone sublines of SKOV3 ovarian cancer cells using an in vivo selection method. These cells showed decreases in ceramide levels and ceramide synthase (CerS) 2 expression. Moreover, CerS2 downregulation in ovarian cancer cells promoted metastasis in vivo and potentiated cell motility and invasiveness. Moreover, CerS2 knock-in suppressed the formation of lamellipodia required for cell motility in this cell line. In order to define specific roles of ceramide species in cell motility controlled by CerS2, the effect of exogenous long- and very long-chain ceramide species on the formation of lamellipodia was evaluated. Treatment with distinct ceramides increased cellular ceramides and had inhibitory effects on the formation of lamellipodia. Interestingly, blocking the recycling pathway of ceramides by a CerS inhibitor was ineffective in the suppression of exogenous C24:1 -ceramide for the formation of lamellipodia. These results suggested that C24:1 -ceramide, a CerS2 metabolite, predominantly suppresses the formation of lamellipodia without the requirement for deacylation/reacylation. Moreover, knockdown of neutral ceramidase suppressed the formation of lamellipodia concomitant with upregulation of C24:1 -ceramide. Collectively, the CerS2-C24:1 -ceramide axis, which may be countered by neutral ceramidase, is suggested to limit cell motility and metastatic potential. These findings may provide insights that lead to further development of ceramide-based therapy and biomarkers for metastatic ovarian cancer.

Rafting Down the Metastatic Cascade: The Role of Lipid Rafts in Cancer Metastasis, Cell Death, and Clinical Outcomes

Lipid rafts are tightly packed, cholesterol- and sphingolipid-enriched microdomains within the plasma membrane that play important roles in many pathophysiologic processes. Rafts have been strongly implicated as master regulators of signal transduction in cancer, where raft compartmentalization can promote transmembrane receptor oligomerization, shield proteins from enzymatic degradation, and act as scaffolds to enhance intracellular signaling cascades. Cancer cells have been found to exploit these mechanisms to initiate oncogenic signaling and promote tumor progression. This review highlights the roles of lipid rafts within the metastatic cascade, specifically within tumor angiogenesis, cell adhesion, migration, epithelial-to-mesenchymal transition, and transendothelial migration. In addition, the interplay between lipid rafts and different modes of cancer cell death, including necrosis, apoptosis, and anoikis, will be described. The clinical role of lipid raft-specific proteins, caveolin and flotillin, in assessing patient prognosis and evaluating metastatic potential of various cancers will be presented. Collectively, elucidation of the complex roles of lipid rafts and raft components within the metastatic cascade may be instrumental for therapeutic discovery to curb prometastatic processes.

The Role of Necroptosis in ROS-Mediated Cancer Therapies and Its Promising Applications

Over the past decades, promising therapies targeting different signaling pathways have emerged. Among these pathways, apoptosis has been well investigated and targeted to design diverse chemotherapies. However, some patients are chemoresistant to these therapies due to compromised apoptotic cell death. Hence, exploring alternative treatments aimed at different mechanisms of cell death seems to be a potential strategy for bypassing impaired apoptotic cell death. Emerging evidence has shown that necroptosis, a caspase-independent form of cell death with features between apoptosis and necrosis, can overcome the predicament of drug resistance. Furthermore, previous studies have also indicated that there is a close correlation between necroptosis and reactive oxygen species (ROS); both necroptosis and ROS play significant roles both under human physiological conditions such as the regulation of inflammation and in cancer biology. Several small molecules used in experiments and clinical practice eliminate cancer cells via the modulation of ROS and necroptosis. The molecular mechanisms of these promising therapies are discussed in detail in this review.

Necroptosis in Immuno-Oncology and Cancer Immunotherapy

Immune-checkpoint blockers (ICBs) have revolutionized oncology and firmly established the subfield of immuno-oncology. Despite this renaissance, a subset of cancer patients remain unresponsive to ICBs due to widespread immuno-resistance. To "break" cancer cell-driven immuno-resistance, researchers have long floated the idea of therapeutically facilitating the immunogenicity of cancer cells by disrupting tumor-associated immuno-tolerance via conventional anticancer therapies. It is well appreciated that anticancer therapies causing immunogenic or inflammatory cell death are best positioned to productively activate anticancer immunity. A large proportion of studies have emphasized the importance of immunogenic apoptosis (i.e., immunogenic cell death or ICD); yet, it has also emerged that necroptosis, a programmed necrotic cell death pathway, can also be immunogenic. Emergence of a proficient immune profile for necroptosis has important implications for cancer because resistance to apoptosis is one of the major hallmarks of tumors. Putative immunogenic or inflammatory characteristics driven by necroptosis can be of great impact in immuno-oncology. However, as is typical for a highly complex and multi-factorial disease like cancer, a clear cause versus consensus relationship on the immunobiology of necroptosis in cancer cells has been tough to establish. In this review, we discuss the various aspects of necroptosis immunobiology with specific focus on immuno-oncology and cancer immunotherapy.

Ceramide/Sphingomyelin Rheostat Regulated by Sphingomyelin Synthases and Chronic Diseases in Murine Models

Ceramide and sphingomyelin (SM) are major components of the double membrane-bound sphingolipids. Ceramide is an essential bioactive lipid involved in numerous cell processes including apoptosis, necrosis, and autophagy-dependent cell death. Inversely, SM regulates opposite cellular processes such as proliferation and migration by changing receptor-mediated signal transduction in the lipid microdomain. SM is generated through a transfer of phosphocholine from phosphatidylcholine to ceramide by SM synthases (SMSs). Research during the past several decades has revealed that the ceramide/SM balance in cellular membranes regulated by SMSs is important to decide the cell fate, survival, and proliferation. In addition, recent experimental studies utilizing SMS knockout mice and murine disease models provide evidence that SMS-regulated ceramide/SM balance is involved in human diseases. Here, we review the basic structural and functional characteristics of SMSs and focus on their cellular functions through the regulation of ceramide/SM balance in membrane microdomains. In addition, we present the pathological or physiological implications of SMSs by analyzing their role in SMS-knockout mice and human disease models. This review finally presents evidence indicating that the regulation of ceramide/SM balance through SMS could be a therapeutic target for human disorders.

Inhibitors of Ceramide- and Sphingosine-Metabolizing Enzymes as Sensitizers in Radiotherapy and Chemotherapy for Head and Neck Squamous Cell Carcinoma

In the treatment of advanced head and neck squamous cell carcinoma (HNSCC), including oral SCC, radiotherapy is a commonly performed therapeutic modality. The combined use of radiotherapy with chemotherapy improves therapeutic effects, but it also increases adverse events. Ceramide, a central molecule in sphingolipid metabolism and signaling pathways, mediates antiproliferative responses, and its level increases in response to radiotherapy and chemotherapy. However, when ceramide is metabolized, prosurvival factors, such as sphingosine-1-phosphate (S1P), ceramide-1-phosphate (C1P), and glucosylceramide, are produced, reducing the antitumor effects of ceramide. The activities of ceramide- and sphingosine-metabolizing enzymes are also associated with radio- and chemo-resistance. Ceramide analogs and low molecular-weight compounds targeting these enzymes exert anticancer effects. Synthetic ceramides and a therapeutic approach using ultrasound have also been developed. Inhibitors of ceramide- and sphingosine-metabolizing enzymes and synthetic ceramides can function as sensitizers of radiotherapy and chemotherapy for HNSCC.

Regulation of Necroptosis by Phospholipids and Sphingolipids

Several non-apoptotic regulated cell death pathways have been recently reported. Necroptosis, a form of necrotic-regulated cell death, is characterized by the involvement of receptor-interacting protein kinases and/or the pore-forming mixed lineage kinase domain-like protein. Recent evidence suggests a key role for lipidic molecules in the regulation of necroptosis. The purpose of this mini-review is to outline the regulation of necroptosis by sphingolipids and phospholipids.

Rubusoside-assisted solubilization of poorly soluble C6-Ceramide for a pilot pharmacokinetic study

Although C₆-Ceramide has attracted much attention as a possible tumor suppressor, the delivery of C₆-Ceramide is still challenging due to its inherent hydrophobicity and insolubility. In this study we explored the use of a natural compound rubusoside (RUB) as a solubilizer to enhance the solubility of a fluorescence-labeled C₆-Ceramide (NBD C₆-Ceramide) and to characterize its pharmacokinetics and tissue distribution in an animal model. RUB significantly enhanced the solubility of NBD C₆-Ceramide by forming nanomicelles, and efficiently delivered NBD C₆-Ceramide in rats by oral and intravenous administration. RUB loaded 1.96 % of NBD C₆-Ceramide in the nanomicelles and solubilized it to a concentration of 3.6 mg/mL in water. NBD C₆-Ceramide in nanomicelles remained stable in aqueous solutions, allowing intravenous administration without the use of any organic solvents or surfactants. After oral administration, NBD C₆-Ceramide rapidly rose to peak plasma concentrations within the first 90 min, distributed to tissues, and remained in vivo for more than 24 h. Tissular levels of NBD C₆-Ceramide from high to low were associated with heart, lung, cerebellum, testicle, spleen, liver, kidney, and brain. Altogether, our study demonstrated that RUB-assisted nanomicelles can serve as an efficient and convenient delivery system for short-chain C₆-Ceramide and enable in vivo evaluation of potential new cancer treatments.

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.

Necroptosis in primate luteolysis: a role for ceramide

The corpus luteum (CL) is a transient endocrine organ, yet molecular mechanisms resulting in its demise are not well known. The presence of phosphorylated mixed lineage kinase domain-like pseudokinase pMLKL(T357/S358) in human and nonhuman primate CL samples (Macaca mulatta and Callithrix jacchus) implied that necroptosis of luteal cells may be involved. In M. mulatta CL, pMLKL positive staining became detectable only from the mid-late luteal phase onwards, pointing to necroptosis during regression of the CL. Cell death, including necroptosis, was previously observed in cultures of human luteal granulosa cells (GCs), an apt model for the study of the human CL. To explore mechanisms of necroptotic cell death in GCs during culture, we performed a proteomic analysis. The levels of 50 proteins were significantly altered after 5 days of culture. Interconnectivity analysis and immunocytochemistry implicated specifically the ceramide salvage pathway to be enhanced. M. mulatta CL transcriptome analysis indicated in vivo relevance. Perturbing endogenous ceramide generation by fumonisin B1 (FB1) and addition of soluble ceramide (C2-CER) yielded opposite actions on viability of GCs and therefore supported the significance of the ceramide pathway. Morphological changes indicated necrotic cell death in the C2-CER treated group. Studies with the pan caspase blocker zVAD-fmk or the necroptosis blocker necrosulfonamid (NSA) further supported that C2-CER induced necroptosis. Our data pinpoint necroptosis in a physiological process, namely CL regression. This raises the possibility that the primate CL could be rescued by pharmacological inhibition of necroptosis or by interaction with ceramide metabolism.

Upregulation of human glycolipid transfer protein (GLTP) induces necroptosis in colon carcinoma cells

Human GLTP on chromosome 12 (locus 12q24.11) encodes a 24 kD amphitropic lipid transfer protein (GLTP) that mediates glycosphingolipid (GSL) intermembrane trafficking and regulates GSL homeostatic levels within cells. Herein, we provide evidence that GLTP overexpression inhibits the growth of human colon carcinoma cells (HT-29; HCT-116), but spares normal colonic cells (CCD-18Co). Mechanistic studies reveal that GLTP overexpression arrested the cell cycle at the G1/S checkpoint via upregulation of cyclin-dependent kinase inhibitor-1B (Kip1/p27) and cyclin-dependent kinase inhibitor 1A (Cip1/p21) at the protein and mRNA levels, and downregulation of cyclin-dependent kinase-2 (CDK2), cyclin-dependent kinase-4 (CDK4), cyclin E and cyclin D1 protein levels. Assessment of the biological fate of HCT-116 cells overexpressing GLTP indicated no increase in cell death suggesting induction of quiescence. However, HT-29 cells overexpressing GLTP underwent cell death by necroptosis as revealed by phosphorylation of human mixed lineage kinase domain-like protein (pMLKL) via receptor-interacting protein kinase-3 (RIPK-3), elevated cytosolic calcium, and plasma membrane permeabilization by pMLKL oligomerization. Overexpression of W96A-GLTP, an ablated GSL binding site mutant, failed to arrest the cell cycle or induce necroptosis. Sphingolipid assessment (ceramide, monohexosylceramide, sphingomyelin, ceramide-1-phosphate, sphingosine, and sphingosine-1-phosphate) of HT-29 cells overexpressing GLTP revealed large decreases (>5-fold) in sphingosine-1-phosphate with minimal change in 16:0-ceramide, tipping the 'sphingolipid rheostat' (S1P/16:0-Cer ratio) towards cell death. Depletion of RIPK-3 or MLKL abrogated necroptosis induced by GLTP overexpression. Our findings establish GLTP upregulation as a previously unknown suppressor of human colon carcinoma HT-29 cells via interference with cell cycle progression and induction of necroptosis.

Emergence of membrane sphingolipids as a potential therapeutic target

BACKGROUND

Though sphingolipids are ubiquitously present in eukaryotic cells, but until the last decade, they were merely considered as a structural component of the plasma membrane with limited function. However, over the last decade, numerous functions have been ascribed to sphingolipids after the seminal discoveries on the bioactivities of several sphingolipids.

SCOPE OF REVIEW

Sphingolipids are now well-recognized signals for fundamental cellular processes. Here we discussed about the advent of several sphingolipids components as potential therapeutic target for both human and plants.

MAJOR CONCLUSIONS

Sphingolipid contents and/or sphingolipid-metabolizing enzyme expression/activity often get impaired during pathophysiological conditions, and hence manipulation of this signaling pathway may be beneficial in disease diagnosis, and the plasma concentrations can serve as an important prognostic and diagnostic marker for the disease.

GENERAL SIGNIFICANCE

Sphingolipids are emerging as a goldmine for new therapeutic drug targets with promising new applications (cosmeceutical and nutraceutical), thereby opening new avenues for pharmaceuticals and nutraceutical industries.

La-Related Protein 4 as a Suppressor for Motility of Ovarian Cancer Cells

The La-related proteins (LARPs) are a family of RNA binding proteins that control the degradation and stabilization of RNAs. As emerging research reveals the biology of each LARP, it is evident that LARPs are dysregulated in some types of cancer. Upregulation of cell motility potentiates the metastatic potential of ovarian cancer cells; however, the roles of LARPs in cell motility remain unknown. In the present study, we investigated the roles of LARPs in the progression of ovarian cancer using SKOV3 human ovarian cancer cells and a public database that integrates microarray-based gene expression data and clinical data. To explore the involvement of LARPs in the cell motility, we performed RNA interference screening for LARP mRNAs in SKOV3 cells. The screening identified LARP4 as a potential suppressor of the formation of lamellipodia. Conversely, enforced expression of LARP4 suppressed the formation of lamellipodia. Moreover, cell migration was significantly increased in LARP4-depleted SKOV3 cells. Mechanistically, LARP4 depletion was associated with the decrease in RhoA protein expression. These results suggest that LARP4 may limit RhoA-dependent cell motility. In a mouse xenograft model with SKOV3 cells, LARP4 depletion potentiated peritoneal metastasis. Upon analysis of a public database of patients with ovarian cancer, the LARP4 mRNA-high expression group (n = 166) showed longer overall survival compared with the LARP4 mRNA-low expression group (n = 489), implying a positive correlation of LARP4 mRNA levels in ovarian cancer tissues with patient prognosis. Taken together, we propose that LARP4 could suppress motility and metastatic potential of ovarian cancer cells.

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.

Turning the Spotlight on Lipids in Non-Apoptotic Cell Death

Although apoptosis has long dominated the spotlight, studies in the past two decades have expanded the repertoire of programmed cell death (PCD). Several forms of non-apoptotic regulated cell death have been identified, with important links to organismal homeostasis and different disease pathologies. Necroptosis, ferroptosis, pyroptosis, and NETosis are the major forms of PCD that have attracted attention. Clear biochemical distinctions differentiate these forms of non-apoptotic PCD at the protein and membrane levels. For instance, pore formation at the plasma membrane is a hallmark of necroptosis and pyroptosis; however, different proteins facilitate pore formation in these processes. Here, we will highlight the role of lipids in different forms of non-apoptotic PCD. In particular, we discuss how lipids can trigger or facilitate the membrane-related changes that result in cell death. We also highlight the use of small molecules in elucidating the mechanisms of non-apoptotic PCD and the potential of lipid biosynthetic pathways to perturb these processes for therapeutic applications as a future avenue of research.