Antitumor activity of sphingosine kinase 2 inhibitor ABC294640 and sorafenib in hepatocellular carcinoma xenografts

SKI-349, a Sphingosine Kinases 1/2 Inhibitor, Suppresses Cell Viability, Invasion, and AKT/mTOR Signaling Pathway, and Shows Synergistic Cytotoxic Effects with Sorafenib in Hepatocellular Carcinoma

SKI-349 is a novel sphingosine kinases (SPHK) inhibitor with anti-tumor effects. This study aimed to assess the effect of SKI-349 on cell biological behaviors, downstream pathways, and its synergistic effect with sorafenib in hepatocellular carcinoma (HCC). HCC cell lines (Huh7 and Hep3B) were treated with SKI-349 at concentrations of 1, 2, 4, or 8 μM. Then, SPHK1/2 activity, cell viability, proliferation, apoptosis, invasion, and protein expressions of phosphorylated-protein kinase B (p-AKT), AKT, phosphorylated-mammalian target of rapamycin (p-mTOR) and mTOR were detected. Combination index values of SKI-349 (0, 1, 2, 4, or 8 μM) and sorafenib (0, 2.5, 5, 10, or 20 μM) were calculated. SKI-349 decreased the relative SPHK1 and SPHK2 activity compared with blank control in a dose-dependent manner in the Huh7 and Hep3B cell lines. Meanwhile, SKI-349 reduced cell viability, 5-ethynyl-2'-deoxyuridine (EdU) positive cells, and invasive cells, while it increased apoptotic cells compared to blank control in a dose-dependent manner in Huh7 and Hep3B cell lines. Based on the western blot assay, SKI-349 decreased the ratio of p-AKT to AKT and that of p-mTOR to mTOR compared with blank control in a dose-dependent manner in the Huh7 and Hep3B cell lines. Additionally, SKI-349 combined with sorafenib declined cell viability with concentration gradient effects compared to SKI-349 sole treatment, and they had synergistic cytotoxic effects in Huh7 and Hep3B cell lines. SKI-349 suppresses SPHK1 and SPHK2 activity, cell viability, invasion, and AKT/mTOR signaling pathway, as well as exhibits a synergistic cytotoxic effect with sorafenib in HCC.

Opaganib (ABC294640) Induces Immunogenic Tumor Cell Death and Enhances Checkpoint Antibody Therapy

Antibody-based cancer drugs that target the checkpoint proteins CTLA-4, PD-1 and PD-L1 provide marked improvement in some patients with deadly diseases such as lung cancer and melanoma. However, most patients are either unresponsive or relapse following an initial response, underscoring the need for further improvement in immunotherapy. Certain drugs induce immunogenic cell death (ICD) in tumor cells in which the dying cells promote immunologic responses in the host that may enhance the in vivo activity of checkpoint antibodies. Sphingolipid metabolism is a key pathway in cancer biology, in which ceramides and sphingosine 1-phosphate (S1P) regulate tumor cell death, proliferation and drug resistance, as well as host inflammation and immunity. In particular, sphingosine kinases are key sites for manipulation of the ceramide/S1P balance that regulates tumor cell proliferation and sensitivity to radiation and chemotherapy. We and others have demonstrated that inhibition of sphingosine kinase-2 by the small-molecule investigational drug opaganib (formerly ABC294640) kills tumor cells and increases their sensitivities to other drugs and radiation. Because sphingolipids have been shown to regulate ICD, opaganib may induce ICD and improve the efficacy of checkpoint antibodies for cancer therapy. This was demonstrated by showing that in vitro treatment with opaganib increases the surface expression of the ICD marker calreticulin on a variety of tumor cell types. In vivo confirmation was achieved using the gold standard immunization assay in which B16 melanoma, Lewis lung carcinoma (LLC) or Neuro-2a neuroblastoma cells were treated with opaganib in vitro and then injected subcutaneously into syngeneic mice, followed by implantation of untreated tumor cells 7 days later. In all cases, immunization with opaganib-treated cells strongly suppressed the growth of subsequently injected tumor cells. Interestingly, opaganib treatment induced crossover immunity in that opaganib-treated B16 cells suppressed the growth of both untreated B16 and LLC cells and opaganib-treated LLC cells inhibited the growth of both untreated LLC and B16 cells. Next, the effects of opaganib in combination with a checkpoint antibody on tumor growth in vivo were assessed. Opaganib and anti-PD-1 antibody each slowed the growth of B16 tumors and improved mouse survival, while the combination of opaganib plus anti-PD-1 strongly suppressed tumor growth and improved survival (p < 0.0001). Individually, opaganib and anti-CTLA-4 antibody had modest effects on the growth of LLC tumors and mouse survival, whereas the combination of opaganib with anti-CTLA-4 substantially inhibited tumor growth and increased survival (p < 0.001). Finally, the survival of mice bearing B16 tumors was only marginally improved by opaganib or anti-PD-L1 antibody alone but was nearly doubled by the drugs in combination (p < 0.005). Overall, these studies demonstrate the ability of opaganib to induce ICD in tumor cells, which improves the antitumor activity of checkpoint antibodies.

Lipid metabolism of hepatocellular carcinoma impacts targeted therapy and immunotherapy

Hepatocellular carcinoma (HCC) is a common malignant tumor that affecting many people's lives globally. The common risk factors for HCC include being overweight and obese. The liver is the center of lipid metabolism, synthesizing most cholesterol and fatty acids. Abnormal lipid metabolism is a significant feature of metabolic reprogramming in HCC and affects the prognosis of HCC patients by regulating inflammatory responses and changing the immune microenvironment. Targeted therapy and immunotherapy are being explored as the primary treatment strategies for HCC patients with unresectable tumors. Here, we detail the specific changes of lipid metabolism in HCC and its impact on both these therapies for HCC. HCC treatment strategies aimed at targeting lipid metabolism and how to integrate them with targeted therapy or immunotherapy rationally are also presented.

A comprehensive review of the relationship between autophagy and sorafenib-resistance in hepatocellular carcinoma: ferroptosis is noteworthy

Patients with hepatocellular carcinoma (HCC) bear a heavy burden of disease and economic burden but have fewer treatment options. Sorafenib, a multi-kinase inhibitor, is the only approved drug that can be used to limit the progression of inoperable or distant metastatic HCC. However, enhanced autophagy and other molecular mechanisms after sorafenib exposure further induce drug resistance in HCC patients. Sorafenib-associated autophagy also generates a series of biomarkers, which may represent that autophagy is a critical section of sorafenib-resistance in HCC. Furthermore, many classic signaling pathways have been found to be involved in sorafenib-associated autophagy, including the HIF/mTOR signaling pathway, endoplasmic reticulum stress, and sphingolipid signaling, among others. In turn, autophagy also provokes autophagic activity in components of the tumor microenvironment, including tumor cells and stem cells, further impacting sorafenib-resistance in HCC through a special autophagic cell death process called ferroptosis. In this review, we summarized the latest research progress and molecular mechanisms of sorafenib-resistance-associated autophagy in detail, providing new insights and ideas for unraveling the dilemma of sorafenib-resistance in HCC.

Mebendazole Impedes the Proliferation and Migration of Pancreatic Cancer Cells through SK1 Inhibition Dependent Pathway

Pancreatic ductal adenocarcinoma (PDAC) has one of the highest mortality rates and requires the development of highly efficacious medications that can improve the efficiency of existing treatment methods. In particular, in PDAC, resistance to conventional chemotherapy reduces the effectiveness of anticancer drugs, decreasing the therapeutic efficiency. Sphingosine 1-phosphate (S1P), produced by sphingosine kinase (SK), plays a vital role in cancer growth, metastasis, chemotherapy, and drug resistance. Focusing on the structural characteristics of mebendazole (MBZ), we studied whether MBZ would affect metastasis, invasion, and drug resistance in cancer by lowering S1P production through inhibition of SK activity. MBZ selectively inhibited SK1 more than SK2 and regulated the levels of sphingolipids. MBZ inhibited the proliferation and migration of cancer cells in other PDAC cell lines. To determine whether the effect of MBZ on cancer cell growth and migration is S1P-mediated, S1P was treated, and the growth and migration of cancer cells were observed. It was found that MBZ inhibited S1P-induced cancer cell growth, and MBZ showed a growth inhibitory effect by regulating the JAK2/STAT3/Bcl-2 pathway. The phosphorylation of focal adhesion kinase (FAK), a transcription factor that regulates migration, was inhibited by MBZ, so it was found that the effect of MBZ regulates the migration of cancer cells through the S1P/FAK/vimentin pathway. In conclusion, our study suggests that the anthelmintic MBZ can be used as a potential therapeutic agent for treating PDAC and for structural synthesis studies of its analogs.

Ablation of sphingosine kinase 2 suppresses fatty liver-associated hepatocellular carcinoma via downregulation of ceramide transfer protein

Hepatocellular carcinoma (HCC) accounts for 90% of primary liver cancer, the third leading cause of cancer-associated death worldwide. With the increasing prevalence of metabolic conditions, non-alcoholic fatty liver disease (NAFLD) is emerging as the fastest-growing HCC risk factor, and it imposes an additional layer of difficulty in HCC management. Dysregulated hepatic lipids are generally believed to constitute a deleterious environment cultivating the development of NAFLD-associated HCC. However, exactly which lipids or lipid regulators drive this process remains elusive. We report herein that sphingosine kinase 2 (SphK2), a key sphingolipid metabolic enzyme, plays a critical role in NAFLD-associated HCC. Ablation of Sphk2 suppressed HCC development in NAFLD livers via inhibition of hepatocyte proliferation both in vivo and in vitro. Mechanistically, SphK2 deficiency led to downregulation of ceramide transfer protein (CERT) that, in turn, decreased the ratio of pro-cancer sphingomyelin (SM) to anti-cancer ceramide. Overexpression of CERT restored hepatocyte proliferation, colony growth and cell cycle progression. In conclusion, the current study demonstrates that SphK2 is an essential lipid regulator in NAFLD-associated HCC, providing experimental evidence to support clinical trials of SphK2 inhibitors as systemic therapies against HCC.

The Sphingosine Kinase 2 Inhibitor Opaganib Protects Against Acute Kidney Injury in Mice

Introduction

Acute kidney injury (AKI) is a common multifactorial adverse effect of surgery, circulatory obstruction, sepsis or drug/toxin exposure that often results in morbidity and mortality. Sphingolipid metabolism is a critical regulator of cell survival and pathologic inflammation processes involved in AKI. Opaganib (also known as ABC294640) is a first-in-class experimental drug targeting sphingolipid metabolism that reduces the production and activity of inflammatory cytokines and, therefore, may be effective to prevent and treat AKI.

Methods

Murine models of AKI were used to assess the in vivo efficacy of opaganib including ischemia-reperfusion (IR) injury induced by either transient bilateral occlusion of renal blood flow (a moderate model) or nephrectomy followed immediately by occlusion of the contralateral kidney (a severe model) and lipopolysaccharide (LPS)-induced sepsis. Biochemical and histologic assays were used to quantify the effects of oral opaganib treatment on renal damage in these models.

Results

Opaganib suppressed the elevations of creatinine and blood urea nitrogen (BUN), as well as granulocyte infiltration into the kidneys, of mice that experienced moderate IR from transient bilateral ligation. Opaganib also markedly decreased these parameters and completely prevented mortality in the severe renal IR model. Additionally, opaganib blunted the elevations of BUN, creatinine and inflammatory cytokines following exposure to LPS.

Conclusion

The data support the hypotheses that sphingolipid metabolism is a key mediator of renal inflammatory damage following IR injury and sepsis, and that this can be suppressed by opaganib. Because opaganib has already undergone clinical testing in other diseases (cancer and Covid-19), the present studies support conducting clinical trials with this drug with surgical or septic patients at risk for AKI.

Opaganib Protects against Radiation Toxicity: Implications for Homeland Security and Antitumor Radiotherapy

Exposure to ionizing radiation (IR) is a lingering threat from accidental or terroristic nuclear events, but is also widely used in cancer therapy. In both cases, host inflammatory responses to IR damage normal tissue causing morbidity and possibly mortality to the victim/patient. Opaganib, a first-in-class inhibitor of sphingolipid metabolism, has broad anti-inflammatory and anticancer activity. Opaganib elevates ceramide and reduces sphingosine 1-phosphate (S1P) in cells, conditions that increase the antitumor efficacy of radiation while concomitantly suppressing inflammatory damage to normal tissue. Therefore, opaganib may suppress toxicity from unintended IR exposure and improve patient response to chemoradiation. To test these hypotheses, we first examined the effects of opaganib on the toxicity and antitumor activity of radiation in mice exposed to total body irradiation (TBI) or IR with partial bone marrow shielding. Oral treatment with opaganib 2 h before TBI shifted the LD75 from 9.5 Gy to 11.5 Gy, and provided substantial protection against gastrointestinal damage associated with suppression of radiation-induced elevations of S1P and TNFα in the small intestines. In the partially shielded model, opaganib provided dose-dependent survival advantages when administered 4 h before or 24 h after radiation exposure, and was particularly effective when given both prior to and following radiation. Relevant to cancer radiotherapy, opaganib decreased the sensitivity of IEC6 (non-transformed mouse intestinal epithelial) cells to radiation, while sensitizing PAN02 cells to in vitro radiation. Next, the in vivo effects of opaganib in combination with radiation were examined in a syngeneic tumor model consisting of C57BL/6 mice bearing xenografts of PAN02 pancreatic cancer cells and a cross-species xenograft model consisting of nude mice bearing xenografts of human FaDu cells. Mice were treated with opaganib and/or IR (plus cisplatin in the case of FaDu tumors). In both tumor models, the optimal suppression of tumor growth was attained by the combination of opaganib with IR (± cisplatin). Overall, opaganib substantially protects normal tissue from radiation damage that may occur through unintended exposure or cancer radiotherapy.

Recent Progress in the Development of Opaganib for the Treatment of Covid-19

The Covid-19 pandemic driven by the SARS-CoV-2 virus continues to exert extensive humanitarian and economic stress across the world. Although antivirals active against mild disease have been identified recently, new drugs to treat moderate and severe Covid-19 patients are needed. Sphingolipids regulate key pathologic processes, including viral proliferation and pathologic host inflammation. Opaganib (aka ABC294640) is a first-in-class clinical drug targeting sphingolipid metabolism for the treatment of cancer and inflammatory diseases. Recent work demonstrates that opaganib also has antiviral activity against several viruses including SARS-CoV-2. A recently completed multinational Phase 2/3 clinical trial of opaganib in patients hospitalized with Covid-19 demonstrated that opaganib can be safely administered to these patients, and more importantly, resulted in a 62% decrease in mortality in a large subpopulation of patients with moderately severe Covid-19. Furthermore, acceleration of the clearance of the virus was observed in opaganib-treated patients. Understanding the biochemical mechanism for the anti-SARS-CoV-2 activity of opaganib is essential for optimizing Covid-19 treatment protocols. Opaganib inhibits three key enzymes in sphingolipid metabolism: sphingosine kinase-2 (SK2); dihydroceramide desaturase (DES1); and glucosylceramide synthase (GCS). Herein, we describe a tripartite model by which opaganib suppresses infection and replication of SARS-CoV-2 by inhibiting SK2, DES1 and GCS. The potential impact of modulation of sphingolipid signaling on multi-organ dysfunction in Covid-19 patients is also discussed.

Lipid alterations in chronic liver disease and liver cancer

Lipids are a complex and diverse group of molecules with crucial roles in many physiological processes, as well as in the onset, progression, and maintenance of cancers. Fatty acids and cholesterol are the building blocks of lipids, orchestrating these crucial metabolic processes. In the liver, lipid alterations are prevalent as a cause and consequence of chronic hepatitis B and C virus infections, alcoholic hepatitis, and non-alcoholic fatty liver disease and steatohepatitis. Recent developments in lipidomics have also revealed that dynamic changes in triacylglycerols, phospholipids, sphingolipids, ceramides, fatty acids, and cholesterol are involved in the development and progression of primary liver cancer. Accordingly, the transcriptional landscape of lipid metabolism suggests a carcinogenic role of increasing fatty acids and sterol synthesis. However, limited mechanistic insights into the complex nature of the hepatic lipidome have so far hindered the development of effective therapies.

Therapeutic Strategies Targeting Urokinase and Its Receptor in Cancer

Several studies have ascertained that uPA and uPAR do participate in tumor progression and metastasis and are involved in cell adhesion, migration, invasion and survival, as well as angiogenesis. Increased levels of uPA and uPAR in tumor tissues, stroma and biological fluids correlate with adverse clinic-pathologic features and poor patient outcomes. After binding to uPAR, uPA activates plasminogen to plasmin, a broad-spectrum matrix- and fibrin-degrading enzyme able to facilitate tumor cell invasion and dissemination to distant sites. Moreover, uPAR activated by uPA regulates most cancer cell activities by interacting with a broad range of cell membrane receptors. These findings make uPA and uPAR not only promising diagnostic and prognostic markers but also attractive targets for developing anticancer therapies. In this review, we debate the uPA/uPAR structure-function relationship as well as give an update on the molecules that interfere with or inhibit uPA/uPAR functions. Additionally, the possible clinical development of these compounds is discussed.

Gene expression profiles of liver cancer cell lines reveal two hepatocyte-like and fibroblast-like clusters

Cancer cell lines are widely used in basic research to study cancer development, growth, invasion, or metastasis. They are also used for the development and screening of anticancer drugs. However, there are no clear criteria for choosing the most suitable cell lines among the wide variety of cancer cell lines commercially available for research, and the choice is often based on previously published reports. Here, we investigated the characteristics of liver cancer cell lines by analyzing the gene expression data available in the Cancer Cell Line Encyclopedia. Unsupervised clustering analysis of 28 liver cancer cell lines yielded two main clusters. One cluster showed a gene expression pattern similar to that of hepatocytes, and the other showed a pattern similar to that of fibroblasts. Analysis of hepatocellular carcinoma gene expression profiles available in The Cancer Genome Atlas showed that the gene expression patterns in most hepatoma tissues were similar to those in the hepatocyte-like cluster. With respect to liver cancer research, our findings may be useful for selecting an appropriate cell line for a specific study objective. Furthermore, our approach of utilizing a public database for comparing the properties of cell lines could be an attractive cell line selection strategy that can be applied to other fields of research.

Rational design of SphK inhibitors using crystal structures aided by computer

Sphingosine kinases (SphKs) are lipid kinases that catalyze the phosphorylation of sphingosine (Sph) to sphingosine-1-phosphate (S1P). As a bioactive lipid, S1P plays a role outside and inside the cell to regulate biological processes. The overexpression of SphKs is related to a variety of pathophysiological conditions. Targeting the S1P signaling pathway is a potential treatment strategy for many diseases. SphKs are key kinases of the S1P signaling pathway. The SphK family includes two isoforms: SphK1 and SphK2. Determination of the co-crystal structure of SphK1 with various inhibitors has laid a solid foundation for the development of small molecule inhibitors targeting SphKs. This paper reviews the differences and connections between the two isoforms and the structure of SphK1 crystals, especially the structure of its Sph "J-shaped" channel binding site. This review also summarizes the recent development of SphK1 and SphK2 selective inhibitors and the exploration of the unresolved SphK2 structure.

Targeting SphK2 Reverses Acquired Resistance of Regorafenib in Hepatocellular Carcinoma

Background: Regorafenib is a second-line therapy drug used for advanced hepatocellular carcinoma (HCC). Unfortunately, the survival benefit of the patients receiving this treatment is modest, which may be attributed to drug resistance. In the present study, sphingosine kinase 2 (SphK2) was targeted to reverse regorafenib resistance in HCC.

Methods: The functions of SphK2 and sphingosine-1-phosphate (S1P), the catalytic product of SphK2 in regorafenib resistance of HCC cells, were evaluated by cell counting kit-8 assay, colony formation, cell cycle evaluation, and annexin V–fluorescein isothiocyanate/propidium iodide double-staining assay. The antitumor activity of combined treatment of regorafenib and the SphK2-specific inhibitor ABC294640 was examined in HCC cells in vitro and xenograft model in vivo. The molecular mechanisms of SphK2/S1P-mediating regorafenib resistance were investigated using cell line establishment and Western blot analysis.

Results: Well-developed regorafenib-resistant HCC cells indicated high expression levels of SphK2. The sensitivity to regorafenib of regorafenib-resistant HCC cells was restored following SphK2 knockdown or pharmacological inhibition by ABC294640. In addition, ectopic expression of SphK2 and exogenous addition of S1P decreased the sensitivity of HCC cells to regorafenib. Furthermore, the combination treatment with ABC294640 sensitized resistant tumor to regorafenib in xenograft model of HCC. The phosphorylation levels of nuclear factor κB (NF-κB), as well as those of signal transducer and activator of transcription 3 (STAT3), were positively associated with SphK2 and S1P.

Conclusions: SphK2/S1P mediates regorafenib resistance of HCC through NF-κB and STAT3 activation. Targeting SphK2 by ABC294640 potently reduces regorafenib resistance of HCC cells both in vitro and in vivo. The combination of ABC294640 and regorafenib could be developed as a novel potential treatment strategy for advanced HCC.

Antiproliferative and Apoptotic Effects of Cardamonin against Hepatocellular Carcinoma HepG2 Cells

Liver cancer is the sixth most common cancer in terms of incidence and the fourth in terms of mortality. Hepatocellular carcinoma (HCC) represents almost 90% of primary liver cancer and has become a major health problem globally. Cardamonin (CADMN) is a natural bioactive chalcone found in several edible plants such as cardamom and Alpinia species. Previous studies have shown that CADMN possesses anticancer activities against breast, lung, prostate and colorectal cancer. In the present study, the mechanisms underlying the anti-hepatocellular carcinoma effects of CADMN were investigated against HepG2 cells. The results demonstrated that CADMN has anti-proliferative effects and apoptotic action on HepG2 cells. CADMN showed potent cytotoxicity against HepG2 cells with an IC₅₀ of 17.1 ± 0.592 μM at 72 h. Flow cytometry analysis demonstrated that CADMN arrests HepG2 cells in G1 phase and induces a significant increase in early and late apoptosis in a time-dependent manner. The mechanism by which CADMN induces apoptotic action was via activation of both extrinsic and intrinsic pathways. Moreover, the findings of this study showed the involvement of reactive oxygen species (ROS), which inhibit the NF-κB pathway and further enhance the apoptotic process. Together, our findings further support the potential anticancer activity of CADMN as an alternative therapeutic agent against HCC.

Antineoplastic Agents Targeting Sphingolipid Pathways

Emerging studies in the enigmatic area of bioactive lipids have made many exciting new discoveries in recent years. Once thought to play a strictly structural role in cellular function, it has since been determined that sphingolipids and their metabolites perform a vast variety of cellular functions beyond what was previously believed. Of utmost importance is their role in cellular signaling, for it is now well understood that select sphingolipids serve as bioactive molecules that play critical roles in both cancer cell death and survival, as well as other cellular responses such as chronic inflammation, protection from intestinal pathogens, and intrinsic protection from intestinal contents, each of which are associated with oncogenesis. Importantly, it has been demonstrated time and time again that many different tumors display dysregulation of sphingolipid metabolism, and the exact profile of said dysregulation has been proven to be useful in determining not only the presence of a tumor, but also the susceptibility to various chemotherapeutic drugs, as well as the metastasizing characteristics of the malignancies. Since these discoveries surfaced it has become apparent that the understanding of sphingolipid metabolism and profile will likely become of great importance in the clinic for both chemotherapy and diagnostics of cancer. The goal of this paper is to provide a comprehensive review of the current state of chemotherapeutic agents that target sphingolipid metabolism that are undergoing clinical trials. Additionally, we will formulate questions involving the use of sphingolipid metabolism as chemotherapeutic targets in need of further research.

Sorafenib Treatment and Modulation of the Sphingolipid Pathway Affect Proliferation and Viability of Hepatocellular Carcinoma In Vitro

Hepatocellular carcinoma (HCC) shows a remarkable heterogeneity and is recognized as a chemoresistant tumor with dismal prognosis. In previous studies, we observed significant alterations in the serum sphingolipids of patients with HCC. This study aimed to investigate the in vitro effects of sorafenib, which is the most widely used systemic HCC medication, on the sphingolipid pathway as well as the effects of inhibiting the sphingolipid pathway in HCC. Huh7.5 and HepG2 cells were stimulated with sorafenib, and inhibitors of the sphingolipid pathway and cell proliferation, viability, and concentrations of bioactive metabolites were assessed. We observed a significant downregulation of cell proliferation and viability and a simultaneous upregulation of dihydroceramides upon sorafenib stimulation. Interestingly, fumonisin B1 (FB1) and the general sphingosine kinase inhibitor SKI II were able to inhibit cell proliferation more prominently in HepG2 and Huh7.5 cells, whereas there were no consistent effects on the formation of dihydroceramides, thus implying an involvement of distinct metabolic pathways. In conclusion, our study demonstrates a significant downregulation of HCC proliferation upon sorafenib, FB1, and SKI II treatment, whereas it seems they exert antiproliferative effects independently from sphingolipids. Certainly, further data would be required to elucidate the potential of FB1 and SKI II as putative novel therapeutic targets in HCC.

The role of the sphingolipid pathway in liver fibrosis: an emerging new potential target for novel therapies

Sphingolipids (SL) are a family of bioactive lipids and a major cellular membrane structural component. SLs include three main compounds: ceramide (Cer), sphingosine (Sp), and sphingosine-1-phosphate (S-1P), all of which have emerging roles in biological functions in cells, especially in the liver. They are under investigation in various liver diseases, including cirrhosis and end-stage liver disease. In this review, we provide an overview on the role of SLs in liver pathobiology and focus on their potential role in the development of hepatic fibrosis. We describe recent evidence and suggest SLs are a promising potential therapeutic target for the treatment of liver disease and fibrosis.

Sphingosine kinase and sphingosine-1-phosphate receptor signaling pathway in inflammatory gastrointestinal disease and cancers: A novel therapeutic target

Inflammatory gastrointestinal (GI) diseases and malignancies are associated with growing morbidity and cancer-related mortality worldwide. GI tumor and inflammatory cells contain activated sphingolipid-metabolizing enzymes, including sphingosine kinase 1 (SphK1) and SphK2, that generate sphingosine-1-phosphate (S1P), a highly bioactive compound. Many inflammatory responses, including lymphocyte trafficking, are directed by circulatory S1P, present in high concentrations in both the plasma and the lymph of cancer patients. High fat and sugar diet, disbalanced intestinal flora, and obesity have recently been linked to activation of inflammation and SphK/S1P/S1P receptor (S1PR) signaling in various GI pathologies, including cancer. SphK1 overexpression and activation facilitate and enhance the development and progression of esophageal, gastric, and colon cancers. SphK/S1P axis, a mediator of inflammation in the tumor microenvironment, has recently been defined as a target for the treatment of GI disease states, including inflammatory bowel disease and colitis. Several SphK1 inhibitors and S1PR antagonists have been developed as novel anti-inflammatory and anticancer agents. In this review, we analyze the mechanisms of SphK/S1P signaling in GI tissues and critically appraise recent studies on the role of SphK/S1P/S1PR in inflammatory GI disorders and cancers. The potential role of SphK/S1PR inhibitors in the prevention and treatment of inflammation-mediated GI diseases, including GI cancer, is also evaluated.

Design of Sphingosine Kinases Inhibitors: Challenges and Recent Developments

BACKGROUND

Sphingosine kinases (SphKs) catalyze the phosphorylation of sphingosine to form the bioactive sphingolipid metabolite sphingosine-1-phosphate (S1P). S1P is an important lipid mediator with a wide range of biological functions; it is also involved in a variety of diseases such as inflammatory diseases, Alzheimer's disease and cancer.

METHODS

This review reports the recent advancement in the research of SphKs inhibitors. Our purpose is also to provide a complete overview useful for underlining the features needed to select a specific pharmacological profile.

DISCUSSION

Two distinct mammalian SphK isoforms have been identified, SphK1 and SphK2. These isoforms are encoded by different genes and exhibit distinct subcellular localizations, biochemical properties and functions. SphK1 and SphK2 inhibition can be useful in different pathological conditions.

CONCLUSION

SphK1 and SphK2 have many common features but different and even opposite biological functions. For this reason, several research groups are interested in understanding the therapeutic usefulness of a selective or non-selective inhibitor of SphKs. Moreover, a compensatory mechanism for the two isoforms has been demonstrated, thus leading to the development of dual inhibitors.

Sphingosine Kinases as Druggable Targets

There is substantial evidence that the enzymes, sphingosine kinase 1 and 2, which catalyse the formation of the bioactive lipid sphingosine 1-phosphate, are involved in pathophysiological processes. In this chapter, we appraise the evidence that both enzymes are druggable and describe how isoform-specific inhibitors can be developed based on the plasticity of the sphingosine-binding site. This is contextualised with the effect of sphingosine kinase inhibitors in cancer, pulmonary hypertension, neurodegeneration, inflammation and sickling.

S1PR1 promotes proliferation and inhibits apoptosis of esophageal squamous cell carcinoma through activating STAT3 pathway

Background

Esophageal squamous cell carcinoma (ESCC) is one of the most common cancers worldwide, which lacks effective biomarkers for prognosis. Therefore, it is urgent to explore new potential molecular markers to discriminate patients with poorer survival in ESCC.

Methods

Bioinformatics analysis, qRT-PCR, and western blot were applied to investigate S1PR1 expression. CCK-8 assay, colony formation assay, flow cytometry dual staining assay, and immunofluorescence were performed to examine cell proliferation ability and apoptosis rate. Mouse xenograft model of TE-13 cells was established to confirm the roles of S1PR1 in vivo. Gene set enrichment analysis (GSEA) was used to investigate the downstream signaling pathways related to S1PR1 functions. Co-IP was performed to verify the direct binding of S1PR1 and STAT3. Western blot was applied to determine the phosphorylation level of STAT3. Immunohistochemistry was conducted to identify protein expression of S1PR1 and p- STAT3 in tumor tissues.

Results

In the present study, we found that S1PR1 expression was higher in ESCC patients and was a potential biomarker for poor prognosis. Silencing S1PR1 expression inhibited proliferation, and increased apoptosis of ESCC cells, while overexpression of S1PR1 had opposite effects. Mechanistically, S1PR1 played the roles of promoting proliferation and attenuating apoptosis through directly activating p-STAT3. Furthermore, in vivo experiments verified this mechanism.

Conclusion

Our findings indicated that S1PR1 enhanced proliferation and inhibited apoptosis of ESCC cells by activating STAT3 signaling pathway. S1PR1 may serve as a prognostic biomarker for clinical applications.

Electronic supplementary material

The online version of this article (10.1186/s13046-019-1369-7) contains supplementary material, which is available to authorized users.

Transcriptome-Wide Effects of Sphingosine Kinases Knockdown in Metastatic Prostate and Breast Cancer Cells: Implications for Therapeutic Targeting

Sphingosine kinases 1 and 2 (SK1 and SK2) are proto-oncogenic isozymes expressed in many human tumors and associated with chemoresistance and poor prognosis. They are well-recognized therapy targets and their inhibition was shown to induce tumor volume reduction and chemosensitization in multiple cancer models. Oncogenic signaling is extremely complex and often cross-regulated. Designing molecular therapies and their combinations requires rational approaches to avoid redundant targeting or developing resistance. In this study, we have performed RNA transcriptome microarray analysis of two breast and two prostate metastatic cancer cell lines treated with siRNAs targeting SK1 or SK2. In prostate cancer cell lines SK1 knockdown (KD) has significantly changed expression of several genes including downregulation of NSUN2, G3BP2 and upregulation of ETS1. SK2 KD also affected expression of multiple genes including downregulation of CAPZA1 NSUN3 and ADPGK and upregulation of VDAC1, IBTK, ETS1, and MKNK2. Similarly, in breast cancer cells SK1 KD led to downregulation of NSUN2, NFATC3, CDK2, and G3BP2 and upregulation of GTF2B, TTC17, and RAB23. SK2 KD in breast cancer cells has decreased expression of ITGAV and CAPZA1 and increased expression of GTF2B and ST13. Gene-set enrichment analysis of known biochemical pathways showed that in prostate and breast cell lines SKs KD have altered multiple pathways. SK1 KD altered chromatin assembly, regulation of G1/S transition and mitosis, Wnt and MAP kinase signaling and cell motility. SK2 KD altered RAS protein signal transduction, regulation of MAP kinase and serine/threonine kinase activity, cell motility, small GTPase mediated signal transduction and phosphatidylinositol 3-kinase (PI3K) signaling. Through genome-wide microarray analysis, we have identified important molecular pathways affected by SK1 and SK2 KD. It appears that while KD of both genes leads to a decrease in individual pro-tumorigenic genes, there is a universal cellular response resulting in upregulation of several known pro-survival and pro-tumorigenic pathways such as MAPK, RAS, and PI3K, which may mediate cancer resistance to anti-SKs therapies. Our data point out to the potential advantage of certain molecular therapy combinations in targeting prostate and breast cancer. Further signaling studies are required to confirm the individual involvement of identified pathways.

Role of Sphingosine Kinase 1 and Sphingosine-1-Phosphate Axis in Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is primarily diagnosed in the latter stages of disease progression and is the third leading cause of cancer deaths worldwide. Thus, there is a need to find biomarkers of early HCC as well as the development of more effective treatments for the disease. Sphingosine-1-phosphate (S1P) is a pleiotropic lipid signaling molecule produced by two isoforms of sphingosine kinase (SphK1 and SphK2) that is involved in regulation of many aspects of mammalian physiology and pathophysiology, including inflammation, epithelial and endothelial barrier function, cancer, and metastasis, among many others. Abundant evidence indicates that SphK1 and S1P promote cancer progression and metastasis in multiple types of cancers. However, the role of SphK/S1P in HCC is less well studied. Here, we review the current state of knowledge of SphKs and S1P in HCC, including evidence for the correlation of SphK1 expression and S1P levels with progression of HCC and negative outcomes, and discuss how this information could lead to the design of more effective diagnostic and treatment modalities for HCC.

MiR-363-3p suppresses tumor growth and metastasis of colorectal cancer via targeting SphK2

Aberrant expression of miR-363-3p is seen in a wide array of cancers. The exact function of miR-363-3p in colorectal cancer (CRC), and the underlying mechanisms remain undefined. In the current study, we observed a down-regulation of miR-363-3p in CRC tissues, along with a strong correlation between low miR-363-3p levels and clinico-pathological parameters like tumor stage and lymph node metastasis. Ectopic overexpression of miR-363-3p in HT29 and HCT116 cell lines effectively inhibited cell proliferation and metastasis, and promoted apoptosis. Concurrently, miR-363-3p inhibition facilitated cell proliferation and suppressed apoptosis. Consistent with the in vitro findings, tumor growth and metastasis were also suppressed by the overexpression of miR-363-3p in vivo. Furthermore, miR-363-3p overexpression resulted in a significant decrease in SphK2 mRNA and protein levels, while miR-363-3p inhibition elevated SphK2 levels in CRC cell lines. Overexpression of SphK2 significantly abrogated the effects of miR-363-3p on cell growth, apoptosis, and metastasis. Taken together, our findings establish miR-363-3p as a potential tumor suppressor in CRC with SphK2 as its downstream target.

Novel Sphingolipid-Based Cancer Therapeutics in the Personalized Medicine Era

Sphingolipids are bioactive lipids that participate in a wide variety of biological mechanisms, including cell death and proliferation. The myriad of pro-death and pro-survival cellular pathways involving sphingolipids provide a plethora of opportunities for dysregulation in cancers. In recent years, modulation of these sphingolipid metabolic pathways has been in the forefront of drug discovery for cancer therapeutics. About two decades ago, researchers first showed that standard of care treatments, e.g., chemotherapeutics and radiation, modulate sphingolipid metabolism to increase endogenous ceramides, which kill cancer cells. Strikingly, resistance to these treatments has also been linked to altered sphingolipid metabolism, favoring lipid species that ultimately lead to cell survival. To this end, many inhibitors of sphingolipid metabolism have been developed to further define not only our understanding of these pathways but also to potentially serve as therapeutic interventions. Therefore, understanding how to better use these new drugs that target sphingolipid metabolism, either alone or in combination with current cancer treatments, holds great potential for cancer control. While sphingolipids in cancer have been reviewed previously (Hannun & Obeid, 2018; Lee & Kolesnick, 2017; Morad & Cabot, 2013; Newton, Lima, Maceyka, & Spiegel, 2015; Ogretmen, 2018; Ryland, Fox, Liu, Loughran, & Kester, 2011) in this chapter, we present a comprehensive review on how standard of care therapeutics affects sphingolipid metabolism, the current landscape of sphingolipid inhibitors, and the clinical utility of sphingolipid-based cancer therapeutics.

Targeting Sphingosine Kinases for the Treatment of Cancer

Sphingosine kinases (SK1 and SK2) are key, druggable targets within the sphingolipid metabolism pathway that promote tumor growth and pathologic inflammation. A variety of isozyme-selective and dual inhibitors of SK1 and SK2 have been described in the literature, and at least one compound has reached clinical testing in cancer patients. In this chapter, we will review the rationale for targeting SKs and summarize the preclinical and emerging clinical data for ABC294640 as the first-in-class selective inhibitor of SK2.

Suppression of c-Myc and RRM2 expression in pancreatic cancer cells by the sphingosine kinase-2 inhibitor ABC294640

Pancreatic cancer remains extremely difficult to treat, with the average lifespan following diagnosis being only 3-6 months, resulting in a death to incidence ratio of 0.94. A major reason for this high mortality rate is resistance to the main chemotherapeutic agent used to treat this disease, gemcitabine. Alterations in nucleoside and gemcitabine metabolism, specifically over-expression of ribonucleotide reductase, have been implicated as a major mechanism of resistance to this drug. Here, we show that inhibition of sphingosine kinase-2 by the specific inhibitor ABC294640 is synergistically cytotoxic with gemcitabine toward three human pancreatic cancer cell lines. Treatment with ABC294640 results in decreased expression of both RRM2 and MYC in all three cell lines. Additionally, expression of c-Myc protein and phosphorylation of Rb at S780 both decrease in a dose-dependent manner in response to ABC294640, while acetylation of H3-K9 and p21 levels increase. Pretreatment with the protein phosphatase 1 inhibitor okadaic acid or the ceramide synthase inhibitor fumonisin B1 fails to prevent the effects of ABC294640 on Rb phosphorylation. These data indicate a role for sphingosine kinase-2 in E2F and c-Myc mediated transcription through alteration of histone acetylation and p21 expression. These effects of ABC294640 suggest that it may be an effective agent for pancreatic cancer, particularly in combination with gemcitabine.

Sphingosine kinase 2 supports the development of BCR/ABL-independent acute lymphoblastic leukemia in mice

Background

Sphingosine kinase (SphK) 2 has been implicated in the development of a range of cancers and inhibitors of this enzyme are currently in clinical trial. We have previously demonstrated a role for SphK2 in the development of acute lymphoblastic leukemia (ALL).

Methods

In this and our previous study we use mouse models: in the previous study the disease was driven by the proto-oncogene BCR/ABL1, while in this study cancer risk was elevated by deletion of the tumor suppressor ARF.

Results

Mice lacking ARF and SphK2 had a significantly reduced incidence of ALL compared mice with wild type SphK2.

Conclusions

These results show that the role of SphK2 in ALL development is not limited to BCR/ABL1 driven disease extending the potential use of inhibitors of this enzyme to ALL patients whose disease have driver mutations other than BCR/ABL1.

Sphingolipid signaling in renal fibrosis

Over the last decade, various sphingolipid subspecies have gained increasing attention as important signaling molecules that regulate a multitude of physiological and pathophysiological processes including inflammation and tissue remodeling. These mediators include ceramide, sphingosine 1-phosphate (S1P), the cerebroside glucosylceramide, lactosylceramide, and the gangliosides GM3 and Gb3. These lipids have been shown to accumulate in various chronic kidney diseases that typically end in renal fibrosis and ultimately renal failure. This review will summarize the effects and contributions of those enzymes that regulate the generation and interconversion of these lipids, notably the acid sphingomyelinase, the acid sphingomyelinase-like protein SMPDL3B, the sphingosine kinases, the S1P lyase, the glucosylceramide synthase, the GM3 synthase, and the α-galactosidase A, to renal fibrotic diseases. Strategies of manipulating these enzymes for therapeutic purposes and the impact of existing drugs on renal pathologies will be discussed.

Sphingolipid metabolism in cancer signalling and therapy

Sphingolipids, including the two central bioactive lipids ceramide and sphingosine-1-phosphate (S1P), have opposing roles in regulating cancer cell death and survival, respectively, and there have been exciting developments in understanding how sphingolipid metabolism and signalling regulate these processes in response to anticancer therapy. Recent studies have provided mechanistic details of the roles of sphingolipids and their downstream targets in the regulation of tumour growth and response to chemotherapy, radiotherapy and/or immunotherapy using innovative molecular, genetic and pharmacological tools to target sphingolipid signalling nodes in cancer cells. For example, structure-function-based studies have provided innovative opportunities to develop mechanism-based anticancer therapeutic strategies to restore anti-proliferative ceramide signalling and/or inhibit pro-survival S1P-S1P receptor (S1PR) signalling. This Review summarizes how ceramide-induced cellular stress mediates cancer cell death through various mechanisms involving the induction of apoptosis, necroptosis and/or mitophagy. Moreover, the metabolism of ceramide for S1P biosynthesis, which is mediated by sphingosine kinase 1 and 2, and its role in influencing cancer cell growth, drug resistance and tumour metastasis through S1PR-dependent or receptor-independent signalling are highlighted. Finally, studies targeting enzymes involved in sphingolipid metabolism and/or signalling and their clinical implications for improving cancer therapeutics are also presented.

Sphingosine 1-phosphate regulates proliferation, cell cycle and apoptosis of hepatocellular carcinoma cells via syndecan-1

Sphingosine 1-phosphate (S1P) plays an important role in hepatocarcinogenesis. We previously demonstrated that S1P induced epithelial-mesenchymal transition of hepatocellular carcinoma (HCC) cells via an MMP-7/Syndecan-1/TGF-β autocrine loop. In the present study, we investigated the regulative role of S1P in cell survival and progression of HCC cells, and tested whether syndecan-1 is required in the S1P action. After transfected with syndecan-1 shRNA, HepG2 and SMMC7721 cells were treated with S1P for 72 h, and then cell proliferation was detected by CCK8 assay, and cell cycle progression and cell apoptosis were detected by flow cytometry. The levels of apoptosis markers including cleaved-Caspase-3 and cleaved-PARP in SMMC7721 cells were examined by western blotting. Results showed that S1P significantly enhanced cell proliferation in HCC cells, which was significantly inhibited by syndecan-1 shRNA. S1P induced the cell proportion in S phase in HCC cells, whereas S1P decreased the proportion of cells in both early and late apoptosis. Syndecan-1 shRNA induced the G2/M arrest in the presence of S1P. In the syndecan-1 shRNA transfected HCC cells, the proportions of late and early apoptotic cells, and levels of cleaved-Caspase-3 and cleaved-PARP were significantly increased in cells with or without S1P treatment. Thus, S1P augments the proportion of cells in S phase of the cell cycle that might translate to enhance HCC cell proliferation and inhibit the cell apoptosis via syndecan-1.

RNAi screen reveals a role of SPHK2 in dengue virus-mediated apoptosis in hepatic cell lines

Hepatic dysfunction is a feature of dengue virus (DENV) infection. Hepatic biopsy specimens obtained from fatal cases of DENV infection show apoptosis, which relates to the pathogenesis of DENV infection. However, how DENV induced liver injury is not fully understood. In this study, we aim to identify the factors that influence cell death by employing an apoptosis-related siRNA library screening. Our results show the effect of 558 gene silencing on caspase 3-mediated apoptosis in DENV-infected Huh7 cells. The majority of genes that contributed to apoptosis were the apoptosis-related kinase enzymes. Tumor necrosis factor superfamily member 12 (TNFSF12), and sphingosine kinase 2 (SPHK2), were selected as the candidate genes to further validate their influences on DENV-induced apoptosis. Transfection of siRNA targeting SPHK2 but not TNFSF12 genes reduced apoptosis determined by Annexin V/PI staining. Knockdown of SPHK2 did not reduce caspase 8 activity; however, did significantly reduce caspase 9 activity, suggesting its involvement of SPHK2 in the intrinsic pathway of apoptosis. Treatment of ABC294649, an inhibitor of SPHK2, reduced the caspase 3 activity, suggesting the involvement of its kinase activity in apoptosis. Knockdown of SPHK2 significantly reduced caspase 3 activity not only in DENV-infected Huh7 cells but also in DENV-infected HepG2 cells. Our results were consistent across all of the four serotypes of DENV infection, which supports the pro-apoptotic role of SPHK2 in DENV-infected liver cells.

The Role of Sphingosine-1-Phosphate and Ceramide-1-Phosphate in Inflammation and Cancer

Inflammation is part of our body's response to tissue injury and pathogens. It helps to recruit various immune cells to the site of inflammation and activates the production of mediators to mobilize systemic protective processes. However, chronic inflammation can increase the risk of diseases like cancer. Apart from cytokines and chemokines, lipid mediators, particularly sphingosine-1-phosphate (S1P) and ceramide-1-phosphate (C1P), contribute to inflammation and cancer. S1P is an important player in inflammation-associated colon cancer progression. On the other hand, C1P has been recognized to be involved in cancer cell growth, migration, survival, and inflammation. However, whether C1P is involved in inflammation-associated cancer is not yet established. In contrast, few studies have also suggested that S1P and C1P are involved in anti-inflammatory pathways regulated in certain cell types. Ceramide is the substrate for ceramide kinase (CERK) to yield C1P, and sphingosine is phosphorylated to S1P by sphingosine kinases (SphKs). Biological functions of sphingolipid metabolites have been studied extensively. Ceramide is associated with cell growth inhibition and enhancement of apoptosis while S1P and C1P are associated with enhancement of cell growth and survival. Altogether, S1P and C1P are important regulators of ceramide level and cell fate. This review focuses on S1P and C1P involvement in inflammation and cancer with emphasis on recent progress in the field.

Sphingosine metabolism as a therapeutic target in cutaneous melanoma

Melanoma is by far the most aggressive type of skin cancer with a poor prognosis in its advanced stages. Understanding the mechanisms involved in melanoma pathogenesis, response, and resistance to treatment has gained a lot of attention worldwide. Recently, the role of sphingolipid metabolism has been studied in cutaneous melanoma. Sphingolipids are bioactive lipid effector molecules involved in the regulation of various cellular signaling pathways such as inflammation, cancer cell proliferation, death, senescence, and metastasis. Recent studies suggest that sphingolipid metabolism impacts melanoma pathogenesis and is a potential therapeutic target. This review focuses on defining the role of sphingolipid metabolism in melanoma carcinogenesis, discussing sphingolipid-based therapeutic approaches, and highlighting the areas that require more extensive research.

Sphingosine Kinases/Sphingosine 1-Phosphate Signaling in Hepatic Lipid Metabolism

The ever-increasing prevalence of metabolic diseases such as dyslipidemia and diabetes in the western world continues to be of great public health concern. Biologically active sphingolipids, such as sphingosine 1-phosphate (S1P) and ceramide, are important regulators of lipid metabolism. S1P not only directly functions as an active intracellular mediator, but also activates multiple signaling pathways via five transmembrane G-protein coupled receptors (GPCRs), S1PR1-5. S1P is exclusively formed by sphingosine kinases (SphKs). Two isoforms of SphKs, SphK1 and SphK2, have been identified. Recent identification of the conjugated bile acid-induced activation of S1PR2 as a key regulator of SphK2 opened new directions for both the sphingolipid and bile acid research fields. The role of SphKs/S1P-mediated signaling pathways in health and various human diseases has been extensively reviewed elsewhere. This review focuses on recent findings related to SphKs/S1P-medaited signaling pathways in regulating hepatic lipid metabolism.

A Phase I Study of ABC294640, a First-in-Class Sphingosine Kinase-2 Inhibitor, in Patients with Advanced Solid Tumors

Purpose: Sphingosine kinases (SK1 and SK2) regulate tumor growth by generating the mitogenic and proinflammatory lipid sphingosine 1-phosphate (S1P). This phase I study investigated the safety, pharmacokinetics, pharmacodynamics, and antitumor activity of ABC294640, a first-in-class orally available inhibitor of SK2.Experimental Design: Escalating doses of ABC294640 were administered orally to patients with advanced solid tumors in sequential cohorts at the following dose levels: 250 mg qd, 250 mg bid, 500 mg bid, and 750 mg bid, continuously in cycles of 28 days. Serial blood samples were obtained to measure ABC294640 concentrations and sphingolipid profiles.Results: Twenty-two patients were enrolled, and 21 received ABC294640. The most common drug-related toxicities were nausea, vomiting, and fatigue. Among the 4 patients at 750 mg bid, one had dose-limiting grade 3 nausea and vomiting, and 2 were unable to complete cycle 1 due to diverse drug-related toxicities. The 500 mg bid dose level was established as the recommended phase II dose. ABC294640 administration resulted in decreases in S1P levels over the first 12 hours, with return to baseline at 24 hours. The best response was a partial response in a patient with cholangiocarcinoma at 250 mg qd, and stable disease was observed in 6 patients with various solid tumors across dose levels.Conclusions: At 500 mg bid, ABC294640 is well tolerated and achieves biologically relevant plasma concentrations. Changes in plasma sphingolipid levels may provide a useful pharmacodynamic biomarker for ABC294640. Clin Cancer Res; 23(16); 4642-50. ©2017 AACR.

Serum sphingolipidomic analyses reveal an upregulation of C16-ceramide and sphingosine-1-phosphate in hepatocellular carcinoma

We have recently shown that major alterations of serum sphingolipid metabolites in chronic liver disease associate significantly with the stage of liver fibrosis in corresponding patients. In the current study we assessed via mass spectrometry serum concentrations of sphingolipid metabolites in a series of 122 patients with hepatocellular carcinoma (HCC) compared to an age- and sex-matched series of 127 patients with cirrhosis. We observed a highly significant upregulation of long and very long chain ceramides (C16-C24) in the serum of patients with HCC as compared to patients with cirrhosis (P < 0.001). Accordingly, dihydro-ceramides, synthetic precursors of ceramides and notably sphingosine, sphingosine-1-phosphate (S1P) and sphinganine-1-phosphate (SA1P) were upregulated in patients with HCC (P < 0.001). Especially the diagnostic accuracy of C16-ceramide and S1P, assessed by receiver operating curve (ROC) analysis, showed a higher area under the curve (AUC) value as compared to alpha fetoprotein (AFP) (0.999 and 0.985 versus 0.823, P < 0.001 respectively). In conclusion, serum levels of sphingolipid metabolites show a significant upregulation in patients with HCC as compared to patients with cirrhosis. Particularly C16-ceramide and S1P may serve as novel diagnostic markers for the identification of HCC in patients with liver diseases. Our data justify further investigations on the role of sphingolipids in HCC.

Evaluation of uttroside B, a saponin from Solanum nigrum Linn, as a promising chemotherapeutic agent against hepatocellular carcinoma

We report, for the first time, the remarkable efficacy of uttroside B, a potent saponin from Solanum nigrum Linn, against liver cancer. The compound has been isolated and characterized from the leaves of Solanum nigrum Linn, a plant widely used in traditional medicine and is a rich resource of several anticancer molecules. Uttroside B, that comprises of β-D-glucopyranosyl unit at C-26 of the furostanol and β-lycotetraosyl unit at C-3, is ten times more cytotoxic to the liver cancer cell line, HepG2 (IC50: 0.5 μM) than sorafenib (IC50: 5.8 μM), the only FDA-approved drug for liver cancer. Moreover, it induces cytotoxicity in all liver cancer cell lines, irrespective of their HBV status, while being non-toxic to normal immortalized hepatocytes. It induces apoptosis in HepG2 cells by down-regulating mainly the activation of MAPK and mTOR pathways. The drastic reduction in HepG2-xenograft tumor size achieved by uttroside B in NOD-SCID mice and substantiation of its biological safety through both acute and chronic toxicity studies in Swiss albino mice warrants clinical validation of the molecule against hepatic cancer, for which, the chemotherapeutic armamentarium currently has limited weapons.

Therapeutic Strategies and Pharmacological Tools Influencing S1P Signaling and Metabolism

During the last two decades the study of the sphingolipid anabolic, catabolic, and signaling pathways has attracted enormous interest. Especially the introduction of fingolimod into market as first p.o. therapeutic for the treatment of multiple sclerosis has boosted this effect. Although the complex regulation of sphingosine-1-phosphate (S1P) and other catabolic and anabolic sphingosine-related compounds is not fully understood, the influence on different (patho)physiological states from inflammation to cytotoxicity as well as the availability of versatile pharmacological tools that represent new approaches to study these states are described. Here, we have summarized various aspects concerning the many faces of sphingolipid function modulation by different pharmacological tools up to clinical candidates. Due to the immense heterogeneity of physiological or pharmacological actions and complex cross regulations, it is difficult to predict their role in upcoming therapeutic approaches. Currently, inflammatory, immunological, and/or antitumor aspects are discussed.

Therapeutic potential of targeting sphingosine kinases and sphingosine 1-phosphate in hematological malignancies

Sphingolipids, such as ceramide, sphingosine and sphingosine 1-phosphate (S1P) are bioactive molecules that have important functions in a variety of cellular processes, which include proliferation, survival, differentiation and cellular responses to stress. Sphingolipids have a major impact on the determination of cell fate by contributing to either cell survival or death. Although ceramide and sphingosine are usually considered to induce cell death, S1P promotes survival of cells. Sphingosine kinases (SPHKs) are the enzymes that catalyze the conversion of sphingosine to S1P. There are two isoforms, SPHK1 and SPHK2, which are encoded by different genes. SPHK1 has recently been implicated in contributing to cell transformation, tumor angiogenesis and metastatic spread, as well as cancer cell multidrug-resistance. More recent findings suggest that SPHK2 also has a role in cancer progression. This review is an overview of our understanding of the role of SPHKs and S1P in hematopoietic malignancies and provides information on the current status of SPHK inhibitors with respect to their therapeutic potential in the treatment of hematological cancers.

The roles of bile acids and sphingosine-1-phosphate signaling in the hepatobiliary diseases

Based on research carried out over the last decade, it has become increasingly evident that bile acids act not only as detergents, but also as important signaling molecules that exert various biological effects via activation of specific nuclear receptors and cell signaling pathways. Bile acids also regulate the expression of numerous genes encoding enzymes and proteins involved in the synthesis and metabolism of bile acids, glucose, fatty acids, and lipoproteins, as well as energy metabolism. Receptors activated by bile acids include, farnesoid X receptor α, pregnane X receptor, vitamin D receptor, and G protein-coupled receptors, TGR5, muscarinic receptor 2, and sphingosine-1-phosphate receptor (S1PR)2. The ligand of S1PR2, sphingosine-1-phosphate (S1P), is a bioactive lipid mediator that regulates various physiological and pathophysiological cellular processes. We have recently reported that conjugated bile acids, via S1PR2, activate and upregulate nuclear sphingosine kinase 2, increase nuclear S1P, and induce genes encoding enzymes and transporters involved in lipid and sterol metabolism in the liver. Here, we discuss the role of bile acids and S1P signaling in the regulation of hepatic lipid metabolism and in hepatobiliary diseases.

Modulation of Autophagy by Sorafenib: Effects on Treatment Response

The multikinase inhibitor sorafenib is, at present, the only drug approved for the treatment of hepatocellular carcinoma (HCC), one of the most lethal types of cancer worldwide. However, the increase in the number of sorafenib tumor resistant cells reduces efficiency. A better knowledge of the intracellular mechanism of the drug leading to reduced cell survival could help to improve the benefits of sorafenib therapy. Autophagy is a bulk cellular degradation process activated in a broad range of stress situations, which allows cells to degrade misfolded proteins or dysfunctional organelles. This cellular route can induce survival or death, depending on cell status and media signals. Sorafenib, alone or in combination with other drugs is able to induce autophagy, but cell response to the drug depends on the complex integrative crosstalk of different intracellular signals. In cancerous cells, autophagy can be regulated by different cellular pathways (Akt-related mammalian target of rapamycin (mTOR) inhibition, 5′ AMP-activated protein kinase (AMPK) induction, dissociation of B-cell lymphoma 2 (Bcl-2) family proteins from Beclin-1), or effects of some miRNAs. Inhibition of mTOR signaling by sorafenib and diminished interaction between Beclin-1 and myeloid cell leukemia 1 (Mcl-1) have been related to induction of autophagy in HCC. Furthermore, changes in some miRNAs, such as miR-30α, are able to modulate autophagy and modify sensitivity in sorafenib-resistant cells. However, although AMPK phosphorylation by sorafenib seems to play a role in the antiproliferative action of the drug, it does not relate with modulation of autophagy. In this review, we present an updated overview of the effects of sorafenib on autophagy and its related activation pathways, analyzing in detail the involvement of autophagy on sorafenib sensitivity and resistance.

Antitumor effect of the novel sphingosine kinase 2 inhibitor ABC294640 is enhanced by inhibition of autophagy and by sorafenib in human cholangiocarcinoma cells

Sphingosine kinase 2 (Sphk2) has an oncogenic role in cancer. A recently developed first-in-class Sphk2 specific inhibitor ABC294640 displays antitumor activity in many cancer models. However, the role of Sphk2 and the antitumor activity of its inhibitor ABC294640 are not known in cholangiocarcinoma. We investigated the potential of targeting Sphk2 for the treatment of cholangiocarcinoma. We found that Sphk2 is overexpressed in five established human cholangiocarcinoma cell lines (WITT, HuCCT1, EGI-1, OZ and HuH28) and a new patient-derived cholangiocarcinoma cell line (LIV27) compared to H69 normal cholangiocytes. Inhibition of Sphk2 by ABC294640 inhibited proliferation and induced caspase-dependent apoptosis. Furthermore, we found that ABC294640 inhibited STAT3 phosphorylation, one of the key signaling pathways regulating cholangiocarcinoma cell proliferation and survival. ABC294640 also induced autophagy. Inhibition of autophagy by bafilomycin A1 or chloroquine potentiated ABC294640-induced cytotoxicity and apoptosis. In addition, ABC294640 in combination with sorafenib synergistically inhibited cell proliferation of cholangiocarcinoma cells. Strong decreases in STAT3 phosphorylation were observed in WITT and HuCCT1 cells exposed to the ABC294640 and sorafenib combination. These findings provide novel evidence that Sphk2 may be a rational therapeutic target in cholangiocarcinoma. Combinations of ABC294640 with sorafenib and/or autophagy inhibitors may provide novel strategies for the treatment of cholangiocarcinoma.