From Sphingosine Kinase to Dihydroceramide Desaturase: A Structure-Activity Relationship (SAR) Study of the Enzyme Inhibitory and Anticancer Activity of 4-((4-(4-Chlorophenyl)thiazol-2-yl)amino)phenol (SKI-II)

TFA-Mediated Synthesis of 1,2,4-Oxadiazoles from Carbamates and Nitriles

An unprecedented protocol for the synthesis of 1,2,4-oxadiazoles from carbamates has been developed by employing nitriles as both substrates and solvents. This one-pot procedure achieves the formation of C═N bonds via TFA-mediated [3+2] annulation. A series of 1,2,4-oxadiazoles are synthesized in moderate to good yields.

Staging of colorectal cancer using lipid biomarkers and machine learning

INTRODUCTION

Colorectal cancer (CRC) is the third most commonly diagnosed cancer worldwide. Alteration in lipid metabolism and chemokine expression are considered hallmark characteristics of malignant progression and metastasis of CRC. Validated diagnostic and prognostic biomarkers are urgently needed to define molecular heterogeneous CRC clinical stages and subtypes, as liver dominant metastasis has poor survival outcomes.

OBJECTIVES

The aim of this study was to integrate lipid changes, concentrations of chemokines, such as platelet factor 4 and interleukin 8, and gene marker status measured in plasma samples, with clinical features from patients at different CRC stages or who had progressed to stage-IV colorectal liver metastasis (CLM).

METHODS

High-resolution liquid chromatography-mass spectrometry (HR-LC-MS) was used to determine the levels of candidate lipid biomarkers in each CRC patient's preoperative plasma samples and combined with chemokine, gene and clinical data. Machine learning models were then trained using known clinical outcomes to select biomarker combinations that best classify CRC stage and group.

RESULTS

Bayesian neural net and multilinear regression-machine learning identified candidate biomarkers that classify CRC (stages I-III), CLM patients and control subjects (cancer-free or patients with polyps/diverticulitis), showing that integrating specific lipid signatures and chemokines (platelet factor-4 and interluken-8; IL-8) can improve prognostic accuracy. Gene marker status could contribute to disease prediction, but requires ubiquitous testing in clinical cohorts.

CONCLUSION

Our findings demonstrate that correlating multiple disease related features with lipid changes could improve CRC prognosis. The identified signatures could be used as reference biomarkers to predict CRC prognosis and classify stages, and monitor therapeutic intervention.

Thiol-promoted intermolecular cyclization to synthesize 1,2,4-oxadiazoles including tioxazafen under transition metal-free conditions

A simple and efficient one-pot intermolecular annulation reaction for the synthesis of 1,2,4-oxadiazoles from amidoximes and benzyl thiols has been developed, in which benzyl thiols act as not only reactants but also organo-catalysts. The control experiments proved that thiol substrates could facilitate the dehydroaromatization step. High yield, functional group diversity and transition metal-free, extra oxidant-free, and mild conditions are the important practical features. Moreover, this protocol provides an effective alternative method for the synthesis of a commercially available broad-spectrum nematicide, tioxazafen.

Pharmacological Elevation of Cellular Dihydrosphingomyelin Provides a Novel Antiviral Strategy against West Nile Virus Infection

The flavivirus life cycle is strictly dependent on cellular lipid metabolism. Polyphenols like gallic acid and its derivatives are promising lead compounds for new therapeutic agents as they can exert multiple pharmacological activities, including the alteration of lipid metabolism. The evaluation of our collection of polyphenols against West Nile virus (WNV), a representative medically relevant flavivirus, led to the identification of N,N'-(dodecane-1,12-diyl)bis(3,4,5-trihydroxybenzamide) and its 2,3,4-trihydroxybenzamide regioisomer as selective antivirals with low cytotoxicity and high antiviral activity (half-maximal effective concentrations [EC₅₀s] of 2.2 and 0.24 μM, respectively, in Vero cells; EC₅₀s of 2.2 and 1.9 μM, respectively, in SH-SY5Y cells). These polyphenols also inhibited the multiplication of other flaviviruses, namely, Usutu, dengue, and Zika viruses, exhibiting lower antiviral or negligible antiviral activity against other RNA viruses. The mechanism underlying their antiviral activity against WNV involved the alteration of sphingolipid metabolism. These compounds inhibited ceramide desaturase (Des1), promoting the accumulation of dihydrosphingomyelin (dhSM), a minor component of cellular sphingolipids with important roles in membrane properties. The addition of exogenous dhSM or Des1 blockage by using the reference inhibitor GT-11 {N-[(1R,2S)-2-hydroxy-1-hydroxymethyl-2-(2-tridecyl-1-cyclopropenyl)ethyl]octanamide} confirmed the involvement of this pathway in WNV infection. These results unveil the potential of novel antiviral strategies based on the modulation of the cellular levels of dhSM and Des1 activity for the control of flavivirus infection.

The Sphingolipid Inhibitors Ceranib-2 and SKI-II Reduce Measles Virus Replication in Primary Human Lymphocytes: Effects on mTORC1 Downstream Signaling

The bioactive sphingolipids ceramide and sphingosine-1-phosphate (S1P) are involved in the regulation of cell homeostasis and activity ranging from apoptosis to proliferation. We recently described that the two compounds ceranib-2 (inhibiting acid ceramidase) and SKI-II [inhibiting the sphingosine kinases 1 and − 2 (SphK1/2)] reduce mTORC1 activity and measles virus (MV) replication in human primary peripheral blood lymphocytes (PBL) by about one log step. We now further investigated whether mTORC1 downstream signaling and viral protein expression may be affected by ceranib-2 and/or SKI-II. Western blot analyses showed that in uninfected cells the phosphorylation of the eukaryotic initiation factor 4E (eIF4E) was reduced by both inhibitors. Interestingly, MV infection led to an increase of rpS6 protein levels and phosphorylation of eIF4E. Treatment with both inhibitors reduced the rpS6 protein expression, and in addition, SKI-II reduced rpS6 phosphorylation. The phosphorylation of eIF4E was slightly reduced by both inhibitors. In addition, SKI-II led to reduced levels of IKK in MV-infected cells. Both inhibitors reduced the expression of viral proteins and the titers of newly synthesized MV by approximately one log step. As expected, SKI-II and rapamycin reduced also the virally encoded GFP expression; however, ceranib-2 astonishingly led to increased levels of GFP fluorescence. Our findings suggest that the inhibitors ceranib-2 and SKI-II act via differential mechanisms on MV replication. The observed effects on mTORC1 downstream signaling, predominantly the reduction of rpS6 levels by both inhibitors, may affect the translational capacity of the cells and contribute to the antiviral effect in human primary PBL.

Lipidomics Profiles in Hepatocytes from Nonalcoholic Steatohepatitis Patients Differ Markedly from In Vitro-Induced Steatotic Hepatocytes

Nonalcoholic steatohepatitis (NASH) is a severe form of liver injury that can be caused by a variety of stimuli and has a significant mortality rate. A common technique to induce in vitro steatosis involves culturing primary human hepatocytes (PHH) in fatty acid-enriched media. This study compared the lipidome of PHH cultured in fatty acid-enriched media to hepatocytes from patients with NASH and healthy controls. Hepatocytes from NASH patients displayed increased total cellular abundance of glycerolipids and phospholipids compared to healthy control hepatocytes. PHH cultured in fatty acid-enriched media demonstrated increased glycerolipids. However, these culture conditions did not induce elevated phospholipid levels. Thus, culturing PHH in fatty acid-enriched media has limited capacity to emulate the environment of hepatocytes in NASH patients.

New N-(3′-acetyl-8-nitro-2,3-dihydro-1H,3′H-spiro[quinoline-4,2′-[1,3,4]thiadiazol]-5′-yl) acetamides induced cell death in MCF-7 cells via G2/M phase cell cycle arrest

A series of new N-(3′-acetyl-8-nitro-2,3-dihydro-1H,3′H-spiro[quinoline-4,2′-[1,3,4]thiadiazol]-5′-yl) acetamide derivatives were synthesized from potent 8-nitroquinoline-thiosemicarbazones.

Resensitising proteasome inhibitor-resistant myeloma with sphingosine kinase 2 inhibition

The introduction of the proteasome inhibitor bortezomib into treatment regimens for myeloma has led to substantial improvement in patient survival. However, whilst bortezomib elicits initial responses in many myeloma patients, this haematological malignancy remains incurable due to the development of acquired bortezomib resistance. With other patients presenting with disease that is intrinsically bortezomib resistant, it is clear that new therapeutic approaches are desperately required to target bortezomib-resistant myeloma. We have previously shown that targeting sphingolipid metabolism with the sphingosine kinase 2 (SK2) inhibitor K145 in combination with bortezomib induces synergistic death of bortezomib-naïve myeloma. In the current study, we have demonstrated that targeting sphingolipid metabolism with K145 synergises with bortezomib and effectively resensitises bortezomib-resistant myeloma to this proteasome inhibitor. Notably, these effects were dependent on enhanced activation of the unfolded protein response, and were observed in numerous separate myeloma models that appear to have different mechanisms of bortezomib resistance, including a new bortezomib-resistant myeloma model we describe which possesses a clinically relevant proteasome mutation. Furthermore, K145 also displayed synergy with the next-generation proteasome inhibitor carfilzomib in bortezomib-resistant and carfilzomib-resistant myeloma cells. Together, these findings indicate that targeting sphingolipid metabolism via SK2 inhibition may be effective in combination with a broad spectrum of proteasome inhibitors in the proteasome inhibitor resistant setting, and is an approach worth clinical exploration.

Therapeutic Potential of SphK1 Inhibitors Based on Abnormal Expression of SphK1 in Inflammatory Immune Related-Diseases

Sphingosine kinase 1(SphK1) a key enzyme that catalyzes the conversion of sphingosine (Sph) to sphingosine 1-phosphate (S1P), so as to maintain the dynamic balance of sphingolipid-rheostat in cells and participate in cell growth and death, proliferation and migration, vasoconstriction and remodeling, inflammation and metabolism. The normal expression of SphK1 maintains the balance of physiological and pathological states, which is reflected in the regulation of inflammatory factor secretion, immune response in traditional immune cells and non-traditional immune cells, and complex signal transduction. However, abnormal SphK1 expression and activity are found in various inflammatory and immune related-diseases, such as hypertension, atherosclerosis, Alzheimer’s disease, inflammatory bowel disease and rheumatoid arthritis. In view of the therapeutic potential of regulating SphK1 and its signal, the current research is aimed at SphK1 inhibitors, such as SphK1 selective inhibitors and dual SphK1/2 inhibitor, and other compounds with inhibitory potency. This review explores the regulatory role of over-expressed SphK1 in inflammatory and immune related-diseases, and investigate the latest progress of SphK1 inhibitors and the improvement of disease or pathological state.

Angiogenesis as a potential treatment strategy for rheumatoid arthritis

Angiogenesis is an early and key event in the pathogenesis of rheumatoid arthritis (RA) and is crucial for the proliferation of synovial tissue and the formation of pannus. This process is regulated by both angiogenesis-stimulating factors and angiogenesis inhibitors, the basis for the "on-off hypothesis of angiogenesis." In RA, inflammation, immune imbalance, and hypoxia can further turn on the switch for blood vessel formation and induce angiogenesis. The new vasculature can recruit white blood cells, induce immune imbalance, and aggravate inflammation. At the same time, it also can provide oxygen and nutrients for the proliferating synovial tissue, which can accelerate the process of RA. The current therapies for RA mainly target the inflammatory response of autoimmune activation. Although these therapies have been greatly improved, there are still many patients whose RA is difficult to treat or who do not fully respond to treatment. Therefore, new innovative therapies are still urgently needed. This review covers the mechanism of synovial angiogenesis in RA, including the detailed process of angiogenesis and the relationship between inflammation, immune imbalance, hypoxia, and synovial angiogenesis, respectively. At the same time, in the context of the development of angiogenesis inhibition therapy for cancer, we also discuss similar treatment strategies for RA, especially the combination of targeted angiogenesis inhibition therapy and immunotherapy.

The effect of dihydroceramide desaturase 1 inhibition on endothelial impairment induced by indoxyl sulfate

Protein-bound uremic toxins (PBUTs) have adverse effects on vascular function, which is imperative in the progression of cardiovascular and renal diseases. The role of sphingolipids in PBUT-mediated vasculo-endothelial pathophysiology is unclear. This study assessed the therapeutic potential of dihydroceramide desaturase 1 (Des1) inhibition, the last enzyme involved in de novo ceramide synthesis, to mitigate the vascular effects of the PBUT indoxyl sulfate (IS). Rat aortic rings were isolated and vascular reactivity was assessed in organ bath experiments followed by immunohistochemical analyses. Furthermore, cultured human aortic endothelial cells were assessed for phenotypic and mechanistic changes. Inhibition of Des1 by a selective inhibitor CIN038 (0.1 to 0.3 μM) improved IS-induced impairment of vasorelaxation and modulated immunoreactivity of oxidative stress markers. Des1 inhibition also reversed IS-induced reduction in endothelial cell migration (1.0 μM) by promoting the expression of angiogenic cytokines and reducing inflammatory and oxidative stress markers. These effects were associated with a reduction of TIMP1 and the restoration of Akt phosphorylation. In conclusion, Des1 inhibition improved vascular relaxation and endothelial cell migration impaired by IS overload. Therefore, Des1 may be a suitable intracellular target to mitigate PBUT-induced adverse vascular effects.

Mesenteric lymphatic dysfunction promotes insulin resistance and represents a potential treatment target in obesity

Visceral adipose tissue (VAT) encases mesenteric lymphatic vessels and lymph nodes through which lymph is transported from the intestine and mesentery. Whether mesenteric lymphatics contribute to adipose tissue inflammation and metabolism and insulin resistance is unclear. Here we show that obesity is associated with profound and progressive dysfunction of the mesenteric lymphatic system in mice and humans. We find that lymph from mice and humans consuming a high-fat diet (HFD) stimulates lymphatic vessel growth, leading to the formation of highly branched mesenteric lymphatic vessels that 'leak' HFD-lymph into VAT and, thereby, promote insulin resistance. Mesenteric lymphatic dysfunction is regulated by cyclooxygenase (COX)-2 and vascular endothelial growth factor (VEGF)-C-VEGF receptor (R)3 signalling. Lymph-targeted inhibition of COX-2 using a glyceride prodrug approach reverses mesenteric lymphatic dysfunction, visceral obesity and inflammation and restores glycaemic control in mice. Targeting obesity-associated mesenteric lymphatic dysfunction thus represents a potential therapeutic option to treat metabolic disease.

Dihydroceramide Desaturase Functions as an Inducer and Rectifier of Apoptosis: Effect of Retinol Derivatives, Antioxidants and Phenolic Compounds

Dihydroceramide desaturase (Degs1) catalyses the introduction of a 4,5-trans double bond into dihydroceramide to form ceramide. We show here that Degs1 is polyubiquitinated in response to retinol derivatives, phenolic compounds or anti-oxidants in HEK293T cells. The functional predominance of native versus polyubiquitinated forms of Degs1 appears to govern cytotoxicity. Therefore, 4-HPR or celecoxib appear to stimulate the de novo ceramide pathway (with the exception of C24:0 ceramide), using native Degs1, and thereby promote PARP cleavage and LC3B-I/II processing (autophagy/apoptosis). The ubiquitin-proteasomal degradation of Degs1 is positively linked to cell survival via XBP-1s and results in a concomitant increase in dihydroceramides and a decrease in C24:0 ceramide levels. However, in the case of 4-HPR or celecoxib, the native form of Degs1 functionally predominates, such that the apoptotic programme is sustained. In contrast, 4-HPA or AM404 do not produce apoptotic ceramide, using native Degs1, but do promote a rectifier function to induce ubiquitin-proteasomal degradation of Degs1 and are not cytotoxic. Therefore, Degs1 appears to function both as an 'inducer' and 'rectifier' of apoptosis in response to chemical cellular stress, the dynamic balance for which is dependent on the nature of chemical stress, thereby determining cytotoxicity. The de novo synthesis of ceramide or the ubiquitin-proteasomal degradation of Degs1 in response to anti-oxidants, retinol derivatives and phenolic compounds appear to involve sensors, and for rectifier function, this might be Degs1 itself.

Sphingolipid imbalance and inflammatory effects induced by uremic toxins in heart and kidney cells are reversed by dihydroceramide desaturase 1 inhibition

Non-dialysable protein-bound uremic toxins (PBUTs) contribute to the development of cardiovascular disease (CVD) in chronic kidney disease (CKD) and vice versa. PBUTs have been shown to alter sphingolipid imbalance. Dihydroceramide desaturase 1 (Des1) is an important gatekeeper enzyme which controls the non-reversible conversion of sphingolipids, dihydroceramide, into ceramide. The present study assessed the effect of Des1 inhibition on PBUT-induced cardiac and renal effects in vitro, using a selective Des1 inhibitor (CIN038). Des1 inhibition attenuated hypertrophy in neonatal rat cardiac myocytes and collagen synthesis in neonatal rat cardiac fibroblasts and renal mesangial cells induced by the PBUTs, indoxyl sulfate and p-cresol sulfate. This is at least attributable to modulation of NF-κB signalling and reductions in β-MHC, Collagen I and TNF-α gene expression. Lipidomic analyses revealed Des1 inhibition restored C16-dihydroceramide levels reduced by indoxyl sulfate. In conclusion, PBUTs play a critical role in mediating sphingolipid imbalance and inflammatory responses in heart and kidney cells, and these effects were attenuated by Des1 inhibition. Therefore, sphingolipid modifying agents may have therapeutic potential for the treatment of CVD and CKD and warrant further investigation.

N-Heterocyclic Carbene-Catalyzed Cyclization of Aldehydes with α-Diazo Iodonium Triflate: Facile Access to 2,5-Disubstituted 1,3,4-Oxadiazoles

Herein, we report a novel organocatalytic process for synthesis of complex 1,3,4-oxadiazoles from readily accessible aldehydes. By exploiting the nucleophilicity of the putative Breslow intermediate and the inherent electrophilicity of α-diazo iodonium triflate, we have found that N-heterocyclic carbene catalyst promotes efficient cyclization of various aldehydes and α-diazo iodonium triflates. The reaction proceeds under mild conditions with a wide range of functional group tolerance. The heterocyclic products can be readily further functionalized, rendering the protocol highly valuable.

A chemical screen for modulators of mRNA translation identifies a distinct mechanism of toxicity for sphingosine kinase inhibitors

We here conducted an image-based chemical screen to evaluate how medically approved drugs, as well as drugs that are currently under development, influence overall translation levels. None of the compounds up-regulated translation, which could be due to the screen being performed in cancer cells grown in full media where translation is already present at very high levels. Regarding translation down-regulators, and consistent with current knowledge, inhibitors of the mechanistic target of rapamycin (mTOR) signaling pathway were the most represented class. In addition, we identified that inhibitors of sphingosine kinases (SPHKs) also reduce mRNA translation levels independently of mTOR. Mechanistically, this is explained by an effect of the compounds on the membranes of the endoplasmic reticulum (ER), which activates the integrated stress response (ISR) and contributes to the toxicity of SPHK inhibitors. Surprisingly, the toxicity and activation of the ISR triggered by 2 independent SPHK inhibitors, SKI-II and ABC294640, the latter in clinical trials, are also observed in cells lacking SPHK1 and SPHK2. In summary, our study provides a useful resource on the effects of medically used drugs on translation, identified compounds capable of reducing translation independently of mTOR and has revealed that the cytotoxic properties of SPHK inhibitors being developed as anticancer agents are independent of SPHKs.

Development and therapeutic potential of 2-aminothiazole derivatives in anticancer drug discovery

Currently, the development of anticancer drug resistance is significantly restricted the clinical efficacy of the most commonly prescribed anticancer drug. Malignant disease is widely prevalent and considered to be the major challenges of this century, which concerns the medical community all over the world. Consequently, investigating small molecule antitumor agents, which could decrease drug resistance and reduce unpleasant side effect is more desirable. 2-aminothiazole scaffold has emerged as a promising scaffold in medicinal chemistry and drug discovery research. This nucleus is a fundamental part of some clinically applied anticancer drugs such as dasatinib and alpelisib. Literature survey documented that different 2-aminothiazole analogs exhibited their potent and selective nanomolar inhibitory activity against a wide range of human cancerous cell lines such as breast, leukemia, lung, colon, CNS, melanoma, ovarian, renal, and prostate. In this paper, we have reviewed the progresses and structural modification of 2-aminothiazole to pursuit potent anticancers and also highlighted in vitro activities and in silico studies. The information will useful for future innovation. Representatives of 2-aminothiazole-containing compounds classification.

Small Molecule Inhibitors Targeting Biosynthesis of Ceramide, the Central Hub of the Sphingolipid Network

Ceramides are composed of a sphingosine and a single fatty acid connected by an amide linkage. As one of the major classes of biologically active lipids, ceramides and their upstream and downstream metabolites have been implicated in several pathological conditions including cancer, neurodegeneration, diabetes, microbial pathogenesis, obesity, and inflammation. Consequently, tremendous efforts have been devoted to deciphering the dynamics of metabolic pathways involved in ceramide biosynthesis. Given that several distinct enzymes can produce ceramide, different enzyme targets have been pursued depending on the underlying disease mechanism. The main objective of this review is to provide a comprehensive overview of small molecule inhibitors reported to date for each of these ceramide-producing enzymes from a medicinal chemistry perspective.

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.

Metabolomes and Lipidomes of the Infective Stages of the Gastrointestinal nematodes, Nippostrongylus brasiliensis and Trichuris muris

Soil-transmitted helminths, including hookworms and whipworms, infect billions of people worldwide. Their capacity to penetrate and migrate through their hosts’ tissues is influenced by the suite of molecules produced by the infective developmental stages. To facilitate a better understanding of the immunobiology and pathogenicity of human hookworms and whipworms, we investigated the metabolomes of the infective stage of Nippostrongylus brasiliensis third-stage larvae (L3) which penetrate the skin and Trichuris muris eggs which are orally ingested, using untargeted liquid chromatography-mass spectrometry (LC-MS). We identified 55 polar metabolites through Metabolomics Standard Initiative level-1 (MSI-I) identification from N. brasiliensis and T. muris infective stages, out of which seven were unique to excretory/secretory products (ESPs) of N. brasiliensis L3. Amino acids were a principal constituent (33 amino acids). Additionally, we identified 350 putative lipids, out of which 28 (all known lipids) were unique to N. brasiliensis L3 somatic extract and four to T. muris embryonated egg somatic extract. Glycerophospholipids and glycerolipids were the major lipid groups. The catalogue of metabolites identified in this study shed light on the biology, and possible therapeutic and diagnostic targets for the treatment of these critical infectious pathogens. Moreover, with the growing body of literature on the therapeutic utility of helminth ESPs for treating inflammatory diseases, a role for metabolites is likely but has received little attention thus far.

Targeting the SphK-S1P-SIPR Pathway as a Potential Therapeutic Approach for COVID-19

The world is currently experiencing the worst health pandemic since the Spanish flu in 1918-the COVID-19 pandemic-caused by the coronavirus severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). This pandemic is the world's third wake-up call this century. In 2003 and 2012, the world experienced two major coronavirus outbreaks, SARS-CoV-1 and Middle East Respiratory syndrome coronavirus (MERS-CoV), causing major respiratory tract infections. At present, there is neither a vaccine nor a cure for COVID-19. The severe COVID-19 symptoms of hyperinflammation, catastrophic damage to the vascular endothelium, thrombotic complications, septic shock, brain damage, acute disseminated encephalomyelitis (ADEM), and acute neurological and psychiatric complications are unprecedented. Many COVID-19 deaths result from the aftermath of hyperinflammatory complications, also referred to as the "cytokine storm syndrome", endotheliitus and blood clotting, all with the potential to cause multiorgan dysfunction. The sphingolipid rheostat plays integral roles in viral replication, activation/modulation of the immune response, and importantly in maintaining vasculature integrity, with sphingosine 1 phosphate (S1P) and its cognate receptors (SIPRs: G-protein-coupled receptors) being key factors in vascular protection against endotheliitus. Hence, modulation of sphingosine kinase (SphK), S1P, and the S1P receptor pathway may provide significant beneficial effects towards counteracting the life-threatening, acute, and chronic complications associated with SARS-CoV-2 infection. This review provides a comprehensive overview of SARS-CoV-2 infection and disease, prospective vaccines, and current treatments. We then discuss the evidence supporting the targeting of SphK/S1P and S1P receptors in the repertoire of COVID-19 therapies to control viral replication and alleviate the known and emerging acute and chronic symptoms of COVID-19. Three clinical trials using FDA-approved sphingolipid-based drugs being repurposed and evaluated to help in alleviating COVID-19 symptoms are discussed.

Design, Synthesis, Radiosynthesis and Biological Evaluation of Fenretinide Analogues as Anticancer and Metabolic Syndrome-Preventive Agents

Fenretinide (4-HPR) is a synthetic derivative of all-trans-retinoic acid (ATRA) characterised by improved therapeutic properties and toxicological profile relative to ATRA. 4-HPR has been mostly investigated as an anti-cancer agent, but recent studies showed its promising therapeutic potential for preventing metabolic syndrome. Several biological targets are involved in 4-HPR's activity, leading to the potential use of this molecule for treating different pathologies. However, although 4-HPR displays quite well-understood multitarget promiscuity with regards to pharmacology, interpreting its precise physiological role remains challenging. In addition, despite promising results in vitro, the clinical efficacy of 4-HPR as a chemotherapeutic agent has not been satisfactory so far. Herein, we describe the preparation of a library of 4-HPR analogues, followed by the biological evaluation of their anti-cancer and anti-obesity/diabetic properties. The click-type analogue 3 b showed good capacity to reduce the amount of lipid accumulation in 3T3-L1 adipocytes during differentiation. Furthermore, it showed an IC₅₀ of 0.53±0.8 μM in cell viability tests on breast cancer cell line MCF-7, together with a good selectivity (SI=121) over noncancerous HEK293 cells. Thus, 3 b was selected as a potential PET tracer to study retinoids in vivo, and the radiosynthesis of [¹⁸ F]3b was successfully developed. Unfortunately, the stability of [¹⁸ F]3b turned out to be insufficient to pursue imaging studies.

Palladium-catalyzed synthesis of 5-amino-1,2,4-oxadiazoles via isocyanide insertion

A convenient and efficient palladium-catalyzed approach has been developed for the synthesis of 5-amino-1,2,4-oxadiazoles from amidoximes and isocyanides. Various 5-amino-1,2,4-oxadiazoles were obtained in moderate to high yields under mild conditions. The key to the success of this strategy involves new C-N bond and C-O bond formation via palladium-catalyzed isocyanide insertion.

Diversity-oriented synthesis and antifungal activities of novel pimprinine derivative bearing a 1,3,4-oxadiazole-5-thioether moiety

Based on the strategy of diversity-oriented synthesis and the structures of natural product pimprinine and streptochlorin, two series of novel pimprinine derivatives containing 1,3,4-oxadiazole-5-thioether moieties were efficiently synthesized under the optimized reaction conditions. Biological assays conducted at Syngenta showed the designed derivatives displayed an altered pattern of biological activity, of which 5h was identified as the most promising compound with strong activity against Pythium dissimile and also a broad antifungal spectrum in primary screening. Further structural optimization of pimprinine and streptochlorin derivatives is well under way, aiming to discover synthetic analogues with improved antifungal activity. Two series of novel pimprinine derivatives containing 1,3,4-oxadiazole-5-thioether moieties were efficiently synthesized through diversity-oriented synthesis strategy under the optimized conditions. Biological assays showed the designed derivatives exhibited potential activity.

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.

Targeting the Sphingolipid System as a Therapeutic Direction for Glioblastoma

Glioblastoma (GBM) is the most commonly diagnosed malignant brain tumor in adults. The prognosis for patients with GBM remains poor and largely unchanged over the last 30 years, due to the limitations of existing therapies. Thus, new therapeutic approaches are desperately required. Sphingolipids are highly enriched in the brain, forming the structural components of cell membranes, and are major lipid constituents of the myelin sheaths of nerve axons, as well as playing critical roles in cell signaling. Indeed, a number of sphingolipids elicit a variety of cellular responses involved in the development and progression of GBM. Here, we discuss the role of sphingolipids in the pathobiology of GBM, and how targeting sphingolipid metabolism has emerged as a promising approach for the treatment of GBM.

Roles of sphingosine-1-phosphate signaling in cancer

The potent pleiotropic lipid mediator sphingosine-1-phosphate (S1P) participates in numerous cellular processes, including angiogenesis and cell survival, proliferation, and migration. It is formed by one of two sphingosine kinases (SphKs), SphK1 and SphK2. These enzymes largely exert their various biological and pathophysiological actions through one of five G protein-coupled receptors (S1PR1–5), with receptor activation setting in motion various signaling cascades. Considerable evidence has been accumulated on S1P signaling and its pathogenic roles in diseases, as well as on novel modulators of S1P signaling, such as SphK inhibitors and S1P agonists and antagonists. S1P and ceramide, composed of sphingosine and a fatty acid, are reciprocal cell fate regulators, and S1P signaling plays essential roles in several diseases, including inflammation, cancer, and autoimmune disorders. Thus, targeting of S1P signaling may be one way to block the pathogenesis and may be a therapeutic target in these conditions. Increasingly strong evidence indicates a role for the S1P signaling pathway in the progression of cancer and its effects. In the present review, we discuss recent progress in our understanding of S1P and its related proteins in cancer progression. Also described is the therapeutic potential of S1P receptors and their downstream signaling cascades as targets for cancer treatment.

Kelch-like protein 5-mediated ubiquitination of lysine 183 promotes proteasomal degradation of sphingosine kinase 1

Sphingosine kinase 1 (SK1) is a signalling enzyme that catalyses the phosphorylation of sphingosine to generate the bioactive lipid sphingosine 1-phosphate (S1P). A number of SK1 inhibitors and chemotherapeutics can induce the degradation of SK1, with the loss of this pro-survival enzyme shown to significantly contribute to the anti-cancer properties of these agents. Here we define the mechanistic basis for this degradation of SK1 in response to SK1 inhibitors, chemotherapeutics, and in natural protein turnover. Using an inducible SK1 expression system that enables the degradation of pre-formed SK1 to be assessed independent of transcriptional or translational effects, we found that SK1 was degraded primarily by the proteasome since several proteasome inhibitors blocked SK1 degradation, while lysosome, cathepsin B or pan caspase inhibitors had no effect. Importantly, we demonstrate that this proteasomal degradation of SK1 was enabled by its ubiquitination at Lys183 that appears facilitated by SK1 inhibitor-induced conformational changes in the structure of SK1 around this residue. Furthermore, using yeast two-hybrid screening, we identified Kelch-like protein 5 (KLHL5) as an important protein adaptor linking SK1 to the cullin 3 (Cul3) ubiquitin ligase complex. Notably, knockdown of KLHL5 or Cul3, use of a cullin inhibitor or a dominant-negative Cul3 all attenuated SK1 degradation. Collectively this data demonstrates the KLHL5/Cul3-based E3 ubiquitin ligase complex is important for regulation of SK1 protein stability via Lys183 ubiquitination, in response to SK1 inhibitors, chemotherapy and for normal SK1 protein turnover.

Use of Acid Ceramidase and Sphingosine Kinase Inhibitors as Antiviral Compounds Against Measles Virus Infection of Lymphocytes in vitro

As structural membrane components and signaling effector molecules sphingolipids influence a plethora of host cell functions, and by doing so also the replication of viruses. Investigating the effects of various inhibitors of sphingolipid metabolism in primary human peripheral blood lymphocytes (PBL) and the human B cell line BJAB we found that not only the sphingosine kinase (SphK) inhibitor SKI-II, but also the acid ceramidase inhibitor ceranib-2 efficiently inhibited measles virus (MV) replication. Virus uptake into the target cells was not grossly altered by the two inhibitors, while titers of newly synthesized MV were reduced by approximately 1 log (90%) in PBL and 70-80% in BJAB cells. Lipidomic analyses revealed that in PBL SKI-II led to increased ceramide levels, whereas in BJAB cells ceranib-2 increased ceramides. SKI-II treatment decreased sphingosine-1-phosphate (S1P) levels in PBL and BJAB cells. Furthermore, we found that MV infection of lymphocytes induced a transient (0.5-6 h) increase in S1P, which was prevented by SKI-II. Investigating the effect of the inhibitors on the metabolic (mTORC1) activity we found that ceranib-2 reduced the phosphorylation of p70 S6K in PBL, and that both inhibitors, ceranib-2 and SKI-II, reduced the phosphorylation of p70 S6K in BJAB cells. As mTORC1 activity is required for efficient MV replication, this effect of the inhibitors is one possible antiviral mechanism. In addition, reduced intracellular S1P levels affect a number of signaling pathways and functions including Hsp90 activity, which was reported to be required for MV replication. Accordingly, we found that pharmacological inhibition of Hsp90 with the inhibitor 17-AAG strongly impaired MV replication in primary PBL. Thus, our data suggest that treatment of lymphocytes with both, acid ceramidase and SphK inhibitors, impair MV replication by affecting a number of cellular activities including mTORC1 and Hsp90, which alter the metabolic state of the cells causing a hostile environment for the virus.

Approaches for probing and evaluating mammalian sphingolipid metabolism

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

Interdiction of Sphingolipid Metabolism Revisited: Focus on Prostate Cancer

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

Current Parallel Solid-Phase Synthesis of Drug-like Oxadiazole and Thiadiazole Derivatives for Combinatorial Chemistry

Solid-phase organic synthesis is a powerful tool in the synthesis of small organic molecules and building of libraries of compounds for drug discovery. Heterocyclic compounds are important components of the drug discovery field as well and serve as a core for hundreds of marketed drugs. In particular, oxadiazole and thiadiazole cores are compounds of great interest due to their comprehensive biological activities and structural features. Therefore, a plethora of oxadiazole and thiadiazole synthesis methodologies have been reported to date, including solution and solid-phase synthesis methodologies. In this review, we concentrate on and summarize solid-phase synthetic approaches of the oxadiazole and thiadiazole derivatives.

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.

An oncogenic role for sphingosine kinase 2

While both human sphingosine kinases (SK1 and SK2) catalyze the generation of the pleiotropic signaling lipid sphingosine 1-phosphate, these enzymes appear to be functionally distinct. SK1 has well described roles in promoting cell survival, proliferation and neoplastic transformation. The roles of SK2, and its contribution to cancer, however, are much less clear. Some studies have suggested an anti-proliferative/pro-apoptotic function for SK2, while others indicate it has a pro-survival role and its inhibition can have anti-cancer effects. Our analysis of gene expression data revealed that SK2 is upregulated in many human cancers, but only to a small extent (up to 2.5-fold over normal tissue). Based on these findings, we examined the effect of different levels of cellular SK2 and showed that high-level overexpression reduced cell proliferation and survival, and increased cellular ceramide levels. In contrast, however, low-level SK2 overexpression promoted cell survival and proliferation, and induced neoplastic transformation in vivo. These findings coincided with decreased nuclear localization and increased plasma membrane localization of SK2, as well as increases in extracellular S1P formation. Hence, we have shown for the first time that SK2 can have a direct role in promoting oncogenesis, supporting the use of SK2-specific inhibitors as anti-cancer agents.

Sphingosine kinase inhibitors: A patent review

Sphingosine kinases (SphKs) catalyze the conversion of the sphingosine to the promitogenic/migratory product, sphingosine-1-phosphate (S1P). SphK/S1P pathway has been linked to the progression of cancer and various other diseases including allergic inflammatory disease, cardiovascular diseases, rejection after transplantation, the central nervous system, and virus infections. Therefore, SphKs represent potential new targets for developing novel therapeutics for these diseases. The history and development of SphK inhibitors are discussed, summarizing SphK inhibitors by their structures, and describing some applications of SphK inhibitors. We concluded: i) initial SphK inhibitors based on sphingosine have low specificity with several important off-targets. Identification the off-targets that would work synergistically with SphKs, and developing compounds that target the unique C4 domain of SphKs should be the focus of future studies. ii) The modifications of SphK inhibitors, which are devoted to increasing the selectivity to one of the two isoforms, now focus on the alkyl length, the spacer between the head and linker rings, and the insertion and the position of lipidic group in tail region. iii) SphK/S1P signaling pathway holds therapeutic values for many diseases. To find the exact function of each isoform of SphKs increasing the number of SphK inhibitor clinical trials is necessary.

Mammalian sphingosine kinase (SphK) isoenzymes and isoform expression: challenges for SphK as an oncotarget

The various sphingosine kinase (SphK) isoenzymes (isozymes) and isoforms, key players in normal cellular physiology, are strongly implicated in cancer and other diseases. Mutations in SphKs, that may justify abnormal physiological function, have not been recorded. Nonetheless, there is a large and growing body of evidence demonstrating the contribution of gain or loss of function and the imbalance in the SphK/S1P rheostat to a plethora of pathological conditions including cancer, diabetes and inflammatory diseases. SphK is expressed as two isozymes SphK1 and SphK2, transcribed from genes located on different chromosomes and both isozymes catalyze the phosphorylation of sphingosine to S1P. Expression of each SphK isozyme produces alternately spliced isoforms. In recent years the importance of the contribution of SpK1 expression to treatment resistance in cancer has been highlighted and, additionally, differences in treatment outcome appear to also be dependent upon SphK isoform expression. This review focuses on an exciting emerging area of research involving SphKs functions, expression and subcellular localization, highlighting the complexity of targeting SphK in cancer and also comorbid diseases. This review also covers the SphK isoenzymes and isoforms from a historical perspective, from their first discovery in murine species and then in humans, their role(s) in normal cellular function and in disease processes, to advancement of SphK as an oncotarget.

Transforming Sphingosine Kinase 1 Inhibitors into Dual and Sphingosine Kinase 2 Selective Inhibitors: Design, Synthesis, and in Vivo Activity

Sphingosine 1-phosphate (S1P) is a pleiotropic signaling molecule that interacts with its five G-protein coupled receptors (S1P1-5) to regulate cell growth and survival and has been implicated in a variety of diseases including cancer and sickle cell disease. As the key mediators in the synthesis of S1P, sphingosine kinase (SphK) isoforms 1 and 2 have attracted attention as viable targets for pharmaceutical inhibition. In this article, we describe the design, synthesis, and biological evaluation of aminothiazole-based guanidine inhibitors of SphK. Surprisingly, combining features of reported SphK1 inhibitors generated SphK1/2 dual inhibitor 20l (SLC4011540) (hSphK1 Ki = 120 nM, hSphK2 Ki = 90 nM) and SphK2 inhibitor 20dd (SLC4101431) (Ki = 90 nM, 100-fold SphK2 selectivity). These compounds effectively decrease S1P levels in vitro. In vivo administration of 20dd validated that inhibition of SphK2 increases blood S1P levels.

Thiadiazole inhibitors: a patent review

INTRODUCTION

Four isomeric structures of thiadiazole motifs have outstanding pharmacological inhibitory applications are reported in this review. Thiadiazole nucleus is present in several biologically active natural products and commercial drugs. Most of thiadiazoles reported herein are emphasized to have broad spectrum of medicinal activities. Areas covered: This review represents the recent inhibitory activities of thiadiazole isomeric scaffolds and their broad-spectrum biological applications published as full texts during 2010-2016 as well as the patents published during 2005-2016. The inhibition areas covered included anti-inflammatory, antimicrobial, antitumor, antioxidant, antitubercular, antiviral, antileishmanial, anticonvulsant, herbicidal and algicidal activities in addition to enzymes, human platelet aggregation and neuroprotective inhibitors. Expert opinion: This survey revealed very interesting data about the applications of thiadiazoles, where some synthetic or natural thiadiazole derivatives were components of drugs available in the market. Many thiadiazole derivatives can be considered as lead compounds for drug synthesis. The most inhibitory active 1,3,4-thiadiazole compounds are those incorporating secondary alkyl(aryl)amido- and/or benzylthio(mercapto) groups at positions 2 and 5. Several thiadiazole derivatives demonstrated higher antibacterial, antitumor and antiviral activities than the standard drugs. Some thiadiazole derivatives exhibited high selective enzymes inhibitory activities based on the electronic properties of the substituents at positions 2 or 5.

A revisit to the Gattermann reaction: interesting synthesis of nitrogen heterocyclic aromatic halides and their fluorescence properties

The Gattermann reaction and an electrophilic substitution reaction, which were conducted in a one-pot reaction, are reported, and four aromatic dihalides of similar structure were obtained. 2-Chloro-5-(3-chloro-4-methoxy-phenyl)-1,3,4-thiadiazole was applied as a highly efficient fluorescence sensor for the detection of TNP.