ABC294640, a sphingosine kinase 2 inhibitor, enhances the antitumor effects of TRAIL in non-small cell lung cancer

Loss of sphingosine kinase 2 protects against cisplatin-induced kidney injury

Cisplatin is an established chemotherapeutic drug for treatment of solid-organ cancers and is the primary drug used in the treatment of head and neck cancer; however, cisplatin-induced nephrotoxicity largely limits its clinical use. Inhibition of sphingosine kinase 2 (SphK2) has been demonstrated to alleviate various kidney diseases. Therefore, we hypothesized that inhibition of SphK2 could also protect against cisplatin-induced nephrotoxicity. Results from the present study showed that the SphK2 inhibitor ABC294640 or knockdown of SphK2 by siRNA blocked the cisplatin-induced increase of cellular injury markers (neutrophil gelatinase-associated lipocalin, kidney injury molecule-1, and cleaved caspase-3) by Western blot analysis in HK-2 cells, a human renal tubular cell line. In addition, SphK2 inhibition blocked cisplatin-induced activation of NF-κB by Western blot analysis and immunostaining analysis. Furthermore, SphK2 inhibition suppressed cisplatin-induced increases of proinflammatory markers (NLR family pyrin domain containing 3, interleukin-1β, and interleukin-6). Genetic deletion of the SphK2 gene in mice further confirmed that inhibition of SphK2 protected against cisplatin-induced kidney damage in vivo. Compared with wild-type mice, SphK2 knockout mice exhibited less renal dysfunction and reduced promotion of kidney injury markers, inflammatory factors, tubular morphology damage, and fibrotic staining. At the same time, the SphK2 inhibitor ABC294640 failed to interfere with the activity of cisplatin or radiation in two cell culture models of head and neck cancer. It is concluded that inhibition of Sphk2 protects against cisplatin-induced kidney injury. SphK2 may be used as a potential therapeutic target for the prevention or treatment of cisplatin-induced kidney injury.NEW & NOTEWORTHY The present study provides new findings that sphingosine kinase 2 (SphK2) is highly expressed in renal tubules, cisplatin treatment increases the expression of SphK2 in proximal tubular cells and kidneys, and inhibition of SphK2 alleviates cisplatin-induced kidney injury by suppressing the activation of NF-κB, production of inflammatory factors, and apoptosis. SphK2 may serve as a potential therapeutic target for the prevention or treatment of cisplatin-induced nephrotoxicity.

Targeting sphingosine kinase 1/2 by a novel dual inhibitor SKI-349 suppresses non-small cell lung cancer cell growth

Sphingosine kinase 1 (SphK1) and sphingosine kinase (SphK2) are both important therapeutic targets of non-small cell lung cancer (NSCLC). SKI-349 is a novel, highly efficient and small molecular SphK1/2 dual inhibitor. Here in primary human NSCLC cells and immortalized cell lines, SKI-349 potently inhibited cell proliferation, cell cycle progression, migration and viability. The dual inhibitor induced mitochondrial depolarization and apoptosis activation in NSCLC cells, but it was non-cytotoxic to human lung epithelial cells. SKI-349 inhibited SphK activity and induced ceramide accumulation in primary NSCLC cells, without affecting SphK1/2 expression. SKI-349-induced NSCLC cell death was attenuated by sphingosine-1-phosphate and by the SphK activator K6PC-5, but was potentiated by the short-chain ceramide C6. Moreover, SKI-349 induced Akt-mTOR inactivation, JNK activation, and oxidative injury in primary NSCLC cells. In addition, SKI-349 decreased bromodomain-containing protein 4 (BRD4) expression and downregulated BRD4-dependent genes (Myc, cyclin D1 and Klf4) in primary NSCLC cells. At last, SKI-349 (10 mg/kg) administration inhibited NSCLC xenograft growth in nude mice. Akt-mTOR inhibition, JNK activation, oxidative injury and BRD4 downregulation were detected in SKI-349-treated NSCLC xenograft tissues. Taken together, targeting SphK1/2 by SKI-349 potently inhibits NSCLC cell growth in vitro and in vivo.

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.

Sphingolipid Metabolism and Signaling in Lung Cancer: A Potential Therapeutic Target

Sphingolipids are important bioactive lipids that not only play an important role in maintaining the barrier function and fluidity of cell membranes but also regulate multiple processes in cancer development by controlling multiple signaling pathways in the signal transduction network. Dysregulation of sphingolipid metabolism is thought to be one of the most important dysregulated pathways in lung cancer, the most prevalent type of cancer in terms of incidence and mortality worldwide. This article focuses on lung cancer, reviewing the important lipids in sphingolipid metabolism and the related enzymes in relation to lung cancer progression and their effects on the tumor microenvironment and discussing their roles in the diagnosis and treatment of lung cancer.

Nephrotoxicity in cancer treatment: An update

It has been estimated that nearly 80% of anticancer drug-treated patients receive potentially nephrotoxic drugs, while the kidneys play a central role in the excretion of anticancer drugs. Nephrotoxicity has long been a serious complication that hampers the effectiveness of cancer treatment and continues to influence both mortality and length of hospitalization among cancer patients exposed to either conventional cytotoxic agents or targeted therapies. Kidney injury arising from anticancer drugs tends to be associated with preexisting comorbidities, advanced cancer stage, and the use of concomitant non-chemotherapeutic nephrotoxic drugs. Despite the prevalence and impact of kidney injury on therapeutic outcomes, the field is sorely lacking in an understanding of the mechanisms driving cancer drug-induced renal pathophysiology, resulting in quite limited and largely ineffective management of anticancer drug-induced nephrotoxicity. Consequently, there is a clear imperative for understanding the basis for nephrotoxic manifestations of anticancer agents for the successful management of kidney injury by these drugs. This article provides an overview of current preclinical research on the nephrotoxicity of cancer treatments and highlights prospective approaches to mitigate cancer therapy-related renal toxicity.

Supramolecular Self-Assembly Mediated by Multiple Hydrogen Bonds and the Importance of C-S···N Chalcogen Bonds in N'-(Adamantan-2-ylidene)hydrazide Derivatives

The present article comprehensively examines six N′-(adamantan-2-ylidene)hydrazide derivatives using the Hirshfeld surface analysis, PIXEL energy for molecular dimers, lattice energies for crystal packing, and topological analysis for intramolecular and intermolecular interactions. The crystal structure of one of the N′-(adamantan-2-ylidene)hydrazide derivatives, namely, N′-(adamantan-2-ylidene)-5-bromothiophene-2-carbohydrazide 1, C₁₅H₁₇N₂OSBr, has been determined and analyzed in detail along with five closely related structures. The molecular conformation of 1 is locked by an intramolecular C–S···N chalcogen bond as found in one of its closely related structure, namely, N′-(adamantan-2-ylidene)thiophene-2-carbohydrazide. Furthermore, a detailed potential energy surface scan analysis has been performed to highlight the importance of a chalcogen bond. Two of these compounds possess syn-orientation for amide units, whereas the corresponding moiety exhibits anti-conformations in the remaining four structures. The Hirshfeld surface and its decomposed fingerprint plots provide a qualitative picture of acyl substituent effects on the intermolecular interactions toward crystal packing of these six structures. Intermolecular interaction energies for dimers observed in these structures calculated by density functional theory (B97D3/def2-TZVP) and PIXEL (MP2/6-31G**) methods are comparable. This study also identifies that multiple hydrogen bonds, including N/C–H···O/N and C–H···π interactions, are collectively responsible for a self-assembled synthon. The nature and strength of these interactions have been studied using atoms in molecule topological analysis. The in vitro antiproliferative activity of compound 1 was assessed against five human tumor cell lines and showed marked antiproliferative activity.

Targeting Sphingolipids for Cancer Therapy

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

Comparative MD Study of Inhibitory Activity of Opaganib and Adamantane-Isothiourea Derivatives toward COVID-19 Main Protease Mpro

In this study, the inhibitory potency of four adamantly- isothiourea derivatives (compounds 1 [4-bromobenzyl (Z)-N'-(adamantan-1-yl)-4-phenylpiperazine-1-carbothioimidate], 2 [3,5-bis(trifluoromethyl)benzyl (Z)-N'-(adamantan-1-yl)-4-phenylpiperazine-1-carbothioimidate], 3 [4-bromobenzyl (Z)-N-(adamantan-1-yl)morpholine-4-carbothioimidate] and 4 [3,5-bis(trifluoromethyl)benzyl (Z)-N-(adamantan-1-yl)morpholine-4-carbothioimidate]) was evaluated against SARS-CoV-2 targeted proteins. The investigated compounds 1-4 possess a similar structure to opaganib, which is used in studies like a potential drug for COVID-19 treatment. Since examined adamantly-isothiourea derivatives (1-4) shown broad-spectrum of antibacterial activity and significant in vitro cytotoxic effects against five human tumor cell lines and shown similarity in structure with opaganib, it was of interest to study their inhibitory potency toward some SARS-CoV-2 proteins such as SARS-CoV-2 main protease Mpro and mutation of SARS-CoV-2 Spike (S) Protein D614G. The inhibitory potency of studied compounds is examined using molecular docking and molecular dynamic simulations. The results of molecular docking simulations indicate compound 1 as the most prominent candidate of inhibition of SARS-CoV-2 main protease Mpro (▵Gbind=11.24 kcal/mol), while almost the same inhibition potency of all studied compounds is exhibited toward D614G. Regarding the results obtained by molecular dynamic simulations, compounds 1 and 4 possess similar inhibitory potency toward SARS-CoV-2 main protease Mpro as opaganib (▵Gbind ≈ 40 kcal/mol).

Harnessing TRAIL-Induced Apoptosis Pathway for Cancer Immunotherapy and Associated Challenges

The immune cytokine tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) has attracted rapidly evolving attention as a cancer treatment modality because of its competence to selectively eliminate tumor cells without instigating toxicity in vivo. TRAIL has revealed encouraging promise in preclinical reports in animal models as a cancer treatment option; however, the foremost constraint of the TRAIL therapy is the advancement of TRAIL resistance through a myriad of mechanisms in tumor cells. Investigations have documented that improvement of the expression of anti-apoptotic proteins and survival or proliferation involved signaling pathways concurrently suppressing the expression of pro-apoptotic proteins along with down-regulation of expression of TRAILR1 and TRAILR2, also known as death receptor 4 and 5 (DR4/5) are reliable for tumor cells resistance to TRAIL. Therefore, it seems that the development of a therapeutic approach for overcoming TRAIL resistance is of paramount importance. Studies currently have shown that combined treatment with anti-tumor agents, ranging from synthetic agents to natural products, and TRAIL could result in induction of apoptosis in TRAIL-resistant cells. Also, human mesenchymal stem/stromal cells (MSCs) engineered to generate and deliver TRAIL can provide both targeted and continued delivery of this apoptosis-inducing cytokine. Similarly, nanoparticle (NPs)-based TRAIL delivery offers novel platforms to defeat barricades to TRAIL therapeutic delivery. In the current review, we will focus on underlying mechanisms contributed to inducing resistance to TRAIL in tumor cells, and also discuss recent findings concerning the therapeutic efficacy of combined treatment of TRAIL with other antitumor compounds, and also TRAIL-delivery using human MSCs and NPs to overcome tumor cells resistance to TRAIL.

Ceramide Metabolism Enzymes-Therapeutic Targets against Cancer

Sphingolipids are both structural molecules that are essential for cell architecture and second messengers that are involved in numerous cell functions. Ceramide is the central hub of sphingolipid metabolism. In addition to being the precursor of complex sphingolipids, ceramides induce cell cycle arrest and promote cell death and inflammation. At least some of the enzymes involved in the regulation of sphingolipid metabolism are altered in carcinogenesis, and some are targets for anticancer drugs. A number of scientific reports have shown how alterations in sphingolipid pools can affect cell proliferation, survival and migration. Determination of sphingolipid levels and the regulation of the enzymes that are implicated in their metabolism is a key factor for developing novel therapeutic strategies or improving conventional therapies. The present review highlights the importance of bioactive sphingolipids and their regulatory enzymes as targets for therapeutic interventions with especial emphasis in carcinogenesis and cancer dissemination.

Revisiting the role of TRAIL/TRAIL-R in cancer biology and therapy

TNF-related apoptosis-inducing ligand (TRAIL), a member of the TNF superfamily, can induce apoptosis in cancer cells, sparing normal cells when bound to its associated death receptors (DR4/DR5). This unique mechanism makes TRAIL a potential anticancer therapeutic agent. However, clinical trials of recombinant TRAIL protein and TRAIL receptor agonist monoclonal antibodies have shown disappointing results due to its short half-life, poor pharmacokinetics and the resistance of the cancer cells. This review summarizes TRAIL-induced apoptotic and survival pathways as well as mechanisms leading to apoptotic resistance. Recent development of methods to overcome cancer cell resistance to TRAIL-induced apoptosis, such as protein modification, combination therapy and TRAIL-based gene therapy, appear promising. We also discuss the challenges and opportunities in the development of TRAIL-based therapies for the treatment of human cancers.

Sphingosine kinase 2 inhibitor ABC294640 suppresses neuronal excitability and inhibits multiple endogenously and exogenously expressed voltage-gated ion channels in cultured cells

Sphingolipids regulate multiple cellular processes, including proliferation, autophagy, and apoptosis. Sphingosine kinases, the key enzymes in the metabolism of sphingolipids, are overexpressed in many cancers, making them important targets for the development of antitumor drugs. ABC294640 is a selective sphingosine kinase 2 (SK2) inhibitor that shows good antitumor activity in vitro. One phase I clinical study of ABC294640 reported that ABC294640 caused a variety of neurological disorders. The mechanism of these phenomena, however, remains unclear. In the present study, we used in vitro cell experiments to test the effects of ABC294640 on the nervous system. We found that ABC294640 suppressed the firing of action potentials in cultured hippocampal neurons from neonatal mice and inhibited endogenous sodium, potassium, and calcium currents in both cultured neurons and SH-SY5Y cells. In addition, we tested four types of human voltage-gated potassium channels transiently expressed in HEK293T cells. All were inhibited by ABC294640, of which K_V4.2 and K_V1.4 were more sensitive than BK and K2P2.1. The effect of ABC294640 on ion channels was different from another SK2 inhibitor K145 and was not affected by S1P. The fast onset and recovery of the inhibition indicated that ABC294640 was likely to inhibit ion channels by acting directly on channel proteins, rather than by inhibiting SK2. These results revealed the mechanism by which ABC294640 interferes with the nervous system. To develop future antitumor drugs, researchers should modify the structure of ABC294640 to avoid its effects on ion channels or should develop compounds that target SK2 or downstream molecules.

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.

Identification of prognostic biomarkers and drug target prediction for colon cancer according to a competitive endogenous RNA network

Colorectal cancer is one of the commoner digestive tract malignant tumor types, and its incidence and mortality rate are high. Accumulating evidence indicates that long‑chain non‑coding RNAs (lncRNAs) and protein‑coding RNAs interact with each other by competing with the same micro(mi)RNA response element (MREs) and serve an important role in the regulation of gene expression in a variety of tumor types. However, the regulatory mechanism and prognostic role of lncRNA‑mediated competing endogenous (ce)RNA networks in colon cancer have yet to be elucidated. The expression profiles of mRNAs, lncRNAs and miRNAs from 471 colon cancer and 41 paracancerous tissue samples were downloaded from The Cancer Genome Atlas database. A lncRNA‑miRNA‑mRNA ceRNA network in colon cancer was constructed and comprised 17 hub lncRNAs, 87 hub miRNA and 144 hub mRNAs. The topological properties of the network were analyzed, and the random walk algorithm was used to identify the nodes significantly associated with colon cancer. Survival analysis using the UALCAN database indicated that 2/17 lncRNAs identified [metastasis‑associated lung adenocarcinoma transcript (MALAT1) and maternally expressed gene 3 (MEG3)] and 5/144 mRNAs [FES upstream region (FURIN), nuclear factor of activated T‑cells 5 (NFAT5), RNA Binding Motif Protein 12B (RBM12B), Ras related GTP binding A (RRAGA) and WD repeat domain phosphoinositide‑interacting protein 2 (WIPI2)] were significantly associated with the overall survival of patients with colon cancer, and may therefore be used as potential prognostic biomarkers of colon cancer. According to extracted lncRNA‑miRNA‑mRNA interaction pairs, the GSE26334 dataset was used to confirm that the lncRNA MALAT1/miR‑129‑5p/NFAT5 axis may represent a novel regulatory mechanism concerning the progression of colon cancer. The clusterProfiler package was used to analyze Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways in colon cancer. Finally, drugs that significantly interact with the core genes identified in colon cancer were predicted using a hypergeometric test. Of these, fostamatinib was identified to be a targeted drug for colon cancer therapy. The present findings provide a novel perspective for improved understanding of the lncRNA‑associated ceRNA network and may facilitate the development of novel targeted therapeutics in colon cancer.

Validated LC-MS/MS method of Sphingosine 1-phosphate quantification in human serum for evaluation of response to radiotherapy in lung cancer

Background

Sphingosine 1‐phosphate (S1P), a bioactive lipid, has been shown to mediate cancer processes. Therefore, accurate qualitative and quantitative determination is essential. The current assay method is still cumbersome to be of practical use worldwide and the aim of this study was therefore to develop a fast, accurate, precise and efficient LC‐MS/MS method for targeted analyses of S1P in serum samples.

Methods

Liquid chromatography‐tandem mass spectrometry (LC‐MS/MS) is an established method used for monitoring and analyzing S1P levels in serum. We determined the level of serum S1P in 256 patients with lung cancer and 36 healthy donors, and used Spearman';s rank correlation analysis to evaluate the difference in serum S1P levels between radiotherapy and nonradiotherapy patients.

Results

Standard curves were linear over ranges of 25–600 ng/mL for S1P with correlation coefficient (r²) greater than 0.9996. The lower limit of quantifications (LLOQs) was 25 ng/mL. The intra‐ and interbatch precisions and accuracy was less than 10% for S1P. The recoveries of the method were found to be 80%–98%. Serum S1P levels in healthy donors were different from those in patients (P < 0.001). Of 256 lung cancer patients, 124 (48.4%) received radiotherapy and were identified to have concomitant low serum S1P levels (222.13 ± 48.63), whereas 132 (51.6%) who had not received radiotherapy were identified to have high levels (315.16 ± 51.06). The serum S1P levels were therefore associated with radiotherapy (Spearman's Rho = −0.653, P < 0.001).

Conclusions

Our results indicated that this new LC‐MS/MS method is rapid, sensitive, specific and reliable for the quantification of S1P levels in serum samples. The level of S1P in serum samples of patients with lung cancer who received radiotherapy was significantly lower than that in patients who did not receive radiotherapy.

Key points

An improved method was established to quantify S1P levels in human serum by LC‐MS/MS, which enabled the change in serum S1P levels in lung cancer patients to be monitored, in combination with radiotherapy, and their clinical significance to be analyzed.

Novel meriolin derivatives as rapid apoptosis inducers

3-(Hetero)aryl substituted 7-azaindoles possessing multikinase inhibitor activity are readily accessed in a one-pot Masuda borylation-Suzuki coupling sequence. Several promising derivatives were identified as apoptosis inducers and, emphasizing the multikinase inhibition potential, as sphingosine kinase 2 inhibitors. Our measurements provide additional insights into the structure-activity relationship of meriolin derivatives, suggesting derivatives bearing a pyridine moiety with amino groups in 2-position as most active anticancer compounds and thus as highly promising candidates for future in vivo studies.

Developing TRAIL/TRAIL death receptor-based cancer therapies

Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) is a member of the TNF superfamily that can initiate the apoptosis pathway by binding to its associated death receptors DR4 and DR5. The activation of the TRAIL pathway in inducing tumor-selective apoptosis leads to the development of TRAIL-based cancer therapies, which include recombinant forms of TRAIL, TRAIL receptor agonists, and other therapeutic agents. Importantly, TRAIL, DR4, and DR5 can all be induced by synthetic and natural agents that activate the TRAIL apoptosis pathway in cancer cells. Thus, understanding the regulation of the TRAIL apoptosis pathway can aid in the development of TRAIL-based therapies for the treatment of human cancer.

Antitumor Effect of Periplocin in TRAIL-Resistant gastric cancer cells via upregulation of death receptor through activating ERK1/2-EGR1 pathway

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), a member of the tumor necrosis factor family, induces apoptosis in a variety of cancer cells. However, gastric cancer (GC) cells are insensitive to TRAIL usually. In the previous study, we showed that Periplocin could induce apoptosis in GC cells via the activation of ERK1/2-EGR1 pathway. In the present study, we have shown that the combination of Periplocin and TRAIL had a greater inhibitory effect on gastric cancer cell viability in vitro and in vivo than Periplocin or TRAIL alone. Through upregulating the expression of DR4 and DR5 at transcriptional and protein levels, Periplocin enhanced the sensitivity of gastric cancer cells to TRAIL. Furthermore, enhanced activity of ERK1/2-EGR1 pathway was responsible for upregulating of DR4 and DR5 uponPeriplocin treatment, subsequently reducing the expression of Mcl-1 and Bcl2 and activating Bid and caspase-3/8. Collectively, these data implied that Periplocin might act as a sensitizer of TRAIL and could be a potential strategy for the treatment of GC.

Targeting sphingosine kinase 2 suppresses cell growth and synergizes with BCL2/BCL-XL inhibitors through NOXA-mediated MCL1 degradation in cholangiocarcinoma

Sphingosine kinase 2 (SPHK2) is a key factor within sphingolipid metabolism, responsible for the conversion of pro-apoptotic sphingosine to the pro-survival sphingosine-1-phosphate. We have previously shown that ABC294640, a first-in-class SPHK2 inhibitor, inhibits growth of cholangiocarcinoma cells. In a Phase I study of ABC294640 in tumors, the best response was achieved in a cholangiocarcinoma patient. These data suggest SPHK2 as a novel therapeutic target of cholangiocarcinoma. However, the antitumor mechanism of ABC294640 in cholangiocarcinoma remains not clear. In the current study, we found that ABC294640 upregulated expression of pro-apoptotic NOXA. In cholangiocarcinoma patients, high NOXA mRNA expression was associated with better overall survival. Also, SPHK2 mRNA expression was negatively correlated with NOXA mRNA expression. NOXA is known to degrade MCL1, an anti-apoptotic BCL2 protein. We showed that ABC294640 directed MCL1 for proteasome degradation. Knockdown of NOXA prevented ABC294640-induced MCL1 degradation and apoptosis. In addition, ABC294640 had a synergistic effect with BCL2/BCL-XL inhibitors ABT-263 and Obatoclax in inhibiting cell growth. Combined treatment with ABC294640 and BCL2/BCL-XL inhibitors induced potent apoptosis. Silencing of MCL1 also potentiated ABT-263-induced cytotoxicity. Furthermore, we found that both SPHK2 and MCL1 protein expression were significantly higher in cholangiocarcinoma than that in nontumoral bile ducts. SPHK2 expression correlated significantly with MCL1 expression. Our study reveals that ABC294640 inhibits cholangiocarcinoma cell growth and sensitizes the antitumor effect of BCL2/BCL-XL inhibitors through NOXA-mediated MCL1 degradation. Combinations of ABC294640 with BCL2/BCL-XL inhibitors may provide novel strategies for the treatment of cholangiocarcinoma.

New insights into the roles and regulation of SphK2 as a therapeutic target in cancer chemoresistance

Chemoresistance is a complicated process developed by most cancers and accounts for the majority of relapse and metastasis in cancer. The main mechanisms of chemoresistance phenotype include increased expression and/or activated drug efflux pumps, altered DNA repair, altered metabolism of therapeutics as well as impaired apoptotic signaling pathways. Aberrant sphingolipid signaling has also recently received considerable attention in chemoresistance. Sphingolipid metabolites regulate main biological processes such as apoptosis, cell survival, proliferation, and differentiation. Two sphingosine kinases, SphK1 and SphK2, convert sphingosine to sphingosine-1-phosphate, an antiapoptotic bioactive lipid mediator. Numerous evidence has revealed the involvement of activated SphK1 in tumorigenesis and resistance, however, contradictory results have been found for the role of SphK2 in these functions. In some studies, overexpression of SphK2 suppressed cell growth and induced apoptosis. In contrast, some others have shown cell proliferation and tumor promotion effect for SphK2. Our understanding of the role of SphK2 in cancer does not have a sufficient integrity. The main focus of this review will be on the re-evaluation of the role of SphK2 in cell death and chemoresistance in light of our new understanding of molecular targeted therapy. We will also highlight the connections between SphK2 and the DNA damage response. Finally, we will provide our insight into the regulatory mechanisms of SphKs by two main categories, micro and long, noncoding RNAs as the novel players of cancer chemoresistance.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

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.

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.

The sphingosine kinase 2 inhibitor ABC294640 displays anti-non-small cell lung cancer activities in vitro and in vivo

Non-small cell lung cancer (NSCLC) accounts for about 85-90% of lung cancer cases, and is the number one killer among cancers in the United States. The majorities of lung cancer patients do not respond well to conventional chemo- and/or radio-therapeutic regimens, and have a dismal 5-year survival rate of ∼15%. The recent introduction of targeted therapy and immunotherapy gives new hopes to NSCLC patients, but even with these agents, not all patients respond, and responses are rarely complete. Thus, there is still an urgent need to identify new therapeutic targets in NSCLC and develop novel anti-cancer agents. Sphingosine kinase 2 (SphK2) is one of the key enzymes in sphingolipid metabolism. SphK2 expression predicts poor survival in NSCLC patients, and is associated with Gefitinib-resistance. In this study, the anti-NSCLC activities of ABC294640, the only first-in-class orally available inhibitor of SphK2, were explored. The results obtained indicate that ABC294640 treatment causes significant NSCLC cell apoptosis, cell cycle arrest and suppression of tumor growth in vitro and in vivo. Moreover, lipidomics analyses revealed the complete signature of ceramide and dihydro(dh)-ceramide species in the NSCLC cell-lines with or without ABC294640 treatment. These findings indicate that sphingolipid metabolism targeted therapy may be developed as a promising strategy against NSCLC.

The sphingosine kinase 2 inhibitor ABC294640 inhibits cervical carcinoma cell growth

ABC294640 is a specific sphingosine kinase 2 (SphK2) inhibitor. The anti-cervical carcinoma activity by ABC294640 was tested in this study. ABC294640 inhibited in vitro growth of the established (C33A and HeLa lines) and primary human cervical carcinoma cells. The SphK2 inhibitor also induced G1-S arrest and apoptosis in cervical carcinoma cells. It was yet non-cytotoxic to SphK2-low human cervical epithelial cells. ABC294640 inhibited SphK activation, causing sphingosine-1-phosphate depletion, signal transducer and activator of transcription 3 in-activation and ceramide production. Bcl-2 is a key resistance factor of ABC294640. Pharmacological Bcl-2 inhibition or Bcl-2 shRNA potentiated ABC294640-induced C33A cell growth inhibition and apoptosis. On the other hand, exogenous over-expression of Bcl-2 attenuated ABC294640's cytotoxicity against C33A cells. In vivo, ABC294640 administration inhibited C33A xenograft tumor growth in mice. Co-administration of the Bcl-2 inhibitor GDC-0199 further potentiated ABC294640's anti-tumor activity. Together, we suggest that ABC294640 might have translational value for the treatment of human cervical carcinoma.

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.

SphK2 over-expression promotes osteosarcoma cell growth

It is needed to explore novel biological markers for early diagnosis and treatment of human osteosarcoma. Sphingosine kinase 2 (SphK2) expression and potential functions in osteosarcoma were studied. We demonstrate that SphK2 is over-expressed in multiple human osteosarcoma tissues and established human osteosarcoma cell lines. Silence of SphK2 by targeted-shRNAs inhibited osteosarcoma cell growth, and induced cell apoptosis. On the other hand, exogenous over-expression of SphK2 could further promote osteosarcoma cell growth. Notably, microRNA-19a-3p ("miR-19a-3p") targets the 3' UTR (untranslated region) of SphK2 mRNA. Remarkably, forced-expression of miR-19a-3p silenced SphK2 and inhibited osteosarcoma cell growth. In vivo, SphK2 silence, by targeted-shRNA or miR-19a-3p, inhibited U2OS tumor growth in nude mice. These results suggest that SphK2 could be a novel and key oncotarget protein for OS cell progression.

AntagomiR-613 protects neuronal cells from oxygen glucose deprivation/re-oxygenation via increasing SphK2 expression

Oxygen glucose deprivation (OGD)/re-oxygenation (OGDR) causes damages to neuronal cells. Sphingosine kinase 2 (SphK2) expression could exert neuroprotective functions. Here, we aim to induce SphK2 expression via inhibiting the anti-SphK2 microRNA: microRNA-613 ("miR-613"). In both SH-SY5Y neuronal cells and primary murine hippocampal neurons, transfection of the miR-613's specific inhibitor, antagomiR-613 ("antamiR-613"), induced miR-613 depletion and SphK2 expression. Reversely, forced over-expression of miR-613 caused SphK2 downregulation in SH-SY5Y cells. OGDR-induced cytotoxicity in neuronal cells was largely attenuated by antamiR-613. SphK2 is required for antamiR-613-induced actions in neuronal cells. SphK2 knockdown (by targeted-shRNAs) or inhibition (by its inhibitor ABC294640) almost completely abolished antamiR-613-mediated neuroprotection against OGDR. Further studies showed that OGDR-induced reactive oxygen species (ROS) production, lipid peroxidation, and DNA damages in SH-SY5Y cells were largely attenuated by antamiR-613, but were intensified by miR-613 expression. Taken together, we conclude that antamiR-613 protects neuronal cells from OGDR probably via inducing SphK2 expression.

SKI-178: A Multitargeted Inhibitor of Sphingosine Kinase and Microtubule Dynamics Demonstrating Therapeutic Efficacy in Acute Myeloid Leukemia Models

AIM

To further characterize the selectivity, mechanism-of-action and therapeutic efficacy of the novel small molecule inhibitor, SKI-178.

METHODS

Using the state-of-the-art Cellular Thermal Shift Assay (CETSA) technique to detect "direct target engagement" of proteins intact cells, in vitro and in vivo assays, pharmacological assays and multiple mouse models of acute myeloid leukemia (AML).

RESULTS

Herein, we demonstrate that SKI-178 directly target engages both Sphingosine Kinase 1 and 2. We also present evidence that, in addition to its actions as a Sphingosine Kinase Inhibitor, SKI-178 functions as a microtubule network disrupting agent both in vitro and in intact cells. Interestingly, we separately demonstrate that simultaneous SphK inhibition and microtubule disruption synergistically induces apoptosis in AML cell lines. Furthermore, we demonstrate that SKI-178 is well tolerated in normal healthy mice. Most importantly, we demonstrate that SKI-178 has therapeutic efficacy in several mouse models of AML.

CONCLUSION

SKI-178 is a multi-targeted agent that functions both as an inhibitor of the SphKs as well as a disruptor of the microtubule network. SKI-178 induced apoptosis arises from a synergistic interaction of these two activities. SKI-178 is safe and effective in mouse models of AML, supporting its further development as a multi-targeted anti-cancer therapeutic agent.

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.

Sphingosine 1-Phosphate: A Novel Target for Lung Disorders

Sphingosine 1-phosphate (S1P) is involved in a wide range of cellular processes, which include proliferation, apoptosis, lymphocyte egress, endothelial barrier function, angiogenesis, and inflammation. S1P is produced by two isoenzymes, namely, sphingosine kinase 1 and 2 (SphK1 and 2) and once produced, S1P can act both in an autocrine and paracrine manner. S1P can be dephosphorylated back to sphingosine by two phosphatases (SGPP 1 and 2) or can be irreversibly cleaved by S1P lyase. S1P has a diverse range of functions, which is mediated in a receptor dependent, through G-protein coupled receptors (S1PR1-5) or receptor independent manner, through intracellular targets such as HDACs and TRAF2. The involvement of S1P signaling has been confirmed in various disease conditions including lung diseases. The SphK inhibitors and S1PR modulators are currently under clinical trials for different pathophysiological conditions. There is a significant effort in targeting various components of S1P signaling for several diseases. This review focuses on the ways in which S1P signaling can be therapeutically targeted in lung disorders.

Targeting sphingosine-1-phosphate signaling in lung diseases

Sphingosine-1-phosphate (S1P), a simple, bioactive sphingolipid metabolite, plays a key role, both intracellularly and extracellularly, in various cellular processes such as proliferation, survival, migration, inflammation, angiogenesis, and endothelial barrier integrity. The cellular S1P level is low and is tightly regulated by its synthesis and degradation. Sphingosine Kinases (SphKs) 1 and 2, catalyze the ATP-dependent phosphorylation of sphingosine to S1P, while the degradation is mediated by the reversible dephosphorylation catalyzed by the S1P phosphatases and lipid phosphate phosphatases and the irreversible degradation to hexadecenal and ethanolamine phosphate by sphingosine-1-phosphate lyase (S1PL). As a ligand for specific G-protein-coupled receptors, S1P1-5, which are differentially expressed in different cell types, S1P generates downstream signals that play crucial role in developmental and disease related pathologies. In addition to acting extracellularly on receptors located on the plasma membrane, S1P can also act intracellularly, independently of S1P1-5, affecting calcium homeostasis and cell proliferation. The SphKs /S1P /S1PL metabolic pathway is implicated in numerous human pathologies including respiratory disorders, thereby raising the possibility that manipulating intracellular S1P levels could offer therapeutic potential in ameliorating lung diseases. This review focuses on the prospects of targeting S1P signaling and S1P metabolizing enzymes using small molecule inhibitors, receptor agonists, and antagonists in the treatment of lung diseases.

Inhibition of ceramide glucosylation sensitizes lung cancer cells to ABC294640, a first-in-class small molecule SphK2 inhibitor

Sphingosine kinase 2 (SphK2) is proposed as a novel oncotarget for lung cancer. Here, we studied the anti-lung cancer cell activity by ABC294640, a first-in-class SphK2 inhibitor. We showed that ABC294640 suppressed growth of primary and A549 human lung cancer cells, but sparing SphK2-low lung epithelial cells. Inhibition of SphK2 by ABC294640 increased ceramide accumulation, but decreased pro-survival sphingosine-1-phosphate (S1P) content, leading to lung cancer cell apoptosis activation. Significantly, we show that glucosylceramide synthase (GCS) might be a major resistance factor of ABC294640. The GCS inhibitor 1-phenyl-2-decanoylamino-3-morpholino-1-propanol (PDMP) or GCS shRNA/siRNA knockdown facilitated ABC294640-induced ceramide production and lung cancer cell apoptosis. Reversely, forced overexpression of GCS reduced ABC294640's sensitivity, resulting in decreased ceramide accumulation and apoptosis induction in A549 cells. These findings provide further evidences to support that targeting SphK2 by ABC294640 may be a rational treatment option for lung cancer. Ceramide glucosylation inhibition may further sensitize lung cancer cells to ABC294640.

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.

The Sphingosine Kinase 2 Inhibitor ABC294640 Reduces the Growth of Prostate Cancer Cells and Results in Accumulation of Dihydroceramides In Vitro and In Vivo

Despite recent advances in the development of novel therapies against castration-resistant prostate cancer, the advanced form of the disease remains a major treatment challenge. Aberrant sphingolipid signaling through sphingosine kinases and their product, sphingosine-1-phosphate, can promote proliferation, drug resistance, angiogenesis, and inflammation. The sphingosine kinase 2 inhibitor ABC294640 is undergoing clinical testing in cancer patients, and in this study we investigated the effects this first-in-class inhibitor in castration-resistant prostate cancer. In vitro, ABC294640 decreased prostate cancer cell viability as well as the expression of c-Myc and the androgen receptor, while lysosomal acidification increased. ABC294640 also induced a greater than 3-fold increase in dihydroceramides that inversely correlated with inhibition of dihydroceramide desaturase (DEGS) activity. Expression of sphingosine kinase 2 was dispensable for the ABC294640-mediated increase in dihydroceramides. In vivo, ABC294640 diminished the growth rate of TRAMP-C2 xenografts in syngeneic hosts and elevated dihydroceramides within tumors as visualized by MALDI imaging mass spectroscopy. The plasma of ABC294640-treated mice contained significantly higher levels of C16- and C24:1-ceramides (but not dihydro-C16-ceramide) compared with vehicle-treated mice. In summary, our results suggest that ABC294640 may reduce the proliferative capacity of castration-resistant prostate cancer cells through inhibition of both sphingosine kinase 2 and dihydroceramide desaturase, thereby providing a foundation for future exploration of this small-molecule inhibitor for the treatment of advanced disease.

Targeting sphingosine kinase 2 (SphK2) by ABC294640 inhibits colorectal cancer cell growth in vitro and in vivo

BACKGROUND

Colorectal cancer (CRC) is a major health problem in China and around the world. It is one of the leading causes of cancer-related deaths. Research groups are thus searching for novel and more efficient anti-CRC agents.

RESULTS

Here we demonstrated that ABC294640, a novel SphK2 inhibitor, induced growth inhibition and apoptosis in transformed and primary CRC cells. The SphK activity was remarkably inhibited by ABC294640, accompanied by sphingosine-1-phosphate (S1P) depletion and ceramide incensement in CRC cells. Exogenously-added S1P inhibited ABC294640-induced HT-29 cell lethality. While C6 ceramide and SphK1 inhibitor SKI-II facilitated ABC294640-induced cytotoxicity against HT-29 cells. ABC294640 inhibited AKT-S6K1, but activated JNK signaling in transformed and primary CRC cells. JNK inhibitors (SP600125 and JNKi-II) alleviated ABC294640-induced CRC cell apoptosis. Moreover, a low concentration of ABC294640 sensitized the activity of 5-FU and cisplatin in vitro. In vivo, ABC294640 oral administration dramatically inhibited HT-29 xenografts growth in nude mice.

CONCLUSIONS

Targeting of SphK2 by ABC294640 potently inhibits CRC cell growth both in vitro and in vivo, ABC294640 could be developed as a novel therapeutic for the treatment of CRC.