The Tumorigenic Effect of Sphingosine Kinase 1 and Its Potential Therapeutic Target

Thymoquinone, artemisinin, and thymol attenuate proliferation of lung cancer cells as Sphingosine kinase 1 inhibitors

Sphingosine-1-phosphate (S1P) formed via catalytic actions of sphingosine kinase 1 (SphK1) behaves as a pro-survival substance and activates downstream target molecules associated with various pathologies, including initiation, inflammation, and progression of cancer. Here, we aimed to investigate the SphK1 inhibitory potentials of thymoquinone (TQ), Artemisinin (AR), and Thymol (TM) for the therapeutic management of lung cancer. We implemented docking, molecular dynamics (MD) simulations, enzyme inhibition assay, and fluorescence measurement studies to estimate binding affinity and SphK1 inhibitory potential of TQ, AR, and TM. We further investigated the anti-cancer potential of these compounds on non-small cell lung cancer (NSCLC) cell lines (H1299 and A549), followed by estimation of mitochondrial ROS, mitochondrial membrane potential depolarization, and cleavage of DNA by comet assay. Enzyme activity and fluorescence binding studies suggest that TQ, AR, and TM significantly inhibit the activity of SphK1 with IC50 values of 35.52 µM, 42.81 µM, and 53.68 µM, respectively, and have an excellent binding affinity. TQ shows cytotoxic effect and anti-proliferative potentials on H1299 and A549 with an IC50 value of 27.96 µM and 54.43 µM, respectively. Detection of mitochondrial ROS and mitochondrial membrane potential depolarization shows promising TQ-induced oxidative stress on H1299 and A549 cell lines. Comet assay shows promising TQ-induced oxidative DNA damage. In conclusion, TQ, AR, and TM act as potential inhibitors for SphK1, with a strong binding affinity. In addition, the cytotoxicity of TQ is linked to oxidative stress due to mitochondrial ROS generation. Overall, our study suggests that TQ is a promising inhibitor of SphK1 targeting lung cancer therapy.

Ferroptosis: a promising target for fumarate hydratase-deficient tumor therapeutics literature review

Background and Objective

This review aims to investigate the ferroptosis mechanism of fumarate hydratase (FH)-related tumors for the purpose of possible treatment of tumors. Ferroptosis is an iron (Fe)-dependent form of regulated cell death caused by lipid peroxidation on the cell membrane. Studies have implicated FH in tumorigenesis. As mutations in the FH gene alter cellular metabolism and increase tumorigenesis risk, particularly in the kidneys. As most tumor cells require higher amounts of ferrous ions (Fe2+) than normal cells, they are more susceptible to ferroptosis. Recent studies have indicated that ferroptosis is inhibited the pathogenesis and progression of FH-deficient tumors by regulating lipid and iron metabolism, glutathione-glutathione peroxidase 4 (GSH-GPX4), nuclear factor-erythroid 2-related factor 2 (NRF2)/heme oxygenase-1 (HO-1) pathways. While the Fe2+ content is significantly lower in FH-deficient tumor cells, than that in normal cells. It is promising to promote ferroptosis by increasing the concentration of Fe2+ in cells to achieve the purpose of tumor treatment.

Methods

In this study, we searched for relevant articles on ferroptosis and FH-deficient tumors using PubMed database.

Key Content and Findings

FH is a tumor suppressor. A number of basic studies have shown that the loss of FH plays an important role in hereditary leiomyomas and tumors such as renal cell carcinoma, ovarian cancer, and other tumors. This type of tumor cells can through induce ferroptosis, inhibit proliferation, migration and invasion of tumor cells, increase the sensitivity of tumor cells to chemotherapy, and reverse the drug resistance through various molecular mechanisms. At present, the research on ferroptosis in FH-related tumors is still in the basic experimental stage.

Conclusions

This article reviews the anti-tumor effects and mechanisms of FH and ferroptosis, in order to further explore the medical value of ferroptosis in FH-related tumor therapy.

TCF12 Transcriptionally Activates SPHK1 to Induce Osteosarcoma Angiogenesis by Promoting the S1P/S1PR4/STAT3 Axis

Transcription factor 12 (TCF12) is a known oncogene in many cancers. However, whether TCF12 can regulate malignant phenotypes and angiogenesis in osteosarcoma is not elucidated. In this study, we demonstrated increased expression of TCF12 in osteosarcoma tissues and cell lines. High TCF12 expression was associated with metastasis and poor survival rate of osteosarcoma patients. Knockdown of TCF12 reduced the proliferation, migration, and invasion of osteosarcoma cells. TCF12 was found to bind to the promoter region of sphingosine kinase 1 (SPHK1) to induce transcriptional activation of SPHK1 expression and enhance the secretion of sphingosine-1-phosphate (S1P), which eventually resulted in the malignant phenotypes of osteosarcoma cells. In addition, S1P secreted by osteosarcoma cells promoted the angiogenesis of HUVECs by targeting S1PR4 on the cell membrane to activate the STAT3 signaling pathway. These findings suggest that TCF12 may induce transcriptional activation of SPHK1 to promote the synthesis and secretion of S1P. This process likely enhances the malignant phenotypes of osteosarcoma cells and induces angiogenesis via the S1PR4/STAT3 signaling pathway.

The emerging roles of sphingosine 1-phosphate and SphK1 in cancer resistance: a promising therapeutic target

Cancer chemoresistance is a problematic dilemma that significantly restrains numerous cancer management protocols. It can promote cancer recurrence, spreading of cancer, and finally, mortality. Accordingly, enhancing the responsiveness of cancer cells towards chemotherapies could be a vital approach to overcoming cancer chemoresistance. Tumour cells express a high level of sphingosine kinase-1 (SphK1), which acts as a protooncogenic factor and is responsible for the synthesis of sphingosine-1 phosphate (S1P). S1P is released through a Human ATP-binding cassette (ABC) transporter to interact with other phosphosphingolipids components in the interstitial fluid in the tumor microenvironment (TME), provoking communication, progression, invasion, and tumor metastasis. Also, S1P is associated with several impacts, including anti-apoptotic behavior, metastasis, mesenchymal transition (EMT), angiogenesis, and chemotherapy resistance. Recent reports addressed high levels of S1P in several carcinomas, including ovarian, prostate, colorectal, breast, and HCC. Therefore, targeting the S1P/SphK signaling pathway is an emerging therapeutic approach to efficiently attenuate chemoresistance. In this review, we comprehensively discussed S1P functions, metabolism, transport, and signaling. Also, through a bioinformatic framework, we pointed out the alterations of SphK1 gene expression within different cancers with their impact on patient survival, and we demonstrated the protein-protein network of SphK1, elaborating its sparse roles. Furthermore, we made emphasis on different machineries of cancer resistance and the tight link with S1P. We evaluated all publicly available SphK1 inhibitors and their inhibition activity using molecular docking and how SphK1 inhibitors reduce the production of S1P and might reduce chemoresistance, an approach that might be vital in the course of cancer treatment and prognosis.

The Oncogenic Lipid Sphingosine-1-Phosphate Impedes the Phagocytosis of Tumor Cells by M1 Macrophages in Diffuse Large B Cell Lymphoma

BACKGROUND

A total of 30-40% of diffuse large B cell lymphoma (DLBCL) patients will either not respond to the standard therapy or their disease will recur. The first-line treatment for DLBCL is rituximab and combination chemotherapy. This treatment involves the chemotherapy-induced recruitment of tumor-associated macrophages that recognize and kill rituximab-opsonized DLBCL cells. However, we lack insights into the factors responsible for the recruitment and functionality of macrophages in DLBCL tumors.

METHODS

We have studied the effects of the immunomodulatory lipid sphingosine-1-phosphate (S1P) on macrophage activity in DLBCL, both in vitro and in animal models.

RESULTS

We show that tumor-derived S1P mediates the chemoattraction of both monocytes and macrophages in vitro and in animal models, an effect that is dependent upon the S1P receptor S1PR1. However, S1P inhibited M1 macrophage-mediated phagocytosis of DLBCL tumor cells opsonized with the CD20 monoclonal antibodies rituximab and ofatumumab, an effect that could be reversed by an S1PR1 inhibitor.

CONCLUSIONS

Our data show that S1P signaling can modulate macrophage recruitment and tumor cell killing by anti-CD20 monoclonal antibodies in DLBCL. The administration of S1PR1 inhibitors could enhance the phagocytosis of tumor cells and improve outcomes for patients.

Targeting sphingosine kinase 1 in p53KO thymic lymphoma

Sphingosine kinase 1 (SK1) is a key sphingolipid enzyme that is upregulated in several types of cancer, including lymphoma which is a heterogenous group of malignancies. Treatment for lymphoma has improved significantly by the introduction of new therapies; however, subtypes with tumor protein P53 (p53) mutations or deletion have poor prognosis, making it critical to explore new therapeutic strategies in this context. SK1 has been proposed as a therapeutic target in different types of cancer; however, the effect of targeting SK1 in cancers with p53 deletion has not been evaluated yet. Previous work from our group suggests that loss of SK1 is a key event in mediating the tumor suppressive effect of p53. Employing both genetic and pharmacological approaches to inhibit SK1 function in Trp53KO mice, we show that targeting SK1 decreases tumor growth of established p53KO thymic lymphoma. Inducible deletion of Sphk1 or its pharmacological inhibition drive increased cell death in tumors which is accompanied by selective accumulation of sphingosine levels. These results demonstrate the relevance of SK1 in the growth and maintenance of lymphoma in the absence of p53 function, positioning this enzyme as a potential therapeutic target for the treatment of tumors that lack functional p53.

The role of sphingosine-1-phosphate in autophagy and related disorders

S1P, also referred to as sphingosine-1-phosphate, is a lipid molecule with bioactive properties involved in numerous cellular processes such as cell growth, movement, programmed cell death, self-degradation, cell specialization, aging, and immune system reactions. Autophagy is a meticulously controlled mechanism in which cells repurpose their elements to maintain cellular balance. There are five stages in autophagy: initiation, nucleation, elongation and maturation, fusion, and degradation. New research has provided insight into the complex connection between S1P and autophagy, uncovering their interaction in both normal and abnormal circumstances. Gaining knowledge about the regulatory mechanism of S1P signaling on autophagy can offer a valuable understanding of its function in well-being and illness, potentially leading to innovative therapeutic concepts for diverse ailments. Hence, this review analyzes the essential stages in mammalian autophagy, with a specific emphasis on recent research exploring the control of each stage by S1P. Additionally, it sheds light on the roles of S1P-induced autophagy in various disorders.

Sphingosine kinase 1 regulates lipid metabolism to promote progression of kidney renal clear cell carcinoma

PURPOSE

To detect the expression of sphingosine kinase 1 (SPHK1) in clear cell renal cell carcinoma (ccRCC) and explore its biological role in the occurrence and development of ccRCC through regulation of fatty acid metabolism.

METHODS

Using the Cancer Genome Atlas database, SPHK1 expression and its clinical significance were detected in clear cell renal cell carcinoma. Immunohistochemistry was performed to detect SPHK1 expression in RCC samples in our hospital. The connection between the SPHK1 levels and clinicopathological features of patients was assessed. Nile Red was used to detect fatty acids in cells. Cell Counting Kit-8 and 5-ethynyl-2'-deoxyuridine assays were performed to determine the effect of SPHK1 on renal cell viability and proliferation, respectively. Additionally, the effects of SPHK1 on the proliferation and metastasis of ccRCC were studied using wound healing and Transwell assays. Fatty acids were added exogenously in recovery experiments and western blotting was performed to determine the effect of SPHK1 on fatty acid metabolism in ccRCC. Finally, the effects of SPHK1 on tumor growth were investigated in a xenograft model.

RESULTS

Bioinformatics analysis revealed that SPHK1 expression was upregulated in kidney RCC. OverSPHK1 expression was associated with poor prognosis for ccRCC patients. High SPHK1 expression was detected in human ccRCC. SPHK1 expression was related to clinicopathological features, such as tumor size and Furman grade. Additionally, cell proliferation, migration, and invasion were inhibited in ccRCC cells with low SPHK1 expression. In rescue experiments, proliferation, migration, and invasion were restored. In vivo, reduced SPHK1 levels correlated with lower expression of fatty acid synthase, stearoyl-CoA desaturase 1, and acetyl CoA carboxylase, and slowed tumor growth.

CONCLUSIONS

SPHK1 is abnormally overexpressed in human ccRCC. Patients with ccRCC may benefit from treatments that target SPHK1, which may also serve as a prognostic indicator.

HOXC11 drives lung adenocarcinoma progression through transcriptional regulation of SPHK1

Lung adenocarcinoma (LUAD) is a fatal threat to human health, while the mechanism remains unclear, and the therapy brings limited therapeutic effects. Transcription factor Homeobox C11 (HOXC11) was previously proved to be related to hind limbs and metanephric development during the embryonic phase, and its role in tumors has been gradually recognized. Our study found that HOXC11 overexpressed in LUAD and was associated with worse overall survival. Moreover, its expression in lung cancer was regulated by IκB kinase α (IKKα), a pivotal kinase in NF-κB signaling, which was related to the ubiquitination of HOXC11. We further proved that HOXC11 could enhance the ability of proliferation, migration, invasion, colony formation, and the progression of the cell cycle in LUAD cells. Meanwhile, it also accelerated the formation of subcutaneous and lung metastases tumors. In contrast, loss of HOXC11 in LUAD cells significantly inhibited these malignant phenotypes. At the same time, HOXC11 regulated the expression of sphingosine kinase 1 (SPHK1) by directly binding to its promoter region. Therefore, we conclude that HOXC11 impacts the development of LUAD and facilitates lung cancer progression by promoting the expression of SPHK1.

Metformin as a Potential Antitumor Agent

Some recent findings suggest that metformin, an oral antidiabetic drug, may have antitumor properties. Studies have shown that metformin can alter cell metabolism, both tumor and immune cells, which can greatly influence disease outcome. In this review, we discuss the potential mechanisms in which metformin can directly induce apoptosis of tumor cells as well as mechanisms in which metformin can elicit or enhance antitumor immune response.

S1P-Induced TNF-α and IL-6 Release from PBMCs Exacerbates Lung Cancer-Associated Inflammation

Sphingosine-1-phosphate (S1P) is involved in inflammatory signaling/s associated with the development of respiratory disorders, including cancer. However, the underlying mechanism/s are still elusive. The aim of this study was to investigate the role of S1P on circulating blood cells obtained from healthy volunteers and non-small cell lung cancer (NSCLC) patients. To pursue our goal, peripheral blood mononuclear cells (PBMCs) were isolated and stimulated with S1P. We found that the administration of S1P did not induce healthy PBMCs to release pro-inflammatory cytokines. In sharp contrast, S1P significantly increased the levels of TNF-α and IL-6 from lung cancer-derived PBMCs. This effect was S1P receptor 3 (S1PR3)-dependent. The pharmacological blockade of ceramidase and sphingosine kinases (SPHKs), key enzymes for S1P synthesis, completely reduced the release of both TNF-α and IL-6 after S1P addition on lung cancer-derived PBMCs. Interestingly, S1P-induced IL-6, but not TNF-α, release from lung cancer-derived PBMCs was mTOR- and K-Ras-dependent, while NF-κB was not involved. These data identify S1P as a bioactive lipid mediator in a chronic inflammation-driven diseases such as NSCLC. In particular, the higher presence of S1P could orchestrate the cytokine milieu in NSCLC, highlighting S1P as a pro-tumor driver.

Development of a Novel Sphingolipid Signaling Pathway-Related Risk Assessment Model to Predict Prognosis in Kidney Renal Clear Cell Carcinoma

This study aimed to explore underlying mechanisms by which sphingolipid-related genes play a role in kidney renal clear cell carcinoma (KIRC) and construct a new prognosis-related risk model. We used a variety of bioinformatics methods and databases to complete our exploration. Based on the TCGA database, we used multiple R-based extension packages for data transformation, processing, and statistical analyses. First, on analyzing the CNV, SNV, and mRNA expression of 29 sphingolipid-related genes in various types of cancers, we found that the vast majority were protective in KIRC. Subsequently, we performed cluster analysis of patients with KIRC using sphingolipid-related genes and successfully classified them into the following three clusters with significant prognostic differences: Cluster 1, Cluster 2, and Cluster 3. We performed differential analyses of transcription factor activity, drug sensitivity, immune cell infiltration, and classical oncogenes to elucidate the unique roles of sphingolipid-related genes in cancer, especially KIRC, and provide a reference for clinical treatment. After analyzing the risk rates of sphingolipid-related genes in KIRC, we successfully established a risk model composed of seven genes using LASSO regression analysis, including SPHK1, CERS5, PLPP1, SGMS1, SGMS2, SERINC1, and KDSR. Previous studies have suggested that these genes play important biological roles in sphingolipid metabolism. ROC curve analysis results showed that the risk model provided good prediction accuracy. Based on this risk model, we successfully classified patients with KIRC into high- and low-risk groups with significant prognostic differences. In addition, we performed correlation analyses combined with clinicopathological data and found a significant correlation between the risk model and patient’s M, T, stage, grade, and fustat. Finally, we developed a nomogram that predicted the 5-, 7-, and 10-year survival in patients with KIRC. The model we constructed had strong predictive ability. In conclusion, we believe that this study provides valuable data and clues for future studies on sphingolipid-related genes in KIRC.

Determining the Anticancer Activity of Sphingosine Kinase Inhibitors Containing Heteroatoms in Their Tail Structure

Sphingosine kinase (SK) enzyme, a central player of sphingolipid rheostat, catalyzes the phosphorylation of sphingosine to the bioactive lipid mediator sphingosine 1 phosphate (S1P), which regulates cancer cell proliferation, migration, differentiation, and angiogenesis through its extracellular five G protein-coupled S1P receptors (S1PR_1–5). Recently, several research studies on SK inhibitors have taken place in order use them for the development of novel anticancer-targeted therapy. In this study, we designed and synthesized analog derivatives of known SK1 inhibitors, namely RB005 and PF-543, by introducing heteroatoms at their tail structure, as well as investigated their anticancer activities and pharmacokinetic parameters in vitro. Compounds 1–20 of RB005 and PF-543 derivatives containing an aliphatic chain or a tail structure of benzenesulfonyl were synthesized. All compounds of set 1 (1–10) effectively reduced cell viability in both HT29 and HCT116 cells, whereas set 2 derivatives (11–20) showed poor anticancer effect. Compound 10, having the highest cytotoxic effect (48 h, HT29 IC₅₀ = 6.223 µM, HCT116 IC₅₀ = 8.694 µM), induced HT29 and HCT116 cell death in a concentration-dependent manner through the mitochondrial apoptotic pathway, which was demonstrated by increased annexin V-FITC level, and increased apoptotic marker cleaved caspase-3 and cleaved PARP. Compound 10 inhibited SK1 by 20%, and, thus, the S1P level decreased by 42%. Unlike the apoptosis efficacy, the SK1 inhibitory effect and selectivity of the PF-543 derivative were superior to that of the RB005 analog. As a result, compounds with an aliphatic chain tail exhibited stronger apoptotic effects. However, this ability was not proportional to the degree of SK inhibition. Compound 10 increased the protein phosphatase 2A (PP2A) activity (1.73 fold) similar to FTY720 (1.65 fold) and RB005 (1.59 fold), whereas compounds 11 and 13 had no effect on PP2A activation. Since the PP2A activity increased in compounds with an aliphatic chain tail, it can be suggested that PP2A activation has an important effect on anticancer and SK inhibitory activities.

SphK1-driven autophagy potentiates focal adhesion paxillin-mediated metastasis in colorectal cancer

Invasion and metastasis are the main causes of colorectal cancer (CRC)‐related death. Accumulating evidence suggested that sphingosine kinase 1 (SphK1) promoted the metastasis of CRC and autophagy played an important role in SphK1 promoting the metastasis of malignancy. However, the mechanism by which SphK1‐driven autophagy promotes invasion and metastasis in CRC remains to be clarified. In the present study, immunohistochemical detection showed the expression of SphK1 and paxillin was higher in human CRC tissues than those of normal colorectal mucosal tissues, they were both associated with TNM staging, lymphatic, and distance metastasis. In addition, study of in situ tumor transplantation model in nude mice showed that the suppression of SphK1 inhibited the growth of colonic orthotopic implantation tumors and the expression of paxillin, p‐paxillin, LC3 in the tumor. So, SphK1 may promote CRC metastasis via inducing the expression of paxillin expression and its phosphorylation, in vivo. Furthermore, results of CCK8 assay, transwell and wound healing assays showed that SphK1 promoted the viability, invasion, and metastasis of CRC cells. Transmission electron microscopy detection showed that SphK1 is the key factor in autophagy induction in CRC cells. Moreover, western blot examination indicated that the expression of LC3Ⅱ/Ⅰ, paxillin, p‐paxillin, MMP‐2, and vimentin was enhanced in SphK1‐overexpressed CRC cells and suppressed in SphK1 knockdown CRC cells, meanwhile, the expression of E‐cadherin was suppressed in SphK1‐overexpressed CRC cells and enhanced in SphK1 knockdown CRC cells. Suppression of autophagy by 3MA reversed the expression of paxillin and its phosphorylation in SphK1‐overexpressed CRC cells, indicated that SphK1‐driven autophagy induced the expression of paxillin and its phosphorylation in CRC cells. Together, these findings reveal that SphK1‐driven autophagy may promote the invasion and metastasis of CRC via promoting the expression of focal adhesion paxillin and its phosphorylation.

Potentiating Therapeutic Effects of Epidermal Growth Factor Receptor Inhibition in Triple-Negative Breast Cancer

Triple-negative breast cancer (TNBC) is a subset of breast cancer with aggressive characteristics and few therapeutic options. The lack of an appropriate therapeutic target is a challenging issue in treating TNBC. Although a high level expression of epidermal growth factor receptor (EGFR) has been associated with a poor prognosis among patients with TNBC, targeted anti-EGFR therapies have demonstrated limited efficacy for TNBC treatment in both clinical and preclinical settings. However, with the advantage of a number of clinically approved EGFR inhibitors (EGFRis), combination strategies have been explored as a promising approach to overcome the intrinsic resistance of TNBC to EGFRis. In this review, we analyzed the literature on the combination of EGFRis with other molecularly targeted therapeutics or conventional chemotherapeutics to understand the current knowledge and to provide potential therapeutic options for TNBC treatment.

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

Simple Summary

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

Abstract

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