A fluorogenic substrate for the detection of lipid amidases in intact cells.

Lipid amidases of therapeutic relevance include acid ceramidase (AC), N-acylethanolamine-hydrolyzing acid amidase, and fatty acid amide hydrolase (FAAH). Although fluorogenic substrates have been developed for the three enzymes and high-throughput methods for screening have been reported, a platform for the specific detection of these enzyme activities in intact cells is lacking. In this article, we report on the coumarinic 1-deoxydihydroceramide RBM1-151, a 1-deoxy derivative and vinilog of RBM14-C12, as a novel substrate of amidases. This compound is hydrolyzed by AC (appKm = 7.0 µM; appVmax = 99.3 nM/min), N-acylethanolamine-hydrolyzing acid amidase (appKm = 0.73 µM; appVmax = 0.24 nM/min), and FAAH (appKm = 3.6 µM; appVmax = 7.6 nM/min) but not by other ceramidases. We provide proof of concept that the use of RBM1-151 in combination with reported irreversible inhibitors of AC and FAAH allows the determination in parallel of the three amidase activities in single experiments in intact cells.

Sphingolipid paracrine signaling impairs keratinocyte adhesion to promote melanoma invasion.

Melanoma is the deadliest form of skin cancer due to its propensity to metastasize. It arises from melanocytes, which are attached to keratinocytes within the basal epidermis. Here, we hypothesize that, in addition to melanocyte-intrinsic modifications, dysregulation of keratinocyte functions could initiate early-stage melanoma cell invasion. We identified the lysolipid sphingosine 1-phosphate (S1P) as a tumor paracrine signal from melanoma cells that modifies the keratinocyte transcriptome and reduces their adhesive properties, leading to tumor invasion. Mechanistically, tumor cell-derived S1P reduced E-cadherin expression in keratinocytes via S1P receptor dependent Snail and Slug activation. All of these effects were blocked by S1P2/3 antagonists. Importantly, we showed that epidermal E-cadherin expression was inversely correlated with the expression of the S1P-producing enzyme in neighboring tumors and the Breslow thickness in patients with early-stage melanoma. These findings support the notion that E-cadherin loss in the epidermis initiates the metastatic cascade in melanoma.

Potential Role of Sphingolipidoses-Associated Lysosphingolipids in Cancer.

Sphingolipids play a key structural role in cellular membranes and/or act as signaling molecules. Inherited defects of their catabolism lead to lysosomal storage diseases called sphingolipidoses. Although progress has been made toward a better understanding of their pathophysiology, several issues still remain unsolved. In particular, whether lysosphingolipids, the deacylated form of sphingolipids, both of which accumulate in these diseases, are simple biomarkers or play an instrumental role is unclear. In the meanwhile, evidence has been provided for a high risk of developing malignancies in patients affected with Gaucher disease, the most common sphingolipidosis. This article aims at analyzing the potential involvement of lysosphingolipids in cancer. Knowledge about lysosphingolipids in the context of lysosomal storage diseases is summarized. Available data on the nature and prevalence of cancers in patients affected with sphingolipidoses are also reviewed. Then, studies investigating the biological effects of lysosphingolipids toward pro or antitumor pathways are discussed. Finally, original findings exploring the role of glucosylsphingosine in the development of melanoma are presented. While this lysosphingolipid may behave like a protumorigenic agent, further investigations in appropriate models are needed to elucidate the role of these peculiar lipids, not only in sphingolipidoses but also in malignant diseases in general.

Adipocyte Extracellular Vesicles Decrease p16INK4A in Melanoma: An Additional Link between Obesity and Cancer.

Obesity is a recognized factor for increased risk and poor prognosis of many cancers, including melanoma. In this study, using genetically engineered mouse models of melanoma (NrasQ61K transgenic expression, associated or not with Cdkn2a heterozygous deletion), we show that obesity increases melanoma initiation and progression by supporting tumor growth and metastasis, thereby reducing survival. This effect is associated with a decrease in p16INK4A expression in tumors. Mechanistically, adipocytes downregulate p16INK4A in melanoma cells through ß-catenin-dependent regulation, which increases cell motility. Furthermore, ß-catenin is directly transferred from adipocytes to melanoma cells in extracellular vesicles, thus increasing its level and activity, which represses CDKN2A transcription. Adipocytes from individuals with obesity have a stronger effect than those from lean individuals, mainly owing to an increase in the number of vesicles secreted, thus increasing the amount of ß-catenin delivered to melanoma cells and, consequently, amplifying their effect. In conclusion, in this study, we reveal that adipocyte extracellular vesicles control p16INK4A expression in melanoma, which promotes tumor progression. This work expands our understanding of the cooperation between adipocytes and tumors, particularly in obesity.

Neutral Sphingomyelinase 2 Heightens Anti-Melanoma Immune Responses and Anti-PD-1 Therapy Efficacy.

Dysregulation of lipid metabolism affects the behavior of cancer cells, but how this happens is not completely understood. Neutral sphingomyelinase 2 (nSMase2), encoded by SMPD3, catalyzes the breakdown of sphingomyelin to produce the anti-oncometabolite ceramide. We found that this enzyme was often downregulated in human metastatic melanoma, likely contributing to immune escape. Overexpression of nSMase2 in mouse melanoma reduced tumor growth in syngeneic wild-type but not CD8-deficient mice. In wild-type mice, nSMase2-overexpressing tumors showed accumulation of both ceramide and CD8+ tumor-infiltrating lymphocytes, and this was associated with increased level of transcripts encoding IFNγ and CXCL9. Overexpressing the catalytically inactive nSMase2 failed to alter tumor growth, indicating that the deleterious effect nSMase2 has on melanoma growth depends on its enzymatic activity. In vitro, small extracellular vesicles from melanoma cells overexpressing wild-type nSMase2 augmented the expression of IL12, CXCL9, and CCL19 by bone marrow-derived dendritic cells, suggesting that melanoma nSMase2 triggers T helper 1 (Th1) polarization in the earliest stages of the immune response. Most importantly, overexpression of wild-type nSMase2 increased anti-PD-1 efficacy in murine models of melanoma and breast cancer, and this was associated with an enhanced Th1 response. Therefore, increasing SMPD3 expression in melanoma may serve as an original therapeutic strategy to potentiate Th1 polarization and CD8+ T-cell-dependent immune responses and overcome resistance to anti-PD-1.

Combining Nivolumab and Ipilimumab with Infliximab or Certolizumab in Patients with Advanced Melanoma: First Results of a Phase Ib Clinical Trial.

PURPOSE: TNF blockers can be used to manage gastrointestinal inflammatory side effects following nivolumab and/or ipilimumab treatment in patients with advanced melanoma. Our preclinical data showed that anti-TNF could promote the efficacy of immune checkpoint inhibitors. PATIENTS AND METHODS: TICIMEL (NTC03293784) is an open-label, two-arm phase Ib clinical trial. Fourteen patients with advanced and/or metastatic melanoma (stage IIIc/IV) were enrolled. Patients were treated with nivolumab (1 mg/kg) and ipilimumab (3 mg/kg) combined to infliximab (5 mg/kg, N = 6) or certolizumab (400/200 mg, N = 8). The primary endpoint was safety and the secondary endpoint was antitumor activity. Adverse events (AEs) were graded according to the NCI Common Terminology Criteria for Adverse Events and response was assessed following RECIST 1.1. RESULTS: Only one dose-limiting toxicity was observed in the infliximab cohort. The two different combinations were found to be safe. We observed lower treatment-related AEs with infliximab as compared with certolizumab. In the certolizumab cohort, one patient was not evaluable for response. In this cohort, four of eight patients exhibited hepatobiliary disorders and seven of seven evaluable patients achieved objective response including four complete responses (CRs) and three partial responses (PRs). In the infliximab cohort, we observed one CR, two PRs, and three progressive diseases. Signs of activation and maturation of systemic T-cell responses were seen in patients from both cohorts. CONCLUSIONS: Our results show that both combinations are safe in human and provide clinical and biological activities. The high response rate in the certolizumab-treated patient cohort deserves further investigations.

Lipid metabolic Reprogramming: Role in Melanoma Progression and Therapeutic Perspectives.

Metabolic reprogramming contributes to the pathogenesis and heterogeneity of melanoma. It is driven both by oncogenic events and the constraints imposed by a nutrient- and oxygen-scarce microenvironment. Among the most prominent metabolic reprogramming features is an increased rate of lipid synthesis. Lipids serve as a source of energy and form the structural foundation of all membranes, but have also emerged as mediators that not only impact classical oncogenic signaling pathways, but also contribute to melanoma progression. Various alterations in fatty acid metabolism have been reported and can contribute to melanoma cell aggressiveness. Elevated expression of the key lipogenic fatty acid synthase is associated with tumor cell invasion and poor prognosis. Fatty acid uptake from the surrounding microenvironment, fatty acid ß-oxidation and storage also appear to play an essential role in tumor cell migration. The aim of this review is (i) to focus on the major alterations affecting lipid storage organelles and lipid metabolism. A particular attention has been paid to glycerophospholipids, sphingolipids, sterols and eicosanoids, (ii) to discuss how these metabolic dysregulations contribute to the phenotype plasticity of melanoma cells and/or melanoma aggressiveness, and (iii) to highlight therapeutic approaches targeting lipid metabolism that could be applicable for melanoma treatment.

New Insights into the Role of Sphingolipid Metabolism in Melanoma.

Cutaneous melanoma is a deadly skin cancer whose aggressiveness is directly linked to its metastatic potency. Despite remarkable breakthroughs in term of treatments with the emergence of targeted therapy and immunotherapy, the prognosis for metastatic patients remains uncertain mainly because of resistances. Better understanding the mechanisms responsible for melanoma progression is therefore essential to uncover new therapeutic targets. Interestingly, the sphingolipid metabolism is dysregulated in melanoma and is associated with melanoma progression and resistance to treatment. This review summarises the impact of the sphingolipid metabolism on melanoma from the initiation to metastatic dissemination with emphasis on melanoma plasticity, immune responses and resistance to treatments.

Are Glucosylceramide-Related Sphingolipids Involved in the Increased Risk for Cancer in Gaucher Disease Patients? Review and Hypotheses.

The roles of ceramide and its catabolites, i.e., sphingosine and sphingosine 1-phosphate, in the development of malignancies and the response to anticancer regimens have been extensively described. Moreover, an abundant literature points to the effects of glucosylceramide synthase, the mammalian enzyme that converts ceramide to ß-glucosylceramide, in protecting tumor cells from chemotherapy. Much less is known about the contribution of ß-glucosylceramide and its breakdown products in cancer progression. In this chapter, we first review published and personal clinical observations that report on the increased risk of developing cancers in patients affected with Gaucher disease, an inborn disorder characterized by defective lysosomal degradation of ß-glucosylceramide. The previously described mechanistic links between lysosomal ß-glucosylceramidase, ß-glucosylceramide and/or ß-glucosylphingosine, and various hallmarks of cancer are reviewed. We further show that melanoma tumor growth is facilitated in a Gaucher disease mouse model. Finally, the potential roles of the ß-glucosylceramidase protein and its lipidic substrates and/or downstream products are discussed.

Resistance of melanoma to immune checkpoint inhibitors is overcome by targeting the sphingosine kinase-1.

Immune checkpoint inhibitors (ICIs) have dramatically modified the prognosis of several advanced cancers, however many patients still do not respond to treatment. Optimal results might be obtained by targeting cancer cell metabolism to modulate the immunosuppressive tumor microenvironment. Here, we identify sphingosine kinase-1 (SK1) as a key regulator of anti-tumor immunity. Increased expression of SK1 in tumor cells is significantly associated with shorter survival in metastatic melanoma patients treated with anti-PD-1. Targeting SK1 markedly enhances the responses to ICI in murine models of melanoma, breast and colon cancer. Mechanistically, SK1 silencing decreases the expression of various immunosuppressive factors in the tumor microenvironment to limit regulatory T cell (Treg) infiltration. Accordingly, a SK1-dependent immunosuppressive signature is also observed in human melanoma biopsies. Altogether, this study identifies SK1 as a checkpoint lipid kinase that could be targeted to enhance immunotherapy.

Corrigendum: The TNF Paradox in Cancer Progression and Immunotherapy.

[This corrects the article DOI: 10.3389/fimmu.2019.01818.].

Anti-TNF, a magic bullet in cancer immunotherapy?

Immune checkpoint blockers (ICB) have revolutionized cancer therapy. However, complete response is observed in a minority of patients and most patients develop immune-related adverse events (irAEs). These include colitis, which can be treated with anti-tumor necrosis factor (TNF) antibodies such as Infliximab. In a recent issue of the Journal for ImmunoTherapy of Cancer, Badran et al. reported that co-administering Infliximab together with ICB to five cancer patients prevents colitis recurrence, with four of them exhibiting overall disease stability. The basis for this treatment strategy stemmed from our pre-clinical demonstration that TNF contributes to resistance to anti-PD-1 therapy. In agreement with this concept, we have shown that TNF blockers improve the anti-tumor therapeutic activity of ICB in mice and based on these findings we are currently evaluating the combination in melanoma patients enrolled in the TICIMEL clinical trial. Herein, (i) we discuss the scientific rationale for combining anti-TNF and ICB in cancer patients, (ii) comment on the paper published by Badran et al. and (iii) provide the TICIMEL clinical trial design.

Sphingomyelin Synthase 1 (SMS1) Downregulation Is Associated With Sphingolipid Reprogramming and a Worse Prognosis in Melanoma.

Sphingolipid (SL) metabolism alterations have been frequently reported in cancer including in melanoma, a bad-prognosis skin cancer. In normal cells, de novo synthesized ceramide is mainly converted to sphingomyelin (SM), the most abundant SL, by sphingomyelin synthase 1 (SMS1) and, albeit to a lesser extent, SMS2, encoded by the SGMS1 and SGMS2 genes, respectively. Alternatively, ceramide can be converted to glucosylceramide (GlcCer) by the GlcCer synthase (GCS), encoded by the UGCG gene. Herein, we provide evidence for the first time that SMS1 is frequently downregulated in various solid cancers, more particularly in melanoma. Accordingly, various human melanoma cells displayed a SL metabolism signature associated with (i) a robust and a low expression of UGCG and SGMS1/2, respectively, (ii) higher in situ enzyme activity of GCS than SMS, and (iii) higher intracellular levels of GlcCer than SM. SMS1 was expressed at low levels in most of the human melanoma biopsies. In addition, several mutations and increased CpG island methylation in the SGMS1 gene were identified that likely affect SMS1 expression. Finally, low SMS1 expression was associated with a worse prognosis in metastatic melanoma patients. Collectively, our study indicates that SMS1 downregulation in melanoma enhances GlcCer synthesis, triggering an imbalance in the SM/GlcCer homeostasis, which likely contributes to melanoma progression. Evaluating SMS1 expression level in tumor samples might serve as a biomarker to predict clinical outcome in advanced melanoma patients.

Lysosomal acid ceramidase ASAH1 controls the transition between invasive and proliferative phenotype in melanoma cells.

Phenotypic plasticity and subsequent generation of intratumoral heterogeneity underly key traits in malignant melanoma such as drug resistance and metastasis. Melanoma plasticity promotes a switch between proliferative and invasive phenotypes characterized by different transcriptional programs of which MITF is a critical regulator. Here, we show that the acid ceramidase ASAH1, which controls sphingolipid metabolism, acted as a rheostat of the phenotypic switch in melanoma cells. Low ASAH1 expression was associated with an invasive behavior mediated by activation of the integrin alphavbeta5-FAK signaling cascade. In line with that, human melanoma biopsies revealed heterogeneous staining of ASAH1 and low ASAH1 expression at the melanoma invasive front. We also identified ASAH1 as a new target of MITF, thereby involving MITF in the regulation of sphingolipid metabolism. Together, our findings provide new cues to the mechanisms underlying the phenotypic plasticity of melanoma cells and identify new anti-metastatic targets.

Targeting the Sphingosine 1-Phosphate Axis Exerts Potent Antitumor Activity in BRAFi-Resistant Melanomas.

BRAF inhibitors (BRAFi) are used to treat patients with melanoma harboring the V600E mutation. However, resistance to BRAFi is inevitable. Here, we identified sphingosine 1-phosphate (S1P) receptors as regulators of BRAFV600E-mutant melanoma cell-autonomous resistance to BRAFi. Moreover, our results reveal a distinct sphingolipid profile, that is, a tendency for increased very long-chain ceramide species, in the plasma of patients with melanoma who achieve a response to BRAFi therapy as compared with patients with progressive disease. Treatment with BRAFi resulted in a strong decrease in S1PR1/3 expression in sensitive but not in resistant cells. Genetic and pharmacologic interventions, that increase ceramide/S1P ratio, downregulated S1PR expression and blocked BRAFi-resistant melanoma cell growth. This effect was associated with a decreased expression of MITF and Bcl-2. Moreover, the BH3 mimetic ABT-737 improved the antitumor activity of approaches targeting S1P-metabolizing enzymes in BRAFi-resistant melanoma cells. Collectively, our findings indicate that targeting the S1P/S1PR axis could provide effective therapeutic options for patients with melanoma who relapse after BRAFi therapy.

Phenotypic and lipidomic characterization of primary human epidermal keratinocytes exposed to simulated solar UV radiation.

BACKGROUND: Ultraviolet (UV) radiation is known to be one of the most important environmental hazards acting on the skin. The most part of UV radiation is absorbed in the epidermis, where keratinocytes are the most abundant and exposed cell type. Lipids have an important role in skin biology, not only for their important contribution to the maintenance of the permeability barrier but also for the production and storage of energy, membrane organization and cell signalling functions. However, the effects on the lipid composition of keratinocytes under UV radiation are little explored. OBJECTIVE: The present work aims to explore the effects on the phenotype and lipid content of primary human keratinocytes exposed to simulated solar UV radiation. METHODS: Keratinocytes were exposed to a single (acute exposure) and repeated simulated solar UV irradiations for 4 weeks (chronic exposure). Cell viability and morphology were explored, as well as the production of reactive oxygen species. Then, lipid extracts were analysed through liquid chromatography coupled to mass spectrometry (LC-MS) and the data generated was processed using the ROIMCR chemometric methodology together with partial least squares discriminant analysis (PLS-DA), to finally reveal the most relevant lipid changes that occurred in keratinocytes upon UV irradiation. Also, the potential induction of keratinocyte differentiation was explored by measuring the increase of involucrin. RESULTS: Under acute irradiation, cell viability and morphology were not altered. However, a general increase of phosphatidylcholines (PC) phosphatidylethanolamines (PE) and phosphatidylglycerol (PG) together with a slight sphingomyelin (SM) decrease were found in UV irradiated cells, among other changes. In addition, keratinocyte cultures did not present any differentiation hallmark. Contrary to acute-irradiated cells, in chronic exposures, cell viability was reduced and keratinocytes presented an altered morphology. Also, hallmarks of differentiation, such as the increase of involucrin protein and the autophagy induction were detected. Among the main lipid changes that accompanied this phenotype, the increase of long-chain ceramides, lysoPC and glycerolipid species were found. CONCLUSION: Important lipid changes were detected under acute and chronic UV irradiation. The lipid profile under chronic exposure may represent a lipid fingerprint of the keratinocyte differentiation phenotype.

Untargeted lipidomic analysis of primary human epidermal melanocytes acutely and chronically exposed to UV radiation.

Ultraviolet (UV) radiation present in sunlight has been related to harmful effects on skin such as premature aging and skin cancer. In order to study the effects of UV radiation on skin, many investigations have been carried out at transcriptomic and proteomic levels. However, studies on the effects of UV radiation on lipid composition are scarce. In this work, primary cultures of melanocytes were exposed to UV radiation in a similar UVA/UVB ratio to that found in solar light. The UV exposure was carried out twice a week and different endpoints were investigated at 0.5 (acute exposure), 1.5 and 3 weeks. As a result, dendrite formation and a progressive reduction in cell viability were observed. Also, cell cycle arrest and a reduced E-cadherin content were detected at 0.5 and 1.5 weeks. In the second stage of the study, lipid extracts of melanocytes were analysed by liquid chromatography coupled to mass spectrometry (LC-MS) and subjected to an untargeted lipidomic approach using the ROIMCR chemometric method. Among the most important changes observed under UV irradiation, lipid raft components such as sphingomyelins and GM3 gangliosides as well as other signalling molecules such as phosphatidylinositols decreased progressively with time. These modifications indicated strong effects on important functions such as cell signalling and recognition. In contrast, triacylglycerol species, associated with energy storage, increased progressively, which could be interpreted as a survival mechanism under adverse conditions. Further studies are needed to better understand the functional implications of the changes observed.