Targeting sphingosine-1-phosphate for cancer therapy

Making a Difference

This is a personal account of one academic scientist who founded two biotechnology companies. Both companies were initially incubated within the walls of the university under a creative student incubator program whereby biology students could pursue their graduate academic degrees while gaining valuable biotechnology experiences. After the companies transitioned out of the university environment, the professor and his students pursued diagnostic and therapeutic drug development resulting in the completion of several clinical trials. The value of international scientific collaborations with colleagues at the University of Padova (Italy) is also described.

Hypogelsolinemia and Decrease in Blood Plasma Sphingosine-1-Phosphate in Patients Diagnosed with Severe Acute Pancreatitis

BACKGROUND

Acute pancreatitis (AP) is a frequent hospitalization cause of patients suffering from gastrointestinal disorders. Gelsolin has an ability to bind bioactive lipids including different sphingolipids engaged in inflammatory response. Importantly, hypogelsolinemia was observed in patients with different states of acute and chronic inflammation.

AIMS

The aim of the present study was to assess the interplay of blood plasma gelsolin and blood plasma sphingosine-1-phosphate (S1P) concentration in patients diagnosed with acute pancreatitis.

MATERIALS AND METHODS

To assess the concentration of gelsolin and S1P, immunoblotting and HPLC technique were employed, respectively. Additionally, the concentrations of amylase, lipase, C-reactive protein (CRP), procalcitonin (PCT) and the number of white blood cells (WBC) and platelet (PLT) were recorded.

RESULTS

We found that both pGSN and S1P concentrations in the plasma of the AP patients were significantly lower (pGSN ~ 15-165 mg/L; S1P ~ 100-360 pmol/mL) when compared to the levels of pGSN and S1P in a control group (pGSN ~ 130-240 mg/L; S1P ~ 260-400 pmol/mL). Additionally, higher concentrations of CRP, WBC, amylase and lipase were associated with low level of gelsolin in the blood of AP patients. No correlations between the level of PCT and PLT with gelsolin concentration were noticed.

CONCLUSION

Plasma gelsolin and S1P levels decrease during severe acute pancreatitis. Simultaneous assessment of pGSN and S1P can be useful in development of more accurate diagnostic strategies for patients with severe acute pancreatitis.

S1PR1 as a Novel Promising Therapeutic Target in Cancer Therapy

Sphingosine-1-phosphate (S1P) can regulate several physiological and pathological processes. S1P signaling via its cell surface receptor S1PR1 has been shown to enhance tumorigenesis and stimulate growth, expansion, angiogenesis, metastasis, and survival of cancer cells. S1PR1-mediated tumorigenesis is supported and amplified by activation of downstream effectors including STAT3, interleukin-6, and NF-κB networks. S1PR1 signaling can also trigger various other signaling pathways involved in carcinogenesis including activation of PI3K/AKT, MAPK/ERK1/2, Rac, and PKC/Ca, as well as suppression of cyclic adenosine monophosphate (cAMP). It also induces immunological tolerance in the tumor microenvironment, while the immunosuppressive function of S1PR1 can also lead to the generation of pre-metastatic niches. Some tumor cells upregulate S1PR1 signaling pathways, which leads to drug resistant cancer cells, mainly through activation of STAT3. This signaling pathway is also implicated in some inflammatory conditions leading to the instigation of inflammation-driven cancers. Furthermore, it can also increase survival via induction of anti-apoptotic pathways, for instance, in breast cancer cells. Therefore, S1PR1 and its signaling pathways can be considered as potential anti-tumor therapeutic targets, alone or in combination therapies. Given the oncogenic nature of S1PR1 and its distribution in a variety of cancer cell types along with its targeting advantages over other molecules of this family, S1PR1 should be considered a favorable target in therapeutic approaches to cancer. This review describes the role of S1PR1 in cancer development and progression, specifically addressing breast cancer, glioma, and hematopoietic malignancies. We also discuss the potential use of S1P signaling modulators as therapeutic targets in cancer therapy.

Molecular Regulation of Sprouting Angiogenesis

The term angiogenesis arose in the 18th century. Several studies over the next 100 years laid the groundwork for initial studies performed by the Folkman laboratory, which were at first met with some opposition. Once overcome, the angiogenesis field has flourished due to studies on tumor angiogenesis and various developmental models that can be genetically manipulated, including mice and zebrafish. In addition, new discoveries have been aided by the ability to isolate primary endothelial cells, which has allowed dissection of various steps within angiogenesis. This review will summarize the molecular events that control angiogenesis downstream of biochemical factors such as growth factors, cytokines, chemokines, hypoxia-inducible factors (HIFs), and lipids. These and other stimuli have been linked to regulation of junctional molecules and cell surface receptors. In addition, the contribution of cytoskeletal elements and regulatory proteins has revealed an intricate role for mobilization of actin, microtubules, and intermediate filaments in response to cues that activate the endothelium. Activating stimuli also affect various focal adhesion proteins, scaffold proteins, intracellular kinases, and second messengers. Finally, metalloproteinases, which facilitate matrix degradation and the formation of new blood vessels, are discussed, along with our knowledge of crosstalk between the various subclasses of these molecules throughout the text. Compr Physiol 8:153-235, 2018.

Unexpected profile of sphingolipid contents in blood and bone marrow plasma collected from patients diagnosed with acute myeloid leukemia

Background

Impaired apoptotic pathways in leukemic cells enable them to grow in an uncontrolled way. Moreover, aberrations in the apoptotic pathways are the main factor of leukemic cells drug resistance.

Methods

To assess the presence of potential abnormalities that might promote dysfunction of leukemic cells growth, HPLC system was used to determine sphingosine (SFO), sphinganine (SFA), sphingosine-1-phosphate (S1P) and ceramide (CER) concentration in the blood collected from patients diagnose with acute myeloblastic leukemia (AML; n = 49) and compare to values of control (healthily) group (n = 51). Additionally, in AML group concentration of SFO, SFA, S1P and CER was determined in bone marrow plasma and compared to respective values in blood plasma. The concentration of S1P and CER binding protein – plasma gelsolin (GSN) was also assessed in collected samples using immunoblotting assay.

Results

We observed that in AML patients the average SFO, SFA and CER concentration in blood plasma was significantly higher (p < 0.001) compare to control group, when blood plasma S1P concentration was significantly lower (p < 0.001). At the same time the CER/S1P ratio in AML patient (44.5 ± 19.4) was about 54% higher compare to control group (20.9 ± 13.1). Interestingly the average concentration of S1P in blood plasma (196 ± 13 pmol/ml) was higher compare to its concentration in plasma collected from bone marrow (154 ± 21 pmol/ml).

Conclusions

We hypothesize that changes in profile of sphingolipids concentration and some of their binding protein partners such as GSN in extracellular environment of blood and bone marrow cells in leukemic patients can be targeted to develop new AML treatment method(s).

Sphingosine-1-Phosphate Metabolism and Its Role in the Development of Inflammatory Bowel Disease

Beyond their role as structural molecules, sphingolipids are involved in many important cellular processes including cell proliferation, apoptosis, inflammation, and migration. Altered sphingolipid metabolism is observed in many pathological conditions including gastrointestinal diseases. Inflammatory bowel disease (IBD) represents a state of complex, unpredictable, and destructive inflammation of unknown origin within the gastrointestinal tract. The mechanisms explaining the pathophysiology of IBD involve signal transduction pathways regulating gastro-intestinal system’s immunity. Progressive intestinal tissue destruction observed in chronic inflammation may be associated with an increased risk of colon cancer. Sphingosine-1-phosphate (S1P), a sphingolipid metabolite, functions as a cofactor in inflammatory signaling and becomes a target in the treatment of IBD, which might prevent its conversion to cancer. This paper summarizes new findings indicating the impact of (S1P) on IBD development and IBD-associated carcinogenesis.

Sphingosine-1-phosphate is involved in the occlusive arteriopathy of pulmonary arterial hypertension

Despite several advances in the pathobiology of pulmonary arterial hypertension (PAH), its pathogenesis is not completely understood. Current therapy improves symptoms but has disappointing effects on survival. Sphingosine-1-phosphate (S1P) is a lysophospholipid synthesized by sphingosine kinase 1 (SphK1) and SphK2. Considering the regulatory roles of S1P in several tissues leading to vasoconstriction, inflammation, proliferation, and fibrosis, we investigated whether S1P plays a role in the pathogenesis of PAH. To test this hypothesis, we used plasma samples and lung tissue from patients with idiopathic PAH (IPAH) and the Sugen5416/hypoxia/normoxia rat model of occlusive PAH. Our study revealed an increase in the plasma concentration of S1P in patients with IPAH and in early and late stages of PAH in rats. We observed increased expression of both SphK1 and SphK2 in the remodeled pulmonary arteries of patients with IPAH and PAH rats. Exogenous S1P stimulated the proliferation of cultured rat pulmonary arterial endothelial and smooth-muscle cells. We also found that 3 weeks of treatment of late-stage PAH rats with an SphK1 inhibitor reduced the increased plasma levels of S1P and the occlusive pulmonary arteriopathy. Although inhibition of SphK1 improved cardiac index and the total pulmonary artery resistance index, it did not reduce right ventricular systolic pressure or right ventricular hypertrophy. Our study supports that S1P is involved in the pathogenesis of occlusive arteriopathy in PAH and provides further evidence that S1P signaling may be a novel therapeutic target.

Lysophosphatidic Acid and Sphingosine-1-Phosphate: A Concise Review of Biological Function and Applications for Tissue Engineering

The presentation and controlled release of bioactive signals to direct cellular growth and differentiation represents a widely used strategy in tissue engineering. Historically, work in this field has primarily focused on the delivery of large cytokines and growth factors, which can be costly to manufacture and difficult to deliver in a sustained manner. There has been a marked increase over the past decade in the pursuit of lipid mediators due to their wide range of effects over multiple cell types, low cost, and ease of scale-up. Lysophosphatidic acid (LPA) and sphingosine-1-phosphate (S1P) are two bioactive lysophospholipids (LPLs) that have gained attention for use as pharmacological agents in tissue engineering applications. While these lipids can have similar effects on cellular response, they possess distinct chemical backbones, mechanisms of synthesis and degradation, and signaling pathways using a discrete set of G-protein-coupled receptors (GPCRs). LPA and S1P predominantly act extracellularly on their GPCRs and can directly regulate cell survival, differentiation, cytokine secretion, proliferation, and migration--each of the important functions that must be considered in regenerative medicine. In addition to these potent physiological functions, these LPLs play pivotal roles in a number of pathophysiological processes. To capitalize on the promise of these molecules in tissue engineering, these lipids have been incorporated into biomaterials for in vivo delivery. Here, we survey the effects of LPA and S1P on both cellular- and tissue-level phenotypes, with an eye toward regulating stem/progenitor cell growth and differentiation. In particular, we examine work that has translational applications for cell-based tissue engineering strategies in promoting cell survival, bone and cartilage engineering, and therapeutic angiogenesis.

Involvement of vacuolar H(+)-ATPase in killing of human melanoma cells by the sphingosine kinase analogue FTY720

Targeting the sphingosine 1-phosphate (S1P)/S1P receptor (S1PR) signalling axis is emerging as a promising strategy in the treatment of cancer. However, the effect of such an approach on survival of human melanoma cells remains less understood. Here, we show that the sphingosine analogue FTY720 that functionally antagonises S1PRs kills human melanoma cells through a mechanism involving the vacuolar H(+) -ATPase activity. Moreover, we demonstrate that FTY720-triggered cell death is characterized by features of necrosis and is not dependent on receptor-interacting protein kinase 1 or lysosome cathepsins, nor was it associated with the activation of protein phosphatase 2A. Instead, it is mediated by increased production of reactive oxygen species and is antagonized by activation of autophagy. Collectively, these results suggest that FTY720 and its analogues are promising candidates for further development as new therapeutic agents in the treatment of melanoma.

Communication between host organism and cancer cells is transduced by systemic sphingosine kinase 1/sphingosine 1-phosphate signalling to regulate tumour metastasis

Mechanisms by which cancer cells communicate with the host organism to regulate lung colonization/metastasis are unclear. We show that this communication occurs via sphingosine 1-phosphate (S1P) generated systemically by sphingosine kinase 1 (SK1), rather than via tumour-derived S1P. Modulation of systemic, but not tumour SK1, prevented S1P elevation, and inhibited TRAMP-induced prostate cancer growth in TRAMP^+/+SK1^−/− mice, or lung metastasis of multiple cancer cells in SK1^−/− animals. Genetic loss of SK1 activated a master metastasis suppressor, Brms1 (breast carcinoma metastasis suppressor 1), via modulation of S1P receptor 2 (S1PR2) in cancer cells. Alterations of S1PR2 using pharmacologic and genetic tools enhanced Brms1. Moreover, Brms1 in S1PR2^−/− MEFs was modulated by serum S1P alterations. Accordingly, ectopic Brms1 in MB49 bladder cancer cells suppressed lung metastasis, and stable knockdown of Brms1 prevented this process. Importantly, inhibition of systemic S1P signalling using a novel anti-S1P monoclonal antibody (mAb), Sphingomab, attenuated lung metastasis, which was prevented by Brms1 knockdown in MB49 cells. Thus, these data suggest that systemic SK1/S1P regulates metastatic potential via regulation of tumour S1PR2/Brms1 axis.

Co-administration phenoxodiol with doxorubicin synergistically inhibit the activity of sphingosine kinase-1 (SphK1), a potential oncogene of osteosarcoma, to suppress osteosarcoma cell growth both in vivo and in vitro

Elucidation of the mechanisms of chemo-resistance and implementation of strategies to overcome it will be pivotal to improve the survival for osteosarcoma (OS) patients. We here suggest that sphingosine kinase-1 (SphK1) might be the key factor contributing to chemo-resistance in OS. Our Western-blots and immunohistochemistry results showed that SphK1 is over-expressed in multiple clinical OS tissues. Over-expression of SphK1 in OS cell line U2OS promoted its growth and endorsed its resistance against doxorubicin, while knocking-down of SphK1 by shRNA inhibited U2OS cell growth and increased its sensitivity to doxorubicin. Co-administration phenoxodiol with doxorubicin synergistically inhibited SphK1 activity to trigger cellular ceramide accumulation, and achieved synergistic anti-OS growth effect, accompanied with a significant increased of apoptosis and cytotoxicity. Increased cellular level of ceramide by the co-administration induced the association between Akt and Protein Phosphatase 1 (PP1) to dephosphorylate Akt, and to introduce a constitutively active Akt (CA-Akt) restored Akt activation and diminished cell growth inhibition. Further, phenoxodiol and doxorubicin synergistically activated apoptosis signal-regulating kinase 1(ASK1)/c-jun-NH2-kinase (JNK) signaling, which also contributed to cell growth inhibition. Significantly, the role of SphK1 in OS cell growth and the synergistic anti-OS effect of phenoxodiol and doxorubicin were also seen in a mice OS xenograft model. In conclusion, our data suggest that SphK1 might be a critical oncogene of OS and co-administration phenoxodiol with doxorubicin synergistically inhibited the activity of SphK1 to suppress osteosarcoma cell growth both in vivo and in vitro.

Blocking S1P interaction with S1P₁ receptor by a novel competitive S1P₁-selective antagonist inhibits angiogenesis

Sphingosine 1-phosphate receptor type 1 (S1P(1)) was shown to be essential for vascular maturation during embryonic development and it has been demonstrated that substantial crosstalk exists between S1P(1) and other pro-angiogenic growth factors, such as vascular endothelial growth factor (VEGF) and basic fibroblast growth factor. We developed a novel S1P(1)-selective antagonist, TASP0277308, which is structurally unrelated to S1P as well as previously described S1P(1) antagonists. TASP0277308 inhibited S1P- as well as VEGF-induced cellular responses, including migration and proliferation of human umbilical vein endothelial cells. Furthermore, TASP0277308 effectively blocked a VEGF-induced tube formation in vitro and significantly suppressed tumor cell-induced angiogenesis in vivo. These findings revealed that S1P(1) is a critical component of VEGF-related angiogenic responses and also provide evidence for the efficacy of TASP0277308 for anti-cancer therapies.

Induction of brain tumor stem cell apoptosis by FTY720: a potential therapeutic agent for glioblastoma

FTY720 is a sphingosine analogue that down regulates expression of sphingosine-1-phosphate receptors and causes apoptosis of multiple tumor cell types, including glioma cells. This study examined the effect of FTY720 on brain tumor stem cells (BTSCs) derived from human glioblastoma (GBM) tissue. FTY720 treatment of BTSCs led to rapid inactivation of ERK MAP kinase, leading to upregulation of the BH3-only protein Bim and apoptosis. In combination with temozolomide (TMZ), the current standard chemotherapeutic agent for GBM, FTY720 synergistically induced BTSC apoptosis. FTY720 also slowed growth of intracranial xenograft tumors in nude mice and augmented the therapeutic effect of TMZ, leading to enhanced survival. Furthermore, the combination of FTY720 and TMZ decreased the invasiveness of BTSCs in mouse brains. FTY720 is known to cross the blood-brain barrier and recently received Food and Drug Administration approval for treatment of relapsing multiple sclerosis. Thus, FTY720 is an excellent potential therapeutic agent for treatment of GBM.

Sphingosine kinase 1 promotes tumour cell migration and invasion via the S1P/EDG1 axis in hepatocellular carcinoma

BACKGROUND/AIMS

Sphingosine kinase 1 (SphK1), which phosphorylates sphingosine to sphingosine-1-phosphate (S1P), is overexpressed in various types of cancers, and may act as an oncogene in tumorigenesis. However, little is known about the precise role of the SphK1/S1P pathway in human liver cancer, especially regarding the metastasis of hepatocellular carcinoma (HCC).

MATERIALS AND METHODS

The expression of SphK1 was detected by quantitative reverse-transcription PCR. In addition, transwell cell migration and invasion assay were carried out for functional analysis. Furthermore, the level of S1P was quantified by ELISA and Rac1/Cdc42 GTPase activation was assessed by western blot analysis.

RESULTS

The levels of SphK1 mRNA are commonly up-regulated in HCC patients and human liver cancer cell migration and invasion can be promoted by the overexpression of SphK1. In addition, inhibition of SphK1 with either a SphK1 inhibitor or siRNA reduced human liver cancer cell migration and invasion. Furthermore, overexpression of SphK1 increased S1P levels, and the exogenous addition of S1P increased liver cell migration and invasion through the EDG1 receptor.

DISCUSSION AND CONCLUSION

The results from this study provide strong evidence of a role for the SphK1/S1P/EDG1 pathway in liver metastasis, thus making it an attractive therapeutic target for the development of new anti-HCC drugs.

Immune regulation by sphingosine 1-phosphate and its receptors

It is well established that the lysophospholipid and signalling molecule sphingosine 1-phosphate (S1P) has many important functions in immune surveillance. S1P is produced from sphingosine by two distinct sphingosine kinases, SphK1 and SphK2, and acts as an intracellular messenger and as an extracellular ligand of five G protein-coupled cell surface receptors designated S1P(1)-S1P(5). S1P not only regulates peripheral lymphocyte circulation, but also influences their differentiation, activation, infiltration, and local positioning. The therapeutic value of modulating S1P metabolism and S1P receptor function is currently tested in clinical trials and holds great promise for treatment of different autoimmune diseases. Despite its obvious contribution to immune regulation, the analysis of S1P is still challenging. A major obstacle is the difficulty to analyze S1P locally in tissues and within cells due to its high metabolic turnover and the limited resolution of current analytical techniques like liquid chromatography and mass spectrometry. This review focuses on recent advancements to our understanding how different sources of S1P contribute to immune function, and how changes in production, secretion, and degradation of S1P can influence immune responses.

Targeting tumour cells at the entrance

Metabolism in tumour cells is adapted to the demands of a growing cell. The Warburg effect and increased use of glutamine are two well-known adaptations of tumour metabolism. Both require transporters to allow uptake of substrates and efflux of products. Differentiated cells are less reliant on these pathways and as a result are less vulnerable to drugs that curtail nutrient uptake. Thus drugs that reduce nutrient uptake are promising candidates for tumour therapy. Detailed understanding of tumour cell biology will allow the generation of new chemotherapeutic drugs with limited side effects. In this issue of the Biochemical Journal, Romero Rosales et al. have identified the mechanism by which the sphingolipid analogue FTY720 inhibits tumour growth.

Sphingosine-1-phosphate antibodies as potential agents in the treatment of cancer and age-related macular degeneration

Sphingosine-1-phosphate (S1P) is a pleiotropic bioactive lipid thought to be dysregulated in a variety of disease conditions. In this review, we discuss the roles of S1P in cancer and in wet age-related macular degeneration. We also explore potential treatment strategies for these disorders, including the utility of anti-S1P antibodies acting as molecular sponges to neutralize dysregulated S1P in relevant tissues.

Current and emerging therapies for the treatment of age-related macular degeneration

Age-related macular degeneration (AMD) is the leading cause of vision loss in the industrialized world. In the last few decades, the mainstay of treatment for choroidal neovascularization (CNV) due to AMD has been thermal laser photocoagulation. In the last decade, photodynamic therapy with verteporfin extended treatment for more patients. While both of these treatments have prevented further vision loss in a subset of patients, improvement in visual acuity is rare. Anti-vascular endothelial growth factor A (VEGF) therapy has revolutionized the treatment of AMD-related CNV. Pegaptanib, an anti-VEGF aptamer prevents vision loss in CNV, although the performance is similar to that of photodynamic therapy. Ranibizumab, an antibody fragment and bevacizumab, a full-length humanized monoclonal antibody against VEGF have both shown promising results with improvements in visual acuity with either agent. VEGF trap, a modified soluble VEGF receptor analogue, binds VEGF more tightly than all other anti-VEGF agents and has also shown promising results in early trials. Other treatment strategies to decrease the effect of VEGF have used small interfering ribonucleic acid (RNA) to inhibit VEGF production and VEGF receptor production. Steroids, including anecortave acetate in the treatment and prevention of CNV, have shown promise in controlled trials. Receptor tyrosine kinase inhibitors, such as vatalanib, inhibit downstream effects of VEGF, and have been effective in the treatment of CNV in early studies. Squalamine lactate inhibits plasma membrane ion channels with downstream effects on VEGF, and has shown promising results with systemic administration. Other growth factors, including pigment epithelium-derived growth factor that has been administered via an adenoviral vector has shown promising initial results. In some patients ciliary neurotrophic factor is currently being studied for the inhibition of progression of geographic atrophy. Combination therapy has been investigated, and may prove to be more effective in the management of AMD-associated CNV. Ongoing and future studies will be crucial for optimizing the treatment of patients with AMD.

Novel synthesis and biological evaluation of enigmols as therapeutic agents for treating prostate cancer

Enigmol is a synthetic, orally active 1-deoxysphingoid base analogue that has demonstrated promising activity against prostate cancer. In these studies, the pharmacologic roles of stereochemistry and N-methylation in the structure of enigmols were examined. A novel enantioselective synthesis of all four possible 2S-diastereoisomers of enigmol (2-aminooctadecane-3,5-diols) from l-alanine is reported, which features a Liebeskind-Srogl cross-coupling reaction between l-alanine thiol ester and (E)-pentadec-1-enylboronic acid as the key step. In vitro biological evaluation of the four enigmol diastereoisomers and 2S,3S,5S-N-methylenigmol against two prostate cancer cell lines (PC-3 and LNCaP) indicates that all but one diastereomer demonstrate potent oncolytic activity. In nude mouse xenograft models of human prostate cancer, enigmol was equally effective as standard prostate cancer therapies (androgen deprivation or docetaxel), and two of the enigmol diastereomers, 2S,3S,5R-enigmol and 2S,3R,5S-enigmol, also caused statistically significant inhibition of tumor growth. A pharmacokinetic profile of enigmol and N-methylenigmol is also presented.

Sphingosine 1-phosphate regulates matrix metalloproteinase-9 expression and breast cell invasion through S1P3-Gαq coupling

Recent evidence suggests that inflammation is involved in malignant progression of breast cancer. Sphingosine 1-phosphate (S1P), acting on the G-protein-coupled receptors, is known as a potent inflammatory mediator. In this study, the effect of the inflammatory lipid S1P on the regulation of invasive/migratory phenotypes of MCF10A human breast epithelial cells was investigated to elucidate a causal relationship between inflammation and the control of invasiveness of breast cells. We show that S1P causes induction of matrix metalloproteinase-9 (MMP-9) in vitro and in vivo, and thus enhances invasion and migration. We also show that fos plays a crucial role in the transcriptional activation of MMP-9 by S1P. In addition, activation of extracellular-signal-regulated kinases 1 and 2 (ERK1/2), p38 and alpha serine/threonine-protein kinase (Akt) are involved in the process of S1P-mediated induction of MMP-9 expression and invasion. Activation of the S1P receptor S1P₃ and G(αq) are required for S1P-induced invasive/migratory responses, suggesting that the enhancement of S1P-mediated invasiveness is triggered by the specific coupling of S1P₃ to the heterotrimeric G(αq) subunit. Activation of phospholipase C-β₄ and intracellular Ca²⁺ release are required for S1P-induced MMP-9 upregulation. Taken together, this study demonstrated that S1P regulates MMP-9 induction and invasiveness through coupling of S1P₃ and G(αq) in MCF10A cells, thus providing a molecular basis for the crucial role of S1P in promoting breast cell invasion.

Characterization of a sphingosine 1-phosphate receptor antagonist prodrug

Sphingosine 1-phosphate (S1P) is a phospholipid that binds to a set of G protein-coupled receptors (S1P(1)-S1P(5)) to initiate an array of signaling cascades that affect cell survival, differentiation, proliferation, and migration. On a larger physiological scale, the effects of S1P on immune cell trafficking, vascular barrier integrity, angiogenesis, and heart rate have also been observed. An impetus for the characterization of S1P-initiated signaling effects came with the discovery that FTY720 [fingolimod; 2-amino-2-(2-[4-octylphenyl]ethyl)-1,3-propanediol] modulates the immune system by acting as an agonist at S1P(1). In the course of structure-activity relationship studies to better understand the functional chemical space around FTY720, we discovered conformationally constrained FTY720 analogs that behave as S1P receptor type-selective antagonists. Here, we present a pharmacological profile of a lead S1P(1/3) antagonist prodrug, 1-(hydroxymethyl)-3-(3-octylphenyl)cyclobutane (VPC03090). VPC03090 is phosphorylated by sphingosine kinase 2 to form the competitive antagonist species 3-(3-octylphenyl)-1-(phosphonooxymethyl)cyclobutane (VPC03090-P) as observed in guanosine 5'-O-(3-[(35)S]thio)triphosphate binding assays, with effects on downstream S1P receptor signaling confirmed by Western blot and calcium mobilization assays. Oral dosing of VPC03090 results in an approximate 1:1 phosphorylated/alcohol species ratio with a half-life of 30 h in mice. Because aberrant S1P signaling has been implicated in carcinogenesis, we applied VPC03090 in an immunocompetent mouse mammary cancer model to assess its antineoplastic potential. Treatment with VPC03090 significantly inhibited the growth of 4T1 primary tumors in mice. This result calls to attention the value of S1P receptor antagonists as not only research tools but also potential therapeutic agents.

Local inactivation of sphingosine 1-phosphate in lymph nodes induces lymphopenia

Sphingosine 1-phosphate (S1P) initiates T and B cell exit from lymphoid tissues by activating the S1P(1) receptor on lymphocytes. To define the mechanistic details of this ligand-receptor interaction, the biological activity of the S1P-blocking Ab Sphingomab was investigated. Treatment of mice with Sphingomab resulted in blood B and T cell lymphopenia. Although Sphingomab blocked S1P(1)-mediated calcium flux and receptor downregulation by S1P in vitro, plasma from Sphingomab-treated mice demonstrated a 4-fold increase in S1P concentration and largely retained its stimulating activity on S1P receptors. Plasma-borne S1P was obviously not sufficiently inactivated by Sphingomab to account for the observed lymphopenia. Therefore, we addressed the local S1P-blocking activity of Sphingomab in spleen and peripheral lymph nodes (pLNs) as a potential cause of PBL depletion. Transwell chemotaxis assays revealed the migration of freshly isolated splenocytes, but not pLN cells to S1P. However, chemotaxis of pLN cells was regained after culture in S1P-low medium, and pLN cells isolated from Sphingomab-treated mice also revealed enhanced chemotaxis to S1P, indicating substantial local inactivation of S1P in pLN after Sphingomab treatment. We conclude that treatment with the S1P-blocking Ab Sphingomab induces lymphopenia by inactivating S1P locally in pLN and not systemically in plasma. Consequently, the presence of local S1P amounts in secondary lymphoid organs contributes to B and T cell egress.

STAT3-induced S1PR1 expression is crucial for persistent STAT3 activation in tumors

Interleukin-6 (IL-6)-Janus kinase (JAK) signaling is viewed as crucial for persistent signal transducer and activator of transcription-3 (STAT3) activation in cancer. However, IL-6-induced STAT3 activation is normally transient. Here we identify a key mechanism for persistent STAT3 activation in tumor cells and the tumor microenvironment. We show that expression of sphingosine-1-phosphate receptor-1 (S1PR1), a G protein-coupled receptor for the lysophospholipid sphingosine-1-phosphate (S1P), is elevated in STAT3-positive tumors. STAT3 is a transcription factor for the S1pr1 gene. Reciprocally, enhanced S1pr1 expression activates STAT3 and upregulates Il6 gene expression, thereby accelerating tumor growth and metastasis in a STAT3-dependent manner. Silencing S1pr1 in tumor cells or immune cells inhibits tumor STAT3 activity, tumor growth and metastasis. S1P-S1PR1-induced STAT3 activation is persistent, in contrast to transient STAT3 activation by IL-6. S1PR1 activates STAT3 in part by upregulating JAK2 tyrosine kinase activity. We show that STAT3-induced S1PR1 expression, as well as the S1P-S1PR1 pathway reciprocal regulation of STAT3 activity, is a major positive feedback loop for persistent STAT3 activation in cancer cells and the tumor microenvironment and for malignant progression.

Regulation of cancer cell migration and invasion by sphingosine-1-phosphate

Sphingosine-1-phosphate (S1P) is a bioactive sphingolipid that has been implicated in regulation of a number of cancer cell malignant behaviors, including cell proliferation, survival, chemotherapeutic resistance and angiogenesis. However, the effects of S1P on cancer cell migration, invasion and metastasis, are perhaps its most complex, due to the fact that, depending upon the S1P receptors that mediate its responses and the crosstalk with other signaling pathways, S1P can either positively or negatively regulate invasion. This review summarizes the effects of S1P on cancer cell invasion and the mechanisms by which it affects this important aspect of cancer cell behavior.

S1P1 and VEGFR-2 form a signaling complex with extracellularly regulated kinase 1/2 and protein kinase C-alpha regulating ML-1 thyroid carcinoma cell migration

Sphingosine 1-phosphate (S1P) and vascular endothelial growth factor receptor 2 (VEGFR-2) signaling have been shown to integrate in many biological processes. The follicular thyroid carcinoma cell line ML-1 expresses VEGFR-2 and secretes substantial amounts of both vascular endothelial growth factor (VEGF)-A and VEGF-C. ML-1 cells also express S1P-receptors (S1P(1-3,5)). S1P is able to phosphorylate VEGFR-2, and inhibiting VEGFR-2 attenuates S1P-induced migration and down-regulates S1P(1) expression in ML-1 cells. In the present study, we focused on the interactions between S1P(1) and VEGFR-2. We show that S1P receptors form complexes with VEGFR-2 and that the S1P(1)/VEGFR-2 complex associates with protein kinase C (PKC)-alpha and ERK1/2. Furthermore, the complex evokes bidirectional signaling since the S1P-induced ERK1/2 phosphorylation is sensitive to VEGFR-2 kinase inhibition and VEGF-A-induced ERK1/2 phosphorylation is sensitive to pertussis toxin treatment as well as S1P(1) small interfering RNA (siRNA) treatment. Both S1P- and VEGF-A-induced haptotaxis is sensitive to pertussis toxin treatment and S1P(1) siRNA treatment. Phosphorylation of ERK1/2 evoked by both VEGF-A and the S1P(1) agonist SEW-2871 is inhibited by PKC-alpha and PKC-betaI siRNA. We hypothesize that VEGFR-2 forms a signaling complex with S1P(1), evoking bidirectional signaling regulating both ERK1/2 phosphorylation and haptotaxis of ML-1 cells.

Erythrocytes serve as a reservoir for cellular and extracellular sphingosine 1-phosphate

Sphingosine 1-phosphate (S1P) in blood is phosphorylated, stored, and transported by red blood cells (RBC). Release of S1P from RBC into plasma is a regulated process that does not occur in plasma- or serum-free media. Plasma fractionation and incubations with isolated and recombinant proteins identified high density lipoprotein (HDL) and serum albumin (SA) as non-redundant endogenous triggers for S1P release from RBC. S1P bound to SA and HDL was able to stimulate the S1P(1) receptor in calcium flux experiments. The binding capability of acceptor molecules triggers S1P release, as demonstrated with the anti-S1P antibody Sphingomab. More S1P was extracted from RBC membranes by HDL than by SA. Blood samples from anemic patients confirmed a reduced capacity for S1P release in plasma. In co-cultures of RBC and endothelial cells (EC), we observed transcellular transportation of S1P as a second function of RBC-associated S1P in the absence of SA and HDL and during tight RBC-EC contact, mimicking conditions in tissue interstitium and capillaries. In contrast to S1P bound to SA and HDL, RBC-associated S1P was significantly incorporated by EC after S1P lyase (SGPL1) inhibition. RBC-associated S1P, therefore, has two functions: (1) It contributes to the cellular pool of SGPL1-sensitive S1P in tissues after transcellular transportation and (2) it helps maintain extracellular S1P levels via SA and HDL independently from SGPL1 activity.

ATX-LPA receptor axis in inflammation and cancer

Lysophosphatidic acid (LPA, 1- or 2-acyl-sn-glycerol 3-phosphate) mediates a plethora of physiological and pathological activities via interactions with a series of high affinity G protein-coupled receptors (GPCR). Both LPA receptor family members and autotaxin (ATX/LysoPLD), the primary LPA-producing enzyme, are aberrantly expressed in many human breast cancers and several other cancer lineages. Using transgenic mice expressing either an LPA receptor or ATX, we recently demonstrated that the ATX-LPA receptor axis plays a causal role in breast tumorigenesis and cancer-related inflammation, further validating the ATX-LPA receptor axis as a rich therapeutic target in cancer.

Novel pathways for implantation and establishment and maintenance of pregnancy in mammals

Uterine receptivity to implantation varies among species, and involves changes in expression of genes that are coordinate with attachment of trophectoderm to uterine lumenal and superficial glandular epithelia, modification of phenotype of uterine stromal cells, silencing of receptors for progesterone and estrogen, suppression of genes for immune recognition, alterations in membrane permeability to enhance conceptus-maternal exchange of factors, angiogenesis and vasculogenesis, increased vascularity of the endometrium, activation of genes for transport of nutrients into the uterine lumen, and enhanced signaling for pregnancy recognition. Differential expression of genes by uterine epithelial and stromal cells in response to progesterone, glucocorticoids, prostaglandins and interferons may influence uterine receptivity to implantation in mammals. Uterine receptivity to implantation is progesterone-dependent; however, implantation is preceded by loss of expression of receptors for progesterone (PGR) so that progesterone most likely acts via PGR-positive stromal cells throughout pregnancy. Endogenous retroviruses expressed by the uterus and/or blastocyst also affect implantation and placentation in various species. Understanding the roles of the variety of hormones, growth factors and endogenous retroviral proteins in uterine receptivity for implantation is essential to enhancing reproductive health and fertility in humans and domestic animals.

Sphingosine 1-phosphate receptor signaling

The sphingosine 1-phosphate (S1P) receptor signaling system is a productive model system. A hydrophobic zwitterionic lysophospholipid ligand with difficult physical properties interacts with five high-affinity G protein-coupled receptors to generate multiple downstream signals. These signals modulate homeostasis and pathology on a steep agonist concentration-response curve. Ligand presence is essential for vascular development and endothelial integrity, while acute increases in ligand concentrations result in cardiac death. Understanding this integrated biochemical system has exemplified the impact of both genetics and chemistry. Developing specific tools with defined biochemical properties for the reversible modulation of signals in real time has been essential to complement insights gained from genetic approaches that may be irreversible and compensated. Despite its knife-edge between life and death, this system, based in part on receptor subtype-selectivity and in part on differential attenuation of deleterious signals, now appears to be on the cusp of meaningful therapy for multiple sclerosis.

Sphingolipids as determinants of apoptosis and chemoresistance in the MCF-7 cell model system

An estimated 182,640 women and 1,990 men were diagnosed with breast cancer in 2008, and approximately 40,480 women and 450 men died from the disease. Thus, continued mechanistic studies are needed to understand the causes and develop additional therapeutics for this complicated disease. The MCF-7 cell system is one of the most recognized models for estrogen receptor (ER)-positive breast cancer and has generated approximately 13,000 publications cited in PubMed to date. A number of clues for biological mechanisms related to apoptotic/anti-apoptotic pathways and chemoresistance were elucidated and summarized in our previous review. The focus of this review is new knowledge of the central role of sphingolipid signaling in apoptotic mechanisms in estrogen receptor-positive breast cancer. The ultimate goal is to target crucial steps in survival signaling pathways that may ultimately provide additional translational solutions to the successful pharmacologic treatment of breast cancer.

Production and characterization of monoclonal anti-sphingosine-1-phosphate antibodies

Sphingosine-1-phosphate (S1P) is a pleiotropic bioactive lipid involved in multiple physiological processes. Importantly, dysregulated S1P levels are associated with several pathologies, including cardiovascular and inflammatory diseases and cancer. This report describes the successful production and characterization of a murine monoclonal antibody, LT1002, directed against S1P, using novel immunization and screening methods applied to bioactive lipids. We also report the successful generation of LT1009, the humanized variant of LT1002, for potential clinical use. Both LT1002 and LT1009 have high affinity and specificity for S1P and do not cross-react with structurally related lipids. Using an in vitro bioassay, LT1002 and LT1009 were effective in blocking S1P-mediated release of the pro-angiogenic and prometastatic cytokine, interleukin-8, from human ovarian carcinoma cells, showing that both antibodies can out-compete S1P receptors in binding to S1P. In vivo anti-angiogenic activity of all antibody variants was demonstrated using the murine choroidal neovascularization model. Importantly, intravenous administration of the antibodies showed a marked effect on lymphocyte trafficking. The resulting lead candidate, LT1009, has been formulated for Phase 1 clinical trials in cancer and age-related macular degeneration. The anti-S1P antibody shows promise as a novel, first-in-class therapeutic acting as a "molecular sponge" to selectively deplete S1P from blood and other compartments where pathological S1P levels have been implicated in disease progression or in disorders where immune modulation may be beneficial.

Regional heterogeneity in expression of the sphingosine-1-phosphate pathway in the female rat lower urinary tract

OBJECTIVE

We investigated the existence and regional distribution of sphingosine-1-phosphate regulatory enzymes and receptors in the lower urinary tract and determined the functional role of sphingosine-1-phosphate receptors in the bladder.

STUDY DESIGN

Lower urinary tract tissue from 10 female rats was harvested for real-time reverse transcriptase-polymerase chain reaction or organ bath physiology, whereas blood serum was obtained for high-performance liquid chromatography determination of sphingosine-1-phosphate levels. Statistical analysis included the Student t test and analysis of variance.

RESULTS

All 3 sphingosine-1-phosphate receptors and major enzymes were expressed throughout the lower urinary tract, but expression and physiologic force generation varied among regions. Sphingosine-1-phosphate was detected in serum.

CONCLUSION

We provide novel data that the sphingosine-1-phosphate signaling pathway regulatory proteins exist throughout the female rat lower urinary tract, but that relative expression exhibits regional heterogeneity corresponding with lower urinary tract contractile response to sphingosine-1-phosphate. Our study suggests that sphingosine-1-phosphate signaling is important in the lower urinary tract and identifies this pathway as a possible target for altering bladder smooth muscle tone.

Sphingosine-1-phosphate protects intestinal epithelial cells from apoptosis through the Akt signaling pathway

OBJECTIVE

The regulation of apoptosis of intestinal mucosal cells is important in maintenance of normal intestinal physiology.

SUMMARY

Sphingosine-1-phosphate (S1P) has been shown to play a critical role in cellular protection to otherwise lethal stimuli in several nonintestinal tissues.

METHODS

The current study determines whether S1P protected normal intestinal epithelial cells (IECs) from apoptosis and whether Akt activation was the central pathway for this effect.

RESULTS

S1P demonstrated significantly reduced levels of apoptosis induced by tumor necrosis factor-alpha (TNF-alpha)/cycloheximide (CHX). S1P induced increased levels of phosphorylated Akt and increased Akt activity, but did not affect total amounts of Akt. This activation of Akt was associated with decreased levels of both caspase-3 protein levels and of caspase-3 activity. Inactivation of Akt by treatment with the PI3K chemical inhibitor LY294002 or by overexpression of the dominant negative mutant of Akt (DNMAkt) prevented the protective effect of S1P on apoptosis. Additionally, silencing of the S1P-1 receptor by specific siRNA demonstrated a lesser decrease in apoptosis to S1P exposure.

CONCLUSION

These results indicate that S1P protects intestinal epithelial cells from apoptosis via an Akt-dependent pathway.

Sphingosine-1-phosphate as a mediator of high-density lipoprotein effects in cardiovascular protection

Sphingosine-1-phosphate (S1P) has gained special attention in the high-density lipoprotein (HDL) field because HDL is the most prominent plasma carrier of S1P and because the S1P content of HDL may be responsible for many of the pleiotropic functions of HDL. This revelation has come from the evidence that HDL employ S1P receptors and signalling pathways to implement several HDL-ascribed biological effects as diverse as endothelial nitric oxide production, vasodilation, survival, and cardioprotection. This review focuses on HDL effects that are completely or partially mediated by the S1P content of the HDL particle and differentiates them from genuine HDL effects that are S1P-independent. In addition, the functional properties of 'free', HDL-unbound S1P are sometimes different from or even contrary to those of HDL-associated S1P. The nature of the physical interactions between HDL and local and systemic S1P production will be discussed as well as their consequences for organ function. Finally, we will elucidate the potential benefits and limitations of S1P analogues as a new class of functional HDL mimetics for cardiovascular therapy.

Anastellin, the angiostatic fibronectin peptide, is a selective inhibitor of lysophospholipid signaling

Angiogenesis is regulated by integrin-dependent cell adhesion and the activation of specific cell surface receptors on vascular endothelial cells by angiogenic factors. Lysophosphatidic acid (LPA) and sphingosine-1 phosphate (S1P) are bioactive lysophospholipids that activate G protein-coupled receptors that stimulate phosphatidylinositol 3-kinase (PI3K), Ras, and Rho effector pathways involved in vascular cell survival, proliferation, adhesion, and migration. Previous studies have shown that anastellin, a fragment of the first type III module of fibronectin, functions as an antiangiogenic peptide suppressing tumor growth and metastasis. We have previously shown that anastellin blocks serum-dependent proliferation of microvessel endothelial cells (MVEC) by affecting extracellular signal-regulated kinase (ERK)-dependent G(1)-S transition. However, the mechanism by which anastellin regulates endothelial cell function remains unclear. In the present study, we mapped several lysophospholipid-mediated signaling pathways in MVEC and examined the effects of anastellin on LPA- and S1P-induced MVEC proliferation, migration, and cytoskeletal organization. Both LPA and S1P activated PI3K, Ras/ERK, and Rho/Rho kinase pathways, leading to migration, G(1)-S cell cycle progression, and stress fiber formation, respectively. Stimulation of proliferation by LPA/S1P occurred through a G(i)-dependent Ras/ERK pathway, which was independent of growth factor receptors and PI3K and Rho/Rho kinase signaling. Although LPA and S1P activated both PI3K/Akt and Ras/ERK signaling through G(i), anastellin inhibited only the Ras/ERK pathway. Stress fiber formation in response to LPA was dependent on Rho/Rho kinase but independent of G(i) and unaffected by anastellin. These results suggest that lysophospholipid mediators of G(i) activation leading to PI3K/Akt and Ras/ERK signaling bifurcate downstream of G(i) and that anastellin selectively inhibits the Ras/ERK arm of the pathway.

Heme oxygenase-1 contributes to an alternative macrophage activation profile induced by apoptotic cell supernatants

Apoptotic cells (AC) are rapidly engulfed by professional phagocytes such as macrophages to avoid secondary necrosis and thus inflammation. Recognition of AC polarizes macrophages toward an anti-inflammatory phenotype, which shows homology to an alternatively activated M2 macrophage. However, mechanistic details provoking these phenotype alterations are incompletely understood. Here, we demonstrate a biphasic up-regulation of heme oxygenase-1 (HO-1), a protein that bears an antiapoptotic as well as an anti-inflammatory potential, in primary human macrophages, which were exposed to the supernatant of AC. Although the first phase of HO-1 induction at 6 h was accomplished by AC-derived sphingosine-1-phosphate (S1P) acting via S1P receptor 1, the second wave of HO-1 induction at 24 h was attributed to autocrine signaling of vascular endothelial growth factor A (VEGFA), whose expression and release were facilitated by S1P. Whereas VEGFA release from macrophages was signal transducer and activator of transcription (STAT) 1-dependent, vascular endothelial growth factor itself triggered STAT1/STAT3 heterodimer formation, which bound to and activated the HO-1 promoter. Knockdown of HO-1 proved its relevance in facilitating enhanced expression of the antiapoptotic proteins Bcl-2 and Bcl-X(L), as well as the anti-inflammatory adenosine receptor A(2A). These findings suggest that HO-1, which is induced by AC-derived S1P, is critically involved in macrophage polarization toward an M2 phenotype.

Clinical significance of sphingosine kinase-1 expression in human astrocytomas progression and overall patient survival

PURPOSE

To characterize the expression of sphingosine kinase-1 (SPHK1) in human astrocytomas and to investigate the association between SPHK1 expression and progression of astrocytomas.

EXPERIMENTAL DESIGN

The expression of SPHK1 in normal human astrocytes, astrocytoma cell lines, and four pairs of matched astrocytoma tissues and their adjacent normal brain tissues were detected by quantitative reverse transcription-PCR and Western blot. In addition, SPHK1 protein expression was examined in 243 cases of histologically characterized astrocytomas by immunohistochemistry. Statistical analyses were applied to test for prognostic and diagnostic associations.

RESULTS

SPHK1 in astrocytoma cell lines was elevated at both mRNA and protein levels, and the SPHK1 mRNA and protein were significantly up-regulated by up to 6.8- and 40-fold, respectively, in primary astrocytomas compared with those in the adjacent noncancerous brain tissues. Immunohistochemical analysis showed that 100 of 243 (41.2%) paraffin-embedded archival astrocytoma biopsies exhibited high expression of SPHK1. Statistical analysis suggested that the up-regulation of SPHK1 was significantly correlated with the histologic grade of astrocytoma (P=0.000) and that patients with high SPHK1 level exhibited shorter survival time (P<0.001). Multivariate analysis revealed that SPHK1 up-regulation might be an independent prognostic indicator for the survival of patients with astrocytoma.

CONCLUSIONS

SPHK1 might represent a novel and useful prognostic marker for astrocytoma and play a role during the development and progression of the disease.

Induction of antiproliferative connective tissue growth factor expression in Wilms' tumor cells by sphingosine-1-phosphate receptor 2

Connective tissue growth factor (CTGF), a member of the CCN family of secreted matricellular proteins, regulates fibrosis, angiogenesis, cell proliferation, apoptosis, tumor growth, and metastasis. However, the role of CTGF and its regulation mechanism in Wilms' tumor remains largely unknown. We found that the bioactive lipid sphingosine-1-phosphate (S1P) induced CTGF expression in a concentration- and time-dependent manner in a Wilms' tumor cell line (WiT49), whereas FTY720-phosphate, an S1P analogue that binds all S1P receptors except S1P2, did not. Further, the specific S1P2 antagonist JTE-013 completely inhibited S1P-induced CTGF expression, whereas the S1P1 antagonist VPC44116 did not, indicating that this effect was mediated by S1P2. This was confirmed by adenoviral transduction of S1P2 in WiT49 cells, which showed that overexpression of S1P2 increased the expression of CTGF. Induction of CTGF by S1P was sensitive to ROCK inhibitor Y-27632 and c-Jun NH2-terminal kinase inhibitor SP600125, suggesting the requirement of RhoA/ROCK and c-Jun NH2-terminal kinase pathways for S1P-induced CTGF expression. Interestingly, the expression levels of CTGF were decreased in 8 of 10 Wilms' tumor tissues compared with matched normal tissues by quantitative real-time PCR and Western blot analysis. In vitro, human recombinant CTGF significantly inhibited the proliferation of WiT49 cells. In addition, overexpression of CTGF resulted in significant inhibition of WiT49 cell growth. Taken together, these data suggest that CTGF protein induced by S1P2 might act as a growth inhibitor in Wilms' tumor.

Anti-sphingosine-1-phosphate monoclonal antibodies inhibit angiogenesis and sub-retinal fibrosis in a murine model of laser-induced choroidal neovascularization

The efficacy of novel monoclonal antibodies that neutralize the pro-angiogenic mediator, sphingosine-1-phosphate (S1P), were tested using in vitro and in vivo angiogenesis models, including choroidal neovascularization (CNV) induced by laser disruption of Bruch's membrane. S1P receptor levels in human brain choroid plexus endothelial cells (CPEC), human lung microvascular endothelial cells, human retinal vascular endothelial cells, and circulating endothelial progenitor cells were examined by semi-quantitative PCR. The ability of murine or humanized anti-S1P monoclonal antibodies (mAbs) to inhibit S1P-mediated microvessel tube formation by CPEC on Matrigel was evaluated and capillary density in subcutaneous growth factor-loaded Matrigel plugs was determined following anti-S1P treatment. S1P promoted in vitro capillary tube formation in CPEC consistent with the presence of cognate S1P(1-5) receptor expression by these cells and the S1P antibody induced a dose-dependent reduction in microvessel tube formation. In a murine model of laser-induced rupture of Bruch's membrane, S1P was detected in posterior cups of mice receiving laser injury, but not in uninjured controls. Intravitreous injection of anti-S1P mAbs dramatically inhibited CNV formation and sub-retinal collagen deposition in all treatment groups (p<0.05 compared to controls), thereby identifying S1P as a previously unrecognized mediator of angiogenesis and subretinal fibrosis in this model. These findings suggest that neutralizing S1P with anti-S1P mAbs may be a novel method of treating patients with exudative age-related macular degeneration by reducing angiogenesis and sub-retinal fibrosis, which are responsible for visual acuity loss in this disease.

Mast cells and cancer--no longer just basic science

The incorporation of new anti-cancer kinase inhibitors within cancer management is rapidly increasing. Mast cells are sensitive to several of these new anti-cancer agents most notably to c-Kit inhibitors. As a result, studies investigating the role of mast cells in tumors may have direct clinical relevance and consequently, important clinical implications. Here we review some of the basic attributes of mast cells, especially those related to the new "targeted" drugs. Mast cell roles such as modulators of regulatory T-cells, inducers of angiogenesis and promoters of clot formation are discussed. We also review recent mouse tumor models and human pathological data which implicate mast cells as having both pro- and anti-tumor growth properties. These studies expose a complex, emerging picture of mast cell involvement in tumor biology. It seems that mast cell modulator drugs may improve the efficacy of anti-tumor therapy under certain circumstances, whilst under others, may negatively affect drug efficacy.

Lysophospholipid signaling in the function and pathology of the reproductive system

BACKGROUND

Lysophosphatidic acid (LPA) and sphingosine-1-phosphate (S1P) are two prominent signaling lysophospholipids (LPs) exerting their functions through a group of G protein-coupled receptors (GPCRs). This review covers current knowledge of the LP signaling in the function and pathology of the reproductive system.

METHODS

PubMed was searched up to May 2008 for papers on lysophospholipids/LPA/S1P/LPC/SPC in combination with each part of the reproductive system, such as testis/ovary/uterus.

RESULTS

LPA and SIP are found in significant amounts in serum and other biological fluids. To date, 10 LP receptors have been identified, including LPA(1-5) and S1P(1-5). In vitro and in vivo studies from the past three decades have demonstrated or suggested the physiological functions of LP signaling in reproduction, such as spermatogenesis, male sexual function, ovarian function, fertilization, early embryo development, embryo spacing, implantation, decidualization, pregnancy maintenance and parturition, as well as pathological roles in ovary, cervix, mammary gland and prostate cancers.

CONCLUSIONS

Receptor knock-out and other studies indicate tissue-specific and receptor-specific functions of LP signaling in reproduction. More comprehensive studies are required to define mechanisms of LP signaling and explore the potential use as a therapeutic target.

A selective sphingosine kinase 1 inhibitor integrates multiple molecular therapeutic targets in human leukemia

The potent bioactive sphingolipid mediator, sphingosine-1-phosphate (S1P), is produced by 2 sphingosine kinase isoenzymes, SphK1 and SphK2. Expression of SphK1 is up-regulated in cancers, including leukemia, and associated with cancer progression. A screen of sphingosine analogs identified (2R,3S,4E)-N-methyl-5-(4'-pentylphenyl)-2-aminopent-4-ene-1,3-diol, designated SK1-I (BML-258), as a potent, water-soluble, isoenzyme-specific inhibitor of SphK1. In contrast to pan-SphK inhibitors, SK1-I did not inhibit SphK2, PKC, or numerous other protein kinases. SK1-I decreased growth and survival of human leukemia U937 and Jurkat cells, and enhanced apoptosis and cleavage of Bcl-2. Lethality of SK1-I was reversed by caspase inhibitors and by expression of Bcl-2. SK1-I not only decreased S1P levels but concomitantly increased levels of its proapoptotic precursor ceramide. Conversely, S1P protected against SK1-I-induced apoptosis. SK1-I also induced multiple perturbations in activation of signaling and survival-related proteins, including diminished phosphorylation of ERK1/2 and Akt. Expression of constitutively active Akt protected against SK1-I-induced apoptosis. Notably, SK1-I potently induced apoptosis in leukemic blasts isolated from patients with acute myelogenous leukemia but was relatively sparing of normal peripheral blood mononuclear leukocytes. Moreover, SK1-I markedly reduced growth of AML xenograft tumors. Our results suggest that specific inhibitors of SphK1 warrant attention as potential additions to the therapeutic armamentarium in leukemia.

Lysophosphatidic acid (LPA) and angiogenesis

Lysophosphatidic acid (LPA) is a simple lipid with many important biological functions such as the regulation of cellular proliferation, cellular migration, differentiation, and suppression of apoptosis. Although a direct angiogenic effect of LPA has not been reported to date, there are indications that LPA promotes angiogenesis. In addition, LPA is a chemoattractant for cultured endothelial cells and promotes barrier function in such cultures. To test the hypothesis that LPA is angiogenic, we used the chicken chorio-allantoic membrane (CAM) assay. Sequence analysis of the cloned, full-length chicken LPA receptor cDNAs revealed three receptor types that are orthologous to the mammalian LPA(1), LPA(2), and LPA(3) receptors. We document herein that LPA is angiogenic in the CAM system and further that synthetic LPA receptor agonists and antagonists mimic or block this response, respectively. Our results predict that LPA receptor antagonists are a possible therapeutic route to interdicting angiogenesis.

Implication of ceramide, ceramide 1-phosphate and sphingosine 1-phosphate in tumorigenesis

In the last two decades there has been considerable progress in our understanding of the role of sphingolipids in controlling signal transduction processes, particularly in the mechanisms leading to regulation of cell growth and death. Ceramide is a well-characterized sphingolipid metabolite and second messenger that can be produced by cancer cells in response to a variety of stimuli, including therapeutic drugs, leading to cell cycle arrest and apoptosis. Although this is a promising aspect when thinking of treating cancer, it should be borne in mind that ceramide production may not always be a growth inhibitory or pro-apoptotic signal. In fact, ceramide can be readily converted to sphingosine 1-phosphate (S1P) by the concerted actions of ceramidases and sphingosine kinases, or to ceramide 1-phosphate (C1P) by the action of ceramide kinase. In general, S1P and C1P have opposing effects to ceramide, acting as pro-survival or mitogenic signals in most cell types. This review will address our current understanding of the many roles of ceramide, S1P and C1P in the regulation of cell growth and survival with special emphasis to the emerging role of these molecules and their metabolizing enzymes in controlling tumor progression and metastasis.

Involvement of sphingosine kinase 2 in p53-independent induction of p21 by the chemotherapeutic drug doxorubicin

Sphingosine-1-phosphate is a potent lipid mediator formed by phosphorylation of sphingosine, a metabolite of sphingolipids, catalyzed by two sphingosine kinase (SphK) isoenzymes, SphK1 and SphK2. Expression of SphK2, which is enriched in the nucleus of MCF7 human breast cancer cells, increased expression of the cyclin-dependent kinase inhibitor p21 but had no effect on p53 or its phosphorylation. The anticancer drug doxorubicin is known to increase p21 via p53-dependent and p53-independent mechanisms. Down-regulation of endogenous SphK2 with small interfering RNA targeted to unique mRNA sequences decreased basal and doxorubicin-induced expression of p21 without affecting increased expression of p53. Down-regulation of SphK2 also decreased G(2)-M arrest and markedly enhanced apoptosis induced by doxorubicin. Moreover, siSphK2 reduced doxorubicin-induced p21 expression in p53-inactivated MCF7 cells. Likewise, in human wild-type p53- and p21-expressing HCT116 colon carcinoma cells, as well as in p53-null counterparts, down-regulation of SphK2 markedly reduced p21 induction by doxorubicin. Knockdown of SphK2 sensitized HCT116 cells to apoptosis induced by doxorubicin with concomitant cleavage of poly(ADP-ribose) polymerase. Collectively, our results show that endogenous SphK2 is important for p53-independent induction of p21 expression by doxorubicin and suggest that SphK2 may influence the balance between cytostasis and apoptosis of human cancer cells.

(Dihydro)ceramide synthase 1 regulated sensitivity to cisplatin is associated with the activation of p38 mitogen-activated protein kinase and is abrogated by sphingosine kinase 1

Resistance to chemotherapeutic drugs often limits their clinical efficacy. Previous studies have implicated the bioactive sphingolipid sphingosine-1-phosphate (S-1-P) in regulating sensitivity to cisplatin [cis-diamminedichloroplatinum(II)] and showed that modulating the S-1-P lyase can alter cisplatin sensitivity. Here, we show that the members of the sphingosine kinase (SphK1 and SphK2) and dihydroceramide synthase (LASS1/CerS1, LASS4/CerS4, and LASS5/CerS5) enzyme families each have a unique role in regulating sensitivity to cisplatin and other drugs. Thus, expression of SphK1 decreases sensitivity to cisplatin, carboplatin, doxorubicin, and vincristine, whereas expression of SphK2 increases sensitivity. Expression of LASS1/CerS1 increases the sensitivity to all the drugs tested, whereas LASS5/CerS5 only increases sensitivity to doxorubicin and vincristine. LASS4/CerS4 expression has no effect on the sensitivity to any drug tested. Reflecting this, we show that the activation of the p38 mitogen-activated protein (MAP) kinase is increased only by LASS1/CerS1, and not by LASS4/CerS4 or LASS5/CerS5. Cisplatin was shown to cause a specific translocation of LASS1/CerS1, but not LASS4/CerS4 or LASS5/CerS5, from the endoplasmic reticulum (ER) to the Golgi apparatus. Supporting the hypothesis that this translocation is mechanistically involved in the response to cisplatin, we showed that expression of SphK1, but not SphK2, abrogates both the increased cisplatin sensitivity in cells stably expressing LASS1/CerS and the translocation of the LASS1/CerS1. The data suggest that the enzymes of the sphingolipid metabolic pathway can be manipulated to improve sensitivity to the widely used drug cisplatin.

Stem cell regulation by lysophospholipids

Lysophosphatidic acid (LPA) and sphingosine 1-phosphate (S1P) regulate a diverse range of mammalian cell processes, largely through engaging multiple G protein-coupled receptors specific for these lysophospholipids. LPA and S1P have been clearly identified to have widespread physiological and pathophysiological actions, controlling events within the reproductive, gastrointestinal, vascular, nervous and immune systems, and also having a prominent role in cancer. Here we review the recent literature showing the additional emerging role for LPA and S1P in the regulation of stem cells and their progenitors. We discuss the role of these lysophospholipids in regulating the proliferation, survival, differentiation and migration of a range of adult and embryonic stem cells and progenitors, and thus are likely to play a substantial role in the maintenance, generation, mobilisation and homing of stem cell and progenitor populations in the body.

Clinical relevance of ceramide metabolism in the pathogenesis of human head and neck squamous cell carcinoma (HNSCC): attenuation of C(18)-ceramide in HNSCC tumors correlates with lymphovascular invasion and nodal metastasis

It has been documented previously that defects in the generation of C(18)-ceramide, a product of ceramide synthase 1 (CerS1), also known as longevity assurance gene 1 (hLASS1), play important roles in the pathogenesis and/or progression of HNSCC. However, whether altered levels of ceramide generation in HNSCC tumors have any clinical relevance remains unknown. In this study, the levels of endogenous ceramides were measured in tumor tissues of 45 HNSCC patients as compared to their normal tissues using high-pressure liquid chromatography/mass spectrometry (LC/MS), and then possible link between ceramide levels and the clinical parameters of HNSCC were examined. The data showed that the levels of C(16)-, C(24)-, C(24:1)-ceramides were significantly elevated in the majority of tumor tissues compared to their normal tissues, while the levels of only C(18)-ceramide were significantly decreased in HNSCC tumors, especially in tumor tissues of male patients. Importantly, it was also shown here that decreased C(18)-ceramide levels in HNSCC tumor tissues were significantly associated with the higher incidences of lymphovascular invasion, and pathologic nodal metastasis. Importantly, attenuation of C(18)-ceramide was also positively linked to the higher overall stages of the primary HNSCC tumors. Therefore, these data suggest, for the first time, that the defects in the generation/accumulation of C(18)-ceramide might have important clinical roles in HNSCC, especially in lymphovascular invasion and nodal disease.

The role of lysosphingolipids in the regulation of biological processes

This review summarizes data on the role of lysosphingolipids (glucosyl- and galactosylsphingosines, sphingosine-1-phosphate, sphingosine-1-phosphocholine) in the regulation of various biological processes in normal and pathological states.