Role of the autotaxin-lysophosphatidate axis in the development of resistance to cancer therapy

The Effect of Ionizing Irradiation on the Autotaxin-Lysophasphatidic Acid Axis and Interleukin-6/8 Secretion in Different Breast Cancer Cell Lines

BACKGROUND

The Autotaxin (ATX)-lysophosphatidic acid (LPA) axis is involved in decreasing radiation sensitivity of breast tumor cells. This study aims to further elucidate the effect of irradiation on the ATX-LPA axis and cytokine secretion in different breast cancer cell lines to identify suitable breast cancer subtypes for targeted therapies.

METHODS

Different breast cancer cell lines (MCF-7 (luminal A), BT-474 (luminal B), SKBR-3 (HER2-positive), MDA-MB-231 and MDA-MB-468 (triple-negative)) and the breast epithelial cell line MCF-10A were irradiated. The influence of irradiation on LPA receptor (LPAR) expression, ATX expression, and Interleukin (IL)-6 and IL-8 secretion was analyzed. Further, the effect of IL-6 and IL-8 on ATX expression of adipose-derived stem cells (ADSC) was investigated.

RESULTS

Irradiation increased ATX and LPAR2 expression in MDA-MB-231 cells. Additionally, IL-6 secretion was enhanced in MDA-MB-231, and IL-8 secretion in MDA-MB-231 and MDA-MB-468. Stimulation of ADSC with IL-6 and IL-8 increased ATX expression in ADSC.

CONCLUSIONS

Targeting ATX or its downstream signaling pathways might enhance the sensitivity of triple-negative breast cancer cells to radiation. Further exploration of the interplay between irradiation, the ATX-LPA axis, and inflammatory cytokines may elucidate novel pathways for overcoming radioresistance and improving individual treatment outcomes.

From Classical to Alternative Pathways of 2-Arachidonoylglycerol Synthesis: AlterAGs at the Crossroad of Endocannabinoid and Lysophospholipid Signaling

2-arachidonoylglycerol (2-AG) is the most abundant endocannabinoid (EC), acting as a full agonist at both CB1 and CB2 cannabinoid receptors. It is synthesized on demand in postsynaptic membranes through the sequential action of phosphoinositide-specific phospholipase Cβ1 (PLCβ1) and diacylglycerol lipase α (DAGLα), contributing to retrograde signaling upon interaction with presynaptic CB1. However, 2-AG production might also involve various combinations of PLC and DAGL isoforms, as well as additional intracellular pathways implying other enzymes and substrates. Three other alternative pathways of 2-AG synthesis rest on the extracellular cleavage of 2-arachidonoyl-lysophospholipids by three different hydrolases: glycerophosphodiesterase 3 (GDE3), lipid phosphate phosphatases (LPPs), and two members of ecto-nucleotide pyrophosphatase/phosphodiesterases (ENPP6-7). We propose the names of AlterAG-1, -2, and -3 for three pathways sharing an ectocellular localization, allowing them to convert extracellular lysophospholipid mediators into 2-AG, thus inducing typical signaling switches between various G-protein-coupled receptors (GPCRs). This implies the critical importance of the regioisomerism of both lysophospholipid (LPLs) and 2-AG, which is the object of deep analysis within this review. The precise functional roles of AlterAGs are still poorly understood and will require gene invalidation approaches, knowing that both 2-AG and its related lysophospholipids are involved in numerous aspects of physiology and pathology, including cancer, inflammation, immune defenses, obesity, bone development, neurodegeneration, or psychiatric disorders.

A combined opposite targeting of p110δ PI3K and RhoA abrogates skin cancer

Malignant melanoma is the most aggressive and deadly skin cancer with an increasing incidence worldwide whereas SCC is the second most common non-melanoma human skin cancer with limited treatment options. Here we show that the development and metastasis of melanoma and SCC cancers can be blocked by a combined opposite targeting of RhoA and p110δ PI3K. We found that a targeted induction of RhoA activity into tumours by deletion of p190RhoGAP-a potent inhibitor of RhoA GTPase-in tumour cells together with adoptive macrophages transfer from δD910A/D910A mice in mice bearing tumours with active RhoA abrogated growth progression of melanoma and SCC tumours. Τhe efficacy of this combined treatment is the same in tumours lacking activating mutations in BRAF and in tumours harbouring the most frequent BRAF(V600E) mutation. Furthermore, the efficiency of this combined treatment is associated with decreased ATX expression in tumour cells and tumour stroma bypassing a positive feedback expression of ATX induced by direct ATX pharmacological inactivation. Together, our findings highlight the importance of targeting cancer cells and macrophages for skin cancer therapy, emerge a reverse link between ATX and RhoA and illustrate the benefit of p110δ PI3K inhibition as a combinatorial regimen for the treatment of skin cancers.

Autotaxin Secretion Is a Stromal Mechanism of Adaptive Resistance to TGFβ Inhibition in Pancreatic Ductal Adenocarcinoma

The TGFβ receptor inhibitor galunisertib demonstrated efficacy in patients with pancreatic ductal adenocarcinoma (PDAC) in the randomized phase II H9H-MC-JBAJ study, which compared galunisertib plus the chemotherapeutic agent gemcitabine with gemcitabine alone. However, additional stromal paracrine signals might confer adaptive resistance that limits the efficacy of this therapeutic strategy. Here, we found that autotaxin, a secreted enzyme that promotes inflammation and fibrosis by generating lysophosphatidic acid (LPA), mediates adaptive resistance to TGFβ receptor inhibition. Blocking TGFβ signaling prompted the skewing of cancer-associated fibroblasts (CAF) toward an inflammatory (iCAF) phenotype. iCAFs were responsible for a significant secretion of autotaxin. Paracrine autotaxin increased LPA-NFκB signaling in tumor cells that triggered treatment resistance. The autotaxin inhibitor IOA-289 suppressed NFκB activation in PDAC cells and overcame resistance to galunisertib and gemcitabine. In immunocompetent orthotopic murine models, IOA-289 synergized with galunisertib in restoring sensitivity to gemcitabine. Most importantly, treatment with galunisertib significantly increased plasma levels of autotaxin in patients enrolled in the H9H-MC-JBAJ study, and median progression-free survival was significantly longer in patients without an increase of autotaxin upon treatment with galunisertib compared with those with increased autotaxin. These results establish that autotaxin secretion by CAFs is increased by TGFβ inhibition and that circulating autotaxin levels predict response to the combination treatment approach of gemcitabine plus galunisertib.

SIGNIFICANCE

TGFβ inhibition skews cancer-associated fibroblasts toward an inflammatory phenotype that secretes autotaxin to drive adaptive resistance in PDAC, revealing autotaxin as a therapeutic target and biomarker of galunisertib response.

The autotaxin-LPA axis promotes membrane trafficking and secretion in yolk sac visceral endoderm cells

Autotaxin, encoded by the Enpp2 gene, is an exoenzyme that produces lysophosphatidic acid, thereby regulating many biologic functions. We previously reported that Enpp2 mRNA was abundantly expressed in yolk sac visceral endoderm (VE) cells and that Enpp2-/- mice were lethal at embryonic day 9.5 owing to angiogenic defects in the yolk sac. Enpp2-/- mice showed lysosome fragmentation in VE cells and embryonic abnormalities including allantois malformation, neural tube defects, no axial turning, and head cavity formation. However, whether the defects in endocytic vesicle formation affect membrane trafficking in VE cells remained to be directly examined. In this study, we found that pinocytosis, transcytosis, and secretion of angiogenic factors such as vascular endothelial growth factor and transforming growth factor β1 were impaired in Enpp2-/- VE cells. Moreover, pharmacologic inhibition of membrane trafficking phenocopied the defects of Enpp2-/- mice. These findings demonstrate that Enpp2 promotes endocytosis and secretion of angiogenic factors in VE cells, thereby regulating angiogenesis/vasculogenesis and embryonic development.

Lysophosphatidic Acid Receptor Signaling in the Human Breast Cancer Tumor Microenvironment Elicits Receptor-Dependent Effects on Tumor Progression

Lysophosphatidic acid receptors (LPARs) are six G-protein-coupled receptors that mediate LPA signaling to promote tumorigenesis and therapy resistance in many cancer subtypes, including breast cancer. Individual-receptor-targeted monotherapies are under investigation, but receptor agonism or antagonism effects within the tumor microenvironment following treatment are minimally understood. In this study, we used three large, independent breast cancer patient cohorts (TCGA, METABRIC, and GSE96058) and single-cell RNA-sequencing data to show that increased tumor LPAR1, LPAR4, and LPAR6 expression correlated with a less aggressive phenotype, while high LPAR2 expression was particularly associated with increased tumor grade and mutational burden and decreased survival. Through gene set enrichment analysis, it was determined that cell cycling pathways were enriched in tumors with low LPAR1, LPAR4, and LPAR6 expression and high LPAR2 expression. LPAR levels were lower in tumors over normal breast tissue for LPAR1, LPAR3, LPAR4, and LPAR6, while the opposite was observed for LPAR2 and LPAR5. LPAR1 and LPAR4 were highest in cancer-associated fibroblasts, while LPAR6 was highest in endothelial cells, and LPAR2 was highest in cancer epithelial cells. Tumors high in LPAR5 and LPAR6 had the highest cytolytic activity scores, indicating decreased immune system evasion. Overall, our findings suggest that potential compensatory signaling via competing receptors must be considered in LPAR inhibitor therapy.

Inhibition of branched-chain alpha-keto acid dehydrogenase kinase augments the sensitivity of ovarian and breast cancer cells to paclitaxel

CONTEXT

Many cancer patients who initially respond to chemotherapy eventually develop chemoresistance, and to address this, we previously conducted a RNAi screen to identify genes contributing to resistance. One of the hits from the screen was branched-chain α-keto acid dehydrogenase kinase (BCKDK). BCKDK controls the metabolism of branched-chain amino acids (BCAAs) through phosphorylation and inactivation of the branched-chain α-keto acid dehydrogenase complex (BCKDH), thereby inhibiting catabolism of BCAAs.

METHODS

We measured the impact on paclitaxel sensitivity of inhibiting BCKDK in ovarian and breast cancer cell lines.

RESULTS

Inhibition of BCKDK using siRNA or two chemical inhibitors (BCKDKi) was synergistic with paclitaxel in both breast and ovarian cancer cells. BCKDKi reduced levels of BCAA and the addition of exogenous BCAA suppressed this synergy. BCKDKi inactivated the mTORC1-Aurora pathway, allowing cells to overcame M-phase arrest induced by paclitaxel. In some cases, cells almost completed cytokinesis, then reverted to a single cell, resulting in multinucleate cells.

CONCLUSION

BCKDK is an attractive target to augment the sensitivity of cancer cells to paclitaxel.

Autotaxin in Breast Cancer: Role, Epigenetic Regulation and Clinical Implications

Autotaxin (ATX), the protein product of Ectonucleotide Pyrophosphatase Phosphodiesterase 2 (ENPP2), is a secreted lysophospholipase D (lysoPLD) responsible for the extracellular production of lysophosphatidic acid (LPA). ATX-LPA pathway signaling participates in several normal biological functions, but it has also been connected to cancer progression, metastasis and inflammatory processes. Significant research has established a role in breast cancer and it has been suggested as a therapeutic target and/or a clinically relevant biomarker. Recently, ENPP2 methylation was described, revealing a potential for clinical exploitation in liquid biopsy. The current review aims to gather the latest findings about aberrant signaling through ATX-LPA in breast cancer and discusses the role of ENPP2 expression and epigenetic modification, giving insights with translational value.

Serum autotaxin levels correlate with the severity of pruritus in intrahepatic cholestasis of pregnancy

PURPOSE

This study aimed to examine autotaxin (ATX) concentrations in the serum of pregnant women complicated with intrahepatic cholestasis of pregnancy (ICP) and compare them with individuals with uncomplicated healthy pregnancies.

METHODS

This prospective case-control study took place with 83 pregnant women. The study group included 43 pregnant women presenting with a singleton pregnancy diagnosed with ICP in their third trimester of pregnancy. The diagnostic power of the ATX variable was examined by receiver operating characteristic analysis, and the cut-off value calculated according to the Youden index was summarized with the related sensitivity and specificity points.

RESULTS

The mean serum concentration of maternal ATX was significantly higher in the ICP cases (8.91 ± 2.69 pg/mL) compared to the pregnant women in the control group (3.59 ± 1.39 ng/mL, p < 0.001). According to the Youden index, a 5.80 ng/mL cut-off value of serum ATX concentrations can be used to diagnose ICP with 97.7% sensitivity and 97.5% specificity. A significant highly positive correlation was found between maternal serum ATX levels and maternal serum total bile acid levels (r = 0.633 and p < 0.001) and itch intensity, which was objectified by the visual analog scale score (r = 0.951 and p < 0.001).

CONCLUSION

Maternal serum ATX levels were significantly increased in ICP patients as compared with healthy pregnant women. Also, serum ATX activity was highly correlated with the itch intensity. We consider that ATX might represent a robust, accurate, and reliable circulating biomarker to diagnose ICP.

KAI1/CD82 gene and autotaxin-lysophosphatidic acid axis in gastrointestinal cancers

The KAI1/CD82 gene inhibits the metastasis of most tumors and is remarkably correlated with tumor invasion and prognosis. Cell metabolism dysregulation is an important cause of tumor occurrence, development, and metastasis. As one of the important characteristics of tumors, cell metabolism dysregulation is attracting increasing research attention. Phospholipids are an indispensable substance in the metabolism in various tumor cells. Phospholipid metabolites have become important cell signaling molecules. The pathological role of lysophosphatidic acid (LPA) in tumors was identified in the early 1990s. Currently, LPA inhibitors have entered clinical trials but are not yet used in clinical treatment. Autotaxin (ATX) has lysophospholipase D (lysoPLD) activity and can regulate LPA levels in vivo. The LPA receptor family and ATX/lysoPLD are abnormally expressed in various gastrointestinal tumors. According to our recent pre-experimental results, KAI1/CD82 might inhibit the migration and metastasis of cancer cells by regulating the ATX-LPA axis. However, no relevant research has been reported. Clarifying the mechanism of ATX-LPA in the inhibition of cancer metastasis by KAI1/CD82 will provide an important theoretical basis for targeted cancer therapy. In this paper, the molecular compositions of the KAI1/CD82 gene and the ATX-LPA axis, their physiological functions in tumors, and their roles in gastrointestinal cancers and target therapy are reviewed.

Phosphatidylcholine-Derived Lipid Mediators: The Crosstalk Between Cancer Cells and Immune Cells

To become resistant, cancer cells need to activate and maintain molecular defense mechanisms that depend on an energy trade-off between resistance and essential functions. Metabolic reprogramming has been shown to fuel cell growth and contribute to cancer drug resistance. Recently, changes in lipid metabolism have emerged as an important driver of resistance to anticancer agents. In this review, we highlight the role of choline metabolism with a focus on the phosphatidylcholine cycle in the regulation of resistance to therapy. We analyze the contribution of phosphatidylcholine and its metabolites to intracellular processes of cancer cells, both as the major cell membrane constituents and source of energy. We further extended our discussion about the role of phosphatidylcholine-derived lipid mediators in cellular communication between cancer and immune cells within the tumor microenvironment, as well as their pivotal role in the immune regulation of therapeutic failure. Changes in phosphatidylcholine metabolism are part of an adaptive program activated in response to stress conditions that contribute to cancer therapy resistance and open therapeutic opportunities for treating drug-resistant cancers.

The ATX-LPA Axis Regulates Vascular Permeability during Cerebral Ischemic-Reperfusion

Endothelial permeability is a major complication that must be addressed during stroke treatment. Study of the mechanisms underlying blood−brain barrier (BBB) disruption and management of the hypoxic stress-induced permeability of the endothelium following reperfusion are both urgently needed for stroke management. Lysophosphatidic acid (LPA), a bioactive lipid essential for basic cellular functions, causes unfavorable outcomes during stroke progression. LPA-producing enzyme autotaxin (ATX) is regulated in ischemic stroke. We used an electrical cell-substrate impedance sensor (ECIS) to measure endothelial permeability. Mitochondrial bioenergetics were obtained using a Seahorse analyzer. AR-2 probe fluorescence assay was used to measure ATX activity. LPA increased endothelial permeability and reduced junctional protein expression in mouse brain microvascular endothelial cells (MBMEC). LPA receptor inhibitors Ki16425 and AM095 attenuated the LPA-induced changes in the endothelial permeability and junctional proteins. LPA significantly diminished mitochondrial function in MBMEC. ATX was upregulated (p < 0.05) in brain microvascular endothelial cells under hypoxic reperfusion. ATX activity and permeability were attenuated with the use of an ATX inhibitor in a mouse stroke model. The upregulation of ATX with hypoxic reperfusion leads to LPA production in brain endothelial cells favoring permeability. Inhibition of the ATX−LPA−LPAR axis could be therapeutically targeted in stroke to achieve better outcomes.

ENPP2 Promoter Methylation Correlates with Decreased Gene Expression in Breast Cancer: Implementation as a Liquid Biopsy Biomarker

Autotaxin (ATX), encoded by the ctonucleotide pyrophosphatase/phosphodiesterase 2 (ENPP2) gene, is a key enzyme in lysophosphatidic acid (LPA) synthesis. We have recently described ENPP2 methylation profiles in health and multiple malignancies and demonstrated correlation to its aberrant expression. Here we focus on breast cancer (BrCa), analyzing in silico publicly available BrCa methylome datasets, to identify differentially methylated CpGs (DMCs) and correlate them with expression. Numerous DMCs were identified between BrCa and healthy breast tissues in the gene body and promoter-associated regions (PA). PA DMCs were upregulated in BrCa tissues in relation to normal, in metastatic BrCa in relation to primary, and in stage I BrCa in relation to normal, and this was correlated to decreased mRNA expression. The first exon DMC was also investigated in circulating cell free DNA (ccfDNA) isolated by BrCa patients; methylation was increased in BrCa in relation to ccfDNA from healthy individuals, confirming in silico results. It also differed between patient groups and was correlated to the presence of multiple metastatic sites. Our data indicate that promoter methylation of ENPP2 arrests its transcription in BrCa and introduce first exon methylation as a putative biomarker for diagnosis and monitoring which can be assessed in liquid biopsy.

Roles of Autotaxin/Autotaxin-Lysophosphatidic Acid Axis in the Initiation and Progression of Liver Cancer

Autotaxin (ATX) is a secreted glycoprotein and catalyzes the hydrolysis of lysophosphatidylcholine to lysophosphatidic acid (LPA), a growth factor-like signaling phospholipid. ATX has been abundantly detected in the culture medium of various cancer cells, tumor tissues, and serum or plasma of cancer patients. Biological actions of ATX are mediated by LPA. The ATX-LPA axis mediates a plethora of activities, such as cell proliferation, survival, migration, angiogenesis, and inflammation, and participates in the regulation of various physiological and pathological processes. In this review, we have summarized the physiological function of ATX and the ATX-LPA axis in liver cancer, analyzed the role of the ATX-LPA axis in tumorigenesis and metastasis, and discussed the therapeutic strategies targeting the ATX-LPA axis, paving the way for new therapeutic developments.

High-Fat Diet Promotes Colorectal Tumorigenesis Through Modulating Gut Microbiota and Metabolites

BACKGROUND AND AIMS

Dietary fat intake is associated with increased risk of colorectal cancer (CRC). We examined the role of high-fat diet (HFD) in driving CRC through modulating gut microbiota and metabolites.

METHODS

HFD or control diet was fed to mice littermates in CRC mouse models of an azoxymethane (AOM) model and Apcmin/+ model, with or without antibiotics cocktail treatment. Germ-free mice for fecal microbiota transplantation were used for validation. Gut microbiota and metabolites were detected using metagenomic sequencing and high-performance liquid chromatography-mass spectrometry, respectively. Gut barrier function was determined using lipopolysaccharides level and transmission electron microscopy.

RESULTS

HFD promoted colorectal tumorigenesis in both AOM-treated mice and Apcmin/+ mice compared with control diet-fed mice. Gut microbiota depletion using antibiotics attenuated colon tumor formation in HFD-fed mice. A significant shift of gut microbiota composition with increased pathogenic bacteria Alistipessp.Marseille-P5997 and Alistipessp.5CPEGH6, and depleted probiotic Parabacteroides distasonis, along with impaired gut barrier function was exhibited in HFD-fed mice. Moreover, HFD-modulated gut microbiota promotes colorectal tumorigenesis in AOM-treated germ-free mice, indicating gut microbiota was essential in HFD-associated colorectal tumorigenesis. Gut metabolites alteration, including elevated lysophosphatidic acid, which was confirmed to promote CRC cell proliferation and impair cell junction, was also observed in HFD-fed mice. Moreover, transfer of stools from HFD-fed mice to germ-free mice without interference increased colonic cell proliferation, impaired gut barrier function, and induced oncogenic genes expression.

CONCLUSIONS

HFD drives colorectal tumorigenesis through inducing gut microbial dysbiosis, metabolomic dysregulation with elevated lysophosphatidic acid, and gut barrier dysfunction in mice.

Anti-fibrosis Attributes; UHPLC-MS/MS-Based pharmacokinetics profiling of a novel ATX inhibitor with excellent vivo efficacy in rat

3,4-Difluorobenzyl(1-ethyl-5-(4-((4-hydroxypiperidin-1-yl)-methyl)thiazol-2-yl)-1H-indol-3-yl)carbamate (NAI59), a small molecule with outstanding therapeutic effectiveness to anti-pulmonary fibrosis, is being developed as an autotaxin inhibitor candidate compound. To evaluate the pharmacokinetics and plasma protein binding of NAI59, a UPLC-MS/MS method was developed to quantity NAI59 in plasma and phosphate-buffered saline. The calibration curve linearity ranged from 9.95 ng·mL^-1 to 1990.00 ng·mL^-1 in plasma. The accuracy was -6.8%-5.9%, and the intra- and inter-day precision were within 15%. The matrix effect and recovery were within the criteria, as well as dilution integrity. The chromatographic and mass spectrometric conditions were also feasible to determine PBS samples, and it's proved that this method had good precision and accuracy in the range from 9.95 ng·mL^-1 to 497.50 ng·mL^-1 in PBS. It's the first time to determine the pharmacokinetics, absolute bioavailability, and plasma protein binding of NAI59 in rats by this established method. As a result, the pharmacokinetic profiles of NAI59 showed a dose-dependent relationship after oral administration, and the absolute bioavailability in rats was 6.3%. In addition, the results of protein binding showed that the combining capacity of NAI59 with plasma protein attained 90% and increased with the increase of drug concentration.

Aberrant ENPP2 expression promotes tumor progression in multiple myeloma

Ectonucleotide pyrophosphatase/phosphodiesterase 2 (ENPP2) has been recently linked to tumor development. However, its role in modulating multiple myeloma (MM) disease progression remains unclear. Here, we demonstrated that CD138+ cells isolated from MM patients presented with higher expression of ENPP2 compared with CD138- cells. Treatment of MM cells with IL-6 resulted in ENPP2 upregulation. ENPP2 overexpression promoted proliferation, inhibited apoptosis, increased lysophosphatidic acid (LPA) generation, and upregulated osteoclastogenesis mediator expression in MM cells. In contrast, ENPP2 inhibition induced apoptosis, suppressed proliferation and survival, decreased LPA generation and downregulated osteoclastogenesis mediator expression. In an MM xenograft mouse model, ENPP2 knockdown significantly reduced MM tumor burden by inhibiting cell proliferation and inducing apoptosis. Furthermore, ENPP2 knockdown decreased the levels of LPA, osteoclastogenesis mediators in sera of mice with MM. Our findings revealed the tumor-promoting role of ENPP2 in MM, thus providing new molecular evidence for targeting the ENPP2-LPA axis in MM therapy.

Lipid metabolism in cancer progression and therapeutic strategies

Dysregulated lipid metabolism represents an important metabolic alteration in cancer. Fatty acids, cholesterol, and phospholipid are the three most prevalent lipids that act as energy producers, signaling molecules, and source material for the biogenesis of cell membranes. The enhanced synthesis, storage, and uptake of lipids contribute to cancer progression. The rewiring of lipid metabolism in cancer has been linked to the activation of oncogenic signaling pathways and cross talk with the tumor microenvironment. The resulting activity favors the survival and proliferation of tumor cells in the harsh conditions within the tumor. Lipid metabolism also plays a vital role in tumor immunogenicity via effects on the function of the noncancer cells within the tumor microenvironment, especially immune‐associated cells. Targeting altered lipid metabolism pathways has shown potential as a promising anticancer therapy. Here, we review recent evidence implicating the contribution of lipid metabolic reprogramming in cancer to cancer progression, and discuss the molecular mechanisms underlying lipid metabolism rewiring in cancer, and potential therapeutic strategies directed toward lipid metabolism in cancer. This review sheds new light to fully understanding of the role of lipid metabolic reprogramming in the context of cancer and provides valuable clues on therapeutic strategies targeting lipid metabolism in cancer.

Development of a selective fluorescence-based enzyme assay for glycerophosphodiesterase family members GDE4 and GDE7

Lysophosphatidic acid (LPA) is a lipid mediator that regulates various processes, including cell migration and cancer progression. Autotaxin (ATX) is a lysophospholipase D-type exoenzyme that produces extracellular LPA. In contrast, glycerophosphodiesterase (GDE) family members GDE4 and GDE7 are intracellular lysophospholipases D that form LPA, depending on Mg²⁺ and Ca²⁺, respectively. Since no fluorescent substrate for these GDEs has been reported, in the present study, we examined whether a fluorescent ATX substrate, FS-3, could be applied to study GDE activity. We found that the membrane fractions of human GDE4- and GDE7-overexpressing human embryonic kidney 293T cells hydrolyzed FS-3 in a manner almost exclusively dependent on Mg²⁺ and Ca²⁺, respectively. Using these assay systems, we found that several ATX inhibitors, including α-bromomethylene phosphonate analog of LPA and 3-carbacyclic phosphatidic acid, also potently inhibited GDE4 and GDE7 activities. In contrast, the ATX inhibitor S32826 hardly inhibited these activities. Furthermore, FS-3 was hydrolyzed in a Mg²⁺-dependent manner by the membrane fraction of human prostate cancer LNCaP cells that express GDE4 endogenously but not by those of GDE4-deficient LNCaP cells. Similar Ca²⁺-dependent GDE7 activity was observed in human breast cancer MCF-7 cells but not in GDE7-deficient MCF-7 cells. Finally, our assay system could selectively measure GDE4 and GDE7 activities in a mixture of the membrane fractions of GDE4- and GDE7-overexpressing human embryonic kidney 293T cells in the presence of S32826. These findings allow high-throughput assays of GDE4 and GDE7 activities, which could lead to the development of selective inhibitors and stimulators as well as a better understanding of the biological roles of these enzymes.

Advances in understanding of relationship between Hhip and Lpar2 gene expression and gastric cancer

Gastric cancer (GC) is a malignant tumor derived from gastric mucosal epithelial cells. In recent years, it has been found that the Hhip and Lpar2 genes play an important role in the development of GC. The Hhip gene can inhibit the proliferation and invasion of GC cells by participating in the Hedgehog signaling pathway, while the Lpar2 gene promotes the development of GC by activating the ATX-LPA signaling pathway. In this paper, we will review the changes of expression levels, molecular mechanism, and clinical application of Hhip and Lpar2 genes in GC patients.

The lysophosphatidic acid axis in fibrosis: Implications for glaucoma

Glaucoma is a common progressive optic neuropathy that results in visual field defects and can lead to irreversible blindness. The pathophysiology of glaucoma involves dysregulated extracellular matrix remodelling in both the trabecular meshwork in the anterior chamber and in the lamina cribrosa of the optic nerve head. Fibrosis in these regions leads to raised intraocular pressure and retinal ganglion cell degeneration, respectively. Lysophosphatidic acid (LPA) is a bioactive lipid mediator which acts via six G-protein coupled receptors on the cell surface to activate intracellular pathways that promote cell proliferation, transcription and survival. LPA signalling has been implicated in both normal wound healing and pathological fibrosis. LPA enhances fibroblast proliferation, migration and contraction, and induces expression of pro-fibrotic mediators such as connective tissue growth factor. The LPA axis plays a major role in diseases such as idiopathic pulmonary fibrosis, where it has been identified as an important pharmacological target. In glaucoma, LPA is present in high levels in the aqueous humour, and its signalling has been found to increase resistance to aqueous humour outflow through altered trabecular meshwork cellular contraction and extracellular matrix deposition. LPA signalling may, therefore, also represent an attractive target for treatment of glaucoma. In this review we wish to describe the role of LPA and its related proteins in tissue fibrosis and glaucoma.

Lysophospholipids in Lung Inflammatory Diseases

The lysophospholipids (LPLs) belong to a group of bioactive lipids that play pivotal roles in several physiological and pathological processes. LPLs are derivatives of phospholipids and consist of a single hydrophobic fatty acid chain, a hydrophilic head, and a phosphate group with or without a large molecule attached. Among the LPLs, lysophosphatidic acid (LPA) and sphingosine-1-phosphate (S1P) are the simplest, and have been shown to be involved in lung inflammatory symptoms and diseases such as acute lung injury, asthma, and chronic obstructive pulmonary diseases. G protein-coupled receptors (GPCRs) mediate LPA and S1P signaling. In this chapter, we will discuss on the role of LPA, S1P, their metabolizing enzymes, inhibitors or agonists of their receptors, and their GPCR-mediated signaling in lung inflammatory symptoms and diseases, focusing specially on acute respiratory distress syndrome, asthma, and chronic obstructive pulmonary disease.

Evaluation of serum ATX and LPA as potential diagnostic biomarkers in patients with pancreatic cancer

BACKGROUND

Pancreatic cancer (PC) is a devastating disease that has a poor prognosis and a total 5-year survival rate of around 5%. The poor prognosis of PC is due in part to a lack of suitable biomarkers that can allow early diagnosis. The lysophospholipase autotaxin (ATX) and its product lysophosphatidic acid (LPA) play an essential role in disease progression in PC patients and are associated with increased morbidity in several types of cancer. In this study, we evaluated both the potential role of serum LPA and ATX as diagnostic markers in PC and their prognostic value for PC either alone or in combination with CA19-9.

METHODS

ATX, LPA and CA19-9 levels were evaluated using ELISA of serum obtained from PC patients (n = 114) healthy volunteers (HVs: n = 120) and patients with benign pancreatic diseases (BPDs: n = 94).

RESULTS

Serum levels of ATX, LPA and CA19-9 in PC patients were substantially higher than that for BPD patients or HVs (p < 0.001). The sensitivity of LPA in early phase PC was 91.74% and the specificity of ATX was 80%. The levels of ATX, LPA and CA19-9 were all substantially higher for early stage PC patients compared to levels in serum from BPD patients and HVs. The diagnostic efficacy of CA19-9 for PC was significantly enhanced by the addition of ATX and LPA (p = 0.0012).

CONCLUSION

Measurement of LPA and ATX levels together with CA19-9 levels can be used for early detection of PC and diagnosis of PC in general.

Structure-Based Discovery of Novel Chemical Classes of Autotaxin Inhibitors

Autotaxin (ATX) is a secreted glycoprotein, widely present in biological fluids, largely responsible for extracellular lysophosphatidic acid (LPA) production. LPA is a bioactive growth-factor-like lysophospholipid that exerts pleiotropic effects in almost all cell types, exerted through at least six G-protein-coupled receptors (LPAR1-6). Increased ATX expression has been detected in different chronic inflammatory diseases, while genetic or pharmacological studies have established ATX as a promising therapeutic target, exemplified by the ongoing phase III clinical trial for idiopathic pulmonary fibrosis. In this report, we employed an in silico drug discovery workflow, aiming at the identification of structurally novel series of ATX inhibitors that would be amenable to further optimization. Towards this end, a virtual screening protocol was applied involving the search into molecular databases for new small molecules potentially binding to ATX. The crystal structure of ATX in complex with a known inhibitor (HA-155) was used as a molecular model docking reference, yielding a priority list of 30 small molecule ATX inhibitors, validated by a well-established enzymatic assay of ATX activity. The two most potent, novel and structurally different compounds were further structurally optimized by deploying further in silico tools, resulting to the overall identification of six new ATX inhibitors that belong to distinct chemical classes than existing inhibitors, expanding the arsenal of chemical scaffolds and allowing further rational design.

Role of Adipose Tissue-Derived Autotaxin, Lysophosphatidate Signaling, and Inflammation in the Progression and Treatment of Breast Cancer

Autotaxin (ATX) is a secreted enzyme that produces lysophosphatidate (LPA), which signals through six G-protein coupled receptors, promoting tumor growth, metastasis, and survival from chemotherapy and radiotherapy. Many cancer cells produce ATX, but breast cancer cells express little ATX. In breast tumors, ATX is produced by tumor-associated stroma. Breast tumors are also surrounded by adipose tissue, which is a major bodily source of ATX. In mice, a high-fat diet increases adipocyte ATX production. ATX production in obesity is also increased because of low-level inflammation in the expanded adipose tissue. This increased ATX secretion and consequent LPA signaling is associated with decreased adiponectin production, which results in adverse metabolic profiles and glucose homeostasis. Increased ATX production by inflamed adipose tissue may explain the obesity-breast cancer association. Breast tumors produce inflammatory mediators that stimulate ATX transcription in tumor-adjacent adipose tissue. This drives a feedforward inflammatory cycle since increased LPA signaling increases production of more inflammatory mediators and cyclooxygenase-2. Inhibiting ATX activity, which has implications in breast cancer adjuvant treatments, attenuates this cycle. Targeting ATX activity and LPA signaling may potentially increase chemotherapy and radiotherapy efficacy, and decrease radiation-induced fibrosis morbidity independently of breast cancer type because most ATX is not derived from breast cancer cells.