Activity of 2-substituted lysophosphatidic acid (LPA) analogs at LPA receptors: discovery of a LPA1/LPA3 receptor antagonist

Group III secreted phospholipase A2 -driven lysophospholipid pathway protects against allergic asthma

Asthma is a chronic inflammatory disease of the airways characterized by recurrent episodes of airway obstruction, hyperresponsiveness, remodeling, and eosinophilia. Phospholipase A2 s (PLA2 s), which release fatty acids and lysophospholipids from membrane phospholipids, have been implicated in exacerbating asthma by generating pro-asthmatic lipid mediators, but an understanding of the association between individual PLA2 subtypes and asthma is still incomplete. Here, we show that group III-secreted PLA2 (sPLA2 -III) plays an ameliorating, rather than aggravating, role in asthma pathology. In both mouse and human lungs, sPLA2 -III was expressed in bronchial epithelial cells and decreased during the asthmatic response. In an ovalbumin (OVA)-induced asthma model, Pla2g3-/- mice exhibited enhanced airway hyperresponsiveness, eosinophilia, OVA-specific IgE production, and type 2 cytokine expression as compared to Pla2g3+/+ mice. Lipidomics analysis showed that the pulmonary levels of several lysophospholipids, including lysophosphatidylcholine, lysophosphatidylethanolamine, and lysophosphatidic acid (LPA), were decreased in OVA-challenged Pla2g3-/- mice relative to Pla2g3+/+ mice. LPA receptor 2 (LPA2 ) agonists suppressed thymic stromal lymphopoietin (TSLP) expression in bronchial epithelial cells and reversed airway hyperresponsiveness and eosinophilia in Pla2g3-/- mice, suggesting that sPLA2 -III negatively regulates allergen-induced asthma at least by producing LPA. Thus, the activation of the sPLA2 -III-LPA pathway may be a new therapeutic target for allergic asthma.

Synthesis and Biological Evaluation of Lysophosphatidic Acid Analogues Using Conformational Restriction and Bioisosteric Replacement Strategies

Lysophosphatidic acid (LPA) is a key player in many physiological and pathophysiological processes. The biological activities of LPA are mediated through interactions with-at least-six subtypes of G-protein-coupled receptors (GPCRs) named LPA1-6. Developing a pharmacological tool molecule that activates LPA subtype receptors selectively will allow a better understanding of their specific physiological roles. Here, we designed and synthesized conformationally restricted 25 1-oleoyl LPA analogues MZN-001 to MZN-025 by incorporating its glycerol linker into dihydropyran, tetrahydropyran, and pyrrolidine rings and variating the lipophilic chain. The agonistic activities of these compounds were evaluated using the TGFα shedding assay. Overall, the synthesized analogues exhibited significantly reduced agonistic activities toward LPA1, LPA2, and LPA6, while demonstrating potent activities toward LPA3, LPA4, and LPA5 compared to the parent LPA. Specifically, MZN-010 showed more than 10 times greater potency (EC50 = 4.9 nM) than the standard 1-oleoyl LPA (EC50 = 78 nM) toward LPA5 while exhibiting significantly lower activity on LPA1, LPA2, and LPA6 and comparable potency toward LPA3 and LPA4. Based on the MZN-010 scaffold, we synthesized additional analogues with improved selectivity and potency toward LPA5. Compound MZN-021, which contains a saturated lipophilic chain, exhibited 50 times more potent activity (EC50 = 1.2 nM) than the natural LPA against LPA5 with over a 45-fold higher selectivity when compared to those of other LPA receptors. Thus, MZN-021 was found to be a potent and selective LPA5 agonist. The findings of this study could contribute to broadening the current knowledge about the stereochemical and three-dimensional arrangement of LPA pharmacophore components inside LPA receptors and paving the way toward synthesizing other subtype-selective pharmacological probes.

The development of modulators for lysophosphatidic acid receptors: A comprehensive review

Lysophosphatidic acids (LPAs) are bioactive phospholipids implicated in a wide range of cellular activities that regulate a diverse array of biological functions. They recognize two types of G protein-coupled receptors (LPARs): LPA_1-3 receptors and LPA_4-6 receptors that belong to the endothelial gene (EDG) family and non-endothelial gene family, respectively. In recent years, the LPA signaling pathway has captured an increasing amount of attention because of its involvement in various diseases, such as idiopathic pulmonary fibrosis, cancers, cardiovascular diseases and neuropathic pain, making it a promising target for drug development. While no drugs targeting LPARs have been approved by the FDA thus far, at least three antagonists have entered phase Ⅱ clinical trials for idiopathic pulmonary fibrosis (BMS-986020 and BMS-986278) and systemic sclerosis (SAR100842), and one radioligand (BMT-136088/¹⁸F-BMS-986327) has entered phase Ⅰ clinical trials for positron emission tomography (PET) imaging of idiopathic pulmonary fibrosis. This article provides an extensive review on the current status of ligand development targeting LPA receptors to modulate LPA signaling and their therapeutic potential in various diseases.

Lysophosphatidic Acid Signaling in Cancer Cells: What Makes LPA So Special?

Lysophosphatidic acid (LPA) refers to a family of simple phospholipids that act as ligands for G protein-coupled receptors. While LPA exerts effects throughout the body in normal physiological circumstances, its pathological role in cancer is of great interest from a therapeutic viewpoint. The numerous LPA receptors (LPARs) are coupled to a variety of G proteins, and more than one LPAR is typically expressed on any given cell. While the individual receptors signal through conventional GPCR pathways, LPA is particularly efficacious in stimulating cancer cell proliferation and migration. This review addresses the mechanistic aspects underlying these pro-tumorigenic effects. We provide examples of LPA signaling responses in various types of cancers, with an emphasis on those where roles have been identified for specific LPARs. While providing an overview of LPAR signaling, these examples also reveal gaps in our knowledge regarding the mechanisms of LPA action at the receptor level. The current understanding of the LPAR structure and the roles of LPAR interactions with other receptors are discussed. Overall, LPARs provide insight into the potential molecular mechanisms that underlie the ability of individual GPCRs (or combinations of GPCRs) to elicit a unique spectrum of responses from their agonist ligands. Further knowledge of these mechanisms will inform drug discovery, since GPCRs are promising therapeutic targets for cancer.

Lysophosphatidic acid (LPA) receptor modulators: Structural features and recent development

Lysophosphatidic acid (LPA) activates six LPA receptors (LPAR_1-6) and regulates various cellular activities such as cell proliferation, cytoprotection, and wound healing. Many studies elucidated the pathological outcomes of LPA are due to the alteration in signaling pathways, which include migration and invasion of cancer cells, fibrosis, atherosclerosis, and inflammation. Current pathophysiological research on LPA and its receptors provides a means that LPA receptors are new therapeutic targets for disorders associated with LPA. Various chemical modulators are developed and are under investigation to treat a wide range of pathological complications. This review summarizes the physiological and pathological roles of LPA signaling, development of various LPA modulators, their structural features, patents, and their clinical outcomes.

A Novel Agonist of the Type 1 Lysophosphatidic Acid Receptor (LPA1), UCM-05194, Shows Efficacy in Neuropathic Pain Amelioration

Neuropathic pain (NP) is a complex chronic pain state with a prevalence of almost 10% in the general population. Pharmacological options for NP are limited and weakly effective, so there is a need to develop more efficacious NP attenuating drugs. Activation of the type 1 lysophosphatidic acid (LPA₁) receptor is a crucial factor in the initiation of NP. Hence, it is conceivable that a functional antagonism strategy could lead to NP mitigation. Here we describe a new series of LPA₁ agonists among which derivative (S)-17 (UCM-05194) stands out as the most potent and selective LPA₁ receptor agonist described so far (E_max = 118%, EC₅₀ = 0.24 μM, K_D = 19.6 nM; inactive at autotaxin and LPA_2-6 receptors). This compound induces characteristic LPA₁-mediated cellular effects and prompts the internalization of the receptor leading to its functional inactivation in primary sensory neurons and to an efficacious attenuation of the pain perception in an in vivo model of NP.

Regulation of tumor cell - Microenvironment interaction by the autotaxin-lysophosphatidic acid receptor axis

The lipid mediator lysophosphatidic acid (LPA) in biological fluids is primarily produced by cleavage of lysophospholipids by the lysophospholipase D enzyme Autotaxin (ATX). LPA has been identified and abundantly detected in the culture medium of various cancer cell types, tumor effusates, and ascites fluid of cancer patients. Our current understanding of the physiological role of LPA established its role in fundamental biological responses that include cell proliferation, metabolism, neuronal differentiation, angiogenesis, cell migration, hematopoiesis, inflammation, immunity, wound healing, regulation of cell excitability, and the promotion of cell survival by protecting against apoptotic death. These essential biological responses elicited by LPA are seemingly hijacked by cancer cells in many ways; transcriptional upregulation of ATX leading to increased LPA levels, enhanced expression of multiple LPA GPCR subtypes, and the downregulation of its metabolic breakdown. Recent studies have shown that overexpression of ATX and LPA GPCR can lead to malignant transformation, enhanced proliferation of cancer stem cells, increased invasion and metastasis, reprogramming of the tumor microenvironment and the metastatic niche, and development of resistance to chemo-, immuno-, and radiation-therapy of cancer. The fundamental role of LPA in cancer progression and the therapeutic inhibition of the ATX-LPA axis, although highly appealing, remains unexploited as drug development to these targets has not reached into the clinic yet. The purpose of this brief review is to highlight some unique signaling mechanisms engaged by the ATX-LPA axis and emphasize the therapeutic potential that lies in blocking the molecular targets of the LPA system.

LPA1 is a key mediator of intracellular signalling and neuroprotection triggered by tetracyclic antidepressants in hippocampal neurons

Both lysophosphatidic acid (LPA) and antidepressants have been shown to affect neuronal survival and differentiation, but whether LPA signalling participates in the action of antidepressants is still unknown. In this study, we examined the role of LPA receptors in the regulation of extracellular signal-regulated protein kinases 1 and 2 (ERK1/2) activity and neuronal survival by the tetracyclic antidepressants, mianserin and mirtazapine in hippocampal neurons. In HT22 immortalized hippocampal cells, antidepressants and LPA induced a time- and concentration-dependent stimulation of ERK1/2 phosphorylation. This response was inhibited by either LPA₁ and LPA_1/3 selective antagonists or siRNA-induced LPA₁ down-regulation, and enhanced by LPA₁ over-expression. Conversely, the selective LPA₂ antagonist H2L5186303 had no effect. Antidepressants induced cyclic AMP response element binding protein phosphorylation and this response was prevented by LPA₁ blockade. ERK1/2 stimulation involved pertussis toxin-sensitive G proteins, Src tyrosine kinases and fibroblast growth factor receptor (FGF-R) activity. Tyrosine phosphorylation of FGF-R was enhanced by antidepressants through LPA₁ . Serum withdrawal induced apoptotic death, as indicated by increased annexin V staining, caspase activation and cleavage of poly-ADP-ribose polymerase. Antidepressants inhibited the apoptotic cascade and this protective effect was curtailed by blockade of either LPA₁ , ERK1/2 or FGF-R activity. Moreover, in primary mouse hippocampal neurons, mianserin acting through LPA₁ increased phospho-ERK1/2 and protected from apoptosis induced by removal of growth supplement. These data indicate that in neurons endogenously expressed LPA₁ receptors mediate intracellular signalling and neuroprotection by tetracyclic antidepressants.

Calcium Signaling of Lysophosphatidylethanolamine through LPA1 in Human SH-SY5Y Neuroblastoma Cells

Lysophosphatidylethanolamine (LPE), a lyso-type metabolite of phosphatidylethanolamine, has been reported to be an intercellular signaling molecule. LPE mobilizes intracellular Ca²⁺ through G-protein-coupled receptor (GPCR) in some cells types. However, GPCRs for lysophosphatidic acid (LPA) were not implicated in the LPE-mediated activities in LPA GPCR overexpression systems or in SK-OV3 ovarian cancer cells. In the present study, in human SH-SY5Y neuroblastoma cells, experiments with LPA₁ antagonists showed LPE induced intracellular Ca²⁺ increases in an LPA₁ GPCR-dependent manner. Furthermore, LPE increased intracellular Ca²⁺ through pertussis-sensitive G proteins, edelfosine-sensitive-phospholipase C, 2-APB-sensitive IP₃ receptors, Ca²⁺ release from intracellular Ca²⁺ stores, and subsequent Ca²⁺ influx across plasma membranes, and LPA acted on LPA₁ and LPA₂ receptors to induce Ca²⁺ response in a 2-APB-sensitive and insensitive manner. These findings suggest novel involvements for LPE and LPA in calcium signaling in human SH-SY5Y neuroblastoma cells.

LPA1 receptor-mediated thromboxane A2 release is responsible for lysophosphatidic acid-induced vascular smooth muscle contraction

Lysophosphatidic acid (LPA) has been recognized recently as an endothelium-dependent vasodilator, but several lines of evidence indicate that it may also stimulate vascular smooth muscle cells (VSMCs), thereby contributing to vasoregulation and remodeling. In the present study, mRNA expression of all 6 LPA receptor genes was detected in murine aortic VSMCs, with the highest levels of LPA₁, LPA₂, LPA₄, and LPA₆ In endothelium-denuded thoracic aorta (TA) and abdominal aorta (AA) segments, 1-oleoyl-LPA and the LPA_1-3 agonist VPC31143 induced dose-dependent vasoconstriction. VPC31143-induced AA contraction was sensitive to pertussis toxin (PTX), the LPA_1&3 antagonist Ki16425, and genetic deletion of LPA₁ but not that of LPA₂ or inhibition of LPA₃, by diacylglycerol pyrophosphate. Surprisingly, vasoconstriction was also diminished in vessels lacking cyclooxygenase-1 [COX1 knockout (KO)] or the thromboxane prostanoid (TP) receptor (TP KO). VPC31143 increased thromboxane A₂ (TXA₂) release from TA of wild-type, TP-KO, and LPA₂-KO mice but not from LPA₁-KO or COX1-KO mice, and PTX blocked this effect. Our findings indicate that LPA causes vasoconstriction in VSMCs, mediated by LPA₁-, G_i-, and COX1-dependent autocrine/paracrine TXA₂ release and consequent TP activation. We propose that this new-found interaction between the LPA/LPA₁ and TXA₂/TP pathways plays significant roles in vasoregulation, hemostasis, thrombosis, and vascular remodeling.-Dancs, P. T., Ruisanchez, E., Balogh, A., Panta, C. R., Miklós, Z., Nüsing, R. M., Aoki, J., Chun, J., Offermanns, S., Tigyi, G., Benyó, Z. LPA₁ receptor-mediated thromboxane A₂ release is responsible for lysophosphatidic acid-induced vascular smooth muscle contraction.

LPA1 Mediates Antidepressant-Induced ERK1/2 Signaling and Protection from Oxidative Stress in Glial Cells

Antidepressants have been shown to affect glial cell functions and intracellular signaling through mechanisms that are still not completely understood. In the present study, we provide evidence that in glial cells the lysophosphatidic acid (LPA) receptor LPA₁ mediates antidepressant-induced growth factor receptor transactivation, ERK1/2 signaling, and protection from oxidative stress. Thus, in C6 glioma cells and rat cortical astrocytes, ERK1/2 activation induced by either amitriptyline or mianserin was antagonized by Ki16425 and VPC 12249 (S), which block LPA₁ and LPA₃ receptors, and by AM966, which selectively blocks LPA₁ Cell depletion of LPA₁ with siRNA treatment markedly reduced antidepressant- and LPA-induced ERK1/2 phosphorylation. LPA₁ blockade prevented antidepressant-induced phosphorylation of the transcription factors CREB and Elk-1. Antidepressants and LPA signaling to ERK1/2 was abrogated by cell treatment with pertussis toxin and by the inhibition of fibroblast growth factor (FGF) receptor (FGF-R) and platelet-derived growth factor receptor (PDGF-R) tyrosine kinases. Both Ki16425 and AM966 suppressed antidepressant-induced phosphorylation of FGF-R. Moreover, blockade of LPA₁ or inhibition of FGF-R and PDGF-R activities prevented antidepressant-stimulated Akt and GSK-3β phosphorylations. Mianserin protected C6 glioma cells and astrocytes from apoptotic cell death induced by H₂O₂, as indicated by increased cell viability, decreased expression of cleaved caspase 3, reduced cleavage of poly-ADP ribose polymerase and inhibition of DNA fragmentation. The protective effects of mianserin were antagonized by AM966. These data indicate that LPA₁ constitutes a novel molecular target of the regulatory actions of tricyclic and tetracyclic antidepressants in glial cells.

Lysophosphatidylethanolamine increases intracellular Ca(2+) through LPA(1) in PC-12 neuronal cells

G protein-coupled receptors (GPCRs) have been implicated in lysophosphatidylethanolamine (LPE)-induced increases in intracellular Ca(2+) ([Ca(2+)]i), but in different cell types, this response may be dependent or independent of lysophosphatidic acid (LPA) GPCR. The effects of LPEs from Grifola frondosa on the neuronal differentiation and apoptosis of PC-12 neuronal cells have been previously reported. In the present study, the authors sought to identify the mechanism responsible for the effects of LPEs in PC-12 neuronal cells. LPE increase [Ca(2+)]i concentration-dependently in PC-12 neuronal cells, but this LPE-induced [Ca(2+)]i increase was less than that elicited by LPA. Studies using specific inhibitors showed that LPE-induced Ca(2+) response was mediated via pertussis toxin-sensitive Gi/o proteins, edelfosine-sensitive phospholipase C, and 2-APB-sensitive IP3 receptor and by Ca(2+) influx across the cell membrane, and that this did not involve the conversion of LPE to LPA. Furthermore, LPE- and LPA-induced responses were found to show homologous and heterologous desensitization in PC-12 cells. VPC32183 and Ki16425 (antagonists of LPA1 and LPA3) inhibited LPE-induced [Ca(2+)]i increases. Furthermore, AM-095 (a specific inhibitor of LPA1) inhibited LPE-induced Ca(2+) response completely in PC-12 cells. These findings indicate LPE increases [Ca(2+)]i via a LPA1/Gi/o proteins/phospholipase C/IP3/Ca(2+) rise/Ca(2+) influx pathway in PC-12 neuronal cells.

The status of the lysophosphatidic acid receptor type 1 (LPA1R)

The current status of the LPA₁receptor and its ligands in the drug development pipeline is reviewed.

Identification of a novel class of autotaxin inhibitors through cross-screening

Starting from the known LPA₁antagonist4, three novel series of autotaxin inhibitors exemplified by7,8and9were identified using a combination of scaffold hopping and ligand-based design.

Lysophospholipid receptor nomenclature review: IUPHAR Review 8

Lysophospholipids encompass a diverse range of small, membrane-derived phospholipids that act as extracellular signals. The signalling properties are mediated by 7-transmembrane GPCRs, constituent members of which have continued to be identified after their initial discovery in the mid-1990s. Here we briefly review this class of receptors, with a particular emphasis on their protein and gene nomenclatures that reflect their cognate ligands. There are six lysophospholipid receptors that interact with lysophosphatidic acid (LPA): protein names LPA1 - LPA6 and italicized gene names LPAR1-LPAR6 (human) and Lpar1-Lpar6 (non-human). There are five sphingosine 1-phosphate (S1P) receptors: protein names S1P1 -S1P5 and italicized gene names S1PR1-S1PR5 (human) and S1pr1-S1pr5 (non-human). Recent additions to the lysophospholipid receptor family have resulted in the proposed names for a lysophosphatidyl inositol (LPI) receptor - protein name LPI1 and gene name LPIR1 (human) and Lpir1 (non-human) - and three lysophosphatidyl serine receptors - protein names LyPS1 , LyPS2 , LyPS3 and gene names LYPSR1-LYPSR3 (human) and Lypsr1-Lypsr3 (non-human) along with a variant form that does not appear to exist in humans that is provisionally named LyPS2L . This nomenclature incorporates previous recommendations from the International Union of Basic and Clinical Pharmacology, the Human Genome Organization, the Gene Nomenclature Committee, and the Mouse Genome Informatix.

Role of LPAR3, PKC and EGFR in LPA-induced cell migration in oral squamous carcinoma cells

Background

Oral squamous cell carcinoma is an aggressive neoplasm with serious morbidity and mortality, which typically spreads through local invasive growth. Lysophosphatidic acid (LPA) is involved in a number of biological processes, and may have a role in cancer cell migration and invasiveness. LPA is present in most tissues and can activate cells through six different LPA receptors (LPAR1-6). Although LPA is predominantly promigratory, some of the receptors may have antimigratory effects in certain cells. The signalling mechanisms of LPA are not fully understood, and in oral carcinoma cells the specific receptors and pathways involved in LPA-stimulated migration are unknown.

Methods

The oral carcinoma cell lines E10, SCC-9, and D2 were investigated. Cell migration was studied in a scratch wound assay, and invasion was demonstrated in organotypic three dimensional co-cultures. Protein and mRNA expression of LPA receptors was studied with Western blotting and qRT-PCR. Activation of signalling proteins was examined with Western blotting and isoelectric focusing, and signalling mechanisms were further explored using pharmacological agents and siRNA directed at specific receptors and pathways.

Results

LPA stimulated cell migration in the two oral carcinoma cell lines E10 and SCC-9, but was slightly inhibitory in D2. The receptor expression profile and the effects of specific pharmacological antagonist and agonists indicated that LPA-stimulated cell migration was mediated through LPAR3 in E10 and SCC-9. Furthermore, in both these cell lines, the stimulation by LPA was dependent on PKC activity. However, while LPA induced transactivation of EGFR and the stimulated migration was blocked by EGFR inhibitors in E10 cells, LPA did not induce EGFR transactivation in SCC-9 cells. In D2 cells, LPA induced EGFR transactivation, but this was associated with slowing of a very high inherent migration rate in these cells.

Conclusion

The results demonstrate LPA-stimulated migration in oral carcinoma cells through LPAR3, mediated further by PKC, which acts either in concert with or independently of EGFR transactivation.

Identification of heparin-binding EGF-like growth factor (HB-EGF) as a biomarker for lysophosphatidic acid receptor type 1 (LPA1) activation in human breast and prostate cancers

Lysophosphatidic acid (LPA) is a natural bioactive lipid with growth factor-like functions due to activation of a series of six G protein-coupled receptors (LPA_1–6). LPA receptor type 1 (LPA₁) signaling influences the pathophysiology of many diseases including cancer, obesity, rheumatoid arthritis, as well as lung, liver and kidney fibrosis. Therefore, LPA₁ is an attractive therapeutic target. However, most mammalian cells co-express multiple LPA receptors whose co-activation impairs the validation of target inhibition in patients because of missing LPA receptor-specific biomarkers. LPA₁ is known to induce IL-6 and IL-8 secretion, as also do LPA₂ and LPA₃. In this work, we first determined the LPA induced early-gene expression profile in three unrelated human cancer cell lines expressing different patterns of LPA receptors (PC3: LPA_1,2,3,6; MDA-MB-231: LPA_1,2; MCF-7: LPA_2,6). Among the set of genes upregulated by LPA only in LPA₁-expressing cells, we validated by QPCR and ELISA that upregulation of heparin-binding EGF-like growth factor (HB-EGF) was inhibited by LPA_1–3 antagonists (Ki16425, Debio0719). Upregulation and downregulation of HB-EGF mRNA was confirmed in vitro in human MDA-B02 breast cancer cells stably overexpressing LPA₁ (MDA-B02/LPA₁) and downregulated for LPA₁ (MDA-B02/shLPA₁), respectively. At a clinical level, we quantified the expression of LPA₁ and HB-EGF by QPCR in primary tumors of a cohort of 234 breast cancer patients and found a significantly higher expression of HB-EGF in breast tumors expressing high levels of LPA₁. We also generated human xenograph prostate tumors in mice injected with PC3 cells and found that a five-day treatment with Ki16425 significantly decreased both HB-EGF mRNA expression at the primary tumor site and circulating human HB-EGF concentrations in serum. All together our results demonstrate that HB-EGF is a new and relevant biomarker with potentially high value in quantifying LPA₁ activation state in patients receiving anti-LPA₁ therapies.

Lysophosphatidic acid receptor type 1 (LPA1) plays a functional role in osteoclast differentiation and bone resorption activity

Lysophosphatidic acid (LPA) is a natural bioactive lipid that acts through six different G protein-coupled receptors (LPA1-6) with pleiotropic activities on multiple cell types. We have previously demonstrated that LPA is necessary for successful in vitro osteoclastogenesis of bone marrow cells. Bone cells controlling bone remodeling (i.e. osteoblasts, osteoclasts, and osteocytes) express LPA1, but delineating the role of this receptor in bone remodeling is still pending. Despite Lpar1(-/-) mice displaying a low bone mass phenotype, we demonstrated that bone marrow cell-induced osteoclastogenesis was reduced in Lpar1(-/-) mice but not in Lpar2(-/-) and Lpar3(-/-) animals. Expression of LPA1 was up-regulated during osteoclastogenesis, and LPA1 antagonists (Ki16425, Debio0719, and VPC12249) inhibited osteoclast differentiation. Blocking LPA1 activity with Ki16425 inhibited expression of nuclear factor of activated T-cell cytoplasmic 1 (NFATc1) and dendritic cell-specific transmembrane protein and interfered with the fusion but not the proliferation of osteoclast precursors. Similar to wild type osteoclasts treated with Ki16425, mature Lpar1(-/-) osteoclasts had reduced podosome belt and sealing zone resulting in reduced mineralized matrix resorption. Additionally, LPA1 expression markedly increased in the bone of ovariectomized mice, which was blocked by bisphosphonate treatment. Conversely, systemic treatment with Debio0719 prevented ovariectomy-induced cancellous bone loss. Moreover, intravital multiphoton microscopy revealed that Debio0719 reduced the retention of CX3CR1-EGFP(+) osteoclast precursors in bone by increasing their mobility in the bone marrow cavity. Overall, our results demonstrate that LPA1 is essential for in vitro and in vivo osteoclast activities. Therefore, LPA1 emerges as a new target for the treatment of diseases associated with excess bone loss.

The Concise Guide to PHARMACOLOGY 2013/14: G protein-coupled receptors

The Concise Guide to PHARMACOLOGY 2013/14 provides concise overviews of the key properties of over 2000 human drug targets with their pharmacology, plus links to an open access knowledgebase of drug targets and their ligands (www.guidetopharmacology.org), which provides more detailed views of target and ligand properties. The full contents can be found at http://onlinelibrary.wiley.com/doi/10.1111/bph.12444/full. G protein-coupled receptors are one of the seven major pharmacological targets into which the Guide is divided, with the others being G protein-coupled receptors, ligand-gated ion channels, ion channels, catalytic receptors, nuclear hormone receptors, transporters and enzymes. These are presented with nomenclature guidance and summary information on the best available pharmacological tools, alongside key references and suggestions for further reading. A new landscape format has easy to use tables comparing related targets. It is a condensed version of material contemporary to late 2013, which is presented in greater detail and constantly updated on the website www.guidetopharmacology.org, superseding data presented in previous Guides to Receptors and Channels. It is produced in conjunction with NC-IUPHAR and provides the official IUPHAR classification and nomenclature for human drug targets, where appropriate. It consolidates information previously curated and displayed separately in IUPHAR-DB and the Guide to Receptors and Channels, providing a permanent, citable, point-in-time record that will survive database updates.

Lysophosphatidic acid induces vasodilation mediated by LPA1 receptors, phospholipase C, and endothelial nitric oxide synthase

Lysophosphatidic acid (LPA) has been implicated as a mediator of several cardiovascular functions, but its potential involvement in the control of vascular tone is obscure. Here, we show that both LPA (18:1) and VPC31143 (a synthetic agonist of LPA1-3 receptors) relax intact mouse thoracic aorta with similar Emax values (53.9 and 51.9% of phenylephrine-induced precontraction), although the EC50 of LPA- and VPC31143-induced vasorelaxations were different (400 vs. 15 nM, respectively). Mechanical removal of the endothelium or genetic deletion of endothelial nitric oxide synthase (eNOS) not only diminished vasorelaxation by LPA or VPC31143 but converted it to vasoconstriction. Freshly isolated mouse aortic endothelial cells expressed LPA1, LPA2, LPA4 and LPA5 transcripts. The LPA1,3 antagonist Ki16425, the LPA1 antagonist AM095, and the genetic deletion of LPA1, but not that of LPA2, abolished LPA-induced vasorelaxation. Inhibition of the phosphoinositide 3 kinase-protein kinase B/Akt pathway by wortmannin or MK-2206 failed to influence the effect of LPA. However, pharmacological inhibition of phospholipase C (PLC) by U73122 or edelfosine, but not genetic deletion of PLCε, abolished LPA-induced vasorelaxation and indicated that a PLC enzyme, other than PLCε, mediates the response. In summary, the present study identifies LPA as an endothelium-dependent vasodilator substance acting via LPA1, PLC, and eNOS.

Development of lysophosphatidic acid pathway modulators as therapies for fibrosis

Lysophosphatidic acid (LPA) is a class of bioactive phospholipid that displays a wide range of cellular effects via LPA receptors, of which six have been identified (LPAR1–6). In serum and plasma, LPA production occurs mainly by the hydrolysis of lysophosphatidylcholine by the phospholipase D activity of autotaxin (ATX). The involvement of the LPA pathway in driving chronic wound-healing conditions, such as idiopathic pulmonary fibrosis, has suggested targets in this pathway could provide potential therapeutic approaches. Mice with LPAR1 knockout or tissue-specific ATX deletion have demonstrated reduced lung fibrosis following bleomycin challenge. Therefore, strategies aimed at antagonizing LPA receptors or inhibiting ATX have gained considerable attention. This Review will summarize the current status of identifying small-molecule modulators of the LPA pathway. The therapeutic utility of LPA modulators for the treatment of fibrotic diseases will soon be revealed as clinical trials are already in progress in this area.

Lysophosphatidylethanolamine utilizes LPA(1) and CD97 in MDA-MB-231 breast cancer cells

Lysophosphatidylethanolamine (LPE) is a lyso-type metabolite of phosphatidylethanolamine (a plasma membrane component), and its intracellular Ca(2+) ([Ca(2+)]i) increasing actions may be mediated through G-protein-coupled receptor (GPCR). However, GPCRs for lysophosphatidic acid (LPA), a structurally similar representative lipid mediator, have not been implicated in LPE-mediated activities in SK-OV3 or OVCAR-3 ovarian cancer cells or in receptor over-expression systems. In the present study, LPE-induced [Ca(2+)]i increase was observed in MDA-MB-231 cells but not in other breast cancer cell lines. In addition, LPE- and LPA-induced responses showed homologous and heterologous desensitization. Furthermore, VPC32183 and Ki16425 (antagonists of LPA1 and LPA3) inhibited LPE-induced [Ca(2+)]i increases, and knockdown of LPA1 by transfection with LPA1 siRNA completely inhibited LPE-induced [Ca(2+)]i increases. Furthermore, the involvement of CD97 (an adhesion GPCR) in the action of LPA1 in MDA-MB-231 cells was demonstrated by siRNA transfection. Pertussis toxin (a specific inhibitor of Gi/o proteins), edelfosine (an inhibitor of phospholipase C), or 2-APB (an inhibitor of IP3 receptor) completely inhibited LPE-induced [Ca(2+)]i increases, whereas HA130, an inhibitor of autotaxin/lysophospholipase D, did not. Therefore, LPE is supposed to act on LPA1-CD97/Gi/o proteins/phospholipase C/IP3/Ca(2+) rise in MDA-MB-231 breast cancer cells.

Engineering vascularized tissues using natural and synthetic small molecules

Vascular growth and remodeling are complex processes that depend on the proper spatial and temporal regulation of many different signaling molecules to form functional vascular networks. The ability to understand and regulate these signals is an important clinical need with the potential to treat a wide variety of disease pathologies. Current approaches have focused largely on the delivery of proteins to promote neovascularization of ischemic tissues, most notably VEGF and FGF. Although great progress has been made in this area, results from clinical trials are disappointing and safer and more effective approaches are required. To this end, biological agents used for therapeutic neovascularization must be explored beyond the current well-investigated classes. This review focuses on potential pathways for novel drug discovery, utilizing small molecule approaches to induce and enhance neovascularization. Specifically, four classes of new and existing molecules are discussed, including transcriptional activators, receptor selective agonists and antagonists, natural product-derived small molecules, and novel synthetic small molecules.

Current progress in non-Edg family LPA receptor research

Lysophosphatidic acid (LPA) is the simplest phospholipid yet possesses myriad biological functions. Until 2003, the functions of LPA were thought to be elicited exclusively by three subtypes of the endothelial differentiation gene (Edg) family of G protein-coupled receptors - LPA(1), LPA(2), and LPA(3). However, several biological functions of LPA could not be assigned to any of these receptors indicating the existence of one or more additional LPA receptor(s). More recently, the discovery of a second cluster of LPA receptors which includes LPA(4), LPA(5), and LPA(6) has paved the way for new avenues of LPA research. Analyses of these non-Edg family LPA receptors have begun to fill in gaps to understand biological functions of LPA such as platelet aggregation and vascular development that could not be ascribed to classical Edg family LPA receptors and are also unveiling new biological functions. Here we review recent progress in the non-Edg family LPA receptor research, with special emphasis on the pharmacology, signaling, and physiological roles of this family of receptors. This article is part of a Special Issue entitled Advances in Lysophospholipid Research.

Role of sphingosine 1-phosphate and lysophosphatidic acid in fibrosis

This review highlights an emerging role for sphingosine 1-phosphate (S1P) and lysophosphatidic acid (LPA) in many different types of fibrosis. Indeed, both LPA and S1P are involved in the multi-process pathogenesis of fibrosis, being implicated in promoting the well-established process of differentiation of fibroblasts to myofibroblasts and the more controversial epithelial-mesenchymal transition and homing of fibrocytes to fibrotic lesions. Therefore, targeting the production of these bioactive lysolipids or blocking their sites/mechanisms of action has therapeutic potential. Indeed, LPA receptor 1 (LPA(1)) selective antagonists are currently being developed for the treatment of fibrosis of the lung as well as a neutralising anti-S1P antibody that is currently in Phase 1 clinical trials for treatment of age related macular degeneration. Thus, LPA- and S1P-directed therapeutics may not be too far from the clinic. This article is part of a Special Issue entitled Advances in Lysophospholipid Research.

Lysophosphatidic acid stimulates epidermal growth factor-family ectodomain shedding and paracrine signaling from human lung fibroblasts

Lysophospatidic acid (LPA) is a bioactive lipid mediator implicated in tissue repair and wound healing. It mediates diverse functional effects in fibroblasts, including proliferation, migration and contraction, but less is known about its ability to evoke paracrine signaling to other cell types involved in wound healing. We hypothesized that human pulmonary fibroblasts stimulated by LPA would exhibit ectodomain shedding of epidermal growth factor receptor (EGFR) ligands that signal to lung epithelial cells. To test this hypothesis, we used alkaline phosphatase-tagged EGFR ligand plasmids transfected into lung fibroblasts, and enzyme-linked immunosorbent assays to detect shedding of native ligands. LPA induced shedding of alkaline phosphatase-tagged heparin-binding epidermal growth factor (HB-EGF), amphiregulin, and transforming growth factor-a; non-transfected fibroblasts shed amphiregulin and HBEGF under baseline conditions, and increased shedding of HB-EGF in response to LPA. Treatment of fibroblasts with LPA resulted in elevated phosphorylation of extracellular signal-regulated kinase 1/2, enhanced expression of mRNA for c-fos, HB-EGF and amphiregulin, and enhanced proliferation at 96 hours. However, none of these fibroblast responses to LPA required ectodomain shedding or EGFR activity. To test the ability of LPA to stimulate paracrine signaling from fibroblasts, we transferred conditioned medium from LPA-stimulated cells, and found enhanced EGFR and extracellular signal-regulated kinase 1/2 phosphorylation in reporter A549 cells in excess of what could be accounted for by transferred LPA alone. These data show that LPA mediates EGF-family ectodomain shedding, resulting in enhanced paracrine signaling from lung fibroblasts to epithelial cells.

Lysophosphatidic acid receptor agonists and antagonists (WO2010051053)

Lysophosphatidic acid (LPA) is a bioactive lipid involved in signaling pathways that result in cell survival, proliferation, migration and invasion. These cellular responses are a critical element of both normal development as well as pathophysiology. In particular, dysregulated LPA production and function have been linked with cancer and cardiovascular disease. RxBio, Inc. has generated several series of LPA analogs with varied agonist/antagonist function at the LPA(1-3) GPCR targets of LPA signaling. These analogs are simplified relative to LPA through deletion of the glycerol moiety linking the LPA phosphate and fatty acid groups. One of the example compounds was shown to protect intestinal crypt cells from radiation-induced apoptosis in mice when whole body irradiation occurred 2 h after oral dosing.

International Union of Basic and Clinical Pharmacology. LXXVIII. Lysophospholipid receptor nomenclature

Lysophospholipids are cell membrane-derived lipids that include both glycerophospholipids such as lysophosphatidic acid (LPA) and sphingoid lipids such as sphingosine 1-phosphate (S1P). These and related molecules can function in vertebrates as extracellular signals by binding and activating G protein-coupled receptors. There are currently five LPA receptors, along with a proposed sixth (LPA₁-LPA₆), and five S1P receptors (S1P₁-S1P₅). A remarkably diverse biology and pathophysiology has emerged since the last review, driven by cloned receptors and targeted gene deletion ("knockout") studies in mice, which implicate receptor-mediated lysophospholipid signaling in most organ systems and multiple disease processes. The entry of various lysophospholipid receptor modulatory compounds into humans through clinical trials is ongoing and may lead to new medicines that are based on this signaling system. This review incorporates IUPHAR Nomenclature Committee guidelines in updating the nomenclature for lysophospholipid receptors ( http://www.iuphar-db.org/DATABASE/FamilyMenuForward?familyId=36).

Pharmacological tools for lysophospholipid GPCRs: development of agonists and antagonists for LPA and S1P receptors

Previous studies on lysophosphatidic acid (LPA) and sphingosine 1-phosphate (S1P) using various approaches have shown that both the molecules can act as intercellular signaling molecules. The discovery of the Edg subfamily of G-protein-coupled receptors (GPCRs) (later renamed LPA(1-3) and S1P(1-5)) for these molecules has opened up a new avenue for pathophysiological research on lysophospholipids. Genetic and molecular studies on lysophospholipid GPCRs have elucidated pathophysiological impacts and roles in cellular signaling pathways. Recently, lysophospholipid GPCR genes have been used to develop receptor subtype-selective agonists and antagonists. The discovery of FTY720, a novel immune modulator, along with other chemical tools, has provided a means of elucidating the functions of each lysophospholipid GPCR on an organ and the whole body level. This communication attempts to retrospectively review the development of agonists and antagonists for lysophospholipid GPCRs, provide integrated information on pharmacological tools for lysophospholipid GPCR signaling, and speculate on future drug development.

Aiming drug discovery at lysophosphatidic acid targets

Lysophosphatidic acid (LPA, 1-radyl-2-hydroxy-sn-glycero-3-phosphate) is the prototype member of a family of lipid mediators and second messengers. LPA and its naturally occurring analogues interact with G protein-coupled receptors on the cell surface and a nuclear hormone receptor within the cell. In addition, there are several enzymes that utilize LPA as a substrate or generate it as a product and are under its regulatory control. LPA is present in biological fluids, and attempts have been made to link changes in its concentration and molecular composition to specific disease conditions. Through their many targets, members of the LPA family regulate cell survival, apoptosis, motility, shape, differentiation, gene transcription, malignant transformation and more. The present review depicts arbitrary aspects of the physiological and pathophysiological actions of LPA and attempts to link them with select targets. Many of us are now convinced that therapies targeting LPA biosynthesis and signalling are feasible for the treatment of devastating human diseases such as cancer, fibrosis and degenerative conditions. However, successful targeting of the pathways associated with this pleiotropic lipid will depend on the future development of as yet undeveloped pharmacons.

LPA(3), a unique G protein-coupled receptor for lysophosphatidic acid

Lysophosphatidic acid (LPA; 1- or 2-acyl-sn-glycerol-3-phosphate) is a phospholipid that is involved in numerous normal physiological and pathological processes such as brain development, blood vessel formation, embryo implantation, hair growth, neuropathic pain, lung fibrosis and colon cancer. Most of these functions are mediated by G protein-coupled receptors (GPCRs) specific to LPA. So far, six GPCRs for LPA have been identified: LPA(1)/Edg2, LPA(2)/Edg4, LPA(3)/Edg7, LPA(4)/GPR23/P2Y9, LPA(5)/GPR92 and LPA(6)/P2Y5. An intracellular target of LPA has also been proposed. Among the LPA receptors, LPA(3) is unique in that it is activated significantly by a specific form of LPA (2-acyl LPA with unsaturated fatty acids) and is expressed in a limited number of tissues such as the reproductive organs. Recent studies have shown that LPA(3)-mediated LPA signaling is essential for proper embryo implantation and have revealed an unexpected genetic linkage between LPA and prostaglandin signaling. Here we review recent advances in the study of LPA(3), especially studies using LPA(3)-deficient mice. In addition, we focus on the agonists and antagonists that are specific to each LPA receptor as important tools for the functional study of LPA signaling.

2D binary QSAR modeling of LPA3 receptor antagonism

A structurally diverse dataset of 119 compounds was used to develop and validate a 2D binary QSAR model for the LPA(3) receptor. The binary QSAR model was generated using an activity threshold of greater than 15% inhibition at 10 microM. The overall accuracy of the model on the training set was 82%. It had accuracies of 55% for active and 91% for inactive compounds, respectively. The model was validated using an external test set of 10 compounds. The accuracy on the external test set was 60% overall, identifying three out of seven actives and all three inactive compounds. This model was combined with similarity searching to rapidly screen libraries and select 14 candidate LPA(3) antagonists. Experimental assays confirmed 13 of these (93%) met the 15% inhibition threshold defining actives. The successful application of the model to select candidates for screening demonstrates the power of this binary QSAR model to prioritize compound selection for experimental consideration.

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.

Structure-based drug design identifies novel LPA3 antagonists

Compound 5 ([5-(3-nitrophenoxy)-1,3-dioxo-1,3-dihydro-2-isoindol-2-yl]acetic acid) was identified as a weak selective LPA(3) antagonist (IC(50)=4504 nM) in a virtual screening effort to optimize a dual LPA(2 and 3) antagonist. Structure-based drug design techniques were used to prioritize similarity search matches of compound 5. This strategy rapidly identified 10 novel antagonists. The two most efficacious compounds identified inhibit activation of the LPA(3) receptor by 200 nM LPA with IC(50) values of 752 nM and 2992 nM. These compounds additionally define changes to our previously reported pharmacophore that will improve its ability to identify more potent and selective LPA(3) receptor antagonists. The results of the combined computational and experimental screening are reported.

Utilization of the Tango beta-arrestin recruitment technology for cell-based EDG receptor assay development and interrogation

Cellular assay development for the endothelial differentiation gene (EDG) family of G-protein-coupled receptors (GPCRs) and related lysophospholipid (LP) receptors is complicated by endogenous receptor expression and divergent receptor signaling. Endogenously expressed LP receptors exist in most tissue culture cell lines. These LP receptors, along with other endogenously expressed GPCRs, contribute to off-target signaling that can complicate interpretation of second-messenger-based cellular assay results. These receptors also activate a diverse and divergent set of cellular signaling pathways, necessitating the use of a variety of assay formats with mismatched procedures and functional readouts. This complicates examination and comparison of these receptors across the entire family. The Tango technology uses the conserved beta-arrestin-dependent receptor deactivation process to allow interrogation of the EDG and related receptors with a single functional assay. This method also isolates the target receptor signal, allowing the use of tissue culture cell lines regardless of their endogenous receptor expression. The authors describe the use of this technique to build cell-based receptor-specific assays for all 8 members of the EDG receptor family as well as the related LPA receptors GPR23, GPR92, and GPR87. In addition, they demonstrate the value of this technology for identification and investigation of functionally selective receptor compounds as demonstrated by the immunosuppressive compound FtY720-P and its action at the EDG(1) and EDG(3) receptors.

Alkoxymethylenephosphonate analogues of (Lyso) phosphatidic acid stimulate signaling networks coupled to the LPA2 receptor

An efficient stereocontrolled synthesis afforded alkoxymethylenephosphonate (MP) analogues of lysophosphatidic acid (LPA) and phosphatidic acid (PA). The pharmacological properties of MP-LPA and MP-PA analogues were characterized for LPA receptor subtype-specific agonist and antagonist activity using Ca(2+)-mobilization assays in RH7777 cells expressing the individual LPA(1)-LPA(3) receptors and CHO cells expressing LPA(4). In addition, activation of a PPARgamma reporter gene construct expressed in CV-1 cells was assessed. These metabolically stabilized LPA analogues exhibited an unexpected pattern of partial agonist/antagonist activity for the LPA G-protein-coupled receptor family and the intracellular LPA receptor PPARgamma. Analogues were compared with 18:1 LPA for activation of downstream signaling in HT-29 colon cancer cells, which exclusively express LPA(2), and both SKOV3 and OVCAR3 ovarian cancer cells, which express LPA(1), LPA(2), and LPA(3). Unexpectedly, reverse phase protein arrays showed that four MP-LPA and MP-PA analogues selectively activated downstream signaling in HT-29 cells with greater potency than LPA. In particular, the oleoyl MP-LPA analogue strongly promoted phosphorylation and activation of AKT, MEK, and pS6 in HT-29 cells in a concentration-dependent manner. In contrast, the four MP-LPA and MP-PA analogues were equipotent with LPA for pathway activation in the SKOV3 and OVCAR3 cells. Taken together, these results suggest that the MP analogues may selectively activate signaling via the LPA(2) receptor subtype, while simultaneously suppressing signaling through the LPA(1) and LPA(3) subtypes.

Lysophospholipid interactions with protein targets

Bioactive lysophospholipids include lysophosphatidic acid (LPA), sphingosine 1-phosphate (S1P), cyclic-phosphatidic acid (CPA) and alkyl glycerolphosphate (AGP). These lipid mediators stimulate a variety of responses that include cell survival, proliferation, migration, invasion, wound healing, and angiogenesis. Responses to lysophospholipids depend upon interactions with biomolecular targets in the G protein-coupled receptor (GPCR) and nuclear receptor families, as well as enzymes. Our current understanding of lysophospholipid interactions with these targets is based on a combination of lysophospholipid analog structure activity relationship studies as well as more direct structural characterization techniques such as X-ray crystallography, nuclear magnetic resonance (NMR) spectroscopy, and experimentally-validated molecular modeling. The direct structural characterization studies are the focus of this review, and provide the insight necessary to stimulate structure-based therapeutic lead discovery efforts in the future.

The lysophosphatidic acid receptor LPA1 links pulmonary fibrosis to lung injury by mediating fibroblast recruitment and vascular leak

Aberrant wound-healing responses to injury have been implicated in the development of pulmonary fibrosis, but the mediators directing these pathologic responses have yet to be fully identified. We show that lysophosphatidic acid levels increase in bronchoalveolar lavage fluid following lung injury in the bleomycin model of pulmonary fibrosis, and that mice lacking one of its receptors, LPA1, are markedly protected from fibrosis and mortality in this model. The absence of LPA1 led to reduced fibroblast recruitment and vascular leak, two responses that may be excessive when injury leads to fibrosis rather than to repair, whereas leukocyte recruitment was preserved during the first week after injury. In persons with idiopathic pulmonary fibrosis, lysophosphatidic acid levels in bronchoalveolar lavage fluid were also increased, and inhibition of LPA1 markedly reduced fibroblast responses to the chemotactic activity of this fluid. LPA1 therefore represents a new therapeutic target for diseases in which aberrant responses to injury contribute to fibrosis, such as idiopathic pulmonary fibrosis.

Alpha-substituted phosphonate analogues of lysophosphatidic acid (LPA) selectively inhibit production and action of LPA

Isoform-selective agonists and antagonists of the lysophosphatidic acid (LPA) G-protein-coupled receptors (GPCRs) have important potential applications in cell biology and therapy. LPA GPCRs regulate cancer cell proliferation, invasion, angiogenesis, and biochemical resistance to chemotherapy- and radiotherapy-induced apoptosis. LPA and its analogues are also feedback inhibitors of the enzyme lysophospholipase D (lysoPLD, also known as autotaxin), a central regulator of invasion and metastasis. For cancer therapy, the ideal therapeutic profile would be a metabolically stabilized pan-LPA receptor antagonist that also inhibits lysoPLD. Herein we describe the synthesis of a series of novel alpha-substituted methylene phosphonate analogues of LPA. Each of these analogues contains a hydrolysis-resistant phosphonate mimic of the labile monophosphate of natural LPA. The pharmacological properties of these phosphono-LPA analogues were characterized in terms of LPA receptor subtype-specific agonist and antagonist activity using Ca(2+) mobilization assays in RH7777 and CHO cells expressing the individual LPA GPCRs. In particular, the methylene phosphonate LPA analogue is a selective LPA(2) agonist, whereas the corresponding alpha-hydroxymethylene phosphonate is a selective LPA(3) agonist. Most importantly, the alpha-bromomethylene and alpha-chloromethylene phosphonates show pan-LPA receptor subtype antagonist activity. The alpha-bromomethylene phosphonates are the first reported antagonists for the LPA(4) GPCR. Each of the alpha-substituted methylene phosphonates inhibits lysoPLD, with the unsubstituted methylene phosphonate showing the most potent inhibition. Finally, unlike many LPA analogues, none of these compounds activate the intracellular LPA receptor PPARgamma.

Synthesis and evaluation of isoxazole derivatives as lysophosphatidic acid (LPA) antagonists

A series of isoxazole derivatives were synthesized and their antagonistic activities against LPA stimulation on both LPA(1)/CHO cells and rHSC cells were evaluated. Among them, 3-(4-[4-[1-(2-chloro-cyclopent-1-enyl)-ethoxycarbonylamino]-isoxazol-3- y]]-benzylsulfanyl)-propionic acid (34) showed the most potent activities.

Role of lipoprotein-associated lysophospholipids in migratory activity of coronary artery smooth muscle cells

The migration of vascular smooth muscle cells (SMCs) is a hallmark of the pathogenesis of atherosclerosis and restenosis after angioplasty. Plasma low-density lipoprotein (LDL), but not high-density lipoprotein (HDL), induced the migration of human coronary artery SMCs (CASMCs). Among bioactive lipids postulated to be present in LDL, lysophosphatidic acid (LPA) appreciably mimicked the LDL action. In fact, the LDL-induced migration was markedly inhibited by pertussis toxin, an LPA receptor antagonist Ki-16425, and a small interfering RNA (siRNA) targeted for LPA(1) receptors. Moreover, LDL contains a higher amount of LPA than HDL does. HDL markedly inhibited LPA- and platelet-derived growth factor (PDGF)-induced migration, and sphingosine 1-phosphate (S1P), the content of which is about fourfold higher in HDL than in LDL, mimicked the HDL action. The inhibitory actions of HDL and S1P were suppressed by S1P(2) receptor-specific siRNA. On the other hand, the degradation of the LPA component of LDL by monoglyceride lipase or the antagonism of LPA receptors by Ki-16425 allowed LDL to inhibit the PDGF-induced migration. The inhibitory effect of LDL was again suppressed by S1P(2) receptor-specific siRNA. In conclusion, LPA/LPA(1) receptors and S1P/S1P(2) receptors mediate the stimulatory and inhibitory migration response to LDL and HDL, respectively. The balance of not only the content of LPA and S1P in lipoproteins but also the signaling activity between LPA(1) and S1P(2) receptors in the cells may be critical in determining whether the lipoprotein is a positive or negative regulator of CASMC migration.