Inhibition of transcellular tumor cell migration and metastasis by novel carba-derivatives of cyclic phosphatidic acid

Phosphatidic acid is an endogenous negative regulator of PIEZO2 channels and mechanical sensitivity

Mechanosensitive PIEZO2 ion channels play roles in touch, proprioception, and inflammatory pain. Currently, there are no small molecule inhibitors that selectively inhibit PIEZO2 over PIEZO1. The TMEM120A protein was shown to inhibit PIEZO2 while leaving PIEZO1 unaffected. Here we find that TMEM120A expression elevates cellular levels of phosphatidic acid and lysophosphatidic acid (LPA), aligning with its structural resemblance to lipid-modifying enzymes. Intracellular application of phosphatidic acid or LPA inhibited PIEZO2, but not PIEZO1 activity. Extended extracellular exposure to the non-hydrolyzable phosphatidic acid and LPA analogue carbocyclic phosphatidic acid (ccPA) also inhibited PIEZO2. Optogenetic activation of phospholipase D (PLD), a signaling enzyme that generates phosphatidic acid, inhibited PIEZO2, but not PIEZO1. Conversely, inhibiting PLD led to increased PIEZO2 activity and increased mechanical sensitivity in mice in behavioral experiments. These findings unveil lipid regulators that selectively target PIEZO2 over PIEZO1, and identify the PLD pathway as a regulator of PIEZO2 activity.

2-Carba cyclic phosphatidic acid regulates blood coagulation and fibrinolysis system for repair after brain injury

Effective blood coagulation prevents inflammation and neuronal loss after brain injury. 2-Carba-cyclic phosphatidic acid (2ccPA), a biotherapeutic for brain injury, inhibits blood extravasation resulting from blood-brain barrier breakdown. However, the hemostasis mechanism of 2ccPA remains unclear. We determined the effects of 2ccPA-injection on blood coagulation and fibrinolysis using a needle-induced brain injury model. 2ccPA suppressed the expression of platelet degranulation-related genes. Immediately after brain injury, 2ccPA increased CD41+ platelet aggregation around the lesions and promoted fibrin aggregation. Additionally, 2ccPA supported fibrinolysis by upregulating plasminogen activator expression. These results suggest the acute effects of 2ccPA on brain hemostasis.

2-carba-cyclic phosphatidic acid modulates astrocyte-to-microglia communication and influences microglial polarization towards an anti-inflammatory phenotype

2-carba-cyclic phosphatidic acid (2ccPA) suppresses microglial and astrocyte inflammation for neuronal survival following traumatic brain injury. However, it remains unknown how 2ccPA regulates microglial activation. In this study, to elucidate the 2ccPA behavior in glial communication, we collected the astrocyte conditioned media (ACM) from primary astrocyte cultures that were treated by lipopolysaccharide (LPS) and 2ccPA and analyzed the alteration of microglial inflammation caused by the ACM treatment. The addition of the ACM derived from LPS- and 2ccPA-double treated astrocytes to microglia decreased the CD86⁺ pro-inflammatory M1 microglia, which were upregulated with the ACM collected from astrocytes treated by LPS without 2ccPA, while the direct addition of LPS and 2ccPA to microglia failed to decrease the CD86⁺ microglia to the basal level. We confirmed that the ACM from LPS- and 2ccPA-treated astrocytes increased the ratio of CD206⁺ anti-inflammatory M2 microglia to total microglia, whereas direct treatment of microglia with LPS and 2ccPA had no effect on the CD206⁺ microglia ratio, demonstrating the importance of astrocyte intervention in microglial polarization. In addition, we examined whether astrocytes modulate the 2ccPA-regulated proinflammatory cytokine production derived from microglia. The addition of the ACM from LPS- and 2ccPA-treated astrocytes to microglia remarkably canceled the LPS-induced upregulation of IL-1β, IL-6, and TNF-α secreted from microglia, while the direct addition of LPS and 2ccPA to microglia showed no affect. Therefore, our results indicate that astrocytes mediate the 2ccPA function to shift microglia towards the M2 phenotype by interfering with the polarization of M1 microglia and to suppress cytokine production.

Effects of 2-carba-cyclic phosphatidic acid derivatives on IL-1β-stimulated human chondrocytes

Osteoarthritis (OA) is a common joint disease characterized by the breakdown of subchondral bone and cartilage damage, most often affecting middle-aged and elderly people. Although the etiology of OA is still unknown, some reports suggest that inflammatory factors such as interleukin (IL)- 1β mediate the progression of OA. To investigate the effect of IL-1β and the possibility of treatment for OA, we applied 2-carba-cyclic phosphatidic acid (2ccPA) and its derivatives on human chondrocytes. 2ccPA is a synthesized phospholipid derived from a bioactive phospholipid mediator: cyclic phosphatidic acid (cPA). It has been previously reported that 2ccPA exhibits anti-inflammatory and chondroprotective effects in an OA animal model. 2ccPA and its ring-opened body (ROB) derivative significantly suppressed IL-1β-induced upregulation of IL-6, matrix metalloproteinase-13, and cyclooxygenase-2, as well as the degradation of type II collagen and aggrecan. However, the other two derivatives, namely the deacylated and ring-opened deacylated bodies, showed little effect on an IL-1β-exposed human chondrosarcoma cell-line. These data suggest that the intactness of 2ccPA and ROB is essential for anti-inflammatory effects on OA. Collectively, this study provides evidence that 2ccPA and ROB would be novel therapeutic agents for OA.

Enantioselective total syntheses of (S)-phosphonothrixin and unexpected cyclic derivative (S)-cyclic phosphonothrixin via enzymatic resolution

(S)-Phosphonothrixin is a phosphonate natural product produced by Saccharothrix sp. ST-888 that exhibits herbicidal activity. The previously reported asymmetric synthesis of (S)-phosphonothrixin is laborious and difficult to reproduce. In this study, we developed a scalable and concise enantioselective total synthesis of (S)-phosphonothrixin via two different synthetic routes by the enzymatic resolution of a known racemic epoxy alcohol. The second-generation synthesis was more efficient in terms of the overall yield (15%) and the number of steps (7) and afforded a unique cyclic phosphonate (phostone) as the product of the C-P bond formation reaction, which was converted to (S)-cyclic phosphonothrixin. Both (S)-phosphonothrixin and (S)-cyclic phosphonothrixin induced chlorosis in the plant Arabidopsis thaliana. However, (S)-cyclic phosphonothrixin exhibited lower activity than (S)-phosphonothrixin owing to its fixed conformation, as evidenced by a structure-activity relationship study. This study paves the way for the elucidation of the detailed mode of action of (S)-phosphonothrixin.

The neuroprotective function of 2-carba-cyclic phosphatidic acid: Implications for tenascin-C via astrocytes in traumatic brain injury

We examined the mechanism how 2-carba-cyclic phosphatidic acid (2ccPA), a lipid mediator, regulates neuronal apoptosis in traumatic brain injury (TBI). First, we found 2ccPA suppressed neuronal apoptosis after the injury, and increased the immunoreactivity of tenascin-C (TN-C), an extracellular matrix protein by 2ccPA in the vicinity of the wound region. 2ccPA increased the mRNA expression levels of Tnc in primary cultured astrocytes, and the conditioned medium of 2ccPA-treated astrocytes suppressed the apoptosis of cortical neurons. The neuroprotective effect of TN-C was abolished by knockdown of TN-C. These results indicate that 2ccPA contributes to neuroprotection via TN-C from astrocytes in TBI.

2-Carba-lysophosphatidic acid is a novel β-lysophosphatidic acid analogue with high potential for lysophosphatidic acid receptor activation and autotaxin inhibition

Cyclic phosphatidic acid (cPA) is a naturally occurring phospholipid mediator that, along with its chemically stabilized analogue 2-carba-cyclic phosphatidic acid (2ccPA), induces various biological activities in vitro and in vivo. Although cPA is similar to lysophosphatidic acid (LPA) in structure and synthetic pathway, some of cPA biological functions apparently differ from those reported for LPA. We previously investigated the pharmacokinetic profile of 2ccPA, which was found to be rapidly degraded, especially in acidic conditions, yielding an unidentified compound. Thus, not only cPA but also its degradation compound may contribute to the biological activity of cPA, at least for 2ccPA. In this study, we determined the structure and examined the biological activities of 2-carba-lysophosphatidic acid (2carbaLPA) as a 2ccPA degradation compound, which is a type of β-LPA analogue. Similar to LPA and cPA, 2carbaLPA induced the phosphorylation of the extracellular signal-regulated kinase and showed potent agonism for all known LPA receptors (LPA_1–6) in the transforming growth factor-α (TGFα) shedding assay, in particular for LPA₃ and LPA₄. 2carbaLPA inhibited the lysophospholipase D activity of autotaxin (ATX) in vitro similar to other cPA analogues, such as 2ccPA, 3-carba-cPA, and 3-carba-LPA (α-LPA analogue). Our study shows that 2carbaLPA is a novel β-LPA analogue with high potential for the activation of some LPA receptors and ATX inhibition.

Enhancement of Cornified Envelope-Related Gene and Protein Expression by Carba Cyclic Phosphatidic Acid in Normal Human Epidermal Keratinocytes

The aim of this study was to examine the effects of carba cyclic phosphatidic acid (ccPA) on cornified envelope (CE) formation and keratinocyte differentiation. ccPA-treated keratinocytes showed higher mRNA and protein levels of differentiation markers and CE components than untreated cells. These results suggest that ccPA could serve as therapeutic targets for treating skin barrier dysfunction because of their roles in upregulating genes and proteins associated with CE formation and keratinocyte differentiation.

Evaluation of the pharmacokinetics of 2-carba-cyclic phosphatidic acid by liquid chromatography-triple quadrupole mass spectrometry

Cyclic phosphatidic acid (cPA) is a lysophospholipid mediator that suppresses cancer metastasis and osteoarthritis. It also has neuroprotective roles in diseases such as multiple sclerosis and delayed neuronal death following transient ischemia. In order to take advantage of the properties of cPA for the development of new therapeutic strategies, we have synthesized several cPA derivatives and discovered 2-carba-cPA (2ccPA) as a promising candidate. To develop 2ccPA as a therapeutic agent, we investigated the pharmacokinetic profile of 2ccPA by liquid chromatography-triple quadrupole mass spectrometry in this study. When 2ccPA was administered intraperitoneally to mice at a dose of 1.6 mg/kg, the half-life of 2ccPA in plasma was 16 min. The 2ccPA, dosed intraperitoneally to mice at 16 mg/kg, distributed to each organ including brain at 20 min after dosing. It was found that 2ccPA was stable in neutral or alkaline conditions (e.g., intestine) but unstable in acidic conditions (e.g., stomach). When 2ccPA was orally administrated to rats as a gastro-resistant form using an enterosoluble capsule, plasma 2ccPA levels peaked at 2 h, slowly declined thereafter and persistently detected even at 10 h after administration. Here, we present the findings on the effect of the continuous release of 2ccPA from the capsule to reduce the lysophospholipase D activity and also decrease plasma levels of lysophosphatidic acid in rat. These findings will be useful in further studies for evaluating the application of 2ccPA in several disorders.

2-Carba cyclic phosphatidic acid inhibits lipopolysaccharide-induced prostaglandin E2 production in a human macrophage cell line

Cyclic phosphatidic acid (cPA) is a naturally occurring phospholipid mediator that contains a unique cyclic phosphate ring at the sn-2 and sn-3 positions of its glycerol backbone. Using mouse models for multiple sclerosis (cuprizone-induced demyelination and experimental autoimmune encephalomyelitis) and traumatic brain injury, we revealed that cPA and its metabolically stabilized cPA derivative, 2-carba-cPA (2ccPA), have potential to protect against neuroinflammation. In this study, we investigated whether 2ccPA has anti-inflammatory effect on peripheral immune function or not using inflammation-induced macrophages-like cell line, THP-1 monocytes differentiated by phorbol 12-myristate 13-acetate (PMA). Lipopolysaccharide (LPS)-stimulated THP-1 cells were found to have higher expression of the mRNAs of several inflammation-related cytokines and of the enzyme cyclooxygenase-2 (Cox-2); however, when THP-1 cells were stimulated by LPS in the presence of 2ccPA, the increase in the expression of pro-inflammatory cytokine and Cox-2 mRNA was attenuated. 2ccPA treatment also decreased the amount of prostaglandin E2 (PGE2) produced by LPS-stimulated THP-1 cells and decreased expression of the mRNA of prostaglandin E receptor 2 (EP2, PTGER2), a PGE2 receptor that mediates inflammation. These results indicate that 2ccPA has anti-inflammatory properties.

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2-Carba cyclic phosphatidic acid inhibits prostaglandin E2 production.

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2-Carba cyclic phosphatidic acid has anti-inflammatory effect.

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2-Carba cyclic phosphatidic acid has effect on peripheral immune function.

When spider and snake get along: Fusion of a snake disintegrin with a spider phospholipase D to explore their synergistic effects on a tumor cell

Venoms of spiders and snakes contain toxins extremely active and, thus, provide a natural source for the development of new biotechnological tools. Among the diversity of toxins present in the venom of spiders from genus Loxosceles, the phospholipases D (PLDs) show high hydrolytic activity upon lysophosphatidylcholine (LPC) and sphingomyelin (SM), generating bioactive phospholipids such as cyclic phosphatidic acid (cPA). Since this mediator has been shown to play a major role in complex signaling pathways, including inhibition of tumor cells, the PLDs may hold the key to learn how toxins could be used for therapeutic purposes. However, the strong platelet aggregation of PLDs and their lack of selectivity impose a major limitation. On the other hand, disintegrins present in the venoms of Viperidae snakes are a potent inhibitor of platelet aggregation and possess high affinity and specificity to molecules called integrins that are highly expressed in some tumor cells, such as murine melanoma B16F10. Therefore, disintegrins might be suitable molecules to carry the PLDs to the malignant cells, so both toxins may work synergistically to eliminate these cells. Thus, in this work, a recombinant PLD from Loxosceles gaucho spider was recombinantly fused to a disintegrin from Echis carinatus snake to form a hybrid toxin called Rechistatin. This recombinant toxin was successfully expressed in bacteria, showed binding activity in B16F10 murine melanoma cells and exerted a synergistic cytotoxicity effect on these cells. Therefore, the approach presented in this work may represent a new strategy to explore new potential applications for spider PLDs.

2-carba cyclic phosphatidic acid suppresses inflammation via regulation of microglial polarisation in the stab-wounded mouse cerebral cortex

Traumatic brain injury (TBI) is caused by physical damage to the brain and it induces blood-brain barrier (BBB) breakdown and inflammation. To diminish the sequelae of TBI, it is important to decrease haemorrhage and alleviate inflammation. In this study, we aimed to determine the effects of 2-carba-cyclic phosphatidic acid (2ccPA) on the repair mechanisms after a stab wound injury as a murine TBI model. The administration of 2ccPA suppressed serum immunoglobulin extravasation after the injury. To elucidate the effects of 2ccPA on inflammation resulting from TBI, we analysed the mRNA expression of inflammatory cytokines. We found that 2ccPA prevents a TBI-induced increase in the mRNA expression of Il-1β, Il-6, Tnf-α and Tgf-β1. In addition, 2ccPA reduces the elevation of Iba1 levels. These data suggest that 2ccPA attenuates the inflammation after a stab wound injury via the modulation of pro-inflammatory cytokines release from microglial cells. Therefore, we focused on the function of 2ccPA in microglial polarisation towards M1 or M2 phenotypes. The administration of 2ccPA decreased the number of M1 and increased the number of M2 type microglial cells, indicating that 2ccPA modulates the microglial polarisation and shifts them towards M2 phenotype. These data suggest that 2ccPA treatment suppresses the extent of BBB breakdown and inflammation after TBI.

Quantitative determination of cyclic phosphatidic acid and its carba analog in mouse organs and plasma using LC-MS/MS

Cyclic phosphatidic acid (cPA), an analog of lysophosphatidic acid, is involved in the regulation of many cellular processes. A sensitive and specific method to quantify the molecular species of cPA is important for studying the physiological and pathophysiological roles of cPA. Here, we developed a liquid chromatography-tandem mass spectrometry (LC-MS/MS)-based quantification method for the simultaneous detection of cPA species having various fatty acids (16:0, 18:0, 18:1, and 18:2) as well as 2-carba-cPA, a chemically synthesized analog of cPA. Chromatography was performed using a reversed-phase C18 column. cPA species were detected using a triple quadrupole mass spectrometer. cPA 17:0 was used as an internal standard. Intra- and interday precision values (CV%) were within 10%. The linear range of detection for each cPA species was 0.01 μg/mL to 5 μg/mL, with correlation coefficients of 0.998 or higher. The developed method was applied to the quantification of cPA species in mouse plasma and organs. The concentrations of cPA 16:0, 18:0, and 18:1 were revealed to be significantly reduced in the brains of cuprizone-treated mice, a model of multiple sclerosis, compared with control mice. These findings could be important for understanding the roles of cPA in the neurodegenerative processes associated with multiple sclerosis.

Protective and therapeutic role of 2-carba-cyclic phosphatidic acid in demyelinating disease

BACKGROUND

Multiple sclerosis is a neuroinflammatory demyelinating and neurodegenerative disease of the central nervous system characterized by recurrent and progressive demyelination/remyelination cycles, neuroinflammation, oligodendrocyte loss, demyelination, and axonal degeneration. Cyclic phosphatidic acid (cPA) is a natural phospholipid mediator with a unique cyclic phosphate ring structure at the sn-2 and sn-3 positions of the glycerol backbone. We reported earlier that cPA elicits a neurotrophin-like action and protects hippocampal neurons from ischemia-induced delayed neuronal death. We designed, chemically synthesized, and metabolically stabilized derivatives of cPA: 2-carba-cPA (2ccPA), a synthesized compound in which one of the phosphate oxygen molecules is replaced with a methylene group at the sn-2 position. In the present study, we investigated whether 2ccPA exerts protective effects in oligodendrocytes and suppresses pathology in the two most common mouse models of multiple sclerosis.

METHODS

To evaluate whether 2ccPA has potential beneficial effects on the pathology of multiple sclerosis, we investigated the effects of 2ccPA on oligodendrocyte cell death in vitro and administrated 2ccPA to mouse models of experimental autoimmune encephalomyelitis (EAE) and cuprizone-induced demyelination.

RESULTS

We demonstrated that 2ccPA suppressed the CoCl₂-induced increase in the Bax/Bcl-2 protein expression ratio and phosphorylation levels of p38MAPK and JNK protein. 2ccPA treatment reduced cuprizone-induced demyelination, microglial activation, NLRP3 inflammasome, and motor dysfunction. Furthermore, 2ccPA treatment reduced autoreactive T cells and macrophages, spinal cord injury, and pathological scores in EAE, the autoimmune multiple sclerosis mouse model.

CONCLUSIONS

We demonstrated that 2ccPA protected oligodendrocytes via suppression of the mitochondrial apoptosis pathway. Also, we found beneficial effects of 2ccPA in the multiperiod of cuprizone-induced demyelination and the pathology of EAE. These data indicate that 2ccPA may be a promising compound for the development of new drugs to treat demyelinating disease and ameliorate the symptoms of multiple sclerosis.

Structural evidence of the species-dependent albumin binding of the modified cyclic phosphatidic acid with cytotoxic properties

Cytotoxic properties of a new phosphorodithioate myristoyl derivative of cyclic phosphatidic acid as well as detailed binding mode of this ligand by human and equine serum albumins based on two crystal structures are presented.

Cyclic phosphatidic acids (cPAs) are naturally occurring, very active signalling molecules, which are involved in several pathological states, such as cancer, diabetes or obesity. As molecules of highly lipidic character found in the circulatory system, cPAs are bound and transported by the main extracellular lipid binding protein–serum albumin. Here, we present the detailed interactions between human serum albumin (HSA) and equine serum albumin (ESA) with a derivative of cPA, 1-O-myristoyl-sn-glycerol-2,3-cyclic phosphorodithioate (Myr-2S-cPA). Initial selection of the ligand used for the structural study was made by the analysis of the therapeutically promising properties of the sulfur containing analogues of cPA in respect to the unmodified lysophospholipids (LPLs). Substitution of one or two non-bridging oxygen atoms in the phosphate group with one or two sulfur atoms increases the cytotoxic effect of cPAs up to 60% on the human prostate cancer (PC) cells. Myr-2S-cPA reduces cancer cell viability in a dose-dependent manner, with IC₅₀ value of 29.0 μM after 24 h incubation, which is almost 30% lower than IC₅₀ of single substituted phosphorothioate cPA. Although, the structural homology between HSA and ESA is big, their crystal complexes with Myr-2S-cPA demonstrate significantly different mode of binding of this LPL analogue. HSA binds three molecules of Myr-2S-cPA, whereas ESA only one. Moreover, none of the identified Myr-2S-cPA binding sites overlap in both albumins.

Autotaxin and LPA1 and LPA5 receptors exert disparate functions in tumor cells versus the host tissue microenvironment in melanoma invasion and metastasis

Autotaxin (ENPP2/ATX) and lysophosphatidic acid (LPA) receptors represent two key players in regulating cancer progression. The present study sought to understand the mechanistic role of LPA G protein-coupled receptors (GPCR), not only in the tumor cells but also in stromal cells of the tumor microenvironment. B16F10 melanoma cells predominantly express LPA5 and LPA2 receptors but lack LPA1. LPA dose dependently inhibited invasion of cells across a Matrigel layer. RNAi-mediated knockdown of LPA5 relieved the inhibitory effect of LPA on invasion without affecting basal invasion. This suggests that LPA5 exerts an anti-invasive action in melanoma cells in response to LPA. In addition, both siRNA-mediated knockdown and pharmacologic inhibition of LPA2 reduced the basal rate invasion. Unexpectedly, when probing the role of this GPCR in host tissues, it was found that the incidence of melanoma-derived lung metastasis was greatly reduced in LPA5 knockout (KO) mice compared with wild-type (WT) mice. LPA1-KO but not LPA2-KO mice also showed diminished melanoma-derived lung metastasis, suggesting that host LPA1 and LPA5 receptors play critical roles in the seeding of metastasis. The decrease in tumor cell residence in the lungs of LPA1-KO and LPA5-KO animals was apparent 24 hours after injection. However, KO of LPA1, LPA2, or LPA5 did not affect the subcutaneous growth of melanoma tumors.

IMPLICATIONS

These findings suggest that tumor and stromal LPA receptors, in particular LPA1 and LPA5, play different roles in invasion and the seeding of metastasis.

Cyclic phosphatidic acid relieves osteoarthritis symptoms

Background

Cyclic phosphatidic acid (cPA) is a naturally occurring phospholipid mediator with a unique cyclic phosphate ring at the sn-2 and sn-3 positions of its glycerol backbone. Natural cPA and its chemically stabilized cPA derivative, 2-carba-cPA (2ccPA), inhibit chronic and acute inflammation, and 2ccPA attenuates neuropathic pain. Osteoarthritis (OA) is a degenerative disease frequently associated with symptoms such as inflammation and joint pain. Because 2ccPA has obvious antinociceptive activity, we hypothesized that 2ccPA might relieve the pain caused by OA. We aimed to characterize the effects of 2ccPA on the pathogenesis of OA induced by total meniscectomy in the rabbit knee joint.

Results

Intra-articular injection of 2ccPA (twice a week for 42 days) significantly reduced pain and articular swelling. Histopathology showed that 2ccPA suppressed cartilage degeneration in OA. We also examined the effects of 2ccPA on the inflammatory and catabolic responses of human OA synoviocytes and chondrosarcoma SW1353 cells in vitro. 2ccPA stimulated synthesis of hyaluronic acid and suppressed production of the metalloproteinases MMP-1, -3, and -13. However, it had no effect on the production of interleukin (IL)-6, an inflammatory cytokine. The suppressive effect of 2ccPA on MMP-1 and -3 production in synoviocytes and on MMP-13 production in SW1353 cells was not mediated by the lysophosphatidic acid receptor, LPA1 receptor (LPA1R).

Conclusions

Our results suggest that 2ccPA significantly reduces the pain response to OA by inducing hyaluronic acid production and suppressing MMP-1, -3, and -13 production in synoviocytes and chondrocytes.

Cyclic phosphatidic acid treatment suppress cuprizone-induced demyelination and motor dysfunction in mice

Multiple sclerosis is a chronic demyelinating disease of the central nervous system leading to progressive cognitive and motor dysfunction, which is characterized by neuroinflammation, demyelination, astrogliosis, loss of oligodendrocytes, and axonal pathologies. Cyclic phosphatidic acid (cPA) is a naturally occurring phospholipid mediator with a unique cyclic phosphate ring structure at the sn-2 and sn-3 positions of the glycerol backbone. cPA elicits a neurotrophin-like action and protects hippocampal neurons from ischemia-induced delayed neuronal death. In this study, we investigated the effects of cPA on cuprizone-induced demyelination, which is a model of multiple sclerosis. Mice were fed a diet containing 0.2% cuprizone for 5 weeks, which induces severe demyelination, astrocyte and microglial activation, and motor dysfunction. Simultaneous administration of cPA effectively attenuated cuprizone-induced demyelination, glial activation, and motor dysfunction. These data indicate that cPA may be a useful treatment to reduce the extent of demyelination and the severity of motor dysfunction in multiple sclerosis. cPA is a potential lead compound in the development of drugs for the treatment of this devastating disease.

Exendin-4 induces cell adhesion and differentiation and counteracts the invasive potential of human neuroblastoma cells

Exendin-4 is a molecule currently used, in its synthetic form exenatide, for the treatment of type 2 diabetes mellitus. Exendin-4 binds and activates the Glucagon-Like Peptide-1 Receptor (GLP-1R), thus inducing insulin release. More recently, additional biological properties have been associated to molecules that belong to the GLP-1 family. For instance, Peptide YY and Vasoactive Intestinal Peptide have been found to affect cell adhesion and migration and our previous data have shown a considerable actin cytoskeleton rearrangement after exendin-4 treatment. However, no data are currently available on the effects of exendin-4 on tumor cell motility. The aim of this study was to investigate the effects of this molecule on cell adhesion, differentiation and migration in two neuroblastoma cell lines, SH-SY5Y and SK-N-AS. We first demonstrated, by Extra Cellular Matrix cell adhesion arrays, that exendin-4 increased cell adhesion, in particular on a vitronectin substrate. Subsequently, we found that this molecule induced a more differentiated phenotype, as assessed by i) the evaluation of neurite-like protrusions in 3D cell cultures, ii) the analysis of the expression of neuronal markers and iii) electrophysiological studies. Furthermore, we demonstrated that exendin-4 reduced cell migration and counteracted anchorage-independent growth in neuroblastoma cells. Overall, these data indicate for the first time that exendin-4 may have anti-tumoral properties.

Protection of neuroblastoma Neuro2A cells from hypoxia-induced apoptosis by cyclic phosphatidic acid (cPA)

Cyclic phosphatidic acid (cPA) is a naturally occurring phospholipid mediator with a unique cyclic phosphate ring at the sn-2 and sn-3 positions of its glycerol backbone. We have previously shown that cPA significantly suppresses ischemia-induced delayed neuronal death and the accumulation of glial fibrillary acidic protein in the CA1 region of the rat hippocampus. These results indicated that the systemic administration of cPA can protect hippocampal neurons against ischemia-induced delayed neuronal cell death. In the current study, we investigated the effects of cPA on neuronal cell death caused by hypoxia in vitro and the molecular mechanisms underlying these effects. We used cobalt chloride (CoCl₂) to expose cells to hypoxic conditions in vitro. Treating mouse neuroblastoma (Neuro2A) cells with CoCl₂ induced nuclear DNA condensation and phosphatidylserine exposure. However, adding cPA led to the suppression of CoCl₂-induced apoptosis in a cPA dose-dependent manner and attenuated the increase in the Bax/Bcl-2 ratio caused by CoCl₂. Quantitative PCR analysis showed that Neuro2A cells strongly express the LPA₁, LPA₂, and LPA₆, which are G-protein coupled receptors that can be activated by cPA. To date, LPA₁ and LPA₂ have been reported to exhibit antiapoptotic activity. Therefore, to assess the roles of LPA₁ and LPA₂ on cPA-induced neuroprotective functions, Ki16425, a selective LPA₁ and LPA₃ antagonist, was adopted to know the LPA₁ function and siRNA was used to knockdown the expression of LPA₂. On the basis of our results, we propose that cPA-induced protection of Neuro2A cells from CoCl₂-induced hypoxia damage is mediated via LPA₂.

Release of cyclic phosphatidic acid from gelatin-based hydrogels inhibit colon cancer cell growth and migration

Microparticle and nanoparticle formulations are widely used to improve the bioavailability of low-solubility drugs and as vehicles for organ- and tissue-specific targeted drug delivery. We investigated the effect of a novel, controlled-release form of a bioactive lipid, cyclic phosphatidic acid (cPA), on human colon cancer cell line functions. We encapsulated cPA in gelatin-based hydrogels and examined its ability to inhibit the viability and migration of HT-29 and DLD-1 cells in vitro and the LPA-induced activity of the transcription factor peroxisome proliferator-activated receptor gamma (PPARγ). The hydrogel delivery system prolonged cPA release into the culture medium. Accordingly, cPA-hydrogel microspheres substantially inhibited LPA-induced PPARγ activity and cell growth and migration compared with that of cells cultured with cPA alone. Thus, hydrogel microspheres are a potential system for stable and efficient delivery of bioactive lipids such as cPA and may offer a new strategy for targeted colon cancer treatment.

Virtual screening for LPA2-specific agonists identifies a nonlipid compound with antiapoptotic actions

Lysophosphatidic acid (LPA) is a highly potent endogenous lipid mediator that protects and rescues cells from programmed cell death. Earlier work identified the LPA₂ G protein-coupled receptor subtype as an important molecular target of LPA mediating antiapoptotic signaling. Here we describe the results of a virtual screen using single-reference similarity searching that yielded compounds 2-((9-oxo-9H-fluoren-2-yl)carbamoyl)benzoic acid (NSC12404), 2-((3-(1,3-dioxo-1H-benzo[de]isoquinolin-2(3H)-yl)propyl)thio)benzoic acid (GRI977143), 4,5-dichloro-2-((9-oxo-9H-fluoren-2-yl)carbamoyl)benzoic acid (H2L5547924), and 2-((9,10-dioxo-9,10-dihydroanthracen-2-yl)carbamoyl) benzoic acid (H2L5828102), novel nonlipid and drug-like compounds that are specific for the LPA₂ receptor subtype. We characterized the antiapoptotic action of one of these compounds, GRI977143, which was effective in reducing activation of caspases 3, 7, 8, and 9 and inhibited poly(ADP-ribose)polymerase 1 cleavage and DNA fragmentation in different extrinsic and intrinsic models of apoptosis in vitro. Furthermore, GRI977143 promoted carcinoma cell invasion of human umbilical vein endothelial cell monolayers and fibroblast proliferation. The antiapoptotic cellular signaling responses were present selectively in mouse embryonic fibroblast cells derived from LPA(1&2) double-knockout mice reconstituted with the LPA₂ receptor and were absent in vector-transduced control cells. GRI977143 was an effective stimulator of extracellular signal-regulated kinase 1/2 activation and promoted the assembly of a macromolecular signaling complex consisting of LPA₂, Na⁺ - H⁺ exchange regulatory factor 2, and thyroid receptor interacting protein 6, which has been shown previously to be a required step in LPA-induced antiapoptotic signaling. The present findings indicate that nonlipid LPA₂-specific agonists represent an excellent starting point for development of lead compounds with potential therapeutic utility for preventing the programmed cell death involved in many types of degenerative and inflammatory diseases.

The Role of PPARγ in the Transcriptional Control by Agonists and Antagonists

In recent years, peroxisome proliferator-activated receptor gamma (PPARγ) has been reported to be a target for the treatment of type II diabetes. Furthermore, it has received attention for its therapeutic potential in many other human diseases, including atherosclerosis, obesity, and cancers. Recent studies have provided evidence that the endogenously produced PPARγ antagonist, 2,3-cyclic phosphatidic acid (cPA), which is similar in structure to lysophosphatidic acid (LPA), inhibits cancer cell invasion and metastasis in vitro and in vivo. We recently observed that cPA negatively regulates PPARγ function by stabilizing the binding of the corepressor protein, silencing mediator of retinoic acid and thyroid hormone receptor. We also showed that cPA prevents neointima formation, adipocyte differentiation, lipid accumulation, and upregulation of PPARγ target gene transcription. We then analyzed the molecular mechanism of cPA's action on PPARγ. In this paper, we summarize the current knowledge on the mechanism of PPARγ-mediated transcriptional activity and transcriptional repression in response to novel lipid-derived ligands, such as cPA.

Controlling cancer through the autotaxin-lysophosphatidic acid receptor axis

LPA (lysophosphatidic acid, 1-acyl-2-hydroxy-sn-glycero-3-phosphate), is a growth factor-like lipid mediator that regulates many cellular functions, many of which are unique to malignantly transformed cells. The simple chemical structure of LPA and its profound effects in cancer cells has attracted the attention of the cancer therapeutics field and drives the development of therapeutics based on the LPA scaffold. In biological fluids, LPA is generated by ATX (autotaxin), a lysophospholipase D that cleaves the choline/serine headgroup from lysophosphatidylcholine and lysophosphatidylserine to generate LPA. In the present article, we review some of the key findings that make the ATX-LPA signalling axis an emerging target for cancer therapy.

Pharmacological evaluation of a novel cyclic phosphatidic acid derivative 3-S-cyclic phosphatidic acid (3-S-cPA)

Cyclic phosphatidic acid (cPA) is a naturally occurring phospholipid mediator possessing cyclic phosphate ring, which is necessary for its specific biological activities. To stabilize cyclic phosphate ring of cPA, we synthesized a series of cPA derivatives. We have shown that racemic 3-S-cPA, with a phosphate oxygen atom replaced with a sulfur atom at the sn-3, was a more effective autotaxin (ATX) inhibitor than cPA. In this study, we showed that racemic 3-S-cPA also had potent biological activities such as inhibition of cancer cell migration, suppression of the nociceptive reflex, and attenuation of ischemia-induced delayed neuronal cell death in the hippocampal CA1. Moreover, we synthesized both enantiomers of palmitoleoyl derivative of 3-S-cPA, and found that the chirality of 3-S-cPA is not involved in ATX inhibition. Based on these findings, racemic 3-S-cPA is suggested as an effective therapeutic compound like cPA.

Antinociceptive effect of cyclic phosphatidic acid and its derivative on animal models of acute and chronic pain

1. Abstract

Benzyl and naphthalene methylphosphonic acid inhibitors of autotaxin with anti-invasive and anti-metastatic activity

Autotaxin (ATX, NPP2) is a member of the nucleotide pyrophosphate phosphodiesterase enzyme family. ATX catalyzes the hydrolytic cleavage of lysophosphatidylcholine (LPC) by lysophospholipase D activity, which leads to generation of the growth-factor-like lipid mediator lysophosphatidic acid (LPA). ATX is highly upregulated in metastatic and chemotherapy-resistant carcinomas and represents a potential target to mediate cancer invasion and metastasis. Herein we report the synthesis and pharmacological characterization of ATX inhibitors based on the 4-tetradecanoylaminobenzylphosphonic acid scaffold, which was previously found to lack sufficient stability in cellular systems. The new 4-substituted benzylphosphonic acid and 6-substituted naphthalen-2-ylmethylphosphonic acid analogues block ATX activity with K(i) values in the low micromolar to nanomolar range against FS3, LPC, and nucleotide substrates through a mixed-mode inhibition mechanism. None of the compounds tested inhibit the activity of related enzymes (NPP6 and NPP7). In addition, the compounds were evaluated as agonists or antagonists of seven LPA receptor (LPAR) subtypes. Analogues 22 and 30 b, the two most potent ATX inhibitors, inhibit the invasion of MM1 hepatoma cells across murine mesothelial and human vascular endothelial monolayers in vitro in a dose-dependent manner. The average terminal half-life for compound 22 is 10±5.4 h and it causes a long-lasting decrease in plasma LPA levels. Compounds 22 and 30 b significantly decrease lung metastasis of B16-F10 syngeneic mouse melanoma in a post-inoculation treatment paradigm. The 4-substituted benzylphosphonic acids and 6-substituted naphthalen-2-ylmethylphosphonic acids described herein represent new lead compounds that effectively inhibit the ATX-LPA-LPAR axis both in vitro and in vivo.

Lysophosphatidic acid is a lipid mediator with wide range of biological activities. Biosynthetic pathways and mechanism of action

Lysophosphatidic acid (LPA) is a lipid mediator required for maintaining homeostasis of numerous physiological functions and also involved in development of some pathological processes through interactions with G protein-coupled receptors. Recently many data have appeared about the role of this phospholipid in humans, but pathways of LPA biosynthesis and mechanisms of its action remain unclear. This review presents modern concepts about biosynthesis, reception, and biological activity of LPA in humans. Natural and synthetic LPA analogs are considered in the view of their possible use in pharmacology as agonists and/or antagonists of G protein-coupled receptors of LPA.

Autotaxin: its role in biology of melanoma cells and as a pharmacological target

Autotaxin (ATX) is an extracellular lysophospholipase D (lysoPLD) released from normal cells and cancer cells. Activity of ATX is detected in various biological fluids. The lysophosphatidic acid (LPA) is the main product of ATX. LPA acting through specific G protein-coupled receptors (LPA₁-LPA₆) affects immunological response, normal development, and malignant tumors' formation and progression. In this review, the impact of autotoxin on biology of melanoma cells and potential treatment is discussed.

Synthesis of enantiopure 2-carba-cyclic phosphatidic acid and effects of its chirality on biological functions

Cyclic phosphatidic acid (cPA) is a naturally occurring phospholipid mediator, which has a quite unique cyclic phosphate ring at sn-2 and sn-3 positions of the glycerol backbone. We have designed and chemically synthesized several metabolically stabilized derivatives of cPA. 2-Carba-cPA (2ccPA) is one of the synthesized compounds in which the phosphate oxygen was replaced with a methylene group at the sn-2 position, and it showed much more potent biological activities than natural cPA. Here, we developed a new method of 2ccPA enantiomeric synthesis. And we examined the effects of 2ccPA enantiomers on autotaxin (ATX) activity, cancer cell invasion and nociceptive reflex. As well as racemic-2ccPA, both enantiomers showed inhibitory effects on ATX activity, cancer cell invasion and nociceptive reflex. As their effects were not significantly different from each other, the chirality of 2ccPA may not be critical for these biological functions of 2ccPA.

Synthesis and pharmacological evaluation of the stereoisomers of 3-carba cyclic-phosphatidic acid

Cyclic phosphatidic acid (CPA) is a naturally occurring analog of lysophosphatidic acid (LPA) in which the sn-2 hydroxy group forms a five-membered ring with the sn-3 phosphate. Here, we describe the synthesis of R-3-CCPA and S-3-CCPA along with their pharmacological properties as inhibitors of lysophospholipase D/autotaxin, agonists of the LPA(5) GPCR, and blockers of lung metastasis of B16-F10 melanoma cells in a C57BL/6 mouse model. S-3CCPA was significantly more efficacious in the activation of LPA(5) compared to the R-stereoisomer. In contrast, no stereoselective differences were found between the two isomers toward the inhibition of autotaxin or lung metastasis of B16-F10 melanoma cells in vivo. These results extend the potential utility of these compounds as potential lead compounds warranting evaluation as cancer therapeutics.

Cyclic phosphatidic acid influences the expression and regulation of cyclic nucleotide phosphodiesterase 3B and lipolysis in 3T3-L1 cells

Cyclic phosphatidic acid (cPA) is found in cells from slime mold to humans and has a largely unknown function. We previously reported that cPA significantly inhibited the lipid accumulation in 3T3-L1 adipocytes through inhibition of PPARγ activation. We find here that cPA reduced intracellular triglyceride levels and inhibited the phosphodiesterase 3B (PDE3B) expression in 3T3-L1 adipocytes. PPARγ activation in adipogenesis that can be blocked by treatment with cPA then participates in adipocyte function through inhibition of PDE3B expression. We also found the intracellular cAMP levels in 3T3-L1 adipocytes increased after exposure to cPA. These findings contribute to the participation of cPA on the lipolytic activity in 3T3-L1 adipocytes. Our studies imply that cPA might be a therapeutic compound in the treatment of obesity and obesity-related diseases.

Cyclic phosphatidic acid decreases proliferation and survival of colon cancer cells by inhibiting peroxisome proliferator-activated receptor γ

Cyclic phosphatidic acid (cPA), a structural analog of lysophosphatidic acid (LPA), is one of the simplest phospholipids found in every cell type. cPA is a specific, high-affinity antagonist of peroxisome proliferator-activated receptor gamma (PPARγ); however, the molecular mechanism by which cPA inhibits cellular proliferation remains to be clarified. In this study, we found that inhibition of PPARγ prevents proliferation of human colon cancer HT-29 cells. cPA suppressed cell growth, and this effect was reversed by the addition of a PPARγ agonist. These results indicate that the physiological effects of cPA are partly due to PPARγ inhibition. Our results identify PPARγ as a molecular mediator of cPA activity in HT-29 cells, and suggest that cPA and the PPARγ pathway might be therapeutic targets in the treatment of colon cancer.

Effects of cyclic phosphatidic acid on delayed neuronal death following transient ischemia in rat hippocampal CA1

Cyclic phosphatidic acid (cPA) is a lipid mediator that elicits a neurotrophin-like action in embryonic hippocampal neurons in vitro. In this study, we investigated the effects of cPA and 2-O-carba-oleoyl-cPA (2ccPA), a metabolically stabilized cPA derivative, on ischemia-induced delayed neuronal death in the rat hippocampal CA1 region. Transient occlusion for 8 min of bilateral carotid arteries besides permanent ligation of bilateral vertebral arteries was performed and morphological changes of the neurons were examined histologically 5 days after occlusion. cPA or 2ccPA was continuously administered for 5 days by means of an osmotic pump that was implanted subcutaneously before occlusion. Five days after occlusion, delayed neuronal death occurred in approximately 85% of the CA1 hippocampal neurons in the 0.2-2% bovine serum albumin vehicle control group. However, administration of cPA significantly increased the number of undamaged neurons in a dose-dependent manner. At the most effective concentration (18 μg/kg/5d), the number of undamaged neurons was increased to 4 times of that in the vehicle control group. 2ccPA also showed a neuroprotective effect, but it was less potent than that of natural cPA. These results indicate that systemic administration of both cPA and 2ccPA can protect neurons from ischemia-induced delayed neuronal death in the hippocampus.

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.

Targeting melanoma growth and viability reveals dualistic functionality of the phosphonothionate analogue of carba cyclic phosphatidic acid

BACKGROUND

Although the incidence of melanoma in the U.S. is rising faster than any other cancer, the FDA-approved chemotherapies lack efficacy for advanced disease, which results in poor overall survival. Lysophosphatidic acid (LPA), autotaxin (ATX), the enzyme that produces LPA, and the LPA receptors represent an emerging group of therapeutic targets in cancer, although it is not known which of these is most effective.

RESULTS

Herein we demonstrate that thio-ccPA 18:1, a stabilized phosphonothionate analogue of carba cyclic phosphatidic acid, ATX inhibitor and LPA1/3 receptor antagonist, induced a marked reduction in the viability of B16F10 metastatic melanoma cells compared with PBS-treated control by 80-100%. Exogenous LPA 18:1 or D-sn-1-O-oleoyl-2-O-methylglyceryl-3-phosphothioate did not reverse the effect of thio-ccPA 18:1. The reduction in viability mediated by thio-ccPA 18:1 was also observed in A375 and MeWo melanoma cell lines, suggesting that the effects are generalizable. Interestingly, siRNA to LPA3 (siLPA3) but not other LPA receptors recapitulated the effects of thio-ccPA 18:1 on viability, suggesting that inhibition of the LPA3 receptor is an important dualistic function of the compound. In addition, siLPA3 reduced proliferation, plasma membrane integrity and altered morphology of A375 cells. Another experimental compound designed to antagonize the LPA1/3 receptors significantly reduced viability in MeWo cells, which predominantly express the LPA3 receptor.

CONCLUSIONS

Thus the ability of thio-ccPA 18:1 to inhibit the LPA3 receptor and ATX are key to its molecular mechanism, particularly in melanoma cells that predominantly express the LPA3 receptor. These observations necessitate further exploration and exploitation of these targets in melanoma.

Lysophosphatidic acid (LPA)-induced vasodilator-stimulated phosphoprotein mediates lamellipodia formation to initiate motility in PC-3 prostate cancer cells

Prostate cancer remains the most frequently diagnosed malignancy and the second leading cause of cancer mortality among men in the United States. Hormone refractory, metastatic disease has no molecular therapeutics to date and survival is poor. Lysophosphatidic acid (LPA) is a bioactive lipid exhibiting motility, invasive, growth, proliferative and survival effects in multiple cancer cell lineages. Cells express different combinations of LPA-specific G protein-coupled receptors, LPA(1), LPA(2) LPA(3), and LPA(4) as well as other LPA receptors, which bind LPA and thereby regulate lipid signaling. The role of specific LPA receptors in functional outcomes of lysolipid signaling remains to be fully elucidated in prostate cancer. We hypothesized that LPA can initiate cell migration through specific LPA receptors by activating actin-associating proteins involved in motility, including the vasodilator-stimulated phosphoprotein (VASP). In the present study, we demonstrate that LPA-induced lamellipodia formation in cells is dependent on LPA receptor-mediated phosphorylation of VASP, demonstrating a previously unknown regulation by LPA. LPA induces phosphorylation of VASP at Ser(157), through protein kinase A (PKA) since the stimulation was abrogated by PKA inhibition. In addition, we found the effects of LPA-induced lamellipodia formation and migration were reduced by knockdown of either VASP or LPA receptor expression, suggesting that LPA receptor-induced VASP phosphorylation is a critical mediator of migration initiation. Thus the LPA(2) and LPA(3) receptors, in addition to the previously implicated LPA(1) receptor, play a role in cellular motility potentially contributing to invasion and metastases. Emerging drugs targeting the LPA pathway may be beneficial for the treatment of metastatic progression in prostate cancer.

Unique ligand selectivity of the GPR92/LPA5 lysophosphatidate receptor indicates role in human platelet activation

Lysophosphatidic acid (LPA) is a ligand for LPA(1-3) of the endothelial differentiation gene family G-protein-coupled receptors, and LPA(4-8) is related to the purinergic family G-protein-coupled receptor. Because the structure-activity relationship (SAR) of GPR92/LPA(5) is limited and whether LPA is its preferred endogenous ligand has been questioned in the literature, in this study we applied a combination of computational and experimental site-directed mutagenesis of LPA(5) residues predicted to interact with the headgroup of LPA. Four residues involved in ligand recognition in LPA(5) were identified as follows: R2.60N mutant abolished receptor activation, whereas H4.64E, R6.62A, and R7.32A greatly reduced receptor activation. We also investigated the SAR of LPA(5) using LPA analogs and other non-lysophospholipid ligands. SAR revealed that the rank order of agonists is alkyl glycerol phosphate > LPA > farnesyl phosphates >> N-arachidonoylglycine. These results confirm LPA(5) to be a bona fide lysophospholipid receptor. We also evaluated several compounds with previously established selectivity for the endothelial differentiation gene receptors and found several that are LPA(5) agonists. A pharmacophore model of LPA(5) binding requirements was developed for in silico screening, which identified two non-lipid LPA(5) antagonists. Because LPA(5) transcripts are abundant in human platelets, we tested its antagonists on platelet activation and found that these non-lipid LPA(5) antagonists inhibit platelet activation. The present results suggest that selective inhibition of LPA(5) may provide a basis for future anti-thrombotic therapies.

Lysophosphatidic acid receptors determine tumorigenicity and aggressiveness of ovarian cancer cells

BACKGROUND

Lysophosphatidic acid (LPA) acts through the cell surface G protein-coupled receptors, LPA1, LPA2, or LPA3, to elicit a wide range of cellular responses. It is present at high levels in intraperitoneal effusions of human ovarian cancer increasing cell survival, proliferation, and motility as well as stimulating production of neovascularizing factors. LPA2 and LPA3 and enzymes regulating the production and degradation of LPA are aberrantly expressed by ovarian cancer cells, but the consequences of these expression changes in ovarian cancer cells were unknown.

METHODS

Expression of LPA1, LPA2, or LPA3 was inhibited or increased in ovarian cancer cells using small interfering RNAs (siRNAs) and lentivirus constructs, respectively. We measured the effects of changes in LPA receptor expression on cell proliferation (by crystal violet staining), cell motility and invasion (using Boyden chambers), and cytokines (interleukin 6 [IL-6], interleukin 8 [IL-8], and vascular endothelial growth factor [VEGF]) production by enzyme-linked immunosorbent assay. The role of LPA receptors in tumor growth, ascites formation, and cytokine production was assessed in a mouse xenograft model. All statistical tests were two-sided.

RESULTS

SKOV-3 cells with increased expression of LPA receptors showed increased invasiveness, whereas siRNA knockdown inhibited both migration (P < .001, Student t test) and invasion. Knockdown of the LPA2 or LPA3 receptors inhibited the production of IL-6, IL-8, and VEGF in SKOV-3 and OVCAR-3 cells. SKOV-3 xenografts expressing LPA receptors formed primary tumors of increased size and increased ascites volume. Invasive tumors in the peritoneal cavity occurred in 75% (n = 4) of mice injected with LPA1 expressing SKOV-3 and 80% (n = 5) of mice injected with LPA2 or LPA3 expressing SKOV-3 cells. Metastatic tumors expressing LPA1, LPA2, and LPA3 were identified in the liver, kidney, and pancreas; tumors expressing LPA2 and LPA3 were detected in skeletal muscle; and tumors expressing LPA2 were also found in the cervical lymph node and heart. The percent survival of mice with tumors expressing LPA2 or LPA3 was reduced in comparison with animals with tumors expressing beta-galactosidase.

CONCLUSIONS

Expression of LPA2 or LPA3 during ovarian carcinogenesis contributes to ovarian cancer aggressiveness, suggesting that the targeting of LPA production and action may have potential for the treatment of ovarian cancer.

Cyclic phosphatidic acid - a unique bioactive phospholipid

Cyclic phosphatidic acid (CPA) is a naturally occurring analog of the growth factor-like phospholipid mediator, lysophosphatidic acid (LPA). The sn-2 hydroxy group of CPA forms a 5-membered ring with the sn-3 phosphate. CPA affects numerous cellular functions, including anti-mitogenic regulation of the cell cycle, induction of stress fiber formation, inhibition of tumor cell invasion and metastasis, and regulation of differentiation and survival of neuronal cells. Interestingly, many of these cellular responses caused by CPA oppose those of LPA despite the activation of apparently overlapping receptor populations. Since the early 1990s, studies on CPA actions gradually developed, and we are now beginning to understand the importance of this lipid. In this review, we focus on the current knowledge about CPA, including enzymatic formation of CPA, unique biological activities and biological targets of CPA, and we also explore metabolically stabilized CPA analogs.

Measurement of autotaxin/lysophospholipase D activity

Lysophosphatidic acid (LPA) is a bioactive lipid mediator present in the blood and other biological fluids at physiologically relevant concentrations. In the cardiovascular system, studies using in vitro and in vivo experimental models indicate that LPA stimulates platelet activation, differentiation and migration of vascular smooth muscle cells, and changes in vascular tone. A growing body of evidence suggests that aberrant production and actions of LPA could play an important role in atherothrombotic disease. Hydrolysis of lysophospholipids by the secreted plasma protein autotaxin/lysophospholipase D (lysoPLD) is a major mechanism for generation of LPA in the blood. This chapter describes methods for determining the activity of recombinant autotaxin/lysoPLD using radiolabeled and fluorogenic substrates.