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

HSP27 Modulates Neuropathic Pain by Inhibiting P2X3 Degradation

The role of heat shock protein 27 (HSP27), a chaperone, in neuropathic pain after nerve injury has not been systematically surveyed despite its neuroprotective and regeneration-promoting effects. In this study, we found that HSP27 expression in sensory neurons of the dorsal root ganglia (DRG) mediated nerve injury-induced neuropathic pain. Neuropathic pain behaviors were alleviated by silencing HSP27 in the DRG of a rat spinal nerve ligation (SNL) model. Local injection of an HSP27-overexpression construct into the DRG of naïve rats elicited neuropathic pain behaviors. HSP27 interacted with a purinergic receptor, P2X3, and their expression patterns corroborated the induction and reversal of neuropathic pain according to two lines of evidence: colocalization immunohistochemically and immunoprecipitation biochemically. In a cell model cotransfected with HSP27 and P2X3, the degradation rate of P2X3 was reduced in the presence of HSP27. Such an alteration was mediated by reducing P2X3 ubiquitination in SNL rats and was reversed after silencing HSP27 in the DRGs of SNL rats. In summary, the interaction of HSP27 with P2X3 provides a new mechanism of injury-induced neuropathic pain that could serve as an alternative therapeutic target.

Direct Binding Methods to Measure Receptor-Ligand Interactions

G-protein-coupled receptors (GPCRs) contribute to numerous physiological processes via complex network mechanisms. While indirect signaling assays (Ca2+ mobilization, cAMP production, and GTPγS binding) have been useful in identifying and characterizing downstream signaling mechanisms of GPCRs, these methods lack measurements of direct binding affinities, kinetics, binding specificity, and selectivity that are important parameters in GPCR drug discovery. In comparison to existing direct methods that use radio- or fluorescent labels, label-free techniques can closely emulate the native interactions around binding partners. Surface plasmon resonance (SPR) is a label-free technique that utilizes the refractive index (RI) property and is applied widely in quantitative GPCR-ligand binding kinetics measurement including small molecules screening. However, purified GPCRs are further embedded in a synthetic lipid environment which is immobilized through different tags to the SPR sensor surface, resulting in a non-native environment. Here, we introduced a methodology that also uses the RI property to measure binding interactions in a label-free, immobilization-free arrangement. The free-solution technique is successfully applied in quantifying the interaction of bioactive lipids to cognate lipid GPCRs, which is not purified but rather present in near-native conditions, i.e., in milieu of other cytoplasmic lipids and proteins. To further consider the wide applicability of these free-solution approaches in biomolecular interaction research, additional applications on a variety of receptor-ligand pairs are imperative.

Design and synthesis of novel pipernonaline derivatives as anti-austerity agents against human pancreatic cancer PANC-1 cells

Pipernonaline (1), one of the components of the spice pepper, preferentially reduced the survival of human pancreatic cancer PANC-1 cells under nutrient-deprived conditions witha PC₅₀ value of 7.2 μM, suggesting that1couldpotentially lead to the development ofnew anticanceragents basedon theanti-austerity strategy. We have synthesized a total of 31 pipernonaline derivatives, revealing clear structure-activity relationships. Compound 9, which showed the strongest preferential cytotoxicity among synthesized derivatives, inhibited Akt activation and cancer cell migration, making it an extremely promising candidate compound for new pancreatic cancer agents based on the anti-austerity strategy.

Novel Antagonist of the Type 2 Lysophosphatidic Acid Receptor (LPA2), UCM-14216, Ameliorates Spinal Cord Injury in Mice

Spinal cord injuries (SCIs) irreversibly disrupt spinal connectivity, leading to permanent neurological disabilities. Current medical treatments for reducing the secondary damage that follows the initial injury are limited to surgical decompression and anti-inflammatory drugs, so there is a pressing need for new therapeutic strategies. Inhibition of the type 2 lysophosphatidic acid receptor (LPA₂) has recently emerged as a new potential pharmacological approach to decrease SCI-associated damage. Toward validating this receptor as a target in SCI, we have developed a new series of LPA₂ antagonists, among which compound 54 (UCM-14216) stands out as a potent and selective LPA₂ receptor antagonist (E_max = 90%, IC₅₀ = 1.9 μM, K_D = 1.3 nM; inactive at LPA_1,3–6 receptors). This compound shows efficacy in an in vivo mouse model of SCI in an LPA₂-dependent manner, confirming the potential of LPA₂ inhibition for providing a new alternative for treating SCI.

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.

Rational Design 2-Hydroxypropylphosphonium Salts as Cancer Cell Mitochondria-Targeted Vectors: Synthesis, Structure, and Biological Properties

It has been shown for a wide range of epoxy compounds that their interaction with triphenylphosphonium triflate occurs with a high chemoselectivity and leads to the formation of (2-hydroxypropyl)triphenylphosphonium triflates 3 substituted in the 3-position with an alkoxy, alkylcarboxyl group, or halogen, which were isolated in a high yield. Using the methodology for the disclosure of epichlorohydrin with alcohols in the presence of boron trifluoride etherate, followed by the substitution of iodine for chlorine and treatment with triphenylphosphine, 2-hydroxypropyltriphenylphosphonium iodides 4 were also obtained. The molecular and supramolecular structure of the obtained phosphonium salts was established, and their high antitumor activity was revealed in relation to duodenal adenocarcinoma. The formation of liposomal systems based on phosphonium salt 3 and L-α-phosphatidylcholine (PC) was employed for improving the bioavailability and reducing the toxicity. They were produced by the thin film rehydration method and exhibited cytotoxic properties. This rational design of phosphonium salts 3 and 4 has promising potential of new vectors for targeted delivery into mitochondria of tumor cells.

Generation of an Lpar1-EGFP Fusion Knock-in Transgenic Mouse Line

Lysophosphatidic acid (LPA) is a lysophospholipid that acts as an extracellular signal through the activation of cognate G protein-coupled receptors (GPCRs). There are six known LPA receptors (LPA_1-6). The first such receptor, LPA₁, was identified in the embryonic brain and has been studied extensively for gene expression throughout the body, including through studies of receptor-null mice. However, identifying receptor protein expression in situ and in vivo within living cells and tissues has been difficult because of biologically low receptor expression and variable antibody specificity. To visualize native LPA₁ receptor expression in situ, we generated a knock-in mouse produced by homologous recombination in murine embryonic stem (ES) cells to replace a wildtype Lpar1 allele with a mutant allele created by in-frame fusion of EGFP to the 4th exon of Lpar1 (Lpar1-EGFP knock-in allele). Homozygous knock-in mice appeared normal and the expected mendelian ratios of knock-in allele transmission were present in females and males. Histological assessments of the fetal and adult central nervous system (CNS) demonstrated expression patterns that were consistent with prior in situ hybridization studies. This new mouse line will be useful for studies of LPA₁ in the developing and adult CNS, as well as other tissues, and for receptor assessments in living tissues and disease models.

Tozasertib Attenuates Neuropathic Pain by Interfering with Aurora Kinase and KIF11 Mediated Nociception

Kinesins are the motor proteins that transport excitatory receptors to the synaptic membrane by forming a complex with receptor cargo leading to central sensitization causing neuropathic pain. Many regulatory proteins govern the transit of receptors by activating kinesin, and Aurora kinases are one of them. In this study, we have performed in silico molecular dynamics simulation to delineate the dynamic interaction of Aurora kinase A with its pharmacological inhibitor, tozasertib. The results from the molecular dynamics study shows that tozasertib-Aurora kinase A complex is stabilized through hydrogen bonding, polar interactions, and water bridges. Findings from the in vitro studies suggest that tozasertib treatment significantly attenuates lipopolysaccharide (LPS)-induced increase in oxidonitrosative stress and kif11 overexpression in C6 glial cell lines. Further, we investigated the regulation of kif11 and its modulation by tozasertib in an animal model of neuropathic pain. Two weeks post-CCI surgery we observed a significant increase in pain hypersensitivity and kif11 overexpression in DRG and spinal cord of nerve-injured rats. Tozasertib treatment significantly attenuates enhanced pain hypersensitivity along with the restoration of kif11 expression in DRG and spinal cord and oxidonitrosative stress in the sciatic nerve of injured rats. Our findings demonstrate the potential role of tozasertib for the management of neuropathic pain.

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.

Novel Approaches, Drug Candidates, and Targets in Pain Drug Discovery

Because of the problems associated with opioids, drug discovery efforts have been employed to develop opioids with reduced side effects using approaches such as biased opioid agonism, multifunctional opioids, and allosteric modulation of opioid receptors. Receptor targets such as adrenergic, cannabinoid, P2X3 and P2X7, NMDA, serotonin, and sigma, as well as ion channels like the voltage-gated sodium channels Nav1.7 and Nav1.8 have been targeted to develop novel analgesics. Several enzymes, such as soluble epoxide hydrolase, sepiapterin reductase, and MAGL/FAAH, have also been targeted to develop novel analgesics. In this review, old and recent targets involved in pain signaling and compounds acting at these targets are summarized. In addition, strategies employed to reduce side effects, increase potency, and efficacy of opioids are also elaborated. This review should aid in propelling drug discovery efforts to discover novel analgesics.

Dual Role of Lysophosphatidic Acid Receptor 2 (LPA2) in Amyotrophic Lateral Sclerosis

Lysophosphatidic acid (LPA) is a pleiotropic extracellular lipid mediator with many physiological functions that signal through six known G protein-coupled receptors (LPA1-6). In the central nervous system (CNS), LPA mediates a wide range of effects including neural progenitor cell physiology, neuronal cell death, axonal retraction, and inflammation. Since inflammation is a hallmark of most neurological conditions, we hypothesized that LPA could be involved in the physiopathology of amyotrophic lateral sclerosis (ALS). We found that LPA2 RNA was upregulated in post-mortem spinal cord samples of ALS patients and in the sciatic nerve and skeletal muscle of SOD1G93A mouse, the most widely used ALS mouse model. To assess the contribution of LPA2 to ALS, we generated a SOD1G93A mouse that was deficient in Lpar2. This animal revealed that LPA2 signaling accelerates disease onset and neurological decline but, unexpectedly, extended the lifespan. To gain insights into the early harmful actions of LPA2 in ALS, we studied the effects of this receptor in the spinal cord, peripheral nerve, and skeletal muscle of ALS mice. We found that LPA2 gene deletion increased microglial activation but did not contribute to motoneuron death, astrogliosis, degeneration, and demyelination of motor axons. However, we observed that Lpar2 deficiency protected against muscle atrophy. Moreover, we also found the deletion of Lpar2 reduced the invasion of macrophages into the skeletal muscle of SOD1G93A mice, linking LPA2 signaling with muscle inflammation and atrophy in ALS. Overall, these results suggest for the first time that LPA2 contributes to ALS, and its genetic deletion results in protective actions at the early stages of the disease but shortens survival thereafter.

Platinum-Based Drugs Cause Mitochondrial Dysfunction in Cultured Dorsal Root Ganglion Neurons

Cisplatin and oxaliplatin are treatment options for a variety of cancer types. While highly efficient in killing cancer cells, both chemotherapeutics cause severe side effects, e.g., peripheral neuropathies. Using a cell viability assay, a mitochondrial stress assay, and live-cell imaging, the effects of cis- or oxaliplatin on the mitochondrial function, reactive oxygen species (ROS) production, and mitochondrial and cytosolic calcium concentration of transient receptor potential ankyrin 1 (TRPA1)- or vanilloid 1 (TRPV1)-positive dorsal root ganglion (DRG) neurons of adult Wistar rats were determined. Mitochondrial functions were impaired after exposure to cis- or oxaliplatin by mitochondrial respiratory chain complex I-III inhibition. The basal respiration, spare respiratory capacity, and the adenosine triphosphate (ATP)-linked respiration were decreased after exposure to 10 µM cis- or oxaliplatin. The ROS production showed an immediate increase, and after reaching the peak, ROS production dropped. Calcium imaging showed an increase in the cytosolic calcium concentration during exposure to 10 µM cis- or oxaliplatin in TRPA1- or TRPV1-positive DRG neurons while the mitochondrial calcium concentration continuously decreased. Our data demonstrate a significant effect of cis- and oxaliplatin on mitochondrial function as an early event of platinum-based drug exposure, suggesting mitochondria as a potential target for preventing chemotherapy-induced neuropathy.

Lysophosphatidic Acid Receptor 1- and 3-Mediated Hyperalgesia and Hypoalgesia in Diabetic Neuropathic Pain Models in Mice

Lysophosphatidic acid (LPA) signaling is known to play key roles in the initiation and maintenance of various chronic pain models. Here we examined whether LPA signaling is also involved in diabetes-induced abnormal pain behaviors. The high-fat diet (HFD) showing elevation of blood glucose levels and body weight caused thermal, mechanical hyperalgesia, hypersensitivity to 2000 or 250 Hz electrical-stimulation and hyposensitivity to 5 Hz stimulation to the paw in wild-type (WT) mice. These HFD-induced abnormal pain behaviors and body weight increase, but not elevated glucose levels were abolished in LPA₁^−/− and LPA₃^−/− mice. Repeated daily intrathecal (i.t.) treatments with LPA_1/3 antagonist AM966 reversed these abnormal pain behaviors. Similar abnormal pain behaviors and their blockade by daily AM966 (i.t.) or twice daily Ki16425, another LPA_1/3 antagonist was also observed in db/db mice which show high glucose levels and body weight. Furthermore, streptozotocin-induced similar abnormal pain behaviors, but not elevated glucose levels or body weight loss were abolished in LPA₁^−/− and LPA₃^−/− mice. These results suggest that LPA₁ and LPA₃ play key roles in the development of both type I and type II diabetic neuropathic pain.

Phenyl(thio)phosphon(amid)ate Benzenesulfonamides as Potent and Selective Inhibitors of Human Carbonic Anhydrases II and VII Counteract Allodynia in a Mouse Model of Oxaliplatin-Induced Neuropathy

Human carbonic anhydrase (CA; EC 4.2.1.1) isoforms II and VII are implicated in neuronal excitation, seizures, and neuropathic pain (NP). Their selective inhibition over off-target CAs is expected to produce an anti-NP action devoid of side effects due to promiscuous CA modulation. Here, a drug design strategy based on the observation of (dis)similarities between the target CA active sites was planned with benzenesulfonamide derivatives and, for the first time, a phosphorus-based linker. Potent and selective CA II/VII inhibitors were identified among the synthesized phenyl(thio)phosphon(amid)ates 3-22. X-ray crystallography depicted the binding mode of phosphonic acid 3 to both CAs II and VII. The most promising derivatives, after evaluation of their stability in acidic media, were tested in a mouse model of oxaliplatin-induced neuropathy. The most potent compound racemic mixture was subjected to HPLC enantioseparation, and the identification of the eutomer, the (S)-enantiomer, allowed to halve the dose totally relieving allodynia in mice.

Lysophosphatidic Acid Receptor Agonism: Discovery of Potent Nonlipid Benzofuran Ethanolamine Structures

Lysophosphatidic acid (LPA) is the natural ligand for two phylogenetically distinct families of receptors (LPA_1-3, LPA_4-6) whose pathways control a variety of physiologic and pathophysiological responses. Identifying the benefit of balanced activation/repression of LPA receptors has always been a challenge because of the high lability of LPA and the limited availability of selective and/or stable agonists. In this study, we document the discovery of small benzofuran ethanolamine derivatives (called CpX and CpY) behaving as LPA_1-3 agonists. Initially found as rabbit urethra contracting agents, their elusive receptors were identified from [³⁵S]GTPγS-binding and β-arrestin2 recruitment investigations and then confirmed by [³H]CpX binding studies (urethra, hLPA_1-2 membranes). Both compounds induced a calcium response in hLPA_1-3 cells within a range of 0.4-1.5-log lower potency as compared with LPA. The contractions of rabbit urethra strips induced by these compounds perfectly matched binding affinities with values reaching the two-digit nanomolar level. The antagonist, KI16425, dose-dependently antagonized CpX-induced contractions in agreement with its affinity profile (LPA₁≥LPA₃>>LPA₂). The most potent agonist, CpY, doubled intraurethral pressure in anesthetized female rats at 3 µg/kg i.v. Alternatively, CpX was shown to inhibit human preadipocyte differentiation, a process totally reversed by KI16425. Together with original molecular docking data, these findings clearly established these molecules as potent agonists of LPA_1-3 and consolidated the pivotal role of LPA₁ in urethra/prostate contraction as well as in fat cell development. The discovery of these unique and less labile LPA_1-3 agonists would offer new avenues to investigate the roles of LPA receptors. SIGNIFICANCE STATEMENT: We report the identification of benzofuran ethanolamine derivatives behaving as potent selective nonlipid LPA_1-3 agonists and shown to alter urethra muscle contraction or preadipocyte differentiation. Unique at this level of potency, selectivity, and especially stability, compared with lysophosphatidic acid, they represent more appropriate tools for investigating the physiological roles of lysophosphatidic acid receptors and starting point for optimization of drug candidates for therapeutic applications.