Design and synthesis of sulfamoyl benzoic acid analogues with subnanomolar agonist activity specific to the LPA2 receptor

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.

High-throughput screening strategies for space-based radiation countermeasure discovery

As humanity begins to venture further into space, approaches to better protect astronauts from the hazards found in space need to be developed. One particular hazard of concern is the complex radiation that is ever present in deep space. Currently, it is unlikely enough spacecraft shielding could be launched that would provide adequate protection to astronauts during long-duration missions such as a journey to Mars and back. In an effort to identify other means of protection, prophylactic radioprotective drugs have been proposed as a potential means to reduce the biological damage caused by this radiation. Unfortunately, few radioprotectors have been approved by the FDA for usage and for those that have been developed, they protect normal cells/tissues from acute, high levels of radiation exposure such as that from oncology radiation treatments. To date, essentially no radioprotectors have been developed that specifically counteract the effects of chronic low-dose rate space radiation. This review highlights how high-throughput screening (HTS) methodologies could be implemented to identify such a radioprotective agent. Several potential target, pathway, and phenotypic assays are discussed along with potential challenges towards screening for radioprotectors. Utilizing HTS strategies such as the ones proposed here have the potential to identify new chemical scaffolds that can be developed into efficacious radioprotectors that are specifically designed to protect astronauts during deep space journeys. The overarching goal of this review is to elicit broader interest in applying drug discovery techniques, specifically HTS towards the identification of radiation countermeasures designed to be efficacious towards the biological insults likely to be encountered by astronauts on long duration voyages.

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 (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.

Assessment of anti-inflammatory-like, antioxidant activities and molecular docking of three alkynyl-substituted 3-ylidene-dihydrobenzo[d]isothiazole 1,1-dioxide derivatives

The presence of enyne and benzoisothiazole functions in the molecular architecture of compounds 1, 2 and 3 were expected to provide biochemical activities. In the present work, we first examined the molecular surface contact of three alkynyl-substituted 3-ylidenedihydrobenzo[d] isothiazole 1,1-dioxides. The analysis of the Hirshfeld surfaces reveals that only compound 3 exhibited a well-defined red spots, indicating intermolecular interactions identified as S-O⋯H, C-H⋯O and C-O⋯H contacts. Comparative fingerprint histograms of the three compounds show that close pair interactions are dominated by C-H⋯H-C contact. By UV-visible analysis, compound 1 showed the most intense absorbances at 407 and 441 nm, respectively. The radical scavenging activity explored in the DPPH test, shows that only 1 exhibited low anti-radical activity. Furthermore, cellular antioxidant capacity of benzoisothiazoles 1-3 was investigated with PMA-activated HL-60 cells using chemiluminescence and fluorescence techniques in the presence of L-012 and Amplex Red probe, respectively. Results highlight that compound 1 exhibited moderate anti-ROS capacity while compounds 2 and 3 enhanced ROS production. The cytotoxicity test performed on HL-60 cells, using the MTS assay, confirmed the lack of toxicity of the tested benzoisothiazole 1 compared to 2 and 3 which show low cytotoxicity (≤30%). Anti-catalytic activity was evaluated by following the inhibitory potential of the benzoisothiazoles on MPO activity and depicted benzoisothiazoles-MPO interactions by docking. Both SIEFED and docking studies demonstrated an anti-catalytic activity of the tested benzoisothiazoles towards MPO with the best activity for compound 2.

LPAR2 receptor activation attenuates radiation-induced disruption of apical junctional complexes and mucosal barrier dysfunction in mouse colon

The tight junction (TJ) and barrier function of colonic epithelium is highly sensitive to ionizing radiation. We evaluated the effect of lysophosphatidic acid (LPA) and its analog, Radioprotein-1, on γ-radiation-induced colonic epithelial barrier dysfunction using Caco-2 and m-IC_C12 cell monolayers in vitro and mice in vivo. Mice were subjected to either total body irradiation (TBI) or partial body irradiation (PBI-BM5). Intestinal barrier function was assessed by analyzing immunofluorescence localization of TJ proteins, mucosal inulin permeability, and plasma lipopolysaccharide (LPS) levels. Oxidative stress was analyzed by measuring protein thiol oxidation and antioxidant mRNA. In Caco-2 and m-IC_C12 cell monolayers, LPA attenuated radiation-induced redistribution of TJ proteins, which was blocked by a Rho-kinase inhibitor. In mice, TBI and PBI-BM5 disrupted colonic epithelial tight junction and adherens junction, increased mucosal permeability, and elevated plasma LPS; TJ disruption by TBI was more severe in Lpar2^-/- mice compared to wild-type mice. RP1, administered before or after irradiation, alleviated TBI and PBI-BM5-induced TJ disruption, barrier dysfunction, and endotoxemia accompanied by protein thiol oxidation and downregulation of antioxidant gene expression, cofilin activation, and remodeling of the actin cytoskeleton. These data demonstrate that LPAR2 receptor activation prevents and mitigates γ-irradiation-induced colonic mucosal barrier dysfunction and endotoxemia.

Lysophosphatidic acid type 2 receptor agonists in targeted drug development offer broad therapeutic potential

The growth factor-like lipid mediator, lysophosphatidic acid (LPA), is a potent signaling molecule that influences numerous physiologic and pathologic processes. Manipulation of LPA signaling is of growing pharmacotherapeutic interest, especially because LPA resembles compounds with drug-like features. The action of LPA is mediated through activation of multiple types of molecular targets, including six G protein-coupled receptors that are clear targets for drug development. However, the LPA signaling has been linked to pathological responses that include promotion of fibrosis, atherogenesis, tumorigenesis, and metastasis. Thus, a question arises: Can we harness, in an LPA-like drug, the many beneficial activities of this lipid without eliciting its dreadful actions? We developed octadecyl thiophosphate (OTP; subsequently licensed as Rx100), an LPA mimic with higher stability in vivo than LPA. This article highlights progress made toward developing analogs like OTP and exploring prosurvival and regenerative LPA signaling. We determined that LPA prevents cell death triggered by various cellular stresses, including genotoxic stressors, and rescues cells condemned to apoptosis. LPA2 agonists provide a new treatment option for secretory diarrhea and reduce gastric erosion caused by nonsteroidal anti-inflammatory drugs. The potential uses of LPA2 agonists like OTP and sulfamoyl benzoic acid-based radioprotectins must be further explored for therapeutic uses.

The LPA2 receptor agonist Radioprotectin-1 spares Lgr5-positive intestinal stem cells from radiation injury in murine enteroids

Rapidly proliferating cells are highly sensitive to ionizing radiation and can undergo apoptosis if the oxidative and genotoxic injury exceed the defensive and regenerative capacity of the cell. Our earlier work has established the antiapoptotic action of the growth factor-like lipid mediator lysophosphatidic acid (LPA). Activation of the LPA₂ GPCR has been hypothesized to elicit antiapoptotic and regenerative actions of LPA. Based on this hypothesis we developed a novel nonlipid agonist of LPA₂, which we designated Radioprotectin-1 (RP-1). We tested RP-1 at the six murine LPA GPCR subtypes using the transforming growth factor alpha shedding assay and found that it had a 25 nM EC₅₀ that is similar to that of LPA18:1 at 32 nM. RP-1 effectively reduced apoptosis induced by γ-irradiation and the radiomimetic drug Adriamycin only in cells that expressed LPA₂ either endogenously or after transfection. RP-1 reduced γ-H2AX levels in irradiated mouse embryonic fibroblasts transduced with the human LPA₂ GPCR but was ineffective in vector transduced MEF control cells and significantly increased clonogenic survival after γ-irradiation. γ-Irradiation induced the expression of lpar2 transcripts that was further enhanced by RP-1 exposure within 30 min after irradiation. RP-1 decreased the mortality of C57BL/6 mice in models of the hematopoietic and gastrointestinal acute radiation syndromes. Using Lgr5-EGFP-CreER;Tdtomato^flox transgenic mice, we found that RP-1 increased the survival and growth of intestinal enteroids via the enhanced survival of Lgr5⁺ intestinal stem cells. Taken together, our results suggest that the LPA₂-specific agonist RP-1 exerts its radioprotective and radiomitigative action through specific activation of the upregulated LPA₂ GPCR in Lgr5⁺ stem cells.

Novel Inhibitory Effect of a Lysophosphatidic Acid 2 Agonist on Allergen-Driven Airway Inflammation

Lysophosphatidic acid (LPA) is a pleiotropic lipid signaling molecule associated with asthma pathobiology. LPA elicits its effects by binding to at least six known cell surface G protein-coupled receptors (LPA1-6) that are expressed in the lung in a cell type-specific manner. LPA2 in particular has emerged as an attractive therapeutic target in asthma because it appears to transduce inhibitory or cell-protective signals. We studied a novel and specific small molecule LPA2 agonist (2-[4-(1,3-dioxo-1H,3H-benzoisoquinolin-2-yl)butylsulfamoyl] benzoic acid [DBIBB]) in a mouse model of house dust mite-induced allergic airway inflammation. Mice injected with DBIBB developed significantly less airway and lung inflammation compared with vehicle-treated controls. Levels of lung Th2 cytokines were also significantly attenuated by DBIBB. We conclude that pharmacologic activation of LPA2 attenuates Th2-driven allergic airway inflammation in a mouse model of asthma. Targeting LPA receptor signaling holds therapeutic promise in allergic asthma.

The autotaxin-LPA2 GPCR axis is modulated by γ-irradiation and facilitates DNA damage repair

In this study we characterized the effects of radiation injury on the expression and function of the autotaxin (ATX)-LPA2 GPCR axis. In IEC-6 crypt cells and jejunum enteroids quantitative RT-PCR showed a time- and dose-dependent upregulation of lpa2 in response to γ-irradiation that was abolished by mutation of the NF-κB site in the lpa2 promoter or by inhibition of ATM/ATR kinases with CGK-733, suggesting that lpa2 is a DNA damage response gene upregulated by ATM via NF-κB. The resolution kinetics of the DNA damage marker γ-H2AX in LPA-treated IEC-6 cells exposed to γ-irradiation was accelerated compared to vehicle, whereas pharmacological inhibition of LPA2 delayed the resolution of γ-H2AX. In LPA2-reconstituted MEF cells lacking LPA1&3 the levels of γ-H2AX decreased rapidly, whereas in Vector MEF were high and remained sustained. Inhibition of ERK1&2 or PI3K/AKT signaling axis by pertussis toxin or the C311A/C314A/L351A mutation in the C-terminus of LPA2 abrogated the effect of LPA on DNA repair. LPA2 transcripts in Lin(-)Sca-1(+)c-Kit(+) enriched for bone marrow stem cells were 27- and 5-fold higher than in common myeloid or lymphoid progenitors, respectively. Furthermore, after irradiation higher residual γ-H2AX levels were detected in the bone marrow or jejunum of irradiated LPA2-KO mice compared to WT mice. We found that γ-irradiation increases plasma ATX activity and LPA level that is in part due to the previously established radiation-induced upregulation of TNFα. These findings identify ATX and LPA2 as radiation-regulated genes that appear to play a physiological role in DNA repair.

Combined mitigation of the gastrointestinal and hematopoietic acute radiation syndromes by an LPA2 receptor-specific nonlipid agonist

Pharmacological mitigation of injuries caused by high-dose ionizing radiation is an unsolved medical problem. A specific nonlipid agonist of the type 2 G protein coupled receptor for lysophosphatidic acid (LPA2) 2-[4-(1,3-dioxo-1H,3H-benzoisoquinolin-2-yl)butylsulfamoyl]benzoic acid (DBIBB) when administered with a postirradiation delay of up to 72 hr reduced mortality of C57BL/6 mice but not LPA2 knockout mice. DBIBB mitigated the gastrointestinal radiation syndrome, increased intestinal crypt survival and enterocyte proliferation, and reduced apoptosis. DBIBB enhanced DNA repair by augmenting the resolution of γ-H2AX foci, increased clonogenic survival of irradiated IEC-6 cells, attenuated the radiation-induced death of human CD34(+) hematopoietic progenitors and enhanced the survival of the granulocyte/macrophage lineage. DBIBB also increased the survival of mice suffering from the hematopoietic acute radiation syndrome after total-body irradiation. DBIBB represents a drug candidate capable of mitigating acute radiation syndrome caused by high-dose γ-radiation to the hematopoietic and gastrointestinal system.