Identification of potent lysophosphatidic acid receptor 5 (LPA5) antagonists as potential analgesic agents.

Lysophosphatidic acid (LPA) plays an important role in a variety of cellular functions. In particular, LPA5 receptor is highly expressed in spinal cord and dorsal root ganglion, which are associated with pain. This fact prompted us to hypothesize that LPA5 antagonists show analgesic effects. To search for potent LPA5 antagonists with blood brain barrier (BBB) permeability, we conducted high throughput screening (HTS). In HTS campaign, we found a 2H-isoquinoline-1-one scaffold showing antagonistic activity against LPA5 and synthesized a series of 2H-isoquinoline-1-one derivatives and evaluated their LPA5 activities. Among these compounds, compound 7e showed potent LPA5 activity with an IC50 value of 0.12 µM, and acceptable BBB permeability. Furthermore, it showed effective analgesic effect in a chronic constriction injury rat model. Therefore, 7e may have a potential as novel pain therapeutic approach.

Design, synthesis, and biological evaluation of novel biphenyl-4-carboxamide derivatives as orally available TRPV1 antagonists.

A new series of transient receptor potential vanilloid type 1 (TRPV1) antagonists were designed and synthesized from N-(3-hydroxyphenyl)-2-(piperidin-1-ylmethyl)biphenyl-4-carboxamide hydrochloride (8). SAR studies identified (R)-N-(1-methyl-2-oxo-1,2,3,4-tetrahydro-7-quinolyl)-2-[(2-methylpyrrolidin-1-yl)methyl]biphenyl-4-carboxamide hydrochloride (ASP8370, 7), as a compound with high aqueous solubility, satisfactory stability in human liver microsomes, and reduced CYP3A4 inhibition. ASP8370 was selected as a clinical development candidate with significant ameliorative effects on neuropathic pain. SAR studies also revealed the structural mechanisms underlying the switching between TRPV1 antagonism and agonism.

Analgesic effects of novel lysophosphatidic acid receptor 5 antagonist AS2717638 in rodents.

Lysophosphatidic acid (LPA) is a bioactive lipid that acts via at least six G protein-coupled receptors, LPA receptors 1-6 (LPA1-6), for various physiological functions. We examined (1) whether LPA5 is involved in pain signaling in the spinal cord; and (2) the pharmacological effects of a novel LPA5 antagonist on intrathecal prostaglandin (PG)- and (S)-α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)-induced allodynia, and neuropathic and inflammatory pain in rodents. Intrathecal injection of a selective LPA5 agonist, geranylgeranyl diphosphate, and a non-selective agonist, LPA, induced allodynia in wild type, but not in LPA5 knockout mice. These novel results suggest that LPA5 is important for pain signal transmission in the spinal cord. AS2717638 (6,7-dimethoxy-2-(5-methyl-1,2-benzoxazol-3-yl)-4-(piperidin-1-ylcarbonyl)isoquinolin-1(2H)-one) bound to the LPA-binding site on LPA5 and selectively inhibited LPA-induced cyclic adenosine monophosphate accumulation in human LPA5-but not LPA1-, 2-, or 3-expressing cells. Further, oral administration of AS2717638 inhibited LPA5 agonist-induced allodynia in mice. AS2717638 also significantly improved PGE2-, PGF2α-, and AMPA-induced allodynia, while both pregabalin and duloxetine alleviated only PGE2-induced allodynia in mice. Similarly, AS2717638 significantly ameliorated static mechanical allodynia and thermal hyperalgesia in rat models of chronic constriction injury (CCI)-induced neuropathic pain. AS2717638 also showed analgesic effects in a rat model of inflammatory pain. These findings suggest that LPA5 antagonists elicit broad analgesic effects against both neuropathic and inflammatory pain. Accordingly, pharmacological LPA5 antagonists are attractive development candidates for potential novel pain therapies.

Rice plastidial N-glycosylated nucleotide pyrophosphatase/phosphodiesterase is transported from the ER-golgi to the chloroplast through the secretory pathway.

A nucleotide pyrophosphatase/phosphodiesterase (NPP) activity that catalyzes the hydrolytic breakdown of ADP-glucose (ADPG) has been shown to occur in the plastidial compartment of both mono- and dicotyledonous plants. To learn more about this enzyme, we purified two NPPs from rice (Oryza sativa) and barley (Hordeum vulgare) seedlings. Both enzymes are glycosylated, since they bind to concanavalin A, stain with periodic acid-Schiff reagent, and are digested by Endo-H. A complete rice NPP cDNA, designated as NPP1, was isolated, characterized, and overexpressed in transgenic plants displaying high ADPG hydrolytic activity. Databank searches revealed that NPP1 belongs to a functionally divergent group of plant nucleotide hydrolases. NPP1 contains numerous N-glycosylation sites and a cleavable hydrophobic signal sequence that does not match with the N-terminal part of the mature protein. Both immunocytochemical analyses and confocal fluorescence microscopy of rice cells expressing NPP1 fused with green fluorescent protein (GFP) revealed that NPP1-GFP occurs in the plastidial compartment. Brefeldin A treatment of NPP1-GFP-expressing cells prevented NPP1-GFP accumulation in the chloroplasts. Endo-H digestibility studies revealed that both NPP1 and NPP1-GFP in the chloroplast are glycosylated. Collectively, these data demonstrate the trafficking of glycosylated proteins from the endoplasmic reticulum-Golgi system to the chloroplast in higher plants.