Amelioration of neuropathic pain by novel transient receptor potential vanilloid 1 antagonist AS1928370 in rats without hyperthermic effect.

Transient receptor potential vanilloid 1 (TRPV1) is activated by a variety of stimulations, such as endogenous ligands and low pH, and is believed to play a role in pain transmission. TRPV1 antagonists have been reported to be effective in several animal pain models; however, some compounds induce hyperthermia in animals and humans. We discovered the novel TRPV1 antagonist (R)-N-(1-methyl-2-oxo-1,2,3,4-tetrahydro-7-quinolyl)-2-[(2-methylpyrrolidin-1-yl)methyl]biphenyl-4-carboxamide (AS1928370) in our laboratory. AS1928370 bound to the resiniferatoxin-binding site on TRPV1 and inhibited capsaicin-mediated inward currents with an IC50 value of 32.5 nM. Although AS1928370 inhibited the capsaicin-induced Ca²(+) flux in human and rat TRPV1-expressing cells, the inhibitory effect on proton-induced Ca²(+) flux was extremely small. In addition, AS1928370 showed no inhibitory effects on transient receptor potential vanilloid 4, transient receptor potential ankyrin 1, and transient receptor potential melastatin 8 in concentrations up to 10 µM. AS1928370 improved capsaicin-induced secondary hyperalgesia and mechanical allodynia in an L5/L6 spinal nerve ligation model in rats with respective ED50 values of 0.17 and 0.26 mg/kg p.o. Furthermore, AS1928370 alleviated inflammatory pain in a complete Freund's adjuvant model at 10 mg/kg p.o. AS1928370 had no effect on rectal body temperature up to 10 mg/kg p.o., although a significant hypothermic effect was noted at 30 mg/kg p.o. In addition, AS1928370 showed no significant effect on motor coordination. These results suggest that blockage of the TRPV1 receptor without affecting the proton-mediated TRPV1 activation is a promising approach to treating neuropathic pain because of the potential wide safety margin against hyperthermic effects. As such, compounds such as ASP1928370 may have potential as new analgesic agents for treating neuropathic pain.

Synthesis and biological evaluation of 3-biphenyl-4-yl-4-phenyl-4H-1,2,4-triazoles as novel glycine transporter 1 inhibitors.

We describe the preparation and evaluation of a novel series of glycine transporter 1 (GlyT1) inhibitors derived from a high-throughput screening hit. The SAR studies resulted in the discovery of 3-biphenyl-4-yl-4-(2-fluorophenyl)-5-isopropyl-4H-1,2,4-triazole (6p). A pharmacokinetic study was also conducted and revealed that 6p had excellent oral bioavailability and ameliorated learning impairment in passive avoidance tasks in mice.

Neuroprotective effects of the selective type 1 metabotropic glutamate receptor antagonist YM-202074 in rat stroke models.

We describe in vitro properties and in vivo neuroprotective effects of a newly synthesized, high-affinity, selective allosteric metabotropic glutamate receptor type 1 (mGluR(1)) antagonist, N-cyclohexyl-6-{[(2-methoxyethyl)(methyl)amino]methyl}-N-methylthiazolo[3,2-a]benzimidazole-2-carboxamide (YM-202074). YM-202074 bound an allosteric site of rat mGluR(1) with a K(i) value of 4.8+/-0.37 nM. YM-202074 also inhibited the mGluR(1)-mediated inositol phosphates production in rat cerebellar granule cells with an IC(50) value of 8.6+/-0.9 nM, while showing selectivity over mGluR(2-7). When YM-202074 was infused intravenously at an initial dose of 20 mg/kg/h for 0.5 h followed by a dose of 5 mg/kg/h for 7.5 h, the free concentration of YM-202074 in the brain rapidly (<12 min) reached approximately 0.3 microM, reaching a steady-state phase within 1.5 h. We first treated rats such that they developed transient middle cerebral artery (MCA) occlusion. Results clearly demonstrate a dose-dependent improvement of neurological deficit and reduction of the infarct volume in both the hemisphere and cortex when YM-202074 was infused intravenously immediately after occlusion at a dose of 10 or 20 mg/kg/h for 0.5 h followed by a dose of 2.5 or 5 mg/kg/h for 23.5 h, respectively. Significant neuroprotection was maintained even when the administration of drugs was delayed by up to 2 h following the onset of ischemia. Furthermore, the improvement of neurological deficit and the reduction of infarct volume were sustained for 1 week following the onset of ischemia. These results suggest that YM-202074 exhibits great potential as a novel neuroprotective agent for the treatment of stroke.

Antinociceptive profile of a selective metabotropic glutamate receptor 1 antagonist YM-230888 in chronic pain rodent models.

Metabotropic glutamate receptor 1 (mGlu(1) receptor) has been suggested to play an important role in pain transmission. In this study, the effects of a newly-synthesized mGlu(1) receptor antagonist, (R)-N-cycloheptyl-6-({[(tetrahydro-2-furyl)methyl]amino}methyl)thieno[2,3-d]pyrimidin-4-ylamine (YM-230888), were examined in a variety of rodent chronic pain models in order to characterize the potential analgesic profile of mGlu(1) receptor blockade. YM-230888 bound an allosteric site of mGlu(1) receptor with a K(i) value of 13+/-2.5 nM and inhibited mGlu(1)-mediated inositol phosphate production in rat cerebellar granule cells with an IC(50) value of 13+/-2.4 nM. It showed selectivity for mGlu(1) versus mGlu(2)-mGlu(7) subtypes and ionotropic glutamate receptors. YM-230888 recovered mechanical allodynia with an ED(50) value of 8.4 mg/kg p.o. in L5/L6 spinal nerve ligation models. It also showed antinociceptive response at doses of 10 and 30 mg/kg p.o. in streptozotocin-induced hyperalgesia models. In addition, it significantly reduced pain parameters at a dose of 30 mg/kg p.o. in complete Freund's adjuvant-induced arthritic pain models. Although YM-230888 showed no significant effect on rotarod performance time at doses of 10 or 30 mg/kg p.o., it significantly decreased it at a dose of 100 mg/kg p.o. On the other hand, YM-230888 showed no significant sedative effect in locomotor activity measurement up to 100 mg/kg p.o. These results suggest that the blockade of mGlu(1) receptors is an attractive target for analgesics. YM-230888 has potential as a new analgesic agent for the treatment of various chronic pain conditions. In addition, YM-230888 may be a useful tool for the investigation of mGlu(1) receptors.

Radioligand binding properties and pharmacological characterization of 6-amino-N-cyclohexyl-N,3-dimethylthiazolo[3,2-a]benzimidazole-2-carboxamide (YM-298198), a high-affinity, selective, and noncompetitive antagonist of metabotropic glutamate receptor type 1.

Metabotropic glutamate receptor type 1 (mGluR1) is thought to play important roles in the neurotransmission and pathogenesis of several neurological disorders. Here, we describe the radioligand binding properties and pharmacological effects of a newly synthesized, high-affinity, selective, and noncompetitive mGluR1 antagonist, 6-amino-N-cyclohexyl-N,3-dimethylthiazolo[3,2-a]benzimidazole-2-carboxamide (YM-298198). YM-298198 inhibited glutamate-induced inositol phosphate production in mGluR1-NIH3T3 cells with an IC50 of 16 +/- 5.8 nM in a noncompetitive manner. Its radiolabeled form, [3H]YM-298198, bound to mGluR1-NIH3T3 cell membranes with a KD of 32 +/- 8.5 nM and a Bmax of 2297 +/- 291 fmol/mg protein. In ligand displacement experiments using rat cerebellum membrane, an existing noncompetitive mGluR1 antagonist 7-(hydroxyimino)cyclo-propa[b]chromen-1a-carboxylate ethyl ester (CPCCOEt) competitively displaced [3H]YM-298198 binding, although glutamate and other mGluR1 ligands acting on a glutamate site failed to inhibit [3H]YM-298198 binding, suggesting that YM-298198 binds to CPCCOEt (allosteric) binding sites but not to glutamate (agonist) binding sites. Specificity was demonstrated for mGluR1 over mGluR subtypes 2 to 7, ionotropic glutamate receptors, and other receptor, transporter, and ion channel targets. In in vivo experiments, orally administered YM-298198 showed a significant analgesic effect in streptozotocin-induced hyperalgesic mice at doses (30 mg/kg) that did not cause Rotarod performance impairment, indicating that it is also useful even for in vivo experiments. In conclusion, YM-298198 is a newly synthesized, high-affinity, selective, and noncompetitive antagonist of mGluR1 that will be a useful pharmacological tool due to its highly active properties in vitro and in vivo. Its radiolabeled form [3H]YM-298198 will also be a valuable tool for future investigation of the mGluR1.

Allodynia and hyperalgesia in adjuvant-induced arthritic rats: time course of progression and efficacy of analgesics.

The complete Freund's adjuvant (CFA)-induced arthritic rat model has extensively served as a laboratory model in the study of arthritic pain. However, the time courses of allodynia and hyperalgesia and the efficacies of different analgesics have not fully been analyzed in this model. Mechanical allodynia, thermal and joint hyperalgesia, and other disease development parameters (body weight, mobility, paw volume, and joint stiffness) were measured on postinoculation days (PIDs) 0 to 28 in rats. Acute analgesic efficacies of drugs were evaluated on PID 9 when degrees of allodynia, hyperalgesia, and joint stiffness in the ipsilateral paw reached almost the maximum, although those in the contralateral paw changed only slightly. In the ipsilateral paw, thermal hyperalgesia reached the maximum on PID 1, whereas mechanical allodynia and joint hyperalgesia progressively developed during the first 7 or 8 days, being tuned in to arthritis development. In the contralateral paw, thermal hyperalgesia never occurred, whereas mechanical allodynia and joint hyperalgesia developed after PID 11. Morphine and tramadol had full efficacies for all the pain parameters tested at sedation-inducing doses. Indomethacin and diclofenac significantly but partially improved thermal and joint hyperalgesia. Amitriptyline significantly reduced thermal and joint hyperalgesia only at sedation-inducing dose. Acetaminophen, carbamazepine, and gabapentin had, at the most, very small efficacies. In conclusion, the present study provided integrated information about the time course of pain and other disease development parameters in the CFA-induced arthritic rats, and clarified acute efficacies of different categories of analgesics for the allodynia and hyperalgesia.

YM872: a selective, potent and highly water-soluble alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid receptor antagonist.

This review focuses on the in vitro and in vivo neuropharmacology of YM872, a potential neuroprotective agent currently undergoing clinical trials in the United States (trial name: AMPA Receptor Antagonist Treatment in Ischemic Stroke - ARTIST). Its neuroprotective properties in rats and cats with induced focal cerebral ischemia are described. YM872, [2,3-dioxo-7-(1H-imidazol-1-yl)-6-nitro-1,2,3,4-tetrahydroquinoxalin-1-yl]-acetic acid monohydrate, is a selective, potent and highly water-soluble competitive alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) receptor antagonist. YM872 has a potent inhibitory effect on [(3)H]AMPA binding with a K(i) value of 0.096 microM. In contrast, YM872 has very low affinity for other ionotropic glutamate receptors. The solubility of YM872 is approximately 500 to 1000 times higher than that of the other competitive AMPA antagonists: YM90K, NBQX, or CNQX. The neuroprotective efficacy of YM872 was investigated in rats and cats subjected to permanent occlusion of the left middle cerebral artery. The animals were assessed either histologically or neurologically following ischemia. In rats with occluded middle cerebral artery (MCAO) YM872, by i.v. infusion, significantly reduced infarct volume measured at 24 h and 1 week after ischemia. Significant neuroprotection was maintained even when drug administration was delayed for up to 2 h after ischemia. In addition, YM872 significantly improved neurological deficit measured at 1 week after ischemia. In cats with MCAO YM872, by i.v. infusion, dose-dependently reduced infarct volume at 6 h after ischemia. YM872 produced no behavioral abnormalities and was not nephrotoxic. The evidence for the neuroprotective efficacy of YM872 suggests its therapeutic potential in the treatment of acute stroke in humans.