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.

AS1069562, the (+)-isomer of indeloxazine, exerts analgesic effects in rat models of nociceptive pain.

OBJECTIVES: The (+)-isomer of indeloxazine AS1069562 has multiple pharmacological actions, such as serotonin (5-HIT) and norepinephrine (NE) reuptake inhibition and analgesic effects in animal models of neuropathic pain. Here, we investigated the analgesic effects of AS1069562 in rat models of inflammatory and noninflammatory nociceptive pain. METHODS: Adjuvant-induced arthritis (AIA) and bradykinin-induced knee joint pain were used as rat models of inflammatory pain. The chronic phase of monoiodoacetate-induced arthritis (MIA) was used as a rat model of noninflammatory pain. Analgesic effects were evaluated by weight-bearing deficit in the AIA and MIA models and by pain response in the bradykinin-induced knee joint pain model. RESULTS: In the AIA model and the bradykinin-induced knee joint pain model, AS1069562 significantly ameliorated the pain-related behavior of weight-bearing deficit and the pain response, respectively. AS1069562 also significantly improved the pain-related behavior of weight-bearing deficit in the chronic phase of the MIA model. Further, following monoiodoacetate injection, repeated administration of AS1069562 or duloxetine significantly improved weight-bearing deficit in the MIA model. Interestingly, the analgesic effect of AS1069562 was sustained for 24 hours after the last administration, although the plasma concentration of AS1069562 was reduced to undetectable levels. In contrast, the analgesic effect of duloxetine did not continue after treatment discontinuation. DISCUSSION: AS1069562 exerts analgesic effects on inflammatory and noninflammatory nociceptive pain in rat models of arthritis pain, and repeated administration of AS1069562 exerts a more persistent analgesic effect on arthritis pain than duloxetine. These findings suggest that AS1069562 has an attractive analgesic profile for the treatment of nociceptive pain.

Antinociceptive effects of AS1069562, the (+)-isomer of indeloxazine, on spinal hypersensitivity induced by intrathecal injection of prostaglandin in mice: comparison with duloxetine and amitriptyline.

The (+)-isomer of indeloxazine AS1069562 exerts multiple pharmacological actions including the inhibition of serotonin (5-HT) and norepinephrine reuptake and analgesia in experimental animal pain models. Here, we evaluated the antinociceptive effects of AS1069562 and the antidepressants duloxetine and amitriptyline in mouse models of prostaglandin-induced spinal hypersensitivity. Prostaglandin E2 (PGE2) and F2α (PGF2α) were intrathecally administered to induce spinal hypersensitivity, causing tactile allodynia in mice. Allodynia induced by PGF2α but not by PGE2 was suppressed by desensitization of C-fibers with systemic pretreatment with resiniferatoxin. C-fiber hyperexcitability might therefore play a role in allodynia induced by PGF2α but not PGE2. In the PGE2-induced allodynia model, AS1069562 and duloxetine significantly suppressed allodynia, whereas amitriptyline did not. In the PGF2α-induced allodynia model, AS1069562 and amitriptyline significantly ameliorated allodynia, whereas duloxetine did not. To demonstrate the broad effects of AS1069562 compared to duloxetine, additional studies were conducted to elucidate other target mechanisms of AS1069562 beyond 5-HT and norepinephrine reuptake inhibition. AS1069562 exhibited affinity for both 5-HT1A and 5-HT3 receptors, and the analgesic effect of AS1069562 on PGF2α-induced allodynia was significantly blocked by the 5-HT1A receptor antagonist (S)-WAY100135 and the 5-HT3 receptor agonist SR57227. Taken together, these results indicate that AS1069562 inhibits both C-fiber- and non-C-fiber-dependent prostaglandin-induced allodynia, while duloxetine inhibits only non-C-fiber-triggered allodynia, and amitriptyline inhibits only C-fiber-triggered allodynia. These broad antinociceptive effects of AS1069562 may be due not only to 5-HT and norepinephrine reuptake inhibition but also to its effects on 5-HT receptors such as 5-HT1A and 5-HT3 receptors.

AS1069562, the (+)-isomer of indeloxazine, exerts analgesic effects in a rat model of neuropathic pain with unique characteristics in spinal monoamine turnover.

AS1069562 [(R)-2-[(1H-inden-7-yloxy)methyl]morpholine monobenzenesulfonate] is the (+)-isomer of indeloxazine, which had been used clinically for the treatment of cerebrovascular diseases with multiple pharmacological actions, including serotonin (5-HT) and norepinephrine (NE) reuptake inhibition. Here we investigated the analgesic effects of AS1069562 in a rat model of chronic constriction injury (CCI)-induced neuropathic pain and the spinal monoamine turnover. These effects were compared with those of the antidepressants duloxetine and amitriptyline. AS1069562 significantly elevated extracellular 5-HT and NE levels in the rat spinal dorsal horn, although its 5-HT and NE reuptake inhibition was much weaker than that of duloxetine in vitro. In addition, AS1069562 increased the ratio of the contents of both 5-HT and NE to their metabolites in rat spinal cord, whereas duloxetine slightly increased only the ratio of the content of 5-HT to its metabolite. In CCI rats, AS1069562 and duloxetine significantly ameliorated mechanical allodynia, whereas amitriptyline did not. AS1069562 and amitriptyline significantly ameliorated thermal hyperalgesia, and duloxetine tended to ameliorate it. Furthermore, AS1069562, duloxetine, and amitriptyline significantly improved spontaneous pain-associated behavior. In a gastric emptying study, AS1069562 affected gastric emptying at the same dose that exerted analgesia in CCI rats. On the other hand, duloxetine and amitriptyline significantly reduced gastric emptying at lower doses than those that exerted analgesic effects. These results indicate that AS1069562 broadly improved various types of neuropathic pain-related behavior in CCI rats with unique characteristics in spinal monoamine turnover, suggesting that AS1069562 may have potential as a treatment option for patients with neuropathic pain, with a different profile from currently available antidepressants.

AS1069562, the (+)-isomer of indeloxazine, but not duloxetine has a curative-like analgesic effect in a rat model of streptozotocin-induced diabetic neuropathy.

AS1069562 is the (+)-isomer of indeloxazine, which had been clinically used as a cerebral activator for the treatment of cerebrovascular diseases with serotonin and norepinephrine reuptake inhibition (SNRI) and neuroprotection. Here, we compared the analgesic effects of repeated treatment with AS1069562 and duloxetine, a selective SNRI, on pain-related behavior in a rat model of streptozotocin (STZ)-induced diabetic neuropathy. Further, we also evaluated the effects on the expression of neurotrophic factors and nerve conduction velocity. AS1069562 and duloxetine by single daily administration for 4 weeks significantly improved mechanical allodynia in STZ-induced diabetic rats and did not affect plasma glucose level or body weight. Interestingly, the analgesic effect of AS1069562 continued after a consecutive 1-week treatment discontinuation, although the plasma concentration of AS1069562 was reduced to undetectable levels. In contrast, the efficacy of duloxetine disappeared after treatment discontinuation. Expression analysis demonstrated that AS1069562 significantly restored decreased insulin-like growth factor 1 and fibroblast growth factor 2 mRNA levels in dorsal root ganglion and spinal cord, respectively, whereas duloxetine did not affect the expression levels of neurotrophic factors. In addition, AS1069562 reversed the slowing of nerve conduction velocity. The results of this study indicate that the analgesic effect of repeated dosing of AS1069562 but not duloxetine is persistent even after a 1-week drug discontinuation in STZ-induced diabetic rats. Restoration of neurotrophic factors may be involved in the curative-like pharmacological effect of this agent. Thus, AS1069562 may potentially offer a better treatment option for patients with painful diabetic neuropathy than duloxetine via different mechanisms.

Minodronic acid, a third-generation bisphosphonate, antagonizes purinergic P2X(2/3) receptor function and exerts an analgesic effect in pain models.

The P2X(2/3) receptor has an important role in the nociceptive transmission. Minodronic acid is a third third-generation bisphosphonate and a potent inhibitor of bone resorption. We found that minodronic acid inhibited alpha,beta-methylene ATP-induced cation uptake with the potency higher than that of suramin in the P2X(2/3) receptor receptor-expressing cells. Other bisphosphonates did not show such activity. Subcutaneously administered (10-50 mg/kg) minodronic acid significantly inhibited the alpha,beta-methylene ATP-, acetic acid- and formalin-induced nociceptive behaviors in mice. These unique effects of minodronic acid would be beneficial for the treatment of accelerated bone turnover diseases accompanied by bone pain, including bone metastases.

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.