Evaluation of cutaneous allodynia following induction of cortical spreading depression in freely moving rats.

BACKGROUND: Cortical spreading depression (CSD) is a wave of depolarization followed by depression of bioelectrical activity that slowly propagates through the cortex. CSD is believed to be the underlying mechanism of aura in migraine; however, whether CSD can elicit pain associated with migraine headache is unclear. METHODS: Awake, freely moving rats were monitored for both CSD events and behavioral responses resulting from dural-cortical pinprick and/or KCl injection to the occipital cortex. RESULTS: We observed tactile allodynia of the face and hindpaws, as well as enhanced Fos expression within the trigeminal nucleus caudalis (TNC) following CSD induced by KCl injection into the cortex, but not by pinprick. Application of KCl onto the dura elicited cutaneous allodynia and increased Fos staining in the TNC but did not elicit CSD events. CONCLUSIONS: These data suggest that sustained activation of trigeminal afferents that may be required to establish cutaneous allodynia may not occur following CSD events in normal animals.

Discovery of fused bicyclic agonists of the orphan G-protein coupled receptor GPR119 with in vivo activity in rodent models of glucose control.

We herein outline the design of a new series of agonists of the pancreatic and GI-expressed orphan G-protein coupled receptor GPR119, a target that has been of significant recent interest in the field of metabolism, starting from our prototypical agonist AR231453. A number of key parameters were improved first by incorporation of a pyrazolopyrimidine core to create a new structural series and secondly by the introduction of a piperidine ether group capped with a carbamate. Chronic treatment with one compound from the series, 3k, showed for the first time that blood glucose and glycated hemoglobin (HbA1c) levels could be significantly reduced in Zucker Diabetic Fatty (ZDF) rats over several weeks of dosing. As a result of these and other data described here, 3k (APD668, JNJ-28630368) was the first compound with this mechanism of action to be progressed into clinical development for the treatment of diabetes.

Medullary pain facilitating neurons mediate allodynia in headache-related pain.

OBJECTIVE: To develop and validate a model of cutaneous allodynia triggered by dural inflammation for pain associated with headaches. To explore neural mechanisms underlying cephalic and extracephalic allodynia. METHODS: Inflammatory mediators (IM) were applied to the dura of unanesthetized rats via previously implanted cannulas, and sensory thresholds of the face and hind-paws were characterized. RESULTS: IM elicited robust facial and hind-paw allodynia, which peaked within 3 hours. These effects were reminiscent of cutaneous allodynia seen in patients with migraine or other primary headache conditions, and were reversed by agents used clinically in the treatment of migraine, including sumatriptan, naproxen, and a calcitonin gene-related peptide antagonist. Consistent with clinical observations, the allodynia was unaffected by a neurokinin-1 antagonist. Having established facial and hind-paw allodynia as a useful animal surrogate of headache-associated allodynia, we next showed that blocking pain-facilitating processes in the rostral ventromedial medulla (RVM) interfered with its expression. Bupivacaine, destruction of putative pain-facilitating neurons, or block of cholecystokinin receptors prevented or significantly attenuated IM-induced allodynia. Electrophysiological studies confirmed activation of pain-facilitating RVM "on" cells and transient suppression of RVM "off" cells after IM. INTERPRETATION: Facial and hind-paw allodynia associated with dural stimulation is a useful surrogate of pain associated with primary headache including migraine and may be exploited mechanistically for development of novel therapeutic strategies for headache pain. The data also demonstrate the requirement for activation of descending facilitation from the RVM for the expression of cranial and extracranial cutaneous allodynia, and are consistent with a brainstem generator of allodynia associated with headache disorders.

Constitutive activity at the cannabinoid CB1 receptor is required for behavioral response to noxious chemical stimulation of TRPV1: antinociceptive actions of CB1 inverse agonists.

The potential modulation of TRPV1 nociceptive activity by the CB(1) receptor was investigated here using CB(1) wild-type (WT) and knock-out (KO) mice as well as selective CB(1) inverse agonists. No significant differences were detected in baseline thermal thresholds of ICR, CB(1)WT or CB(1)KO mice. Intraplantar capsaicin produced dose- and time-related paw flinch responses in ICR and CB(1)WT mice and induced plasma extravasation yet minimal responses were seen in CB(1)KO animals with no apparent differences in TRPV1 channel expression. Capsaicin-evoked CGRP release from spinal cord tissue and capsaicin-evoked action potentials on isolated skin-nerve preparation were significantly decreased in CB(1)KO mice. Pretreatment with intraplantar galanin and bradykinin, compounds known to sensitize TRPV1 receptors, restored capsaicin-induced flinching in CB(1)KO mice. The possibility that constitutive activity at the CB(1) receptor is required to maintain the TRPV1 receptor in a "sensitized" state was tested using CB(1) inverse agonists. The CB(1) inverse agonists elicited concentration-related inhibition of capsaicin-induced calcium influx in F-11 cells and produced dose-related inhibition of capsaicin-induced flinching in ICR mice. These data suggest that constitutive activity at the CB(1) receptor maintains the TRPV1 channel in a sensitized state responsive to noxious chemical stimuli. Treatment with CB(1) inverse agonists may promote desensitization of the channel resulting in antinociceptive actions against chemical stimulus modalities. These studies propose possible therapeutic exploitation of a novel mechanism providing pain relief by CB(1) inverse agonists.

The ORL-1 receptor system: are there opportunities for antagonists in pain therapy?

Following the cloning of the classical opioid receptors (mu, delta and kappa), the opioid receptor like-1 (ORL-1) was identified as a G-protein coupled receptor (GPCR) with 65% structure homology to the other members of the opioid family. Its endogenous ligand nociception/orphanin FQ (N/OFQ) was discovered shortly thereafter, becoming the subject of investigation in numerous studies. Since activation of the ORL-1 receptor by N/OFQ leads to G alpha(i)-coupling and signal transduction similar to that of opioid receptors, N/OFQ was thought to have a role in pain modulation, similar to that of the endogenous opioids. Surprisingly, studies characterizing N/OFQ's effects on pain transmission yielded conflicting results, attributing to N/OFQ both pronociceptive and antinociceptive actions, depending on doses and routes of administration as well as species and sex of the subjects. With the development of selective and potent ORL-1 antagonists, many scientists believed these contradicting actions would be elucidated. Here we review the recent literature reporting the use of novel ORL-1 antagonists, both peptide and non-peptide, in different models of pain and discuss their use as research tools or potential drug candidates.

Discovery of the first potent and orally efficacious agonist of the orphan G-protein coupled receptor 119.

GPR119 is a rhodopsin-like GPCR expressed in pancreatic beta-cells and incretin releasing cells in the GI tract. As with incretins, GPR119 increases cAMP levels in these cell types, thus making it a highly attractive potential target for the treatment of diabetes. The discovery of the first reported potent agonist of GPR119, 2-fluoro-4-methanesulfonyl-phenyl)-{6-[4-(3-isopropyl-[1,2,4]oxadiazol-5-yl)-piperidin-1-yl]-5-nitro-pyrimidin-4-yl}-amine (8g, AR231453), is described starting from an initial inverse agonist screening hit. Compound 8g showed in vivo activity in rodents and was active in an oral glucose tolerance test in mice following oral administration.