Pharmacology/Drug Development

The σ receptor has attracted intense interest in cancer imaging, psychiatric disease, neuropathic pain and other areas of biology. Here we determined the crystal structure of this receptor in complex with the clinical candidate roluperidone and the tool compound PB28. These structures templated a large-scale docking screen of 490 million virtual molecules, of which 484 compounds were synthesized and tested. We identified 127 new chemotypes with affinities superior to 1 μM, 31 of which had affinities superior to 50 nM. The hit rate fell smoothly and monotonically with docking score. We optimized three hits for potency and selectivity, and achieved affinities that ranged from 3 to 48 nM, with up to 250-fold selectivity versus the σ receptor. Crystal structures of two ligands bound to the σ receptor confirmed the docked poses. To investigate the contribution of the σ receptor in pain, two potent σ-selective ligands and one potent σ/σ non-selective ligand were tested for efficacy in a mouse model of neuropathic pain. All three ligands showed time-dependent decreases in mechanical hypersensitivity in the spared nerve injury model, suggesting that the σ receptor has a role in nociception. This study illustrates the opportunities for rapid discovery of in vivo probes through structure-based screens of ultra large libraries, enabling study of underexplored areas of biology.

High molecular weight hyaluronan (HMWH) is an agonist at cluster of differentiation 44 (CD44), the cognate hyaluronan receptor, on nociceptors, where it acts to induce anti-hyperalgesia in preclinical models of inflammatory and neuropathic pain. In the present experiments we studied the CD44 second messengers that mediate HMWH-induced attenuation of pain associated with oxaliplatin and paclitaxel chemotherapy-induced peripheral neuropathy (CIPN). While HMWH attenuates CIPN only in male rats, following ovariectomy or intrathecal administration of an oligodeoxynucleotide (ODN) antisense to G-protein coupled estrogen receptor (GPR30) mRNA, female rats are also sensitive to HMWH. Intrathecal administration of ODN antisense to CD44 mRNA markedly attenuates HMWH-induced anti-hyperalgesia in male rats with CIPN induced by oxaliplatin or paclitaxel. Intradermal administration of inhibitors of CD44 second messengers, RhoGTPases (RhoA), phospholipase C (PLC) and PI3Kγ attenuates HMWH-induced anti-hyperalgesia, as does intrathecal administration of an oligodeoxynucleotide (ODN) antisense to PI3Kγ. Our results demonstrate that HMWH-induces anti-hyperalgesia in CIPN, mediated by its action at CD44, and downstream signaling by RhoA, PLC and PI3Kγ.

Obstructive sleep apnea (OSA), characterized by low arterial oxygen saturation during sleep, is associated with an increased risk of orofacial pain. In this study, we simulated chronic intermittent hypoxia (CIH) during the sleep/rest phase (light phase) to determine the role of transient receptor potential vanilloid 1 (TRPV1) in mediating enhanced orofacial nocifensive behavior and trigeminal spinal subnucleus caudalis (Vc) neuronal responses to capsaicin stimulation in a rat model of OSA. Rats were subjected to CIH (nadir O, 5%) during the light phase for 8 or 16 consecutive days. CIH yielded enhanced behavioral responses to capsaicin, a TRPV1 agonist, after application to the ocular surface and intraoral mucosa, which was reversed under normoxic conditions. The percentage of TRPV1-immunoreactive trigeminal ganglion neurons was greater in CIH rats than in normoxic rats and recovered under normoxic conditions after CIH. The ratio of large-sized TRPV1-immunoreactive trigeminal ganglion neurons increased in CIH rats. The density of TRPV1 positive primary afferent terminals in the superficial laminae of Vc was higher in CIH rats. The phosphorylated extracellular signal-regulated kinase (pERK)-immunoreactive cells intermingled with central terminal of TRPV1 positive afferents in the Vc. The number of pERK-immunoreactive cells following low-dose capsaicin (0.33 µM) application to the tongue was significantly greater in the middle portion of the Vc of CIH rats than in normoxic rats and recovered under normoxic conditions after CIH. These data suggest that CIH during the sleep (light) phase is sufficient to transiently enhance pain on the ocular surface and intraoral mucosa via TRPV1-dependent mechanisms.

Pain is responsible for inducing physical and mental stress, interfering negatively in patients' quality of life. Classic analgesic drugs, such as opioids and non-steroidal anti-inflammatory drugs, are known for their wide range of adverse effects, making it important to develop new drugs. Thus, this study aimed to analyze the action of the hybrid compound cis- (±) -acetate of 4-chloro-6- (naphthalene-1-yl) -tetrahydro-2h-pyran -2-yl) methyl2- (2- (2,6-dichlorophenylamine) phenyl (LS19) under acute nociceptive conditions, and deepened the understanding of the responsible mechanisms. Male swiss mice were evaluated in the acetic acid-induced abdominal writhing, formalin, tail-flick, capsaicin- and glutamate-induced nociception, thermal stimulation in animals injected with capsaicin and rotarod tests besides the acute and subchronic toxicological evaluation. The compound showed effect on the acetic acid-induced abdominal writhing, formalin (both phases), tail-flick, thermal stimulation in animals injected with capsaicin and capsaicin-induced nociception tests. In the study of the mechanism of action was observed reversion of the antihyperalgesic effect of the compound from the previous intraperitoneal and intrathecal administration of naloxone, nor-binaltorphimine, naltrindole, methylnaltrexone, 7-nitroindazole, L-NAME, ODQ, glibenclamide on the tail flick test. In the thermal stimulation in animals injected with capsaicin, the compound showed antinociceptive effect by oral and intraplantar routes, besides to reducing the levels of TNF-α, IL-1β and PGE in the paws previously administered with capsaicin. There were no signs of acute and subchronic intoxication with the compound. In summary, the compound LS19 presented spinal and local antihyperalgesic effect, demonstrating participation of the opioid/NO/cGMP/K+ ATP pathway and TRPV1 receptors and it demonstrated safety in its use in mice.