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Opioids are the most effective painkillers, but their benefit-risk balance often hinder their therapeutic use. WLB-73502 is a dual, bispecific compound that binds sigma-1 (S1R) and mu-opioid (MOR) receptors. WLB-73502 is an antagonist at the S1R. It behaved as a partial MOR agonist at the G-protein pathway and produced no/unsignificant β -arrestin-2 recruitment, thus demonstrating low intrinsic efficacy on MOR at both signalling pathways. Despite its partial MOR agonism, WLB-73502 exerted full antinociceptive efficacy, with potency superior to morphine and similar to oxycodone against nociceptive, inflammatory and osteoarthritis pain, and superior to both morphine and oxycodone against neuropathic pain. WLB-73502 crosses the blood–brain barrier and binds brain S1R and MOR to an extent consistent with its antinociceptive effect. Contrary to morphine and oxycodone, tolerance to its antinociceptive effect did not develop after repeated 4-week administration. Also, contrary to opioid comparators, WLB-73502 did not inhibit gastrointestinal transit or respiratory function in rats at doses inducing full efficacy, and it was devoid of proemetic effect (retching and vomiting) in ferrets at potentially effective doses. WLB-73502 benefits from its bivalent S1R antagonist and partial MOR agonist nature to provide an improved antinociceptive and safety profile respect to strong opioid therapy. WLB-73502 is a bispecific sigma-1 antagonist and partial mu-opioid agonist (low intrinsic efficacy at G i/o -protein activation and undetectable β -arrestin-2 recruitment) with improved antinociceptive and safety profile respect to strong opioids. [Display omitted] [ABSTRACT FROM AUTHOR]

A new mitogen-activated protein kinase (MAPK)-like enzyme which functions as a MAPK-activated protein (MAPKAP) kinase-2 reactivating kinase (RK) is identified in Saccharomyces cerevisiae. MAPKAP kinase-2 is activated by the p44 and p42 isoforms of MAPK and also by sodium arsenite, osmotic stress and heat shock. The RK of MAPKAP kinase-2 is identified by the raising of antiserum against Xenopus MAPK. The ability of RK to activate RK kinase also enables its identification.

Abstract: Sigma 1 receptor (σ1 receptor) is a unique ligand-regulated molecular chaperone located mainly in the endoplasmic reticulum and the plasma membrane. σ1 receptor is activated under stress or pathological conditions and interacts with several neurotransmitter receptors and ion channels to modulate their function. The effects reported preclinically with σ1 receptor ligands are consistent with a role for σ1 receptor in central sensitization and pain hypersensitivity and suggest a potential therapeutic use of σ1 receptor antagonists for the management of neuropathic pain as monotherapy. Moreover, data support their use in opioid adjuvant therapy: combination of σ1 receptor antagonists and opioids results in potentiation of opioid analgesia, without significant increases in opioid-related unwanted effects. Results from clinical trials using selective σ1 receptor antagonists in several pain conditions are eagerly awaited to ascertain the potential of σ1 receptor modulation in pain therapy. [Copyright &y& Elsevier]

Abstract: Sigma-1 (σ1) receptors play a role in different types of pain and in central sensitization mechanisms; however, it is unknown whether they are involved in chemotherapy-induced neuropathic pain. We compared the ability of paclitaxel to induce cold (acetone test) and mechanical (electronic Von Frey test) allodynia in wild-type (WT) and σ1 receptor knockout (σ1-KO) mice. We also tested the effect on paclitaxel-induced painful neuropathy of BD-1063 (16–64 mg/kg, subcutaneously) and S1RA (32–128 mg/kg, subcutaneously), 2 selective σ1 receptor antagonists that bind to the σ1 receptor with high affinity and competitively. The responses to cold and mechanical stimuli were similar in WT and σ1-KO mice not treated with paclitaxel; however, treatment with paclitaxel (2 mg/kg, intraperitoneally, once per day during 5 consecutive days) produced cold and mechanical allodynia and an increase in spinal cord diphosphorylated extracellular signal-regulated kinase (pERK) in WT but not in σ1-KO mice. The administration of BD-1063 or S1RA 30 minutes before each paclitaxel dose prevented the development of cold and mechanical allodynia in WT mice. Moreover, the acute administration of both σ1 receptor antagonists dose dependently reversed both types of paclitaxel-induced allodynia after they had fully developed. These results suggest that σ1 receptors play a key role in paclitaxel-induced painful neuropathy. Perspective: Antagonists of the σ1 receptor may have therapeutic value for the treatment and/or prevention of paclitaxel-induced neuropathic pain. This possibility is especially interesting in the context of chemotherapy-induced neuropathy, where the onset of nerve damage is predictable and preventive treatment could be administered. [Copyright &y& Elsevier]

Drug combination for the treatment of pain is common clinical practice. Co-crystal of Tramadol-Celecoxib (CTC) consists of two active pharmaceutical ingredients (APIs), namely the atypical opioid tramadol and the preferential cyclooxygenase-2 inhibitor celecoxib, at a 1:1 molecular ratio. In this study, a non-formulated ‘raw’ form of CTC administered in suspension (referred to as ctc susp ) was compared with both tramadol and celecoxib alone in a rat plantar incision postoperative pain model. For comparison, the strong opioids morphine and oxycodone, and a tramadol plus acetaminophen combination at a molecular ratio of 1:17 were also tested. Isobolographic analyses showed that ctc susp exerted synergistic mechanical antiallodynic (experimental ED 50 = 2.0 ± 0.5 mg/kg, i.p.; theoretical ED 50 = 3.8 ± 0.4 mg/kg, i.p.) and thermal (experimental ED 50 = 2.3 ± 0.5 mg/kg, i.p.; theoretical ED 50 = 9.8 ± 0.8 mg/kg, i.p.) antihyperalgesic effects in the postoperative pain model. In contrast, the tramadol and acetaminophen combination showed antagonistic effects on both mechanical allodynia and thermal hyperalgesia. No synergies between tramadol and celecoxib on locomotor activity, motor coordination, ulceration potential and gastrointestinal transit were observed after the administration of ctc susp . Overall, rat efficacy and safety data revealed that ctc susp provided synergistic analgesic effects compared with each API alone, without enhancing adverse effects. Moreover, ctc susp showed similar efficacy but improved safety ratio (80, measured as gastrointestinal transit vs postoperative pain ED 50 ratios) compared with the strong opioids morphine (2.5) and oxycodone (5.8). The overall in vivo profile of ctc susp supports the further investigation of CTC in the clinical management of moderate-to-severe acute pain as an alternative to strong opioids. [ABSTRACT FROM AUTHOR]

Abstract: While opioids are potent analgesics widely used in the management of pain, a number of well-known adverse effects limit their use. The sigma-1 receptor is a ligand-regulated molecular chaperone involved in pain processing, including modulation of opioid antinociception. However, data supporting the potential use of sigma-1 receptor ligands as suitable opioid adjuvants are based on studies that use non selective ligands. Also, safety issues derived from combination therapy are poorly addressed. In this study we used the new selective sigma-1 receptor antagonist S1RA (E-52862) to characterize the effect of selective sigma-1 receptor blockade on opioid-induced efficacy- and safety-related outcomes in mice. S1RA (40mg/kg) had no effect in the tail-flick test but did enhance the antinociceptive potency of several opioids by a factor between 2 and 3.3. The potentiating effect of S1RA on morphine antinociception did not occur in sigma-1 receptor knockout mice, which supports the selective involvement of the sigma-1 receptor. Interestingly, S1RA co-administration restored morphine antinociception in tolerant mice and reverted the reward effects of morphine in the conditioned place preference paradigm. In addition, enhancement of antinociception was not accompanied by potentiation of other opioid-induced effects, such as the development of morphine analgesic tolerance, physical dependence, inhibition of gastrointestinal transit, or mydriasis. The use of sigma-1 receptor antagonists as opioid adjuvants could represent a promising pharmacological strategy to enhance opioid potency and, most importantly, to increase the safety margin of opioids. S1RA is currently in phase II clinical trials for the treatment of several pain conditions. [Copyright &y& Elsevier]

Abstract: We studied the modulation of morphine-induced mechanical antinociception and side effects by σ1 receptor inhibition. Both wild-type (WT) and σ1 receptor knockout (σ1-KO) mice showed similar responses to paw pressure (100–600 g). The systemic (subcutaneous) or local (intraplantar) administration of σ1 antagonists (BD-1063, BD-1047, NE-100 and S1RA) was devoid of antinociceptive effects in WT mice. However, σ1-KO mice exhibited an enhanced mechanical antinociception in response to systemic morphine (1–16 mg/kg). Similarly, systemic treatment of WT mice with σ1 antagonists markedly potentiated morphine-induced antinociception, and its effects were reversed by the selective σ1 agonist PRE-084. Although the local administration of morphine (50–200 μg) was devoid of antinociceptive effects in WT mice, it induced dose-dependent antinociception in σ1-KO mice. This effect was limited to the injected paw. Enhancement of peripheral morphine antinociception was replicated in WT mice locally co-administered with σ1 antagonists and the opioid. None of the σ1 antagonists tested enhanced morphine-antinociception in σ1-KO mice, confirming a σ1-mediated action. Morphine-induced side-effects (hyperlocomotion and inhibition of gastrointestinal transit) were unaltered in σ1-KO mice. These results cannot be explained by a direct interaction of σ1 ligands with μ-opioid receptors or adaptive changes of μ-receptors in σ1-KO mice, given that [3H]DAMGO binding in forebrain, spinal cord, and hind-paw skin membranes was unaltered in mutant mice, and none of the σ1 drugs tested bound to μ-opioid receptors. These results show that σ1 receptor inhibition potentiates morphine-induced mechanical analgesia but not its acute side effects, and that this enhanced analgesia can be induced at peripheral level. [Copyright &y& Elsevier]

By using a new polyclonal antibody raised against a 21-amino acid peptide sequence corresponding to the fragment 138–157 of the cloned rat σ1-receptor, we demonstrated by immunoperoxidase and double immunofluorescence techniques, that rat oligodendrocytes express the σ1-receptor. Experiments in vivo and in vitro showed that σ1-receptor colocalized with specific markers of progenitor (A2B5) and mature oligodendrocytes (GalC, RIP). These results suggest that σ1-receptor in oligodendrocytes might be involved in myelination by direct implication in cholesterol biosynthesis or by interaction with endogenous ligands such as neurosteroids. [Copyright &y& Elsevier]