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TWIK-related K+ (TREK) channels are potential analgesic targets. However, selective activators for TREK with both defined action mechanism and analgesic ability for chronic pain have been lacking. Here we report C3001a, a selective activator for TREK against other two-pore domain K+ (K2P) channels. C3001a binds to the cryptic binding site formed by P1 and TM4 in TREK-1, as suggested by computational modeling and experimental analysis. Further, we identify the carboxyl group of C3001a as a structural determinant for the binding to TREK-1/2, and the key residue that defines the subtype-selectivity of C3001a. C3001a targets TREK channels in peripheral nervous system to reduce the excitability of nociceptive neurons. In neuropathic pain, C3001a alleviated spontaneous pain and cold hyperalgesia. In a mouse model of acute pancreatitis, C3001a alleviated mechanical allodynia and inflammation. Together, C3001a represents a lead compound which could advance the rational design of peripherally-acting analgesics targeting K2P channels without opioid-like adverse effects.
Learn More >Four novel fluorinated cyclic analogues of biphalin with excellent to modest binding affinity for μ-, δ- and κ-receptors were synthesized. The cyclic peptides have a combination of piperazine or hydrazine linker with or without a xylene bridge. Among the ligands, MACE3 demonstrated a better activity than biphalin after intravenous administration, and its corresponding analogue incorporating the hydrazine linker (MACE2) was able to induce longer lasting analgesia following subcutaneous administration. An analogue of MACE2 containing 2,6-dimethyl-L-tyrosine (MACE4) showed the best potency and in vivo antinociceptive activity of this series.
Learn More >Neuropathic pain (NP) is a complex chronic pain state with a prevalence of almost 10% in the general population. Pharmacological options for NP are limited and slightly effective, so there is a need of developing more efficacious NP attenuating drugs. Activation of the type 1 lysophosphatidic acid (LPA1) receptor is a crucial factor in the initiation of NP. Hence, it is conceivable that a functional antagonism strategy could lead to NP mitigation. Here we describe a new series of LPA1 agonists among which derivative (S)-17 (UCM-05194) stands out as the most potent and selective LPA1 receptor agonist described so far (Emax=118%, EC50=0.24 µM, KD=19.6 nM; inactive at autotaxin and LPA2-6 receptors). This compound induces characteristic LPA1-mediated cellular effects and prompts the internalization of the receptor leading to its functional inactivation in primary sensory neurons and to an efficacious attenuation of the pain perception in an in vivo model of NP.
Learn More >Migraine is a highly disabling neurovascular disorder characterized by a severe headache (associated with nausea, photophobia and/or phonophobia), and trigeminovascular system activation involving the release of calcitonin-gene related peptide (CGRP). Novel anti-migraine drugs target CGRP signaling through either stimulation of 5-HT receptors on trigeminovascular nerves (resulting in inhibition of CGRP release) or direct blockade of CGRP or its receptor. Lasmiditan is a highly selective 5-HT receptor agonist and, unlike the triptans, is devoid of vasoconstrictive properties, allowing its use in patients with cardiovascular risk. Since lasmiditan can actively penetrate the blood-brain barrier, central therapeutic as well as side effects mediated by 5-HT receptor activation should be further investigated. Other novel anti-migraine drugs target CGRP signaling directly. This neuropeptide can be targeted by the monoclonal antibodies eptinezumab, fremanezumab and galcanezumab, or by CGRP-neutralizing L-aptamers called Spiegelmers. The CGRP receptor can be targeted by the monoclonal antibody erenumab, or by small-molecule antagonists called gepants. Currently, rimegepant and ubrogepant have been developed for acute migraine treatment, while atogepant is studied for migraine prophylaxis. Of these drugs targeting CGRP signaling directly, eptinezumab, erenumab, fremanezumab, galcanezumab, rimegepant and ubrogepant have been approved for clinical use, while atogepant is in the last stage before approval. Although all of these drugs seem highly promising for migraine treatment, their safety should be investigated in the long-term. Moreover, the exact mechanism(s) of action of these drugs need to be elucidated further, to increase both safety and efficacy and to increase the number of responders to the different treatments, so that all migraine patients can satisfactorily be treated.
Learn More >Dezocine is an opioid analgesic widely used in China, occupying over 45% of the domestic market of opioid analgesics. We have recently demonstrated that dezocine produced mechanical antiallodynia and thermal antihyperalgesia through spinal μ-opioid receptor activation and norepinephrine reuptake inhibition in neuropathic pain. This study further explored the dual μ-opioid receptor and norepinephrine reuptake mechanisms underlying dezocine-induced mechanical antiallodynia in bone cancer pain, compared with tapentadol, the first recognized analgesic in this class. Dezocine and tapentadol, given subcutaneously, exerted profound mechanical antiallodynia in bone cancer pain rats in a dose-dependent manner, yielding similar maximal effects but different potencies: EDs of 0.6 mg/kg for dezocine and 7.5 mg/kg for tapentadol, respectively. Furthermore, their mechanical antiallodynia was partially blocked by intrathecal injection of the specific μ-opioid receptor antagonist CTAP, but not κ-opioid receptor antagonists GNTI and nor-BNI or δ-opioid receptor antagonist naltrindole. Intrathecal administrations of the specific norepinephrine depletor 6-OHDA (but not the serotonin depletor PCPA) for three consecutive days and single injection of the α-adrenoceptor antagonist phentolamine/α2-adrenoceptor antagonist yohimbine partially blocked dezocine- and tapentadol-induced mechanical antiallodynia. Strikingly, the combination of CTAP and yohimbine nearly completely blocked dezocine- and tapentadol-induced mechanical antiallodynia. Our results illustrate that both dezocine and tapentadol exert mechanical antiallodynia in bone cancer pain through dual mechanisms of μ-opioid receptor activation and norepinephrine reuptake inhibition, and suggest that the μ-opioid receptor and norepinephrine reuptake dual-targeting opioids are effective analgesics in cancer pain.
Learn More >Acid-sensing ion channels (ASICs) are proton-gated cation channels that contribute to neurotransmission, as well as initiation of pain and neuronal death following ischemic stroke. As such, there is a great interest in understanding the in vivo regulation of ASICs, especially by endogenous neuropeptides that potently modulate ASICs. The most potent endogenous ASIC modulator known to date is the opioid neuropeptide big dynorphin (BigDyn). BigDyn is up-regulated in chronic pain and increases ASIC-mediated neuronal death during acidosis. Understanding the mechanism and site of action of BigDyn on ASICs could thus enable the rational design of compounds potentially useful in the treatment of pain and ischemic stroke. To this end, we employ a combination of electrophysiology, voltage-clamp fluorometry, synthetic BigDyn analogs, and noncanonical amino acid-mediated photocrosslinking. We demonstrate that BigDyn binding results in an ASIC1a closed resting conformation that is distinct from open and desensitized states induced by protons. Using alanine-substituted BigDyn analogs, we find that the BigDyn modulation of ASIC1a is primarily mediated through electrostatic interactions of basic amino acids in the BigDyn N terminus. Furthermore, neutralizing acidic amino acids in the ASIC1a extracellular domain reduces BigDyn effects, suggesting a binding site at the acidic pocket. This is confirmed by photocrosslinking using the noncanonical amino acid azidophenylalanine. Overall, our data define the mechanism of how BigDyn modulates ASIC1a, identify the acidic pocket as the binding site for BigDyn, and thus highlight this cavity as an important site for the development of ASIC-targeting therapeutics.
Learn More >Uncontrolled cancer pain is a significant problem in palliative medicine. Opioids are often first-line treatment that increase risks of analgesic tolerance and hyperalgesia. Topical ketamine with other adjuvant pain medications is an often-overlooked treatment, yet may be most effective in difficult-to-treat cancer pain. We report a case series of hospice patients with uncontrolled cancer pain who were suboptimally treated with opioids and nerve blocks, whose symptoms responded to topical ketamine with other adjuvants. We review the pronociceptive properties of opioids and how topical multimodal treatment of cancer pain can be more effective than standard opioids, other topical adjuvant medications, and nerve blocks. We discuss the shortcomings of the World Health Organization (WHO) stepladder for the treatment of cancer pain and suggest an adjuvant treatment algorithm, directing physicians to appropriate adjuvant pain agents based on pain type and distinct receptor actions. This is a retrospective case series of patients who responded to topical multimodal pain treatment with implementation of findings into an addendum to the WHO stepladder. Subjects were from a case series of community-based hospice patients with previously uncontrolled cancer pain. Measurement was made by self-report of pain levels using the 10-point numeric pain rating scale. Patients' pain was controlled with topical adjuvant medications with return to previously lost function and prevention of otherwise escalating opioid dosing. These patient cases reveal how ketamine-based topical treatment for cancer pain can be more effective than standard opioids, other topical adjuvant medications, and nerve blocks with no noted side effects and observed reduction in opioid consumption.
Learn More >To evaluate the efficacy and safety of duloxetine in the treatment of patients with osteoarthritis (OA) or chronic low back pain (CLBP).
Learn More >Prolonged use of opioids causes analgesic tolerance and adverse effects including constipation and dependence. Evidence exists that molecules targeting imidazoline-2 receptors (I2Rs) potentiate opioid analgesia in rodents. We investigated whether combination with the I2R ligand CR4056 could improve efficacy and safety of morphine, and explored the mechanisms of CR4056-opioid interaction.
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