Pharmacology/Drug Development

Chemokines are important regulators of immune, inflammatory, and neuronal responses in peripheral and central pain pathway. The aim of this study was to investigate whether chemokine (C-X-C motif) ligand 13 (CXCL13) and its receptor (C-X-C chemokine receptor type 5, CXCR5) involve in the development of bone cancer pain (BCP) and the regulation of morphine analgesia in rats. The change of pain behaviors in BCP rats were measured by testing paw withdrawal threshold (PWT). The levels of CXCL13, CXCR5 and signal pathway proteins (p-p38, p-ERK and p-AKT etc) in the spinal cord were measured via western blots. The expression of CXCL13 and CXCR5 in spinal cord were increased in BCP rats. The BCP rats showed decrease of PWTs, which was relieved by CXCR5i. Intrathecally injection of murine recombinant CXCL13 (mrCXCL13) decreased the PWTs of BCP rats and opposed morphine-induced analgesia in BCP rats. In BCP rats, the signal pathway proteins (p38, ERK and AKT) in the spinal cord were activated. CXCL13 and morphine had contrary effect on the phosphorylation of these proteins. MrCXCL13 directly increased the levels of p-p38, p-ERK and p-AKT in BCP rats. However, morphine decreased the levels of these proteins in BCP rats. While blocking the activation of p-p38, p-ERK and p-AKT, morphine analgesia was enhanced. These results suggest CXCL13 participated in bone cancer pain and opposed morphine analgesia via p38, ERK and AKT pathways. It may be a target to enhance pain management in cancer pain patients.

Highly effective and safe drugs for the treatment of neuropathic pain are urgently required and it was shown that blocking T-type calcium channels can be a promising strategy for drug development for neuropathic pain. We have developed pyrrolidine-based T-type calcium channel inhibitors by structural hybridization and subsequent assessment of in vitro activities against Ca3.1 and Ca3.2 channels. Profiling of in vitro ADME properties of compounds was also carried out. The representative compound 17h showed comparable in vivo efficacy to gabapentin in the SNL model, which indicates T-type calcium channel inhibitors can be developed as effective therapeutics for neuropathic pain.

The 5-HT receptor has recently gained much attention due to its involvement in multiple physiological functions and diseases. The insufficient quality of the available molecular probes prompted design of fluorinated 3-(1-alkyl-1H-imidazol-5-yl)-1H-indoles as a new generation of selective 5-HT receptor agonists. A potent and drug-like agonist, 3-(1-ethyl-1H-imidazol-5-yl)-5-iodo-4-fluoro-1H-indole (AGH-192, 35, K = 4 nM), was identified by optimizing the halogen bond formation with Ser5.42 as the supposed partner. The compound was characterized by excellent water solubility, high selectivity over related CNS targets, high metabolic stability, oral bioavailability and low cytotoxicity. Rapid absorption into the blood, medium half-life and a high peak concentration in the brain C = 1069 ng/g were found after i.p. (2.5 mg/kg) administration in mice. AGH-192 may thus serve as the long-sought tool compound in the study of 5-HT receptor function, as well as a potential analgesic, indicated by the antinociceptive effect observed in a mouse model of neuropathic pain.

The endogenous cannabinoid system is involved in the physiological inhibitory control of pain and is of particular interest for the development of therapeutic approaches for pain management. Selective activation of the peripheral CB1 cannabinoid receptor has been shown to suppress the heightened firing of primary afferents, which is the peripheral mechanism underlying neuropathic pain after nerve injury. However, the mechanism underlying this effect of CB1 receptor remains unclear. The large-conductance calcium-activated potassium (BK) channels have been reported to participate in anticonvulsant and vasorelaxant effects of cannabinoids. We asked whether BK channels participate in cannabinoids-induced analgesia and firing-suppressing effects in primary afferents after nerve injury. Here, using mice with chronic constriction injury(CCI)-induced neuropathic pain, antinociception action and firing-suppressing effect of HU210 were measured before and after BK channel blocker application. We found that local peripheral application of HU210 alleviated CCI-induced pain behavior and suppressed the heightened firing of injured fibers. Co-administration of IBTX with HU210 significantly reversed the analgesia and the firing-suppressing effect of HU210. This result indicated that the peripheral analgesic effects of cannabinoids depends on activation of BK channels.