Cannabinoid receptor 2-selective agonist JWH015 attenuates bone cancer pain through the amelioration of impaired autophagy flux induced by inflammatory mediators in the spinal cord

Bone cancer pain (BCP) is a severe complication of advanced bone cancer. Although cannabinoid receptor 2 (CB2) agonists may have an analgesic effect, the underlying mechanism remains unclear. CB2 serves a protective role in various pathological states through the activation of autophagy. Therefore, the present study aimed to determine whether the analgesic effects of the selective CB2 agonist JWH015 was mediated by the activation of autophagy in BCP. BCP was induced by the intra-femur implantation of NCTC2472 fibrosarcoma cells in C3H/HeN mice. The pain behaviors were assessed on the following postoperative days. The selective CB2 agonist JWH015 (1 and 2 µg) was intrathecally administered on day 14 following implantation. AM630 (1 µg), a CB2 antagonist, was injected 30 min before JWH015 administration. Lipopolysaccharide (LPS; 100 nM)-stimulated primary neurons were treated with JWH015 (1 µM) and AM630 (1 µM) to further verify the mechanism by which CB2 affects autophagy. The results demonstrated that autophagy flux was impaired in spinal neurons during BCP, as indicated by the increased ratio of microtubule-associated protein 1 light chain 3β (LC3B)-II/LC3B-I and increased expression of p62. Intrathecal administration of JWH015 attenuated BCP, which was accompanied by the amelioration of impaired autophagy flux (decreased LC3B-II/LC3B-I ratio and decreased p62expression). In addition, the activation of glia cells and upregulation of the glia-derived inflammatory mediators, interleukin (IL)-1β and IL-6 were suppressed by JWH015. In LPS-stimulated primary neurons, IL-1β and IL-6 were increased, and autophagy flux was impaired; whereas treatment with JWH015 decreased the expression of IL-1β and IL-6, LC3B-II/LC3B-I ratio and expression of p62. These effects were by pretreatment with the CB2-selective antagonist AM630. The results of the present study suggested that the impairment of autophagy flux was induced by glia-derived inflammatory mediators in spinal neurons. Intrathecal administration of the selective CB2 agonist JWH015 ameliorated autophagy flux through the downregulation of IL-1β and IL-6 and attenuated BCP.