Involvement of Spinal CCR5/PKCγ Signaling Pathway in the Maintenance of Cancer-Induced Bone Pain.

Cancer-induced bone pain (CIBP) is a challenging medical problem that considerably influences cancer patients' quality of life. Currently, few treatments have been developed to conquer CIBP because of a poor understanding of the potential mechanisms. Our previous work has proved that spinal RANTES (a major ligand for CCR5) was involved in the maintenance of CIBP. In this study, we attempted to investigate whether spinal CCR5 and its downstream PKCγ pathway is involved in the maintenance of CIBP. Inoculation of Walker 256 cells into the tibia could induce a marked mechanical allodynia with concomitant upregulation of spinal CCR5 and p-PKCγ expression from day 6 to day 15 after inoculation. Spinal CCR5 was prominently expressed in microglia, and mechanical allodynia was attenuated by intrathecal injection of DAPTA (a specific antagonist of CCR5) with downregulation of spinal CCR5 and p-PKCγ expression levels at day 15 in inoculated rats. Pre-intrathecal injection of RANTES could reverse the anti-allodynia effects of DAPTA. Intrathecal administration of GF109203X (an inhibitor of PKC) could alleviate mechanical allodynia as well as decrease of spinal p-PKCγ expression level, but no influence on spinal CCR5 level. Our findings suggest that CCR5/PKCγ signaling pathway in microglia may contribute to the maintenance of CIBP in rats.

Spinal SET7/9 may contribute to the maintenance of cancer-induced bone pain in mice.

Cancer-induced bone pain (CIBP) profoundly influences patients' quality of life. Exploring the mechanisms by which CIBP occurs is essential for developing efficacious therapies. Various studies have shown that proinflammatory factors were involved in CIBP. SET domain containing lysine methyltransferase 7/9 (SET7/9) may modulate the expression of NF-κB-dependent proinflammatory genes in vitro. However, whether SET7/9 may participate in the maintenance of CIBP remains unknown. In this study, NCTC 2472 cells were inoculated into the intramedullary space of the femur to establish a mouse model of CIBP. Upregulation of spinal SET7/9 expression was related to pain behaviours in tumour-inoculated mice. Intrathecal cyproheptadine (10 or 20 nmol) attenuated response to painful stimuli in a dose-dependent manner. Moreover, there was a concomitant decrease in spinal SET7/9 and RANTES expression. The antinociceptive effects of cyproheptadine were abolished by pre-intrathecal administration of SET 7/9 (0.2 µg) for 30 minutes before intrathecal cyproheptadine (20 nmol) administration. These results indicated that spinal SET7/9 may contribute to the maintenance of CIBP in mice. Hence, targeting of spinal SET7/9 might be a useful alternative therapy for the treatment of CIBP.

Connexin 43 Mediates CXCL12 Production from Spinal Dorsal Horn to Maintain Bone Cancer Pain in Rats.

Tumor metastasis to bone can subsequently lead to bone cancer pain (BCP). Currently, BCP is difficult to conquer due to a poor understanding of the potential mechanisms. Several studies have indicated that astrocyte-specific connexin 43 (Cx43) was involved in the neuropathic pain, and Cx43 induced the release of chemokine CXCL12 in bone marrow stromal cells. However, whether spinal Cx43 mediates the production of CXCL12 to participate in the maintenance of BCP is still unknown. Here we showed that Walker 256 tumor cells inoculation into the tibia induced a significant mechanical allodynia, which was accompanied by upregulation of spinal p-Cx43 and CXCL12 expression levels from day 6 to day 18 after inoculation. Spinal Cx43 was mainly expressed in astrocytes, and intrathecal (43)Gap26 (a selective Cx43 blocker) markedly attenuated mechanical allodynia as well as reduced p-Cx43 and CXCL12 expression at day 18 after inoculation. Pre-intrathecal administration of CXCL12 almost abolished the attenuated mechanical allodynia by (43)Gap26. Furthermore, intrathecal injection of anti-CXCL12 neutralizing antibody could ameliorate mechanical allodynia with concomitant inhibition of upregulation of CXCL12 expression, but not influence on p-Cx43 expression. Our results indicate that Cx43 mediates CXCL12 production from spinal dorsal horn in astrocytes to maintain bone cancer pain in rats. These findings may improve our understanding of the underlying mechanisms of BCP and provide a novel target for the treatment of BCP.

Involvement of Spinal Bv8/Prokineticin 2 in a Rat Model of Cancer-Induced Bone Pain.

Cancer-induced bone pain (CIBP) is seriously disruptive to the quality of life in cancer patients, and present therapies are limited. The Bv8/prokineticin 2, a new family of chemokines, has been demonstrated to be involved in inflammatory and neuropathic pain. However, whether it is involved in CIBP remains unclear. This study was designed to examine whether spinal Bv8 was involved in the development of CIBP in rats. A rat CIBP model was constructed by injecting Walker 256 carcinoma cells into the medullary cavity of rat tibia. Tibia inoculation with Walker 256 tumour cells resulted in the development of mechanical hyperalgesia. Compared with sham rats, spinal Bv8 mRNA and protein levels were markedly and time-dependently increased in CIBP rats. Intrathecal administration of Bv8 neutralizing antibody (5 ng) could markedly attenuate pain behaviour as well as up-regulation of spinal TNF-α expression at day 18 after inoculation. Intrathecal pre-treatment with synthetic Bv8 (50 pg) almost completely abolished these effects. These data suggested that spinal Bv8/prokineticin 2 participated in the development of CIBP. Targeting of spinal Bv8 might be a promising strategy for the management of cancer-induced bone pain.

Evidence for involvement of spinal RANTES in the antinociceptive effects of triptolide, a diterpene triepoxide, in a rat model of bone cancer pain.

It has been shown that triptolide has beneficial effects in the treatment of neuropathic pain, but its effects on bone cancer pain (BCP) remain unclear. In this study, we aimed to explore the potential role of spinal regulated activation of normal T cell expressed and secreted (RANTES) in the antinociceptive effects of triptolide on BCP. A BCP model was induced by injecting Walker 256 mammary gland carcinoma cells into the intramedullary space of rat tibia. Intrathecal administration of triptolide (0.5, 1, 2 µg) could dose-dependently alleviate mechanical hyperalgesia and spontaneous pain. In addition, there were also concomitant decreases in RANTES mRNA and protein expression levels in spinal dorsal horn. These results suggest that the antinociceptive effects of triptolide are related with inhibition of spinal RANTES expression in BCP rats. The findings of this study may provide a promising drug for the treatment of BCP.

Involvement of spinal CC chemokine ligand 5 in the development of bone cancer pain in rats.

In this study, we aimed to investigate the role of spinal CC chemokine ligand 5 (CCL5) in the development of bone cancer pain (BCP). A BCP model was established by inoculation of Walker 256 cells into the intramedullary space of rat tibia. The levels of spinal CCL5 mRNA and protein expression significantly and time dependently increased in BCP rats compared with sham rats. On day 15 after inoculation, intrathecal administration of anti-CCL5 neutralizing antibody (4 µg) significantly attenuated the established mechanical hyperalgesia in the Walker 256 cells-injected rats, and the effect was abolished by intrathecal pre-treatment with recombinant rat CCL5 (0.2 µg). These results suggest that the spinal CCL5 may be involved in the development of BCP. The findings of this study may provide an evidence for developing novel analgesic agents to treat BCP.