Role of the CXCR4/ALK5/Smad3 Signaling Pathway in Cancer-Induced Bone Pain

Esketamine inhibits the c-Jun N-terminal kinase pathway in the spinal dorsal horn to relieve bone cancer pain in rats

Cancer-induced bone pain (CIBP) is one of the most common and feared symptoms in patients with advanced tumors. The X-C motif chemokine ligand 12 (CXCL12) and the CXCR4 receptor have been associated with glial cell activation in bone cancer pain. Moreover, mitogen-activated protein kinases (MAPKs), as downstream CXCL12/CXCR4 signals, and c-Jun, as activator protein AP-1 components, contribute to the development of various types of pain. However, the specific CIBP mechanisms remain unknown. Esketamine is a non-selective N-methyl-d-aspartic acid receptor (NMDA) inhibitor commonly used as an analgesic in the clinic, but its analgesic mechanism in bone cancer pain remains unclear. We used a tumor cell implantation (TCI) model and explored that CXCL12/CXCR4, p-MAPKs, and p-c-Jun were stably up-regulated in the spinal cord. Immunofluorescence images showed activated microglia in the spinal cord on day 14 after TCI and co-expression of CXCL12/CXCR4, p-MAPKs (p-JNK, p-ERK, p-p38 MAPK), and p-c-Jun in microglia. Intrathecal injection of the CXCR4 inhibitor AMD3100 reduced JNK and c-Jun phosphorylations, and intrathecal injection of the JNK inhibitor SP600125 and esketamine also alleviated TCI-induced pain and reduced the expression of p-JNK and p-c-Jun in microglia. Overall, our data suggest that the CXCL12/CXCR4-JNK-c-Jun signaling pathway of microglia in the spinal cord mediates neuronal sensitization and pain hypersensitivity in cancer-induced bone pain and that esketamine exerts its analgesic effect by inhibiting the JNK-c-Jun pathway.

[Pirfenidone inhibits proliferation of rabbit tenon fibroblasts by down-regulating TGF-β3 in the TGF-β/Smad pathway]

OBJECTIVE

To investigate the molecular mechanism by which pirfenidone inhibits scar formation through the TGF-β/Smad pathway.

METHODS

Cultured rabbit tenon fibroblasts (RTFs) were treated with different concentrations of pirfenidone to determine its initial active concentration and optimum concentration of pirfenidone for inhibiting RTF proliferation using CCK-8 assay. In RTFs treated with pirfenidone at the initial and optimal concentrations, expressions of TGF-β3, collagen I and collagen III were examined with both immunofluorescence assay and Western blotting, and their mRNA expression levels were detected using RT-PCR.

RESULTS

The initial and optimal concentrations of pirfenidone for inhibiting RTF proliferation were 0.1 mg/mL and 0.27 mg/mL, respectively. In RTFs treated with pirfenidone at the two concentrations for 24 h, both immunofluorescence assay and Western blotting showed significantly lowered protein expressions of TGF-β3, collagen I and collagen III as compared with those in the control group (P < 0.05). The mRNA expressions of TGF-β3, collagen I and collagen III in the RTFs were also significantly lowered after treatment with pirfenidone at the initial and optimal concentrations (P < 0.05).

CONCLUSIONS

Pirfenidone concentration-dependently inhibits the proliferation of RTFs possibly by down-regulating the expression of TGF-β3 in the TGF-β/Smad pathway.

Multifarious Targets and Recent Developments in the Therapeutics for the Management of Bone Cancer Pain

Bone cancer pain (BCP) is a distinct pain state showing characteristics of both neuropathic and inflammatory pain. On average, almost 46% of cancer patients exhibit BCP with numbers flaring up to as high as 76% for terminally ill patients. Patients suffering from BCP experience a compromised quality of life, and the unavailability of effective therapeutics makes this a more devastating condition. In every individual cancer patient, the pain is driven by different mechanisms at different sites. The mechanisms behind the manifestation of BCP are very complex and poorly understood, which creates a substantial barrier to drug development. Nevertheless, some of the key mechanisms involved have been identified and are being explored further to develop targeted molecules. Developing a multitarget approach might be beneficial in this case as the underlying mechanism is not fixed and usually a number of these pathways are simultaneously dysregulated. In this review, we have discussed the role of recently identified novel modulators and mechanisms involved in the development of BCP. They include ion channels and receptors involved in sensing alteration of temperature and acidic microenvironment, immune system activation, sodium channels, endothelins, protease-activated receptors, neurotrophins, motor proteins mediated trafficking of glutamate receptor, and some bone-specific mechanisms. Apart from this, we have also discussed some of the novel approaches under preclinical and clinical development for the treatment of bone cancer pain.