The contribution of stem cell factor and its receptor c-Kit to cancer-induced bone pain.

Cancer-induced bone pain (CIBP) is among the most common and debilitating symptoms in patients with bone metastasis. Current treatments are somewhat effective but have severe side effects. For the future development of safer CIBP treatments, in this study, we sought to investigate the mechanisms whereby the nerve-cancer interaction controls CIBP. We found that c-Kit, a receptor tyrosine kinase, was activated in the dorsal root ganglia (DRG) sensory neurons of mice with CIBP and that c-Kit's sole ligand, stem cell factor (SCF), was enhanced in the bone marrow with bone metastasis. When DRGs were treated with SCF or conditioned medium from high SCF-expressing cancer cells, in vitro nerve sprouting was enhanced, and this effect was abolished with c-Kit inhibitors. Mice inoculated intrafemorally with cancer cells that had varying levels of SCF expression developed CIBP and enhanced peripheral nerve sprouting in an SCF-dependent manner. Downstream proteomic analysis revealed that SCF upregulated and activated fibroblast growth factor 1 (FGF1) in DRGs. When FGF1 was knocked down in DRGs, SCF-mediated nerve sprouting was prevented. Taken together, our studies demonstrate the importance of the SCF/c-Kit axis in CIBP and nerve sprouting and identify the SCF/c-Kit/FGF1 pathway as a potential therapeutic target for CIBP.