Myeloid cell reprogramming combined with zoledronic acid effectively suppresses bone metastasis

Bone metastases are refractory to current therapies, primarily owing to the immunosuppressive metastasis tumor microenvironment (TME), which is dominated by myeloid cells. However, the function and regulatory mechanisms of myeloid compartments within the bone TME are incompletely understood. Herein we sought to delineate the role of the DKK1-CKAP4 axis in shaping myeloid cell-mediated immunosuppression in bone metastases and to identify potential therapeutic strategies targeting this pathway.

The composition and phenotypic characteristics of myeloid cells in the bone TME were analyzed. Mechanistic studies were conducted using ex vivo co-culture systems and an in vivo Ckap4^fl/flS100a8^Cre (neutrophil-specific Ckap4 knockout) mouse model to delineate the role of the DKK1-CKAP4 axis in regulating neutrophil maturation, osteoclast-like cell differentiation, and macrophage polarization. The therapeutic efficacy of DKK1 blockade in combination with zoledronic acid, as well as the impact on remodeling the TME, was further validated in bone metastasis mouse models.

Significant expansion and predominance of myeloid cells within the bone TME was noted. Mechanistically, the DKK1-CKAP4 axis regulated the development and function of multiple myeloid populations. The DKK1-CKAP4 axis drove neutrophils toward an immature-like, immunosuppressive phenotype, promoted osteoclast-like cell differentiation, and induced macrophage polarization into an M2-like phenotype. Importantly, combined therapy with DKK1 blockade and zoledronic acid reprogrammed immunosuppressive myeloid cells, restored antitumor immunity, and significantly reduced tumor burden in bone metastasis models.

The findings herein showed the DKK1-CKAP4 axis to be a key regulator of myeloid-driven immunosuppression in the bone TME. The combination of DKK1 blockade with zoledronic acid represents a potential therapeutic strategy for bone metastases.