CXCL8 mediates macrophage migration in canine oral malignant melanoma

Tumor-associated macrophage (TAM) infiltration is associated with poor prognosis in human patients with melanoma. However, the mechanism by which TAMs infiltrate tumor tissues in dogs remains unclear. Therefore, the present study aimed to identify macrophage chemotactic factors involved in macrophage migration in canine oral malignant melanoma (OMM). We first analyzed RNA-seq data of canine OMM, then performed immunohistochemistry of OMM tissue, and finally performed a macrophage migration assay using factors secreted from a canine melanoma cell line. The RNA-seq and immunohistochemistry revealed high TAM infiltration in canine oral malignant melanoma. Migration assays were performed using macrophage cell lines and culture supernatants from seven canine melanoma cell lines to identify macrophage chemotactic factors. The analysis of chemokine expression in canine melanoma cell lines revealed a positive correlation between CXCL8 expression and macrophage migration. Furthermore, macrophage migration was significantly reduced by CXCL8 gene knockout and anti-CXCL8-neutralizing monoclonal antibody. Additionally, the addition of recombinant CXCL8 protein rescued the reduction in migratory macrophage cells caused by CXCL8 knockout. These findings indicate that CXCL8 plays a crucial role in macrophage migration and that targeting CXCL8 may be a novel therapeutic approach for canine melanoma.