Stromal cell‐derived CSF‐1 blockade prolongs xenograft survival of CSF‐1‐negative neuroblastoma

Abstract

The molecular mechanisms of tumor–host interactions that render neuroblastoma (NB) cells highly invasive are unclear. Cancer cells upregulate host stromal cell colony‐stimulating factor‐1 (CSF‐1) production to recruit tumor‐associated macrophages (TAMs) and accelerate tumor growth by affecting extracellular matrix remodeling and angiogenesis. By coculturing NB with stromal cells in vitro, we showed the importance of host CSF‐1 expression for macrophage recruitment to NB cells. To examine this interaction in NB in vivo, mice bearing human CSF‐1‐expressing SK‐N‐AS and CSF‐1‐negative SK‐N‐DZ NB xenografts were treated with intratumoral injections of small interfering RNAs directed against mouse CSF‐1. Significant suppression of both SK‐N‐AS and SK‐N‐DZ NB growth by these treatments was associated with decreased TAM infiltration, matrix metalloprotease (MMP)‐12 levels and angiogenesis compared to controls, while expression of tissue inhibitors of MMPs increased following mouse CSF‐1 blockade. Furthermore, Tie‐2‐positive and ‐negative TAMs recruited by host CSF‐1 were identified in NB tumor tissue by confocal microscopy and flow cytometry. However, host‐CSF‐1 blockade prolonged survival only in CSF‐1‐negative SK‐N‐DZ NB. These studies demonstrated that increased CSF‐1 production by host cells enhances TAM recruitment and NB growth and that the CSF‐1 phenotype of NB tumor cells adversely affects survival.