Cancer-associated fibroblasts produce Netrin-1 to control cancer cell plasticity.

Netrin-1 is upregulated in a large fraction of human neoplasms. In multiple animal models, interference with netrin-1 is associated with inhibition of tumor growth and metastasis. Although netrin-1 upregulation was initially described in cancer cells, we report here that in the human colorectal cancer database, the expression of netrin-1 and its receptor UNC5B correlates with a cancer-associated fibroblasts (CAF) signature. Both colon and lung CAF secreted netrin- 1 when cocultured with respective cancer cells, and netrin- 1 upregulation in CAF was associated with increased cancer cell stemness. Pharmacologic inhibition of netrin-1 with a netrin-1-mAb (Net1-mAb) abrogated the CAF-mediated increase of cancer stem-ness both in coculture experiments and in mice. Net-1-mAb inhibited intercellular signaling between CAF and cancer cells by modulating CAF-mediated expression of cytokines such as IL6. Together these data demonstrate that netrin-1 is upregulated not only in cancer cells but also in cancer-associated stromal cells. In addition to its direct activity on cancer cells, inhibition of netrin-1 may reduce proneoplastic CAF-cancer cell cross-talk, thus inhibiting cancer plasticity. Significance: Netrin-1, a navigation cue during embryonic development, is upregulated in cancer-associated fibroblasts and regulates cancer cell stemness.