Metastatic colorectal cancer cells maintain the TGFβ program and use TGFBI to fuel angiogenesis

Colorectal cancer (CRC) cells are traditionally considered unresponsive to TGF beta due to mutations in the receptors and/or downstream signaling molecules. TGF beta influences CRC cells only indirectly via stromal cells, such as cancer-associated fibroblasts. However, CRC cell ability to directly respond to TGF beta currently remains unexplored. This represents a missed opportunity for diagnostic and therapeutic interventions.Methods: We examined whether cancer cells from primary CRC and liver metastases respond to TGF beta by inducing TGF beta-induced protein ig-h3 (TGFBI) expression, and the contribution of canonical and non-canonical TGF beta signaling pathways to this effect. We then investigated in vitro and in vivo TGFBI impact on metastasis formation and angiogenesis. Using patient serum samples and an orthotopic mouse model of CRC liver metastases we assessed the diagnostic/tumor targeting value of novel antibodies against TGFBI.Results: Metastatic CRC cells, such as circulating tumor cells, directly respond to TGF beta. These cells were characterized by the absence of TGF beta receptor mutations and the frequent presence of p53 mutations. The pro-tumorigenic program orchestrated by TGF beta in CRC cells was mediated through TGFBI, the expression of which was positively regulated by non-canonical TGF beta signaling cascades. TGFBI inhibition was sufficient to significantly reduce liver metastasis formation in vivo. Moreover, TGFBI pro-tumorigenic function was linked to its ability to stimulate angiogenesis. TGFBI levels were higher in serum samples from untreated patients with CRC than in patients who were receiving chemotherapy. A radiolabeled anti-TGFBI antibody selectively targeted metastatic lesions in vivo, underscoring its diagnostic and therapeutic potential.Conclusions: TGF beta signaling in CRC cells directly contributes to their metastatic potential and stromal cell-independence. Proteins downstream of activated TGF beta, such as TGFBI, represent novel diagnostic and therapeutic targets for more specific anti-metastatic therapies.