Co-migration of colon cancer cells and CAFs induced by TGFβ₁ enhances liver metastasis.

Colorectal cancer (CRC) cells often metastatize to the liver. Cancer-associated fibroblasts (CAFs) enhance metastasis by providing cytokines that create a favorable microenvironment and by inducing co-dissemination with tumor cells. However, the mechanisms of co-metastatization remain elusive. The aim of this study is to assess the role of TGFβ1 in CRC cell-CAFs attachment and its impact on liver metastasis. CAFs were obtained after xenotransplantation of Mc38 cells into EGFP-C57BL/6 mice. Attachment experiments with CRC cells and CAFs (with or without TGFβ1 and the inhibitory peptide P17) were carried out, as well as in vivo liver metastasis assays. TGFβ1 induced adhesion of CRC cells to CAFs, whereas exposure to P17 abrogated this effect. Co-injection of Mc38 cells with CAFs intrasplenically increased liver metastasis, as compared to injection of tumor cells alone. Pretreatment of Mc38 cells with TGFβ1 enhanced the metastatic burden, in comparison to untreated Mc38 + CAFs. TGFβ1-pretreated Mc38 cells co-metastatized with CAFs to the liver in a highly efficient way. Importantly, the metastatic burden was significantly reduced (p < 0.001) when P17 was administered in mice. The number of PCNA+ and CD-31+ cells was also reduced by P17 in these animals, indicating a decrease in proliferation and angiogenesis upon TGFβ1 signaling blockade. Through microarray analysis, we identified potential TGFβ1-regulated genes that may mediate cancer cell-stroma interactions to increase metastasis. In conclusion, TGFβ1 promotes co-travelling of CRC cells and CAFs to the liver to enhance metastasis. Our results strongly support the use of TGFβ1 targeted drugs as a novel strategy to reduce liver metastasis in CRC patients.