Epithelial to mesenchymal transition and cancer stem cell phenotypes leading to liver metastasis are abrogated by the novel TGFβ1-targeting peptides P17 and P144

Colorectal cancer (CRC) frequently metastasizes to the liver, a phenomenon that involves the participation of transforming-growth-factor-β1 (TGFβ1). Blockade of the protumorigenic effects elicited by TGFβ1 in advanced CRC could attenuate liver metastasis. We aimed in the present study to assess the antimetastatic effect of TGFβ1-blocking peptides P17 and P144, and to study mechanisms responsible for this activity in a mouse model. Colon adenocarcinoma cells expressing luciferase were pretreated with TGFβ1 (Mc38-lucTGFβ1 cells), injected into the spleen of mice and monitored for tumor development. TGFβ1 increased primary tumor growth and liver metastasis, whereas systemic treatment of mice with either P17 or P144 significantly reduced tumor burden (p<0.01). In metastatic nodules, mitotic/apoptotic ratio, mesenchymal traits and angiogenesis (evaluated by CD-31, as well as circulating endothelial and progenitor cells) induced by TGFβ1 were consistently reduced following injection of peptides. In vitro experiments revealed a direct effect of TGFβ1 in Mc38 cells, which resulted in activation of Smad2, Smad3 and Smad1/5/8, and increased invasion and transendothelial migration, whereas blockade of TGFβ1-signaling reverted these features. Because TGFβ1-mediated epithelial–mesenchymal transition (EMT) has been suggested to induce a cancer stem cell (CSC) phenotype, we analyzed the ability of this cytokine to induce tumorsphere formation and the expression of CSC markers. In TGFβ1-treated cells, tumorspheres were enriched in CD44 and SOX2, which were diminished in the presence of P17. Our data provide a preclinical rationale to evaluate P17 and P144 as potential therapeutic options for the treatment of metastatic CRC.