Tigecycline suppresses colon cancer stem cells and impairs tumor engraftment by targeting SNAI1-regulated epithelial-mesenchymal transition.

Cancer stem cells (CSCs) play a key role in the progression of colorectal cancer (CRC). The high heterogeneity of CSCs has hindered the clinical application of CSC-targeting therapies. Tetracyclines are drugs with therapeutic potentials beyond their antibiotic activity. We previously demonstrated the efficacy of tigecycline, a third-generation tetracycline, against a model of colitis-associated colorectal cancer, primarily focusing on its immunomodulatory role with a preliminary assessment of its impact on stemness. In this study we characterize the effects of tigecycline on colon CSCs in vitro and in a CRC xenograft model, with special attention on the signaling pathways involved and the modulation of the gut microbiota. We generated secondary colonospheres from two colon tumor cell lines HCT116 and CMT93, and evaluated the effect of tigecycline on CSCs properties. We showed that tigecycline (25, 50 μM) effectively reduced colon CD133(+)CD44(+)LGR5(+)ALDH(+) subpopulations and their viability, self-renewal and migratory capacity. Moreover, tigecycline treatment hindered epithelial-mesenchymal transition (EMT) process through targeting SNAI1 and β-catenin, resulting in an upregulation of epithelial markers (E-cadherin) and a downregulation of pluripotency and mesenchymal ones (Vimentin, N-cadherin, SOX2, NANOG, MIR155, MIR146). This effect was confirmed in two independent CRC-xenograft murine models in which tigecycline administration led to a reduction in tumor volume. Finally, CRC samples were taken from HCT116 xenograft model mice for analysis of CSCs-related signaling pathways and stools were collected for gut microbiome metagenomic analysis. We found that the antibiotic modulated gut dysbiosis by increasing the abundance of beneficial bacterial species such as Parabacteroides sp., which were involved in metabolic pathways that hindered SNAI1-Wnt-β-catenin signaling. These results reinforce the new role of tigecycline in the therapy of CRC and demonstrate for the first time the effect of tigecycline on colon CSCs and their malignancies.