Bacterial Cyclodipeptides Inhibit Invasiveness and Metastasis Progression in the Triple-Negative Breast Cancer MDA-MB-231 Mouse Model

Background: Triple-negative breast cancer (TNBC) is an aggressive subtype associated with a high metastatic rate and low survival worldwide. Bacterial cyclodipeptides (CDPs) exhibit anticancer properties by targeting multiple signaling pathways. Methods: The effect of CDPs on the metastasis of the TNBC MDA-MB-231 cell line was evaluated both in vitro and in advanced-stage tumors in immunosuppressed female mice. Results: CDPs more effectively reduced the migratory and invasive abilities of the MDA-MB-231 cell line than methotrexate (MTX). The anti-metastatic effect correlated with inhibition of the Akt/mTOR/S6K pathway, evidenced by decreased expression of markers such as Gab1, Vimentin, and FOXO1. Mice with MDA-MB-231 xenografts treated with CDPs, alone or in combination with MTX, showed near-complete suppression of primary tumor growth and metastatic foci in tumor and organ tissues. Key proteins involved in signaling pathways associated with tumor progression and metastasis such as p-Akt, p-Gab1, and FOXO1 were markedly reduced expression in tumor tissues following xenografted mice CDPs treated. Notably, genes involved in EMT, invasiveness, and metastasis—including PTEN, SNAIL, CXCL1, BRCA1, GADD45A, and PD-L1—were dysregulated in the livers of animals with TNBC, but CDPs treatment restored them to healthy levels more effectively than MTX. Conclusions: The anti-metastatic effects of CDPs in the MDA-MB-231 line involve inhibiting phosphorylation of components of the Akt/mTOR/S6K pathway and reducing metastasis markers and proliferation regulators, as demonstrated in cultures of the MDA-MB-231 line and in tumor and liver tissues from the TNBC xenograft mouse model. The anti-metastatic activity of CDPs was more effective than MTX alone; however, combined treatment produced a synergistic effect, increasing efficacy. These findings offer new insights into the mechanism of action of CDPs and their potential as candidates for further preclinical development.