Thiostrepton Modulates TLR4 Expression and Induces Apoptosis in MDA MB 231 cells: An In Vitro and In Silico Analysis

Abstract

Objective: Toll-like receptors (TLRs) are key pattern recognition receptors involved in tumorigenesis, apoptosis, and metastasis. Triple-negative breast cancer (TNBC) is a highly aggressive malignancy with a poor prognosis. Although the role of TLRs in breast cancer remains underexplored, recent studies suggest targeting TLRs in TNBC could be beneficial. In this study Thiostrepton, an antibiotic and novel inhibitor of TLR7-9 in psoriatic inflammation, was investigated for its effects on TLR3, TLR4, and TLR9 expression in TNBC cells (MDA-MB-231). Materials and Methods: The cytotoxicity of thiostrepton was assessed using the MTT assay. RT-PCR was used to measure gene expression levels of TLR3, TLR4, TLR9, Bax, Bcl-2, Nf-κB, and E-cadherin. Cell morphology changes were analyzed with Acridine Orange/Ethidium Bromide (AO/EtBr) staining. Molecular docking and dynamics simulations examined interactions between thiostrepton and the TLR4-MD-2 complex. Results: Thiostrepton led to a concentration- and time-dependent decrease in cell viability. It significantly inhibited TLR4, Bcl-2 gene expression and increased TLR3, Bax, and Nf-κB levels. The changes in Bax and Bcl-2 gene expression, along with alterations in cell morphology, demonstrated that thiostrepton promoted apoptosis in MDA-MB-231 cells. While TLR9 expression reduction was not significant, thiostrepton notably increased TLR3 expression and decreased TLR4 expression. The three independent molecular dynamics simulations demonstrated that thiostrepton binds stably to the TLR4-MD2 domain, exhibiting a high binding affinity as indicated by the binding free energy calculations. Conclusion: Thiostrepton effectively induces apoptosis and reduces cell viability in TNBC cells. In silico analysis suggest thiostrepton could modulate TLR4, highlighting its potential as a candidate for further research and therapeutic development.