Thymoquinone Enhances Tamoxifen Efficacy Against Triple-Negative Breast Cancer by Targeting EMT Signaling

The variety of available therapies for treating TNBC is constrained by the minimal or no expression of receptors such as estrogen (ER), progesterone (PR), and human epidermal growth factor 2 (HER2). However, estrogen receptor β (ERβ) has emerged as a potential therapeutic target for TNBCs. Tamoxifen (TAM) is used as an endocrine therapy against ER-positive cancer but has minimal impact on ER-negative cancers like TNBC. Thymoquinone (TQ) is an active natural compound with anticancer properties, as evidenced by a cumulative number of reports. A combinatorial approach to targeting EMT in TNBC is one strategy that may improve TAM activity. In this study, we evaluated the binding affinity and stability of TQ and TAM with ERβ in silico and assessed their cytotoxic potential individually and in combination in vitro. Docking and molecular dynamics (MD) studies confirmed interactions between ERβ and TQ, TAM, and GEN. The IC₅₀ values for TQ and TAM were approximately 18.44 and 11.76 μM, respectively, for MDA-MB-468, and 22.06 and 15.73 μM, respectively, for MDA-MB-231. An in vitro study demonstrated enhanced cytotoxic effects when TQ (20 μM) and TAM (13 μM) were combined. Further analysis revealed downregulation of the mesenchymal markers CDH2 (N-cadherin) and vinculin, which are responsible for cell migration. Additionally, low vimentin and enhanced E-cadherin expression lead to downregulation of core EMT regulators, including SNAIL1 and ZEB1. In conclusion, TQ showed potential chemomodulatory effects on TAM against TNBC by reducing the expression of EMT-associated markers.