Increased TGF-β signaling during antiestrogen therapy in triple-negative breast cancer cells

Antiestrogen therapies, such as Tamoxifen (TAM), are widely used in managing estrogen receptor-positive (ER+) breast cancer (BC); however, resistance to these agents remains a significant clinical challenge. Triple-negative breast cancer (TNBC) represents the most aggressive subtype of breast cancer, lacking approved targeted therapies and exhibiting poor patient outcomes. Transforming growth factor-β (TGF-β), a dual-functional cytokine involved in tumor suppression and progression, has gained attention for its crucial role in breast cancer development and metastasis. Therefore, evaluating the impact of antiestrogens on TGF-β pathway components may help identify novel therapeutic targets for TNBC. This study investigated the expressions of TGF-β1, TGF-β2, and SMAD-3 in four human BC cell lines (MCF-7, MDA-MB-231, MDA-MB-468, and SK-BR-3) following treatment with optimal cell-line-specific doses of TAM and its active metabolite, 4-Hydroxytamoxifen (4-OH-TAM). In TNBC cells, antiestrogen treatment resulted in elevated TGF-β1 expression, accompanied by increased TGF-β2 and SMAD-3, particularly in metastatic MDA-MB-231 cells. Gene expression analysis also revealed that TGF-β1 was upregulated in short-term TAM treatment in MDA-MB-231 cells, whereas 4-OH-TAM had minimal impact. Long-term exposure led to opposite patterns with TGF-β1 decreasing in TAM of MDA-MB-231 cells but increasing in MCF-7 cells, while TGF-β1 elevates in 4-OH-TAM in MDA-MB-231 cells, suggesting cell line and duration-specific responses. Functional assays further showed differential anti-migratory effects, with TAM more effective in MDA-MB-231 and 4-OH-TAM in MCF-7 cells. These findings highlight TGF-β1 as a potential biomarker for TNBC and for predicting responses to antiestrogen therapies, warranting further mechanistic and functional validation.