Tangeretin suppresses HER2-driven breast cancer via PI3K/AKT/mTOR inhibition and caspase-dependent apoptosis

Tangeretin, a citrus-derived polymethoxylated flavone, exhibits potent and selective anti-cancer activity against HER2-positive breast cancer. It demonstrated cytotoxicity in SKBR3 cells (IC₅₀ = 19.5 ± 1.7 µM) and MCF-7 cells (IC₅₀ = 36.2 ± 2.4 µM), while sparing non-tumorigenic MCF-10A cells (>90% viability; IC₅₀ = 327.5 ± 18.2 µM). Tangeretin markedly reduced clonogenic survival (51.4 ± 3.1 colonies in SKBR3; 78.1 ± 3.7 in MCF-7) and induced pronounced apoptosis, as evidenced by late apoptotic staining (50.6 ± 2.3%), DNA laddering, and strong activation of caspase-3/7 (3.4 ± 0.1-fold) and caspase-9 (2.9 ± 0.1-fold). Flow cytometry revealed significant G₂/M phase arrest in SKBR3 cells (38.9 ± 2.0%). Mechanistically, tangeretin suppressed AKT kinase activity (0.4 ± 0.04-fold), comparable to MK-2206 (0.3 ± 0.0-fold), and reduced the expression of phosphorylated HER2 (p-HER2), p-PI3K, p-AKT, p-mTOR, p-p70S6K, and cyclin D1. These findings establish tangeretin as a selective HER2-targeted anti-cancer candidate that acts through dual inhibition of the PI3K/AKT/mTOR pathway and induction of mitochondrial apoptosis.