Synergistic anticancer effects of Chrysin and trastuzumab in HER2-Positive breast cancer cells

HER2-positive breast cancer is an aggressive subtype with limited therapeutic options. Trastuzumab, a monoclonal antibody targeting the HER2 receptor, has improved clinical outcomes; however, its efficacy remains a critical challenge in the HER2-positive model. This study investigated the potential of chrysin, a naturally occurring flavonoid, to enhance the efficacy of trastuzumab in HER2-positive SKBR3 and BT-474 breast cancer cells. The effects of chrysin and trastuzumab, alone or in combination, were evaluated in SKBR3 and BT-474 cells. Cell viability was evaluated using an MTT assay, and the combination index (CI) value was determined using Compusyn software. Apoptosis and HER2 expression were analyzed by flow cytometry. The morphological characteristics of apoptosis were evaluated using the DAPI-TUNEL staining. Protein expression of STAT3 and PDL-1 was detected by western blotting. Real-time PCR was employed to quantify the angiogenesis-related genes. Chrysin enhanced the anticancer effects of trastuzumab, achieving an optimal combination index (CI) of 0.39 in SKBR3 cells and a similarly strong synergistic profile in BT-474 cells (CI = 0.54). Chrysin synergistically enhanced trastuzumab-induced apoptosis in both cell lines (p < 0.01 and p < 0.001). Trastuzumab significantly reduced HER2 expression on SKBR3 and BT-474 cells (p < 0.001) and, surprisingly, chrysin also reduced HER2 expression in a significant manner (p < 0.001). Combination therapy further intensified this effect in SKBR3 and BT-474 cells (p < 0.001 and p < 0.01, respectively). Additionally, the combination therapy significantly decreased p-STAT3 and PD-L1 protein levels in SKBR3 and reduced mRNA levels of Tie2 and VEGFR2 in both cell lines. Chrysin synergistically enhances the efficacy of trastuzumab in HER2-positive SKBR3 and BT-474 breast cancer cells. These findings warrant further investigation in immune-competent and in vivo models to assess clinical applicability and underlying mechanisms.