Apigenin promotes apoptosis of 4T1 cells through PI3K/AKT/Nrf2 pathway and improves tumor immune microenvironment in vivo

Background and purpose: 2022 U.S. cancer statistics reveal breast cancer is among the most common cancers in women. Apigenin (API) is endowed with anti-cancer activities among naturally occurring plant flavonoids. However, its mechanism of action on breast cancer, the fourth largest cancer in women, has not yet been clarified. Experimental approach: In vitro, we used MTT, transwell, staining, and western blotting to investigate the inhibitory effect of apigenin on 4T1 and the underlying molecular mechanism. In vivo by establishing a xenograft tumor model, using immunohistochemistry, and flow cytometry to study the inhibitory effect of apigenin on breast solid tumors and its effect on the tumor immune microenvironment. Key results: API significantly suppressed 4T1 cells proliferation, migration, and invasion. Furthermore, API treatment reduced MMP and upgraded intracellular ROS production. API could regulate Bcl-2 family proteins and activate caspase-3 to promote cell apoptosis. At the same time, the PI3K/AKT/Nrf2 pathway of API-treated 4T1 cells was inhibited in a concentration-dependent manner. Moreover, API inhibited breast tumor growth in mice, and significantly reduced PCNA content in tumor tissue. We also found that the proportion of regulatory T (Treg) cells in TDLN was decreased in the API-treated group. In addition, API can prolong the survival of mice with mammary gland tumors. Conclusions and implications: Our research show that apigenin can induce breast cancer cell apoptosis through the PI3K/AKT/Nrf2 pathway, and can improve the tumor immune microenvironment in mice with breast tumors, thereby inhibiting the growth of breast cancer. Thus, API may be a promising agent for breast cancer treatment.