Formononetin Restrains Tumorigenesis of Breast Tumor by Restraining STING-NF-κB and Interfering with the Activation of PD-L1.

Abstract

Breast cancer (BC), a common tumor in women, has high morbidity and mortality. Formononetin, an active ingredient in red clover and Astragalus membranaceus, has a wide range of pharmacological applications, including as an anticancer agent. Since immunotherapy is a hot topic in the treatment strategy of BC, it was dedicated to appraising the specific mechanism of formononetin in BC immunotherapy in this research. Different formononetin concentrations (0, 20, 40, 60, 80, 100 μM) were used to treat BC cells transfected with pcDNA3.1-Programmed death ligand 1 (PD-L1) or Short-hairpin RNA (sh)-PD-L1. Cells were separated into four subgroups: CTRL, pcDNA3.1-PD-L1, sh-CTRL, and sh-PD-L1. Cell viability and cell cycle were assessed through Methylthiazolyldiphenyl-tetrazolium bromide (MTT) assay and flow cytometry. Programmed death ligand 1 (PD-L1) mRNA concentration was validated via quantitative real-time reverse transcription polymerase chain reaction (qRT-PCR). Cell metastasis was evaluated via cloning assay and transwell assay. The p-STING/stimulator of interferon genes (STING), p-p65/p65, and PD-L1 concentrations were determined by western blot. Formononetin restrained the proliferation of MCF-7 and MDA-MB-468 cells, and reduced PD-L1 mRNA, p-STING/STING, and p-p65/p65 protein concentrations. Whereas PD-L1 inhibition restrained the viability of BC cells, pcDNA3.1-PD-L1 intervention had the opposite result. STING pathway inhibitor C-176 combined with formononetin treatment further restrained cell proliferation, colony formation, and cell invasion, in contrast to cells treated with formononetin alone. Formononetin can restrain the proliferation of BC cells, which may be mediated through the interference of PD-L1 and suppression of the activation of the STING-NF-κB pathway.