β-Sitosterol targets ASS1 for Nrf2 ubiquitin-dependent degradation, inducing ROS-mediated apoptosis via the PTEN/PI3K/AKT signaling pathway in ovarian cancer

The exploration of drugs derived from natural sources holds significant promise in addressing current limitations in ovarian cancer (OC) treatments. While previous studies have highlighted the remarkable anti-cancer properties of the natural compound β-sitosterol (SIT) across various tumors, its specific role in OC treatment remains unexplored. This study aims to investigate the anti-tumor activity of SIT in OC using in vitro and in vivo models, delineate potential mechanisms, and establish a preclinical theoretical foundation for future clinical trials, thus fostering further research. Utilizing network pharmacology, we pinpoint SIT as a promising candidate for OC treatment and predict its potential targets and pathways. Through a series of in vitro and in vivo experiments, we unveil a novel mechanism through which SIT mitigates the malignant biological behaviors of OC cells by modulating redox status. Specifically, SIT selectively targets argininosuccinate synthetase 1 (ASS1), a protein markedly overexpressed in OC tissues and cells. Inhibiting ASS1, SIT enhances the interaction between Nrf2 and Keap1, instigating the ubiquitin-dependent degradation of Nrf2, subsequently diminishing the transcriptional activation of downstream antioxidant genes HO-1 and NQO1. The interruption of the antioxidant program by SIT results in the substantial accumulation of reactive oxygen species (ROS) in OC cells. This, in turn, upregulates PTEN, exerting negative regulation on the phosphorylation activation of AKT. The suppression of AKT signaling disrupted downstream pathways associated with cell cycle, cell survival, apoptosis, migration, and invasion, ultimately culminating in the death of OC cells. Our research uncovers new targets and mechanisms of SIT against OC, contributing to the existing knowledge on the anti-tumor effects of natural products in the context of OC. Additionally, this research unveils a novel role of ASS1 in regulating the Nrf2-mediated antioxidant program and governing redox homeostasis in OC, providing a deeper understanding of this complex disease.