Cucurbitacin B Inhibits Hepatocellular Carcinoma by Inducing Ferroptosis and Activating the cGAS-STING Pathway

The incidence of primary liver cancer is increasing annually, with extremely high mortality and suboptimal therapeutic outcomes. The inefficient presentation of tumor antigens and low infiltration of specific cytotoxic T lymphocytes (CTLs) result in insufficient immunogenicity, which limits the efficacy of immunotherapy. Despite the popularity of immune checkpoint inhibitors (ICIs), insufficient immune activation means only a small subset of hepatocellular carcinoma (HCC) patients exhibit clinical responses to ICIs, showing significant inter-individual variability. The activation of the cyclic GMP-AMP synthase(cGAS)- stimulator of interferon genes(STING) pathway initiates the expression of type I interferons (IFNs) and inflammatory cytokines, promoting the formation of a pro-inflammatory environment at the tumor site. This pathway enhances anti-tumor immune responses by facilitating antigen processing and presentation, T cell priming and activation, and remodeling of the immunosuppressive microenvironment. Our research found that cucurbitacin B (CuB), a natural component derived from traditional Chinese medicine, had significant anti-hepatocellular carcinoma properties and exerted anti-tumor effects through the cGAS-STING pathway. Specifically, CuB regulated ferroptosis by down-regulating the expression of Solute Carrier Family 7 Member 11 (SLC7A11) and Glutathione Peroxidase 4 (GPX4) and upregulating the expression of Transferrin Receptor Protein 1 (TFR1) and Long-chain Acyl-CoA Synthetase 4 (ACSL4). These actions involved lipid substrates, iron ion homeostasis, and antioxidant defense systems. The release of mitochondrial DNA (mtDNA) triggered by ferroptosis activated the cGAS-STING immune signaling pathway, leading to the up-regulation of cGAS, phosphorylated STING (p-STING), phosphorylated TANK-binding kinase 1 (TBK1), phosphorylated Interferon regulatory factor3 (IRF3), and Interferon-β (IFN-β). This cascade activation pattern provides new insights into the drug treatment of tumors.