Simvastatin induces ferroptosis and activates anti-tumor immunity to sensitize anti-PD-1 immunotherapy in microsatellite stable gastric cancer

Background: Gastric cancer (GC), especially the case with microsatellite stability (MSS) phenotype, has limited efficacy for immune checkpoint blockade (ICB) therapy. Metabolism reprogramming is newly recognized to affect tumor immune microenvironment (TIME). However, the relationship between metabolism reprogramming and immunotherapy for MSS GC has not been reported. Methods: A metabolic stratification for GC was developed based on the glycolysis/cholesterol synthesis axis using the R package "ConsensusClusterPlus". The T cell inflamed score was used to define "immune-hot" and "immune- cold" phenotypes in MSS GC. The anti-tumor and immunological effects of simvastatin were explored using in vitro and in vivo experiments. Results: Three metabolic subtypes were identified in GC patients, including cholesterol, glycolysis and quiescent subtypes. The cholesterol subtype was associated with poorer clinical features and higher tumor purity. Correspondingly, we demonstrated that simvastatin, a specific inhibitor of cholesterol synthesis, significantly inhibited the proliferation, migration, and induced ferroptosis in GC cells. Interestingly, simvastatin markedly inhibited tumor growth in immunocompetent mice, while no significant effect in immunodeficient mice. Upregulation of chemokines and increased recruitment of CD8+ T cells were observed after simvastatin treatment. Consistently, the cholesterol subtype exhibited a less inflamed TIME and coincided significantly with the "immune-cold" phenotype of MSS GC. Finally, we confirmed simvastatin enhanced PD-1 blockade efficacy via modulating the TIME and activating anti-tumor immunity in tumor-bearing mice. Conclusion: Our data revealed the significance of cholesterol synthesis in GC and demonstrated simvastatin served as a promising sensitizer for ICB therapy by inducing ferroptosis and anti-tumor immunity in MSS GC patients.