Targeting SIRT2 induces MLH1 deficiency and boosts antitumor immunity in preclinical colorectal cancer models

Abstract

Low tumor mutation burden and an immunosuppressive tumor microenvironment (TME) of colorectal cancers (CRCs) contribute to resistance to immune-checkpoint inhibitors in patients. Understanding the mechanisms of cancer immune evasion will be helpful to develop new therapeutic strategies. Here, leveraging mass spectrometry-based proteomic profiling data and clinical validation, we identified that low sirtuin 2 (SIRT2) expression was associated with improved prognosis and an immune-active TME in CRC. Specifically, genetic knockdown or pharmacological inhibition of SIRT2 resulted in enhanced infiltration and cytotoxicity of CD8⁺ T cells, leading to tumor regression across multiple CRC mouse models and patient-derived organoids. Further in vitro experimental analysis demonstrated that SIRT2 interacted with and deacetylated MutL protein homolog 1 (MLH1) at Lys^402/443/461, thereby preventing MLH1 ubiquitination and degradation. SIRT2 knockdown or inhibition down-regulated MLH1, increasing DNA damage and activating the cyclic GMP-AMP synthase-stimulator of interferon genes (cGAS-STING) pathway. In addition, both in vivo and in vitro experiments indicated that SIRT2 inhibition stimulated the production of tumor neoantigens and enhanced major histocompatibility complex class I (MHC-I) expression, reprogramming the TME toward an immune-active status and inducing long-lasting immune memory. Last, a combination strategy using SIRT2 inhibitor 2-cyano-3-[5-(2,5-dichlorophenyl)-2-furanyl]-N-5-quinolinyl-2-propenamide (AGK2) and anti-programmed cell death protein-1 (PD-1) therapy enhanced immune response, making tumors susceptible to immunotherapy and driving substantial tumor regression in vivo. Our study uncovers a role of SIRT2 in reprogramming TME and underscores the potential of targeting SIRT2 to sensitize CRC to immunotherapy.