Metabolic reprogramming in GNSOR-deficient cancer
S-nitrosoglutathione reductase (GSNOR) is a denitrosylase enzyme which has been suggested to play a tumor suppressor role, although the responsible mechanisms are still largely unclear. In this study, we show that GSNOR deficiency in tumors was associated with poor prognostic histopathological features and poor survival in colorectal cancer (CRC) patients. Besides, GSNOR-low tumors were characterized by an immunosuppressive microenvironment with exclusion of cytotoxic CD8+ T cells. Notably, GSNOR-low tumors exhibited an immunoevasive proteomic signature along with an altered energy metabolism characterized by impaired oxidative   phosphorylation (OXPHOS) and energetic dependence on glycolytic activity. CRISPR-Cas9–mediated generation of GSNOR gene knockout (KO) in CRC cells confirmed in vitro and in vivo that GSNOR-deficiency conferred higher tumorigenic and tumor initiating capacities. Moreover, GSNOR-KO cells possessed enhanced immunoevasive properties and resistance to immunotherapy, as revealed by their xenografting into humanized murine models. Importantly, GSNOR-KO cells were characterized by a metabolic shift from OXPHOS to glycolysis to produce energy, as indicated by increased lactate secretion, higher sensitivity to 2-deoxyglucose (2-DG) and fragmented mitochondrial network. Real-time metabolic analysis revealed that GSNOR-KO cells operated close to their maximal glycolytic rate, as compensation for lower OXPHOS levels, explaining their higher sensitivity to 2-DG. Remarkably, this higher susceptibility to glycolysis inhibition with 2-DG was validated in patient derived xenografts and organoids from clinical GSNOR-low tumors. In conclusion, our data support that metabolic reprogramming induced by GSNOR deficiency is an important mechanism for tumor progression and immunoevasion in CRC and that the metabolic vulnerabilities associated with the deficiency of this denitrosylase can be therapeutically exploited.