Proteome Instability Is a Therapeutic Vulnerability in Mismatch Repair-Deficient Cancer

Deficient DNA mismatch repair (dMMR) induces a hypermutator phenotype that can lead to tumorigenesis; however, the functional impact of the high mutation burden resulting from this phenotype remains poorly explored. Here, we demonstrate that dMMR-induced destabilizing mutations lead to proteome instability in dMMR tumors, resulting in an abundance of misfolded protein aggregates. To compensate, dMMR cells utilize a Nedd8-mediated degradation pathway to facilitate clearance of misfolded proteins. Blockade of this Nedd8 clearance pathway with MLN4924 causes accumulation of misfolded protein aggregates, ultimately inducing immunogenic cell death in dMMR cancer cells. To leverage this immunogenic cell death, we combined MLN4924 treatment with PD1 inhibition and found the combination was synergistic, significantly improving efficacy over either treatment alone. [Display omitted] •Abundant destabilizing mutations lead to proteome instability in MSI cancers•MSI cancers rely on Nedd8-mediated clearance of destabilized/misfolded proteins•Inhibiting neddylation with MLN4924 induces immunogenic cell death•Potentiating MLN4924 therapy's immunogenicity with anti-PD1 provides potent synergy McGrail et al. find that the abundance of destabilizing mutations in microsatellite unstable (MSI) tumors causes proteome instability and accumulation of misfolded proteins. To compensate, MSI tumors rely on a Nedd8-mediated pathway to clear misfolded aggregates, which can be therapeutically targeted by MLN4924.