Combination with SGT-53 overcomes tumor resistance to a checkpoint inhibitor.

The tumor suppressor p53 responds to genotoxic and oncogenic stresses by inducing cell cycle arrest and apoptosis. Recent studies suggest that p53 also participates in the regulation of cellular immune responses. Here, we have investigated the potential of p53 gene therapy to augment immune checkpoint inhibition by combining an anti-programmed cell death protein 1 (PD1) antibody with SGT-53, our investigational nanomedicine carrying a plasmid encoding human wild-type p53. In three syngeneic mouse tumor models examined including a breast cancer, a non-small cell lung carcinoma, and a glioblastoma, SGT-53 sensitized otherwise refractory tumors to anti-PD1 antibody. The involvement of p53 in enhancing anti-PD1 immunotherapy appears to be multifaceted, since SGT-53 treatment increased tumor immunogenicity, enhanced both innate and adaptive immune responses, and reduced tumor-induced immunosuppression in a 4T1 breast tumor model. In addition, SGT-53 alleviates a fatal xenogeneic hypersensitivity associated with the anti-PD1 antibody in this model. Our data suggest that restoring p53 function by SGT-53 is able to boost anti-tumor immunity to augment anti-PD1 therapy by sensitizing tumors otherwise insensitive to anti-PD1 immunotherapy while reducing immune-related adverse events.