Conditional fusogenic lipid nanocarriers for cytosolic delivery of macromolecular therapeutics

Macromolecular therapeutics designed for intracellular targets must overcome systemic delivery barriers, target cell membrane impermeability, and inefficient endosomal escape. Here, we engineer a class of conditional fusogenic liposomes (C-FLIPs) that harness the catalytic activity of extracellular proteases present in the pathological microenvironment. This context-specific activation enables on-target membrane fusion with cells in diseased tissue, resulting in cytosolic delivery of therapeutic payloads. We describe the cytoplasmic delivery of three prototypic macromolecular therapeutic classes: peptide degraders, cytotoxic proteins, and ribonucleoprotein particles (RNPs). We further develop C-FLIP to deliver granzyme B (GzmB) to the cytoplasm of cancer cells in vivo and induce pyroptosis in immunologically-inert tumors. Treatment with C-FLIP/GzmB reprograms the immunosuppressive tumor microenvironment and synergizes with checkpoint blockade to result in the regression of established tumors and induce immunological memory. This modular, non-viral, cytosolic delivery platform represents a promising approach to leverage pathological protease activity for targeted delivery of biologics.