Cytosolic Delivery of Anionic Cyclic Dinucleotide STING Agonists with Locally Supercharged Viral Capsids

Cyclic dinucleotide (CDN) STING agonists represent a powerful new immunotherapy treatment modality and are a class of nucleotide-based therapies with broad clinical potential. However, they face practical challenges in administration, largely due to their poor pharmacological properties. We report the development of a drug delivery platform for CDNs and other anionic small-molecule drugs using bacteriophage MS2 viral capsids with engineered cationic residues. Relative to viral capsids lacking locally supercharged regions, these assemblies exhibit substantial increases in mammalian cell uptake while avoiding cell toxicity and hemolysis. A synthetic strategy was developed to attach CDN drugs covalently to the interior capsid surfaces through reductively cleavable disulfide linkers, which allowed for traceless drug release upon cell entry and exposure to reductive cytosolic environments. MS2-mediated CDN delivery into immune cell populations resulted in an approximately 100-fold increase in delivery efficiency compared with free drugs and showed enhanced STING activation as well as downstream cytokine release.