Polyelectrolyte nanoparticles enable intracellular delivery of STING protein fragments for ovarian cancer immunotherapy.

Therapeutic activation of stimulator of interferon genes (STING) signaling shows promise as a method of inflaming the tumor microenvironment to generate an anti-cancer immune response. Frequent loss of STING expression in many human cancers renders small-molecule agonists ineffective in cancer cells. We previously demonstrated that delivering a fragment of the STING protein, dubbed STINGΔTM, to the cytosol can bypass this challenge by directly activating downstream signaling molecules in the cytosol; however, this strategy requires an effective cytosolic protein delivery vehicle to be therapeutically active. In this work, we develop a poly(β-amino ester) (PBAE) degradable polycation nanoparticle formulation to target ovarian cancer and deliver bioactive STINGΔTM protein to the cytosol. Screening experiments reveal that increasing PBAE hydrophobicity enables efficient protein encapsulation and delivery to the cytosol. We then develop a pH-shift-mediated method to assemble smaller, negatively charged nanoparticles composed of STINGΔTM protein, PBAE, and a polyanion. The polyanion can tune the cell type specificity of STING signaling activation in vitro, with poly(L-glutamate) and poly(L-aspartate) preferentially activating signaling in ovarian cancer cells. In a syngeneic mouse model of ovarian cancer, nanoparticles accumulate preferentially in tumors throughout the abdomen, slow tumor growth, and extend survival. Overall, the development of a tumor-targeted PBAE nanoparticle enabled the treatment of ovarian cancer through the direct intracellular delivery of STING protein, yielding an immunotherapy that shows promise for the treatment of cancers with dysregulated STING.