(209h) Nanoscale Polymer Complexes Deliver Sting Protein Fragments to Activate Innate Immunity in Ovarian Cancer

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. Recent evidence highlights benefits of activating STING signaling in cancer cells specifically, however, frequent loss of STING expression in human cancer makes this impossible for a large fraction of patients using existing small-molecule agonists. We previously reported on a strategy capable of bypassing this challenge, by delivering a fragment of the STING protein dubbed STINGΔTM to the cytosol. STINGΔTM directly interacts with downstream signaling molecules, activating signaling even in cells that do not express functional STING. However, an effective cytosolic protein delivery strategy is required to apply STINGΔTM to the treatment of cancer.

In this work, we develop and characterize a nanoscale polymer ternary complex formulation to facilitate the cytosolic delivery of STINGΔTM protein and demonstrate its ability to activate signaling in STING-silenced ovarian cancer models. Poly(beta-amino esters) (PBAEs) were screened with a functional delivery assay, which led to the discovery of a hydrophobic PBAE that can effectively deliver active STINGΔTM to the cytosol. Additional characterization allowed for the development of a pH-shift-mediated process to near completely encapsulate STINGΔTM in PBAE particles. Polyanions were incorporated into this formulation to generate ternary complexes, smaller, negatively charged nanoparticles with greatly improved stability and strong delivery efficacy. These ternary complexes were able to activate STING signaling in a variety of ovarian cancer cell lines including spheroids generated with a STING-silent ovarian cancer cell line, evidenced by a strong chemokine and cytokine production upon treatment. Overall, this work serves as an in vitro demonstration of a nanoparticle formulation that enables cytosolic STINGΔTM delivery, motivates its ongoing evaluation in in vivo models, and shows its potential application for the treatment of STING-silenced ovarian cancer.