A novel polymeric peptide delivery platform and association with targeted co-delivery of antigens and STING agonists with antitumor immune response.

Abstract

2564 Background: Use of tumor antigens for the development of patient-specific cancer vaccines has been a promising therapeutic strategy. However, challenges remain in delivering subunit vaccine components in a coordinated fashion to elicit antitumor immune responses. To overcome these, we developed rationally designed vaccines using a novel nanoplatform called the Protein-Like Polymer (PLP), in reference to its globular structure reminiscent of native proteins, with unique characteristics that allow for sustained/targeted delivery of tumor antigens in conjunction with STING agonists. Methods: PLPs containing a model melanoma antigen were synthesized via ring-opening metathesis polymerization (ROMP) and characterized. A library of compounds were generated with different sidechain linkage chemistries (amide, ester, or disulfide), degrees of polymerization, and inclusion/exclusion of Oligo(ethylene glycol) (OEG) side chains. In vitro uptake and functional assays using gp100-specific T Cells were conducted with fluorescently-labeled and non-labeled polymers respectively. In vivo experiments were done using a B16F10 murine melanoma tumor model over-expressing gp100. Ability of PLPs to co-deliver immunomodulatory compounds was tested by electrostatically coupling a small molecule STING agonist 2’3’ cGAMP which formed stable nanostructures. The optimized construct was also tested in an OVA system to prove generalizability. Results: Conjugating peptide antigens using a cleavable disulfide linkage, which reduces intracellularly in antigen presenting cells (APCs), resulted in increased endosomal localization and efficacy. Incorporating a diluent amount of OEG side chains increased resistance to enzymatic degradation while improving bioactivity and uptake by APCs. In vivo studies using PLPs conjugated with gp100 resulted in significant increases in survival time and reduced tumor burden in B16 melanoma. Increasing the DP, and therefore the density of antigen side chains, improved vaccine efficacy and resistance to proteolysis. Mice treated with STING-PLP complexes showed significantly smaller tumors vs control at day 14 (0.038g vs 0.76g; p < 0.0001) and allowed for subcutaneous administration of 2’3’ cGAMP, which otherwise diffuses rapidly away from the injection site. OVA-PLPs behaved similarly in their cognate system but showed no activity when tested on gp100-specific cells and vice versa demonstrating antigen-specificity. Conclusions: This work validates the potential of PLPs to overcome major limitations in cancer vaccine development. The modularity of the platform allows for complex nano-architectures including systems capable of delivering challenging compounds, ie small molecule STING agonists, subcutaneously through electrostatic coupling. This technology has the potential to revolutionize cancer vaccinology.