Protective antigen-mediated delivery of biomolecules

Abstract

The intracellular delivery of therapeutic biomolecules such as oligonucleotides and proteins remains a key challenge today. Protective antigen, a naturally evolved protein translocase derived from Bacillus anthracis, has shown promise as a platform of protein delivery due to its ability to form a transmembrane pore that allows the cargo to have cytosolic access. We and others have used the LFN/PA system to deliver a wide variety of natural and non-natural peptides and proteins. Despite the significant progress made with the LFN/PA delivery platform, some aspects including cargo selection and targeting still remain limited. In the first part of the thesis, we greatly expand the application of the platform by demonstration of efficient delivery of peptide nucleic acids (PNAs), an oligonucleotide analog. Using this technology, we successfully exploited a cancer- specific gene dependency by the intracellular delivery of an anti-sense PNA in a receptor-dependent manner. In addition to exploiting new types of cargo for delivery, we developed a new strategy to target the LFN/PA system to specific cell types. In the second part of the thesis, we chemically conjugated a full-length immunoglobulin G (IgG) to a mutant PA (mPA). Significantly, we took advantage of the fact that PA activation is protease-dependent and created highly specific delivery vehicles that can only be activated by the concurrent presence of two entities on the cell surface. We showed a protein toxin delivered by these IgG-mPA variants effectively inhibited cell growth in different cancer cell lines and exhibited a significantly increased therapeutic window over previously reported PA variants both in vitro and in vivo. In the last part of the thesis, we explored the possibility of simplifying the LFN/PA system by directly ligating protein cargos to PA. In the absence of LFN, the chemically created single-component system significantly increased the amount of delivered cargo. Moreover, the single-component system combined with a short N-terminal polylysine tag further improved the delivery efficiency by more than 100-fold. Our findings raise the prospect of a simpler PA-mediated delivery platform..