Bio-inspired pH-responsive polymers for intracellular delivery of macromolecules and cell engineering applications

Abstract

Biological macromolecules including peptides, proteins and antibodies can act as therapeutic agents. When delivered intracellularly to their desired target site within the cell, they can modify cell behaviour. However, a long-standing challenge is the efficient delivery of such materials to their intracellular target sites. Although effective in some applications, existing technologies to improve delivery, namely viral vectors, have key limitations in their toxicity and safety. There is thus a need for more effective intracellular delivery tools. This thesis explores the use of bio-inspired pH-responsive polymers as intracellular delivery platforms for the enhanced uptake of macromolecules. PP50, an anionic polymer comprised of a poly-L-lysine isophthalamide backbone grafted with the hydrophobic amino acid L- phenylalanine at a stoichiometric percentage of 50 mol%, was capable of delivering FITC- dextran, peptides and antibodies into the cell interior when the pH environment was lowered to pH 6.5. Additionally, the ability of PP50 to facilitate the uptake of the ribosome-inactivating protein saporin to induce apoptosis and cell death in 2D monolayer and multicellular spheroids highlights the potential use of PP50 for a wide range of therapeutic applications. PLP-NDA18, another anionic polymer comprised of a poly-L-lysine isophthalamide backbone grafted with decylamine at 18 mol%, also showed enhanced uptake and cytotoxicity of saporin when co-incubated with cells. For cell engineering applications, two cationic polymers, CP1 and CP2, were investigated for their ability to improve the direct cytoplasmic delivery of the target antigen ovalbumin peptide and induce antigen presentation by DCs. Whilst CP1 displayed superior membrane lytic capabilities at pH 6.5, CP2 showed to be the most promising polymer for the upregulation of MHC I and cytoplasmic delivery of the antigen peptide. In the future, a more comprehensive investigation into the underlying mechanisms of cationic mediated antigen delivery will help to understand the full capabilities of these cationic polymers as intracellular delivery platforms. Altogether, this work demonstrates that pH-responsive polymers are promising candidates as intracellular delivery platforms for a wide range of applications. Further studies and research are required for each polymer to reach its full potential as a widely adopted intracellular delivery agent.