Polyion complex micelle formation from double-hydrophilic block copolymers composed of charged and non-charged segments in aqueous media

Hydrolytically Degradable PEGylated Polyelectrolyte Nanocomplexes for Protein Delivery

Novel oppositely charged polyphosphazene polyelectrolytes containing grafted poly(ethylene glycol) (PEG) chains were synthesized as modular components for the assembly of biodegradable PEGylated protein delivery vehicles. These macromolecular counterparts, which contained either carboxylic acid or tertiary amino groups, were then formulated at near physiological conditions into supramolecular assemblies of nanoscale level, below 100 nm. Nanocomplexes with electroneutral surface charge, as assessed by zeta potential measurements, were stable in aqueous solutions, which suggests their compact polyelectrolyte complex "core"-hydrophilic PEG "shell" structure. Investigation of PEGylated polyphosphazene nanocomplexes as agents for noncovalent PEGylation of the therapeutic protein l-asparaginase (L-ASP) in vitro demonstrated their ability to dramatically reduce protein antigenicity, as measured by antibody binding using enzyme linked immunosorbent assay (ELISA). Encapsulation in nanocomplexes did not affect enzymatic activity of L-ASP, but improved its thermal stability and proteolytic resistance. Gel permeation chromatography (GPC) experiments revealed that all synthesized polyphosphazenes exhibited composition controlled hydrolytic degradability in aqueous solutions at neutral pH and showed greater stability at lower temperatures. Overall, novel hydrolytically degradable polyphosphazene polyelectrolytes capable of spontaneous self-assembly into PEGylated nanoparticulates in aqueous solutions can potentially enable a simple and effective approach to modifying therapeutic proteins without the need for their covalent modification.

Polyion Complex Micelles for Protein Delivery

Proteins are ubiquitous in life and next to water, they are the most abundant compounds found in human bodies. Proteins have very specific roles in the body and depending on their function, they are for example classified as enzymes, antibodies or transport proteins. Recently, therapeutic proteins have made an impact in the drug market. However, some proteins can be subject to quick hydrolytic degradation or denaturation depending on the environment and therefore require a protective layer. A range of strategies are available to encapsulate and deliver proteins, but techniques based on polyelectrolyte complex formation stand out owing to their ease of formulation. Depending on their isoelectric point, proteins are charged and can condense with oppositely charged polymers. Using block copolymers with a neutral block and a charged block results in the formation of polyion complex (PIC) micelles when mixed with the oppositely charged protein. The neutral block stabilises the charged protein–polymer core, leading to nanoparticles. The types of micelles are also known under the names interpolyelectrolyte complex, complex coacervate core micelles, and block ionomer complexes. In this article, we discuss the formation of PIC micelles and their stability. Strategies to enhance the stability such as supercharging the protein or crosslinking the PIC micelles are discussed.