Disulfide-crosslinked polyion micelles for delivery of protein therapeutics.

New protein delivery systems are needed that efficiently encapsulate proteins and avoid formulation processes that affect protein structure and function. We have developed a protein delivery system termed disulfide-crosslinked polyion micelles (DCPMs), which consist of nanocomplexes formed by electrostatic self-assembly of a protein with a poly(ethylene glycol)-poly(L-lysine) block copolymer (PEG-PLL). The PEG-PLL amines are modified with crosslinkable dithiopyridine groups, using a Michael addition reaction that preserves the positive charges on the PLL chain to optimize polyionic complexation and disulfide crosslinking. DCPMs for vaccine delivery were prepared with ovalbumin and immunostimulatory CpG-DNA and are designed to release the vaccine intracellularly through reduction of disulfide crosslinks. DCPMs were also developed as a long-circulating enzyme carrier that maintains the enzymatic activity of the anti-oxidant enzyme catalase within the micelle core. Ovalbumin and catalase were each modified with SPDP to tether the protein in the micelle core, resulting in a high degree of protein retention under SDS-PAGE. DCPMs efficiently encapsulate and retain functional proteins in a stable polyionic complex and are a versatile delivery system for enzymes, vaccine antigens, and other protein therapeutics.