The current gold standard to reduce non-specific cellular uptake of drug delivery vehicles is by covalent attachment of poly(ethylene glycol) (PEG). It is thought that PEG can reduce protein adsorption and thereby confer a stealth effect. Here, we show that polystyrene nanocarriers that have been modified with PEG or poly(ethyl ethylene phosphate) (PEEP) and exposed to plasma proteins exhibit a low cellular uptake, whereas those not exposed to plasma proteins show high non-specific uptake. Mass spectrometric analysis revealed that exposed nanocarriers formed a protein corona that contains an abundance of clusterin proteins (also known as apolipoprotein J). When the polymer-modified nanocarriers were incubated with clusterin, non-specific cellular uptake could be reduced. Our results show that in addition to reducing protein adsorption, PEG, and now PEEPs, can affect the composition of the protein corona that forms around nanocarriers, and the presence of distinct proteins is necessary to prevent non-specific cellular uptake.

Biodegradable polymers are of current interest and chemical functionality in such materials is often demanded in advanced biomedical applications. Functional groups often are not tolerated in the polymerization process of ring-opening polymerization (ROP) and therefore protective groups need to be applied. Advantageously, several orthogonally reactive functions are available, which do not demand protection during ROP. We give an insight into available, orthogonally reactive cyclic monomers and the corresponding functional synthetic and biodegradable polymers, obtained from ROP. Functionalities in the monomer are reviewed, which are tolerated by ROP without further protection and allow further post-modification of the corresponding chemically functional polymers after polymerization. Synthetic concepts to these monomers are summarized in detail, preferably using precursor molecules. Post-modification strategies for the reported functionalities are presented and selected applications highlighted.

Protein-polymer conjugates are widely used to improve the pharmacokinetic properties of therapeutic proteins. Commercially available conjugates employ poly(ethylene glycol) (PEG) as the protective polymer; however, PEG has a number of shortcomings, including non-biodegradability and immunogenicity, that call for the development of alternatives. Here, the synthesis of biodegradable poly(phosphate), that is, poly(ethyl ethylene phosphate) (PEEP), by organo-catalyzed anionic ring-opening polymerization exhibiting dispersity values Ð < 1.3 is reported. Polymers with molecular weights between 2000 and 33 200 g mol are then ω-functionalized with a succinimidyl carbonate group and subsequently conjugated to model proteins. These are the first conjugates based on polyphosphates which degraded upon exposure to phosphodiesterase. As is the case for PEGylated therapeutics, residual in vitro activity of the PPEylated conjugates depends on the extent of protein modification. These results suggest that PEEP exhibits the desired properties of a biopolymer for use in next generation, fully degradable drug delivery systems.