Poly(2-ethyl-2-oxazoline) Featuring a Central Amino Moiety

Deciphering Polymer Interactions in Bioconjugates with Different Architectures by Structural Analysis via Time-Resolved Limited Proteolysis Mass Spectrometry

Therapeutic proteins are commonly conjugated with polymers to modulate their pharmacokinetics but often lack a description of the polymer-protein interaction. We deployed limited proteolysis mass spectrometry (LiP-MS) to reveal the interaction of polyethylene glycol (PEG) and PEG alternative polymers with interferon-α2a (IFN). Target conjugates were digested with the specific protease trypsin and a "heavy" 15N-IFN wild type (IFN-WT) for time-resolved quantification of the cleavage dynamics. Interactions between IFN-α2a and its high-affinity receptor were detailed by LiP-MS. Then, 10 kDa polymers of PEG, linear polyglycerol (LPG), and poly(2-oxazoline) (POX) with two different cyclooctyne linkers (BCN/DBCO) were used for site-specific bioconjugation to azide functionalized IFN-α2a. Tryptic events at each cleavage site and in different structural environments (loops/helices) were compared. PEG and LPG were similar, and POX showed a reduced interaction profile with the IFN-α2a surface. All-atom molecular dynamics simulations of IFN-DBCO-polymer conjugates revealed distinct and transient (below 50 ns) protein-interaction profiles for PEG, LPG, and POX. Cleavage dynamics of IFN-polymer conjugates from the BCN handle were homogeneous, pointing to a more conserved IFN structure than DBCO-polymer conjugates. In summary, time-resolved LiP-MS for quantification of cleavage events enhances the structural understanding of transient IFN-polymer interactions, which may be extended to other bioconjugate types.

Cryogels Based on Poly(2-oxazoline)s through Development of Bi- and Trifunctional Cross-Linkers Incorporating End Groups with Adjustable Stability

1,4-Bis(iodomethyl)benzene and 1,3,5-tris(iodomethyl)benzene were used as initiators for the cationic ring-opening polymerization (CROP) of 2-ethyl-2-oxazoline (EtOx) and its copolymerization with tert-butyl (3-(4,5-dihydrooxazol-2-yl)propyl)carbamate (BocOx) or methyl 3-(4,5-dihydrooxazol-2-yl)propanoate (MestOx). Kinetic studies confirmed the applicability of these initiators. Termination with suitable nucleophiles resulted in two- and three-armed cross-linkers featuring acrylate, methacrylate, piperazine-acrylamide, and piperazine-methacrylamide as polymerizable ω-end groups. Matrix-assisted laser desorption/ionization mass spectrometry and nuclear magnetic resonance (NMR) spectroscopy confirmed the successful attachment of the respective ω-end groups at all initiation sites for every prepared cross-linkers. Except for acrylate, each ω-end group remained stable during deprotection of BocOx containing cross-linkers. The cryogels were prepared using EtOx-based cross-linkers, as confirmed by solid-state NMR spectroscopy, scanning electron microscopy, and thermogravimetric analysis. Stability tests revealed a complete dissolution of the acrylate-containing gels at pH = 14, whereas the piperazine-acrylamide-based cryogels featured excellent hydrolytic stability.

Protected amine-functional initiators for the synthesis of α-amine homo- and heterotelechelic poly(2-ethyl-2-oxazoline)s

Screening a series of protected amine cationic ring-opening polymerization initiators revealed the commercially available N-(3-bromopropyl)phthalimide as the most suitable to achieve defined polymers with high degree of amine functionalization.

Molecular Insights into Site-Specific Interferon-α2a Bioconjugates Originated from PEG, LPG, and PEtOx

Conjugation of biologics with polymers modulates their pharmacokinetics, with polyethylene glycol (PEG) as the gold standard. We compared alternative polymers and two types of cyclooctyne linkers (BCN/DBCO) for bioconjugation of interferon-α2a (IFN-α2a) using 10 kDa polymers including linear mPEG, poly(2-ethyl-2-oxazoline) (PEtOx), and linear polyglycerol (LPG). IFN-α2a was azide functionalized via amber codon expansion and bioorthogonally conjugated to all cyclooctyne linked polymers. Polymer conjugation did not impact IFN-α2a's secondary structure and only marginally reduced IFN-α2a's bioactivity. In comparison to PEtOx, the LPG polymer attached via the less rigid cyclooctyne linker BCN was found to stabilize IFN-α2a against thermal stress. These findings were further detailed by molecular modeling studies which showed a modulation of protein flexibility upon PEtOx conjugation and a reduced amount of protein native contacts as compared to PEG and LPG originated bioconjugates. Polymer interactions with IFN-α2a were further assessed via a limited proteolysis (LIP) assay, which resulted in comparable proteolytic cleavage patterns suggesting weak interactions with the protein's surface. In conclusion, both PEtOx and LPG bioconjugates resulted in a similar biological outcome and may become promising PEG alternatives for bioconjugation.