Site-Specific POxylation of Interleukin-4

Polymer conjugated biologics form a multibillion dollar market, dominated by poly(ethylene glycol) (PEG). Recent reports linked PEGs to immunological concerns, fueling the need for alternative polymers. Therefore, we are presenting a strategy replacing PEG by poly(2-oxazoline) (POx) polymers using genetically engineered interleukin-4 (IL-4) featuring an unnatural amino acid for site-specific conjugation through bioorthogonal copper-catalyzed azide alkyne cycloaddition (CuAAC). Conjugation yields of IL-4-PEG were poor and did not respond to an increase in the copper catalyst. In contrast, POxylated IL-4 conjugates resulted in homogeneous conjugate outcome, as demonstrated electrophoretically by size exclusion chromatography and analytical ultracentrifugation. Furthermore, POxylation did not impair thermal and chemical stability, and preserved wild-type IL-4 activity for the conjugates as demonstrated by TF-1 cell proliferation and STAT-6 phosphorylation in HEK293T cells, respectively. In conclusion, POxylation provides an interesting alternative to PEGylation with superior outcome for the synthesis yield by CuAAC and resulting in conjugates with excellent thermal and chemical stress profiles as well as biological performances.