Reversible Chemical Protein Modification to Endogenous Glutathione and Its Utilities in the Manufacture of Transcellular Pro-Enzymes

Proteins have been perceived as being an intriguing modality of therapeutics for the treatment of intractable diseases in view of their superlative precision and versatility. Nonetheless, proteins' intrinsic characters, particularly their being hydrophilic macromolecules with unmethodical charges, have imposed the exceeding challenge of seeking transcellular trafficking into cells' interiors. To circumvent this drawback, we have attempted to employ triple-functional amine-reactive 4-(2-((2-(((4-nitrophenoxy)carbonyl)oxy)ethyl)disulfaneyl)ethoxy)-4-oxobutanoic acid for the efficient incorporation of the anionic carboxyl moiety into amine-enriched enzymes, resulting in overall negatively charged pro-enzymes. The resulting pro-enzymes could be readily electrostatically assembled with cationic species [for instance: block copolymers of poly(ethylene glycol)-polylysine] into core–shell architectural delivery nanoparticles for their facilitated endocytosis into cells. Noteworthy is the aforementioned carboxylation chemistry designed to allow facile reversal of the pro-enzymes to the original amine groups due to the thiolysis of intermediate disulfide linkage for subsequent cascade reactions in response to the cytosol-enriched glutathione. Therefore, cytosol-selective structural disassembly for the liberation and activation of the pro-enzymes was accomplished. Our subsequent investigations utilizing ribonuclease A and catalase as the model enzymes demonstrated appreciable transcellular transportation of the active enzymes to the cell interiors, exerting overwhelming cytotoxic potencies and H2O2 scavenging capacities, respectively. Hence, we reported an unprecedented redox-stimulated charge reversal strategy in engineering cytosol-activatable pro-enzymes, manifesting a simple and efficient approach in the manufacture of transcellular proteinic therapeutics, which should be highlighted to promote their wide availability for use with diverse functional proteins as molecular biological tools and precision therapeutics.