Reduction Sensitive Poly(l‑glutamic acid) (PGA)-Protein Conjugates Designed for Polymer Masked–Unmasked Protein Therapy

Protein therapeutics have become an important class of medicines for a large variety of diseases. However, they have disadvantages such as rapid elimination/metabolism leading to the need for repeated doses, immunogenicity/antigenicity, and aggregation/degradation during formulation and storage. The concept of polymer masked–unmasked protein therapy (PUMPT) makes use of polymer–protein multivalent conjugation with biodegradable carriers, which mask the protein activity during transport and increase its stability, but is capable of specifically triggering an unmasking effect at the disease site, allowing its therapeutic action. The aim of this study was to widen the PUMPT concept by designing reduction sensitive poly-l-glutamic acid (PGA)-based conjugates, in which the protein release and unmasking effect takes place in the reducing environments found intracellularly as well as in the tumor microenvironment. Lysozyme was used as the model protein to achieve proof of concept. Overall, the synthesized platform showed to be promising for the delivery of anticancer proteins as well as for enzyme replacement therapeutic approaches aiming to treat lysosomal storage disorders.