Approximately 25% of new drugs approved by the American Food and Drug Administration are peptides or proteins. Unfortunately, many of these therapeutic agents are rapidly eliminated by the body and/or are recognized by the immune system. For the past 30 years, these issues have been mainly addressed by grafting polymer chains to the peptide/protein, thus masking it from the immune system and preventing rapid elimination by increasing its size. One major obstacle to this approach lies in the loss of activity of the therapeutic agent, especially when specific binding events are involved.
A recent direction taken in this field is to release the native peptide or protein from the polymer with time in the body, a process referred to as “reversible PEGylation” (rPEGylation). However, it is currently difficult to predictably and finely control the rate of release over a useful range in a biofluid, which would permit control over pharmacokinetics.
We have recently reported coupling chemistry for selective conjugation of polymers to arginine residues on proteins. In this project, we will adapt our findings to achieve the selective, yet reversible, modification of arginine residues. Control of the rate of release of the polymer from the peptide or protein should be achievable through structural modifications to the reagent, and/or by altering the local micro-environment at the conjugation site. We will examine the stability of the prepared conjugates in model buffers and in biofluids for both a peptide containing a single arginine residue, and lysozyme, which contains multiple arginine residues.
The research proposed herein is important because it addresses important needs in the field of rPEGylation. Such an innovation will be of great value for altering pharmacokinetics, in particular for well-defined mono-PEGylated peptides or proteins for which release kinetics cannot be altered by increasing the number of conjugated polymer chains. This research is of broad interest because conjugation can, a priori, be achieved between any peptide or protein containing at least one arginine residue, to entities such as polymers or small molecule ligands such as lipids or cell-penetrating peptides, etc. Applications of selective reversible conjugation to proteins can also be found in sensor and protein sorting applications.