For Research Use Only. Not for Clinical Use.

Overview of PEGylation Based Half-Life Extension

PEGylation, a very popular technology for the modification of proteins, was introduced in the early 70s. The peptide chain is covalently attached to one or more high molecular weight chains of PEG, a molecule built of repetitive units of ethylene oxide (CH₂-CH₂-O). This elongation works by hiding antigenic determinants of the peptide so that antibodies cannot recognize it as a foreign body, and increasing protein size so that it won't be cleared out by kidneys very easily. PEG itself is an uncharged hydrophilic polymer that is non-biodegradable, mostly non-toxic, and non-immunogenic. Highly flexible PEG molecules can be easily attached to a therapeutic molecule. PEGylation also helps absorption enhancement by making the proteins more water-soluble and masks the molecules from proteolytic degradation.

First-generation PEGylation used the linear chain of PEG attached to peptide while 2^nd generation came up with the idea of branched-chain PEG and PEG derivative attachment. Over the years far better PEGylation strategies were developed to reduce the non-specific activity of peptides as well as increase their stability. There are > 10 peptide therapeutics already in the market, with a number of potential drugs designed based on this technology currently under clinical trial.

Fig. 1 Examples of PEGylation chemistry. (van Witteloostuijn, 2016)

Examples of PEGylation Application

The very first works of Frank Davis and coworkers in the 70s generated the first commercial PEGylated form of protein drug, modified adenosine deaminase (ADA). Enzyme ADA is used to treat severe combined immunodeficiency disease (SCID) mainly in young adults. Like most enzymes, ADA has a very short plasma half-life of a few minutes. Conjugating PEG to bovine ADA prolonged its half-life to 24 h in mice. In subsequent studies, PEG-ADA was tested on two children by intramuscular (IM) injection. The enzyme was found to be absorbed rapidly from the injection site to plasma, showing an elongated half-life of 48-72 h. Once a week administration of 15 U/kg bodyweights of the enzyme successfully maintained a plasma ADA activity which is 2-3 folds higher than erythrocyte ADA activity in normal subjects.

Another noted success using PEGylation technology was long-lasting hemophilia drugs. Hemophilia is a rare blood disorder due to clotting factor deficiency. Therefore, it is treated with recombinant factor VIII products. Products available in the market had half-lives of 12h and needed at least 3 injections per week. PEGylated anti-hemophilia agent, Adynovate (PEG-FVIII) has extended the half-life to 13.4-14.7 h.

Fig. 2 PEGylation influences physicochemical properties and biological effects of nanoparticles (NPs). (Mozar, 2018)

References

1. van Witteloostuijn, S. B.; et al. Half-Life Extension of Biopharmaceuticals using Chemical Methods: Alternatives to PEGylation. ChemMedChem. 2016, 11(22): 2474-2495.
2. Mozar, F. S. and Chowdhury, E. H. Impact of PEGylated Nanoparticles on Tumor Targeted Drug Delivery. Curr Pharm Des. 2018, 24(28): 3283-3296.