What are polyethylene glycol and pegylation?
Polyethylene glycol (PEG) is a linear polymer formed by the polymerization of ethylene oxide. The molecular formula is abbreviated as H(OCH2CH2)nOH, with n represents the number of ethoxy units. It is a widely used ingredient in the development of new drugs. PEG can be dissolved in water and some organic solvents. When adding other organic solvents, it can precipitate from the original solution.
Unlike polysaccharides, only the terminal hydroxyl groups of PEG can be activated and react with proteins, which can avoid the complexity of the reaction and the product. However, PEG has two hydroxyl groups. If it reacts with protein, it may also form "PEG-protein-PEG-protein" conjugates with different degrees of cross-linking, and precipitation may even occur.
Is it possible to find a polyethylene glycol with only one terminal hydroxyl group? The researchers discovered monomethoxy polyethylene glycol (mPEG). The difference between mPEG and the conventional PEG is that one end is a monomethoxy group, and the other end is a hydroxyl group. The molecular formula is CH3(OCH2CH2)nOH. By activating this hydroxyl group to introduce an activated group and react with the protein, the PEG-protein conjugate can only be formed at the hydroxyl end, and no cross-linked product can be formed.
By the end of the 1960s, when the DNA recombination technology was not yet available on the market, researchers often used animal-derived proteins when preparing drugs, which led to serious immunogenicity problems. When developing new drugs, polyethylene glycol polymer chains are chemically coupled to protein molecules, and the volume of the drug molecules is increased to effectively extend the drug half-life in the body, and at the same time, the immune sites are shielded to significantly reduce the immunogenicity. This is one of the most effective long-acting protein preparation technologies recognized internationally.
Advantages of coupling PEG to protein molecules
Coupling the activated PEG with the protein molecule can improve the three-dimensional state of the protein and cause the various biochemical properties of the protein to change. Compared with unmodified drugs, PEG-modified drugs have the following advantages:
(1) Stronger biological activity
(2) Liposomes have a stronger passive targeting effect on tumors
(3) Longer half-life
(4) Lower maximum blood concentration
(5) Smaller fluctuations in blood concentration
(6) Less enzyme degradation
(7) Less immunogenicity and antigenicity
(8) Less toxicity
(9) Better solubility
(10) Reduced medication frequency
(11) Improve patient compliance, improve quality of life, and reduce treatment costs
Safety of PEG-modified drugs
In the early FDA-approved lyophilized human blood gamma globulin powder, PEG was used as one of the ingredients. However, the PEG added here is polyethylene glycol with a hydroxyl group at both ends, that is, conventional PEG. Some people have done animal safety experiments and discussed the metabolism of conventional PEG in the 1940s. Studies have shown that a small molecular weight PEG, such as only a few hundred kDa, can be nephrotoxic. When the molecular weight is greater than 1000 kDa, the toxicity is not obvious. Experiments on the metabolism have shown that renal elimination is the main way to clear low molecular weight PEG from the body. As the molecular weight increases, fecal elimination becomes an additional method of removal.
mPEG is very similar to PEG, except that one hydroxyl group at the end is replaced. Therefore, people initially inferred from the early PEG animal test data that mPEG is also biologically safe. There are also articles showing that interferon with a molecular weight of 40,000 mPEG is excreted from the body through feces and liver metabolism. However, in recent years, studies have found that mPEG-modified protein drugs can cause the body to produce antibodies against PEG, thereby accelerating the elimination of the drug. The production of this antibody may be related to the single methoxy group at its end.
Creative Proteomics provides a comprehensive PEGylated Protein Analysis Service for our customers.
