Pegylation – in search of balance and enhanced bioavailability

In the process of finding better therapeutics, thousands of new molecules are synthesised every day. Many of these can be poorly soluble in water, leading to a potentially promising drug being rejected during testing due to its poor solubility. Polyethylene glycol (PEG) has become known as an excellent modification to remedy this and was initially used to increase circulation time and reduce the immunogenicity of therapeutic proteins. Thus significantly increasing their safety and range of use. Another group of compounds in which significant benefits of pegylation have been seen are photosensitisers. Used in photodynamic therapy, they are often characterised by very high hydrophobicity. Pegylation of their structure significantly increases their affinity for cancer cells and facilitates their penetration through cell membranes. Classical small-molecule drugs can benefit from temporary combinations hydrolysed in the body or very short PEG chains. This approach allows a significant increase in the bioavailability of the drug while avoiding the disadvantages of small molecule pegylation. However, the most common motive for pegylation recently is the creation of drug carriers. Liposomes and nanoparticles make it possible to exploit the advantages of PEG to stabilise their structure and increase circulation time while not modifying the structure of the active compound. Unfortunately, PEGs also have their drawbacks. The first is their high molecular weight range, especially for longer chains, which poses difficulties in purification. Another is the emergence of antibodies directed against PEG. Nevertheless, pegylation is still an up-and-coming method for modifying pharmaceutically active molecules.