The development of biological therapeutics

The development of biological therapeutics has advanced medicine dramatically in the 20th century. Protein-based drugs are now commonly used in treatment of disease. Technologies to improve the pharmacokinetic properties of these drugs are at the cutting edge of research within the pharmaceutical industry. I have evaluated a novel thiol-selective specific linker (PermaLinkTM,, Glythera Ltd) for the attachment of chemical groups such as polyethylene glycol (PEG) to cysteine via a stable thio-ether bond. Proteins are often PEGylated to improve their serum half-life, reduce their immunogenicity and prevent renal clearance by increasing their overall size. The linkers which attach these PEG molecules to a protein are an essential part of this modification as these affect where the molecule is attached and consequently whether the protein stays biologically active. In this study, I have compared PermaLinkTM-PEG with commercially available maleimide-PEG for the attachment of PEG groups to proteins. Initially I established a protocol to reduce the test protein prior to reaction with PermaLinkTM-PEG or maleimide-PEG. Agarose resin-linked Tris(2-carboxyethyl) phosphine (TCEP) was used to reduce cysteines prior to the addition of thiol-reactive compounds. Using this reduction approach, I observed that PermaLinkTM-PEG demonstrated an increased apparent cystiene selectively compared to maleimide-PEG. PermaLinkTM-PEG attached the predicted number of PEG molecules based on the number of available cysteines while non-specific multi-pegylation was observed with maleimide-PEG. Based on my results I propose that PermaLinkTM-PEG selectively targets cysteine thiol groups compared to maleimide-PEG. Overall I propose that PermaLinkTM technology could be used to develop new therapeutic proteins with reduced non-specific PEGylation.