Engineering Polymer Conjugation For Better Therapeutic Proteins

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Polymer covalent conjugation, especially with polyethylene glycol (PEG), is a consolidated strategy for improving the therapeutic performance of bioactive substances, like proteins, peptides, small drugs and oligonucleotides. Furthermore, this approach is playing an important role for introducing biocompatibility and increased in vivo half-life of other drug delivery systems such as liposomes, nanoparticles, nanotubes, etc. In general, polymer conjugation is performed to prolong the pharmacokinetic of a fast body-cleared molecule and to reduce immunogenicity. The former advantage is reached by decreasing the rates of both kidney clearance and degradation, while the last is achieved by a shielding effect of the polymer’s chains over the immunogenic sites of a protein. So far the polymer conjugation to protein was obtained by few chemical strategies thus limiting the possibility to direct the polymer coupling to a desired site in view to minimize the activity lost.
Now this field is renewing by taking advantages of the use of enzymes to mediate the polymer coupling to new sites in a protein, opening the possibility to obtain site-selective protein conjugates also in the case of very complex and high molecular weight proteins. In general enzymatic conjugation is very specific for a predetermined site in a protein, and the conjugate formation is fast and often quantitative also in physiological conditions of reaction buffers.
Among the several enzymes introduced for PEGylation this presentation will focus especially on the use of microbial transglutaminase.