PEGYLATION OF CYTOKINES AND OTHER THERAPEUTIC PROTEINS AND PEPTIDES -THE IMPORTANCE OF BIOLOGICAL OPTIMIZATION OF COUPLING TECHNIQUES

Polyethylene glycol (PEG) modification, PEGylation, is a well establis hed technique which has the capacity to solve or ameliorate many of th e problems of protein and peptide pharmaceuticals. It is one of the mo st important of the molecule altering structural chemistry (MASC) tech niques and in many settings is enabling technology. The use of PEG as a linker molecule is also beginning to make a contribution to the prod uction of exciting new products. We have previously reviewed the marke d differences between methods of PEGylation and the surprising and dra matic impact of different coupling techniques (using different activat ed PEGs) on factors such as retention of bioactivity, stability and im munogenicity of the resulting PEGylated proteins and peptides. Numerou s factors play a part in this variation: the presence or absence of li nkers between the PEG and the target molecule; the nature and stabilit y of the bond(s) between the PEG, linker and target; the impact of PEG attachment on surface charge; the coupling conditions; and the relati ve toxicity of the activated polymer and/or coproduct(s). These are no t, however, the only sources of qualitative differences in PEGylated p roducts. Our own experience whilst developing a linkerless PEGylation technique (i.e. one attaching only PEG to the target molecule), which we devised to overcome all the major problems of pre-existing PEGylati on techniques, was that considerable modification of the prototype met hod and a process of 'biological optimisation' was required to achieve good results in terms of conservation of bioactivity. Biological opti misation has not, as far as we are aware, been systematically applied by other groups working in PEGylation. It is the term we use to descri be an iterative process for examining and refining all the steps in th e PEGylation process, including manufacturing the activated polymer, i n order to achieve the best possible conservation of bioactivity and o ther beneficial features of the method. The application of this biolog ically optimised PEGylation technique, using tresyl monomethoxy PEG (T MPEG), to a variety of target proteins reveals, as outlined in this re view, an exceptional ability to conserve biological activity of the ta rget. This, and the benefit of adding nothing other than PEG itself (w hich has an excellent safety record), to the protein, as well as other manufacturing and practical advantages, makes the method ideal for th e modification of cytokines and other therapeutic proteins. (C) 1998 E lsevier Science Ireland Ltd. All rights reserved.