SOLID-PHASE AGGREGATION OF PROTEINS UNDER PHARMACEUTICALLY RELEVANT CONDITIONS

In order to successfully employ proteins as pharmaceuticals, it is ess ential to understand mechanistically the stability issues relevant to their formulation and delivery. Various deleterious processes may occu r in protein formulations, thereby diminishing their therapeutic value . This review focuses upon one aspect of this problem, namely aggregat ion of solid proteins under pharmaceutically relevant conditions (elev ated temperature and water activity). Strategies to pursue such studie s are presented with an emphasis on a mechanistic analysis of aggregat e formation. Both covalent and noncovalent aggregation pathways have b een elucidated. Proteins that contain disulfide bonds as well as free thiol residues may aggregate via thiol-disulfide interchange. For prot eins which contain disulfides but not free thiol residues, intermolecu lar disulfide bonding may still occur when intact disulfides undergo b eta-elimination, yielding free thiols which can catalyze disulfide scr ambling. Finally, proteins containing no cysteine/cystine residues may aggregate by other covalent pathways or by noncovalent routes. On the basis of these, pathways, some rational stabilization strategies have been proposed and verified. Ultimately, application of this knowledge should lead to more stable and effective pharmaceutical protein formu lations.