PEGylation of Antibody Fragments to Improve Pharmacodynamics and Pharmacokinetics

Covalent attachment of polyethylene glycol (PEG) with therapeutic proteins (PEGylation) e.g., antibodies, antibody fragments, and enzymes, has been emerged as an effective strategy to enhance the pharmacodynamics and pharmacological properties of biopharmaceuticals. For example conjugation of PEG to proteins increases the solubility, protects against enzymatic digestion, and slows filtration by kidneys, thus enhancing the pharmacokinetic (PK) profiles. PEG scaffolds were also constructed for the multimerization of small proteins. However, random PEGylation leads to loss of biological potency of many proteins and as well as heterogeneous molecular configured mixtures. Hence a novel PEGylation approach is needed to retain biological properties and at the same time enhance PK profiles. Site-specific PEGylation with cysteine engineered protein at a defined site will meet both requirements of the therapeutic proteins. Here we describe a step wise approach for site-specific PEGylation of two cysteine engineered antibody fragments of 25 and 50kDa respectively to target human breast cancer cells. Purification and analysis of immunoreactivity of the PEGylated immunoconjugates is also explained.