Chemical and Enzymatic Site Specific PEGylation of hGH: The Stability and in vivo Activity of PEG-N-Terminal-hGH and PEG-Gln141-hGH Conjugates

The use of therapeutic proteins is often impaired by their short in vivo half-lives. PEGylation has been exploited to enhance protein stability and to prolong the pharmacokinetic. The biophysical characterization of two site-specific mono-PEGylated forms of human growth hormone (hGH) - chemically N-terminal PEGylated hGH (PEG-Nter-hGH) and enzymatically Gln141 PEGylated hGH (PEG-Gln141-hGH) via transglutaminase - is outlined here and their pharmacodynamics are compared. The thermal stability of PEG-Nter-hGH was increased with respect to that of hGH and PEG-Gln141-hGH. Pharmacodynamic studies in rats showed that a single injection of the conjugates had a better or comparable potency with respect to a daily hGH on a week schedule in terms of weight gain, femoral length, and tibial diaphysis width. Two different site-specific monoPEGylated forms of hGH are prepared using a chemical, N-terminal PEGylation and enzymatic, transglutaminase-based conjugation approaches. The N-terminal PEGylation yielded a conjugate with a higher thermal stability and, of particular interest, one that is able to recover the secondary structure after thermal denaturation.