Evaluation of the rapid plasma elimination of recombinant alpha 1-proteinase inhibitor: synthesis of polyethylene glycol conjugates with improved therapeutic potential.

Plasma-derived alpha 1-proteinase inhibitor (alpha 1PlI) is used for replacement therapy in patients with emphysema who have a deficiency of the protein. Future therapy with alpha 1PI with reactive site mutants of this inhibitor will probably require the use of recombinant-derived alpha 1PI (r alpha 1PI). However, the pharmacologic efficacy of r alpha 1PI in humans has been hindered, since r alpha 1PI is rapidly cleared from the circulation of experimental animals. Our studies of the metabolism of r alpha 1PI in mice demonstrate that the rapid clearance of r alpha 1PI is due to renal filtration. However, after preventing renal filtration by ligation of the renal arteries, we find that r alpha 1PI is metabolized in a manner similar to alpha 1PI. Conjugation of r alpha 1PI to polyethylene glycol of Mr approximately 4000 (PEG-4) greatly slows the clearance of r alpha 1PI. The PEG-4 r alpha 1PI conjugate is metabolized in a manner similar to alpha 1PI and has similar kinetic properties before and after oxidation with N-chlorosuccinimide. Moreover, proteinase complexes of PEG-4-r alpha 1PI are catabolized by the same hepatocyte receptor that binds alpha 1PI-proteinase complexes. The results of these studies lay the groundwork for the synthesis of pharmacologically effective r alpha 1PI derivatives with acceptable plasma retention times.