Transglutaminase-Mediated Dual and Site-Specific Incorporation of Poly(ethylene glycol) Derivatives into a Chimeric Interleukin-2

To expand the applications of poly(ethylene glycol) (PEG)-protein conjugates for clinical use, we have developed a novel method for dual and site-specific incorporations of PEG derivatives into proteins using a substrate peptide (AQQIVM, named TG2) and transglutaminase (TGase). In our previous studies, TG2 was shown to be a special peptide with two adjacent Gln substrates for guinea pig liver transglutaminase (G-TGase). We have now constructed a chimeric protein (named rTG2-IL-2) of human interleukin-2 (IL-2), in which TG2 was fused to the N-terminus of IL-2. For the G-TGase-catalyzed reaction, rTG2-IL-2 was dually and site-specifically modified with alkylamine derivatives of PEG (PEG10, average M(r) 10 kDa) at both the Gln2 and Gln3 residues in the appended tag. To demonstrate the effectiveness of the G-TGase-catalyzed PEG-incorporation, we have compared the characteristics and the biological properties of PEG10-rTG2-IL-2 species with two PEG10 molecules attached to rTG2-IL-2 [(PEG10)(2)-rTG2-IL-2] with that of (PEG10)(2)-rhIL-2(R), in which PEG10 was randomly incorporated into rhIL-2 by a general procedure using a N-hydroxysuccinimidyl ester of PEG (PEG10-COOSu) (M(r) 10 kDa). (PEG10)(2)-rTG2-IL-2 was found to be superior in its in vitro bioactivities and equivalent in its pharmacokinetic profiles to (PEG10)(2)-rhIL-2(R). Unlike most previous methods, this approach can place dual PEG chains at designed sites on chimeric proteins without decreasing their bioactivities. Thus, TGase-catalyzed PEG-incorporation would improve the therapeutic utility of PEG-protein conjugates.