Poly(L-glutamic acid)-co-poly(ethylene glycol) block copolymers for protein conjugation

Poly(L-glutamic acid)-co-poly(ethylene glycol) block copolymers (PLE-PEG) are here investigated as polymers for conjugation to therapeutic proteins such as granulocyte colony stimulating factor (G-CSF) and human growth hormone (hGH). PLE-PEG block copolymers are able to stabilize and protect proteins from degradation and to prolong their residence time in the blood stream, features that are made possible thanks to PEG's intrinsic properties and the simultaneous presence of the biodegradable anionic PLE moiety. When PLE-PEG copolymers are selectively tethered to the N-terminus of G-CSF and hGH, they yield homogeneous monoconjugates that preserve the protein's secondary structure. During the current study the pharmacokinetics of PLE₁₀-PEG_20k-G-CSF and PLE₂₀-PEG_20k-G-CSF derivatives and their ability to induce granulopoiesis were, respectively, assessed in Sprague-Dawley rats and in C57BL6 mice. Our results show that the bioavailability and bioactivity of the derivatives are comparable to or better than those of PEG_20k-Nter-G-CSF (commercially known as Pegfilgrastim). The therapeutic effects of PLE₁₀-PEG_20k-hGH and PLE₂₀-PEG_20k-hGH derivatives tested in hypophysectomized rats demonstrate that the presence of a negatively charged PLE block enhances the biological properties of the conjugates additionally with respect to PEG_20k-Nter-hGH.