Conjugation of high-molecular weight poly(ethylene glycol) to cytokines: Granulocyte-macrophage colony-stimulating factors as model substrates

The ability of the small receptor-binding protein, recombinant murine granulocyte-macrophage colony-stimulating factor (GM-CSF), to increase the abundance of certain blood cell types in mice was enhanced markedly by covalent attachment of a single long strand of PEG (30-40 kDa). Potency was not increased further by coupling a second strand. Such conjugates can be synthesized efficiently by reaction of protein amino groups with PEG propionaldehydes in the presence of NaBH(3)CN or with PEG p-nitrophenyl carbonates. Both methods have been used to prepare recombinant human GM-CSF conjugates of predetermined composition, e.g. PEG(1)GM-CSF and PEG(2)GM-CSF, in high yield. These compounds, or analogous derivatives of other cytokines, purified by ion-exchange and size-exclusion chromatography, may be suitable candidates for pharmaceutical development.