Selective enhancement of thrombopoietic activity of PEGylated interleukin 6 by a simple procedure using a reversible amino-protective reagent

We developed a novel method for the chemical modification of cytokines with synthetic polymers to increase the therapeutic efficacy of the former in v ivo. A pH-reversible amino-protective reagent, dimethylmaleic anhydride (DM MAn), was used for modification of interleukin-6 (IL-6) with polyethylene g lycol (PEG). The novel PEG-conjugated IL-6 (DmPEG-IL-6), which had been pre treated with DMMAn before PEGylation, showed up to a 140% increase in in vi tro specific activity compared with PEG-IL-6 that had been synthesized by t he previous method. Moreover, DmPEG-IL-6 caused thrombopoiesis more potentl y in mice than PEG-IL-6. The DmPEG-IL-6 Fr.1, having 3-4 PEG chains attache d to the cytokine, showed the strongest thrombopoietic effect among the DmP EG-IL-6s with different molecular sizes that were tested. PEG-IL-6 Fr.1 had a 500-fold higher potency in stimulating thrombopoiesis than native IL-6 a nd DmPEG-IL-6 Fr.1 achieved a threefold higher thrombopoietic effect than P EG-IL-6 Fr.1. In addition, side-effects, such as an increase in the plasma fibrinogen level, were not observed after injection of either PEG-IL-6s or DmPEG-IL-6s. These results suggest that PEGylation with DMMAn pretreatment may become a useful means for clinical cytokine delivery.