Many injectable drugs require delivery strategies for enhancing their
pharmacokinetics due to rapid loss via renal filtration if possess low molecular weight (<60-70 kDa) and/or clearance by the body‟s components (e.g., proteases, antibodies, high-efficiency receptors) in their native form. FDA-approved polyethylene glycol [PEG] is a vehicle for improving therapeutics, but artificial polymers have potential biocompatibility and immunogenicity liabilities. Here we utilized a natural vertebrate carbohydrate, heparosan [HEP], the biosynthetic precursor of heparan sulfate and heparin, to enhance performance of a biologic drug. The heparosan polysaccharide was stable with a long half-life (~8 days for 99-kDa chain) in the non-human primate bloodstream, but was efficiently degraded to very short oligosaccharides when internalized by cells, and then excreted into urine and feces. Several heparosanmodified
human granulocyte-colony stimulating factor [G-CSF] conjugates were
synthesized with defined quasi-monodisperse HEP polysaccharide chains. Single
dosing of 55- or 99-kDa HEP-G-CSF in rats increased blood neutrophil levels
comparable to PEG-G-CSF conjugates. Repeated dosing of HEP-G-CSF or heparosan alone for 2 weeks did not cause heparosan-specific toxic effects in rats. Heparosan did not possess the anticoagulant behavior of its daughter, heparin, based on testing in rats or clinical diagnostic assays with human plasma. Neither anti-heparosan IgG nor IgM antibodies were detected in a long-term (9 doses over 7 months) immunogenicity study of the HEP-drug conjugate with rats. These proof-of-concept experiments with HEP-GCSF indicate that it is a valid drug candidate for neutropenia and suggest the potential of this HEP-based platform as a safe alternative delivery vehicle for other therapeutics.