Refolding and purification of cGMP-grade recombinant human neurturin from Escherichia coli inclusion bodies

Neurturin is a potent neurotrophic factor that has been investigated as a potential therapeutic agent for the treatment of neurodegenerative diseases, including Parkinson's disease, and, more recently, for the treatment of type II diabetes. However, purification of Neurturin for clinical applications has been hampered by its low solubility in aqueous solutions. Here we describe the development of a scalable manufacturing process for recombinant Neurturin from E. coli. inclusion bodies. Neurturin was refolded from solubilized inclusion bodies by fed-batch dilution refolding with a titer of 90 mg per liter refold and a refold yield of 89%. A two-step purification process using cation exchange and hydrophobic interaction chromatography, followed by formulation using tangential flow filtration resulted in an overall process yield of about 56 mg purified Neurturin per liter refold. Solubility of Neurturin during the purification process was maintained by the addition of 15% (w/v) glycerol to all buffers. For clinical applications and parenteral administration glycerol was replaced by 15% (w/v) sulfobutyl ether-beta-cyclodextrin (i.e. Captisol) in the drug substance formulation buffer. The final purified product had low or undetectable levels of product-related impurities and concentrations of process-related contaminants such as host cell proteins, host cell DNA, endotoxins and Triton X-100 were reduced more than 10,000-fold or below the limit of detection. Bioactivity of purified recombinant Neurturin was demonstrated in a cell-based assay by activation of the MAPK signaling pathway.