Authors: Kristen Skvorak, Nick Agard, Chinping Chng, Nikki Dellas, William Hallows, Matt Miller, Jinsong Shen, Judy Viduya, Xiyun Zhang, Cynthia Zhu, Raphael Schiffmann, and Gjalt Huisman
Inborn errors of metabolism (IEM) are inherited disorders characterized by single gene defects that lead to impairment of metabolic pathways and the accumulation of toxic substrates. For some of these disorders, enzyme replacement therapy (ERT) is available. However, issues that commonly compromise the efficacy of ERTs are short in vivo half-life and the development of antidrug antibodies. This limits efficacy of treatment, and may cause side-effects. Therefore, development of ERTs with enhanced stability and reduced immunogenicity would be beneficial. To establish proof of concept, we engineered α-galactosidase A (GLA) for such properties as a potentially more effective treatment of Fabry disease. Intravenously administered ERTs for treatment of Fabry disease are known to have a short in vivo half-life and induce an immune response in patients. Applying CodeEvolver® protein engineering technology, we looked to improve stability of the enzyme to the conditions in serum and in the lysosome, as well as reduce the predicted immunogenicity of the enzyme. Over eight rounds of enzyme optimization and screening of more than 12,000 variants, new GLA enzymes were discovered that met our objectives of improved stability in both serum and the lysosome while retaining full activity. These improved properties were obtained with the introduction of ~12 mutations. Another 10 mutations removed all predicted immunogenic epitopes. In a mouse model of Fabry disease, such GLA variants showed prolonged half-life in both the serum and lysosome.