Enzyme replacement therapy using a modified α-N-acetylgalactosaminidase to suppress progressive glycolipid accumulation and escape from antidrug antibody formation in young human NAGA-transgenic/Gla-knockout mice

Enzyme replacement therapy (ERT) using recombinant human α-galactosidase A (AGAL) is a standard therapy for Fabry disease. However, systemic reviews have reported that recurrent injection of the enzyme can induce the formation of harmful antidrug antibodies (ADAs) in male patients with Fabry disease. Unfortunately, to date no recommended ERT drugs facilitating escape from ADA formation have yet been established. Accordingly, we focused on α-N-acetylgalactosaminidase (NAGA), which has a protein structure that is similar to that of AGAL. Previously, we had prepared a modified NAGA (p. S188E and p. A191L) and determined the biochemical properties of the new enzyme. In this study we verified the efficacy of the modified NAGA, both in silico and via cell and animal experiments. The molecular dynamics simulation results suggested that the enzyme has an affinity for α-D-galactose (α-Gal) as a ligand. Moreover, these results also suggested that the modified NAGA may hydrolyze the terminal α-Gal moieties of glycoconjugates. The cell experiments revealed that the modified NAGA incorporated into cultured Fabry fibroblasts was more stable than recombinant human AGAL, despite the specific enzyme activity of the former being lower than that of the latter. Additional animal experiments revealed that human NAGA-transgenic/Gla-knockout mice were tolerant of recurrent administration of the modified NAGA, and that the modified NAGA notably did not induce the formation of ADAs. Moreover, the enzyme also suppressed the progressive accumulation of globotriaosylceramide and globotriaosylsphingosine in organs/tissues, thereby improving morphological changes in young mice. Overall, these findings suggest that the modified NAGA is a promising ERT drug candidate for patients with Fabry disease, especially for those who are likely to produce anti-AGAL antibodies.