Characterization of a chemically modified plant cell culture expressed human α-Galactosidase-A enzyme for treatment of Fabry disease

Fabry disease is an X-linked recessive disorder caused by the loss of function of the lysosomal enzyme α-Galactosidase-A. Although two enzyme replacement therapies (ERTs) are commercially available, they may not effectively reverse some of the Fabry pathology. PRX-102 is a novel enzyme for the therapy of Fabry disease expressed in a BY2 Tobacco cell culture. PRX-102 is chemically modified, resulting in a cross-linked homo-dimer. We have characterized the in-vitro and in-vivo properties of PRX-102 and compared the results with the two commercially produced α-Galactosidase-A enzymes. Results show that PRX-102 has prolonged in-vitro stability in plasma, after 1h incubation it retains 30% activity compared with complete inactivation of the commercial enzymes. Under lysosomal-like conditions PRX-102 maintains over 80% activity following 10days of incubation, while commercial enzymes become inactive after 2days. Pharmacokinetic profile of PRX-102 measured in male Fabry mice shows a 10 fold increase in t_1/2 in mice (581min) compared to approved drugs. The enzyme has significantly different kinetic parameters to the alternative ERTs available (p-value<0.05, one way ANOVA), although these differences do not indicate any significant biochemical variations. PRX-102 is uptaken to primary human Fabry fibroblasts. The repeat administration of the enzyme to Fabry mice caused significant reduction (p-value<0.05) of Gb₃ in various tissues (the measured residual content was 64% in kidney, liver was cleaned, 23% in heart, 5.7% in skin and 16.2% in spleen). PRX-102 has a relatively simple glycosylation pattern, characteristic to plants, having mainly tri-mannose structures with the addition of either α(1-3)-linked fucose or β(1-2)-linked xylose, or both, in addition to various high mannose structures, while agalsidase beta has a mixture of sialylated glycans in addition to high mannose structures. This study concludes that PRX-102 is equivalent in functionality to the current ERTs available, with superior stability and prolonged circulatory half-life. Therefore we propose that PRX-102 is a promising alternative for treatment of Fabry disease.