Enzyme replacement therapy – a brief history

Excerpt

The concept of enzyme replacement therapy for lysosomal storage diseases was enunciated by de Duve in 1964. However, much cell biology had to be learned before lysosomal enzymes could be developed into pharmaceuticals. A model system, consisting of cultured skin fibroblasts from patients with mucopolysaccharidoses (MPS), showed that their defective glycosaminoglycan catabolism could be corrected by factors derived from cells of a different genotype. The corrective factors were identified as lysosomal enzymes with a special feature, or recognition signal, that would permit efficient uptake. As the recognition signal was absent from a number of lysosomal enzymes secreted by fibroblasts from patients with I-cell disease (a monogenic disorder), it was postulated to be a post-translational modification of the lysosomal enzymes. It was subsequently shown to be a carbohydrate and identified as mannose-6-phosphate (M6P), which was recognized by ubiquitous M6P receptors. A second model system was the clearance, in vivo, of lysosomal enzymes from plasma. The recognition signal for this system was identified as mannose, and clearance was shown to be mediated by the mannose receptor of the reticuloendothelial system. This second system was immediately put to use for the treatment of Gaucher disease type I, in which macrophages are the affected cells. Native, and later recombinant, glucocerebrosidase was modified to expose terminal mannose residues; it became the first successful pharmaceutical for a lysosomal storage disease. Recombinant lysosomal enzymes containing the M6P signal have been developed (or are in the advanced stages of development) into pharmaceuticals for the treatment of Fabry disease, MPS I, MPS II, MPS VI and Pompe disease.