Lipoprotein Receptor Binding, Cellular Uptake, and Lysosomal Delivery of Fusions between the Receptor-associated Protein (RAP) and α-l-Iduronidase or Acid α-Glucosidase

Abstract

Enzyme replacement therapy for lysosomal storage disorders depends on efficient uptake of recombinant enzyme into the tissues of patients. This uptake is mediated by oligosaccharide receptors including the cation-independent mannose 6-phosphate receptor and the mannose receptor. We have sought to exploit alternative receptor systems that are independent of glycosylation but allow for efficient delivery to the lysosome. Fusions of the human lysosomal enzymes ␣-L-iduronidase or acid ␣-glucosidase with the receptor-associated protein were efficiently endocytosed by lysosomal storage disorder patient fibroblasts, rat C6 glioma cells, mouse C2C12 myoblasts, and recombinant Chinese hamster ovary cells expressing individual members of the low-density lipoprotein receptor family. Uptake of the fusions exceeded that of phosphorylated enzyme in all cases, often by an order of magnitude or greater. Uptake was specifically mediated by members of the low-density lipoprotein receptor protein family and was followed by delivery of the fusions to the lysosome. The advantages of the lipoprotein receptor system over oligosaccharide receptor systems include more efficient cellular delivery and the potential for transcytosis of ligands across tight endothelia, including the blood-brain barrier.Enzyme replacement therapy for lysosomal storage disorders relies on the efficient delivery of recombinant enzyme to all of the affected tissues of the patient (1). Uptake of enzyme from the blood following intravenous administration requires specific oligosaccharides on the enzyme itself and corresponding oligosaccharide receptors on target cells. Examples include the binding of phosphorylated high-mannose oligosaccharides on ␣-L-iduronidase by the cation-independent mannose 6-phosphate receptor (MPR) 1 and binding of high-mannose oligosaccharides on glucocerebrosidase by the mannose receptor (2, 3). The former system is the basis for treatment of patients with Hurler syndrome, the latter for Gaucher syndrome. Factors that limit uptake by these systems include the extent to which the recombinant enzyme is modified with the necessary oligosaccharides and the density of the oligosaccharide receptors on different tissues. The absence of quality control mechanisms for oligosaccharide modifications in the secretory pathway can lead to poorly modified recombinant enzymes. This deficiency has been addressed, with varying success, by post-secretory modification of recombinant enzymes with glycosidases or glycosyltransferases (4). Another solution to the problem is to utilize alternative uptake mechanisms that rely on proteinbased, rather than oligosaccharide-based, targeting determinants. Some studies have focused on the use of small, basic peptides, like human immunodeficiency virus TAT, for this purpose (5, 6). Others have demonstrated the feasibility of this approach using insulin-like growth factor-2, a peptide ligand for the MPR (7). The low density lipoprotein receptor (LDLR) family is one of the most widely distributed and intensively utili...

Carbohydrate-remodelled acid α-glucosidase with higher affinity for the cation-independent mannose 6-phosphate receptor demonstrates improved delivery to muscles of Pompe mice

“…Alternative targeting strategies that have been described for lysosomal enzymes include the generation of fusion proteins containing ligands for either the IGF II (insulin-like growth factor II) or the RAP (receptor-associated protein) [48,49]. Although these glycosylation-independent targeting strategies offer some advantages such as ease of production, they also have limitations.…”

Delivery of Acid Sphingomyelinase in Normal and Niemann-Pick Disease Mice Using Intercellular Adhesion Molecule-1-Targeted Polymer Nanocarriers

“…6 and 7) reduces the efficacy of this strategy. Targeting ERTs to specific cell surface determinants (e.g., using chimeric enzymes containing targeting moieties; Xia et al, 2001;LeBowitz et al, 2004;Prince et al, 2004;Zhang et al, 2007) may facilitate delivery to the desired pathological sites.…”

Lysosomes and Nanotherapeutics: Diseases, Treatments, and Side Effects

“…48 Examples of this strategy have shown to improve delivery of β-glucuronidase (MPS type VII), α-L-iduronidase (Hurler syndrome), and α-glucosidase (Pompe disease) through use of insulin-like growth factor II (ILF-II) peptides to target M6P receptors, receptor-associated protein (RAP) that binds to low-density lipoprotein receptors (LDLRs), or others, all of which result in clathrin-dependent endocytosis and lysosomal transport. 34,91,92 Chimeras containing protein transduction domains (e.g. HIV Tat) have also been used in the case of β-glucuronidase (MPS type VII), glucocerebrosidase (Gaucher disease), and galactocerebrosidase (Krabbe disease) to improve charge-mediated binding to the plasmalemma and internalization via passive uptake within endocytic vesicles and/or direct penetration through the plasmalemma.…”