Lysosomal storage diseases arise from a genetic loss-of-function defect in enzymes mediating key catabolic steps resulting in accumulation of substrate within the lysosome. Treatment of several of these disorders has been achieved by enzyme replacement therapy (ERT), in which a recombinant version of the defective enzyme is expressed in vitro and administered by infusion. However, in many cases the biodistribution of the administered protein does not match that of the accumulated substrate due to the glycosylation-mediated clearance of the enzymes from circulation, resulting in poor or absent substrate clearance from some tissues. To overcome this limitation, we have evaluated several peptide-based targeting motifs to redirect recombinant human alpha-galactosidase (rhalphaGal) to specific receptors. A reversible thiol-based PEGylation chemistry was developed to achieve multivalent peptide display with lysosomal release. In vitro, cell uptake was peptide dependent and independent of the normal mannose-6-phosphate receptor mediated pathway. Surprisingly, despite increased plasma half-life and decreased liver uptake, none of the peptide conjugates showed significantly altered biodistribution in alphaGal-knockout mice. This suggests that these peptide-based targeting motifs are unlikely to provide substantial therapeutic benefit likely due to the complexity of factors affecting PK and biodistribution.
"New approaches rely on the uptake mechanisms different from the M6P-based using protein-based mechanisms. Recently, a non-carbohydrate targeting platform for lysosomal proteins was evaluated . The authors described that a fusion protein of β-glucuronidase with IGF-II, a high-affinity M6PR ligand, improved the targeting to podocytes in Mucopolysacccharidosis VII, another lysosomal disorder, where the podocyte is the most severely-affected kidney cell-type . "
[Show abstract][Hide abstract] ABSTRACT: Injury to the glomerular podocyte is a key mechanism in human glomerular disease and podocyte repair is an important therapeutic target. In Fabry disease, podocyte injury is caused by the intracellular accumulation of globotriaosylceramide. This study identifies in the human podocyte three endocytic receptors, mannose 6-phosphate/insulin-like growth II receptor, megalin, and sortilin and demonstrates their drug delivery capabilities for enzyme replacement therapy. Sortilin, a novel α-galactosidase A binding protein, reveals a predominant intracellular expression but also surface expression in the podocyte. The present study provides the rationale for the renal effect of treatment with α-galactosidase A and identifies potential pathways for future non-carbohydrate based drug delivery to the kidney podocyte and other potential affected organs.
PLoS ONE 09/2011; 6(9):e25065. DOI:10.1371/journal.pone.0025065 · 3.23 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Abstract A major driver of aging is catabolic insufficiency, the inability of our bodies to break down certain substances that accumulate slowly throughout the life span. Even though substance buildup is harmless while we are young, by old age the accumulations can reach a toxic threshold and cause disease. This includes some of the most prevalent diseases in old age-atherosclerosis and macular degeneration. Atherosclerosis is associated with the buildup of cholesterol and its oxidized derivatives (particularly 7-ketocholesterol) in the artery wall. Age-related macular degeneration is associated with carotenoid lipofuscin, primarily the pyridinium bisretinoid A2E. Medical bioremediation is the concept of reversing the substance accumulations by using enzymes from foreign species to break down the substances into forms that relieve the disease-related effect. We report on an enzyme discovery project to survey the availability of microorganisms and enzymes with these abilities. We found that such microorganisms and enzymes exist. We identified numerous bacteria having the ability to transform cholesterol and 7-ketocholesterol. Most of these species initiate the breakdown by same reaction mechanism as cholesterol oxidase, and we have used this enzyme directly to reduce the toxicity of 7-ketocholesterol, the major toxic oxysterol, to cultured human cells. We also discovered that soil fungi, plants, and some bacteria possess peroxidase and carotenoid cleavage oxygenase enzymes that effectively destroy with varied degrees of efficiency and selectivity the carotenoid lipofuscin found in macular degeneration.
Rejuvenation Research 12/2009; 12(6):411-9. DOI:10.1089/rej.2009.0917 · 3.31 Impact Factor
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