title: Biochemical characterization of fluorescent-labeled recombinant human alpha-L-iduronidase in vitro.
abstract: In vivo tracking of the delivery of therapeutic proteins is a useful tool for preclinical studies. However, many labels are too large to use without disrupting the normal uptake, function, or other properties of the protein. Low-molecular-weight fluorescent labels allow in vivo and ex vivo tracking of the distribution of therapeutic proteins, and should not alter the protein's characteristics. We tested the in vitro properties of fluorescent-labeled recombinant human alpha-l-iduronidase (rhIDU, the enzyme deficient in Hurler syndrome) and compared labeled to unlabeled proteins. Labeled rhIDU retained full enzymatic activity and showed similar kinetics to nonlabeled rhIDU. Uptake of labeled rhIDU into human Hurler fibroblasts, measured by activity assay, was equivalent to unlabeled rhIDU enzyme and showed an uptake constant of 0.72 nM. Labeled rhIDU was also able to enter cells via the mannose 6-phospate receptor pathway and reduce glycosaminoglycan storage in Hurler fibroblasts. Subcellular localization was verified within lysosomes by confocal microscopy. These findings suggest that fluorescent labeling does not significantly interfere with enzymatic activity, stability, or uptake, and validates this method as a way to track exogenously administered enzyme.
authors.affiliation: Division of Medical Genetics, Los Angeles Biomedical Research Institute at Harbor-UCLA Medical Center, Torrance, CA 90502, USA.
authors.forename: Brigette L
authors.initials: BL
authors.lastname: Tippin
authors.forename: Larisa
authors.initials: L
authors.lastname: Troitskaya
authors.forename: Shih-hsin
authors.initials: SH
authors.lastname: Kan
authors.forename: Amanda K
authors.initials: AK
authors.lastname: Todd
authors.forename: Steven Q
authors.initials: SQ
authors.lastname: Le
authors.forename: Patricia I
authors.initials: PI
authors.lastname: Dickson
mesh_terms: D002478:Cells, Cultured; D005347:Fibroblasts / Q000378:metabolism; D005456:Fluorescent Dyes / Q000737:chemistry; D006025:Glycosaminoglycans / Q000378:metabolism; D006801:Humans; D007068:Iduronidase / Q000032:analysis* / Q000737:chemistry / Q000378:metabolism*; D008247:Lysosomes / Q000201:enzymology*; D008970:Molecular Weight; D008059:Mucopolysaccharidosis I / Q000201:enzymology; D017527:Receptor, IGF Type 2 / Q000378:metabolism; D011994:Recombinant Proteins / Q000032:analysis / Q000737:chemistry / Q000378:metabolism
chemical_list: D005456:Fluorescent Dyes; D006025:Glycosaminoglycans; D017527:Receptor, IGF Type 2; D011994:Recombinant Proteins; D007068:Iduronidase