title: Pyrimethamine as a potential pharmacological chaperone for late-onset forms of GM2 gangliosidosis.
abstract: Late-onset GM2 gangliosidosis is composed of two related, autosomal recessive, neurodegenerative diseases, both resulting from deficiency of lysosomal, heterodimeric beta-hexosaminidase A (Hex A, alphabeta). Pharmacological chaperones (PC) are small molecules that can stabilize the conformation of a mutant protein, allowing it to pass the quality control system of the endoplasmic reticulum. To date all successful PCs have also been competitive inhibitors. Screening for Hex A inhibitors in a library of 1040 Food Drug Administration-approved compounds identified pyrimethamine (PYR (2,4-diamino 5-(4-chlorophenyl)-6-ethylpyrimidine)) as the most potent inhibitor. Cell lines from 10 late-onset Tay-Sachs (11 alpha-mutations, 2 novel) and 7 Sandhoff (9 beta-mutations, 4 novel) disease patients, were cultured with PYR at concentrations corresponding to therapeutic doses. Cells carrying the most common late-onset mutation, alphaG269S, showed significant increases in residual Hex A activity, as did all 7 of the beta-mutants tested. Cells responding to PC treatment included those carrying mutants resulting in reduced Hex heat stability and partial splice junction mutations of the inherently less stable alpha-subunit. PYR, which binds to the active site in domain II, was able to function as PC even to domain I beta-mutants. We concluded that PYR functions as a mutation-specific PC, variably enhancing residual lysosomal Hex A levels in late-onset GM2 gangliosidosis patient cells.
authors.affiliation: Division of Clinical and Metabolic Genetics, Department of Pediatrics, Hospital for Sick Children, Toronto, Ontario M5G 1X8, Canada.
authors.forename: Gustavo H B
authors.initials: GH
authors.lastname: Maegawa
authors.forename: Michael
authors.initials: M
authors.lastname: Tropak
authors.forename: Justin
authors.initials: J
authors.lastname: Buttner
authors.forename: Tracy
authors.initials: T
authors.lastname: Stockley
authors.forename: Fernando
authors.initials: F
authors.lastname: Kok
authors.forename: Joe T R
authors.initials: JT
authors.lastname: Clarke
authors.forename: Don J
authors.initials: DJ
authors.lastname: Mahuran
mesh_terms: D019281:Dimerization; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005347:Fibroblasts / Q000378:metabolism; D005493:Folic Acid Antagonists / Q000494:pharmacology; D020143:Gangliosidoses, GM2 / Q000188:drug therapy* / Q000378:metabolism*; D054818:Hexosaminidase A; D006801:Humans; D008247:Lysosomes / Q000378:metabolism; D008958:Models, Molecular; D018832:Molecular Chaperones; D009154:Mutation; D020125:Mutation, Missense; D017510:Protein Folding; D011739:Pyrimethamine / Q000494:pharmacology*; D001619:beta-N-Acetylhexosaminidases / Q000037:antagonists & inhibitors
chemical_list: D004791:Enzyme Inhibitors; D005493:Folic Acid Antagonists; D018832:Molecular Chaperones; D054818:Hexosaminidase A; D001619:beta-N-Acetylhexosaminidases; D011739:Pyrimethamine