title: Cyanine dye N744 inhibits tau fibrillization by blocking filament extension: implications for the treatment of tauopathic neurodegenerative diseases.
abstract: Tau fibrillization is a potential therapeutic target for Alzheimer's and other neurodegenerative diseases. Small molecules capable of both inhibiting aggregation and promoting filament disaggregation have been discovered, but knowledge of their mechanism of action and potential for testing in biological models is fragmentary. To clarify these issues, the interaction between a small-molecule inhibitor of tau fibrillization, 3,3'-bis(beta-hydroxyethyl)-9-ethyl-5,5'-dimethoxythiacarbocyanine iodide (N744), and full-length four-repeat tau protein was characterized in vitro using transmission electron microscopy and fluorescence spectroscopy. Analysis of reaction time courses performed in the presence of anionic fibrillization inducers revealed that increasing concentrations of N744 decreased the total filament length without modulating lag time, indicating that filament extension but not nucleation was affected by inhibitor under the conditions that were investigated. Critical concentration measurements confirmed that N744 shifted equilibria at filament ends away from the fibrillized state, resulting in endwise filament disaggregation when it was added to synthetic filaments. Both increasing bulk tau concentrations and filament stabilizing modifications such as pseudophosphorylation and glycation antagonized N744 activity. The results illustrate the importance of mechanism for the design and interpretation of pharmacological studies in biological models of tau aggregation.
authors.affiliation: Biophysics Program, The Ohio State University College of Medicine, Columbus, Ohio 43210, USA.
authors.forename: Mihaela
authors.initials: M
authors.lastname: Necula
authors.forename: Carmen N
authors.initials: CN
authors.lastname: Chirita
authors.forename: Jeff
authors.initials: J
authors.lastname: Kuret
mesh_terms: D052160:Benzothiazoles; D001667:Binding, Competitive; D002232:Carbocyanines / Q000737:chemistry* / Q000378:metabolism / Q000494:pharmacology; D006801:Humans; D007700:Kinetics; D008956:Models, Chemical; D009419:Nerve Tissue Proteins / Q000037:antagonists & inhibitors* / Q000378:metabolism*; D011499:Protein Processing, Post-Translational; D012995:Solubility; D024801:Tauopathies / Q000188:drug therapy* / Q000378:metabolism*; D013844:Thiazoles / Q000737:chemistry* / Q000378:metabolism / Q000494:pharmacology; D016875:tau Proteins
chemical_list: C487610:3-(2-hydroxyethyl)-2-(2-((3-(2-hydroxyethyl)-5-methoxy-2-benzothiazolylidene)methyl)-1-butenyl)-5-methoxybenzothiazolium; D052160:Benzothiazoles; D002232:Carbocyanines; C054369:MAPT protein, human; D009419:Nerve Tissue Proteins; D013844:Thiazoles; C505137:cyanine dye N744; D016875:tau Proteins; C009462:thioflavin T