Iodine Atoms: A New Molecular Feature for the Design of Potent Transthyretin Fibrillogenesis Inhibitors (original) (raw)
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Biochemical Journal, 2005
Ex vivo and in vitro studies have revealed the remarkable amyloid inhibitory potency and specificity of iododiflunisal in relation to transthyretin [Almeida, Macedo, Cardoso, Alves, Valencia, Arsequell, Planas and Saraiva (2004) Biochem. J. 381, 351–356], a protein implicated in familial amyloidotic polyneuropathy. In the present paper, the crystal structure of transthyretin complexed with this diflunisal derivative is reported, which enables a detailed analysis of the protein–ligand interactions. Iododiflunisal binds very deep in the hormone-binding channel. The iodine substituent is tightly anchored into a pocket of the binding site and the fluorine atoms provide extra hydrophobic contacts with the protein. The carboxylate substituent is involved in an electrostatic interaction with the Nζ of a lysine residue. Moreover, ligand-induced conformational alterations in the side chain of some residues result in the formation of new intersubunit hydrogen bonds. All these new interactions...
PLoS ONE, 2009
Transthyretin (TTR) is one of thirty non-homologous proteins whose misfolding, dissociation, aggregation, and deposition is linked to human amyloid diseases. Previous studies have identified that TTR amyloidogenesis can be inhibited through stabilization of the native tetramer state by small molecule binding to the thyroid hormone sites of TTR. We have evaluated a new series of b-aminoxypropionic acids (compounds 5-21), with a single aromatic moiety (aryl or fluorenyl) linked through a flexible oxime tether to a carboxylic acid. These compounds are structurally distinct from the native ligand thyroxine and typical halogenated biaryl NSAID-like inhibitors to avoid off-target hormonal or anti-inflammatory activity. Based on an in vitro fibril formation assay, five of these compounds showed significant inhibition of TTR amyloidogenesis, with two fluorenyl compounds displaying inhibitor efficacy comparable to the well-known TTR inhibitor diflunisal. Fluorenyl 15 is the most potent compound in this series and importantly does not show off-target anti-inflammatory activity. Crystal structures of the TTR:inhibitor complexes, in agreement with molecular docking studies, revealed that the aromatic moiety, linked to the sp 2 -hybridized oxime carbon, specifically directed the ligand in either a forward or reverse binding mode. Compared to the aryl family members, the bulkier fluorenyl analogs achieved more extensive interactions with the binding pockets of TTR and demonstrated better inhibitory activity in the fibril formation assay. Preliminary optimization efforts are described that focused on replacement of the C-terminal acid in both the aryl and fluorenyl series (compounds 22-32). The compounds presented here constitute a new class of TTR inhibitors that may hold promise in treating amyloid diseases associated with TTR misfolding. (JCS) . These authors contributed equally to this work.
Biochemical …, 2004
In familial amyloidotic polyneuropathy, TTR (transthyretin) variants are deposited as amyloid fibrils. It is thought that this process involves TTR tetramer dissociation, which leads to partially unfolded monomers that aggregate and polymerize into amyloid fibrils. This process can be counteracted by stabilization of the tetramer. Several small compounds, such as diclofenac, diflunisal and flufenamic acid, have been reported to bind to TTR in vitro, in the T 4 (thyroxine) binding channel that runs through the TTR tetramer, and consequently are considered to stabilize TTR. However, if these agents bind plasma proteins other than TTR, decreased drug availability will occur, compromising their use as therapeutic agents for TTR amyloidosis. In the present work, we compared the action of these compounds and of new derivatives designed to increase both selectivity of binding to TTR and inhibitory potency in relation to TTR amyloid fibril formation. We found two diflunisal derivatives that, in contrast with diclofenac, flufenamic acid and diflunisal, displaced T 4 from TTR in plasma preferentially over binding to albumin and thyroxine binding globulin. The same diflunisal derivatives also had a stabilizing effect on TTR tetramers in plasma, as studied by isoelectric focusing of whole plasma under semi-denaturing conditions. In addition, by transmission electron microscopy, we demonstrated that, in contrast with other proposed TTR stabilizers (namely diclofenac, flufenamic acid and diflunisal), one of the diflunisal derivatives tested efficiently inhibited TTR aggregation. Taken together, our ex vivo and in vitro studies present evidence for the selectivity and efficiency of novel diflunisal derivates as TTR stabilizers and as inhibitors of fibril formation.
Journal of Enzyme Inhibition and Medicinal Chemistry, 2016
Transthyretin (TTR), a b-sheet-rich tetrameric protein, in equilibrium with an unstable amyloidogenic monomeric form is responsible for extracellular deposition of amyloid fibrils, is associated with the onset of neurodegenerative diseases, such as senile systemic amyloidosis, familial amyloid polyneuropathy and familial amyloid cardiomyopathy. One of the therapeutic strategies is to use small molecules to stabilize the TTR tetramer and thus curb amyloid fibril formation. Here, we report the synthesis, the in vitro evaluation of several halogen substituted 9-fluorenyl-and di-benzophenon-based ligands and their three-dimensional crystallographic analysis in complex with TTR. The synthesized compounds bind TTR and stabilize the tetramer with different potency. Of these compounds, 2c is the best inhibitor. The dual binding mode prevalent in the absence of substitutions on the fluorenyl ring, is disfavored by (2,7-dichlorofluoren-9-ylideneaminooxy)-acetic acid (1b), (2,7-dibromo-fluoren-9-ylideneaminooxy)-acetic acid (1c) and (E/Z)-((3,4-dichloro-phenyl)-methyleneaminooxy)-acetic acid (2c), all with halogen substitutions.
Journal of the American Chemical Society, 2010
Transthyretin aggregation-associated proteotoxicity appears to cause several human amyloid diseases. Rate-limiting tetramer dissociation and monomer misfolding of transthyretin (TTR) occur before its aggregation into cross-β-sheet amyloid fibrils. Small molecule binding to and preferential stabilization of the tetrameric state of TTR over the dissociative transition state raises the kinetic barrier for dissociation, imposing kinetic stabilization on TTR and preventing aggregation. This is an effective strategy to halt neurodegeneration associated with polyneuropathy, according to recent placebo-controlled clinical trial results. In three recent papers, we systematically ranked possibilities for the three substructures composing a typical TTR kinetic stabilizer, using fibril inhibition potency and plasma TTR binding selectivity data. Herein, we have successfully employed a substructure combination strategy to use these data to develop potent and selective TTR kinetic stabilizers that rescue cells from the cytotoxic effects of TTR amyloidogenesis. Of the 92 stilbene and dihydrostilbene analogues synthesized, nearly all potently inhibit TTR fibril formation. Seventeen of these exhibit a binding stoichiometry of > 1.5 of a maximum of 2 to plasma TTR, while displaying minimal binding to the thyroid hormone receptor (< 20%). Six analogues were definitively categorized as kinetic stabilizers by evaluating dissociation time-courses. High resolution TTR• (kinetic stabilizer) 2 crystal structures (1.31-1.70 Å) confirmed the anticipated binding orientation of the 3,5-dibromo-4-hydroxyphenyl substructure and revealed a strong preference of the isosteric 3,5dibromo-4-aminophenyl substructure to bind to the inner thyroxine binding pocket.
Inhibiting transthyretin amyloid fibril formation via protein stabilization
Proceedings of the National Academy of Sciences, 1996
Transthyretin (TTR) amyloid fibril formation is observed systemically in familial amyloid polyneuropathy and senile systemic amyloidosis and appears to be the causative agent in these diseases. Herein, we demonstrate conclusively that thyroxine (10.8 M) inhibits TTR fibril formation efficiently in vitro and does so by stabilizing the tetramer against dissociation and the subsequent conformational changes required for amyloid fibril formation. In addition, the nonnative ligand 2,4,6-triiodophenol, which binds to TTR with slightly increased affinity also inhibits TTR fibril formation by this mechanism. Sedimentation velocity experiments were employed to show that TTR undergoes dissociation (linked to a conformational change) to form the monomeric amyloidogenic intermediate, which self-assembles into amyloid in the absence, but not in the presence of thyroxine. These results demonstrate the feasibility of using small molecules to stabilize the native fold of a potentially amyloidogenic human protein, thus preventing the conformational changes, which appear to be the common link in several human amyloid diseases. This strategy and the compounds resulting from further development should prove useful for critically evaluating the amyloid hypothesis-i.e., the putative cause-and-effect relationship between TTR amyloid deposition and the onset of familial amyloid polyneuropathy and senile systemic amyloidosis.
FEBS Letters, 2013
a b s t r a c t Several classes of chemicals are able to bind to the thyroxine binding sites of transthyretin (TTR), stabilizing its native state and inhibiting in vitro the amyloidogenic process. The amyloidogenic I84S TTR variant undergoes a large conformational change at moderately acidic pH. Structural evidence has been obtained by X-ray analysis for the native state stabilization of I84S TTR by two chemically distinct fibrillogenesis inhibitors. In fact, they fully prevent the acidic pH-induced protein conformational change as a result of a long-range stabilizing effect. This study provides further support to the therapeutic strategy based on the use of TTR stabilizers as anti-amyloidogenic drugs.
ACS Combinatorial Science, 2015
Two series of iododiflunisal and diflunisal analogues have been obtained by using a two step sequential reaction solution-phase parallel synthesis. The synthesis combined an aqueous Suzuki-Miyaura cross-coupling and a mild electrophilic aromatic iodination step using a new polymersupported iodonium version of Barluenga's reagent. From a selected set of 77 noniodinated and 77 iodinated diflunisal analogues, a subset of good transthyretin amyloid inhibitors has been obtained with improved turbidimetry inhibition constants, high binding affinity to transthyretin, and good selectivity for TTR compared to other thyroxine binding proteins.
Inhibiting transthyretin conformational changes that lead to amyloid fibril formation
Proceedings of the National Academy of Sciences of the United States of America, 1998
Insoluble protein fibrils resulting from the self-assembly of a conformational intermediate are implicated as the causative agent in several severe human amyloid diseases, including Alzheimer's disease, familial amyloid polyneuropathy, and senile systemic amyloidosis. The latter two diseases are associated with transthyretin (TTR) amyloid fibrils, which appear to form in the acidic partial denaturing environment of the lysosome. Here we demonstrate that flufenamic acid (Flu) inhibits the conformational changes of TTR associated with amyloid fibril formation. The crystal structure of TTR complexed with Flu demonstrates that Flu mediates intersubunit hydrophobic interactions and intersubunit hydrogen bonds that stabilize the normal tetrameric fold of TTR. A small-molecule inhibitor that stabilizes the normal conformation of a protein is desirable as a possible approach to treat amyloid diseases. Molecules such as Flu also provide the means to rigorously test the amyloid hypothesis...
Journal of Combinatorial Chemistry, 2005
Stabilization of tetrameric transthyretin (TTR) by binding of small ligands is a current strategy aimed at inhibiting amyloid fibrillogenesis in transthyretin-associated pathologies, such as senile systemic amyloidosis (SSA) and familial amyloidotic polyneuropathy (FAP). A kinetic assay is developed for rapid evaluation of compounds as potential in vitro inhibitors in a high-throughput screening format. It is based on monitoring the time-dependent increase of absorbance due to turbidity occurring by acid-induced protein aggregation. The method uses the highly amyloidogenic Y78F mutant of human transthyretin (heterogously expressed in Escherichia coli cells). Initial rates of protein aggregation at different inhibitor concentrations follow a monoexponential dose-response curve from which inhibition parameters are calculated. For the assay development, thyroid hormones and nonsteroidal antiinflamatory drugs were chosen among other reference compounds. Some of them are already known to be in vitro inhibitors of TTR amyloidogenesis. Analysis time is optimized to last 1.5 h, and the method is implemented in microtiter plates for screening of libraries of potential fibrillogenesis inhibitors.