Design, synthesis, and evaluation of oxazole transthyretin amyloidogenesis inhibitors

Drug Discovery and Development in Rare Diseases: Taking a Closer Look at the Tafamidis Story

Rare diseases are increasingly recognized as a global public health priority. Governments worldwide currently provide important incentives to stimulate the discovery and development of orphan drugs for the treatment of these conditions, but substantial scientific, clinical, and regulatory challenges remain. Tafamidis is a first-in-class, disease-modifying transthyretin (TTR) kinetic stabilizer that represents a major breakthrough in the treatment of transthyretin amyloidosis (ATTR amyloidosis). ATTR amyloidosis is a rare, progressive, and fatal systemic disorder caused by aggregation of misfolded TTR and extracellular deposition of amyloid fibrils in various tissues and organs, including the heart and nervous systems. In this review, we present the successful development of tafamidis spanning 3 decades, marked by meticulous laboratory research into disease mechanisms and natural history, and innovative clinical study design and implementation. These efforts established the safety and efficacy profile of tafamidis, leading to its regulatory approval, and enabled post-approval initiatives that further support patients with ATTR amyloidosis.

Review on the Structures and Activities of Transthyretin Amyloidogenesis Inhibitors

Transthyretin (TTR) is a tetrameric protein, and its dissociation, aggregation, deposition, and misfolding are linked to several human amyloid diseases. As the main transporter for thyroxine (T4) in plasma and cerebrospinal fluid, TTR contains two T4-binding sites, which are docked with T4 and subsequently maintain the structural stability of TTR homotetramer. Affected by genetic disorders and detrimental environmental factors, TTR degrades to monomer and/or form amyloid fibrils. Reasonably, stabilization of TTR might be an efficient strategy for the treatment of TTR-related amyloidosis. However, only 10-25% of T4 in the plasma is bound to TTR under physiological conditions. Expectedly, T4 analogs with different structures aiming to bind to T4 pockets may displace the functions of T4. So far, a number of compounds including both natural and synthetic origin have been reported. In this paper, we summarized the potent inhibitors, including bisaryl structure-based compounds, flavonoids, crown ethers, and carboranes, for treating TTR-related amyloid diseases and the combination modes of some compounds binding to TTR protein.

The Binding of BF-227-Like Benzoxazoles to Human α-Synuclein and Amyloid β Peptide Fibrils

Development of an α-synuclein (α-Syn) positron emission tomography agent for the diagnosis and evaluation of Parkinson disease therapy is a key goal of neurodegenerative disease research. BF-227 has been described as an α-Syn binder and hence was employed as a lead to generate a library of α-Syn-binding compounds. [³H]BF-227 bound to α-Syn and amyloid β peptide (Aβ) fibrils with affinities (K_D) of 46.0 nM and 15.7 nM, respectively. Affinities of BF-227-like compounds (expressed as K_i) for α-Syn and Aβ fibrils were determined, along with 5 reference compounds (flutafuranol, flutemetamol, florbetapir, BF-227, and PiB). Selectivity for α-Syn binding, defined as the K_i(Aβ)/K_i(α-Syn) ratio, was 0.23 for BF-227. A similar or lower ratio was measured for analogues decorated with alkyl or oxyethylene chains attached to the oxygen at the 6 position of BF-227, suggesting a lack of involvement of the side chain in fibril binding. BF-227-like iodobenzoxazoles had lower affinities and poor α-Syn selectivity. However, BF-227-like fluorobenzoxazoles had improved α-Syn selectively having K_i(Aβ)/K_i(α-Syn) ranging from 2.2 to 5.1 with appreciable fibril affinity, although not sufficient to warrant further investigation. Compounds based on fluorobenzoxazoles might offer an approach to obtaining an α-Syn imaging agent with an appropriate affinity and selectivity.

A comprehensive review on biological activities of oxazole derivatives

The utility of oxazole as intermediates for the synthesis of new chemical entities in medicinal chemistry have been increased in the past few years. Oxazole is an important heterocyclic nucleus having a wide spectrum of biological activities which drew the attention of researchers round the globe to synthesize various oxazole derivatives and screen them for their various biological activities. The present review article aims to review the work reported on therapeutic potentials of oxazole scaffolds which are valuable for medical applications during new millennium.

Design, synthesis and biological evaluation of 3-(2-aminooxazol-5-yl)-2H-chromen-2-one derivatives

BACKGROUND

In view of wide range of biological activities of oxazole, a new series of oxazole analogues was synthesized and its chemical structures were confirmed by spectral data (Proton/Carbon-NMR, IR, MS etc.). The synthesized oxazole derivatives were screened for their antimicrobial and antiproliferative activities.

RESULTS AND DISCUSSION

The antimicrobial activity was performed against selected fungal and bacterial strains using tube dilution method. The antiproliferative potential was evaluated against human colorectal carcinoma (HCT116) and oestrogen- positive human breast carcinoma (MCF7) cancer cell lines using Sulforhodamine B assay and, results were compared to standard drugs, 5-fluorouracil and tamoxifen, respectively.

CONCLUSION

The performed antimicrobial activity indicated that compounds 3, 5, 6, 8 and 14 showed promising activity against selected microbial species. Antiproliferative screening found compound 14 to be the most potent compound against HCT116 (IC₅₀ = 71.8 µM), whereas Compound 6 was the most potent against MCF7 (IC₅₀ = 74.1 µM). Further, the molecular docking study has been carried to find out the interaction between active oxazole compounds with CDK8 (HCT116) and ER-α (MCF7) proteins indicated that compound 14 and 6 showed good dock score with better potency within the ATP binding pocket and may be used as a lead for rational drug designing of the anticancer molecule.

Semi-quantitative models for identifying potent and selective transthyretin amyloidogenesis inhibitors

Rate-limiting dissociation of the tetrameric protein transthyretin (TTR), followed by monomer misfolding and misassembly, appears to cause degenerative diseases in humans known as the transthyretin amyloidoses, based on human genetic, biochemical and pharmacologic evidence. Small molecules that bind to the generally unoccupied thyroxine binding pockets in the native TTR tetramer kinetically stabilize the tetramer, slowing subunit dissociation proportional to the extent that the molecules stabilize the native state over the dissociative transition state-thereby inhibiting amyloidogenesis. Herein, we use previously reported structure-activity relationship data to develop two semi-quantitative algorithms for identifying the structures of potent and selective transthyretin kinetic stabilizers/amyloidogenesis inhibitors. The viability of these prediction algorithms, in particular the more robust in silico docking model, is perhaps best validated by the clinical success of tafamidis, the first-in-class drug approved in Europe, Japan, South America, and elsewhere for treating transthyretin aggregation-associated familial amyloid polyneuropathy. Tafamidis is also being evaluated in a fully-enrolled placebo-controlled clinical trial for its efficacy against TTR cardiomyopathy. These prediction algorithms will be useful for identifying second generation TTR kinetic stabilizers, should these be needed to ameliorate the central nervous system or ophthalmologic pathology caused by TTR aggregation in organs not accessed by oral tafamidis administration.

CSP-1103 (CHF5074) stabilizes human transthyretin in healthy human subjects

Hereditary amyloid polyneuropathy is a type of protein misfolding disease. Transthyretin (TTR) is a homotetrameric serum protein and TTR tetramer dissociation is the limiting step in amyloid fibril formation. Thus, prevention of TTR dissociation is a promising therapeutic approach and some TTR stabilizers have been approved for the treatment of TTR amyloidosis. CSP-1103 (CHF5074) is a non-steroidal anti-inflammatory derivative that lacks cyclooxygenase inhibitory activity. In vitro, CSP-1103 stabilizes the TTR tetramer by binding to the thyroxine (T4) binding site. We have previously shown that serum TTR levels were increased by oral CSP-1103 administration through stabilization of TTR tetramers in humanized mice at both the Ttr locus and the Rbp4 locus. To determine whether CSP-1103 stabilizes TTR tetramers in humans, multiple CSP-1103 oral doses were administered for two weeks to 48 healthy human volunteers in a double-blind, placebo-controlled, parallel-group study. CSP-1103 treatment stabilized TTR tetramers in a dose-dependent manner under normal or denaturing stress conditions, thereby increasing serum TTR levels. Preincubation of serum with CSP-1103 or diflunisal in vitro increased the TTR tetramer stability. Computer simulation analysis revealed that the binding affinities of CSP-1103 with TTR at pH 7.0 were similar to those of tafamidis, thus confirming that CSP-1103 has potent TTR-stabilizing activity.

DDQ-promoted direct C5-alkylation of oxazoles with alkylboronic acids via palladium-catalysed C–H bond activation

The first protocol for the direct C5-alkylation of oxazoles through transition-metal-catalysed C(5)–H bond activation.

Synthesis and anticholinesterase activity of new substituted benzo[d]oxazole-based derivatives

A series of novel benzo[d]oxazole derivatives (6a-n) have been synthesized and biologically evaluated as potential inhibitors of acetylcholinesterases (AChE) and butyrylcholinesterase (BChE). The chemical structures of all final compounds were confirmed by spectroscopic methods. In vitro studies showed that most of the synthesized compounds are potent acetylcholinesterase and butyrylcholinesterase inhibitors. Among them, compounds 6a and 6j strongly inhibited AChE and BChE activities with IC₅₀ values of 1.03-1.35 and 6.6-8.1 μm, respectively. Docking studies also provided the binding modes of action and identified hydrophobic pi forces as the main interaction.

Current and future treatment of amyloid diseases

There are more than 30 human proteins whose aggregation appears to cause degenerative maladies referred to as amyloid diseases or amyloidoses. These disorders are named after the characteristic cross-β-sheet amyloid fibrils that accumulate systemically or are localized to specific organs. In most cases, current treatment is limited to symptomatic approaches and thus disease-modifying therapies are needed. Alzheimer's disease is a neurodegenerative disorder with extracellular amyloid β-peptide (Aβ) fibrils and intracellular tau neurofibrillary tangles as pathological hallmarks. Numerous clinical trials have been conducted with passive and active immunotherapy, and small molecules to inhibit Aβ formation and aggregation or to enhance Aβ clearance; so far such clinical trials have been unsuccessful. Novel strategies are therefore required and here we will discuss the possibility of utilizing the chaperone BRICHOS to prevent Aβ aggregation and toxicity. Type 2 diabetes mellitus is symptomatically treated with insulin. However, the underlying pathology is linked to the aggregation and progressive accumulation of islet amyloid polypeptide as fibrils and oligomers, which are cytotoxic. Several compounds have been shown to inhibit islet amyloid aggregation and cytotoxicity in vitro. Future animal studies and clinical trials have to be conducted to determine their efficacy in vivo. The transthyretin (TTR) amyloidoses are a group of systemic degenerative diseases compromising multiple organ systems, caused by TTR aggregation. Liver transplantation decreases the generation of misfolded TTR and improves the quality of life for a subgroup of this patient population. Compounds that stabilize the natively folded, nonamyloidogenic, tetrameric conformation of TTR have been developed and the drug tafamidis is available as a promising treatment.

Repositioning tolcapone as a potent inhibitor of transthyretin amyloidogenesis and associated cellular toxicity

Transthyretin (TTR) is a plasma homotetrameric protein implicated in fatal systemic amyloidoses. TTR tetramer dissociation precedes pathological TTR aggregation. Native state stabilizers are promising drugs to treat TTR amyloidoses. Here we repurpose tolcapone, an FDA-approved molecule for Parkinson's disease, as a potent TTR aggregation inhibitor. Tolcapone binds specifically to TTR in human plasma, stabilizes the native tetramer in vivo in mice and humans and inhibits TTR cytotoxicity. Crystal structures of tolcapone bound to wild-type TTR and to the V122I cardiomyopathy-associated variant show that it docks better into the TTR T4 pocket than tafamidis, so far the only drug on the market to treat TTR amyloidoses. These data indicate that tolcapone, already in clinical trials for familial amyloid polyneuropathy, is a strong candidate for therapeutic intervention in these diseases, including those affecting the central nervous system, for which no small-molecule therapy exists.

CHF5074 (CSP-1103) stabilizes human transthyretin in mice humanized at the transthyretin and retinol-binding protein loci

Familial amyloidotic polyneuropathy is one type of protein misfolding disease. Transthyretin (TTR) tetramer dissociation is the limiting step for amyloid fibril formation. CHF5074 (CSP-1103) stabilizes TTR tetramer in vitro by binding to the T4 binding site. Here, we used three strains of double humanized mice (mTtr(hTTRVal30/hTTRVal30), mTtr(hTTRVal30/hTTRMet30), and mTtr(hTTRMet30/hTTRMet30)) to assess whether CHF5074 stabilizes TTR tetramers in vivo. Treatment of mice with CHF5074 increased serum TTR levels by stabilizing TTR tetramers. Although the binding affinities of CHF5074 and diflunisal with TTRMet30 were similar, CHF5074 bound TTRVal30 more strongly than did diflunisal, suggesting the potent TTR-stabilizing activity of CHF5074.

Aromatic sulfonyl fluorides covalently kinetically stabilize transthyretin to prevent amyloidogenesis while affording a fluorescent conjugate

Molecules that bind selectively to a given protein and then undergo a rapid chemoselective reaction to form a covalent conjugate have utility in drug development. Herein a library of 1,3,4-oxadiazoles substituted at the 2 position with an aryl sulfonyl fluoride and at the 5 position with a substituted aryl known to have high affinity for the inner thyroxine binding subsite of transthyretin (TTR) was conceived of by structure-based design principles and was chemically synthesized. When bound in the thyroxine binding site, most of the aryl sulfonyl fluorides react rapidly and chemoselectively with the pKa-perturbed K15 residue, kinetically stabilizing TTR and thus preventing amyloid fibril formation, known to cause polyneuropathy. Conjugation t50s range from 1 to 4 min, ~1400 times faster than the hydrolysis reaction outside the thyroxine binding site. X-ray crystallography confirms the anticipated binding orientation and sheds light on the sulfonyl fluoride activation leading to the sulfonamide linkage to TTR. A few of the aryl sulfonyl fluorides efficiently form conjugates with TTR in plasma. Eleven of the TTR covalent kinetic stabilizers synthesized exhibit fluorescence upon conjugation and therefore could have imaging applications as a consequence of the environment sensitive fluorescence of the chromophore.

The transthyretin amyloidoses: from delineating the molecular mechanism of aggregation linked to pathology to a regulatory-agency-approved drug

Transthyretin (TTR) is one of the many proteins that are known to misfold and aggregate (i.e., undergo amyloidogenesis) in vivo. The process of TTR amyloidogenesis causes nervous system and/or heart pathology. While several of these maladies are associated with mutations that destabilize the native TTR quaternary and/or tertiary structure, wild-type TTR amyloidogenesis also leads to the degeneration of postmitotic tissue. Over the past 20 years, much has been learned about the factors that influence the propensity of TTR to aggregate. This biophysical information led to the development of a therapeutic strategy, termed "kinetic stabilization," to prevent TTR amyloidogenesis. This strategy afforded the drug tafamidis which was recently approved by the European Medicines Agency for the treatment of TTR familial amyloid polyneuropathy, the most common familial TTR amyloid disease. Tafamidis is the first and currently the only medication approved to treat TTR familial amyloid polyneuropathy. Here we review the biophysical basis for the kinetic stabilization strategy and the structure-based drug design effort that led to this first-in-class pharmacologic agent.

Chemical and biological approaches for adapting proteostasis to ameliorate protein misfolding and aggregation diseases: progress and prognosis

Maintaining the proteome to preserve the health of an organism in the face of developmental changes, environmental insults, infectious diseases, and rigors of aging is a formidable task. The challenge is magnified by the inheritance of mutations that render individual proteins subject to misfolding and/or aggregation. Maintenance of the proteome requires the orchestration of protein synthesis, folding, degradation, and trafficking by highly conserved/deeply integrated cellular networks. In humans, no less than 2000 genes are involved. Stress sensors detect the misfolding and aggregation of proteins in specific organelles and respond by activating stress-responsive signaling pathways. These culminate in transcriptional and posttranscriptional programs that up-regulate the homeostatic mechanisms unique to that organelle. Proteostasis is also strongly influenced by the general properties of protein folding that are intrinsic to every proteome. These include the kinetics and thermodynamics of the folding, misfolding, and aggregation of individual proteins. We examine a growing body of evidence establishing that when cellular proteostasis goes awry, it can be reestablished by deliberate chemical and biological interventions. We start with approaches that employ chemicals or biological agents to enhance the general capacity of the proteostasis network. We then introduce chemical approaches to prevent the misfolding or aggregation of specific proteins through direct binding interactions. We finish with evidence that synergy is achieved with the combination of mechanistically distinct approaches to reestablish organismal proteostasis.

A competition assay to identify amyloidogenesis inhibitors by monitoring the fluorescence emitted by the covalent attachment of a stilbene derivative to transthyretin

Herein we demonstrate that competition between candidate kinetic stabilizer binding to transthyretin (TTR) and stilbene binding to and reaction with the same thyroxine sites within TTR can be utilized to discover potent and highly selective non-covalent TTR amyloidogenesis inhibitors. We report two stilbenes, S1 and S2, for use in distinct competition assays. Each bind selectively to TTR and then chemoselectively react to form an amide bond with the Lys-15 residue of TTR, creating a fluorescent conjugate. We used 28 TTR kinetic stabilizers exhibiting a known spectrum of plasma TTR binding selectivities and TTR amyloid fibril inhibition efficacies to validate the 'TTR fluorescence conjugate competition assay'. The kinetic stabilizers competed with S1 for binding to recombinant TTR in buffer and with S2 for binding to endogenous levels of TTR in human blood serum. In both assay scenarios, we demonstrate that the lower the TTR-stilbene conjugate fluorescence after a 3 h competition, the greater the binding selectivity and potency of the candidate TTR kinetic stabilizer. These assays, particularly the assay utilizing S2 in human serum, replace two assays previously utilized to gather the same information. While not the focus of this manuscript, it is clear that the 'TTR fluorescence conjugate competition assay' could be adapted for high throughput screening applications.

Structure-based design of kinetic stabilizers that ameliorate the transthyretin amyloidoses

Small molecules that bind to normally unoccupied thyroxine (T(4)) binding sites within transthyretin (TTR) in the blood stabilize the tetrameric ground state of TTR relative to the dissociative transition state and dramatically slow tetramer dissociation, the rate-limiting step for the process of amyloid fibril formation linked to neurodegeneration and cell death. These so-called TTR kinetic stabilizers have been designed using structure-based principles and one of these has recently been shown to halt the progression of a human TTR amyloid disease in a clinical trial, providing the first pharmacologic evidence that the process of amyloid fibril formation is causative. Structure-based design has now progressed to the point where highly selective, high affinity TTR kinetic stabilizers that lack undesirable off-target activities can be produced with high frequency.

Toward optimization of the second aryl substructure common to transthyretin amyloidogenesis inhibitors using biochemical and structural studies

Transthyretin (TTR) amyloidogenesis inhibitors are typically composed of two aromatic rings and a linker. We have previously established optimal structures for one aromatic ring and the linker. Herein, we employ a suboptimal linker and an optimal aryl-X substructure to rank order the desirability of aryl-Z substructures--using a library of 56 N-(3,5-dibromo-4-hydroxyphenyl)benzamides. Coconsideration of amyloid inhibition potency and ex vivo plasma TTR binding selectivity data reveal that 2,6, 2,5, 2, 3,4,5, and 3,5 substituted aryls bearing small substituents generate the most potent and selective inhibitors, in descending order. These benzamides generally lack undesirable thyroid hormone receptor binding and COX-1 inhibition activity. Three high-resolution TTR.inhibitor crystal structures (1.31-1.35 A) provide insight into why these inhibitors are potent and selective, enabling future structure-based design of TTR kinetic stabilizers.

Iodine atoms: a new molecular feature for the design of potent transthyretin fibrillogenesis inhibitors

The thyroid hormone and retinol transporter protein known as transthyretin (TTR) is in the origin of one of the 20 or so known amyloid diseases. TTR self assembles as a homotetramer leaving a central hydrophobic channel with two symmetrical binding sites. The aggregation pathway of TTR into amiloid fibrils is not yet well characterized but in vitro binding of thyroid hormones and other small organic molecules to TTR binding channel results in tetramer stabilization which prevents amyloid formation in an extent which is proportional to the binding constant. Up to now, TTR aggregation inhibitors have been designed looking at various structural features of this binding channel others than its ability to host iodine atoms. In the present work, greatly improved inhibitors have been designed and tested by taking into account that thyroid hormones are unique in human biochemistry owing to the presence of multiple iodine atoms in their molecules which are probed to interact with specific halogen binding domains sitting at the TTR binding channel. The new TTR fibrillogenesis inhibitors are based on the diflunisal core structure because diflunisal is a registered salicylate drug with NSAID activity now undergoing clinical trials for TTR amyloid diseases. Biochemical and biophysical evidence confirms that iodine atoms can be an important design feature in the search for candidate drugs for TTR related amyloidosis.

Toward optimization of the linker substructure common to transthyretin amyloidogenesis inhibitors using biochemical and structural studies

To develop potent and highly selective transthyretin (TTR) amyloidogenesis inhibitors, it is useful to systematically optimize the three substructural elements that compose a typical TTR kinetic stabilizer: the two aryl rings and the linker joining them. Herein, we evaluated 40 bisaryl molecules based on 10 unique linker substructures to determine how these linkages influence inhibitor potency and selectivity. These linkers connect one unsubstituted aromatic ring to either a 3,5-X 2 or a 3,5-X 2-4-OH phenyl substructure (X = Br or CH 3). Coconsideration of amyloid inhibition and ex vivo plasma TTR binding selectivity data reveal that direct connection of the two aryls or linkage through nonpolar E-olefin or -CH 2CH 2- substructures generates the most potent and selective TTR amyloidogenesis inhibitors exhibiting minimal undesirable binding to the thyroid hormone nuclear receptor or the COX-1 enzyme. Five high-resolution TTR.inhibitor crystal structures (1.4-1.8 A) provide insight into why such linkers afford inhibitors with greater potency and selectivity.

Novel 5-(3-(Substituted)-4,5-dihydroisoxazol-5-yl)-2-methoxyphenyl Derivatives: Synthesis and Anticancer Activity

Thirty novel 5-(3-(substituted phenyl)-4,5-dihydroisoxazol-5-yl)-2-methoxyphenyl derivatives were synthesized and evaluated for their antitumour activity. The bioassays showed that the 2-fluorobenzoyl derivative 6ai, the 4-trifluoromethylbenzoyl derivative 6ah, and the 3-trifluoromethyl isoxazole derivatives (6ch and 6ci) were highly effective against PC-3 cells. The IC50 values of 6ah and 6ai against PC-3 cells were 1.5 and 1.8 μg mL–1, respectively.

Models for binding cooperativities of inhibitors with transthyretin

Here, molecular dynamics (MD) simulations are performed to study the differences of binding channel shapes of TTR with two inhibitors, flufenamic acid (FLU) and one kind of N-phenyl phenoxazine (BPD). The asymmetries of global structure including the central binding channel are found to be intrinsic. Moreover, the conformational changes of the binding channel are responsible for negative cooperativity (NC) or independent cooperativity (IC) of ligands. The results suggested a possible binding mechanism addressing NC of FLU and IC of BPD. For FLU, when the first ligand binds with TTR, it leads to expansion of the second binding site which may weaken the interaction of the second FLU with TTR. But for BPD, the first ligand's binding changes the second site's shape slightly, the second ligand has similar binding ability with TTR in the second site like the first binding event.

Orally administered diflunisal stabilizes transthyretin against dissociation required for amyloidogenesis

OBJECTIVE

Rate-limiting transthyretin (TTR) tetramer dissociation and monomer misfolding enable misassembly into numerous aggregate morphologies including amyloid, a process genetically linked to and thought to cause amyloid pathology. T119M TTR trans-suppressor subunit inclusion into tetramers otherwise composed of disease-associated subunits ameliorates human amyloidosis by increasing the tetramer dissociation barrier. Diflunisal binding to the 99% unoccupied L-thyroxine binding sites in TTR also increases the tetramer dissociation barrier; hence, we investigated the feasibility of using diflunisal for the treatment of human TTR amyloidosis using healthy volunteers.

METHODS

Diflunisal (125, 250 or 500 mg bid) was orally administered to groups of 10 subjects for 7 days to evaluate serum diflunisal concentration, diflunisal binding stoichiometry to TTR, and the extent of diflunisal imposed TTR kinetic stabilization against urea- and acid-mediated TTR denaturation in human serum. The rates of urea-mediated tetramer dissociation and acid-mediated aggregation as a function of diflunisal concentration were also evaluated in vitro, utilizing physiologically relevant concentrations identified by the above experiments.

RESULTS

In the 250 mg bid group, 12 h after the 13th oral dose, the diflunisal serum concentration of 146 +/- 39 microM was sufficient to afford a TTR binding stoichiometry exceeding 0.95 +/- 0.13 ( approximately 1.75 corrected). Diflunisal binding to TTR at this dose slowed urea-mediated dissociation and acid-mediated TTR aggregation at least, threefold (p < 0.05) in serum and in vitro, consistent with kinetic stabilization of TTR.

CONCLUSION

Diflunisal-mediated kinetic stabilization of TTR should ameliorate TTR amyloidoses, provided that the nonsteroidal anti-inflammatory drug liabilities can be managed clinically.

Diflunisal stabilizes familial amyloid polyneuropathy-associated transthyretin variant tetramers in serum against dissociation required for amyloidogenesis

Transthyretin (TTR) tetramer dissociation, misfolding and misassembly are required for the process of amyloid fibril formation associated with familial amyloid polyneuropathy (FAP). Preferential stabilization of the native TTR tetramer over the dissociative transition state by small molecule binding raises the kinetic barrier of tetramer dissociation, preventing amyloidogenesis. Two NSAIDs, diflunisal and flufenamic acid, and trivalent chromium have this ability. Here, we investigated the feasibility of using these molecules for the treatment of FAP utilizing serum samples from 37 FAP patients with 10 different mutations. We demonstrated that the TTR heterotetramer structures in FAP patients serum are significantly less stable than that in normal subjects, indicating the instability of the variant TTR structure is a fundamental cause of TTR amyloidosis. We also demonstrated that therapeutic serum concentrations of diflunisal (100-200 microM) stabilized serum variant TTR tetramer better than those of flufenamic acid (35-70 microM). Trivalent chromium at levels obtained by oral supplementation did not stabilize TTR in a statistically significant fashion. Importantly, diflunisal increased serum TTR stability in FAP patients beyond the level of normal controls.

Native state kinetic stabilization as a strategy to ameliorate protein misfolding diseases: a focus on the transthyretin amyloidoses

Small molecule-mediated protein stabilization inside or outside of the cell is a promising strategy to treat protein misfolding/misassembly diseases. Herein we focus on the transthyretin (TTR) amyloidoses and demonstrate that preferential ligand binding to and stabilization of the native state over the dissociative transition state raises the kinetic barrier of dissociation (rate-limiting for amyloidogenesis), slowing and in many cases preventing TTR amyloid fibril formation. Since T119M-TTR subunit incorporation into tetramers otherwise composed of disease-associated subunits also imparts kinetic stability on the tetramer and ameliorates amyloidosis in humans, it is likely that small molecule-mediated native state kinetic stabilization will also alleviate TTR amyloidoses.

Genistein, a natural product from soy, is a potent inhibitor of transthyretin amyloidosis

The misfolding of transthyretin (TTR), including rate-limiting tetramer dissociation and partial monomer denaturation, is sufficient for TTR misassembly into amyloid and other abnormal quaternary structures associated with three amyloid diseases: senile systemic amyloidosis, familial amyloid polyneuropathy, and familial amyloid cardiomyopathy. Small molecules can bind to one or both of the unoccupied TTR thyroid hormone-binding sites, stabilizing the native tetramer more than the dissociative transition state, thereby raising the kinetic barrier for tetramer dissociation. Herein we demonstrate that genistein, the major isoflavone natural product in soy, works in this fashion and is an excellent inhibitor of transthyretin tetramer dissociation and amyloidogenesis, reducing acid-mediated fibril formation to <10% of that exhibited by TTR alone. Genistein also inhibits the amyloidogenesis of the most common familial amyloid polyneuropathy and familial amyloid cardiomyopathy mutations in TTR: V30M and V122I, respectively. Genistein additionally inhibits tetramer dissociation under physiological conditions thought to lead to slow amyloidogenesis in humans. Furthermore, this natural product exhibits highly selective binding to TTR in plasma over all of the other plasma proteins. Isothermal titration calorimetry shows that genistein binds to TTR with negative cooperativity (K(d1) = 40 nM, K(d2) = 1.4 microM). The benefits of using a nutraceutical such as genistein to treat orphan diseases such as the TTR amyloidoses include known oral bioavailability and safety data. It is conceivable that some patients could benefit from simply increasing their intake of soy products or supplements.