tolcapone and tafamidis

Often considered a rare disease, cardiac amyloidosis is increasingly recognized by practicing clinicians. The increased rate of diagnosis is in part due the aging of the population and increasing incidence and prevalence of cardiac amyloidosis with advancing age, as well as the advent of noninvasive methods using nuclear scintigraphy to diagnose transthyretin cardiac amyloidosis due to either variant or wild type transthyretin without a biopsy. Perhaps the most important driver of the increased awareness is the elucidation of the biologic mechanisms underlying the pathogenesis of cardiac amyloidosis which have led to the development of several effective therapies with differing mechanisms of actions. In this review, the mechanisms underlying the pathogenesis of cardiac amyloidosis due to light chain (AL) or transthyretin (ATTR) amyloidosis are delineated as well as the rapidly evolving therapeutic landscape that has emerged from a better pathophysiologic understanding of disease development.

Topics: Aging; Alkylating Agents; Amyloid; Amyloid Neuropathies, Familial; Amyloidosis; Antibodies, Monoclonal; Benzoates; Benzoxazoles; Bridged Bicyclo Compounds, Heterocyclic; Cardiomyopathies; Catechol O-Methyltransferase Inhibitors; Heart Transplantation; Humans; Immunomodulating Agents; Oligonucleotides; Proteasome Inhibitors; Protein Folding; Pyrazoles; RNA, Small Interfering; Stem Cell Transplantation; Sulfonamides; Tolcapone

Transthyretin (TTR) tetramer dissociation is rate limiting for aggregation and subunit exchange. Slowing of TTR tetramer dissociation

Topics: Amyloid; Amyloid Neuropathies, Familial; Benzoates; Benzoxazoles; Cardiomyopathies; Diflunisal; Humans; Kinetics; Prealbumin; Protein Aggregates; Protein Binding; Protein Multimerization; Protein Subunits; Pyrazoles; Tolcapone

Transthyretin (TTR) is a homotetrameric protein involved in human amyloidosis, including familial amyloid polyneuropathy (FAP). Discovering small-molecule stabilizers of the TTR tetramer is a therapeutic strategy for these diseases. Tafamidis, the only approved drug for FAP treatment, is not effective for all patients. Herein, we discovered that benzbromarone (BBM), a uricosuric drug, is an effective TTR stabilizer and inhibitor against TTR amyloid fibril formation. BBM rendered TTR more resistant to urea denaturation, similarly to iododiflunisal (IDIF), a very potent TTR stabilizer. BBM competes with thyroxine for binding in the TTR central channel, with an IC

Topics: Amyloid; Benzbromarone; Benzoxazoles; Binding Sites; Binding, Competitive; Crystallography, X-Ray; Diflunisal; Drug Repositioning; Gene Expression; Humans; Hydrogen Bonding; Kinetics; Molecular Docking Simulation; Neuroprotective Agents; Prealbumin; Protein Binding; Protein Conformation, alpha-Helical; Protein Conformation, beta-Strand; Protein Interaction Domains and Motifs; Protein Multimerization; Protein Stability; Recombinant Proteins; Thermodynamics; Thyroxine; Tolcapone

Dissociation of the native transthyretin (TTR) tetramer is widely accepted as the critical step in TTR amyloid fibrillogenesis. It is modelled by exposure of the protein to non-physiological low pH in vitro and is inhibited by small molecule compounds, such as the drug tafamidis. We have recently identified a new mechano-enzymatic pathway of TTR fibrillogenesis in vitro, catalysed by selective proteolytic cleavage, which produces a high yield of genuine amyloid fibrils. This pathway is efficiently inhibited only by ligands that occupy both binding sites in TTR. Tolcapone, which is bound with similar high affinity in both TTR binding sites without the usual negative cooperativity, is therefore of interest. Here we show that TTR fibrillogenesis by the mechano-enzymatic pathway is indeed more potently inhibited by tolcapone than by tafamidis but neither, even in large molar excess, completely prevents amyloid fibril formation. In contrast, mds84, the prototype of our previously reported bivalent ligand TTR 'superstabiliser' family, is notably more potent than the monovalent ligands and we show here that this apparently reflects the critical additional interactions of its linker within the TTR central channel. Our findings have major implications for therapeutic approaches in TTR amyloidosis.

Topics: Amyloid; Benzophenones; Benzoxazoles; Binding Sites; Fenamates; Humans; Models, Molecular; Molecular Structure; Nitrophenols; Prealbumin; Protein Binding; Protein Multimerization; Proteolysis; Tolcapone

The quaternary structure stability of proteins is typically studied under conditions that accelerate their aggregation/unfolding processes on convenient laboratory time scales. Such conditions include high temperature or pressure, chaotrope-mediated unfolding, or low or high pH. These approaches have the limitation of being nonphysiological and that the concentration of the protein in solution is changing as the reactions proceed. We describe a methodology to define the quaternary structure stability of the amyloidogenic homotetrameric protein transthyretin (TTR) under physiological conditions. This methodology expands from a described approach based on the measurement of the rate of subunit exchange of TTR with a tandem flag-tagged (FT₂) TTR counterpart. We demonstrate that subunit exchange of TTR with FT₂·TTR can be analyzed and quantified using a semi-native polyacrylamide gel electrophoresis technique. In addition, we biophysically characterized two FT₂·TTR variants derived from wild-type and the amyloidogenic variant Val122Ile TTR, both of which are associated with cardiac amyloid deposition late in life. The FT₂·TTR variants have similar amyloidogenic potential and similar thermodynamic and kinetic stabilities compared to those of their nontagged counterparts. We utilized the methodology to study the potential of the small molecule SOM0226, a repurposed drug under clinical development for the prevention and treatment of the TTR amyloidoses, to stabilize TTR. The results enabled us to characterize the binding energetics of SOM0226 to TTR. The described technique is well-suited to study the quaternary structure of other human aggregation-prone proteins under physiological conditions.

Topics: Amino Acid Substitution; Amyloid; Amyloidosis, Familial; Benzophenones; Benzoxazoles; Binding Sites; Drugs, Investigational; Fluorescent Dyes; Humans; Kinetics; Models, Molecular; Mutant Proteins; Nitrophenols; Nootropic Agents; Prealbumin; Protein Aggregation, Pathological; Protein Stability; Protein Structure, Quaternary; Protein Unfolding; Recombinant Proteins; Thermodynamics; Tolcapone