Mechanism of Action and Clinical Application of Tafamidis in Hereditary Transthyretin Amyloidosis

Transthyretin mutagenesis: impact on amyloidogenesis and disease

Transthyretin (TTR), a homotetrameric protein found in plasma, cerebrospinal fluid, and the eye, plays a pivotal role in the onset of several amyloid diseases with high morbidity and mortality. Protein aggregation and fibril formation by wild-type TTR and its natural more amyloidogenic variants are hallmarks of ATTRwt and ATTRv amyloidosis, respectively. The formation of soluble amyloid aggregates and the accumulation of insoluble amyloid fibrils and deposits in multiple tissues can lead to organ dysfunction and cell death. The most frequent manifestations of ATTR are polyneuropathies and cardiomyopathies. However, clinical manifestations such as carpal tunnel syndrome, leptomeningeal, and ocular amyloidosis, among several others may also occur. This review provides an up-to-date listing of all single amino-acid mutations in TTR known to date. Of approximately 220 single-point mutations, 93% are considered pathogenic. Aspartic acid is the residue mutated with the highest frequency, whereas tryptophan is highly conserved. "Hot spot" mutation regions are mainly assigned to β-strands B, C, and D. This manuscript also reviews the protein aggregation models that have been proposed for TTR amyloid fibril formation and the transient conformational states that convert native TTR into aggregation-prone molecular species. Finally, it compiles the various in vitro TTR aggregation protocols currently in use for research and drug development purposes. In short, this article reviews and discusses TTR mutagenesis and amyloidogenesis, and their implications in disease onset.

Outcomes of Octogenarian Patients Treated with Tafamidis for Transthyretin Amyloid Cardiomyopathy

Patients with transthyretin amyloid cardiomyopathy (ATTR-CM) benefit from disease-modifying agents such as tafamidis. However, the survival benefit of tafamidis in elderly patients (age ≥80 years) is not reported. This study aimed to assess the survival of patients with ATTR-CM aged 80 years and older who were treated with tafamidis compared with patients aged <80 years. We conducted a retrospective analysis of patients with ATTR-CM who underwent tafamidis treatment, aged 45 to 97 years at the time of diagnosis between January 1, 2008, and May 31, 2021. A total of 484 patients were included, with 208 in the ≥80 years group and 276 in the <80 years group. The cohort was followed up for mortality outcomes, and hazard ratios with 95% confidence intervals were calculated. After a median follow-up of 18.5 months, 72 deaths were recorded in the entire cohort. Kaplan-Meier curves showed no differences in survival probability between the 2 groups at 30 months (p for log-rank test = 0.76). The survival rates for patients aged ≥80 years who underwent treatment at 1, 2, 3, 4, and 5 years were 94.7%, 86.0%, 77.0%, 77.0%, and 38.5%, respectively. The corresponding rates for patients aged <80 years who underwent treatment were 93.2, 84.8, 74.4, 68.2, and 64.6%, respectively. In the multivariable analysis, the hazard ratio (95% confidence interval) of the mortality comparing treatment patients aged ≥80 years with those aged <80 years was 0.81 (0.41 to 1.61). In conclusion, tafamidis treatment is associated with similar reductions in mortality in older and younger patients with ATTR-CM.

Tafamidis improves myocardial longitudinal strain in A97S transthyretin cardiac amyloidosis

Background

Transthyretin cardiomyopathy (ATTR-CM) is a debilitating disease that has received much attention since the emergence of novel treatments. The Transthyretin Cardiomyopathy Clinical Trial showed that tafamidis, a transthyretin tetramer stabilizer, effectively reduced the declines in functional capacity and quality of life. However, Ala97Ser (A97S) hereditary ATTR-CM is underrepresented in major ATTR-CM tafamidis trials.

Objectives

We aim to investigate the change in global longitudinal strain (GLS) of A97S ATTR-CM patients after 12 months of tafamidis treatment.

Methods

We retrospectively analysed a prospective cohort of patients with A97S ATTR-CM who received tafamidis meglumine (61 mg/day) at the National Taiwan University Hospital. Echocardiography with speckle tracking strain analysis was performed at baseline and 12 months after treatment.

Results

In all, 20 patients were included in the cohort. The baseline left ventricular ejection fraction (LVEF) and interventricular septum (IVS) thickness were 59.20 ± 13.23% and 15.10 ± 3.43 mm, respectively. After 12 months of tafamidis treatment, the LVEF and IVS were 61.83 ± 15.60% (p = 0.244) and 14.59 ± 3.03 mm (p = 0.623), respectively. GLS significantly improved from -12.70 ± 3.31% to -13.72 ± 3.17% (p = 0.048), and longitudinal strain (LS) in apical and middle segments significantly improved from -16.05 ± 4.82% to -17.95 ± 3.48% (p = 0.039) and -11.89 ± 4.38% to -13.58 ± 3.12% (p = 0.039), respectively. Subgroup analysis showed that patients with LVEF < 50% had a better treatment response and improvement in GLS. The patients with an IVS ⩾ 13 mm had an improvement in two-chamber LS from -10.92 ± 4.25% to -13.15 ± 3.87% (p = 0.042) and an improvement in apical left ventricular LS from -15.30 ± 5.35% to -17.82 ± 3.99% (p = 0.031).

Conclusion

Tafamidis significantly improved GLS, and particularly apical and middle LS in A97S ATTR-CM patients.

Efficacy of tafamidis in transthyretin amyloid cardiomyopathy: a systematic review and meta-analysis

In May 2019, the U.S. Food and Drug Administration approved tafamidis as the first conservative management of transthyretin amyloid cardiomyopathy (ATTR-CM). Our aim in conducting this systematic review and meta-analysis was to assess the efficacy of tafamidis on patients with ATTR-CM. For that purpose, we thoroughly searched PubMed, ScienceDirect, and Clinical trails.gov by using the appropriate search strategy and following predefined inclusion and exclusion criteria, which retrieved 235 articles initially. Of which two randomized controlled trials (RCTs) and one observational study matched our inclusion criteria. A total of 876 patients are included in this analysis. Based on results, tafamidis significantly reduced cardiovascular (CV) mortality in the ATTR-ACT trial and Ochi et al. (OR 0.58; 95% CI: [0.41-0.83], P=0.003, I 2=87%). A subgroup analysis was conducted for CV mortality due to heart failure (OR 0.89; 95% CI: [0.63-1.25], P=0.50, I 2=93%). The results exhibit that tafamidis reduced all causes of mortality (OR 0.45; 95% CI: [0.32-0.64], P≤0.00001, I 2=22%). Furthermore, mortality remained statistically insignificant in patients with heart transplants (OR 1.18; 95% CI: [0.52-2.70], P=0.70, I 2=0%) and patients with cardiac mechanical assist devices (OR 4.15; 95% CI: [0.48-35.66], P=0.20, I 2=0%). This meta-analysis suggests that tafamidis is a safe and efficient drug to use in patients with ATTR-CM and can possess the potential to be a milestone in enhancing the conservative management of the patients.

Mapping cellular response to destabilized transthyretin reveals cell- and amyloidogenic protein-specific signatures

BACKGROUND

In ATTR amyloidosis, transthyretin (TTR) protein is secreted from the liver and deposited as toxic aggregates at downstream target tissues. Despite recent advancements in treatments for ATTR amyloidosis, the mechanisms underlying misfolded TTR-mediated cellular damage remain elusive.

METHODS

In an effort to define early events of TTR-associated stress, we exposed neuronal (SH-SY5Y) and cardiac (AC16) cells to wild-type and destabilized TTR variants (TTRV122I (p.V142I) and TTRL55P (p.L70P)) and performed transcriptional (RNAseq) and epigenetic (ATACseq) profiling. We subsequently compared TTR-responsive signatures to cells exposed to destabilized antibody light chain protein associated with AL amyloidosis as well as ER stressors (thapsigargin, heat shock).

RESULTS

In doing so, we observed overlapping, yet distinct cell type- and amyloidogenic protein-specific signatures, suggesting unique responses to each amyloidogenic variant. Moreover, we identified chromatin level changes in AC16 cells exposed to mutant TTR that resolved upon pre-incubation with kinetic stabilizer tafamidis.

CONCLUSIONS

Collectively, these data provide insight into the mechanisms underlying destabilized protein-mediated cellular damage and provide a robust resource representing cellular responses to aggregation-prone proteins and ER stress.

Variation of tafamidis plasma levels during the treatment of TTR amyloidosis patients with Glu89Gln mutation

PURPOSE

The transthyretin kinetic stabilizer tafamidis, used as a first-line therapy of amyloidosis patients, binds selectively to the transthyretin protein structure and thus prevents its dissociation. The limited information regarding tafamidis application in Glu89Gln amyloidosis patients imposed our research team to determine and evaluate its individual mean plasma levels and their biological variation.

METHODS

The present cohort study investigated Bulgarian amyloidosis patients, grouped by gender, age, and therapy duration. A total of sixty patients aged 40-75 years and therapy duration up to 9 years were included. A precise and accurate high-performance liquid chromatography method with ultraviolet detection was used for plasma concentration measurement.

RESULTS

Mean plasma concentrations were 5.13 ± 2.64 µmol/L and showed low intra-individual (18.50%) and high inter-individual variability (51.43%). No significant difference was observed between tafamidis plasma levels and therapy duration with p = 0.5941 (p < 0.05 considered significant), but a significant positive correlation was found between plasma concentration, gender, and age with obtained results about p-value 0.0001 and 0.0235, respectively.

CONCLUSION

The summary results of the study showed differences that may be based on some specific clinical features of the Glu89Gln mutation.

Hereditary transthyretin amyloidosis: a comprehensive review with a focus on peripheral neuropathy

Amyloidoses represent a group of diseases characterized by the pathological accumulation in the extracellular area of insoluble misfolded protein material called "amyloid". The damage to the tissue organization and the direct toxicity of the amyloidogenic substrates induce progressive dysfunctions in the organs involved. They are usually multisystem diseases involving several vital organs, such as the peripheral nerves, heart, kidneys, gastrointestinal tract, liver, skin, and eyes. Transthyretin amyloidosis (ATTR) is related to abnormalities of transthyretin (TTR), a protein that acts as a transporter of thyroxine and retinol and is produced predominantly in the liver. ATTR is classified as hereditary (ATTRv) and wild type (ATTRwt). ATTRv is a severe systemic disease of adults caused by mutations in the TTR gene and transmitted in an autosomal dominant manner with incomplete penetrance. Some pathogenic variants in TTR are preferentially associated with a neurological phenotype (progressive peripheral sensorimotor polyneuropathy); others are more frequently associated with restrictive heart failure. However, many mutations express a mixed phenotype with neurological and cardiological involvement. ATTRv is now a treatable disease. A timely and definite diagnosis is essential in view of the availability of effective therapies that have revolutionized the management of affected patients. The purpose of this review is to familiarize the clinician with the disease and with the correct diagnostic pathways in order to obtain an early diagnosis and, consequently, the possibility of an adequate treatment.

A case of disappearing amyloid on technetium pyrophosphate scan

Technetium-99mm pyrophosphate (Tc-PYP) scintigraphy is a highly accurate non-invasive method for the diagnosis of transthyretin (ATTR) cardiac amyloidosis. Prognosis for this disease is improved following treatment with the transthyretin (TTR) stabilizer tafamidis. Although tafamidis slows disease progression, its effects on myocardial amyloid and Tc-PYP uptake remain unclear. We present a patient with ATTR cardiac amyloidosis who had a strongly positive initial Tc-PYP scan, with a dramatic decrease in Tc-PYP uptake on repeat scan after 3 years of tafamidis treatment. However, myocardial biopsy showed persistent diffuse amyloid deposits. This case highlights the need for further studies regarding the utility of serial Tc-PYP scans in monitoring the progress of ATTR cardiomyopathy.

EGCG-Mediated Protection of Transthyretin Amyloidosis by Stabilizing Transthyretin Tetramers and Disrupting Transthyretin Aggregates

Transthyretin amyloidosis (ATTR) is a progressive and systemic disease caused by the misfolding and amyloid aggregation of transthyretin (TTR). Stabilizing the TTR tetramers and disrupting the formed TTR aggregation are treated as a promising strategy for the treatment of ATTR. Previous studies have reported that epigallocatechin gallate (EGCG) can participate in the whole process of TTR aggregation to prevent ATTR. However, the interaction mechanism of EGCG in this process is still obscure. In this work, we performed molecular dynamics simulations to investigate the interactions between EGCG and TTR tetramers, and between EGCG and TTR aggregates formed by the V30M mutation. The obtained results suggest that EGCG at the binding site of the V30M TTR tetramer can form stable hydrogen bonds with residues in the flexible AB-loop and EF-helix-loop, which reduces the structural mobility of these regions significantly. Additionally, the polyaromatic property of EGCG contributes to the increasement of hydrophobicity at the binding site and thus makes the tetramer difficult to be solvated and dissociated. For V30M-TTR-generated aggregates, EGCG can promote the dissociation of boundary β-strands by destroying key residue interactions of TTR aggregates. Moreover, EGCG is capable of inserting into the side-chain of residues of neighboring β-strands and disrupting the highly structured aggregates. Taken together, this study elucidates the role of EGCG in preventing TTR amyloidosis, which can provide important theoretical support for the future of drug design for ATTR.

Advances in the synthetic strategies of benzoxazoles using 2-aminophenol as a precursor: an up-to-date review

Benzoxazole is a resourceful and important member of the heteroarenes that connects synthetic organic chemistry to medicinal, pharmaceutical, and industrial areas. It is a bicyclic planar molecule and is the most favorable moiety for researchers because it has been extensively used as a starting material for different mechanistic approaches in drug discovery. The motif exhibits a high possibility of broad substrate scope and functionalization to offer several biological activities like anti-microbial, anti-fungal, anti-cancer, anti-oxidant, anti-inflammatory effects, and so on. There has been a large upsurge in the synthesis of benzoxazole via different pathways. The present article presents recent advances in synthetic strategies for benzoxazole derivatives since 2018. A variety of well-organized synthetic methodologies for benzoxazole using 2-aminophenol with aldehydes, ketones, acids, alcohols, isothiocyanates, ortho-esters, and alkynones under different reaction conditions and catalysts, viz. nanocatalysts, metal catalysts, and ionic liquid catalysts, with other miscellaneous techniques has been summarized.

Myricetin: A Potent Anti-Amyloidogenic Polyphenol against Superoxide Dismutase 1 Aggregation

Amyotrophic lateral sclerosis (ALS) is believed to be caused by the aggregation of misfolded or mutated superoxide dismutase 1 (SOD1). As there is currently no treatment, research into aggregation inhibitors continues. Based on docking, molecular dynamics (MD) simulations, and experimental observations, we propose that myricetin, a plant flavonoid, can act as a potent anti-amyloidogenic polyphenol against SOD1 aggregation. Our MD simulation results showed that myricetin stabilizes the protein interface, destabilizes the preformed fibril, and decreases the rate of fibril elongation. Myricetin inhibits the aggregation of SOD1 in a dose-dependent manner as shown by the ThT aggregation kinetics curves. Our transmission electron microscopy, dynamic light scattering, and circular dichroism experiments indicate that fewer shorter fibrils have formed. Fluorescence spectroscopy results predict the involvement of a static quenching mechanism characterized by a strong binding between protein and myricetin. Importantly, size exclusion chromatography revealed the potential of myricetin for fibril destabilization and depolymerization. These experimental observations complement the MD results. Thus, myricetin is a potent SOD1 aggregation inhibitor that can reduce the fibril load. Using the structure of myricetin as a reference, it is possible to design more effective therapeutic inhibitors against ALS that prevent the disease and reverse its effects.

Brazilian consensus for diagnosis, management and treatment of hereditary transthyretin amyloidosis with peripheral neuropathy: second edition

Hereditary transthyretin amyloidosis with peripheral neuropathy (ATTRv-PN) is an autosomal dominant inherited sensorimotor and autonomic polyneuropathy with over 130 pathogenic variants identified in the TTR gene. Hereditary transthyretin amyloidosis with peripheral neuropathy is a disabling, progressive and life-threatening genetic condition that leads to death in ∼ 10 years if untreated. The prospects for ATTRv-PN have changed in the last decades, as it has become a treatable neuropathy. In addition to liver transplantation, initiated in 1990, there are now at least 3 drugs approved in many countries, including Brazil, and many more are being developed. The first Brazilian consensus on ATTRv-PN was held in the city of Fortaleza, Brazil, in June 2017. Given the new advances in the area over the last 5 years, the Peripheral Neuropathy Scientific Department of the Brazilian Academy of Neurology organized a second edition of the consensus. Each panelist was responsible for reviewing the literature and updating a section of the previous paper. Thereafter, the 18 panelists got together virtually after careful review of the draft, discussed each section of the text, and reached a consensus for the final version of the manuscript.

Real-World Efficacy of Tafamidis in Patients With Transthyretin Amyloidosis and Heart Failure

Tafamidis was associated with a reduction in cardiovascular hospitalizations and all-cause mortality in patients with transthyretin amyloid cardiomyopathy (ATTR-CM) in the ATTR-ACT trial. However, real-world data on the efficacy of tafamidis are limited. We conducted a retrospective, observational cohort study using the TriNetX research network. Patients with wild-type TTR amyloidosis and heart failure (HF) were divided into 2 groups based on treatment with tafamidis. Propensity score matching (PSM) was performed, and rates of heart failure exacerbations (HFE) and all-cause mortality at 12 months were compared. After PSM, 421 patients were in each group (tafamidis vs nontafamidis). During the 12-month follow-up period, patients treated with tafamidis experienced significantly less HFE and all-cause mortality. A higher probability of event-free survival for HFE and all-cause mortality was noted with tafamidis. This real-world analysis supports that tafamidis use is associated with reduced HFE and all-cause mortality in patients with wild-type TTR amyloidosis and HF. Longer-term follow-up is needed to better understand the utility of tafamidis, given the increasing recognition of ATTR-CM and the high cost of tafamidis.

Genetic causes of heart failure with preserved ejection fraction: emerging pharmacological treatments

Heart failure with preserved ejection fraction (HFpEF) is a major driver of cardiac morbidity and mortality in developed countries, due to ageing populations and the increasing prevalence of comorbidities. While heart failure with reduced ejection fraction is dominated by left ventricular impairment, HFpEF results from a complex interplay of cardiac remodelling, peripheral circulation, and concomitant features including age, hypertension, obesity, and diabetes. In an important subset, however, HFpEF is subtended by specific diseases of the myocardium that are genetically determined, have distinct pathophysiology, and are increasingly amenable to targeted, innovative treatments. While each of these conditions is rare, they collectively represent a relevant subset within HFpEF cohorts, and their prompt recognition has major consequences for clinical practice, as access to dedicated, disease-specific treatments may radically change the quality of life and outcome. Furthermore, response to standard heart failure treatment will generally be modest for these individuals, whose inclusion in registries and trials may dilute the perceived efficacy of treatments targeting mainstream HFpEF. Finally, a better understanding of the molecular underpinnings of monogenic myocardial disease may help identify therapeutic targets and develop innovative treatments for selected HFpEF phenotypes of broader epidemiological relevance. The field of genetic cardiomyopathies is undergoing rapid transformation due to recent, groundbreaking advances in drug development, and deserves greater awareness within the heart failure community. The present review addressed existing and developing therapies for genetic causes of HFpEF, including hypertrophic cardiomyopathy, cardiac amyloidosis, and storage diseases, discussing their potential impact on management and their broader implications for our understanding of HFpEF at large.

Updated Evaluation of the Safety, Efficacy and Tolerability of Tafamidis in the Treatment of Hereditary Transthyretin Amyloid Polyneuropathy

Hereditary amyloid transthyretin (ATTRv) amyloidosis is a devastating hereditary multisystemic disease affecting predominantly the peripheral and autonomic nervous systems and the heart. ATTRv is caused by mutations in the transthyretin (TTR) gene, leading to extracellular deposition of amyloid fibrils in multiple organs including the peripheral nervous system. If untreated, it is associated with a fatal outcome 10-12 years after disease onset. Different treatments are available for patients with ATTRv polyneuropathy. Tafamidis 20 mg is approved in Europe since 2011 for early stages of ATTRv polyneuropathy (stage I - able to walk without support) and it is recommended as first-line therapy in these patients. Tafamidis is a TTR stabilizer that selectively binds to TTR and kinetically stabilizes both wild-type native TTR and mutant TTR. Consequently, it has the potential to prevent the amyloidogenic cascade initiated by TTR tetramer dissociation into its monomers and subsequent misfolding and aggregation. Tafamidis is an oral drug, taken once per day, with proved efficacy, safety and tolerability in ATTRv-PN patients as demonstrated in different clinical trials and open-label extension studies as well in clinical practice setting with around 10 years of experience. Tafamidis treatment started in the earliest stages of the disease is associated with better neurological outcomes. A multidisciplinary approach in referral centres is also fundamental for monitoring patients to assess individual response to treatment.

Inhibition of Amyloid Protein Aggregation Using Selected Peptidomimetics

Aberrant protein aggregation leads to the formation of amyloid fibrils. This phenomenon is linked to the development of more than 40 irremediable diseases such as Alzheimer's disease, Parkinson's disease, type 2 diabetes, and cancer. Plenty of research efforts have been given to understanding the underlying mechanism of protein aggregation, associated toxicity, and the development of amyloid inhibitors. Recently, the peptidomimetic approach has emerged as a potential tool to modulate several protein-protein interactions (PPIs). In this review, we discussed selected peptidomimetic-based approaches for the modulation of important amyloid proteins (Islet Amyloid Polypeptide, Amyloid Beta, α-synuclein, mutant p53, and insulin) aggregation. This approach holds a powerful platform for creating an essential stepping stone for the vital development of anti-amyloid therapeutic agents.

Amyloid Disassembly: What Can We Learn from Chaperones?

Protein aggregation and subsequent accumulation of insoluble amyloid fibrils with cross-β structure is an intrinsic characteristic of amyloid diseases, i.e., amyloidoses. Amyloid formation involves a series of on-pathway and off-pathway protein aggregation events, leading to mature insoluble fibrils that eventually accumulate in multiple tissues. In this cascade of events, soluble oligomeric species are formed, which are among the most cytotoxic molecular entities along the amyloid cascade. The direct or indirect action of these amyloid soluble oligomers and amyloid protofibrils and fibrils in several tissues and organs lead to cell death in some cases and organ disfunction in general. There are dozens of different proteins and peptides causing multiple amyloid pathologies, chief among them Alzheimer's, Parkinson's, Huntington's, and several other neurodegenerative diseases. Amyloid fibril disassembly is among the disease-modifying therapeutic strategies being pursued to overcome amyloid pathologies. The clearance of preformed amyloids and consequently the arresting of the progression of organ deterioration may increase patient survival and quality of life. In this review, we compiled from the literature many examples of chemical and biochemical agents able to disaggregate preformed amyloids, which have been classified as molecular chaperones, chemical chaperones, and pharmacological chaperones. We focused on their mode of action, chemical structure, interactions with the fibrillar structures, morphology and toxicity of the disaggregation products, and the potential use of disaggregation agents as a treatment option in amyloidosis.

Controlling amyloid formation of intrinsically disordered proteins and peptides: slowing down or speeding up?

The pathological assembly of intrinsically disordered proteins/peptides (IDPs) into amyloid fibrils is associated with a range of human pathologies, including neurodegeneration, metabolic diseases and systemic amyloidosis. These debilitating disorders affect hundreds of millions of people worldwide, and the number of people affected is increasing sharply. However, the discovery of therapeutic agents has been immensely challenging largely because of (i) the diverse number of aggregation pathways and the multi-conformational and transient nature of the related proteins or peptides and (ii) the under-development of experimental pipelines for the identification of disease-modifying molecules and their mode-of-action. Here, we describe current approaches used in the search for small-molecule modulators able to control or arrest amyloid formation commencing from IDPs and review recently reported accelerators and inhibitors of amyloid formation for this class of proteins. We compare their targets, mode-of-action and effects on amyloid-associated cytotoxicity. Recent successes in the control of IDP-associated amyloid formation using small molecules highlight exciting possibilities for future intervention in protein-misfolding diseases, despite the challenges of targeting these highly dynamic precursors of amyloid assembly.

Phase 1/1b Studies of UCB0599, an Oral Inhibitor of α-Synuclein Misfolding, Including a Randomized Study in Parkinson's Disease

BACKGROUND

Parkinson's disease (PD) and its progression are thought to be caused and driven by misfolding of α-synuclein (ASYN). UCB0599 is an oral, small-molecule inhibitor of ASYN misfolding, aimed at slowing disease progression.

OBJECTIVE

The aim was to investigate safety/tolerability and pharmacokinetics (PK) of single and multiple doses of UCB0599.

METHODS

Safety/tolerability and PK of single and multiple doses of UCB0599 and its metabolites were investigated in two phase 1 studies in healthy participants (HPs), where food effect and possible interaction with itraconazole (ITZ) were assessed (UP0030 [randomized, placebo-controlled, dose-escalation, crossover study, N = 65] and UP0078 [open-label study, N = 22]). Safety/tolerability and multi-dose PK of UCB0599 were subsequently investigated in a phase 1b randomized, double-blind, placebo-controlled study of participants with PD (UP0077 [NCT04875962], N = 31).

RESULTS

Across all studies, UCB0599 displayed rapid absorption with linear, time-independent PK properties; PK of multiple doses of UCB0599 were predictable from single-dose exposures. No notable food-effect was observed; co-administration with ITZ affected UCB0599 disposition (maximum plasma concentration and area under the curve increased ~1.3- and ~2 to 3-fold, respectively) however, this did not impact the safety profile. Hypersensitivity reactions were reported in UP0030 (n = 2) and UP0077 (n = 2). Treatment-related adverse events occurred in 43% (UCB0599), and 30% (placebo) of participants with PD were predominantly mild-to-moderate in intensity and were not dose related.

CONCLUSIONS

Seventy-three HPs and 21 participants with PD received UCB0599 doses; an acceptable safety/tolerability profile and predictable PK support continued development of UCB0599 for the slowing of PD progression. A phase 2 study in early-stage PD is underway (NCT04658186). © 2022 UCB Pharma. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Influence of denaturants on amyloid β42 aggregation kinetics

Amyloid formation is linked to devastating neurodegenerative diseases, motivating detailed studies of the mechanisms of amyloid formation. For Aβ, the peptide associated with Alzheimer’s disease, the mechanism and rate of aggregation have been established for a range of variants and conditions in vitro and in bodily fluids. A key outstanding question is how the relative stabilities of monomers, fibrils and intermediates affect each step in the fibril formation process. By monitoring the kinetics of aggregation of Aβ42, in the presence of urea or guanidinium hydrochloride (GuHCl), we here determine the rates of the underlying microscopic steps and establish the importance of changes in relative stability induced by the presence of denaturant for each individual step. Denaturants shift the equilibrium towards the unfolded state of each species. We find that a non-ionic denaturant, urea, reduces the overall aggregation rate, and that the effect on nucleation is stronger than the effect on elongation. Urea reduces the rate of secondary nucleation by decreasing the coverage of fibril surfaces and the rate of nucleus formation. It also reduces the rate of primary nucleation, increasing its reaction order. The ionic denaturant, GuHCl, accelerates the aggregation at low denaturant concentrations and decelerates the aggregation at high denaturant concentrations. Below approximately 0.25 M GuHCl, the screening of repulsive electrostatic interactions between peptides by the charged denaturant dominates, leading to an increased aggregation rate. At higher GuHCl concentrations, the electrostatic repulsion is completely screened, and the denaturing effect dominates. The results illustrate how the differential effects of denaturants on stability of monomer, oligomer and fibril translate to differential effects on microscopic steps, with the rate of nucleation being most strongly reduced.

The Journey of Human Transthyretin: Synthesis, Structure Stability, and Catabolism

Transthyretin (TTR) is a homotetrameric protein mainly synthesised by the liver and the choroid plexus whose function is to carry the thyroid hormone thyroxine and the retinol-binding protein bound to retinol in plasma and cerebrospinal fluid. When the stability of the tetrameric structure is lost, it breaks down, paving the way for the aggregation of TTR monomers into insoluble fibrils leading to transthyretin (ATTR) amyloidosis, a progressive disorder mainly affecting the heart and nervous system. Several TTR gene mutations have been characterised as destabilisers of TTR structure and are associated with hereditary forms of ATTR amyloidosis. The reason why also the wild-type TTR is intrinsically amyloidogenic in some subjects is largely unknown. The aim of the review is to give an overview of the TTR biological life cycle which is largely unknown. For this purpose, the current knowledge on TTR physiological metabolism, from its synthesis to its catabolism, is described. Furthermore, a large section of the review is dedicated to examining in depth the role of mutations and physiological ligands on the stability of TTR tetramers.

ATF6 Activation Reduces Amyloidogenic Transthyretin Secretion through Increased Interactions with Endoplasmic Reticulum Proteostasis Factors

The extracellular aggregation of destabilized transthyretin (TTR) variants is implicated in the onset and pathogenesis of familial TTR-related amyloid diseases. One strategy to reduce the toxic, extracellular aggregation of TTR is to decrease the population of aggregation-prone proteins secreted from mammalian cells. The stress-independent activation of the unfolded protein response (UPR)-associated transcription factor ATF6 preferentially decreases the secretion and subsequent aggregation of destabilized, aggregation-prone TTR variants. However, the mechanism of this reduced secretion was previously undefined. Here, we implement a mass-spectrometry-based interactomics approach to identify endoplasmic reticulum (ER) proteostasis factors involved in ATF6-dependent reductions in destabilized TTR secretion. We show that ATF6 activation reduces amyloidogenic TTR secretion and subsequent aggregation through a mechanism involving ER retention that is mediated by increased interactions with ATF6-regulated ER proteostasis factors including BiP and PDIA4. Intriguingly, the PDIA4-dependent retention of TTR is independent of both the single TTR cysteine residue and the redox activity of PDIA4, indicating that PDIA4 retains destabilized TTR in the ER through a redox-independent mechanism. Our results define a mechanistic basis to explain the ATF6 activation-dependent reduction in destabilized, amyloidogenic TTR secretion that could be therapeutically accessed to improve treatments of TTR-related amyloid diseases.

A Rare Case of I127V Heterozygous Transthyretin Amyloidosis With Atypical Transthoracic Echocardiogram Findings Presenting As Upper Extremity Sensorimotor Polyneuropathy

Hereditary transthyretin amyloidosis (hATTR) is a class of disorders with various systemic clinical manifestations, most often cardiac and neurologic in origin. The I127V mutation is a known but uncommon type of hATTR that typically affects males in their sixth or seventh decade of life. We present a case of this rare genetic variant with an atypical presentation of upper, followed by lower extremity sensorimotor polyneuropathy, with an uncharacteristic transthoracic echocardiogram (TTE) pattern but strongly positive pyrophosphate (PYP) scan, confirming the amyloidosis (AL) diagnosis.

New Advanced Imaging Parameters and Biomarkers—A Step Forward in the Diagnosis and Prognosis of TTR Cardiomyopathy

Transthyretin amyloid cardiomyopathy (ATTR-CM) is an infiltrative disorder characterized by extracellular myocardial deposits of amyloid fibrils, with poor outcome, leading to heart failure and death, with significant treatment expenditure. In the era of a novel therapeutic arsenal of disease-modifying agents that target a myriad of pathophysiological mechanisms, timely and accurate diagnosis of ATTR-CM is crucial. Recent advances in therapeutic strategies shown to be most beneficial in the early stages of the disease have determined a paradigm shift in the screening, diagnostic algorithm, and risk classification of patients with ATTR-CM. The aim of this review is to explore the utility of novel specific non-invasive imaging parameters and biomarkers from screening to diagnosis, prognosis, risk stratification, and monitoring of the response to therapy. We will summarize the knowledge of the most recent advances in diagnostic, prognostic, and treatment tailoring parameters for early recognition, prediction of outcome, and better selection of therapeutic candidates in ATTR-CM. Moreover, we will provide input from different potential pathways involved in the pathophysiology of ATTR-CM, on top of the amyloid deposition, such as inflammation, endothelial dysfunction, reduced nitric oxide bioavailability, oxidative stress, and myocardial fibrosis, and their diagnostic, prognostic, and therapeutic implications.

Enhancing autophagy in Alzheimer's disease through drug repositioning

Alzheimer's disease (AD) is one of the biggest human health threats due to increases in aging of the global population. Unfortunately, drugs for treating AD have been largely ineffective. Interestingly, downregulation of macroautophagy (autophagy) plays an essential role in AD pathogenesis. Therefore, targeting autophagy has drawn considerable attention as a therapeutic approach for the treatment of AD. However, developing new therapeutics is time-consuming and requires huge investments. One of the strategies currently under consideration for many diseases is "drug repositioning" or "drug repurposing". In this comprehensive review, we have provided an overview of the impact of autophagy on AD pathophysiology, reviewed the therapeutics that upregulate autophagy and are currently used in the treatment of other diseases, including cancers, and evaluated their repurposing as a possible treatment option for AD. In addition, we discussed the potential of applying nano-drug delivery to neurodegenerative diseases, such as AD, to overcome the challenge of crossing the blood brain barrier and specifically target molecules/pathways of interest with minimal side effects.

Transthyretin -Related Familial Amyloid Polyneuropathy (TTR-FAP) Polineuropathy – Challenge Diagnosis and Case Presentation

Introduction Transthyretin -Related Familial Amyloid Polyneuropathy (TTR-FAP) is a rare cause of polyneuropathy, mainly in Romania, but also in other geographic area of Europe, Japan and north America.

Polyneuropathies are common in neurology practice, but prevalence and incidence are not known, usually are underreported and misdiagnosis. Almost one third of polyneuropathies remain idiopathic, in spite of extensive work-out to identify etiology. Transthyretin-related familial amyloid polyneuropathy (TTR-FAP) is a multisystemic disease neurological manifestation caused by the accumulation of amyloidogenic transthyretin (TTR) protein in tissues. It is an autosomal dominant syndrome, and there are more than 100 forms of TTr associated with FAP. The disease is characterized by progressive peripheral and autonomic neuropathy, and visceral amyloid involvement like cardiac amyloidosis.

Case presentation We present the case of a male, aged 48, who experienced from 18 month paresthesias of distal inferior limb and fatigue, with an important weight loss. The patient was diagnosed with mixed polyneuropathy, and he was extensively investigated. Etiology was not established. He began to feel dizziness and faints several times, and these new features lead to our final diagnosis.

Conclusions Etiology of a polyneuropathy case could be very challenging for general neurologist due to a numerous causes. A large variety of signs and symptoms lead the clinician to a narrow diagnostic possibilities and still this might take a long time. Polyneuropathy and cardiac involvement make a mark for life threatening disease but potentially curable

The Discovery of Peptide Macrocycle Rescuers of Pathogenic Protein Misfolding and Aggregation by Integrating SICLOPPS Technology and Ultrahigh-Throughput Screening in Bacteria

The phenomenon of protein misfolding and aggregation has been widely associated with numerous human diseases, such as Alzheimer's disease, systemic amyloidosis and type 2 diabetes, the vast majority of which remain incurable. To advance early stage drug discovery against these diseases, investigation of molecular libraries with expanded diversities and ultrahigh-throughput screening methodologies that allow deeper investigation of chemical space are urgently required. Toward this, we describe how Escherichia coli can be engineered so as to enable (1) the production of expanded combinatorial libraries of short, drug-like, head-to-tail cyclic peptides and (2) their simultaneous functional screening for identifying effective inhibitors of protein misfolding and aggregation using a genetic assay that links protein folding and misfolding to cell fluorescence. In this manner, cyclic peptides with the ability to inhibit pathogenic protein misfolding and/or aggregation can be readily selected by flow cytometric cell sorting in an ultrahigh-throughput fashion. This biotechnological approach accelerates significantly the identification of hit/lead molecules with potentially therapeutic properties against devastating diseases.

Targeting transthyretin in Alzheimer's disease: Drug discovery of small-molecule chaperones as disease-modifying drug candidates for Alzheimer's disease

Transthyretin (TTR) has a well-established role in neuroprotection in Alzheimer's Disease (AD). We have setup a drug discovery program of small-molecule compounds that act as chaperones enhancing TTR/Amyloid-beta peptide (Aβ) interactions. A combination of computational drug repurposing approaches and in vitro biological assays have resulted in a set of molecules which were then screened with our in-house validated high-throughput screening ternary test. A prioritized list of chaperones was obtained and corroborated with ITC studies. Small-molecule chaperones have been discovered, among them our lead compound Iododiflunisal (IDIF), a molecule in the discovery phase; one investigational drug (luteolin); and 3 marketed drugs (sulindac, olsalazine and flufenamic), which could be directly repurposed or repositioned for clinical use. Not all TTR tetramer stabilizers behave as chaperones in vitro. These chemically diverse chaperones will be used for validating TTR as a target in vivo, and to select one repurposed drug as a candidate to enter clinical trials as AD disease-modifying drug.

Targeted treatments of AL and ATTR amyloidosis

The therapeutic landscape for cardiac amyloidosis is rapidly evolving. In the last decade, our focus has shifted from dealing with the inevitable complications of continued extracellular infiltration of amyloid fibrils to earlier identification of these patients with prompt initiation of targeted therapy to prevent further deposition. Although much of the focus on novel targeted therapies is within the realm of transthyretin amyloidosis, light chain amyloidosis has benefited due to an overlap particularly in the final common pathway of fibrillogenesis and extraction of amyloid fibrils from the heart. Here, we review the targeted therapeutics for transthyretin and light chain amyloidosis. For transthyretin amyloidosis, the list of current and future therapeutics continues to evolve; and therefore, it is crucial to become familiar with the underlying mechanistic pathways of the disease. Although targeted therapeutic choices in AL amyloidosis are largely driven by the hematology team, the cardiac adverse effect profiles of these therapies, particularly in those with advanced amyloidosis, provide an opportunity for early recognition to prevent decompensation and can help inform recommendations regarding therapy changes when required.

Effects of a Domino Liver Transplantation Program on Patient Survival and Waiting List Time: A Single-Center Retrospective Study

Explanted livers from patients with familial amyloid polyneuropathy have often been used for domino liver transplantation (DLT). This has expanded the organ pool for liver transplantation. We evaluated the effects of a single-center DLT program on waiting list duration and patient survival. Liver transplants conducted from 2007 to 2017 were analyzed. Selected patients, all liver transplant candidates above the age of 60 years and patients with hepatocellular carcinoma, were offered DLT. Survival, time on waiting list, and operative factors were evaluated. The study group included 485 patients transplanted with grafts from deceased donors (conventional liver transplantation) and 149 patients who were offered and accepted a potential DLT, of whom 34 underwent DLT and 115 did not; these patients received a deceased donor graft (non-DLT). Five-year and overall estimated survival rates respectively were 79% and 54.4% for DLT and 67.6% and 46.7% for non-DLT (P = .67, log rank test). No differences were noted in survival (P = .816) or waiting times (P = 1.0) between DLT and non-DLT groups. As expected, survival time in the conventional liver transplantation group was longer (84.7% and 60.6%, P < .001). Donor age and ischemia time were significantly different between DLT and non-DLT (P < .001). DLT has enabled 6% additional transplantations without affecting waiting time or survival (34/600).

Diagnostic Work-Up of Cardiac Amyloidosis Using Cardiovascular Imaging: Current Standards and Practical Algorithms

Among non-ischemic cardiomyopathies, cardiac amyloidosis is one of the most common, being caused by extracellular depositions of amyloid fibrils in the myocardium. Two main forms of cardiac amyloidosis are known so far, including 1) light-chain (AL) amyloidosis caused by monoclonal production of light-chains, and 2) transthyretin (ATTR) amyloidosis, caused by dissociation of the transthyretin tetramer into monomers. Both AL and ATTR amyloidosis are progressive diseases with median survival from diagnosis of less than 6 months and 3 to 5 years, respectively, if untreated. In this regard, death occurs in most patients due to cardiac causes, mainly congestive heart failure, which can be prevented due to the presence of effective, life-saving treatment regimens. Therefore, early diagnosis of cardiac amyloidosis is crucial more than ever. However, diagnosis of cardiac amyloidosis may be challenging due to variable clinical manifestations and the perceived rarity of the disease. In this regard, clinical and laboratory reg flags are available, which may help clinicians to raise suspicion of cardiac amyloidosis. In addition, advances in cardiovascular imaging have already revealed a higher prevalence of cardiac amyloidosis in specific populations, so that the diagnosis especially of ATTR amyloidosis has experienced a >30-fold increase during the past ten years. The goal of our review article is to summarize these findings and provide a practical approach for clinicians on how to use cardiovascular imaging techniques, such as echocardiography, cardiac magnetic resonance, bone scintigraphy and, if required, organ biopsy within predefined diagnostic algorithms for the diagnostic work-up of patients with suspected cardiac amyloidosis. In addition, two clinical cases and practical tips are provided in this context.

Prognostic Value of N-Terminal Pro-Brain Natriuretic Peptide and High-Sensitivity Troponin T Levels in the Natural History of Transthyretin Amyloid Cardiomyopathy and Their Evolution after Tafamidis Treatment

BACKGROUND

We assesse the evolution and prognostic value of N-terminal pro-brain natriuretic peptide (NT-proBNP) and high-sensitivity troponin T (cTnT-HS) in transthyretin amyloid cardiomyopathy (ATTR-CA) before and after tafamidis treatment.

METHODS AND RESULTS

454 ATTR-CA patients without tafamidis (Cohort A) and 248 ATTR-CA with tafamidis (Cohort B) were enrolled. Event-free survival (EFS) events were death, heart transplant, or acute heart failure. In Cohort A, 27% of patients maintained NT-proBNP < 3000 ng/L and 14% cTnT-HS < 50 ng/L at 12 months relative to baseline levels. In Cohort B, the proportions were 49% and 29%, respectively. In Cohort A, among the 333 patients without an increased NT-proBNP > 50% relative to baseline EFS was extended compared to the 121 patients with an increased NT-proBNP > 50% (HR: 0.75 [0.57; 0.98]; p = 0.032). In Cohort A, baseline NT-proBNP > 3000 ng/L and cTnT-HS > 50 ng/L and a relative increase of NT-proBNP > 50% during follow-up were independent prognostic factors of EFS. The slopes of logs NT-proBNP and cTnT-HS increased with time before and stabilized after tafamidis.

CONCLUSION

ATTR-CA patients with increasing NT-proBNP had an increased risk of EFS. Tafamidis stabilize NT-proBNP and cTnT-HS increasing, even if initial NT-proBNP levels were >3000 ng/L. Thus suggesting that all patients, irrespective of baseline NT-proBNP levels, may benefit from tafamidis.

Modeling of Survival and Frequency of Cardiovascular-Related Hospitalization in Patients with Transthyretin Amyloid Cardiomyopathy Treated with Tafamidis

Introduction

ATTR-ACT (Tafamidis in Transthyretin Cardiomyopathy Clinical Trial) demonstrated the efficacy and safety of tafamidis in transthyretin amyloid cardiomyopathy (ATTR-CM). Model-based analyses from ATTR-ACT can examine predictor effects on dose–response/exposure–response relationships.

Methods

Parametric hazard distributions were developed for all-cause mortality and frequency of cardiovascular-related hospitalization. Time-to-event models were fitted to survival data, and repeated time-to-event models were fitted to hospitalization data. Disease-specific characteristics were assessed as baseline predictors of event hazards.

Results

There were 441 patients in this analysis. At month 30, 70.5% (tafamidis) and 57.1% (placebo) of patients were alive, with 154/441 deaths reported; 495 cardiovascular-related hospitalizations occurred. The cumulative risk of death was 42.1% (95% confidence interval [CI] 24.2–58.0) lower with tafamidis than with placebo, regardless of New York Heart Association (NYHA) class; significant predictors of decreased risk were genotype (wild-type), greater 6-Minute Walk Test (6MWT) distance, higher left ventricular ejection fraction (LVEF), and lower blood urea nitrogen (BUN) and N-terminal pro-B-type natriuretic peptide concentrations. The average cumulative risk of cardiovascular-related hospitalization up to 30 months was 40.8% (95% CI 31.0–49.7) lower with tafamidis in NYHA class I/II patients. Significant predictors of reduced risk were greater 6MWT distance, higher LVEF, and lower BUN and troponin I concentrations.

Conclusions

Tafamidis reduced cumulative mortality and hospitalization risk versus placebo in patients with ATTR-CM. Baseline predictors of outcome were consistent with the cardiovascular nature of the disease and suggested that earlier treatment may improve outcomes.

Clinical Trials.gov Identifier

NCT01994889 (date of registration: November 26, 2013).

Supplementary Information

The online version contains supplementary material available at 10.1007/s40256-021-00464-y.

Symptomatic Val122del mutated hereditary transthyretin amyloidosis: Need for early diagnosis and prioritization for heart and liver transplantation

BACKGROUND

Hereditary transthyretin (ATTRv) amyloidosis is an autosomal dominant disease linked to transthyretin gene mutations which cause instability of the transthyretin tetramer. After dissociation and misfolding they reassemble as insoluble fibrils (i.e. amyloid). Apart from the common Val30Met mutation there is a very heterogeneous group of non-Val30Met mutations. In some cases, the clinical picture is dominated by a rapidly evolving restrictive and hypertrophic cardiomyopathy.

METHODS

A case series of four liver recipients with the highly clinically relevant, rare and particularly aggressive Val122del mutation is presented. Medical and surgical therapeutic options, waiting list policy for ATTRv-amyloidosis, including the need for heart transplantation, and status of heart-liver transplantation are discussed.

RESULTS

Three patients needed a staged (1 patient) or simultaneous (2 patients) heart-liver transplant due to rapidly progressing cardiac failure and/or neurologic disability. Domino liver transplantation was impossible in two due to fibrotic hepatic transformation caused by cardiomyopathy. After a follow-up ranging from 3.5 to 9.5 years, cardiac (allograft) function was maintained in all patients, but neuropathy progressed in three patients, one of whom died after 80 months.

CONCLUSIONS

This is the first report in (liver) transplant literature about the rare Val122del ATTRv mutation. Due to its aggressiveness, symptomatic patients should be prioritized on the liver and, in cases with cardiomyopathy, heart waiting lists in order to avoid the irreversible neurological and cardiac damage that leads to a rapid lethal outcome.

Disease-associated mutations impacting BC-loop flexibility trigger long-range transthyretin tetramer destabilization and aggregation

Hereditary transthyretin amyloidosis (ATTR) is an autosomal dominant disease characterized by the extracellular deposition of the transport protein transthyretin (TTR) as amyloid fibrils. Despite the progress achieved in recent years, understanding why different TTR residue substitutions lead to different clinical manifestations remains elusive. Here, we studied the molecular basis of disease-causing missense mutations affecting residues R34 and K35. R34G and K35T variants cause vitreous amyloidosis, whereas R34T and K35N mutations result in amyloid polyneuropathy and restrictive cardiomyopathy. All variants are more sensitive to pH-induced dissociation and amyloid formation than the wild-type (WT)-TTR counterpart, specifically in the variants deposited in the eyes amyloid formation occurs close to physiological pHs. Chemical denaturation experiments indicate that all the mutants are less stable than WT-TTR, with the vitreous amyloidosis variants, R34G and K35T, being highly destabilized. Sequence-induced stabilization of the dimer–dimer interface with T119M rendered tetramers containing R34G or K35T mutations resistant to pH-induced aggregation. Because R34 and K35 are among the residues more distant to the TTR interface, their impact in this region is therefore theorized to occur at long range. The crystal structures of double mutants, R34G/T119M and K35T/T119M, together with molecular dynamics simulations indicate that their strong destabilizing effect is initiated locally at the BC loop, increasing its flexibility in a mutation-dependent manner. Overall, the present findings help us to understand the sequence-dynamic-structural mechanistic details of TTR amyloid aggregation triggered by R34 and K35 variants and to link the degree of mutation-induced conformational flexibility to protein aggregation propensity.

Identification of Transthyretin Tetramer Kinetic Stabilizers That Are Capable of Inhibiting the Retinol-Dependent Retinol Binding Protein 4-Transthyretin Interaction: Potential Novel Therapeutics for Macular Degeneration, Transthyretin Amyloidosis, and Their Common Age-Related Comorbidities

Dissociation of transthyretin (TTR) tetramers may lead to misfolding and aggregation of proamyloidogenic monomers, which underlies TTR amyloidosis (ATTR) pathophysiology. ATTR is a progressive disease resulting from the deposition of toxic fibrils in tissues that predominantly presents clinically as amyloid cardiomyopathy and peripheral polyneuropathy. Ligands that bind to and kinetically stabilize TTR tetramers prohibit their dissociation and may prevent ATTR onset. Drawing from clinically investigated AG10, we designed a constrained congener (14) that exhibits excellent TTR tetramer binding potency, prevents TTR aggregation in a gel-based assay, and possesses desirable pharmacokinetics in mice. Additionally, 14 significantly lowers murine serum retinol binding protein 4 (RBP4) levels despite a lack of binding at that protein's all-trans-retinol site. We hypothesize that kinetic stabilization of TTR tetramers via 14 is allosterically hindering all-trans-retinol-dependent RBP4-TTR tertiary complex formation and that the compound could present ancillary therapeutic utility for indications treated with RBP4 antagonists, such as macular degeneration.

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.

Canadian Guidelines for Hereditary Transthyretin Amyloidosis Polyneuropathy Management

Hereditary transthyretin-mediated (hATTR) amyloidosis is a progressive disease caused by mutations in the TTR gene leading to multisystem organ dysfunction. Pathogenic TTR aggregation, misfolding, and fibrillization lead to deposition of amyloid in multiple body organs and frequently involve the peripheral nerve system and the heart. Common neurologic manifestations include: sensorimotor polyneuropathy (PN), autonomic neuropathy, small-fiber PN, and carpal tunnel syndrome. Many patients have significant progression due to diagnostic delays as hATTR PN is not considered within the differential diagnosis. Recently, two effective novel disease-modifying therapies, inotersen and patisiran, were approved by Health Canada for the treatment of hATTR PN. Early diagnosis is crucial for the timely introduction of these disease-modifying treatments that reduce impairments, improve quality of life, and extend survival. In this guideline, we aim to improve awareness and outcomes of hATTR PN by making recommendations directed to the diagnosis, monitoring, and treatment in Canada.

Population pharmacokinetic modelling and simulation of tafamidis in healthy subjects and patients with transthyretin amyloidosis

AIMS

Since the first approval for transthyretin amyloid polyneuropathy patients, new formulations and different strength of tafamidis have been developed and tested in a different population (transthyretin amyloid cardiomyopathy). The objective of this analysis was to develop a unified population pharmacokinetic (PK) model of tafamidis, which can describe the PK of various different formulations in healthy subjects as well as patients with TTR amyloidosis, and to understand effects of intrinsic and extrinsic factors on the PK variability.

METHODS

Pooled data from 23 clinical studies (17 Phase 1 and 6 Phase 2/3 studies) were used for the analysis. The plasma concentration-time data were analysed using a nonlinear mixed effects modelling methodology. Covariate analysis was performed using a stepwise covariate model building procedure.

RESULTS

The final model was a 2-compartment model with first-order absorption and elimination coupled with an absorption lag time for nonsolution formations. Body weight, food and tafamidis formulations were incorporated as structural covariates on PK parameters. Covariate analysis further identified age ≥65 years (14.5% decrease) and moderate hepatic impairment effects (57.6% increase) on apparent clearance and transthyretin amyloid polyneuropathy effect (17.3% decrease) on F. However, model-based clinical trial simulation results indicated that tafamidis steady-state exposure changes were not clinically meaningful under the tested conditions.

CONCLUSIONS

The unified population PK model of tafamidis was developed based on 23 studies. Subsequent clinical trial simulations indicated that no significant changes in tafamidis exposure necessitating a dose modification are expected due to either extrinsic or intrinsic factors. The model was used to support labelling statements for dose recommendations in special populations.

Tafamidis: A Review in Transthyretin Amyloid Cardiomyopathy

Transthyretin amyloid cardiomyopathy (ATTR-CM) is a progressive, life-threatening disease characterized by the aggregation and deposition of amyloidogenic misfolded transthyretin (TTR) in the myocardium. The gradual accumulation of insoluble TTR amyloid fibrils can result in restrictive cardiomyopathy and heart failure. Tafamidis (Vyndaqel^®; Vyndamax^®), a TTR stabilizer, has been approved for use in the treatment of adults with ATTR-CM in several countries. Tafamidis stabilizes both wild-type and mutant TTR, inhibiting the formation of TTR amyloid fibrils. In the pivotal phase III ATTR-ACT trial, tafamidis significantly reduced all-cause mortality and frequency of cardiovascular-related hospitalizations relative to placebo in patients with ATTR-CM. In addition, tafamidis recipients experienced significantly less deterioration in 6-minute walk test distance and quality of life than placebo recipients over the 30-month treatment period. Treatment benefits were largely consistent between patients with wild-type TTR and patients with a variant TTR genotype. Tafamidis was generally well tolerated in patients with ATTR-CM and, with a safety profile similar to that of placebo, tafamidis is suitable for long-term use. Given that treatment for this condition has in the past been largely limited to symptom management, tafamidis constitutes a valuable disease-modifying therapy for patients with ATTR-CM.

Modulation of the Mechanisms Driving Transthyretin Amyloidosis

Transthyretin (TTR) amyloidoses are systemic diseases associated with TTR aggregation and extracellular deposition in tissues as amyloid. The most frequent and severe forms of the disease are hereditary and associated with amino acid substitutions in the protein due to single point mutations in the TTR gene (ATTRv amyloidosis). However, the wild type TTR (TTR wt) has an intrinsic amyloidogenic potential that, in particular altered physiologic conditions and aging, leads to TTR aggregation in people over 80 years old being responsible for the non-hereditary ATTRwt amyloidosis. In normal physiologic conditions TTR wt occurs as a tetramer of identical subunits forming a central hydrophobic channel where small molecules can bind as is the case of the natural ligand thyroxine (T₄). However, the TTR amyloidogenic variants present decreased stability, and in particular conditions, dissociate into partially misfolded monomers that aggregate and polymerize as amyloid fibrils. Therefore, therapeutic strategies for these amyloidoses may target different steps in the disease process such as decrease of variant TTR (TTRv) in plasma, stabilization of TTR, inhibition of TTR aggregation and polymerization or disruption of the preformed fibrils. While strategies aiming decrease of the mutated TTR involve mainly genetic approaches, either by liver transplant or the more recent technologies using specific oligonucleotides or silencing RNA, the other steps of the amyloidogenic cascade might be impaired by pharmacologic compounds, namely, TTR stabilizers, inhibitors of aggregation and amyloid disruptors. Modulation of different steps involved in the mechanism of ATTR amyloidosis and compounds proposed as pharmacologic agents to treat TTR amyloidosis will be reviewed and discussed.

Functional and Biochemical Consequences of Disease Variants in Neurotransmitter Transporters: A Special Emphasis on Folding and Trafficking Deficits

Neurotransmitters, such as γ-aminobutyric acid, glutamate, acetyl choline, glycine and the monoamines, facilitate the crosstalk within the central nervous system. The designated neurotransmitter transporters (NTTs) both release and take up neurotransmitters to and from the synaptic cleft. NTT dysfunction can lead to severe pathophysiological consequences, e.g. epilepsy, intellectual disability, or Parkinson’s disease. Genetic point mutations in NTTs have recently been associated with the onset of various neurological disorders. Some of these mutations trigger folding defects in the NTT proteins. Correct folding is a prerequisite for the export of NTTs from the endoplasmic reticulum (ER) and the subsequent trafficking to their pertinent site of action, typically at the plasma membrane. Recent studies have uncovered some of the key features in the molecular machinery responsible for transporter protein folding, e.g., the role of heat shock proteins in fine-tuning the ER quality control mechanisms in cells. The therapeutic significance of understanding these events is apparent from the rising number of reports, which directly link different pathological conditions to NTT misfolding. For instance, folding-deficient variants of the human transporters for dopamine or GABA lead to infantile parkinsonism/dystonia and epilepsy, respectively. From a therapeutic point of view, some folding-deficient NTTs are amenable to functional rescue by small molecules, known as chemical and pharmacological chaperones.

Oligomerization Profile of Human Transthyretin Variants with Distinct Amyloidogenicity

One of the molecular hallmarks of amyloidoses is ordered protein aggregation involving the initial formation of soluble protein oligomers that eventually grow into insoluble fibrils. The identification and characterization of molecular species critical for amyloid fibril formation and disease development have been the focus of intense analysis in the literature. Here, using photo-induced cross-linking of unmodified proteins (PICUP), we studied the early stages of oligomerization of human transthyretin (TTR), a plasma protein involved in amyloid diseases (ATTR amyloidosis) with multiple clinical manifestations. Upon comparison, the oligomerization processes of wild-type TTR (TTRwt) and several TTR variants (TTRV30M, TTRL55P, and TTRT119M) clearly show distinct oligomerization kinetics for the amyloidogenic variants but a similar oligomerization mechanism. The oligomerization kinetics of the TTR amyloidogenic variants under analysis showed a good correlation with their amyloidogenic potential, with the most amyloidogenic variants aggregating faster (TTRL55P > TTRV30M > TTRwt). Moreover, the early stage oligomerization mechanism for these variants involves stepwise addition of monomeric units to the growing oligomer. A completely different behavior was observed for the nonamyloidogenic TTRT119M variant, which does not form oligomers in the same acidic conditions and even for longer incubation times. Thorough characterization of the initial steps of TTR oligomerization is critical for better understanding the origin of ATTR cytotoxicity and developing novel therapeutic strategies for the treatment of ATTR amyloidosis.

Diagnosis and treatment of cardiac amyloidosis: an interdisciplinary consensus statement

The prevalence and significance of cardiac amyloidosis have been considerably underestimated in the past; however, the number of patients diagnosed with cardiac amyloidosis has increased significantly recently due to growing awareness of the disease, improved diagnostic capabilities and demographic trends. Specific therapies that improve patient prognosis have become available for certain types of cardiac amyloidosis. Thus, the earliest possible referral of patients with suspicion of cardiac amyloidosis to an experienced center is crucial to ensure rapid diagnosis, early initiation of treatment, and structured patient care. This requires intensive collaboration across several disciplines, and between resident physicians and specialized centers. The aim of this consensus statement is to provide guidance for the rapid and efficient diagnosis and treatment of light-chain amyloidosis and transthyretin amyloidosis, which are the most common forms of cardiac amyloidosis.