Potent kinetic stabilizers that prevent transthyretin-mediated cardiomyocyte proteotoxicity

Diflunisal for ATTR cardiac amyloidosis

Transthyretin (TTR) cardiac amyloidosis is an important, often under-recognized and potentially modifiable cause of heart failure with a preserved ejection fraction. The only proven treatment is liver or combined heart/liver transplantation, which, although effective, is not suitable for the vast majority of older adults with this condition. Diflunisal, a nonsteroidal anti-inflammatory drug, can stabilize the TTR tetramer in vitro and may prevent misfolding monomers and dimers from forming amyloid deposits in the heart. It is one of two small molecules assessed in animal safety studies and human clinical trials of TTR polyneuropathy. The authors conducted a single-arm, open-label investigation with a mean follow-up of 0.9 ± 0.3 years to determine the safety and efficacy of diflunisal administration in a cohort of 13 patients with confirmed wild-type or mutant TTR cardiac amyloidosis. Diflunisal was well tolerated from a hematologic standpoint, although a 6% decline in estimated glomerular filtration rate was noted. Therapy was discontinued in one patient who rapidly developed volume overload. There was no significant mean change in cardiac structure (left ventricular mass: -53 g/m(2) change, P=.36), function (ejection fraction: -2% change, P=.61), or biomarkers (Troponin I: +0.03 ng/mL, P=.08; BNP: +93 pg/mL change, P=.52) during the course of therapy. These data suggest that at low dosages and with careful monitoring, diflunisal can be safely administered to compensated patients with cardiac TTR amyloidosis. Further study in a randomized placebo-controlled trial is warranted.

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.

Small-molecule targeting of proliferating cell nuclear antigen chromatin association inhibits tumor cell growth

Proliferating cell nuclear antigen (PCNA), a potential anticancer target, forms a homotrimer and is required for DNA replication and numerous other cellular processes. The purpose of this study was to identify novel small molecules that modulate PCNA activity to affect tumor cell proliferation. An in silico screen of a compound library against a crystal structure of PCNA and a subsequent structural similarity search of the ZINC chemical database were carried out to derive relevant docking partners. Nine compounds, termed PCNA inhibitors (PCNA-Is), were selected for further characterization. PCNA-I1 selectively bound to PCNA trimers with a dissociation constant (K(d)) of ~0.2 to 0.4 μM. PCNA-Is promoted the formation of SDS-refractory PCNA trimers. PCNA-I1 dose- and time-dependently reduced the chromatin-associated PCNA in cells. Consistent with its effects on PCNA trimer stabilization, PCNA-I1 inhibited the growth of tumor cells of various tissue types with an IC(50) of ~0.2 μM, whereas it affected the growth of nontransformed cells at significantly higher concentrations (IC(50), ~1.6 μM). Moreover, uptake of BrdU was dose-dependently reduced in cells treated with PCNA-I1. Mechanistically the PCNA-Is mimicked the effect of PCNA knockdown by siRNA, inducing cancer cell arrest at both the S and G(2)/M phases. Thus, we have identified a class of compounds that can directly bind to PCNA, stabilize PCNA trimers, reduce PCNA association with chromatin, and inhibit tumor cell growth by inducing a cell cycle arrest. They are valuable tools in studying PCNA function and may be useful for future PCNA-targeted cancer therapy.

Familial amyloidotic polyneuropathy and transthyretin

There has been much progress in our understanding of transthyretin (TTR)-related amyloidosis including familial amyloidotic polyneuropathy (FAP), senile systemic amyloidosis and its related disorders from many clinical and experimental aspects. FAP is an inherited severe systemic amyloidosis caused by mutated TTR, and characterized by amyloid deposition mainly in the peripheral nervous system and the heart. Liver transplantation is the only available treatment for the disease. FAP is now recognized not to be a rare disease, and to have many variations based on genetical and biochemical variations of TTR. This chapter covers the recent advances in the clinical and pathological aspects of, and therapeutic approaches to FAP, and the trend as to the molecular pathogenesis of TTR.