Differential Transthyretin Stabilization in Patients With Wild Type and Variant Transthyretin Amyloidosis

Background: Transthyretin amyloid cardiomyopathy (ATTR-CM) is a progressive, often fatal disease caused by transthyretin (TTR) tetramer destabilization, leading to amyloid deposition from either age-related wild type TTR or pathogenic TTR variants. TTR variants are less stable than wild type TTR, leading to lower serum TTR (sTTR) and worse clinical outcomes. TTR stabilizers, tafamidis and acoramidis, are approved for treatment of patients with ATTR-CM. Objectives: The aim of this study was to evaluate the differences in stabilizing effect and magnitude of sTTR increases for acoramidis and tafamidis using data from the ATTRibute-CM (Efficacy and Safety of AG10 in Subjects With Transthyretin Amyloid Cardiomyopathy) trial. Methods: Stabilizing potency was analyzed using sTTR as an in vivo readout and by applying 2 orthogonal pharmacodynamic assays: Western blot and fluorescent probe exclusion. In vitro analyses used blood samples from patients with variant ATTR-CM at clinically relevant concentrations of acoramidis (10 μM) and tafamidis (16-26 μM). Results: In ATTRibute-CM, treatment with acoramidis (n = 234) resulted in a greater rise in sTTR from baseline to month 30 vs placebo plus tafamidis (n = 34). Acoramidis achieved greater TTR stabilization than placebo plus tafamidis at month 30 by Western blot (90.2% [n = 83] vs 60.6% [n = 6]) and fluorescent probe exclusion (99.7% [n = 71] vs 68.0% [n = 4]), although this was limited by a small sample size. Subsequent in vitro analysis corroborated acoramidis was a more effective TTR stabilizer than tafamidis across all 51 individual participant samples tested, representing 17 unique variants. Conclusions: Acoramidis is a near-complete stabilizer of wild type and variant TTR. Although in vitro comparisons between acoramidis and tafamidis suggest greater stabilization by acoramidis, randomized prospective trial data comparing these TTR stabilizers are lacking, and further investigation is warranted. (Efficacy and Safety of AG10 in Subjects With Transthyretin Amyloid Cardiomyopathy [ATTRibute-CM]; NCT03860935).