Vutrisiran-Mediated Knockdown of Transthyretin in Patients with ATTR Amyloidosis

Background and objective: We assessed the consistency of serum transthyretin (TTR) knockdown with the RNA interference therapeutic vutrisiran across subpopulations of patients with hereditary TTR amyloidosis (ATTR) with polyneuropathy (ATTRv-PN) in HELIOS-A (NCT03759379) and ATTR with cardiomyopathy (ATTR-CM) in HELIOS-B (NCT04153149). Methods: Patients received vutrisiran 25 mg subcutaneously every 3 months (Q3M). Serum TTR was measured during randomized treatment through Month 18 in HELIOS-A (post-dose/peak and pre-dose/trough sampling) and Month 30 in HELIOS-B (trough only, except Week 6). The effects of intrinsic/extrinsic factors on serum TTR knockdown from baseline were assessed. Pharmacokinetic/pharmacodynamic modeling was used to support consistency in TTR knockdown between studies. Results: Observed median (95% confidence interval [CI]) serum TTR knockdown with vutrisiran was 64.2% (61.6-67.8) at Week 3 (n = 114), with steady-state trough knockdown 86.2% (84.1-92.6) (n = 118) in HELIOS-A, and 69.0% (66.0-72.0) at Week 6 (n = 294), with steady-state trough knockdown 82.5% (80.5-84.9) (n = 307) in HELIOS-B. There were no meaningful differences in serum TTR percent knockdown across subgroups defined by baseline characteristics, including age, sex, ethnicity/race, weight, TTR genotype, N-terminal pro-B-type natriuretic peptide, and serum TTR concentration (both studies), and ATTRwt/ATTRv, disease stage/severity, troponin I, and tafamidis use (HELIOS-B), or anti-drug antibodies. Model-predicted peak serum TTR knockdown in HELIOS-B was sustained and consistent with observed knockdown in HELIOS-A; predicted median (95% CI) reduction at Month 30 was 87.1% (84.8-89.4). Conclusions: Vutrisiran led to rapid, sustained, and consistent TTR knockdown in HELIOS-A and HELIOS-B, supporting fixed-dose vutrisiran 25 mg Q3M across patients with ATTRv-PN and ATTR-CM.