Clinical Evaluation of the Effect of Aficamten on <scp>QT</scp>/<scp>QTc</scp> Interval in Healthy Participants

Aficamten is a next-in-class, small-molecule, cardiac myosin inhibitor in development for treating hypertrophic cardiomyopathy (HCM). This 2-part study evaluated aficamten's impact on QTc interval in healthy participants. Part A (n = 10) was an open-label study to find the appropriate dose for thorough QT (TQT) evaluation in Part B. Part B (n = 34) was a double-blind, 3-way crossover TQT study conducted as per ICH E14 guidance using negative (placebo) and positive (moxifloxacin) controls. A single 50 mg aficamten dose achieved exposures (C_max range: 124-1660 ng/mL) comparable to the highest clinical dose (20 mg QD) in obstructive HCM patients (NCT05186818; [C_max range: 131-1230 ng/mL]) and was chosen for TQT evaluation. Using concentration-QT (C-QT) modeling, the placebo- and baseline-corrected QT interval using Fridericia's correction (ΔΔQTcF) was -1.82 msec (90% CI: -3.43, -0.214) at peak aficamten concentrations (298.3 ng/mL) following the 50 mg dose. The 90% CI upper bound of ΔΔQTcF for aficamten was < 10 msec at all post-dose time points. Assay sensitivity was established by the 90% CI lower bound for moxifloxacin (ΔΔQTcF) exceeding 5 msec. Aficamten did not cause QTc prolongation (using C-QT and by time point analyses) within observed plasma concentrations up to 1660 ng/mL (aficamten), 213 ng/mL (metabolite CK-3834282), and 343 ng/mL (metabolite CK-3834283). No clinically meaningful effect on electrocardiogram parameters, including absolute QTcF (≤ 450 msec) and change from baseline in QTcF (≤ 30 msec) was noted in aficamten-treated participants. Aficamten was generally well tolerated. In conclusion, there was no evidence of aficamten-mediated QTc prolongation across the therapeutic concentration range in a formal TQT study.