Dose-finding Study to Evaluate the Safety, Tolerability, Pharmacokinetics, and Pharmacodynamics of CK-3773274 in Adults With Hypertrophic Cardiomyopathy

This was a Phase 2, multi-center, randomized, placebo-controlled, double-blind, dose-finding study in participants with symptomatic HCM. The study consisted of 4 cohorts. For Cohorts 1 and 2, participants with obstructive HCM (oHCM) and not receiving disopyramide were randomized 2:1 to active or placebo treatment and received up to 3 escalating doses of aficamten (5, 10, and 15 mg once daily in Cohort 1 and 10, 20, and 30 mg once daily in Cohort 2) or placebo based on site-read echocardiographic guidance. Cohort 3 consisted of participants with oHCM whose background HCM therapy included disopyramide. All participants in Cohort 3 received up to 3 escalating doses of aficamten (5, 10, and 15 mg once daily) based on echocardiographic guidance. Cohort 4 consisted of participants with non-obstructive HCM (nHCM) on standard of care background therapy. Cohort 4 participants received up to 3 doses of aficamten (5, 10, and 15 mg once daily), titrated based on site-read echocardiographic guidance.

In all 4 cohorts, treatment duration was 10 weeks with a 4-week follow-up period after the last dose.

Inclusion criteria

• Males and females between 18 and 85 years of age at screening.
• Body weight is ≥45 kg at screening.
• Diagnosed with HCM per the following criteria:

• Has left ventricular (LV) hypertrophy with non-dilated LV chamber in the absence of other cardiac disease.
• Has minimal wall thickness ≥15 mm (minimal wall thickness ≥13 mm is acceptable with a positive family history of HCM or with a known disease-causing gene mutation).
• Adequate acoustic windows for echocardiography.
• For Cohorts 1, 2 and 3 has LVOT-G during screening as follows:

• Resting gradient ≥50 mmHg OR
• Resting gradient ≥30 mmHg and <50 mmHg with post-Valsalva LVOT-G ≥50 mmHg
• For Cohort 4 has resting and post-Valsalva LVOT-G < 30 mmHg at the time of screening
• For Cohort 4 has elevated NT-proBNP > 300 pg/mL at the time of screening
• LVEF ≥60% at screening.
• New York Heart Association (NYHA) Class II or III at screening.
• Patients on beta-blockers, verapamil, diltiazem, or ranolazine should have been on stable doses for >4 weeks prior to randomization and anticipate remaining on the same medication regimen during the study.
• For Cohort 3: Patients must be taking disopyramide. Patients should have been on stable disopyramide doses for >4 weeks prior to screening and anticipate remaining on the same medication regimen during the study.

Exclusion criteria

• Aortic stenosis or fixed subaortic obstruction.
• Known infiltrative or storage disorder causing cardiac hypertrophy that mimics oHCM (eg, Noonan syndrome, Fabry disease, amyloidosis).
• History of LV systolic dysfunction (LVEF <45%) at any time during their clinical course.
• Documented history of current obstructive coronary artery disease (>70% stenosis in one or more epicardial coronary arteries) or documented history of myocardial infarction.
• Has been treated with septal reduction therapy (surgical myectomy or percutaneous alcohol septal ablation) or has plans for either treatment during the study period (Cohorts 1, 2, and 3 only). Patients having undergone septal reduction therapy > 12 months prior to screening who remain symptomatic from nHCM, and who meet all other criteria for inclusion, may be enrolled in Cohort 4.
• For Cohorts 1, 2 and 4: Has been treated with disopyramide or antiarrhythmic drugs that have negative inotropic activity within 4 weeks prior to screening. (For Cohort 3, use of disopyramide is required).
• Has any ECG abnormality considered by the investigator to pose a risk to patient safety (eg, second degree atrioventricular block type II).
• Paroxysmal atrial fibrillation or flutter documented during the screening period.
• Paroxysmal or permanent atrial fibrillation requiring rhythm restoring treatment (eg, direct-current cardioversion, ablation procedure, or antiarrhythmic therapy) ≤6 months prior to screening. (This exclusion does not apply if atrial fibrillation has been treated with anticoagulation and adequately rate-controlled for >6 months).
• History of syncope or sustained ventricular tachyarrhythmia with exercise within 6 months prior to screening.
• Has received prior treatment with CK-3773274 or mavacamten.
• For Cohort 4: has any documented history of LVOT-G ≥ 30 mmHg at rest, with Valsalva, or with exercise (for subjects who have had prior septal reduction therapy, this exclusion criteria only applies to gradients detected following septal reduction therapy).