Preclinical characterization of CK-4021586, a new class of cardiac myosin inhibitors for the treatment of hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy (HCM) is the most common monogenetic heart disease, with an estimated carrier prevalence of ∼1 in 500. Hypercontractility of the cardiac sarcomere is a common driver of the pathological hypertrophic cardiac remodeling that is a hallmark of the disease. Clinical trials of the selective cardiac myosin inhibitors mavacamten and aficamten have demonstrated that inhibition of the biochemical activity of cardiac myosin can induce cardiac remodeling and improve both patient symptoms and exercise capacity in HCM with left ventricular outflow tract obstruction (oHCM). The diverse genetic underpinnings of HCM suggest that it is possible that additional classes of cardiac myosin inhibitors with distinct biochemical mechanisms-of-action may also have a salutary impact on disease expression. While both mavacamten and aficamten bind to the single-headed motor domain of myosin (subfragment-1) and inhibit its ATPase activity, CK-4021586 (CK-586) is a new class of cardiac myosin inhibitor that inhibits the ATPase activity of two-headed heavy meromyosin (HMM) but not single-headed subfragment-1. CK-586 is a partial inhibitor of cardiac myofibrillar ATPase activity (EC50 2.9 µM, maximal inhibition ∼50%) that requires the regulatory light chain. Notably, fractional shortening of electrically-paced adult rat ventricular cardiomyocytes was inhibited almost completely (>80% at 5 µM) without alterations in the calcium (Ca2+) transient. In normal Sprague Dawley rats, CK-586 reduced cardiac fractional shortening in a dose and concentration-dependent manner. In conclusion, CK-586 is a novel, small molecule, cardiac myosin inhibitor that reduces cardiac contractility in vitro and in vivo. CK-586 has a biochemical mechanism of action distinct from both mavacamten and aficamten, providing an additional tool to decrease the number of functionally-available myosin heads and treat the cardiac hypercontractility that forms the pathologic basis of HCM.