Abstract Or301: Preclinical characterization of CK-4021586, a new class of cardiac myosin inhibitors, for the treatment of heart failure with preserved ejection fraction

Clinical trials of cardiac myosin inhibitors, including mavacamten and aficamten , have been shown to induce cardiac remodeling and improve exercise capacity of patients with hypertrophic cardiomyopathy (HCM) with left ventricular outflow tract obstruction. A subset of patients with heart failure with preserved ejection fraction (HFpEF) have overlapping features with HCM including hypercontractility (EF >65%), thickened heart walls and impaired diastolic function. This similarity suggests myosin inhibitors could be therapeutic in treating HFpEF. Here, we describe the preclinical characterization of a novel cardiac myosin inhibitor, CK-4021586 (CK-586), which has a distinct mechanism of action from both mavacamten and aficamten . CK-586 is a partial inhibitor of cardiac myofibrillar ATPase activity (EC50: 2.9 µM, maximal biochemical inhibition ~50%) which requires the presence of two-headed heavy meromyosin (HMM) and the regulatory light chain. CK-586 potently inhibited sarcomere shortening in both rat and human adult ventricular cardiomyocytes, with IC50 values of 3.2 µM and 2.8 µM respectively, achieving over 80% inhibition at 10 µM. Importantly, even at high concentrations up to 20 µM, CK-586 did not affect calcium transients in rat myocytes. Similarly, CK-586 effectively normalized contractile function in engineered heart tissues derived from human iPSC-cardiomyocytes carrying the HCM-associated R403Q myosin mutation. At 2 µM, the compound restored contractile force and relaxation time (RT90) to near-normal levels, while showing >80% force inhibition at 10 µM. In the ZSF1 obese HFpEF rat model, 16 weeks of CK-586 treatment reduced fractional shortening (vehicle: 52.7 ± 2.9% vs. CK-586: 48.1 ± 2.6%) and as a measure of diastolic function, improved isovolumic relaxation time (vehicle: 27.0 ± 2.2 ms vs. CK-586: 23.3 ± 2.3 ms). ZSF1 obese rats treated with CK-586 also demonstrated approximately 50% lower interstitial fibrosis compared to untreated controls. In conclusion, CK-586 is a novel, small molecule, cardiac myosin inhibitor that reduces contractility in vitro and in vivo . These findings suggest that targeting cardiac myosin to reduce contractility could help reverse some of the structural changes associated with HFpEF and improve cardiac relaxation.