Abstract 10925: A Small Molecule Inhibitor of Sarcomere Contractility Acutely Relieves Prolonged Relaxation in Human-Induced Pluripotent Stem Cell-Derived Cardiomyocytes With Hypertrophic Cardiomyopathy

Abstract

Hypertrophic cardiomyopathy (HCM) is one of the most common genetic cardiac diseases primarily caused by mutations in sarcomeric genes. However, HCM is also associated with mutations in non-sarcomeric proteins and a Finnish founder mutation for HCM in non-sarcomeric protein junctophilin-2 (JPH2) has been identified. MYK-461 is a recently described mechanistically novel small molecule that acts at the sarcomere to specifically inhibit contractility that has been proposed as a treatment for HCM. Here, we use MYK-461 to test whether direct reduction in contractility is sufficient to relieve phenotypic characteristics in human-induced pluripotent stem cell derived cardiomyocytes (hiPSC-CMs) carrying JPH2 mutation T161K. Hypothesis: Currently all HCM patients are treated the same regardless of the underlying genetic defect. Current medication does not prevent or stop the thickening of the heart muscle; only the symptoms and arrhythmias can be controlled with beta-blockers or calcium blockers. MYK-461 decreases adenosine triphosphatase activity of the cardiac myosin heavy chain to reduce contractility, thus modifying the characteristic pathology of HCM. Methods: Skin fibroblasts from a Finnish patient with HCM causing JPH2 p.(Thr161Lys) were reprogrammed into hiPSCs and further differentiated into CMs. As a control line, an isogenic counterpart was generated using the CRISPR/Cas9 genome editing method. We evaluated the effect of MYK-461 treatment to T161K-hiPSC-CMs by their functional characteristics associated with JPH2 mutation. Results: By video microscopy, we identified increased contractility (BPM; 41±6 SEM, n=9) and prolonged diastolic phase (ms; 394.8±29.7 SEM, n=9) in T161K-hiPSC-CMs. Treatment with MYK-461 reduced contractility (BPM; 36±3 SEM, n=10) and relaxation phase (ms; 293.1±33.6 SEM, n=10) in a dose-dependent manner, displaying functional characteristics closer to isogenic-hiPSC-CMs control group. Conclusions: In conclusion, the results demonstrate that acute reduction in contractility is sufficient to relieve prolonged relaxation. Further, these studies suggest that T161K-hiPSC-CMs provide adequate in vitro platform for modelling the functional effect of MYK-461.