Myosin in autoinhibited off state(s), stabilized by mavacamten, can be recruited via inotropic effectors.

Abstract

Mavacamten is a novel investigational small molecule designed to regulate cardiac function at the sarcomere level by selectively but reversibly inhibiting the enzymatic activity of myosin. It shifts myosin towards ordered off states close to the thick filament backbone. However, the likelihood of recruiting these mavacamten-induced, off-state myosin heads upon increasing physiological demands of the heart has not been systematically explored. Here, we show that cardiac myosins stabilized in these off state(s) by mavacamten are recruitable by 1) Ca2+, 2) stretch and 3) β-adrenergic receptor (β-AR) stimulation, three inotropic effectors. At the molecular level, we find that Ca2+ increases myosin ATPase activity by shifting mavacamten-stabilized myosin heads from the inactive super-relaxed (SRX) state to the active disordered relaxed (DRX) state. At the sarcomere level, both Ca2+ and passive lengthening can shift mavacamten-ordered off myosin heads from positions close to the thick filament backbone to disordered on states closer to the thin filaments. And finally, in vivo, we show that β-AR stimulation can increase left-ventricular function and stroke volume in the setting of mavacamten. In conclusion, these data demonstrate that the mavacamten-promoted off states of myosin in the thick filament are activable, thus leading to the preservation of the cardiac reserve. These results not only provide a potential mechanistic explanation for the clinical observation of increased peak oxygen uptake (pVO2) with exercise in HCM patients receiving mavacamten but also lay out a fresh outlook on the safety and reversibility of this drug. This project is supported by grant P30 GM138395 from the NIGMS of the NIH; the Ministry of Education, Science and Technological Development of the Republic of Serbia through Contracts No. 451-03-68/2022-14/200378; MyoKardia Inc., a wholly owned subsidiary of Bristol Myers Squibb.