Perspectives of a myosin motor activator agent with increased selectivity.

Clinical treatment of heart failure is still not fully solved. A novel class of agents, the myosin motor activators, acts directly on cardiac myosin resulting in an increased force generation and prolongation of contraction. Omecamtiv mecarbil, the lead molecule of this group, is now in human phase 3 displaying promising clinical performance. However, omecamtiv mecarbil is not selective to myosin, because it readily binds to and activates cardiac ryanodine receptors (RyR-2), an effect that may cause complications in case of overdose. In this study, in silico analysis was performed to investigate the docking of omecamtiv mecarbil and other structural analogues to cardiac myosin heavy chain and RyR-2 to select the structure that has a higher selectivity to myosin over RyR-2. In silico docking studies revealed that omecamtiv mecarbil has comparable affinity to myosin and RyR-2: the respective Kd values are 0.60 and 0.87 µmol/L. Another compound, CK-1032100, has much lower affinity to RyR-2 than omecamtiv mecarbil, while it still has a moderate affinity to myosin. It was concluded that further research starting from the chemical structure of CK-1032100 may result a better myosin activator burdened probably less by the RyR-2 binding side effect. It also is possible, however, that the selectivity of omecamtiv mecarbil to myosin over RyR-2 cannot be substantially improved, because similar moieties seem to be responsible for the high affinity to both myosin and RyR-2.

The myosin activator omecamtiv mecarbil: a promising new inotropic agent.

Heart failure became a leading cause of mortality in the past few decades with a progressively increasing prevalence. Its current therapy is restricted largely to the suppression of the sympathetic activity and the renin-angiotensin system in combination with diuretics. This restrictive strategy is due to the potential long-term adverse effects of inotropic agents despite their effective influence on cardiac function when employed for short durations. Positive inotropes include inhibitors of the Na+/K+ pump, ß-receptor agonists, and phosphodiesterase inhibitors. Theoretically, Ca2+ sensitizers may also increase cardiac contractility without resulting in Ca2+ overload; nevertheless, their mechanism of action is frequently complicated by other pleiotropic effects. Recently, a new positive inotropic agent, the myosin activator omecamtiv mecarbil, has been developed. Omecamtiv mecarbil binds directly to ß-myosin heavy chain and enhances cardiac contractility by increasing the number of the active force-generating cross-bridges, presumably without major off-target effects. This review focuses on recent in vivo and in vitro results obtained with omecamtiv mecarbil, and discusses its mechanism of action at a molecular level. Based on clinical data, omecamtiv mecarbil is a promising new tool in the treatment of systolic heart failure.