Myosin
IIs, actin-based motors that utilize the chemical energy
of adenosine 5′-triphosphate (ATP) to generate force, have
potential as therapeutic targets. Their heavy chains differentiate
the family into muscle (skeletal [SkMII], cardiac, smooth) and nonmuscle
myosin IIs. Despite the therapeutic potential for muscle disorders,
SkMII-specific inhibitors have not been reported and characterized.
Here, we present the discovery, synthesis, and characterization of
“skeletostatins,” novel derivatives of the pan-myosin
II inhibitor blebbistatin, with selectivity 40- to 170-fold for SkMII
over all other myosin II family members. In addition, the skeletostatins
bear improved potency, solubility, and photostability, without cytotoxicity.
Based on its optimal in vitro profile, MT-134’s in vivo tolerability, efficacy, and pharmacokinetics were
determined. MT-134 was well-tolerated in mice, impaired motor performance,
and had excellent exposure in muscles. Skeletostatins are useful probes
for basic research and a strong starting point for drug development.