Biophysical Society Thematic Meeting | Canterbury 2023

Towards a More Perfect Union: Multi-Scale Models of Muscle and Their Experimental Validation

Poster Abstracts

11-POS Board 11 SKELETAL MYOSIN INHIBITOR EDG-4131 EXHIBITS A DISTINCT MECHANISM FOR MODULATING MUSCLE FUNCTION Sarah J Lehman 1 ; Weikang Ma 2 ; Mike DuVall 1 ; Benjamin Barthel 1 ; Molly R Madden 1 ; Marc Evanchik 1 ; Thomas C Irving 2 ; Alan J Russell 1 ; 1 Edgewise Therapeutics, Boulder, CO, USA 2 Illinois Institute of Technology, Center for Synchrotron Radiation Research and Instrumentation, Chicago, IL, USA Skeletal myopathies are genetic diseases that lead to progressive muscle degeneration, leading to weakness and loss of ambulation. While etiologies vary, many types of myopathies are characterized by contraction-induced injury. Small molecules that limit sarcomeric contraction have shown slowing of skeletal muscle disease progression in animal models. One class of molecules targets myosin, inhibiting the enzymatic function of the motor protein and/or sequestering myosin in a state unable to bind actin, leading to reduced muscle contractility. EDG-4131 inhibited the ATPase activity in rabbit psoas myosin S1 (IC 50 =1.1µM) and force production in fast skeletal muscle fibers. Further biochemical assessment of the super-relaxed state of rabbit psoas heavy meromyosin showed that EDG-4131 significantly increased the super-relaxed state (36µM EDG-4131: 60 ± 10% vs. DMSO: 72 ± 4%, p=0.02), reducing the number of available myosin heads for interaction with actin. Interestingly, X-ray diffraction patterns in rat EDL muscle showed that, in contrast to other myosin inhibitors such as blebbistatin that order the myosin heads close to thick filament backbone, EDG-4131 shifted the myosin heads towards actin (I 1 /I 0 : EDG-4131 = 0.28 vs Ctrl = 0.36) accompanied with a loss of helical ordering of the myosin heads under resting conditions (I M3 : EDG-4131 = 1.83 vs Ctrl = 1.31, I MLL1 : EDG-4131 = 1.46 vs Ctrl = 0.80). These data suggest that EDG-4131 does not inhibit myosin function by stabilizing the folded-back state of myosin heads but may lead to an undefined structural state of myosin that results in slowed ATP turnover and reduces lattice spacing below the optimal contractile range.

82