Inhibition of Muscle-Specific Protein Kinase (MuSK) Releases Organophosphate-Aged Acetylcholinesterase (AChE) from C2C12 Cells.

Mechanistically, OPs inhibit acetylcholinesterase (AChE), an enzyme that terminates cholinergic transmission, triggering a sustained activation of acetylcholine receptors. A component of the treatment for OP intoxication is oximes as AChE reactivators. However, oximes may not be efficacious and could worsen OP effects. Further, dealkylation of the AChE-OP adducts prevents oxime reactivation. Therefore, other approaches are needed to rescue AChE activity. We propose that replacing aged extracellular AChE with active intracellular enzymes may be an effective approach. Thus, molecular screening was used to identify small molecules that could displace aged AChE. C2C12 myoblasts were treated with 20 μM of diisopropylfluorophosphate (DFP) for one hour, followed by a drug panel. AChE activity and surface abundance were measured after 6 h. From the chemical screen, a promising hit, Pz-1 (a tyrosine kinase inhibitor), was identified, which decreased surface AChE on DFP-exposed C2C12 myoblasts in a dose-dependent manner without impacting viability. Additionally, AChE presence and activity were recovered after washing and supplementing the media with 100 nM of acetylcholine. Biochemically, Pz-1 inhibits muscle-specific protein kinase (MuSK), a kinase that interacts with AChE. These results suggest that altering MuSK activity may disrupt protein-protein interactions, destabilizing AChE, which may lead to the discovery of new countermeasures for OP exposures.