Targeted inhibition of the Shroom3–Rho kinase protein–protein interaction circumvents Nogo66 to promote axon outgrowth

BACKGROUND: Inhibitory molecules in the adult central nervous system, including NogoA, impede neural repair by blocking axon outgrowth. The actin-myosin regulatory protein Shroom3 directly interacts with Rho kinase and conveys axon outgrowth inhibitory signals from Nogo66, a C-terminal inhibitory domain of NogoA. The purpose of this study was to identify small molecules that block the Shroom3–Rho kinase protein–protein interaction as a means to modulate NogoA signaling and, in the longer term, enhance axon outgrowth during neural repair. RESULTS: A high throughput screen for inhibitors of the Shroom3–Rho kinase protein–protein interaction identified CCG-17444 (Chem ID: 2816053). CCG-17444 inhibits the Shroom3–Rho kinase interaction in vitro with micromolar potency. This compound acts through an irreversible, covalent mechanism of action, targeting Shroom3 Cys1816 to inhibit the Shroom3–Rho kinase protein–protein interaction. Inhibition of the Shroom3–Rho kinase protein–protein interaction with CCG-17444 counteracts the inhibitory action of Nogo66 and enhances neurite outgrowth. CONCLUSIONS: This study identifies a small molecule inhibitor of the Shroom3–Rho kinase protein–protein interaction that circumvents the inhibitory action of Nogo66 in neurons. Identification of a small molecule compound that blocks the Shroom3–Rho kinase protein–protein interaction provides a first step towards a potential new strategy for enhancing neural repair.