Structure–Activity Relationship Analysis of Rhosin, a RhoA GTPase Inhibitor, Reveals a New Class of Antiplatelet Agents

Current antiplatelet therapies have several clinical complications and are mostly irreversible in terms of suppressing platelet activity; hence, there is a need to develop improved therapeutic agents. Previous studies have implicated RhoA in platelet activation. Here, we further characterized the lead RhoA inhibitor, Rhosin/G04, in platelet function and present structure–activity relationship (SAR) analysis. A screening for Rhosin/G04 analogs in our chemical library by similarity and substructure searches revealed compounds that showed enhanced antiplatelet activity and suppressed RhoA activity and signaling. A screening for Rhosin/G04 analogs in our chemical library using similarity and substructure searches revealed compounds that showed enhanced antiplatelet activity and suppressed RhoA activity and signaling. SAR analysis revealed that the active compounds have a quinoline group optimally attached to the hydrazine at the 4-position and halogen substituents at the 7- or 8-position. Having indole, methylphenyl, or dichloro-phenyl substituents led to better potency. Rhosin/G04 contains a pair of enantiomers, and S-G04 is significantly more potent than R-G04 in inhibiting RhoA activation and platelet aggregation. Furthermore, the inhibitory effect is reversible, and S-G04 is capable of inhibiting diverse-agonist-stimulated platelet activation. This study identified a new generation of small-molecule RhoA inhibitors, including an enantiomer capable of broadly and reversibly modulating platelet activity.