ML-161 is an allosteric, reversible inhibitor of proteinase-activated receptor 1 (PAR1) on platelets, preventing surface expression of P-selectin induced by the peptide SFLLRN with an IC50 value of 0.26 μM. It blocks platelet activation induced by thrombin as well as by SFLLRN but not by PMA , U-46619 , or collagen.