AC-55541 is a highly selective protease-activated receptor 2 ( PAR2 ) agonist ( pEC 50 =6.7), displays no activity at other PAR subtypes or at over 30 other receptors involved in nociception and inflammation. AC-55541 has pEC 50 values of 5.9 and 6.6 in PI hydrolysis assays and Ca 2+ mobilization assays and exhibits pronociceptive activity in vivo.