Upamostat, also known as Mesupron and WX-671, is an orally bioavailable second-generation serine protease inhibitor prodrug derived from 3-amidinophenylalanine. It targets the human urokinase plasminogen activator (uPA) system and exhibits potential antineoplastic and antimetastatic properties. After oral administration, the serine protease inhibitor WX-671 is converted into its active form, Nα-(2,4,6-triisopropylphenylsulfonyl)-3-amidinophenylalanine-4-ethoxycarbonylpiperazinylamide (WX-UK1), which inhibits multiple serine proteases, especially uPA, potentially hindering tumor growth and metastasis.