Obtustatin is a highly potent and selective inhibitor of the binding of α1β1 integrin to collagen IV, however, does not show inhibitory activity toward other integrins, including α2β1, αIIbβ3, αvβ3, α4β1, α5β1, α6β1, and α9β1, α4β7 integrins. It displays antitumor efficacy.