A20FMDV2 is a selective αvβ6 integrin inhibitor ( IC 50 : 3 nM), with an activity 1,000-fold more selective for αvβ6 than for other RGD-directed integrins ( αvβ3 , αvβ5 , and α5β1 ). A20FMDV2 can be derived from the foot-and-mouth disease virus. A20FMDV2 can be radiolabeled for the PET imaging of αvβ6 integrin-positive tumors.