A new cyclic peptide containing the isoDGR motif that, after coupling to albumin, selectively binds αvβ3, an integrin overexpressed in the tumor vasculature. IsoDGR-tagged albumin binds tumor vessels and can be exploited as a carrier for the preparation of tumor vasculature-selective nanomedicines, such as gold nanoparticles (Au) carrying tumor necrosis factor α (TNF), a potent vascular damaging agent.