Antagonists for modifying protein-protein interactions involving certain amino acid sequences within MMP-9 and/or β1 integrins are described. Such antagonists inhibit angiogenesis, tumor growth and disease states. Example antagonists are polypeptide and non-polypeptide molecules, including the novel antibody Mab FM155 and the novel synthetic peptide FRIP-1. Methods for inhibiting angiogenesis and disease states by administering such antagonists are disclosed. Methods for identifying antagonists that modify protein-protein interactions involving certain amino acid sequences within MMP-9 and/or β1 integrins are also described.