An ammonium salt with potential antiangiogenic and antitumor activities. Tetrathiomolybdate has been found to deplete systemic copper reserves through an unknown mechanism. This agent has been shown to inhibit the activities of cuproenzymes, including superoxide dismutase 1 (SOD1) and cytochrome c oxidase (COX), which may contribute to its antiangiogenic and antitumor effects.