A method of treating a disease in which inhibiting of a proteasome is advantageous is provided. The method comprises administering to the subject a therapeutically effective amount of a compound which binds to a proteasome of a cell, the compound comprising a copper bound to a ligand, the ligand being configured such that upon binding to the proteasome, the copper interacts with cysteine 31 of a Beta2 subunit of the proteasome and further interacts with cysteine 118 of a Beta3 subunit of the proteasome, thereby treating the disease. Additional novel proteasome inhibitors are also provided as well as methods of identifying proteasome inhibitors.