Abstract: The present invention relates to new treatments of multidrug resistant disorders, particularly cancers. There is provided a method of treating a cancer including administering an effective amount of a semicarbazone or hydrazone compound to a patient that has cancer, the cancer including a cancerous cell that includes an active efflux mechanism; wherein the compound is a substrate of the active efflux mechanism and the compound is able to form a chelation complex with a metal species in the cancerous cell, the chelation complex being cytotoxic to the cancerous cell.