Calicheamicin

Calicheamicin is a class of enediyne antitumor antibiotics with potent cytotoxic activity against cancer cells. The molecule binds in the minor groove of DNA and undergoes a Bergman type cyclization that generates a reactive diradical species, which pulls hydrogen atoms from the sugar backbone of DNA and breaks both strands. Scientists at Lederle Laboratories isolated it from the bacterium Micromonospora echinospora in the mid 1980s, found in caliche soil deposits near Kerrville, Texas. Because it is too toxic to give on its own, it is instead attached to a targeting antibody as an antibody drug conjugate; inotuzumab ozogamicin, sold as Besponsa, carries a calicheamicin derivative to CD22 positive cells and gained United States approval in August 2017 for relapsed or refractory B cell precursor acute lymphoblastic leukemia.