The calicheamicins are a class of enediyne antibiotics derived from the bacterium Micromonospora echinospora, with calicheamicin γ1 being the most notable. It was isolated originally in the mid-1980's from the chalky soil, or "calichi pits", located in Kerrville, Texas. The sample was collected by a scientist working for Lederle Labs. It is extremely toxic to all cells and in the year 2000, a CD33 antigen-targeted immunoconjugate N-acetyl dimethyl hydrazide calichiamicin was developed and marketed as targeted therapy against the non-solid tumor cancer acute myeloid leukemia (AML). Calicheamicin γ1 and the related enediyne esperamicin are the two of the most potent antitumor agents known.

Calicheamicins target DNA, causing strand scission. Calicheamicins bind with DNA in the minor groove, where they then undergo a reaction analogous to the Bergman cyclization, generating a diradical species. Like all enediynes, this diradical, 1,4-dehydrobenzene, then abstracts hydrogen atoms from the deoxyribose (sugar) backbone of DNA, which results in strand scission.