actinomycin (ăkˌtənōmĪˈsən) [key], any one of a group of antibiotics produced by bacteria of the genus Streptomyces. Actinomycin was the first antibiotic reported to be able to halt cancer; however, it is not widely used to treat cancers because it is highly toxic to humans, interfering with the genetic material of cells. It is mainly used as an investigative tool in cell biology.
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