Actinomycin is an antibiotic obtained from species of Streptomyces, filamentous soil bacteria known for producing an array of natural products. This compound inhibits the transcription of DNA to RNA, thus causing the death of cells. The ability to cause cell suicide made actinomycin D an early chemotherapy drug. This compound is highly toxic to normal cells, so it is only used on certain specialized types of cancers. An alternate name for the drug is dactinomycin.
Streptomyces is a gram positive bacterium that is a member of the actinomycete group. These soil bacteria are renowned for producing antibiotics and other natural products. Competition among microorganisms in the soil is fierce, and the production of compounds that kill other organisms helps the actinomycetes to survive.
Part of the reason that actinomycin is such a successful antibiotic is that its chemical structure includes two cyclic peptides. This unusual grouping of amino acids is very difficult for other organisms to degrade. It also includes a D amino acid in each of the cyclic peptide rings. Usually, amino acids are found in the L configuration. The use of such atypical biochemical attributes contributes to the success of this actinomycete in the soil.
The isolation of actinomycin in 1940 earned the Nobel Prize for Selman Waksman. Studies of the mechanism of action of this antibiotic showed that it acted by binding to double-stranded DNA and stopping the transcription of this DNA into RNA. By being bound in this manner, actinomycin inhibited RNA polymerase from moving forward. This activity caused the cells to commit suicide, a process known as apoptosis.
The ability to cause apoptosis is a valuable property. Cancerous cells spread much more quickly than the cells in neighboring, normal tissue because they have lost control and do not undergo as much apoptosis. Drugs that cause apoptosis have potential as cancer treatments. A drug that is injected intravenously and circulated throughout the blood to kill cancer cells is known as an anti-neoplastic agent--a chemotherapy drug.
Actinomycin D has been used as a chemotherapy drug for many years. The power of this class of drugs is their specificity in killing cells that are dividing. This makes it more likely that they will kill cancer cells, rather than the cells of non-cancerous tissue. The compound is highly toxic to normal cells, however. The drug is very carefully monitored when it is used.
Aside from its uses in cancer treatment and as an antibiotic, the ability of actinomycin to bind DNA has made this compound useful for studies in biochemistry and cell biology. It is used to inhibit RNA synthesis. Also, a fluorescent derivative can be created that is known as 7-aminoactinomycin D. This chemical is used to stain DNA that is single-stranded. It is a valuable marker to determine whether cells have died or not.
