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Actinomycin D is a cytotoxic antibiotic from Streptomyces parvullus that binds DNA and blocks RNA synthesis. In the clinic the same molecule is called dactinomycin; in the lab it is the classic tool for shutting off transcription to measure how fast an mRNA decays. This page is general information for researchers and lab or clinic staff, not medical advice.
Short answer
Actinomycin D inhibits transcription by binding DNA and immobilising the transcription complex, so growing RNA chains cannot elongate. The FDA label for dactinomycin describes it as “a cytotoxic actinomycin that binds DNA and inhibits RNA synthesis.” The same property makes it a long-standing research reagent and a regulated chemotherapy drug, and the label directs that it be handled and disposed of as a cytotoxic drug.
What actinomycin D is
The FDA label for Dactinomycin for Injection, USP (label effective 2020-11-13, read via openFDA on 2026-11-07) describes dactinomycin as an actinomycin produced by Streptomyces parvullus, with molecular formula C62H86N12O16 and a molecular weight of 1255.42 daltons. “Actinomycin D” and “dactinomycin” therefore refer to the same compound in everyday use: research suppliers and papers tend to say actinomycin D, while the drug label and clinical literature say dactinomycin. The label’s own distribution study used 3H-actinomycin D.
How actinomycin D inhibits transcription
Mechanism of action
Sobell (PNAS 1985;82:5328-31, “Actinomycin and DNA transcription”, PMC390561) proposes that actinomycin binds a premelted DNA conformation present within the transcriptional complex. This immobilises the complex and interferes with the elongation of growing RNA chains. The FDA label states the clinical-facing version of the same idea in a single sentence: the drug binds DNA and inhibits RNA synthesis (label section 12.1).
Why that matters in practice
Because the block acts on elongation of RNA chains, treated cells stop producing new transcripts while existing RNA continues to decay. That is the basis of the research use described next. The label also reports that radiolabelled actinomycin D concentrated in nucleated cells and did not cross the blood-brain barrier (section 12.3).
Clinical versus research use
One molecule, two settings. The table below separates what the FDA label says from what the methods literature says; every row traces to the source named in it.
| Item | Clinical (dactinomycin) | Research (actinomycin D) |
|---|---|---|
| Source | FDA label, Dactinomycin for Injection, USP (openFDA, read 2026-11-07) | Lai et al., Methods 2019;155:77-87 (PMC6392460) |
| What it is used for | Listed indications include Wilms tumor, rhabdomyosarcoma, Ewing sarcoma, metastatic nonseminomatous testicular cancer, gestational trophoblastic neoplasia, and regional perfusion for locally recurrent solid malignancies. Except gestational trophoblastic neoplasia, which may be single-agent, each is “as part of” combination chemotherapy. | Inhibiting transcription in cultured metazoan cells to monitor mRNA turnover; the authors describe it as probably the method with the longest history for measuring mRNA decay. |
| Known cautions | Warnings and precautions on the label include secondary malignancy, veno-occlusive disease, extravasation, myelosuppression, hepatotoxicity, renal and mucocutaneous effects, and that live vaccines are not recommended. | The approach has been criticised as prone to artifacts and as ineffective for some promoters; the authors say that with appropriate guidelines and controls it is versatile. |
| Handling | The label says it is a cytotoxic drug and to follow applicable special handling and disposal procedures. The supplied form is a lyophilised 500 mcg vial with 20 mg mannitol, stored at 20-25 C, protected from light and humidity. | Refer to the supplier safety data sheet and your institution’s chemical-hygiene plan. |
Where it matters in the lab
mRNA stability (“chase”) experiments
Lai et al. (2019) review the use of actinomycin D to stop transcription in cultured cells and follow the disappearance of an mRNA over time. They note that measured half-lives range from minutes to many days. They also flag the main weakness: the method can introduce artifacts, and it may not work for some promoters. The practical implication, in the authors’ framing, is that results need appropriate controls and should be read with those caveats in mind rather than as an unconditional number.
Handling and waste
The label classes the drug as cytotoxic and calls for special handling and disposal. For the general frame, see our guides to the NIOSH hazardous drugs list, cytotoxicity and how to obtain a safety data sheet, and the dictionary entry on universal waste disposal requirements. Your institution’s chemical-hygiene plan and the supplier’s safety data sheet set the actual procedures.
Common misunderstandings
- “Actinomycin D and dactinomycin are different drugs.” They are two names for the same actinomycin; the label’s distribution study itself used 3H-actinomycin D.
- “It is a general-purpose cancer drug.” The label lists specific indications, and nearly all are as part of combination chemotherapy.
- “It cleanly switches off all transcription.” The methods literature records artifacts and promoters for which it is ineffective, so controls matter.
- “It is only a lab reagent.” It is also an FDA-labelled cytotoxic drug, with the handling expectations that implies.
Frequently asked questions
What is the mechanism of action of actinomycin D?
It binds DNA and inhibits RNA synthesis (FDA label, section 12.1). Sobell (1985) proposes that it binds a premelted DNA conformation within the transcriptional complex, immobilising the complex and blocking elongation of growing RNA chains.
How does actinomycin D inhibit transcription?
By interfering with RNA chain elongation: binding to DNA within the transcription complex stalls it, so new RNA is not extended (Sobell, PNAS 1985).
What class of drug is actinomycin D?
The FDA label calls it a cytotoxic actinomycin, an antibiotic-derived compound produced by Streptomyces parvullus.
What is the most aggressive chemotherapy drug?
No source we draw on ranks chemotherapy drugs by “aggressiveness”, so we do not name one. Toxicity and suitability depend on the drug, the regimen and the patient, which is a question for an oncology team.
How much does dactinomycin cost?
This page does not state prices; the label and research literature do not give them, and prices vary by supplier, formulation and setting.
Sources
- U.S. FDA label, Dactinomycin for Injection, USP, via openFDA (set ID 2aaca42a-3b79-4151-a727-83253556a540; label effective 2020-11-13), read 2026-11-07: openFDA drug label record.
- Sobell HM. Actinomycin and DNA transcription. Proc Natl Acad Sci USA 1985;82(16):5328-31. PMC390561, abstract read 2026-11-07.
- Lai WS, et al. Inhibiting transcription in cultured metazoan cells with actinomycin D to monitor mRNA turnover. Methods 2019;155:77-87. PMC6392460, abstract read 2026-11-07.
