Dactinomycin
Summary
Dactinomycin (Actinomycin D) is a chemotherapeutic antibiotic that intercalates into DNA to inhibit RNA polymerase and transcription. It is classically used in pediatric tumors like Wilms tumor, rhabdomyosarcoma, and Ewing sarcoma, often remembered by the mnemonic 'sounds like dactinomycin, used in children.' Its major toxicity is myelosuppression.
Detail
Dactinomycin is a natural antibiotic derived from Streptomyces species that acts as an antitumor agent rather than an antimicrobial due to its toxicity profile. Mechanistically, it intercalates between adjacent guanine-cytosine base pairs in the DNA double helix, which blocks the movement of RNA polymerase and thereby inhibits RNA synthesis (transcription) at low doses and DNA replication at higher doses. It is classified as a cell-cycle nonspecific agent. Clinically, dactinomycin is primarily used in combination chemotherapy regimens for pediatric solid tumors, including Wilms tumor (nephroblastoma), rhabdomyosarcoma, and Ewing sarcoma, often paired with vincristine and cyclophosphamide (VAC regimen). It also has a role in treating gestational trophoblastic disease (choriocarcinoma) and some testicular cancers. Adverse effects include significant myelosuppression (leukopenia, thrombocytopenia), nausea/vomiting, mucositis, alopecia, and the potential for severe tissue necrosis if extravasation occurs during IV administration. Like other antineoplastics, it carries risk of secondary malignancies. A high-yield board association is the 'children's tumor antibiotic' pairing and its mechanism distinguishing it from topoisomerase inhibitors like doxorubicin, though both intercalate DNA.
Sources
- First Aid for the USMLE Step 1
- Katzung's Basic and Clinical Pharmacology
- Goodman & Gilman's The Pharmacological Basis of Therapeutics
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