antitumor antibiotics
Summary
Antitumor antibiotics are chemotherapeutic agents derived from Streptomyces species that interfere with DNA structure/function to kill rapidly dividing cancer cells. Key drugs include anthracyclines (doxorubicin, daunorubicin), bleomycin, and dactinomycin. They are cell-cycle nonspecific (except bleomycin, which is G2/M specific) and are used in various solid tumors and hematologic malignancies.
Detail
Antitumor antibiotics work via multiple mechanisms: (1) Anthracyclines (doxorubicin, daunorubicin, epirubicin, idarubicin) intercalate into DNA, inhibit topoisomerase II, and generate free radicals causing DNA strand breaks and lipid peroxidation of cell membranes. Major dose-limiting toxicity is cardiotoxicity (dilated cardiomyopathy) due to free radical damage to myocytes, which is cumulative dose-dependent and can be mitigated with dexrazoxane (iron chelator). (2) Bleomycin causes DNA strand breaks via free radical formation and is cell-cycle specific for G2/M phase; its major toxicity is pulmonary fibrosis due to minimal inactivating hydrolase enzyme in lung tissue. (3) Dactinomycin (actinomycinD) intercalates into DNA, blocking RNA polymerase and transcription; used classically in pediatric tumors like Wilms tumor, Ewing sarcoma, and rhabdomyosarcoma (think 'children act out'). Clinical uses span Hodgkin and non-Hodgkin lymphoma (ABVD regimen includes doxorubicin and bleomycin), breast cancer, sarcomas, testicular cancer (bleomycin), and leukemias (daunorubicin in AML induction). Key boards associations: doxorubicin/daunorubicin = cardiotoxicity (monitor with echocardiogram/MUGA scan), bleomycin = pulmonary fibrosis (monitor with PFTs), dactinomycin = myelosuppression and GI toxicity. All require careful dosing due to narrow therapeutic index and irreversible organ-specific toxicities.
Sources
- Katzung's Basic and Clinical Pharmacology
- First Aid for the USMLE Step 1
- Goodman & Gilman's The Pharmacological Basis of Therapeutics
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