Antitumor antibiotics

Anthracyclines - Red Devil's Heartbreak

• Mechanism of Action: Triple threat:

  • Intercalates between DNA base pairs, blocking replication & transcription.
  • Inhibits topoisomerase II, leading to irreversible DNA strand breaks.
  • Generates oxygen free radicals via its quinone moiety (Fenton reaction), causing significant oxidative damage to tissues, especially the heart.

• Key Drugs: Doxorubicin, Daunorubicin, Epirubicin, Idarubicin.

  • 📌 All end in "-rubicin," like a "ruby" for their red color.

• Clinical Use: Broad-spectrum against solid tumors (breast, lung) and hematologic malignancies (leukemias, lymphomas).

• Adverse Effects:

  • Cardiotoxicity: Acute (arrhythmias) and chronic (dose-dependent dilated cardiomyopathy). This is the dose-limiting toxicity.
  • Myelosuppression: Severe.
  • Red Discoloration: Urine and sweat turn red. 📌 "Red Devil".
  • Alopecia.

⭐ High-Yield: Cardiotoxicity is cumulative and often irreversible. Monitor cardiac function (e.g., ECHO, MUGA scan) before and during therapy. The iron chelator Dexrazoxane can be used prophylactically to mitigate cardiotoxicity.

Bleomycin - The Lung Crusher

• Mechanism: Induces oxidative damage by chelating iron (Fe²⁺), creating free radicals that cause single and double-strand DNA breaks.

  • Cell cycle-specific for the G2 phase.

• Clinical Use:

  • Testicular Cancer (BEP regimen)
  • Hodgkin Lymphoma (ABVD regimen)

• Adverse Effects:

  • ⚠️ Pulmonary Fibrosis: Dose-limiting, often irreversible. "Bleomycin lung."
  • Skin: Hyperpigmentation, striae.
  • Mucositis.
  • 📌 Mnemonic: Blows Lungs Every Once.

⭐ High-Yield: Unlike most chemotherapy agents, Bleomycin causes minimal myelosuppression, making it useful in combination regimens.

Other Agents - The Niche Players

• Dactinomycin (Actinomycin D)

  • MoA: Intercalates in DNA, inhibiting transcription by blocking RNA polymerase.
  • Clinical Use: Key for pediatric tumors.

  ⭐ Used for Wilms tumor, Ewing sarcoma, and rhabdomyosarcoma. 📌 Mnemonic: Children ACT out.

• Mitomycin (Mitomycin C)

  • MoA: Metabolically activated to an alkylating agent that cross-links DNA.
  • Niche: Most effective in hypoxic environments of solid tumors.
  • Clinical Use: Anal, bladder, pancreas, and stomach cancers.

High‑Yield Points - ⚡ Biggest Takeaways

• Anthracyclines (e.g., Doxorubicin) generate free radicals, causing dose-limiting cardiotoxicity (dilated cardiomyopathy). Dexrazoxane is cardioprotective.
• Bleomycin induces free radical damage, leading to dose-limiting pulmonary fibrosis and skin hyperpigmentation.
• The core mechanism for most involves DNA intercalation, inhibiting topoisomerase II, and disrupting DNA/RNA synthesis.
• Actinomycin D (Dactinomycin) is crucial for treating pediatric tumors like Wilms tumor and Ewing sarcoma.
• Remember the unique toxicities: Doxorubicin → Heart, Bleomycin → Lungs.