Topoisomerase Inhibitors and Antitumor Antibiotics

Camptothecins, anthracyclines, etoposide, bleomycin, and actinomycin D

ARDS = acute respiratory distress syndrome  ·  BEACOPP = bleomycin, etoposide, doxorubicin, cyclophosphamide, vincristine, procarbazine, prednisone  ·  BEP = bleomycin, etoposide, cisplatin  ·  DLCO = diffusing capacity for carbon monoxide  ·  DSB = double-strand break  ·  FEC = fluorouracil, epirubicin, cyclophosphamide  ·  FOLFIRI = fluorouracil, leucovorin, irinotecan  ·  KMT2A = lysine methyltransferase 2A (formerly MLL)  ·  LVEF = left ventricular ejection fraction  ·  PLD = pegylated liposomal doxorubicin  ·  ROS = reactive oxygen species  ·  SCLC = small cell lung cancer  ·  UGT1A1 = UDP-glucuronosyltransferase isoform 1A1

Topoisomerase I vs II Inhibitors: Mechanism and Safety Profile
Topoisomerase I Inhibitors
Camptothecins: Irinotecan & Topotecan
  • Single-strand nick → cleavable complex → lethal DSB only at replication fork
  • S-phase specific
  • No secondary leukemia risk; no cumulative cardiotoxicity
  • Irinotecan: prodrug → SN-38 (active) via carboxylesterase
  • UGT1A1*28 homozygotes: impaired SN-38 glucuronidation → severe toxicity; consider dose reduction
  • Irinotecan early diarrhea: cholinergic → atropine; late diarrhea: SN-38 mucosal → loperamide
Topoisomerase II Inhibitors
Anthracyclines & Etoposide
  • DSBs in any cell cycle phase
  • Anthracyclines: cumulative cardiomyopathy (topo II-beta + ROS in cardiomyocytes)
  • Doxorubicin limit: 450–550 mg/m²; epirubicin limit: ~900 mg/m²
  • Etoposide: secondary AML (KMT2A rearrangement, latency 1–3 years, de novo AML)
  • Etoposide risk: ~1–2% in BEP; ~3–5% in BEACOPP
  • Dexrazoxane: only approved cardioprotectant; 10:1 ratio before doxorubicin
Doxorubicin: Three Simultaneous Mechanisms
Mechanism Detail Clinical Consequence
DNA intercalation + topo II-alpha inhibition Planar chromophore inserts between base pairs; stabilizes cleavable complex → persistent DSBs Antitumor activity; also topo II-beta DSBs in cardiomyocytes
ROS generation via semiquinone radical One-electron reduction → superoxide → hydroxyl radical (Fenton chemistry) DNA, protein, lipid damage; cardiomyocytes especially vulnerable (low catalase)
Cardiolipin binding Intercalates into mitochondrial inner membrane lipid cardiolipin Disrupts electron transport chain; mitochondrial apoptosis in cardiomyocytes
Antitumor Antibiotics
Bleomycin
DNA Strand Scission & Pulmonary Risk
  • Mechanism: iron chelation → ROS → direct DNA strand cleavage
  • G2/M phase specific; low bleomycin hydrolase in lung → organ-specific toxicity
  • Pulmonary toxicity: ~10% at BEP doses; risk above 400 units cumulative
  • Monitor: serial DLCO measurements
  • Anesthesia risk: high FiO&sub2; → ARDS (no safe time threshold after bleomycin)
  • Indications: BEP (testicular GCT), Hodgkin lymphoma (ABVD)
Actinomycin D (Dactinomycin)
RNA Polymerase Blockade
  • Intercalates at GC base pairs → blocks RNA polymerase movement
  • Inhibits all RNA species (mRNA, rRNA, tRNA)
  • Potent radiation sensitizer (blocks DNA repair enzyme transcription)
  • Indications: Wilms tumor, gestational trophoblastic disease, Ewing sarcoma, rhabdomyosarcoma
  • Dose-limiting toxicity: myelosuppression, mucositis
  • Extreme vesicant: extravasation prevention essential
Bleomycin Anesthesia Rule: No Safe Oxygen Threshold
Any patient with prior bleomycin exposure requires FiO&sub2; kept at the minimum consistent with safe oxygenation (SpO&sub2; target 93–95%) during and after general anesthesia. There is no established safe interval after bleomycin treatment beyond which normal FiO&sub2; can be used. Document bleomycin history prominently in every patient chart and communicate it to the anesthesia team before any elective or emergency procedure.