Induction of Neuronal Apoptosis by Camptothecin, an Inhibitor of DNA Topoisomerase-I: Evidence for Cell Cycle-Independent Toxicity

• Published in: The Journal of cell biology Vol. 134; no. 3; pp. 757 - 770
• Main Authors: Morris, Erick J., Geller, Herbert M.
• Format: Journal Article
• Language: English
• Published: United States Rockefeller University Press 01.08.1996; The Rockefeller University Press
• Subjects: Animals; Antineoplastic Agents, Phytogenic - pharmacology; Aphidicolin - pharmacology; Apoptosis; Apoptosis - drug effects; Astrocytes; Astrocytes - cytology; Astrocytes - drug effects; Aurintricarboxylic Acid - pharmacology; Camptothecin - analogs & derivatives; Camptothecin - pharmacology; Cell Cycle; Cell death; Cell lines; Cell Survival; Cells; Cells, Cultured; Cellular biology; Cerebral Cortex; Cultured cells; DNA; DNA - analysis; DNA - biosynthesis; DNA Topoisomerases, Type I - analysis; DNA Topoisomerases, Type I - physiology; Enzyme Inhibitors - pharmacology; Enzymes; Models, Neurological; Neuroglia; Neurons; Neurons - cytology; Neurons - drug effects; Neurons - enzymology; Protein Synthesis Inhibitors - pharmacology; Rats; Rats, Sprague-Dawley; RNA; RNA - biosynthesis; Stereoisomerism; Topoisomerase I Inhibitors
• ISSN: 0021-9525; 1540-8140
• DOI: 10.1083/jcb.134.3.757

Camptothecin is an S-phase-specific anticancer agent that inhibits the activity of the enzyme DNA topoisomerase-I (topo-I). Irreversible DNA double-strand breaks are produced during DNA synthesis in the presence of camptothecin, suggesting that this agent should not be toxic to nondividing cells, such as neurons. Unexpectedly, camptothecin induced significant, dose-dependent cell death of postmitotic rat cortical neurons in vitro; astrocytes were more resistant. Aphidicolin, an inhibitor of DNA polymerase α, did not prevent camptothecin-induced neuronal death, while death was prevented by actinomycin D and 5,6-dichloro-1-beta-D-ribofuranosyl benzimidazole as well as cycloheximide and anisomycin, inhibitors of RNA and protein synthesis, respectively. Camptothecininduced neuronal death was apoptotic, as characterized by chromatin condensation, cytoplasmic shrinking, plasma membrane blebbing, and fragmentation of neurites. DNA fragmentation was also confirmed by the use of the in situ DNA end labeling assay. In addition, aurintricarboxylic acid, an inhibitor of the apoptotic endonuclease, partially protected against camptothecininduced neuronal death. The toxicity of stereoisomers of a camptothecin analogue was stereospecific, demonstrating that toxicity was a result of inhibition of topo-I. The difference in sensitivity to camptothecin between neurons and astrocytes correlated with their transcriptional activity and level of topo-I protein expression. These data indicate important roles for topo-I in postmitotic neurons and suggest that topo-I inhibitors can induce apoptosis independent of DNA synthesis. We suggest a model based on transcriptionally mediated DNA damage, a novel mechanism of action of topo-I poisons.