Dual topoisomerase I and II inhibition by intoplicine (RP-60475), a new antitumor agent in early clinical trials.

Abstract

The mechanisms of action of intoplicine (RP-60475), a 7H-benzo[e]pyrido[4,3-b]indole derivative that is presently in early clinical trials, have been investigated. Intoplicine induced both topoisomerase I- and II-mediated DNA strand breaks, using purified topoisomerases. The topoisomerase cleavage site patterns induced by intoplicine were unique, relative to those of camptothecin, 4'-(9-acridinylamino)methanesulfon-m-anisidide (m-AMSA), and other known topoisomerase inhibitors. Both topoisomerase I- and II-induced DNA breaks decreased at drug concentrations higher than 1 microM, which is consistent with the DNA-intercalating activity of intoplicine. DNA damage was investigated in KB cells in culture by using alkaline elution. Intoplicine induced single-strand breaks (SSB) in a bell-shaped manner with respect to drug concentration (maximum frequency at 1 microM approximately 220 rad-equivalents). SSB formation was fast, whereas reversal after drug removal was slow. Similar bell-shaped curves were obtained for DNA double-strand breaks (DSB) and DNA-protein cross-links. SSB and DNA-protein cross-link frequencies were approximately equal, and no protein-free breaks were detectable, indicating the protein concealment of the breaks, as expected for topoisomerase inhibition. Comparison of SSB and DSB frequencies indicated that intoplicine produced a significant amount of SSB not related to DSB, which is consistent with concomitant inhibition of both DNA topoisomerases I and II in cells. Data derived from resistant cell lines indicated that multidrug-resistant cells were cross-resistant to intoplicine but that m-AMSA- and camptothecin-resistant cells were sensitive to intoplicine. Hence, intoplicine might circumvent topoisomerase I-mediated and topoisomerase II-mediated resistance by poisoning both enzymes simultaneously.

• Authors: B Poddevin, J F Riou, F Lavelle, Y Pommier
• Journal: Molecular pharmacology (Mol Pharmacol) Vol. 44 Issue 4 Pg. 767-74 (Oct 1993) ISSN: 0026-895X [Print] United States
• PMID: 8232227 (Publication Type: Comparative Study, Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• Antineoplastic Agents
• DNA, Neoplasm
• Indoles
• Pyridines
• Topoisomerase I Inhibitors
• Topoisomerase II Inhibitors
• intoplicine

Topics

• Animals
• Antineoplastic Agents (pharmacology, toxicity)
• DNA Damage
• DNA, Neoplasm (drug effects, metabolism)
• Humans
• Indoles (pharmacology, toxicity)
• KB Cells
• Kinetics
• Leukemia P388 (drug therapy)
• Mice
• Pyridines (pharmacology, toxicity)
• Topoisomerase I Inhibitors
• Topoisomerase II Inhibitors
• Tumor Cells, Cultured