The topoisomerase II poison clerocidin alkylates non-paired guanines of DNA: implications for irreversible stimulation of DNA cleavage

Abstract

Clerocidin, a diterpenoid with antibacterial and antitumor activity, stimulates in vitro DNA cleavage mediated by mammalian and bacterial topoisomerase (topo) II. Different from the classical topoisomerase poisons, clerocidin-stimulated breaks at guanines immediately preceding the sites of DNA cleavage are not resealed upon heat or salt treatment. To understand the mechanism of irreversible trapping of the topo II-cleavable complex, we have investigated the reactivity of clerocidin per se towards DNA. We show here that the drug is able to nick negatively supercoiled plasmids. DNA cleavage by clerocidin in enzyme-free medium is due to the ability of the drug to form covalent adducts with guanines. Indeed, clerocidin was able to specifically react with short oligonucleotides when the guanines were unpaired and exposed as in bulges or in the single-strand form. The clerocidin epoxy group attacks the nitrogen at position 7 of guanines, leading to strand scission at the modified site. Our findings also demonstrate that trapping of topoisomerases by clerocidin is specific for type II enzymes. The guanine-alkylating ability of clerocidin suggests an unprecedented mechanism of topo II poisoning, according to which the enzyme renders the drug reactive toward DNA by distorting the double-helical structure of the nucleic acid at the cleavage site.

Mangrove dolabrane‐type of diterpenes tagalsins suppresses tumor growth viaROS‐mediated apoptosis and ATM/ATR–Chk1/Chk2‐regulated cell cycle arrest

“…Two diterpenoids, clerocidin and salvicine, have been shown to exert their cytotoxicity by inducing DNA double‐strand breaks (DSBs) 14, 15, 16. Therefore, we asked whether tagalsins also induce cell death via DNA damage.…”

“…Therefore, we conclude that tagalsins induce DNA damage mainly via oxidative DNA damage. Several terpenoids, e.g., artesunate, clerocidin and salvicine, have been shown to induce DSBs 14, 15, 16, 31. Oxidative DNA damage was implicated to be the reason for the anticancer effect of artesunate 31.…”

“…Oxidative DNA damage was implicated to be the reason for the anticancer effect of artesunate 31. Clerocidin and salvicine were shown to induce DNA DSBs by topoisomerase inhibition 14, 15, 16. It was shown that clerocidin alkylates non‐paired guanines of DNA resulting in irreversible stimulation of DNA cleavage 15.…”

“…Clerocidin and salvicine were shown to induce DNA DSBs by topoisomerase inhibition 14, 15, 16. It was shown that clerocidin alkylates non‐paired guanines of DNA resulting in irreversible stimulation of DNA cleavage 15. Thus, terpenoids may induce DNA damage through different mechanisms.…”

Transcriptional inhibition of the estrogen response element by antiestrogenic piperidinediones correlates with intercalation into DNA measured by energy calculations

“…The ligand was removed from the complex and energy of the DNA and ligand were measured as above. The total energy of interaction of the ligand with the DNA was calculated by the energy of the complex, minus the energy of the ligand, minus the energy of the DNA: E interaction = E complex − (E ligand + E DNA ) [43]. Note that because the energies are expressed as negative numbers, the greater the value in kcal, the more favorable the interaction of a given ligand with DNA.…”