biostudies-literatureBossaert MLigue Contre le CancerCancéropôle Grand OuestAgence Nationale de la Recherchee65184https://www.ebi.ac.uk/biostudies/studies/S-EPMC8279764biostudies-literatureUnknown10G-quadruplexes (G4) are non-canonical DNA structures found in the genome of most species including human. Small molecules stabilizing these structures, called G4 ligands, have been identified and, for some of them, shown to induce cytotoxic DNA double-strand breaks. Through the use of an unbiased genetic approach, we identify here topoisomerase 2α (TOP2A) as a major effector of cytotoxicity induced by two clastogenic G4 ligands, pyridostatin and CX-5461, the latter molecule currently undergoing phase I/II clinical trials in oncology. We show that both TOP2 activity and transcription account for DNA break production following G4 ligand treatments. In contrast, clastogenic activity of these G4 ligands is countered by topoisomerase 1 (TOP1), which limits co-transcriptional G4 formation, and beLifeTranscription-associated topoisomerase 2α (TOP2A) activity is a major effector of cytotoxicity induced by G-quadruplex ligands.PMC8279764ANR-10-INBS-09ANR-17-CE18-0002-01Equipe Labellisée 2018Emergence funding "CX-Break"ANR-16-CE11-0006-01Pipier ARiou JFNoirot CCalsou PSerre RFBouchez OBossaert MNguyen LTBritton SGomez DDefrancq EfalseTranscription-associated topoisomerase 2α (TOP2A) activity is a major effector of cytotoxicity induced by G-quadruplex ligands.G-quadruplexes (G4) are non-canonical DNA structures found in the genome of most species including human. Small molecules stabilizing these structures, called G4 ligands, have been identified and, for some of them, shown to induce cytotoxic DNA double-strand breaks. Through the use of an unbiased genetic approach, we identify here topoisomerase 2α (TOP2A) as a major effector of cytotoxicity induced by two clastogenic G4 ligands, pyridostatin and CX-5461, the latter molecule currently undergoing phase I/II clinical trials in oncology. We show that both TOP2 activity and transcription account for DNA break production following G4 ligand treatments. In contrast, clastogenic activity of these G4 ligands is countered by topoisomerase 1 (TOP1), which limits co-transcriptional G4 formation, and b2021-01-01T00:00:00Z2021 Jun2026-05-07T20:48:40.167Z2022-02-10T19:49:49.283ZS-EPMC82797643418039210.7554/eLife.65184