DNA repair controls the outcome of several anticancer therapies. As such there is a huge interest for novel small molecules modulating DNA repair. In the DDR lab, we decipher how cells respond to DNA damage, more specifically to the most harmful type, DNA Double-Strand Breaks (DSBs). We use the resulting knowledge to design and perform targeted and phenotypical based screens to identify new modulators of specific aspects of the DNA damage response. To achieve our goals, we rely on high- and super-resolution imaging, molecular and cell biology, genomics, small molecules screening, chemical probes and on multiple collaborations with structural biologists and chemists. We recently implemented in the lab several complementary approaches to decipher how biologically active small molecules act (Bombarde et al. Mol Cancer Ther 2017; Bossaert, Pipier et al. 2021; Demange, Joly, Marcoux et al. eLife 2022).

The interplay between DNA repair mechanisms

Two principal DSB repair mechanisms co-exist in human cells: Non- Homologous End Joining (NHEJ) and Homologous Recombination (HR). Using a new method for imaging NHEJ proteins, we recently discovered the main mechanism antagonizing NHEJ proteins association to special DSBs, thereby allowing HR to proceed. We established that these mechanisms are druggable and that their inhibition triggers toxic DNA repair events in response to some anticancer agents (Britton et al. 2013 J Cell Biol; Chanut, Britton et al. 2016 Nat Commun; Britton, Chanut et al. 2020 Nucleic Acids Res).

How DNA repair proteins associate on damaged chromatin

We recently characterized how the repair factors APLF and XLF associate with the NHEJ core protein Ku at DNA damage, thereby characterizing two new interaction interfaces at the functional and structural levels (Nemoz, Ropars, Frit et al. 2018 Nat Struct Mol Biol; Seif-El-Dahan, Kefala-Stavridi, Frit, Hardwick et al. 2023). We also investigate how the genomic context, such as heterochromatin and transcription, affect DNA repair and genome stability. Using laser micro-irradiation and live imaging, we discovered a novel mechanism promoting the exclusion of a large number of RNA-binding proteins from DNA damage sites, thereby preventing the local accumulation of R-loops (Britton, Dernoncourt et al. Nucleic Acids Res 2014).

How stabilizing specific DNA structures triggers DNA damage

Small molecules stabilizing secondary DNA structures, such as G-quadruplexes (G4) ligands, trigger DNA damage (Zell et al. 2020 RSC Chem Biol). Through an unbiased genomic approach, we recently discovered that DNA topoisomerase 2 alpha is responsible for the production of DSB by several G4 ligands (Bossaert, Pipier et al. 2021 eLife), including CX-5461 a molecule undergoing clinical trials in oncology. We also contributed to develop novel ligands of another secondary structure, the Three-way Junction, and established that they also trigger DNA damage by a mechanism that we are currently investigating (Duskova 2019 J Med Chem; Duskova et al. 2020 J Am Chem Soc; Zell et al. Nucleic Acids Res 2021).