Characterisation of DNA Double-Strand Break Repair by Alternative End-Joining: Potential Targets for Cancer Therapy

Project Information

altEJrepair

Grant agreement ID: 714162

DOI

10.3030/714162

Project closed

EC signature date 3 May 2017

Start date 1 July 2017

End date 30 June 2023

Funded under

• EXCELLENT SCIENCE - European Research Council (ERC)

Total cost

€ 1 498 750,00

EU contribution

€ 1 498 750,00

Coordinated by

INSTITUT CURIE
France

Periodic Reporting for period 4 - altEJrepair (Characterisation of DNA Double-Strand Break Repair by Alternative End-Joining: Potential Targets for Cancer Therapy)

Reporting period: 2022-01-01 to 2023-06-30

Summary of the context and overall objectives of the project

In the altEJrepair proposal, we aimed at deciphering the molecular functions of the poorly characterized alternative end joining (alt-EJ) DNA repair pathway with the final hope to uncover new drug targets for the treatment of HDR cancer. First, we aim to provide with a global understanding of the pathway in human by unravelling the composition, regulation and function of the alt-EJ repair. Second, since the alt-EJ is also required for the survival of breast and ovarian cancers with defects in homologous recombination (the so-called Homologous Recombination Deficient (HRD) tumors, inhibiting components of the alt-EJ pathway is predicted to kill HRD tumors. For this reason, uncovering new alt-EJ players will provide with new drug targets for the treatment of these cancers.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

We made important contributions to the field of genome stability and tumor biology by shedding light on new mechanisms and pathways controlling genome stability and HRD tumor survival.
One of the objectives of our ERC StG was to understand the mechanisms of action of polymerase theta and the underlying reason for the synthetic lethality with HR. We have solved this question, by showing the Polθ repairs DSB during mitosis and that this function is essential for the survival of HR deficient cells. More generally, in our ERC StG project, we aimed at discovering additional DNA repair related vulnerabilities of HR-deficient tumors. We discovered new targetable synthetic lethality with HR-defect. One of our studies unveils nuclear NAD+-mediated DAN repair as a novel vulnerability of BRCA1/2-mutated cancer cells and its potential as druggable signaling pathway to tackle PARPi resistance. In another work, we discovered that BRCA1/2-mutated tumors show frequent events of nuclear envelop rupture and that inhibiting the repair of these ruptures kills BRCA1/2-mutated cells. This constitutes a novel and targetable vulnerability, which we termed NE vulnerability.

Our reseach and results were disseminated by several members of our groups (PI, postdocs and PhD) through various means to the scientific community and to non-specialist audiences. First, we published new biological insights in high quality, international peer-reviewed open access journals to allow for a maximum dissemination (Nature, Nature Cancer, Molecular Cell). Second, we have presented our work at national and international conferences dedicated to basic biophysical, DNA replication and DNA repair studies such as EMBO conferences, Keystone symposia and biophysical societies. Third, we have presented seminars to several research institute in Europe. These events are important as they represent an opportunity to reach out to all components of our scientific community (technician, undergrads, PhD, administrative), and not only those attending international conferences. Finally, we have presented our research and discoveries to non-specialist audiences (communication at elementary school, radio, TV), and at national and local science events. Innovation also took a part important of our action. We have also demonstrated our potential to bridge basic to translational science by developing the first-in-class Polθ inhibitor (now in clinical trials), filing 5 patents, obtaining funds for innovation (i.e. ERC PoC) and by creating a startup developing new anti-cancer therapeutics.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

Our main achievements and publications go beyond the state of the art thus forcing another lecture of various aspects of genome stability. In addition, we show how a more accurate understanding of genome stability mechanisms can be exploited for developing alternative anti-cancer treatment.
1/ DNA repair in mitosis was proven impossible by several groups over the past two decades until our recent study showed that DNA polymerase theta (Polθ) repairs mitotic DSBs. We showed that Polθ get specifically activated during mitosis allowing end-joining repair of DNA double strand breaks. Although DNA repair has been studied for decades, it remains extremely poorly understood in mitosis. We believe our work (Gelot et al, Nature 2023) has open a new field of investigation (i.e. mitotic repair).

2/ The nuclear envelope (NE) separates the nucleus from the cytosol. NE integrity is maintained by the lamina. Mechanical forces can lead to NE rupture, and this process has been studied extensively. However, spontaneous events of NE rupture have been observed in tumor cells. The source, mechanism and consequences of these spontaneous NE rupture events remain completely unknown. We showed that the kinase ATR mediates NE rupture. Interestingly, BRCA-mutated tumors show frequent events of NE rupture. Inhibiting the repair of NE ruptures kills BRCA-mutated cells. This constitutes a novel and targetable vulnerability, which we termed NE vulnerability. In summary, we described a new mechanism that lies at the intersection of genome stability and structural organization of the cell. We strongly believe that our research will be of wide interest to the scientific community as well as a cornerstone of future research (Kovacs et al. Molecular Cell, 2023). 2 patents arise from this publication.

3/ Finally, one of the first challenges my laboratory at Institut Curie has taken is the discovery and co-development of the first-in-class Polθ inhibitor. We screened more than 25,000 small molecules against the ATPase activity of Polθ. We have shown that one compound, Novobiocin (NVB), disturbingly induces BRCA cell death without affecting non-BRCA cell survival. Moreover, the use of this inhibitor in several preclinical mouse models has demonstrated the efficacy of NVB in inducing the death of BRCA tumors. Importantly, NVB is also effective against certain BRCA tumors that have acquired resistance to PARP inhibitors. NVB could be used as monotherapy as an alternative to PARP inhibitors or in combination with them to limit the emergence of chemoresistance in these tumors. Recently, the FDA (Food and Drug Administration) authorized a clinical trial to evaluate the efficacy of NVB in the treatment of chemoresistant BRCA tumors. (Zhou et al., Nature Cancer 2021 (D’Andrea and Ceccaldi as co-corresponding authors). 2 patents arise from this publication.

Overall stagety and goal of the altEJRepair project