Abstract 1352: Inactivation of factors of DNA double-strand break repair by homologous recombination or non-homologous end-joining leads to frequent catastrophic genomic events in murine and human tumors
Authors: Ratnaparkhe Manasi , Wong John , Wei Pei-Chi , Hlevnjak Mario , Northcott Paul , Jones David T. , Kool Marcel , Jauch Anna , Pastorczak Agata , Korshunov Andrey , Kumar Rajiv , Downing Susanna M. , Pfister Stefan M. , Zapatka Marc , McKinnon Peter J. , Alt Frederick W. , Lichter Peter , Ernst Aurelie 
Published: August 2018

Abstract
Chromothripsis and chromoanasynthesis are two forms of genomic instability leading to complex genomic rearrangements that affect one or very few chromosomes. These one-off catastrophic events play a role in numerous tumor entities as well as in some congenital diseases. The availability of murine models recapitulating both phenomena would substantially facilitate the investigation of the mechanistic aspects underlying catastrophic genomic events.
Homologous recombination repair (HR) and canonical Non-Homologous-End-Joining (cNHEJ) represent the two major processes for DNA double-strand break repair in mammalian cells. Conditional inactivation of key factors of either of these two pathways, such as Brca2 for HR and Xrcc4 or Lig4 for cNHEJ in nestin-expressing or Emx1-expressing murine neural progenitor cells leads to medulloblastomas and gliomas in a p53-deficient background. We showed by whole-genome sequencing that these tumors frequently display chromothripsis or chromoanasynthesis (33 to 73% of the analyzed tumors, n= 27) and that catastrophic rearrangements drive tumor development.
FISH analysis identified a link between chromoanasynthesis and increased numerical and structural aberrations and with the presence of marker chromosomes. In addition, amplifications of c-Myc and n-Myc likely facilitate catastrophic events. Detailed analysis of the microhomologies at the breakpoint junctions on the chromosomes affected by complex genomic rearrangements identified cNHEJ and alternative end-joining as likely repair processes involved in chromothripsis and chromoanasynthesis.
Treatment of cells derived from the mouse tumors with inhibitors of HR and/or alternative end-joining (e.g. RAD51 and PARP inhibitors, respectively) in combination with DNA damage revealed the dependence of these tumor cells on specific repair processes and showed that these DNA repair deficiencies can be utilized for synthetic lethality approaches.
Comparison of the mouse tumors with whole-genome sequencing data from human medulloblastomas (n=68) and gliomas (n=32) identified an association between chromothripsis and deficiencies in repair processes, by analyzing copy-number level aberrations affecting repair factors and mutational signatures of DNA double-strand break repair defects. This link between DNA repair deficiency and chromothripsis was further confirmed in additional tumor entities such as breast cancer (n=356) and melanoma (n=69).
In analogy to the clinical use of PARP inhibitors in the context of BRCA-deficient breast cancer, our findings point towards therapeutic opportunities to target DNA repair defects in tumors with complex genomic rearrangements.
Citation Format: Manasi Ratnaparkhe, John Wong, Pei-Chi Wei, Mario Hlevnjak, Paul Northcott, David T. Jones, Marcel Kool, Anna Jauch, Agata Pastorczak, Andrey Korshunov, Rajiv Kumar, Susanna M. Downing, Stefan M. Pfister, Marc Zapatka, Peter J. McKinnon, Frederick W. Alt, Peter Lichter, Aurelie Ernst. Inactivation of factors of DNA double-strand break repair by homologous recombination or non-homologous end-joining leads to frequent catastrophic genomic events in murine and human tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1352.