Abstract 2567: TRACERx: Intra-tumor subclonal driver mutation results in defective DNA damage response (DDR) and genome instability

Abstract TRACERx is a longitudinal clinical study, which explores the evolutionary trajectories of NSCLC by temporally dissecting genomic aberrations through multi-region sequencing. Analysis of the first 100 patients revealed extensive intra-tumor heterogeneity (ITH) and chromosomal instability (CIN), manifesting as subclonal somatic mutations and copy number aberrations. Although mutations in “trunk” clonal drivers such as Ras, C-Myc, p53 or MAPK pathway have been thoroughly characterized after the herculean efforts of TCGA consortium, the roles of sub-clonal drivers remain largely obscure as their identification is only made possible by multi-region sequencing. Harnessing the power of the TracerX consortium, we investigate the molecular mechanisms that underpins the role of sub-clonal drivers in ITH. By means of high content imaging of DNA damage markers and tracking human artificial chromosome loss, we aim to elucidate the link between subclonal drivers and CIN events (Zalmas et al, in press). Importantly, we found the ablation of a large proportion of subclonal drivers result in genomic instability. This suggests that genome instability is not merely a standalone hallmarks of cancer, but also a major step that drivers sub-clonal expansion and functionally connect genome instability to tumor evolution. However, the molecular pathways directly linking genome maintenance, chromosomal instability events and cancer evolution is unclear. More intriguingly, only a fraction of these subclonal drivers has been previously reported to be involved in canonical DNA damage response (DDR). This suggests the error-prone DNA repair is favored during tumor clonal evolution. Here, we present previously uncharacterized subclonal driver that are important for error-free DNA repair pathway. The ablation of these genes causes mis-localization of key homologous repair (HR) proteins, such as BRCA1 and Rad51, to DNA damage sites after IR irradiation. Strikingly, early signaling events such as ATM phosphorylation, phosphorylation and ubiquitylation of histone H2A.X, and 53BP1 localization remain unaffected. The exact molecular mechanism the leads to DNA repair pathway selection will be discussed. Citation Format: Wei-ting Lu, Lykourgos-Panagiotis Zalmas, Thomas Webber, Nnennaya Kanu, Charles Swanton. TRACERx: Intra-tumor subclonal driver mutation results in defective DNA damage response (DDR) and genome instability [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2567.