Abstract 6217: TP53 loss with whole genome doubling mediates heterogeneous intra-patient therapy response in EGFR-driven lung adenocarcinoma: A TRACERx study
Authors: Hobor Sebastijan , Bakir Maise Al , Skrzypski Marcin , Frankell Alexander M. , Bakker Bjorn , Watkins Thomas B. , Markovets Aleksandra , Dry Jonathan R. , Brown Andrew P. , van der Aart Jasper , Oukrif Dahmane , Novelli Marco , Renshaw Matthew J. , Hill William , Bos Hilda van den , Spierings Diana C. , Chmielecki Juliann , Barrett Carl , Litchfield Kevin , de Bruin Elza , Foijer Floris , Vousden Karen H. ,   TRACERx consortium, Hynds Robert E. , Hiley Crispin T. , Kanu Nnennaya , Zaccaria Simone , Gronroos Eva C. , Swanton Charles 
Published: June 2022

Abstract
Introduction: Mutations in the epidermal growth factor receptor (EGFR) are often found in never-smokers who develop lung adenocarcinoma (LUAD) and resistance to receptor-targeted tyrosine kinase inhibitors (TKIs) generally occurs within five years of treatment. Mixed responses, where individual tumor lesions within the same patient respond differently to treatment, contribute to early treatment failure and indicate the involvement of multiple genomic alterations. TP53 loss of function has been associated with both tolerance to chromosomal instability (CIN) and with shortened progression free survival in EGFR-driven tumors. The aim of this study was to investigate the hypothesis that CIN, together with loss of p53 function, may lead to diverse genotypes that underlie the mixed responses observed in EGFR-driven LUAD.
Experimental Procedures: We used genetically engineered mouse models (GEMMs), driven by EGFR with or without concomitant Trp53 loss and human isogenic cell lines to investigate cellular evolution and the effect of whole genome doubling on targeted therapy responses and mechanisms of resistance. Next generation sequencing and shallow whole genome single cell analyses, together with longitudinal imaging analysis from the Aura clinical trials (AURA2, AURA3 and the AURA extension cohort, Identifiers: NCT02094261, NCT02151981 and NCT01802632) was used to investigate the effect of p53 loss on tumor evolution.
Results: EGFR mutant tumors with clonal Trp53 loss or TP53 pathway disruption displayed increased Weighted Genome Integrity Index (wGII) and higher cell to cell variation in both the mouse and TRACERx data sets. We found that TP53 loss of function increased the incidence of mixed responses and resistance to targeted therapy in both mouse and human tumors leading to early treatment failure and reduced survival. Whole-exome sequencing (median depth of 92x, range: 58-169x) of nine erlotinib-resistant EGFR mouse tumors identified four EGFR bypassing mutations (oncogenic KRAS mutations; Q61H, Q61R, and two G12D mutations) and one likely driver mutation in FGFR2 (C286R). We could only identify one known resistance associated mutation, EGFRT790M, in EGFR mutant tumors with concomitant loss of Trp53. In depth analysis revealed no major copy number differences in treatment naÏve vs resistant EGFR mutant tumors. In contrast, 70% of all tumors with concomitant Trp53 loss had amplified a region of mouse chromosome 7, harboring MET and BRAF. Investigating an isogenic EGFR/TP53 mutant cell model system revealed whole genome doubling as advantageous in overcoming the selection pressure induced by targeted therapy.
Conclusion: We find that loss of TP53 in the context of mutated EGFR leads to an altered and plastic genomic landscape, with multiple copy number changes, which in turn facilitates therapy resistance.
Citation Format: Sebastijan Hobor, Maise Al Bakir, Marcin Skrzypski, Alexander M. Frankell, Bjorn Bakker, Thomas B. Watkins, Aleksandra Markovets, Jonathan R. Dry, Andrew P. Brown, Jasper van der Aart, Dahmane Oukrif, Marco Novelli, Matthew J. Renshaw, William Hill, Hilda van den Bos, Diana C. Spierings, Juliann Chmielecki, Carl Barrett, Kevin Litchfield, Elza de Bruin, Floris Foijer, Karen H. Vousden, TRACERx consortium, Robert E. Hynds, Crispin T. Hiley, Nnennaya Kanu, Simone Zaccaria, Eva C. Gronroos, Charles Swanton. TP53 loss with whole genome doubling mediates heterogeneous intra-patient therapy response in EGFR-driven lung adenocarcinoma: A TRACERx study [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 6217.