Abstract 3158: Defining the mechanisms that lead to mutational heterogeneity in the normal respiratory epithelium

Abstract

Abstract It is well established that tobacco smoking causes lung cancer and this is thought to be the result of a progressive accumulation of genomic mutations induced by tobacco smoke exposure; however, until recently a detailed understanding of the effects of smoke exposure on the genomes of cells in the normal bronchial epithelium was lacking. To address this, we defined the genomic architecture of normal airway basal cells in children and non-smoking, smoking and ex-smoking adults. We discovered two populations of basal cells in individuals with a smoking history: those with high mutational burden, driver gene mutations and tobacco-associated mutational signatures, and those with low mutational burden, similar to basal cells from never smokers and with an absence of mutational signatures associated with tobacco exposure. These cells expand preferentially in ex-smokers, accounting for 20-40% of basal cells compared with 2-5% in current smokers. We hypothesise that these cells are cancer-protective and their expansion reduces the risk of lung cancer development after smoking cessation. Understanding the functional differences between high- and low-mutant airway basal cells and the mechanisms by which some cells resist the accumulation of smoking-induced mutations will be crucial to understanding the earliest stages of lung carcinogenesis. To address this, we performed RNAseq on a subset of whole-genome sequenced airway basal cells. Preliminary data show that expression of markers of stemness is significantly different between high- and low-mutant basal cells. In addition, initial analysis shows that pathways such as carcinogen metabolism and MHC class I antigen presentation are higher in high-mutant basal cells. Further analysis in more patients is ongoing. To complement these data, we expanded whole-genome sequenced basal cell clones in culture and performed a range of assays to assess their progenitor and differentiation capacity. We assessed proliferation, colony-forming efficiency, longevity and differentiation and found no apparent differences between low- and high-mutant basal cells. Initial analysis suggests that carcinogen metabolism and MHC class I antigen presentation may be key pathways in establishing heterogeneity in mutational burden and clonal dynamics in the normal airway epithelium. Additional assays and analysis are ongoing and will be the focus of future research. Citation Format: Kate H. Gowers, Sarah E. Clarke, Ayu Hutami Syaraf, Kenichi Yoshida, Moritz J. Przybilla, Hugh Selway, Adam Pennycuick, Peter J. Campbell, Sam M. Janes. Defining the mechanisms that lead to mutational heterogeneity in the normal respiratory epithelium [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 3158.