There are more than 90 million smokers in the United States who are at elevated risk for lung adenocarcinoma (LUAD), the most common lung cancer subtype. LUADs in smokers frequently (more than 25%) exhibit mutations in the Kras oncogene. Relative to other LUADs found in smokers, Kras mutant LUAD displays dismal prognosis. Attempts to pharmacologically target Kras have, for the most part, failed, warranting the need for new strategies for prevention and early treatment of this fatal disease. Despite this urgency, we have a poor understanding of events that drive development of Kras mutant LUAD in smokers and that would constitute targets for early treatment. Previous work revealed that visually normal smoking exposed airways carry alterations that are characteristic of adjacent LUADs, an effect referred to as ?airway field of injury?. While this field is enriched with malignant properties, we do not know which field changes are induced or progress in normal or premalignant cells to give rise to Kras mutant LUAD and, if so, how we can impede this process. Our goal is to address this gap in knowledge, first determining molecular alterations in the progression of the normal-appearing airway field of injury to a Kras mutant LUAD phenotype, and second identifying agents that target these field alterations and prevent development of the malignancy. In our preliminary data, we found that mice with knockout of G-protein coupled receptor 5A (Gprc5a-/-), a retinoid-regulated gene that is prominently suppressed in human LUADs compared to normal lung, not only developed, in contrast to wild type littermates, premalignant lesions (PMLs) and LUADs after tobacco carcinogen exposure but also that these lesions harbored somatic Kras mutations, the same variants thought to act as drivers of human LUAD in smokers. We then studied the effects of tobacco carcinogen on gene expression in normal airways of Gprc5a-/- mice in order to understand early events in Kras mutant LUAD pathogenesis. Using RNA-sequencing, we found activation of oncogenic pathways in tobacco carcinogen exposed normal airways when compared to non-exposed cells at baseline, suggestive of an airway field of injury induced prior to onset of Kras mutant LUAD. We will use the tobacco carcinogen exposed Gprc5a-/- mouse as a model to study and target progression of the airway field of injury to Kras mutant LUAD.
In Aim 1, we will survey, by exome sequencing, mutations that characterize the evolution of smoking exposed airway cells to Kras mutant PMLs and LUADs.
In Aim 2, we will determine evolutionarily conserved airway expression profiles that progress with time following onset of smoking and signify the development of Kras mutant PMLs and LUADs.
In Aim 3, we will harness the field signatures and use computational drug discovery approaches to identify agents that prevent the development of Kras mutant PMLs and inhibit progression of PMLs to LUADs. At the conclusion of our studies, we will have started to understand the evolution of Kras mutant LUAD, pointed to chemoprevention approaches for this fatal disease and contributed novel models for studying LUAD pathogenesis and tumor promoting field effects.

Public Health Relevance

Lung adenocarcinoma (LUAD) patients with activating mutations in the Kras oncogene have very poor clinical outcome. There are limited strategies to prevent or treat early Kras mutant LUAD largely due to our poor knowledge of the earliest events in its development. Using unique experimental models and state-of-the-art computation, we propose to understand the progression of normal smoking exposed airway epithelium to Kras mutant LUAD and to identify drugs that impede this process and prevent development of the malignancy.

National Institute of Health (NIH)
National Cancer Institute (NCI)
Research Project (R01)
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Special Emphasis Panel (ZCA1)
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Szabo, Eva
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University of Texas MD Anderson Cancer Center
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