Lung adenocarcinoma (LUAD) is the most common cancer diagnosed in lifetime smokers of whom there are more than 90 million in the United States. Smokers with LUAD frequently (more than 25%) harbor somatic activating mutations in the Kras oncogene. Kras-mutant LUAD (KM-LUAD) displays very poor clinical outcome and inferior response to therapy. Despite the urgent need of new strategies for early treatment of this fatal disease, we still do not understand targetable changes that promote onset of KM-LUAD. Using a human- relevant genetically engineered mouse model comprised of tobacco exposure and high somatic mutation burdens including driver Kras variants, features that constitute a perfect storm for LUAD pathogenesis in humans, we identified significant progressive changes in gut microbiome composition that were coexistent with reduced levels of gut and circulating bacterial metabolites and closely associated with evolution of KM-LUAD. Similar microbial phenotypes were observed in mice exposed to combustible cigarette smoke (CCS). We further found in lungs of the mice up-regulation of pro-tumor inflammatory cues including activation of the IL-6 /STAT3 pathway which we have previously shown to promote KM-LUAD development by immune reprogramming. Also, we noted that lipocalin 2 (LCN2), a host defense antimicrobial protein that is released from cells during microbiome imbalance, was markedly progressively up-regulated in normal airway cells prior to onset of Kras-mutant preneoplasias and LUADs. Genetic deletion of Lcn2 in these mice markedly increased KM-LUAD development concomitant with global changes in the gut microbiome and heightened pro-tumor lung inflammation. Despite these insights, the interplay between the host microbiome and key immune responses in the pathogenesis of KM-LUAD are poorly understood. We hypothesize that the host microbiome (derived from the gut and possibly the lung) promotes tobacco-associated KM-LUAD development through activation of the IL-6/STAT3 pathway and changes in systemic and lung immune contexture. We will address our hypothesis using the following three aims.
In Aim 1, using sequencing, metagenomics, as well as bacterial metabolite and immune profiling approaches, we will discern evolving microbiome changes that are functionally linked to tobacco carcinogen- and CCS-associated KM-LUAD development as well as probe downstream systemic and local (in lung) immunomodulatory effects including those on the pro-tumor IL- 6/STAT3 pathway.
In Aim 2, we will determine the role of host antimicrobial and immunomodulatory cues mediated by LCN2 induction in KM-LUAD pathogenesis.
In Aim 3, we will investigate chemopreventive and early therapeutic effects of microbiome intervention, alone or in combination with immunotherapy, against KM- LUAD. At the conclusion of our studies, we will have shed light on uncharted host processes in the evolution of KM-LUAD, paved the way for identification of new targets to guide chemoprevention and early detection of this fatal disease in smokers and contributed novel models for studying LUAD pathogenesis.

Public Health Relevance

Smokers with Kras-mutant lung adenocarcinoma (KM-LUAD) display very poor clinical outcome largely due to our poor understanding of targetable molecular changes in the development of the malignancy. While it is now appreciated that the host microbiome has a major impact on health and is a key orchestrator of tumor promoting inflammation and cancer therapy, the role of microbiome changes in development of KM-LUAD is not known. Using unique human-relevant experimental models as well as state-of-the-art metagenomics, immune profiling, and computation, we propose to first interrogate how the gut, and possibly lung, microbiome sways KM-LUAD pathogenesis, pro-tumor inflammatory pathways and tumor immunity and then to develop and test gut microbiome intervention strategies that prevent development of this fatal disease.

National Institute of Health (NIH)
National Cancer Institute (NCI)
Research Project (R01)
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Cancer Prevention Study Section (CPSS)
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Daschner, Phillip J
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University of Texas MD Anderson Cancer Center
United States
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