Evolution Of The Gut Amicrobiome During The Pathogenesis Of Smoking-Associated Kras-Mutant Lung Cancer

Relative to other tumors in smokers, KRAS-mutant lung adenocarcinomas (LUADs) display dismal prognosis warranting the need for early management of this disease. Limiting these advances is our gap in knowledge of events that drive KRAS-mutant LUAD oncogenesis. Host defense systems, such as those elicited by the gut microbiome, were recently shown to influence tumors external to the gastrointestinal tract (e.g. melanomas), thus highlighting the microbiome as an orchestrator of oncogenesis. Yet, gut microbiome changes in early stages of KRAS-mutant LUAD development are not known. We recently reported that mice with knockout of G-protein coupled receptor 5A (Gprc5a-/-), in contrast to wild type (WT) littermates, develop LUADs which are accelerated following exposure to tobacco carcinogen (nicotine-specific nitrosamine ketone/NNK). LUADs in the tobacco exposed Gprc5a-/- mouse model exhibit high somatic mutation burdens, driver Kras variants and other co-occurring drivers, features constituting a “perfect storm” for LUAD pathogenesis in smokers. Using this human-relevant model, we performed 16S-Seq of fecal samples collected prior to and at several time points post-NNK exposure during LUAD development. We found significant, some progressive, microbial changes during the pathogenesis of LUAD, including abolishment of phylum Verrucomicrobia, progressive increase in tumor-promoting genera Odoribacter spp., gradual decrease in Akkermansia spp., which was previously shown to be associated with response to PD-1 blockade, as well as reduced abundance of Ruminococcus which was previously reported to be suppressed during colon carcinogenesis. Additionally, and prior to tumor onset, lungs and immune cells of these Gprc5a-/- mice exhibited markedly elevated expression of lipocalin 2 (LCN2), an antimicrobial protein released from host cells during microbiome imbalance and inflammation. We further found that Gprc5a-/- mice with knockout of Lcn2 exhibited increased tumors compared to similarly exposed Gprc5a-/- with intact Lcn2. These effects were accompanied by widespread changes in the gut microbiome including increased abundance of tumor-promoting Alistipes spp. and, conversely, reduced abundance of Lactobacillus spp. Our data show that host defense mediated by LCN2 counteracts Kras-mutant LUAD development by restricting gut microbiome imbalance (i.e., maintaining gut microbiome homeostasis and diversity), suggesting a protective role during Kras-mutant LUAD development. Our overall findings inform on novel pathways implicating antimicrobial host defense mechanisms in the development of smoking-associated Kras-mutant LUAD. Efforts are underway to discern specific microbiome profiles that are likely causally related to smoking-associated Kras-mutant LUAD development as well as to develop and test preclinical microbiome intervention strategies for this malignancy. Citation Format: Warapen Treekitkarnmongkol, Casey Finnicum, Ansam Sinjab, Maya Hassane, Christel Davis, Gareth E. Davies, Kristi L. Hoffman, Junya Fujimoto, Florencia McAllister, Boris Sepesi, Tina Cascone, Robert R. Jenq, Joseph Petrosino, Erik Ehli, Seyed J. Moghaddam, Humam Kadara. Evolution of the gut microbiome during the pathogenesis of smoking-associated Kras-mutant lung cancer [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 3349.