STAT3, NF-κB, and Estrogen Receptor Beta: The Balance of Inflammation in K-ras Mutant Lung Adenocarcinoma

K-ras mutant lung adenocarcinoma (KM-LUAD) is a difficult-to-treat cancer subtype in which chronic inflammation pervades the tumor immune microenvironment (TIME). Pro-inflammatory pathways dampen the response to treatments, including immune checkpoint inhibitors, necessitating therapies that target this inflammatory signaling network in the TIME. This network is underpinned by interaction and coordination of two inflammatory pathways: signal transducer and activator of transcription 3 (STAT3) and nuclear factor kappa B (NF-κB). The balance of these transcription factors determines the degree of anti- vs. pro-tumor immunity, and a skewing towards STAT3 is known to promote tumor development and a pro-tumor TIME. It is also well documented in lung cancer that there are disparities in incidence and survival based on sex, with more cases of lung cancer occurring in female patients but yielding a lower mortality rate than males. A proposed mechanism for this disparity involves the interaction of estrogen signaling with STAT3 and NF-κB. From these observations, two independent but related research projects were developed. The first wing of this study was to test the anti-tumor and early immunotherapeutic efficacy of TTI-101, a selective small-molecule inhibitor of canonical STAT3 signaling, in a K-rasG12D mutant lung cancer mouse model (CC-LR). Treatment of CC-LR mice with TTI-101 resulted in reduced tumor burden while increasing dendritic cell (DC) and T helper 1 (Th1) infiltration into the TIME. TTI-101 treatment decreased pY-STAT3 expression in tumors with accompanying increases in several NF-κB anti-tumor target genes including CXCL9, a chemokine for primed T cells. Transcriptional profiling of the TIME revealed improved immune activation and anti-tumor skewing, as well as B cell signaling enrichment. Analysis of human LUAD data demonstrated negative correlations between STAT3 and Th1/DC infiltration, with DC infiltration also conferring improved survival in LUAD patients with low STAT3. The second wing of this study was to generate a KM-LUAD mouse model with conditional deletion of estrogen receptor β (ERβ), the main form of ER expressed in lung tissue. The resulting mice developed a lower tumor burden than matched controls, and RNA and protein analyses indicated a shift from STAT3- to NF-κB-driven inflammation. The results of these two research arms highlight the importance of STAT3 in driving early tumorigenesis and the anti-tumor benefits of repolarization of the TIME towards NF-κB-driven inflammation. These results also offer a preventative treatment window for high-risk individuals and patients with early-stage KM-LUAD, as well as potential stratification criteria and therapeutic targets.