Serine/Threonine Kinase 11 (STK11) encodes an important tumor suppressor that is frequently mutated in lung adenocarcinoma. Clinical studies have shown that mutations in STK11 resulting in loss of function correlate with resistance to anti-PD-1 monoclonal antibody therapy in KRAS-driven non-small cell lung cancer (NSCLC), but the molecular mechanisms responsible remain unclear. Despite this uncertainty, STK11 functional status is emerging as a reliable biomarker for predicting non-response to anti-PD-1 therapy in NSCLC patients. The clinical utility of this biomarker ultimately depends upon accurate classification of STK11 variants. For nonsense variants occurring early in the STK11 coding region, this assessment is straightforward. However, rigorously demonstrating the functional impact of missense variants remains an unmet challenge. Here we present data characterizing four STK11 splice-site variants by analyzing tumor mRNA, and 28 STK11 missense variants using an in vitro kinase assay combined with a cell-based p53-dependent luciferase reporter assay. The variants we report were identified in primary human NSCLC biopsies in collaboration with the University of Vermont Genomic Medicine group. Additionally, we compare our experimental results with data from 22 in silico predictive algorithms. Our work highlights the power, utility and necessity of functional variant assessment and will aid STK11 variant curation, provide a platform to assess novel STK11 variants and help guide anti-PD-1 therapy utilization in KRAS-driven NSCLCs.

Serine Threonine Kinase 11 (STK11) loss of function (LoF) correlates with anti-PD-1 therapy resistance in patients with KRAS-driven lung adenocarcinoma (LUAD). The molecular mechanisms governing this observation remain unclear and represent a critical outstanding question in the field of lung oncology. As an initial approach to understand this phenomenon, we knocked out STK11 in multiple KRAS-driven, STK11-competent human LUAD cell lines and performed whole transcriptome analyses to identify STK11-loss-dependent differential gene expression. Subsequent pathway enrichment studies highlighted activation of the HIPPO/YAP1 signaling axis, along with the induction of numerous tumor-intrinsic cytokines. To validate that YAP1-mediated transcriptional activation occurs in response to STK11 loss, we pursued YAP1 perturbation as a strategy to restore an STK11-competent gene expression profile in STK11-KO LUAD cell lines. Together, our data link STK11loss with YAP1-mediated transcriptional activation, including the upregulation of immune-evasion promoting cytokines IL-6, CXCL8 and CXCL2. Further, our results raise the intriguing possibility that YAP1 antagonism may represent a therapeutic approach to counter anti-PD-1 therapy resistance in STK11-null, KRAS-driven LUADs by modulating tumor-intrinsic gene expression to promote a “hot” tumor immune microenvironment.

Non-small cell lung adenocarcinomas with concurrent oncogenic KRAS and SKT11 loss-of-function mutations represent an aggressive subtype that is characterized, in part, by increased metastasis and enhanced dependence on glutamine metabolism. The purpose of this study was to elucidate the metabolic rewiring of STK11-null KRAS-driven lung adenocarcinoma cells and determine how such altered metabolism may promote metastasis. Both parental and ΔSTK11 cells, generated via CRISPR-Cas9, were assessed for metabolic flux and measures of metastatic potential at baseline, and when deprived of exogenous glutamine. Seahorse analysis revealed a “metabolically exhausted” mitochondrial phenotype in ΔSTK11 cells at baseline. Upon exogenous glutamine deprivation, both ΔSTK11 and parental cells similarly decreased mitochondrial respiration, however, through the employment of RNA sequencing and heavy carbon labeling, we demonstrate an upregulation of the hexosamine biosynthetic pathway (HBP) in ΔSTK11 cells. Moreover, we observed an increase in global O-GlcNAcylation, the product of the HBP, in ΔSTK11 cells. The HBP is an offshoot of glycolysis/gluconeogenesis that serves as a central hub to regulate many cancer fitness pathways via O-GlcNAcylation, and it has been established that cancer cells upregulate the HBP resulting in activation of proteins involved in promoting metastasis. To assess transcriptional characteristics of metastatic spread, KEGG pathway analysis was performed on transcriptomic data obtained from parental vs ΔSTK11 cells subjected to glutamine deprivation and revealed significant upregulation of NFkB and MAPK signaling in ΔSTK11 cells. Additionally, EMT markers downstream of these pathways, such as SNAI2 and ZEB1, were upregulated in ΔSTK11 cells. Trypan Blue staining was used as a preliminary method to measure anoikis resistance, an additional characteristic of metastatic potential. Results revealed a significant increase in live detached cells upon glutamine deprivation-induced detachment in ΔSTK11 cells. Correspondingly, differential gene expression indicated significant upregulation of BCL2A1, an anti-apoptotic protein, in ΔSTK11 cells following glutamine deprivation. Future studies aim to further clarify the altered metabolic profile of ΔSTK11 lung adenocarcinoma cells to identify the mechanism(s) by which such metabolic rewiring drives metastatic progression. In conclusion, this work reveals novel findings regarding the molecular mechanisms altered downstream of STK11-loss that influence glutamine metabolism and enhanced metastasis in KRAS-driven lung adenocarcinomas. Citation Format: Shannon M. Prior, Sean M. Lenahan, Hailey M. Sarausky, David J. Seward, Paula B. Deming. Metabolic rewiring and metastatic potential in STK11-null lung adenocarcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 270.

Our work demonstrates RNAscope allows simultaneous quantitative assessment of multiple transcripts in situ using formalin fixed paraffin embedded (FFPE) human non-small cell lung cancer (NSCLC) biopsies and suggests this methodology could be used as a rapid surrogate biomarker for genotype/transcriptome profiling stemming for Serine Threonine Kinase 11 (STK11) loss of function (LoF). Recent clinical studies have correlated anti-PD1 therapy resistance in NSCLC with somatic disruption of STK11. Historically, rapid assessment of STK11 status using immunohistochemistry (IHC) has been a challenge. Our work in human NSCLC cell lines suggests that STK11 loss correlates with changes in tumor intrinsic cytokine expression. Several recent studies have suggested such changes may drive immune evasion. We therefore wondered whether cytokine expression profiles from primary human NSCLC biopsies might be used as a reliable biomarker to predict anti-PD1 therapy response. Here we present our findings using multiplexed RNAscope probes on KRAS-driven primary human NSCLC biopsies with and without STK11 loss. This initial work focuses on cytokines identified using our cell culture models as a proof of principle approach. Using CRISPR-Cas9 we engineered paired STK11 KO cell lines derived from 3 independent KRAS-driven human lung adenocarcinomas (NCI-H441, NCI-H1792, NCI-H2009). RNAseq and differential gene expression analysis revealed STK11-loss-dependent increases in IL-6, IL-8 and IL-32 in all three lines. We then created FFPE cell blocks using these cell lines and validated the RNAseq expression changes with multiplexed RNAscope probes in situ. Next, we informatically searched the molecular pathology archives at the UVM medical center and identified primary KRAS-driven human NSCLC biopsies with and without predicted STK11 loss. We then performed multiplexed RNAscope analysis on these samples to quantify IL-6, IL-8 and IL-32 gene expression as a function of tumor genotype in vivo. Our data suggest RNAscope represents a valid methodology to exploit quantitative differential gene expression as a reliable and reproducible surrogate biomarker of somatic STK11 disruption in NSCLC. Our future studies aim to establish whether genotype-dependent cytokine profiles predict anti-PD1 therapy response in KRAS-driven lung adenocarcinomas. Citation Format: Hailey M. Sarausky, Sean M. Lenahan, David Joseph Seward. Utilizing RNAscope to assess STK11-LoF-dependent transcriptional phenotypes in human NSCLC biopsies and evaluate its potential to predict anti-PD1 therapy response [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 2706.

Glutamine amidotransferase-1 domain-containing AraC-family transcriptional regulators (GATRs) are present in the genomes of many bacteria, including all Pseudomonas species. The involvement of several characterized GATRs in amine-containing compound metabolism has been determined, but the full scope of GATR ligands and regulatory networks are still unknown. Here, we characterize Pseudomonas putida’s detection of the animal-derived amine compound, creatine, a compound particularly enriched in muscle and ciliated cells by a creatine-specific GATR, PP_3665, here named CahR (Creatine amidohydrolase Regulator). cahR is necessary for transcription of the gene encoding creatinase (PP_3667/creA) in the presence of creatine and is critical for P. putida’s ability to utilize creatine as a sole source of nitrogen. The CahR/creatine regulon is small and electrophoretic mobility shift demonstrates strong and specific CahR binding only at the creA promoter, supporting the conclusion that much of the regulon is dependent on downstream metabolites. Phylogenetic analysis of creA orthologs associated with cahR orthologs highlights a strain distribution and organization supporting likely horizontal gene transfer, particularly evident within the genus Acinetobacter. This study identifies and characterizes the GATR that transcriptionally controls P. putida metabolism of creatine, broadening the scope of known GATR ligands and suggesting GATR diversification during evolution of metabolism for aliphatic nitrogen compounds.