Metabolic reprogramming driven by EZH2 inhibition depends on cell-matrix interactions.

EZH2 (Enhancer of Zeste Homolog 2), a subunit of Polycomb Repressive Complex 2 (PRC2), catalyzes the trimethylation of histone H3 at lysine 27 (H3K27me3), which represses expression of genes. It also has PRC2-independent functions, including transcriptional coactivation of oncogenes, and is frequently overexpressed in lung cancers. Clinically, EZH2 inhibition can be achieved with the FDA-approved drug EPZ-6438 (tazemetostat). To realize the full potential of EZH2 blockade, it is critical to understand how cell-cell/cell-matrix interactions present in 3D tissue and cell culture systems influences this blockade in terms of growth-related metabolic functions. Here, we show that EZH2 suppression reduced growth of human lung adenocarcinoma A549 cells in 2D cultures but stimulated growth in 3D cultures. To understand the metabolic underpinnings, we employed [13C6]-glucose stable isotope-resolved metabolomics to determine the effect of EZH2 suppression on metabolic networks in 2D versus 3D A549 cultures. The Krebs cycle, neoribogenesis, γ-aminobutyrate metabolism, and salvage synthesis of purine nucleotides were activated by EZH2 suppression in 3D spheroids but not in 2D cells, consistent with the growth effect. Using simultaneous 2H7-glucose + 13C5,15N2-Gln tracers and EPZ-6438 inhibition of H3 trimethylation, we delineated the effects on the Krebs cycle, γ-aminobutyrate metabolism, gluconeogenesis, and purine salvage to be PRC2-dependent. Furthermore, the growth/metabolic effects differed for mouse Matrigel versus self-produced A549 extracellular matrix. Thus, our findings highlight the importance of the presence and nature of extracellular matrix in studying the function of EZH2 and its inhibitors in cancer cells for modeling the in vivo outcomes.

Using Artificial Intelligence to Identify Tumor Microenvironment Heterogeneity in Non-Small Cell Lung Cancers.

Lung cancer heterogeneity is a major barrier to effective treatments and encompasses not only the malignant epithelial cell phenotypes and genetics but also the diverse tumor-associated cell types. Current techniques used to investigate the tumor microenvironment can be time-consuming, expensive, complicated to interpret, and often involves destruction of the sample. Here we use standard hematoxylin and eosin-stained tumor sections and the HALO AI nuclear phenotyping software to characterize 6 distinct cell types (epithelial, mesenchymal, macrophage, neutrophil, lymphocyte, and plasma cells) in both murine lung cancer models and human lung cancer samples. CD3 immunohistochemistry and lymph node sections were used to validate lymphocyte calls, while F4/80 immunohistochemistry was used for macrophage validation. Consistent with numerous prior studies, we demonstrated that macrophages predominate the adenocarcinomas, whereas neutrophils predominate the squamous cell carcinomas in murine samples. In human samples, we showed a strong negative correlation between neutrophils and lymphocytes as well as between mesenchymal cells and lymphocytes and that higher percentages of mesenchymal cells correlate with poor prognosis. Taken together, we demonstrate the utility of this AI software to identify, quantify, and compare distributions of cell types on standard hematoxylin and eosin-stained slides. Given the simplicity and cost-effectiveness of this technique, it may be widely beneficial for researchers designing new therapies and clinicians working to select favorable treatments for their patients.

The Epithelial Sodium Channel Is a Modifier of the Long-Term Nonprogressive Phenotype Associated with F508del CFTR Mutations.

Cystic fibrosis (CF) remains the most lethal genetic disease in the Caucasian population. However, there is great variability in clinical phenotypes and survival times, even among patients harboring the same genotype. We identified five patients with CF and a homozygous F508del mutation in the CFTR gene who were in their fifth or sixth decade of life and had shown minimal changes in lung function over a longitudinal period of more than 20 years. Because of the rarity of this long-term nonprogressive phenotype, we hypothesized these individuals may carry rare genetic variants in modifier genes that ameliorate disease severity. Individuals at the extremes of survival time and lung-function trajectory underwent whole-exome sequencing, and the sequencing data were filtered to include rare missense, stopgain, indel, and splicing variants present with a mean allele frequency of <0.2% in general population databases. Epithelial sodium channel (ENaC) mutants were generated via site-directed mutagenesis and expressed for Xenopus oocyte assays. Four of the five individuals carried extremely rare or never reported variants in the SCNN1D and SCNN1B genes of the ENaC. Separately, an independently enriched rare variant in SCNN1D was identified in the Exome Variant Server database associated with a milder pulmonary disease phenotype. Functional analysis using Xenopus oocytes revealed that two of the three variants in δ-ENaC encoded by SCNN1D exhibited hypomorphic channel activity. Our data suggest a potential role for δ-ENaC in controlling sodium reabsorption in the airways, and advance the plausibility of ENaC as a therapeutic target in CF.

Using 3-Dimensional Cultures to Propagate Genetically Modified Lung Organoids.

Transformed lung organoids have extensive applications in lung cancer modeling and drug screening. Traditional two-dimensional (2D) cultures fail to propagate a large subpopulation of murine primary tumors in vitro. However, three-dimensional (3D) air-liquid interface (ALI) cultures, which are employed to grow normal lung organoids, can be used to efficiently culture cancerous lung tumor cells. Here, we detail a procedure for cultivating genetically modified lung organoids in 3D-ALI cultures. This protocol contains two parts. The first part describes how to transduce lung epithelial cells, which are either freshly sorted from lungs or from actively growing murine organoids, with virus in order to modify gene expression. The target lung cells are incubated with virus for 1-2 h for transduction. Then, the transduced cells are thoroughly washed and mixed with stromal support cells and Matrigel and are loaded into transwell inserts for culture and validated for genetic modifications through downstream assays. The second part describes how to isolate tumor cells growing orthotopically in genetically engineered mouse models to produce organoid cell lines that can be used for ex vivo drug discovery assays. For this protocol, tumors are isolated from lungs of mice, finely chopped and washed. Then, tumor chunks are mixed with Matrigel for 3D-ALI culture. Finally, organoids budding from tumor chunks are trypsinized and passaged to establish an organoid line. Together these two protocols provide a promising platform to study the genesis, progression, and treatment of lung cancer.

Isolation, Culture, and Phenotypic Analysis of Murine Lung Organoids.

Three-dimensional (3D) organoid cultures retain self-renewing stem cells that differentiate into multiple cell types that display spatial organization and functional key features, providing a highly physiological relevant system. Here we describe a strategy for the generation of 3D murine lung organoids derived from freshly isolated primary tracheal and distal lung epithelial stem cells. Isolated tracheas are subjected to enzymatic digestion to release the epithelial layer that is then dissociated into a single cell suspension for organoid culture. Lung epithelial cells are obtained from dissected lobes, which are applied to mechanical and enzymatic dissociation. After flow sorting, organoids are established from tracheal basal, secretory club, and alveolar type 2 cells in the defined conditioned medium that is required to sustain organoid growth and generate the differentiated cells. Multi-cell-type organoid co-culture replicates niches for distal epithelial stem cells to differentiate into bronchiolar and alveolar cell types. Established organoids can be fixed for wholemount staining and paraffin embedding, or passaged for further culture. Taken together, this protocol provides an efficient and validated approach to generate murine lung organoids, as well as a platform for further analysis.

EZH2 Inhibition Promotes Tumor Immunogenicity in Lung Squamous Cell Carcinomas.

Two important factors that contribute to resistance to immune checkpoint inhibitors (ICI) are an immune-suppressive microenvironment and limited antigen presentation by tumor cells. In this study, we examine whether inhibition of the methyltransferase enhancer of zeste 2 (EZH2) can increase ICI response in lung squamous cell carcinomas (LSCC). Our in vitro experiments using two-dimensional human cancer cell lines as well as three-dimensional murine and patient-derived organoids treated with two inhibitors of the EZH2 plus IFNγ showed that EZH2 inhibition leads to expression of both MHC class I and II (MHCI/II) expression at both the mRNA and protein levels. Chromatin immunoprecipitation sequencing confirmed loss of EZH2-mediated histone marks and gain of activating histone marks at key loci. Furthermore, we demonstrate strong tumor control in models of both autochthonous and syngeneic LSCC treated with anti-PD1 immunotherapy with EZH2 inhibition. Single-cell RNA sequencing and immune cell profiling demonstrated phenotypic changes toward more tumor suppressive phenotypes in EZH2 inhibitor-treated tumors. These results indicate that EZH2 inhibitors could increase ICI responses in patients undergoing treatment for LSCC. SIGNIFICANCE: The data described here show that inhibition of the epigenetic enzyme EZH2 allows derepression of multiple immunogenicity factors in LSCC, and that EZH2 inhibition alters myeloid cells in vivo. These data support clinical translation of this combination therapy for treatment of this deadly tumor type.

Methionine Restriction Reduces Lung Cancer Progression and Increases Chemotherapy Response.

Targeting tumor metabolism through dietary interventions is an area of growing interest, and may help to improve the significant mortality of aggressive cancers, including non-small cell lung cancer (NSCLC). Here we show that the restriction of methionine in the aggressive KRAS /Lkb1- mutant NSCLC autochthonous mouse model drives decreased tumor progression and increased carboplatin treatment efficacy. Importantly, methionine restriction during early stages of tumorigenesis prevents the lineage switching known to occur in the model, and alters the tumor immune microenvironment (TIME) to have fewer tumor-infiltrating neutrophils. Mechanistically, mutations in LKB1 are linked to anti-oxidant production through changes to cystathionine-ß-synthase (CBS) expression. Human cell lines with rescued LKB1 show increased CBS levels and resistance to carboplatin, which can be partially rescued by methionine restriction. Furthermore, LKB1 rescued cells, but not mutant cells, show less G2- M arrest and apoptosis in high methionine conditions. Knock-down of CBS sensitized both LKB1 mutant and non-mutated lines to carboplatin, again rescuing the carboplatin resistance of the LKB1 rescued lines. Given that immunotherapy is commonly combined with chemotherapy for NSCLC, we next wanted to understand if T cells are impaired by MR. Therefore, we examined the ability of T cells from MR and control tumor bearing mice to proliferate in culture and found that T cells from MR treated mice had no defects in proliferation, even though we continued the MR conditions ex vivo . We also identified that CBS is most highly correlated with smoking, adenocarcinomas with alveolar and bronchiolar features, and adenosquamous cell carcinomas, implicating its roles in oxidative stress response and lineage fate in human tumors. Taken together, we have shown the importance of MR as a dietary intervention to slow tumor growth and improve treatment outcomes for NSCLC.

EZH2 inhibition promotes tumor immunogenicity in lung squamous cell carcinomas.

Two important factors that contribute to resistance to immune checkpoint inhibitors (ICIs) are an immune-suppressive microenvironment and limited antigen presentation by tumor cells. In this study, we examine if inhibition of the methyltransferase EZH2 can increase ICI response in lung squamous cell carcinomas (LSCCs). Our in vitro experiments using 2D human cancer cell lines as well as 3D murine and patient derived organoids treated with two inhibitors of the EZH2 plus interferon-γ (IFNγ) showed that EZH2 inhibition leads to expression of both major histocompatibility complex class I and II (MHCI/II) expression at both the mRNA and protein levels. ChIP-sequencing confirmed loss of EZH2-mediated histone marks and gain of activating histone marks at key loci. Further, we demonstrate strong tumor control in models of both autochthonous and syngeneic LSCC treated with anti-PD1 immunotherapy with EZH2 inhibition. Single-cell RNA sequencing and immune cell profiling demonstrated phenotypic changes towards more tumor suppressive phenotypes in EZH2 inhibitor treated tumors. These results indicate that this therapeutic modality could increase ICI responses in patients undergoing treatment for LSCC.

Crizotinib induces Par-4 secretion from normal cells and GRP78 expression on the cancer cell surface for selective tumor growth inhibition.

Lung cancer is the leading cause of cancer-related deaths. Lung cancer cells develop resistance to apoptosis by suppressing the secretion of the tumor suppressor Par-4 protein (also known as PAWR) and/or down-modulating the Par-4 receptor GRP78 on the cell surface (csGRP78). We sought to identify FDA-approved drugs that elevate csGRP78 on the surface of lung cancer cells and induce Par-4 secretion from the cancer cells and/or normal cells in order to inhibit cancer growth in an autocrine or paracrine manner. In an unbiased screen, we identified crizotinib (CZT), an inhibitor of activated ALK/MET/ROS1 receptor tyrosine kinase, as an inducer of csGRP78 expression in ALK-negative, KRAS or EGFR mutant lung cancer cells. Elevation of csGRP78 in the lung cancer cells was dependent on activation of the non-receptor tyrosine kinase SRC by CZT. Inhibition of SRC activation in the cancer cells prevented csGRP78 translocation but promoted Par-4 secretion by CZT, implying that activated SRC prevented Par-4 secretion. In normal cells, CZT did not activate SRC and csGRP78 elevation but induced Par-4 secretion. Consequently, CZT induced Par-4 secretion from normal cells and elevated csGRP78 in the ALK-negative tumor cells to cause paracrine apoptosis in cancer cell cultures and growth inhibition of tumor xenografts in mice. Thus, CZT induces differential activation of SRC in normal and cancer cells to trigger the pro-apoptotic Par-4-GRP78 axis. As csGRP78 is a targetable receptor, CZT can be repurposed to elevate csGRP78 for inhibition of ALK-negative lung tumors.

EZH2 inhibition confers PIK3CA-driven lung tumors enhanced sensitivity to PI3K inhibition.

Members of the PI3K signaling pathway, especially PIK3CA, the gene encoding the catalytic subunit of the PI3K complex, are highly mutated and amplified in various cancer types, including non-small cell lung cancer. Although PI3K inhibitors have been used in clinics for follicular lymphoma and chronic lymphocytic leukemia, no agents targeting PI3K aberrations in lung cancer have been approved by the FDA so far. In this study, we observed that PIK3CA-E545K, the most common mutation in lung cancer, harbored a modest induction of stem-like properties in lung epithelial cells, and drove development of adenocarcinoma autochthonously when paired with p53 loss in a murine mouse model. We also found that PIK3CA-mutant of amplified lung cancer cells were sensitive to EZH2 inhibition. EZH2 inhibition synergized with PI3K inhibition in human cancer cells in vitro and worked together efficiently in vivo. Mechanistically, EZH2 inhibition cooperated with PI3K inhibition to produce a more potent suppression of phospho-AKT downstream of PI3K. This study suggests a promising combination therapy to combat lung cancers with PIK3CA mutation or amplification. Both copanlisib, the PI3K inhibitor, and tazemetostat, the EZH2 inhibitor, are FDA-approved, which should enhance the clinical translation of this work.

The kinase PLK1 promotes the development of Kras/Tp53-mutant lung adenocarcinoma through transcriptional activation of the receptor RET.

Increased abundance of polo-like kinase 1 (PLK1) is observed in various tumor types, particularly in lung adenocarcinoma (LUAD). Here, we found that PLK1 accelerated the progression of LUAD through a mechanism that was independent of its role in mediating mitotic cell division. Analysis of human tumor databases revealed that increased PLK1 abundance in LUAD correlated with mutations in KRAS and p53, with tumor stage, and with reduced survival in patients. In a mouse model of KRASG12D-driven, p53-deficient LUAD, PLK1 overexpression increased tumor burden, decreased tumor cell differentiation, and reduced animal survival. PLK1 overexpression in cultured cells and mice indirectly increased the expression of the gene encoding the receptor tyrosine kinase RET by phosphorylating the transcription factor TTF-1. Signaling by RET and mutant KRAS in these tumors converged to activate the mitogen-activated protein kinase (MAPK) pathway. Pharmacological inhibition of the MAPK pathway kinase MEK combined with inhibition of either RET or PLK1 markedly suppressed tumor growth. Our findings show that PLK1 can amplify MAPK signaling and reveal a potential target for stemming progression in lung cancers with high PLK1 abundance.

Cellular Origins of EGFR-Driven Lung Cancer Cells Determine Sensitivity to Therapy.

Targeting the epidermal growth factor receptor (EGFR) with tyrosine kinase inhibitors (TKIs) is one of the major precision medicine treatment options for lung adenocarcinoma. Due to common development of drug resistance to first- and second-generation TKIs, third-generation inhibitors, including osimertinib and rociletinib, have been developed. A model of EGFR-driven lung cancer and a method to develop tumors of distinct epigenetic states through 3D organotypic cultures are described here. It is discovered that activation of the EGFR T790M/L858R mutation in lung epithelial cells can drive lung cancers with alveolar or bronchiolar features, which can originate from alveolar type 2 (AT2) cells or bronchioalveolar stem cells, but not basal cells or club cells of the trachea. It is also demonstrated that these clones are able to retain their epigenetic differences through passaging orthotopically in mice and crucially that they have distinct drug vulnerabilities. This work serves as a blueprint for exploring how epigenetics can be used to stratify patients for precision medicine decisions.

Description of a Lung Cancer Hotspot: Disparities in Lung Cancer Histology, Incidence, and Survival in Kentucky and Appalachian Kentucky.

INTRODUCTION: Kentucky is recognized as the state with the highest lung cancer burden for more than 2 decades, but how lung cancer differs in Kentucky relative to other US populations is not fully understood. PATIENTS AND METHODS: We examined lung cancer reported to the Surveillance, Epidemiology, and End Results (SEER) Program by Kentucky and the other SEER regions for patients diagnosed between 2012 and 2016. Our analyses included histologic types, incidence rates, stage at diagnosis, and survival in Kentucky and Appalachian Kentucky relative to other SEER regions. RESULTS: We found that both squamous cell carcinomas and small-cell lung cancers represent larger proportions of lung cancer diagnoses in Kentucky and Appalachian Kentucky than they do in the SEER registries. Furthermore, age-adjusted cancer incidence rates were higher in Kentucky for every subtype of lung cancer examined. Most notably, for Appalachian women the rate of small-cell carcinomas was 3.5-fold higher, and for Appalachian men the rate of squamous cell carcinoma was 3.1-fold higher, than the SEER rates. In Kentucky, lung cancers were diagnosed at later stages and lung cancer survival was lower for adenocarcinoma and neuroendocrine carcinomas than in SEER registries. Squamous cell carcinomas and small-cell carcinomas were most lethal in Appalachian Kentucky. CONCLUSION: Together, these data highlight the considerable disparities among lung cancer cases in the United States and demonstrate the continuing high burden and poor survival of lung cancer in Kentucky and Appalachian Kentucky. Strategies to identify and rectify causes of these disparities are discussed.

Brain glycogen serves as a critical glucosamine cache required for protein glycosylation.

Glycosylation defects are a hallmark of many nervous system diseases. However, the molecular and metabolic basis for this pathology is not fully understood. In this study, we found that N-linked protein glycosylation in the brain is metabolically channeled to glucosamine metabolism through glycogenolysis. We discovered that glucosamine is an abundant constituent of brain glycogen, which functions as a glucosamine reservoir for multiple glycoconjugates. We demonstrated the enzymatic incorporation of glucosamine into glycogen by glycogen synthase, and the release by glycogen phosphorylase by biochemical and structural methodologies, in primary astrocytes, and in vivo by isotopic tracing and mass spectrometry. Using two mouse models of glycogen storage diseases, we showed that disruption of brain glycogen metabolism causes global decreases in free pools of UDP-N-acetylglucosamine and N-linked protein glycosylation. These findings revealed fundamental biological roles of brain glycogen in protein glycosylation with direct relevance to multiple human diseases of the central nervous system.

BRG1 Loss Predisposes Lung Cancers to Replicative Stress and ATR Dependency.

Inactivation of SMARCA4/BRG1, the core ATPase subunit of mammalian SWI/SNF complexes, occurs at very high frequencies in non-small cell lung cancers (NSCLC). There are no targeted therapies for this subset of lung cancers, nor is it known how mutations in BRG1 contribute to lung cancer progression. Using a combination of gain- and loss-of-function approaches, we demonstrate that deletion of BRG1 in lung cancer leads to activation of replication stress responses. Single-molecule assessment of replication fork dynamics in BRG1-deficient cells revealed increased origin firing mediated by the prelicensing protein, CDC6. Quantitative mass spectrometry and coimmunoprecipitation assays showed that BRG1-containing SWI/SNF complexes interact with RPA complexes. Finally, BRG1-deficient lung cancers were sensitive to pharmacologic inhibition of ATR. These findings provide novel mechanistic insight into BRG1-mutant lung cancers and suggest that their dependency on ATR can be leveraged therapeutically and potentially expanded to BRG1-mutant cancers in other tissues. SIGNIFICANCE: These findings indicate that inhibition of ATR is a promising therapy for the 10% of non-small cell lung cancer patients harboring mutations in SMARCA4/BRG1. GRAPHICAL ABSTRACT: http://cancerres.aacrjournals.org/content/canres/80/18/3841/F1.large.jpg.