Abstract 4713: BET bromodomain inhibition synergizes with PD-1 blockade to facilitate anti-tumor response in Kras-mutant non-small cell lung cancer

KRAS mutation is present in about 30% of human lung adenocarcinomas. While recent advances in targeted therapy have shown great promise, KRAS remains undruggable and concurrent alterations in tumor suppressors render KRAS mutant tumors even more resistant to existing therapies. Contributing to the refractoriness of KRAS mutant tumors harboring these co-mutations are immunosuppressive mechanisms such as increased presence of suppressive Tregs in tumors and elevated expression of the inhibitory receptor PD-1 on tumor-infiltrating T cells. BET bromodomain inhibitors demonstrate clinical benefit in hematologic malignancies, and prior reports demonstrate their Treg-disruptive effects in a NSCLC model. Targeting PD-1 inhibitory signals through anti-PD-1 antibody blockade has also shown substantial therapeutic impact in lung cancer although these outcomes are still limited to a minor pool of patients. We therefore hypothesized that the BET bromodomain inhibitor JQ1 would synergize with PD-1 blockade to promote robust anti-tumor response in lung cancer. In the present study, using Kras+/LSL-G12D; Trp53L/L (KP) mouse models of non-small cell lung cancer, we identified cooperative effects among JQ1 and anti-PD-1 that included reduced numbers of tumor-infiltrated Tregs and enhanced activation of tumor-infiltrating T cells, which exhibited a Th1 cytokine profile that favored their demonstrated improved effector function. Furthermore, lung-tumor-bearing mice under this combinatorial treatment regimen showed robust and long-lasting anti-tumor responses compared to either agent alone, culminating in substantial improvement in the survival of treated mice. Thus, combining BET bromodomain inhibition with immune checkpoint blockade offers a promising therapeutic approach for solid malignancies such as lung adenocarcinoma.

Citation Format: Dennis O. Adeegbe, Shengwu Liu, Michaela Bowden, Peter S. Hammerman, James E. Bradner, Anil K. Rustgi, Adam J. Bass, Gordon J. Freeman, Huawei Chen, kwok-Kin Wong. BET bromodomain inhibition synergizes with PD-1 blockade to facilitate anti-tumor response in Kras-mutant non-small cell lung cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4713.

Comparative Molecular Analysis of Gastrointestinal Adenocarcinomas

We analyzed 921 adenocarcinomas of the esophagus, stomach, colon, and rectum to examine shared and distinguishing molecular characteristics of gastrointestinal tract adenocarcinomas (GIACs). Hypermutated tumors were distinct regardless of cancer type and comprised those enriched for insertions/deletions, representing microsatellite instability cases with epigenetic silencing of MLH1 in the context of CpG island methylator phenotype, plus tumors with elevated single-nucleotide variants associated with mutations in POLE. Tumors with chromosomal instability were diverse, with gastroesophageal adenocarcinomas harboring fragmented genomes associated with genomic doubling and distinct mutational signatures. We identified a group of tumors in the colon and rectum lacking hypermutation and aneuploidy termed genome stable and enriched in DNA hypermethylation and mutations in KRAS, SOX9, and PCBP1.

Abundant PD-L1 expression in Epstein-Barr Virus-infected gastric cancers

Gastric cancer (GC) is a deadly disease with limited treatment options. Recent studies with PD-1 inhibition have shown promising results in GC, but key questions remain regarding which GC subclass may respond best. In other cancers, expression of the PD-1 ligand PD-L1 has been shown to identify cancers with greater likelihood of response to PD-1 blockade. We here show with immunohistochemistry that Epstein-Barr Virus (EBV)+ GCs (n = 32) have robust PD-L1 expression not seen in other GCs. In EBV+ GC, we observed PD-L1 staining in tumor cells in 50% (16/32) and immune cells in 94% (30/32) of cases. Among EBV-negative GCs, PD-L1 expression within tumors cells was observed only in cases with microsatellite instability (MSI), although 35% of EBV-/MSS GCs possessed PD-L1 expression of inflammatory cells. Moreover, distinct classes of GC showed different patterns of PD-L1+ immune cell infiltrations. In both EBV+ and MSI tumors, PD-L1+ inflammatory cells were observed to infiltrate the tumor. By contrast, such cells remained at the tumor border of EBV-/MSS GCs. Consistent with these findings, we utilized gene expression profiling of GCs from The Cancer Genome Atlas study to demonstrate that an interferon-γ driven gene signature, an additional proposed marker of sensitivity to PD-1 therapy, were enriched in EBV+ and MSI GC. These data suggest that patients with EBV+ and MSI GC may have greater likelihood of response to PD-1 blockade and that EBV and MSI status should be evaluated as variables in clinical trials of these emerging inhibitors.

Whole exome sequencing of urachal adenocarcinoma reveals recurrent NF1 mutations

Urachal adenocarcinoma is a rare bladder malignancy arising from the urachal remnant. Given its rarity and the lack of knowledge about its genetic characteristics, optimal management of this cancer is not well defined. Practice patterns vary and outcomes remain poor. In order to identify the genomic underpinnings of this malignancy, we performed whole exome sequencing using seven tumor/normal pairs of formalin fixed archival specimens. We identified recurrent evidence of MAP-kinase pathway activation as three patients had neurofibromin 1 (NF1) mutations, with one of these patients also harboring an oncogenic KRAS G13D mutation. We also observed recurrent evidence of Wnt/β-catenin pathway activation as three patients had oncogenic mutations in APC or RNF43. In addition, somatic copy number analysis revealed focal chromosome 12p amplifications in three samples, resembling findings from testicular germ cell tumors. We describe the genomic landscape of this malignancy in our institutional cohort and propose investigation of the therapeutic potential for MAP-K pathway inhibition in the subset of patients who show evidence of its activation.

Suppression of Adaptive Responses to Targeted Cancer Therapy by Transcriptional Repression

Acquired drug resistance is a major factor limiting the effectiveness of targeted cancer therapies. Targeting tumors with kinase inhibitors induces complex adaptive programs that promote the persistence of a fraction of the original cell population, facilitating the eventual outgrowth of inhibitor-resistant tumor clones. We show that the addition of a newly identified CDK7/12 inhibitor, THZ1, to targeted therapy enhances cell killing and impedes the emergence of drug-resistant cell populations in diverse cellular and in vivo cancer models. We propose that targeted therapy induces a state of transcriptional dependency in a subpopulation of cells poised to become drug tolerant, which THZ1 can exploit by blocking dynamic transcriptional responses, promoting remodeling of enhancers and key signaling outputs required for tumor cell survival in the setting of targeted therapy. These findings suggest that the addition of THZ1 to targeted therapies is a promising broad-based strategy to hinder the emergence of drug-resistant cancer cell populations.Significance: CDK7/12 inhibition prevents active enhancer formation at genes, promoting resistance emergence in response to targeted therapy, and impedes the engagement of transcriptional programs required for tumor cell survival. CDK7/12 inhibition in combination with targeted cancer therapies may serve as a therapeutic paradigm for enhancing the effectiveness of targeted therapies. Cancer Discov; 8(1); 59-73. ©2017 AACR.See related commentary by Carugo and Draetta, p. 17This article is highlighted in the In This Issue feature, p. 1.

Indoleamine 2,3-Dioxygenase 1, Increased in Human Gastric Pre-Neoplasia, Promotes Inflammation and Metaplasia in Mice and Is Associated With Type II Hypersensitivity/Autoimmunity

BACKGROUND & AIMS

Chronic gastrointestinal inflammation increases the risk of cancer by mechanisms that are not well understood. Indoleamine-2,3-dioxygenase 1 (IDO1) is a heme-binding enzyme that regulates the immune response via catabolization and regulation of tryptophan availability for immune cell uptake. IDO1 expression is increased during the transition from chronic inflammation to gastric metaplasia. We investigated whether IDO1 contributes to the inflammatory response that mediates loss of parietal cells leading to metaplasia.

METHODS

Chronic gastric inflammation was induced in Ido1^-/- and CB57BL/6 (control) mice by gavage with Helicobacter felis or overexpression of interferon gamma in gastric parietal cells. We also performed studies in Jh^-/- mice, which are devoid of B cells. Gastric tissues were collected and analyzed by flow cytometry, immunostaining, and real-time quantitative polymerase chain reaction. Plasma samples were analyzed by enzyme-linked immunosorbent assay. Gastric tissues were obtained from 20 patients with gastric metaplasia and 20 patients without gastric metaplasia (controls) and analyzed by real-time quantitative polymerase chain reaction; gastric tissue arrays were analyzed by immunohistochemistry. We collected genetic information on gastric cancers from The Cancer Genome Atlas database.

RESULTS

H felis gavage induced significantly lower levels of pseudopyloric metaplasia in Ido1^-/- mice, which had lower frequencies of gastric B cells, than in control mice. Blood plasma from H felis-infected control mice had increased levels of autoantibodies against parietal cells, compared to uninfected control mice, but this increase was lower in Ido1^-/- mice. Chronically inflamed stomachs of Ido1^-/- mice had significantly lower frequencies of natural killer cells in contact with parietal cells, compared with stomachs of control mice. Jh^-/- mice had lower levels of pseudopyloric metaplasia than control mice in response to H felis infection. Human gastric pre-neoplasia and carcinoma specimens had increased levels of IDO1 messenger RNA compared with control gastric tissues, and IDO1 protein colocalized with B cells. Co-clustering of IDO1 messenger RNA with B-cell markers was corroborated by The Cancer Genome Atlas database.

CONCLUSIONS

IDO1 mediates gastric metaplasia by regulating the B-cell compartment. This process appears to be associated with type II hypersensitivity/autoimmunity. The role of autoimmunity in the progression of pseudopyloric metaplasia warrants further investigation.

Fibroblast growth factor receptor 2 expression, but not its genetic amplification, is associated with tumor growth and worse survival in esophagogastric junction adenocarcinoma

Background

Fibroblast growth factor receptor 2 (FGFR2) genetic alterations lead to tumor cell proliferation in various types of cancer. We hypothesized that FGFR2 amplification is associated with FGFR2 expression, resulting in tumor growth and poorer outcome in esophagogastric junction (EGJ) adenocarcinoma.

Patients and Methods

A total of 176 consecutive chemo-naive patients with EGJ adenocarcinoma were enrolled from two academic institutions. FGFR2 amplification was examined by real-time PCR (N = 140) and FGFR2 expression with immunohistochemical staining (N = 176), and compared against clinicopathological factors and patient outcomes. The effects of FGFR2 inhibition or overexpression on cell proliferation, cell cycle, and apoptosis assays were investigated in EGJ adenocarcinoma cell lines. Downstream FGFR2, AKT and ERK were also examined.

Results

Based on the correlation between FGFR2 levels and FGFR2 overexpression in vitro, FGFR2 amplification was defined as copy number > 3.0. In clinical samples, FGFR2 amplification and FGFR2 IHC expression were 15% and 61%, respectively. Although these two statuses were significantly correlated (P < 0.05), only FGFR2 IHC expression was significantly associated with tumor depth (multivariate P < 0.001) and overall survival of patients (univariate P = 0.007). Supporting these findings, FGFR2 overexpression was associated with tumor cell proliferation, cell cycle progression, and anti-apoptosis. Selective inhibition of FGFR2 sufficiently suppressed tumor cell proliferation through de-phosphorylation of AKT and ERK.

Conclusions

FGFR2 amplification was significantly associated with FGFR2 expression. FGFR2 expression (but not FGFR2 amplification) was associated with tumor growth and patient outcomes. Our findings support FGFR2 as a novel therapeutic target for EGJ adenocarcinoma.

Interplay between Notch1 and Notch3 promotes EMT and tumor initiation in squamous cell carcinoma

Notch1 transactivates Notch3 to drive terminal differentiation in stratified squamous epithelia. Notch1 and other Notch receptor paralogs cooperate to act as a tumor suppressor in squamous cell carcinomas (SCCs). However, Notch1 can be stochastically activated to promote carcinogenesis in murine models of SCC. Activated form of Notch1 promotes xenograft tumor growth when expressed ectopically. Here, we demonstrate that Notch1 activation and epithelial–mesenchymal transition (EMT) are coupled to promote SCC tumor initiation in concert with transforming growth factor (TGF)-β present in the tumor microenvironment. We find that TGFβ activates the transcription factor ZEB1 to repress Notch3, thereby limiting terminal differentiation. Concurrently, TGFβ drives Notch1-mediated EMT to generate tumor initiating cells characterized by high CD44 expression. Moreover, Notch1 is activated in a small subset of SCC cells at the invasive tumor front and predicts for poor prognosis of esophageal SCC, shedding light upon the tumor promoting oncogenic aspect of Notch1 in SCC.

Notch receptors can exert different roles in cancer. In this manuscript, the authors reveal that Notch1 activation and EMT promote tumor initiation and cancer cell heterogeneity in squamous cell carcinoma, while the repression of Notch3 by ZEB1 limits Notch1-induced differentiation, permitting Notch1-mediated EMT.

Tumor PDCD1LG2 (PD-L2) Expression and the Lymphocytic Reaction to Colorectal Cancer

Expression of the immune checkpoint ligand CD274 (programmed cell death 1 ligand 1, PD-L1, from gene CD274) contributes to suppression of antitumor T cell-mediated immune response in various tumor types. However, the role of PDCD1LG2 (PD-L2, CD273, from gene PDCD1LG2) in the tumor microenvironment remains unclear. We hypothesized that tumor PDCD1LG2 expression might be inversely associated with lymphocytic reactions to colorectal cancer. We examined tumor PDCD1LG2 expression by IHC in 823 colon and rectal carcinoma cases within two U.S.-nationwide cohort studies and categorized tumors into quartiles according to the percentage of PDCD1LG2-expressing carcinoma cells. We conducted multivariable ordinal logistic regression analysis to assess the associations of tumor PDCD1LG2 expression with Crohn-like lymphoid reaction, peritumoral lymphocytic reaction, intratumoral periglandular reaction, or tumor-infiltrating lymphocytes, controlling for potential confounders, including microsatellite instability, CpG island methylator phenotype, long-interspersed nucleotide element-1 methylation, and KRAS, BRAF, and PIK3CA mutations. Tumor PDCD1LG2 expression was inversely associated with Crohn-like lymphoid reaction (P_trend = 0.0003). For a unit increase in the three-tiered ordinal categories of Crohn-like lymphoid reaction, a multivariable OR in the highest (vs. lowest) quartile of the percentage of PDCD1LG2-expressing tumor cells was 0.38 (95% confidence interval, 0.22-0.67). Tumor PDCD1LG2 expression was not associated with peritumoral lymphocytic reaction, intratumoral periglandular reaction, tumor-infiltrating lymphocytes, or patient survival (P_trend > 0.13). Thus, tumor PDCD1LG2 expression is inversely associated with Crohn-like lymphoid reaction to colorectal cancer, suggesting a possible role of PDCD1LG2-expressing tumor cells in inhibiting the development of tertiary lymphoid tissues during colorectal carcinogenesis. Cancer Immunol Res; 5(11); 1046-55. ©2017 AACR.

Genomic Heterogeneity as a Barrier to Precision Medicine in Gastroesophageal Adenocarcinoma

Gastroesophageal adenocarcinoma (GEA) is a lethal disease where targeted therapies, even when guided by genomic biomarkers, have had limited efficacy. A potential reason for the failure of such therapies is that genomic profiling results could commonly differ between the primary and metastatic tumors. To evaluate genomic heterogeneity, we sequenced paired primary GEA and synchronous metastatic lesions across multiple cohorts, finding extensive differences in genomic alterations, including discrepancies in potentially clinically relevant alterations. Multiregion sequencing showed significant discrepancy within the primary tumor (PT) and between the PT and disseminated disease, with oncogene amplification profiles commonly discordant. In addition, a pilot analysis of cell-free DNA (cfDNA) sequencing demonstrated the feasibility of detecting genomic amplifications not detected in PT sampling. Lastly, we profiled paired primary tumors, metastatic tumors, and cfDNA from patients enrolled in the personalized antibodies for GEA (PANGEA) trial of targeted therapies in GEA and found that genomic biomarkers were recurrently discrepant between the PT and untreated metastases. Divergent primary and metastatic tissue profiling led to treatment reassignment in 32% (9/28) of patients. In discordant primary and metastatic lesions, we found 87.5% concordance for targetable alterations in metastatic tissue and cfDNA, suggesting the potential for cfDNA profiling to enhance selection of therapy.Significance: We demonstrate frequent baseline heterogeneity in targetable genomic alterations in GEA, indicating that current tissue sampling practices for biomarker testing do not effectively guide precision medicine in this disease and that routine profiling of metastatic lesions and/or cfDNA should be systematically evaluated. Cancer Discov; 8(1); 37-48. ©2017 AACR.See related commentary by Sundar and Tan, p. 14See related article by Janjigian et al., p. 49This article is highlighted in the In This Issue feature, p. 1.

Aspirin exerts high anti-cancer activity in PIK3CA-mutant colon cancer cells

Evidence suggests that nonsteroidal anti-inflammatory drug aspirin (acetylsalicylic acid) may improve patient survival in PIK3CA-mutant colorectal carcinoma, but not in PIK3CA-wild-type carcinoma. However, whether aspirin directly influences the viability of PIK3CA-mutant colon cancer cells is poorly understood. We conducted in vitro experiments to test our hypothesis that the anti-proliferative activity of aspirin might be stronger for PIK3CA-mutant colon cancer cells than for PIK3CA-wild-type colon cancer cells. We measured the anti-proliferative effect of aspirin at physiologic concentrations in seven PIK3CA-mutant and six PIK3CA-wild-type human colon cancer cell lines. After exposure to aspirin, the apoptotic index and cell cycle phase of colon cancer cells were assessed. In addition, the effect of aspirin was examined in parental SW48 cells and SW48 cell clones with individual knock-in PIK3CA mutations of either c.3140A>G (p.H1047R) or c.1633G>A (p.E545K). Aspirin induced greater dose-dependent loss of cell viability in PIK3CA-mutant cells than in PIK3CA-wild-type cells after treatment for 48 and 72 hours. Aspirin treatment also led to higher proportions of apoptotic cells and G0/G1 phase arrest in PIK3CA-mutant cells than in PIK3CA-wild-type cells. Aspirin treatment of isogenic SW48 cells carrying a PIK3CA mutation, either c.3140A>G (p.H1047R) or c.1633G>A (p. E545K), resulted in a more significant loss of cell viability compared to wild-type controls. Our findings indicate that aspirin causes cell cycle arrest, induces apoptosis, and leads to loss of cell viability more profoundly in PIK3CA-mutated colon cancer cells than in PIK3CA-wild-type colon cancer cells. These findings support the use of aspirin to treat patients with PIK3CA-mutant colon cancer.

Sporadic Early-Onset Diffuse Gastric Cancers Have High Frequency of Somatic CDH1 Alterations, but Low Frequency of Somatic RHOA Mutations Compared With Late-Onset Cancers

BACKGROUND & AIMS

Early-onset gastric cancer, which develops in patients younger than most gastric cancers, is usually detected at advanced stages, has diffuse histologic features, and occurs more frequently in women. We investigated somatic genomic alterations associated with the unique characteristics of sporadic diffuse gastric cancers (DGCs) from younger patients.

METHODS

We conducted whole exome and RNA sequence analyses of 80 resected DGC samples from patients 45 years old or younger in Korea. Patients with pathogenic germline mutations in CDH1, TP53, and ATM were excluded from the onset of this analysis, given our focus on somatic alterations. We used MutSig2CV to evaluate the significance of mutated genes. We recruited 29 additional early-onset Korean DGC samples and performed SNP6.0 array and targeted sequencing analyses of these 109 early-onset DGC samples (54.1% female, median age, 38 years). We compared the SNP6.0 array and targeted sequencing data of the 109 early-onset DGC samples with those from diffuse-type stomach tumor samples collected from 115 patients in Korea who were 46 years or older (late onset) at the time of diagnosis (controls; 29.6% female, median age, 67 years). We compared patient survival times among tumors from different subgroups and with different somatic mutations. We performed gene silencing of RHOA or CDH1 in DGC cells with small interfering RNAs for cell-based assays.

RESULTS

We identified somatic mutations in the following genes in a significant number of early-onset DGCs: the cadherin 1 gene (CDH1), TP53, ARID1A, KRAS, PIK3CA, ERBB3, TGFBR1, FBXW7, RHOA, and MAP2K1. None of 109 early-onset DGC cases had pathogenic germline CDH1 mutations. A higher proportion of early-onset DGCs had mutations in CDH1 (42.2%) or TGFBR1 (7.3%) compared with control DGCs (17.4% and 0.9%, respectively) (P < .001 and P = .014 for CDH1 and TGFBR1, respectively). In contrast, a smaller proportion of early-onset DGCs contained mutations in RHOA (9.2%) than control DGCs (19.1%) (P = .033). Late-onset DGCs in The Cancer Genome Atlas also contained less frequent mutations in CDH1 and TGFBR1 and more frequent RHOA mutations, compared with early-onset DGCs. Early-onset DGCs from women contained significantly more mutations in CDH1 or TGFBR1 than early-onset DGCs from men. CDH1 alterations, but not RHOA mutations, were associated with shorter survival times in patients with early-onset DGCs (hazard ratio, 3.4; 95% confidence interval, 1.5-7.7). RHOA activity was reduced by an R5W substitution-the RHOA mutation most frequently detected in early-onset DGCs. Silencing of CDH1, but not RHOA, increased migratory activity of DGC cells.

CONCLUSIONS

In an integrative genomic analysis, we found higher proportions of early-onset DGCs to contain somatic mutations in CDH1 or TGFBR1 compared with late-onset DGCs. However, a smaller proportion of early-onset DGCs contained somatic mutations in RHOA than late-onset DGCs. CDH1 alterations, but not RHOA mutations, were associated with shorter survival times of patients, which might account for the aggressive clinical course of early-onset gastric cancer. Female predominance in early-onset gastric cancer may be related to relatively high rates of somatic CDH1 and TGFBR1 mutations in this population.

Tumour CD274 (PD-L1) expression and T cells in colorectal cancer

OBJECTIVE

Evidence suggests that CD274 (programmed death-ligand 1, B7-H1) immune checkpoint ligand repress antitumour immunity through its interaction with the PDCD1 (programmed cell death 1, PD-1) receptor of T lymphocytes in various tumours. We hypothesised that tumour CD274 expression levels might be inversely associated with T-cell densities in colorectal carcinoma tissue.

DESIGN

We evaluated tumour CD274 expression by immunohistochemistry in 823 rectal and colon cancer cases within the Nurses' Health Study and Health Professionals Follow-up Study. We conducted multivariable ordinal logistic regression analyses to examine the association of tumour CD274 expression with CD3⁺, CD8⁺, CD45RO (PTPRC)⁺ or FOXP3⁺ cell density in tumour tissue, controlling for potential confounders including tumour status of microsatellite instability (MSI), CpG island methylator phenotype, long interspersed nucleotide element-1 methylation level and KRAS, BRAF and PIK3CA mutations.

RESULTS

CD274 expression in tumour cells or stromal cells (including immune cells) was detected in 731 (89%) or 44 (5%) cases, respectively. Tumour CD274 expression level correlated inversely with FOXP3⁺ cell density in colorectal cancer tissue (outcome) (p_trend=0.0002). For a unit increase in outcome quartile categories, multivariable OR in the highest (vs lowest) CD274 expression score was 0.22 (95% CI 0.10 to 0.47). Tumour CD274 expression was inversely associated with MSI-high status (p=0.001). CD274 expression was not significantly associated with CD3⁺, CD8⁺ or CD45RO⁺ cell density, pathological lymphocytic reactions or patient survival prognosis.

CONCLUSIONS

Tumour CD274 expression is inversely associated with FOXP3⁺ cell density in colorectal cancer tissue, suggesting a possible influence of CD274-expressing carcinoma cells on regulatory T cells in the tumour microenvironment.

In vivo genome editing and organoid transplantation models of colorectal cancer and metastasis

In vivo interrogation of the function of genes implicated in tumorigenesis is limited by the need to generate and cross germline mutant mice. Here we describe approaches to model colorectal cancer (CRC) and metastasis, which rely on in situ gene editing and orthotopic organoid transplantation in mice without cancer-predisposing mutations. Autochthonous tumor formation is induced by CRISPR-Cas9-based editing of the Apc and Trp53 tumor suppressor genes in colon epithelial cells and by orthotopic transplantation of Apc-edited colon organoids. ApcΔ/Δ;KrasG12D/+;Trp53Δ/Δ (AKP) mouse colon organoids and human CRC organoids engraft in the distal colon and metastasize to the liver. Finally, we apply the orthotopic transplantation model to characterize the clonal dynamics of Lgr5+ stem cells and demonstrate sequential activation of an oncogene in established colon adenomas. These experimental systems enable rapid in vivo characterization of cancer-associated genes and reproduce the entire spectrum of tumor progression and metastasis.

Long-lived keratin 15+ esophageal progenitor cells contribute to homeostasis and regeneration

The esophageal lumen is lined by a stratified squamous epithelium comprised of proliferative basal cells that differentiate while migrating toward the luminal surface and eventually desquamate. Rapid epithelial renewal occurs, but the specific cell of origin that supports this high proliferative demand remains unknown. Herein, we have described a long-lived progenitor cell population in the mouse esophageal epithelium that is characterized by expression of keratin 15 (Krt15). Genetic in vivo lineage tracing revealed that the Krt15 promoter marks a long-lived basal cell population able to self-renew, proliferate, and generate differentiated cells, consistent with a progenitor/stem cell population. Transcriptional profiling demonstrated that Krt15+ basal cells are molecularly distinct from Krt15- basal cells. Depletion of Krt15-derived cells resulted in decreased proliferation, thereby leading to atrophy of the esophageal epithelium. Further, Krt15+ cells were radioresistant and contributed to esophageal epithelial regeneration following radiation-induced injury. These results establish the presence of a long-lived and indispensable Krt15+ progenitor cell population that provides additional perspective on esophageal epithelial biology and the widely prevalent diseases that afflict this epithelium.

Somatic copy number alterations in gastric adenocarcinomas among Asian and Western patients

Gastric cancer, a leading worldwide cause of cancer mortality, shows high geographic and ethnic variation in incidence rates, which are highest in East Asia. The anatomic locations and clinical behavior also differ by geography, leading to the controversial idea that Eastern and Western forms of the disease are distinct. In view of these differences, we investigated whether gastric cancers from Eastern and Western patients show distinct genomic profiles. We used high-density profiling of somatic copy-number aberrations to analyze the largest collection to date of gastric adenocarcinomas and utilized genotyping data to rigorously annotate ethnic status. The size of this collection allowed us to accurately identify regions of significant copy-number alteration and separately to evaluate tumors arising in Eastern and Western patients. Among molecular subtypes classified by The Cancer Genome Atlas, the frequency of gastric cancers showing chromosomal instability was modestly higher in Western patients. After accounting for this difference, however, gastric cancers arising in Easterners and Westerners have highly similar somatic copy-number patterns. Only one genomic event, focal deletion of the phosphatase gene PTPRD, was significantly enriched in Western cases, though also detected in Eastern cases. Thus, despite the different risk factors and clinical features, gastric cancer appears to be a fundamentally similar disease in both populations and the divergent clinical outcomes cannot be ascribed to different underlying structural somatic genetic aberrations.

Multiparametric profiling of non-small-cell lung cancers reveals distinct immunophenotypes

BACKGROUND. Immune checkpoint blockade improves survival in a subset of patients with non-small-cell lung cancer (NSCLC), but robust biomarkers that predict response to PD-1 pathway inhibitors are lacking. Furthermore, our understanding of the diversity of the NSCLC tumor immune microenvironment remains limited. METHODS. We performed comprehensive flow cytometric immunoprofiling on both tumor and immune cells from 51 NSCLCs and integrated this analysis with clinical and histopathologic characteristics, next-generation sequencing, mRNA expression, and PD-L1 immunohistochemistry (IHC). RESULTS. Cytometric profiling identified an immunologically "hot" cluster with abundant CD8⁺ T cells expressing high levels of PD-1 and TIM-3 and an immunologically "cold" cluster with lower relative abundance of CD8⁺ T cells and expression of inhibitory markers. The "hot" cluster was highly enriched for expression of genes associated with T cell trafficking and cytotoxic function and high PD-L1 expression by IHC. There was no correlation between immunophenotype and KRAS or EGFR mutation, or patient smoking history, but we did observe an enrichment of squamous subtype and tumors with higher mutation burden in the "hot" cluster. Additionally, approximately 20% of cases had high B cell infiltrates with a subset producing IL-10. CONCLUSIONS. Our results support the use of immune-based metrics to study response and resistance to immunotherapy in lung cancer. FUNDING. The Robert A. and Renée E. Belfer Family Foundation, Expect Miracles Foundation, Starr Cancer Consortium, Stand Up to Cancer Foundation, Conquer Cancer Foundation, International Association for the Study of Lung Cancer, National Cancer Institute (R01 CA205150), and the Damon Runyon Cancer Research Foundation.

Sox2 Suppresses Gastric Tumorigenesis in Mice

Sox2 expression marks gastric stem and progenitor cells, raising important questions regarding the genes regulated by Sox2 and the role of Sox2 itself during stomach homeostasis and disease. By using ChIP-seq analysis, we have found that the majority of Sox2 targets in gastric epithelial cells are tissue specific and related to functions such as endoderm development, Wnt signaling, and gastric cancer. Unexpectedly, we found that Sox2 itself is dispensable for gastric stem cell and epithelial self-renewal, yet Sox2(+) cells are highly susceptible to tumorigenesis in an Apc/Wnt-driven mouse model. Moreover, Sox2 loss enhances, rather than impairs, tumor formation in Apc-deficient gastric cells in vivo and in vitro by inducing Tcf/Lef-dependent transcription and upregulating intestinal metaplasia-associated genes, providing a mechanistic basis for the observed phenotype. Together, these data identify Sox2 as a context-dependent tumor suppressor protein that is dispensable for normal tissue regeneration but restrains stomach adenoma formation through modulation of Wnt-responsive and intestinal genes.

Abstract A37: The role of IL-6 in the interaction between fibroblasts and tumor cells in esophageal adenocarcinoma

Often described as wounds that do not heal, cancer cells depend on interactions with the surrounding stroma to develop and progress. Among the various stromal components, cancer-associated fibroblasts (CAFs) play a critical role in promoting tumor growth and invasion, leading to treatment resistance and poor survival in a number of cancers, including esophageal adenocarcinoma. Mechanistically, CAFs communicate with tumor cells in large part via secreted signaling factors. One such factor, interleukin-6 (IL-6), has been shown to be secreted by CAFs to promote angiogenesis, epithelial-to-mesenchymal transition (EMT), tumor cell stemness, and treatment resistance in adenocarcinomas of the colon, pancreas, stomach, and breast. In EAC, the upregulation of IL-6 signaling among tumor cells, particularly as a result of exposure to reflux, is well characterized. However, the role of IL-6 as a potential mediator of the CAF-tumor cell interaction in EAC remains poorly understood.

To confirm that IL-6 is indeed involved in this interaction, we used ELISA to study the dynamics of IL-6 secretion by activated fibroblasts (FEF3303, FEF3 and PDF.G.P) and EAC cells (OE-19 and OE-33) in the setting of mono- and co-culture. We found that the interaction of CAFs and EAC cells in co-culture dramatically increased IL-6 levels compared to either EAC cells or fibroblasts alone. Next, we considered the relevance of these findings to human disease by examining human EAC biopsy specimens for patterns of IL-6 expression via immunohistochemical staining. IL-6 was strongly expressed in the tumor-associated stroma of 10/10 EAC biopsy specimens, with 5/10 showing tumor expression as well, which in several cases was localized to the invasive edge near the tumor-stromal interface. In addition, to assess for IL-6 signaling, we stained the sections for downstream mediators of IL-6 signaling, namely STAT3 and ERK1/2. We found nuclear localization of STAT3 and ERK in 10/10 and 7/10 samples, respectively, indicating activation of these pathways.

In summary, our findings indicate that IL-6 is involved in the communication between CAFs and tumor cells in EAC. Furthermore, we have reason to believe, especially in cases where both tumor cells and stroma have strong IL-6 expression, that IL-6 may be a mediator of a bidirectional “crosstalk” between these two cell types. Additional investigation, for instance with the use of a 3-D organotypic model of EAC, will help to further characterize the functional role of IL-6 in this context. This is the first report describing a potential role for IL-6 in mediating crosstalk between CAFs and tumor cells in EAC.

Citation Format: Eric W. Lin, Tatiana A. Karakasheva, Sarah Derks, Kwok K. Wong, Adam J. Bass, Anil K. Rustgi. The role of IL-6 in the interaction between fibroblasts and tumor cells in esophageal adenocarcinoma. [abstract]. In: Proceedings of the AACR Special Conference: Function of Tumor Microenvironment in Cancer Progression; 2016 Jan 7–10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2016;76(15 Suppl):Abstract nr A37.

Abstract A32: Il-6 initiates a self-sustaining signaling loop to promote nurturing tumor microenvironment

Desmoplasia, or deposition of connective tissue proper in the stroma, is a key feature of esophageal squamous cell carcinoma (ESCC), a common malignancy worldwide. The cellular component of connective tissue proper is comprised of fibroblasts, and cancer-associated fibroblasts (CAFs) are widely recognized as a major constituent of the tumor microenvironment (TME). The purpose of this study was to investigate the cross-talk between CAFs and tumor cells in ESCC, as well as identify factors that mediate this cross-talk and evaluate these factors as therapeutic targets in ESCC and potentially other squamous cell carcinomas.

We have observed that co-culture with CAFs prompts ESCC cells to acquire a more mesenchymal phenotype and express potent mediators of cell migration and invasion, such as matricellular proteins (periostin, fibrillin, osteonectin) and growth factors (EGF, HGF, VEGF). Furthermore, co-culture of ESCC cells with CAFs promotes tumor cell migration in our 3D organotypic culture, while co-transplantation of ESCC cells with fibroblasts leads to enhanced tumor growth in vivo, compared to tumors transplanted without fibroblasts.

In order to identify potential mediators of ESCC-CAF cross-talk, we have performed a comprehensive cytokine array and found that interleukin 6 (IL-6) is significantly overexpressed in conditioned media from co-culture of esophageal CAFs and ESCC cells, compared to mono-culture. IL-6 is known to play important roles in the development of multiple types of cancer, mostly via activation of the STAT3 signaling pathway. To confirm relevance of our in vitro findings, we have performed immunohistochemical staining of tissue samples from ESCC patients and found that, compared to normal esophagus, expression of IL-6 is enhanced in ESCC in both epithelial cells and fibroblasts.

Interestingly, knockdown of IL-6 resulted in altered morphology of ESCC cells in 3D organotypic culture. This was accompanied by restored membrane localization of E-cadherin and reduced activation of STAT3 signaling. In order to investigate the importance of STAT3 and MEK/ERK signaling (the latter being another pathway activated by IL-6 in cancer) on ESCC cell biology, we have treated 3D organotypic cultures with stattic and trametinib (inhibitors of STAT3 and MEK, respectively). This treatment resulted in impaired invasion, reduced proliferation and enhanced apoptosis of ESCC cells, accompanied by decreased expression of the basal cell marker p63. Furthermore, treatment with stattic and trametinib leads to reduced secretion of IL-6 by these cultures. These effects were more pronounced upon treatment with combination of stattic and trametinib.

Since we found IL-6 to be important for ESCC progression in vitro, we have conducted a therapeutic study utilizing tocilizumab (an FDA-approved anti-human IL-6R neutralizing antibody). Subcutaneous xenograft tumors comprised of human ESCC and CAF cell lines, were treated with tocilizumab, which resulted in suppressed tumor growth, accompanied by decreased activation of STAT3 and ERK within the tumor, compared to control IgG-treated tumors. Furthermore, tocilizumab-treated animals had reduced numbers of splenic monocytic immature myeloid cells (CD11b+Ly-6C+), which is in agreement with previously published findings regarding MDSCs in murine models of ESCC.

In summary, our findings indicate that IL-6, at least in part, is responsible for migration, proliferation, survival and poor differentiation of ESCC cells, promoted by CAFs in the TME. We also report that these effects of IL-6 are mediated by STAT3 and ERK signaling. Finally, we demonstrate that inhibition of IL-6 signaling suppresses ESCC tumor growth in vivo. This is the first report of anti-tumorigenic activity of tocilizumab in ESCC, which makes it a promising candidate for ESCC therapy.

Supported by NCI P01 CA098101.

Citation Format: Tatiana A. Karakasheva, Monica Soni, Todd J. Waldron, Eric W. Lin, Philip D. Hicks, Andres Klein-Szanto, Kwok K. Wong, Adam J. Bass, Anil K. Rustgi. Il-6 initiates a self-sustaining signaling loop to promote nurturing tumor microenvironment. [abstract]. In: Proceedings of the AACR Special Conference: Function of Tumor Microenvironment in Cancer Progression; 2016 Jan 7–10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2016;76(15 Suppl):Abstract nr A32.

ERBB2 emerges as a new target for colorectal cancer

ERBB2 mutations and amplifications are present in 7% of colorectal cancers. The presence of these alterations may be a marker of resistance to anti-EGFR therapy and, more importantly, could help identify patients who would benefit from ERBB2-directed therapy.

Oesophageal adenocarcinoma and gastric cancer: should we mind the gap?

Over recent decades we have witnessed a shift in the anatomical distribution of gastric cancer (GC), which increasingly originates from the proximal stomach near the junction with the oesophagus. In parallel, there has been a dramatic rise in the incidence of oesophageal adenocarcinoma (OAC) in the lower oesophagus, which is associated with antecedent Barrett oesophagus (BO). In this context, there has been uncertainty regarding the characterization of adenocarcinomas spanning the area from the lower oesophagus to the distal stomach. Most relevant to this discussion is the distinction, if any, between OAC and intestinal-type GC of the proximal stomach. It is therefore timely to review our current understanding of OAC and intestinal-type GC, integrating advances from cell-of-origin studies and comprehensive genomic alteration analyses, ultimately enabling better insight into the relationship between these two cancers.

FBXO4 loss facilitates carcinogen induced papilloma development in mice

Cyclin D1 is frequently overexpressed in esophageal squamous cell carcinoma (ESCC) and is considered a key driver of this disease. Mutations in FBXO4, F-box specificity factor that directs SCF-mediated ubiquitylation of cyclin D1, occur in ESCC with concurrent overexpression of cyclin D1 suggesting a potential tumor suppressor role for FBXO4. To evaluate the contribution of FBXO4-dependent regulation cyclin D1 in esophageal squamous cell homeostasis, we exposed FBXO4 knockout mice to N-nitrosomethylbenzylamine (NMBA), an esophageal carcinogen. Our results revealed that loss of FBXO4 function facilitates NMBA induced papillomas in FBXO4 het (+/-) and null (-/-) mice both by numbers and sizes 11 months after single dose NMBA treatment at 2mg/kg by gavage when compared to that in wt (+/+) mice (P < 0.01). No significant difference was noted between heterozygous or nullizygous mice consistent with previous work. To assess cyclin D1/CDK4 dependence, mice were treated with the CDK4/6 specific inhibitor, PD0332991, for 4 weeks. PD0332991 treatment (150mg/kg daily), reduced tumor size and tumor number. Collectively, our data support a role for FBXO4 as a suppressor of esophageal tumorigenesis.

Gastric Adenocarcinoma: An Update on Genomics, Immune System Modulations, and Targeted Therapy

Gastric adenocarcinoma (GAC) is a global health burden on all societies, and it was the third-leading cause of cancer-related mortality in 2012, causing 723,000 deaths worldwide. The prognosis of patients with metastatic GAC remains poor, with a median overall survival of less than 1 year in patients treated with currently available therapies. A limited number of therapeutic agents is currently available. Recent additions to the armamentarium include trastuzumab and ramucirumab, which have shown some survival advantage when added to cytotoxic(s). Genomic analyses have defined various genotypes of GACs. The novel genomic knowledge can lead to discovery of novel targets and novel therapeutic agents. In this update, we focus on the current genomic data, targeted therapies including immune system modulators, and expand on HER2/neu testing and the use of agents against this target. Several other facets of GAC and its therapy are not to be included in this review but have been discussed elsewhere.