Chronic Obstructive Pulmonary Disease Alters Immune Cell Composition and Immune Checkpoint Inhibitor Efficacy in Non-Small Cell Lung Cancer

RATIONALE

Chronic obstructive pulmonary disease (COPD) and non-small cell lung cancer (NSCLC) are interrelated diseases with substantial mortality, and the pathogenesis of both involves aberrant immune functioning.

OBJECTIVES

To profile immune cell composition and function in patients with NSCLC and describe the effects of COPD on lung and tumor microenvironments.

METHODS

We profiled resected lung and tumor tissue using flow cytometry and T-cell receptor sequencing in patients with and without COPD from a prospective cohort of patients undergoing resection of NSCLC. A murine cigarette smoke exposure model was used to evaluate the effect on pulmonary immune populations. A separate retrospective cohort of patients who received immune checkpoint inhibitors (ICIs) was analyzed, and their survival was quantified.

MEASUREMENTS AND MAIN RESULTS

We observed an increased number of IFN-γ-producing CD8⁺ and CD4⁺ (T-helper cell type 1 [Th1]) lymphocytes in the lungs of patients with COPD. In both humans and mice, increased Th17 content was seen with smoke exposure, but was not associated with the development or severity of COPD. COPD-affected lung tissue displayed increased Th1 differentiation that was recapitulated in the matching tumor sample. PD-1 (programmed cell death protein 1) expression was increased in tumors of patients with COPD, and the presence of COPD was associated with progression-free survival in patients treated with ICIs.

CONCLUSIONS

In patients with COPD, Th1 cell populations were expanded in both lung and tumor microenvironments, and the presence of COPD was associated with longer progression-free intervals in patients treated with ICIs. This has implications for understanding the immune mediators of COPD and developing novel therapies for NSCLC.

Lung Cancer Subtypes Generate Unique Immune Responses

Lung cancer, the leading cause of cancer-related deaths worldwide, is a heterogeneous disease comprising multiple histologic subtypes that harbor disparate mutational profiles. Immune-based therapies have shown initial promise in the treatment of lung cancer patients but are limited by low overall response rates. We sought to determine whether the host immune response to lung cancer is dictated, at least in part, by histologic and genetic differences, because such correlations would have important clinical ramifications. Using mouse models of lung cancer, we show that small cell lung cancer (SCLC) and lung adenocarcinoma (ADCA) exhibit unique immune cell composition of the tumor microenvironment. The total leukocyte content was markedly reduced in SCLC compared with lung ADCA, which was validated in human lung cancer specimens. We further identified key differences in immune cell content using three models of lung ADCA driven by mutations in Kras, p53, and Egfr Although Egfr-mutant cancers displayed robust myeloid cell recruitment, they failed to mount a CD8⁺ immune response. In contrast, Kras-mutant tumors displayed significant expansion of multiple immune cell types, including CD8⁺ cells, regulatory T cells, IL-17A-producing lymphocytes, and myeloid cells. A human tissue microarray annotated for KRAS and EGFR mutations validated the finding of reduced CD8⁺ content in human lung ADCA. Taken together, these findings establish a strong foundational knowledge of the immune cell contexture of lung ADCA and SCLC and suggest that molecular and histological traits shape the host immune response to cancer.

Insulin receptor substrate-1 deficiency drives a proinflammatory phenotype in KRAS mutant lung adenocarcinoma

Insulin receptor substrate-1 (IRS-1) is a signaling adaptor protein that interfaces with many pathways activated in lung cancer. It has been assumed that IRS-1 promotes tumor growth through its ability to activate PI3K signaling downstream of the insulin-like growth factor receptor. Surprisingly, tumors with reduced IRS-1 staining in a human lung adenocarcinoma tissue microarray displayed a significant survival disadvantage, especially within the Kirsten rat sarcoma viral oncogene homolog (KRAS) mutant subgroup. Accordingly, adenoviral Cre recombinase (AdCre)-treated LSL-Kras/Irs-1(fl/fl) (Kras/Irs-1(-/-)) mice displayed increased tumor burden and mortality compared with controls. Mechanistically, IRS-1 deficiency promotes Janus kinase/signal transducers and activators of transcription (JAK/STAT) signaling via the IL-22 receptor, resulting in enhanced tumor-promoting inflammation. Treatment of Kras/Irs-1(+/+) and Kras/Irs-1(-/-) mice with JAK inhibitors significantly reduced tumor burden, most notably in the IRS-1-deficient group.

Abstract PR04: Inflammatory responses within the lung tumor microenvironment correlate with oncogenic mutation and histologic subtype

Lung cancer is a heterogeneous disease comprised of multiple histologic subtypes that harbor disparate mutational landscapes. Small cell lung carcinoma (SCLC), in which RB1 and TP53 mutations are common, accounts for 10-20% of lung cancer diagnoses. Approximately half of non-small cell lung carcinoma cases are classified as lung adenocarcinomas (ADCA), in which KRAS, EGFR, and TP53 mutations are the predominant genetic drivers. Novel immunotherapeutic strategies have offered new hope for the management of ADCA and SCLC, but the clinical success of immunomodulatory agents will depend on a strong foundational knowledge of the cells that comprise the lung tumor microenvironment (TME) in these molecularly and histologically distinct diseases. We therefore sought to determine whether the host immune response to lung cancer is predicated, at least in part, by histologic and genetic differences, as such correlations would have important clinical ramifications.

Using three mouse models of lung ADCA KrasLSL-G12D, KrasLSL-G12D;Trp53Fl/Fl, and EgfrL858R as well as the Rb1Fl/Fl;Trp53Fl/Fl model of SCLC, we show that SCLC and ADCA tumors exhibit unique immune cell composition. Lung specimens from tumor-bearing and control animals (n ≥ 5 per cohort) were harvested at multiple time points and subjected to histological assessment and comprehensive flow cytometric immunophenotyping. Tumor-associated inflammation was discernibly lower in SCLC compared to all ADCA models. Moreover, the leukocyte composition of SCLC was dominated by cells of the adaptive rather than innate arm of the host immune system, a finding subsequently validated in 2 human SCLC surgical specimens. We further identified key differences in leukocyte content of mouse ADCA that correlated with oncogenic mutation. Although Egfr-mutant cancers displayed robust myeloid cell recruitment, they failed to mount a CD8+ cellular immune response. In contrast, Kras-mutant tumors displayed significant expansion of multiple immune cell types, including CD8+ cells, regulatory T cells, IL17-producing lymphocytes, and myeloid cells. Although loss of Trp53 promoted malignancy, it had minimal effect on immune cell composition within the Kras TME. Pre-clinical in vivo investigations with immune checkpoint inhibitor compounds are currently being conducted to assess the importance of these distinct immune responses to tumor progression and survival.

To determine whether the differential inflammatory responses observed in mice are clinically relevant, we conducted an immune profiling study of a large lung cancer patient cohort that included 55 ADCA specimens. Notably, patients with EGFR mutations (n = 5) exhibited fewer total CD8+ T cells, as well as decreased exhausted CD8+PD1+ and CD8+TIM3+ content, compared to all other ADCA cases, thereby substantiating the murine phenotype. Taken together, these findings establish a strong foundational knowledge of the immune cell contexture of lung ADCA and SCLC and suggest that molecular and histological traits shape the host immune response to cancer.

This abstract is also presented as Poster A01.

Citation Format: Stephanie E. Busch, Julia Kargl, Mark L. Hanke, Heather E. Metz, Kyoung-Hee Kim, A McGarry Houghton. Inflammatory responses within the lung tumor microenvironment correlate with oncogenic mutation and histologic subtype. [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 PR04.

Abstract 3182: Reduced tumor burden and mortality in IL-17RA-deficient EGFR mutant mice

Lung cancer is the leading cause of cancer death in the United States, with the five-year survival rates currently around 15%. Resistance to cancer therapies, like those that target epidermal growth factor receptor (EGFR), is an important clinical problem. The most common mechanism of resistance to targeted therapies in EGFR-mutant lung cancer is the T790M mutation. Given the lack of efficacy of the targeted therapy combinations tested so far, the ideal partner to an EGFR targeted therapy may be a drug that acts by an entirely different mechanism, possibly one that targets the tumor microenvironment. To dissect the role of the tumor microenvironment in lung cancer pathology we utilized mice engineered to express the L858R activating mutation within EGFR (TetO-EgfrL858R;Ccsp-rtTA) or the T790M resistance mutation (TetO-EgfrL858R/T790M;Ccsp-rtTA). Previous studies from our group indicate that KRAS mutant NSCLC is associated with a robust inflammatory response characterized by infiltrating immune cells, particularly macrophages and neutrophils. Neutrophils, which require IL-17 for recruitment and T cell suppression, promote tumor growth; and the infiltration of Th17 cells in human cancers is associated with a poor prognosis, making IL-17 an attractive therapeutic target for NSCLC.

Activation of the L858R or the T790M Egfr mutation within the lung was characterized by an abundant infiltration of alveolar macrophages, 8- and 14-fold increases respectively. In contrast, the number of neutrophils and CD8 T cells remained relatively unchanged after the expression of either Egfr mutation. In addition, the few CD8 T cells that were present within the tumor microenvironment appeared to exhibit a more exhausted phenotype within mice expressing the T790M mutation. The lack of expanded CD8 T cell number was also observed in a limited number of human EGFR lung specimens (n = 3). EGFR activation did however result in amplified numbers of both T regulatory cells and IL-17 producing T cells. Increased expression of the IL-17 differentiating cytokines TGF-β and IL-6, as well as the Th17 proliferative cytokine IL-1β was also observed by qRT-PCR gene expression analysis within L858R EGFR mutant mice. To further dissect the role of IL-17 in tumor growth TetO-EgfrL858R;Ccsp-rtTA mice were crossed to IL-17RA deficient mice. IL-17RA deficient EGFR mutant mice displayed enhanced survival and decreased tumor burden when compared to IL-17RA sufficient controls. IL-17RA loss also resulted in a less robust immune response within EGFR mutant mice as the bronchial alveolar lavage fluid showed decreased infiltration of macrophages, neutrophils and lymphocytes. Further examination of EGFR mutant lung tissue displayed alterations in immune cell-recruiting chemokines and cytokines after the loss of IL-17RA. Taken together, our data demonstrate a role for IL-17 in EGFR mediated lung tumorigenesis and suggest the use of IL-17 antagonism as a possible therapy for EGFR patients.

Citation Format: Mark L. Hanke, Stephanie E. Busch, Julia Kargl, Kyoung Hee Kim, A McGarry Houghton. Reduced tumor burden and mortality in IL-17RA-deficient EGFR mutant mice. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 3182. doi:10.1158/1538-7445.AM2015-3182

Abstract 2354: Insulin receptor substrate-1 regulates immune cell content in lung adenocarcinoma

Lung cancer is the leading cause of cancer deaths worldwide. In the United States, lung cancer accounts for ∼160,000 deaths per year while the five-year survival rate remains stagnant at ∼15%. A better understanding of the pathobiology for this disease is imperative for development of novel therapeutics to improve mortality rates. Lung adenocarcinoma (ADCA) accounts for over 50% of non-small lung cancer cases. Within this subset, K-ras is the most common activating mutation accounting for ∼35% of cases. Our group previously showed that K-ras activation generates an inflammatory response in lung tumors, mediated largely through the increased production of CC/CXC chemokines by tumor cells. The corresponding influx of neutrophils increased tumor growth, which was associated with degradation of the intracellular protein insulin receptor substrate-1 (IRS-1). Since IRS-1 is generally thought of as a pro-tumor entity, we decided to undertake a controlled study to further elucidate its pro-host role. We performed a study using a well-annotated human lung ADCA TMA (n = 136) and found that positive IRS-1 staining provided a 75-month median survival advantage among all cases (p = 0.01) and an 81-month median advantage within the K-ras subtype (p = 0.006). EGFR and non-K-ras/non-EGFR cases did not display differences. To further dissect the role of IRS-1 in tumor growth we generated LSL-K-ras/IRS-1fl/fl mice and studied them over a time course. LSL-K-ras/IRS-1-/- mice displayed highly significant early mortality (p<0.0001) and increased tumor burden when compared to LSL-K-ras/IRS-1+/+ controls (p<0.01). Surprisingly, IRS-1 loss in tumor cells generated a robust immune response. The bronchial alveolar lavage fluid of LSL-K-ras/IRS-1-/- mice had increased infiltration of macrophages (∼2.5x), neutrophils (∼40x) and lymphocytes (∼5x). Significant increases in many immune cell-recruiting chemokines were observed in the LSL-K-ras/IRS-1-/- mice compared to controls. Many cancers are able to manipulate the host immune response through signaling pathways that interface with IRS-1, including: phosphoinositol 3-kinase (PI3K), extracellular signal regulated kinase (MEK/ERK) and Janus kinase/signal transducer and activator of transcription (JAK/STAT). An array of IRS-1 silenced A549 cells versus controls displayed no change in CC/CXC chemokine production. Evaluation of the tumor microenvironment, however, provided evidence for a role for IL-17 and IL-22 producing cells, which are present at tumor sites in human lung cancer cases and LSL-K-ras mice. We found that loss of IRS-1 increases pSTAT3 production in vivo and in vitro in the presence of IL-22, triggering chemokine release and the generation of a pro-tumor immune response. This is the first description of a pro-host role for IRS-1 in human cancer. This study provides an important marker in a subset (K-ras) of lung ADCA with a very poor prognosis that may be susceptible to JAK/STAT antagonism.

Citation Format: Heather Metz, Stephanie E. Busch, Julia Kargl, Mark L. Hanke, Kyoung-Hee Kim, A. McGarry Houghton. Insulin receptor substrate-1 regulates immune cell content in lung adenocarcinoma. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 2354. doi:10.1158/1538-7445.AM2015-2354

Abstract 3181: EGFR and KRAS activation generate discrete inflammatory responses within the lung tumor microenvironment

Despite decades of research, non-small cell lung carcinoma (NSCLC) remains one of the world's deadliest cancers. Approximately half of NSCLC cases are classified as lung adenocarcinomas (ADCA), in which KRAS, EGFR, and TP53 mutations are the predominant genetic drivers. Although patients with EGFR mutations are initially responsive to targeted therapies, drug resistance uniformly occurs within one year. KRAS mutant ADCA have proven even more intractable, as scant progress has been made in the development of therapeutics for this patient population. Recent breakthroughs in the field of immunotherapy have offered new hope for the management of NSCLC, but the clinical success of immunomodulatory agents will depend on a strong foundational knowledge of the immune cells that comprise the ADCA microenvironment.

Activating mutations in KRAS and EGFR induce the aberrant function of numerous signaling pathways that may influence the host immune response in different ways. However, the discrete impact of KRAS and EGFR mutations on the immune composition of ADCA remains largely undefined. To address this question, we profiled the tumor microenvironments (TME) of four mouse models of ADCA: adenoviral Cre-infected KrasLSL-G12D and KrasLSL-G12D;Trp53Fl/Fl mice, as well as TetO-EgfrL858R;Ccsp-rtTA and TetO-EgfrL858R;T790M;Ccsp-rtTA mice. Lung specimens from tumor-bearing and control animals (n ≥ 5 per cohort) were harvested at multiple time points and subjected to histological assessment, gene expression analysis by qRT-PCR, and flow cytometric immunophenotyping, in which 23 markers were used to identify 12 unique cell types. The Kras subtype exhibited robust inflammation and expansion of both the lymphoid and myeloid cell compartments. In particular, significant increases were observed in the number of CD8+ T cells (3-fold), B cells (2.5-fold), and macrophages (16-fold). Although loss of Trp53 promoted tumor growth and malignancy, it had little effect on cytokine expression or immune cell recruitment into the Kras TME. In contrast, while EgfrL858R mutations produced similar total levels of inflammation, leukocyte recruitment into the Egfr TME was largely restricted to macrophage expansion (increased 8-fold). Introduction of the T790M resistance mutation to Egfr-mutant animals further amplified the macrophage dominant signal (14-fold). Expression of the cytokine IL-6 was correspondingly elevated in the Egfr but not Kras subtypes, a finding replicated in EGFR-transfected primary human endobronchial cells. Most notably, CD8+ cytotoxic T cell numbers were unaltered at all time points examined in the Egfr animals, a finding which raises concerns about the efficacy of most currently developed immune checkpoint blockers in EGFR patients. In summary, KRAS and EGFR mutations give rise to distinct immune responses that may require oncogene-specific immunotherapy regimens.

Citation Format: Stephanie E. Busch, Mark L. Hanke, Kyoung Hee Kim, Julia Kargl, A. McGarry Houghton. EGFR and KRAS activation generate discrete inflammatory responses within the lung tumor microenvironment. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 3181. doi:10.1158/1538-7445.AM2015-3181

Abstract 1290: Distinct immune cell composition for lung squamous cell carcinoma (SCCA) and adenocarcinoma (ADCA)

Lung cancer is the leading cause of cancer deaths worldwide, with ∼15% of lung cancer patients surviving for five years. Recent approaches in cancer therapy target immunosuppressive factors in the tumor microenvironment (TME) capable of derailing an effective immune response, using checkpoint inhibitors (e.g. anti-PD-1/PDL-1). Unfortunately, only ∼20% of patients benefit from these treatments and appropriate studies are of importance to determine the underlying molecular mechanisms.

Lung cancer is a heterogeneous disease classified by multiple histologic subtypes, with ADCA and SCCA representing the majority of non-small cell lung cancer (NSCLC).

To evaluate the complexity of the immune cell composition of the TME of human NSCLC we examined tumor and non-adjacent lung tissue from the same patients. Tissue specimen (n = 43) with corresponding clinicopathologic information were analyzed by flow cytometry and immunohistochemistry. Next generation sequencing for TCRs was performed to assess the TCR repertoire.

Surprisingly we found that immune cells comprise ∼80% of the tumor mass in NSCLC. Many immune cell types are significantly increased in tumor tissue, when compared to normal lung, such as CD3+ and CD4+ T-cells, as well as B-cells. Notably, CD4+ cell subtypes including Th17 and regulatory T cells (Treg), and IL-17-expressing γδ T cells are increased. In contrast, decreased presence of Th1 cells was observed in tumor tissue.

Remarkably, immune cell compositions are unique for lung ADCA and SCCA. In SCCA we observed a Treg (p<0.0001) predominant signature with additional increased infiltration of PMNs (p = 0.047) and significant decreases in Th1 (p = 0.034) and Th17 cells (p = 0.035) when compared to ADCA. SCCA displays immune suppressive cell content indicated by low levels of CD8 effector memory RA cells (CD8+CCR7−CD45RA+, p = 0.0081), high expression of exhaustion markers on CD8 cells (e.g. PD-1, p = 0.089) as well as significantly more EpCAM+ cells expressing PDL-1 (p = 0.0073). Further, a more clonal TCR β-chain repertoire (p = 0.018) and higher frequency of the top 10 clones (p = 0.049) were observed in SCCA. The presence of PMNs at the sites of tumorigenesis inversely correlates with CD8+ cell content (ADCA: R2 = 0.24, p = 0.022; SCCA R2 = 0.84, p = 0.0002).

In contrast, ADCA represents a Th17 signature, revealing elevated levels of IL17-expressing CD4+ T-cells and γδ T cells. While SCCA immune cell content clusters well, immune cell composition in ADCA is very heterogeneous. Preliminary data suggest that driver-mutations in ADCA such as EGFR predict distinct immune cell composition.

These data provide evidence that the immune cell composition present within different NSCLC subtypes displays unique phenotypes and identifying the immunosuppressive factors in different subsets will be important for successful immune-based therapy.

Citation Format: Julia Kargl, Kyoung-Hee Kim, Stephanie E. Busch, Mark L. Hanke, Heather E. Metz, Martin W. McIntosh, A McGarry Houghton. Distinct immune cell composition for lung squamous cell carcinoma (SCCA) and adenocarcinoma (ADCA). [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1290. doi:10.1158/1538-7445.AM2015-1290

Abstract 4860: Insulin receptor substrate-1 regulates immune cell content in lung adenocarcinoma

Lung cancer is the leading cause of cancer deaths worldwide. In the United States, lung cancer accounts for ∼160,000 deaths per year while the five-year survival rate remains stagnant at ∼15%. A better understanding of the pathobiology for this disease is imperative for development of novel therapeutics to improve mortality rates. One of the most common activating mutations in lung cancer is K-ras. Our group previously showed that K-ras activation generates an inflammatory response in lung tumors, mediated largely through the increased production of neutrophil chemokines by tumor cells. The corresponding increase in neutrophil recruitment in this model increased tumor growth, which was associated with degradation of the intracellular protein insulin receptor substrate-1 (IRS-1). A study of non-small cell lung cancer demonstrated that IRS-1 was low or absent in 46% of cases. To further dissect the role of IRS-1 in tumor growth we generated LSL-K-ras/IRS-1 fl/fl mice and subjected them to adenoviral cre. LSL-K-ras/IRS-1-/- mice displayed early mortality and increased tumor burden when compared to LSL-K-ras/IRS-1+/+ controls. Surprisingly, IRS-1 loss in tumor cells generated a robust immune response. The bronchial alveolar lavage fluid of LSL-K-ras/IRS-1-/- mice showed increased infiltration of macrophages, neutrophils and lymphocytes. Further examination of the chemokine profiles of LSL-K-ras/IRS-1-/- and LSL-K-ras/IRS-1+/+ mice showed a significant increase in many immune cell-recruiting chemokines in the LSL-K-ras/IRS-1-/- mice including CCL2, CCL3, CCL4, CXCL1, CXCL2 and CXCl12. Many cancers are able to manipulate the host immune response through signaling pathways that interface with IRS-1, including: phosphoinositol 3-kinase (PI3K), extracellular signal regulated kinase (MEK/ERK) and Janus kinase/signal transducer and activator of transcription (JAK/STAT). As some cytokines can activate IRS-1 via JAK/STAT signaling, we suspected that IL-17 and IL-22 might function in this regard. Loss of IRS-1 increases pSTAT3 production, which triggers chemokine release and the generation of a pro-tumor immune response. Preliminary data to support this hypothesis include: 1) presence of IL-17 and IL-22 producing cells (e.g. Th17) at sites of tumor in LSL-K-ras mice, 2) induction of pTyr-IRS-1 upon IL-17 and IL-22 stimulation in A549 cells, and 3) increased CC and CXC chemokines in IRS-1 deficient cells upon IL-17 and IL-22 stimulation. Experimentation is ongoing to further elucidate the mechanism behind this phenotype.

Citation Format: Heather E. Metz, Stephanie E. Busch, Mark L. Hanke, Julia Kargl, Kyoung-Hee Kim, A McGarry Houghton. Insulin receptor substrate-1 regulates immune cell content in lung adenocarcinoma. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4860. doi:10.1158/1538-7445.AM2014-4860

CTCF haploinsufficiency destabilizes DNA methylation and predisposes to cancer

Epigenetic alterations, particularly in DNA methylation, are ubiquitous in cancer, yet the molecular origins and the consequences of these alterations are poorly understood. CTCF, a DNA-binding protein that regulates higher-order chromatin organization, is frequently altered by hemizygous deletion or mutation in human cancer. To date, a causal role for CTCF in cancer has not been established. Here, we show that Ctcf hemizygous knockout mice are markedly susceptible to spontaneous, radiation-, and chemically induced cancer in a broad range of tissues. Ctcf(+/-) tumors are characterized by increased aggressiveness, including invasion, metastatic dissemination, and mixed epithelial/mesenchymal differentiation. Molecular analysis of Ctcf(+/-) tumors indicates that Ctcf is haploinsufficient for tumor suppression. Tissues with hemizygous loss of CTCF exhibit increased variability in CpG methylation genome wide. These findings establish CTCF as a prominent tumor-suppressor gene and point to CTCF-mediated epigenetic stability as a major barrier to neoplastic progression.

ARF inhibits the growth and malignant progression of non-small-cell lung carcinoma

Non-small-cell lung carcinoma (NSCLC) is among the deadliest of human cancers. The CDKN2A locus, which houses the INK4a and ARF tumor suppressor genes, is frequently altered in NSCLC. However, the specific role of ARF in pulmonary tumorigenesis remains unclear. KRAS and other oncogenes induce the expression of ARF, thus stabilizing p53 activity and arresting cell proliferation. To address the role of ARF in Kras-driven NSCLC, we compared the susceptibility of NIH/Ola strain wild-type and Arf-knockout mice to urethane-induced lung carcinogenesis. Lung tumor size, malignancy and associated morbidity were significantly increased in Arf(-/-) compared with Arf(+/+) animals at 25 weeks after induction. Pulmonary tumors from Arf-knockout mice exhibited increased cell proliferation and DNA damage compared with wild-type mice. A subgroup of tumors in Arf(-/-) animals presented as dedifferentiated and metastatic, with many characteristics of pulmonary sarcomatoid carcinoma, a neoplasm previously undocumented in mouse models. Our finding of a role for ARF in NSCLC is consistent with the observation that benign adenomas from Arf(+/+) mice robustly expressed ARF, while ARF expression was markedly reduced in malignant adenocarcinomas. ARF expression also frequently colocalized with the expression of p21(CIP1), a transcriptional target of p53, arguing that ARF induces the p53 checkpoint to arrest cell proliferation in vivo. Taken together, these findings demonstrate that induction of ARF is an early response in lung tumorigenesis that mounts a strong barrier against tumor growth and malignant progression.

ARF suppresses hepatic vascular neoplasia in a carcinogen-exposed murine model

Hepatic haemangiosarcoma is a deadly malignancy whose aetiology remains poorly understood. Inactivation of the CDKN2A locus, which houses the ARF and p16(INK4a) tumour suppressor genes, is a common event in haemangiosarcoma patients, but the precise role of ARF in vascular tumourigenesis is unknown. To determine the extent to which ARF suppresses vascular neoplasia, we examined the incidence of hepatic vascular lesions in Arf-deficient mice exposed to the carcinogen urethane [intraperitoneal (i.p.), 1 mg/g]. Loss of Arf resulted in elevated morbidity and increased the incidence of both haemangiomas and incipient haemangiosarcomas. Suppression of vascular lesion development by ARF was heavily dependent on both Arf gene-dosage and the genetic strain of the mouse. Trp53-deficient mice also developed hepatic vascular lesions after exposure to urethane, suggesting that ARF signals through a p53-dependent pathway to inhibit the development of hepatic haemangiosarcoma. Our findings provide strong evidence that inactivation of Arf is a causative event in vascular neoplasia and suggest that the ARF pathway may be a novel molecular target for therapeutic intervention in haemangiosarcoma patients.

Abstract A34: Arf suppresses the growth and progression of Kras-driven lung tumors

Non-small cell lung carcinoma (NSCLC) is among the deadliest of human cancers, with an overall five-year survival rate of 10–20%. Activating mutations in the Kras proto-oncogene occur in approximately one-third of NSCLC patients, but tumor suppression in the lung remains poorly elucidated. The Cdkn2a locus, which houses both the p16lnk4a and Arf tumor suppressor genes, is frequently altered in NSCLC; however, the specific role of Arf in lung tumorigenesis has not been well characterized. Several lines of evidence indicate that Kras and other oncogenes induce the expression of Art, which in turn stabilizes p53 activity and arrests the growth of transformed cells. To determine the extent to which Arf suppresses NSCLC development in vivo, we employed the urethane chemical carcinogenesis model of Kras-driven NSCLC. We treated both wild-type and Arf-deficient mice with urethane and found that early-stage lung adenomas in wild-type mice robustly expressed Arf, In contrast to adenomas, malignant lung adenocarcinomas exhibited little induction of Art. Moreover, Arf-deficient mice exposed to urethane displayed accelerated lung tumor-associated morbidity and significantly increased lung tumor size compared to Arf wild-type and heterozygous littermates. Malignant progression of adenomas to adenocarcinomas was also markedly elevated in Arf-deficient mice. These data demonstrate that Arf functions as a barrier to tumor promotion and progression in a carcinogen model of Kras-driven NSCLC.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the Second AACR International Conference on Frontiers in Basic Cancer Research; 2011 Sep 14-18; San Francisco, CA. Philadelphia (PA): AACR; Cancer Res 2011;71(18 Suppl):Abstract nr A34.

Maternal activation of gap genes in the hover fly Episyrphus

The metameric organization of the insect body plan is initiated with the activation of gap genes, a set of transcription-factor-encoding genes that are zygotically expressed in broad and partially overlapping domains along the anteroposterior (AP) axis of the early embryo. The spatial pattern of gap gene expression domains along the AP axis is generally conserved, but the maternal genes that regulate their expression are not. Building on the comprehensive knowledge of maternal gap gene activation in Drosophila, we used loss- and gain-of-function experiments in the hover fly Episyrphus balteatus (Syrphidae) to address the question of how the maternal regulation of gap genes evolved. We find that, in Episyrphus, a highly diverged bicoid ortholog is solely responsible for the AP polarity of the embryo. Episyrphus bicoid represses anterior zygotic expression of caudal and activates the anterior and central gap genes orthodenticle, hunchback and Krüppel. In bicoid-deficient Episyrphus embryos, nanos is insufficient to generate morphological asymmetry along the AP axis. Furthermore, we find that torso transiently regulates anterior repression of caudal and is required for the activation of orthodenticle, whereas all posterior gap gene domains of knirps, giant, hunchback, tailless and huckebein depend on caudal. We conclude that all maternal coordinate genes have altered their specific functions during the radiation of higher flies (Cyclorrhapha).