Allyson G. McLoed

A Critical Role for Macrophages in Promotion of Urethane-Induced Lung Carcinogenesis

Macrophages have established roles in tumor growth and metastasis, but information about their role in lung tumor promotion is limited. To assess the role of macrophages in lung tumorigenesis, we developed a method of minimally invasive, long-term macrophage depletion by repetitive intratracheal instillation of liposomal clodronate. Compared with controls treated with repetitive doses of PBS-containing liposomes, long-term macrophage depletion resulted in a marked reduction in tumor number and size at 4 mo after a single i.p. injection of the carcinogen urethane. After urethane treatment, lung macrophages developed increased M1 macrophage marker expression during the first 2–3 wk, followed by increased M2 marker expression by week 6. Using a strategy to reduce alveolar macrophages during tumor initiation and early promotion stages (weeks 1–2) or during late promotion and progression stages (weeks 4–16), we found significantly fewer and smaller lung tumors in both groups compared with controls. Late-stage macrophage depletion reduced VEGF expression and impaired vascular growth in tumors. In contrast, early-stage depletion of alveolar macrophages impaired urethane-induced NF-κB activation in the lungs and reduced the development of premalignant atypical adenomatous hyperplasia lesions at 6 wk after urethane injection. Together, these studies elucidate an important role for macrophages in lung tumor promotion and indicate that these cells have distinct roles during different stages of lung carcinogenesis.

EPITHELIAL NUCLEAR FACTOR-κB SIGNALING PROMOTES LUNG CARCINOGENESIS VIA RECRUITMENT OF REGULATORY T LYMPHOCYTES

The mechanisms by which chronic inflammatory lung diseases, particularly chronic obstructive pulmonary disease, confer enhanced risk for lung cancer are not well-defined. To investigate whether nuclear factor (NF)-κB, a key mediator of immune and inflammatory responses, provides an interface between persistent lung inflammation and carcinogenesis, we utilized tetracycline-inducible transgenic mice expressing constitutively active IκB kinase β in airway epithelium (IKTA (IKKβ trans-activated) mice). Intraperitoneal injection of ethyl carbamate (urethane), or 3-methylcholanthrene (MCA) and butylated hydroxytoluene (BHT) was used to induce lung tumorigenesis. Doxycycline-treated IKTA mice developed chronic airway inflammation and markedly increased numbers of lung tumors in response to urethane, even when transgene expression (and therefore epithelial NF-κB activation) was begun after exposure to carcinogen. Studies using a separate tumor initiator/promoter model (MCA+BHT) indicated that NF-κB functions as an independent tumor promoter. Enhanced tumor formation in IKTA mice was preceded by increased proliferation and reduced apoptosis of alveolar epithelium, resulting in increased formation of premalignant lesions. Investigation of inflammatory cells in lungs of IKTA mice revealed a substantial increase in macrophages and lymphocytes, including functional CD4+/CD25+/FoxP3+ regulatory T lymphocytes (Tregs). Importantly, Treg depletion using repetitive injections of anti-CD25 antibodies limited excessive tumor formation in IKTA mice. At 6 weeks following urethane injection, antibody-mediated Treg depletion in IKTA mice reduced the number of premalignant lesions in the lungs in association with an increase in CD8 lymphocytes. Thus, persistent NF-κB signaling in airway epithelium facilitates carcinogenesis by sculpting the immune/inflammatory environment in the lungs.

Distal Regions of the Human IFNG Locus Direct Cell Type-Specific Expression

Genes, such as IFNG, which are expressed in multiple cell lineages of the immune system, may employ a common set of regulatory elements to direct transcription in multiple cell types or individual regulatory elements to direct expression in individual cell lineages. By employing a bacterial artificial chromosome transgenic system, we demonstrate that IFNG employs unique regulatory elements to achieve lineage-specific transcriptional control. Specifically, a one 1-kb element 30 kb upstream of IFNG activates transcription in T cells and NKT cells but not in NK cells. This distal regulatory element is a Runx3 binding site in Th1 cells and is needed for RNA polymerase II recruitment to IFNG, but it is not absolutely required for histone acetylation of the IFNG locus. These results support a model whereby IFNG uses cis-regulatory elements with cell type-restricted function.

Interleukin-5 Facilitates Lung Metastasis by Modulating the Immune Microenvironment

Although the lung is the most common metastatic site for cancer cells, biologic mechanisms regulating lung metastasis are not fully understood. Using heterotopic and intravenous injection models of lung metastasis in mice, we found that IL5, a cytokine involved in allergic and infectious diseases, facilitates metastatic colonization through recruitment of sentinel eosinophils and regulation of other inflammatory/immune cells in the microenvironment of the distal lung. Genetic IL5 deficiency offered marked protection of the lungs from metastasis of different types of tumor cells, including lung cancer, melanoma, and colon cancer. IL5 neutralization protected subjects from metastasis, whereas IL5 reconstitution or adoptive transfer of eosinophils into IL5-deficient mice exerted prometastatic effects. However, IL5 deficiency did not affect the growth of the primary tumor or the size of metastatic lesions. Mechanistic investigations revealed that eosinophils produce CCL22, which recruits regulatory T cells to the lungs. During early stages of metastasis, Treg created a protumorigenic microenvironment, potentially by suppressing IFNγ-producing natural killer cells and M1-polarized macrophages. Together, our results establish a network of allergic inflammatory circuitry that can be co-opted by metastatic cancer cells to facilitate lung colonization, suggesting interventions to target this pathway may offer therapeutic benefits to prevent or treat lung metastasis.

Chronic NF-κB activation links COPD and lung cancer through generation of an immunosuppressive microenvironment in the lungs

Nuclear Factor (NF)-κB is positioned to provide the interface between COPD and carcinogenesis through regulation of chronic inflammation in the lungs. Using a tetracycline-inducible transgenic mouse model that conditionally expresses activated IκB kinase β (IKKβ) in airway epithelium (IKTA), we found that sustained NF-κB signaling results in chronic inflammation and emphysema by 4 months. By 11 months of transgene activation, IKTA mice develop lung adenomas. Investigation of lung inflammation in IKTA mice revealed a substantial increase in M2-polarized macrophages and CD4+/CD25+/FoxP3+ regulatory T lymphocytes (Tregs). Depletion of alveolar macrophages in IKTA mice reduced Tregs, increased lung CD8+ lymphocytes, and reduced tumor numbers following treatment with the carcinogen urethane. Alveolar macrophages from IKTA mice supported increased generation of inducible Foxp3+ Tregs ex vivo through expression of TGFβ and IL-10. Targeting of TGFβ and IL-10 reduced the ability of alveolar macrophages from IKTA mice to induce Foxp3 expression on T cells. These studies indicate that sustained activation of NF-κB pathway links COPD and lung cancer through generation and maintenance of a pro-tumorigenic inflammatory environment consisting of alternatively activated macrophages and regulatory T cells.

p52 Overexpression Increases Epithelial Apoptosis, Enhances Lung Injury, and Reduces Survival after Lipopolysaccharide Treatment

Although numerous studies have demonstrated a critical role for canonical NF-κB signaling in inflammation and disease, the function of the noncanonical NF-κB pathway remains ill-defined. In lung tissue from patients with acute respiratory distress syndrome, we identified increased expression of the noncanonical pathway component p100/p52. To investigate the effects of p52 expression in vivo, we generated a novel transgenic mouse model with inducible expression of p52 in Clara cell secretory protein–expressing airway epithelial cells. Although p52 overexpression alone did not cause significant inflammation, p52 overexpression caused increased lung inflammation, injury, and mortality following intratracheal delivery of Escherichia coli LPS. No differences in cytokine/chemokine expression were measured between p52-overexpressing mice and controls, but increased apoptosis of Clara cell secretory protein–positive airway epithelial cells was observed in transgenic mice after LPS stimulation. In vitro studies in lung epithelial cells showed that p52 overexpression reduced cell survival and increased the expression of several proapoptotic genes during cellular stress. Collectively, these studies demonstrate a novel role for p52 in cell survival/apoptosis of airway epithelial cells and implicate noncanonical NF-κB signaling in the pathogenesis of acute respiratory distress syndrome.

Epithelial NF-κB signaling promotes EGFR-driven lung carcinogenesis via macrophage recruitment

ABSTRACT Several studies have demonstrated that NF-κB activation is common in lung cancer; however, the mechanistic links between NF-κB signaling and tumorigenesis remain to be fully elucidated. We investigated the function of NF-κB signaling in epidermal growth factor receptor (EGFR)-mutant lung tumors using a transgenic mouse model with doxycycline (dox)-inducible expression of oncogenic EGFR in the lung epithelium with or without a dominant inhibitor of NF-κB signaling. NF-κB inhibition resulted in a significant reduction in tumor burden in both EGFR tyrosine kinase inhibitor (TKI)-sensitive and resistant tumors. However, NF-κB inhibition did not alter epithelial cell survival in vitro or in vivo, and no changes were detected in activation of EGFR downstream signaling pathways. Instead, we observed an influx of inflammatory cells (macrophages and neutrophils) in the lungs of mice with oncogenic EGFR expression that was blocked in the setting of NF-κB inhibition. To investigate whether inflammatory cells play a role in promoting EGFR-mutant lung tumors, we depleted macrophages and neutrophils during tumorigenesis and found that neutrophil depletion had no effect on tumor formation, but macrophage depletion caused a significant reduction in tumor burden. Together, these data suggest that epithelial NF-κB signaling supports carcinogenesis in a non-cell autonomous manner in EGFR-mutant tumors through recruitment of pro-tumorigenic macrophages.

p52 expression enhances lung cancer progression

While many studies have demonstrated that canonical NF-κB signaling is a central pathway in lung tumorigenesis, the role of non-canonical NF-κB signaling in lung cancer remains undefined. We observed frequent nuclear accumulation of the non-canonical NF-κB component p100/p52 in human lung adenocarcinoma. To investigate the impact of non-canonical NF-κB signaling on lung carcinogenesis, we employed transgenic mice with doxycycline-inducible expression of p52 in airway epithelial cells. p52 over-expression led to increased tumor number and progression after injection of the carcinogen urethane. Gene expression analysis of lungs from transgenic mice combined with in vitro studies suggested that p52 promotes proliferation of lung epithelial cells through regulation of cell cycle-associated genes. Using gene expression and patient information from The Cancer Genome Atlas (TCGA) database, we found that expression of p52-associated genes was increased in lung adenocarcinomas and correlated with reduced survival, even in early stage disease. Analysis of p52-associated gene expression in additional human lung adenocarcinoma datasets corroborated these findings. Together, these studies implicate the non-canonical NF-κB component p52 in lung carcinogenesis and suggest modulation of p52 activity and/or downstream mediators as new therapeutic targets.

Abstract 3667: Attenuation of NF-κB signaling in myeloid cells enhances urethane-induced lung tumorigenesis via neutrophil-derived IL-1β

Proceedings: AACR Annual Meeting 2014; April 5-9, 2014; San Diego, CA The transcription factor Nuclear Factor κB (NF-κB) is a master regulator of inflammation, and its activation is associated with tumorigenesis in a variety of cancers. Our group and others have shown that NF-κB signaling in lung epithelial cells is critical for lung carcinogenesis. However, pharmaceutical inhibition of NF-κB signaling has not been effective for the treatment of lung tumorigenesis in animals or humans for reasons that remain unknown. We hypothesized that attenuation of NF-κB signaling in myeloid cells contributes to inefficacy of NF-κB-targeted therapies by unmasking pro-tumorigenic characteristics of inflammatory cells. For our studies, we utilized mice with IKKβ deleted specifically in myeloid cells (IKKβΔmye) and induced lung tumorigenesis with a single intraperitoneal injection of the lung carcinogen urethane (1g/kg). We found that IKKβΔmye mice developed more atypical adenomatous hyperplasia (AAH) lesions at 6 weeks and more lung tumors at 16 weeks after urethane compared to WT mice. These histological differences were correlated with enhanced lung inflammation in IKKβΔmye mice which was observed 1 week after urethane and persisted for up to 6 weeks. Flow cytometric analysis of myeloid cell populations revealed that IKKβΔmye mice contained more pulmonary neutrophils at 1 and 6 weeks after urethane compared to WT mice. In bone marrow chimeras generated by transplantation of bone marrow from IKKβΔmye or WT donors into recipient NF-κB reporter mice, we showed that depletion of neutrophils using Ly6G antibody treatment (100 ug/twice weekly IP injection) during the first 6 weeks of lung carcinogenesis blocked NF-κB activation in stromal cells and reduced tumor multiplicity in IKKβΔmye mice to levels observed in urethane-treated WT mice. Thus, these studies indicated that neutrophils play an important role in lung tumorigenesis during early tumor development and may do so by limiting NF-κB activation in lung epithelial cells. Evaluation of cytokines in the lungs of WT and IKKβΔmye mice at 1 week after urethane revealed higher levels of IL-1β in IKKβΔmye mice compared to WT mice. Further examination of myeloid cells sorted 1 week after urethane identified neutrophils as the key producers of IL-1β in the lungs of IKKβΔmye mice. Neutralization of IL-1 signaling by IL-1 receptor antagonist (IL-1ra) treatment during the first 4 weeks of carcinogenesis decreased the number of AAH lesions in IKKβΔmye mice 6 weeks after urethane and reduced the number of tumors at 16 weeks in IKKβΔmye mice. Taken together, our data suggest that neutrophils can support tumor promotion through production and secretion of IL-1β, which may activate pro-tumorgenic NF-κB signaling in the lung epithelium. We speculate that the paradoxical increase in inflammation and IL-1β production resulting from NF-κB inhibition in myeloid cells contributes to the lack of effectiveness of NF-κB inhibitors in patients with lung cancer. Citation Format: Allyson McLoed, Rinat Zaynagetdinov, Taylor Sherrill, Fiona Yull, Timothy Blackwell. Attenuation of NF-κB signaling in myeloid cells enhances urethane-induced lung tumorigenesis via neutrophil-derived IL-1β. [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 3667. doi:10.1158/1538-7445.AM2014-3667

Abstract 2875: NF-κB signaling in myeloid cells limits urethane-induced lung tumorigenesis.

The transcription factor Nuclear Factor κB (NF-κB) is a master regulator of inflammation, and its activation is associated with tumorigenesis in a variety of cancers. Our group has shown that NF-κB signaling in lung epithelial cells is critical for lung tumor formation. However, the role of NF-κB in other cell types, such as myeloid cells, during lung carcinogenesis is uncertain. We hypothesized that NF-κB signaling in myeloid cells (macrophages, monocytes, and neutrophils) promotes lung tumorigenesis by facilitating lung inflammation. Surprisingly, we found that mice with myeloid cell-targeted IKKβ deletion (IKKβΔmye mice) developed significantly more tumors than wild-type (WT) mice 4 months following a single intraperitoneal (IP) injection of the lung carcinogen urethane (1g/kg). IKKβΔmye mice exhibited a paradoxical increase in the proinflammatory cytokines IL-1β, TNFα, and CXCL1 at 1 and 2 weeks after urethane treatment, and a more than 3-fold higher influx of CD11b+Ly-6G+ cells into IKKβΔmye lungs compared to WT lungs was observed by flow cytometry 1 week post-urethane. By 6 weeks after urethane, IKKβΔmye mice developed more lung inflammation than WT mice, which was accompanied by an increased burden of atypical adenomatous hyperplasia lesions. Flow cytometric analysis of inflammatory cell populations at this time point revealed a sustained increase in granulocytic cells, indicated by significantly higher numbers of CD11b+Gr-1hi cells in the lungs of IKKβΔmye mice compared to WT mice. Depletion of granulocytic cells using Ly-6G antibody treatment (50ug/weekly IP injection) during the first 6 weeks of urethane-induced lung carcinogenesis reduced lung NF-κB activation and lung tumor incidence in IKKβΔmye mice to levels observed in urethane-treated WT mice, indicating that granulocytic cells play an important role in lung tumorigenesis during early tumor development and may do so by limiting NF-κB activation in lung epithelial cells. Together, our data suggest that the impact of NF-κB signaling on lung tumorigenesis is cell type specific and that myeloid NF-κB signaling limits urethane-induced inflammation and lung tumorigenesis. Granulocytes are important players during early lung tumor promotion, and we propose that they promote lung carcinogenesis through interactions that increase survival and/or proliferation of mutated lung epithelial cells. Citation Format: Allyson McLoed, Rinat Zaynagetdinov, Taylor Sherrill, Fiona Yull, Timothy Blackwell. NF-κB signaling in myeloid cells limits urethane-induced lung tumorigenesis. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 2875. doi:10.1158/1538-7445.AM2013-2875