KEAP1 mutation in lung adenocarcinoma promotes immune evasion and immunotherapy resistance

Lung cancer treatment has benefited greatly through advancements in immunotherapies. However, immunotherapy often fails in patients with specific mutations like KEAP1, which are frequently found in lung adenocarcinoma. We established an antigenic lung cancer model and used it to explore how Keap1 mutations remodel the tumor immune microenvironment. Using single-cell technology and depletion studies, we demonstrate that Keap1-mutant tumors diminish dendritic cell and T cell responses driving immunotherapy resistance. This observation was corroborated in patient samples. CRISPR-Cas9-mediated gene targeting revealed that hyperactivation of the NRF2 antioxidant pathway is responsible for diminished immune responses in Keap1-mutant tumors. Importantly, we demonstrate that combining glutaminase inhibition with immune checkpoint blockade can reverse immunosuppression, making Keap1-mutant tumors susceptible to immunotherapy. Our study provides new insight into the role of KEAP1 mutations in immune evasion, paving the way for novel immune-based therapeutic strategies for KEAP1-mutant cancers.

IL-18-secreting CAR T cells targeting DLL3 are highly effective in small cell lung cancer models

Patients with small cell lung cancer (SCLC) generally have a poor prognosis and a median overall survival of only about 13 months, indicating the urgent need for novel therapies. Delta-like protein 3 (DLL3) has been identified as a tumor-specific cell surface marker on neuroendocrine cancers, including SCLC. In this study, we developed a chimeric antigen receptor (CAR) against DLL3 that displays antitumor efficacy in xenograft and murine SCLC models. CAR T cell expression of the proinflammatory cytokine IL-18 greatly enhanced the potency of DLL3-targeting CAR T cell therapy. In a murine metastatic SCLC model, IL-18 production increased the activation of both CAR T cells and endogenous tumor-infiltrating lymphocytes. We also observed an increased infiltration, repolarization, and activation of antigen-presenting cells. Additionally, human IL-18-secreting anti-DLL3 CAR T cells showed an increased memory phenotype, less exhaustion, and induced durable responses in multiple SCLC models, an effect that could be further enhanced with anti-PD-1 blockade. All together, these results define DLL3-targeting CAR T cells that produce IL-18 as a potentially promising novel strategy against DLL3-expressing solid tumors.

Inference of single cell profiles from histology stains with the Single-Cell omics from Histology Analysis Framework (SCHAF)

Tissue biology involves an intricate balance between cell-intrinsic processes and interactions between cells organized in specific spatial patterns, which can be respectively captured by single-cell profiling methods, such as single-cell RNA-seq (scRNA-seq), and histology imaging data, such as Hematoxylin-and-Eosin (H&E) stains. While single-cell profiles provide rich molecular information, they can be challenging to collect routinely and do not have spatial resolution. Conversely, histological H&E assays have been a cornerstone of tissue pathology for decades, but do not directly report on molecular details, although the observed structure they capture arises from molecules and cells. Here, we leverage adversarial machine learning to develop SCHAF (Single-Cell omics from Histology Analysis Framework), to generate a tissue sample's spatially-resolved single-cell omics dataset from its H&E histology image. We demonstrate SCHAF on two types of human tumors-from lung and metastatic breast cancer-training with matched samples analyzed by both sc/snRNA-seq and by H&E staining. SCHAF generated appropriate single-cell profiles from histology images in test data, related them spatially, and compared well to ground-truth scRNA-Seq, expert pathologist annotations, or direct MERFISH measurements. SCHAF opens the way to next-generation H&E2.0 analyses and an integrated understanding of cell and tissue biology in health and disease.

The ectonucleotidase CD39 identifies tumor-reactive CD8+ T cells predictive of immune checkpoint blockade efficacy in human lung cancer

Improved identification of anti-tumor T cells is needed to advance cancer immunotherapies. CD39 expression is a promising surrogate of tumor-reactive CD8+ T cells. Here, we comprehensively profiled CD39 expression in human lung cancer. CD39 expression enriched for CD8+ T cells with features of exhaustion, tumor reactivity, and clonal expansion. Flow cytometry of 440 lung cancer biospecimens revealed weak association between CD39+ CD8+ T cells and tumoral features, such as programmed death-ligand 1 (PD-L1), tumor mutation burden, and driver mutations. Immune checkpoint blockade (ICB), but not cytotoxic chemotherapy, increased intratumoral CD39+ CD8+ T cells. Higher baseline frequency of CD39+ CD8+ T cells conferred improved clinical outcomes from ICB therapy. Furthermore, a gene signature of CD39+ CD8+ T cells predicted benefit from ICB, but not chemotherapy, in a phase III clinical trial of non-small cell lung cancer. These findings highlight CD39 as a proxy of tumor-reactive CD8+ T cells in human lung cancer.

Inhibition of XPO1 Sensitizes Small Cell Lung Cancer to First- and Second-Line Chemotherapy

Small cell lung cancer (SCLC) is an aggressive malignancy characterized by early metastasis and extreme lethality. The backbone of SCLC treatment over the past several decades has been platinum-based doublet chemotherapy, with the recent addition of immunotherapy providing modest benefits in a subset of patients. However, nearly all patients treated with systemic therapy quickly develop resistant disease, and there is an absence of effective therapies for recurrent and progressive disease. Here we conducted CRISPR-Cas9 screens using a druggable genome library in multiple SCLC cell lines representing distinct molecular subtypes. This screen nominated exportin-1, encoded by XPO1, as a therapeutic target. XPO1 was highly and ubiquitously expressed in SCLC relative to other lung cancer histologies and other tumor types. XPO1 knockout enhanced chemosensitivity, and exportin-1 inhibition demonstrated synergy with both first- and second-line chemotherapy. The small molecule exportin-1 inhibitor selinexor in combination with cisplatin or irinotecan dramatically inhibited tumor growth in chemonaïve and chemorelapsed SCLC patient-derived xenografts, respectively. Together these data identify exportin-1 as a promising therapeutic target in SCLC, with the potential to markedly augment the efficacy of cytotoxic agents commonly used in treating this disease. SIGNIFICANCE: CRISPR-Cas9 screening nominates exportin-1 as a therapeutic target in SCLC, and exportin-1 inhibition enhances chemotherapy efficacy in patient-derived xenografts, providing a novel therapeutic opportunity in this disease.

Rlf-Mycl Gene Fusion Drives Tumorigenesis and Metastasis in a Mouse Model of Small Cell Lung Cancer

Small cell lung cancer (SCLC) has limited therapeutic options and an exceptionally poor prognosis. Understanding the oncogenic drivers of SCLC may help define novel therapeutic targets. Recurrent genomic rearrangements have been identified in SCLC, most notably an in-frame gene fusion between RLF and MYCL found in up to 7% of the predominant ASCL1-expressing subtype. To explore the role of this fusion in oncogenesis and tumor progression, we used CRISPR/Cas9 somatic editing to generate a Rlf-Mycl-driven mouse model of SCLC. RLF-MYCL fusion accelerated transformation and proliferation of murine SCLC and increased metastatic dissemination and the diversity of metastatic sites. Tumors from the RLF-MYCL genetically engineered mouse model displayed gene expression similarities with human RLF-MYCL SCLC. Together, our studies support RLF-MYCL as the first demonstrated fusion oncogenic driver in SCLC and provide a new preclinical mouse model for the study of this subtype of SCLC.

SIGNIFICANCE

The biological and therapeutic implications of gene fusions in SCLC, an aggressive metastatic lung cancer, are unknown. Our study investigates the functional significance of the in-frame RLF-MYCL gene fusion by developing a Rlf-Mycl-driven genetically engineered mouse model and defining the impact on tumor growth and metastasis. This article is highlighted in the In This Issue feature, p. 2945.

MAPK pathway activation selectively inhibits ASCL1-driven small cell lung cancer

Activation of mitogenic signaling pathways is a common oncogenic driver of many solid tumors including lung cancer. Although activating mutations in the mitogen-activated protein kinase (MAPK) pathway are prevalent in non-small cell lung cancers, MAPK pathway activity, counterintuitively, is relatively suppressed in the more aggressively proliferative small cell lung cancer (SCLC). Here, we elucidate the role of the MAPK pathway and how it interacts with other signaling pathways in SCLC. We find that the most common SCLC subtype, SCLC-A associated with high expression of ASCL1, is selectively sensitive to MAPK activation in vitro and in vivo through induction of cell-cycle arrest and senescence. We show strong upregulation of ERK negative feedback regulators and STAT signaling upon MAPK activation in SCLC-A lines. These findings provide insight into the complexity of signaling networks in SCLC and suggest subtype-specific mitogenic vulnerabilities.

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MAPK activation causes cell-cycle arrest and senescence selectively in SCLC-A subtype

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MAPK-induced growth inhibition is independent of NOTCH signaling

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MAPK activation increases ERK negative feedback and activates STAT3 signaling

Signatures of plasticity, metastasis, and immunosuppression in an atlas of human small cell lung cancer

Small cell lung cancer (SCLC) is an aggressive malignancy that includes subtypes defined by differential expression of ASCL1, NEUROD1, and POU2F3 (SCLC-A, -N, and -P, respectively). To define the heterogeneity of tumors and their associated microenvironments across subtypes, we sequenced 155,098 transcriptomes from 21 human biospecimens, including 54,523 SCLC transcriptomes. We observe greater tumor diversity in SCLC than lung adenocarcinoma, driven by canonical, intermediate, and admixed subtypes. We discover a PLCG2-high SCLC phenotype with stem-like, pro-metastatic features that recurs across subtypes and predicts worse overall survival. SCLC exhibits greater immune sequestration and less immune infiltration than lung adenocarcinoma, and SCLC-N shows less immune infiltrate and greater T cell dysfunction than SCLC-A. We identify a profibrotic, immunosuppressive monocyte/macrophage population in SCLC tumors that is particularly associated with the recurrent, PLCG2-high subpopulation.

Comprehensive molecular characterization of lung tumors implicates AKT and MYC signaling in adenocarcinoma to squamous cell transdifferentiation

BACKGROUND

Lineage plasticity, the ability to transdifferentiate among distinct phenotypic identities, facilitates therapeutic resistance in cancer. In lung adenocarcinomas (LUADs), this phenomenon includes small cell and squamous cell (LUSC) histologic transformation in the context of acquired resistance to targeted inhibition of driver mutations. LUAD-to-LUSC transdifferentiation, occurring in up to 9% of EGFR-mutant patients relapsed on osimertinib, is associated with notably poor prognosis. We hypothesized that multi-parameter profiling of the components of mixed histology (LUAD/LUSC) tumors could provide insight into factors licensing lineage plasticity between these histologies.

METHODS

We performed genomic, epigenomics, transcriptomics and protein analyses of microdissected LUAD and LUSC components from mixed histology tumors, pre-/post-transformation tumors and reference non-transformed LUAD and LUSC samples. We validated our findings through genetic manipulation of preclinical models in vitro and in vivo and performed patient-derived xenograft (PDX) treatments to validate potential therapeutic targets in a LUAD PDX model acquiring LUSC features after osimertinib treatment.

RESULTS

Our data suggest that LUSC transdifferentiation is primarily driven by transcriptional reprogramming rather than mutational events. We observed consistent relative upregulation of PI3K/AKT, MYC and PRC2 pathway genes. Concurrent activation of PI3K/AKT and MYC induced squamous features in EGFR-mutant LUAD preclinical models. Pharmacologic inhibition of EZH1/2 in combination with osimertinib prevented relapse with squamous-features in an EGFR-mutant patient-derived xenograft model, and inhibition of EZH1/2 or PI3K/AKT signaling re-sensitized resistant squamous-like tumors to osimertinib.

CONCLUSIONS

Our findings provide the first comprehensive molecular characterization of LUSC transdifferentiation, suggesting putative drivers and potential therapeutic targets to constrain or prevent lineage plasticity.

Multi-omic analysis of lung tumors defines pathways activated in neuroendocrine transformation

Lineage plasticity is implicated in treatment resistance in multiple cancers. In lung adenocarcinomas (LUADs) amenable to targeted therapy, transformation to small cell lung cancer (SCLC) is a recognized resistance mechanism. Defining molecular mechanisms of neuroendocrine (NE) transformation in lung cancer has been limited by a paucity of pre-/post-transformation clinical samples. Detailed genomic, epigenomic, transcriptomic, and protein characterization of combined LUAD/SCLC tumors, as well as pre-/post-transformation samples, support that NE transformation is primarily driven by transcriptional reprogramming rather than mutational events. We identify genomic contexts in which NE transformation is favored, including frequent loss of the 3p chromosome arm. We observed enhanced expression of genes involved in PRC2 complex and PI3K/AKT and NOTCH pathways. Pharmacological inhibition of the PI3K/AKT pathway delayed tumor growth and NE transformation in an EGFR-mutant patient-derived xenograft model. Our findings define a novel landscape of potential drivers and therapeutic vulnerabilities of neuroendocrine transformation in lung cancer.

Abstract 420: Rlf-Mycl1 gene fusion as a novel oncogenic driver in a mouse model of small cell lung cancer

Background: Small cell lung cancer (SCLC) is the most aggressive subtype of lung cancer, accounting for about 15% of all lung cancer cases and approximately 200,000 deaths per year. SCLC genetic alterations are characterized by near-universal loss of function of the tumor suppressor genes TP53 and RB1. Several in-frame gene fusions have been identified in SCLC tumors and cell lines, with recurrent fusion events noted in up to 5% of cases. However, the biological and therapeutic implications of these fusions, including the recurrent in-frame RLF-MYCL1 gene fusion, are unknown. MYCL1 is frequently expressed in SCLC and differential expression of MYC family members has been associated with different SCLC subtypes. Here we investigate the functional significance of the RLF-MYCL1 gene fusion by developing a novel Rlf-Mycl1-driven genetically engineered mouse model (GEMM) of SCLC using CRISPR-Cas9 genome engineering.

Methods: SgRNAs targeting intronic sequences of the Rlf and Mycl1 genes were cloned into a Cas9-expressing plasmid and co-transfected in NIH/3T3 cells. The presence of the Rlf-Mycl1 fusion was confirmed at the DNA and protein level. To test whether the RLF-MYCL1 gene fusion is important for the oncogenic switch during early SCLC development, we transduced Rb1Δ/Δ;Trp53Δ/Δ;Rbl2+/Δ precancerous neuroendocrine cells (preSCs), which were isolated from an early stage in tumorigenesis, with a lentiviral vector encoding Cas9 and with the dual sgRNAs targeting Rlf and Mycl1 genes (P-RM).

Results: The P-RM transduced preSCs formed significantly more colonies in soft agar than those infected with non-targeting sgRNAs (P-NT) (p<0.02). To assess the effect of Rlf-Mycl1 gene fusion in vivo, we injected P-RM and P-NT cells into the flank of athymic nude mice (n=4/5). P-RM injected mice developed detectable tumors significantly earlier than P-NT injected mice (p<0.01). To induce the Rlf-Mycl1 rearrangement in vivo, we transduced a cohort (n=12) of adult GEMM Rb1fl/fl;Trp53fl/fl;Rbl2fl/fl;Rosa26LSL-Cas9-GFP mice by intratracheal administration of a lentiviral vector encoding sgRNAs targeting Rlf and Mycl1. Mice transduced with the Rlf-Mycl1 lentiviral vector had a significantly higher tumor burden than controls by quantitative monitoring with MRI of pulmonary tumors over 6 months. These GEMMs are currently being monitored for survival assessment.

Summary: A major hurdle to SCLC clinical advancement is the absence of targetable driver mutations. Our findings indicate that the Rlf-Mycl1 gene fusion accelerates SCLC tumor growth. Defining mechanisms by which Rlf-Mycl1 accelerates tumorigenesis may identify therapeutic strategies to target SCLC harboring this fusion oncogene. Our study further supports a careful analysis of the involvement of other gene-fusions in SCLC.

Citation Format: Metamia Ciampricotti, Triantafyllia Karakousi, Alvaro Quintanal Villalonga, Viola Allaj, Andrea Ventura, Triparna Sen, JT Poirier, Thales Papagiannakopoulos, Charles M. Rudin. Rlf-Mycl1 gene fusion as a novel oncogenic driver in a mouse model of small cell lung cancer [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 420.

Therapeutic targeting of macrophages enhances chemotherapy efficacy by unleashing type I interferon response

Recent studies have revealed a role for macrophages and neutrophils in limiting chemotherapy efficacy; however, the mechanisms underlying the therapeutic benefit of myeloid-targeting agents in combination with chemotherapy are incompletely understood. Here, we show that targeting tumour-associated macrophages by colony-stimulating factor-1 receptor (CSF-1R) blockade in the K14cre;Cdh1^F/F;Trp53^F/F transgenic mouse model for breast cancer stimulates intratumoural type I interferon (IFN) signalling, which enhances the anticancer efficacy of platinum-based chemotherapeutics. Notably, anti-CSF-1R treatment also increased intratumoural expression of type I IFN-stimulated genes in patients with cancer, confirming that CSF-1R blockade is a powerful strategy to trigger an intratumoural type I IFN response. By inducing an inflamed, type I IFN-enriched tumour microenvironment and by further targeting immunosuppressive neutrophils during cisplatin therapy, antitumour immunity was activated in this poorly immunogenic breast cancer mouse model. These data illustrate the importance of breaching multiple layers of immunosuppression during cytotoxic therapy to successfully engage antitumour immunity in breast cancer.

Mammary tumor-derived CCL2 enhances pro-metastatic systemic inflammation through upregulation of IL1β in tumor-associated macrophages

Patients with primary solid malignancies frequently exhibit signs of systemic inflammation. Notably, elevated levels of neutrophils and their associated soluble mediators are regularly observed in cancer patients, and correlate with reduced survival and increased metastasis formation. Recently, we demonstrated a mechanistic link between mammary tumor-induced IL17-producing γδ T cells, systemic expansion of immunosuppressive neutrophils and metastasis formation in a genetically engineered mouse model for invasive breast cancer. How tumors orchestrate this systemic inflammatory cascade to facilitate dissemination remains unclear. Here we show that activation of this cascade relies on CCL2-mediated induction of IL1β in tumor-associated macrophages. In line with these findings, expression of CCL2 positively correlates with IL1Β and macrophage markers in human breast tumors. We demonstrate that blockade of CCL2 in mammary tumor-bearing mice results in reduced IL17 production by γδ T cells, decreased neutrophil expansion and enhanced CD8⁺ T cell activity. These results highlight a new role for CCL2 in facilitating the breast cancer-induced pro-metastatic systemic inflammatory γδ T cell – IL17 – neutrophil axis.

Abstract A20: Mammary tumor-derived CCL2 enhances pro-metastatic systemic inflammation through upregulation of macrophage-derived IL1beta

Metastatic breast cancer remains a major cause of cancer-related death among women. Metastasis is regulated by extensive crosstalk between cancer cells and immune cells. Besides the onset of a local inflammatory microenvironment, tumors frequently induce a systemic inflammatory state characterized by the release of various cytokines, chemokines and growth factors to mobilize myeloid cells that support metastasis, emphasizing the notion that cancer should be regarded as a systemic disease. Utilizing the K14cre;Cdh1F/F;Trp53F/F (KEP) conditional mouse model of metastatic breast cancer, we have recently unraveled a novel mechanistic link between mammary tumor-induced IL17-producing gamma delta T cells, systemic expansion of immunosuppressive neutrophils and metastasis formation. We identified tumor-derived IL1beta as one of the drivers of this cascade by inducing IL17 release from gamma delta T cells. However, it remains unclear how other inflammatory mediators are involved in this systemic inflammatory cascade. In the current study, we identified the pro-inflammatory cytokine CCL2 as a key regulator of the gamma delta T cell IL17 neutrophil axis. CCL2 blockade resulted in reduced IL17-production by gamma delta T cells, decreased systemic neutrophil accumulation and enhanced CD8+ T cell activity. We show that activation of this cascade relies on CCL2-mediated release of IL1beta from CCR2+ tumor-associated macrophages. These results indicate that CCL2, via IL1beta, acts as a key player in regulating the pro-metastatic gamma delta T cell IL17 neutrophil systemic inflammatory cascade and might be an interesting candidate for therapeutic targeting.

Citation Format: Kelly Kersten, Seth B. Coffelt, Niels J. Verstegen, Kim Vrijland, Metamia Ciampricotti, Chris W. Doornebal, Cheei-Sing Hau, Parul Doshi, Karin E. de Visser. Mammary tumor-derived CCL2 enhances pro-metastatic systemic inflammation through upregulation of macrophage-derived IL1beta. [abstract]. In: Proceedings of the AACR Special Conference on Tumor Metastasis; 2015 Nov 30-Dec 3; Austin, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(7 Suppl):Abstract nr A20.

IL-17-producing γδ T cells and neutrophils conspire to promote breast cancer metastasis

Metastatic disease remains the primary cause of death for patients with breast cancer. The different steps of the metastatic cascade rely on reciprocal interactions between cancer cells and their microenvironment. Within this local microenvironment and in distant organs, immune cells and their mediators are known to facilitate metastasis formation. However, the precise contribution of tumour-induced systemic inflammation to metastasis and the mechanisms regulating systemic inflammation are poorly understood. Here we show that tumours maximize their chance of metastasizing by evoking a systemic inflammatory cascade in mouse models of spontaneous breast cancer metastasis. We mechanistically demonstrate that interleukin (IL)-1β elicits IL-17 expression from gamma delta (γδ) T cells, resulting in systemic, granulocyte colony-stimulating factor (G-CSF)-dependent expansion and polarization of neutrophils in mice bearing mammary tumours. Tumour-induced neutrophils acquire the ability to suppress cytotoxic T lymphocytes carrying the CD8 antigen, which limit the establishment of metastases. Neutralization of IL-17 or G-CSF and absence of γδ T cells prevents neutrophil accumulation and downregulates the T-cell-suppressive phenotype of neutrophils. Moreover, the absence of γδ T cells or neutrophils profoundly reduces pulmonary and lymph node metastases without influencing primary tumour progression. Our data indicate that targeting this novel cancer-cell-initiated domino effect within the immune system--the γδ T cell/IL-17/neutrophil axis--represents a new strategy to inhibit metastatic disease.

Abstract IA07: Cancer-associated inflammation facilitates metastatic breast cancer and counteracts chemoresponsiveness

Over 90% of breast cancer deaths are due to complications as a consequence of metastasis formation. Much progress has been made in understanding primary breast cancer formation; however, metastatic disease is still largely unexplored, poorly understood and incurable. Clearly, there is an urgent need for novel therapies with efficacious anti-metastatic activity. The different steps of the metastatic cascade are largely regulated by reciprocal interactions between cancer cells and their microenvironment. Accumulating evidence indicates that cells and mediators of the immune system can facilitate metastasis formation. To mechanistically study how immune cells and their mediators modulate breast cancer metastasis, we have recently developed a mouse model of spontaneous breast cancer metastasis that mimics the clinical course of metastatic disease in humans. The basis is the K14cre;EcadF/F;p53F/F transgenic mouse that develops breast cancer resembling human invasive lobular carcinoma. We orthotopically transplant invasive lobular carcinoma fragments from these mice into mammary glands of wild-type syngeneic mice. Once primary tumors are established, we mimic the clinical setting and perform a mastectomy. Following surgery, the mice develop clinically overt metastases in lymph nodes, lungs, liver and other distant organs. This novel mouse model of breast cancer metastasis accurately mimics each step of the metastatic cascade in humans. It provides a unique tool to further explore the biology of metastatic breast cancer with the aim to contribute to the development of more effective treatment strategies.

Neutrophils make up a significant proportion of the inflammatory infiltrate in many tumors and their accumulation in breast cancer patients has been associated with metastasis formation. Also in our spontaneous breast cancer metastasis mouse model, metastasis formation is accompanied by a very pronounced accumulation of neutrophils in circulation and distant organs. Antibody-mediated depletion of neutrophils did not affect primary breast cancer outgrowth, but did result in a profound decrease in lung and lymph node metastasis. Using biological and genomic approaches, we have uncovered a novel communication network between gamma delta T cells and neutrophils that is critical for breast cancer metastasis. We are currently dissecting the mechanisms by which neutrophils facilitate breast cancer metastasis formation.

Besides regulating metastatic disease, the immune system also modulates responsiveness of cancer to conventional forms of therapy. Using the K14cre;EcdF/F;p53F/F mouse mammary tumor model, we study the ability of the immune system to influence the anti-cancer efficacy of chemotherapy. We have observed that it is very important to optimally match chemotherapeutic drugs with immunomodulatory compounds. In addition, combining chemotherapy with an immunomodulatory drug can trigger a rewiring of the inflammatory tumor microenvironment resulting in immune-dependent therapy resistance. Taken together, through mechanistic understanding of the crosstalk between the immune system and cancer, we aim to contribute to the design of novel immunomodulatory strategies to fight metastatic breast cancer and to increase the efficacy of conventional anti-cancer therapies.

(Supported by the Dutch Cancer Society grant 2011-5004, NWO/VIDI 91796307, AICR 11-0677 and FP7 MCA-ITN 317445)

Citation Format: Seth B. Coffelt, Chris W. Doornebal, Metamia Ciampricotti, Camilla Salvagno, Kelly Kersten, Kim Vrijland, Cheei-Sing Hau, Jos Jonkers, Karin E. De Visser. Cancer-associated inflammation facilitates metastatic breast cancer and counteracts chemoresponsiveness. [abstract]. In: Abstracts: AACR Special Conference on Cellular Heterogeneity in the Tumor Microenvironment; 2014 Feb 26-Mar 1; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2015;75(1 Suppl):Abstract nr IA07. doi:10.1158/1538-7445.CHTME14-IA07

Abstract A083: Neutrophils promote metastasis of invasive lobular carcinoma

The multistep process of metastasis is highly dependent on the intrinsic mutations that accumulate in cancer cells. However, recent experimental evidence has shown that these mutations are not sufficient to facilitate metastatic disease. Cues from the tumor microenvironment are also required. In order to understand how systemic changes might affect metastasis formation, we profiled the cellular and molecular alterations in various organs of K14cre;EcdF/F;p53F/F mammary tumor-bearing mice – a model of invasive lobular breast cancer. Among all immune cells, increased neutrophil accumulation was the most pronounced. To test the functional importance of neutrophils in the metastatic process, we utilized our recently described model of spontaneous metastasis. This model is based on the transplantation of K14cre;EcdF/F;p53F/F tumor pieces into wild-type recipient mice, and subsequent surgical removal of the primary tumor, permitting us to investigate neutrophil function in both the neoadjuvant and adjuvant settings. Interestingly, mice treated with neutrophil-depleting antibodies in the neoadjuvant setting displayed a profound reduction in pulmonary metastasis, whereas metastases in the adjuvant group were equivalent to controls. These data indicate that neutrophils play a prominent role during the very early stages of the metastatic cascade. Our preliminary data suggest that these tumor-educated neutrophils can suppress the activation of T cells, as one mechanism by which they may promote metastasis. In addition, cytokine analysis of K14cre;EcdF/F;p53F/F mammary tumors demonstrated an increase in the IL17 pathway when compared to wild-type mammary glands. Subsets of T cells are known producers of IL17 and this pathway regulates neutrophil expansion indirectly. In accordance with this, K14cre;EcdF/F;p53F/F mice lacking the adaptive immune system displayed reduced IL17 levels and reduced circulating neutrophils. Current efforts are underway to determine whether T cells play a role in the pro-metastatic function of neutrophils. Together, these findings indicate that neutrophils are crucial for the establishment of breast cancer metastasis.

Citation Format: Seth B. Coffelt, Chris W. Doornebal, Kelly Kersten, Metamia Ciampricotti, Cheei-Sing Hau, Kim Vrijland, Jorieke Weiden, Jos Jonkers, Karin E. de Visser. Neutrophils promote metastasis of invasive lobular carcinoma. [abstract]. In: Proceedings of the AACR Special Conference on Advances in Breast Cancer Research: Genetics, Biology, and Clinical Applications; Oct 3-6, 2013; San Diego, CA. Philadelphia (PA): AACR; Mol Cancer Res 2013;11(10 Suppl):Abstract nr A083.

Abstract A96: The impact of the inflammatory microenvironment on breast cancer metastasis and chemotherapy responsiveness

After decades of research, breast cancer still remains the leading cause of cancer mortality in women. The majority of these breast cancer deaths is due to metastasis, which is still poorly understood and incurable. Recently it has been appreciated that the tumor microenvironment plays a significant role in both tumor progression and response to chemotherapy. However, its role in metastasis formation is still largely unclear. In this project we focus on the role of the inflammatory microenvironment on metastatic breast cancer and chemotherapy responsiveness.

In our research we make use of the conditional K14cre;EcdF/F;P53F/F breast cancer mouse model that spontaneously develops mammary tumors resembling human invasive lobular carcinomas (ILC). These tumors reside in an inflammatory microenvironment which is characterized by expression of inflammatory cytokines resulting in infiltration of large numbers of immune cells. About 50% of K14cre;EcdF/F;P53F/F animals develop micrometastases in distant organs like lung, lymph node and spleen, however they do not succumb to metastatic disease. We hypothesize that the inflammatory tumor microenvironment plays a role in breast cancer metastasis formation and possibly in chemotherapy efficacy. Exploiting the K14cre;EcdF/F;P53F/F model, mouse ILC (mILC) pieces are transplanted into the 4th mammary gland of wild type recipient mice. Tumors are allowed to grow to a specific size upon which a mastectomy is performed mimicking the clinical situation. Mice are sacrificed as soon as they show clinical signs of metastatic disease. This transplantable model allows us to study the effect of the microenvironment on breast cancer metastasis and chemotherapy responsiveness in two distinct settings: a neo-adjuvant setting (treatment targeting primary tumor growth) and an adjuvant setting (treatment after mastectomy specifically targeting metastatic outgrowth). Using this model we set out to study the effect of the inflammatory microenvironment in breast cancer metastasis formation and chemotherapy responsiveness. We found that neo-adjuvant chemotherapy treatment resulted in a significant delay of primary tumor growth. As a result, metastasis-free survival was significantly increased compared to controls. Also adjuvant chemotherapy treatment resulted in a survival benefit compared to controls. We are currently studying the effect of inflammatory cytokine inhibition on chemotherapy responsiveness and formation of distant metastases. Therefore we are analyzing different populations of immune cells in the inflammatory tumor microenvironment by flow cytometry. Subsequently, we are looking into the pattern of metastasis formation throughout the body. This research is funded by the Dutch Cancer Society; 2011-5004.

Citation Format: Kelly Kersten, Metamia Ciampricotti, Chris W. Doornebal, Cheei-Sing Hau, Seth B. Coffelt, Karin de Visser. The impact of the inflammatory microenvironment on breast cancer metastasis and chemotherapy responsiveness. [abstract]. In: Proceedings of the AACR Special Conference on Tumor Invasion and Metastasis; Jan 20-23, 2013; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2013;73(3 Suppl):Abstract nr A96.

Developmental stage-specific contribution of LGR5(+) cells to basal and luminal epithelial lineages in the postnatal mammary gland

The leucine-rich repeat-containing heterotrimeric guanine nucleotide-binding protein-coupled receptor 5 (LGR5) has been identified as a marker of cycling stem cells in several epithelial tissues, including small intestine, colon, stomach and hair follicle. To investigate whether LGR5 also marks mammary epithelial stem cells, we performed in situ lineage-tracing studies and mammary gland reconstitutions with LGR5-expressing mammary epithelial cells. Interestingly, the LGR5 progeny population in mammary epithelium switches from the luminal to the myoepithelial compartment during the first 12 days of postnatal development, likely reflecting local changes in Wnt signalling. Together, our findings point to a stage-specific contribution of LGR5-expressing cells to luminal and basal epithelial lineages during postnatal mammary gland development.

A preclinical mouse model of invasive lobular breast cancer metastasis

Metastatic disease accounts for more than 90% of cancer-related deaths, but the development of effective antimetastatic agents has been hampered by the paucity of clinically relevant preclinical models of human metastatic disease. Here, we report the development of a mouse model of spontaneous breast cancer metastasis, which recapitulates key events in its formation and clinical course. Specifically, using the conditional K14cre;Cdh1(F/F);Trp53(F/F) model of de novo mammary tumor formation, we orthotopically transplanted invasive lobular carcinoma (mILC) fragments into mammary glands of wild-type syngeneic hosts. Once primary tumors were established in recipient mice, we mimicked the clinical course of treatment by conducting a mastectomy. After surgery, recipient mice succumbed to widespread overt metastatic disease in lymph nodes, lungs, and gastrointestinal tract. Genomic profiling of paired mammary tumors and distant metastases showed that our model provides a unique tool to further explore the biology of metastatic disease. Neoadjuvant and adjuvant intervention studies using standard-of-care chemotherapeutics showed the value of this model in determining therapeutic agents that can target early- and late-stage metastatic disease. In obtaining a more accurate preclinical model of metastatic lobular breast cancer, our work offers advances supporting the development of more effective treatment strategies for metastatic disease.

Bmp signaling exerts opposite effects on cardiac differentiation

RATIONALE

The importance for Bmp signaling during embryonic stem cell differentiation into myocardial cells has been recognized. The question when and where Bmp signaling in vivo regulates myocardial differentiation has remained largely unanswered.

OBJECTIVE

To identify when and where Bmp signaling regulates cardiogenic differentiation.

METHODS AND RESULTS

Here we have observed that in zebrafish embryos, Bmp signaling is active in cardiac progenitor cells prior to their differentiation into cardiomyocytes. Bmp signaling is continuously required during somitogenesis within the anterior lateral plate mesoderm to induce myocardial differentiation. Surprisingly, Bmp signaling is actively repressed in differentiating myocardial cells. We identified the inhibitory Smad6a, which is expressed in the cardiac tissue, to be required to inhibit Bmp signaling and thereby promote expansion of the ventricular myocardium.

CONCLUSION

Bmp signaling exerts opposing effects on myocardial differentiation in the embryo by promoting as well as inhibiting cardiac growth.

Development of metastatic HER2(+) breast cancer is independent of the adaptive immune system

The tumour-modulating effects of the endogenous adaptive immune system are rather paradoxical. Whereas some clinical and experimental observations offer compelling evidence for the existence of immunosurveillance, other studies have revealed promoting effects of the adaptive immune system on primary cancer development and metastatic disease. We examined the functional significance of the adaptive immune system as a regulator of spontaneous HER2(+) breast tumourigenesis and pulmonary metastasis formation, using the MMTV-NeuT mouse model in which mammary carcinogenesis is induced by transgenic expression of the activated HER2/neu oncogene. Although T and B lymphocytes infiltrate human and experimental HER2(+) breast tumours, genetic elimination of the adaptive immune system does not affect development of premalignant hyperplasias or primary breast cancers. In addition, we demonstrate that pulmonary metastasis formation in MMTV-NeuT mice is not dependent on the adaptive immune system. Thus, our findings reveal that spontaneous HER2-driven mammary tumourigenesis and metastasis formation are neither suppressed, nor altered by immunosurveillance mechanisms, nor promoted by the adaptive immune system.