Premetastatic Lung Research Articles

CircRNAs expression profile and potential roles of circRERE-PMN in pre-metastatic lungs.

The successful pulmonary metastasis of malignant cancer cells depends on the survival of circulating tumor cells in a distant and hostile microenvironment. The formation of a pre-metastatic niche (PMN) creates a supportive environment for subsequent metastasis. Circular RNAs (circRNAs) are increasingly acknowledged as crucial elements in the mechanisms of metastasis due to their stable structures and functions, making them promising early metastasis detection markers. However, the specific expression patterns and roles of circRNAs in the lungs before metastasis remain largely unexplored. Our research aims to chart the circRNA expression profile and assess their impact on the lung PMN. We developed a lung PMN model and employed comprehensive RNA sequencing to analyze the differences in circRNA expression between normal and pre-metastatic lungs. We identified 38 significantly different circRNAs, primarily involved in metabolism, apoptosis, and inflammation pathways. We then focused on one specific circRNA, circ:chr4:150406196 - 150406664 (circRERE-PMN), which exhibited a significant change in expression and was prevalent in myeloid-derived suppressor cells (MDSCs), alveolar epithelial cells, and macrophages within the pre-metastatic lung environment. CircRERE-PMN was found to potentially regulate apoptosis and the expression of cytokines and chemokines through its interaction with the downstream target HUR in alveolar epithelial cells. Overall, our study highlights the crucial role of circRNAs in the formation of lung PMNs, supporting their potential as diagnostic or therapeutic targets for lung metastasis.

Abstract PO4-25-02: Long-range Deployment of Tumor-antigen Specific Cytotoxic T Lymphocytes Inhibits Lung Metastasis of Breast Cancer

Abstract Effector Immune Cell Deployment (EICD) refers to systemic deployment of anti-tumor effector immune cells in cancer patients, including the priming, circulation, trafficking, activity and fate of the immunocytes, and is a panorama to reflect the generation, distribution and development of anti-tumor immunity. Tumor antigen-specific T cells are the main component of effector immune cells in anti-tumor immune responses, but their systemic deployment in breast cancer patients and the underlying mechanisms remain largely unknown. Here, we identified a cluster of CD8+ T cell exhibiting tissue-resident memory (TRM) phenotype in the tumor-draining lymph nodes (TDLNs) of 487 breast cancer patients, whose abundancy specifically predicts improved lung, but not other target organ metastasis-free survival. Also, high lung CD8+ TRM infiltration is associated with lower metastatic burden in breast cancer patients. Using single-cell RNA sequencing, we observed that in multiple mouse cancer models, CD8+TRM accumulate at early tumor stages when lung metastasis was not identified. Functionally, the CD8+TRM isolated from pre-metastatic lungs of the animals were tumor antigen specific and cytotoxic to the tumor cells. Nevertheless, the abundancy of CD8+TRM in the lungs were dramatically decreased in the lungs upon metastasis establishment. Moreover, in Cd8cre/+ Itgaeloxp/+-diphtheria toxin receptor conditional knockout mice, we unambiguously demonstrated that specific depletion of the CD8+ TRM subset facilitates lung metastasis in vivo, while adoptive transfer of CD8+ TRM successfully inhibited lung metastasis and prolonged survival of the mice. Mechanistically, using cell-tracing techniques in the photo-convertible Kaede-Tg mice, we found that tumor-specific CD8+ TRM were generated in the TDLNs of the mice and were recruited to the lungs via CCL25/CCR9 signaling axis. However, the circulating exosomes secreted by primary tumor cells were taken up by alveolar macrophages and polarized them to release IDO1 and impaired anti-tumor T cell immunity, facilitating lung metastasis. More importantly, inhibition of IDO1 effectively retrieves TRM-mediated protection against lung metastasis. Collectively, we have revealed a cross-talk between tumor cells and the inflammatory environment of distant organs, which could drive lung metastasis by impairing EICD. Our findings also highlight the therapeutic potential of orchestrating EICD in turning “cold” metastatic tumor foci to “hot” ones. Citation Format: Yue Xing, Shicheng Su, Erwei Song. Long-range Deployment of Tumor-antigen Specific Cytotoxic T Lymphocytes Inhibits Lung Metastasis of Breast Cancer [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO4-25-02.

Abstract 1495: Lipocalin-2 promotes breast cancer metastasis via tumor cell intrinsic and extrinsic mechanisms

Abstract While metastasis is the primary factor predicting poor outcomes in solid tumors, survival is lowest in patients initially diagnosed with a localized malignancy that then progresses to metastatic disease. Notably, nearly 25% of early-stage breast cancers (BCs) metastasize during treatment or following an initial positive response to therapeutic intervention. To define the molecular and cellular factors that contribute to metastatic progression of BC, we previously developed the Py230-C57Bl/6 syngeneic experimental metastasis model for interrogating mechanisms by which soluble factors condition premetastatic lung tissue to potentiate BC cell seeding/expansion. Using this model and the TCGA, we identified lipocalin-2 (Lcn2) as a molecular candidate that is upregulated in lung-tropic Py230 cells and other human triple-negative breast cancer (TNBC) cells, and that predicts poor outcomes in human BCs. While Lcn2 has been previously reported to mediate BC progression in genetically engineered mouse models, its mechanism(s) of action remain undefined. Here, we demonstrate that Py230 cell-secreted Lcn2 is necessary for optimal reprogramming of the premetastatic lung during metastatic progression. In agreement with these data, we defined a cell intrinsic role for Lcn2 in BC cell organoid assembly/invasion and expression of proinflammatory factors. To define BC cell extrinsic roles for Lcn2 in remodeling the premetastatic lung, we collected global transcriptome and single-cell spatial proteome data for lung tissue from C57Bl/6 mice systemically educated with mock media or media conditioned with Py8119 (Lcn2low) or Py230 (Lcn2hi) BC cells. Mice receiving Py230 conditioned media treatments were further divided between two groups – one receiving an isotype control IgG and the other receiving an Lcn2 immunoneutralizing antibody. Global transcriptome data was used to determine novel gene set enrichment signatures and clinically relevant interactomes – notable candidates predicted to cooperate with Lcn2 in decreasing patient survival were affiliated with cilia biogenesis and function. Single-cell spatial proteome data were analyzed for 28 different cell populations within the premetastatic lung. Interestingly, Py230 cell-derived Lcn2 did not affect the percentage of ciliated epithelial cells indicating that the global transcriptome data referenced above represent a real increase in expression of cilia-related genes and not an increase in cilia-positive cell types. Notably, we identified that Lcn2 increased the percentage of CD45neg/Despos mechanomodulatory cells and proliferating CD45pos/CD3pos/CD4neg/CD8pos cytotoxic T cells in the premetastatic lung. Taken together, these data define new targets around which new therapeutic strategies can be developed to improve BC patient outcomes. Citation Format: Joshua Gamez, Francesca Sanchez, Gabriela Ortiz-Soto, Jane Cox, Amir Gerami, Jonathan A. Kelber. Lipocalin-2 promotes breast cancer metastasis via tumor cell intrinsic and extrinsic mechanisms [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 1495.

Myeloid Cells Pave the Metastatic Road in Breast Cancer.

Current immunotherapeutic approaches are tailored towards biomarkers and mechanisms presented in the primary tumor microenvironment, yet few are designed against targets that arise in the metastatic site. In a recent Cancer Discovery article, Yofe and colleagues spatially and temporally mapped the evolving breast tumor metastatic environment within the lung at single-cell resolution to identify immunologic cell types and mechanisms underlying the formation of metastatic nodules. The authors identified myeloid cell, monocyte, and neutrophil phenotypes as the most significant differences between the primary tumor and metastatic site. The authors also revealed the existence of a metastasis-specific population of macrophages expressing Trem2 in both human and murine models that exhibit immunosuppressive features. Interestingly, Trem2+ macrophages are enriched at the invasive border of metastatic nodules compared with the metastatic core, suggesting they play an exclusionary role within the site. Characterization of the premetastatic lung in conjunction with pseudotime lineage analysis revealed that Fn1+ monocytes precede metastasis formation and are the likely source of Trem2+ macrophages in developed nodules. This study supports the characterization of metastatic immune microenvironments to identify novel immunotherapeutic targets that may not exist within the primary site but play a significant role in patient outcome.

Unveiling the role of osteosarcoma-derived secretome in premetastatic lung remodelling

BackgroundLung metastasis is the most adverse clinical factor and remains the leading cause of osteosarcoma-related death. Deciphering the mechanisms driving metastatic spread is crucial for finding open therapeutic windows for successful organ-specific interventions that may halt or prevent lung metastasis.MethodsWe employed a mouse premetastatic lung-based multi-omics integrative approach combined with clinical features to uncover the specific changes that precede lung metastasis formation and identify novel molecular targets and biomarker of clinical utility that enable the design of novel therapeutic strategies.ResultsWe found that osteosarcoma-bearing mice or those preconditioned with the osteosarcoma cell secretome harbour profound lung structural alterations with airway damage, inflammation, neutrophil infiltration, and extracellular matrix remodelling with increased deposition of fibronectin and collagens by resident stromal activated fibroblasts, favouring the adhesion of disseminated tumour cells. Systemic-induced microenvironmental changes, supported by transcriptomic and histological data, promoted and accelerated lung metastasis formation. Comparative proteome profiling of the cell secretome and mouse plasma identified a large number of proteins involved in extracellular-matrix organization, cell-matrix adhesion, neutrophil degranulation, and cytokine-mediated signalling, consistent with the observed lung microenvironmental changes. Moreover, we identified EFEMP1, an extracellular matrix glycoprotein exclusively secreted by metastatic cells, in the plasma of mice bearing a primary tumour and in biopsy specimens from osteosarcoma patients with poorer overall survival. Depletion of EFEMP1 from the secretome prevents the formation of lung metastasis.ConclusionsIntegration of our data uncovers neutrophil infiltration and the functional contribution of stromal-activated fibroblasts in ECM remodelling for tumour cell attachment as early pro-metastatic events, which may hold therapeutic potential in preventing or slowing the metastatic spread. Moreover, we identified EFEMP1, a secreted glycoprotein, as a metastatic driver and a potential candidate prognostic biomarker for lung metastasis in osteosarcoma patients.Graphical abstractOsteosarcoma-derived secreted factors systemically reprogrammed the lung microenvironment and fostered a growth-permissive niche for incoming disseminated cells to survive and outgrow into overt metastasis.Daily administration of osteosarcoma cell secretome mimics the systemic release of tumour-secreted factors of a growing tumour in mice during PMN formation;Transcriptomic and histological analysis of premetastatic lungs revealed inflammatory-induced stromal fibroblast activation, neutrophil infiltration, and ECM remodelling as early onset pro-metastatic events;Proteome profiling identified EFEMP1, an extracellular secreted glycoprotein, as a potential predictive biomarker for lung metastasis and poor prognosis in osteosarcoma patients.Osteosarcoma patients with EFEMP1 expressing biopsies have a poorer overall survival.

Targeting acidic pre-metastatic niche in lungs by pH low insertion peptide and its utility for anti-metastatic therapy.

Dysregulated extracellular pH, the universal feature of tumor, works as an evolutional force to drive dissemination of tumor cells. It is well-established that tumor acidity is associated with tumor growth and metastasis. However, the pH of pre-metastatic niche remains unclear. We hypothesized that primary tumor cells remotely prime acidity in secondary organ to achieve metastatic colonization. Herein, we demonstrated that the pH responsive probe pH Low Insertion Peptide (pHLIP) was notably accumulated in pre-metastatic lungs of 4T1.2 breast tumor-bearing mice. The pHLIP-targeted lungs showed high amounts of lactate and overexpressed glycolysis-related proteins. Pharmacological inhibition of glycolysis suppressed the lung acidification induced by 4T1.2 cancer cell culture supernatant and delayed subsequent metastatic burden of disseminated tumor cells. In the acidic lungs, pHLIP was primarily localized in alveolar type 2 cells which strongly expressed glycolysis-related proteins. 4T1.2-derived extracellular vesicles expressed some of the glycolysis-related proteins, and their administration increased pHLIP accumulation and glycolytic enhancement in lungs. pHLIP-conjugated dexamethasone effectively attenuated lung metastatic burden by disrupting pro-inflammatory response in the acidic lungs. From these results, targeting the metastasis-supporting microenvironment by pHLIP technology creates possibility to identify pre-metastatic organ and prevent metastatic recurrence.

Primary breast tumor induced extracellular matrix remodeling in premetastatic lungs

The premetastatic niche hypothesis proposes an active priming of the metastatic site by factors secreted from the primary tumor prior to the arrival of the first cancer cells. We investigated several extracellular matrix (ECM) structural proteins, ECM degrading enzymes, and ECM processing proteins involved in the ECM remodeling of the premetastatic niche. Our in vitro model consisted of lung fibroblasts, which were exposed to factors secreted by nonmalignant breast epithelial cells, nonmetastatic breast cancer cells, or metastatic breast cancer cells. We assessed ECM remodeling in vivo in premetastatic lungs of female mice growing orthotopic primary breast tumor xenografts, as compared to lungs of control mice without tumors. Premetastatic lungs contained significantly upregulated Collagen (Col) Col4A5, matrix metalloproteinases (MMPs) MMP9 and MMP14, and decreased levels of MMP13 and lysyl oxidase (LOX) as compared to control lungs. These in vivo findings were consistent with several of our in vitro cell culture findings, which showed elevated Col14A1, Col4A5, glypican-1 (GPC1) and decreased Col5A1 and Col15A1 for ECM structural proteins, increased MMP2, MMP3, and MMP14 for ECM degrading enzymes, and decreased LOX, LOXL2, and prolyl 4-hydroxylase alpha-1 (P4HA1) for ECM processing proteins in lung fibroblasts conditioned with metastatic breast cancer cell media as compared to control. Taken together, our data show that premetastatic priming of lungs by primary breast tumors resulted in significant ECM remodeling which could facilitate metastasis by increasing interstitial fibrillar collagens and ECM stiffness (Col14A1), disruptions of basement membranes (Col4A5), and formation of leaky blood vessels (MMP2, MMP3, MMP9, and MMP14) to promote metastasis.

Pulmonary interleukin 1 beta/serum amyloid A3 axis promotes lung metastasis of hepatocellular carcinoma by facilitating the pre-metastatic niche formation

BackgroundIncreasing evidence suggests a vital role of the pre-metastatic niche in the formation of distant metastasis of many cancers. However, how the pre-metastatic niche is formed and promotes pulmonary metastasis of hepatocellular carcinoma (HCC) remains unknown.MethodsOrthotopic liver tumor models and RNA-Seq were used to identify dysregulated genes in the pre-metastatic lung. Il1b knockout (Il1b−/−) mice and lentivirus-mediated gene knockdown/overexpression were utilized to demonstrate the role of interleukin 1 beta (IL-1β)/serum amyloid A3 (SAA3) in the pre-metastatic niche formation and pulmonary metastasis. The potential molecular mechanisms were investigated by RNA-Seq, real-time quantitative PCR (qPCR), western blotting, immunohistochemistry (IHC), flow cytometry, luciferase reporter assay, double immunofluorescent staining and H&E staining.ResultsAccumulation of myeloid cells and upregulation of IL-1β were observed in the pre-metastatic lung of orthotopic liver tumor models. Myeloid cells accumulation and pulmonary metastasis were suppressed in Il1b−/− mice and Il1r1-silencing mice. Mechanistically, SAA3 and matrix metallopeptidase 9 (MMP9) were identified as potential downstream targets of IL-1β. Overexpression of SAA3 in the lungs of Il1b−/− mice restored myeloid cells accumulation and pulmonary metastasis of the orthotopic HCC xenografts. Moreover, alveolar macrophages-derived IL-1β dramatically enhanced SAA3 expression in alveolar epithelial cells in an NF-κB dependent manner and increased MMP9 levels in an autocrine manner. Furthermore, SAA3 recruited myeloid cells to the lung without affecting the expression of MMP9 in myeloid cells.ConclusionsOur study suggests a key role of pulmonary IL-1β and SAA3 in creating a permissive lung pre-metastatic niche by enhancing MMP9 expression and recruiting myeloid cells, respectively, thus promoting pulmonary metastasis of HCC.

Abstract 66: Galectin-1 mediated chronic tumoral-STING activation promotes metastasisthrough MDSC recruitment

Abstract Tumor cells alter the immune microenvironment to facilitate metastatic progression. Galectin-1 (Gal1) is a known modulator of tumor growth and progression in multiple cancer types including head and neck cancer (HNC). However, its contribution to the regulation of metastasis is poorly understood. Through this study we report a previously unknown role for Gal1 in modulating the STING pathway to regulate metastasis. The cGAS-STING pathway has paradoxical roles in cancer depending on the kinetics and strength of its induction, with chronic STING activation being linked to immune suppression and tumor progression while acute activation being associated with immune activation. However, little is known about the pathways that promote chronic STING activation. Using HNC and lung cancer models, we show that Gal-1 enhances STING protein stability, leading to sustained NF-κΒ activation and heightened chemokine-driven recruitment of myeloid derived suppressor cells (MDSCs). We show that Gal1-STING connection fosters the establishment of pre-metastatic niche through polymorphonuclear MDSCs (PMN-MDSCs), which modify the local lung microenvironment to support metastatic spread. Notably, RNA sequencing of MDSCs isolated from pre-metastatic lungs indicate the role of PMN-MDSCs in remodeling collagen and the extracellular matrix in the pre-metastatic compartment. Our findings reveal an unexpected role of STING activation in metastatic progression of HNC and lung cancer models and establish Gal1 as an endogenous positive regulator of STING. Citation Format: Dhanya K. Nambiar, Vignesh Vignesh Viswanathan, Hongbin Cao, Weiruo Zhang, Li Guan, Manish Chamoli, Brittany Holmes, Christina Kong, Rachel Hildebrand, Amanda Koong, Rie Eyben, Amato Giaccia, Lingyin Li, Edgar Engleman, Quynh Thu Le. Galectin-1 mediated chronic tumoral-STING activation promotes metastasisthrough MDSC recruitment [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 66.

An HLA-G/SPAG9/STAT3 axis promotes brain metastases

Brain metastases (BM) are the most common brain neoplasm in adults. Current BM therapies still offer limited efficacy and reduced survival outcomes, emphasizing the need for a better understanding of the disease. Herein, we analyzed the transcriptional profile of brain metastasis initiating cells (BMICs) at two distinct stages of the brain metastatic cascade-the "premetastatic" or early stage when they first colonize the brain and the established macrometastatic stage. RNA sequencing was used to obtain the transcriptional profiles of premetastatic and macrometastatic (non-premetastatic) lung, breast, and melanoma BMICs. We identified that lung, breast, and melanoma premetastatic BMICs share a common transcriptomic signature that is distinct from their non-premetastatic counterparts. Importantly, we show that premetastatic BMICs exhibit increased expression of HLA-G, which we further demonstrate functions in an HLA-G/SPAG9/STAT3 axis to promote the establishment of brain metastatic lesions. Our findings suggest that unraveling the molecular landscape of premetastatic BMICs allows for the identification of clinically relevant targets that can possibly inform the development of preventive and/or more efficacious BM therapies.

Abstract B009: Tumoral activation of endothelium drives macrophages-mediated metastatic niche formation and promotes lung metastasis

Abstract Primary tumor induces macrophages-enriched environment to establish metastatic niche which enhances homing and colonization of circulating tumor cells. However, the molecular mechanism underlying endothelial remodeling that favors macrophages infiltration and subsequent niche formation is not fully understood. Here, we found that tumor-derived factors activated endothelial cells to increase adhesive efficacy of monocytes to the endothelium, leading to macrophage infiltration. In mouse models of pulmonary metastasis, this endothelial activation triggered formation of premetastatic niche via accumulation of macrophages in the lungs. Of note, macrophages primed the metastatic microenvironment through enhancing expression of niche-related genes including S100A8, S100A9, MMP9 and fibronectin within the premetastatic lungs and directly transmitted survival signal to tumor cells in a contact-dependent manner. Furthermore, we demonstrated that depletion of macrophages specifically during premetastatic stages reduced niche formation and also resulted in reduced metastatic burden. These findings suggest that endothelial remodeling at metastatic site is a key step for initiation of premetastatic niche formation supported by macrophages. Targeting this step could present an opportunity for therapeutic intervention of metastatic spread in patients with malignant cancers. Citation Format: Hyewon Chung, Sang Wha Kim, Seung Hyeok Seok. Tumoral activation of endothelium drives macrophages-mediated metastatic niche formation and promotes lung metastasis [abstract]. In: Proceedings of the AACR Special Conference: Cancer Metastasis; 2022 Nov 14-17; Portland, OR. Philadelphia (PA): AACR; Cancer Res 2022;83(2 Suppl_2):Abstract nr B009.

Xiaoliu Pingyi Pecipe Inhibits Lung Pre-Metastatic Niche Formation and Prevents Myeloid-Derived Suppressor Cells Recruitment.

Metastasis, a leading cause of cancer-related deaths, involves complex mechanisms. The premetastatic niche (PMN) is a crucial contributor to this process. Myeloid-derived suppressor cells (MDSCs) play an important role in PMN formation and promote tumor progression and metastasis. The Xiaoliu Pingyi recipe (XLPYR), a traditional Chinese medicine, is effective in preventing postoperative recurrence and metastasis in cancer patients. This study investigated the effects of XLPYR on MDSCs recruitment and on the expression of PMN markers and elucidated the mechanisms involved in the prevention of tumor metastasis. C57BL/6 mice were subcutaneously injected with Lewis cells and treated with cisplatin and XLPYR. Tumors were resected after 14 days after the establishment of a model of lung metastasis, and tumor volume and weight were measured. Lung metastases were observed 21 days after resection. MDSCs in the lung, spleen, and peripheral blood were detected by flow cytometry. Western blotting, qRT-PCR and ELISA were used to detect the expression of S100A8, S100A9, MMP9, LOX, and IL-6/STAT3 in premetastatic lung tissue. XLPYR treatment inhibited tumor growth and prevented lung metastasis. Compared to mice without subcutaneous tumor cell transplantation, the model group had an increased proportion of MDSCs, higher expression of S100A8, S100A9, MMP9, and LOX in the premetastatic lung. XLPYR treatment reduced the proportion of MDSCs, S100A8, S100A9, MMP9, and LOX expression, and downregulated the IL-6/STAT3 pathway. XLPYR may prevent MDSCs recruitment and reduce the expression of S100A8, MMP9, LOX, and IL6/STAT3 in premetastatic lung tissue, thus reducing lung metastases.

Tumor-derived Cav-1 promotes pre-metastatic niche formation and lung metastasis in breast cancer.

Rationale: Breast cancer (BC), as one of the most frequently diagnosed cancer, has a poor prognosis due to the development of distant metastasis. Among the BC metastatic sites, lung is one of the most common sites. Caveolin-1 (Cav-1) is a functional membrane protein that plays a vital role in tumor metastasis. Although studies have revealed that Cav-1 levels were elevated in patients with advanced cancer, whether Cav-1 affects BC lung metastasis by influencing the formation of pre-metastatic niche (PMN) through exosomes has not been explored. Methods: Differential ultracentrifugation, transmission electron microscopy and nanoparticle tracking analysis were used to verify the presence of exosomes. Transwell assays were used to examine the biological effects of exosomes containing Cav-1. Both in vitro cell cultures and mammary tumor cell-induced mouse models were used to assess the lung metastasis. The regulatory mechanisms of PMN formation were revealed using western blot, flow cytometry, RT-qPCR, immunofluorescence assays, gene overexpression assays and RNA interference assays. Results: Exosomes have critical functions in transporting Cav-1 between primary BC and metastatic organ microenvironments. Cav-1 in BC-derived exosomes can act as a signaling molecule to mediate intercellular communication and regulate the PMN before lung metastasis by regulating the expression of PMN marker genes and inflammatory chemokines in lung epithelial cells, promoting the secretion of tenascin-C (TnC) in lung fibroblasts to cause extracellular matrix (ECM) deposition, and inhibiting the PTEN/CCL2/VEGF-A signaling pathway in lung macrophages to facilitate their M2-type polarization and angiogenesis. Conclusion: Our study investigated the mechanisms of lung PMN formation induced by Cav-1 in BC-derived exosomes. Our data may provide new directions for exploring the mechanisms and developing treatment strategies of BC lung metastasis.

Host CLIC4 expression in the tumor microenvironment is essential for breast cancer metastatic competence.

The TGF-β-regulated Chloride Intracellular Channel 4 (CLIC4) is an essential participant in the formation of breast cancer stroma. Here, we used data available from the TCGA and METABRIC datasets to show that CLIC4 expression was higher in breast cancers from younger women and those with early-stage metastatic disease. Elevated CLIC4 predicted poor outcome in breast cancer patients and was linked to the TGF-β pathway. However, these associations did not reveal the underlying biological contribution of CLIC4 to breast cancer progression. Constitutive ablation of host Clic4 in two murine metastatic breast cancer models nearly eliminated lung metastases without reducing primary tumor weight, while tumor cells ablated of Clic4 retained metastatic capability in wildtype hosts. Thus, CLIC4 was required for host metastatic competence. Pre- and post-metastatic proteomic analysis identified circulating pro-metastatic soluble factors that differed in tumor-bearing CLIC4-deficient and wildtype hosts. Vascular abnormalities and necrosis increased in primary tumors from CLIC4-deficient hosts. Transcriptional profiles of both primary tumors and pre-metastatic lungs of tumor-bearing CLIC4-deficient hosts were consistent with a microenvironment where inflammatory pathways were elevated. Altogether, CLIC4 expression in human breast cancers may serve as a prognostic biomarker; therapeutic targeting of CLIC4 could reduce primary tumor viability and host metastatic competence.

Abstract 3999: HLA-G, SPAG9 and STAT3 signalling: An alliance that promotes early-stage brain metastases

Abstract Brain metastases (BM) are the most common brain tumours in adults and a prominent cause of cancer-related mortality globally. Leading sources of BM are cancers of the lung, breast and melanoma, which together account for approximately 80% of all BM. Unfortunately, current clinical modalities for BM including surgery, radiation therapy and chemotherapy still offer limited efficacy and median survival times of 4 - 12 months in treated patients, emphasizing the need for more effective therapeutic strategies and generally a better understanding of the disease. We recently identified the presence of stem-like cells termed “brain metastasis-initiating cells” or BMICs in patient-derived BM from lung, breast and melanoma cancers that are able to recapitulate the complete brain metastatic cascade in pre-clinical models of BM. Through these models, we serendipitously captured lung, breast and melanoma BMICs at the “pre-metastatic” stage of BM - a stage where circulating metastatic cells have seeded the brain, but not yet formed full-blown (macro-metastatic) brain lesions. Transcriptomic analysis of pre-metastatic and macro-metastatic lung, breast and melanoma BMICs revealed a unique genetic profile in pre-metastatic BMICs that was distinct from their macro-metastatic counterparts. Further analysis identified several genes commonly up-regulated in all pre-metastatic BMIC cohorts irrespective of their primary tumour of origin. Intriguingly, we found that inhibition of the non-classical human leukocyte class I antigen-G or HLA-G gene (one of the top up-regulated genes in the pre-metastatic cohorts), reduced the ability of BMICs to form mature brain lesions. Correspondingly, HLA-G over-expression increased the capacity of BMICs to establish secondary brain tumours. Mechanistically, we discovered that over-expressing HLA-G levels in BMICs (to simulate the high levels that occurs in pre-metastatic BMICs), increased the activation of STAT3 signalling and this was mediated in part via a novel HLA-G binding partner - SPAG9. Our work thus uncovered a potential cooperative role between HLA-G, SPAG9 and STAT3 signalling during the early stages of BM. Indeed, attenuation of SPAG9 protein levels or STAT3 signalling in HLA-G over-expressing BMICs using CRISPR knockout and a STAT3 inhibitor respectively obstructed the ability of high HLA-G levels to promote mature brain lesions. This is the first study to reveal a role for an HLA-G-SPAG9-STAT3 axis in BM and highlights the potential of targeting this axis to inhibit BM, which will markedly extend patient survival. Citation Format: Blessing I. Bassey-Archibong, Chirayu R. Chokshi, Nikoo Aghaei, Agata Kieliszek, Nazanin Tatari, Dillon McKenna, Mohini Singh, Minomi Subapanditha, Arun Parmar, Neil Savage, Yu Lu, Chitra Venugopal, Sheila Singh. HLA-G, SPAG9 and STAT3 signalling: An alliance that promotes early-stage brain metastases [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3999.

Abstract 3138: The lung pro-thrombotic niche drives cancer-associated thromboembolism via exosomal ITGB2

Abstract Thromboembolism (TE) is a common complication in cancer patients and the second leading cause of cancer-related deaths. The incidence of TE varies in different cancer types, with the highest risk in lung cancer and pancreatic ductal adenocarcinoma (PDAC), and in advanced-stage and metastatic cancers. Despite the benefits associated with thromboprophylaxis for symptomatic TE, the prevention of TE still remains an unmet clinical need due to lack of biomarkers predictive of TE risk and the bleeding risk associated with the routine use of anti-coagulants. Exosomes are small circulating extracellular vesicles that mediate cell-to-cell communication. Cancer cells and the tumor microenvironment release large numbers of exosomes into the blood circulation and have displayed a therapeutic and predictive value in systemic diseases. Integrins expressed on the surface of exosomes drive their selective organotropism and prepare distant sites for metastatic seeding by establishing favorable pre-metastatic niches. Here we show that exosomes from metastasis-bearing lungs or pre-metastatic lungs of mice with melanoma, breast, lung and pancreatic cancer induce TE in mice and express high levels of integrin beta 2 (ITGB2). Instead, exosomes from tumor cell lines, primary tumors or other metastasis-bearing organs did not show any pro-thrombotic properties. Myeloid cells including monocytes/macrophages and neutrophils infiltrating pre- and post-metastatic lungs were the main source of ITGB2+ pro-thrombotic exosomes. Blockade of ITGB2 on lung-derived exosomes, or systemically in mice, prevented exosome-induced platelet aggregation and TE, and reduced metastasis. Examination of the mechanisms of ITGB2-induced TE showed that exosomal ITGB2 interact directly or through fibrin with different binding partners on platelets, and induce their activation and aggregation. Importantly, we found that exosomal ITGB2 levels are elevated in the plasma of PDAC patients prior to TE events in comparison to PDAC patients with no history of TE, and thus might serve as prognostic biomarker of TE. Together, our results provide the first evidence of the establishment of a pro-thrombotic lung niche in different cancer types. Moreover, we identify exosomal ITGB2 as a new target for the prevention and/or treatment of TE, as well as a potential “liquid biopsy” analyte for the early stratification of patients at high risk of TE. Citation Format: Serena Lucotti, Yusuke Ogitani, Candia M. Kenific, Linda Bojmar, Michele Cioffi, Pernille Lauritzen, Henrik Molina, Soren Heissel, Harry B. Lengel, Xiaohong Jing, Haiying Zhang, Irina Matei, Eileen M. O'Reilly, William R. Jarnagin, David R. Jones, James B. Bussel, David Kelsen, Jacqueline F. Bromberg, Diane M. Simeone, David Lyden. The lung pro-thrombotic niche drives cancer-associated thromboembolism via exosomal ITGB2 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3138.

Lin28B-high breast cancer cells promote immune suppression in the lung pre-metastatic niche via exosomes and support cancer progression

The formation of pre-metastatic niche is a key step in the metastatic burden. The pluripotent factor Lin28B is frequently expressed in breast tumors and is particularly upregulated in the triple negative breast cancer subtype. Here, we demonstrate that Lin28B promotes lung metastasis of breast cancer by building an immune-suppressive pre-metastatic niche. Lin28B enables neutrophil recruitment and N2 conversion. The N2 neutrophils are then essential for immune suppression in pre-metastatic lung by PD-L2 up-regulation and a dysregulated cytokine milieu. We also identify that breast cancer-released exosomes with low let-7s are a prerequisite for Lin28B-induced immune suppression. Moreover, Lin28B-induced breast cancer stem cells are the main sources of low-let-7s exosomes. Clinical data further verify that high Lin28B and low let-7s in tumors are both indicators for poor prognosis and lung metastasis in breast cancer patients. Together, these data reveal a mechanism by which Lin28B directs the formation of an immune-suppressive pre-metastatic niche.

NKG2D signaling regulates IL-17A-producing γδT cells in mice to promote cancer progression.

γδT cells are unconventional T cells particularly abundant in mucosal tissues that play an important role in tissue surveillance, homeostasis, and cancer. γδT cells recognize stressed cells or cancer cells through the NKG2D receptor to kill these cells and maintain normality. Contrary to the well-established anti-tumor function of these NKG2D-expressing γδT cells, we show here that, in mice, NKG2D regulates a population of pro-tumor γδT cells capable of producing IL-17A. Germline deletion of Klrk1, the gene encoding NKG2D, reduced the frequency of γδT cells in the tumor microenvironment and delayed tumor progression. We further show that blocking NKG2D reduced the capability of γδT cells to produce IL-17A in the pre-metastatic lung and that co-culture of lung T cells with NKG2D ligand-expressing tumor cells specifically increased the frequency of γδT cells. Together, these data support the hypothesis that, in a tumor microenvironment where NKG2D ligands are constitutively expressed, γδT cells accumulate in an NKG2D-dependent manner and drive tumor progression by secreting pro-inflammatory cytokines, such as IL-17A.

Abstract IA16: Immune suppression in cancer and strategies for its reversal

Abstract The microenvironment is involved in multiple aspect of cancer progression. Tumor metastasis is a critical step in the progression of solid tumors that is associated with patient mortality, and the metastatic microenvironment is key regulator of this process. The pre-metastatic niche is the microenvironment important for metastatic initiation that is established at distant sites in response to primary tumor factors during cancer progression. We characterized this microenvironment which involves changes in both stromal and immune populations in the lungs of sarcoma-bearing mice and in the liver in pancreatic- bearing mice by flow cytometry and RNA sequencing approaches. We identified a gene signature in pre-metastatic niche formation that demonstrates upregulation of immune suppression genes that is consistent across different metastatic tissue including lung and liver as well as across species with commonalities in murine and human early metastatic microenvironments. Performing single cell RNA sequencing of the pre-metastatic niche revealed key immune suppressive genes were found in the myeloid cell clusters. In addition to the increase of myeloid cells and immunosuppressive pathways, we discovered that T cell populations are reduced in pre-metastatic lungs. We hypothesized that reversing this immunosuppressive environment would restore T cell function and antitumor immunity. We designed a novel approach in which we generated Genetically-Engineered Myeloid cells (GEMys) to deliver IL-12, a potent antitumor molecule, into the pre-metastatic microenvironment. We evaluated the lungs by flow cytometry and observed that IL12-GEMy-treated mice had increased numbers of T cells and enhanced expression of activation markers, resulting in reduced metastasis and increased survival. This model was effective in an aggressive experimental metastasis model of pancreatic liver metastasis and was not only able to limit metastatic progression but was able to cure a subset of mice compared to rapid metastatic progression in the liver within a month in the untreated pancreatic cancer mice. When combined with chemotherapy pre-conditioning, IL12-GEMys cured mice of established tumors and generated long-lived T cell memory, as these mice were immune to subsequent tumor challenge. These studies demonstrate that IL12-GEMys can functionally modulate the core program of immune suppression in the pre-metastatic niche to successfully rebalance the dysregulated metastatic microenvironment in cancer. Citation Format: Rosandra N. Kaplan. Immune suppression in cancer and strategies for its reversal [abstract]. In: Abstracts: AACR Virtual Special Conference: Tumor Immunology and Immunotherapy; 2021 Oct 5-6. Philadelphia (PA): AACR; Cancer Immunol Res 2022;10(1 Suppl):Abstract nr IA16.

Extracellular vesicles in cancer progression.

Cancer cells release a variety of factors that contribute to the alteration of proximal and distal tissues to promote metastasis. Recent studies have demonstrated that aggressive cancer cells release extracellular vesicles with higher protein content and in excess than extracellular vesicles isolated from patients with less aggressive disease or healthy individuals. We found that melanoma tumor-derived extracellular vesicles (TEV) downregulate type I interferon receptor subunit 1 (IFNAR1), suppress expression of the interferon stimulated gene cholesterol 25-hydroxylase (CH25H). Loss of CH25H is observed in the leukocytes from melanoma patients, which correlated with metastasis and poor survival. Similarly, mice also exhibit loss of IFNAR1 following TEV administration. Moreover, loss of CH25H increased TEV uptake and TEV-induced pre metastatic niche and lung metastasis. Use of the anti-hypertensive drug, reserpine, mimicked the effects of the CH25H product 25-hydroxycholesterol to suppress TEV uptake and TEV-mediated tumor growth, pre-metastatic niche formation, and lung metastasis. These results suggest the importance of CH25H in suppressing TEV mediate cancer progression and importance of developing strategies to suppress TEV uptake and TEV-mediated disease progression.