Spatial and Temporal Mapping of Breast Cancer Lung Metastases Identify TREM2 Macrophages as Regulators of the Metastatic Boundary

Macrophage niche imprinting as a determinant of macrophage identity and function

Macrophage niches are the anatomical locations within organs or tissues consisting of various cells, intercellular and extracellular matrix, transcription factors, and signaling molecules that interact to influence macrophage self-maintenance, phenotype, and behavior. The niche, besides physically supporting macrophages, imposes a tissue- and organ-specific identity on the residing and infiltrating monocytes and macrophages. In this review, we give examples of macrophage niches and the modes of communication between macrophages and surrounding cells. We also describe how macrophages, acting against their immune defensive nature, can create a hospitable niche for pathogens and cancer cells.

Galectin-3 depletion tames pro-tumoural microglia and restrains cancer cells growth

Galectin-3 (Gal-3) is a multifunctional protein that plays a pivotal role in the initiation and progression of various central nervous system diseases, including cancer. Although the involvement of Gal-3 in tumour progression, resistance to treatment and immunosuppression has long been studied in different cancer types, mainly outside the central nervous system, its elevated expression in myeloid and glial cells underscores its profound impact on the brain's immune response. In this context, microglia and infiltrating macrophages, the predominant non-cancerous cells within the tumour microenvironment, play critical roles in establishing an immunosuppressive milieu in diverse brain tumours. Through the utilisation of primary cell cultures and immortalised microglial cell lines, we have elucidated the central role of Gal-3 in promoting cancer cell migration, invasion, and an immunosuppressive microglial phenotypic activation. Furthermore, employing two distinct in vivo models encompassing primary (glioblastoma) and secondary brain tumours (breast cancer brain metastasis), our histological and transcriptomic analysis show that Gal-3 depletion triggers a robust pro-inflammatory response within the tumour microenvironment, notably based on interferon-related pathways. Interestingly, this response is prominently observed in tumour-associated microglia and macrophages (TAMs), resulting in the suppression of cancer cells growth.

Improving the predictive accuracy of efficacy evaluation using tumor orthotopic transplant and resection model

Preclinical efficacy evaluation and tumor drug sensitivity analysis are two main applications of efficacy evaluation. Preclinical efficacy evaluation is to predict whether candidate drugs or therapies may improve patient outcomes in clinical trials. Tumor drug sensitivity analysis is an approach for the personalized evaluation and optimization of approved anti-cancer drugs and treatment regimens. Overall survival (OS) is the gold standard to evaluate the outcome of drugs or therapies in both clinical trials and clinical treatment. Many efficacy evaluation models, such as cell model, tumor cell-line transplant model, patient-derived tumor xenograft model, tumor organoid model, have been developed to assess the inhibitory effect of tested drugs or therapies on tumor growth. In fact, many treatments may also lead to malignant progression of tumors, such as chemotherapy, which can lead to metastasis. Therefore, tumor growth inhibition does not necessarily predict OS benefit. Whether it can prevent or inhibit tumor recurrence and metastasis is the key to whether drugs and therapies can improve patient outcomes. In this perspective, we summarize the current understanding of the pathological progression of tumor recurrence and metastasis, point out the shortcomings of existing tumor transplant models for simulating the clinical scenario of malignant progression of tumors, and propose five improved indicators for comprehensive efficacy evaluation to predict OS benefit using tumor orthotopic transplant and resection model. Improvement in the accuracy of efficacy evaluation will accelerate the development process of anti-cancer drugs or therapies, optimize treatment regimens to improve OS benefit, and reduce drug development and cancer treatment costs.

Extracellular-vesicle-packaged S100A11 from osteosarcoma cells mediates lung premetastatic niche formation by recruiting gMDSCs

The premetastatic niche (PMN) contributes to lung-specific metastatic tropism in osteosarcoma. However, the crosstalk between primary tumor cells and lung stromal cells is not clearly defined. Here, we dissect the composition of immune cells in the lung PMN and identify granulocytic myeloid-derived suppressor cell (gMDSC) infiltration as positively associated with immunosuppressive PMN formation and tumor cell colonization. Osteosarcoma-cell-derived extracellular vesicles (EVs) activate lung interstitial macrophages to initiate the influx of gMDSCs via secretion of the chemokine CXCL2. Proteomic profiling of EVs reveals that EV-packaged S100A11 stimulates the Janus kinase 2/signal transducer and activator of transcription 3 signaling pathway in macrophages by interacting with USP9X. High level of S100A11 expression or circulating gMDSCs correlates with the presentation of lung metastasis and poor prognosis in osteosarcoma patients. In summary, we identify a key role of tumor-derived EVs in lung PMN formation, providing potential strategies for monitoring or preventing lung metastasis in osteosarcoma.

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.

Aberrant activation of wound healing programs within the metastatic niche facilitates lung colonization by osteosarcoma cells

Purpose

Lung metastasis is responsible for nearly all deaths caused by osteosarcoma, the most common pediatric bone tumor. How malignant bone cells coerce the lung microenvironment to support metastatic growth is unclear. This study delineates how osteosarcoma cells educate the lung microenvironment during metastatic progression.

Experimental design

Using single-cell transcriptomics (scRNA-seq), we characterized genome- and tissue-wide molecular changes induced within lung tissues by disseminated osteosarcoma cells in both immunocompetent murine models of metastasis and patient samples. We confirmed transcriptomic findings at the protein level and determined spatial relationships with multi-parameter immunofluorescence. We evaluated the ability of nintedanib to impair metastatic colonization and prevent osteosarcoma-induced education of the lung microenvironment in both immunocompetent murine osteosarcoma and immunodeficient human xenograft models.

Results

Osteosarcoma cells induced acute alveolar epithelial injury upon lung dissemination. scRNA-seq demonstrated that the surrounding lung stroma adopts a chronic, non-resolving wound-healing phenotype similar to that seen in other models of lung injury. Accordingly, metastasis-associated lung demonstrated marked fibrosis, likely due to the accumulation of pathogenic, pro-fibrotic, partially-differentiated epithelial intermediates. Inhibition of fibrotic pathways with nintedanib prevented metastatic progression in multiple murine and human xenograft models.

Conclusions

Our work demonstrates that osteosarcoma cells co-opt fibrosis to promote metastatic outgrowth. When harmonized with data from adult epithelial cancers, our results support a generalized model wherein aberrant mesenchymal-epithelial interactions are critical for promoting lung metastasis. Adult epithelial carcinomas induce fibrotic pathways in normal lung fibroblasts, whereas osteosarcoma, a pediatric mesenchymal tumor, exhibits fibrotic reprogramming in response to the aberrant wound-healing behaviors of an otherwise normal lung epithelium, which are induced by tumor cell interactions.

Statement of translational relevance

Therapies that block metastasis have the potential to save the majority of lives lost due to solid tumors. Disseminated tumor cells must educate the foreign, inhospitable microenvironments they encounter within secondary organs to facilitate metastatic colonization. Our study elucidated that disseminated osteosarcoma cells survive within the lung by co-opting and amplifying the lung's endogenous wound healing response program. More broadly, our results support a model wherein mesenchymal-epithelial cooperation is a key driver of lung metastasis. Osteosarcoma, a pediatric mesenchymal tumor, undergoes lung epithelial induced fibrotic activation while also transforming normal lung epithelial cells towards a fibrosis promoting phenotype. Conversely, adult epithelial carcinomas activate fibrotic signaling in normal lung mesenchymal fibroblasts. Our data implicates fibrosis and abnormal wound healing as key drivers of lung metastasis across multiple tumor types that can be targeted therapeutically to disrupt metastasis progression.