Impact of breast cancer cells´ secretome on the brain metastatic niche remodeling

The signature of extracellular vesicles in hypoxic breast cancer and their therapeutic engineering

Breast cancer (BC) currently ranks second in the global cancer incidence rate. Hypoxia is a common phenomenon in BC. Under hypoxic conditions, cells in the tumor microenvironment (TME) secrete numerous extracellular vesicles (EVs) to achieve intercellular communication and alter the metabolism of primary and metastatic tumors that shape the TME. In addition, emerging studies have indicated that hypoxia can promote resistance to tumor treatment. Engineered EVs are expected to become carriers for cancer treatment due to their high biocompatibility, low immunogenicity, high drug delivery efficiency, and ease of modification. In this review, we summarize the mechanisms of EVs in the primary TME and distant metastasis of BC under hypoxic conditions. Additionally, we highlight the potential applications of engineered EVs in mitigating the malignant phenotypes of BC cells under hypoxia.

Nerve growth factor inducible (VGF) is a secreted mediator for metastatic breast cancer tropism to the brain

Brain metastases are one of the most serious clinical problems in breast cancer (BC) progression, associated with lower survival rates and a lack of effective therapies. Thus, to dissect the early stages of the brain metastatic process, we studied the impact of brain organotropic BC cells' secretomes on the establishment of the brain pre-metastatic niche (PMN). We found that BC cells with specific tropism to the brain caused significant blood-brain barrier (BBB) disruption, as well as microglial activation, in both in vitro and in vivo models. Further, we searched for a brain-organotropic metastatic signature, as a promising source for the discovery of new biomarkers involved in brain metastatic progression. Of relevance, we identified VGF (nerve growth factor inducible) as a key mediator in this process, also impacting the BBB and microglial functions both in vitro and in vivo. In a series of human breast tumors, VGF was found to be expressed in both cancer cells and the adjacent stroma. Importantly, VGF-positive tumors showed a significantly worse prognosis and were associated with HER2 (human epidermal growth factor receptor 2) overexpression and triple-negative molecular signatures. Further clinical validation in primary tumors from metastatic BC cases showed a significant association between VGF and the brain metastatic location, clearly and significantly impacting on the prognosis of BC patients with brain metastasis. In conclusion, our study reveals a unique secretome signature for BC with a tropism for the brain, highlighting VGF as a crucial mediator in this process. Furthermore, its specific impact as a poor prognostic predictor for BC patients with brain metastasis opens new avenues to target VGF to control the progression of brain metastatic disease. © 2024 The Pathological Society of Great Britain and Ireland.

Pre-metastatic niche: formation, characteristics and therapeutic implication

Distant metastasis is a primary cause of mortality and contributes to poor surgical outcomes in cancer patients. Before the development of organ-specific metastasis, the formation of a pre-metastatic niche is pivotal in promoting the spread of cancer cells. This review delves into the intricate landscape of the pre-metastatic niche, focusing on the roles of tumor-derived secreted factors, extracellular vesicles, and circulating tumor cells in shaping the metastatic niche. The discussion encompasses cellular elements such as macrophages, neutrophils, bone marrow-derived suppressive cells, and T/B cells, in addition to molecular factors like secreted substances from tumors and extracellular vesicles, within the framework of pre-metastatic niche formation. Insights into the temporal mechanisms of pre-metastatic niche formation such as epithelial-mesenchymal transition, immunosuppression, extracellular matrix remodeling, metabolic reprogramming, vascular permeability and angiogenesis are provided. Furthermore, the landscape of pre-metastatic niche in different metastatic organs like lymph nodes, lungs, liver, brain, and bones is elucidated. Therapeutic approaches targeting the cellular and molecular components of pre-metastatic niche, as well as interventions targeting signaling pathways such as the TGF-β, VEGF, and MET pathways, are highlighted. This review aims to enhance our understanding of pre-metastatic niche dynamics and provide insights for developing effective therapeutic strategies to combat tumor metastasis.

Electrophysiological and morphological modulation of neuronal-glial network by breast cancer and nontumorigenic mammary cell conditioned medium

Breast cancer is a significant global health concern, with the overexpression of human epidermal growth factor receptor 2 (HER2/ERBB2) being a driver oncogene in 20%-30% of cases. Indeed, HER2/ERBB2 plays a crucial role in regulating cell growth, differentiation, and survival via a complex signaling network. Overexpression of HER2/ERBB2 is associated with more aggressive behavior and increased risk of brain metastases, which remains a significant clinical challenge for treatment. Recent research has highlighted the role of breast cancer secretomes in promoting tumor progression, including excessive proliferation, immune invasion, and resistance to anti-cancer therapy, and their potential as cancer biomarkers. In this study, we investigated the impact of ERBB2+ breast cancer SKBR-3 cell line compared with MCF10-A mammary non-tumorigenic cell conditioned medium on the electrophysiological activity and morphology of neural networks derived from neurons differentiated from human induced pluripotent stem cells. Our findings provide evidence of active modulation of neuronal-glial networks by SKBR-3 and MCF10-A conditioned medium. These results provide insights into the complex interactions between breast cancer cells and the surrounding microenvironment. Further research is necessary to identify the specific factors within breast cancer conditioned medium that mediate these effects and to develop targeted therapies that disrupt this interaction.

Profiling of Secreted Proteins in Serum-Containing Media Using BONCAT and Pulsed SILAC

Secreted proteins play pivotal roles in signal transduction and cell-to-cell communication. Despite increasing interest in secretome analysis over the past decade, most studies on this topic have utilized serum-free medium (SFM). However, fetal bovine serum (FBS) is the most widely used serum supplement for cell culture, and secretome analysis using serum-containing medium (SCM) is important to identify proteins secreted under realistic conditions and to understand their physiological roles. In this chapter, we describe a simple and robust protocol based on bioorthogonal non-canonical amino acid tagging (BONCAT) and pulsed stable isotope labeling by amino acids in cell culture (pSILAC), for identification and quantitation of the cell secretome in SCM. In this protocol, the secretome of SFM is compared with that of SCM to confirm the effect of FBS. Additionally, for mass spectrometric data processing, we provide parameters that increase true positives and decrease both false positives and false negatives.

Radiotherapeutic Strategies to Overcome Resistance of Breast Cancer Brain Metastases by Considering Immunogenic Aspects of Cancer Stem Cells

Breast cancer is the most diagnosed cancer in women, and symptomatic brain metastases (BCBMs) occur in 15-20% of metastatic breast cancer cases. Despite technological advances in radiation therapy (RT), the prognosis of patients is limited. This has been attributed to radioresistant breast cancer stem cells (BCSCs), among other factors. The aim of this review article is to summarize the evidence of cancer-stem-cell-mediated radioresistance in brain metastases of breast cancer from radiobiologic and radiation oncologic perspectives to allow for the better interpretability of preclinical and clinical evidence and to facilitate its translation into new therapeutic strategies. To this end, the etiology of brain metastasis in breast cancer, its radiotherapeutic treatment options, resistance mechanisms in BCSCs, and effects of molecularly targeted therapies in combination with radiotherapy involving immune checkpoint inhibitors are described and classified. This is considered in the context of the central nervous system (CNS) as a particular metastatic niche involving the blood-brain barrier and the CNS immune system. The compilation of this existing knowledge serves to identify possible synergistic effects between systemic molecularly targeted therapies and ionizing radiation (IR) by considering both BCSCs' relevant resistance mechanisms and effects on normal tissue of the CNS.

Immune Checkpoint Inhibitors and Other Immune Therapies in Breast Cancer: A New Paradigm for Prolonged Adjuvant Immunotherapy

Background: Breast cancer is the most common form of cancer in women worldwide. Advances in the early diagnosis and treatment of cancer in the last decade have progressively decreased the cancer mortality rate, and in recent years, immunotherapy has emerged as a relevant tool against cancer. HER2+ and triple-negative breast cancers (TNBCs) are considered more immunogenic and suitable for this kind of treatment due to the higher rate of tumor-infiltrating lymphocytes (TILs) and programmed death ligand 1 (PD-L1) expression. In TNBC, genetic aberrations further favor immunogenicity due to more neo-antigens in cancer cells. Methods: This review summarizes the principal ongoing conventional and investigational immunotherapies in breast cancer. Particularly, immune checkpoint inhibitors (ICIs) and their use alone or combined with DNA damage repair inhibitors (DDRis) are described. Then, the issue on immunotherapy with monoclonal antibodies against HER-2 family receptors is updated. Other investigational immunotherapies include a new schedule based on the interferon beta-interleukin-2 sequence that was given in ER+ metastatic breast cancer patients concomitant with anti-estrogen therapy, which surprisingly showed promising results. Results: Based on the scientific literature and our own findings, the current evaluation of tumor immunogenicity and the conventional model of adjuvant chemotherapy (CT) are questioned. Conclusions: A novel strategy based on additional prolonged adjuvant immunotherapy combined with hormone therapy or alternated with CT is proposed.

Small extracellular vesicles: from promoting pre-metastatic niche formation to therapeutic strategies in breast cancer

Breast cancer is the most common cancer in females, and to date, the mortality rate of breast cancer metastasis cannot be ignored. The metastasis of breast cancer is a complex, staged process, and the pattern of metastatic spread is not random. The pre-metastatic niche, as an organ-specific home for metastasis, is a favourable environment for tumour cell colonization. As detection techniques improve, the role of the pre-metastatic niche in breast cancer metastasis is being uncovered. sEVs (small extracellular vesicles) can deliver cargo, which is vital for the formation of pre-metastatic niches. sEVs participate in multiple aspects of creating a distant microenvironment to promote tumour invasion, including the secretion of inflammatory molecules, immunosuppression, angiogenesis and enhancement of vascular permeability, as well as regulation of the stromal environment. Here, we discuss the multifaceted mechanisms through which breast cancer-derived sEVs contribute to pre-metastatic niches. In addition, sEVs as biomarkers and antimetastatic therapies are also discussed, particularly their use in transporting exosomal microRNAs. The study of sEVs may provide insight into immunotherapy and targeted therapies for breast cancer, and we also provide an overview of their potential role in antitumour metastasis.

Characteristics of the cancer stem cell niche and therapeutic strategies

Distinct regions harboring cancer stem cells (CSCs) have been identified within the microenvironment of various tumors, and as in the case of their healthy counterparts, these anatomical regions are termed “niche.” Thus far, a large volume of studies have shown that CSC niches take part in the maintenance, regulation of renewal, differentiation and plasticity of CSCs. In this review, we summarize and discuss the latest findings regarding CSC niche morphology, physical terrain, main signaling pathways and interactions within them. The cellular and molecular components of CSCs also involve genetic and epigenetic modulations that mediate and support their maintenance, ultimately leading to cancer progression. It suggests that the crosstalk between CSCs and their niche plays an important role regarding therapy resistance and recurrence. In addition, we updated diverse therapeutic strategies in different cancers in basic research and clinical trials in this review. Understanding the complex heterogeneity of CSC niches is a necessary pre-requisite for designing superior therapeutic strategies to target CSC-specific factors and/or components of the CSC niche.

The theory of tumor ecosystem

Cancer cells can be conceived as “living organisms” interacting with cellular or non‐cellular components in the host internal environment, not only the local tumor microenvironment but also the distant organ niches, as well as the immune, nervous and endocrine systems, to construct a self‐sustainable tumor ecosystem. With increasing evidence for the systemic tumor‐host interplay, we predict that a new era of cancer therapy targeting the ecosystemic vulnerability of human malignancies has come. Revolving around the tumor ecosystem scoped as different hierarchies of primary, regional, distal and systemic onco‐spheres, we comprehensively review the tumor‐host interaction among cancer cells and their local microenvironment, distant organ niches, immune, nervous and endocrine systems, highlighting material and energy flow with tumor ecological homeostasis as an internal driving force. We also substantiate the knowledge of visualizing, modelling and subtyping this dynamically intertwined network with recent technological advances, and discuss ecologically rational strategies for more effective cancer therapies.

Brain Vascular Microenvironments in Cancer Metastasis

Primary tumours, particularly from major solid organs, are able to disseminate into the blood and lymphatic system and spread to distant sites. These secondary metastases to other major organs are the most lethal aspect of cancer, accounting for the majority of cancer deaths. The brain is a frequent site of metastasis, and brain metastases are often fatal due to the critical role of the nervous system and the limited options for treatment, including surgery. This creates a need to further understand the complex cell and molecular biology associated with the establishment of brain metastasis, including the changes to the environment of the brain to enable the arrival and growth of tumour cells. Local changes in the vascular network, immune system and stromal components all have the potential to recruit and foster metastatic tumour cells. This review summarises our current understanding of brain vascular microenvironments, fluid circulation and drainage in the context of brain metastases, as well as commenting on current cutting-edge experimental approaches used to investigate changes in vascular environments and alterations in specialised subsets of blood and lymphatic vessel cells during cancer spread to the brain.

Identification of immune-related cells and genes in the breast invasive carcinoma microenvironment

The clinical prognosis of breast cancer is closely related to its infiltrating immune status. The study sought to explore tumor-infiltrating immune cells (TILs) and immune-associated genes in the tumor microenvironment of breast invasive carcinoma (BRCA). The ESTIMATE algorithm was used to evaluate the microenvironment of breast cancer patients in TCGA database. The tumor's matrix score and immune score were obtained. The median was divided into two sub groups according to the median of the score, and the correlation between the score and prognosis was also discussed. Differentially expressed genes were screened from two subgroups with high and low score of breast cancer, and the differentially expressed genes were analyzed by GO and KEGG enrichment to explore their possible molecular functions, biological processes, cellular components and signal pathways involved in gene enrichment. It was found that there was a significant correlation between immune score and five-year survival rate, and the high score group had a better prognosis. Macrophage M1 and T cell CD8+ cells were positively related to 5-year overall survival in patients with breast invasive carcinoma. However, Macrophage M2 was negatively related to 5-year overall survival. We also observed that the low expression of four genes (CLEC3A, MCTS1, PDP1 and TCP1,) was related to favorable survival outcomes. High expression of FOXP3, CXCL9, CCR5, CXCR3, and CD37 was related to a high overall survival rate in BRCA. We identified a list of immune - related cells and genes that are useful for Prognostic evaluation and individualized treatment of BRCA.

Type V collagen alpha 1 chain promotes the malignancy of glioblastoma through PPRC1-ESM1 axis activation and extracellular matrix remodeling

Glioblastoma (GBM) is a fatal cancer. Existing therapies do not have significant efficacy for GBM patients. Previous studies have shown that the collagen family is involved in the regulation of the extracellular environment of cancer cells, and these conditions could become an important factor for effective treatment. Therefore, we screened various collagen types and observed that the type V collagen α1 chain (COL5A1) gene plays a pivotal role in GBM. We further examined whether the overexpression of COL5A1 is common in mesenchymal subtypes and is related to the survival rate of GBM patients through several in silico cohorts. In addition, our cohort also showed a consistent trend in COL5A1 protein levels. Most importantly, we validated the cell mobility, metastatic ability and actin polymerization status caused by COL5A1 with two-way models. Based on these results, we established a transcriptomics dataset based on COL5A1. Moreover, PPRC1, GK and ESM1 were predicted by ingenuity pathway analysis (IPA) to be transcription factors or to participate downstream. We investigated the involvement of COL5A1 in extracellular remodeling and the regulation of actin filaments in the metastasis of GBM. Our results indicate that the COL5A1-PPRC1-ESM1 axis may represent a novel therapeutic target in GBM.

Integrated Bioinformatics and Experimental Approaches Identified the Role of NPPA in the Proliferation and the Malignant Behavior of Breast Cancer

Breast cancer is the 3rd most common type of malignant tumor worldwide with high heterogeneity, frequent recurrence, and high metastasis tendency. In this study, we aimed to demonstrate the value of extracellular matrix- (ECM-) related genes in breast cancer patients. The overall expression of ECM is assessed with a novel SC3 clustering method, and patients were divided into two clusters with diverse recurrence rate. We established the Cox regression model in breast cancer patients and identified NPPA as an independent prognostic marker. The NPPA expression is downregulated in breast cancer patients, independent of the ER status, PR status, stemness score, and immune infiltrating condition. And we observed the enhanced proliferation, migration, and invasion potential of breast cancer cells after NPPA depletion. Further, we predicted the transcription modulation of NPPA with PROMO and JASPAR. And we further validated the binding of MZF1 to the -318 bp~-452 bp region of the NPPA promoter with chromatin immunoprecipitation and dual luciferase assay. Together, our study identified NPPA as a potential prognostic biomarker for breast cancer patients, whose downregulation is associated with an enhanced malignant behavior of breast cancer cells both in vivo and in vitro and identified the transcription regulation of NPPA by MZF1.

A glitch in the matrix: organ-specific matrisomes in metastatic niches

Modification of the extracellular matrix (ECM) is a critical aspect of developing a metastasis-supportive organ niche. Recent work investigating ECM changes that facilitate metastasis has revealed ways in which different metastatic organ niches are similar as well as the distinct characteristics that make them unique. In this review, we present recent findings regarding how ECM modifications support metastasis in four frequent metastatic sites: the lung, liver, bone, and brain. We discuss ways in which these modifications are shared between metastatic organs as well as features specific to each location. We also discuss areas of technical innovation that could be advantageous to future research and areas of inquiry that merit further investigation.

CIRCULATING TUMOR CELLS: WHERE WE LEFT OFF?

Cancer metastasis and recurrence are the leading causes of cancer-related death. Tumor cells which leave the primary or secondary tumors and shed into the bloodstream are called circulating tumor cells (CTC). These cells are the key drivers of cancer dissemination to surrounding tissues and to distant organs. The use of CTC in clinical practice necessitates the deep insight into their biology, as well as into their role in cancer evasion of immune surveillance, tumor resistance to chemo- radio- and immunotherapies and metastatic dormancy. Aim. The purpose of the work was to review the current knowledge on the CTC biology, as well as the prospects for their use for the diagnosis and targeted treatment of metastatic disease. Methods. The work proposed the integrative literature review using MEDLINE, Biological Abstracts and EMBASE databases. Results. This review summarizes and discusses historical milestones and current data concerning СTС biology, the main stages of their life cycle, their role in metastatic cascade, clinical prospects for their use as markers for the diagnosis and prognostication of the disease course, as well as targets for cancer treatment. Conclusions. Significant progress in the area of CTC biology and their use in cancer theranostics convincingly proved the attractiveness of these cells as targets for cancer prognosis and therapy. The effective use of liquid biopsy with quantitative and phenotypic characteristics of CTCs is impeded by the imperfection of the methodology for taking biological material and by the lack of reliable markers for assessing the metastatic potential of CTCs of various origins. The variety of mechanisms of tumor cells migration and invasion requires the development of complex therapeutic approaches for anti-metastatic therapy targeting CTCs. Efforts to address these key issues could help developing new and effective cancer treatment strategies.

Characteristics of pre-metastatic niche: the landscape of molecular and cellular pathways

Metastasis is a major contributor to cancer-associated deaths. It involves complex interactions between primary tumorigenic sites and future metastatic sites. Accumulation studies have revealed that tumour metastasis is not a disorderly spontaneous incident but the climax of a series of sequential and dynamic events including the development of a pre-metastatic niche (PMN) suitable for a subpopulation of tumour cells to colonize and develop into metastases. A deep understanding of the formation, characteristics and function of the PMN is required for developing new therapeutic strategies to treat tumour patients. It is rapidly becoming evident that therapies targeting PMN may be successful in averting tumour metastasis at an early stage. This review highlights the key components and main characteristics of the PMN and describes potential therapeutic strategies, providing a promising foundation for future studies.

Management of Brain and Leptomeningeal Metastases from Breast Cancer

The management of breast cancer (BC) has rapidly evolved in the last 20 years. The improvement of systemic therapy allows a remarkable control of extracranial disease. However, brain (BM) and leptomeningeal metastases (LM) are frequent complications of advanced BC and represent a challenging issue for clinicians. Some prognostic scales designed for metastatic BC have been employed to select fit patients for adequate therapy and enrollment in clinical trials. Different systemic drugs, such as targeted therapies with either monoclonal antibodies or small tyrosine kinase molecules, or modified chemotherapeutic agents are under investigation. Major aims are to improve the penetration of active drugs through the blood-brain barrier (BBB) or brain-tumor barrier (BTB), and establish the best sequence and timing of radiotherapy and systemic therapy to avoid neurocognitive impairment. Moreover, pharmacologic prevention is a new concept driven by the efficacy of targeted agents on macrometastases from specific molecular subgroups. This review aims to provide an overview of the clinical and molecular factors involved in the selection of patients for local and/or systemic therapy, as well as the results of clinical trials on advanced BC. Moreover, insight on promising therapeutic options and potential directions of future therapeutic targets against BBB and microenvironment are discussed.

Supportive roles of brain macrophages in CNS metastases and assessment of new approaches targeting their functions

Metastases to the central nervous system (CNS) occur frequently in adults and their frequency increases with the prolonged survival of cancer patients. Patients with CNS metastases have short survival, and modern therapeutics, while effective for extra-cranial cancers, do not reduce metastatic burden. Tumor cells attract and reprogram stromal cells, including tumor-associated macrophages that support cancer growth by promoting tissue remodeling, invasion, immunosuppression and metastasis. Specific roles of brain resident and infiltrating macrophages in creating a pre-metastatic niche for CNS invading cancer cells are less known. There are populations of CNS resident innate immune cells such as: parenchymal microglia and non-parenchymal, CNS border-associated macrophages that colonize CNS in early development and sustain its homeostasis. In this study we summarize available data on potential roles of different brain macrophages in most common brain metastases. We hypothesize that metastatic cancer cells exploit CNS macrophages and their cytoprotective mechanisms to create a pre-metastatic niche and facilitate metastatic growth. We assess current pharmacological strategies to manipulate functions of brain macrophages and hypothesize on their potential use in a therapy of CNS metastases. We conclude that the current data strongly support a notion that microglia, as well as non-parenchymal macrophages and peripheral infiltrating macrophages, are involved in multiple stages of CNS metastases. Understanding their contribution will lead to development of new therapeutic strategies.