Advances in decoding breast cancer brain metastasis

Biological profile of breast cancer brain metastasis

Breast cancer is one of the leading causes of death worldwide. The aggressive behaviour of breast tumor results from their metastasis. Notably, the brain tissue is one of the common regions of metastasis, thereby reducing the overall survival of patients. Moreover, the metastatic tumors demonstrate poor response or resistance to therapies. In addition, breast cancer brain metastasis provides the poor prognosis of patients. Therefore, it is of importance to understand the mechanisms in breast cancer brain metastasis. Both cell lines and animal models have been developed for the evaluation of breast cancer brain metastasis. Moreover, different tumor microenvironment components and other factors such as lymphocytes and astrocytes can affect brain metastasis. The breast cancer cells can disrupt the blood-brain barrier (BBB) during their metastasis into brain, developing blood-tumor barrier to enhance carcinogenesis. The breast cancer brain metastasis can be increased by the dysregulation of chemokines, STAT3, Wnt, Notch and PI3K/Akt. On the other hand, the effective therapeutics have been developed for the brain metastasis such as introduction of nanoparticles. Moreover, the disruption of BBB by ultrasound can increase the entrance of bioactive compounds to the brain tissue. In order to improve specificity and selectivity, the nanoparticles for the delivery of therapeutics and crossing over BBB have been developed to suppress breast cancer brain metastasis.

Bridging the gap: unlocking the potential of emerging drug therapies for brain metastasis

Brain metastasis remains an unmet clinical need in advanced cancers with an increasing incidence and poor prognosis. The limited response to various treatments is mainly derived from the presence of the substantive barrier, blood-brain barrier (BBB) and brain-tumour barrier (BTB), which hinders the access of potentially effective therapeutics to the metastatic tumour of the brain. Recently, the understanding of the structural and molecular features of the BBB/BTB has led to the development of efficient strategies to enhance BBB/BTB permeability and deliver drugs across the BBB/BTB to elicit the anti-tumour response against brain metastasis. Meanwhile, novel agents capable of penetrating the BBB have rapidly developed and been evaluated in preclinical studies and clinical trials, with both targeted therapies and immunotherapies demonstrating impressive intracranial activity against brain metastasis. In this review, we summarize the recent advances in the biological properties of the BBB/BTB and the emerging strategies for BBB/BTB permeabilization and drug delivery across the BBB/BTB. We also discuss the emerging targeted therapies and immunotherapies against brain metastasis tested in clinical trials. Additionally, we provide our viewpoints on accelerating clinical translation of novel drugs into clinic for patients of brain metastasis. Although still challenging, we expect this review to benefit the future development of novel therapeutics, specifically from a clinical perspective.

Comprehensive integrated single-cell RNA sequencing analysis of brain metastasis and glioma microenvironment: Contrasting heterogeneity landscapes

Understanding the specific type of brain malignancy, source of brain metastasis, and underlying transformation mechanisms can help provide better treatment and less harm to patients. The tumor microenvironment plays a fundamental role in cancer progression and affects both primary and metastatic cancers. The use of single-cell RNA sequencing to gain insights into the heterogeneity profiles in the microenvironment of brain malignancies is useful for guiding treatment decisions. To comprehensively investigate the heterogeneity in gliomas and brain metastasis originating from different sources (lung and breast), we integrated data from three groups of single-cell RNA-sequencing datasets obtained from GEO. We gathered and processed single-cell RNA sequencing data from 90,168 cells obtained from 17 patients. We then employed the R package Seurat for dataset integration. Next, we clustered the data within the UMAP space and acquired differentially expressed genes for cell categorization. Our results underscore the significance of macrophages as abundant and pivotal constituents of gliomas. In contrast, lung-to-brain metastases exhibit elevated numbers of AT2, cytotoxic CD4+ T, and exhausted CD8+ T cells. Conversely, breast-to-brain metastases are characterized by an abundance of epithelial and myCAF cells. Our study not only illuminates the variation in the TME between brain metastasis with different origins but also opens the door to utilizing established markers for these cell types to differentiate primary brain metastatic cancers.

New insights of miRNA molecular mechanisms in breast cancer brain metastasis and therapeutic targets

Brain metastases in breast cancer (BC) patients are often associated with a poor prognosis. Recent studies have uncovered the critical roles of miRNAs in the initiation and progression of BC brain metastasis, highlighting the disease's underlying molecular pathways. miRNA-181c, miRNA-10b, and miRNA-21, for example, are all overexpressed in BC patients. It has been shown that these three miRNAs help tumors grow and metastasize by targeting genes that control how cells work. On the other hand, miRNA-26b5p, miRNA-7, and miRNA-1013p are all downregulated in BC brain metastasis patients. They act as tumor suppressors by controlling the expression of genes related to cell adhesion, angiogenesis, and invasion. Therapeutic miRNA targeting has considerable promise in treating BC brain metastases. Several strategies have been proposed to modulate miRNA expression, including miRNA-Mimics, antagomirs, and small molecule inhibitors of miRNA biogenesis. This review discusses the aberrant expression of miRNAs and metastatic pathways that lead to the spread of BC cells to the brain. It also explores miRNA therapeutic target molecular mechanisms and BC brain metastasis challenges with advanced strategies. The targeting of certain miRNAs opens a new door for the development of novel therapeutic approaches for this devastating disease.

Tumor microenvironment and exosomes in brain metastasis: Molecular mechanisms and clinical application

Metastasis is one of the important biological features of malignant tumors and one of the main factors responsible for poor prognosis. Although the widespread application of newer clinical technologies and their continuous development have significantly improved survival in patients with brain metastases, there is no uniform standard of care. More effective therapeutic measures are therefore needed to improve prognosis. Understanding the mechanisms of tumor cell colonization, growth, and invasion in the central nervous system is of particular importance for the prevention and treatment of brain metastases. This process can be plausibly explained by the “seed and soil” hypothesis, which essentially states that tumor cells can interact with various components of the central nervous system microenvironment to produce adaptive changes; it is this interaction that determines the development of brain metastases. As a novel form of intercellular communication, exosomes play a key role in the brain metastasis microenvironment and carry various bioactive molecules that regulate receptor cell activity. In this paper, we review the roles and prospects of brain metastatic tumor cells, the brain metastatic tumor microenvironment, and exosomes in the development and clinical management of brain metastases.

Intracranial Response Rate in Patients with Breast Cancer Brain Metastases after Systemic Therapy

Simple Summary

For many years, patients with breast cancer and brain metastases were excluded from participation in clinical trials. It was believed that anticancer drugs could not cross the blood–brain barrier. However, recent evidence strongly suggests that some drugs can act against brain metastases, with the greatest intracranial response rate reported in the case of capecitabine, neratinib plus capecitabine, trastuzumab deruxtecan and tucatinib plus trastuzumab and capecitabine. In this article, we discuss the achievements in systemic therapy of breast cancer patients with brain metastases. We stress on the newest clinical trial results which indicate tremendous progress in HER2-positive breast cancer. On the other hand, in patients with triple-negative breast cancer or hormone-receptor-positive brain metastases, much fewer compounds were discovered. Based on the presented results, patients with active brain metastases should be routinely included in clinical trials with novel agents.

Abstract

Brain metastases are detected in 5% of patients with breast cancer at diagnosis. The rate of brain metastases is higher in HER2-positive and triple-negative breast cancer patients (TNBC). In patients with metastatic breast cancer, the risk of brain metastases is much higher, with up to 50% of the patients having two aggressive biological breast cancer subtypes. The prognosis for such patients is poor. Until recently, little was known about the response to systemic therapy in brain metastases. The number of trials dedicated to breast cancer with brain metastases was scarce. Our review summarizes the current knowledge on this topic including very significant results of clinical trials which have been presented very recently. We focus on the intracranial response rate of modern drugs, including new antibody–drug conjugates, HER2- targeted tyrosine kinase inhibitors and other targeted therapies. We highlight the most effective and promising drugs. On the other hand, we also suggest that further efforts are needed to improve the prognosis, especially patients with TNBC and brain metastases. The information contained in this article can help oncologists make treatment-related decisions.

Can stress promote the pathophysiology of brain metastases? A critical review of biobehavioral mechanisms

Chronic stress can promote tumor growth and progression through immunosuppressive effects and bi-directional interactions between tumor cells and their microenvironment. β-Adrenergic receptor signaling plays a critical role in mediating stress-related effects on tumor progression. Stress-related mechanisms that modulate the dissemination of tumor cells to the brain have received scant attention. Brain metastases are highly resistant to chemotherapy and contribute considerably to morbidity and mortality in various cancers, occurring in up to 20% of patients in some cancer types. Understanding the mechanisms promoting brain metastasis could help to identify interventions that improve disease outcomes. In this review, we discuss biobehavioral, sympathetic, neuroendocrine, and immunological mechanisms by which chronic stress can impact tumor progression and metastatic dissemination to the brain. The critical role of the inflammatory tumor microenvironment in tumor progression and metastatic dissemination to the brain, and its association with stress pathways are delineated. We also discuss translational implications for biobehavioral and pharmacological interventions.

Evolving treatment strategies of brain metastases from breast cancer: current status and future direction

Remarkable progress in breast cancer treatment has improved patient survival, resulting in an increased incidence of brain metastasis (BM). Current treatment options for BM are limited and are generally used for palliative purposes. Historically, local treatment, consisting of radiotherapy and surgery, is the standard of care due to delivery limitations of systemic treatments through the blood-brain barrier. However, as novel biological mechanisms for tumors and BM have been discovered, several innovative systemic agents, such as small-molecular-targeted therapy and immunotherapy, have begun to change the treatment paradigm. In addition, efforts to maximize antitumor effects have been attempted using combination therapy, informed by tumor biology. In this comprehensive review, we will highlight various clinical trials investigating the treatment of BM in breast cancer patients, discuss presently available treatment options, and suggest potential directions of future therapeutic targets.

Circulating Tumor Cells Exhibit Metastatic Tropism and Reveal Brain Metastasis Drivers

Hematogenous metastasis is initiated by a subset of circulating tumor cells (CTC) shed from primary or metastatic tumors into the blood circulation. Thus, CTCs provide a unique patient biopsy resource to decipher the cellular subpopulations that initiate metastasis and their molecular properties. However, one crucial question is whether CTCs derived and expanded ex vivo from patients recapitulate human metastatic disease in an animal model. Here, we show that CTC lines established from patients with breast cancer are capable of generating metastases in mice with a pattern recapitulating most major organs from corresponding patients. Genome-wide sequencing analyses of metastatic variants identified semaphorin 4D as a regulator of tumor cell transmigration through the blood-brain barrier and MYC as a crucial regulator for the adaptation of disseminated tumor cells to the activated brain microenvironment. These data provide the direct experimental evidence of the promising role of CTCs as a prognostic factor for site-specific metastasis. SIGNIFICANCE: Interests abound in gaining new knowledge of the physiopathology of brain metastasis. In a direct metastatic tropism analysis, we demonstrated that ex vivo-cultured CTCs from 4 patients with breast cancer showed organotropism, revealing molecular features that allow a subset of CTCs to enter and grow in the brain.This article is highlighted in the In This Issue feature, p. 1.

Oxymatrine Promotes S-Phase Arrest and Inhibits Cell Proliferation of Human Breast Cancer Cells in Vitro through Mitochondria-Mediated Apoptosis

Breast cancer is one of the most lethal malignancies in the world. Oxymatrine is the major effective and toxic alkaloid component which is derived from the root of Sophora flavescens AIT, a traditional Chinese medicine which is widely distributed in Asia and the Pacific Islands. In the current research study, we investigated the effects and mechanisms of action of oxymatrine on breast cancer cells. We demonstrated that the viability and single cell proliferation capability of MCF-7 and MDA-MB-231, two breast cancer cell lines which are widely used in in vitro study, were significantly suppressed in a time- and concentration-dependent manner. Furthermore, the cell cycle of breast cancer cells treated with oxymatrine was arrested at the S-phase of the cell cycle. Oxymatrine also triggered apoptosis in breast cancer cells by modulating apoptosis-related proteins, such as cleaved Caspase-3, cleaved Caspase-9 and poly(ADP-ribose)polymerase (PARP). The remarkable reduction in the ratio of Bcl-2/Bax was also observed in oxymatrine treated breast cancer cells. In conclusion, our research demonstrated that oxymatrine plays a critical role in suppressing carcinogenesis of breast cancer cells through cell cycle arrest and induction of mitochondria-mediated apoptosis, which suggests a promising application of this drug in breast cancer therapy.