Astrocytic laminin-211 drives disseminated breast tumor cell dormancy in brain

Improved Liver Intravital Microscopic Imaging Using a Film-Assisted Stabilization Method

Intravital microscopy (IVM) is a valuable method for biomedical characterization of dynamic processes, which has been applied to many fields such as neuroscience, oncology, and immunology. During IVM, vibration suppression is a major challenge due to the inevitable respiration and heartbeat from live animals. In this study, taking liver IVM as an example, we have unraveled the vibration inhibition effect of liquid bridges by studying the friction characteristics of a moist surface on the mouse liver. We confirmed the presence of liquid bridges on the liver through fluorescence imaging, which can provide microscale and nondestructive liquid connections between adjacent surfaces. Liquid bridges were constructed to sufficiently stabilize the liver after abdominal dissection by covering it with a polymer film, taking advantage of the high adhesion properties of liquid bridges. We further prototyped a microscope-integrated vibration-damping device with adjustable film tension to simplify the sample preparation procedure, which remarkably decreased the liver vibration. In practical application scenarios, we observed the process of liposome phagocytosis by liver Kupffer cells with significantly improved image and video quality. Collectively, our method not only provided a feasible solution to vibration suppression in the field of IVM, but also has the potential to be applied to vibration damping of precision instruments or other fields that require nondestructive ″soft″ vibration damping.

Differential stiffness between brain vasculature and parenchyma promotes metastatic infiltration through vessel co-option

In brain metastasis, cancer cells remain in close contact with the existing vasculature and can use vessels as migratory paths-a process known as vessel co-option. However, the mechanisms regulating this form of migration are poorly understood. Here we use ex vivo brain slices and an organotypic in vitro model for vessel co-option to show that cancer cell invasion along brain vasculature is driven by the difference in stiffness between vessels and the brain parenchyma. Imaging analysis indicated that cells move along the basal surface of vessels by adhering to the basement membrane extracellular matrix. We further show that vessel co-option is enhanced by both the stiffness of brain vasculature, which reinforces focal adhesions through a talin-dependent mechanism, and the softness of the surrounding environment that permits cellular movement. Our work reveals a mechanosensing mechanism that guides cell migration in response to the tissue's intrinsic mechanical heterogeneity, with implications in cancer invasion and metastasis.

Distinct tumor architectures and microenvironments for the initiation of breast cancer metastasis in the brain

Brain metastasis, a serious complication of cancer, hinges on the initial survival, microenvironment adaptation, and outgrowth of disseminated cancer cells. To understand the early stages of brain colonization, we investigated two prevalent sources of cerebral relapse, triple-negative (TNBC) and HER2+ (HER2BC) breast cancers. Using mouse models and human tissue samples, we found that these tumor types colonize the brain, with a preference for distinctive tumor architectures, stromal interfaces, and autocrine programs. TNBC models tend to form perivascular sheaths with diffusive contact with astrocytes and microglia. In contrast, HER2BC models tend to form compact spheroids driven by autonomous tenascin C production, segregating stromal cells to the periphery. Single-cell transcriptomics of the tumor microenvironment revealed that these architectures evoke differential Alzheimer's disease-associated microglia (DAM) responses and engagement of the GAS6 receptor AXL. The spatial features of the two modes of brain colonization have relevance for leveraging the stroma to treat brain metastasis.

Quiescent cancer cells induced by high-density cultivation reveals cholesterol-mediated survival and lung metastatic traits

BACKGROUND

The metastatic cascade, a multifaceted and highly aggressive process, is the primary cause of mortality. The survival of quiescent cancer cells in circulatory system during metastasis is crucial, yet our comprehension is constrained by the absence of universally accepted quiescent cancer models.

METHOD

We developed a quiescent cancer cell model using high-density cultivation. Based on the scRNA-seq analysis, IP-MS, metabolomics, mouse lung metastasis models, cholesterol assay, PLA and other molecular experiments, we explored the molecular mechanism. Immunofluorescence, atomic force microscope, FluidFM, and shear stress stimulation were used to analyze the cytoskeleton and membrane properties contributing to mechanical force resistance.

RESULT

We established a quiescent cancer cell model induced by high-density cultivation. Single-cell RNA sequencing (scRNA-seq) analysis reveals that CDC25A plays a crucial role in the transition to quiescence, with its expression significantly elevated in the quiescent state. Depletion of CDC25A leads to an increased proliferative capacity, and reduced metastasis under high-density conditions. Mechanistically, upregulated CDC25A in quiescent cells enhances cholesterol metabolism via endosome pathways, leading to cell cycle arrest. This increase in cholesterol reinforces the cytoskeleton, alters membrane properties, and improves resistance to mechanical forces in circulatory system.

CONCLUSION

CDC25A significantly increased the cholesterol metabolism through endosome pathway in quiescent cancer cells, leading to the significant changes in cytoskeleton and membrane properties so as to enhance the resistance of mechanical force in circulatory system, facilitating lung metastasis. In high-density cultivation, quiescent cancer cells, up-regulate cholesterol metabolism by CDC25A through endosome pathway, enhancing the resistance to mechanical force in circulatory system, facilitating lung metastasis.

Accessing the vasculature in cancer: revising an old hallmark

The classic cancer hallmark, inducing angiogenesis, was born out of the long-held notion that tumours could grow only if new vessels were formed. The attempts, based on this premise, to therapeutically restrain angiogenesis in hopes of controlling tumour growth have been less effective than expected. This is partly because primary and metastatic tumours can grow without angiogenesis. The discovery of nonangiogenic cancers and the mechanisms they use to exploit normal vessels, called 'vessel co-option,' has opened a new field in cancer biology. Consequently, the cancer hallmark, 'inducing angiogenesis,' has been modified to 'inducing or accessing vasculature.'

Biomechanical properties of laminins and their impact on cancer progression

Laminins (LMs) constitute a family of heterotrimeric glycoproteins essential for the formation of basement membranes (BM). They act as molecular bridges between cells and the extracellular matrix (ECM), thereby transmitting signals influencing cell behavior and tissue organization. In the realm of cancer pathobiology, LMs regulate key processes such as migration, differentiation, or fibrosis. This review critically examines the multifaceted impact of LMs on tumor progression, with a particular focus on the isoform-specific structure-function relationships, and how this structural diversity contributes to the biomechanical properties of BMs. LM interactions with integrin and non-integrin cell surface receptors, as well as with other ECM proteins, modify the response of cancer cells to the ECM stiffness, ultimately influencing the capacity of malignant cells to breach the BM, a limiting step in metastatic dissemination. Comprehension of the mechanisms underlying LM-driven tumor biomechanics holds potential for better understand cancer pathobiology and design new targeted therapeutic strategies.

Multifaceted interactions between cancer cells and glial cells in brain metastasis

Cancer brain metastasis has a poor prognosis, is commonly observed in clinical practice, and the number of cases is increasing as overall cancer survival improves. However, experiments in mouse models have shown that brain metastasis itself is an inefficient process. One reason for this inefficiency is the brain microenvironment, which differs significantly from that of other organs, making it difficult for cancer cells to adapt. The brain microenvironment consists of unique resident cell types such as neurons, oligodendrocytes, astrocytes, and microglia. Accumulating evidence over the past decades suggests that the interactions between cancer cells and glial cells can positively or negatively influence the development of brain metastasis. Nevertheless, elucidating the complex interactions between cancer cells and glial cells remains challenging, in part due to the limitations of existing experimental models for glial cell culture. In this review, we first provide an overview of glial cell culture methods and then examine recent discoveries regarding the interactions between brain metastatic cancer cells and the surrounding glial cells, with a special focus on astrocytes and microglia. Finally, we discuss future perspectives for understanding the multifaceted interactions between cancer cells and glial cells for the treatment of metastatic brain tumors.

Multiphoton fluorescence microscopy for in vivo imaging

Multiphoton fluorescence microscopy (MPFM) has been a game-changer for optical imaging, particularly for studying biological tissues deep within living organisms. MPFM overcomes the strong scattering of light in heterogeneous tissue by utilizing nonlinear excitation that confines fluorescence emission mostly to the microscope focal volume. This enables high-resolution imaging deep within intact tissue and has opened new avenues for structural and functional studies. MPFM has found widespread applications and has led to numerous scientific discoveries and insights into complex biological processes. Today, MPFM is an indispensable tool in many research communities. Its versatility and effectiveness make it a go-to technique for researchers investigating biological phenomena at the cellular and subcellular levels in their native environments. In this Review, the principles, implementations, capabilities, and limitations of MPFM are presented. Three application areas of MPFM, neuroscience, cancer biology, and immunology, are reviewed in detail and serve as examples for applying MPFM to biological research.

Unraveling the Connection: Extracellular Vesicles and Non-Small Cell Lung Cancer

Extracellular vesicles (EVs) are nanoscale lipid bilayer vesicles released during cell activation, cellular damage, or apoptosis. They carry nucleic acids, proteins, and lipids facilitating intercellular communication and activate signaling pathways in target cells. In non-small cell lung cancer (NSCLC), EVs may contribute to tumor growth and metastasis by modulating immune responses, facilitating epithelial-mesenchymal transition, and promoting angiogenesis, while potentially contributing to resistance to chemotherapy drugs. EVs in liquid biopsies serve as non-invasive biomarkers for early cancer detection and diagnosis. Due to their small size, inherent molecular transport properties, and excellent biocompatibility, EVs also act as natural drug delivery vehicles in NSCLC therapy.

Laminin I mediates resistance to lapatinib in HER2-positive brain metastatic breast cancer cells in vitro

The role of extracellular matrix (ECM) prevalent in the brain metastatic breast cancer (BMBC) niche in mediating cancer cell growth, survival, and response to therapeutic agents is not well understood. Emerging evidence suggests a vital role of ECM of the primary breast tumor microenvironment (TME) in tumor progression and survival. Possibly, the BMBC cells are also similarly influenced by the ECM of the metastatic niche; therefore, understanding the effect of the metastatic ECM on BMBC cells is imperative. Herein, we assessed the impact of various ECM components (i.e., Tenascin C, Laminin I, Collagen I, Collagen IV, and Fibronectin) on brain metastatic human epidermal growth factor receptor 2 (HER2)-positive and triple negative breast cancer (TNBC) cell lines in vitro. The highly aggressive TNBC cell line was minimally affected by ECM components exhibiting no remarkable changes in viability and morphology. On the contrary, amongst various ECM components tested, the HER2-positive cell line was significantly affected by Laminin I with higher viability and demonstrated a distinct spread morphology. In addition, HER2-positive BMBC cells exhibited resistance to Lapatinib in presence of Laminin I. Mechanistically, Laminin I-induced resistance to Lapatinib was mediated in part by phosphorylation of Erk 1/2 and elevated levels of Vimentin. Laminin I also significantly enhanced the migratory potential and replicative viability of HER2-positive BMBC cells. In sum, our findings show that presence of Laminin I in the TME of BMBC cells imparts resistance to targeted therapeutic agent Lapatinib, while increasing the possibility of its dispersal and clonogenic survival.

Role of Extracellular Vesicles in the Progression of Brain Tumors

Brain tumors, and, in particular, glioblastoma (GBM), are among the most aggressive forms of cancer. In spite of the advancement in the available therapies, both diagnosis and treatments are still unable to ensure pathology-free survival of the GBM patients for more than 12-15 months. At the basis of the still poor ability to cope with brain tumors, we can consider: (i) intra-tumor heterogeneity; (ii) heterogeneity of the tumor properties when we compare different patients; (iii) the blood-brain barrier (BBB), which makes difficult both isolation of tumor-specific biomarkers and delivering of therapeutic drugs to the brain. Recently, it is becoming increasingly clear that cancer cells release large amounts of extracellular vesicles (EVs) that transport metabolites, proteins, different classes of RNAs, DNA, and lipids. These structures are involved in the pathological process and characterize any particular form of cancer. Moreover, EVs are able to cross the BBB in both directions. Starting from these observations, researchers are now evaluating the possibility to use EVs purified from organic fluids (first of all, blood and saliva), in order to obtain, through non-invasive methods (liquid biopsy), tumor biomarkers, and, perhaps, also for obtaining nanocarriers for the targeted delivering of drugs.

Mouse Models of Metastasis and Dormancy

Metastasis is the ultimate and often lethal stage of cancer. Metastasis occurs in three phases that may vary across individuals: First, dissemination from the primary tumor. Second, tumor dormancy at the metastatic site where micrometastatic cancer cells remain quiescent or, in dynamic cycles of proliferation and elimination, remaining clinically undetectable. Finally, cancer cells are able to overcome microenvironmental constraints for outgrowth, or the formation of clinically detectable macrometastases that colonize distant organs and are largely incurable. A variety of approaches have been used to model metastasis to elucidate molecular mechanisms and identify putative therapeutic targets. In particular, metastatic dormancy has been challenging to model in vivo due to the sparse numbers of cancer cells in micrometastasis nodules and the long latency times required for tumor outgrowth. Here, we review state-of-the art genetically engineered mouse, syngeneic, and patient-derived xenograft approaches for modeling metastasis and dormancy. We describe the advantages and limitations of various metastasis models, novel findings enabled by such approaches, and highlight opportunities for future improvement.

Matrix stiffness influences response to chemo and targeted therapy in brain metastatic breast cancer cells

Breast cancer is the most common malignancy accounting for 12.5% of all newly diagnosed cancer cases across the globe. Breast cancer cells are known to metastasize to distant organs (i.e., brain), wherein they can exhibit a dormant phenotype for extended time periods. These dormant cancer cells exhibit reduced proliferation and therapeutic resistance. However, the mechanisms by which dormant cancer cells exhibit resistance to therapy, in the context of brain metastatic breast cancer (BMBC), is not well understood. Herein, we utilized hyaluronic acid (HA) hydrogels with varying stiffnesses to study drug responsiveness in dormant vs. proliferative BMBC cells. It was found that cells cultured on soft HA hydrogels (∼0.4 kPa) that showed a non-proliferative (dormant) phenotype exhibited resistance to Paclitaxel or Lapatinib. In contrast, cells cultured on stiff HA hydrogels (∼4.5 kPa) that showed a proliferative phenotype exhibited responsiveness to Paclitaxel or Lapatinib. Moreover, dormancy-associated resistance was found to be due to upregulation of the serum/glucocorticoid regulated kinase 1 (SGK1) gene which was mediated, in part, by the p38 signaling pathway. Accordingly, SGK1 inhibition resulted in a dormant-to-proliferative switch and response to therapy. Overall, our study demonstrates that matrix stiffness influences dormancy-associated therapy response mediated, in part, via the p38/SGK1 axis.

Protocol for generating dormant human brain metastatic breast cancer spheroids in vitro

Here, we present a protocol to generate dormant brain metastatic breast cancer (BMBC) spheroids utilizing hyaluronic acid (HA) hydrogels. We describe the steps for construction of spheroids from human BMBC cell lines MDA-MB-231Br and BT474Br3, HA hydrogel preparation, and spheroid plating on HA hydrogels and in suspension culture. We then detail the impact of HA hydrogel on the dormant phenotype of spheroids by measuring spheroid cross-sectional area, cell numbers, and EdU staining. For complete details on the use and execution of this protocol, please refer to Kondapaneni et al.1.

Breast cancer exploits neural signaling pathways for bone-to-meninges metastasis

The molecular mechanisms that regulate breast cancer cell (BCC) metastasis and proliferation within the leptomeninges (LM) are poorly understood, which limits the development of effective therapies. In this work, we show that BCCs in mice can invade the LM by abluminal migration along blood vessels that connect vertebral or calvarial bone marrow and meninges, bypassing the blood-brain barrier. This process is dependent on BCC engagement with vascular basement membrane laminin through expression of the neuronal pathfinding molecule integrin α6. Once in the LM, BCCs colocalize with perivascular meningeal macrophages and induce their expression of the prosurvival neurotrophin glial-derived neurotrophic factor (GDNF). Intrathecal GDNF blockade, macrophage-specific GDNF ablation, or deletion of the GDNF receptor neural cell adhesion molecule (NCAM) from BCCs inhibits breast cancer growth within the LM. These data suggest integrin α6 and the GDNF signaling axis as new therapeutic targets against breast cancer LM metastasis.

From pre-clinical to translational brain metastasis research: current challenges and emerging opportunities

Brain metastasis, characterized by poor clinical outcomes, is a devastating disease. Despite significant mechanistic and therapeutic advances in recent years, pivotal improvements in clinical interventions have remained elusive. The heterogeneous nature of the primary tumor of origin, complications in drug delivery across the blood-brain barrier, and the distinct microenvironment collectively pose formidable clinical challenges in developing new treatments for patients with brain metastasis. Although current preclinical models have deepened our basic understanding of the disease, much of the existing research on brain metastasis has employed a reductionist approach. This approach, which often relies on either in vitro systems or in vivo injection models in young and treatment-naive mouse models, does not give sufficient consideration to the clinical context. Given the translational importance of brain metastasis research, we advocate for the design of preclinical experimental models that take into account these unique clinical challenges and align more closely with current clinical practices. We anticipate that aligning and simulating real-world patient conditions will facilitate the development of more translatable treatment regimens. This brief review outlines the most pressing clinical challenges, the current state of research in addressing them, and offers perspectives on innovative metastasis models and tools aimed at identifying novel strategies for more effective management of clinical brain metastasis.

Advances in the molecular regulation mechanism of tumor dormancy and its therapeutic strategy

Tumor dormancy is a stage in the growth and development of malignant cells and is one of the biological characteristics of malignant cells. Complex transitions involving dormant tumor cells between quiescent and proliferative states pose challenges for tumor eradication. This paper explores the biological features and molecular mechanisms of tumor dormancy and highlights emerging therapies. The strategies discussed promise innovative clinical potential against malignant tumors. Understanding the mechanisms of dormancy can help provide valuable insights into the diagnosis and treatment of malignant tumors to advance the fight against this world problem.

Lung endothelium exploits susceptible tumor cell states to instruct metastatic latency

In metastasis, cancer cells travel around the circulation to colonize distant sites. Due to the rarity of these events, the immediate fates of metastasizing tumor cells (mTCs) are poorly understood while the role of the endothelium as a dissemination interface remains elusive. Using a newly developed combinatorial mTC enrichment approach, we provide a transcriptional blueprint of the early colonization process. Following their arrest at the metastatic site, mTCs were found to either proliferate intravascularly or extravasate, thereby establishing metastatic latency. Endothelial-derived angiocrine Wnt factors drive this bifurcation, instructing mTCs to follow the extravasation-latency route. Surprisingly, mTC responsiveness towards niche-derived Wnt was established at the epigenetic level, which predetermined tumor cell behavior. Whereas hypomethylation enabled high Wnt activity leading to metastatic latency, methylated mTCs exhibited low activity and proliferated intravascularly. Collectively the data identify the predetermined methylation status of disseminated tumor cells as a key regulator of mTC behavior in the metastatic niche.

Unveiling cancer dormancy: Intrinsic mechanisms and extrinsic forces

Tumor cells disseminate in various distant organs at early stages of cancer progression. These disseminated tumor cells (DTCs) can stay dormant/quiescent without causing patient symptoms for years or decades. These dormant tumor cells survive despite curative treatments by entering growth arrest, escaping immune surveillance, and/or developing drug resistance. However, these dormant cells can reactivate to proliferate, causing metastatic progression and/or relapse, posing a threat to patients' survival. It's unclear how cancer cells maintain dormancy and what triggers their reactivation. What are better approaches to prevent metastatic progression and relapse through harnessing cancer dormancy? To answer these remaining questions, we reviewed the studies of tumor dormancy and reactivation in various types of cancer using different model systems, including the brief history of dormancy studies, the intrinsic characteristics of dormant cells, and the external cues at the cellular and molecular levels. Furthermore, we discussed future directions in the field and the strategies for manipulating dormancy to prevent metastatic progression and recurrence.

Embracing cancer complexity: Hallmarks of systemic disease

The last 50 years have witnessed extraordinary developments in understanding mechanisms of carcinogenesis, synthesized as the hallmarks of cancer. Despite this logical framework, our understanding of the molecular basis of systemic manifestations and the underlying causes of cancer-related death remains incomplete. Looking forward, elucidating how tumors interact with distant organs and how multifaceted environmental and physiological parameters impinge on tumors and their hosts will be crucial for advances in preventing and more effectively treating human cancers. In this perspective, we discuss complexities of cancer as a systemic disease, including tumor initiation and promotion, tumor micro- and immune macro-environments, aging, metabolism and obesity, cancer cachexia, circadian rhythms, nervous system interactions, tumor-related thrombosis, and the microbiome. Model systems incorporating human genetic variation will be essential to decipher the mechanistic basis of these phenomena and unravel gene-environment interactions, providing a modern synthesis of molecular oncology that is primed to prevent cancers and improve patient quality of life and cancer outcomes.

Astrocyte-induced mGluR1 activates human lung cancer brain metastasis via glutamate-dependent stabilization of EGFR

There are limited methods to stably analyze the interactions between cancer cells and glial cells in vitro, which hinders our molecular understanding. Here, we develop a simple and stable culture method of mouse glial cells, termed mixed-glial culture on/in soft substrate (MGS), which serves well as a platform to study cancer-glia interactions. Using this method, we find that human lung cancer cells become overly dependent on metabotropic glutamate receptor 1 (mGluR1) signaling in the brain microenvironment. Mechanistically, interactions with astrocytes induce mGluR1 in cancer cells through the Wnt-5a/prickle planar cell polarity protein 1 (PRICKLE1)/RE1 silencing transcription factor (REST) axis. Induced mGluR1 directly interacts with and stabilizes the epidermal growth factor receptor (EGFR) in a glutamate-dependent manner, and these cells then become responsive to mGluR1 inhibition. Our results highlight increased dependence on mGluR1 signaling as an adaptive strategy and vulnerability of human lung cancer brain metastasis.

Outlook and opportunities for engineered environments of breast cancer dormancy

Dormant, disseminated breast cancer cells resist treatment and may relapse into malignant metastases after decades of quiescence. Identifying how and why these dormant breast cancer cells are triggered into outgrowth is a key unsolved step in treating latent, metastatic breast cancer. However, our understanding of breast cancer dormancy in vivo is limited by technical challenges and ethical concerns with triggering the activation of dormant breast cancer. In vitro models avoid many of these challenges by simulating breast cancer dormancy and activation in well-controlled, bench-top conditions, creating opportunities for fundamental insights into breast cancer biology that complement what can be achieved through animal and clinical studies. In this review, we address clinical and preclinical approaches to treating breast cancer dormancy, how precisely controlled artificial environments reveal key interactions that regulate breast cancer dormancy, and how future generations of biomaterials could answer further questions about breast cancer dormancy.

It's all about the base: stromal cells are central orchestrators of metastasis

The tumor microenvironment (TME) is an integral part of tumors and plays a central role in all stages of carcinogenesis and progression. Each organ has a unique and heterogeneous microenvironment, which affects the ability of disseminated cells to grow in the new and sometimes hostile metastatic niche. Resident stromal cells, such as fibroblasts, osteoblasts, and astrocytes, are essential culprits in the modulation of metastatic progression: they transition from being sentinels of tissue integrity to being dysfunctional perpetrators that support metastatic outgrowth. Therefore, better understanding of the complexity of their reciprocal interactions with cancer cells and with other components of the TME is essential to enable the design of novel therapeutic approaches to prevent metastatic relapse.

Epigenetic alterations fuel brain metastasis via regulating inflammatory cascade

Brain metastasis (BrM) is a major threat to the survival of melanoma, breast, and lung cancer patients. Circulating tumor cells (CTCs) cross the blood-brain barrier (BBB) and sustain in the brain microenvironment. Genetic mutations and epigenetic modifications have been found to be critical in controlling key aspects of cancer metastasis. Metastasizing cells confront inflammation and gradually adapt in the unique brain microenvironment. Currently, it is one of the major areas that has gained momentum. Researchers are interested in the factors that modulate neuroinflammation during BrM. We review here various epigenetic factors and mechanisms modulating neuroinflammation and how this helps CTCs to adapt and survive in the brain microenvironment. Since epigenetic changes could be modulated by targeting enzymes such as histone/DNA methyltransferase, deacetylases, acetyltransferases, and demethylases, we also summarize our current understanding of potential drugs targeting various aspects of epigenetic regulation in BrM.

Cell cycle control by cell-matrix interactions

Cell adhesion to the extracellular matrix (ECM) is required for normal cell cycle progression and accurate cell division. However, how cell adhesion to the wide range of ECM proteins found in human tissues influences the cell cycle is not fully understood. The composition and physical properties of the ECM can have profound effects on cell proliferation but can also promote cell cycle exit and quiescence. Furthermore, during tumor development and progression, changes in the ECM can drive both cancer cell proliferation and dormancy. Cell-matrix adhesion is primarily sensed via integrin-associated adhesion complexes, which in turn are regulated by the cell cycle machinery. In particular, cyclin-dependent kinase 1 (CDK1) has been shown to play a crucial role in regulating adhesion complexes during interphase and entry into mitosis. These reciprocal links between cell cycle progression and cell-matrix interactions are now being identified.

Cell-cell communication characteristics in breast cancer metastasis

Breast cancer, a highly fatal disease due to its tendency to metastasize, is the most prevalent form of malignant tumors among women worldwide. Numerous studies indicate that breast cancer exhibits a unique predilection for metastasis to specific organs including the bone, liver, lung, and brain. However, different types of, The understanding of the heterogeneity of metastatic breast cancer has notably improved with the recent advances in high-throughput sequencing techniques. Focusing on the modification in the microenvironment of the metastatic organs and the crosstalk between tumor cells and in situ cells, noteworthy research points include the identification of two distinct modes of tumor growth in bone metastases, the influence of type II pneumocyte on lung metastases, the paradoxical role of Kupffer cells in liver metastases, and the breakthrough of the blood-brain barrier (BBB) breach in brain metastases. Overall, this review provides a comprehensive overview of the characteristics of breast cancer metastases, shedding light on the pivotal roles of immune and resident cells in the development of distinct metastatic foci.

New insights into the correlations between circulating tumor cells and target organ metastasis

Organ-specific metastasis is the primary cause of cancer patient death. The distant metastasis of tumor cells to specific organs depends on both the intrinsic characteristics of the tumor cells and extrinsic factors in their microenvironment. During an intermediate stage of metastasis, circulating tumor cells (CTCs) are released into the bloodstream from primary and metastatic tumors. CTCs harboring aggressive or metastatic features can extravasate to remote sites for continuous colonizing growth, leading to further lesions. In the past decade, numerous studies demonstrated that CTCs exhibited huge clinical value including predicting distant metastasis, assessing prognosis and monitoring treatment response et al. Furthermore, increasingly numerous experiments are dedicated to identifying the key molecules on or inside CTCs and exploring how they mediate CTC-related organ-specific metastasis. Based on the above molecules, more and more inhibitors are being developed to target CTCs and being utilized to completely clean CTCs, which should provide promising prospects to administer advanced tumor. Recently, the application of various nanomaterials and microfluidic technologies in CTCs enrichment technology has assisted to improve our deep insights into the phenotypic characteristics and biological functions of CTCs as a potential therapy target, which may pave the way for us to make practical clinical strategies. In the present review, we mainly focus on the role of CTCs being involved in targeted organ metastasis, especially the latest molecular mechanism research and clinical intervention strategies related to CTCs.

The Interaction of LAMA2 and Duration of Illness Affects the Thickness of the Right Transverse Temporal Gyrus in Major Depressive Disorder

Background

Depression is a heritable brain disorder. Laminin genes were recently identified to affect the brain's overall thickness through neurogenesis, differentiation, and migration in depression. This study aims to explore the effects of the LAMA2's single nucleotide polymorphisms (SNP), a subunit gene of laminin, on the detected brain regions of patients with major depressive disorder (MDD).

Methods

The study included 89 patients with MDD and 60 healthy controls with T1-weighted structural magnetic resonance imaging and blood samples for genotyping. The interactions between LAMA2 gene SNPs and diagnosis as well as duration of illness (DOI) were explored on brain measures controlled for age, gender, and site.

Results

The right transverse temporal gyrus and right parahippocampal gyrus showed reduced thickness in MDD. Almost all seven LAMA2 SNPs showed significant interactions with diagnosis on both gyrus (corrected p < 0.05 or trending). In MDD, rs6569604, rs2229848, rs2229849, rs2229850, and rs2784895 interacted with DOI on the right transverse temporal gyrus (corrected p < 0.05), but not the right parahippocampal gyrus.

Conclusion

The thickness of the right transverse temporal gyrus in patients with MDD may be affected by LAMA2 gene and DOI.

Harnessing immunotherapy for brain metastases: insights into tumor-brain microenvironment interactions and emerging treatment modalities

Brain metastases signify a deleterious milestone in the progression of several advanced cancers, predominantly originating from lung, breast and melanoma malignancies, with a median survival timeframe nearing six months. Existing therapeutic regimens yield suboptimal outcomes; however, burgeoning insights into the tumor microenvironment, particularly the immunosuppressive milieu engendered by tumor-brain interplay, posit immunotherapy as a promising avenue for ameliorating brain metastases. In this review, we meticulously delineate the research advancements concerning the microenvironment of brain metastases, striving to elucidate the panorama of their onset and evolution. We encapsulate three emergent immunotherapeutic strategies, namely immune checkpoint inhibition, chimeric antigen receptor (CAR) T cell transplantation and glial cell-targeted immunoenhancement. We underscore the imperative of aligning immunotherapy development with in-depth understanding of the tumor microenvironment and engendering innovative delivery platforms. Moreover, the integration with established or avant-garde physical methodologies and localized applications warrants consideration in the prevailing therapeutic schema.

From adhesion complex to signaling hub: the dual role of dystroglycan

Dystroglycan (DG) is a transmembrane protein widely expressed in multiple cells and tissues. It is formed by two subunits, α- and β-DG, and represents a molecular bridge between the outside and the inside of the cell, which is essential for the mechanical and structural stability of the plasma membrane. The α-subunit is a cell-surface protein that binds to the extracellular matrix (ECM) and is tightly associated with the plasma membrane via a non-covalent interaction with the β-subunit, which, in turn, is a transmembrane protein that binds to the cytoskeletal actin. DG is a versatile molecule acting not only as a mechanical building block but also as a modulator of outside-inside signaling events. The cytoplasmic domain of β-DG interacts with different adaptor and cytoskeletal proteins that function as molecular switches for the transmission of ECM signals inside the cells. These interactions can modulate the involvement of DG in different biological processes, ranging from cell growth and survival to differentiation and proliferation/regeneration. Although the molecular events that characterize signaling through the ECM-DG-cytoskeleton axis are still largely unknown, in recent years, a growing list of evidence has started to fill the gaps in our understanding of the role of DG in signal transduction. This mini-review represents an update of recent developments, uncovering the dual role of DG as an adhesion and signaling molecule that might inspire new ideas for the design of novel therapeutic strategies for pathologies such as muscular dystrophy, cardiomyopathy, and cancer, where the DG signaling hub plays important roles.

New Insights into YAP/TAZ-TEAD-Mediated Gene Regulation and Biological Processes in Cancer

The Hippo pathway is conserved across species. Key mammalian Hippo pathway kinases, including MST1/2 and LATS1/2, inhibit cellular growth by inactivating the TEAD coactivators, YAP, and TAZ. Extensive research has illuminated the roles of Hippo signaling in cancer, development, and regeneration. Notably, dysregulation of Hippo pathway components not only contributes to tumor growth and metastasis, but also renders tumors resistant to therapies. This review delves into recent research on YAP/TAZ-TEAD-mediated gene regulation and biological processes in cancer. We focus on several key areas: newly identified molecular patterns of YAP/TAZ activation, emerging mechanisms that contribute to metastasis and cancer therapy resistance, unexpected roles in tumor suppression, and advances in therapeutic strategies targeting this pathway. Moreover, we provide an updated view of YAP/TAZ's biological functions, discuss ongoing controversies, and offer perspectives on specific debated topics in this rapidly evolving field.

Recent progress on the effect of extracellular matrix on occurrence and progression of breast cancer

Breast cancer (BC) metastasis is an enormous challenge targeting BC therapy. The extracellular matrix (ECM), the principal component of the BC metastasis niche, is the pivotal driver of breast tumor development, whose biochemical and biophysical characteristics have attracted widespread attention. Here, we review the biological effects of ECM constituents and the influence of ECM stiffness on BC metastasis and drug resistance. We provide an overview of the relative signal transduction mechanisms, existing metastasis models, and targeted drug strategies centered around ECM stiffness. It will shed light on exploring more underlying targets and developing specific drugs aimed at ECM utilizing biomimetic platforms, which are promising for breast cancer treatment.

Dormancy in Breast Cancer

The pattern of delayed recurrence in a subset of breast cancer patients has long been explained by a model that incorporates a variable period of cellular or tumor mass dormancy prior to disease relapse. In this review, we critically evaluate existing data to develop a framework for inferring the existence of dormancy in clinical contexts of breast cancer. We integrate these clinical data with rapidly evolving mechanistic insights into breast cancer dormancy derived from a broad array of genetically engineered mouse models as well as experimental models of metastasis. Finally, we propose actionable interventions and discuss ongoing clinical trials that translate the wealth of knowledge gained in the laboratory to the long-term clinical management of patients at a high risk of developing recurrence.

Critical functions of extracellular matrix in brain metastasis seeding

Human brain is characterized by extremely sparse extracellular matrix (ECM). Despite its low abundance, the significance of brain ECM in both physiological and pathological conditions should not be underestimated. Brain metastasis is a serious complication of cancer, and recent findings highlighted the contribution of ECM in brain metastasis development. In this review, we provide a comprehensive outlook on how ECM proteins promote brain metastasis seeding. In particular, we discuss (1) disruption of the blood-brain barrier in brain metastasis; (2) role of ECM in modulating brain metastasis dormancy; (3) regulation of brain metastasis seeding by ECM-activated integrin signaling; (4) functions of brain-specific ECM protein reelin in brain metastasis. Lastly, we consider the possibility of targeting ECM for brain metastasis management.

The origin of brain malignancies at the blood-brain barrier

Despite improvements in extracranial therapy, survival rate for patients suffering from brain metastases remains very poor. This is coupled with the incidence of brain metastases continuing to rise. In this review, we focus on core contributions of the blood-brain barrier to the origin of brain metastases. We first provide an overview of the structure and function of the blood-brain barrier under physiological conditions. Next, we discuss the emerging idea of a pre-metastatic niche, namely that secreted factors and extracellular vesicles from a primary tumor site are able to travel through the circulation and prime the neurovasculature for metastatic invasion. We then consider the neurotropic mechanisms that circulating tumor cells possess or develop that facilitate disruption of the blood-brain barrier and survival in the brain's parenchyma. Finally, we compare and contrast brain metastases at the blood-brain barrier to the primary brain tumor, glioma, examining the process of vessel co-option that favors the survival and outgrowth of brain malignancies.

A new time dimension in the fight against metastasis

Despite advances in uncovering vulnerabilities, identifying biomarkers, and developing more efficient treatments, cancer remains a threat because of its ability to progress while acquiring resistance to therapy. The circadian rhythm governs most of the cellular functions implicated in cancer progression, and its exploitation therefore opens new promising directions in the fight against metastasis. In this review we summarize the role of the circadian rhythm in tumor development and progression, with emphasis on the circadian rhythm-regulated elements that control the generation of circulating tumor cells (CTCs) and metastasis. We then present data on chronotherapy and discuss how circadian rhythm investigations may open new paths to more effective anticancer treatments.

Molecular signaling network and therapeutic developments in breast cancer brain metastasis

Breast cancer (BC) is one of the most frequently diagnosed cancers in women worldwide. It has surpassed lung cancer as the leading cause of cancer-related death. Breast cancer brain metastasis (BCBM) is becoming a major clinical concern that is commonly associated with ER-ve and HER2+ve subtypes of BC patients. Metastatic lesions in the brain originate when the cancer cells detach from a primary breast tumor and establish metastatic lesions and infiltrate near and distant organs via systemic blood circulation by traversing the BBB. The colonization of BC cells in the brain involves a complex interplay in the tumor microenvironment (TME), metastatic cells, and brain cells like endothelial cells, microglia, and astrocytes. BCBM is a significant cause of morbidity and mortality and presents a challenge to developing successful cancer therapy. In this review, we discuss the molecular mechanism of BCBM and novel therapeutic strategies for patients with brain metastatic BC.

Biglycan and reduced glycolysis are associated with breast cancer cell dormancy in the brain

Exit of quiescent disseminated cancer cells from dormancy is thought to be responsible for metastatic relapse and a better understanding of dormancy could pave the way for novel therapeutic approaches. We used an in vivo model of triple negative breast cancer brain metastasis to identify differences in transcriptional profiles between dormant and proliferating cancer cells in the brain. BGN gene, encoding a small proteoglycan biglycan, was strongly upregulated in dormant cancer cells in vivo. BGN expression was significantly downregulated in patient brain metastases as compared to the matched primary breast tumors and BGN overexpression in cancer cells inhibited their growth in vitro and in vivo. Dormant cancer cells were further characterized by a reduced expression of glycolysis genes in vivo, and inhibition of glycolysis in vitro resulted in a reversible growth arrest reminiscent of dormancy. Our study identified mechanisms that could be targeted to induce/maintain cancer dormancy and thereby prevent metastatic relapse.

The covert symphony: cellular and molecular accomplices in breast cancer metastasis

Breast cancer has emerged as the most commonly diagnosed cancer and primary cause of cancer-related deaths among women worldwide. Although significant progress has been made in targeting the primary tumor, the effectiveness of systemic treatments to prevent metastasis remains limited. Metastatic disease continues to be the predominant factor leading to fatality in the majority of breast cancer patients. The existence of a prolonged latency period between initial treatment and eventual recurrence in certain patients indicates that tumors can both adapt to and interact with the systemic environment of the host, facilitating and sustaining the progression of the disease. In order to identify potential therapeutic interventions for metastasis, it will be crucial to gain a comprehensive framework surrounding the mechanisms driving the growth, survival, and spread of tumor cells, as well as their interaction with supporting cells of the microenvironment. This review aims to consolidate recent discoveries concerning critical aspects of breast cancer metastasis, encompassing the intricate network of cells, molecules, and physical factors that contribute to metastasis, as well as the molecular mechanisms governing cancer dormancy.

Metastasis

Most cancer-associated deaths occur due to metastasis, yet our understanding of metastasis as an evolving, heterogeneous, systemic disease and of how to effectively treat it is still emerging. Metastasis requires the acquisition of a succession of traits to disseminate, variably enter and exit dormancy, and colonize distant organs. The success of these events is driven by clonal selection, the potential of metastatic cells to dynamically transition into distinct states, and their ability to co-opt the immune environment. Here, we review the main principles of metastasis and highlight emerging opportunities to develop more effective therapies for metastatic cancer.

The evolving tumor microenvironment: From cancer initiation to metastatic outgrowth

Cancers represent complex ecosystems comprising tumor cells and a multitude of non-cancerous cells, embedded in an altered extracellular matrix. The tumor microenvironment (TME) includes diverse immune cell types, cancer-associated fibroblasts, endothelial cells, pericytes, and various additional tissue-resident cell types. These host cells were once considered bystanders of tumorigenesis but are now known to play critical roles in the pathogenesis of cancer. The cellular composition and functional state of the TME can differ extensively depending on the organ in which the tumor arises, the intrinsic features of cancer cells, the tumor stage, and patient characteristics. Here, we review the importance of the TME in each stage of cancer progression, from tumor initiation, progression, invasion, and intravasation to metastatic dissemination and outgrowth. Understanding the complex interplay between tumor cell-intrinsic, cell-extrinsic, and systemic mediators of disease progression is critical for the rational development of effective anti-cancer treatments.

Regulation of dormancy during tumor dissemination: the role of the ECM

The study of the metastatic cascade has revealed the complexity of the process and the multiple cellular states that disseminated cancer cells must go through. The tumor microenvironment and in particular the extracellular matrix (ECM) plays an important role in regulating the transition from invasion, dormancy to ultimately proliferation during the metastatic cascade. The time delay from primary tumor detection to metastatic growth is regulated by a molecular program that maintains disseminated tumor cells in a non-proliferative, quiescence state known as tumor cell dormancy. Identifying dormant cells and their niches in vivo and how they transition to the proliferative state is an active area of investigation, and novel approaches have been developed to track dormant cells during dissemination. In this review, we highlight the latest research on the invasive nature of disseminated tumor cells and their link to dormancy programs. We also discuss the role of the ECM in sustaining dormant niches at distant sites.

Dormant cancer cells: programmed quiescence, senescence, or both?

Metastasis is the overwhelming driver of cancer mortality, accounting for the majority of cancer deaths. Many patients present with metastatic relapse years after eradication of the primary lesion. Disseminated cancer cells can undergo a durable proliferative arrest and lie dormant in secondary tissues before reentering the cell cycle to seed these lethal relapses. This process of cancer cell dormancy remains poorly understood, largely due to difficulties in studying these dormant cells. In the face of these challenges, the application of knowledge from the cellular senescence and quiescence fields may help to guide future thinking on the study of dormant cancer cells. Both senescence and quiescence are common programs of proliferative arrest that are integral to tissue development and homeostasis. Despite phenotypic differences, these two states also share common characteristics, and both likely play a role in cancer dormancy and delayed metastatic relapse. Understanding the cell biology behind these states, their overlaps and unique characteristics is critical to our future understanding of dormant cancer cells, as these cells likely employ some of the same molecular programs to promote survival and dissemination. In this review, we highlight the biology underlying these non-proliferative states, relate this knowledge to what we currently know about dormant cancer cells, and discuss implications for future work toward targeting these elusive metastatic seeds.

The genomic regulation of metastatic dormancy

The genomics and pathways governing metastatic dormancy are critically important drivers of long-term patient survival given the considerable portion of cancers that recur aggressively months to years after initial treatments. Our understanding of dormancy has expanded greatly in the last two decades, with studies elucidating that the dormant state is regulated by multiple genes, microenvironmental (ME) interactions, and immune components. These forces are exerted through mechanisms that are intrinsic to the tumor cell, manifested through cross-talk between tumor and ME cells including those from the immune system, and regulated by angiogenic processes in the nascent micrometastatic niche. The development of new in vivo and 3D ME models, as well as enhancements to decades-old tumor cell pedigree models that span the development of metastatic dormancy to aggressive growth, has helped fuel what arguably is one of the least understood areas of cancer biology that nonetheless contributes immensely to patient mortality. The current review focuses on the genes and molecular pathways that regulate dormancy via tumor-intrinsic and ME cells, and how groups have envisioned harnessing these therapeutically to benefit patient survival.

The Journey of Cancer Cells to the Brain: Challenges and Opportunities

Cancer metastases into the brain constitute one of the most severe, but not uncommon, manifestations of cancer progression. Several factors control how cancer cells interact with the brain to establish metastasis. These factors include mediators of signaling pathways participating in migration, infiltration of the blood-brain barrier, interaction with host cells (e.g., neurons, astrocytes), and the immune system. Development of novel therapies offers a glimpse of hope for increasing the diminutive life expectancy currently forecasted for patients suffering from brain metastasis. However, applying these treatment strategies has not been sufficiently effective. Therefore, there is a need for a better understanding of the metastasis process to uncover novel therapeutic targets. In this review, we follow the journey of various cancer cells from their primary location through the diverse processes that they undergo to colonize the brain. These processes include EMT, intravasation, extravasation, and infiltration of the blood-brain barrier, ending up with colonization and angiogenesis. In each phase, we focus on the pathways engaging molecules that potentially could be drug target candidates.

M2-like macrophage-derived exosomes facilitate metastasis in non-small-cell lung cancer by delivering integrin αVβ3

Metastasis is the most prevalent cause of cancer deaths, and immunological components of the tumor microenvironment, especially tumor-associated macrophages (TAMs), play a vital role in cancer metastasis. However, the underlying mechanisms of TAMs on non-small-cell lung cancer (NSCLC) metastasis remain largely unexplored. Herein, we demonstrated that M2-like TAMs facilitate the migration and invasion of cancer cells in vitro and in vivo through intercellular delivery of M2-like macrophage-derived exosomes (M2-exos). Importantly, we found that M2-exos had considerably higher levels of integrin (ITG) αV and β3. The impact of M2-like macrophage-mediated invasion and migration of NSCLC cells was clearly decreased when ITG αVβ3 was blocked. Mechanistically, exosomal ITG αVβ3 produced from M2-like macrophages successfully triggered the focal adhesion kinase signaling pathway in recipient cells, boosting the migratory and invasive abilities of NSCLC cells. Clinically, we found that metastatic NSCLC patients had greater ITG αV and β3 expression, which was associated with a worse prognosis. This study reveals a novel mechanism by which M2-exos significantly increased NSCLC cell migration and invasion by delivering integrin αVβ3. Exosomal ITG αVβ3 can be used as a potential prognostic marker, and blocking ITG αVβ3 could be a viable treatment option for preventing tumor metastasis.

Biology, vulnerabilities and clinical applications of circulating tumour cells

In recent years, exceptional technological advances have enabled the identification and interrogation of rare circulating tumour cells (CTCs) from blood samples of patients, leading to new fields of research and fostering the promise for paradigm-changing, liquid biopsy-based clinical applications. Analysis of CTCs has revealed distinct biological phenotypes, including the presence of CTC clusters and the interaction between CTCs and immune or stromal cells, impacting metastasis formation and providing new insights into cancer vulnerabilities. Here we review the progress made in understanding biological features of CTCs and provide insight into exploiting these developments to design future clinical tools for improving the diagnosis and treatment of cancer.

Distinct tumor architectures for metastatic colonization of the brain

Brain metastasis is a dismal cancer complication, hinging on the initial survival and outgrowth of disseminated cancer cells. To understand these crucial early stages of colonization, we investigated two prevalent sources of cerebral relapse, triple-negative (TNBC) and HER2+ breast cancer (HER2BC). We show that these tumor types colonize the brain aggressively, yet with distinct tumor architectures, stromal interfaces, and autocrine growth programs. TNBC forms perivascular sheaths with diffusive contact with astrocytes and microglia. In contrast, HER2BC forms compact spheroids prompted by autonomous extracellular matrix components and segregating stromal cells to their periphery. Single-cell transcriptomic dissection reveals canonical Alzheimer's disease-associated microglia (DAM) responses. Differential engagement of tumor-DAM signaling through the receptor AXL suggests specific pro-metastatic functions of the tumor architecture in both TNBC perivascular and HER2BC spheroidal colonies. The distinct spatial features of these two highly efficient modes of brain colonization have relevance for leveraging the stroma to treat brain metastasis.

Intravital imaging to study cancer progression and metastasis

Navigation through the bulk tumour, entry into the blood vasculature, survival in the circulation, exit at distant sites and resumption of proliferation are all steps necessary for tumour cells to successfully metastasize. The ability of tumour cells to complete these steps is highly dependent on the timing and sequence of the interactions that these cells have with the tumour microenvironment (TME), including stromal cells, the extracellular matrix and soluble factors. The TME thus plays a major role in determining the overall metastatic phenotype of tumours. The complexity and cause-and-effect dynamics of the TME cannot currently be recapitulated in vitro or inferred from studies of fixed tissue, and are best studied in vivo, in real time and at single-cell resolution. Intravital imaging (IVI) offers these capabilities, and recent years have been a time of immense growth and innovation in the field. Here we review some of the recent advances in IVI of mammalian models of cancer and describe how IVI is being used to understand cancer progression and metastasis, and to develop novel treatments and therapies. We describe new techniques that allow access to a range of tissue and cancer types, novel fluorescent reporters and biosensors that allow fate mapping and the probing of functional and phenotypic states, and the clinical applications that have arisen from applying these techniques, reporters and biosensors to study cancer. We finish by presenting some of the challenges that remain in the field, how to address them and future perspectives.