Cystine/glutamate antiporter xCT deficiency reduces metastasis without impairing immune system function in breast cancer mouse models

BACKGROUND

The upregulation of antioxidant mechanisms is a common occurrence in cancer cells, as they strive to maintain balanced redox state and prevent oxidative damage. This includes the upregulation of the cystine/glutamate antiporter xCT, which plays a crucial role in protecting cancer cells from oxidative stress. Consequently, targeting xCT has become an attractive strategy for cancer treatment. However, xCT is also expressed by several types of immune cells where it has a role in proliferation and effector functions. In light of these observations, a comprehensive understanding of the specific role of xCT in the initiation and progression of cancer, as well as its potential impact on the immune system within the tumor microenvironment and the anti-tumor response, require further investigation.

METHODS

We generated xCTnull BALB/c mice to investigate the role of xCT in the immune system and xCTnull/Erbb2-transgenic BALB-neuT mice to study the role of xCT in a mammary cancer-prone model. We also used mammary cancer cells derived from BALB-neuT/xCTnull mice and xCTKO 4T1 cells to test the contribution of xCT to malignant properties in vitro and in vivo.

RESULTS

xCT depletion in BALB-neuT/xCTnull mice does not alter autochthonous tumor initiation, but tumor cells isolated from these mice display proliferation and redox balance defects in vitro. Although xCT disruption sensitizes 4T1 cells to oxidative stress, it does not prevent transplantable tumor growth, but reduces cell migration in vitro and lung metastasis in vivo. This is accompanied by an altered immune cell recruitment in the pre-metastatic niche. Finally, systemic depletion of xCT in host mice does not affect transplantable tumor growth and metastasis nor impair the proper mounting of both humoral and cellular immune responses in vivo.

CONCLUSIONS

xCT is dispensable for proper immune system function, thus supporting the safety of xCT targeting in oncology. Nevertheless, xCT is involved in several processes required for the metastatic seeding of mammary cancer cells, thus broadening the scope of xCT-targeting approaches.

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.

Hepatic Progenitor Cells in the Form of Ductular Structures within a GIST Liver Metastasis: Supporting a Putative Role in the Hepatic Metastatic Niche

INTRODUCTION

Recent studies have highlighted the presence of hepatic progenitor cells (HPCs) in metastatic liver carcinomas. We provide further evidence of this phenomenon, presenting a case of a gastrointestinal stromal tumour (GIST) liver metastasis with evidence of intra- and peritumoral HPC.

CASE DESCRIPTION

A 64-year-old man presented with a gastric mass diagnosed as a high-risk KIT-mutated GIST. The patient was treated with imatinib, recurring 5 years later with a liver mass. Liver biopsy disclosed a GIST metastasis, hallmarked by a proliferation of ductular structures without cytological atypia intermingled with the tumour cells, with a CK7/CK19/CD56-positive immunophenotype and rare CD44 positivity. The patient underwent liver resection, and the same ductular structures were present in the tumour interior and at its periphery.

CONCLUSION

We document for the time the presence of HPC in the form of ductular structures in a GIST liver metastasis, further supporting their role in the liver metastatic niche.

Lineage plasticity in prostate cancer: Looking beyond intrinsic alterations

Emergence of small cell prostate cancer is linked to the plasticity of tumour cells and avoidance of environmental pressures. This process is thought to be reversable, however to-date evidence of this has been demonstrated in small-cell prostate cancer. To study the plasticity of prostate tumours, we look to clinical cohorts of patients covering the spectra of malignancy subtypes and utilise in vitro and in vivo models of disease progression. Current models have assisted in the understanding of the extremities of this plasticity, elucidating internal mechanisms and adaptations to stressors through transition to altered cell states. By interrogating the tumour microenvironment and earlier time points, we are beginning to form a deeper understanding of the full spectra of tumour plasticity. It could be proffered that this deeper understanding will lead to better patient outcome, with earlier interventions more likely to reverse plasticity and prevent trans-differentiation to the aggressive, small cell phenotype.

Cancer extracellular vesicles, tumoroid models, and tumor microenvironment

Cancer extracellular vesicles (EVs), or exosomes, promote tumor progression through enhancing tumor growth, initiating epithelial-to-mesenchymal transition, remodeling the tumor microenvironment, and preparing metastatic niches. Three-dimensionally (3D) cultured tumoroids / spheroids aim to reproduce some aspects of tumor behavior in vitro and show increased cancer stem cell properties. These properties are transferred to their EVs that promote tumor growth. Moreover, recent tumoroid models can be furnished with aspects of the tumor microenvironment, such as vasculature, hypoxia, and extracellular matrix. This review summarizes tumor tissue culture and engineering platforms compatible with EV research. For example, the combination experiments of 3D-tumoroids and EVs have revealed multifunctional proteins loaded in EVs, such as metalloproteinases and heat shock proteins. EVs or exosomes are able to transfer their cargo molecules to recipient cells, whose fates are often largely altered. In addition, the review summarizes approaches to EV labeling technology using fluorescence and luciferase, useful for studies on EV-mediated intercellular communication, biodistribution, and metastatic niche formation.

Targeting bone microenvironments for treatment and early detection of cancer bone metastatic niches

Bone tissues are the main metastatic sites of many cancers, and bone metastasis is an important cause of death. When bone metastasis occurs, dynamic interactions between tumor cells and bone tissues promote changes in the tumor-bone microenvironments that are conducive to tumor growth and progression, which also promote several related diseases, including pathological fracture, bone pain, and hypercalcemia. Accordingly, it has obvious clinical benefits for improving the cure rate and reducing the occurrence of related diseases through targeting bone microenvironments for the treatment and early detection of cancer bone metastasis niches. In this review, we briefly analyzed the relationship between bone microstructures and tumor metastasis, as well as microenvironmental changes in osteoblasts, osteoclasts, immune cells, and extracellular and bone matrixes caused when metastatic tumor cells colonize bones. We also discuss novel designs in nanodrugs for inhibiting tumor proliferation and migration through targeting to tumor bone metastases and abnormal bone-microenvironment components. In addition, related researches on the early detection of bone and multi-organ metastases by nanoprobes are also introduced. And we look forward to provide some useful proposals and enlightenments on nanotechnology-based drug delivery and probes for the treatment and early detection of bone metastasis.

Pericytes cross-talks within the tumor microenvironment

Cancer cells are embedded within the tumor microenvironment and interact dynamically with its components during tumor progression. Understanding the molecular mechanisms by which the tumor microenvironment components communicate is crucial for the success of therapeutic applications. Recent studies show, by using state-of-the-art technologies, including sophisticated in vivo inducible Cre/loxP mediated systems and CRISPR-Cas9 gene editing, that pericytes communicate with cancer cells. The arising knowledge on cross-talks within the tumor microenvironment will be essential for the development of new therapies against cancer. Here, we review recent progress in our understanding of pericytes roles within tumors.

Tumor-on-chip modeling of organ-specific cancer and metastasis

Every year, cancer claims millions of lives around the globe. Unfortunately, model systems that accurately mimic human oncology - a requirement for the development of more effective therapies for these patients - remain elusive. Tumor development is an organ-specific process that involves modification of existing tissue features, recruitment of other cell types, and eventual metastasis to distant organs. Recently, tissue engineered microfluidic devices have emerged as a powerful in vitro tool to model human physiology and pathology with organ-specificity. These organ-on-chip platforms consist of cells cultured in 3D hydrogels and offer precise control over geometry, biological components, and physiochemical properties. Here, we review progress towards organ-specific microfluidic models of the primary and metastatic tumor microenvironments. Despite the field's infancy, these tumor-on-chip models have enabled discoveries about cancer immunobiology and response to therapy. Future work should focus on the development of autologous or multi-organ systems and inclusion of the immune system.

The liver metastatic niche: modelling the extracellular matrix in metastasis

Dissemination of malignant cells from primary tumours to metastatic sites is a key step in cancer progression. Disseminated tumour cells preferentially settle in specific target organs, and the success of such metastases depends on dynamic interactions between cancer cells and the microenvironments they encounter at secondary sites. Two emerging concepts concerning the biology of metastasis are that organ-specific microenvironments influence the fate of disseminated cancer cells, and that cancer cell-extracellular matrix interactions have important roles at all stages of the metastatic cascade. The extracellular matrix is the complex and dynamic non-cellular component of tissues that provides a physical scaffold and conveys essential adhesive and paracrine signals for a tissue's function. Here, we focus on how extracellular matrix dynamics contribute to liver metastases - a common and deadly event. We discuss how matrix components of the healthy and premetastatic liver support early seeding of disseminated cancer cells, and how the matrix derived from both cancer and liver contributes to the changes in niche composition as metastasis progresses. We also highlight the technical developments that are providing new insights into the stochastic, dynamic and multifaceted roles of the liver extracellular matrix in permitting and sustaining metastasis. An understanding of the contribution of the extracellular matrix to different stages of metastasis may well pave the way to targeted and effective therapies against metastatic disease.

Fibronectin as a multiregulatory molecule crucial in tumor matrisome: from structural and functional features to clinical practice in oncology

Deciphering extracellular matrix (ECM) composition and architecture may represent a novel approach to identify diagnostic and therapeutic targets in cancer. Among the ECM components, fibronectin and its fibrillary assembly represent the scaffold to build up the entire ECM structure, deeply affecting its features. Herein we focus on this extraordinary protein starting from its complex structure and defining its role in cancer as prognostic and theranostic marker.

TGFβ Signaling in the Tumor Microenvironment

Transforming growth factor beta (TGFβ) is a pleiotropic growth factor. Under normal physiological conditions, TGFβ maintains homeostasis in mammalian tissues by restraining the growth of cells and stimulating apoptosis. However, the role of TGFβ signaling in the carcinogenesis is complex. TGFβ acts as a tumor suppressor in the early stages of disease and as a tumor promoter in its later stages where cancer cells have been relieved from TGFβ growth controls. Overproduction of TGFβ by cancer cells lead to a local fibrotic and immune-suppressive microenvironment that fosters tumor growth and correlates with invasive and metastatic behavior of the cancer cells. Here, we present an overview of the complex biology of the TGFβ family, and we discuss the roles of TGFβ signaling in carcinogenesis and how this knowledge is being leveraged to develop TGFβ inhibition therapies against the tumor.

Imaging Early-Stage Metastases Using an 18F-Labeled VEGFR-1-Specific Single Chain VEGF Mutant

PURPOSE

Metastatic breast cancer is the second leading cause of cancer-related death in women. The 5-year survival rate for metastatic breast cancer has remained near 26.9 % for over a decade. The recruitment of hematopoietic stem cells with high expression of the vascular endothelial growth factor receptor 1 (VEGFR-1) has been implicated in early stages of metastasis formation. We propose the use of an ¹⁸F-labeled single-chain version of VEGF121, re-engineered to be selective for VEGFR-1 (scVR1), as a positron emission tomography (PET) imaging agent to non-invasively image early-stage metastases.

PROCEDURES

scVR1 was ¹⁸F-labeled via a biorthogonal click reaction between site-specifically trans-cyclooctene functionalized scVR1 and an Al¹⁸F labeled tetrazine-NODA (1,4,7-triazacyclononane-1,4-diiacetic acid). The [¹⁸F]AlF-NODA-scVR1 was purified using a PD10 column and subsequently analyzed on HPLC to determine radiochemical purity. Animal experiments were performed in 6-8-week-old female BALB/c mice bearing orthotopic primary 4T1 breast tumors or 4T1 metastatic lesions. The [¹⁸F]AlF-NODA-scVR1 tracer was administered via tail vein injection; PET imaging and ex vivo analysis was performed 2 h post-injection.

RESULTS

The [¹⁸F]AlF-NODA-scVR1 was prepared with a 98.2 ± 1.5 % radiochemical purity and an apparent molar activity of 7.5 ± 1.2 GBq/μmol. The specific binding of scVR1 to VEGFR-1 was confirmed via bead-based assay. The ex vivo biodistribution showed tumor uptake of 3.5 ± 0.5 % ID/g and was readily observable in PET images. Metastasis formation was detected with [¹⁸F]AlF-NODA-scVR1 tracer showing colocalization with bioluminescent imaging as well as ex vivo autoradiography and immunofluorescent staining of VEGFR-1.

CONCLUSIONS

The diagnostic capabilities of the [¹⁸F]AlF-NODA-scVR1 PET tracer was confirmed in both orthotopic and metastatic murine cancer models. These results support the potential use of [¹⁸F]AlF-NODA-scVR1 as a PET tracer that could image metastases, providing clinicians with an additional tool to assess a patient's need for adjuvant therapies.

The enhancement of glycolysis regulates pancreatic cancer metastasis

Pancreatic ductal adenocarcinoma is prone to distant metastasis and is expected to become the second leading cause of cancer-related death. In an extremely nutrient-deficient and hypoxic environment resulting from uncontrolled growth, vascular disturbances and desmoplastic reactions, pancreatic cancer cells utilize "metabolic reprogramming" to satisfy their energy demand and support malignant behaviors such as metastasis. Notably, pancreatic cancer cells show extensive enhancement of glycolysis, including glycolytic enzyme overexpression and increased lactate production, and this is caused by mitochondrial dysfunction, cancer driver genes, specific transcription factors, a hypoxic tumor microenvironment and stromal cells, such as cancer-associated fibroblasts and tumor-associated macrophages. The metabolic switch from oxidative phosphorylation to glycolysis in pancreatic cancer cells regulates the invasion-metastasis cascade by promoting epithelial-mesenchymal transition, tumor angiogenesis and the metastatic colonization of distant organs. In addition to aerobic glycolysis, oxidative phosphorylation also plays a critical role in pancreatic cancer metastasis in ways that remain unclear. In this review, we expound on the intracellular and extracellular causes of the enhancement of glycolysis in pancreatic cancer and the strong association between glycolysis and cancer metastasis, which we expect will yield new therapeutic approaches targeting cancer metabolism.

The extracellular matrix in tumor progression and metastasis

The extracellular matrix (ECM) constitutes the scaffold of tissues and organs. It is a complex network of extracellular proteins, proteoglycans and glycoproteins, which form supramolecular aggregates, such as fibrils and sheet-like networks. In addition to its biochemical composition, including the covalent intermolecular cross-linkages, the ECM is also characterized by its biophysical parameters, such as topography, molecular density, stiffness/rigidity and tension. Taking these biochemical and biophysical parameters into consideration, the ECM is very versatile and undergoes constant remodeling. This review focusses on this remodeling of the ECM under the influence of a primary solid tumor mass. Within this tumor stroma, not only the cancer cells but also the resident fibroblasts, which differentiate into cancer-associated fibroblasts (CAFs), modify the ECM. Growth factors and chemokines, which are tethered to and released from the ECM, as well as metabolic changes of the cells within the tumor bulk, add to the tumor-supporting tumor microenvironment. Metastasizing cancer cells from a primary tumor mass infiltrate into the ECM, which variably may facilitate cancer cell migration or act as barrier, which has to be proteolytically breached by the infiltrating tumor cell. The biochemical and biophysical properties therefore determine the rates and routes of metastatic dissemination. Moreover, primed by soluble factors of the primary tumor, the ECM of distant organs may be remodeled in a way to facilitate the engraftment of metastasizing cancer cells. Such premetastatic niches are responsible for the organotropic preference of certain cancer entities to colonize at certain sites in distant organs and to establish a metastasis. Translational application of our knowledge about the cancer-primed ECM is sparse with respect to therapeutic approaches, whereas tumor-induced ECM alterations such as increased tissue stiffness and desmoplasia, as well as breaching the basement membrane are hallmark of malignancy and diagnostically and histologically harnessed.

Evaluation of metastatic niches in distant organs after surgical removal of tumor-bearing lymph nodes

Background

Surgical removal of primary tumors can promote the incidence of tumor metastasis. However, molecular mechanisms underlying this process remain unclear.

Methods

We inoculated tumor cells expressing luciferase gene  into subiliac lymph node (SiLN) of the MXH10/Mo-lpr/lpr mice. The tumor-bearing SiLNs were surgically removed at a certain period of time after inoculation.

Results

In vivo bioluminescence imaging system and histological staining revealed metastasis in lung, proper axillary lymph node (PALN) and liver. The lung metastasis rate in SiLN removal groups was significantly higher than in the control group using Fisher exact test. Mann-Whitney U-test indicated that the luciferase-positive tumor cells in the lung and liver were significantly higher than in the control groups. The lung samples in SiLN removal groups had strong expression of lysine oxidase (LOX). Moreover, the number of CD11b⁺ cells in the lung and liver in the SiLN removal groups was significantly increased, which was positively correlated with LOX expression level. In addition, the condition of LOX and CD11b in liver was similar to lung. In the SiLN surgical removal groups, the matrix metalloproteinase (MMP)-2 and VEGFA expression in the lung tissues was significantly higher than in the control groups; the collagen fibers per area around the pulmonary vessels was quite significantly lower and negatively correlated with the expression of MMP-2 by Spearman’s analysis. Our data indicated that the reticular fibers were deposited and disordered in the tumor tissues of the lungs in the removal groups, and the reticular fibers per area was higher than in the control groups. The tumor cells in the PALN of control groups were significantly higher than in the SiLN removal groups, and CD169⁺ and CD11c⁺ cells were also higher than in the SiLN removal groups.

Conclusions

Altogether, surgical removal of the tumor-bearing lymph node promoted tumor metastasis through changing the niche in lung and liver. Treatment targeting the metastatic niche might be an effective strategy to prevent tumor metastasis, thereby possibly increasing the survival and reducing the incidence of metastasis in cancer patients.

The key role of extracellular vesicles in the metastatic process

Extracellular vesicles (EVs), including exosomes, have a key role in the paracrine communication between organs and compartments. EVs shuttle virtually all types of biomolecules such as proteins, lipids, nucleic acids, metabolites and even pharmacological compounds. Their ability to transfer their biomolecular cargo into target cells enables EVs to play a key role in intercellular communication that can regulate cellular functions such as proliferation, apoptosis and migration. This has led to the emergence of EVs as a key player in tumor growth and metastasis through the formation of "tumor niches" in target organs. Recent data have also been shown that EVs may transform the microenvironment of primary tumors thus favoring the selection of cancer cells with a metastatic behavior. The release of EVs from resident non-malignant cells may contribute to the metastatic processes as well. However, cancer EVs may induce malignant transformation in resident mesenchymal stem cells, suggesting that the metastatic process is not exclusively due to circulating tumor cells. In this review, we outline and discuss evidence-based roles of EVs in actively regulating multiple steps of the metastatic process and how we can leverage EVs to impair metastasis.

The multifaceted role of periostin in priming the tumor microenvironments for tumor progression

Tumor microenvironment consists of tumor cells, stromal cells, extracellular matrix and a plethora of soluble components. The complex array of interactions between tumor cells and their surrounding tumor microenvironments contribute to the determination of the fate of tumor cells during tumorigenesis and metastasis. Matricellular protein periostin is generally absent in most adult tissues but is highly expressed in tumor microenvironments. Current evidence reveals that periostin plays a critical role in establishing and remodeling tumor microenvironments such as the metastatic niche, cancer stem cell niche, perivascular niche, pre-metastatic niche, fibrotic microenvironment and bone marrow microenvironment. Here, we summarize the current knowledge of the multifaceted role of periostin in the tumor microenvironments.

Pathophysiology of bone metastases from solid malignancies

Bone metastases are common complications of many cancers. Among the mechanisms that set the scene for the development of bone metastases, several are shared by all forms of metastatic dissemination (pre-metastatic niche formation and chemotactic attraction of malignant cells, which invade the host tissue) and others are specific of bone tissue (homing of malignant cells to bone marrow niches and acquisition of an osteomimetic cell phenotype). After a latency period that can last several years, the malignant cells can proliferate into tumors that alter the normal bone remodeling process by inducing dysregulation of osteoblast and osteoclast function. These metastases may be lytic, characterized by major bone destruction; sclerotic, with excess bone formation; or mixed. Osteolysis occurs when the tumor cells stimulate osteoclast activity and inhibit osteoblast activity, whereas the opposite effects lead to bone sclerosis. Moreover, the mineralized bone matrix plays a major role in the formation of bone metastases, as its degradation releases growth factors and calcium that exert mitogenic effects on tumor cells. Thus, bone metastases are the site of a vicious circle in which mechanisms involved in bone resorption/formation promote tumor growth and vice versa.

The influence of the pre-metastatic niche on breast cancer metastasis

The emergence of metastatic disease constitutes a significant life-threatening development during cancer progression. To date, intensive efforts have been focused on understanding the intrinsic properties that confer malignant potential to cancer cells, as well as the role of the primary tumour microenvironment in promoting cancer metastasis. Beyond events occurring at the primary site, the metastatic cascade is composed of numerous barriers that must be overcome in order for disseminating cancer cells to form distal metastases. The most formidable of these is the ability of cancer cells to seed and grow in a completely foreign microenvironment. Interestingly, solid malignancies often display a particular tropism for specific tissue sites. For example, breast patients with metastatic disease will often develop bone, lung, liver or brain metastases. This mini-review will explore aspects of pre-existing and induced metastatic niches and focus on how the unique composition and function of diverse niche components, within common sites of breast cancer metastasis, enable the survival and growth of disseminated cancer cells. These common supportive functions of the niche are provided by a complex array of stromal components and molecular mechanisms that are, in part, reflective of the tissue in which the metastases arise. Finally, the metastatic niche is a dynamic structure that is continually altered and sculpted by the cancer cells during progression of the metastatic lesion.

Bone metastasis and the metastatic niche

The bone marrow has been long known to host a unique environment amenable to colonization by metastasizing tumor cells. Yet, the underlying molecular interactions within this specialized microenvironment which give rise to the high incidence of bone metastasis in breast and prostate cancer patients have long remained uncharacterized. With the recent description of the bone metastatic "niche," considerable focus has been placed on understanding how the bone stroma contributes to each step of metastasis. Discoveries within this field have demonstrated that when cancer cells home to the niche in which hematopoietic and mesenchymal stem/progenitor cells normally reside, a bidirectional crosstalk emerges between the tumor cells and the bone metastatic stroma. This communication modulates every step of cancer cell metastasis to the bone, including the initial homing and seeding, formation of micrometastases, outgrowth of macrometastases, and the maintenance of long-term dormancy of disseminated tumor cells in the bone. In clinical practice, targeting the bone metastatic niche is evolving into a promising avenue for the prevention of bone metastatic relapse, therapeutic resistance, and other aspects of cancer progression. Here, we review the current knowledge concerning the role of the bone metastatic niche in bone metastasis.

Extracellular vesicles as modulators of the cancer microenvironment

The tumour microenvironment is a highly complex and dynamic tissue. It comprises not only neoplastic cells, but also other resident cells within the milieu such as stroma and vascular cells in addition to a variable cellular infiltrate from the periphery. A host of soluble factors such as growth factors, chemokines, eicosanoids soluble metabolites and extracellular matrix components have been extensively documented as factors which modulate this environment. However, in recent years there has also been growing interests in the potential roles of extracellular vesicles (EV) in many of the processes governing the nature of cancerous tissue. In this brief review, we have assembled evidence describing several distinct functions for extracellular vesicles in modulating the microenvironment with examples that include immune evasion, angiogenesis and stromal activation. Whilst there remains a great deal to be learnt about the interplay between vesicles and the cancerous environment, it is becoming clear that vesicle-mediated communication has a major influence on key aspects of cancer growth and progression. We conclude that the design of future therapeutics should acknowledge the existence and roles of extracellular vesicles, and seriously consider strategies for circumventing their effects in vivo.

Proof of prometastatic niche induction by hepatic stellate cells

BACKGROUND

An interaction between tumor cells and the microenvironment, as well as the development of angiogenesis, are required to form liver metastases (LMs).

MATERIAL AND METHODS

Immunofluorescence detection of α-smooth muscle actin, desmin, Ki67, laminin, and CD31 was used to analyze the kinetics of tumor angiogenesis determinants, especially the contribution of hepatic stellate cells (HSCs) to angiogenesis in hepatic metastasis produced by intrasplenically injected LS174 colorectal cancer cells. Immunostaining was performed at various times (days 9, 14, 28, and 39).

RESULTS

At the earliest stage, micrometastases consisted of proliferating cancer cells, a well-organized network of activated HSCs and laminin deposits. No vascular network was observed. As the LMs grew in size, an organized vascular network appeared; the laminin network colocalized with CD31 immunostaining. At the later stages, all the immunostained markers became peripheral as a central necrosis developed. Purified activated HSCs isolated from transgenic mice livers developing hepatocellular carcinoma secreted laminin and showed enhanced human umbilical vein EC network formation in a Matrigel assay. In a coinjection LM experiment, activated HSCs enhanced the metastatic process. Moreover, colorectal LMs from six patients were analyzed, and a pattern of marker distribution similar to the coinjection experiment was found in human LMs.

CONCLUSIONS

For the first time, our results show that HSCs play a crucial role in organizing and accelerating the progression of metastasis in modulating the prometastatic niche, interacting with colorectal cancer cell recruitment, and the organization of angiogenesis during colorectal LM development. Therefore, HSCs may be an early therapeutic target in colorectal cancer therapies.

Modifying the osteoblastic niche with zoledronic acid in vivo-potential implications for breast cancer bone metastasis

INTRODUCTION

Bone metastasis is the most common complication of advanced breast cancer. The associated cancer-induced bone disease is treated with bone-sparing agents like zoledronic acid. Clinical trials have shown that zoledronic acid also reduces breast cancer recurrence in bone; potentially by modifying the bone microenvironment surrounding disseminated tumour cells. We have characterised the early effects of zoledronic acid on key cell types of the metastatic niche in vivo, and investigated how these modify the location of breast tumour cells homing to bone.

METHODS

Female mice were treated with a single, clinically achievable dose of zoledronic acid (100μg/kg) or PBS. Bone integrity, osteoclast and osteoblast activity and number/mm trabecular bone on 1, 3, 5 and 10days after treatment were assessed using μCT, ELISA (TRAP, PINP) and bone histomorphometry, respectively. The effect of zoledronic acid on osteoblasts was validated in genetically engineered mice with GFP-positive osteoblastic cells. The effects on growth plate cartilage were visualised by toluidine blue staining. For tumour studies, mice were injected i.c. with DID-labelled MDA-MB-231-NW1-luc2 breast cancer cells 5days after zoledronic acid treatment, followed by assessment of tumour cell homing to bone and soft tissues by multiphoton microscopy, flow cytometry and ex vivo cultures.

RESULTS

As early as 3days after treatment, animals receiving zoledronic acid had significantly increased trabecular bone volume vs. control. This rapid bone effect was reflected in a significant reduction in osteoclast and osteoblast number/mm trabecular bone and reduced bone marker serum levels (day 3-5). These results were confirmed in mice expressing GFP in osteoblastic linage cells. Pre-treatment with zoledronic acid caused accumulation of an extra-cellular matrix in the growth plate associated with a trend towards preferential [1] homing of tumour cells to osteoblast-rich areas of bone, but without affecting the total number of tumour cells. The number of circulating tumour cells was reduced in ZOL treated animals.

CONCLUSION

A single dose of zoledronic acid caused significant changes in the bone area suggested to contain the metastatic niche. Tumour cells arriving in this modified bone microenvironment appeared to preferentially locate to osteoblast-rich areas, supporting that osteoblasts may be key components of the bone metastasis niche and therefore a potential therapeutic target in breast cancer.

Polymeric micelles loaded with platinum anticancer drugs target preangiogenic micrometastatic niches associated with inflammation

Nanocarriers have been used for specific delivery of therapeutic agents to solid tumors based on the enhanced permeability and retention in cancerous tissues. Despite metastasis is the main reason of cancer-related death and a priority for nanocarrier-based therapies, the targeting ability of nanocarriers to the metastatic disease is poorly understood, especially for preangiogenic micrometastases as nanocarriers usually use the malignant neovasculature for enhancing their accumulation. Thus, herein, we studied the ability of micellar nanocarriers incorporating (1,2-diaminocyclohexane)platinum(II) (DACHPt) for treating liver metastases of bioluminescent murine colon adenocarcinoma C-26, during overt and preangiogenic metastatic stages. After intravenous injection, DACHPt-loaded micelles (DACHPt/m) effectively inhibited the tumor growth in both metastatic tumor models. While the anticancer activity of the micelles against overt metastases was associated with their selective accumulation in cancerous tissues having neovasculature, the ability of DACHPt/m to target preangiogenic metastases was correlated with the inflammatory microenvironment of the niche. This targeting capability of polymeric micelles to preangiogenic metastasis may provide a novel approach for early diagnosis and treatment of metastases.

Extracellular matrix components in breast cancer progression and metastasis

The extracellular matrix (ECM) is composed of highly variable and dynamic components that regulate cell behavior. The protein composition and physical properties of the ECM govern cell fate through biochemical and biomechanical mechanisms. This requires a carefully orchestrated and thorough regulation considering that a disturbed ECM can have serious consequences and lead to pathological conditions like cancer. In breast cancer, many ECM proteins are significantly deregulated and specific matrix components promote tumor progression and metastatic spread. Intriguingly, several ECM proteins that are associated with breast cancer development, overlap substantially with a group of ECM proteins induced during the state of tissue remodeling such as mammary gland involution. Fibrillar collagens, fibronectin, hyaluronan and matricellular proteins are matrix components that are common to both involution and cancer. Moreover, some of these proteins have in recent years been identified as important constituents of metastatic niches in breast cancer. In addition, specific ECM molecules, their receptors or enzymatic modifiers are significantly involved in resistance to therapeutic intervention. Further analysis of these ECM proteins and the downstream ECM mediated signaling pathways may provide a range of possibilities to identify druggable targets against advanced breast cancer.

Tumor microenvironment: bone marrow-mesenchymal stem cells as key players

Tumor progression is a multistep phenomenon in which tumor-associated stromal cells perform an intricate cross-talk with tumor cells, supplying appropriate signals that may promote tumor aggressiveness. Among several cell types that constitute the tumor stroma, the discovery that bone marrow-derived mesenchymal stem cells (BM-MSC) have a strong tropism for tumors has achieved notoriety in recent years. Not only are the BM-MSC recruited, but they can also engraft at tumor sites and transdifferentiate into cells such as activated fibroblasts, perivascular cells and macrophages, which will perform a key role in tumor progression. Whether the BM-MSC and their derived cells promote or suppress the tumor progression is a controversial issue. Recently, it has been proposed that proinflammatory stimuli can be decisive in driving BM-MSC polarization into cells with either tumor-supportive or tumor-repressive phenotypes (MSC1/MSC2). These considerations are extremely important both to an understanding of tumor biology and to the putative use of BM-MSC as "magic bullets" against tumors. In this review, we discuss the role of BM-MSC in many steps in tumor progression, focusing on the factors that attract BM-MSC to tumors, BM-MSC differentiation ability, the role of BM-MSC in tumor support or inhibition, the immunomodulation promoted by BM-MSC and metastatic niche formation by these cells.

The role of the tumor-microenvironment in lung cancer-metastasis and its relationship to potential therapeutic targets

Non-small cell lung cancer (NSCLC) accounts for >80% of lung cancer cases and currently has an overall five-year survival rate of only 15%. Patients presenting with advanced stage NSCLC die within 18-months of diagnosis. Metastatic spread accounts for >70% of these deaths. Thus elucidation of the mechanistic basis of NSCLC-metastasis has potential to impact on patient quality of life and survival. Research on NSCLC metastasis has recently expanded to include non-cancer cell components of tumors-the stromal cellular compartment and extra-cellular matrix components comprising the tumor-microenvironment. Metastasis (from initial primary tumor growth through angiogenesis, intravasation, survival in the bloodstream, extravasation and metastatic growth) is an inefficient process and few released cancer cells complete the entire process. Micro-environmental interactions assist each of these steps and discovery of the mechanisms by which tumor cells co-operate with the micro-environment are uncovering key molecules providing either biomarkers or potential drug targets. The major sites of NSCLC metastasis are brain, bone, adrenal gland and the liver. The mechanistic basis of this tissue-tropism is beginning to be elucidated offering the potential to target stromal components of these tissues thus targeting therapy to the tissues affected. This review covers the principal steps involved in tumor metastasis. The role of cell-cell interactions, ECM remodeling and autocrine/paracrine signaling interactions between tumor cells and the surrounding stroma is discussed. The mechanistic basis of lung cancer metastasis to specific organs is also described. The signaling mechanisms outlined have potential to act as future drug targets minimizing lung cancer metastatic spread and morbidity.

Targeting tumor-stromal interactions in bone metastasis

Bone metastasis is a frequent occurrence in late stage solid tumors, including breast cancers, prostate or lung. However, the causes for this proclivity have only recently been elucidated. Significant progress has been made in the past decade toward understanding the molecular underpinnings of bone metastasis, and much of this research reveals a crucial role of the host stroma in each step of the metastatic cascade. Tumor-stromal interactions are crucial in engineering a pre-metastatic niche, accommodating metastatic seeding, and establishing the vicious cycle of bone metastasis. Current treatments in bone metastasis focus on latter steps of the metastatic cascade, with most treatments targeting the process of bone remodeling; however, emerging research identifies many other candidates as promising targets. Host stromal cells including platelets and endothelial cells are important in the early steps of metastatic homing, attachment and extravasation while a variety of immune cells, parenchymal cells and mesenchymal cells of the bone marrow are important in the establishment of overt, immune-suppressed metastatic lesions. Many participants during these steps have been identified and functionally validated. Significant contributors include integrins, (αvβ3, α2β1, α4β1), TGFβ family members, bone resident proteins (BSP, OPG, SPARC, OPN), RANKL, and PTHrP. In this review, we will discuss the contribution of host stromal cells to pre-metastatic niche conditioning, seeding, dormancy, bone-remodeling, immune regulation, and chemotherapeutic shielding in bone metastasis. Research exploring these interactions between bone metastases and stromal cells has yielded many therapeutic targets, and we will discuss both the current and future therapeutic avenues in treating bone metastasis.