Definition of molecular determinants of prostate cancer cell bone extravasation

Extravasation of immune and tumor cells from an endothelial perspective

Crossing the vascular endothelium is a necessary stage for circulating cells aiming to reach distant organs. Leukocyte passage through the endothelium, known as transmigration, is a multistep process during which immune cells adhere to the vascular wall, migrate and crawl along the endothelium until they reach their exit site. Similarly, circulating tumor cells (CTCs), which originate from the primary tumor or reseed from early metastatic sites, disseminate using the blood circulation and also must cross the endothelial barrier to set new colonies in distant organs. CTCs are thought to mimic arrest and extravasation utilized by leukocytes; however, their extravasation also requires processes that, from an endothelial perspective, are specific to cancer cells. Although leukocyte extravasation relies on maintaining endothelial impermeability, it appears that cancer cells can indoctrinate endothelial cells into promoting their extravasation independently of their normal functions. In this Review, we summarize the common and divergent mechanisms of endothelial responses during extravasation of leukocytes (in inflammation) and CTCs (in metastasis), and highlight how these might be leveraged in the development of anti-metastatic treatments.

FUCA1: An Underexplored p53 Target Gene Linking Glycosylation and Cancer Progression

Cancer is a difficult-to-cure disease with high worldwide incidence and mortality, in large part due to drug resistance and disease relapse. Glycosylation, which is a common modification of cellular biomolecules, was discovered decades ago and has been of interest in cancer research due to its ability to influence cellular function and to promote carcinogenesis. A variety of glycosylation types and structures regulate the function of biomolecules and are potential targets for investigating and treating cancer. The link between glycosylation and carcinogenesis has been more recently revealed by the role of p53 in energy metabolism, including the p53 target gene alpha-L-fucosidase 1 (FUCA1), which plays an essential role in fucosylation. In this review, we summarize roles of glycan structures and glycosylation-related enzymes to cancer development. The interplay between glycosylation and tumor microenvironmental factors is also discussed, together with involvement of glycosylation in well-characterized cancer-promoting mechanisms, such as the epidermal growth factor receptor (EGFR), phosphatidylinositol-3-kinase/protein kinase B (PI3K/Akt) and p53-mediated pathways. Glycan structures also modulate cell-matrix interactions, cell-cell adhesion as well as cell migration and settlement, dysfunction of which can contribute to cancer. Thus, further investigation of the mechanistic relationships among glycosylation, related enzymes and cancer progression may provide insights into potential novel cancer treatments.

Cancer on motors: How kinesins drive prostate cancer progression?

Prostate cancer causes numerous male deaths annually. Although great progress has been made in the diagnosis and treatment of prostate cancer during the past several decades, much about this disease remains unknown, especially its pathobiology. The kinesin superfamily is a pivotal group of motor proteins, that contains a microtubule-based motor domain and features an adenosine triphosphatase activity and motility characteristics. Large-scale sequencing analyses based on clinical samples and animal models have shown that several members of the kinesin family are dysregulated in prostate cancer. Abnormal expression of kinesins could be linked to uncontrolled cell growth, inhibited apoptosis and increased metastasis ability. Additionally, kinesins may be implicated in chemotherapy resistance and escape immunologic cytotoxicity, which creates a barrier to cancer treatment. Here we cover the recent advances in understanding how kinesins may drive prostate cancer progression and how targeting their function may be a therapeutic strategy. A better understanding of kinesins in prostate cancer tumorigenesis may be pivotal for improving disease outcomes in prostate cancer patients.

The role of galectins in mediating the adhesion of circulating cells to vascular endothelium

Vascular cell adhesion is a complex orchestration of events that commonly feature lectin-ligand interactions between circulating cells, such as immune, stem, and tumor cells, and endothelial cells (ECs) lining post-capillary venules. Characteristically, circulating cell adherence to the vasculature endothelium is initiated through interactions between surface sialo-fucosylated glycoprotein ligands and lectins, specifically platelet (P)- or endothelial (E)-selectin on ECs or between leukocyte (L)-selectin on circulating leukocytes and L-selectin ligands on ECs, culminating in circulating cell extravasation. This lectin-ligand interplay enables the migration of immune cells into specific tissue sites to help maintain effective immunosurveillance and inflammation control, the homing of stem cells to bone marrow or tissues in need of repair, and, unfortunately, in some cases, the dissemination of circulating tumor cells (CTCs) to distant metastatic sites. Interestingly, there is a growing body of evidence showing that the family of β-galactoside-binding lectins, known as galectins, can also play pivotal roles in the adhesion of circulating cells to the vascular endothelium. In this review, we present contemporary knowledge on the significant roles of host- and/or tumor-derived galectin (Gal)-3, -8, and -9 in facilitating the adhesion of circulating cells to the vascular endothelium either directly by acting as bridging molecules or indirectly by triggering signaling pathways to express adhesion molecules on ECs. We also explore strategies for interfering with galectin-mediated adhesion to attenuate inflammation or hinder the metastatic seeding of CTCs, which are often rich in galectins and/or their glycan ligands.

Synthesis and Biological Evaluation of Cyclobutane-Based β3 Integrin Antagonists: A Novel Approach to Targeting Integrins for Cancer Therapy

The Arg-Gly-Asp (RGD)-binding family of integrin receptors, and notably the β3 subfamily, are key to multiple physiological processes involved in tissue development, cancer proliferation, and metastatic dissemination. While there is compelling preclinical evidence that both αvβ3 and αIIbβ3 are important anticancer targets, most integrin antagonists developed to target the β3 integrins are highly selective for αvβ3 or αIIbβ3. We report the design, synthesis, and biological evaluation of a new structural class of ligand-mimetic β3 integrin antagonist. These new antagonists combine a high activity against αvβ3 with a moderate affinity for αIIbβ3, providing the first evidence for a new approach to integrin targeting in cancer.

Mechanobiology and survival strategies of circulating tumor cells: a process towards the invasive and metastatic phenotype

Metastatic progression is the deadliest feature of cancer. Cancer cell growth, invasion, intravasation, circulation, arrest/adhesion and extravasation require specific mechanical properties to allow cell survival and the completion of the metastatic cascade. Circulating tumor cells (CTCs) come into contact with the capillary bed during extravasation/intravasation at the beginning of the metastatic cascade. However, CTC mechanobiology and survival strategies in the bloodstream, and specifically in the microcirculation, are not well known. A fraction of CTCs can extravasate and colonize distant areas despite the biomechanical constriction forces that are exerted by the microcirculation and that strongly decrease tumor cell survival. Furthermore, accumulating evidence shows that several CTC adaptations, via molecular factors and interactions with blood components (e.g., immune cells and platelets inside capillaries), may promote metastasis formation. To better understand CTC journey in the microcirculation as part of the metastatic cascade, we reviewed how CTC mechanobiology and interaction with other cell types in the bloodstream help them to survive the harsh conditions in the circulatory system and to metastasize in distant organs.

Cancer metastasis chemoprevention prevents circulating tumour cells from germination

The war against cancer traces back to the signature event half-a-century ago when the US National Cancer Act was signed into law. The cancer crusade costs trillions with disappointing returns, teasing the possibility of a new breakthrough. Cure for cancer post-metastases still seems tantalisingly out of reach. Once metastasized, cancer-related death is extremely difficult, if not impossible, to be reversed. Here we present cancer pre-metastasis chemoprevention strategy that can prevent circulating tumour cells (CTCs) from initiating metastases safely and effectively, and is disparate from the traditional cancer chemotherapy and cancer chemoprevention. Deep learning of the biology of CTCs and their disseminating organotropism, complexity of their adhesion to endothelial niche reveals that if the adhesion of CTCs to their metastasis niche (the first and the most important part in cancer metastatic cascade) can be pharmaceutically interrupted, the lethal metastatic cascade could be prevented from getting initiated. We analyse the key inflammatory and adhesive factors contributing to CTC adhesion/germination, provide pharmacological fundamentals for abortifacients to intervene CTC adhesion to the distant metastasis sites. The adhesion/inhibition ratio (AIR) is defined for selecting the best cancer metastasis chemopreventive candidates. The successful development of such new therapeutic modalities for cancer metastasis chemoprevention has great potential to revolutionise the current ineffective post-metastasis treatments.

Targeting HECTD3-IKKα axis inhibits inflammation-related metastasis

Metastasis is the leading cause of cancer-related death. The interactions between circulating tumor cells and endothelial adhesion molecules in distant organs is a key step during extravasation in hematogenous metastasis. Surgery is a common intervention for most primary solid tumors. However, surgical trauma-related systemic inflammation facilitates distant tumor metastasis by increasing the spread and adhesion of tumor cells to vascular endothelial cells (ECs). Currently, there are no effective interventions to prevent distant metastasis. Here, we show that HECTD3 deficiency in ECs significantly reduces tumor metastasis in multiple mouse models. HECTD3 depletion downregulates expression of adhesion molecules, such as VCAM-1, ICAM-1 and E-selectin, in mouse primary ECs and HUVECs stimulated by inflammatory factors and inhibits adhesion of tumor cells to ECs both in vitro and in vivo. We demonstrate that HECTD3 promotes stabilization, nuclear localization and kinase activity of IKKα by ubiquitinating IKKα with K27- and K63-linked polyubiquitin chains at K296, increasing phosphorylation of histone H3 to promote NF-κB target gene transcription. Knockout of HECTD3 in endothelium significantly inhibits tumor cells lung colonization, while conditional knockin promotes that. IKKα kinase inhibitors prevented LPS-induced pulmonary metastasis. These findings reveal the promotional role of the HECTD3-IKKα axis in tumor hematogenous metastasis and provide a potential strategy for tumor metastasis prevention.

Fucosylation in Urological Cancers

Fucosylation is an oligosaccharide modification that plays an important role in immune response and malignancy, and specific fucosyltransferases (FUTs) catalyze the three types of fucosylations: core-type, Lewis type, and H type. FUTs regulate cancer proliferation, invasiveness, and resistance to chemotherapy by modifying the glycosylation of signaling receptors. Oligosaccharides on PD-1/PD-L1 proteins are specifically fucosylated, leading to functional modifications. Expression of FUTs is upregulated in renal cell carcinoma, bladder cancer, and prostate cancer. Aberrant fucosylation in prostate-specific antigen (PSA) could be used as a novel biomarker for prostate cancer. Furthermore, elucidation of the biological function of fucosylation could result in the development of novel therapeutic targets. Further studies are needed in the field of fucosylation glycobiology in urological malignancies.

The Heterogeneity of Neutrophil Recruitment in the Tumor Microenvironment and the Formation of Premetastatic Niches

The recruitment of neutrophil to the primary cancer has been shown to be steered by neoplastic cells or tumor-educated mesenchymal stromal cells and has a prometastatic effect. However, the neutrophil chemotaxis and their interaction with tumor cells in the distal metastasized tissues remain elusive. In this review, we discussed emerging research on the interaction between neutrophil recruitment and tumor metastasis, which is essential for studying tumor cell invasion and related immunotherapy.

Bone Targeting Agents in Patients with Metastatic Prostate Cancer: State of the Art

Simple Summary

Over the disease course of metastatic prostate cancer, approximately the 90% of patients develops bone metastases, with bone involvement frequently leading to various skeletal complications including pathological fractures, spinal cord compression, and pain. Notably enough, the peculiar inclination of prostate cancer cells to seed the bone is considered an important cause of morbidity for prostate cancer patients. Recent years have witnessed the advent of several novel treatments for prostate cancer, and therapeutic paradigms are rapidly shifting. In this review, we aim at giving an overview of current knowledge on the relationship between prostate cancer and bone, especially focusing on the use of bone-targeted agents in this setting.

Abstract

Bone health represents a major issue in castration-resistant prostate cancer (CRPC) patients with bone metastases; in fact, the frequently prolonged use of hormonal agents causes important modifications in physiological bone turnover and most of these men will develop skeletal-related events (SREs), including spinal cord compression, pathologic fractures and need for surgery or radiation to bone, which are estimated to occur in almost half of this patient population. In the last decade, several novel therapeutic options have entered into clinical practice of bone metastatic CRPC, with recent approval of enzalutamide and abiraterone acetate, cabazitaxel chemotherapy and radium-223, on the basis of survival benefit suggested by landmark Phase III trials assessing these agents in this setting. Conversely, although bone-targeted agents (BTAs)—such as the bisphosphonate zoledronic acid and the receptor activator of nuclear factor kappa-B (RANK) ligand inhibitor denosumab—are approved for the prevention of SREs, these compounds have not shown benefit in terms of overall survival. However, emerging evidence has suggested that the combination of BTAs and abiraterone acetate, enzalutamide and the radiopharmaceutical radium-223 could result in improved clinical outcomes and prolonged survival in bone metastatic CRPC. In this review, we will provide an overview on bone tropism of prostate cancer and on the role of BTAs in metastatic hormone-sensitive and castration-resistant prostate cancer.

Probing Intravascular Adhesion and Extravasation of Tumor Cells with Microfluidics

Cancer metastasis is a multistep process during which tumor cells leave the primary tumor mass and form distant secondary colonies that are lethal. Circulating tumor cells (CTCs) are transported by body fluids to reach distant organs, where they will extravasate and either remain dormant or form new tumor foci. Development of methods to study the behavior of CTCs at the late stages of the intravascular journey is thus required to dissect the molecular mechanisms at play. Using recently developed microfluidics approaches, we have demonstrated that CTCs arrest intravascularly, through a two-step process: (a) CTCs stop using low energy and rapidly activated adhesion receptors to form transient metastable adhesions and (b) CTCs stabilize their adhesions to the endothelial layer with high energy and slowly activated adhesion receptors. In this methods chapter, we describe these easy-to-implement quantitative methods using commercially available microfluidic channels. We detail the use of fast live imaging combined to fine-tuned perfusion to measure the adhesion potential of CTC depending on flow velocities. We document how rapidly engaged early metastable adhesion can be discriminated from slower activated stable adhesion using microfluidics. Finally, CTC extravasation potential can be assessed within this setup using long-term cell culture under flow. Altogether, this experimental pipeline can be adapted to probe the adhesion (to the endothelial layer) and extravasation potential of any circulating cell.

MicroRNA-92a Targets SERTAD3 and Regulates the Growth, Invasion, and Migration of Prostate Cancer Cells via the P53 Pathway

Background

The miR-17-92 cluster, consisting of six mature miRNAs including miR-17, miR-18a, miR-19a, miR-19b, miR-20a, and miR-92a, plays a key role in the tumorigenesis and development of various cancers. The dysregulation of the cluster correlates with the biological mechanism of tumor growth and metastasis in vivo. However, the relationship between miR-17-92 cluster and malignancy of prostate cancer remains unclear, and its regulatory mechanism is worth investigating for controlling the proliferation and invasion of prostate cancer.

Materials and Methods

The expressions of miR-17-92 cluster members were measured using real-time quantitative RT-PCR. WB and real-time quantitative RT-PCR were used to detect the expression of SERTAD3, p38, p21, p53 protein levels and transcription levels. Cell proliferation and apoptosis were evaluated using cell proliferation assay, EdU and Hoechst assay, colony formation experiment and flow cytometry analyses. Cell migration and invasion were determined via transwell assays. The TargetScan, miRDB, starBase databases and luciferase reporter assays were used to confirm the target gene of miR-92a.

Results

The relative expression of miR-92a was threefold higher in the metastatic PC-3 cells compared with the non-metastatic LNCaP cells. Down-regulation of miR-92a in PC-3 cells led to the inhibition of cell proliferation, migration, and invasion, while its overexpression in LNCaP cells resulted in the promotion of cell proliferation, migration, and invasion. The role of SERTAD3 in prostate cancer can be alleviated by miR-92a inhibitor.

Conclusion

SERTAD3 was the direct target gene of miR-92a in prostate cancer cells; inhibition of SERTAD3-dependent miR-92a alleviated the growth, invasion, and migration of prostate cancer cells by regulating the expression of the key genes of the p53 pathway, including p38, p53 and p21. These results suggested that targeting SERTAD3 by the induction of overexpression of miR-92a may be a treatment option in prostate cancer.

Cancer immunotherapy needs to learn how to stick to its guns

Cancer immunotherapy and its budding effectiveness at improving patient outcomes has revitalized our hope to fight cancer in a logical and safe manner. Immunotherapeutic approaches to reengage the immune system have largely focused on reversing immune checkpoint inhibitor pathways, which suppress the antitumor response. Although these approaches have generated much excitement, they still lack absolute success. Interestingly, newly described host-tumor sugar chains (glycosylations) and glycosylation-binding proteins (lectins) play key roles in evading the immune system to determine cancer progression. In this issue of the JCI, Nambiar et al. used patient head and neck tumors and a mouse model system to investigate the role of galactose-binding lectin 1 (Gal1) in immunotherapy resistance. The authors demonstrated that Gal1 can affect immune checkpoint inhibitor therapy by increasing immune checkpoint molecules and immunosuppressive signaling in the tumor. Notably, these results suggest that targeting a tumor's glycobiological state will improve treatment efficacy.

Engineered Models of Metastasis with Application to Study Cancer Biomechanics

Three-dimensional complex biomechanical interactions occur from the initial steps of tumor formation to the later phases of cancer metastasis. Conventional monolayer cultures cannot recapitulate the complex microenvironment and chemical and mechanical cues that tumor cells experience during their metastatic journey, nor the complexity of their interactions with other, noncancerous cells. As alternative approaches, various engineered models have been developed to recapitulate specific features of each step of metastasis with tunable microenvironments to test a variety of mechanistic hypotheses. Here the main recent advances in the technologies that provide deeper insight into the process of cancer dissemination are discussed, with an emphasis on three-dimensional and mechanical factors as well as interactions between multiple cell types.

I-branched carbohydrates as emerging effectors of malignant progression

Cell surface carbohydrates, termed "glycans," are ubiquitous posttranslational effectors that can tune cancer progression. Often aberrantly displayed or found at atypical levels on cancer cells, glycans can impact essentially all progressive steps, from malignant transformation to metastases formation. Glycans are structural entities that can directly bind promalignant glycan-binding proteins and help elicit optimal receptor-ligand activity of growth factor receptors, integrins, integrin ligands, lectins, and other type-1 transmembrane proteins. Because glycans play an integral role in a cancer cell's malignant activity and are frequently uniquely expressed, preclinical studies on the suitability of glycans as anticancer therapeutic targets and their promise as biomarkers of disease progression continue to intensify. While sialylation and fucosylation have predominated the focus of cancer-associated glycan modifications, the emergence of blood group I antigens (or I-branched glycans) as key cell surface moieties capable of modulating cancer virulence has reenergized investigations into the role of the glycome in malignant progression. I-branched glycans catalyzed principally by the I-branching enzyme GCNT2 are now indicated in several malignancies. In this Perspective, the putative role of GCNT2/I-branching in cancer progression is discussed, including exciting insights on how I-branches can potentially antagonize the cancer-promoting activity of β-galactose-binding galectins.

Glycosylation in the Tumor Microenvironment: Implications for Tumor Angiogenesis and Metastasis

Just as oncogene activation and tumor suppressor loss are hallmarks of tumor development, emerging evidence indicates that tumor microenvironment-mediated changes in glycosylation play a crucial functional role in tumor progression and metastasis. Hypoxia and inflammatory events regulate protein glycosylation in tumor cells and associated stromal cells in the tumor microenvironment, which facilitates tumor progression and also modulates a patient's response to anti-cancer therapeutics. In this review, we highlight the impact of altered glycosylation on angiogenic signaling and endothelial cell adhesion, and the critical consequences of these changes in tumor behavior.

Bone vascular niche E-selectin induces mesenchymal-epithelial transition and Wnt activation in cancer cells to promote bone metastasis

How disseminated tumor cells (DTCs) engage specific stromal components in distant organs for survival and outgrowth is a critical but poorly understood step of the metastatic cascade. Previous studies have demonstrated the importance of the epithelial-mesenchymal transition (EMT) in promoting the cancer stem cell properties needed for metastasis initiation, while the reverse process of mesenchymal-epithelial transition (MET) is required for metastatic outgrowth. Here we report that this paradoxical requirement for simultaneous induction of both MET and cancer stem cell traits in DTCs is provided by bone vascular niche E-selectin, whose direct binding to cancer cells promotes bone metastasis by inducing MET and activating Wnt signaling. E-selectin binding activity mediated by α1–3 Fucosyltransferases Fut3/Fut6 and Glg1 are instrumental to the formation of bone metastasis. These findings provide unique insights into the functional role of E-selectin as a component of the vascular niche critical for metastatic colonization in bone.

Bone as a Preferential Site for Metastasis

Bone marrow provides a unique microenvironment favoring the colonization and outgrowth of metastatic tumor cells. Despite the high incidence of bone metastasis in breast and prostate cancer patients, many of the molecular mechanisms controlling metastatic progression remain unclear. Several gene signatures associated with bone metastasis have been reported, but no metastasis-specific gene alterations have been identified. Therefore, there has been considerable interest in understanding how the bone microenvironment impacts the behavior of disseminated tumor cells (DTCs) prior to and following colonization of the bone. Substantial evidence indicates that disruption of normal bone homeostasis by tumor-derived factors establishes a premetastatic niche within the bone that favors DTC colonization. Following dissemination, bone resident cells and the surrounding stroma provide critical signals that support tumor cell colonization, survival, and eventual outgrowth. Clinical data suggest that patients can harbor DTCs for years to decades prior to developing overt bone metastases, suggesting a period of tumor dormancy occurs in the bone marrow. Several dormancy-promoting factors have been recently identified; however, critical questions surrounding the molecular triggers and timing of tumor cell emergence from dormancy remain. Here, we review how metastatic tumor cells co-opt the bone marrow microenvironment for metastatic progression and discuss emerging insights into how to more effectively target DTCs and prevent metastasis. © 2018 The Authors. JBMR Plus published by Wiley Periodicals, Inc. on behalf of American Society for Bone and Mineral Research.

Genetics and biology of prostate cancer

Despite the high long-term survival in localized prostate cancer, metastatic prostate cancer remains largely incurable even after intensive multimodal therapy. The lethality of advanced disease is driven by the lack of therapeutic regimens capable of generating durable responses in the setting of extreme tumor heterogeneity on the genetic and cell biological levels. Here, we review available prostate cancer model systems, the prostate cancer genome atlas, cellular and functional heterogeneity in the tumor microenvironment, tumor-intrinsic and tumor-extrinsic mechanisms underlying therapeutic resistance, and technological advances focused on disease detection and management. These advances, along with an improved understanding of the adaptive responses to conventional cancer therapies, anti-androgen therapy, and immunotherapy, are catalyzing development of more effective therapeutic strategies for advanced disease. In particular, knowledge of the heterotypic interactions between and coevolution of cancer and host cells in the tumor microenvironment has illuminated novel therapeutic combinations with a strong potential for more durable therapeutic responses and eventual cures for advanced disease. Improved disease management will also benefit from artificial intelligence-based expert decision support systems for proper standard of care, prognostic determinant biomarkers to minimize overtreatment of localized disease, and new standards of care accelerated by next-generation adaptive clinical trials.

Loss of GCNT2/I-branched glycans enhances melanoma growth and survival

Cancer cells often display altered cell-surface glycans compared to their nontransformed counterparts. However, functional contributions of glycans to cancer initiation and progression remain poorly understood. Here, from expression-based analyses across cancer lineages, we found that melanomas exhibit significant transcriptional changes in glycosylation-related genes. This gene signature revealed that, compared to normal melanocytes, melanomas downregulate I-branching glycosyltransferase, GCNT2, leading to a loss of cell-surface I-branched glycans. We found that GCNT2 inversely correlated with clinical progression and that loss of GCNT2 increased melanoma xenograft growth, promoted colony formation, and enhanced cell survival. Conversely, overexpression of GCNT2 decreased melanoma xenograft growth, inhibited colony formation, and increased cell death. More focused analyses revealed reduced signaling responses of two representative glycoprotein families modified by GCNT2, insulin-like growth factor receptor and integrins. Overall, these studies reveal how subtle changes in glycan structure can regulate several malignancy-associated pathways and alter melanoma signaling, growth, and survival.

Analysis of adhesion kinetics of cancer cells on inflamed endothelium using a microfluidic platform

Metastasis is the ultimate cause of death among the vast majority of cancer patients. This process is comprised of multiple steps, including the migration of circulating cancer cells across microvasculature. This trans-endothelial migration involves the adhesion and eventual penetration of cancer cells to the vasculature of the target organ. Many of these mechanisms remain poorly understood due to poor control of pathophysiological conditions in tumor models. In this work, a microfluidic device was developed to support the culture and observation of engineered microvasculature with systematic control of the environmental characteristics. This device was then used to study the adhesion of circulating cancer cells to an endothelium under varying conditions to delineate the effects of hemodynamics and inflammations. The resulting understanding will help to establish a quantitative and biophysical mechanism of interactions between cancer cells and endothelium.

Bone Marrow Microenvironment as a Regulator and Therapeutic Target for Prostate Cancer Bone Metastasis

Bone is the most common site of prostate cancer metastasis. Once prostate cancer cells metastasize to bone, the mortality rate of prostate cancer patients increases significantly. Furthermore, bone metastases produce multiple skeletal complications, including bone pain that impairs the patients' quality of life. Effective therapies for bone metastatic disease are underdeveloped with most current therapies being primarily palliative with modest survival benefit. Although the exact mechanisms through which prostate cancer metastasizes to bone are unclear, growing evidence suggests that the bone marrow microenvironment, particularly its hematopoietic activity, is a significant mediator of prostate cancer bone tropism. Moreover, the bone microenvironment may regulate metastatic prostate cancer cells between dormant and proliferative states. In this review, we discuss (1) how prostate cancer cells interact with the bone microenvironment to establish bone metastases and (2) current and future potential treatments for prostate cancer patients with bone metastases.

Potent Inhibition of miR-34b on Migration and Invasion in Metastatic Prostate Cancer Cells by Regulating the TGF-β Pathway

The importance of miRNAs in the progression of prostate cancer (PCa) has further been supported by the finding that miRNAs have been identified as potential oncogenes or tumor suppressors in PCa. Indeed, in eukaryotes, miRNAs have been found to regulate and control gene expression by degrading mRNA at the post-transcriptional level. In this study, we investigated the expression of miR-34 family members, miR-34b and miR-34c, in different PCa cell lines, and discussed the molecular mechanism of miR-34b in the invasion and migration of PCa cells in vitro. The difference analyses of the transcriptome between the DU145 and PC3 cell lines demonstrated that both miR-34b and -34c target critical pathways that are involved in metabolism, such as proliferation, and migration, and invasion. The molecular expression of miR-34b/c were lower in PC3 cells. Moreover, over-expression of miR-34b/c in PC3 cells caused profound phenotypic changes, including decreased cell proliferation, migration and invasion. Moreover, the players that regulate expression levels of transforming growth factor-β (TGF-β), TGF-β receptor 1 (TGF-βR1), and p53 or phosphorylation levels of mothers against decapentaplegic 3 (SMAD3) in the TGF-β/Smad3 signaling pathway have yet to be elucidated, and will provide novel tools for diagnosis and treatment of metastatic PCa.

Cancer-associated fibroblasts promote directional cancer cell migration by aligning fibronectin

Cancer-associated fibroblasts (CAFs) are major components of the carcinoma microenvironment that promote tumor progression. However, the mechanisms by which CAFs regulate cancer cell migration are poorly understood. In this study, we show that fibronectin (Fn) assembled by CAFs mediates CAF-cancer cell association and directional migration. Compared with normal fibroblasts, CAFs produce an Fn-rich extracellular matrix with anisotropic fiber orientation, which guides the cancer cells to migrate directionally. CAFs align the Fn matrix by increasing nonmuscle myosin II- and platelet-derived growth factor receptor α-mediated contractility and traction forces, which are transduced to Fn through α5β1 integrin. We further show that prostate cancer cells use αv integrin to migrate efficiently and directionally on CAF-derived matrices. We demonstrate that aligned Fn is a prominent feature of invasion sites in human prostatic and pancreatic carcinoma samples. Collectively, we present a new mechanism by which CAFs organize the Fn matrix and promote directional cancer cell migration.

Liver Metastasis Is Facilitated by the Adherence of Circulating Tumor Cells to Vascular Fibronectin Deposits

The interaction between circulating tumor cells (CTC) and endothelial cells during extravasation is a critical process during metastatic colonization, but its mechanisms remain poorly characterized. Here we report that the luminal side of liver blood vessels contains fibronectin deposits that are enriched in mice bearing primary tumors and are also present in vessels from human livers affected with metastases. Cancer cells attached to endothelial fibronectin deposits via talin1, a major component of focal adhesions. Talin1 depletion impaired cancer cell adhesion to the endothelium and transendothelial migration, resulting in reduced liver metastasis formation in vivo Talin1 expression levels in patient CTC's correlated with prognosis and therapy response. Together, our findings uncover a new mechanism for liver metastasis formation involving an active contribution of hepatic vascular fibronectin and talin1 in cancer cells. Cancer Res; 77(13); 3431-41. ©2017 AACR.

T-lymphocyte homing: an underappreciated yet critical hurdle for successful cancer immunotherapy

Advances in cancer immunotherapy have offered new hope for patients with metastatic disease. This unfolding success story has been exemplified by a growing arsenal of novel immunotherapeutics, including blocking antibodies targeting immune checkpoint pathways, cancer vaccines, and adoptive cell therapy (ACT). Nonetheless, clinical benefit remains highly variable and patient-specific, in part, because all immunotherapeutic regimens vitally hinge on the capacity of endogenous and/or adoptively transferred T-effector (T_eff) cells, including chimeric antigen receptor (CAR) T cells, to home efficiently into tumor target tissue. Thus, defects intrinsic to the multi-step T-cell homing cascade have become an obvious, though significantly underappreciated contributor to immunotherapy resistance. Conspicuous have been low intralesional frequencies of tumor-infiltrating T-lymphocytes (TILs) below clinically beneficial threshold levels, and peripheral rather than deep lesional TIL infiltration. Therefore, a T_eff cell 'homing deficit' may arguably represent a dominant factor responsible for ineffective immunotherapeutic outcomes, as tumors resistant to immune-targeted killing thrive in such permissive, immune-vacuous microenvironments. Fortunately, emerging data is shedding light into the diverse mechanisms of immune escape by which tumors restrict T_eff cell trafficking and lesional penetrance. In this review, we scrutinize evolving knowledge on the molecular determinants of T_eff cell navigation into tumors. By integrating recently described, though sporadic information of pivotal adhesive and chemokine homing signatures within the tumor microenvironment with better established paradigms of T-cell trafficking under homeostatic or infectious disease scenarios, we seek to refine currently incomplete models of T_eff cell entry into tumor tissue. We further summarize how cancers thwart homing to escape immune-mediated destruction and raise awareness of the potential impact of immune checkpoint blockers on T_eff cell homing. Finally, we speculate on innovative therapeutic opportunities for augmenting T_eff cell homing capabilities to improve immunotherapy-based tumor eradication in cancer patients, with special focus on malignant melanoma.

Determinants of Organotropic Metastasis

The spread of cancer from a primary tumor to distant organ sites is the most devastating aspect of malignancy. Dissemination to specific organs depends upon blood flow patterns and characteristics of the distant organ environment, such as the vascular architecture, stromal cell content, and the biochemical milieu of growth factors, signaling molecules, and metabolic substrates, which can be permissive or antagonistic to metastatic colonization. Metastatic tumor cells possess intrinsic cellular properties selected for adaptation to specific organ environments, where they co-opt growth and survival signals, undergo metabolic reprogramming, and subvert resident stromal cell activities to promote extravasation, immune evasion, angiogenesis, and overt metastatic growth. Recent work and new experimental models of metastatic organotropism are uncovering crucial details of how malignant cells metastasize to specific tissues, revealing key mediators that prepare metastatic niches in specific organs and identifying new targets that offer attractive options for therapeutic intervention.

On the trail of the glycan codes stored in cancer-related cell adhesion proteins

Changes in the profile of protein glycosylation are a hallmark of ongoing neoplastic transformation. A unique set of tumor-associated carbohydrate antigens expressed on the surface of malignant cells may serve as powerful diagnostic and therapeutic targets. Cell-surface proteins with altered glycosylation affect the growth, proliferation and survival of those cells, and contribute to their acquisition of the ability to migrate and invade. They may also facilitate tumor-induced immunosuppression and the formation of distant metastases. Deciphering the information encoded in these particular glycan portions of glycoconjugates may shed light on the mechanisms of cancer progression and metastasis. A majority of the related review papers have focused on overall changes in the patterns of cell-surface glycans in various cancers, without pinpointing the molecular carriers of these glycan structures. The present review highlights the ways in which particular tumor-associated glycan(s) coupled with a given membrane-bound protein influence neoplastic cell behavior during the development and progression of cancer. We focus on altered glycosylated cell-adhesion molecules belonging to the cadherin, integrin and immunoglobulin-like superfamilies, examined in the context of molecular interactions.

2,3,5,4'-tetrahydroxystilbene-2-O-β-D-glucoside suppresses human colorectal cancer cell metastasis through inhibiting NF-κB activation

2,3,5,4'-tetrahydroxystilbene-2-O-β-D-glucoside (THSG), a major component of Polygonum multiflorum Thunb (He-Shou-Wu), has been reported to exhibit antioxidant and anti-inflammatory effects. However, its anti-metastatic effect against colorectal cancer is still unclear. In this study, cell migration, invasion and adhesion abilities as well as metastasis-associated protein and NF-κB pathway signaling factor expression were analyzed after treating HT-29 cells with THSG. According to the results, the migration and invasiveness of HT-29 cells were reduced after treatment with 5 or 10 mM THSG (p<0.05). Additionally, the levels of matrix metalloproteinase-2 (MMP-2) and phosphorylated VE-cadherin in HT-29 cells were reduced and the transepithelial electrical resistance (TEER) of EA.hy926 endothelial cell monolayers was increased after incubation in THSG for 24 h (p<0.05). Cell adhesion ability and the E-selectin and intercellular adhesion molecule-1 (ICAM-1) protein levels were reduced when EA.hy926 endothelial cells were treated with THSG (p<0.05). In addition, the cytoplasmic phosphorylation of IκB, the nuclear p65 level and the DNA-binding activity of NF-κB were reduced after treating HT-29 or EA.hy926 cells with 5 or 10 mM THSG (p<0.05). These results suggest that THSG inhibits HT-29 cell metastasis by suppressing cell migration, invasion and adhesion. Furthermore, THSG inhibits metastasis-associated protein expression by suppressing NF-κB pathway activation.

Effects of Panax notoginseng on the Metastasis of Human Colorectal Cancer Cells

The goal of this study was to investigate the effect of the Panax notoginseng ethanol extract (PNEE) on the regulation of human colorectal cancer (CRC) metastasis. The migratory, invasive, and adhesive abilities and the expression of metastasis-associated regulatory molecules in cultured human CRC cells (HCT-116) treated with the PNEE were analyzed in this study. The migratory and invasive abilities of HCT-116 cells were reduced after PNEE treatment. The incubation of HCT-116 cells with the PNEE for 24 h decreased MMP-9 expression and increased E-cadherin expression compared with the control group. The adhesion reaction assay indicated that treatment with the PNEE led to significantly decreased HCT-116 adhesion to endothelial cells (EA.hy926 cells). The integrin-1 protein levels in HCT-116 cells were significantly decreased following treatment with the PNEE. Similarly, the protein levels of E-selectin and intercellular adhesion molecule-1 (ICAM-1) were significantly decreased by treatment of the EA.hy926 endothelial cells with PNEE. A scanning electron microscope (SEM) examination indicated that HCT-116 cells treated with LPS combined with the PNEE had a less flattened and retracted shape compared with LPS-treated cells, and this change in shape was found to be a phenomenon of extravasation invasion. The transepithelial electrical resistance (TEER) of the EA.hy926 endothelial cell monolayer increased after incubation with the PNEE for 24 h. A cell-cell permeability assay indicated that HCT-116 cells treated with the PNEE displayed significantly reduced levels of phosphorylated VE-cadherin (p-VE-cadherin). These results demonstrate the antimetastatic properties of the PNEE and show that the PNEE affects cells by inhibiting cell migration, invasion, and adhesion and regulating the expression of metastasis-associated signaling molecules.

Quantification of cancer cell extravasation in vivo

Cancer cell 'invasiveness' is one of the main driving forces in cancer metastasis, and assays that quantify this key attribute of cancer cells are crucial in cancer metastasis research. The research goal of many laboratories is to elucidate the signaling pathways and effectors that are responsible for cancer cell invasion, but many of these experiments rely on in vitro methods that do not specifically simulate individual steps of the metastatic cascade. Cancer cell extravasation is arguably the most important example of invasion in the metastatic cascade, whereby a single cancer cell undergoes transendothelial migration, forming invasive processes known as invadopodia to mediate translocation of the tumor cell from the vessel lumen into tissue in vivo. We have developed a rapid, reproducible and economical technique to evaluate cancer cell invasiveness by quantifying in vivo rates of cancer cell extravasation in the chorioallantoic membrane (CAM) of chicken embryos. This technique enables the investigator to perform well-powered loss-of-function studies of cancer cell extravasation within 24 h, and it can be used to identify and validate drugs with potential antimetastatic effects that specifically target cancer cell extravasation. A key advantage of this technique over similar assays is that intravascular cancer cells within the capillary bed of the CAM are clearly distinct from extravasated cells, which makes cancer cell extravasation easy to detect. An intermediate level of experience in injections of the chorioallantoic membrane of avian embryos and cell culture techniques is required to carry out the protocol.

Carcinoma-associated fucosylated antigens are markers of the epithelial state and can contribute to cell adhesion through CLEC17A (Prolectin)

Terminal fucosylated motifs of glycoproteins and glycolipid chains are often altered in cancer cells. We investigated the link between fucosylation changes and critical steps in cancer progression: epithelial-to-mesenchymal transition (EMT) and lymph node metastasis.Using mammary cell lines, we demonstrate that during EMT, expression of some fucosylated antigens (e.g.: Lewis Y) is decreased as a result of repression of the fucosyltransferase genes FUT1 and FUT3. Moreover, we identify the fucose-binding bacterial lectin BC2L-C-Nt as a specific probe for the epithelial state.Prolectin (CLEC17A), a human lectin found on lymph node B cells, shares ligand specificities with BC2L-C-Nt. It binds preferentially to epithelial rather than to mesenchymal cells, and microfluidic experiments showed that prolectin behaves as a cell adhesion molecule for epithelial cells. Comparison of paired primary tumors/lymph node metastases revealed an increase of prolectin staining in metastasis and high FUT1 and FUT3 mRNA expression was associated with poor prognosis. Our data suggest that tumor cells invading the lymph nodes and expressing fucosylated motifs associated with the epithelial state could use prolectin as a colonization factor.

When the endothelium scores an own goal: endothelial cells actively augment metastatic extravasation through endothelial-mesenchymal transition

Endothelial-mesenchymal transition (EndMT) is an important mechanism during organ development and in certain pathological conditions. For example, EndMT contributes to myofibroblast formation during organ fibrosis, and it has been identified as an important source of cancer-associated fibroblasts, facilitating tumor progression. Recently, EndMT was proposed to modulate endothelial function during intravasation and extravasation of metastatic tumor cells. Evidence suggests that endothelial cells are not passive actors during transendothelial migration (TEM) of cancer cells, as there are profound changes in endothelial junctional protein expression, signaling, permeability, and contractility. This review describes these alterations in endothelial characteristics during TEM of metastatic tumor cells and discusses them in the context of EndMT. EndMT could play an important role during metastatic intravasation and extravasation, a novel hypothesis that may lead to new therapeutic approaches to tackle metastatic disease.

MicroRNA-34a regulates WNT/TCF7 signaling and inhibits bone metastasis in Ras-activated prostate cancer

Aberrant activation of Ras and WNT signaling are key events that have been shown to be up-regulated in prostate cancer that has metastasized to the bone. However, the regulatory mechanism of combinatorial Ras and WNT signaling in advanced prostate cancer is still unclear. TCF7, a WNT signaling-related gene, has been implicated as a critical factor in bone metastasis, and here we show that TCF7 is a direct target of miR-34a. In samples of prostate cancer patients, miR-34a levels are inversely correlated with TCF7 expression and a WNT dependent gene signature. Ectopic miR-34a expression inhibited bone metastasis and reduced cancer cell proliferation in a Ras-dependent xenograft model. We demonstrate that miR-34a can directly interfere with the gene expression of the anti-proliferative BIRC5, by targeting BIRC5 3′UTR. Importantly, BIRC5 overexpression was sufficient to reconstitute anti-apoptotic signaling in cells expressing high levels of miR-34a. In prostate cancer patients, we found that BIRC5 levels were positively correlated with a Ras signaling signature expression. Our data show that the bone metastasis and anti-apoptotic effects found in Ras signaling-activated prostate cancer cells require miR-34a deficiency, which in turn aids in cell survival by activating the WNT and anti-apoptotic signaling pathways thereby inducing TCF7 and BIRC5 expressions.

Identification of Bone-Derived Factors Conferring De Novo Therapeutic Resistance in Metastatic Prostate Cancer

Resistance to currently available targeted therapies significantly hampers the survival of patients with prostate cancer with bone metastasis. Here we demonstrate an important resistance mechanism initiated from tumor-induced bone. Studies using an osteogenic patient-derived xenograft, MDA-PCa-118b, revealed that tumor cells resistant to cabozantinib, a Met and VEGFR-2 inhibitor, reside in a "resistance niche" adjacent to prostate cancer-induced bone. We performed secretome analysis of the conditioned medium from tumor-induced bone to identify proteins (termed "osteocrines") found within this resistance niche. In accordance with previous reports demonstrating that activation of integrin signaling pathways confers therapeutic resistance, 27 of the 90 osteocrines identified were integrin ligands. We found that following cabozantinib treatment, only tumor cells positioned adjacent to the newly formed woven bone remained viable and expressed high levels of pFAK-Y397 and pTalin-S425, mediators of integrin signaling. Accordingly, treatment of C4-2B4 cells with integrin ligands resulted in increased pFAK-Y397 expression and cell survival, whereas targeting integrins with FAK inhibitors PF-562271 or defactinib inhibited FAK phosphorylation and reduced the survival of PC3-mm2 cells. Moreover, treatment of MDA-PCa-118b tumors with PF-562271 led to decreased tumor growth, irrespective of initial tumor size. Finally, we show that upon treatment cessation, the combination of PF-562271 and cabozantinib delayed tumor recurrence in contrast to cabozantinib treatment alone. Our studies suggest that identifying paracrine de novo resistance mechanisms may significantly contribute to the generation of a broader set of potent therapeutic tools that act combinatorially to inhibit metastatic prostate cancer.

E-selectin ligand-1 controls circulating prostate cancer cell rolling/adhesion and metastasis

Circulating prostate cancer (PCa) cells preferentially roll and adhere on bone marrow vascular endothelial cells, where abundant E-selectin and stromal cell-derived factor 1 (SDF-1) are expressed, subsequently initiating a cascade of activation events that eventually lead to the development of metastases. To elucidate the roles of circulating PCa cells' rolling and adhesion behaviors in cancer metastases, we applied a dynamic cylindrical flow-based microchannel device that is coated with E-selectin and SDF-1, mimicking capillary endothelium. Using this device we captured a small fraction of rolling PCa cells. These rolling cells display higher static adhesion ability, more aggressive cancer phenotypes and stem-like properties. Importantly, mice received rolling PCa cells, but not floating PCa cells, developed cancer metastases. Genes coding for E-selectin ligands and genes associated with cancer stem cells and metastasis were elevated in rolling PCa cells. Knock down of E-selectin ligand 1(ESL-1), significantly impaired PCa cells' rolling capacity and reduced cancer aggressiveness. Moreover, ESL-1 activates RAS and MAP kinase signal cascade, consequently inducing the downstream targets. In summary, circulating PCa cells' rolling capacity contributes to PCa metastasis, and that is in part controlled by ESL-1.

The role of "bone immunological niche" for a new pathogenetic paradigm of osteoporosis

Osteoporosis is characterized by low bone mass and microarchitectural deterioration of bone tissue. The etiology and pathogenetic mechanisms of osteoporosis have not been clearly elucidated. Osteoporosis is linked to bone resorption by the activation of the osteoclastogenic process. The breakdown of homeostasis among pro- and antiosteoclastogenic cells causes unbalanced bone remodeling. The complex interactions among these cells in the bone microenvironment involve several mediators and proinflammatory pathways. Thus, we may consider the bone microenvironment as a complex system in which local and systemic immunity are regulated and we propose to consider it as an "immunological niche." The study of the "bone immunological niche" will permit a better understanding of the complex cell trafficking which regulates bone resorption and disease. The goal of a perfect therapy for osteoporosis would be to potentiate good cells and block the bad ones. In this scenario, additional factors may take part in helping or hindering the proosteoblastogenic factors. Several proosteoblastogenic and antiosteoclastogenic agents have already been identified and some have been developed and commercialized as biological therapies for osteoporosis. Targeting the cellular network of the "bone immunological niche" may represent a successful strategy to better understand and treat osteoporosis and its complications.

SDF-1alpha concentration dependent modulation of RhoA and Rac1 modifies breast cancer and stromal cells interaction

Background

The interaction of SDF-1alpha with its receptor CXCR4 plays a role in the occurrence of distant metastasis in many solid tumors. This interaction increases migration from primary sites as well as homing at distant sites.

Methods

Here we investigated how SDF-1α could modulate both migration and adhesion of cancer cells through the modulation of RhoGTPases.

Results

We show that different concentrations of SDF-1α modulate the balance of adhesion and migration in cancer cells. Increased migration was obtained at 50 and 100 ng/ml of SDF-1α; however migration was reduced at 200 ng/ml. The adhesion between breast cancer cells and BMHC was significantly increased by SDF-1α treatment at 200 ng/ml and reduced using a blocking monoclonal antibody against CXCR4. We showed that at low SDF-1α concentration, RhoA was activated and overexpressed, while at high concentration Rac1 was promoting SDF-1α mediating-cell adhesion.

Conclusion

We conclude that SDF-1α concentration modulates migration and adhesion of breast cancer cells, by controlling expression and activation of RhoGTPases.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-015-1556-7) contains supplementary material, which is available to authorized users.

Quantitative Characterization of E-selectin Interaction with Native CD44 and P-selectin Glycoprotein Ligand-1 (PSGL-1) Using a Real Time Immunoprecipitation-based Binding Assay

Selectins (E-, P-, and L-selectins) interact with glycoprotein ligands to mediate the essential tethering/rolling step in cell transport and delivery that captures migrating cells from the circulating flow. In this work, we developed a real time immunoprecipitation assay on a surface plasmon resonance chip that captures native glycoforms of two well known E-selectin ligands (CD44/hematopoietic cell E-/L-selectin ligand and P-selectin glycoprotein ligand-1) from hematopoietic cell extracts. Here we present a comprehensive characterization of their binding to E-selectin. We show that both ligands bind recombinant monomeric E-selectin transiently with fast on- and fast off-rates, whereas they bind dimeric E-selectin with remarkably slow on- and off-rates. This binding requires the sialyl Lewis x sugar moiety to be placed on both O- and N-glycans, and its association, but not dissociation, is sensitive to the salt concentration. Our results suggest a mechanism through which monomeric selectins mediate initial fast on and fast off kinetics to help capture cells out of the circulating shear flow; subsequently, tight binding by dimeric/oligomeric selectins is enabled to significantly slow rolling.

Exosomes serve as tumour markers for personalized diagnostics owing to their important role in cancer metastasis

Exosomes, membrane vesicles of 40–100 nm in diameter, are derived from endosomes in various cells. The bioactive molecules specifically packed into exosomes can be horizontally transferred into recipient cells changing their biological properties, by which tumour cells continuously modify their surrounding microenvironment and distant target cells favouring cancer metastasis. It has been suspected for a long time that exosomes participate in the whole process of tumour metastasis. Although there is much unknown and many controversies in the role of cancer exosome, the major contribution of tumour-associated exosomes to different steps of cancer metastasis are demonstrated in this review. Mainly because these exosomes are easily accessible and capable of representing their parental cells, exosomes draw much attention as a promising biomarker for tumour screening, diagnosis and prognosis. Currently, researchers have found numerous biomarkers in exosomes with great potential to be utilized in personalized medicine. In this article, we summarize the roles of biomarkers, which are validated by clinical samples. Even though many conundrums remain, such as exosome extraction, large multicentre validation of biomarkers and data interpretation, exosomes are certain to be used in clinical practice in the near future as the field rapidly expands.

PKCε Is an Essential Mediator of Prostate Cancer Bone Metastasis

The bone is a preferred site for metastatic homing of prostate cancer cells. Once prostate cancer patients develop skeletal metastases, they eventually succumb to the disease; therefore, it is imperative to identify key molecular drivers of this process. This study examines the involvement of protein kinase C epsilon (PKCε), an oncogenic protein that is abnormally overexpressed in human tumor specimens and cell lines, on prostate cancer cell bone metastasis. PC3-ML cells, a highly invasive prostate cancer PC3 derivative with bone metastatic colonization properties, failed to induce skeletal metastatic foci upon inoculation into nude mice when PKCε expression was silenced using shRNA. Interestingly, while PKCε depletion had only marginal effects on the proliferative, adhesive, and migratory capacities of PC3-ML cells in vitro or in the growth of xenografts upon s.c. inoculation, it caused a significant reduction in cell invasiveness. Notably, PKCε was required for transendothelial cell migration (TEM) as well as for the growth of PC3-ML cells in a bone biomimetic environment. At a mechanistic level, PKCε depletion abrogates the expression of IL1β, a cytokine implicated in skeletal metastasis. Taken together, PKCε is a key factor for driving the formation of bone metastasis by prostate cancer cells and is a potential therapeutic target for advanced stages of the disease.

IMPLICATIONS

This study uncovers an important new function of PKCε in the dissemination of cancer cells to the bone; thus, highlighting the promising potential of this oncogenic kinase as a therapeutic target for skeletal metastasis.

Targeting bone metastases in prostate cancer: improving clinical outcome

Bone metastases develop in most patients with metastatic castration-resistant prostate cancer (mCRPC). They affect the structural integrity of bone, manifesting as pain and skeletal-related events (SREs), and are the primary cause of patient disability, reduced quality of life (QOL) and death. Understanding the pathophysiology of bone metastases resulted in the development of agents that improve clinical outcome, suggesting that managing both the systemic disease and associated bone events is important. Historically, the treatment of CRPC bone metastases with early radiopharmaceuticals and external beam radiation therapy was largely supportive; however, now, zoledronic acid and denosumab are integral to the therapeutic strategy for mCRPC. These agents substantially reduce skeletal morbidity and improve patient QOL. Radium-223 dichloride is the first bone-targeting agent to show improved survival and reduced pain and symptomatic skeletal events in patients with mCRPC without visceral disease. Five other systemic agents are currently approved for use in mCRPC based on their ability to improve survival. These include the cytotoxic drugs docetaxel and cabazitaxel, the hormone-based therapies, abiraterone and enzalutamide, and the immunotherapeutic vaccine sipuleucel-T. Abiraterone and enzalutamide are able to reduce SREs and improve survival in this setting. Novel agents targeting tumour and bone cells are under clinical development.

Endothelial-mesenchymal transition of brain endothelial cells: possible role during metastatic extravasation

Cancer progression towards metastasis follows a defined sequence of events described as the metastatic cascade. For extravasation and transendothelial migration metastatic cells interact first with endothelial cells. Yet the role of endothelial cells during the process of metastasis formation and extravasation is still unclear, and the interaction between metastatic and endothelial cells during transendothelial migration is poorly understood. Since tumor cells are well known to express TGF-β, and the compact endothelial layer undergoes a series of changes during metastatic extravasation (cell contact disruption, cytoskeletal reorganization, enhanced contractility), we hypothesized that an EndMT may be necessary for metastatic extravasation. We demonstrate that primary cultured rat brain endothelial cells (BEC) undergo EndMT upon TGF-β1 treatment, characterized by the loss of tight and adherens junction proteins, expression of fibronectin, β1-integrin, calponin and α-smooth muscle actin (SMA). B16/F10 cell line conditioned and activated medium (ACM) had similar effects: claudin-5 down-regulation, fibronectin and SMA expression. Inhibition of TGF-β signaling during B16/F10 ACM stimulation using SB-431542 maintained claudin-5 levels and mitigated fibronectin and SMA expression. B16/F10 ACM stimulation of BECs led to phosphorylation of Smad2 and Smad3. SB-431542 prevented SMA up-regulation upon stimulation of BECs with A2058, MCF-7 and MDA-MB231 ACM as well. Moreover, B16/F10 ACM caused a reduction in transendothelial electrical resistance, enhanced the number of melanoma cells adhering to and transmigrating through the endothelial layer, in a TGF-β-dependent manner. These effects were not confined to BECs: HUVECs showed TGF-β-dependent SMA expression when stimulated with breast cancer cell line ACM. Our results indicate that an EndMT may be necessary for metastatic transendothelial migration, and this transition may be one of the potential mechanisms occurring during the complex phenomenon known as metastatic extravasation.

Cancer cells remodel themselves and vasculature to overcome the endothelial barrier

Metastasis refers to the spread of cancer cells from a primary tumor to distant organs mostly via the bloodstream. During the metastatic process, cancer cells invade blood vessels to enter circulation, and later exit the vasculature at a distant site. Endothelial cells that line blood vessels normally serve as a barrier to the movement of cells into or out of the blood. It is thus critical to understand how metastatic cancer cells overcome the endothelial barrier. Epithelial cancer cells acquire increased motility and invasiveness through epithelial-to-mesenchymal transition (EMT), which enables them to move toward vasculature. Cancer cells also express a variety of adhesion molecules that allow them to attach to vascular endothelium. Finally, cancer cells secrete or induce growth factors and cytokines to actively prompt vascular hyperpermeability that compromises endothelial barrier function and facilitates transmigration of cancer cells through the vascular wall. Elucidation of the mechanisms underlying metastatic dissemination may help develop new anti-metastasis therapeutics.

Talin1 phosphorylation activates β1 integrins: a novel mechanism to promote prostate cancer bone metastasis

Talins are adaptor proteins that regulate focal adhesion signaling by conjugating integrins to the cytoskeleton. Talins directly bind integrins and are essential for integrin activation. We previously showed that β1 integrins are activated in metastatic prostate cancer (PCa) cells, increasing PCa metastasis to lymph nodes and bone. However, how β1 integrins are activated in PCa cells is unknown. In this study, we identified a novel mechanism of β1 integrin activation. Using knockdown experiments, we first demonstrated talin1, but not talin2, is important in β1 integrin activation. We next showed that talin1 S425 phosphorylation, but not total talin1 expression, correlates with metastatic potential of PCa cells. Expressing a non-phosphorylatable mutant, talin1^S425A, in talin1-silenced PC3-MM2 and C4-2B4 PCa cells, decreased activation of β1 integrins, integrin-mediated adhesion, motility, and increased the sensitivity of the cells to anoikis. In contrast, re-expression of the phosphorylation-mimicking mutant talin1^S425D led to increased β1 integrin activation and generated biologic effects opposite to talin1^S425A expression. In the highly metastatic PC3-MM2 cells, expression of a non-phosphorylatable mutant, talin1^S425A, in talin1-silenced PC3-MM2 cells, abolished their ability to colonize in the bone following intracardiac injection, while re-expression of phosphorylation-mimicking mutant talin1^S425D restored their ability to metastasize to bone. Immunohistochemical staining demonstrated that talin S425 phosphorylation is significantly increased in human bone metastases when compared to normal tissues, primary tumors, or lymph node metastases. We further showed that p35 expression, an activator of Cdk5, and Cdk5 activity were increased in metastatic tumor cells, and that Cdk5 kinase activity is responsible for talin1 phosphorylation and subsequent β1 integrin activation. Together, our study reveals Cdk5-mediated phosphorylation of talin1 leading to β1 integrin activation is a novel mechanism that increases metastatic potential of PCa cells.

Anterior gradient protein-2 is a regulator of cellular adhesion in prostate cancer

Anterior Gradient Protein (AGR-2) is reported to be over-expressed in many epithelial cancers and promotes metastasis. A clear-cut mechanism for its observed function(s) has not been previously identified. We found significant upregulation of AGR-2 expression in a bone metastatic prostate cancer cell line, PC3, following culturing in bone marrow-conditioned medium. Substantial AGR-2 expression was also confirmed in prostate cancer tissue specimens in patients with bone lesions. By developing stable clones of PC3 cells with varying levels of AGR-2 expression, we identified that abrogation of AGR-2 significantly reduced cellular attachment to fibronectin, collagen I, collagen IV, laminin I and fibrinogen. Loss of cellular adhesion was associated with sharp decrease in the expression of α4, α5, αV, β3 and β4 integrins. Failure to undergo apoptosis following detachment is a hallmark of epithelial cancer metastasis. The AGR-2-silenced PC3 cells showed higher resistance to Tumor necrosis factor-related apoptosis- inducing ligand (TRAIL) induced apoptosis in vitro. This observation was also supported by significantly reduced Caspase-3 expression in AGR-2-silenced PC3 cells, which is a key effector of both extrinsic and intrinsic death signaling pathways. These data suggest that AGR-2 influence prostate cancer metastasis by regulation of cellular adhesion and apoptosis.