前列腺癌的骨转移机制

前列腺癌骨转移的分子与细胞机制仍不清楚.前列腺癌骨转移过程中肿瘤细胞的趋化性,肿瘤细胞与骨骼微环境之间各种分子的相互作用以及肿瘤细胞、破骨细胞、成骨细胞和骨基质之间的恶性循环是近年来前列腺癌骨转移研究的热点.     

Breast cancer-derived factors facilitate osteolytic bone metastasis

Bone is the most common site of breast cancer metastasis. Skeletal metastases resulting from breast cancer are most often osteolytic, and contribute to the morbidity and mortality associated with this disease. Over the past several years, significant effort has been focused on elucidating the molecular mechanisms that govern this process. To accomplish this task, animal model systems have been generated to study the process of breast cancer metastasis to bone. These include: intraosseous injection that models tumor growth in the bone marrow, cardiac injections that permit cancer cell dissemination to the bone marrow from the bloodstream, and spontaneous bone metastasis originating from the mammary gland. Importantly, these various model systems have been combined with gene expression profiling to compare breast cancer populations with distinct bone metastatic potentials in the hopes of finding the genes that facilitate this process. The result has been the accumulation of an impressive body of evidence detailing a complex web of interactions between breast cancer cells, the mineralized bone matrix and host cells resident in bone; such as osteoblasts, osteoclasts and bone marrow endothelium. In this review we will address new developments that underscore the importance of secreted proteins and cell surface receptors expressed on breast cancer cells that play key roles in promoting bone resorption and tumor growth. Recent results from both basic and clinical research reveal that similar metastatic functions, such as adhesion and invasion, are conserved across a variety of bone metastatic breast cancer cells and different sets of genes can fulfill these requirements.     

Biology of breast cancer bone metastasis

Breast carcinoma ranks among the most prevalent malignancies in women. Breast carcinoma frequently metastasizes to bone and approximately 70% of patients with breast cancer have bone metastases, which generally are osteolytic lesions. They cause major morbidity and mortality in patients; and the available treatment options are limited. Bone-specific homing and colonization of cancer cells are important and interesting features of metastasis. There are complex and multiple steps in the process of bone metastasis; and the elaborate interaction between breast carcinoma and bone involves various cytokines, growth factors and cellular signals, which results in a vicious cycle and promotes tumor cell accumulation and osteolysis. Recent advances in molecular biology have resulted in major breakthroughs in our understanding of the pathogenesis of bone metastasis in breast cancer, which is critical in preventing metastasis, designing novel and targeted treatments and prolonging survival in this devastating condition.     

Human bone marrow-derived MSCs can home to orthotopic breast cancer tumors and promote bone metastasis

American women have a nearly 25% lifetime risk of developing breast cancer, with 20% to 40% of these patients developing life-threatening metastases. More than 70% of patients presenting with metastases have skeletal involvement, which signals progression to an incurable stage. Tumor-stroma cell interactions are only superficially understood, specifically regarding the ability of stromal cells to affect metastasis. In vivo models show that exogenously supplied human bone marrow-derived stem cells (hBMSC) migrate to breast cancer tumors, but no reports have shown endogenous hBMSC migration from the bone to primary tumors. Here, we present a model of in vivo hBMSC migration from a physiologic human bone environment to human breast tumors. Furthermore, hBMSCs alter tumor growth and bone metastasis frequency. These may home to certain breast tumors based on tumor-derived TGF-β1. Moreover, at the primary tumor level, interleukin 17B (IL-17B)/IL-17BR signaling may mediate interactions between hBMSCs and breast cancer cells.     

Immune cells as mediators of solid tumor metastasis

Outgrowths of disseminated metastases remain the primary cause of mortality in cancer patients; however, molecular and cellular mechanisms regulating metastatic spread remain largely elusive. Recent insights into these mechanisms have refined the seed and soil hypothesis and it is now recognized that metastasis of solid tumors requires collaborative interactions between malignant cells and a diverse assortment of “activated” stromal cells at both primary and secondary tumor locations. Specifically, persistent pro-tumor immune responses (inflammation), now generally accepted as potentiating primary tumor development, are also being recognized as mediators of cancer metastasis. Thus, novel anti-cancer therapeutic strategies targeting molecular and/or cellular mechanisms regulating these collaborative interactions may provide efficacious relief for metastatic disease. This review focuses on recent literature revealing new mechanisms whereby immune cells regulate metastatic progression, with a primary focus on breast cancer.     

Transforming growth factor-β signaling at the tumor–bone interface promotes mammary tumor growth and osteoclast activation

Understanding the cellular and molecular changes in the bone microenvironment is important for developing novel therapeutics to control breast cancer bone metastasis. Although the underlying mechanism(s) of bone metastasis has been the focus of intense investigation, relatively little is known about complex molecular interactions between malignant cells and bone stroma. Using a murine syngeneic model that mimics osteolytic changes associated with human breast cancer, we examined the role of tumor–bone interaction in tumor-induced osteolysis and malignant growth in the bone microenvironment. We identified transforming growth factor-β receptor 1 (TGF-βRI) as a commonly upregulated gene at the tumor-bone (TB) interface. Moreover, TGF-βRI expression and activation, analyzed by nuclear localization of phospho-Smad2, was higher in tumor cells and osteoclasts at the TB interface as compared to the tumor-alone area. Furthermore, attenuation of TGF-β activity by neutralizing antibody to TGF-β or TGF-βRI kinase inhibitor reduced mammary tumor-induced osteolysis, TGF-βRI expression and its activation. In addition, we demonstrate a potential role of TGF-β as an important modifier of receptor activator of NF-κB ligand (RANKL)-dependent osteoclast activation and osteolysis. Together, these studies demonstrate that inhibition of TGF-βRI signaling at the TB interface will be a therapeutic target in the treatment of breast cancer-induced osteolysis. ( Cancer Sci 2009; 100: 71–81)     

乳腺癌骨转移研究进展

骨是乳腺癌最常见的转移部位之一,乳腺癌骨转移以溶骨性病变为主,也有少部分为成骨性病变,目前的研究表明趋化因子、整合素、血管生成以及骨微环境与癌细胞的相互作用等在乳腺癌骨转移的过程中起了重要作用.     

Breast cancer metastasis in a human bone NOD/SCID mouse model

A major dilemma facing patients with breast cancer is how to decide between over treating indolent tumors and failing to adequately treat aggressive, potentially lethal cancers. Determination of the metastatic potential of a patient's breast cancer would clearly help guide those treatment decisions. Breast cancer commonly spreads to bone in 70% of women with advanced disease. However, the mechanism of bone metastasis is not well understood. One possibility is that the microenvironment within bone marrow, highly rich in growth factors and cytokines, is suitable for the proliferation of breast cancer cells. In this study, we developed a method for implanting human bone in NOD/SCID mice and show that the human bone implants are viable for more than 20 weeks. This human bone NOD/SCID mouse model provides an opportunity to functionally characterize human breast cancer cell behavior in an in vivo human microenvironment. Several breast tumor cell lines have been shown to grow in the human-bone-NOD/SCID model system, however each line has a different functional profile. Here we show that cotransplantation of GFP-MDA-MB-231 breast cancer cells with morcellized human bone allows for tissue specific metastasis to an initially tumor free bone implant. Furthermore, metastasis of breast tumor cells to implanted tumor-free human bone was seen when patient bone containing a metastatic breast tumor was implanted in the host mouse. With this model, we can distinguish between primary invasive breast tumors with and without bone metastatic potential.     

乳腺癌移植转移模型的建立与应用

乳腺癌是女性最常见的恶性肿瘤之一,而转移是乳腺癌患者死亡的主要原因。乳腺癌转移模型是筛选乳腺癌转移相关基因、探讨肿瘤转移分子机制和评价抗转移实验性治疗疗效的重要工具。乳腺癌转移模型主要包括自发性转移模型、诱发性转移模型、转基因肿瘤转移模型和移植性转移模型。移植性肿瘤转移模型以其操作简单、重复性好和生物学性状稳定等优点应用最为广泛。乳腺癌移植性转移模型按建立方法可分为实验性转移模型和自发性转移模型。乳腺癌实验性转移模型是直接将瘤细胞注入血液循环系统后在远处驻留增殖形成转移灶,实验周期短、转移发生率高,费用低,但缺少原发灶的形成和肿瘤细胞从原发灶逃逸的过程。乳腺癌自发性转移模型是将瘤细胞或瘤块接种于皮下、肌肉和乳腺脂肪垫组织,在局部形成原发癌后自发转移,涉及了从原发灶产生到转移灶形成的乳腺癌转移的完整过程,是较好的研究乳腺癌转移机制的工具。近年来对移植转移模型转移灶的检测有了较大进展,采用活体动物成像技术不但能在肿瘤发生早期探测到各组织器官内的微小转移灶,还可以动态监测肿瘤细胞在动物体内的转移状态。本文对乳腺癌移植性转移模型的分类、模型建立方法、转移灶的检测,以及该类模型在乳腺癌转移分子机制和抗转移治疗研究中的应用进行综述。     

Adaptation of energy metabolism in breast cancer brain metastases

Brain metastases are among the most feared complications in breast cancer, as no therapy exists that prevents or eliminates breast cancer spreading to the brain. New therapeutic strategies depend on specific knowledge of tumor cell properties that allow breast cancer cell growth within the brain tissue. To provide information in this direction, we established a human breast cancer cell model for brain metastasis based on circulating tumor cells from a breast cancer patient and variants of these cells derived from bone or brain lesions in immunodeficient mice. The brain-derived cells showed an increased potential for brain metastasis in vivo and exhibited a unique protein expression profile identified by large-scale proteomic analysis. This protein profile is consistent with either a selection of predisposed cells or bioenergetic adaptation of the tumor cells to the unique energy metabolism of the brain. Increased expression of enzymes involved in glycolysis, tricarboxylic acid cycle, and oxidative phosphorylation pathways suggests that the brain metastatic cells derive energy from glucose oxidation. The cells further showed enhanced activation of the pentose phosphate pathway and the glutathione system, which can minimize production of reactive oxygen species resulting from an enhanced oxidative metabolism. These changes promoted resistance of brain metastatic cells to drugs that affect the cellular redox balance. Importantly, the metabolic alterations are associated with strongly enhanced tumor cell survival and proliferation in the brain microenvironment. Thus, our data support the hypothesis that predisposition or adaptation of the tumor cell energy metabolism is a key element in breast cancer brain metastasis, and raise the possibility of targeting the functional differentiation in breast cancer brain lesions as a novel therapeutic strategy.     

Immune system augmentation via humanization using stem/progenitor cells and bioengineering in a breast cancer model study

Despite significant advances, most current in vivo models fail to fully recapitulate the biological processes that occur in humans. Here we aimed to develop an advanced humanized model with features of an organ bone by providing different bone tissue cellular compartments including preosteoblasts, mesenchymal stem/stromal (MSCs), endothelial and hematopoietic cells in an engineered microenvironment. The bone compartment was generated by culturing the human MSCs, umbilical vein endothelial cells with gelatin methacryloyl hydrogels in the center of a melt‐electrospun polycaprolactone tubular scaffolds, which were seeded with human preosteoblasts. The tissue engineered bone (TEB) was subcutaneously implanted into the NSG mice and formed a morphologically and functionally organ bone. Mice were further humanized through the tail vein injection of human cord blood derived CD34+ cells, which then populated in the mouse bone marrow, spleen and humanized TEB (hTEB). 11 weeks after CD34+ transplantation, metastatic breast cancer cells (MDA‐MB‐231BO) were orthotopically injected. Cancer cell injection resulted in the formation of a primary tumor and metastasis to the hTEB and mouse organs. Less frequent metastasis and lower tumor burden were observed in hematochimeric mice, suggesting an immune‐mediated response against the breast cancer cells. Overall, our results demonstrate the efficacy of tissue engineering approaches to study species‐specific cancer‐bone interactions. Further studies using genetically modified hematopoietic stem cells and bioengineered microenvironments will enable us to address the specific roles of signaling molecules regulating hematopoietic niches and cancer metastasis in vivo.     

Crucial contribution of GPR56/ADGRG1, expressed by breast cancer cells,to bone metastasis formation

From a mouse triple-negative breast cancer cell line, 4T1, we previously established 4T1.3 clone with a high capacity to metastasize to bone after its orthotopic injection into mammary fat pad of immunocompetent mice. Subsequent analysis demonstrated that the interaction between cancer cells and fibroblasts in a bone cavity was crucial for bone metastasis focus formation arising from orthotopic injection of 4T1.3 cells. Here, we demonstrated that a member of the adhesion G-protein–coupled receptor (ADGR) family, G-protein–coupled receptor 56 (GPR56)/adhesion G-protein–coupled receptor G1 (ADGRG1), was expressed selectively in 4T1.3 grown in a bone cavity but not under in vitro conditions. Moreover, fibroblasts present in bone metastasis sites expressed type III collagen, a ligand for GPR56/ADGRG1. Consistently, GPR56/ADGRG1 proteins were detected in tumor cells in bone metastasis foci of human breast cancer patients. Deletion of GPR56/ADGRG1 from 4T1.3 cells reduced markedly intraosseous tumor formation upon their intraosseous injection. Conversely, intraosseous injection of GPR56/ADGRG1-transduced 4T1, TS/A (mouse breast cancer cell line), or MDA-MB-231 (human breast cancer cell line) exhibited enhanced intraosseous tumor formation. Furthermore, we proved that the cleavage at the extracellular region was indispensable for GPR56/ADGRG1-induced increase in breast cancer cell growth upon its intraosseous injection. Finally, inducible suppression of Gpr56/Adgrg1 gene expression in 4T1.3 cells attenuated bone metastasis formation with few effects on primary tumor formation in the spontaneous breast cancer bone metastasis model. Altogether, GPR56/ADGRG1 can be a novel target molecule to develop a strategy to prevent and/or treat breast cancer metastasis to bone.     

Tumor alphavbeta3 integrin is a therapeutic target for breast cancer bone metastases

In breast cancer bone metastasis, tumor cells stimulate osteoclast-mediated bone resorption, and bone-derived growth factors released from resorbed bone stimulate tumor growth. The alphavbeta3 integrin is an adhesion receptor expressed by breast cancer cells and osteoclasts. It is implicated in tumor cell invasion and osteoclast-mediated bone resorption. Here, we hypothesized that the therapeutic targeting of tumor alphavbeta3 integrin would prevent bone metastasis formation. We first showed that, compared with mock-transfected cells, the i.v. inoculation of alphavbeta3-overexpressing MDA-MB-231 breast cancer cells in animals increased bone metastasis incidence and promoted both skeletal tumor burden and bone destruction. The direct inoculation of alphavbeta3-overexpressing transfectants into the tibial bone marrow cavity did not however enhance skeletal tumor burden and bone destruction, suggesting that alphavbeta3 controls earlier events during bone metastasis formation. We next examined whether a nonpeptide antagonist of alphavbeta3 (PSK1404) exhibits meaningful antitumor effects in experimental breast and ovarian cancer bone metastasis. A continuous PSK1404 treatment, which inhibited osteoclast-mediated bone resorption in an animal model of bone loss, substantially reduced bone destruction and decreased skeletal tumor burden. Importantly, a short-term PSK1404 treatment that did not inhibit osteoclast activity also decreased skeletal tumor burden and bone destruction. This dosing regimen caused a profound and specific inhibition of bone marrow colonization by green fluorescent protein, alphavbeta3-expressing tumor cells in vivo and blocked tumor cell invasion in vitro. Overall, our data show that tumor alphavbeta3 integrin stands as a therapeutic target for the prevention of skeletal metastases.     

Cathepsin B inhibition limits bone metastasis in breast cancer

Metastasis to bone is a major cause of morbidity in breast cancer patients, emphasizing the importance of identifying molecular drivers of bone metastasis for new therapeutic targets. The endogenous cysteine cathepsin inhibitor stefin A is a suppressor of breast cancer metastasis to bone that is coexpressed with cathepsin B in bone metastases. In this study, we used the immunocompetent 4T1.2 model of breast cancer which exhibits spontaneous bone metastasis to evaluate the function and therapeutic targeting potential of cathepsin B in this setting of advanced disease. Cathepsin B abundancy in the model mimicked human disease, both at the level of primary tumors and matched spinal metastases. RNA interference-mediated knockdown of cathepsin B in tumor cells reduced collagen I degradation in vitro and bone metastasis in vivo. Similarly, intraperitoneal administration of the highly selective cathepsin B inhibitor CA-074 reduced metastasis in tumor-bearing animals, a reduction that was not reproduced by the broad spectrum cysteine cathepsin inhibitor JPM-OEt. Notably, metastasis suppression by CA-074 was maintained in a late treatment setting, pointing to a role in metastatic outgrowth. Together, our findings established a prometastatic role for cathepsin B in distant metastasis and illustrated the therapeutic benefits of its selective inhibition in vivo.     

Combination of anti‐angiogenic therapies reduces osteolysis and tumor burden in experimental breast cancer bone metastasis

The clinical efficacy of anti‐angiogenic monotherapies in metastatic breast cancer is less than originally anticipated, and it is not clear what the response of bone metastasis to anti‐angiogenic therapies is. Here, we examined the impact of neutralizing tumor‐derived vascular endothelial growth factor (VEGF) in animal models of subcutaneous tumor growth and bone metastasis formation. Silencing of VEGF expression (Sh‐VEGF) in osteotropic human MDA‐MB‐231/B02 breast cancer cells led to a substantial growth inhibition of subcutaneous Sh‐VEGF B02 tumor xenografts, as a result of reduced angiogenesis, when compared to that observed with animals bearing mock‐transfected (Sc‐VEGF) B02 tumors. However, there was scant evidence that either the silencing of tumor‐derived VEGF or the use of a VEGF‐neutralizing antibody (bevacizumab) affected B02 breast cancer bone metastasis progression in animals. We also examined the effect of vatalanib (a VEGF receptor tyrosine kinase inhibitor) in this mouse model of bone metastasis. However, vatalanib failed to inhibit bone metastasis caused by B02 breast cancer cells. In sharp contrast, vatalanib in combination with bevacizumab reduced not only bone destruction but also skeletal tumor growth in animals bearing breast cancer bone metastases, when compared with either agent alone. Thus, our study highlights the importance of targeting both the tumor compartment and the host tissue (i.e., skeleton) to efficiently block the development of bone metastasis. We believe this is a crucially important observation as the clinical benefit of anti‐angiogenic monotherapies in metastatic breast cancer is relatively modest.     

乳腺癌骨转移机制与靶向治疗进展

乳腺癌骨转移是晚期乳腺癌常见的症状,乳腺癌细胞通过局部浸润、渗入血管和或淋巴管、随循环系统转移到骨、移出血管和或淋巴管、在骨定居并增殖引起溶骨性骨损伤。乳腺癌骨转移的发生发展取决于乳腺癌细胞与骨局部微环境之间相互作用,最后形成骨的结构破坏及功能受损。本文主要从分子水平阐述乳腺癌骨转移机制,并且综述针对乳腺癌骨转移关键靶点的抗骨转移药物的临床应用。     

Current status in human breast cancer micrometastasis

PURPOSE OF REVIEW: Current research and clinical developments on hematogeneous micrometastasis in breast cancer patients are summarized. RECENT FINDINGS: Distant metastasis is the leading cause of cancer-related death in breast cancer and bone marrow is a common homing organ for blood-borne disseminated tumor cells derived from primary breast carcinomas. Sensitive immunocytochemical or molecular assays now allow the detection of single disseminated tumor cells in bone marrow or the peripheral blood at a frequency of 10 and these cells are detected in 10-60% of breast cancer patients without clinical or even histopathologic signs of metastasis. Recently, evidence has emerged that the detection of disseminated tumor cells and circulating tumor cells may provide important prognostic information, and in particular might help to monitor efficacy of therapy. Moreover, the characterization of disseminated tumor cells/circulating tumor cells has shed new light on the complex process underlying early tumor cell dissemination and metastatic progression in cancer patients. SUMMARY: Research on disseminated tumor cells/circulating tumor cells will help to identify novel targets for biological therapies aimed at preventing metastatic relapse and to monitor the efficacy of these therapies. In particular, understanding tumor dormancy and identifying metastatic stem cells might result in the development of new concepts for antimetastatic therapies.