Hedgehog signaling in tumor cells facilitates osteoblast-enhanced osteolytic metastases

DNA methylation markers for risk of metastasis in a cohort of men with localized prostate cancer

Accurately identifying life-threatening prostate cancer (PCa) at time of diagnosis remains an unsolved problem. We evaluated whether DNA methylation status of selected candidate genes can predict the risk of metastasis beyond clinical risk factors in men with untreated PCa. A nested case-control study was conducted among men diagnosed with localized PCa at Kaiser Permanente California between 01/01/1997-12/31/2006 who did not receive curative treatments. Cases were those who developed metastasis within 10 years from diagnosis. Controls were selected using density sampling. Ninety-eight candidate genes were selected from functional categories of cell cycle control, metastasis/tumour suppressors, cell signalling, cell adhesion/motility/invasion, angiogenesis, and immune function, and 41 from pluripotency genes. Cancer DNA from diagnostic biopsy blocks were extracted and analysed. Associations of methylation status were assessed using CpG site level and principal components-based analysis in conditional logistic regressions. In 215 cases and 404 controls, 27 candidate genes were found to be statistically significant in at least one of the two analytical approaches. The agreement between the methods was 25.9% (7 candidate genes, including 2 pluripotency markers). The DNA methylation status of several candidate genes was significantly associated with risk of metastasis in untreated localized PCa patients. These findings may inform future risk prediction models for PCa metastasis beyond clinical characteristics.

Higher Expressions of SHH and AR Are Associated with a Positive Receptor Status and Have Impact on Survival in a Cohort of Croatian Breast Cancer Patients

Breast cancers (BC) are usually classified into four molecular subtypes according to the expression of estrogen (ER), progesterone (PR), and human epidermal growth factor 2 (HER2) receptors and proliferation marker Ki-67. Despite available anti-hormonal therapies and due to the inherent propensity of some subtypes to develop metastasis, there is a permanent need to discover new prognostic and predictive biomarkers, as well as therapeutic targets for BC. In this study, we used immunohistochemical staining to determine the expression of androgen receptor (AR) and sonic hedgehog protein (SHH), the main ligand of the Hedgehog-GLI (HH-GLI) signaling pathway, in 185 archival primary BC tissue samples and correlated it with clinicopathological characteristics, molecular subtypes, receptors statuses, and survival in a cohort of Croatian BC patients. Results showed that higher SHH and AR expressions were associated with positive receptor status, but increased SHH expression had a negative impact on survival in receptor-negative BCs. On the contrary, higher AR expression was mostly protective. However, multivariate analysis showed that only higher AR expression could be considered as an independent prognostic biomarker for poorer overall survival in triple-negative breast cancer patients (TNBC) (HR 10.9, 95% CI 1.43-83.67; p = 0.021), what could be Croatian population-related. SHH could be a potential target for treating TNBCs and HER2-enriched BCs, in cases where HH-GLI signaling is canonical (SHH-dependent).

Expression of Neurokinin B Receptor in the Gingival Squamous Cell Carcinoma Bone Microenvironment

Gingival squamous cell carcinoma (SCC) frequently invades the maxillary or mandibular bone, and bone destruction is known as a key prognostic factor in gingival SCCs. Recently, Neurokinin 3 receptor (NK-3R), the receptor ligand for NK-3, which is a member of the tachykinin family expressed in the central nervous system, was identified through pathway analysis as a molecule expressed in osteoclasts induced by the hedgehog signal. Although the expression of NK-3R has been detected in osteoclast and SCC cells at the bone invasion front, the relationship between NK-3R expression and the prognosis of gingival SCC patients remains unclear. In the present study, we retrospectively reviewed 27 patients with gingival SCC who had undergone surgery with curative intent. Significantly higher NK-3R expression in tumor cells was found in a case of jawbone invasion than in a case of exophytic poor jawbone invasion. On the other hand, no significant association was observed between NK-3R tumor-positive cases and tumor size, TNM stage, or tumor differentiation. The survival rate tended to be lower in NK-3R tumor-positive cases, but not significantly. However, the disease-specific survival rate was significantly lower in patients with a large number of NK-3R-positive osteoclasts than in those with a small number of them at the tumor bone invasion front. Our results suggest that NK-3R signaling in the gingival SCC bone microenvironment plays an important role in tumor bone destruction and should be considered a potential therapeutic target in advanced gingival SCC with bone destruction.

Two Sides of the Same Coin: The Role of Developmental pathways and pluripotency factors in normal mammary stem cells and breast cancer metastasis

Breast cancer initiation and progression are often observed as the result of dysregulation of normal developmental processes and pathways. Studies focused on normal mammary stem/progenitor cell activity have led to an understanding of how breast cancer cells acquire stemness-associated properties including tumor initiation, survival and multi-lineage differentiation into heterogeneous tumors that become difficult to target therapeutically. Importantly, more recent investigations have provided valuable insight into how key developmental regulators can impact multiple phases of metastasis, where they are repurposed to not only promote metastatic phenotypes such as migration, invasion and EMT at the primary site, but also to regulate the survival, initiation and maintenance of metastatic lesions at secondary organs. Herein, we discuss findings that have led to a better understanding of how embryonic and pluripotency factors contribute not only to normal mammary development, but also to metastatic progression. We further examine the therapeutic potential of targeting these developmental pathways, and discuss how a better understanding of compensatory mechanisms, crosstalk between pathways, and novel experimental models could provide critical insight into how we might exploit embryonic and pluripotency regulators to inhibit tumor progression and metastasis.

Genetic and pharmacological activation of Hedgehog signaling inhibits osteoclastogenesis and attenuates titanium particle-induced osteolysis partly through suppressing the JNK/c-Fos-NFATc1 cascade

Rationale: Wear particle-induced periprosthetic osteolysis (PPO) is a common long-term complication of total joint arthroplasty, and represents the major cause of aseptic loosening and subsequent implant failure. Previous studies have identified the central role of osteoclast-mediated bone resorption in the pathogenesis of PPO. Thus, therapeutic approaches of inhibiting osteoclast formation and activity are considered to be of great potential to prevent and treat this osteolytic disease. Hedgehog (Hh) signaling has been shown to play an important role in promoting osteoblast differentiation and bone formation. While Hh signaling is also implicated in regulating osteoclastogenesis, whether it can directly inhibit osteoclast differentiation and bone resorption remains controversial. Moreover, its potential therapeutic effects on PPO have never been assessed. In this study, we explored the cell-autonomous role of Hh signaling in regulating osteoclastogenesis and its therapeutic potential in preventing wear particle-induced osteolysis. Methods: Hh signaling was activated in macrophages by genetically ablating Sufu in these cells using LysM-Cre or by treating them with purmorphamine (PM), a pharmacological activator of Smoothened (Smo). In vitro cell-autonomous effects of Hh pathway activation on RANKL-induced osteoclast differentiation and activity were evaluated by TRAP staining, phalloidin staining, qPCR analyses, and bone resorption assays. In vivo evaluation of its therapeutic efficacy against PPO was performed in a murine calvarial model of titanium particle-induced osteolysis by μCT and histological analyses. Mechanistic details were explored in RANKL-treated macrophages through Western blot analyses. Results: We found that Sufu deletion or PM treatment potently activated Hh signaling in macrophages, and strongly inhibited RANKL-induced TRAP+ osteoclast production, F-actin ring formation, osteoclast-specific gene expression, and osteoclast activity in vitro. Furthermore, we found that Sufu deletion or PM administration significantly attenuated titanium particle-induced osteoclast formation and bone loss in vivo. Our mechanistic study revealed that activation of Hh signaling suppressed RANKL-induced activation of JNK pathway and downregulated protein levels of two key osteoclastic transcriptional factors, c-Fos and its downstream target NFATc1. Conclusions: Both genetic and pharmacological activation of Hh signaling can cell-autonomously inhibit RANKL-induced osteoclast differentiation and activity in vitro and protect against titanium particle-induced osteolysis in vivo. Mechanistically, Hh signaling hinders osteoclastogenesis partly through suppressing the JNK/c-Fos-NFATc1 cascade. Thus, Hh signaling may serve as a promising therapeutic target for the prevention and treatment of PPO and other osteolytic diseases.

Role of Hedgehog Signaling in Breast Cancer: Pathogenesis and Therapeutics

Breast cancer (BC) is the leading cause of cancer-related mortality in women, only followed by lung cancer. Given the importance of BC in public health, it is essential to identify biomarkers to predict prognosis, predetermine drug resistance and provide treatment guidelines that include personalized targeted therapies. The Hedgehog (Hh) signaling pathway plays an essential role in embryonic development, tissue regeneration, and stem cell renewal. Several lines of evidence endorse the important role of canonical and non-canonical Hh signaling in BC. In this comprehensive review we discuss the role of Hh signaling in breast development and homeostasis and its contribution to tumorigenesis and progression of different subtypes of BC. We also examine the efficacy of agents targeting different components of the Hh pathway both in preclinical models and in clinical trials. The contribution of the Hh pathway in BC tumorigenesis and progression, its prognostic role, and its value as a therapeutic target vary according to the molecular, clinical, and histopathological characteristics of the BC patients. The evidence presented here highlights the relevance of the Hh signaling in BC, and suggest that this pathway is key for BC progression and metastasis.

Inhibition of Hedgehog signaling reprograms the dysfunctional immune microenvironment in breast cancer

Host responses to tumor cells include tumor suppressing or promoting mechanisms. We sought to detail the effect of Hedgehog (Hh) pathway inhibition on the composition of the mammary tumor immune portfolio. We hypothesized that Hh signaling mediates a crosstalk between breast cancer cells and macrophages that dictates alternative polarization of macrophages and consequently supports a tumor-promoting microenvironment. We used an immunocompetent, syngeneic mouse mammary cancer model to inhibit Hh signaling with the pharmacological inhibitor, Vismodegib. Using molecular and functional assays, we identified that Hedgehog (Hh) signaling mediates a molecular crosstalk between mammary cancer cells and macrophages that culminates in alternative polarization of macrophages. We carried out an unbiased kinomics and genomics assessment to unravel changes in global kinomic and gene signatures impacted by Hh signaling. Our investigations reveal that in an immunocompetent mammary cancer model, the administration of Vismodegib led to changes in the portfolio of tumor-infiltrating immune cells. This was characterized by a marked reduction in immune-suppressive innate and adaptive cells concomitant with an enrichment of cytotoxic immune cells. Breast cancer cells induce M2 polarization of macrophages via a crosstalk mediated by Hh ligands that alters critical kinomic and genomic signatures. Macrophage depletion improved the benefit of Hedgehog inhibition on eliciting an immunogenic, pro-inflammatory profile. We define a novel role for Hh signaling in disabling anti-tumor immunity. Inhibition of Hh signaling presents with dual advantages of tumor cell-targeting as well as re-educating a dysfunctional tumor microenvironment.

Widespread Expression of Hedgehog Pathway Components in a Large Panel of Human Tumor Cells and Inhibition of Tumor Growth by GANT61: Implications for Cancer Therapy

The sonic Hedgehog/GLI signaling pathway (HH) is critical for maintaining tissue polarity in development and contributes to tumor stemness. Transcription factors GLI1–3 are the downstream effectors of HH and activate oncogenic targets. To explore the completeness of the expression of HH components in tumor cells, we performed a screen for all HH proteins in a wide spectrum of 56 tumor cell lines of various origin using Western blot analysis. Generally, all HH proteins were expressed. Important factors GLI1 and GLI2 were always expressed, only exceptionally one of them was lowered, suggesting the functionality of HH in all tumors tested. We determined the effect of a GLI inhibitor GANT61 on proliferation in 16 chosen cell lines. More than half of tumor cells were sensitive to GANT61 to various extents. GANT61 killed the sensitive cells through apoptosis. The inhibition of reporter activity containing 12xGLI consensus sites by GANT61 and cyclopamine roughly correlated with cell proliferation influenced by GANT61. Our results recognize the sensitivity of tumor cell types to GANT61 in cell culture and support a critical role for GLI factors in tumor progression through restraining apoptosis. The use of GANT61 in combined targeted therapy of sensitive tumors, such as melanomas, seems to be immensely helpful.

Osteomimicry: How the Seed Grows in the Soil

Metastasis is defined as a very inefficient process, since less than 0.01% of cancer cells injected into the circulation will engraft in a distant organ, where they must acquire the ability to survive and proliferate inside a "foreign" environment. In bone metastases, the interaction with the host organ is much more favoured if tumour cells gain "osteomimicry", that is the ability to resemble a resident bone cell (i.e. the osteoblast), thus intruding in the physiology of the bone. This is accomplished by the expression of osteoblast markers (e.g. alkaline phosphatase) and the production of bone matrix proteins and paracrine factors which deregulate the physiology of bone, fuelling the so-called "vicious cycle". The main challenge of researchers is therefore to identify the genetic profile determining the osteotropism of tumour cells, which would eventually lead to bone colonisation. This could likely provide the answer to a quite intriguing question, that is why some cancers, such as prostate and breast, have a specific predilection to metastasise to the bone. Therefore, it is important to completely address the molecular mechanisms underlying this aspect of bone oncology, identifying relevant pathways, the targeting of which could make any type of bone metastasis curable or avoidable.

Alteration of osteoblast arrangement via direct attack by cancer cells: New insights into bone metastasis

Intact bone tissue exhibits a characteristic anisotropic microstructure derived from collagen fiber alignment and the related c-axis orientation of apatite crystals, which govern the mechanical properties of bone tissue. In contrast, tumor-invaded bone exhibits a disorganized, less-aligned microstructure that results in severely disrupted mechanical function. Despite its importance both in basic principle and in therapeutic applications, the classical understanding of bone metastasis is limited to alterations in bone mass regulated by metastatic cancer cells. In this study, we demonstrate a novel mechanism underlying the disruption of bone tissue anisotropy in metastasized bone. We observed that direct attack by cancer cells on osteoblasts induces the less-organized osteoblast arrangement. Importantly, the crystallographic anisotropy of bone tissue is quantitatively determined by the level of osteoblast arrangement. Osteoblast arrangement was significantly disrupted by physical contact with cancer cells such as osteolytic melanoma B16F10, breast cancer MDA-MB-231, and osteoblastic prostate cancer MDA-PCa-2b cells. The present findings demonstrate that the abnormal arrangement of osteoblasts induced by physical contact with cancer cells facilitates the disorganized microstructure of metastasized bone.

Loss of Merlin induces metabolomic adaptation that engages dependence on Hedgehog signaling

The tumor suppressor protein Merlin is proteasomally degraded in breast cancer. We undertook an untargeted metabolomics approach to discern the global metabolomics profile impacted by Merlin in breast cancer cells. We discerned specific changes in glutathione metabolites that uncovered novel facets of Merlin in impacting the cancer cell metabolome. Concordantly, Merlin loss increased oxidative stress causing aberrant activation of Hedgehog signaling. Abrogation of GLI-mediated transcription activity compromised the aggressive phenotype of Merlin-deficient cells indicating a clear dependence of cells on Hedgehog signaling. In breast tumor tissues, GLI1 expression enhanced tissue identification and discriminatory power of Merlin, cumulatively presenting a powerful substantiation of the relationship between these two proteins. We have uncovered, for the first time, details of the tumor cell metabolomic portrait modulated by Merlin, leading to activation of Hedgehog signaling. Importantly, inhibition of Hedgehog signaling offers an avenue to target the vulnerability of tumor cells with loss of Merlin.

What Is Breast in the Bone?

The normal developmental program that prolactin generates in the mammary gland is usurped in the cancerous process and can be used out of its normal cellular context at a site of secondary metastasis. Prolactin is a pleiotropic peptide hormone and cytokine that is secreted from the pituitary gland, as well as from normal and cancerous breast cells. Experimental and epidemiologic data suggest that prolactin is associated with mammary gland development, and also the increased risk of breast tumors and metastatic disease in postmenopausal women. Breast cancer spreads to the bone in approximately 70% of cases with advanced breast cancer. Despite treatment, new bone metastases will still occur in 30%–50% of patients. Only 20% of patients with bone metastases survive five years after the diagnosis of bone metastasis. The breast cancer cells in the bone microenvironment release soluble factors that engage osteoclasts and/or osteoblasts and result in bone breakdown. The breakdown of the bone matrix, in turn, enhances the proliferation of the cancer cells, creating a vicious cycle. Recently, it was shown that prolactin accelerated the breast cancer cell-mediated osteoclast differentiation and bone breakdown by the regulation of breast cancer-secreted proteins. Interestingly, prolactin has the potential to affect multiple proteins that are involved in both breast development and likely bone metastasis, as well. Prolactin has normal bone homeostatic roles and, combined with the natural “recycling” of proteins in different tissues that can be used for breast development and function, or in bone function, increases the impact of prolactin signaling in breast cancer bone metastases. Thus, this review will focus on the role of prolactin in breast development, bone homeostasis and in breast cancer to bone metastases, covering the molecular aspects of the vicious cycle.

Hedgehog signaling: modulation of cancer properies and tumor mircroenvironment

Cancer poses a serious health problem in society and is increasingly surpassing cardiovascular disease as the leading cause of mortality in the United States. Current therapeutic strategies for cancer are extreme and harsh to patients and often have limited success; the danger of cancer is intensified as it metastasizes to secondary locations such as lung, bone, and liver, posing a dire threat to patient treatment and survival. Hedgehog signaling is an important pathway for normal development. Initially identified in Drosophila, the vertebrate and mammalian equivalent of the pathway has been studied extensively for its role in cancer development and progression. As this pathway regulates key target genes involved in development, its action also allows for the modulation of the microenvironment to prepare a tumor-suitable niche by manipulating tumor cell growth, differentiation, and immune regulation, thus creating an enabling environment for progression and metastasis. In this review, we will summarize recent scientific discoveries reporting the impact of the Hedgehog signaling pathway on the tumor initiation process and metastatic cascade, shedding light on the ability of the tumor to take over a mechanism crucially intended for development and normal function.

Hedgehog signaling: modulation of cancer properies and tumor mircroenvironment

Cancer poses a serious health problem in society and is increasingly surpassing cardiovascular disease as the leading cause of mortality in the United States. Current therapeutic strategies for cancer are extreme and harsh to patients and often have limited success; the danger of cancer is intensified as it metastasizes to secondary locations such as lung, bone, and liver, posing a dire threat to patient treatment and survival. Hedgehog signaling is an important pathway for normal development. Initially identified in Drosophila, the vertebrate and mammalian equivalent of the pathway has been studied extensively for its role in cancer development and progression. As this pathway regulates key target genes involved in development, its action also allows for the modulation of the microenvironment to prepare a tumor-suitable niche by manipulating tumor cell growth, differentiation, and immune regulation, thus creating an enabling environment for progression and metastasis. In this review, we will summarize recent scientific discoveries reporting the impact of the Hedgehog signaling pathway on the tumor initiation process and metastatic cascade, shedding light on the ability of the tumor to take over a mechanism crucially intended for development and normal function.

Survivin, a novel target of the Hedgehog/GLI signaling pathway in human tumor cells

Survivin, an important antiapoptotic protein, is expressed in tumors, whereas in normal tissues the expression of this protein is extremely low, defining a role for survivin as a cancer gene. Survivin exhibits multifunctional activity in tumor cells. However, why survivin expression is sharply and invariably restricted to tumor tissue remains unclear. Here, we identified 11 putative consensus binding sites for GLI transcription factors in the survivin promoter and characterized the promoter activity. Inhibitors of the Hedgehog/GLI pathway, cyclopamine and GANT61, decreased the promoter activity in reporter assays. ΔNGLI2 (which lacks the repressor domain) was the most potent vector in activating the survivin promoter–reporter. Moreover, GANT61, a GLI1/2 inhibitor, repressed endogenous survivin protein and mRNA expression in most cells across a large panel of tumor cell lines. Chromatin immunoprecipitation showed GLI2 binding to the survivin promoter. The ectopic GLI2-evoked expression of endogenous survivin was observed in normal human fibroblasts. GANT61 decreased survivin level in nude mice tumors, mimicking the activity of GANT61 in cultured cells. The immunohistochemistry and double immunofluorescence of human tumors revealed a correlation between the tissue regions showing high GLI2 and survivin positivity. Thus, these results demonstrated that survivin is a classical transcriptional target of GLI2, a Hedgehog pathway signaling effector. This potentially reflects the high expression of survivin in human tumor cells. As the Hedgehog pathway is upregulated in virtually all types of cancer cells, these findings substantially contribute to the explanation of uniform survivin expression in tumors as a potential target for the development of a more effective treatment of cancers through the inhibition of GLI2 to restrain survivin activity.

The Role of Prolactin in Bone Metastasis and Breast Cancer Cell-Mediated Osteoclast Differentiation

BACKGROUND

Metastasis to the bone is a deleterious aspect of breast cancer and is a preferred site that results in bone loss. Hormones such as prolactin (PRL) have not yet been studied for their role in modulating the secondary tumor bone microenvironment.

METHODS

We used quantitative immunohistochemistry with 134 samples of human primary breast cancer and 17 matched primary breast cancers and bone metastases. A Cox proportional hazards regression model was fitted to evaluate the associations between high prolactin receptor (PRLR) expression and time to bone metastasis, adjusting for estrogen receptor status, lymph node status, and chemotherapy status. We assessed osteoclast differentiation, osteoclast size, and measured pit formation in dentine slices. Statistical tests were two-sided.

RESULTS

High PRLR expression in the primary breast tumor was associated with a shorter time to metastasis that includes bone (PRLRAQUA Max-per 100 unit hazard ratio = 1.04, 95% confidence interval = 1.00 to 1.07, P = .03). We observed the PRLR in rare samples of bone metastases and matched primary breast cancer. PRL treatment of breast cancer cells induced osteoclast differentiation and bone lysis via secreted factors and was abrogated by a PRLR antagonist (delta1-9-G129R-hPRL). We demonstrated that sonic hedgehog is a PRL-regulated cytokine in breast cancer cells and part of the mechanism that induces osteoclast differentiation.

CONCLUSIONS

Our evidence indicates that PRL-PRLR can escalate the impact of breast cancer on bone metastasis and that the presence of the PRLR in the tumor microenvironment of breast cancer bone metastasis has the potential to modulate the microenvironment to induce lytic osteoclast formation.

The active role of osteoporosis in the interaction between osteoblasts and bone metastases

INTRODUCTION

To minimize the severity of bone metastases and to delay their onset, it is important to analyze the underlying biological mechanisms. The present study focused on the link between OP and metastatic cells, with particular attention to osteoblast behavior.

METHODS

Osteoblasts (OB) were isolated from the trabecular bone of iliac crest of healthy (SHAM) and ovariectomized (OVX) adult female rats and co-cultured with MRMT-1 rat breast carcinoma cells as conditioned medium (CM) or alone (CTR) for 24h, 7 and 14 days and tested for cell viability, morphology and synthetic activity, i.e. C-terminal procollagen type I, alkaline phosphatase, osteoprotegerin, receptor activator for nuclear factor KB ligand and interleukin-8.

RESULTS

Osteoblast morphology showed a reduced organization in the OVX group, in particular in the CM condition. Conversely, the analysis of cell viability revealed significantly higher values in the OVXCM group with respect to the SHAMCM group at all experimental times, whereas the OVXCTR group had significantly lower values at 7 and 14 days in comparison to those of the SHAM group. ALP release was significantly lower in the CM condition than that of CTR at all timepoints, and so was procollagen type I at 7 and 14 days. The RANKL/OPG ratio showed significantly higher values in OVX osteoblasts in comparison with those of the SHAM group, both in CTR and in CM conditions at each experimental time. Finally, OVXCM showed significantly higher values of IL-8 than those of SHAMCM at 7 and 14 days.

CONCLUSIONS

The results clearly indicate an influence of the metastatic cells on the osteoblastic physiology at different levels: morphology, viability, release of typical proteins, and also IL-8 as a proinflammatory cytokine, especially marked by osteoporosis. Further investigations might highlight the relationship between osteoblasts and breast cancer cells, which might be useful to improve common drugs used against osteoporosis and bone metastases, by enhancing the bone deposition/tumor progression ratio.

A microRNA code for prostate cancer metastasis

Although the development of bone metastasis is a major detrimental event in prostate cancer, the molecular mechanisms responsible for bone homing and destruction remain largely unknown. Here we show that loss of miR-15 and miR-16 in cooperation with increased miR-21 expression promote prostate cancer spreading and bone lesions. This combination of microRNA endows bone-metastatic potential to prostate cancer cells. Concomitant loss of miR-15/miR-16 and gain of miR-21 aberrantly activate TGF-β and Hedgehog signaling, that mediate local invasion, distant bone marrow colonization and osteolysis by prostate cancer cells. These findings establish a new molecular circuitry for prostate cancer metastasis that was validated in patients' cohorts. Our data indicate a network of biomarkers and druggable pathways to improve patient treatment.

Biomechanical forces in the skeleton and their relevance to bone metastasis: biology and engineering considerations

Bone metastasis represents the leading cause of breast cancer related-deaths. However, the effect of skeleton-associated biomechanical signals on the initiation, progression, and therapy response of breast cancer bone metastasis is largely unknown. This review seeks to highlight possible functional connections between skeletal mechanical signals and breast cancer bone metastasis and their contribution to clinical outcome. It provides an introduction to the physical and biological signals underlying bone functional adaptation and discusses the modulatory roles of mechanical loading and breast cancer metastasis in this process. Following a definition of biophysical design criteria, in vitro and in vivo approaches from the fields of bone biomechanics and tissue engineering that may be suitable to investigate breast cancer bone metastasis as a function of varied mechano-signaling will be reviewed. Finally, an outlook of future opportunities and challenges associated with this newly emerging field will be provided.

Nitidine chloride inhibits hepatic cancer growth via modulation of multiple signaling pathways

Background

The development of hepatic cancer is tightly regulated by multiple intracellular signaling pathways. Therefore, most currently-used anti-tumor agents, which typically target single intracellular pathway, might not always be therapeutically effective. Additionally, long-term use of these agents probably generates drug resistance and unacceptable adverse effects. These problems increase the necessity for the development of new chemotherapeutic approaches. Nitidine chloride (NC), a natural benzophenanthridine alkaloid, has been shown to inhibit cancer growth via induction of cell apoptosis and suppression of cancer angiogenesis. But the precise mechanisms of its tumorcidal activity are not well understood.

Methods

To further elucidate the precise mechanisms of its anti-tumor activity, using a hepatic cancer mouse xenograft model, the human hepatic cancer cell lines (HepG2, HCCLM3, Huh7), and umbilical vein endothelial cells (HUVEC), here we evaluate the effect of NC on tumor growth in vivo and in vitro and investigated the underlying molecular mechanisms.

Results

We found that NC treatment resulted in significant decrease in tumor volume and tumor weight respectively, but didn’t affect body weight changes. Additionally, NC treatment dose- and time-dependently reduced the cell viability of all three hepatic cell lines. Moreover, NC suppressed the activation of STAT3, ERK and SHH pathways; and altered the expression of critical target genes including Bcl-2, Bax, Cyclin D1, CDK4, VEGF-A and VEGFR2. These molecular effects resulted in the promotion of apoptosis, inhibition of cell proliferation and tumor angiogenesis.

Conclusions

Our findings suggest that NC possesses a broad range of anti-cancer activities due to its ability to affect multiple intracellular targets, suggesting that NC could be a novel multi-potent therapeutic agent for the treatment of hepatic cancer and other cancers.

BMP9 regulates cross-talk between breast cancer cells and bone marrow-derived mesenchymal stem cells

PURPOSE

Breast cancer cells frequently metastasize to distant organs, including bone. Interactions between breast cancer cells and the bone microenvironment are known to enhance tumor growth and osteolytic damage. Here we investigated whether BMP9 (a secretary protein) may change the bone microenvironment and, by doing so, regulate the cross-talk between breast cancer cells and bone marrow-derived mesenchymal stem cells.

METHODS

After establishing a co-culture system composed of MDA-MB-231 breast cancer cells and HS-5 bone marrow-derived mesenchymal stem cells, and exposure of this system to BMP9 conditioned media, we assessed putative changes in migration and invasion capacities of MDA-MB-231 cells and concomitant changes in osteogenic marker expression in HS-5 cells and metastases-related genes in MDA-MB-231 cells.

RESULTS

We found that BMP9 can inhibit the migration and invasion of MDA-MB-231 cells, and promote osteogenesis and proliferation of HS-5 cells, in the co-culture system. We also found that the BMP9-induced inhibition of migration and invasion of MDA-MB-231 cells may be caused by a decreased RANK ligand (RANKL) secretion by HS-5 cells, leading to a block in the AKT signaling pathway.

CONCLUSIONS

From our data we conclude that BMP9 inhibits the migration and invasion of breast cancer cells, and promotes the osteoblastic differentiation and proliferation of bone marrow-derived mesenchymal stem cells by regulating cross-talk between these two types of cells through the RANK/RANKL signaling axis.

Serotonin regulates calcium homeostasis in lactation by epigenetic activation of hedgehog signaling

Calcium homeostasis during lactation is critical for maternal and neonatal health. We previously showed that nonneuronal/peripheral serotonin [5-hydroxytryptamine (5-HT)] causes the lactating mammary gland to synthesize and secrete PTHrP in an acute fashion. Here, using a mouse model, we found that genetic inactivation of tryptophan hydroxylase 1 (Tph1), which catalyzes the rate-limiting step in peripheral 5-HT synthesis, reduced circulating and mammary PTHrP expression, osteoclast activity, and maternal circulating calcium concentrations during the transition from pregnancy to lactation. Tph1 inactivation also reduced sonic hedgehog signaling in the mammary gland during lactation. Each of these deficiencies was rescued by daily injections of 5-hydroxy-L-tryptophan (an immediate precursor of 5-HT) to Tph1-deficient dams. We used immortalized mouse embryonic fibroblasts to demonstrate that 5-HT induces PTHrP through a sonic hedgehog-dependent signal transduction mechanism. We also found that 5-HT altered DNA methylation of the Shh gene locus, leading to transcriptional initiation at an alternate start site and formation of a variant transcript in mouse embryonic fibroblasts in vitro and in mammary tissue in vivo. These results support a new paradigm of 5-HT-mediated Shh regulation involving DNA methylation remodeling and promoter switching. In addition to having immediate implications for lactation biology, identification and characterization of a novel functional regulatory relationship between nonneuronal 5-HT, hedgehog signaling, and PTHrP offers new avenues for the study of these important factors in development and disease.

Implications of stemness-related signaling pathways in breast cancer response to therapy

There is accumulating evidence that breast cancer may arise from a small subpopulation of transformed mammary stem/progenitor cells, termed breast cancer-initiating cells (BCICs), responsible for initiation and maintenance of cancer. BCICs have been identified in clinical specimens based on CD44(+)/CD24(-/low) membrane expression and/or enzymatic activity of aldehyde dehydrogenase 1 (ALDH1+), or isolated and in vitro propagated as non-adherent spheres. This cell population has been demonstrated to be able to recreate, when injected in mice even at very low concentrations, the same histopathological features of the tumor they were derived from and to escape from current therapeutic strategies. Alterations in genes involved in stemness-related pathways, such as Wnt, Notch, and Sonic Hedgehog, have been proven to play a role in breast cancer progression. Targeting these key elements represents an attractive option, with a solid rationale, although possible concerns may derive from the poor knowledge of tolerance and efficacy of inhibiting these mechanisms without inducing severe side effects. In addition, efforts to develop alternative BCIC-targeted therapies against stemness markers (CD44 and ALDH1) and molecules involved in regulating EMT- and HER2-related pathways, or able to reverse the multi-drug resistance phenotype, or to induce differentiation and to control cell survival pathways are currently ongoing and encouraging results from pre-clinical studies have already been obtained using in vitro and in vivo models.

Hedgehog pathway inhibitor-4 suppresses malignant properties of chondrosarcoma cells by disturbing tumor ciliogenesis

Chondrosarcoma is a type of malignant bone tumor secreting cartilage-like matrix. In clinical treatment, there is no frequently used drug treatment option except for surgical resection. Hedgehog (HH) pathway is a classical signaling pathway that regulates normal cartilage cell development. In order to detect the role that HH pathway plays in chondrosarcoma, we used immunohistochemistry and found this tumor clearly expressed HH pathway-related proteins. Treatment with HH pathway inhibitor-4 (HPI-4) could significantly decrease human chondrosarcoma cell proliferation, invasion and migration ability. Furthermore, HPI-4 could distinctly disturb HH pathway-mediated ciliogenesis and suppress primary cilia-related protein intraflagellar transport protein IFT88 expression. HH downstream effect molecular GLI2 was restrained to block parathyroid hormone-related protein and affect MAPK/ERK-regulated matrix metalloproteinases (MMP2 and MMP9). These results indicated that activated HH pathway existed in chondrosarcoma and HPI-4 could be a new therapeutic option specific to chondrosarcoma expressing elevated levels of HH pathway.

Role of osteopontin in the pathophysiology of cancer

Osteopontin (OPN) is a multifunctional cytokine that impacts cell proliferation, survival, drug resistance, invasion, and stem like behavior. Due to its critical involvement in regulating cellular functions, its aberrant expression and/or splicing is functionally responsible for undesirable alterations in disease pathologies, specifically cancer. It is implicated in promoting invasive and metastatic progression of many carcinomas. Due to its autocrine and paracrine activities OPN has been shown to be a crucial mediator of cellular cross talk and an influential factor in the tumor microenvironment. OPN has been implicated as a prognostic and diagnostic marker for several cancer types. It has also been explored as a possible target for treatment. In this article we hope to provide a broad perspective on the importance of OPN in the pathophysiology of cancer.

The Hedgehog inhibitor cyclopamine antagonizes chemoresistance of breast cancer cells

Chemoresistance of cancer cells has been a severe problem in multiple types of cancers. One possibility is to combine different drugs with chemotherapy for improved efficacy. Cyclopamine blocks Hedgehog signaling by antagonizing Smo function, which induces tumor apoptosis. Here, we show that the combined use of cyclopamine and paclitaxel (chemotherapy drugs) was able to induce breast cancer cell apoptosis both in vivo and in vitro. The results suggest that Hedgehog signaling is a prospective drug target for chemoresistant cancer cells.

Ursolic acid inhibits colorectal cancer angiogenesis through suppression of multiple signaling pathways

Angiogenesis plays a critical role in the development of solid tumors by supplying nutrients and oxygen to support continuous growth of tumor as well as providing an avenue for hematogenous metastasis. Tumor angiogenesis is highly regulated by multiple intracellular signaling transduction cascades such as Hedgehog, STAT3, Akt and p70S6K pathways that are known to malfunction in many types of cancer including colorectal cancer (CRC). Therefore, suppression of tumor angiogenesis through targeting these signaling pathways has become a promising strategy for cancer chemotherapy. Ursolic acid (UA) is a major active compound present in many medicinal herbs that have long been used in China for the clinical treatment of various types of cancer. Although previous studies have demonstrated an antitumor effect for UA, the precise mechanisms of its anti-angiogenic activity are not well understood. To further elucidate the mechanism(s) of the tumorcidal activity of UA, using a CRC mouse xenograft model, chick embryo chorioallantoic membrane (CAM) model, the human colon carcinoma cell line HT-29 and human umbilical vein endothelial cells (HUVECs), in the present study we evaluated the efficacy of UA against tumor growth and angiogenesis in vivo and in vitro and investigated the underlying molecular mechanisms. We found that administration of UA significantly inhibited tumor volume but had no effect on body weight changes in CRC mice, suggesting that UA can suppress colon cancer growth in vivo without noticeable signs of toxicity. In addition, UA treatment reduced intratumoral microvessel density (MVD) in CRC mice, decreased the total number of blood vessels in the CAM model, and dose and time-dependently inhibited the proliferation, migration and tube formation of HUVECs, demonstrating UA's antitumor angiogenesis in vivo and in vitro. Moreover, UA treatment inhibited the expression of critical angiogenic factors, such as VEGF-A and bFGF. Furthermore, UA suppressed the activation of sonic hedgehog (SHH), STAT3, Akt and p70S6K pathways. Collectively, our findings suggest that inhibition of tumor angiogenesis via suppression of multiple signaling pathways might be one of the mechanisms whereby UA can be effective in cancer treatment.

The Hedgehog signalling pathway in breast development, carcinogenesis and cancer therapy

Despite the progress achieved in breast cancer screening and therapeutic innovations, the basal-like subtype of breast cancer (BLBC) still represents a particular clinical challenge. In order to make an impact on survival in this type of aggressive breast cancer, new targeted therapeutic agents are urgently needed. Aberrant activation of the Hedgehog (Hh) signalling pathway has been unambiguously tied to cancer development and progression in a variety of solid malignancies, and the recent approval of vismodegib, an orally bioavailable small-molecule inhibitor of Smoothened, validates Hh signalling as a valuable therapeutic target. A number of recent publications have highlighted a role for Hh signalling in breast cancer models and clinical specimens. Interestingly, Hh ligand overexpression is associated with the BLBC phenotype and a poor outcome in terms of metastasis and breast cancer-related death. In this review, we provide a comprehensive overview of the canonical Hh signalling pathway in mammals, highlight its roles in mammary gland development and breast carcinogenesis and discuss its potential therapeutic value in BLBC.

Emerging targeted agents in metastatic breast cancer

Extensive preclinical experimentation has conceptually changed the way we perceive breast cancer, with the wide spectrum of genomic alterations governing its malignant progression now being recognized. Functional genomics has helped us identify important genetic defects that can be pharmaceutically targeted in the setting of metastatic disease. Rationally chosen combination regimens are now under clinical investigation. Recent data underline the functional importance of the tumour-associated stroma, with several candidate molecular targets now emerging. Data elucidating a cellular hierarchy within the breast cancer cellular compartment support the existence of a therapy-resistant subpopulation of breast cancer stem cells. Identification of the developmental pathways that dictate their malignant phenotype and use of high-throughput screening techniques are leading to new therapeutic avenues. In this Review, we present the biological rationale for the clinical development of more than 15 different classes of targeted agents in breast cancer, along with evidence supporting rational combinations. However, metastatic breast cancer resembles a Darwinian evolutionary system, with 'driver' mutations and epigenetic changes determining clonal selection according to branching trajectories. This evolution is reflected in the molecular heterogeneity of the disease and poses severe impediments to the successful clinical development of emerging targeted agents.

Pathways to breast cancer recurrence

Breast cancer remains a deadly disease, even with all the recent technological advancements. Early intervention has made an impact, but an overwhelmingly large number of breast cancer patients still live under the fear of “recurrent” disease. Breast cancer recurrence is clinically a huge problem and one that is largely not well understood. Over the years, a number of factors have been studied with an overarching aim of being able to prognose recurrent disease. This paper attempts to provide an overview of our current knowledge of breast cancer recurrence and its associated challenges. Through a survey of the literature on cancer stem cells (CSCs), epithelial-mesenchymal transition (EMT), various signaling pathways such as Notch/Wnt/hedgehog, and microRNAs (miRNAs), we also examine the hypotheses that are currently under investigation for the prevention of breast cancer recurrence.

Crosstalk between TGF-β and hedgehog signaling in cancer

Hedgehog (HH) and TGF-β signals control various aspects of embryonic development and cancer progression. While their canonical signal transduction cascades have been well characterized, there is increasing evidence that these pathways are able to exert overlapping activities that challenge efficient therapeutic targeting. We herein review the current knowledge on HH signaling and summarize the recent findings on the crosstalks between the HH and TGF-β pathways in cancer.