Molecular mechanisms of osteolytic bone metastases

A mechanobiological model of bone metastasis reveals that mechanical stimulation inhibits the pro-osteolytic effects of breast cancer cells

Bone is highly susceptible to cancer metastasis, and both tumor and bone cells enable tumor invasion through a "vicious cycle" of biochemical signaling. Tumor metastasis into bone also alters biophysical cues to both tumor and bone cells, which are highly sensitive to their mechanical environment. However, the mechanobiological feedback between these cells that perpetuate this cycle has not been studied. Here, we develop highly advanced in vitro and computational models to provide an advanced understanding of how tumor growth is regulated by the synergistic influence of tumor-bone cell signaling and mechanobiological cues. In particular, we develop a multicellular healthy and metastatic bone model that can account for physiological mechanical signals within a custom bioreactor. These models successfully recapitulated mineralization, mechanobiological responses, osteolysis, and metastatic activity. Ultimately, we demonstrate that mechanical stimulus provided protective effects against tumor-induced osteolysis, confirming the importance of mechanobiological factors in bone metastasis development.

Calcium-Sensing Receptor Expression in Breast Cancer

The calcium-sensing receptor (CaSR) plays a crucial role in maintaining the balance of calcium in the body. Altered signaling through the CaSR has been linked to the development of various tumors, such as colorectal and breast tumors. This retrospective study enrolled 79 patients who underwent surgical removal of invasive breast carcinoma of no special type (NST) to explore the expression of the CaSR in breast cancer. The patients were categorized based on age, tumor size, hormone receptor status, HER2 status, Ki-67 proliferation index, tumor grade, and TNM staging. Immunohistochemistry was conducted on core needle biopsy samples to assess CaSR expression. The results revealed a positive correlation between CaSR expression and tumor size, regardless of the tumor surrogate subtype (p = 0.001). The expression of ER exhibited a negative correlation with CaSR expression (p = 0.033). In contrast, a positive correlation was observed between CaSR expression and the presence of HER2 receptors (p = 0.002). Increased CaSR expression was significantly associated with lymph node involvement and the presence of distant metastasis (p = 0.001 and p = 0.038, respectively). CaSR values were significantly higher in the patients with increased Ki-67 (p = 0.042). Collectively, higher CaSR expression in breast cancer could suggest a poor prognosis and treatment outcome regardless of the breast cancer subtype.

Metastatic Breast Cancer: Review of Emerging Nanotherapeutics

Metastases of breast cancer (BC) are often referred to as stage IV breast cancer due to their severity and high rate of mortality. The median survival time of patients with metastatic BC is reduced to 3 years. Currently, the treatment regimens for metastatic BC are similar to the primary cancer therapeutics and are limited to conventional chemotherapy, immunotherapy, radiotherapy, and surgery. However, metastatic BC shows organ-specific complex tumor cell heterogeneity, plasticity, and a distinct tumor microenvironment, leading to therapeutic failure. This issue can be successfully addressed by combining current cancer therapies with nanotechnology. The applications of nanotherapeutics for both primary and metastatic BC treatments are developing rapidly, and new ideas and technologies are being discovered. Several recent reviews covered the advancement of nanotherapeutics for primary BC, while also discussing certain aspects of treatments for metastatic BC. This review provides comprehensive details on the recent advancement and future prospects of nanotherapeutics designed for metastatic BC treatment, in the context of the pathological state of the disease. Furthermore, possible combinations of current treatment with nanotechnology are discussed, and their potential for future transitions in clinical settings is explored.

Schwann Cell Insulin-like Growth Factor Receptor Type-1 Mediates Metastatic Bone Cancer Pain in Mice

Insulin growth factor-1 (IGF-1), an osteoclast-dependent osteolysis biomarker, contributes to metastatic bone cancer pain (MBCP), but the underlying mechanism is poorly understood. In mice, the femur metastasis caused by intramammary inoculation of breast cancer cells resulted in IGF-1 increase in femur and sciatic nerve, and IGF-1-dependent stimulus/non-stimulus-evoked pain-like behaviors. Adeno-associated virus-based shRNA selective silencing of IGF-1 receptor (IGF-1R) in Schwann cells, but not in dorsal root ganglion (DRG) neurons, attenuated pain-like behaviors. Intraplantar IGF-1 evoked acute nociception and mechanical/cold allodynia, which were reduced by selective IGF-1R silencing in DRG neurons and Schwann cells, respectively. Schwann cell IGF-1R signaling promoted an endothelial nitric oxide synthase-mediated transient receptor potential ankyrin 1 (TRPA1) activation and release of reactive oxygen species that, via macrophage-colony stimulating factor-dependent endoneurial macrophage expansion, sustained pain-like behaviors. Osteoclast derived IGF-1 initiates a Schwann cell-dependent neuroinflammatory response that sustains a proalgesic pathway that provides new options for MBCP treatment.

The RANK/RANKL/OPG system and tumor bone metastasis: Potential mechanisms and therapeutic strategies

With the markedly increased diagnosis and incidence of cancer in the population, tumor bone metastasis has become a frequent event in tumor patients. Healthy bone integrity is maintained by a delicate balance between bone formation and bone resorption. Unfortunately, many tumors, such as prostate and breast, often metastasize to the bone, and the alterations to the bone homeostasis can particularly favor tumor homing and consequent osteolytic or osteoblastic lesions. Receptor activator of NF-κB ligand (RANKL), its receptor RANK, and osteoprotegerin (OPG) are involved in the regulation of the activation, differentiation, and survival of osteoclasts, which play critical roles in bone metastasis formation. High rates of osteoclastic bone resorption significantly increase fracture risk, cause severe bone pain, and contribute to homing tumor cells in bone and bone marrow. Consequently, suppression of the RANK/RANKL/OPG system and osteoclastic activity can not only ameliorate bone resorption but may also prevent tumor bone metastases. This review summarizes the important role of the RANK/RANKL/OPG system and osteoclasts in bone homeostasis and its effect on tumor bone metastasis and discusses therapeutic strategies based on RANKL inhibition.

The association between the severity of periodontitis and osteonecrosis of the jaw in patients with different cancer locations: a nationwide population-based study

OBJECTIVES

To determine the relation between the severity of periodontitis and osteonecrosis of the jaw (ONJ) occurrence among different cancer locations and estimate the effect of dental care on ONJ prevention in cancer patients.

MATERIALS AND METHODS

This population-based cross-sectional study was conducted through the Longitudinal Health Insurance Database, Taiwan. Patients with malignancies were collected and subdivided into groups according to their different cancer locations, the severity of periodontitis, and dental care. Multivariable logistic regression analysis was performed to assess the associations between ONJ and ONJ-related factors.

RESULTS

A total of 8,234 ONJ patients and 32,912 control patients were investigated. Lip, oral cavity, and pharynx malignancies had the highest ONJ risk among all cancer locations (OR from 3.07 to 9.56, P < 0.01). There is a linear relationship between different severities of periodontitis and ONJ. Patients with radiotherapy and severe periodontitis had the highest ONJ risk (adjusted OR, 9.56; 95% CI, 5.34-17.1). Patients with good dental care had a lower ONJ risk.

CONCLUSIONS

The periodontal condition and cancer location showed a significant impact on the risk of developing ONJ after adjusting for bisphosphonate use. Good dental care could decrease the risk of ONJ in cancer patients. The severity of periodontitis might be a target to predict the potency of ONJ.

CLINICAL RELEVANCE

Dentists must be vigilant about the increased risk of ONJ in cancer patients with periodontitis, especially in the head and neck cancer population. Good dental care is advised for cancer patients with severe periodontitis.

Recent Advances in the Treatment of Bone Metastases and Primary Bone Tumors: An Up-to-Date Review

In the last decades, the treatment of primary and secondary bone tumors has faced a slow-down in its development, being mainly based on chemotherapy, radiotherapy, and surgical interventions. However, these conventional therapeutic strategies present a series of disadvantages (e.g., multidrug resistance, tumor recurrence, severe side effects, formation of large bone defects), which limit their application and efficacy. In recent years, these procedures were combined with several adjuvant therapies, with different degrees of success. To overcome the drawbacks of current therapies and improve treatment outcomes, other strategies started being investigated, like carrier-mediated drug delivery, bone substitutes for repairing bone defects, and multifunctional scaffolds with bone tissue regeneration and antitumor properties. Thus, this paper aims to present the types of bone tumors and their current treatment approaches, further focusing on the recent advances in new therapeutic alternatives.

Imaging features of hypercalcemia: A primer for emergency radiologists

Hypercalcemia is a marker for a wide variety of underlying etiologies, and its presentation in the emergency setting may be asymptomatic, incidental, or a primary complaint with associated symptoms and physical exam findings. While the workup is initially driven through serum laboratory testing, imaging plays an important role in diagnosis and post-treatment follow up. This review covers multiple common and uncommon etiologies of hypercalcemia, details their underlying mechanisms, and identifies the most important associated imaging findings. It is important for radiologists to be familiar with these etiologies and imaging findings, particularly in the emergency setting since hypercalcemia may represent the only significant laboratory abnormality associated with the presenting condition. Furthermore, the radiologist's interpretation of a study may be directly influenced by knowing about a patient's hypercalcemia.

Role of Osteocytes in Cancer Progression in the Bone and the Associated Skeletal Disease

PURPOSE OF REVIEW

The goal of this manuscript is to review the current knowledge on the role of osteocytes in cancer in the bone, discuss the potential of osteocytes as a therapeutic target, and propose future research needed to understand the crosstalk between cancer cells and osteocytes in the tumor niche.

RECENT FINDINGS

Numerous studies have established that cancer cells manipulate osteocytes to facilitate invasion and tumor progression in bone. Moreover, cancer cells dysregulate osteocyte function to disrupt physiological bone remodeling, leading to the development of bone disease. Targeting osteocytes and their derived factors has proven to effectively interfere with the progression of cancer in the bone and the associated bone disease. Osteocytes communicate with cancer cells and are also part of the vicious cycle of cancer in the bone. Additional studies investigating the role of osteocytes on metastases to the bone and the development of drug resistance are needed.

A Role for TGFβ Signaling in Preclinical Osteolytic Estrogen Receptor-Positive Breast Cancer Bone Metastases Progression

While tumoral Smad-mediated transforming growth factor β (TGFβ) signaling drives osteolytic estrogen receptor α-negative (ER-) breast cancer bone metastases (BMETs) in preclinical models, its role in ER+ BMETs, representing the majority of clinical BMETs, has not been documented. Experiments were undertaken to examine Smad-mediated TGFβ signaling in human ER+ cells and bone-tropic behavior following intracardiac inoculation of estrogen (E2)-supplemented female nude mice. While all ER+ tumor cells tested (ZR-75-1, T47D, and MCF-7-derived) expressed TGFβ receptors II and I, only cells with TGFβ-inducible Smad signaling (MCF-7) formed osteolytic BMETs in vivo. Regulated secretion of PTHrP, an osteolytic factor expressed in >90% of clinical BMETs, also tracked with osteolytic potential; TGFβ and E2 each induced PTHrP in bone-tropic or BMET-derived MCF-7 cells, with the combination yielding additive effects, while in cells not forming BMETs, PTHrP was not induced. In vivo treatment with 1D11, a pan-TGFβ neutralizing antibody, significantly decreased osteolytic ER+ BMETs in association with a decrease in bone-resorbing osteoclasts at the tumor-bone interface. Thus, TGFβ may also be a driver of ER+ BMET osteolysis. Moreover, additive pro-osteolytic effects of tumoral E2 and TGFβ signaling could at least partially explain the greater propensity for ER+ tumors to form BMETs, which are primarily osteolytic.

Osteolytic effects of tumoral estrogen signaling in an estrogen receptor-positive breast cancer bone metastasis model

AIM

Estrogen receptor α-positive (ER+) subtypes of breast cancer have the greatest predilection for forming osteolytic bone metastases (BMETs). Because tumor-derived factors mediate osteolysis, a possible role for tumoral ERα signaling in driving ER+ BMET osteolysis was queried using an estrogen (E2)-dependent ER+ breast cancer BMET model.

METHODS

Female athymic Foxn1nu mice were inoculated with human ER+ MCF-7 breast cancer cells via the left cardiac ventricle post-E2 pellet placement, and age- and dose-dependent E2 effects on osteolytic ER+ BMET progression, as well as direct bone effects of E2, were determined.

RESULTS

Osteolytic BMETs, which did not form in the absence of E2 supplementation, occurred with the same frequency in young (5-week-old) vs. skeletally mature (16-week-old) E2 (0.72 mg)-treated mice, but were larger in young mice where anabolic bone effects of E2 were greater. However, in mice of a single age and across a range of E2 doses, anabolic E2 bone effects were constant, while osteolytic ER+ BMET lesion incidence and size increased in an E2-dose-dependent fashion. Osteoclasts in ER+ tumor-bearing (but not tumor-naive) mice increased in an E2-dose dependent fashion at the bone-tumor interface, while histologic tumor size and proliferation did not vary with E2 dose. E2-inducible tumoral secretion of the osteolytic factor parathyroid hormone-related protein (PTHrP) was dose-dependent and mediated by ERα, with significantly greater levels of secretion from ER+ BMET-derived tumor cells.

CONCLUSION

These results suggest that tumoral ERα signaling may contribute to ER+ BMET-associated osteolysis, potentially explaining the greater predilection for ER+ tumors to form clinically-evident osteolytic BMETs.

Novel bone-targeted parathyroid hormone-related peptide antagonists inhibit breast cancer bone metastases

Patients with advanced breast cancer often develop bone metastases. Treatment is limited to palliative care. Parathyroid hormone (PTH)/parathyroid hormone-related peptide (PTHrP) antagonists for bone metastases failed clinically due to short half-life and inadequate concentration in bone. We synthesized two novel PTHrP antagonists fused to an inert bacterial collagen binding domain (CBD) that directs drugs to bone. PTH(7-33)-CBD is an N-terminal truncated PTHrP antagonist. [W2]PTH(1-33)-CBD is an PTHrP inverse-agonist. The aim of this study was to assess PTH(7-33)-CBD to reduce breast cancer bone metastases and prevent osteolytic destruction in mice and to assess both drugs for apoptosis of breast cancer cells in vitro and inhibition of PTH receptor (PTHR1). PTH(7-33)-CBD (1000 µg/kg, subcutaneous) or vehicle was administered 24 h prior to MDA-MB-231 breast cancer cell inoculation into the tibia marrow. Weekly tumor burden and bone density were measured. Pharmacokinetic analysis of PTH(7-33)-CBD in rat serum was evaluated. Drug effect on cAMP accumulation in SaOS-2 osteosarcoma cells and apoptosis of MDA-MB-231 cells was assessed. PTH(7-33)-CBD reduced MDA-MB-231 tumor burden and osteolytic destruction in mice 4-5 weeks post-treatment. PTH(7-33)-CBD (1000 μg/kg i.v. and subcutaneous) in rats was rapidly absorbed with peak concentration 5-min and terminal half-life 3-h. Bioavailability by the subcutaneous route was 43% relative to the i.v. route. PTH(7-33)-CBD was detected only on rat periosteal bone surfaces that stained positive for collagen-1. PTH(7-33)-CBD and [W2]PTH(1-33)-CBD (10-8M) blocked basal and PTH agonist-induced cAMP accumulation in SaOS-2 osteosarcoma cells. Both drugs induced PTHR1-dependent apoptosis of MDA-MB-231 cells in vitro. Novel bone-targeted PTHrP antagonists represent a new paradigm for treatment of breast cancer bone metastases.

Printing the Pathway Forward in Bone Metastatic Cancer Research: Applications of 3D Engineered Models and Bioprinted Scaffolds to Recapitulate the Bone-Tumor Niche

Breast cancer commonly metastasizes to bone, resulting in osteolytic lesions and poor patient quality of life. The bone extracellular matrix (ECM) plays a critical role in cancer cell metastasis by means of the physical and biochemical cues it provides to support cellular crosstalk. Current two-dimensional in-vitro models lack the spatial and biochemical complexities of the native ECM and do not fully recapitulate crosstalk that occurs between the tumor and endogenous stromal cells. Engineered models such as bone-on-a-chip, extramedullary bone, and bioreactors are presently used to model cellular crosstalk and bone-tumor cell interactions, but fall short of providing a bone-biomimetic microenvironment. Three-dimensional bioprinting allows for the deposition of biocompatible materials and living cells in complex architectures, as well as provides a means to better replicate biological tissue niches in-vitro. In cancer research specifically, 3D constructs have been instrumental in seminal work modeling cancer cell dissemination to bone and bone-tumor cell crosstalk in the skeleton. Furthermore, the use of biocompatible materials, such as hydroxyapatite, allows for printing of bone-like microenvironments with the ability to be implanted and studied in in-vivo animal models. Moreover, the use of bioprinted models could drive the development of novel cancer therapies and drug delivery vehicles.

'Educated' Osteoblasts Reduce Osteoclastogenesis in a Bone-Tumor Mimetic Microenvironment

Breast cancer (BC) metastases to bone disrupt the balance between osteoblasts and osteoclasts, leading to excessive bone resorption. We identified a novel subpopulation of osteoblasts with tumor-inhibitory properties, called educated osteoblasts (EOs). Here we sought to examine the effect of EOs on osteoclastogenesis during tumor progression. We hypothesized that EOs affect osteoclast development in the bone-tumor niche, leading to suppressed pre-osteoclast fusion and bone resorption. Conditioned media (CM) was analyzed for protein expression of osteoclast factors receptor activator of nuclear factor kappa-β ligand (RANKL), osteoprotegerin (OPG), and tumor necrosis factor alpha (TNFα) via ELISA. EOs were co-cultured with pre-osteoclasts on a bone mimetic matrix to assess osteoclast resorption. Pre-osteoclasts were tri-cultured with EOs plus metastatic BC cells and assessed for tartrate-resistance acid phosphatase (TRAP)-positive, multinucleated (≥3 nuclei), mature osteoclasts. Tumor-bearing murine tibias were stained for TRAP to determine osteoclast number in-vivo. EO CM expressed reduced amounts of soluble TNFα and OPG compared to naïve osteoblast CM. Osteoclasts formed in the presence of EOs were smaller and less in number. Upon co-culture on a mimetic bone matrix, a 50% reduction in the number of TRAP-positive osteoclasts formed in the presence of EOs was observed. The tibia of mice inoculated with BC cells had less osteoclasts per bone surface in bones with increased numbers of EO cells. These data suggest EOs reduce osteoclastogenesis and bone resorption. The data imply EOs provide a protective effect against bone resorption in bone metastatic BC.

Demethoxycucumin protects MDA-MB-231 cells induced bone destruction through JNK and ERK pathways inhibition

Bone is the most common late metastasis of breast cancer. Bone metastasis causes not only severe bone pain, but also bone-related diseases such as pathological fractures, which are closely related to osteoclasts. The effects of demethoxycurcumin (DMC) on osteoclast biology has not been investigated. In this study, we explored the effects of DMC on MDA-MB-231 cells, MCF-7 cells, and osteoclasts induced by RANKL in vitro, as well as the protective effect on bone destruction of tumor bone metastasis in vivo. DMC showed inhibitory effect on the migration and promotes the apoptosis of MDA-MB-231 and MCF-7 cells. At the same time, DMC inhibited osteoclast maturation and mature osteoclast bone resorption in a dose-dependent manner, and suppressed the expression of osteoclast marker genes TRAP, CTSK, MMP9, V-ATPase-d2 and DC-STAMP significantly. Biochemical data showed that DMC inhibited tumor cells and osteoclasts by inhibiting the early activation of ERK and JNK MAPK pathway. Consistent with the results in vitro, we confirmed that DMC protects bone destruction caused by tumor metastasis in vivo. In short, our study confirmed that DMC could be used as a potential drug for the treatment of tumor bone destruction.

Pharmacological Inhibition of NFκB Reduces Prostate Cancer Related Osteoclastogenesis In Vitro and Osteolysis Ex Vivo

NFκB is implicated in cancer and bone remodelling, and we have recently reported that the verified NFκB inhibitor Parthenolide (PTN) reduced osteolysis and skeletal tumour growth in models of metastatic breast cancer. Here, we took advantage of in vitro and ex vivo bone cell and organ cultures to study the effects of PTN on the ability of prostate cancer cells and their derived factors to regulate bone cell activity and osteolysis. PTN inhibited the in vitro growth of a panel of human, mouse and rat prostate cancer cells in a concentration-dependent manner with a varying degree of potency. In prostate cancer cell-osteoclast co-cultures, the rat Mat-Ly-Lu, but not human PC3 or mouse RM1-BT, enhanced RANKL stimulated osteoclast formation and PTN reduced these effects without affecting prostate cancer cell viability. In the absence of cancer cells, PTN reduced the support of Mat-Ly-Lu conditioned medium for the adhesion and spreading of osteoclast precursors, and survival of mature osteoclasts. Pre-exposure of osteoblasts to PTN prior to the addition of conditioned medium from Mat-Ly-Lu cells suppressed their ability to support the formation of osteoclasts by inhibition of RANKL/OPG ratio. PTN enhanced the ability of Mat-Ly-Lu derived factors to increase calvarial osteoblast differentiation and growth. Ex vivo, PTN enhanced bone volume in calvaria organ-Mat-Ly-Lu cell co-culture, without affecting Mat-Ly-Lu viability or apoptosis. Mechanistic studies in osteoclasts and osteoblasts confirmed that PTN inhibit NFκB activation related to derived factors from Mat-Ly-Lu cells. Collectively, these findings suggest that pharmacological inhibition of the skeletal NFκB signalling pathway reduces prostate cancer related osteolysis, but further studies in the therapeutic implications of NFκB inhibition in cells of the osteoblastic lineage are needed.

15-Deoxy-Δ12,14-prostaglandin J2 as a potential regulator of bone metabolism via PPARγ-dependent and independent pathways: a review

Bone metabolism is a complex physiological process that primarily involves osteoblast-mediated bone formation and osteoclast-mediated bone resorption, both of which are regulated by a variety of biological factors. There is increasing evidence that peroxisome proliferator-activated receptor γ (PPARγ) is a member of the nuclear receptor superfamily and plays an important role in lipid metabolism and bone metabolism. Through the PPARγ-dependent pathway, 15-deoxy-Δ^12,14-prostaglandin J₂ (15d-PGJ₂) promotes the formation of marrow adipocytes and inhibits the formation of osteoblasts, resulting in bone loss and increasing the risk of fracture and osteoporosis. Recent studies have found that through the PPARγ-independent pathway, 15d-PGJ₂ plays a regulatory role in bone metastasis of breast cancer, which can inhibit osteoclastogenesis and reduce bone destruction. The purpose of our review is to summarize the recent progress in elucidating the mechanisms and effects of 15d-PGJ₂ in bone metabolism, which can serve as a novel therapeutic target for bone tumors, osteoporosis, rheumatoid arthritis (RA), and other bone diseases.

Bisphosphonates and Cancer: A Relationship Beyond the Antiresorptive Effects

Bisphosphonates (BPs) are stable analogues of the Inorganic Pyrophosphate (PPi), an endogenous regulator of bone mineralization, which can resist the hydrolysis in the gastrointestinal tract. Their conformation allows targeting the bone as a result of their three-dimensional structure, which makes them primary agents against osteoclast-mediated bone loss. They are used in many bone pathological conditions, like bone metastasis, because of its ability to modulate bone metabolism into a less favorable place to cancer cell growth, through the inhibition of osteoclastogenesis and bone resorption. This review is focused on the mechanisms of action through which BPs affect the cellular activity and survival, mainly on their antitumoral effects. In conclusion, BPs are considered the primary therapy for skeletal disorders due to its high affinity for bone, but now they are also considered as potential antitumor agents due to its ability to induce tumor cell apoptosis, inhibition of cell adhesion, invasion and proliferation, modulation of the immune system to target and eliminate cancer cells as well as affect the angiogenic mechanisms. Like any other drug, they also have some adverse effects, but the most common, the acute phase reaction, can be minimized with the intake of calcium and vitamin D.

The Emerging Role of Osteocytes in Cancer in Bone

Advances in the last decade have established the osteocyte, the most abundant cell in bone, as a dynamic and multifunctional cell capable of controlling bone homeostasis by regulating the function of both osteoblasts and osteoclasts. In addition, accumulating evidence demonstrates that osteocyte function is altered in several skeletal disorders, and targeting osteocytes and their derived factors improves skeletal health. Despite the remarkable progress in our understanding of osteocyte biology, there has been a paucity of information regarding the role of osteocytes in the progression of cancer in bone. Exciting, recent discoveries suggest that tumor cells communicate with osteocytes to generate a microenvironment that supports the growth and survival of cancer cells and stimulates bone destruction. This review features these novel findings and discussions regarding the impact of chemotherapy on osteocyte function and the potential of targeting osteocytes for the treatment of cancer in bone. © 2019 The Authors. JBMR Plus published by Wiley Periodicals, Inc. on behalf of American Society for Bone and Mineral Research.

Small molecule nAS-E targeting cAMP response element binding protein (CREB) and CREB-binding protein interaction inhibits breast cancer bone metastasis

Bone is the most common metastatic site for breast cancer. The excessive osteoclast activity in the metastatic bone lesions often produces osteolysis. The cyclic-AMP (cAMP)-response element binding protein (CREB) serves a variety of biological functions including the transformation and immortalization of breast cancer cells. In addition, evidence has shown that CREB plays a key role in osteoclastgenesis and bone resorption. Small organic molecules with good pharmacokinetic properties and specificity, targeting CREB-CBP (CREB-binding protein) interaction to inhibit CREB-mediated gene transcription have attracted more considerations as cancer therapeutics. We recently identified naphthol AS-E (nAS-E) as a cell-permeable inhibitor of CREB-mediated gene transcription through inhibiting CREB-CBP interaction. In this study, we tested the effect of nAS-E on breast cancer cell proliferation, survival, migration as well as osteoclast formation and bone resorption in vitro for the first time. Our results demonstrated that nAS-E inhibited breast cancer cell proliferation, migration, survival and suppressed osteoclast differentiation as well as bone resorption through inhibiting CREB-CBP interaction. In addition, the in vivo effect of nAS-E in protecting against breast cancer-induced osteolysis was evaluated. Our results indicated that nAS-E could reverse bone loss induced by MDA-MB-231 tumour. These results suggest that small molecules targeting CREB-CBP interaction to inhibit CREB-mediated gene transcription might be a potential approach for the treatment of breast cancer bone metastasis.

Cancer Metastases to Bone: Concepts, Mechanisms, and Interactions with Bone Osteoblasts

The skeleton is a unique structure capable of providing support for the body. Bone resorption and deposition are controlled in a tightly regulated balance between osteoblasts and osteoclasts with no net bone gain or loss. However, under conditions of disease, the balance between bone resorption and deposition is upset. Osteoblasts play an important role in bone homeostasis by depositing new bone osteoid into resorption pits. It is becoming increasingly evident that osteoblasts additionally play key roles in cancer cell dissemination to bone and subsequent metastasis. Our laboratory has evidence that when osteoblasts come into contact with disseminated breast cancer cells, the osteoblasts produce factors that initially reduce breast cancer cell proliferation, yet promote cancer cell survival in bone. Other laboratories have demonstrated that osteoblasts both directly and indirectly contribute to dormant cancer cell reactivation in bone. Moreover, we have demonstrated that osteoblasts undergo an inflammatory stress response in late stages of breast cancer, and produce inflammatory cytokines that are maintenance and survival factors for breast cancer cells and osteoclasts. Advances in understanding interactions between osteoblasts, osteoclasts, and bone metastatic cancer cells will aid in controlling and ultimately preventing cancer cell metastasis to bone.

Bisphosphonates in Oncology: Physiopathologic Bases and Clinical Activity

Osteoclastic activation is the ultimate way of bone resorption in neoplasia, induced by the combined effects of tumor-secreted humoral factors (especially parathyroid hormone-related peptides) and osteoclastic-osteoblastic interaction. Bisphosphonates inhibit the osteoclast activity and reduce bone resorption and are a valuable supportive measure for bone disease of neoplasms. Experimental models also suggest an activity of bisphosphonates against cancer cells. Controlled studies, especially in advanced breast cancer and multiple myeloma, indicate different effectiveness against the distinct skeletal-related events. Intravenous clodronate and, especially, pamidronate and zoledronate are the first-choice drugs for hypercalcemia, and they play a significant role in reducing metastatic bone pain. Their prolonged use delays, without hampering, the progression of bone disease, including the appearance of osteolysis and the occurrence of pathologic fractures. This effect is probably more valuable when bisphosphonates are administered early in the course of the disease. The evidence that adjuvant bisphosphonates improve survival needs to be confirmed in ongoing studies. Although poorly absorbed by the gastrointestinal tract, oral bisphosphonates are effective in preventing and treating cancer-induced osteoporosis in long-living patients with operable breast cancer. At present, there is little hope that newer bisphosphonates are more effective than those currently used.

Prostate Cancer Progression and Surrounding Microenvironment

Bidirectional cellular interactions between prostate cancer and prostate or bone stroma are needed for local tumor growth and distant metastasis. The genetics of cancer cells is affected by the host microenvironment and, reciprocally, permanent gene expression changes occur in the stroma surrounding epithelial cancer cells. The immune-mediated micromilieu also affects the progression of prostate cancer; the role of the immune system in controlling the growth of prostate cancer cells is complex, with immune escape mechanisms prevailing over effective antitumor response. Moreover, tumor stem cell models to explain the origin and progression of prostate cancer require appropriate environmental conditions. On the basis of a review of the literature, this article aims to outline the recent advances in the elucidation of the molecular mechanisms underlying the interactions between prostate cancer and its microenvironment.

The cell biology and role of resorptive cells in diseases: A review

Resorptive cells are responsible for the resorption of mineralized matrix of hard tissues. Bone-resorbing cells are called osteoclasts; however, they can resorb mineralized dental tissues or calcified cartilage and then they are called odontoclasts and chondroclasts, respectively. Resorptive cells form when mononuclear precursors derived from a monocyte–macrophage cell lineage are attracted to certain mineralized surfaces and subsequently fuse and adhere onto them for exerting their resorbing activity. These cells are responsible for degradation of calcified extracellular matrix composed of organic molecules and hydroxyapatite. The activity of these cells can be observed in both physiological and pathological processes throughout life and their activity is mainly required in bone turnover and growth, spontaneous and induced (orthodontic) tooth movement, tooth eruption, and bone fracture healing, as well as in pathological conditions such as osteoporosis, osteoarthritis, and bone metastasis. In addition, they are responsible for daily control of calcium homeostasis. Clastic cells also resorb the primary teeth for shedding before the permanent teeth erupt into the oral cavity.

miRNAs in bone metastasis

Bone metastasis is one of the most common forms of metastasis from a number of different primary carcinomas. MicroRNAs (miRNAs) are short, endogenous RNAs that negatively regulate gene expression to control essential pathways, including those involved in bone organogenesis and homeostasis. As these pathways are often hijacked during bone metastasis, it is not surprising that miRNAs can also influence bone metastasis formation. Areas covered: In this review, we first summarize the major signalling pathways involved in normal bone development and bone metastasis. We will then discuss the overall roles of miRNAs in cancer metastasis and highlight the recent findings on the effects of miRNAs in bone metastasis. To this aim, we have performed a literature search in PubMed by using the search words 'miRNAs' and 'bone metastasis', selecting relevant scientific articles published between 2010 and 2016. Seminal publications before 2010 on the metastatic role of miRNAs have also been considered. Expert commentary: With the lack of current diagnostic biomarkers and effective targeted therapies for bone metastasis, the significant role of miRNAs in the regulation of bone homeostasis and bone metastasis may support the future use of miRNAs as diagnostic biomarkers and therapeutic targets.

Disease- and Treatment-related Complication on F-18-Fluorodeoxyglucose Positron Emission Tomography/Computed Tomography in Oncology Practice: A Pictorial Review

F-18-fluorodeoxyglucose positron emission tomography/computed tomography (PET/CT) is routinely performed in oncology patients for various indications including staging, restaging, recurrence detection, and treatment response evaluation. Many disease- and treatment-related complications can be incidentally detected on PET/CT, which may be due to the complication of radiotherapy, chemotherapy, intervention, or primary tumor itself. Some of these complications could be life threatening and need urgent intervention. Therefore, these incidental findings should be recognized on PET/CT and immediately informed to the treating physicians if required urgent intervention.

Transforming Growth Factor Beta is regulated by a Glucocorticoid-Dependent Mechanism in Denervation Mouse Bone

Bone growth and remodeling is inhibited by denervation in adults and children, resulting in alterations of linear growth and bone mass and increased risk for osteoporosis and pathologic fractures. Transforming growth factor beta (TGF-β) isoforms are a key group of growth factors that enhance bone formation. To explore the relation between denervation-induced reduction of bone formation and TGF-β gene expression, we measured mRNA levels of TGF-β in denervation mouse bone and found decreased mRNA levels of TGF-β1, TGF-β2 and TGF-β3. These changes were accompanied by diminishing weight loss, bone mineral density (BMD), trabecular thickness, trabecular separation and trabecular number of femur and lumbar, serum osteocalcin, total calcium, intact parathyroid hormone, and increased serum C telopeptide. Recombinant human TGF-β1 (rhTGF-β1) prevented denervation-induced reduction of BMD further supporting our hypothesis that denervation-induced reduction of bone formation is a result of inhibition of TGF-β gene expression. In addition, antiprogestins RU 38486 blunted the denervation-induced decrease in mRNA levels of TGF-β group, while dexamethasone (DEX) decreased TGF-β group mRNA levels in normal mice. Furthermore, the denervated-mice exhibited a threefold increase in plasma corticosterone. These results suggest that denervation-induced reduction of bone formation may be regulated by glucocorticoids via inhibition of TGF-β gene expression at least in part.

Altered bone microarchitecture and gene expression profile due to calcium deficiency in a mouse model of myeloma

It is not clear why patients with an indolent form of multiple myeloma (MM) develop into an aggressive form with poor prognostic. We investigated the effect of a dietary calcium deficiency on tumor growth, osteolysis and gene expression in the 5T2MM murine model. Two groups of C57BL/KaLwRij mice received 5T2MM cells and started a diet with normal (0.8%; "normal-Ca-MM") or low calcium content (0.05%; "low-Ca-MM"). Two control groups (without 5T2MM cells) received either a normal or low calcium diet (normal-Ca and low-Ca groups). Tumor growth, osteolysis and marrow gene expression of the Wnt pathway, RANKL and MIP-1α were monitored at 6, 8 and 10 weeks (w) after cell injection. In low-Ca mice, serum level of PTH was higher after 10w; microCT showed trabecular bone loss and decrease of cortical thickness at the tibia. A higher M-protein level was evidenced at 10w and 4 mice developed paraplegia at 8/9w in low-Ca-MM group only. Numerous cortical perforations of the tibia were observed in MM groups with a marked decrease in cortical thickness in low-Ca-MM. At 6w, osteoclast number from the endosteum was significantly higher in low-Ca-MM compared to normal-Ca MM. This observation was not found at 8 and 10w. MicroCT of the lumbar vertebrae showed dramatic bone destruction in the low-Ca-MM group. qPCR revealed no difference in RANKL expression whereas differences were obtained in the expression of Lrp5/Lrp6 and MIP-1α from 6w. A low calcium diet induced higher bone destruction in the tibia and vertebra associated with an earlier decrease in bone formation level and a higher increase in bone resorption level at early time in the MM development.

Emerging therapeutic targets in cancer induced bone disease: A focus on the peripheral type 2 cannabinoid receptor

Skeletal complications are a common cause of morbidity in patients with primary bone cancer and bone metastases. The type 2 cannabinoid (Cnr2) receptor is implicated in cancer, bone metabolism and pain perception. Emerging data have uncovered the role of Cnr2 in the regulation of tumour-bone cell interactions and suggest that agents that target Cnr2 in the skeleton have potential efficacy in the reduction of skeletal complications associated with cancer. This review aims to provide an overview of findings relating to the role of Cnr2 receptor in the regulation of skeletal tumour growth, osteolysis and bone pain, and highlights the many unanswered questions and unmet needs. This review argues that development and testing of peripherally-acting, tumour-, Cnr2-selective ligands in preclinical models of metastatic cancer will pave the way for future research that will advance our knowledge about the basic mechanism(s) by which the endocannabinoid system regulate cancer metastasis, stimulate the development of a safer cannabis-based therapy for the treatment of cancer and provide policy makers with powerful tools to assess the science and therapeutic potential of cannabinoid-based therapy. Thus, offering the prospect of identifying selective Cnr2 ligands, as novel, alternative to cannabis herbal extracts for the treatment of advanced cancer patients.

Calcium role in human carcinogenesis: a comprehensive analysis and critical review of literature

The central role played by calcium ion in biological systems has generated an interest for its potential implication in human malignancies. Thus, lines of research, on possible association of calcium metabolism regulation with tumorigenesis, implying disruptions and/or alterations of known molecular pathways, have been extensively researched in the recent decades. This paper is a critical synthesis of these findings, based on a functional approach of the calcium signaling toolkit. It provides strong support that this ubiquitous divalent cation is involved in cancer initiation, promotion, and progression. Different pathways have been outlined, involving equally different molecular and cellular structures. However, if the association between calcium and cancer can be described as constant, it is not always linear. We have identified several influencing factors among which the most relevant are (i) the changes in local or tissular concentrations of free calcium and (ii) the histological and physiological types of tissue involved. Such versatility at the molecular level may probably account for the conflicting findings reported by the epidemiological literature on calcium dietary intake and the risk to develop certain cancers such as the prostatic or mammary neoplasms. However, it also fuels the hypothesis that behind each cancer, a specific calcium pathway can be evidenced. Identifying such molecular interactions is probably a promising approach for further understanding and treatment options for the disease.

Inhibition of KPNA4 attenuates prostate cancer metastasis

Prostate cancer (PCa) is a common cancer in men. Although current treatments effectively palliate symptoms and prolong life, the metastatic PCa remains incurable. It is important to find biomarkers and targets to improve metastatic PCa diagnosis and treatment. Here we report a novel correlation between karyopherin α4 (KPNA4) and PCa pathological stages. KPNA4 mediates the cytoplasm-to-nucleus translocation of transcription factors, including nuclear factor kappa B, although its role in PCa was largely unknown. We find that knockdown of KPNA4 reduces cell migration in multiple PCa cell lines, suggesting a role of KPNA4 in PCa progression. Indeed, stable knockdown of KPNA4 significantly reduces PCa invasion and distant metastasis in mouse models. Functionally, KPNA4 alters tumor microenvironment in terms of macrophage polarization and osteoclastogenesis by modulating tumor necrosis factor (TNF)-α and -β. Further, KPNA4 is proved as a direct target of miR-708, a tumor-suppressive microRNA. We disclose the role of miR-708-KPNA4-TNF axes in PCa metastasis and KPNA4's potential as a novel biomarker for PCa metastasis.

Murine models of breast cancer bone metastasis

Bone metastases cause significant morbidity and mortality in late-stage breast cancer patients and are currently considered incurable. Investigators rely on translational models to better understand the pathogenesis of skeletal complications of malignancy in order to identify therapeutic targets that may ultimately prevent and treat solid tumor metastasis to bone. Many experimental models of breast cancer bone metastases are in use today, each with its own caveats. In this methods review, we characterize the bone phenotype of commonly utilized human- and murine-derived breast cell lines that elicit osteoblastic and/or osteolytic destruction of bone in mice and report methods for optimizing tumor-take in murine models of bone metastasis. We then provide protocols for four of the most common xenograft and syngeneic inoculation routes for modeling breast cancer metastasis to the skeleton in mice, including the intra-cardiac, intra-arterial, orthotopic and intra-tibial methods of tumor cell injection. Recommendations for in vivo and ex vivo assessment of tumor progression and bone destruction are provided, followed by discussion of the strengths and limitations of the available tools and translational models that aid investigators in the study of breast cancer metastasis to bone.

Targeting Bone Metastases in Metastatic Castration-Resistant Prostate Cancer

Skeletal involvement in metastatic castrate-resistant prostate cancer (mCRPC) is common and results in significant morbidity and mortality. The interaction of prostate cancer with the bone microenvironment contributes to progression of cancer in the bone leading to skeletal-related events (SREs). Studies aimed at targeting the bone have been carried out over the recent years. Bisphosphonates are synthetic pyrophosphate analogs first investigated for their role in SRE prevention with zoledronic acid as the main bisphosphonate that is approved by the US Food and Drug Administration for retardation of skeletal events in men with metastatic prostate cancer. Denosumab is another bone-targeted agent against uncontrolled osteolysis and serves as a RANK ligand inhibitor, superior to zoledronic acid in delaying SREs. Radiopharmaceuticals have played a role in targeting the bone microenvironment mainly in pain palliation in mCRPC utilizing strontium or samarium in the remote past, but only radium-223 is the first radiopharmaceutical that has yielded improvement in overall survival. The combination and sequencing strategies of these agents is the subject of multiple ongoing trials to guide the best use of these emerging agents.

Targeting Bone Metastases in Metastatic Castration-Resistant Prostate Cancer

Skeletal involvement in metastatic castrate-resistant prostate cancer (mCRPC) is common and results in significant morbidity and mortality. The interaction of prostate cancer with the bone microenvironment contributes to progression of cancer in the bone leading to skeletal-related events (SREs). Studies aimed at targeting the bone have been carried out over the recent years. Bisphosphonates are synthetic pyrophosphate analogs first investigated for their role in SRE prevention with zoledronic acid as the main bisphosphonate that is approved by the US Food and Drug Administration for retardation of skeletal events in men with metastatic prostate cancer. Denosumab is another bone-targeted agent against uncontrolled osteolysis and serves as a RANK ligand inhibitor, superior to zoledronic acid in delaying SREs. Radiopharmaceuticals have played a role in targeting the bone microenvironment mainly in pain palliation in mCRPC utilizing strontium or samarium in the remote past, but only radium-223 is the first radiopharmaceutical that has yielded improvement in overall survival. The combination and sequencing strategies of these agents is the subject of multiple ongoing trials to guide the best use of these emerging agents.

Cytokines as Mediators of Pain-Related Process in Breast Cancer

Pain is a clinical sign of inflammation found in a wide variety of chronic pathologies, including cancer. The occurrence of pain in patients carrying breast tumors is reported and is associated with aspects concerning disease spreading, treatment, and surgical intervention. The persistence of pain in patients submitted to breast surgery is estimated in a range from 21% to 55% and may affect patients before and after surgery. Beyond the physical compression exerted by the metastatic mass expansion and tissue injury found in breast cancer, inflammatory components that are significantly produced by the host-tumor interaction can significantly contribute to the generation of pain. In this context, cytokines have been studied aiming to establish a cause-effect relationship in cancer pain-related syndromes, especially the proinflammatory ones. Few reports have investigated the relationship between pain and cytokines in women carrying advanced breast cancer. In this scenario, the present review analyzes the main cytokines produced in breast cancer and discusses the evidences from literature regarding its role in specific clinical features related with this pathology.

Bone-immune cell crosstalk: bone diseases

Bone diseases are associated with great morbidity; thus, the understanding of the mechanisms leading to their development represents a great challenge to improve bone health. Recent reports suggest that a large number of molecules produced by immune cells affect bone cell activity. However, the mechanisms are incompletely understood. This review aims to shed new lights into the mechanisms of bone diseases involving immune cells. In particular, we focused our attention on the major pathogenic mechanism underlying periodontal disease, psoriatic arthritis, postmenopausal osteoporosis, glucocorticoid-induced osteoporosis, metastatic solid tumors, and multiple myeloma.

Quetiapine inhibits osteoclastogenesis and prevents human breast cancer-induced bone loss through suppression of the RANKL-mediated MAPK and NF-κB signaling pathways

Bone loss is one of the major complications of advanced cancers such as breast cancer, prostate cancer, and lung cancer. Extensive research has revealed that the receptor activator of NF-κB ligand (RANKL), which is considered to be a key factor in osteoclast differentiation, plays an important role in cancer-associated bone resorption. Therefore, agents that can suppress this bone loss have therapeutic potential. In this study, we detected whether quetiapine (QUE), a commonly used atypical antipsychotic drug, can inhibit RANKL-induced osteoclast differentiation in vitro and prevent human breast cancer-induced bone loss in vivo. RAW 264.7 cells and bone marrow-derived macrophages (BMMs) were used to detect inhibitory effect of QUE on osteoclastogenesis in vitro. Mouse model of breast cancer metastasis to bone was used to test suppressive effect of QUE on breast cancer-induced bone loss in vivo. Our results show that QUE can inhibit RANKL-induced osteoclast differentiation from RAW 264.7 cells and BMMs without signs of cytotoxicity. Moreover, QUE reduced the occurrence of MDA-MB-231 cell-induced osteolytic bone loss by suppressing the differentiation of osteoclasts. Finally, molecular analysis revealed that it is by inhibiting RANKL-mediated MAPK and NF-κB signaling pathways that QUE suppressed the osteoclast differentiation. We demonstrate, for the first time, the novel suppressive effects of QUE on RANKL-induced osteoclast differentiation in vitro and human breast cancer-induced bone loss in vivo, suggesting that QUE may be a potential therapeutic drug for osteolysis treatment.

Immune regulation of bone metastasis

Metastases to bone occur in about 70% of patients with metastatic prostate and breast cancers. Unfortunately, bone metastases result in significant morbidity and mortality and treatment options are limited. Thus, significant effort has focused on understanding the mechanisms that drive tumor dissemination to bone. Bone metastases are typically characterized by a self-perpetuating 'vicious' cycle wherein tumor cells and bone-resorbing cells (osteoclasts) are locked in a cycle that leads to osteoclast-driven bone destruction and the release of bone-stored factors that in turn stimulate tumor cell proliferation and survival. To break this 'vicious' cycle, potent antiresorptive agents such as zoledronic acid (ZOL) have been used. However, in the clinical setting, ZOL failed to improve the overall survival of cancer patients even though it inhibited osteoclast resorptive activity. Thus, other cells in addition to osteoclasts are likely involved in modulating tumor growth in the bone. The immune system has the ability to eliminate tumor cells. Nevertheless, tumor cells can acquire the ability to escape immune control. Our recent observations indicated that a decline in the ability of the immune cells to recognize and kill the tumor drives tumor dissemination to bone even when osteoclasts are inhibited by potent antiresorptive agents. This review focuses on the antitumor and protumor effects of various immune cell populations involved in the bone metastatic process. We also discuss strategies to enhance antitumor immune responses and bypass cancer immune resistance.

Managing bone metastases and reducing skeletal related events in prostate cancer

Advanced-stage prostate cancer is associated with skeletal complications related to metastatic disease and its treatment. On the one hand, metastatic disease to bone is commonly associated with skeletal-related events (SREs); on the other hand, treatment with androgen-deprivation therapy (ADT) leads to loss in bone mineral density (BMD) and increased risk of fracture. Despite osteoblastic appearance on radiography, bone metastases from prostate cancer are associated with increased osteoblast and osteoclast activity providing the rationale for treatment with osteoclast-targeted agents. The bisphosphonate zoledronic acid and the monoclonal antibody denosumab reduce the incidence of SREs in metastatic castration-resistant prostate cancer (mCRPC). A number of agents prevent loss of BMD associated with ADT, but only denosumab is approved to reduce fractures in patients with non-metastatic prostate cancer. Another recently approved agent-radium-223-improves survival and delays SREs in mCRPC. The inhibitors of androgen receptor signalling, abiraterone and enzalutamide, improve survival in mCRPC and delay SREs, although the latter is likely related to control of disease rather than a direct effect on bone. Finally, the tyrosine kinase inhibitor cabozantinib shows promising activity in bone metastases from mCRPC. This Review addresses the skeletal morbidity associated with prostate cancer and the therapeutic options that exist to treat it.

Cadherin-11 in renal cell carcinoma bone metastasis

Bone is one of the common sites of metastases from renal cell carcinoma (RCC), however the mechanism by which RCC preferentially metastasize to bone is poorly understood. Homing/retention of RCC cells to bone and subsequent proliferation are necessary steps for RCC cells to colonize bone. To explore possible mechanisms by which these processes occur, we used an in vivo metastasis model in which 786-O RCC cells were injected into SCID mice intracardially, and organotropic cell lines from bone, liver, and lymph node were selected. The expression of molecules affecting cell adhesion, angiogenesis, and osteolysis were then examined in these selected cells. Cadherin-11, a mesenchymal cadherin mainly expressed in osteoblasts, was significantly increased on the cell surface in bone metastasis-derived 786-O cells (Bo-786-O) compared to parental, liver, or lymph node-derived cells. In contrast, the homing receptor CXCR4 was equivalently expressed in cells derived from all organs. No significant difference was observed in the expression of angiogenic factors, including HIF-1α, VEGF, angiopoeitin-1, Tie2, c-MET, and osteolytic factors, including PTHrP, IL-6 and RANKL. While the parental and Bo-786-O cells have similar proliferation rates, Bo-786-O cells showed an increase in migration compared to the parental 786-O cells. Knockdown of Cadherin-11 using shRNA reduced the rate of migration in Bo-786-O cells, suggesting that Cadherin-11 contributes to the increased migration observed in bone-derived cells. Immunohistochemical analysis of cadherin-11 expression in a human renal carcinoma tissue array showed that the number of human specimens with positive cadherin-11 activity was significantly higher in tumors that metastasized to bone than that in primary tumors. Together, these results suggest that Cadherin-11 may play a role in RCC bone metastasis.

Andrographolide prevents human breast cancer-induced osteoclastic bone loss via attenuated RANKL signaling

Bone metastasis is a common and serious complication in advanced cancers such as breast cancer, prostate cancer, and multiple myeloma. Agents that prevent bone loss could be used to develop an alternative therapy for bone metastasis. RANKL, a member of the tumor necrosis factor superfamily, has been shown to play a significant role in cancer-associated bone loss. In this study, we examined the efficacy of the natural compound andrographolide (AP), a diterpenoid lactone isolated from the traditional Chinese and Indian medicinal plant Andrographis paniculata, in reducing breast cancer-induced osteolysis. AP prevented human breast cancer-induced bone loss by suppressing RANKL-mediated and human breast cancer cell-induced osteoclast differentiation. Molecular analysis revealed that AP prevented osteoclast function by inhibiting RANKL-induced NF-κB and ERK signaling pathway in lower dose (20 μM), as well as inducing apoptosis at higher dose (40 μM). Thus, AP is a potent inhibitor of breast cancer-induced bone metastasis.

The endothelin axis in urologic tumors: mechanisms of tumor biology and therapeutic implications

Endothelin (ET)-1 and its receptors ET-A and ET-B, referred to commonly as the endothelin axis, have been identified in various human cancers, especially gynecologic tumors, such as breast cancer or ovarian cancer, but also including urologic tumor entities. They play a key role in tumor growth and progression by influencing critical cancer pathways, such as apoptosis, angiogenesis and proliferation. In prostate cancer, overexpression of the ET-A receptor increases with tumor progression, and clinical trials with selective ET-A receptor antagonists, such as atrasentan (ABT-627), have shown promising early results. In preclinical models of bladder cancer, overexpression of the ET axis has been demonstrated and ET-targeting agents are under investigation. This paper reviews the role of the ET axis in human cancers and focuses on preclinical and clinical studies in urologic tumor entities to further define the role of ET-targeting agents as targeted molecular therapy.

Bisphosphonates and bone metastases: current status and future directions

Since bone metastases in advanced cancer are common and frequently lead to skeletal-related morbid complications, their treatment remains a major challenge in cancer therapy. Bisphosphonates not only significantly decreased the odds ratios for fracture, need for radiotherapy, and incidence of hypercalcemia, but also had proven ability in the preservation of the 3D microstructure of bone that is responsible for bone stability. Bisphosphonates are well tolerated and have a very low incidence of serious side effects. Consequently, bisphosphonates have become the standard of care for the treatment of malignant bone disease. Benefits of bisphosphonate treatment appears to be more pronounced with longer treatment, indicating that they should be continued until no longer clinically relevant. As this advice has substantial implications on resources, it is essential that the use of bisphosphonates is evidence based.