Novel bone-targeted strategies in oncology

Current comprehensive understanding of denosumab (the RANKL neutralizing antibody) in the treatment of bone metastasis of malignant tumors, including pharmacological mechanism and clinical trials

Denosumab, a fully humanized monoclonal neutralizing antibody, inhibits activation of the RANK/RANKL/OPG signaling pathway through competitive binding with RANKL, thereby inhibiting osteoclast-mediated bone resorption. Denosumab inhibits bone loss; therefore, it is used to treat metabolic bone diseases (including postmenopausal osteoporosis, male osteoporosis, and glucocorticoid-induced osteoporosis), in clinical practice. Since then, multiple effects of denosumab have been discovered. A growing body of evidence suggests that denosumab has a variety of pharmacological activities and broad potential in clinical diseases such as osteoarthritis, bone tumors, and other autoimmune diseases. Currently, Denosumab is emerging as a treatment for patients with malignancy bone metastases, and it also shows direct or indirect anti-tumor effects in preclinical models and clinical applications. However, as an innovative drug, its clinical use for bone metastasis of malignant tumors is still insufficient, and its mechanism of action needs to be further investigated. This review systematically summarizes the pharmacological mechanism of action of denosumab and the current understanding and clinical practice of the use of denosumab for bone metastasis of malignant tumors to help clinicians and researchers deepen their understanding of denosumab.

Effect of cachexia on bone turnover in cancer patients: a case-control study

Background

Increased bone turnover is frequently observed in advanced cancer and predominantly related to bone metastases or therapy. Cachexia represents an important cause of morbidity and mortality in cancer patients. Key features are weight loss, muscle wasting and chronic inflammation, which induce profound metabolic changes in several organs, including the bone. However, whether cachexia contributes to abnormal bone metabolism in cancer patients is unknown. Aim of the present study was to determine the potential correlation of bone turnover markers with body composition and laboratory parameters in treatment-naïve cancer patients.

Methods

In this cross-sectional study we measured the levels of carboxy terminal telopeptide of collagen (CTX), an indicator of bone resorption, as well as osteocalcin (Ocn) and procollagen type I N-terminal propeptide (PINP), indicators of bone formation, in 52 cancer patients and correlated with body composition and laboratory parameters. Univariate and multivariate logistic analysis were performed to identify determinants of negative bone remodeling balance, estimated by CTX/Ocn and CTX/PINP ratio.

Results

Based on weight loss, body mass index and muscle mass, patients were divided into a cachectic (59.6%) and a control (40.4%) group. After correcting for the presence of bone metastases, our results showed a significant upregulation of CTX in cachectic patients compared to non-cachectic cancer patients (median 0.38 vs 0.27 ng/mL, p < 0.05), with no difference in Ocn and PINP levels (mean 14 vs. 16 ng/ml, p = 0.2 and median 32 vs. 26 μg/L, p = 0.5, respectively). In addition, the CTX/Ocn and the CTX/PINP ratio were indicative of bone resorption in 68% and 60% of cachexia patients, respectively (vs. 20% and 31% in the control group, p = 0.002 and p = 0.06). The main determinants of the unbalanced bone turnover were hypoalbuminemia for the CTX/Ocn ratio (OR 19.8, p < 0.01) and high CRP for the CTX/PINP ratio (OR 5.3, p < 0.01) in the multivariate regression analysis.

Conclusions

CTX is substantially higher in cachectic patients compared to non-cachectic oncological patients and hypoalbuminemia as well as elevated CRP concentrations are independent predictors of a negative bone remodeling balance in cancer patients. These results strongly indicate that cachexia correlates with exacerbated bone turnover in cancer.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12885-021-08518-9.

Trial Watch: Monoclonal antibodies in cancer therapy

Since the advent of hybridoma technology, dating back to 1975, monoclonal antibodies have become an irreplaceable diagnostic and therapeutic tool for a wide array of human diseases. During the last 15 years, several monoclonal antibodies (mAbs) have been approved by FDA for cancer therapy. These mAbs are designed to (1) activate the immune system against tumor cells, (2) inhibit cancer cell-intrinsic signaling pathways, (3) bring toxins in the close proximity of cancer cells, or (4) interfere with the tumor-stroma interaction. More recently, major efforts have been made for the development of immunostimulatory mAbs that either enhance cancer-directed immune responses or limit tumor- (or therapy-) driven immunosuppression. Some of these antibodies, which are thought to facilitate tumor eradication by initiating or sustaining a tumor-specific immune response, have already entered clinical trials. In this Trial Watch, we will review and discuss the clinical progress of the most important mAbs that are have entered clinical trials after January 2008.

Comparing the Efficacy and Safety of Denosumab with Bisphosphonates in Increasing Bone Mineral Density in Patients with Prostate Cancer and Breast Cancer on Antihormonal Treatment

Osteoporosis is a common condition prevalent in both sexes that can be primary and secondary. Secondary osteoporosis may occur in cancer patients undergoing antihormonal treatment, leading to an increased risk of fractures. Androgen deprivation therapy (ADT) in patients with prostate cancer and aromatase inhibitors (AI) in patients with breast cancer can drastically increase the risk of osteoporosis. Bisphosphonates are one of the key medications in managing these patients and are widely prescribed. A monoclonal antibody called denosumab, which is a relatively new treatment option, is also used in this population group. To conduct a detailed comparison of these groups, we performed a thorough literature search using Pubmed and Google Scholar to extract data in the form of research papers/clinical trials. A total of 18 research papers were extracted using Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) guidelines and other inclusion and exclusion criteria. Seven of these papers were based on randomized controlled trials (RCTs) comparing denosumab with either placebo or bisphosphonates in patients with breast cancer and prostate cancer. Two meta-analyses comparing the safety and efficacy of both these drugs in this population group were also included. Denosumab was found to significantly increase bone mineral density (BMD) for up to two years and showed better results than bisphosphonates, while both had a comparable safety profile. More trials should be conducted in patients with prostate cancer or breast cancer on ADT or AI therapy, respectively, for longer durations to assess the long-term safety of these drugs in this population.

Sclerostin inhibition alleviates breast cancer-induced bone metastases and muscle weakness

Breast cancer bone metastases often cause a debilitating non-curable condition with osteolytic lesions, muscle weakness and a high mortality. Current treatment comprises chemotherapy, irradiation, surgery and anti-resorptive drugs that restrict but do not revert bone destruction. In metastatic breast cancer cells, we determined the expression of sclerostin, a soluble Wnt inhibitor that represses osteoblast differentiation and bone formation. In mice with breast cancer bone metastases, pharmacological inhibition of sclerostin using an anti-sclerostin antibody (Scl-Ab) reduced metastases without tumor cell dissemination to other distant sites. Sclerostin inhibition prevented the cancer-induced bone destruction by augmenting osteoblast-mediated bone formation and reducing osteoclast-dependent bone resorption. During advanced disease, NF-κB and p38 signaling was increased in muscles in a TGF-β1-dependent manner, causing muscle fiber atrophy, muscle weakness and tissue regeneration with an increase in Pax7-positive satellite cells. Scl-Ab treatment restored NF-κB and p38 signaling, the abundance of Pax7-positive cells and ultimately muscle function. These effects improved the overall health condition and expanded the life span of cancer-bearing mice. Together, these results demonstrate that pharmacological inhibition of sclerostin reduces bone metastatic burden and muscle weakness with a prolongation of the survival time. This might provide novel options for treating musculoskeletal complications in breast cancer patients. .

Systems Modeling of Bortezomib and Dexamethasone Combinatorial Effects on Bone Homeostasis in Multiple Myeloma Patients

Osteolytic bone disease is one of the most debilitating manifestations of multiple myeloma (MM). Bortezomib is a proteasome inhibitor that shows both anticancer and bone anabolic properties and is being evaluated for its positive effects in MM patients with skeletal complications. Dexamethasone is a potent corticosteroid that is often given in combination with bortezomib for its antineoplastic effects; however, bone loss and osteoporosis are major adverse effects of long-term steroid-based therapies. In this study, a small systems pharmacological model was developed to integrate the bone anabolic effects of bortezomib with the osteolytic activity of dexamethasone in MM patients with bone disease. The final model parameters were all estimated with good precision. The interaction model is based on codifying multiple regulatory mechanisms of drug action and provides a platform for probing optimized bortezomib and dexamethasone combination dosing regimens to minimize skeletal side effects during myeloma therapy.

Myeloma Bone Disease: Update on Pathogenesis and Novel Treatment Strategies

Bone disease, including osteolytic lesions and/or osteoporosis, is a common feature of multiple myeloma (MM). The consequences of skeletal involvement are severe pain, spinal cord compressions, and bone fractures, which have a dramatic impact on patients’ quality of life and, ultimately, survival. During the past few years, several landmark studies significantly enhanced our insight into MM bone disease (MBD) by identifying molecular mechanisms leading to increased bone resorption due to osteoclast activation, and decreased bone formation by osteoblast inhibition. Bisphosphonates were the mainstay to prevent skeletal-related events in MM for almost two decades. Excitingly, the most recent approval of the receptor activator of NF-kappa B ligand (RANKL) inhibitor, denosumab, expanded treatment options for MBD, for patients with compromised renal function, in particular. In addition, several other bone-targeting agents, including bone anabolic drugs, are currently in preclinical and early clinical assessment. This review summarizes our up-to-date knowledge on the pathogenesis of MBD and discusses novel state-of-the-art treatment strategies that are likely to enter clinical practice in the near future.

Denosumab for the treatment of bone disease in solid tumors and multiple myeloma

Bone is a common site for malignant involvement, either as a site of metastasis, especially in breast or prostate cancer, or as a defining characteristic of the disease, as in multiple myeloma. Bone disease is a major source of morbidity, and half of patients with bone involvement develop skeletal-related events such as pathological fractures or cord compression requiring surgery and/or radiation. Skeletal involvement also increases mortality, as pathologic fractures increase the risk of dying by 20-40%. Osteoclast inhibition with bisphosphonates such as zoledronic acid and recently denosumab has been a significant improvement for bone disease. This review will focus on denosumab in the treatment of bone metastases and highlight the recent findings in multiple myeloma.

CYR61/CCN1 stimulates proliferation and differentiation of osteoblasts in vitro and contributes to bone remodeling in vivo in myeloma bone disease

Cysteine-rich 61 (CYR61/CCN1), a secreted protein in bone marrow (BM) microenvironment, has diverse effects on many cellular activities such as growth and differentiation. However, the effect of CCN1 on osteoblasts (OBs) in myeloma bone disease remains unclear. In our study, the level of CCN1 in multiple myeloma (MM) patients was detected by ELISA and RT-PCR. The proliferation and differentiation of OBs from MM patients were observed after stimulated by CCN1 in vitro. The myeloma cells transduced with CYR61 gene (RPMI‑8226/CYR61) were injected in a mouse model to evaluate the efficacy of CCN1 in vivo and compare with zoledronic acid. The results showed that CYR61/CCN1 levels in BM supernatant and OBs both elevated significantly in all newly diagnosed MM patients, especially in patients without bone disease (P=0.001 and P<0.001). After 30 ng/l CCN1 stimulation for 24 h, the quantity and mineralization of OBs increased significantly in vitro (P=0.046 and 0.048). The transcription factors of Wnt pathway, runt-related transcription factor 2 (Runx2) and β-catenin were upregulated in OBs after CCN1 stimulation (P=0.012 and 0.011). After injection of RPMI‑8226 cells, bone lesions were observed obviously by microCT and histochemistry at 7 weeks. Radiographic analysis of the bones showed decreased resorption in CCN1 overexpression group and zoledronic acid group, while severe resorption in negative control. Furthermore, trabecular bone volume in CCN1 overexpression group (1.7539±0.16949) was significantly higher than zoledronic acid group (1.2839±0.077) (P=0.012). In conclusion, CCN1 can stimulate the proliferation and differentiation of OBs in vitro and contribute to bone remodeling in vivo in MBD.

Bone targeted therapy for preventing skeletal-related events in metastatic breast cancer

Cancer cells can alter physiological mechanisms within bone resulting in high bone turnover, and consequently in skeletal-related events (SREs), causing severe morbidity in affected patients. The goals of bone targeted therapy, as bisphosphonates and denosumab, are the reduction of incidence and the delay in occurrence of the SREs, to improve quality of life and pain control. The toxicity profile is similar between bisphosphonates and denosumab, even if pyrexia, bone pain, arthralgia, renal failure and hypercalcemia are more common with bisphosphonates, while hypocalcemia and toothache are more frequently reported with denosumab. Osteonecrosis of the jaw (ONJ) occurred infrequently without statistically significant difference. The present review aims to provide an assessment on bone targeted therapies for preventing the occurrence of SREs in bone metastatic breast cancer patients, critically analyzing the evidence available so far on their effectiveness, in light of the different mechanisms of action. Thus, we try to provide tools for the most fitting treatment of bone metastatic breast cancer patients. We also provide an overview on the usefulness of bone turnover markers in clinical practice and new molecules currently under study for the treatment of bone metastatic disease.

Role of decorin in multiple myeloma (MM) bone marrow microenvironment

Decorin is a small, leucine-rich proteoglycan found in the extracellular matrix of various connective tissues with potential effective tumor suppressive properties. Recent data suggest low levels of decorin in multiple myeloma (MM) patients compared to healthy volunteers, as well as in patients with osteolytic bone lesions compared to non-osteolytic lesions. In the present report, we investigated the role of decorin in the MM microenvironment or niche. Our data suggests that decorin is produced by osteoblasts (OBs) but not by MM cells. Furthermore, MM cells decrease OB-induced decorin secretion and this effect is mediated by CCL3. Importantly, neutralizing CCL3 from MM cells restores decorin levels in OBs as does proteasome inhibitors such as carfilzomib. These findings indicate that decorin may indirectly act as an antagonist to MM cell survival and that the interplay between MM and decorin may be an important target to explore in manipulating the tumor niche to inhibit tumorigenesis.

Therapy monitoring of skeletal metastases with whole-body diffusion MRI

Current methods of assessing tumor response at skeletal sites with metastatic disease use a combination of imaging tests, serum and urine biochemical markers, and symptoms assessment. These methods do not always enable the positive assessment of therapeutic benefit to be made but instead provide an evaluation of progression, which then guides therapy decisions in the clinic. Functional imaging techniques such as whole-body diffusion magnetic resonance imaging (MRI) when combined with anatomic imaging and other emerging "wet" biomarkers can improve the classification of therapy response in patients with metastatic bone disease. A range of imaging findings can be seen in the clinic depending on the type of therapy and duration of treatment. Successful response to systemic therapy is usually depicted by reductions in signal intensity accompanied by apparent diffusion coefficient (ADC) increases. Rarer patterns of successful treatment include no changes in signal intensity accompanying increases in ADC values (T2 shine-through pattern) or reductions in signal intensity without ADC value changes. Progressive disease results in increases in extent/intensity of disease on high b-value images with variable ADC changes. Diffusion MRI therapy response criteria need to be developed and tested in prospective studies in order to address current, unmet clinical and pharmaceutical needs for reliable measures of tumor response in metastatic bone disease.

A novel Bruton's tyrosine kinase inhibitor CC-292 in combination with the proteasome inhibitor carfilzomib impacts the bone microenvironment in a multiple myeloma model with resultant antimyeloma activity

Bruton's tyrosine kinase (Btk) modulates B-cell development and activation and has an important role in antibody production. Interestingly, Btk may also affect human osteoclast (OC) function; however, the mechanism was unknown. Here we studied a potent and specific Btk inhibitor, CC-292, in multiple myeloma (MM). In this report, we demonstrate that, although CC-292 increased OC differentiation, it inhibited OC function via inhibition of c-Src, Pyk2 and cortactin, all involved in OC-sealing zone formation. As CC-292 did not show potent in vitro anti-MM activity, we next evaluated it in combination with the proteasome inhibitor, carfilzomib. We first studied the effect of carfilzomib on OC. Carfilzomib did not have an impact on OC-sealing zone formation but significantly inhibited OC differentiation. CC-292 combined with carfilzomib inhibited both sealing zone formation and OC differentiation, resulting in more profound inhibition of OC function than carfilzomib alone. Moreover, the combination treatment in an in vivo MM mouse model inhibited tumor burden compared with CC-292 alone; it also increased bone volume compared with carfilzomib alone. These results suggest that CC-292 combined with carfilzomib augments the inhibitory effects against OC within the bone microenvironment and has promising therapeutic potential for the treatment of MM and related bone disease.

Analysis on survival and prognostic factors for cancer patients with malignancy-associated hypercalcemia

OBJECTIVE

To explore the incidence, clinical characteristics, diagnosis and treatment strategies, prognosis of patients with malignancy-associated hypercalcemia (MAH).

METHODS

The data of 115 patients with MAH who were treated at the Medical Oncology Department of Chinese PLA General Hospital from Jan., 2001 to Dec., 2010 was retrospectively reviewed. Survival analysis was performed using the Kaplan-Meier method and the Cox proportional hazard model with statistic software SPSS 18.0.

RESULTS

The patients had blood calcium levels ranging from 2.77 to 4.87 mmol/L. Except for 9 cases who died or were discharged within 5 days after admission, all other patients recovered to normal blood calcium level after treatment with bisphosphonates or intravenous hydration and diuretics; their survival after occurrence of MAH was from 1 day to 4,051 days, and the median survival time was only 50 days. In the log-rank test, the male, renal metastasis, central nervous system symptoms and hypercalcemia occurring over 140 days after cancer diagnosis were predictors of poor survival (P=0.002, P=0.046, P=0.000, P=0.009). In the COX analysis, being male, central nervous system symptoms and hypercalcemia lasting over 140 days after cancer diagnosis were independent prognostic factors for survival time (RR=2.131, P=0.027; RR=3.054, P=0.002; RR=2.403, P=0.001). According to these factors, a score system was established to predict the patient prognosis and adjust the treatment.

CONCLUSION

Cancer patients with MAH have an extremely poor median survival. Some independent factors indicate poor prognosis, including male gender, central nervous system symptoms and hypercalcemia lasting over 140 days after cancer diagnosis. The prognostic score can serve as a reference for MAH prognosis and treatment, worthy of further investigation.

New insights, recent advances, and current challenges in the biological treatment of multiple myeloma

INTRODUCTION

The availability of thalidomide, lenalidomide, and bortezomib has radically changed multiple myeloma (MM) treatment and significantly improved patients' outcome. Nevertheless, MM is still an incurable disease due to the development of resistance and relapse practically in all patients. Unraveling MM pathogenesis, identifying prognostically high-risk patient populations, and optimizing current treatment strategies are among the challenges we are facing to reach a cure for this disease.

AREAS COVERED

This article reviews recent advances of the genomic analysis of malignant plasma cells and summarizes new insights into the pathophysiologic role of the MM microenvironment and the clinical assessment of derived novel therapeutic strategies. Moreover, current efforts to improve risk stratification and drug development are discussed, and most recent results of Phase II and III clinical trials that aim to optimize existing treatment regimens and to assess the next-generation anti-MM strategies are discussed. A systematic search was conducted of the Pubmed Medline, Embase, and Cochrane Library databases for primary articles, as well as of conference abstracts (e.g., of the American Society of Hematology, the American Society of Clinical Oncology, the American Association of Cancer Research, the European Hematology Association, and the Multiple Myeloma Workshop 2013), practice guidelines, and registries of clinical trials.

EXPERT OPINION

Given continuing advances to overcome current treatment challenges in MM, we are confident that long-lasting responses can be expected in many of our patients within the next decade.

The metastasis-promoting roles of tumor-associated immune cells

Tumor metastasis is driven not only by the accumulation of intrinsic alterations in malignant cells, but also by the interactions of cancer cells with various stromal cell components of the tumor microenvironment. In particular, inflammation and infiltration of the tumor tissue by host immune cells, such as tumor-associated macrophages, myeloid-derived suppressor cells, and regulatory T cells, have been shown to support tumor growth in addition to invasion and metastasis. Each step of tumor development, from initiation through metastatic spread, is promoted by communication between tumor and immune cells via the secretion of cytokines, growth factors, and proteases that remodel the tumor microenvironment. Invasion and metastasis require neovascularization, breakdown of the basement membrane, and remodeling of the extracellular matrix for tumor cell invasion and extravasation into the blood and lymphatic vessels. The subsequent dissemination of tumor cells to distant organ sites necessitates a treacherous journey through the vasculature, which is fostered by close association with platelets and macrophages. Additionally, the establishment of the pre-metastatic niche and specific metastasis organ tropism is fostered by neutrophils and bone marrow-derived hematopoietic immune progenitor cells and other inflammatory cytokines derived from tumor and immune cells, which alter the local environment of the tissue to promote adhesion of circulating tumor cells. This review focuses on the interactions between tumor cells and immune cells recruited to the tumor microenvironment and examines the factors allowing these cells to promote each stage of metastasis.

Molecular communication between tumor-associated fibroblasts and head and neck squamous cell carcinoma

Over the past few decades, it has become increasingly clear that the lethality of cancers depends on more than the malignant cells themselves. The environment those malignant cells are exposed to is just as important a determinant of their behavior. Head and neck squamous cell carcinoma (HNSCC) is both common and deadly. It is the 6th most frequently occurring cancers, and prognosis is still generally poor. Recent evidence indicates that activated fibroblasts residing within the tumor stroma play a significant role in promoting the aggressive spread often seen in head and neck cancer. Tumor associated fibroblasts (TAFs) have also been implicated in facilitating angiogenesis and suppressing the normal anti-tumor function of immune cells. Studying the signaling molecules involved in these processes will facilitate the development of promising targets and inhibitors to prevent tumor-associated fibroblasts from exerting their reinforcing effects on the tumor. In this article, we review the recent literature on the signals used in tumor associated fibroblast communication, with a focus on potential therapeutic targets. Further, we highlight the lead candidates for TAF-targeted therapeutic interventions. Future anti-cancer strategies may achieve better results than current approaches by targeting the support cells in tumor stroma in addition to the cancerous cells.

Denosumab, a RANK ligand inhibitor, for the management of bone loss in cancer patients

Bone loss is a common side effect of cancer treatments, especially antihormonal treatments used in the treatment of breast and prostate cancer. Denosumab is a monoclonal antibody given subcutaneously that inhibits osteoclast activity by targeting the RANK ligand. It is effective in settings ranging from preventing skeletal-related complications in cancer patients with metastatic disease to increasing bone mineral density in patients with osteoporosis. In cancer patients with early stage disease, denosumab can attenuate bone loss from antihormonal treatments, and in prostate cancer, may reduce disease progression. Here, we will discuss the important role denosumab may play in the management of bone loss in patients with cancer.

Novel aspects of mevalonate pathway inhibitors as antitumor agents

The mevalonate pathway for cholesterol biosynthesis and protein prenylation has been implicated in various aspects of tumor development and progression. Certain classes of drugs, such as statins and bisphosphonates, inhibit mevalonate metabolism and therefore have also been tested as antitumor agents. This concept is strongly supported by the recent finding that mutant p53, which is present in more than half of all human cancers, can significantly upregulate mevalonate metabolism and protein prenylation in carcinoma cells. The first evidence that mevalonate pathway inhibitors may have the potential to reverse the malignant phenotype has already been obtained. Moreover, recently discovered immunomodulatory properties of statins and bisphosphonates may also contribute to their known anticancer effects. Drug-induced inhibition of protein prenylation may induce sequential cellular stress responses, including the unfolded protein response and autophagy, that eventually translate into inflammasome-dependent and caspase-1-mediated activation of innate immunity. This review focuses on these novel capabilities of mevalonate pathway inhibitors to beneficially affect tumor biology and contribute to tumor immune surveillance.

Dasatinib as a bone-modifying agent: anabolic and anti-resorptive effects

BACKGROUND

Bone loss, in malignant or non-malignant diseases, is caused by increased osteoclast resorption and/or reduced osteoblast bone formation, and is commonly associated with skeletal complications. Thus, there is a need to identify new agents capable of influencing bone remodeling. We aimed to further pre-clinically evaluate the effects of dasatinib (BMS-354825), a multitargeted tyrosine kinase inhibitor, on osteoblast and osteoclast differentiation and function.

METHODS

For studies on osteoblasts, primary human bone marrow mensenchymal stem cells (hMSCs) together with the hMSC-TERT and the MG-63 cell lines were employed. Osteoclasts were generated from peripheral blood mononuclear cells (PBMC) of healthy volunteers. Skeletally-immature CD1 mice were used in the in vivo model.

RESULTS

Dasatinib inhibited the platelet derived growth factor receptor-β (PDGFR-β), c-Src and c-Kit phosphorylation in hMSC-TERT and MG-63 cell lines, which was associated with decreased cell proliferation and activation of canonical Wnt signaling. Treatment of MSCs from healthy donors, but also from multiple myeloma patients with low doses of dasatinib (2-5 nM), promoted its osteogenic differentiation and matrix mineralization. The bone anabolic effect of dasatinib was also observed in vivo by targeting endogenous osteoprogenitors, as assessed by elevated serum levels of bone formation markers, and increased trabecular microarchitecture and number of osteoblast-like cells. By in vitro exposure of hemopoietic progenitors to a similar range of dasatinib concentrations (1-2 nM), novel biological sequelae relative to inhibition of osteoclast formation and resorptive function were identified, including F-actin ring disruption, reduced levels of c-Fos and of nuclear factor of activated T cells 1 (NFATc1) in the nucleus, together with lowered cathepsin K, αVβ3 integrin and CCR1 expression.

CONCLUSIONS

Low dasatinib concentrations show convergent bone anabolic and reduced bone resorption effects, which suggests its potential use for the treatment of bone diseases such as osteoporosis, osteolytic bone metastasis and myeloma bone disease.

[Denosumab for treatment of postmenopausal osteoporosis]

BACKGROUND

Treatment with bisphosphonates reduces the risk of new fractures and is the treatment of choice for osteoporosis. Denosumab inhibits bone resorption via a different mechanism than bisphosphonates, and is a new option in the treatment of osteoporosis. In this paper we give an overview of the mode of action and clinical effects.

MATERIAL AND METHODS

The paper is based on a non-systematic literature search in Pubmed/Medline.

RESULTS

Denosumab is a human monoclonal antibody to receptor-activated nuclear factor kappa B (RANKL), a member of the TNF family that is formed in the osteoblast. Binding to RANKL results in reduced recruitment and activity of osteoclasts. Denosumab 60 mg given subcutaneously every six months is shown to inhibit bone resorption to a greater degree than bisphosphonates. In a three-year study of 7,868 women with postmenopausal osteoporosis, a reduction in the relative risk of vertebral, non-vertebral and hip fractures compared to placebo was found (68. 20 and 40 %, correspondingly). In the clinical trials with denosumab, the safety profile was similar to placebo, except for a slightly higher incidence of cellulitis and exanthema. Denosumab has also shown promising skeletal effects in the treatment of cancer and rheumatoid arthritis.

INTERPRETATION

Treatment with denosumab has an effect on postmenopausal osteoporosis and may be an alternative to treatment with bisphosphonates. There are few adverse effects and it is simple to administer.

Bony metastases: assessing response to therapy with whole-body diffusion MRI

There are no universally accepted methods for assessing tumour response in skeletal sites with metastatic disease; response is assessed by a combination of imaging tests, serum and urine biochemical markers and symptoms assessments. Whole-body diffusion magnetic resonance imaging excels at bone marrow assessments at diagnosis and for therapy evaluations. It can potentially address unmet clinical and pharmaceutical needs for a reliable measure of tumour response. Signal intensity on high b-value images and apparent diffusion coefficient values can be related to underlying biophysical properties of skeletal metastases. Four patterns of change in response to therapy are described this review. Therapy response criteria need to be tested in prospective clinical studies that incorporate conventional measures of patient benefit.

Formulated siRNAs targeting Rankl prevent osteolysis and enhance chemotherapeutic response in osteosarcoma models

The development of osteosarcoma, the most common malignant primary bone tumor is characterized by a vicious cycle established between tumor proliferation and paratumor osteolysis. This osteolysis is mainly regulated by the receptor activator of nuclear factor κB ligand (RANKL). Preclinical studies have demonstrated that Rankl blockade by soluble receptors is an effective strategy to prevent osteolytic lesions leading to osteosarcoma inhibition. A new therapeutic option could be to directly inhibit Rankl expression by small interfering RNAs (Rkl-siRNAs) and combine these molecules with chemotherapy to counteract the osteosarcoma development more efficiently. An efficient siRNA sequence directed against both mouse and rat mRNAs coding Rankl was first validated in vitro and tested in two models of osteosarcoma: a syngenic osteolytic POS-1 model induced in immunocompetent mice and a xenograft osteocondensant model of rat OSRGA in athymic mice. Intratumor injections of Rankl-directed siRNAs in combination with the cationic liposome RPR209120/DOPE reduced the local and systemic Rankl production and protected bone from paratumor osteolysis. Although Rkl-siRNAs alone had no effect on tumor development in both osteosarcoma models, it significantly blocked tumor progression when combined with ifosfamide compared with chemotherapy alone. Our results indicate that siRNAs could be delivered using cationic liposomes and thereby could inhibit Rankl production in a specific manner in osteosarcoma models. Moreover, the Rankl inhibition mediated by RNA interference strategy improves the therapeutic response of primary osteosarcoma to chemotherapy.

Therapeutic targets for bone metastases in breast cancer

Breast cancer is prone to metastasize to bone. Once metastatic cells are in the bone marrow, they do not, on their own, destroy bone. Instead, they alter the functions of bone-resorbing (osteoclasts) and bone-forming cells (osteoblasts), resulting in skeletal complications that cause pathological fractures and pain. In this review, we describe promising molecular bone-targeted therapies that have arisen from recent advances in our understanding of the pathogenesis of breast cancer bone metastases. These therapies target osteoclasts (receptor activator of nuclear factor kB ligand, integrin αvβ3, c-Src, cathepsin K), osteoblasts (dickkopf-1, activin A, endothelin A) and the bone marrow microenvironment (transforming growth factor β, bone morphogenetic proteins, chemokine CXCL-12 and its receptor CXCR4). The clinical exploitation of these bone-targeted agents will provide oncologists with novel therapeutic strategies for the treatment of skeletal lesions in breast cancer.

Therapeutic targets for bone metastases in breast cancer

Breast cancer is prone to metastasize to bone. Once metastatic cells are in the bone marrow, they do not, on their own, destroy bone. Instead, they alter the functions of bone-resorbing (osteoclasts) and bone-forming cells (osteoblasts), resulting in skeletal complications that cause pathological fractures and pain. In this review, we describe promising molecular bone-targeted therapies that have arisen from recent advances in our understanding of the pathogenesis of breast cancer bone metastases. These therapies target osteoclasts (receptor activator of nuclear factor kB ligand, integrin αvβ3, c-Src, cathepsin K), osteoblasts (dickkopf-1, activin A, endothelin A) and the bone marrow microenvironment (transforming growth factor β, bone morphogenetic proteins, chemokine CXCL-12 and its receptor CXCR4). The clinical exploitation of these bone-targeted agents will provide oncologists with novel therapeutic strategies for the treatment of skeletal lesions in breast cancer.

Bone metastasis: mechanisms and therapeutic opportunities

The skeleton is one of the most common sites for metastatic cancer, and tumors arising from the breast or prostate possess an increased propensity to spread to this site. The growth of disseminated tumor cells in the skeleton requires tumor cells to inhabit the bone marrow, from which they stimulate local bone cell activity. Crosstalk between tumor cells and resident bone and bone marrow cells disrupts normal bone homeostasis, which leads to tumor growth in bone. The metastatic tumor cells have the ability to elicit responses that stimulate bone resorption, bone formation or both. The net result of these activities is profound skeletal destruction that can have dire consequences for patients. The molecular mechanisms that underlie these painful and often incurable consequences of tumor metastasis to bone are beginning to be recognized, and they represent promising new molecular targets for therapy.

Leukocytes as paracrine regulators of metastasis and determinants of organ-specific colonization

It is now well recognized that tumor cell-host interactions regulate all aspects of cancer development. Amongst the various host response programs that facilitate primary cancer development, an emerging body of literature points to a critical role for leukocytes and their soluble mediators as regulating discrete events during primary tumor development and metastasis. This review focuses on the multiple aspects of leukocytes and their effector molecules as regulators of the metastatic process.