Therapeutic efficacy of soluble receptor activator of nuclear factor-kappa B-Fc delivered by nonviral gene transfer in a mouse model of osteolytic osteosarcoma

Tumor growth for remodeling process: A 2D approach

This paper aims to present a comprehensive framework for coupling tumor-bone remodeling processes in a 2-dimensional geometry. This is achieved by introducing a bio-inspired damage that represents the growing tumor, which subsequently affects the main populations involved in the remodeling process, namely, osteoclasts, osteoblasts, and bone tissue. The model is constructed using a set of differential equations based on the Komarova's and Ayati's models, modified to incorporate the bio-inspired damage that may result in tumor mass formation. Three distinct models were developed. The first two models are based on the Komarova's governing equations, with one demonstrating an osteolytic behavior and the second one an osteoblastic model. The third model is a variation of Ayati's model, where the bio-inspired damage is induced through the paracrine and autocrine parameters, exhibiting an osteolytic behavior. The obtained results are consistent with existing literature, leading us to believe that our in-silico experiments will serve as a cornerstone for paving the way towards targeted interventions and personalized treatment strategies, ultimately improving the quality of life for those affected by these conditions.

Biomechanical Aspects in Bone Tumor Engineering

In the past decades, anticancer drug development brought the field of tumor engineering to a new level by the need of robust test systems. Simulating tumor microenvironment in vitro remains a challenge, and osteosarcoma-the most common primary bone cancer-is no exception. The growing evidence points to the inevitable connection between biomechanical stimuli and tumor chemosensitivity and aggressiveness, thus making this component of the microenvironment a mandatory requirement to the developed models. In this review, we addressed the question: is the "in vivo - in vitro" gap in osteosarcoma engineering bridged from the perspective of biomechanical stimuli? The most notable biomechanical cues in the tumor cell microenvironment are observed and compared in the contexts of in vivo conditions and engineered three-dimensional in vitro models. Impact statement The importance of biomechanical stimuli in three-dimensional in vitro models for drug testing is becoming more pronounced nowadays. This review might assist in understanding the key players of the biophysical environment of primary bone cancer and the current state of bone tumor engineering from this perspective.

Investigation of the activity of a novel tropolone in osteosarcoma

Osteosarcoma (OS) is a primary malignant bone tumor characterized by frequent metastasis, rapid disease progression, and a high rate of mortality. Treatment options for OS have remained largely unchanged for decades, consisting primarily of cytotoxic chemotherapy and surgery, thus necessitating the urgent need for novel therapies. Tropolones are naturally occurring seven-membered non-benzenoid aromatic compounds that possess antiproliferative effects in a wide array of cancer cell types. MO-OH-Nap is an α-substituted tropolone that has activity as an iron chelator. Here, we demonstrate that MO-OH-Nap activates all three arms of the unfolded protein response (UPR) pathway and induces apoptosis in a panel of human OS cell lines. Co-incubation with ferric chloride or ammonium ferrous sulfate completely prevents the induction of apoptotic and UPR markers in MO-OH-Nap-treated OS cells. MO-OH-Nap upregulates transferrin receptor 1 (TFR1) protein levels, as well as TFR1, divalent metal transporter 1 (DMT1), iron-regulatory proteins (IRP1, IRP2), ferroportin (FPN), and zinc transporter 14 (ZIP14) transcript levels, demonstrating the impact of MO-OH-Nap on iron-homeostasis pathways in OS cells. Furthermore, MO-OH-Nap treatment restricts the migration and invasion of OS cells in vitro. Lastly, metabolomic profiling of MO-OH-Nap-treated OS cells revealed distinct changes in purine and pyrimidine metabolism. Collectively, we demonstrate that MO-OH-Nap-induced cytotoxic effects in OS cells are dependent on the tropolone's ability to alter cellular iron availability and that this agent exploits key metabolic pathways. These studies support further evaluation of MO-OH-Nap as a novel treatment for OS.

Anoikis patterns exhibit distinct prognostic and immune landscapes in Osteosarcoma

OBJECTIVES

Osteosarcoma is highly aggressive and prone to metastasis, with a poor prognosis. Increasing evidence identified anoikis has a critical effect in tumor metastasis and invasion. However, the prognostic value of anoikis-related genes (ANRGs) in osteosarcoma and their role in the immune landscape of osteosarcoma remain unclear.

METHODS

The RNA sequencing and clinical data of patients with osteosarcoma were extracted from the TARGET and GEO databases, and ANRGs were identified from the GeneCards database. Unsupervised clustering analysis was employed to identify anoikis-related patterns. The ESTIMATE, TIMER and ssGSEA algorithms were used to assess the immune microenvironment of different subtypes. A prognostic signature based on the identified ANRGs was constructed via univariate, LASSO and multivariate Cox regression analyses. KEGG, GO and GSEA were used for functional enrichment of genes associated with different risk subtypes. qPCR, WB and IHC were used to validate the expression of candidate genes.

RESULTS

Two anoikis-related patterns with distinct clinical features and immune statuses were identified based on prognosis-related ANRGs. Cluster 2 had more active immunogenicity and a better prognosis than Cluster 1. Subsequently, we developed and validated an anoikis prognostic signature demonstrating excellent predictive ability for the prognosis of osteosarcoma. Anoikis risk score was positively associated with osteosarcoma metastasis and was identified as an independent prognostic marker. Additionally, a nomogram was established to predict the 3- and 5-year survival probability of patients with osteosarcoma. Functional enrichment analysis revealed that immune dysregulation was correlated with poor prognosis. Besides, patients in the low-risk group had higher infiltration levels of immune cells and more active immune function than patients in the high-risk group. Drug sensitivity analysis revealed several chemotherapeutic agents for the treatment of different subtypes of osteosarcoma.

CONCLUSION

Our study demonstrated the role of ANRGs in osteosarcoma progression, providing insights into clinical decision making in osteosarcoma.

Osteosarcoma and Metastasis

Osteosarcoma is the most common primary bone malignancy in adolescents. Its high propensity to metastasize is the leading cause for treatment failure and poor prognosis. Although the research of osteosarcoma has greatly expanded in the past decades, the knowledge and new therapy strategies targeting metastatic progression remain sparse. The prognosis of patients with metastasis is still unsatisfactory. There is resonating urgency for a thorough and deeper understanding of molecular mechanisms underlying osteosarcoma to develop innovative therapies targeting metastasis. Toward the goal of elaborating the characteristics and biological behavior of metastatic osteosarcoma, it is essential to combine the diverse investigations that are performed at molecular, cellular, and animal levels from basic research to clinical translation spanning chemical, physical sciences, and biology. This review focuses on the metastatic process, regulatory networks involving key molecules and signaling pathways, the role of microenvironment, osteoclast, angiogenesis, metabolism, immunity, and noncoding RNAs in osteosarcoma metastasis. The aim of this review is to provide an overview of current research advances, with the hope to discovery druggable targets and promising therapy strategies for osteosarcoma metastasis and thus to overcome this clinical impasse.

Osteosarcoma and Metastasis Associated Bone Degradation-A Tale of Osteoclast and Malignant Cell Cooperativity

Cancer-induced bone degradation is part of the pathological process associated with both primary bone cancers, such as osteosarcoma, and bone metastases originating from, e.g., breast, prostate, and colon carcinomas. Typically, this includes a cancer-dependent hijacking of processes also occurring during physiological bone remodeling, including osteoclast-mediated disruption of the inorganic bone component and collagenolysis. Extensive research has revealed the significance of osteoclast-mediated bone resorption throughout the course of disease for both primary and secondary bone cancer. Nevertheless, cancer cells representing both primary bone cancer and bone metastasis have also been implicated directly in bone degradation. We will present and discuss observations on the contribution of osteoclasts and cancer cells in cancer-associated bone degradation and reciprocal modulatory actions between these cells. The focus of this review is osteosarcoma, but we will also include relevant observations from studies of bone metastasis. Additionally, we propose a model for cancer-associated bone degradation that involves a collaboration between osteoclasts and cancer cells and in which both cell types may directly participate in the degradation process.

RANK-RANKL signalling in cancer

Oncogenic events combined with a favourable environment are the two main factors in the oncological process. The tumour microenvironment is composed of a complex, interconnected network of protagonists, including soluble factors such as cytokines, extracellular matrix components, interacting with fibroblasts, endothelial cells, immune cells and various specific cell types depending on the location of the cancer cells (e.g. pulmonary epithelium, osteoblasts). This diversity defines specific "niches" (e.g. vascular, immune, bone niches) involved in tumour growth and the metastatic process. These actors communicate together by direct intercellular communications and/or in an autocrine/paracrine/endocrine manner involving cytokines and growth factors. Among these glycoproteins, RANKL (receptor activator nuclear factor-κB ligand) and its receptor RANK (receptor activator nuclear factor), members of the TNF and TNFR superfamilies, have stimulated the interest of the scientific community. RANK is frequently expressed by cancer cells in contrast with RANKL which is frequently detected in the tumour microenvironment and together they participate in every step in cancer development. Their activities are markedly regulated by osteoprotegerin (OPG, a soluble decoy receptor) and its ligands, and by LGR4, a membrane receptor able to bind RANKL. The aim of the present review is to provide an overview of the functional implication of the RANK/RANKL system in cancer development, and to underline the most recent clinical studies.

Osteosarcoma: Cells-of-Origin, Cancer Stem Cells, and Targeted Therapies

Osteosarcoma (OS) is the most common type of primary solid tumor that develops in bone. Although standard chemotherapy has significantly improved long-term survival over the past few decades, the outcome for those patients with metastatic or recurrent OS remains dismally poor and, therefore, novel agents and treatment regimens are urgently required. A hypothesis to explain the resistance of OS to chemotherapy is the existence of drug resistant CSCs with progenitor properties that are responsible of tumor relapses and metastasis. These subpopulations of CSCs commonly emerge during tumor evolution from the cell-of-origin, which are the normal cells that acquire the first cancer-promoting mutations to initiate tumor formation. In OS, several cell types along the osteogenic lineage have been proposed as cell-of-origin. Both the cell-of-origin and their derived CSC subpopulations are highly influenced by environmental and epigenetic factors and, therefore, targeting the OS-CSC environment and niche is the rationale for many recently postulated therapies. Likewise, some strategies for targeting CSC-associated signaling pathways have already been tested in both preclinical and clinical settings. This review recapitulates current OS cell-of-origin models, the properties of the OS-CSC and its niche, and potential new therapies able to target OS-CSCs.

Bone Tumor Environment as a Potential Therapeutic Target in Ewing Sarcoma

Ewing sarcoma is the second most common pediatric bone tumor, with three cases per million worldwide. In clinical terms, Ewing sarcoma is an aggressive, rapidly fatal malignancy that mainly develops not only in osseous sites (85%) but also in extra-skeletal soft tissue. It spreads naturally to the lungs, bones, and bone marrow with poor prognosis in the two latter cases. Bone lesions from primary or secondary (metastases) tumors are characterized by extensive bone remodeling, more often due to osteolysis. Osteoclast activation and subsequent bone resorption are responsible for the clinical features of bone tumors, including pain, vertebral collapse, and spinal cord compression. Based on the “vicious cycle” concept of tumor cells and bone resorbing cells, drugs, which target osteoclasts, may be promising agents as adjuvant setting for treating bone tumors, including Ewing sarcoma. There is also increasing evidence that cellular and molecular protagonists present in the bone microenvironment play a part in establishing a favorable “niche” for tumor initiation and progression. The purpose of this review is to discuss the potential therapeutic value of drugs targeting the bone tumor microenvironment in Ewing sarcoma. The first part of the review will focus on targeting the bone resorbing function of osteoclasts by means of bisphosphonates or drugs blocking the pro-resorbing cytokine receptor activator of NF-kappa B ligand. Second, the role of this peculiar hypoxic microenvironment will be discussed in the context of resistance to chemotherapy, escape from the immune system, or neo-angiogenesis. Therapeutic interventions based on these specificities could be then proposed in the context of Ewing sarcoma.

Bone microenvironment signals in osteosarcoma development

The bone is a complex connective tissue composed of many different cell types such as osteoblasts, osteoclasts, chondrocytes, mesenchymal stem/progenitor cells, hematopoietic cells and endothelial cells, among others. The interaction between them is finely balanced through the processes of bone formation and bone remodeling, which regulates the production and biological activity of many soluble factors and extracellular matrix components needed to maintain the bone homeostasis in terms of cell proliferation, differentiation and apoptosis. Osteosarcoma (OS) emerges in this complex environment as a result of poorly defined oncogenic events arising in osteogenic lineage precursors. Increasing evidence supports that similar to normal development, the bone microenvironment (BME) underlies OS initiation and progression. Here, we recapitulate the physiological processes that regulate bone homeostasis and review the current knowledge about how OS cells and BME communicate and interact, describing how these interactions affect OS cell growth, metastasis, cancer stem cell fate and therapy outcome.

RANK and RANK ligand expression in primary human osteosarcoma

Receptor activator of nuclear factor kappa-B ligand (RANKL) is an essential mediator of osteoclast formation, function and survival. In patients with solid tumor metastasis to the bone, targeting the bone microenvironment by inhibition of RANKL using denosumab, a fully human monoclonal antibody (mAb) specific to RANKL, has been demonstrated to prevent tumor-induced osteolysis and subsequent skeletal complications. Recently, a prominent functional role for the RANKL pathway has emerged in the primary bone tumor giant cell tumor of bone (GCTB). Expression of both RANKL and RANK is extremely high in GCTB tumors and denosumab treatment was associated with tumor regression and reduced tumor-associated bone lysis in GCTB patients. In order to address the potential role of the RANKL pathway in another primary bone tumor, this study assessed human RANKL and RANK expression in human primary osteosarcoma (OS) using specific mAbs, validated and optimized for immunohistochemistry (IHC) or flow cytometry.

Our results demonstrate RANKL expression was observed in the tumor element in 68% of human OS using IHC. However, the staining intensity was relatively low and only 37% (29/79) of samples exhibited≥10% RANKL positive tumor cells. RANK expression was not observed in OS tumor cells. In contrast, RANK expression was clearly observed in other cells within OS samples, including the myeloid osteoclast precursor compartment, osteoclasts and in giant osteoclast cells. The intensity and frequency of RANKL and RANK staining in OS samples were substantially less than that observed in GCTB samples. The observation that RANKL is expressed in OS cells themselves suggests that these tumors may mediate an osteoclastic response, and anti-RANKL therapy may potentially be protective against bone pathologies in OS. However, the absence of RANK expression in primary human OS cells suggests that any autocrine RANKL/RANK signaling in human OS tumor cells is not operative, and anti-RANKL therapy would not directly affect the tumor.

Human mesenchymal stem cells as delivery of osteoprotegerin gene: homing and therapeutic effect for osteosarcoma

Biological treatments have been studied extensively and previous studies have proved that osteoprotegerin (OPG) can inhibit the development and progress of human osteosarcoma. However, the utility of biologic agents for cancer therapy has a short half-life, which can hardly deliver to and function in tumor sites efficiently. Mesenchymal stem cells (MSCs) have the potential to migrate to tumor sites. In this study, MSCs transfected with adenoviruses carrying the OPG gene (MSCs-OPG) were used via the tail vein to treat athymic nude mice (nu/nu) bearing osteosarcoma. In vivo and ex vivo images were used to validate the MSCs homing to tumors. The therapeutic effect for osteosarcoma was evaluated by observations on growth of tumors and bone destruction. The results showed that infected MSCs-OPG labeled with red fluorescent protein (RFP) can migrate to tumor sites and express OPG protein. The treatment by MSCs-OPG reduced the tumor growth and inhibited bone destruction in vivo. All these indicated that MSCs can deliver OPG to tumor sites, which could be a new direction of biological treatment for human osteosarcoma.

RANK ligand blockade with denosumab in combination with sorafenib in chemorefractory osteosarcoma: a possible step forward?

BACKGROUND

There is no established systemic treatment option for unresectable osteosarcoma progressing after standard chemotherapy. A recently published clinical trial has demonstrated some activity of sorafenib in this situation. Preclinical research suggests a role for the inhibition of the receptor activator of nuclear factor-ĸB ligand (RANKL), but no clinical data have been reported so far.

CASE REPORT

A 37-year-old man was diagnosed with unresectable osteoblastic, osteoblastoma-like osteosarcoma in the C7/Th1 vertebra. The tumour progressed locally despite two lines of chemotherapy and stereotactic radiotherapy. On treatment with sorafenib and denosumab, a complete metabolic remission was achieved and is ongoing for over 18 months. Immunohistochemistry revealed an overexpression of RANK and RANKL in the patient's primary tumour.

DISCUSSION

This is the first report of activity achieved by the combination of the tyrosine kinase inhibitor sorafenib and the RANKL inhibitor denosumab in a patient with osteosarcoma. It confirms preclinical data on RANK/RANKL inhibition in osteosarcoma and could serve as a hypothesis-generating approach for clinical trials in this patient population.

Orthotopic murine model of a primary malignant bone tumor in the spine: functional, bioluminescence, and histological correlations

OBJECT

There is currently no reproducible animal model of human primary malignant bone tumors in the spine to permit laboratory investigation of the human disease. Therefore, the authors sought to adapt their previously developed orthotopic model of spinal metastasis to a model for primary malignant bone tumors of the spine.

METHODS

A transperitoneal surgical approach was used to implant osteosarcoma (Krib-1) into the L-3 vertebral body of nude mice via a drill hole. Motor function was evaluated daily using the previously validated qualitative key milestones of tail dragging, dorsal stepping, hindlimb sweeping, and paralysis. A subset of these animals was euthanized upon reaching the various milestones, and the spines were removed, sectioned, and stained. The degree of spinal cord compression was correlated with the occurrence of milestones and assessed by a ratio between the neural elements divided by the area of the spinal canal. Another subset of animals received stably transfected Krib-1 cells with the luciferase gene, and bioluminescence was measured at 10, 20, and 30 days postimplantation.

RESULTS

Osteosarcoma xenografts grew in all animals according to a reliable and reproducible time course; the mean time for development of behavioral milestones was noted in relation to the day of implantation (Day 1). Tail dragging (Milestone 1) occurred on Day 19.06 (95% CI 16.11-22.01), dorsal stepping (Milestone 2) occurred on Day 28.78 (95% CI 26.79-30.77), hindlimb sweeping (Milestone 3) occurred on Day 35.61 (95% CI 32.9-38.32), and paralysis of the hindlimb (Milestone 4) occurred on Day 41.78 (95% CI 39.31-44.25). These clinically observed milestones correlated with increasing compression of the spinal cord on histological sections. The authors observed a progressive increase in the local bioluminescence (in photons/cm²/sec) of the implanted level over time with a mean of 2.17 (range 0.0-8.61) at Day 10, mean 4.68 (range 1.17-8.52) at Day 20, and mean 5.54 (range 1.22-9.99) at Day 30.

CONCLUSIONS

The authors have developed the first orthotopic murine model of a primary malignant bone tumor in the spine, in which neurological decline reproducibly correlates with tumor progression as evidenced by pathological confirmation and noninvasive bioluminescence measurements. Although developed for osteosarcoma, this model can be expanded to study other types of primary malignant bone tumors in the spine. This model will potentially allow animal testing of targeted therapies against specific primary malignant tumor types.

Therapeutic effect of nanogel-based delivery of soluble FGFR2 with S252W mutation on craniosynostosis

Apert syndrome is an autosomal dominantly inherited disorder caused by missense mutations in fibroblast growth factor receptor 2 (FGFR2). Surgical procedures are frequently required to reduce morphological and functional defects in patients with Apert syndrome; therefore, the development of noninvasive procedures to treat Apert syndrome is critical. Here we aimed to clarify the etiological mechanisms of craniosynostosis in mouse models of Apert syndrome and verify the effects of purified soluble FGFR2 harboring the S252W mutation (sFGFR2IIIc^S252W) on calvarial sutures in Apert syndrome mice in vitro. We observed increased expression of Fgf10, Esrp1, and Fgfr2IIIb, which are indispensable for epidermal development, in coronal sutures in Apert syndrome mice. Purified sFGFR2IIIc^S252W exhibited binding affinity for fibroblast growth factor (Fgf) 2 but also formed heterodimers with FGFR2IIIc, FGFR2IIIc^S252W, and FGFR2IIIb^S252W. Administration of sFGFR2IIIc^S252W also inhibited Fgf2-dependent proliferation, phosphorylation of intracellular signaling molecules, and mineralization of FGFR2^S252W-overexpressing MC3T3-E1 osteoblasts. sFGFR2IIIc^S252W complexed with nanogels maintained the patency of coronal sutures, whereas synostosis was observed where the nanogel without sFGFR2^S252W was applied. Thus, based on our current data, we suggest that increased Fgf10 and Fgfr2IIIb expression may induce the onset of craniosynostosis in patients with Apert syndrome and that the appropriate delivery of purified sFGFR2IIIc^S252W could be effective for treating this disorder.

Extracellular Membrane Vesicles Derived from 143B Osteosarcoma Cells Contain Pro-Osteoclastogenic Cargo: A Novel Communication Mechanism in Osteosarcoma Bone Microenvironment

The bone microenvironment (BME) is the main hub of all skeletal related pathological events in osteosarcoma leading to tumor induced bone destruction, and decreasing overall bone quality and bone strength. The role of extra-cellular membrane vesicles (EMVs) as mediators of intercellular communication in modulating osteosarcoma-BME is unknown, and needs to be investigated. It is our hypothesis that osteosarcoma-EMVs contain pro-osteoclastogenic cargo which increases osteoclastic activity, and dysregulated bone remodeling in the osteosarcoma-BME. In this study, EMVs were isolated from the conditioned media of 143B and HOS human osteosarcoma cell cultures using differential ultracentrifugation. Nano-particle tracking analysis determined EMVs in the size range of 50-200 nm in diameter. The EMV yield from 143B cells was relatively higher compared to HOS cells. Transmission electron microscopy confirmed the ultrastructure of 143B-EMVs and detected multivesicular bodies. Biochemical characterization of 143B-EMVs detected the expression of bioactive pro-osteoclastic cargo including matrix metalloproteinases-1 and -13 (MMP-1, -13), transforming growth factor-β (TGF-β), CD-9, and receptor activator of nuclear factor kappa-β ligand (RANKL). Detection of a protein signature that is uniquely pro-osteoclastic in 143B-EMVs is a novel finding, and is significant as EMVs represent an interesting mechanism for potentially mediating bone destruction in the osteosarcoma-BME. This study further demonstrates that 143B cells actively mobilize calcium in the presence of ionomycin, and forskolin, and induce cytoskeleton rearrangements leading to vesicular biogenesis. In conclusion, this study demonstrates that 143B osteosarcoma cells generate EMVs mainly by mechanisms involving increased intracellular calcium or cAMP levels, and contain pro-osteoclastic cargo.

Novel RANK antagonists for the treatment of bone-resorptive disease: theoretical predictions and experimental validation

Receptor activator of nuclear factor-κB (RANK) and RANK ligand (RANKL) play a pivotal role in bone metabolism, and selective targeting of RANK signaling has become a promising therapeutic strategy in the management of resorptive bone diseases. Existing antibody-based therapies and novel inhibitors currently in development were designed to target the ligand, rather than the membrane receptor expressed on osteoclast precursors. We describe here an alternative approach to designing small peptides able to specifically bind to the hinge region of membrane RANK responsible for the conformational change upon RANKL association. A nonapeptide generated by this method was validated for its biological activity in vitro and in vivo and served as a lead compound for the generation of a series of peptide RANK antagonists derived from the original sequence. Our study presents a structure- and knowledge-based strategy for the design of novel effective and affordable small peptide inhibitors specifically targeting the receptor RANK and opens a new therapeutic opportunity for the treatment of resorptive bone disease.

Novel strategies for the treatment of chondrosarcomas: targeting integrins

Chondrosarcomas are a heterogeneous group of malignant bone tumors that are characterized by the production of cartilaginous extracellular matrix. They are the second most frequently occurring type of bone malignancy. Surgical resection remains the primary mode of treatment for chondrosarcomas, since conventional chemotherapy and radiotherapy are largely ineffective. Treatment of patients with high-grade chondrosarcomas is particularly challenging, owing to the lack of effective adjuvant therapies. Integrins are cell surface adhesion molecules that regulate a variety of cellular functions. They have been implicated in the initiation, progression, and metastasis of solid tumors. Deregulation of integrin expression and/or signaling has been identified in many chondrosarcomas. Therefore, the development of new drugs that can selectively target regulators of integrin gene expression and ligand-integrin signaling might hold great promise for the treatment of these cancers. In this review, we provide an overview of the current understanding of how growth factors, chemokines/cytokines, and other inflammation-related molecules can control the expression of specific integrins to promote cell migration. We also review the roles of specific subtypes of integrins and their signaling mechanisms, and discuss how these might be involved in tumor growth and metastasis. Finally, novel therapeutic strategies for targeting these molecules will be discussed.

Drugs targeting the bone microenvironment: new therapeutic tools in Ewing's sarcoma?

INTRODUCTION

Ewing's sarcoma (ES) is the second most frequent malignant primary bone tumour in children, adolescents and young adults. The overall survival is 60 - 70% at 5 years but still very poor for patients with metastases, disease relapse or for those not responding to chemotherapy. For these high risk patients, new therapeutic approaches are needed beyond conventional therapies (chemotherapy, surgery and radiation) such as targeted therapies.

AREAS COVERED

Transcriptomic and genomic analyses in ES have revealed alterations in genes that control signalling pathways involved in many other cancer types. To set up more specific approaches, it is reasonable to think that the particular microenvironment of these bone tumours is essential for their initiation and progression, including in ES. To support this hypothesis, preclinical studies using drugs targeting bone cells (bisphosphonate zoledronate, anti-receptor activator of NF-κB ligand strategies) showed promising results in animal models. This review will discuss the new targeted therapeutic options in ES, focusing more particularly on the ones modulating the bone microenvironment.

EXPERT OPINION

Targeting the microenvironment represents a new option for patients with ES. The proof-of-concept has been demonstrated in preclinical studies using relevant animal models, especially for zoledronate, which induced a strong inhibition of tumour progression in an orthotopic bone model.

Children's Oncology Group's 2013 blueprint for research: bone tumors

In the US, approximately 650 children are diagnosed with osteosarcoma and Ewing sarcoma (ES) each year. Five-year survival ranges from 65% to 75% for localized disease and <30% for patients with metastases. Recent findings include interval-compressed five drug chemotherapy improves survival with localized ES. In osteosarcoma a large international trial investigating the addition of ifosfamide/etoposide or interferon to standard therapy has completed accrual. For ES an ongoing trial explores the addition of cyclophosphamide/topotecan to interval-compressed chemotherapy. Trials planned by the Children's Oncology Group will investigate new target(s) including IGF-1R and mTOR in ES, and RANKL and GD2 in osteosarcoma.

Bone sarcomas: from biology to targeted therapies

Primary malignant bone tumours, osteosarcomas, and Ewing sarcomas are rare diseases which occur mainly in adolescents and young adults. With the current therapies, some patients remain very difficult to treat, such as tumour with poor histological response to preoperative CT (or large initial tumour volume for Ewing sarcomas not operated), patients with multiple metastases at or those who relapsed. In order to develop new therapies against these rare tumours, we need to unveil the key driving factors and molecular abnormalities behind the malignant characteristics and to broaden our understanding of the phenomena sustaining the metastatic phenotype and treatment resistance in these tumours. In this paper, starting with the biology of these tumours, we will discuss potential therapeutic targets aimed at increasing local tumour control, limiting metastatic spread, and finally improving patient survival.

Anti-RANKL therapy for bone tumours: Basic, pre-clinical and clinical evidences

Bone remodelling is related to coordinated phases of bone resorption and bone apposition allowing the maintenance of bone integrity, the phosphocalcic homoeostasis all along the life and consequently the bone adaptation to mechanical constraints or/and to endocrine fluctuations. Unfortunately, bone is a frequent site of tumour development originated from bone cell lineages (primary bone tumours: bone sarcomas) or from nonosseous origins (bone metastases: carcinomas). These tumour cells disrupt the balance between osteoblast and osteoclast activities resulting in a disturbed bone remodelling weakening the bone tissue, in a strongly altered bone microenvironment and consequently facilitating the tumour growth. At the early stage of tumour development, osteoclast differentiation and recruitment of mature osteoclasts are strongly activated resulting in a strong bone matrix degradation and release of numerous growth factors initially stored into this organic/calcified matrix. In turn these soluble factors stimulate the proliferation of tumour cells and exacerbate their migration and their ability to initiate metastases. Because Receptor Activator of NFκB Ligand (RANKL) is absolutely required for in vivo osteoclastogenesis, its role in the bone tumour growth has been immediately pointed out and has consequently allowed the development of new targeted therapies of these malignant diseases. The present review summarises the role of RANKL in the bone tumour microenvironment, the most recent pre-clinical and clinical evidences of its targeting in bone metastases and bone sarcomas. The following sections position RANKL targeted therapy among the other anti-resorptive therapies available and underline the future directions which are currently under investigations.

Relevance of the POS-1 orthotopic model as an "imaging model" for in vivo and simultaneous monitoring of tumor proliferation and bone remodeling in osteosarcoma

INTRODUCTION

Osteosarcoma (OS) management requires a better understanding of tumor/bone interactions in vivo during disease progression. Using [(18)F]-FDG and [(99m)Tc]-HMDP imaging, we assessed a methodology for an in vivo quantitative characterization of an orthotopic model of osteolytic OS on the basis of (1) tumor proliferation, (2) tumor and bone metabolic activities, and (3) bone remodeling.

METHODS

POS-1 tumor bearing mice were monitored in vivo over a 26-day period, with tumor and bone metabolic volumes (TMV and BMV, respectively) being determined from [(18)F]-FDG, bone remodeling from [(99m)Tc]-HMDP, and tumoral volume from micro- computed tomography scans.

RESULTS

From day 10, [(18)F]-FDG strongly accumulated within POS-1 tumor, with a tumor/muscle ratio of 3.7 ± 0.8. TMV and BMV increased as pathology progressed: TMV increased at early stage of pathology (from 56%) whereas BMV strongly increased (from 113%) during late stage. From [(99m)Tc]-HMDP imaging, bone remodeling features were evidenced within the distal region of tibia bearing the tumor, with a mean scintigraphic ratio of 1.36 ± 0.11 at day 12, that reached value of 2.53 ± 0.19 at day 26.

CONCLUSIONS

Our results validated the POS-1 orthotopic model as "OS imaging model," that could serve for evaluating in vivo therapies targeting tumor proliferation and/or bone remodeling in OS.

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.

Effect of zoledronic acid and amputation on bone invasion and lung metastasis of canine osteosarcoma in nude mice

Osteosarcoma (OSA) is an aggressive, highly metastatic and lytic primary bone neoplasm commonly affecting the appendicular skeleton of dogs and children. Current treatment options include amputation of the afflicted limb, limb-sparing procedures, or palliative radiation with or without adjunct chemotherapy. Therapies that inhibit bone resorption, such as the bisphosphonates, may be an effective palliative therapy by limiting the local progression of OSA in those patients that are not viable candidates for amputation. We have developed a mouse model of canine skeletal OSA following intratibial inoculation of OSCA40 cells that spontaneously metastasized to the lungs. We demonstrated that therapy with a nitrogen-containing bisphosphonate, zoledronic acid (Zol), reduced OSA-induced bone lysis; however, Zol monotherapy or in combination with amputation was not effective at inhibiting pulmonary metastasis. While not reaching statistical significance, amputation of the tumor-bearing limb reduced the average incidence of lung metastases; however, this effect was nullified when Zol was added to the treatment protocol. In untreated mice, the magnitude of proximal tibial lysis was significantly correlated with the incidence of metastasis. The data support amputation alone for the management of appendicular OSA rather than combining amputation with Zol. However, in patients that are not viable candidates for amputation, Zol may be a useful palliative therapy for OSA by reducing the magnitude of lysis and therefore bone pain, despite the risk of increased pulmonary metastasis.

Systemic RANK-Fc protein therapy is efficacious against primary osteosarcoma growth in a murine model via activity against osteoclasts

OBJECTIVES

Osteosarcoma (OS) is the most common primary malignant bone tumour, and mainly affects adolescents and young adults. Although there has been substantial improvement in management of OS with surgery and chemotherapy, further survival increase has not been achieved over the past two decades.

METHODS

We focused on the receptor activator of nuclear factor kappaB ligand (RANKL)-osteoclast (OCL) system as a biological target for OS. RANKL is a critical factor for OCL formation and bone resorption activity. The primary lesion in bone and ensuing metastasis in OS both require the induction of OCLs. RANK-Fc is a potent RANKL antagonist and inhibitor of OCL formation and activity.

KEY FINDINGS

In an orthotopic model in Balb/c nu/nu mice, a twice weekly dosing regimen of 350 microg of RANK-Fc per mouse subcutaneously (n= 5) reduced lung metastasis (P > 0.05), preserved bone structure and reduced tartrate-resistant acid phosphatase (TRAP)(+) OCLs (P < 0.005) in OS-bearing bone. In vitro, RANK-Fc suppressed OCL formation (P < 0.005), bone resorption activity (P < 0.005) and RANKL-induced anti-apoptosis (P < 0.5) of OCLs.

Safety concern between autologous fat graft, mesenchymal stem cell and osteosarcoma recurrence

BACKGROUND

Osteosarcoma is the most common malignant primary bone tumour in young adult treated by neo adjuvant chemotherapy, surgical tumor removal and adjuvant multidrug chemotherapy. For correction of soft tissue defect consecutive to surgery and/or tumor treatment, autologous fat graft has been proposed in plastic and reconstructive surgery.

PRINCIPAL FINDINGS

We report here a case of a late local recurrence of osteosarcoma which occurred 13 years after the initial pathology and 18 months after a lipofilling procedure. Because such recurrence was highly unexpected, we investigated the possible relationship of tumor growth with fat injections and with mesenchymal stem/stromal cell like cells which are largely found in fatty tissue. Results obtained in osteosarcoma pre-clinical models show that fat grafts or progenitor cells promoted tumor growth.

SIGNIFICANCE

These observations and results raise the question of whether autologous fat grafting is a safe reconstructive procedure in a known post neoplasic context.