Smoothened as a new therapeutic target for human osteosarcoma

Amicis Omnia Sunt Communia: NF-κB Inhibition as an Alternative to Overcome Osteosarcoma Heterogeneity

Tumor heterogeneity poses a significant challenge in osteosarcoma (OS) treatment. In this regard, the "omics" era has constantly expanded our understanding of biomarkers and altered signaling pathways (i.e., PI3K/AKT/mTOR, WNT/β-catenin, NOTCH, SHH/GLI, among others) involved in OS pathophysiology. Despite different players and complexities, many commonalities have been described, among which the nuclear factor kappa B (NF-κB) stands out. Its altered activation is pervasive in cancer, with pleiotropic action on many disease-relevant traits. Thus, in the scope of this article, we highlight the evidence of NF-κB dysregulation in OS and its integration with other cancer-related pathways while we summarize the repertoire of compounds that have been described to interfere with its action. In silico strategies were used to demonstrate that NF-κB is closely coordinated with other commonly dysregulated signaling pathways not only by functionally interacting with several of their members but also by actively participating in the regulation of their transcription. While existing inhibitors lack selectivity or act indirectly, the therapeutic potential of targeting NF-κB is indisputable, first for its multifunctionality on most cancer hallmarks, and secondly, because, as a common downstream effector of the many dysregulated pathways influencing OS aggressiveness, it turns complex regulatory networks into a simpler picture underneath molecular heterogeneity.

Hedgehog pathway in sarcoma: from preclinical mechanism to clinical application

Sarcomas are a diverse group of malignant neoplasms of mesenchymal origin. They develop rarely, but due to poor prognosis, they are a challenging and significant clinical problem. Currently, available therapeutic options have very limited activity. A better understating of sarcomas' pathogenesis may help develop more effective therapies in the future. The Sonic hedgehog (Shh) signaling pathway is involved in both embryonic development and mature tissue repair and carcinogenesis. Shh pathway inhibitors are presently used in the treatment of basal cell carcinoma. Its increased activity has been demonstrated in many sarcomas, including osteosarcoma, Ewing sarcoma, chondrosarcoma, rhabdomyosarcoma, leiomyosarcoma, and malignant rhabdoid tumor. In vitro studies have demonstrated the effectiveness of inhibitors of the Hedgehog pathway in inhibiting proliferation in those sarcomas in which the components of the pathway are overexpressed. These results were confirmed by in vivo studies, which additionally proved the influence of Shh pathway inhibitors on limiting the metastatic potential of sarcoma cells. However, until now, the efficacy of sarcomas treatment with Shh pathway inhibitors has not been established in clinical trials. The reason for that may be the non-canonical activation of the pathway or interactions with other signaling pathways, such as Wnt or Notch. In this review, we present the Shh signaling pathway's role in the pathogenesis of sarcomas, including both canonical and non-canonical signaling. We also propose how this knowledge could be potentially translated into clinics.

Ligand-dependent hedgehog signaling maintains an undifferentiated, malignant osteosarcoma phenotype

TP53 and RB1 loss-of-function mutations are common in osteosarcoma. During development, combined loss of TP53 and RB1 function leads to downregulation of autophagy and the aberrant formation of primary cilia, cellular organelles essential for the transmission of canonical Hedgehog (Hh) signaling. Excess cilia formation then leads to hypersensitivity to Hedgehog (Hh) ligand signaling. In mouse and human models, we now show that osteosarcomas with mutations in TP53 and RB1 exhibit enhanced ligand-dependent Hh pathway activation through Smoothened (SMO), a transmembrane signaling molecule required for activation of the canonical Hh pathway. This dependence is mediated by hypersensitivity to Hh ligand and is accompanied by impaired autophagy and increased primary cilia formation and expression of Hh ligand in vivo. Using a conditional genetic mouse model of Trp53 and Rb1 inactivation in osteoblast progenitors, we further show that deletion of Smo converts the highly malignant osteosarcoma phenotype to benign, well differentiated bone tumors. Conversely, conditional overexpression of SHH ligand, or a gain-of-function SMO mutant in committed osteoblast progenitors during development blocks terminal bone differentiation. Finally, we demonstrate that the SMO antagonist sonidegib (LDE225) induces growth arrest and terminal differentiation in vivo in osteosarcomas that express primary cilia and Hh ligand combined with mutations in TP53. These results provide a mechanistic framework for aberrant Hh signaling in osteosarcoma based on defining mutations in the tumor suppressor, TP53.

Research progress in the mechanism and treatment of osteosarcoma

ABSTRACT

Osteosarcoma (OS) is the most common primary malignant bone tumor that more commonly occurs in children and adolescents. The most commonly used treatment for OS is surgery combined with chemotherapy, but the treatment outcomes are typically unsatisfactory. High rates of metastasis and post-treatment recurrence rates are major challenges in the treatment of OS. This underlines the need for studying the in-depth characterization of the pathogenetic mechanisms of OS and development of more effective therapeutic modalities. Previous studies have demonstrated the important role of the bone microenvironment and the regulation of signaling pathways in the occurrence and development of OS. In this review, we discussed the available evidence pertaining to the mechanisms of OS development and identified therapeutic targets for OS. We also summarized the available treatment modalities for OS and identified future priorities for therapeutics research.

Deciphering the Signaling Mechanisms of Osteosarcoma Tumorigenesis

Osteosarcoma (OS) is the predominant primary bone tumor in the pediatric and adolescent populations. It has high metastatic potential, with the lungs being the most common site of metastasis. In contrast to many other sarcomas, OS lacks conserved translocations or genetic mutations; instead, it has heterogeneous abnormalities, including somatic DNA copy number alteration, ploidy, chromosomal amplification, and chromosomal loss and gain. Unfortunately, clinical outcomes have not significantly improved in over 30 years. Currently, no effective molecularly targeted therapies are available for this disease. Several genomic studies showed inactivation in the tumor suppressor genes, including p53, RB, and ATRX, and hyperactivation of the tumor promoter genes, including MYC and MDM2, in OS. Alterations in the major signaling pathways, including the PI3K/AKT/mTOR, JAK/STAT, Wnt/β-catenin, NOTCH, Hedgehog/Gli, TGF-β, RTKs, RANK/RANKL, and NF-κB signaling pathways, have been identified in OS development and metastasis. Although OS treatment is currently based on surgical excision and systematic multiagent therapies, several potential targeted therapies are in development. This review focuses on the major signaling pathways of OS, and we propose a biological rationale to consider novel and targeted therapies in the future.

Bioinformatics Screen Reveals Gli-Mediated Hedgehog Signaling as an Associated Pathway to Poor Immune Infiltration of Dedifferentiated Liposarcoma

Liposarcomas are the most diagnosed soft tissue sarcoma, with most cases consisting of well-differentiated (WDLPS) or dedifferentiated (DDLPS) histological subtypes. While both tumor subtypes can have clinical recurrence due to incomplete resections, DDLPS often has worse prognosis due to a higher likelihood of metastasis compared to its well-differentiated counterpart. Unfortunately, targeted therapeutic interventions have lagged in sarcoma oncology, making the need for molecular targeted therapies a promising future area of research for this family of malignancies. In this work, previously published data were analyzed to identify differential pathways that may contribute to the dedifferentiation process in liposarcoma. Interestingly, Gli-mediated Hedgehog signaling appeared to be enriched in dedifferentiated adipose progenitor cells and DDLPS tumors, and coincidentally Gli1 is often co-amplified with MDM2 and CDK4, given its genomic proximity along chromosome 12q13-12q15. However, we find that Gli2, but not Gli1, is differentially expressed between WDLPS and DDLPS, with a noticeable co-expression signature between Gli2 and genes involved in ECM remodeling. Additionally, Gli2 co-expression had a noticeable transcriptional signature that could suggest Gli-mediated Hedgehog signaling as an associated pathway contributing to poor immune infiltration in these tumors.

Self-Renewal and Pluripotency in Osteosarcoma Stem Cells' Chemoresistance: Notch, Hedgehog, and Wnt/β-Catenin Interplay with Embryonic Markers

Osteosarcoma is a highly malignant bone tumor derived from mesenchymal cells that contains self-renewing cancer stem cells (CSCs), which are responsible for tumor progression and chemotherapy resistance. Understanding the signaling pathways that regulate CSC self-renewal and survival is crucial for developing effective therapies. The Notch, Hedgehog, and Wnt/β-Catenin developmental pathways, which are essential for self-renewal and differentiation of normal stem cells, have been identified as important regulators of osteosarcoma CSCs and also in the resistance to anticancer therapies. Targeting these pathways and their interactions with embryonic markers and the tumor microenvironment may be a promising therapeutic strategy to overcome chemoresistance and improve the prognosis for osteosarcoma patients. This review focuses on the role of Notch, Hedgehog, and Wnt/β-Catenin signaling in regulating CSC self-renewal, pluripotency, and chemoresistance, and their potential as targets for anti-cancer therapies. We also discuss the relevance of embryonic markers, including SOX-2, Oct-4, NANOG, and KLF4, in osteosarcoma CSCs and their association with the aforementioned signaling pathways in overcoming drug resistance.

Targeting hedgehog signaling in pancreatic ductal adenocarcinoma

Pancreatic ductal adenocarcinoma (PDAC) remains a leading cause of cancer related death. The urgent need for effective therapies is highlighted by the lack of adequate targeting. In PDAC, hedgehog (Hh) signaling is known to be aberrantly activated, which prompted the pathway as a possible target for effective treatment for PDAC patients. Unfortunately, specific targeting of upstream molecules within the Hh signaling pathway failed to bring clinical benefit. This led to the ongoing debate on Hh targeting as a therapeutic treatment for PDAC patients. Additionally, concurrent non-canonical activation routes also result in translocation of Gli transcription factors into the nucleus. Therefore, different downstream targets of the Hh signaling pathway were identified and evaluated in preclinical and clinical research. In this review we summarize the variety of Hh signaling antagonists in different preclinical models of PDAC. Furthermore, we discuss published and ongoing clinical trials that evaluated Hh antagonists and point out the current hurdles and future perspectives in the light of redesigning Hh-targeting therapies for the treatment of PDAC patients.

Expression of the hedgehog signaling pathway and the effect of inhibition at the level of Smoothened in canine osteosarcoma cell lines

Osteosarcoma (OSA) is the most common malignant bone cancer in dogs. Canine and human OSA share several features, including tumor environments, response to traditional treatment, and several molecular pathways. Hedgehog (Hh) signaling is known to contribute to tumorigenesis and progression of various cancers, including human OSA. This study aimed to identify the role of the Hh signaling pathway in canine OSA cell lines, including Abrams, D17, and Moresco, focusing on the signal transducer Smoothened (SMO). mRNA and protein levels of Hh pathway components, including SHH, IHH, SMO, and PTCH1, were aberrant in all examined OSA cell lines compared with canine osteoblast cells. The SMO inhibitor cyclopamine significantly decreased cell viability and colony-forming ability in the canine OSA cell lines in a dose-dependent manner. Moresco cells, which expressed the highest level of SMO protein, were the most sensitive to the anticancer effect of cyclopamine among the three canine OSA cell lines tested. Hh downstream target gene and protein expression in canine OSA cell lines were downregulated after cyclopamine treatment. In addition, cyclopamine significantly increased apoptotic cell death in Abrams and Moresco cells. The findings that Hh/SMO is activated in canine OSA cell lines and cyclopamine suppresses OSA cell survival via inhibition of SMO suggest that the Hh/SMO signaling pathway might be a novel therapeutic target for canine OSA. This article is protected by copyright. All rights reserved.

Aberrant activation of the Hedgehog signaling pathway in granulosa cells from patients with polycystic ovary syndrome

The molecular mechanism that triggers polycystic ovary syndrome (PCOS) is mysterious. Abnormal development of ovarian granulosa cells (GCs) is one of the causes of PCOS. Herein, our study was carried out using RNA-seq to detect the different gene expression levels in ovarian GCs between three patients with PCOS and four normal controls. To verify the RNA-seq data, GCs from 22 patients with PCOS and 21 controls with normal ovulation were collected to perform the RT-PCR analysis. Hedgehog signaling pathway (Hh) members, Ihh and Ptch2 were abnormally highly expressed in the PCOS tissue (PT). The qPCR also indicated that the expression levels of Hh signaling pathway downstream members, Ptch1, Gli1, and Gli2 in the PT were significantly higher than those in the normal tissue (NT). Besides, the expression of TNF-α mRNA in PCOS patients was higher than that in the control group. Through the chromatin immunoprecipitation assay (ChIP), we found that the Gli1-IP-DNA enriched from the granular cells of PCOS patients was higher than that of the control group. Finally, the Hh signaling pathway inhibitor, cyclopamine, can decrease the apoptosis of PCOS ovarian granulosa cells. These results suggest that abnormal activation of Hh signaling pathway, especially Ihh signal, may have a profound influence on PCOS.

Excellent Early Outcomes of Combined Chemotherapy With Arsenic Trioxide for Stage 4/M Neuroblastoma in Children: A Multicenter Nonrandomized Controlled Trial

This nonrandomized, multicenter cohort, open-label clinical trial evaluated the efficacy and safety of combined chemotherapy with arsenic trioxide (ATO) in children with stage 4/M neuroblastoma (NB). We enrolled patients who were newly diagnosed with NB and assessed as stage 4/M and received either traditional chemotherapy or ATO combined with chemotherapy according to their own wishes. Twenty-two patients were enrolled in the trial group (ATO combined with chemotherapy), and 13 patients were enrolled in the control group (traditional chemotherapy). Objective response rate (ORR) at 4 weeks after completing induction chemotherapy was defined as the main outcome, and adverse events were monitored and graded in the meantime. Data cutoff date was December 31, 2019. Finally, we found that patients who received ATO combined with chemotherapy had a significantly higher response rate than those who were treated with traditional chemotherapy (ORR: 86.36% vs. 46.16%, p=0.020). Reversible cardiotoxicity was just observed in three patients who were treated with ATO, and no other differential adverse events were observed between the two groups. ATO combined with chemotherapy can significantly improve end-induction response in high-risk NB, and our novel regimen is well tolerated in pediatric patients. These results highlight the superiority of chemotherapy with ATO, which creates new opportunity for prolonging survival. In addition, this treatment protocol minimizes therapeutic costs compared with anti-GD2 therapy, MIBG, and proton therapy and can decrease the burden to families and society. However, we also need to evaluate more cases to consolidate our conclusion.

STAT3 is required for Smo-dependent signaling and mediates Smo-targeted treatment resistance and tumorigenesis in Shh medulloblastoma

Sonic hedgehog (Shh)‐driven medulloblastoma (Shh MB) cells are dependent on constitutive Shh signaling, but targeted treatment of Shh MB has been ineffective due to drug resistance. The purpose of this study was to address the critical role of signal transducer and activator of transcription 3 (STAT3) in Shh signaling and drug resistance in Shh MB cells. Herein, we show that STAT3 is required for Smoothened (Smo)‐dependent Shh signaling and, in turn, is reciprocally regulated by Shh signaling, and demonstrate that STAT3 activity is critical for expression of HCK proto‐oncogene, Src family tyrosine kinase (Hck) in Shh MB. We also demonstrate that maintained STAT3 activity suppresses p21 expression and promotes colony formation of Shh MB cells, whereas dual treatment with inhibitors of both Smo and STAT3 results in marked synergistic killing and overcomes drug resistance in vitro of Smo antagonist‐resistant Shh MB cells. Finally, STAT3 inhibitor treatment significantly prevents in vivo tumor formation in genetically engineered Shh MB mice. Collectively, we show that STAT3 is necessary to maintain Shh signaling and thus is a potential therapeutic target to treat Shh MB and overcome anti‐Smo drug resistance.

Drug Resistance in Osteosarcoma: Emerging Biomarkers, Therapeutic Targets and Treatment Strategies

Simple Summary

Despite the adoption of aggressive, multimodal treatment schedules, the cure rate of high-grade osteosarcoma (HGOS) has not significantly improved in the last 30 years. The most relevant problem preventing improvement in HGOS prognosis is drug resistance. Therefore, validated novel biomarkers that help to identify those patients who could benefit from innovative treatment options and the development of drugs enabling personalized therapeutic protocols are necessary. The aim of this review was to give an overview on the most relevant emerging drug resistance-related biomarkers, therapeutic targets and new agents or novel candidate treatment strategies, which have been highlighted and suggested for HGOS to improve the success rate of clinical trials.

Abstract

High-grade osteosarcoma (HGOS), the most common primary malignant tumor of bone, is a highly aggressive neoplasm with a cure rate of approximately 40–50% in unselected patient populations. The major clinical problems opposing the cure of HGOS are the presence of inherent or acquired drug resistance and the development of metastasis. Since the drugs used in first-line chemotherapy protocols for HGOS and clinical outcome have not significantly evolved in the past three decades, there is an urgent need for new therapeutic biomarkers and targeted treatment strategies, which may increase the currently available spectrum of cure modalities. Unresponsive or chemoresistant (refractory) HGOS patients usually encounter a dismal prognosis, mostly because therapeutic options and drugs effective for rescue treatments are scarce. Tailored treatments for different subgroups of HGOS patients stratified according to drug resistance-related biomarkers thus appear as an option that may improve this situation. This review explores drug resistance-related biomarkers, therapeutic targets and new candidate treatment strategies, which have emerged in HGOS. In addition to consolidated biomarkers, specific attention has been paid to the role of non-coding RNAs, tumor-derived extracellular vesicles, and cancer stem cells as contributors to drug resistance in HGOS, in order to highlight new candidate markers and therapeutic targets. The possible use of new non-conventional drugs to overcome the main mechanisms of drug resistance in HGOS are finally discussed.

The value of the hedgehog signal in osteoblasts in fluoride-induced bone-tissue injury

OBJECTIVE

This study was designed to observe the expression of important hedgehog (Hh) signal factors in the bone tissue of rats with chronic fluorosis and cultured osteoblasts in order to investigate the role and significance of the Hh signal in fluoride-induced bone injury.

METHODS

Healthy Sprague-Dawley (SD) rats were randomly divided into four groups: the control group, the fluorosis group (F Group), the fluoride + blocker group (F + Cycl group: rats were treated with fluoride + cyclopamine), and the fluoride + blocker control group (F + DMSO group). After 6 months of intervention, the urinary fluoride content of rats in each group was detected. The primary osteoblasts of rats were selected for cell experiment, and the experiment was carried out after the cells were passaged from the second to the fourth generation.

RESULTS

The proliferation rate of primary rat osteoblasts presented time-affected and dose-affected relationships in a short time under treatment with a low dose of sodium fluoride (NaF), but the proliferation of osteoblasts was inhibited by long-term and high-dose NaF exposure. In the F group, the alkaline phosphatase (ALP) activity of osteoblasts increased gradually. The ALP activity was lower in the F + Cycl group than in the F group, and there was no significant difference between the F + DMSO group and F group. With the increase in fluoride exposure, the expression of Hh signal factors and osteogenic-related factor proteins increased gradually. The expressions of Indian hedgehog (Ihh), smoothened (Smo), Glioma-associated oncogene homolog (Gli) 2, and Runt-related transcription factor 2 (Runx2)in the F + Cycl group increased with the dose of fluoride but they were significantly inhibited compared with the F group. Compared with the control group, the content of urinary fluoride in the F group was significantly higher (P < 0.05), but there was no significant change in urinary fluoride content in the F + Cycl group and the F + DMSO group. Compared with the control group, the serum bone alkaline phosphatase (BALP) contents of rats in the other groups increased after 6 months' intake of fluoride water (P < 0.05). After drug blocking, the serum BALP content in the F + Cycl group was lower than that in the F + DMSO group (P < 0.05). The BALP content in the F + DMSO group was similar to that in the F group: it did not decrease. The mRNA expressions of Ihh, Smo, Gli2, and Runx2 in bone tissue of the F group were significantly higher than those in the control group (P < 0.05). After cyclopamine blocking, the expressions decreased (P < 0.05), but the differences between the F + DMSO group and F group were not statistically significant.

CONCLUSION

Hh signal plays an important role in fluoride-induced bone injury. The effective inhibition of cyclopamine is expected to be a new target for the treatment of skeletal damage caused by fluorosis.

Studying the role of the immune system on the antitumor activity of a Hedgehog inhibitor against murine osteosarcoma

Recent evidence demonstrates that the efficacy of conventional anticancer therapies including chemotherapy requires a functional immune system. Here, we addressed the possibility that the antitumor effect of a selective Smoothened antagonist and Hedgehog (Hh) pathway inhibitor (LDE225), a promising anticancer drug, might at least partially depend on the immune system. To this aim, we used tumor cell lines derived from a murine model of radiation-induced osteosarcoma. In vitro treatment of osteosarcoma cells with LDE225 resulted in a decreased ability of tumor cells to proliferate, but had no effect on their viability. Flow cytometry analysis demonstrated that LDE225-treatment did not detectably modulate the immunogenicity of tumor cells. Moreover, LDE225 did not display any pro-apoptotic properties on osteosarcoma cells, highlighting that its antitumor profile mainly derives from a cytostatic effect. Furthermore, calreticulin exposure, a key feature of immunogenic cell death, was not provoked by LDE225, neither alone nor combined with recognized immunogenic drugs. Finally, the oral administration of LDE225 to osteosarcoma-bearing mice did significantly delay the tumor growth even in an immunocompromised setting. These data suggest that inhibiting Hh signaling can control osteosarcoma cell proliferation but does not modulate the immunogenic profile of these cells.

Sonic Hedgehog Signature in Pediatric Primary Bone Tumors: Effects of the GLI Antagonist GANT61 on Ewing's Sarcoma Tumor Growth

Simple Summary

The poor clinical outcomes for Osteosarcoma (OS) and Ewing’s sarcoma (ES) patients underscore the urgency of developing novel therapeutic strategies for these pathologies. In this context, the emerging role of Sonic hedgehog (SHH) signaling in cancer has been critically evaluated, focusing on the potential for targeting SHH signaling as an anticancer strategy. The aims of this work were (1) to highlight and to compare a possible SHH/Gli signature between OS and ES, (2) to strengthen our knowledge concerning the role of EWS-FLI1 in the SHH signature in ES and (3) to evaluate the effect of the specific Gli inhibitor GANT61 in vivo on the growth of ES tumors using an orthotopic mice model. Our work identifies Gli1 as a promising therapeutic target in ES and demonstrates that GANT61, through inhibition of Gli1 transcriptional activity, may be a promising therapeutic strategy hindering ES tumor progression, and specifically primary tumor growth.

Abstract

Osteosarcoma (OS) and Ewing’s sarcoma (ES) are the most common malignant bone tumors in children and adolescents. In many cases, the prognosis remains very poor. The Sonic hedgehog (SHH) signaling pathway, strongly involved in the development of many cancers, regulate transcription via the transcriptional factors Gli1-3. In this context, RNAseq analysis of OS and ES cell lines reveals an increase of some major compounds of the SHH signaling cascade in ES cells, such as the transcriptional factor Gli1. This increase leads to an augmentation of the transcriptional response of Gli1 in ES cell lines, demonstrating a dysregulation of Gli1 signaling in ES cells and thus the rationale for targeting Gli1 in ES. The use of a preclinical model of ES demonstrates that GANT61, an inhibitor of the transcriptional factor Gli1, reduces ES primary tumor growth. In vitro experiments show that GANT61 decreases the viability of ES cell, mainly through its ability to induce caspase-3/7-dependent cell apoptosis. Taken together, these results demonstrates that GANT61 may be a promising therapeutic strategy for inhibiting the progression of primary ES tumors.

Tumor-Associated Macrophages in Osteosarcoma: From Mechanisms to Therapy

Osteosarcomas (OSs) are bone tumors most commonly found in pediatric and adolescent patients characterized by high risk of metastatic progression and recurrence after therapy. Effective therapeutic management of this disease still remains elusive as evidenced by poor patient survival rates. To achieve a more effective therapeutic management regimen, and hence patient survival, there is a need to identify more focused targeted therapies for OSs treatment in the clinical setting. The role of the OS tumor stroma microenvironment plays a significant part in the development and dissemination of this disease. Important components, and hence potential targets for treatment, are the tumor-infiltrating macrophages that are known to orchestrate many aspects of OS stromal signaling and disease progression. In particular, increased infiltration of M2-like tumor-associated macrophages (TAMs) has been associated with OS metastasis and poor patient prognosis despite currently used aggressive therapies regimens. This review aims to provide a summary update of current macrophage-centered knowledge and to discuss the possible roles that macrophages play in the process of OS metastasis development focusing on the potential influence of stromal cross-talk signaling between TAMs, cancer-stem cells and additional OSs tumoral microenvironment factors.

Cancer Stem Cell Functions in Hepatocellular Carcinoma and Comprehensive Therapeutic Strategies

Hepatocellular carcinoma (HCC) is a significant cause of cancer-related mortality owing to resistance to traditional treatments and tumor recurrence after therapy, which leads to poor therapeutic outcomes. Cancer stem cells (CSC) are a small subset of tumor cells with the capability to influence self-renewal, differentiation, and tumorigenesis. A number of surface markers for liver cancer stem cell (LCSC) subpopulations (EpCAM, CD133, CD44, CD13, CD90, OV-6, CD47, and side populations) in HCC have been identified. LCSCs play critical roles in regulating HCC stemness, self-renewal, tumorigenicity, metastasis, recurrence, and therapeutic resistance via genetic mutations, epigenetic disruption, signaling pathway dysregulation, or alterations microenvironment. Accumulating studies have shown that biomarkers for LCSCs contribute to diagnosis and prognosis prediction of HCC, supporting their utility in clinical management and development of therapeutic strategies. Preclinical and clinical analyses of therapeutic approaches for HCC using small molecule inhibitors, oncolytic measles viruses, and anti-surface marker antibodies have demonstrated selective, efficient, and safe targeting of LCSC populations. The current review focuses on recent reports on the influence of LCSCs on HCC stemness, tumorigenesis, and multiple drug resistance (MDR), along with LCSC-targeted therapeutic strategies for HCC.

Evaluation of canonical Hedgehog signaling pathway inhibition in canine osteosarcoma

Canine osteosarcoma (OSA), the most common canine primary bone malignancy, has a highly aggressive biologic behavior. Despite current standard of care therapies, including amputation and adjuvant chemotherapy, most dogs still succumb to metastatic disease. Further investigations into molecular mechanisms and pathways driving OSA are needed to improve therapeutic options. The Hedgehog (HH) cell-signaling pathway has demonstrated involvement in human OSA. Several studies in canine OSA have found changes in expression of some HH pathway genes and demonstrated a role for HH transcription factors. However, the role of this pathway as well as the translational value of its targeting in canine OSA are still undefined. The objectives of this study were to determine the expression of HH components directly in canine OSA tissues and to evaluate the biologic impact of HH signaling inhibition in canine OSA cells. In situ hybridization was used to detect HH family mRNA expression in archived canine OSA tissues and revealed variable expression levels of these mRNAs in canine OSA tissues. The effect of a commercially available Smoothened inhibitor, vismodegib, was studied in established canine OSA cell lines. Alterations in cellular growth as well as assessment of downstream HH targets were evaluated. Although changes in cell growth were noted following Smoothened inhibition, inconsistent decreases in target gene expression were found. While treatment with vismodegib had a negative impact on canine OSA cell growth and viability, the mechanism remains unclear. Further studies are warranted to evaluate the clinical significance of canonical HH signaling in canine OSA.

The multiple function of long noncoding RNAs in osteosarcoma progression, drug resistance and prognosis

Osteosarcoma is a bone tumor prevalent in children and young adults. LncRNAs are a family of non-protein-coding transcripts longer than 200 nucleotides. The tumor-related pathological functions of lncRNAs include proliferation, migration, and chemotherapy resistance, all of which have been widely acknowledged in research on osteosarcoma. In addition, compelling evidence suggests that lncRNAs could serve as diagnostic indicators, prognostic biomarkers, and targets for disease treatment. In this review, we systematically summarize how lncRNAs regulate tumorigenesis, invasion and therapeutic resistance. By deepening our knowledge of the relationship between lncRNAs and osteosarcoma, we hope to translate research findings into clinical applications as soon as possible.

The YAP/TAZ Pathway in Osteogenesis and Bone Sarcoma Pathogenesis

YAP and TAZ are intracellular messengers communicating multiple interacting extracellular biophysical and biochemical cues to the transcription apparatus in the nucleus and back to the cell/tissue microenvironment interface through the regulation of cytoskeletal and extracellular matrix components. Their activity is negatively and positively controlled by multiple phosphorylation events. Phenotypically, they serve an important role in cellular plasticity and lineage determination during development. As they regulate self-renewal, proliferation, migration, invasion and differentiation of stem cells, perturbed expression of YAP/TAZ signaling components play important roles in tumorigenesis and metastasis. Despite their high structural similarity, YAP and TAZ are functionally not identical and may play distinct cell type and differentiation stage-specific roles mediated by a diversity of downstream effectors and upstream regulatory molecules. However, YAP and TAZ are frequently looked at as functionally redundant and are not sufficiently discriminated in the scientific literature. As the extracellular matrix composition and mechanosignaling are of particular relevance in bone formation during embryogenesis, post-natal bone elongation and bone regeneration, YAP/TAZ are believed to have critical functions in these processes. Depending on the differentiation stage of mesenchymal stem cells during endochondral bone development, YAP and TAZ serve distinct roles, which are also reflected in bone tumors arising from the mesenchymal lineage at different developmental stages. Efforts to clinically translate the wealth of available knowledge of the pathway for cancer diagnostic and therapeutic purposes focus mainly on YAP and TAZ expression and their role as transcriptional co-activators of TEAD transcription factors but rarely consider the expression and activity of pathway modulatory components and other transcriptional partners of YAP and TAZ. As there is a growing body of evidence for YAP and TAZ as potential therapeutic targets in several cancers, we here interrogate the applicability of this concept to bone tumors. To this end, this review aims to summarize our current knowledge of YAP and TAZ in cell plasticity, normal bone development and bone cancer.

SHH Signaling Pathway Drives Pediatric Bone Sarcoma Progression

Primary bone tumors can be divided into two classes, benign and malignant. Among the latter group, osteosarcoma and Ewing sarcoma are the most prevalent malignant primary bone tumors in children and adolescents. Despite intensive efforts to improve treatments, almost 40% of patients succumb to the disease. Specifically, the clinical outcome for metastatic osteosarcoma or Ewing sarcoma remains poor; less than 30% of patients who present metastases will survive 5 years after initial diagnosis. One common and specific point of these bone tumors is their ability to deregulate bone homeostasis and remodeling and divert them to their benefit. Over the past years, considerable interest in the Sonic Hedgehog (SHH) pathway has taken place within the cancer research community. The activation of this SHH cascade can be done through different ways and, schematically, two pathways can be described, the canonical and the non-canonical. This review discusses the current knowledge about the involvement of the SHH signaling pathway in skeletal development, pediatric bone sarcoma progression and the related therapeutic options that may be possible for these tumors.

Melarsomine suppresses canine osteosarcoma cell survival via inhibition of Hedgehog-GLI signaling

The Hedgehog-GLI signaling pathway is activated in human and canine osteosarcoma (OSA) and represents a potential therapeutic target for cancers, including OSA. Arsenic trioxide represses GLI expression. Melarsomine, an arsenic compound-containing drug, has been approved for the treatment of canine heartworm disease. Hence, we hypothesized that melarsomine inhibits GLI signaling in canine OSA cell lines. The present study aimed to assess this hypothesis. Cell viability and colony formation were decreased in the canine OSA cell lines Abrams and D17 after treatment with melarsomine. Melarsomine-induced apoptotic cell death was assessed via cell cycle analysis using propidium iodide staining. Quantitative real-time reverse transcription polymerase chain reaction and western blot analyses revealed a downregulation of genes downstream of the Hedgehog signaling pathway, including GLI1, GLI2, and PTCH, after melarsomine treatment. The present results suggest that melarsomine exerts antitumor effects and serves as a GLI inhibitor in canine OSA cells. Additional studies are required to evaluate and confirm the anticancer effect and relevant therapeutic dose of melarsomine in vivo.

Nuclear localization and Overexpression of Smoothened in Pancreatic and Colorectal Cancers

Smoothened (SMO) is a significant signalling protein which functions as a key transducer for the hedgehog signalling pathway, an important signalling mechanism with key roles in development and oncogenesis. The correlation of expression dynamics of SMO with pancreatic and colorectal cancer genesis has been known but with ambiguity. Therefore, in this study, we investigated messenger RNA (mRNA) and protein expression of SMO in pancreatic and colorectal cancers in our population and assessed relationship with various clinicopathological parameters. Surgically resected tumour and adjacent histologically normal tissues from 33 and 61 pancreatic and colorectal cancer patients were investigated in the present study. Expression of SMO was analysed by quantitative real-time polymerase chain reaction and immunohistochemistry. At mRNA level, SMO was overexpressed in 72.72% (24 of 33) and 50.81% (31 of 61) of the pancreatic and colorectal cancer cases as compared with their adjacent normal tissues. SMO immunohistochemical analysis revealed nuclear localization and overexpression was observed in 51.51% (17 of 33) and 40.98% (25 of 61) of pancreatic and colorectal cancer tissues. SMO overexpression was significantly associated with smoking, late-stage disease and lymph node metastasis in patients with Colorectal cancer. Our results showed that SMO is dysregulated in pancreatic and colorectal cancers and may be considered as a target in cancer therapeutics.

Effect of RAB31 silencing on osteosarcoma cell proliferation and migration through the Hedgehog signaling pathway

Osteosarcoma (OS) is a prevalent cancer that plagues people worldwide. Identifying prognostic markers would be useful in treating human OS. In this study, we aimed to explore the functions of Ras-related protein Rab-31 (RAB31) in OS-cell proliferation, migration, and invasion as well as its roles in the Hedgehog signaling pathway for better understanding of the mechanism. To assess the detailed regulatory mechanism of RAB31 silencing on OS, both RT-qPCR and Western blot analysis were employed to evaluate the expressions of RAB31 as well as the Hedgehog signaling pathway-related genes. Besides, we also investigated the effects of silenced RAB31 both in vitro and in vivo. First, we found that in OS tissues, both mRNA and protein expressions of RAB31 and PCNA had a significant increase. Second, the Hedgehog signaling pathway was detected to play an integral role in OS progression. Finally, after transfection of RAB31-siRNA to reduce the expression of RAB31, the Hedgehog signaling pathway was suppressed, along with cell proliferation, invasion, and migration. Therefore, we conclude that RAB31 plays an important role in OS development and its silencing delays the OS progression via suppression of the Hedgehog signaling pathway.

miR-210 promotes human osteosarcoma cell migration and invasion by targeting FGFRL1

Osteosarcoma is a common bone tumor and a frequently occuring cancer-associated threat to children. Notably, the prognosis of osteosarcoma is very poor when it is diagnosed with metastasis. A growing number of studies have indicated that various microRNAs (miRs) serve important regulatory roles in the pathogeny of different types of cancer. However, the functions of miR-210 in osteosarcoma need to be elucidated comprehensively. The aim of the present study was to investigate the potential roles of miR-210 in osteosarcoma by targeting fibroblast growth factor receptor-like 1 (FGFRL1). Reverse transcription-quantitative polymerase chain reaction results revealed that the expression of miR-210 was highly elevated while FGFRL1 expression was reduced inversely in osteosarcoma tissues compared with matched normal tissues. The results of Transwell assays showed that miR-210 promoted osteosarcoma cell migration and invasion. Furthermore, the luciferase reporter assay results suggested that miR-210 could directly bind to FGFRL1 in osteosarcoma cells. In addition, the present findings demonstrated that miR-210 could negatively regulate FGFRL1 expression by targeting the 3′untranslated region. In conclusion, the findings of the present study suggested that miR-210 exerted tumor carcinogenic functions in osteosarcoma by targeting FGFRL1. The findings of this study demonstrated that FGFRL1 was a direct target of miR-210 in osteosarcoma involved in the promoting functions mediated by miR-210 in the invasion and migration of osteosarcoma, suggesting that miR-210/FGFRL1 may be promising for discovering diagnostic and prognostic biomarkers for the therapies of osteosarcoma.

Advances in sarcoma diagnostics and treatment

The heterogeneity of sarcomas with regard to molecular genesis, histology, clinical characteristics, and response to treatment makes management of these rare yet diverse neoplasms particularly challenging. This review encompasses recent developments in sarcoma diagnostics and treatment, including cytotoxic, targeted, epigenetic, and immune therapy agents. In the past year, groups internationally explored the impact of adding mandatory molecular testing to histological diagnosis, reporting some changes in diagnosis and/or management; however, the impact on outcomes could not be adequately assessed. Transcriptome sequencing techniques have brought forward new diagnostic tools for identifying fusions and/or characterizing unclassified entities. Next-generation sequencing and advanced molecular techniques were also applied to identify potential targets for directed and epigenetic therapy, where preclinical studies reported results for agents active within the receptor tyrosine kinase, mTOR, Notch, Wnt, Hedgehog, Hsp90, and MDM2 signaling networks. At the level of clinical practice, modest developments were seen for some sarcoma subtypes in conventional chemotherapy and in therapies targeting the pathways activated by various receptor tyrosine kinases. In the burgeoning field of immune therapy, sarcoma work is in its infancy; however, elaborate protocols for immune stimulation are being explored, and checkpoint blockade agents advance from preclinical models to clinical studies.

Novel smoothened antagonists as anti-neoplastic agents for the treatment of osteosarcoma

Osteosarcoma (OS) is an ultra-rare highly malignant tumor of the skeletal system affecting mainly children and young adults and it is characterized by an extremely aggressive clinical course. OS patients are currently treated with chemotherapy and complete surgical resection of cancer tissue. However, resistance to chemotherapy and the recurrence of disease, as pulmonary metastasis, remain the two greatest challenges in the management, and treatment of this tumor. For these reasons, it is of primary interest to find alternative therapeutic strategies for OS. Dysregulated Hedgehog signalling is involved in the development of various types of cancers including OS. It has also been implicated in tumor/stromal interaction and cancer stem cell biology, and therefore presents a novel therapeutic strategy for cancer treatment. In our work, we tested the activity of five potent Smoothened (SMO) inhibitors, four acylguanidine and one acylthiourea derivatives, against an OS cell line. We found that almost all our compounds were able to inhibit OS cells proliferation and to reduce Gli1 protein levels. Our results also indicated that SMO inhibition in OS cells by such compounds, induces apoptosis with a nanomolar potency. These findings suggest that inactivation of SMO may be a useful approach to the treatment of patients with OS.

Cell division cycle 20 promotes cell proliferation and invasion and inhibits apoptosis in osteosarcoma cells

Cdc20 (cell division cycle 20 homologue) has been reported to exhibit an oncogenic role in human tumorigenesis. However, the function of Cdc20 in osteosarcoma (OS) has not been investigated. In the current study, we aim to explore the role of Cdc20 in human OS cells. Multiple approaches were used to measure cell growth, apoptosis, cell cycle, migration and invasion in OS cells after depletion of Cdc20 or overexpression of Cdc20. We found that down-regulation of Cdc20 inhibited cell growth, induced apoptosis and triggered cell cycle arrest in OS cells. Moreover, Cdc20 down-regulation let to inhibition of cell migration and invasion in OS cells. Consistently, overexpression of Cdc20 in OS cells promoted cell growth, inhibited apoptosis, enhanced cell migration and invasion. Mechanistically, our Western blotting results showed that overexpression of Cdc20 reduced the expression of Bim and p21, whereas depletion of Cdc20 upregulated Bim and p21 levels in OS cells. Altogether, our findings demonstrated that Cdc20 exerts its oncogenic role partly due to regulation of Bim and p21 in OS cells, suggesting that targeting Cdc20 could be useful for the treatment of OS.

S-phase kinase-associated protein 2 promotes cell growth and motility in osteosarcoma cells

Skp2 (S-phase kinase-associated protein 2) plays an oncogenic role in a variety of human cancers. However, the function of Skp2 in osteosarcoma (OS) is elusive. Therefore, in the current study, we explore whether Skp2 exerts its oncogenic function in OS. The cell growth, apoptosis, invasion and cell cycle were measured in OS cells after Skp2 overexpression. We found that overexpression of Skp2 enhanced cell growth, and inhibited cell apoptosis in OS cells. Moreover, we observed that upregulation of Skp2 accelerated cell cycle progression in OS cells. Furthermore, the ability of migration and invasion was enhanced in Skp2 overexpressing OS cells. Mechanically, our Western blotting data suggested that Skp2 decreased the expression of E-cadherin, Foxo1, p21, and p57, but increased MMP-9 in OS cells. In conclusion, our study demonstrated that Skp2 exhibited an oncogenic function in OS cells, suggesting that inhibition of Skp2 may be a novel approach for the treatment of OS.

Inhibition of Skp2 suppresses the proliferation and invasion of osteosarcoma cells

Osteosarcoma (OS) is a common bone tumor that mainly affects children and young adults. S-phase kinase‑associated protein 2 (Skp2) has been characterized to play a critical oncogenic role in a variety of human malignancies. However, the biological function of Skp2 in OS remains largely obscure. In the present study, we elucidated the role of Skp2 in cell growth, cell cycle, apoptosis and migration in OS cells. We found that depletion of Skp2 inhibited cell growth in both MG-63 and SW 1353 cells. Moreover, we observed that depletion of Skp2 triggered cell apoptosis in two OS cell lines. Furthermore, downregulation of Skp2 induced cell cycle arrest in the G0/G1 phase in OS cells. Notably, our wound healing assay results revealed that inhibition of Skp2 suppressed cell migration in OS cells. Invariably, our western blot results demonstrated that depletion of Skp2 in OS cells inhibited activation of pAkt and increased p27 expression in OS cells, suggesting that Skp2 exerted its oncogenic function partly through the regulation of Akt and p27. Our findings revealed that targeting Skp2 could be a promising therapeutic strategy for the treatment of OS.

Itraconazole induces apoptosis and cell cycle arrest via inhibiting Hedgehog signaling in gastric cancer cells

BACKGROUND

Itraconazole has been proved therapeutically effective against a variety of human cancers. This study assessed the effect of itraconazole on the Hedgehog (Hh) pathway and proliferation of human gastric cancer cells.

METHODS

CCK-8 assay and colony formation assay were used to assess the effects of itraconazole on proliferation of gastric cancer cells. The expression of Hh signaling components in gastric cancer cells treated with itraconazole was evaluated by reverse-transcription polymerase chain reaction, immunoblotting and dual luciferase assay. Tumor xenograft models were used to assess the inhibitory effect of itraconazole on the proliferation of gastric cancer cells in vivo.

RESULTS

Itraconazole could remarkably inhibit the proliferation of gastric cancer cells. When in combination with 5-FU, itraconazole significantly reduced the proliferation rate of cancer cells. Furthermore, itraconazole could regulate the G₁-S transition and induce apoptosis of gastric cancer cells. Hh signaling was abnormally activated in human gastric cancer samples. In vitro, studies showed that the expression of glioma-associated zinc finger transcription factor 1 (Gli1) was decreased at both transcriptional and translational levels after treatment with itraconazole. Dual luciferase assay also indicated that itraconazole could inhibit the transcription of Gli1. In vivo studies demonstrated that monotherapy with itraconazole by oral administration could inhibit the growth of xenografts, and that itraconazole could significantly enhance the antitumor efficacy of the chemotherapeutic agent 5-FU.

CONCLUSIONS

Hh signaling is activated in gastric tumor and itraconazole can inhibit the growth of gastric cancer cells by inhibiting Gli1 expression.

CNOT1 cooperates with LMNA to aggravate osteosarcoma tumorigenesis through the Hedgehog signaling pathway

While treatments for childhood osteosarcoma have improved, the overall survival for this common type of bone cancer has not changed for three decades, and thus, new targets for therapeutic development are needed. To identify tumor-related proteins in osteosarcoma, we used isobaric tags in a relative and absolute quantitation proteomic approach to analyze the differentially expressed proteins between osteosarcoma cells and human osteoblastic cells. Through clinical screening and functional evaluation, CCR4-NOT transcription complex subunit 1 (CNOT1) correlated with the growth of osteosarcoma cells. To date, the mechanisms and regulatory roles of CNOT1 in tumors, including osteosarcoma, remain largely elusive. Here, we present evidence that knockdown of CNOT1 inhibits the growth of osteosarcoma in vitro and in vivo. Mechanistically, we observed that CNOT1 interacted with LMNA (lamin A) and functioned as a positive regulator of this intermediate filament protein. The RNA-seq analysis revealed that CNOT1 depletion inhibited the Hedgehog signaling pathway in osteosarcoma cells. A rescue study showed that the decreased growth of osteosarcoma cells and inhibition of the Hedgehog signaling pathway by CNOT1 depletion were reversed by LMNA overexpression, indicating that the activity of CNOT1 was LMNA dependent. Notably, the CNOT1 expression was significantly associated with tumor recurrence, Enneking stage, and poor survival in patients with osteosarcoma. Examination of clinical samples confirmed that CNOT1 expression positively correlated with LMNA protein expression. Taken together, these results suggest that the CNOT1-LMNA-Hedgehog signaling pathway axis exerts an oncogenic role in osteosarcoma progression, which could be a potential target for gene therapy.

Characterization of Hedgehog Acyltransferase Inhibitors Identifies a Small Molecule Probe for Hedgehog Signaling by Cancer Cells

The Sonic Hedgehog (Shh) signaling pathway plays a critical role during embryonic development and cancer progression. N-terminal palmitoylation of Shh by Hedgehog acyltransferase (Hhat) is essential for efficient signaling, raising interest in Hhat as a novel drug target. A recently identified series of dihydrothienopyridines has been proposed to function via this mode of action; however, the lead compound in this series (RUSKI-43) was subsequently shown to possess cytotoxic activity unrelated to canonical Shh signaling. To identify a selective chemical probe for cellular studies, we profiled three RUSKI compounds in orthogonal cell-based assays. We found that RUSKI-43 exhibits off-target cytotoxicity, masking its effect on Hhat-dependent signaling, hence results obtained with this compound in cells should be treated with caution. In contrast, RUSKI-201 showed no off-target cytotoxicity, and quantitative whole-proteome palmitoylation profiling with a bioorthogonal alkyne-palmitate reporter demonstrated specific inhibition of Hhat in cells. RUSKI-201 is the first selective Hhat chemical probe in cells and should be used in future studies of Hhat catalytic function.

Inhibition of casein kinase 2 prevents growth of human osteosarcoma

High-dose chemotherapy and surgical treatment have improved the prognosis of osteosarcoma. However, more than 20% of patients with osteosarcoma still have a poor prognosis. We investigated the expression and function of casein kinase 2 (CK2) in osteosarcoma growth. We then examined the effects of CX-4945, a CK2 inhibitor, on osteosarcoma growth in vitro and in vivo to apply our findings to the clinical setting. We examined the expression of CK2α and CK2β by western blot analysis, and performed WST-1 assays using CK2α and CK2β siRNA or CX-4945. Flow cytometry and western blot analyses were performed to evaluate apoptotic cell death. Xenograft models were used to examine the effect of CX-4945 in vivo. Western blot analysis revealed upregulation of CK2α and CK2β in human osteosarcoma cell lines compared with human osteoblast cells or mesenchymal stem cells. WST assay showed that knockdown of CK2α or CK2β by siRNA inhibited the proliferation of human osteosarcoma cells. Treatment with 3 µM of CX-4945 inhibited osteosarcoma cell proliferation; however, the same concentration of CX-4945 did not affect the proliferation of human mesenchymal stem cells. Additionally, treatment with CX-4945 inhibited the proliferation of human osteosarcoma cells in a dose-dependent manner. Western blot and flow cytometry analyses showed that treatment with CX-4945 promoted apoptotic death of osteosarcoma cells. The xenograft model showed that treatment with CX-4945 significantly prevented osteosarcoma growth in vivo compared with control vehicle treatment. Our findings indicate that CK2 may be an attractive therapeutic target for treating osteosarcoma.

Personalized comprehensive molecular profiling of high risk osteosarcoma: Implications and limitations for precision medicine

Background

Despite advances in molecular medicine over recent decades, there has been little advancement in the treatment of osteosarcoma. We performed comprehensive molecular profiling in two cases of metastatic and chemotherapy-refractory osteosarcoma to guide molecularly targeted therapy.

Patients and Methods

Hybridization capture of >300 cancer-related genes plus introns from 28 genes often rearranged or altered in cancer was applied to >50 ng of DNA extracted from tumor samples from two patients with recurrent, metastatic osteosarcoma. The DNA from each sample was sequenced to high, uniform coverage. Immunohistochemical probes and morphoproteomics analysis were performed, in addition to fluorescence in situ hybridization. All analyses were performed in CLIA-certified laboratories. Molecularly targeted therapy based on the resulting profiles was offered to the patients. Biomedical analytics were performed using QIAGEN's Ingenuity^® Pathway Analysis.

Results

In Patient #1, comprehensive next-generation exome sequencing showed MET amplification, PIK3CA mutation, CCNE1 amplification, and PTPRD mutation. Immunohistochemistry-based morphoproteomic analysis revealed c-Met expression [(p)-c-Met (Tyr1234/1235)] and activation of mTOR/AKT pathway [IGF-1R (Tyr1165/1166), p-mTOR [Ser2448], p-Akt (Ser473)] and expression of SPARC and COX2. Targeted therapy was administered to match the P1K3CA, c-MET, and SPARC and COX2 aberrations with sirolimus+ crizotinib and abraxane+ celecoxib. In Patient #2, aberrations included NF2 loss in exons 2–16, PDGFRα amplification, and TP53 mutation. This patient was enrolled on a clinical trial combining targeted agents temsirolimus, sorafenib and bevacizumab, to match NF2, PDGFRα and TP53 aberrations. Both the patients did not benefit from matched therapy.

Conclusions

Relapsed osteosarcoma is characterized by complex signaling and drug resistance pathways. Comprehensive molecular profiling holds great promise for tailoring personalized therapies for cancer. Methods for such profiling are evolving and need to be refined to better assist clinicians in making treatment decisions based on the large amount of data that results from this type of testing. Further research in this area is warranted.

Hedgehog Pathway in Pediatric Cancers: They're Not Just for Brain Tumors Anymore

The Hedgehog (HH) pathway regulates fundamental processes in embryonic development, including stem cell maintenance, cell differentiation, tissue polarity, and cell proliferation. In the vertebrate pathway, Sonic hedgehog (SHH) binds to Patched1 (PTCH1), which relieves its inhibition of Smoothened (SMO), allowing the GLI family of transcription factors to translocate to the nucleus and activate HH target genes such as GLI1, GLI2, PTCH1, CYCLIN D1, BCL-2, and MYCN. The HH pathway is also an active participant in tumorigenesis. In 1996, loss-of-function mutation in PTCH1 was discovered to be the cause of nevoid basal cell carcinoma syndrome (NBCCS, or Gorlin syndrome), an autosomal dominant disease associated with increased rates of basal cell carcinoma (BCC), medulloblastoma (MB), and rarely, rhabdomyosarcoma. It is now estimated that 100% of sporadic BCC and up to 20% to 30% of MB also harbor activating HH pathway mutations. Together, these discoveries firmly established the linkage between HH pathway activation and cancer development. Intense research has since been focused on further defining the role of the HH pathway in BCC and MB and potential therapeutic strategies to inhibit HH signaling. Early clinical trials of SMO inhibitors have shown promising results in the treatment of adult BCC and SHH-driven MB. More recently, a number of other pediatric cancers have been reported to show HH activity, making these tumors potential candidates for HH inhibitor therapy. To date however, no HH pathway mutations have been identified in other pediatric cancers. This review will describe the HH pathway signaling in development and cancer with a focus on recent evidence for HH pathway activation in central nervous system (CNS) and non-CNS pediatric cancers.

Osteosarcoma: prognosis plateau warrants retinoblastoma pathway targeted therapy

Osteosarcoma (OS) is the most common primary bone cancer in children and adolescents, affecting ~560 young patients in the United States annually. The term OS describes a diverse array of subtypes with varying prognoses, but the majority of tumors are high grade and aggressive. Perhaps because the true etiology of these aggressive tumors remains unknown, advances in OS treatment have reached a discouraging plateau, with only incremental improvements over the past 40 years. Thus, research surrounding the pathogenesis of OS is essential, as it promises to unveil novel therapeutic targets that can attack tumor cells with greater specificity and lower toxicity. Among the candidate molecular targets in OS, the retinoblastoma (RB) pathway demonstrates the highest frequency of inactivation and thus represents a particularly promising avenue for molecular targeted therapy. This review examines the present thinking and practices in OS treatment and specifically highlights the relevance of the RB pathway in osteosarcomagenesis. Through further investigation into RB pathway-related novel therapeutic targets, we believe that a near-term breakthrough in improved OS prognosis is possible.

Targeting the Sonic Hedgehog Signaling Pathway: Review of Smoothened and GLI Inhibitors

The sonic hedgehog (Shh) signaling pathway is a major regulator of cell differentiation, cell proliferation, and tissue polarity. Aberrant activation of the Shh pathway has been shown in a variety of human cancers, including, basal cell carcinoma, malignant gliomas, medulloblastoma, leukemias, and cancers of the breast, lung, pancreas, and prostate. Tumorigenesis, tumor progression and therapeutic response have all been shown to be impacted by the Shh signaling pathway. Downstream effectors of the Shh pathway include smoothened (SMO) and glioma-associated oncogene homolog (GLI) family of zinc finger transcription factors. Both are regarded as important targets for cancer therapeutics. While most efforts have been devoted towards pharmacologically targeting SMO, developing GLI-targeted approach has its merit because of the fact that GLI proteins can be activated by both Shh ligand-dependent and -independent mechanisms. To date, two SMO inhibitors (LDE225/Sonidegib and GDC-0449/Vismodegib) have received FDA approval for treating basal cell carcinoma while many clinical trials are being conducted to evaluate the efficacy of this exciting class of targeted therapy in a variety of cancers. In this review, we provide an overview of the biology of the Shh pathway and then detail the current landscape of the Shh-SMO-GLI pathway inhibitors including those in preclinical studies and clinical trials.

Downregulation of IDH2 exacerbates the malignant progression of osteosarcoma cells via increased NF-κB and MMP-9 activation

Isocitrate dehydrogenase 2 (IDH2) is a mitochondrial NADP-dependent isocitrate dehydrogenase. It is considered to be a novel tumor suppressor in several types of tumors. However, the role and related mechanism of IDH2 in osteosarcoma remain unknown. The expression and significance of IDH2 were investigated by immunohistochemistry in formalin-fixed paraffin sections from 44 osteosarcoma patients. IDH2 was downregulated via lentiviral vector‑mediated RNA interference (RNAi) in the Saos-2 and MG-63 human osteosarcoma cell lines. The effect of IDH2 downregulation on human osteosarcoma was studied in vitro by MTT, flow cytometry and invasion assays. Nuclear factor-κB (NF-κB) and matrix metalloproteinase-9 (MMP-9) assays were also used to study the likely molecular mechanism of IDH2 downregulation on the malignant progression of osteosarcoma cells. The results revealed that the expression of IDH2 was inversely correlated with pathological grade and metastasis in osteosarcoma. IDH2 downregulation promoted a pro-proliferative effect on the Saos-2 and MG-63 osteosarcoma cell lines. IDH2 downregulation accelerated cell cycle progression from S to G2/M phase. The pro-proliferative effect induced by IDH2 downregulation may be ascribed to increased NF-κB activity via IκBα phosphorylation. The invasive activity of osteosarcoma cells was also significantly promoted by IDH2 downregulation and may result from elevated MMP-9 activity. In conclusion, IDH2 downregulation may exacerbate malignant progression via increased NF-κB and MMP-9 activity and may implicate the potential biological importance of IDH2 targeting in osteosarcoma cells. Downregulation of IDH2 exacerbates the malignant progression of osteosarcoma cells via increased NF-κB and MMP-9 activation.

Combination of Hedgehog inhibitors and standard anticancer agents synergistically prevent osteosarcoma growth

High-dose chemotherapy and surgical intervention have improved long-term prognosis for non-metastatic osteosarcoma to 50-80%. However, metastatic osteosarcoma exhibits resistance to standard chemotherapy. We and others have investigated the function of Hedgehog pathway in osteosarcoma. To apply our previous findings in clinical settings, we examined the effects of Hedgehog inhibitors including arsenic trioxide (ATO) and vismodegib combined with standard anticancer agents. We performed WST-1 assays using ATO, cisplatin (CDDP), ifosfamide (IFO), doxorubicin (DOX), and vismodegib. Combination-index (CI) was used to examine synergism using CalcuSyn software. Xenograft models were used to examine the synergism in vivo. WST-1 assays showed that 143B and Saos2 cell proliferation was inhibited by ATO combined with CDDP, IFO, DOX, and vismodegib. Combination of ATO and CDDP, IFO, DOX or vismodegib was synergistic when the two compounds were used on proliferating 143B and Saos2 human osteosarcoma cells. An osteosarcoma xenograft model showed that treatment with ATO and CDDP, IFO, or vismodegib significantly prevented osteosarcoma growth in vivo compared with vehicle treatment. Our findings indicate that combination of Hedgehog pathway inhibitors and standard FDA-approved anticancer agents with established safety for human use may be an attractive therapeutic method for treating osteosarcoma.

Molecular pathways: novel approaches for improved therapeutic targeting of Hedgehog signaling in cancer stem cells

The Hedgehog (Hh) signaling pathway is critical for embryonic development. In adult tissues, Hh signaling is relatively quiescent with the exception of roles in tissue maintenance and repair. Aberrant activation of Hh signaling is implicated in multiple aspects of transformation, including the maintenance of the cancer stem cell (CSC) phenotype. Preclinical studies indicate that CSCs from many tumor types are sensitive to Hh pathway inhibition and that Hh-targeted therapeutics block many aspects of transformation attributed to CSCs, including drug resistance, relapse, and metastasis. However, to date, Hh inhibitors, specifically those targeting Smoothened [such as vismodegib, BMS-833923, saridegib (IPI-926), sonidegib/erismodegib (LDE225), PF-04449913, LY2940680, LEQ 506, and TAK-441], have demonstrated good efficacy as monotherapy in patients with basal cell carcinoma and medulloblastoma, but have shown limited activity in other tumor types. This lack of success is likely due to many factors, including a lack of patient stratification in early trials, cross-talk between Hh and other oncogenic signaling pathways that can modulate therapeutic response, and a limited knowledge of Hh pathway activation mechanisms in CSCs from most tumor types. Here, we discuss Hh signaling mechanisms in the context of human cancer, particularly in the maintenance of the CSC phenotype, and consider new therapeutic strategies that hold the potential to expand considerably the scope and therapeutic efficacy of Hh-directed anticancer therapy.

Resveratrol and curcumin synergistically induces apoptosis in cigarette smoke condensate transformed breast epithelial cells through a p21(Waf1/Cip1) mediated inhibition of Hh-Gli signaling

Combination therapy using two or more small molecule inhibitors of aberrant signaling cascade in aggressive breast cancers is a promising therapeutic strategy over traditional monotherapeutic approaches. Here, we have studied the synergistic mechanism of resveratrol and curcumin induced apoptosis using in vitro (cigarette smoke condensate mediated transformed breast epithelial cell, MCF-10A-Tr) and in vivo (tumor xenograft mice) model system. Resveratrol exposure increased the intracellular uptake of curcumin in a dose dependent manner and caused apoptosis in MCF-10A-Tr cells. Approximately, ten fold lower IC50 value was noted in cells treated with the combination of resveratrol (3μM) and curcumin (3μM) in comparison to 30μM of resveratrol or curcumin alone. Resveratrol+curcumin combination caused apoptosis by increasing Bax/Bcl-xL ratio, Cytochrome C release, cleaved product of PARP and caspase 3 in cells. Interestingly, this combination unaltered the protein expressions of WNT-TCF and Notch signaling components, β-catenin and cleaved notch-1 val1744, respectively. Furthermore, the combination also significantly decreased the intermediates of Hedgehog-Gli cascade including SMO, SHH, Gli-1, c-MYC, Cyclin-D1, etc. and increased the level of p21(Waf/Cip1) in vitro and in vivo. A significant reduction of Gli- promoter activity was noted in combinational drug treated cells in comparison to individual drug treatment. Un-alteration of the expressions of the above proteins and Gli1 promoter activity in p21(Waf/Cip1) knockout cells suggests this combination caused apoptosis through p21(Waf/Cip1). Thus, our findings revealed resveratrol and curcumin synergistically caused apoptosis in cigarette smoke induced breast cancer cells through p2(Waf/Cip1) mediated inhibition of Hedgehog-Gli cascade.

Matrix metalloproteinase 9 expression and survival of patients with osteosarcoma: a meta-analysis

Several studies have evaluated the effect of matrix metalloproteinase-9 (MMP-9) expression on the overall survival of patients with osteosarcoma, but the results remain conflicting. To examine the prognostic significance of MMP-9 expression in osteosarcoma risk, we conducted this meta-analysis to systematically review the published studies. We searched the commonly used electronic databases updated to September 2013 for relevant studies which evaluated the correction between MMP-9 expression and survival of patients with osteosarcoma. Overall, a total of eight studies including 437 cases were screened out. No significant heterogeneity was observed between studies. The MMP-9 was expressed in 73.9% (323/437) of cases, and the results showed that MMP-9 expression was associated with increased mortality rate of osteosarcoma during the follow-up (risk ratio = 2.79, 95% confidence interval, CI = 1.96-3.97, P < 0.00001). By ethnicity analysis, a significant correction was also found between MMP-9 expression and osteosarcoma risk among Asian and non-Asian population (P < 0.001), indicating that MMP-9 was an indicator of prognosis of osteosarcoma. In conclusion, this meta-analysis indicated that MMP-9 expression might be a biomarker of poor prognosis for patients with osteosarcoma. However, the prognostic value of MMP-9 on survival of osteosarcoma patients still needs further large-scale trials to be clarified.

Genomic instability of osteosarcoma cell lines in culture: impact on the prediction of metastasis relevant genes

Background

Osteosarcoma is a rare but highly malignant cancer of the bone. As a consequence, the number of established cell lines used for experimental in vitro and in vivo osteosarcoma research is limited and the value of these cell lines relies on their stability during culture. Here we investigated the stability in gene expression by microarray analysis and array genomic hybridization of three low metastatic cell lines and derivatives thereof with increased metastatic potential using cells of different passages.

Principal Findings

The osteosarcoma cell lines showed altered gene expression during in vitro culture, and it was more pronounced in two metastatic cell lines compared to the respective parental cells. Chromosomal instability contributed in part to the altered gene expression in SAOS and LM5 cells with low and high metastatic potential. To identify metastasis-relevant genes in a background of passage-dependent altered gene expression, genes involved in "Pathways in cancer" that were consistently regulated under all passage comparisons were evaluated. Genes belonging to "Hedgehog signaling pathway" and "Wnt signaling pathway" were significantly up-regulated, and IHH, WNT10B and TCF7 were found up-regulated in all three metastatic compared to the parental cell lines.

Conclusions

Considerable instability during culture in terms of gene expression and chromosomal aberrations was observed in osteosarcoma cell lines. The use of cells from different passages and a search for genes consistently regulated in early and late passages allows the analysis of metastasis-relevant genes despite the observed instability in gene expression in osteosarcoma cell lines during culture.

Hedgehog signaling inhibitors as anti-cancer agents in osteosarcoma

Osteosarcoma is a rare type of cancer associated with a poor clinical outcome. Even though the pathologic characteristics of OS are well established, much remains to be understood, particularly at the molecular signaling level. The molecular mechanisms of osteosarcoma progression and metastases have not yet been fully elucidated and several evolutionary signaling pathways have been found to be linked with osteosarcoma pathogenesis, especially the hedgehog signaling (Hh) pathway. The present review will outline the importance and targeting the hedgehog signaling (Hh) pathway in osteosarcoma tumor biology. Available data also suggest that aberrant Hh signaling has pro-migratory effects and leads to the development of osteoblastic osteosarcoma. Activation of Hh signaling has been observed in osteosarcoma cell lines and also in primary human osteosarcoma specimens. Emerging data suggests that interference with Hh signal transduction by inhibitors may reduce osteosarcoma cell proliferation and tumor growth thereby preventing osteosarcomagenesis. From this perspective, we outline the current state of Hh pathway inhibitors in osteosarcoma. In summary, targeting Hh signaling by inhibitors promise to increase the efficacy of osteosarcoma treatment and improve patient outcome.