Activation of the hedgehog pathway confers a poor prognosis in embryonal and fusion gene-negative alveolar rhabdomyosarcoma

We need to talk-how muscle stem cells communicate

Skeletal muscle is one of the tissues with the highest ability to regenerate, a finely controlled process which is critically depending on muscle stem cells. Muscle stem cell functionality depends on intrinsic signaling pathways and interaction with their immediate niche. Upon injury quiescent muscle stem cells get activated, proliferate and fuse to form new myofibers, a process involving the interaction of multiple cell types in regenerating skeletal muscle. Receptors in muscle stem cells receive the respective signals through direct cell-cell interaction, signaling via secreted factors or cell-matrix interactions thereby regulating responses of muscle stem cells to external stimuli. Here, we discuss how muscle stem cells interact with their immediate niche focusing on how this controls their quiescence, activation and self-renewal and how these processes are altered in age and disease.

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.

Rhabdomyosarcoma: Current Therapy, Challenges, and Future Approaches to Treatment Strategies

Rhabdomyosarcoma is a rare cancer arising in skeletal muscle that typically impacts children and young adults. It is a worldwide challenge in child health as treatment outcomes for metastatic and recurrent disease still pose a major concern for both basic and clinical scientists. The treatment strategies for rhabdomyosarcoma include multi-agent chemotherapies after surgical resection with or without ionization radiotherapy. In this comprehensive review, we first provide a detailed clinical understanding of rhabdomyosarcoma including its classification and subtypes, diagnosis, and treatment strategies. Later, we focus on chemotherapy strategies for this childhood sarcoma and discuss the impact of three mechanisms that are involved in the chemotherapy response including apoptosis, macro-autophagy, and the unfolded protein response. Finally, we discuss in vivo mouse and zebrafish models and in vitro three-dimensional bioengineering models of rhabdomyosarcoma to screen future therapeutic approaches and promote muscle regeneration.

Identify potential driver genes for PAX-FOXO1 fusion-negative rhabdomyosarcoma through frequent gene co-expression network mining

Background

Rhabdomyosarcoma (RMS) is a soft tissue sarcoma usually originated from skeletal muscle. Currently, RMS classification based on PAX-FOXO1 fusion is widely adopted. However, compared to relatively clear understanding of the tumorigenesis in the fusion-positive RMS, little is known for that in fusion-negative RMS (FN-RMS).

Methods

We explored the molecular mechanisms and the driver genes of FN-RMS through frequent gene co-expression network mining (fGCN), differential copy number (CN) and differential expression analyses on multiple RMS transcriptomic datasets.

Results

We obtained 50 fGCN modules, among which five are differentially expressed between different fusion status. A closer look showed 23% of Module 2 genes are concentrated on several cytobands of chromosome 8. Upstream regulators such as MYC, YAP1, TWIST1 were identified for the fGCN modules. Using in a separate dataset we confirmed that, comparing to FP-RMS, 59 Module 2 genes show consistent CN amplification and mRNA overexpression, among which 28 are on the identified chr8 cytobands. Such CN amplification and nearby MYC (also resides on one of the above cytobands) and other upstream regulators (YAP1, TWIST1) may work together to drive FN-RMS tumorigenesis and progression. Up to 43.1% downstream targets of Yap1 and 45.8% of the targets of Myc are differentially expressed in FN-RMS vs. normal comparisons, which also confirmed the driving force of these regulators.

Discussion

We discovered that copy number amplification of specific cytobands on chr8 and the upstream regulators MYC, YAP1 and TWIST1 work together to affect the downstream gene co-expression and promote FN-RMS tumorigenesis and progression. Our findings provide new insights for FN-RMS tumorigenesis and offer promising targets for precision therapy. Experimental investigation about the functions of identified potential drivers in FN-RMS are in progress.

Targeting the Hedgehog Pathway in Rhabdomyosarcoma

Aberrant activation of the Hedgehog (Hh) signalling pathway is known to play an oncogenic role in a wide range of cancers; in the particular case of rhabdomyosarcoma, this pathway has been demonstrated to be an important player for both oncogenesis and cancer progression. In this review, after a brief description of the pathway and the characteristics of its molecular components, we describe, in detail, the main activation mechanisms that have been found in cancer, including ligand-dependent, ligand-independent and non-canonical activation. In this context, the most studied inhibitors, i.e., SMO inhibitors, have shown encouraging results for the treatment of basal cell carcinoma and medulloblastoma, both tumour types often associated with mutations that lead to the activation of the pathway. Conversely, SMO inhibitors have not fulfilled expectations in tumours-among them sarcomas-mostly associated with ligand-dependent Hh pathway activation. Despite the controversy existing regarding the results obtained with SMO inhibitors in these types of tumours, several compounds have been (or are currently being) evaluated in sarcoma patients. Finally, we discuss some of the reasons that could explain why, in some cases, encouraging preclinical data turned into disappointing results in the clinical setting.

Sterol regulation of developmental and oncogenic Hedgehog signaling

The Hedgehog (Hh) family of lipid-modified signaling proteins directs embryonic tissue patterning and postembryonic tissue homeostasis, and dysregulated Hh signaling drives familial and sporadic cancers. Hh ligands bind to and inhibit the tumor suppressor Patched and allow the oncoprotein Smoothened (SMO) to accumulate in cilia, which in turn activates the GLI family of transcription factors. Recent work has demonstrated that endogenous cholesterol and oxidized cholesterol derivatives (oxysterols) bind and modulate SMO activity. Here we discuss the myriad sterols that activate or inhibit the Hh pathway, with emphasis on endogenous 24(S),25-epoxycholesterol and 3β,5α-dihydroxycholest-7-en-6-one, and propose models of sterol regulation of SMO. Synthetic inhibitors of SMO have long been the focus of drug development efforts. Here, we discuss the possible utility of steroidal SMO ligands or inhibitors of enzymes involved in sterol metabolism as cancer therapeutics.

Role of aberrant Sonic hedgehog signaling pathway in cancers and developmental anomalies

Development is a sophisticated process maintained by various signal transduction pathways, including the Hedgehog (Hh) pathway. Several important functions are executed by the Hh signaling cascade such as organogenesis, tissue regeneration, and tissue homeostasis, among various others. Considering the multiple functions carried out by this pathway, any mutation causing aberrant Hh signaling may lead to myriad developmental abnormalities besides cancers. In the present review article, we explored a wide range of diseases caused by aberrant Hh signaling, including developmental defects and cancers. Finally, we concluded this mini-review with various treatment strategies for Hh-induced diseases.

Genetic Characterization, Current Model Systems and Prognostic Stratification in PAX Fusion-Negative vs. PAX Fusion-Positive Rhabdomyosarcoma

Rhabdomyosarcoma (RMS) is the most common soft tissue sarcoma in children and adolescents and accounts for approximately 2% of soft tissue sarcomas in adults. It is subcategorized into distinct subtypes based on histological features and fusion status (PAX-FOXO1/VGLL2/NCOA2). Despite advances in our understanding of the pathobiological and molecular landscape of RMS, the prognosis of these tumors has not significantly improved in recent years. Developing a better understanding of genetic abnormalities and risk stratification beyond the fusion status are crucial to developing better therapeutic strategies. Herein, we aim to highlight the genetic pathways/abnormalities involved, specifically in fusion-negative RMS, assess the currently available model systems to study RMS pathogenesis, and discuss available prognostic factors as well as their importance for risk stratification to achieve optimal therapeutic management.

Rhabdomyosarcoma: How Advanced Molecular Methods Are Shaping the Diagnostic and Therapeutic Paradigm

For the past 40 years, progress in rhabdomyosarcoma (RMS) has been focused on understanding its molecular basis and characterizing the mutations that drive its tumorigenesis and progression. Genetic predisposition to RMS has allowed discovery of key genetic pathways and driver mutations. Subclassification of RMS into embryonal (ERMS) and alveolar (ARMS) subtypes has shifted from histology to PAX-FOXO1 fusion status, and new driver mutations have been found in spindle cell RMS. Comprehensive molecular profiling leveraging genome-scale next-generation sequencing (NGS) indicates that the RAS/RAF/PI3K axis is mutated in the majority of ERMS and modulated by downstream effects of PAX-FOXO1 fusions in ARMS. Because of the continued poor outcome of high-risk RMS, a variety of molecular targets have been or are now being tested in current or recent therapy trials. New techniques such as single cell sequencing, spatial multi-omics, and CRISPR/Cas9 genome editing offer potential for further discovery, but a need for clinically annotated specimens persists.

Progression and Differentiation of Alveolar Rhabdomyosarcoma Is Regulated by PAX7 Transcription Factor-Significance of Tumor Subclones

Rhabdomyosarcoma (RMS), is the most frequent soft tissue tumor in children that originates from disturbances in differentiation process. Mechanisms leading to the development of RMS are still poorly understood. Therefore, by analysis of two RMS RH30 cell line subclones, one subclone PAX7 negative, while the second one PAX7 positive, and comparison with other RMS cell lines we aimed at identifying new mechanisms crucial for RMS progression. RH30 subclones were characterized by the same STR profile, but different morphology, rate of proliferation, migration activity and chemotactic abilities in vitro, as well as differences in tumor morphology and growth in vivo. Our analysis indicated a different level of expression of adhesion molecules (e.g., from VLA and ICAM families), myogenic microRNAs, such as miR-206 and transcription factors, such as MYOD, MYOG, SIX1, and ID. Silencing of PAX7 transcription factor with siRNA confirmed the crucial role of PAX7 transcription factor in proliferation, differentiation and migration of RMS cells. To conclude, our results suggest that tumor cell lines with the same STR profile can produce subclones that differ in many features and indicate crucial roles of PAX7 and ID proteins in the development of RMS.

Context-dependent modulation of aggressiveness of pediatric tumors by individual oncogenic RAS isoforms

A prototypic pediatric cancer that frequently shows activation of RAS signaling is embryonal rhabdomyosarcoma (ERMS). ERMS also show aberrant Hedgehog (HH)/GLI signaling activity and can be driven by germline mutations in this pathway. We show, that in ERMS cell lines derived from sporadic tumors i.e. from tumors not caused by an inherited genetic variant, HH/GLI signaling plays a subordinate role, because oncogenic mutations in HRAS, KRAS, or NRAS (collectively named oncRAS) inhibit the main HH target GLI1 via the MEK/ERK-axis, but simultaneously increase proliferation and tumorigenicity. oncRAS also modulate expression of stem cell markers in an isoform- and context-dependent manner. In Hh-driven murine ERMS that are caused by a Patched mutation, oncHRAS and mainly oncKRAS accelerate tumor development, whereas oncNRAS induces a more differentiated phenotype. These features occur when the oncRAS mutations are induced at the ERMS precursor stage, but not when induced in already established tumors. Moreover, in contrast to what is seen in human cell lines, oncRAS mutations do not alter Hh signaling activity and marginally affect expression of stem cell markers. Together, all three oncRAS mutations seem to be advantageous for ERMS cell lines despite inhibition of HH signaling and isoform-specific modulation of stem cell markers. In contrast, oncRAS mutations do not inhibit Hh-signaling in Hh-driven ERMS. In this model, oncRAS mutations seem to be advantageous for specific ERMS populations that occur within a specific time window during ERMS development. In addition, this window may be different for individual oncRAS isoforms, at least in the mouse.

MTOR promotes basal cell carcinoma growth through atypical PKC

Advanced basal cell carcinomas (BCCs) are driven by the Hedgehog (HH) pathway and often possess inherent resistance to SMO inhibitors. Identifying and targeting pathways that bypass SMO could provide alternative treatments for patients with advanced or metastatic BCC. Here, we use a combination of RNA-sequencing analysis of advanced human BCC tumor-normal pairs and immunostaining of human and mouse BCC samples to identify an MTOR expression signature in BCC. Pharmacological inhibition of MTOR activity in BCC cells significantly reduces cell proliferation without affecting HH signalling. Similarly, treatment of the Ptch1 ^fl/fl ; Gli1-Cre^ERT2 mouse BCC tumor model with everolimus reduces tumor growth. aPKC, a downstream target of MTOR, shows reduced activity, suggesting that MTOR promotes tumor growth by activating aPKC and demonstrating that suppressing MTOR could be a promising target for BCC patients.

MYBPC2 and MYL1 as Significant Gene Markers for Rhabdomyosarcoma

BACKGROUND

Rhabdomyosarcoma is the most common soft tissue tumor in children. Rhabdomyosarcoma commonly results in pain and bleeding caused by tumor compression and is prone to early metastasis and recurrence, which can seriously affect the therapeutic outcomes and long-term prognosis. Up to 37.7% of rhabdomyosarcomas may metastasize. Therefore, the molecular mechanisms underlying rhabdomyosarcoma must be explored to identify an effective target for its early diagnosis and specific treatment.

METHODS

A dataset of 18 rhabdomyosarcoma tissue samples and 6 healthy skeletal muscle samples was downloaded. Differentially expressed genes between rhabdomyosarcoma and healthy tissue samples were identified by GEO2R. Kyoto Encyclopedia of Genes and Genomes and gene ontology pathway enrichment analyses were performed. A protein-protein interaction network was constructed, and hub genes were identified. Expression and survival analyses of hub genes were performed. Additionally, 30 patients with rhabdomyosarcoma were recruited, and overall survival information and samples were collected. Reverse transcription quantitative real-time polymerase chain reaction assays were performed to verify the expression of MYBPC2 and MYL1 in rhabdomyosarcoma tumor tissues. The Kaplan-Meier method was used to explore overall survival based on our clinical data.

RESULTS

In total, 164 genes were up-regulated and 394 were down-regulated in rhabdomyosarcoma tumor tissues. Gene ontology analysis revealed that variations were predominantly enriched in the cell cycle, muscle contraction, muscle system processes, cytoskeleton, nucleotide binding, and cytoskeletal protein binding. The protein-protein interaction network revealed 3274 edges, and 441 nodes were constructed. Ten hub genes were identified; of these, MYBPC2 and MYL1 were significantly up-regulated in rhabdomyosarcoma. Compared with the healthy group, patients with rhabdomyosarcoma exhibiting high expression of MYBPC2 and MYL1 exhibited significantly worse overall survival.

CONCLUSIONS

We found differentially expressed genes between rhabdomyosarcoma and healthy tissue samples. MYBPC2 and MYL1 may be involved in the pathogenesis of rhabdomyosarcoma and therefore deserve further exploration.

Signaling pathways in Rhabdomyosarcoma invasion and metastasis

Rhabdomyosarcoma (RMS) is an aggressive childhood mesenchymal tumor with two major molecular and histopathologic subtypes: fusion-positive (FP)RMS, characterized by the PAX3-FOXO1 fusion protein and largely of alveolar histology, and fusion-negative (FN)RMS, the majority of which exhibit embryonal tumor histology. Metastatic disease continues to be associated with poor overall survival despite intensive treatment strategies. Studies on RMS biology have provided some insight into autocrine as well as paracrine signaling pathways that contribute to invasion and metastatic propensity. Such pathways include those driven by the PAX3-FOXO1 fusion oncoprotein in FPRMS and signaling pathways such as IGF/RAS/MEK/ERK, PI3K/AKT/mTOR, cMET, FGFR4, and PDGFR in both FP and FNRMS. In addition, specific cytoskeletal proteins, G protein coupled receptors, Hedgehog, Notch, Wnt, Hippo, and p53 pathways play a role, as do specific microRNA. Paracrine factors, including secreted proteins and RMS-derived exosomes that carry cargo of protein and miRNA, have also recently emerged as potentially important players in RMS biology. This review summarizes the known factors contributing to RMS invasion and metastasis and their implications on identifying targets for treatment and a better understanding of metastatic RMS.

Biallelic PTCH1 Inactivation Is a Dominant Genomic Change in Sporadic Keratocystic Odontogenic Tumors

Keratocystic odontogenic tumors (KCOTs) are locally aggressive odontogenic neoplasms with recurrence rates of up to 60%. Approximately 5% of KCOTs are associated with nevoid basal cell carcinoma (Gorlin) syndrome and 90% of these show genomic inactivation of the PTCH1 gene encoding Patched 1. Sporadic KCOTs reportedly have PTCH1 mutations in 30% of cases, but previous genomic analyses have been limited by low tumor DNA yield. The aim of this study was to identify recurrent genomic aberrations in sporadic KCOTs using a next-generation sequencing panel with complete exonic coverage of sonic hedgehog (SHH) pathway members PTCH1, SMO, SUFU, GLI1, and GLI2. Included were 44 sporadic KCOTs from 23 female and 21 male patients with a median age of 50 years (range, 10 to 82 y) and located in the mandible (N=33) or maxilla (N=11). Sequencing identified PTCH1 inactivating mutations in 41/44 (93%) cases, with biallelic inactivation in 35 (80%) cases; 9q copy neutral loss of heterozygosity targeting the PTCH1 locus was identified in 15 (34%) cases. No genomic aberrations were identified in other sequenced SHH pathway members. In summary, we demonstrate PTCH1 inactivating mutations in 93% of sporadic KCOTs, indicating that SHH pathway alterations are a near-universal event in these benign but locally aggressive neoplasms. The high frequency of complete PTCH1 loss of function may provide a rational target for SHH pathway inhibitors to be explored in future studies.

Up-regulation of GLI1 in vincristine-resistant rhabdomyosarcoma and Ewing sarcoma

Background

The clinical significance of GLI1 expression either through canonical Hedgehog signal transduction or through non-canonical mechanisms in rhabdomyosarcoma (RMS) or Ewing sarcoma (EWS) is incompletely understood. We tested a role for Hedgehog (HH) signal transduction and GL11 expression in development of vincristine (VCR) resistance in RMS and EWS.

Methods

We characterized baseline expression and activity of HH pathway components in 5 RMS (RD, Rh18, Ruch-2, Rh30, and Rh41) and 5 EWS (CHLA9, CHLA10, TC32, CHLA258, and TC71) cell lines. We then established VCR-resistant RMS and EWS cell lines by exposing cells to serially increasing concentrations of VCR and determining the IC₅₀. We defined resistance as a ≥ 30-fold increase in IC₅₀ compared with parental cells. We determined changes in gene expression in the VCR-resistant cells compared with parental cells using an 86-gene cancer drug resistance array that included GLI1 and tested the effect of GLI1 inhibition with GANT61 or GLI1 siRNA on VCR resistance.

Results

We found evidence for HH pathway activity and GLI1 expression in RMS and EWS cell lines at baseline, and evidence that GLI1 contributes to survival and proliferation of these sarcoma cells. We were able to establish 4 VCR-resistant cell lines (Ruch-2VR, Rh30VR, Rh41VR, and TC71VR). GLI1 was significantly up-regulated in the Rh30VR, Rh41VR, and TC71VR cells. The only other gene in the drug resistance panel that was significantly up-regulated in each of these VCR-resistant cell lines compared with their corresponding parental cells was the GLI1 direct target and multidrug resistance gene, ATP-binding cassette sub-family B member 1 (MDR1). We established major vault protein (MVP), which was up-regulated in both vincristine-resistant alveolar RMS cell lines (Rh30VR and Rh41VR), as another direct target of GLI1 during development of drug resistance. Treatment of the VCR-resistant cell lines with the small molecule inhibitor GANT61 or GLI1 siRNA together with VCR significantly decreased cell viability at doses that did not reduce viability individually.

Conclusions

These experiments demonstrate that GLI1 up-regulation contributes to VCR resistance in RMS and EWS cell lines and suggest that targeting GLI1 may benefit patients with RMS or EWS by reducing multidrug resistance.

Co-inhibition of BET proteins and PI3Kα triggers mitochondrial apoptosis in rhabdomyosarcoma cells

Remodeling transcription by targeting bromodomain and extraterminal (BET) proteins has emerged as promising anticancer strategy. Here, we identify a novel synergistic interaction of the BET inhibitor JQ1 with the PI3Kα-specific inhibitor BYL719 to trigger mitochondrial apoptosis and to suppress tumor growth in models of rhabdomyosarcoma (RMS). RNA-Seq revealed that JQ1/BYL719 co-treatment shifts the overall balance of BCL-2 family gene expression towards apoptosis and upregulates expression of BMF, BCL2L11 (BIM), and PMAIP1 (NOXA) while downregulating BCL2L1 (BCL-xL). These changes were confirmed by qRT-PCR and western blot analysis. Ingenuity pathway analysis (IPA) of RNA-Seq data followed by validation qRT-PCR and western blot identified MYC and FOXO3a as potential transcription factors (TFs) upstream of the observed gene expression pattern. Immunoprecipitation (IP) studies showed that JQ1/BYL719-stimulated increase in BIM expression enhances the neutralization of antiapoptotic BCL-2, BCL-xL, and MCL-1. This promotes the activation of BAK and BAX and caspase-dependent apoptosis, as (1) individual silencing of BMF, BIM, NOXA, BAK, or BAX, (2) overexpression of BCL-2 or MCL-1 or (3) the caspase inhibitor N-Benzyloxycarbonyl-Val-Ala-Asp(O-Me) fluoromethylketone (zVAD.fmk) all rescue JQ1/BYL719-induced cell death. In conclusion, co-inhibition of BET proteins and PI3Kα cooperatively induces mitochondrial apoptosis by proapoptotic re-balancing of BCL-2 family proteins. This discovery opens exciting perspectives for therapeutic exploitation of BET inhibitors in RMS.

Targeting cancer stem cell pathways for cancer therapy

Since cancer stem cells (CSCs) were first identified in leukemia in 1994, they have been considered promising therapeutic targets for cancer therapy. These cells have self-renewal capacity and differentiation potential and contribute to multiple tumor malignancies, such as recurrence, metastasis, heterogeneity, multidrug resistance, and radiation resistance. The biological activities of CSCs are regulated by several pluripotent transcription factors, such as OCT4, Sox2, Nanog, KLF4, and MYC. In addition, many intracellular signaling pathways, such as Wnt, NF-κB (nuclear factor-κB), Notch, Hedgehog, JAK-STAT (Janus kinase/signal transducers and activators of transcription), PI3K/AKT/mTOR (phosphoinositide 3-kinase/AKT/mammalian target of rapamycin), TGF (transforming growth factor)/SMAD, and PPAR (peroxisome proliferator-activated receptor), as well as extracellular factors, such as vascular niches, hypoxia, tumor-associated macrophages, cancer-associated fibroblasts, cancer-associated mesenchymal stem cells, extracellular matrix, and exosomes, have been shown to be very important regulators of CSCs. Molecules, vaccines, antibodies, and CAR-T (chimeric antigen receptor T cell) cells have been developed to specifically target CSCs, and some of these factors are already undergoing clinical trials. This review summarizes the characterization and identification of CSCs, depicts major factors and pathways that regulate CSC development, and discusses potential targeted therapy for CSCs.

Current and Future Treatment Strategies for Rhabdomyosarcoma

Rhabdomyosarcoma (RMS) is the most common soft tissue sarcoma in children, and can be subcategorized histologically and/or based on PAX-FOXO1 fusion gene status. Over the last four decades, there have been no significant improvements in clinical outcomes for advanced and metastatic RMS patients, underscoring a need for new treatment options for these groups. Despite significant advancements in our understanding of the genomic landscape and underlying biological mechanisms governing RMS that have informed the identification of novel therapeutic targets, development of these therapies in clinical trials has lagged far behind. In this review, we summarize the current frontline multi-modality therapy for RMS according to pediatric protocols, highlight emerging targeted therapies and immunotherapies identified by preclinical studies, and discuss early clinical trial data and the implications they hold for future clinical development.

IL-24 Inhibits Lung Cancer Growth by Suppressing GLI1 and Inducing DNA Damage

Aberrant expression of GLI1 is responsible for aggressive tumor behavior and survival due to its effects on the DNA damage response (DDR). We investigated whether interleukin (IL)-24, a tumor suppressor, inhibits GLI1 and the associated DDR pathway in human NSCLCs. IL-24 treatment reduces mRNA and protein expression of GLI1 in lung tumor cells, but not in normal cells. GLI1 reporter assay and mRNA studies demonstrated that IL-24 regulates GLI1 at the post-transcriptional level by favoring mRNA degradation. Associated with GLI1 inhibition was marked suppression of the ATM-mediated DDR pathway resulting in increased DNA damage, as evidenced by γ-H2AX foci and Comet assay. Furthermore, attenuation of GLI1-associated DDR by IL-24 increased caspase-3 and PARP activity, resulting in cancer cell apoptosis. GLI1 inhibition and overexpression confirmed that IL-24-mediated anti-tumor effects involved the GLI-dependent pathway. Finally, we observed that IL-24-mediated alteration in GLI1 is independent of the canonical hedgehog-signaling pathway. Our study provides evidence that IL-24 treatment induces DNA damage, and reduces GLI1 expression and offers an opportunity for testing IL-24-based therapy for inhibiting GLI1 in lung cancer.

Concomitant targeting of Hedgehog signaling and MCL-1 synergistically induces cell death in Hedgehog-driven cancer cells

In the present study, we show that concomitant inhibition of Hedgehog (HH) signaling by the glioma-associated oncogene homolog1 (GLI1)-targeting agent GANT61 and the antiapoptotic BCL-2 protein family member MCL-1 by A-1210477 synergistically induces cell death in HH-driven cancers, i.e. rhabdomyosarcoma (RMS) and medulloblastoma (MB) cells. Combined genetic and pharmacological inhibition emphasized that co-treatment of GANT61 and A-1210477 indeed relies on inhibition of GLI1 (by GANT61) and MCL-1 (by A-1210477). Mechanistic studies revealed that A-1210477 triggers the release of BIM from MCL-1 and its shuttling to BCL-x_L and BCL-2. Indeed, BIM proved to be required for GANT61/A-1210477-induced cell death, as genetic silencing of BIM using siRNA significantly rescues cell death upon GANT61/A-1210477 co-treatment. Similarly, genetic silencing of NOXA results in a significant reduction of GANT61/A-1210477-mediated cell death. Also, overexpression of MCL-1 or BCL-2 significantly protects RMS cells from GANT61/A-1210477-triggered cell death. Addition of the pan-caspase inhibitor zVAD.fmk significantly decreases GANT61/A-1210477-stimulated cell demise, indicating apoptotic cell death. In conclusion, GANT61 and A-1210477 synergize to engage mitochondrial apoptosis. These findings provide the rationale for further evaluation of dual inhibition of HH signaling and MCL-1 in HH-driven cancers.

Genetics, epigenetics and redox homeostasis in rhabdomyosarcoma: Emerging targets and therapeutics

Rhabdomyosarcoma (RMS) is the most common soft tissue sarcoma accounting for 5-8% of malignant tumours in children and adolescents. Children with high risk disease have poor prognosis. Anti-RMS therapies include surgery, radiation and combination chemotherapy. While these strategies improved survival rates, they have plateaued since 1990s as drugs that target differentiation and self-renewal of tumours cells have not been identified. Moreover, prevailing treatments are aggressive with drug resistance and metastasis causing failure of several treatment regimes. Significant advances have been made recently in understanding the genetic and epigenetic landscape in RMS. These studies have identified novel diagnostic and prognostic markers and opened new avenues for treatment. An important target identified in high throughput drug screening studies is reactive oxygen species (ROS). Indeed, many drugs in clinical trials for RMS impact tumour progression through ROS. In light of such emerging evidence, we discuss recent findings highlighting key pathways, epigenetic alterations and their impacts on ROS that form the basis of developing novel molecularly targeted therapies in RMS. Such targeted therapies in combination with conventional therapy could reduce adverse side effects in young survivors and lead to a decline in long-term morbidity.

Structural optimization on a virtual screening hit of smoothened receptor

The Hedgehog (Hh) pathway plays a critical role during embryonic development by controlling cell patterning, growth and migration. In adults, the function of Hh pathway is curtailed to tissue repair and maintenance. Aberrant reactivation of Hh signaling has been linked to tumorigenesis in various cancers, such as basal cell carcinoma (BCC) and medulloblastoma. The Smoothened (Smo) receptor, a key component of the Hh pathway which is central to the signaling transduction, has emerged as an attractive therapeutic target for the treatment of human cancers. Taking advantage of the availability of several crystal structures of Smo in complex with different antagonists, we have previously conducted a molecular docking-based virtual screening to identify several compounds which exhibited significant inhibitory activity against the Hh pathway activation (IC₅₀ < 10 μM) in a Gli-responsive element (GRE) reporter gene assay. The most potent compound (ChemDiv ID C794-1677: 47 nM) showed comparable Hh signaling inhibition to the marketed drug vismodegib (46 nM). Herein, we report our structural optimization based on the virtual screening hit C794-1677. Our efforts are aimed to improve potency, decrease cLogP, and remove potentially metabolic labile/toxic pyrrole and aniline functionalities presented in C794-1677. The optimization led to the identification of numerous potent compounds exemplified by 25 (7.1 nM), which was 7 folds more potent compared with vismodegib. In addition, 25 was much less lipophilic compared with C794-1677 and devoid of the potentially metabolic labile/toxic pyrrole and aniline functional groups. Furthermore, 25 exhibited promising efficacy in inhibiting Gli1 mRNA expression in NIH3T3 cells with either wildtype Smo or D473H Smo mutant. These results represented significant improvement over the virtual screening hit C794-1677 and suggested that compound 25 can be used as a good starting point to support lead optimization.

Misactivation of Hedgehog signaling causes inherited and sporadic cancers

The Hedgehog pathway is critical for the development of diverse organs. Misactivation of the Hedgehog pathway can cause developmental abnormalities and cancers, including medulloblastoma, the most common pediatric brain tumor, and basal cell carcinoma, the most common cancer in the United States. Here, we review how basic, translational, and clinical studies of the Hedgehog pathway have helped reveal how cells communicate, how intercellular communication controls development, how signaling goes awry to cause cancer, and how to use targeted molecular agents to treat both inherited and sporadic cancers.

Rhabdomyosarcoma

Rhabdomyosarcoma (RMS) is the most common soft tissue sarcoma in children and represents a high-grade neoplasm of skeletal myoblast-like cells. Decades of clinical and basic research have gradually improved our understanding of the pathophysiology of RMS and helped to optimize clinical care. The two major subtypes of RMS, originally characterized on the basis of light microscopic features, are driven by fundamentally different molecular mechanisms and pose distinct clinical challenges. Curative therapy depends on control of the primary tumour, which can arise at many distinct anatomical sites, as well as controlling disseminated disease that is known or assumed to be present in every case. Sophisticated risk stratification for children with RMS incorporates various clinical, pathological and molecular features, and that information is used to guide the application of multifaceted therapy. Such therapy has historically included cytotoxic chemotherapy as well as surgery, ionizing radiation or both. This Primer describes our current understanding of RMS epidemiology, disease susceptibility factors, disease mechanisms and elements of clinical care, including diagnostics, risk-based care of newly diagnosed and relapsed disease and the prevention and management of late effects in survivors. We also outline potential opportunities to further translate new biological insights into improved clinical outcomes.

Soft Tissue Sarcoma Cancer Stem Cells: An Overview

Soft tissue sarcomas (STSs) are an uncommon group of solid tumors that can arise throughout the human lifespan. Despite their commonality as non-bony cancers that develop from mesenchymal cell precursors, they are heterogeneous in their genetic profiles, histology, and clinical features. This has made it difficult to identify a single target or therapy specific to STSs. And while there is no one cell of origin ascribed to all STSs, the cancer stem cell (CSC) principle—that a subpopulation of tumor cells possesses stem cell-like properties underlying tumor initiation, therapeutic resistance, disease recurrence, and metastasis—predicts that ultimately it should be possible to identify a feature common to all STSs that could function as a therapeutic Achilles' heel. Here we review the published evidence for CSCs in each of the most common STSs, then focus on the methods used to study CSCs, the developmental signaling pathways usurped by CSCs, and the epigenetic alterations critical for CSC identity that may be useful for further study of STS biology. We conclude with discussion of some challenges to the field and future directions.

Different Response of Ptch Mutant and Ptch Wildtype Rhabdomyosarcoma Toward SMO and PI3K Inhibitors

Rhabdomyosarcoma (RMS) is the most common pediatric soft tissue sarcoma with poor prognosis. RMS frequently show Hedgehog (HH) pathway activity, which is predominantly seen in the embryonal subtype (ERMS). They also show activation of Phosphatidylinositol-4,5-bisphosphate 3-kinase (PI3K) signaling. Here we compared the therapeutic effectiveness and the impact on HH target gene expression of Smoothened (SMO) antagonists with those of the PI3K inhibitor pictilisib in ERMS with and without mutations in the HH receptor Patched1 (PTCH). Our data demonstrate that growth of ERMS showing canonical Hh signaling activity due to Ptch germline mutations is efficiently reduced by SMO antagonists. This goes along with strong downregulation of the Hh target Gli1. Likewise Ptch mutant tumors are highly responsive toward the PI3K inhibitor pictilisib, which involves modulation of AKT and caspase activity. Pictilisib also modulates Hh target gene expression, which, however, is rather not correlated with its antitumoral effects. In contrast, sporadic ERMS, which usually express HH target genes without having PTCH mutation, apparently lack canonical HH signaling activity. Thus, stimulation by Sonic HE (SHH) or SAG (Smoothened agonist) or inhibition by SMO antagonists do not modulate HH target gene expression. In addition, SMO antagonists do not provoke efficient anticancer effects and rather exert off-target effects. In contrast, pictilisib and other PI3K/AKT/mTOR inhibitors potently inhibit cellular growth. They also efficiently inhibit HH target gene expression. However, of whether this is correlated with their antitumoral effects it is not clear. Together, these data suggest that PI3K inhibitors are a good and reliable therapeutic option for all ERMS, whereas SMO inhibitors might only be beneficial for ERMS driven by PTCH mutations.

Hedgehog Signaling Pathway and Autophagy in Cancer

Hedgehog (Hh) pathway controls complex developmental processes in vertebrates. Abnormal activation of Hh pathway is responsible for tumorigenesis and maintenance of multiple cancers, and thus addressing this represents promising therapeutic opportunities. In recent years, two Hh inhibitors have been approved for basal cell carcinoma (BCC) treatment and show extraordinary clinical outcomes. Meanwhile, a series of novel agents are being developed for the treatment of several cancers, including lung cancer, leukemia, and pancreatic cancer. Unfortunately, Hh inhibition fails to show satisfactory benefits in these cancer types compared with the success stories in BCC, highlighting the need for better understanding of Hh signaling in cancer. Autophagy, a conserved biological process for cellular component elimination, plays critical roles in the initiation, progression, and drug resistance of cancer, and therefore, implied potential to be targeted. Recent evidence demonstrated that Hh signaling interplays with autophagy in multiple cancers. Importantly, modulating this crosstalk exhibited noteworthy capability to sensitize primary and drug-resistant cancer cells to Hh inhibitors, representing an emerging opportunity to reboot the efficacy of Hh inhibition in those insensitive tumors, and to tackle drug resistance challenges. This review will highlight recent advances of Hh pathway and autophagy in cancers, and focus on their crosstalk and the implied therapeutic opportunities.

SNAIL is a key regulator of alveolar rhabdomyosarcoma tumor growth and differentiation through repression of MYF5 and MYOD function

Rhabdomyosarcoma (RMS) is a mesenchymal tumor of soft tissue in children that originates from a myogenic differentiation defect. Expression of SNAIL transcription factor is elevated in the alveolar subtype of RMS (ARMS), characterized by a low myogenic differentiation status and high aggressiveness. In RMS patients SNAIL level increases with higher stage. Moreover, SNAIL level negatively correlates with MYF5 expression. The differentiation of human ARMS cells diminishes SNAIL level. SNAIL silencing in ARMS cells inhibits proliferation and induces differentiation in vitro, and thereby completely abolishes the growth of human ARMS xenotransplants in vivo. SNAIL silencing induces myogenic differentiation by upregulation of myogenic factors and muscle-specific microRNAs, such as miR-206. SNAIL binds to the MYF5 promoter suppressing its expression. SNAIL displaces MYOD from E-box sequences (CANNTG) that are associated with genes expressed during differentiation and G/C rich in their central dinucleotides. SNAIL silencing allows the re-expression of MYF5 and canonical MYOD binding, promoting ARMS cell myogenic differentiation. In differentiating ARMS cells SNAIL forms repressive complex with histone deacetylates 1 and 2 (HDAC1/2) and regulates their expression. Accordingly, in human myoblasts SNAIL silencing induces differentiation by upregulation of myogenic factors. Our data clearly point to SNAIL as a key regulator of myogenic differentiation and a new promising target for future ARMS therapies.

Hedgehog signaling negatively co-regulates BH3-only protein Noxa and TAp73 in TP53-mutated cells

In the present study, we show that pharmacological repression by the Hedgehog (Hh) pathway inhibitor (HPI) GANT61 induces expression of the proapoptotic protein Noxa in TP53-mutated embryonal pediatric tumor cells driven by Hh signaling (i.e. rhabdomyosarcoma (RMS) and medulloblastoma (MB)). Similarly, genetic silencing of Gli1 by siRNA causes increased Noxa mRNA and protein levels, while overexpression of Gli1 results in decreased Noxa expression. Furthermore, TAp73 mRNA and protein levels are increased upon Gli1 knockdown, while Gli1 overexpression reduces TAp73 mRNA and protein levels. However, knockdown of TAp73 fails to block Noxa induction in GANT61-treated cells, suggesting that Noxa is not primarily regulated by TAp73. Interestingly, mRNA levels of the transcription factor EGR1 correlate with those of Noxa and TAp73. Silencing of EGR1 results in decreased Noxa and TAp73 mRNA levels, indicating that EGR1 is involved in regulating transcriptional activity of Noxa and TAp73. These findings suggest that Gli1 represses Noxa and TAp73, possibly via EGR1. These findings could be exploited for the treatment of Hh-driven tumors, e.g. for their sensitization to chemotherapeutic agents.

Dual degradation signals destruct GLI1: AMPK inhibits GLI1 through β-TrCP-mediated proteasome degradation

Overexpression of the GLI1 gene has frequently been found in various cancer types, particularly in brain tumors, in which aberrant GLI1 induction promotes cancer cell growth. Therefore, identifying the molecular players controlling GLI1 expression is of clinical importance. Previously, we reported that AMPK directly phosphorylated and destabilized GLI1, resulting in the suppression of the Hedgehog signaling pathway. The current study not only demonstrates that AMPK inhibits GLI1 nuclear localization, but further reveals that β-TrCP plays an essential role in AMPK-induced GLI1 degradation. We found that activation of AMPK promotes the interaction between β-TrCP and GLI1, and induces β-TrCP-mediated GLI1-ubiquitination and degradation. Inhibiting AMPK activity results in the dissociation of the β-TrCP and GLI1 interaction, and diminishes β-TrCP-mediated-GLI1 ubiquitination and degradation. On GLI1, substitution of AMPK phosphorylation sites to aspartic acid (GLI1^3E) results in stronger binding affinity of GLI1 with β-TrCP, accompanied by enhanced GLI1 ubiquitination and later degradation. In contrast, the GLI1 alanine mutant (GLI1^3A) shows weaker binding with β-TrCP, which is accompanied by reduced β-TrCP-mediated ubiquitination and degradation. Together, these results demonstrate that AMPK regulates GLI1 interaction with β-TrCP by phosphorylating GLI1 and thus both post-translational modifications by AMPK and β-TrCP ultimately impact GLI1 degradation.

The NOTCH1/SNAIL1/MEF2C Pathway Regulates Growth and Self-Renewal in Embryonal Rhabdomyosarcoma

Tumor-propagating cells (TPCs) share self-renewal properties with normal stem cells and drive continued tumor growth. However, mechanisms regulating TPC self-renewal are largely unknown, especially in embryonal rhabdomyosarcoma (ERMS)-a common pediatric cancer of muscle. Here, we used a zebrafish transgenic model of ERMS to identify a role for intracellular NOTCH1 (ICN1) in increasing TPCs by 23-fold. ICN1 expanded TPCs by enabling the de-differentiation of zebrafish ERMS cells into self-renewing myf5+ TPCs, breaking the rigid differentiation hierarchies reported in normal muscle. ICN1 also had conserved roles in regulating human ERMS self-renewal and growth. Mechanistically, ICN1 upregulated expression of SNAIL1, a transcriptional repressor, to increase TPC number in human ERMS and to block muscle differentiation through suppressing MEF2C, a myogenic differentiation transcription factor. Our data implicate the NOTCH1/SNAI1/MEF2C signaling axis as a major determinant of TPC self-renewal and differentiation in ERMS, raising hope of therapeutically targeting this pathway in the future.

Clinical and mutational spectrum of highly differentiated, paired box 3:forkhead box protein o1 fusion-negative rhabdomyosarcoma: A report from the Children's Oncology Group

BACKGROUND

Pediatric paired box 3:forkhead box protein O1 fusion-negative (PF-) rhabdomyosarcoma (RMS) represents a diverse spectrum of tumors with marked differences in histology, myogenic differentiation, and clinical behavior.

METHODS

This study sought to evaluate the clinical and mutational spectrum of 24 pediatric PF- human RMS tumors with high levels of myogenic differentiation. Tumors were sequenced with OncoPanel v.2, a panel consisting of the coding regions of 504 genes previously linked to human cancer.

RESULTS

Most of the tumors (19 of 24) arose at head/neck or genitourinary sites, and the overall survival rate was 100% with a median follow-up time of 4.6 years (range, 1.4-8.6 years). RAS pathway gene mutations were the most common mutations in PF-, highly differentiated RMS tumors. In addition, Hedgehog (Hh) and mechanistic target of rapamycin (mTOR) gene mutations with evidence for functional relevance (high-impact) were identified in subsets of tumors. The presence of Hh and mTOR pathway gene mutations was mutually exclusive and was associated with high-impact RAS pathway gene mutations in 3 of 4 Hh-mutated tumors and in 1 of 6 mTOR-mutated tumors.

CONCLUSIONS

Interestingly, Hh and mTOR gene mutations were previously associated with rhabdomyomas, which are also known to preferentially arise at head/neck and genitourinary sites. Findings from this study further support the idea that PF-, highly differentiated RMS tumors and rhabdomyomas may represent a continuous spectrum of tumors. Cancer 2018;124:1973-81. © 2018 American Cancer Society.

FOXM1 in sarcoma: role in cell cycle, pluripotency genes and stem cell pathways

FOXM1 is a pro-proliferative transcription factor that promotes cell cycle progression at the G1-S, and G2-M transitions. It is activated by phosphorylation usually mediated by successive cyclin – cyclin dependent kinase complexes, and is highly expressed in sarcoma. p53 down regulates FOXM1 and FOXM1 inhibition is also partly dependent on Rb and p21. Abnormalities of p53 or Rb are frequent in sporadic sarcomas with bone or soft tissue sarcoma, accounting for 36% of index cancers in the high penetrance TP53 germline disorder, Li-Fraumeni syndrome.

FOXM1 stimulates transcription of pluripotency related genes including SOX2, KLF4, OCT4, and NANOG many of which are important in sarcoma, a disorder of mesenchymal stem cell/ partially committed progenitor cells. In a selected specific, SOX2 is uniformly expressed in synovial sarcoma. Embryonic pathways preferentially used in stem cell such as Hippo, Hedgehog, and Wnt dominate in FOXM1 stoichiometry to alter rates of FOXM1 production or degradation. In undifferentiated pleomorphic sarcoma, liposarcoma, and fibrosarcoma, dysregulation of the Hippo pathway increases expression of the effector co-transcriptional activator Yes-Associated Protein (YAP). A complex involving YAP and the transcription factor TEAD elevates FOXM1 in these sarcoma subtypes. In another scenario 80% of desmoid tumors have nuclear localization of β-catenin, the Wnt pathway effector molecule. Thiazole antibiotics inhibit FOXM1 and because they have an auto-regulator loop FOXM1 expression is also inhibited. Current systemic treatment of sarcoma is of limited efficacy and inhibiting FOXM1 represents a potential new strategy.

Hedgehog Pathway Drives Fusion-Negative Rhabdomyosarcoma Initiated From Non-myogenic Endothelial Progenitors

Rhabdomyosarcoma (RMS) is a pediatric soft tissue sarcoma that histologically resembles embryonic skeletal muscle. RMS occurs throughout the body and an exclusively myogenic origin does not account for RMS occurring in sites devoid of skeletal muscle. We previously described an RMS model activating a conditional constitutively active Smoothened mutant (SmoM2) with aP2-Cre. Using genetic fate mapping, we show SmoM2 expression in Cre-expressing endothelial progenitors results in myogenic transdifferentiation and RMS. We show that endothelium and skeletal muscle within the head and neck arise from Kdr-expressing progenitors, and that hedgehog pathway activation results in aberrant expression of myogenic specification factors as a potential mechanism driving RMS genesis. These findings suggest that RMS can originate from aberrant development of non-myogenic cells.

Ligand-dependent Hedgehog pathway activation in Rhabdomyosarcoma: the oncogenic role of the ligands

BACKGROUND

Rhabdomyosarcoma (RMS) is the most common type of soft tissue sarcoma in children. The Hedgehog (HH) pathway is known to develop an oncogenic role in RMS. However, the molecular mechanism that drives activation of the pathway in RMS is not well understood.

METHODS

The expression of HH ligands was studied by qPCR, western blot and immunohistochemistry. Functional and animal model studies were carried out with cells transduced with shRNAs against HH ligands or treated with HH-specific inhibitors (Vismodegib and MEDI-5304). Finally, the molecular characterisation of an off-target effect of Vismodegib was also made.

RESULTS

The results showed a prominent expression of HH ligands supporting an autocrine ligand-dependent activation of the pathway. A comparison of pharmacologic Smoothened inhibition (Vismodegib) and HH ligand blocking (MEDI-5304) is also provided. Interestingly, a first description of pernicious off-target effect of Vismodegib is also reported.

CONCLUSIONS

The clarification of the HH pathway activation mechanism in RMS opens a door for targeted therapies against HH ligands as a possible alternative in the future development of better treatment protocols. Moreover, the description of a pernicious off-target effect of Vismodegib, via unfolded protein response activation, may mechanistically explain its previously reported inefficiency in several ligand-dependent cancers.

Hedgehog Pathway Inhibition Hampers Sphere and Holoclone Formation in Rhabdomyosarcoma

Rhabdomyosarcoma (RMS) is the most common type of soft tissue sarcoma in children and can be divided into two main subtypes: embryonal (eRMS) and alveolar (aRMS). Among the cellular heterogeneity of tumors, the existence of a small fraction of cells called cancer stem cells (CSC), thought to be responsible for the onset and propagation of cancer, has been demonstrated in some neoplasia. Although the existence of CSC has been reported for eRMS, their existence in aRMS, the most malignant subtype, has not been demonstrated to date. Given the lack of suitable markers to identify this subpopulation in aRMS, we used cancer stem cell-enriched supracellular structures (spheres and holoclones) to study this subpopulation. This strategy allowed us to demonstrate the capacity of both aRMS and eRMS cells to form these structures and retain self-renewal capacity. Furthermore, cells contained in spheres and holoclones showed significant Hedgehog pathway induction, the inhibition of which (pharmacologic or genetic) impairs the formation of both holoclones and spheres. Our findings point to a crucial role of this pathway in the maintenance of these structures and suggest that Hedgehog pathway targeting in CSC may have great potential in preventing local relapses and metastases.

The heparanase/heparan sulfate proteoglycan axis: A potential new therapeutic target in sarcomas

Heparanase, the only known mammalian endoglycosidase degrading heparan sulfate (HS) chains of HS proteoglycans (HSPG), is a highly versatile protein affecting multiple events in tumor cells and their microenvironment. In several malignancies, deregulation of the heparanase/HSPG system has been implicated in tumor progression, hence representing a valuable therapeutic target. Currently, multiple agents interfering with the heparanase/HSPG axis are under clinical investigation. Sarcomas are characterized by a high biomolecular complexity and multiple levels of interconnection with microenvironment sustaining their growth and progression. The clinical management of advanced diseases remains a challenge. In several sarcoma subtypes, high levels of heparanase expression have been correlated with poor prognosis associated factors. On the other hand, expression of cell surface-associated HSPGs (i.e. glypicans and syndecans) has been found altered in specific sarcoma subtypes. Recent studies provided the preclinical proof-of-principle of the role of the heparanase/HSPG axis as therapeutic target in various sarcoma subtypes. Although currently there are no clinical trials evaluating agents targeting heparanase and/or HSPGs in sarcomas, we here provide arguments for this strategy as potentially able to implement the therapeutic options for sarcoma patients.

Arsenic trioxide induces Noxa-dependent apoptosis in rhabdomyosarcoma cells and synergizes with antimicrotubule drugs

The prognosis of metastatic or relapsed rhabdomyosarcoma (RMS) is poor, highlighting the need of new treatment options. In the present study, we evaluated the in vitro efficacy of arsenic trioxide (ATO) in RMS, a FDA-approved drug used in pediatric leukemia. Here, we report that ATO exerts antitumor activity against RMS cells both as single agent and in combination with microtubule-targeting drugs. Monotherapy with ATO reduces cell viability, triggers apoptosis and suppresses clonogenic survival of RMS cells, at least in part, by transcriptional induction of the proapoptotic BH3-only protein Noxa. siRNA-mediated knockdown of Noxa significantly rescues ATO-mediated cell death, demonstrating that Noxa is required for cell death. Also, ATO suppresses endogenous Hedgehog (Hh) signaling, as it significantly reduces Gli1 transcriptional activity and expression levels of several Hh target genes. Furthermore, we identify synergistic induction of apoptosis by ATO together with several antimicrotubule agents including vincristine (VCR), vinblastine and eribulin. The addition of the broad-range caspase inhibitor zVAD.fmk or overexpression of the antiapoptotic protein Bcl-2 significantly reduce ATO/VCR-induced cell death, indicating that the ATO/VCR combination triggers caspase-dependent apoptosis via the mitochondrial pathway. In summary, ATO exerts antitumor activity against RMS, especially in combination with antimicrotubule drugs. These findings have important implications for the development of novel therapeutic strategies for RMS.

Synthetic Small Molecule Inhibitors of Hh Signaling As Anti-Cancer Chemotherapeutics

The hedgehog (Hh) pathway is a developmental signaling pathway that is essential to the proper embryonic development of many vertebrate systems. Dysregulation of Hh signaling has been implicated as a causative factor in the development and progression of several forms of human cancer. As such, the development of small molecule inhibitors of Hh signaling as potential anti-cancer chemotherapeutics has been a major area of research interest in both academics and industry over the past ten years. Through these efforts, synthetic small molecules that target multiple components of the Hh pathway have been identified and advanced to preclinical or clinical development. The goal of this review is to provide an update on the current status of several synthetic small molecule Hh pathway inhibitors and explore the potential of several recently disclosed inhibitory scaffolds.

Targeting the Hedgehog signaling pathway in cancer: beyond Smoothened

An essential role for Hedgehog (Hh) signaling in human cancer has been established beyond doubt. At present, targeting Hh signaling has mainly been investigated with SMO inhibitors. Unfortunately, resistance against currently used SMO inhibitors has already been observed in basal cell carcinoma (BCC) patients. Therefore, the use of Hh inhibitors targeting the signaling cascade more downstream of SMO could represent a more promising strategy. Furthermore, besides the classical canonical way of Hh signaling activation, non-canonical activation of the GLI transcription factors by multiple important signaling pathways (e.g. MAPK, PI3K, TGFβ) has also been described, pinpointing the importance of targeting the transcription factors GLI1/2. The most promising agent in this context is probably the GLI1/2 inhibitor GANT61 which has been investigated preclinically in numerous tumor types in the last few years. In this review, the emerging role of Hh signaling in cancer is critically evaluated focusing on the potential of targeting Hh signaling more downstream of SMO, i.e. at the level of the GLI transcription factors. Furthermore, the working mechanism and therapeutic potential of the most extensively studied GLI inhibitor in human cancer, i.e. GANT61, is discussed in detail. In conclusion, GANT61 appears to be highly effective against human cancer cells and in xenograft mouse models, targeting almost all of the classical hallmarks of cancer and could hence represent a promising treatment option for human cancer.

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.

Identification of a novel synthetic lethality of combined inhibition of hedgehog and PI3K signaling in rhabdomyosarcoma

We previously reported that aberrant HH pathway activation confers a poor prognosis in rhabdomyosarcoma (RMS). Searching for new treatment strategies we therefore targeted HH signaling. Here, we identify a novel synthetic lethality of concomitant inhibition of HH and PI3K/AKT/mTOR pathways in RMS by GLI1/2 inhibitor GANT61 and PI3K/mTOR inhibitor PI103. Synergistic drug interaction is confirmed by calculation of combination index (CI < 0.2). Similarly, genetic silencing of GLI1/2 significantly increases PI103-induced apoptosis. GANT61 and PI103 also synergize to induce apoptosis in cultured primary RMS cells emphasizing the clinical relevance of this combination. Importantly, GANT61/PI103 cotreatment suppresses clonogenic survival, three-dimensional sphere formation and tumor growth in an in vivo model of RMS. Mechanistic studies reveal that GANT61 and PI103 cooperate to trigger caspase-dependent apoptosis via the mitochondrial pathway, as demonstrated by several lines of evidence. First, GANT61/PI103 cotreatment increases mRNA and protein expression of NOXA and BMF, which is required for apoptosis, since knockdown of NOXA or BMF significantly reduces GANT61/PI103-induced apoptosis. Second, GANT61/PI103 cotreatment triggers BAK/BAX activation, which contributes to GANT61/PI103-mediated apoptosis, since knockdown of BAK provides protection. Third, ectopic expression of BCL-2 or non-degradable phospho-mutant MCL-1 significantly rescue GANT61/PI103-triggered apoptosis. Fourth, GANT61/PI103 cotreatment initiate activation of the caspase cascade via apoptosome-mediated cleavage of the initiator caspase-9, as indicated by changes in the cleavage pattern of caspases (e.g. accumulation of the caspase-9 p35 cleavage fragment) upon addition of the caspase inhibitor zVAD.fmk. Thus, combined GLI1/2 and PI3K/mTOR inhibition represents a promising novel approach for synergistic apoptosis induction and tumor growth reduction with implications for new treatment strategies in RMS.

Contextualizing the Genes Altered in Bladder Neoplasms in Pediatric andTeen Patients Allows Identifying Two Main Classes of Biological ProcessesInvolved and New Potential Therapeutic Targets

Research on bladder neoplasms in pediatric and teen patients (BNPTP) has described 21 genes, which are variously involved in this disease and are mostly responsible for deregulated cell proliferation. However, due to the limited number of publications on this subject, it is still unclear what type of relationships there are among these genes and which are the chances that, while having different molecular functions, they i) act as downstream effector genes of well-known pro- or anti- proliferative stimuli and/or interplay with biochemical pathways having oncological relevance or ii) are specific and, possibly, early biomarkers of these pathologies. A Gene Ontology (GO)-based analysis showed that these 21 genes are involved in biological processes, which can be split into two main classes: cell regulation-based and differentiation/development-based. In order to understand the involvement/overlapping with main cancer-related pathways, we performed a meta-analysis dependent on the 189 oncogenic signatures of the Molecular Signatures Database (OSMSD) curated by the Broad Institute. We generated a binary matrix with 53 gene signatures having at least one hit; this analysis i) suggests that some genes of the original list show inconsistencies and might need to be experimentally re- assessed or evaluated as biomarkers (in particular, ACTA2) and ii) allows hypothesizing that important (proto)oncogenes (E2F3, ERBB2/HER2, CCND1, WNT1, and YAP1) and (putative) tumor suppressors (BRCA1, RBBP8/CTIP, and RB1-RBL2/p130) may participate in the onset of this disease or worsen the observed phenotype, thus expanding the list of possible molecular targets for the treatment of BNPTP.

Genetics of Bladder Malignant Tumors in Childhood

Bladder masses are represented by either benign or malignant entities. Malignant bladder tumors are frequent causes of disease and death in western countries. However, in children they are less common. Additionally, different features are found in childhood, in which non epithelial tumors are more common than epithelial ones. Rhabdomyosarcoma is the most common pediatric bladder tumor, but many other types of lesions may be found, such as malignant rhabdoid tumor (MRT), inflammatory myofibroblastic tumor and neuroblastoma. Other rarer tumors described in literature include urothelial carcinoma and other epithelial neoplasms. Rhabdomyosarcoma is associated to a variety of genetic syndromes and many genes are involved in tumor development. PAX3-FKHR and PAX7-FKHR (P-F) fusion state has important implications in the pathogenesis and biology of RMS, and different genes alterations are involved in the pathogenesis of P-F negative and embryonal RMS, which are the subsets of tumors most frequently affecting the bladder. These genes include p53, MEF2, MYOG, Ptch1, Gli1, Gli3, Myf5, MyoD1, NF1, NRAS, KRAS, HRAS, FGFR4, PIK3CA, CTNNB1, FBXW7, IGF1R, PDGFRA, ERBB2/4, MET, BCOR. Malignant rhabdoid tumor (MRT) usually shows SMARCB1/INI1 alterations. Anaplastic lymphoma kinase (ALK) gene translocations are the most frequently associated alterations in inflammatory myofibroblastic tumor (IMT). Few genes alterations in urothelial neoplasms have been reported in the paediatric population, which are mainly related to deletion of p16/lnk4, overexpression of CK20 and overexpression of p53. Here, we reviewed available literature to identify genes associated to bladder malignancies in children and discussed their possible relationships with these tumors.

Clinicopathological factors predictive of postoperative seizures in patients with gliomas

PURPOSE

Epilepsy is one of the most common manifestations in gliomas and has a severe effect on the life expectancy and quality of life of patients. The aim of our study was to assess the potential connections between clinicopathological factors and postoperative seizure.

METHOD

We retrospectively investigated a group of 147 Chinese high-grade glioma (HGG) patients with preoperative seizure to examine the correlation between postoperative seizure and clinicopathological factors and prognosis. Univariate analyses and multivariate logistic regression analyses were performed to identify factors associated with postoperative seizures. Survival function curves were calculated using the Kaplan-Meier method.

RESULTS

53 patients (36%) were completely seizure-free (Engel class I), and 94 (64%) experienced a postoperative seizure (Engel classes II, III, and IV). A Chi-squared analysis showed that anaplastic oligodendroglioma/anaplastic oligoastrocytoma (AO/AOA) (P=0.05), epidermal growth factor receptor (EGFR) expression (P=0.0004), O(6)-methylguanine DNA methyltransferase (MGMT) expression (P=0.011), and phosphatase and tensin homolog (PTEN) expression (P=0.045) were all significantly different. A logistic regression analysis showed that MGMT expression (P=0.05), EGFR expression (P=0.001), and AO/AOA (P=0.038) are independent factors of postoperative seizure. Patients with lower MGMT and EGFR expression and AO/AOA showed more frequent instances of postoperative seizure. Postoperative seizure showed no statistical significance on overall survival (OS) and progression-free survival (PFS).

CONCLUSION

Our study identified clinicopathological factors related to postoperative seizure in HGGs and found two predictive biomarkers of postoperative seizure: MGMT and EGFR. These findings provided insight treatment strategies aimed at prolonging survival and improving quality of life.