Arsenic trioxide inhibits human cancer cell growth and tumor development in mice by blocking Hedgehog/GLI pathway

Noncanonical GLI1 signaling promotes stemness features and in vivo growth in lung adenocarcinoma

Aberrant Hedgehog/GLI signaling has been implicated in a diverse spectrum of human cancers, but its role in lung adenocarcinoma (LAC) is still under debate. We show that the downstream effector of the Hedgehog pathway, GLI1, is expressed in 76% of LACs, but in roughly half of these tumors, the canonical pathway activator, Smoothened, is expressed at low levels, possibly owing to epigenetic silencing. In LAC cells including the cancer stem cell compartment, we show that GLI1 is activated noncanonically by MAPK/ERK signaling. Different mechanisms can trigger the MAPK/ERK/GLI1 cascade including KRAS mutation and stimulation of NRP2 by VEGF produced by the cancer cells themselves in an autocrine loop or by stromal cells as paracrine cross talk. Suppression of GLI1, by silencing or drug-mediated, inhibits LAC cells proliferation, attenuates their stemness and increases their susceptibility to apoptosis in vitro and in vivo. These findings provide insight into the growth of LACs and point to GLI1 as a downstream effector for oncogenic pathways. Thus, strategies involving direct inhibition of GLI1 may be useful in the treatment of LACs.

Hedgehog signaling contributes to basic fibroblast growth factor-regulated fibroblast migration

Fibroblast migration is a central process in skin wound healing, which requires the coordination of several types of growth factors. bFGF, a well-known fibroblast growth factor (FGF), is able to accelerate fibroblast migration; however, the underlying mechanism of bFGF regulation fibroblast migration remains unclear. Through the RNA-seq analysis, we had identified that the hedgehog (Hh) canonical pathway genes including Smoothened (Smo) and Gli1, were regulated by bFGF. Further analysis revealed that activation of the Hh pathway via up-regulation of Smo promoted fibroblast migration, invasion, and skin wound healing, but which significantly reduced by GANT61, a selective antagonist of Gli1/Gli2. Western blot analyses and siRNA transfection assays demonstrated that Smo acted upstream of phosphoinositide 3-kinase (PI3K)-c-Jun N-terminal kinase (JNK)-β-catenin to promote cell migration. Moreover, RNA-seq and qRT-PCR analyses revealed that Hh pathway genes including Smo and Gli1 were under control of β-catenin, suggesting that β-catenin turn feedback activates Hh signaling. Taken together, our analyses identified a new bFGF-regulating mechanism by which Hh signaling regulates human fibroblast migration, and the data presented here opens a new avenue for the wound healing therapy.

Selective targeting of HDAC1/2 elicits anticancer effects through Gli1 acetylation in preclinical models of SHH Medulloblastoma

SHH Medulloblastoma (SHH-MB) is a pediatric brain tumor characterized by an inappropriate activation of the developmental Hedgehog (Hh) signaling. SHH-MB patients treated with the FDA-approved vismodegib, an Hh inhibitor that targets the transmembrane activator Smoothened (Smo), have shown the rapid development of drug resistance and tumor relapse due to novel Smo mutations. Moreover, a subset of patients did not respond to vismodegib because mutations were localized downstream of Smo. Thus, targeting downstream Hh components is now considered a preferable approach. We show here that selective inhibition of the downstream Hh effectors HDAC1 and HDAC2 robustly counteracts SHH-MB growth in mouse models. These two deacetylases are upregulated in tumor and their knockdown inhibits Hh signaling and decreases tumor growth. We demonstrate that mocetinostat (MGCD0103), a selective HDAC1/HDAC2 inhibitor, is a potent Hh inhibitor and that its effect is linked to Gli1 acetylation at K518. Of note, we demonstrate that administration of mocetinostat to mouse models of SHH-MB drastically reduces tumor growth, by reducing proliferation and increasing apoptosis of tumor cells and prolongs mouse survival rate. Collectively, these data demonstrate the preclinical efficacy of targeting the downstream HDAC1/2-Gli1 acetylation in the treatment of SHH-MB.

Hedgehog Signaling: From Basic Biology to Cancer Therapy

The Hedgehog (HH) signaling pathway was discovered originally as a key pathway in embryonic patterning and development. Since its discovery, it has become increasingly clear that the HH pathway also plays important roles in a multitude of cancers. Therefore, HH signaling has emerged as a therapeutic target of interest for cancer therapy. In this review, we provide a brief overview of HH signaling and the key molecular players involved and offer an up-to-date summary of our current knowledge of endogenous and exogenous small molecules that modulate HH signaling. We discuss experiences and lessons learned from the decades-long efforts toward the development of cancer therapies targeting the HH pathway. Challenges to develop next-generation cancer therapies are highlighted.

Cryptotanshinone enhances the effect of Arsenic trioxide in treating liver cancer cell by inducing apoptosis through downregulating phosphorylated- STAT3 in vitro and in vivo

Background

Arsenic trioxide (ATO) is approved for treating terminal-stage liver cancer in China. Cryptotanshinone (CT), a STAT3 inhibitor, has exhibited certain anti-tumor potency; however, the use of CT enhanced ATO for treating liver cancer has not been reported. Here we try to elucidate how CT could enhance the efficacy of ATO for treating liver cancer and its correlation to STAT3 in vitro and in vivo.

Methods

Cell viability of ATO combined with CT was assessed by ¹MTT assay. Cell apoptosis induced by ATO combined with CT was detected by Annexin V/PI staining and apoptosis-related proteins were detected by western blotting. STAT3-related proteins were analysis by western blotting analysis and Immunofluorescence assays. Efficacy evaluation of ATO combined with CT on xenograft was carried in nude mice and related proteins were analysis by Immunohistochemistry assays.

Results

First we evaluated cell vitality, and our data indicated that the ATO combined with CT showed obvious growth inhibition of Bel-7404 cells compared to ATO or CT alone. Next we found that ATO combined with CT induced cell apoptosis in Bel-7404 cells and upregulated the activation of apoptosis-related proteins cleaved-caspase-3, cleaved-caspase-9, and cleaved-poly(ADP-ribose) polymerase in a time-dependent manner. Next, we found that ATO combined with CT not only inhibited the constitutive levels of phosphorylated-JAK2 and phosphorylated-STAT3^Tyr705 but did so in a time-dependent manner. We also found that ATO combined with CT reversed the upregulated expression of phosphorylated-STAT3^Tyr705 stimulated by interleukin-6 and downregulated STAT3 direct target genes and the anti-apoptotic proteins Bcl-2, XIAP, and survivin but obviously upregulated the promoting apoptosis proteins Bak,.In vivo studies showed that ATO combined with CT decreased tumor growth. Tumors from ATO combined with CT–treated mice showed decreased levels of phosphorylated-STAT3^Tyr705 and the anti-apoptotic protein Bcl-2 but an increased level of pro-apoptotic protein Bax.

Conclusions

Our study provides strong evidence that CT could enhance the efficacy of ATO in treating liver cancer both in vitro and in vivo. Downregulation of phosphorylated-STAT3 expression may play an important role in inducing apoptosis of Bel-7404 cells.

Solasonine, A Natural Glycoalkaloid Compound, Inhibits Gli-Mediated Transcriptional Activity

The major obstacle limiting the efficacy of current Smoothened (Smo) inhibitors is the primary and acquired resistance mainly caused by Smo mutations and Gli amplification. In this context, developing Hh inhibitors targeting Gli, the final effector of this signaling pathway, may combat the resistance. In this study we found that solasonine, a natural glycoalkaloid compound, significantly inhibited the hedgehog (Hh) pathway activity. Meanwhile, solasonine may obviously inhibit the alkaline phosphatase (ALP) activity in C3H10T1/2 cells, concomitantly with reductions of the mRNA expression of Gli1 and Ptch1. However, we found that solasonine exhibited no effect on the transcriptional factors activities provoked by TNF-α and PGE2, thus suggesting its selectivity against Hh pathway activity. Furthermore, we identified that solasonine inhibited the Hh pathway activity by acting on its transcriptional factor Gli using a series of complementary data. We also observed that solasonine obviously inhibited the Gli-luciferase activity provoked by ectopic expression of Smo mutants which may cause the resistance to the current Smo inhibitors. Our study suggests that solasonine may significantly inhibit the Hh pathway activity by acting on Gli, therefore indicating the possibility to use solasonine as a lead compound to develop anticancer drugs for combating the resistance of current Smo inhibitors.

In vitro models of cancer stem cells and clinical applications

Cancer cells, stem cells and cancer stem cells have for a long time played a significant role in the biomedical sciences. Though cancer therapy is more effective than it was a few years ago, the truth is that still none of the current non-surgical treatments can cure cancer effectively. The reason could be due to the subpopulation called “cancer stem cells” (CSCs), being defined as those cells within a tumour that have properties of stem cells: self-renewal and the ability for differentiation into multiple cell types that occur in tumours.

The phenomenon of CSCs is based on their resistance to many of the current cancer therapies, which results in tumour relapse. Although further investigation regarding CSCs is still needed, there is already evidence that these cells may play an important role in the prognosis of cancer, progression and therapeutic strategy. Therefore, long-term patient survival may depend on the elimination of CSCs. Consequently, isolation of pure CSC populations or reprogramming of cancer cells into CSCs, from cancer cell lines or primary tumours, would be a useful tool to gain an in-depth knowledge about heterogeneity and plasticity of CSC phenotypes and therefore carcinogenesis. Herein, we will discuss current CSC models, methods used to characterize CSCs, candidate markers, characteristic signalling pathways and clinical applications of CSCs. Some examples of CSC-specific treatments that are currently in early clinical phases will also be presented in this review.

Arsenic trioxide potentiates the effectiveness of etoposide in Ewing sarcomas

Ewing sarcomas (ES) are rare mesenchymal tumours, most commonly diagnosed in children and adolescents. Arsenic trioxide (ATO) has been shown to efficiently and selectively target leukaemic blasts as well as solid tumour cells. Since multidrug resistance often occurs in recurrent and metastatic ES, we tested potential additive effects of ATO in combination with the cytostatic drugs etoposide and doxorubicin. The Ewing sarcoma cell lines A673, RD-ES and SK-N-MC as well as mesenchymal stem cells (MSC) for control were treated with ATO, etoposide and doxorubicin in single and combined application. Viability and proliferation (MTS assay, colony formation, 3D spheroid culture) as well as cell death induction (western blot analysis, flow cytometry) were analysed. In the MTS viability assays ATO treatment significantly reduced the metabolic activity of all three ES cell lines (A673, RD-ES and SK-N-MC) examined. Moreover, all ES cell lines were sensitive to etoposide, whereas MSC remained unaffected by the drug concentrations used. With the exception of ATO in RD-ES cells, all drugs induced apoptosis in the ES cell lines, indicated by caspase-3 and PARP cleavage. Combination of the agents potentiated the reduction of viability as well as the inhibitory effect on clonal growth. In addition, cell death induction was obviously enhanced in RD-ES and SK-N-MC cells by a combination of ATO and etoposide compared to single application. Summarised, the combination of low dose, physiologically easily tolerable ATO with commonly used etoposide and doxorubicin concentrations efficiently and selectively suppressed viability and colony formation in ES cell lines, whereas a combination of ATO and etoposide was favourable for cell death induction. In addition to an increase of the effectiveness of the cytostatic drugs and prevention of potential drug resistance, this approach may also reduce toxicity effects, since the individual doses can be reduced.

The hedgehog pathway in triple-negative breast cancer

Treatment of triple‐negative breast cancer (TNBC) remains challenging due to the underlying heterogeneity of this disease coupled with the lack of predictive biomarkers and effective targeted therapies. Intratumoral heterogeneity, particularly enrichment for breast cancer stem cell‐like subpopulations, has emerged as a leading hypothesis for systemic therapy resistance and clinically aggressive course of poor prognosis TNBC. A growing body of literature supports the role of the stem cell renewal Hedgehog (Hh) pathway in breast cancer. Emerging preclinical data also implicate Hh signaling in TNBC pathogenesis. Herein, we review the evidence for a pathophysiologic role of Hh signaling in TNBC and explore mechanisms of crosstalk between the Hh pathway and other key signaling networks as well as their potential implications for Hh‐targeted interventions in TNBC.

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.

From molecular interaction to acute promyelocytic leukemia: Calculating leukemogenesis and remission from endogenous molecular-cellular network

Acute promyelocytic leukemia (APL) remains the best example of a malignancy that can be cured clinically by differentiation therapy. We demonstrate that APL may emerge from a dynamical endogenous molecular-cellular network obtained from normal, non-cancerous molecular interactions such as signal transduction and translational regulation under physiological conditions. This unifying framework, which reproduces APL, normal progenitor, and differentiated granulocytic phenotypes as different robust states from the network dynamics, has the advantage to study transition between these states, i.e. critical drivers for leukemogenesis and targets for differentiation. The simulation results quantitatively reproduce microarray profiles of NB4 and HL60 cell lines in response to treatment and normal neutrophil differentiation, and lead to new findings such as biomarkers for APL and additional molecular targets for arsenic trioxide therapy. The modeling shows APL and normal states mutually suppress each other, both in "wiring" and in dynamical cooperation. Leukemogenesis and recovery under treatment may be a consequence of spontaneous or induced transitions between robust states, through "passes" or "dragging" by drug effects. Our approach rationalizes leukemic complexity and constructs a platform towards extending differentiation therapy by performing "dry" molecular biology experiments.

Manganese-Enhanced Magnetic Resonance Imaging as a Diagnostic and Dispositional Tool after Mild-Moderate Blast Traumatic Brain Injury

Traumatic brain injury (TBI) caused by explosive munitions, known as blast TBI, is the signature injury in recent military conflicts in Iraq and Afghanistan. Diagnostic evaluation of TBI, including blast TBI, is based on clinical history, symptoms, and neuropsychological testing, all of which can result in misdiagnosis or underdiagnosis of this condition, particularly in the case of TBI of mild-to-moderate severity. Prognosis is currently determined by TBI severity, recurrence, and type of pathology, and also may be influenced by promptness of clinical intervention when more effective treatments become available. An important task is prevention of repetitive TBI, particularly when the patient is still symptomatic. For these reasons, the establishment of quantitative biological markers can serve to improve diagnosis and preventative or therapeutic management. In this study, we used a shock-tube model of blast TBI to determine whether manganese-enhanced magnetic resonance imaging (MEMRI) can serve as a tool to accurately and quantitatively diagnose mild-to-moderate blast TBI. Mice were subjected to a 30 psig blast and administered a single dose of MnCl2 intraperitoneally. Longitudinal T1-magnetic resonance imaging (MRI) performed at 6, 24, 48, and 72 h and at 14 and 28 days revealed a marked signal enhancement in the brain of mice exposed to blast, compared with sham controls, at nearly all time-points. Interestingly, when mice were protected with a polycarbonate body shield during blast exposure, the marked increase in contrast was prevented. We conclude that manganese uptake can serve as a quantitative biomarker for TBI and that MEMRI is a minimally-invasive quantitative approach that can aid in the accurate diagnosis and management of blast TBI. In addition, the prevention of the increased uptake of manganese by body protection strongly suggests that the exposure of an individual to blast risk could benefit from the design of improved body armor.

Knockdown of EphB1 receptor decreases medulloblastoma cell growth and migration and increases cellular radiosensitization

The expression of members of the Eph family of receptor tyrosine kinases and their ephrin ligands is frequently dysregulated in medulloblastomas. We assessed the expression and functional role of EphB1 in medulloblastoma cell lines and engineered mouse models. mRNA and protein expression profiling showed expression of EphB1 receptor in the human medulloblastoma cell lines DAOY and UW228. EphB1 downregulation reduced cell growth and viability, decreased the expression of important cell cycle regulators, and increased the percentage of cells in G1 phase of the cell cycle. It also modulated the expression of proliferation, and cell survival markers. In addition, EphB1 knockdown in DAOY cells resulted in significant decrease in migration, which correlated with decreased β1-integrin expression and levels of phosphorylated Src. Furthermore, EphB1 knockdown enhanced cellular radiosensitization of medulloblastoma cells in culture and in a genetically engineered mouse medulloblastoma model. Using genetically engineered mouse models, we established that genetic loss of EphB1 resulted in a significant delay in tumor recurrence following irradiation compared to EphB1-expressing control tumors. Taken together, our findings establish that EphB1 plays a key role in medulloblastoma cell growth, viability, migration, and radiation sensitivity, making EphB1 a promising therapeutic target.

Survival regulation of leukemia stem cells

Leukemia stem cells (LSCs) are a subpopulation cells at the apex of hierarchies in leukemia cells and responsible for disease continuous propagation. In this article, we discuss some cellular and molecular components, which are critical for LSC survival. These components include intrinsic signaling pathways and extrinsic microenvironments. The intrinsic signaling pathways to be discussed include Wnt/β-catenin signaling, Hox genes, Hh pathway, Alox5, and some miRNAs, which have been shown to play important roles in regulating LSC survival and proliferation. The extrinsic components to be discussed include selectins, CXCL12/CXCR4, and CD44, which involve in LSC homing, survival, and proliferation by affecting bone marrow microenvironment. Potential strategies for eradicating LSCs will also discuss.

Arsenic trioxide inhibits cancer stem-like cells via down-regulation of Gli1 in lung cancer

Cancer stem cells (CSCs) are responsible for the tumorigenesis and recurrence, so targeting CSCs is a potential effective method to cure cancers. Activated Hedgehog signaling pathway has been proved to be implicated in the maintenance of self-renewal of CSCs, and arsenic trioxide (As2O3) has been reported to inhibit Gli1, a key transcription factor of Hedgehog pathway. In this study, we evaluated whether As2O3 has inhibitory effects on cancer stem-like cells (CSLCs) in lung cancer and further explored the possible mechanism. CCK8 assay and colony formation assay were performed to demonstrate the ability of As2O3 to inhibit the growth of NCI-H460 and NCI-H446 cells, which represented non-small cell lung cancer (NSCLC) and small cell lung cancer (SCLC), respectively. Tumor sphere formation assay was carried out to evaluate the effects of As2O3 on stem cell-like subpopulations. The expression of stem cell biomarkers CD133 and stem cell transcription factors such as Sox2 and Oct4 were detected. Moreover, the effects of As2O3 on expression of Gli1 and its target genes were observed. We found that As2O3 inhibited the cell proliferation and reduced the colony formation ability. Importantly, As2O3 decreased the formation of tumor spheres. The expression of stem cell biomarker CD133 and stem cell transcription factors such as Sox2 and Oct4 were markedly reduced by As2O3 treatment. Furthermore, As2O3 decreased the expression of Gli1, N-myc and GAS1. Our results suggested that As2O3 is a promising agent to inhibit CSLCs in lung cancer. In addition, the mechanism of CSLCs inhibition might involve Gli1 down-regulation.

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.

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.

DYRK1B as therapeutic target in Hedgehog/GLI-dependent cancer cells with Smoothened inhibitor resistance

A wide range of human malignancies displays aberrant activation of Hedgehog (HH)/GLI signaling, including cancers of the skin, brain, gastrointestinal tract and hematopoietic system. Targeting oncogenic HH/GLI signaling with small molecule inhibitors of the essential pathway effector Smoothened (SMO) has shown remarkable therapeutic effects in patients with advanced and metastatic basal cell carcinoma. However, acquired and de novo resistance to SMO inhibitors poses severe limitations to the use of SMO antagonists and urgently calls for the identification of novel targets and compounds.Here we report on the identification of the Dual-Specificity-Tyrosine-Phosphorylation-Regulated Kinase 1B (DYRK1B) as critical positive regulator of HH/GLI signaling downstream of SMO. Genetic and chemical inhibition of DYRK1B in human and mouse cancer cells resulted in marked repression of HH signaling and GLI1 expression, respectively. Importantly, DYRK1B inhibition profoundly impaired GLI1 expression in both SMO-inhibitor sensitive and resistant settings. We further introduce a novel small molecule DYRK1B inhibitor, DYRKi, with suitable pharmacologic properties to impair SMO-dependent and SMO-independent oncogenic GLI activity. The results support the use of DYRK1B antagonists for the treatment of HH/GLI-associated cancers where SMO inhibitors fail to demonstrate therapeutic efficacy.

Arsenic Attenuates GLI Signaling, Increasing or Decreasing its Transcriptional Program in a Context-Dependent Manner

The metalloid arsenic is a worldwide environmental toxicant, exposure to which is associated with many adverse outcomes. Arsenic is also an effective therapeutic agent in certain disease settings. Arsenic was recently shown to regulate the activity of the Hedgehog (HH) signal transduction pathway, and this regulation of HH signaling was proposed to be responsible for a subset of arsenic's biologic effects. Surprisingly, these separate reports proposed contradictory activities for arsenic, as either an agonist or antagonist of HH signaling. Here we provide in vitro and in vivo evidence that arsenic acts as a modulator of the activity of the HH effector protein glioma-associated oncogene family zinc finger (GLI), activating or inhibiting GLI activity in a context-dependent manner. This arsenic-induced modulation of HH signaling is observed in cultured cells, patients with colorectal cancer who have received arsenic-based therapy, and a mouse colorectal cancer xenograft model. Our results show that arsenic activates GLI signaling when the intrinsic GLI activity is low but inhibits signaling in the presence of high-level GLI activity. Furthermore, we show that this modulation occurs downstream of primary cilia, evidenced by experiments in suppressor of fused homolog (SUFU) deficient cells. Combining our findings with previous reports, we present an inclusive model in which arsenic plays dual roles in GLI signaling modulation: when GLIs are primarily in their repressor form, arsenic antagonizes their repression capacity, leading to low-level GLI activation, but when GLIs are primarily in their activator form, arsenic attenuates their activity.

Non-canonical Hedgehog/AMPK-Mediated Control of Polyamine Metabolism Supports Neuronal and Medulloblastoma Cell Growth

Developmental Hedgehog signaling controls proliferation of cerebellar granule cell precursors (GCPs), and its aberrant activation is a leading cause of medulloblastoma. We show here that Hedgehog promotes polyamine biosynthesis in GCPs by engaging a non-canonical axis leading to the translation of ornithine decarboxylase (ODC). This process is governed by AMPK, which phosphorylates threonine 173 of the zinc finger protein CNBP in response to Hedgehog activation. Phosphorylated CNBP increases its association with Sufu, followed by CNBP stabilization, ODC translation, and polyamine biosynthesis. Notably, CNBP, ODC, and polyamines are elevated in Hedgehog-dependent medulloblastoma, and genetic or pharmacological inhibition of this axis efficiently blocks Hedgehog-dependent proliferation of medulloblastoma cells in vitro and in vivo. Together, these data illustrate an auxiliary mechanism of metabolic control by a morphogenic pathway with relevant implications in development and cancer.

High neuropeptide Y release associates with Ewing sarcoma bone dissemination - in vivo model of site-specific metastases

Ewing sarcoma (ES) develops in bones or soft tissues of children and adolescents. The presence of bone metastases is one of the most adverse prognostic factors, yet the mechanisms governing their formation remain unclear. As a transcriptional target of EWS-FLI1, the fusion protein driving ES transformation, neuropeptide Y (NPY) is highly expressed and released from ES tumors. Hypoxia up-regulates NPY and activates its pro-metastatic functions. To test the impact of NPY on ES metastatic pattern, ES cell lines, SK-ES1 and TC71, with high and low peptide release, respectively, were used in an orthotopic xenograft model. ES cells were injected into gastrocnemius muscles of SCID/beige mice, the primary tumors excised, and mice monitored for the presence of metastases. SK-ES1 xenografts resulted in thoracic extra-osseous metastases (67%) and dissemination to bone (50%) and brain (25%), while TC71 tumors metastasized to the lungs (70%). Bone dissemination in SK-ES1 xenografts associated with increased NPY expression in bone metastases and its accumulation in bone invasion areas. The genetic silencing of NPY in SK-ES1 cells reduced bone degradation. Our study supports the role for NPY in ES bone invasion and provides new models for identifying pathways driving ES metastases to specific niches and testing anti-metastatic therapeutics.

Basal cell naevus syndrome: an update on genetics and treatment

Basal cell naevus syndrome is an autosomal dominant disorder that stems from mutations in multiple genes, most commonly patched 1 (PTCH1). The classic triad of symptoms consists of basal cell carcinomas, jaw keratocysts and cerebral calcifications, although there are many other systemic manifestations. Because of the broad range of symptoms and development of several types of tumours, early diagnosis and close monitoring are essential to preserve quality of life. Targeting treatment is often difficult because of tumour prevalence. Newer inhibitors of the hedgehog signalling pathway and proteins involved in proliferative growth have shown therapeutic promise. In addition, preventive medications are being devised. We propose a method for determining appropriate treatment for cutaneous tumours.

Evolving molecular era of childhood medulloblastoma: time to revisit therapy

Currently medulloblastoma is treated with a uniform therapeutic approach based on histopathology and clinico-radiological risk stratification, resulting in unpredictable treatment failure and relapses. Improved understanding of the biological, molecular and genetic make-up of these tumors now clearly identifies it as a compendium of four distinct subtypes (WNT, SHH, group 3 and 4). Advances in utilization of the genomic and epigenomic machinery have now delineated genetic aberrations and epigenetic perturbations in each subgroup as potential druggable targets. This has resulted in endeavors to profile targeted therapy. The challenge and future of medulloblastoma therapeutics will be to keep pace with the evolving novel biological insights and translating them into optimal targeted treatment regimens.

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.

Identification of Novel Ezrin Inhibitors Targeting Metastatic Osteosarcoma by Screening Open Access Malaria Box

Ezrin is a member of the ERM (ezrin, radixin, moesin) family of proteins and functions as a linker between the plasma membrane and the actin cytoskeleton. Ezrin is a key driver of tumor progression and metastatic spread of osteosarcoma. We discovered a quinoline-based small molecule, NSC305787, that directly binds to ezrin and inhibits its functions in promoting invasive phenotype. NSC305787 possesses a very close structural similarity to commonly used quinoline-containing antimalarial drugs. On the basis of this similarity and of recent findings that ezrin has a likely role in the pathogenesis of malaria infection, we screened antimalarial compounds in an attempt to identify novel ezrin inhibitors with better efficacy and drug properties. Screening of Medicines for Malaria Venture (MMV) Malaria Box compounds for their ability to bind to recombinant ezrin protein yielded 12 primary hits with high selective binding activity. The specificity of the hits on ezrin function was confirmed by inhibition of the ezrin-mediated cell motility of osteosarcoma cells. Compounds were further tested for phenocopying the morphologic defects associated with ezrin suppression in zebrafish embryos as well as for inhibiting the lung metastasis of high ezrin-expressing osteosarcoma cells. The compound MMV667492 exhibited potent anti-ezrin activity in all biologic assays and had better physicochemical properties for drug-likeness than NSC305787. The drug-like compounds MMV020549 and MMV666069 also showed promising activities in functional assays. Thus, our study suggests further evaluation of antimalarial compounds as a novel class of antimetastatic agents for the treatment of metastatic osteosarcoma.

Effects of altered ephrin-A5 and EphA4/EphA7 expression on tumor growth in a medulloblastoma mouse model

Background

Members of the Eph/ephrin gene families act as key regulators of cerebellar development during embryogenesis. Aberrant signaling of Eph family of receptor tyrosine kinases and their ephrin ligands has also been implicated in human cancers. Medulloblastoma is an aggressive primitive neuroectodermal tumor that originates from granule neuron precursors in the cerebellum. Previous studies have suggested a role for the ephrin-A5 ligand and its receptors, EphA4 and EphA7, in granule cell-precursor formation and in guiding cell migration. In the present study, we investigated the effects of genetic loss of ephrin-A5, EphA4, and EphA7 on the spatiotemporal development of medulloblastoma tumors in the context of the smoothened transgenic mouse model system.

Findings

Radiographic magnetic resonance imaging (MRI) was performed to monitor tumor growth in a genetically engineered mouse model of medulloblastoma. Tumor tissue was harvested to determine changes in the expression of phosphorylated Akt by Western blotting. This helped to establish a correlation between genotype and/or tumor size and survival. Our in vivo data establish that in ND2-SmoA1 transgenic mice, the homozygous deletion of ephrin-A5 resulted in a consistent pattern of tumor growth inhibition compared to their ephrin-A5 wild-type littermate controls, while the loss of EphA4/EphA7 failed to produce consistent effects versus EphA4/EphA7 wild-type mice. A positive correlation was evident between tumor size, p-Akt, and proliferating cell nuclear antigen (PCNA) expression in our transgenic mouse model system, regardless of genotype.

Conclusions

Taken together, our findings underscore the importance of targeting specific members of the Eph/ephrin families in conjunction with the Akt pathway in order to inhibit medulloblastoma tumor growth and progression.

Pharmacological GLI2 inhibition prevents myofibroblast cell-cycle progression and reduces kidney fibrosis

Chronic kidney disease is characterized by interstitial fibrosis and proliferation of scar-secreting myofibroblasts, ultimately leading to end-stage renal disease. The hedgehog (Hh) pathway transcriptional effectors GLI1 and GLI2 are expressed in myofibroblast progenitors; however, the role of these effectors during fibrogenesis is poorly understood. Here, we demonstrated that GLI2, but not GLI1, drives myofibroblast cell-cycle progression in cultured mesenchymal stem cell-like progenitors. In animals exposed to unilateral ureteral obstruction, Hh pathway suppression by expression of the GLI3 repressor in GLI1+ myofibroblast progenitors limited kidney fibrosis. Myofibroblast-specific deletion of Gli2, but not Gli1, also limited kidney fibrosis, and induction of myofibroblast-specific cell-cycle arrest mediated this inhibition. Pharmacologic targeting of this pathway with darinaparsin, an arsenical in clinical trials, reduced fibrosis through reduction of GLI2 protein levels and subsequent cell-cycle arrest in myofibroblasts. GLI2 overexpression rescued the cell-cycle effect of darinaparsin in vitro. While darinaparsin ameliorated fibrosis in WT and Gli1-KO mice, it was not effective in conditional Gli2-KO mice, supporting GLI2 as a direct darinaparsin target. The GLI inhibitor GANT61 also reduced fibrosis in mice. Finally, GLI1 and GLI2 were upregulated in the kidneys of patients with high-grade fibrosis. Together, these data indicate that GLI inhibition has potential as a therapeutic strategy to limit myofibroblast proliferation in kidney fibrosis.

Bone Sarcomas in Pediatrics: Progress in Our Understanding of Tumor Biology and Implications for Therapy

The pediatric bone sarcomas osteosarcoma and Ewing sarcoma represent a tremendous challenge for the clinician. Though less common than acute lymphoblastic leukemia or brain tumors, these aggressive cancers account for a disproportionate amount of the cancer morbidity and mortality in children, and have seen few advances in survival in the past decade, despite many large, complicated, and expensive trials of various chemotherapy combinations. To improve the outcomes of children with bone sarcomas, a better understanding of the biology of these cancers is needed, together with informed use of targeted therapies that exploit the unique biology of each disease. Here we summarize the current state of knowledge regarding the contribution of receptor tyrosine kinases, intracellular signaling pathways, bone biology and physiology, the immune system, and the tumor microenvironment in promoting and maintaining the malignant phenotype. These observations are coupled with a review of the therapies that target each of these mechanisms, focusing on recent or ongoing clinical trials if such information is available. It is our hope that, by better understanding the biology of osteosarcoma and Ewing sarcoma, rational combination therapies can be designed and systematically tested, leading to improved outcomes for a group of children who desperately need them.

Druggable glycolytic requirement for Hedgehog-dependent neuronal and medulloblastoma growth

Aberrant activation of SHH pathway is a major cause of medulloblastoma (MB), the most frequent brain malignancy of the childhood. A few Hedgehog inhibitors, all antagonizing the membrane transducer Smo, have been approved or are under clinical trials for the treatment of human MB. However, the efficacy of these drugs is limited by the occurrence of novel mutations or by activation of downstream or non-canonical Hedgehog components. Thus, the identification of novel druggable downstream pathways represents a critical step to overcome this problem. In the present work we demonstrate that aerobic glycolysis is a valuable HH-dependent downstream target, since its inhibition significantly counteracts the HH-mediated growth of normal and tumor cells. Hedgehog activation induces transcription of hexokinase 2 (HK2) and pyruvate kinase M2 (PKM2), two key gatekeepers of glycolysis. The process is mediated by the canonical activation of the Gli transcription factors and causes a robust increase of extracellular lactate concentration. We show that inhibition of glycolysis at different levels blocks the Hedgehog-induced proliferation of granule cell progenitors (GCPs), the cells from which medulloblastoma arises. Remarkably, we demonstrate that this glycolytic transcriptional program is also upregulated in SHH-dependent tumors and that pharmacological targeting with the pyruvate kinase inhibitor dichloroacetate (DCA) efficiently represses MB growth in vitro and in vivo. Together, these data illustrate a previously uncharacterized pharmacological strategy to target Hedgehog dependent growth, which can be exploited for the treatment of medulloblastoma patients.

Chinese medicines for prevention and treatment of human hepatocellular carcinoma: current progress on pharmacological actions and mechanisms

Hepatocellular carcinoma (HCC) is one of leading causes of death in the world. Although various treatments have been developed, the therapeutic side effects are far from desirable. Chinese medicines (CMs, including plants, animal parts and minerals) have drawn a great deal of attention in recent years for their potential in the treatment of HCC. Most studies have shown that CMs may be able to retard HCC progression with multiple actions, either alone or in combination with other conventional therapies to improve quality of life in HCC patients. Additionally, CMs are used for preventing HCC occurrence. The aim of this study is to review the potential prophylactic and curative effects of CMs on human HCC and the possible mechanisms that underlie these pharmacological actions. Publications were collected and reviewed from PubMed and China National Knowledge Infrastructure from 2000 to 2014. Keywords for literature searches include "Chinese medicine", "Chinese herb", "traditional Chinese Medicine", "hepatocellular carcinoma" and "liver cancer". CMs in forms of pure compounds, isolated fractions, and composite formulas are included. Combination therapies are also considered. Both in vitro and in vivo efficacies of CMs are being discussed and the translational potential to bedside is to be discussed with clinical cases, which show the actions of CMs on HCC may include tumor growth inhibition, antimetastatic activities, anti-inflammation, anti-liver cancer stem cells, reversal on multi-drug resistance and induction/reduction of oxidative stress. Multiple types of molecules are found to contribute in the above actions. The review paper indicated that CMs might have potential to both prevent HCC occurrence and retard HCC progression with several molecular targets involved.

EWS/FLI1 Target Genes and Therapeutic Opportunities in Ewing Sarcoma

Ewing sarcoma is an aggressive bone malignancy that affect children and young adults. Ewing sarcoma is the second most common primary bone malignancy in pediatric patients. Although significant progress has been made in the treatment of Ewing sarcoma since it was first described in the 1920s, in the last decade survival rates have remained unacceptably invariable, thus pointing to the need for new approaches centered in the molecular basis of the disease. Ewing sarcoma driving mutation, EWS–FLI1, which results from a chromosomal translocation, encodes an aberrant transcription factor. Since its first characterization in 1990s, many molecular targets have been described to be regulated by this chimeric transcription factor. Their contribution to orchestrate Ewing sarcoma phenotype has been reported over the last decades. In this work, we will focus on the description of a selection of EWS/FLI1 targets, their functional role, and their potential clinical relevance. We will also discuss their role in other types of cancer as well as the need for further studies to be performed in order to achieve a broader understanding of their particular contribution to Ewing sarcoma development.

Hedgehog Signaling in Malignant Pleural Mesothelioma

Malignant pleural mesothelioma (MPM) is a cancer associated with exposure to asbestos fibers, which accumulate in the pleural space, damage tissue and stimulate regeneration. Hedgehog signaling is a pathway important during embryonic mesothelium development and is inactivated in adult mesothelium. The pathway is reactivated in some MPM patients with poor clinical outcome, mainly mediated by the expression of the ligands. Nevertheless, mutations in components of the pathway have been observed in a few cases. Data from different MPM animal models and primary culture suggest that both autocrine and paracrine Hedgehog signaling are important to maintain tumor growth. Drugs inhibiting the pathway at the level of the smoothened receptor (Smo) or glioma-associated protein transcription factors (Gli) have been used mostly in experimental models. For clinical development, biomarkers are necessary for the selection of patients who can benefit from Hedgehog signaling inhibition.

Management of pediatric and adult patients with medulloblastoma

OPINION STATEMENT

Approximately 70 % of newly diagnosed children with medulloblastoma (MB) will be classified as "standard risk": their tumor is localized to the posterior fossa, they undergo a near or gross total resection, the tumor does not meet the criteria for large cell/anaplastic histology, and there is no evidence of neuroaxis dissemination by brain/spine MRI and lumbar puncture for cytopathology. Following surgical recovery, they are treated with craniospinal radiation therapy with a boost to the posterior fossa or tumor bed. Adjuvant therapy for approximately 1 year follows anchored by the use of alkylators, platinators, and microtubule inhibitors. This approach to standard risk MB works; greater than 80 % of patients will be cured, and such approaches are arguably the standard of care worldwide for such children. Despite this success, some children with standard risk features will relapse and die of recurrent disease despite aggressive salvage therapy. Moreover, current treatment, even when curative causes life-long morbidity in those who survive, and the consequences are age dependent. For the 20-year-old patient, damage to the cerebellum from surgery conveys greater risk than craniospinal radiation; however, for the 3-year-old patient, the opposite is true. The challenge for the neuro-oncologist today is how to identify accurately patients who need less therapy as well as those for whom current therapy is inadequate. As molecular diagnostics comes of age in brain tumors, the question becomes how to best implement novel methods of risk stratification. Are we able to obtain specific information about the tumor's biology in an increasingly rapid and reliable way, and utilize these findings in the upfront management of these tumors? Precision medicine should allow us to tailor therapy to the specific drivers of each patient's tumor. Regardless of how new approaches are implemented, it is likely that we will no longer be able to have a single standard approach to standard risk medulloblastoma in the near future.

Digging a hole under Hedgehog: downstream inhibition as an emerging anticancer strategy

Hedgehog signaling is a key regulator of development and stem cell fate and its aberrant activation is a leading cause of a number of tumors. Activating germline or somatic mutations of genes encoding Hh pathway components are found in Basal Cell Carcinoma (BCC) and Medulloblastoma (MB). Ligand-dependent Hedgehog hyperactivation, due to autocrine or paracrine mechanisms, is also observed in a large number of malignancies of the breast, colon, skin, bladder, pancreas and other tissues. The key tumorigenic role of Hedgehog has prompted effort aimed at identifying inhibitors of this signaling. To date, only the antagonists of the membrane transducer Smo have been approved for therapy or are under clinical trials in patients with BCC and MB linked to Ptch or Smo mutations. Despite the good initial response, patients treated with Smo antagonists have eventually developed resistance due to the occurrence of compensating mechanisms. Furthermore, Smo antagonists are not effective in tumors where the Hedgehog hyperactivation is due to mutations of pathway components downstream of Smo, or in case of non-canonical, Smo-independent activation of the Gli transcription factors. For all these reasons, the research of Hh inhibitors acting downstream of Smo is becoming an area of intensive investigation. In this review we illustrate the progresses made in the identification of effective Hedgehog inhibitors and their application in cancer, with a special emphasis on the newly identified downstream inhibitors. We describe in detail the Gli inhibitors and illustrate their mode of action and applications in experimental and/or clinical settings.

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.

Merkel Cell Carcinoma with a Suppressor of Fused (SUFU) Mutation: Case Report and Potential Therapeutic Implications

Introduction

Merkel cell carcinoma is a neuroendocrine malignancy. Suppressor of fused (SUFU) is a tumor suppressor oncogene that participates in the Hedgehog (Hh) signaling pathway. The aim of the study was to describe a patient whose Merkel cell carcinoma demonstrated a SUFU genomic alteration.

Case Study

The Hh signaling pathway is involved in the pathogenesis of several tumors, including nevoid basal cell carcinoma syndrome that is associated with an alteration of the patched-1 (PTCH1) gene. Targeted molecular therapy against smoothened (SMO) with vismodegib has been shown to be an effective therapeutic intervention for patients with PTCH-1 mutation. The reported patient was presented with metastatic Merkel cell carcinoma. Analysis of his tumor, using a next-generation sequencing-based assay, demonstrated a genomic aberration of SUFU protein, a component of the Hh signaling pathway that acts downstream to SMO and, therefore, is unlikely to be responsive to vismodegib. Of interest, arsenic trioxide or bromo and extra C-terminal inhibitors impact signals downstream to SUFU, making this aberration conceivably druggable. His tumor has initially been managed with chemotherapy (carboplatin and etoposide) and subsequent radiation therapy is planned.

Conclusion

The pathogenesis of Merkel cell carcinoma is multifactorial, and related to ultraviolet radiation exposure, immunosuppression, and Merkel cell polyomavirus. We report a patient with a mutation in SUFU, a potentially actionable component of the Hh signaling pathway.

Electronic supplementary material

The online version of this article (doi:10.1007/s13555-015-0074-5) contains supplementary material, which is available to authorized users.

Cooperative integration between HEDGEHOG-GLI signalling and other oncogenic pathways: implications for cancer therapy

The HEDGEHOG-GLI (HH-GLI) signalling is a key pathway critical in embryonic development, stem cell biology and tissue homeostasis. In recent years, aberrant activation of HH-GLI signalling has been linked to several types of cancer, including those of the skin, brain, lungs, prostate, gastrointestinal tract and blood. HH-GLI signalling is initiated by binding of HH ligands to the transmembrane receptor PATCHED and is mediated by transcriptional effectors that belong to the GLI family, whose activity is finely tuned by a number of molecular interactions and post-translation modifications. Several reports suggest that the activity of the GLI proteins is regulated by several proliferative and oncogenic inputs, in addition or independent of upstream HH signalling. The identification of this complex crosstalk and the understanding of how the major oncogenic signalling pathways interact in cancer is a crucial step towards the establishment of efficient targeted combinatorial treatments. Here we review recent findings on the cooperative integration of HH-GLI signalling with the major oncogenic inputs and we discuss how these cues modulate the activity of the GLI proteins in cancer. We then summarise the latest advances on SMO and GLI inhibitors and alternative approaches to attenuate HH signalling through rational combinatorial therapies.

Hedgehog/GLI and PI3K signaling in the initiation and maintenance of chronic lymphocytic leukemia

The initiation and maintenance of a malignant phenotype requires complex and synergistic interactions of multiple oncogenic signals. The Hedgehog (HH)/GLI pathway has been implicated in a variety of cancer entities and targeted pathway inhibition is of therapeutic relevance. Signal cross-talk with other cancer pathways including PI3K/AKT modulates HH/GLI signal strength and its oncogenicity. In this study, we addressed the role of HH/GLI and its putative interaction with the PI3K/AKT cascade in the initiation and maintenance of chronic lymphocytic leukemia (CLL). Using transgenic mouse models, we show that B-cell-specific constitutive activation of HH/GLI signaling either at the level of the HH effector and drug target Smoothened or at the level of the GLI transcription factors does not suffice to initiate a CLL-like phenotype characterized by the accumulation of CD5⁺ B cells in the lymphatic system and peripheral blood. Furthermore, Hh/Gli activation in Pten-deficient B cells with activated Pi3K/Akt signaling failed to enhance the expansion of leukemic CD5⁺ B cells, suggesting that genetic or epigenetic alterations leading to aberrant HH/GLI signaling in B cells do not suffice to elicit a CLL-like phenotype in mice. By contrast, we identify a critical role of GLI and PI3K signaling for the survival of human primary CLL cells. We show that combined targeting of GLI and PI3K/AKT/mTOR signaling can have a synergistic therapeutic effect in cells from a subgroup of CLL patients, thereby providing a basis for the evaluation of future combination therapies targeting HH/GLI and PI3K signaling in this common hematopoietic malignancy.

Arsenic trioxide inhibits growth of human chondrosarcoma cells through G2/M arrest and apoptosis as well as autophagy

It has been demonstrated that Gli1 is expressed in chondrosarcoma but not in the normal articular cartilage tissues. Downregulating Gli1 by small interfering RNA inhibited chondrosarcoma cells growth. Arsenic trioxide (ATO) has been demonstrated to suppress human cancer cell growth by targeting Gli1. The aim of this study was to investigate the effect of ATO on antineoplastic capability of chondrosarcoma cells. We found that ATO inhibited the growth of chondrosarcoma cells in dose-dependent and time-dependent manners via MTT and colony formation assays. In addition, ATO treatment induced apoptosis and promoted G2/M phase arrest in SW1353 cells as analyzed by flow cytometry assays and Western blotting. Furthermore, we observed that ATO also triggered autophagy by regulating mammalian target of rapamycin (mTOR) phosphorylation. Finally, we found that ATO-mediated cell death could be averted by autophagy inhibitor. Taken together, the current study suggested that ATO had therapeutic efficacy in human chondrosarcoma cells through the promotion of G2/M arrest and induction of both apoptosis as well as autophagy. ATO administration could be a novel therapeutic strategy for treating chondrosarcomas.

Metformin sensitizes hepatocellular carcinoma to arsenic trioxide-induced apoptosis by downregulating Bcl2 expression

Hepatocellular carcinoma (HCC) is a highly malignant tumor that can evolve rapidly to acquire resistance to conventional chemotherapies. Arsenic trioxide (ATO) is a traditional Asian medicine, and a phase II study has shown that treatment with ATO alone was not effective against HCC. Bcl2 is an antiapoptotic protein that regulates chemotherapy in HCC. Metformin is reported to decrease Bcl2 expression, and the purpose of this study was to verify whether metformin could potentiate the anti-HCC efficacy of ATO in vitro. In the present study, we used metformin and ATO alone or in combination and then tested proliferation, apoptosis, and Bcl2 level of HCC cells. The results showed that metformin enhanced both the proliferation-inhibiting and apoptosis-inducing effects of ATO on HCC cell lines HepG2 and BEL7402. Furthermore, this activity proceeded via a mechanism involving metformin-induced downregulation of Bcl2. A combination of ATO and metformin is therefore a potentially promising approach for HCC therapy.

Gli1/DNA interaction is a druggable target for Hedgehog-dependent tumors

Hedgehog signaling is essential for tissue development and stemness, and its deregulation has been observed in many tumors. Aberrant activation of Hedgehog signaling is the result of genetic mutations of pathway components or other Smo-dependent or independent mechanisms, all triggering the downstream effector Gli1. For this reason, understanding the poorly elucidated mechanism of Gli1-mediated transcription allows to identify novel molecules blocking the pathway at a downstream level, representing a critical goal in tumor biology. Here, we clarify the structural requirements of the pathway effector Gli1 for binding to DNA and identify Glabrescione B as the first small molecule binding to Gli1 zinc finger and impairing Gli1 activity by interfering with its interaction with DNA. Remarkably, as a consequence of its robust inhibitory effect on Gli1 activity, Glabrescione B inhibited the growth of Hedgehog-dependent tumor cells in vitro and in vivo as well as the self-renewal ability and clonogenicity of tumor-derived stem cells. The identification of the structural requirements of Gli1/DNA interaction highlights their relevance for pharmacologic interference of Gli signaling.

Darinaparsin inhibits prostate tumor-initiating cells and Du145 xenografts and is an inhibitor of hedgehog signaling

Prostate cancer is the leading cause of cancer-related death in men in the United States. A major cause of drug resistance in prostate and other epithelial tumors may be due to the presence of a fraction of tumor cells that retain the ability to initiate tumors and hence are termed tumor-initiating cells (TIC) or cancer stem cells. Here, we report that darinaparsin, an organic derivative of arsenic trioxide, is cytotoxic to prostate cancer cell lines as well as fresh prostate cancer cells from patients at low micromolar concentrations, and importantly inhibits the TIC subpopulations. It also inhibits growth of the castrate-resistant Du145 prostate tumor propagated as xenograft in mice and inhibits the tumor-initiating potential of prostate cancer cells. Although the mechanism by which darinaparsin acts is not completely known, we show that it kills prostate cancer cells by blocking cells in the G2-M phase of the cell cycle and inhibits Hedgehog signaling by downregulating Gli-2 transcriptional activity. These data provide a rationale for evaluating darinaparsin in patients with castrate-resistant prostate cancer.

Integration of Network Biology and Imaging to Study Cancer Phenotypes and Responses

Ever growing "omics" data and continuously accumulated biological knowledge provide an unprecedented opportunity to identify molecular biomarkers and their interactions that are responsible for cancer phenotypes that can be accurately defined by clinical measurements such as in vivo imaging. Since signaling or regulatory networks are dynamic and context-specific, systematic efforts to characterize such structural alterations must effectively distinguish significant network rewiring from random background fluctuations. Here we introduced a novel integration of network biology and imaging to study cancer phenotypes and responses to treatments at the molecular systems level. Specifically, Differential Dependence Network (DDN) analysis was used to detect statistically significant topological rewiring in molecular networks between two phenotypic conditions, and in vivo Magnetic Resonance Imaging (MRI) was used to more accurately define phenotypic sample groups for such differential analysis. We applied DDN to analyze two distinct phenotypic groups of breast cancer and study how genomic instability affects the molecular network topologies in high-grade ovarian cancer. Further, FDA-approved arsenic trioxide (ATO) and the ND2-SmoA1 mouse model of Medulloblastoma (MB) were used to extend our analyses of combined MRI and Reverse Phase Protein Microarray (RPMA) data to assess tumor responses to ATO and to uncover the complexity of therapeutic molecular biology.

Arsenic inhibits hedgehog signaling during P19 cell differentiation

Arsenic is a toxicant found in ground water around the world, and human exposure mainly comes from drinking water or from crops grown in areas containing arsenic in soils or water. Epidemiological studies have shown that arsenic exposure during development decreased intellectual function, reduced birth weight, and altered locomotor activity, while in vitro studies have shown that arsenite decreased muscle and neuronal cell differentiation. The sonic hedgehog (Shh) signaling pathway plays an important role during the differentiation of both neurons and skeletal muscle. The purpose of this study was to investigate whether arsenic can disrupt Shh signaling in P19 mouse embryonic stem cells, leading to changes muscle and neuronal cell differentiation. P19 embryonic stem cells were exposed to 0, 0.25, or 0.5 μM of sodium arsenite for up to 9 days during cell differentiation. We found that arsenite exposure significantly reduced transcript levels of genes in the Shh pathway in both a time and dose-dependent manner. This included the Shh ligand, which was decreased 2- to 3-fold, the Gli2 transcription factor, which was decreased 2- to 3-fold, and its downstream target gene Ascl1, which was decreased 5-fold. GLI2 protein levels and transcriptional activity were also reduced. However, arsenic did not alter GLI2 primary cilium accumulation or nuclear translocation. Moreover, additional extracellular SHH rescued the inhibitory effects of arsenic on cellular differentiation due to an increase in GLI binding activity. Taken together, we conclude that arsenic exposure affected Shh signaling, ultimately decreasing the expression of the Gli2 transcription factor. These results suggest a mechanism by which arsenic disrupts cell differentiation.

Hedgehog signaling pathway: a novel target for cancer therapy: vismodegib, a promising therapeutic option in treatment of basal cell carcinomas

The Hedgehog signaling pathway is one of the major regulators of cell growth and differentiation during embryogenesis and early development. It is mostly quiescent in adults but inappropriate mutation or deregulation of the pathway is involved in the development of cancers. Therefore; recently it has been recognized as a novel therapeutic target in cancers. Basal cell carcinomas (BCC) and medulloblastomas are the two most common cancers identified with mutations in components of the hedgehog pathway. The discovery of targeted Hedgehog pathway inhibitors has shown promising results in clinical trials, several of which are still undergoing clinical evaluation. Vismodegib (GDC-0449), an oral hedgehog signaling pathway inhibitor has reached the farthest in clinical development. Initial clinical trials in basal cell carcinoma and medulloblastoma have shown good efficacy and safety and hence were approved by U.S. FDA for use in advanced basal cell carcinomas. This review highlights the molecular basis and the current knowledge of hedgehog pathway activation in different types of human cancers as well as the present and future prospects of the novel drug vismodegib.

Direct binding of arsenic trioxide to AMPK and generation of inhibitory effects on acute myeloid leukemia precursors

Arsenic trioxide (As2O3) exhibits potent antineoplastic effects and is used extensively in clinical oncology for the treatment of a subset of patients with acute myeloid leukemia (AML). Although As2O3 is known to regulate activation of several signaling cascades, the key events, accounting for its antileukemic properties, remain to be defined. We provide evidence that arsenic can directly bind to cysteine 299 in AMPKα and inhibit its activity. This inhibition of AMPK by arsenic is required in part for its cytotoxic effects on primitive leukemic progenitors from patients with AML, while concomitant treatment with an AMPK activator antagonizes in vivo the arsenic-induced antileukemic effects in a xenograft AML mouse model. A consequence of AMPK inhibition is activation of the mTOR pathway as a negative regulatory feedback loop. However, when AMPK expression is lost, arsenic-dependent activation of the kinase RSK downstream of MAPK activity compensates the generation of regulatory feedback signals through phosphorylation of downstream mTOR targets. Thus, therapeutic regimens with As2O3 will need to include inhibitors of both the mTOR and RSK pathways in combination to prevent engagement of negative feedback loops and maximize antineoplastic responses.

Context-dependent signal integration by the GLI code: the oncogenic load, pathways, modifiers and implications for cancer therapy

Canonical Hedgehog (HH) signaling leads to the regulation of the GLI code: the sum of all positive and negative functions of all GLI proteins. In humans, the three GLI factors encode context-dependent activities with GLI1 being mostly an activator and GLI3 often a repressor. Modulation of GLI activity occurs at multiple levels, including by co-factors and by direct modification of GLI structure. Surprisingly, the GLI proteins, and thus the GLI code, is also regulated by multiple inputs beyond HH signaling. In normal development and homeostasis these include a multitude of signaling pathways that regulate proto-oncogenes, which boost positive GLI function, as well as tumor suppressors, which restrict positive GLI activity. In cancer, the acquisition of oncogenic mutations and the loss of tumor suppressors - the oncogenic load - regulates the GLI code toward progressively more activating states. The fine and reversible balance of GLI activating GLI(A) and GLI repressing GLI(R) states is lost in cancer. Here, the acquisition of GLI(A) levels above a given threshold is predicted to lead to advanced malignant stages. In this review we highlight the concepts of the GLI code, the oncogenic load, the context-dependency of GLI action, and different modes of signaling integration such as that of HH and EGF. Targeting the GLI code directly or indirectly promises therapeutic benefits beyond the direct blockade of individual pathways.