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Concept: Hedgehog signaling pathway

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The Hedgehog (Hh) proteins comprise a group of secreted proteins that regulate cell growth, differentiation and survival. Inappropriate activation of the Hh signaling pathway has been implicated in the development of a variety of cancers. Hh pathway inhibitors are a relatively new class of therapeutic agents that act by targeting the proteins involved in the regulation of Hh pathway (PTCH, SMO and Gli). Together, they serve as exciting new prospects, with a bright future, both alone or as an adjuvant to the more traditional anti-cancer drugs.

Concepts: Immune system, DNA, Protein, Gene expression, Developmental biology, Endoplasmic reticulum, Chemotherapy, Hedgehog signaling pathway

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Alterations in hedgehog signaling are implicated in the pathogenesis of basal-cell carcinoma. Although most basal-cell carcinomas are treated surgically, no effective therapy exists for locally advanced or metastatic basal-cell carcinoma. A phase 1 study of vismodegib (GDC-0449), a first-in-class, small-molecule inhibitor of the hedgehog pathway, showed a 58% response rate among patients with advanced basal-cell carcinoma.

Concepts: Cancer, Lung cancer, Carcinoma, Squamous cell carcinoma, Basal cell carcinoma, Hedgehog signaling pathway

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Recognition of the multiple roles of Hedgehog signaling in cancer has prompted intensive efforts to develop targeted pathway inhibitors. Leading inhibitors in clinical development act by binding to a common site within Smoothened, a critical pathway component. Acquired Smoothened mutations, including SMO(D477G), confer resistance to these inhibitors. Here, we report that itraconazole and arsenic trioxide, two agents in clinical use that inhibit Hedgehog signaling by mechanisms distinct from that of current Smoothened antagonists, retain inhibitory activity in vitro in the context of all reported resistance-conferring Smoothened mutants and GLI2 overexpression. Itraconazole and arsenic trioxide, alone or in combination, inhibit the growth of medulloblastoma and basal cell carcinoma in vivo, and prolong survival of mice with intracranial drug-resistant SMO(D477G) medulloblastoma.

Concepts: Pharmacology, Cancer, Oncology, Squamous cell carcinoma, Basal cell carcinoma, Hedgehog signaling pathway, Arsenic trioxide, Cyclopamine

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Hedgehog pathway inhibition has been suggested as a potential maintenance treatment approach in ovarian cancer through disruption of tumor-stromal interactions. Vismodegib is an orally available Hedgehog pathway inhibitor with clinical activity in advanced basal cell carcinoma and medulloblastoma. This phase II, randomized, double-blind, placebo-controlled trial was designed to provide a preliminary estimate of efficacy in patients with ovarian cancer in second or third complete remission (CR).

Concepts: Vitamin D, Metastasis, Hereditary nonpolyposis colorectal cancer, BRCA2, Adenocarcinoma, Squamous cell carcinoma, Basal cell carcinoma, Hedgehog signaling pathway

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BACKGROUND: The Hedgehog Signaling Pathway is one of signaling pathways that are very important toembryonic development. The participation of inhibitors in the Hedgehog Signal Pathway cancontrol cell growth and death, and searching novel inhibitors to the functioning of thepathway are in a great demand. As the matter of fact, effective inhibitors could provideefficient therapies for a wide range of malignancies, and targeting such pathway in cellsrepresents a promising new paradigm for cell growth and death control. Current researchmainly focuses on the syntheses of the inhibitors of cyclopamine derivatives, which bindspecifically to the Smo protein, and can be used for cancer therapy. While quantitativelystructure-activity relationship (QSAR) studies have been performed for these compounds among different cell lines, none of them have achieved acceptable results in the prediction ofactivity values of new compounds. In this study, we proposed a novel collaborative QSARmodel for inhibitors of the Hedgehog Signaling Pathway by integration the information frommultiple cell lines. Such a model is expected to substantially improve the QSAR ability fromsingle cell lines, and provide useful clues in developing clinically effective inhibitors andmodifications of parent lead compounds for target on the Hedgehog Signaling Pathway. RESULTS: In this study, we have presented: (1) a collaborative QSAR model, which is used to integrateinformation among multiple cell lines to boost the QSAR results, rather than only a singlecell line QSAR modeling. Our experiments have shown that the performance of our model issignificantly better than single cell line QSAR methods; and (2) an efficient feature selectionstrategy under such collaborative environment, which can derive the commonly importantfeatures related to the entire given cell lines, while simultaneously showing their specificcontributions to a specific cell-line. Based on feature selection results, we have proposedseveral possible chemical modifications to improve the inhibitor affinity towards multipletargets in the Hedgehog Signaling Pathway. CONCLUSIONS: Our model with the feature selection strategy presented here is efficient, robust, and flexible,and can be easily extended to model large-scale multiple cell line/QSAR data. The data andscripts for collaborative QSAR modeling are available in the Additional file 1.

Concepts: Protein, Cell, Signal transduction, Cell biology, Model organism, Cell culture, Hedgehog signaling pathway, Cyclopamine

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Activation of sonic hedgehog (HH) signaling pathway has been implicated in aggressiveness and progression of gastrointestinal tumors. We planned this study to identify a subgroup of gastric cancer (GC) patients with HH activation and to assess the effect of a HH inhibitor in HH activated GC in vitro. We surveyed HH pathway activation among 512 GC specimens for protein expression of various target genes involved in HH pathway: Indian hedgehog (IHH), patched-1 (PTCH1), smoothened (SMO), GLI2, and FOXA2. We analyzed the correlations between the expression of these factors and clinicopathological features and prognosis. In vitro, ten gastric cancer cell lines were screened for anti-tumoractivity of an HH inhibitor, GDC-0449. Among the 512 specimens, 105 (20.0 %), 83 (16.3 %), 130 (25.5 %), 61 (12.0 %), and 206 (40.8 %) were positive for IHH, PTCH1, GLI2, SMO, and FOXA2 expression, respectively. PTCH1 expression was more frequently observed in well- or moderately differentiated tubular adenocarcinoma, intestinal type and low stage GC. GLI2 was correlated with lymphovascular invasion and intestinal type GC. A high-stage and negative PTCH1 staining were identified as unfavorable independent risk factors for overall survival in multivariate analysis (P < 0.001, 0.045, respectively). For IHH, SMO, and FOXA2, there was no statistical difference in clinicopathologic variables and survival outcome. An HH inhibitor had particularly potent effects on GC cell lines with SMO mRNA overexpression. This is the largest report to analyze the hedgehog pathway in GC. PTCH1 overexpression was an independent prognostic factor for survival and SMO overexpression which was found in 12.0 % of GC patients might be the potential predictive marker of HH inhibitor.

Concepts: DNA, Genetics, Gene expression, Cell, Cancer, Lung cancer, Sonic hedgehog, Hedgehog signaling pathway

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Vismodegib is the first Hedgehog pathway inhibitor to be approved in the USA, where it is indicated for the treatment of adults with metastatic basal cell carcinoma (BCC), or with locally advanced BCC that has recurred following surgery or who are not candidates for surgery, and who are not candidates for radiation. In an ongoing, noncomparative, phase II trial, oral vismodegib was effective in and had an acceptable tolerability profile in the treatment of patients with locally advanced or metastatic BCC.

Concepts: Clinical trial, Cancer, Metastasis, United States, Chemotherapy, Squamous cell carcinoma, Basal cell carcinoma, Hedgehog signaling pathway

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Sonic hedgehog (Shh) determines cerebellar granule cell (GC) progenitor proliferation and medulloblastoma pathogenesis. However, the pathways regulating GC progenitors during embryogenesis before Shh production by Purkinje neurons and their roles in tumorigenesis remain unclear. The cilium-localized G-protein-coupled receptor Gpr161 suppresses Shh-mediated signaling in the neural tube. Here, by deleting Gpr161 in mouse neural stem cells or GC progenitors, we establish Gpr161 as a tumor suppressor in Shh subtype medulloblastoma. Irrespective of Shh production in the cerebellum, Gpr161 deletion increased downstream activity of the Shh pathway by restricting Gli3-mediated repression, causing more extensive generation and proliferation of GC progenitors. Moreover, earlier deletion of Gpr161 during embryogenesis increased tumor incidence and severity. GC progenitor overproduction during embryogenesis from Gpr161 deletion was cilium dependent, unlike normal development. Low GPR161 expression correlated with poor survival of SHH subtype medulloblastoma patients. Gpr161 restricts GC progenitor production by preventing premature and Shh-dependent pathway activity, highlighting the importance of basal pathway suppression in tumorigenesis.

Concepts: Central nervous system, Neuron, Brain, Cerebellum, Purkinje cell, Sonic hedgehog, Hedgehog signaling pathway, Parallel fiber

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In developing tissues, cells estimate their spatial position by sensing graded concentrations of diffusible signaling proteins called morphogens. Morphogen-sensing pathways exhibit diverse molecular architectures, whose roles in controlling patterning dynamics and precision remain unclear. Here, combining cell-based in vitro gradient reconstitution, genetic re-wiring, and mathematical modeling, we systematically analyzed the unique architectural features of the Sonic Hedgehog pathway. The combination of double-negative regulatory logic and negative feedback through the PTCH receptor accelerates gradient formation and improves robustness to variation in the morphogen production rate compared to alternative designs. The ability to isolate morphogen patterning from concurrent developmental processes, and to compare the patterning behaviors of alternative, re-wired, pathway architectures offers a powerful way to understand and engineer multicellular patterning.

Concepts: Mathematics, Engineering, Cell signaling, Control theory, Sonic hedgehog, Hedgehog signaling pathway, Architecture, Morphogens

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Neurogenesis impairment starting from early developmental stages is a key determinant of intellectual disability in Down syndrome (DS). Previous evidence provided a causal relationship between neurogenesis impairment and malfunctioning of the mitogenic Sonic Hedgehog (Shh) pathway. In particular, excessive levels of AICD (amyloid precursor protein intracellular domain), a cleavage product of the trisomic gene APP (amyloid precursor protein) up-regulate transcription of Ptch1 (Patched1), the Shh receptor that keeps the pathway repressed. Since AICD results from APP cleavage by γ-secretase, the goal of the current study was to establish whether treatment with a γ-secretase inhibitor normalises AICD levels and restores neurogenesis in trisomic neural precursor cells. We found that treatment with a selective γ-secretase inhibitor (ELND006; ELN) restores proliferation in neurospheres derived from the subventricular zone (SVZ) of the Ts65Dn mouse model of DS. This effect was accompanied by reduction of AICD and Ptch1 levels and was prevented by inhibition of the Shh pathway with cyclopamine. Treatment of Ts65Dn mice with ELN in the postnatal period P3-P15 restored neurogenesis in the SVZ and hippocampus, hippocampal granule cell number and synapse development, indicating a positive impact of treatment on brain development. In addition, in the hippocampus of treated Ts65Dn mice there was a reduction in the expression levels of various genes that are transcriptionally regulated by AICD, including APP, its origin substrate. Inhibitors of γ-secretase are currently envisaged as tools for the cure of Alzheimer’s disease because they lower βamyloid levels. Current results provide novel evidence that γ-secretase inhibitors may represent a strategy for the rescue of neurogenesis defects in DS.

Concepts: Alzheimer's disease, Neuron, Gene, Gene expression, Hippocampus, Inhibitor, Sonic hedgehog, Hedgehog signaling pathway