Smo Antagonist Research Articles

Impact of the Smoothened Inhibitor, IPI-926, on Smoothened Ciliary Localization and Hedgehog Pathway Activity

A requisite step for canonical Hedgehog (Hh) pathway activation by Sonic Hedgehog (Shh) ligand is accumulation of Smoothened (Smo) to the primary cilium (PC). Activation of the Hh pathway has been implicated in a broad range of cancers, and several Smo antagonists are being assessed clinically, one of which is approved for the treatment of advanced basal cell carcinoma. Recent reports demonstrate that various Smo antagonists differentially impact Smo localization to the PC while still exerting inhibitory activity. In contrast to other synthetic small molecule Smo antagonists, the natural product cyclopamine binds to and promotes ciliary accumulation of Smo and “primes” cells for Hh pathway hyper-responsiveness after compound withdrawal. We compared the properties of IPI-926, a semi-synthetic cyclopamine analog, to cyclopamine with regard to potency, ciliary Smo accumulation, and Hh pathway activity after compound withdrawal. Like cyclopamine, IPI-926 promoted accumulation of Smo to the PC. However, in contrast to cyclopamine, IPI-926 treatment did not prime cells for hyper-responsiveness to Shh stimulation after compound withdrawal, but instead demonstrated continuous inhibition of signaling. By comparing the levels of drug-induced ciliary Smo accumulation with the degree of Hh pathway activity after compound withdrawal, we propose that a critical threshold of ciliary Smo is necessary for “priming” activity to occur. This “priming” appears achievable with cyclopamine, but not IPI-926, and is cell-line dependent. Additionally, IPI-926 activity was evaluated in a murine tumor xenograft model and a pharmacokinetic/pharmacodynamic relationship was examined to assess for in vivo evidence of Hh pathway hyper-responsiveness. Plasma concentrations of IPI-926 correlated with the degree and duration of Hh pathway suppression, and pathway activity did not exceed baseline levels out to 96 hours post dose. The overall findings suggest that IPI-926 possesses unique biophysical and pharmacological properties that result in Hh pathway inhibition in a manner that differentiates it from cyclopamine.

Therapeutic Opportunities for Medulloblastoma Come of Age

In this issue of Cancer Cell, Kool and colleagues reveal clear genetically defined subclasses of the sonic hedgehog (SHH) subclass of medulloblastoma. This molecular dissection of the SHH subclass is not simply a cutting-edge advance; the data have profound impact on clinical trial design and decision-making.

Discovery and Exploitation of Novel Targets by Approved Drugs

Discovery and Exploitation of Novel Targets by Approved Drugs

Primary cilia mediate sonic hedgehog signaling to regulate neuronal‐like differentiation of bone mesenchymal stem cells for resveratrol induction in vitro

Mesenchymal stem cells (MSCs) can differentiate into neuronal-like cell types under specific conditions. The classical antioxidant inducers such as β-mercaptoethanol (BME), butylated hydroxyanisol (BHA), and dimethylsulfoxide (DMSO) are limited in clinical because of toxicity. Resveratrol, a safer, natural antioxidant, can stimulate osteoblastic differentiation of MSCs. However, its effect of inducing MSCs to differentiate into neuronal-like cells is less well studied, and its differentiated mechanisms are not well understood. Sonic hedgehog (Shh) signaling, mediated by the primary cilia, is crucial for embryonic development and tissue differentiation, but relatively little is known about the role of Shh signaling and primary cilia in neuronal-like differentiation of MSCs. Here we show that primary cilia, harboring patched 1 (Ptc1), are present in growth-arrested MSCs and that smoothened (Smo) and Gli1 are present in cytoplasm of MSCs, which are important components of the Shh signaling pathway. After resveratrol induction, MSCs acquire neuronal-like cell morphologies and phenotypes, Smo translocates to the primary cilia, Gli1 enters the nucleus, and expressions of Smo and Gli1 proteins increase, which can be inhibited by cyclopamine, a Smo antagonist. Meanwhile, Smo agonist (SAG) attains similar effects compared with the resveratrol group. These data indicate that resveratrol can induce MSCs to differentiate into neuronal-like cells and activate Shh signaling pathway in the primary cilia. Moreover, the primary cilia and Shh signaling are essential for resveratrol inducing neuronal-like differentiation of MSCs. Our finding is important for understanding the neuronal-like differentiation mechanism of MSCs for resveratrol and promoting its clinical therapeutic utility.

The human oncogene SCL/TAL1 interrupting locus is required for mammalian dopaminergic cell proliferation through the Sonic hedgehog pathway

The human oncogene SCL/TAL1 interrupting locus (Stil) is highly conserved in all vertebrate species. In humans, the expression of Stil regulates cancer cell proliferation and survival. In this study, we examined the function of Stil in neural progenitor cell proliferation and neural differentiation using the mammalian dopaminergic (DA) PC12 cells. Stil is expressed in both proliferating and differentiated PC12 cells. The RNAi-mediated knockdown of Stil expression yielded a decreased proliferation rate of PC12 cells, whereas the overexpression of Stil transcript increased PC12 cell proliferation. The up- and down-regulation of the Sonic hedgehog (Shh) pathway by pharmacological approaches targeting Smoothened (Smo) demonstrated that Stil functions in the Shh pathway for PC12 proliferation. Smo antagonist cyclopamine decreased the proliferation rate of PC12 cells, whereas the overexpression of Stil rescued the cyclopamine-induced decrease in cell proliferation. Oppositely, the application of Smo agonist purmorphamine increased the rate of PC12 cell proliferation. However, the proliferation defect caused by Stil knockdown remained evident after activating the Shh pathway by purmorphamine. The expression of Stil is not required for PC12 cell neural differentiation. In PC12 cells transfected with Stil shRNA plasmids, the outgrowth of neurites persisted after treatment with nerve growth factor (NGF), whereas overexpression of Stil did not increase neurite growth in response to NGF induction. Together, the results from this study suggest a novel role for the oncogene Stil in neural progenitor cells through the Shh pathway, and further introduces Stil as a bio-marker for DA cells.

Structure du récepteur Smoothened

The Smoothened (Smo) receptor is a major component involved in signal transduction of the Hedgehog (Hh) morphogens both during embryogenesis and in the adult. Smo antagonists represent a promi-sing alternative for the treatment of cancers linked to abnormal Hh signalling. The crystal structure of the human Smo receptor bound to an antitumour agent demonstrates that this receptor belongs to the superfamily of G-protein coupled receptors. The antagonist binds to a pocket localized at the extracellular side formed by the seven transmembrane domains and the complex arrangement of the unusually long extracellular loops. The structure of the Smo receptor will promote the development of small molecules interacting with a key therapeutic target with interests in regenerative medicine and cancer.

Smoothened Inhibition Leads to Decreased Proliferation and Induces Apoptosis in Esophageal Adenocarcinoma Cells

The Hedgehog (Hh) pathway is known to be active in Barrett's carcinogenesis. Therefore, we evaluated the efficacy and underlying mechanisms of inhibition of cancer cell growth by the smoothened (Smo) antagonist BMS-833923 in esophageal adenocarcinoma (EAC) cell lines. Cell proliferation and apoptosis were evaluated by flow cytometry, Western blotting, immunofluorescence, and quantitative reverse transcription polymerase chain reactions. Results showed that the Smo antagonist led to reduced Hh pathway activity, resulting in decreased cell proliferation and induction of apoptosis via the intrinsic pathway in the esophageal cancer cells. In conclusion, the Smo antagonist may have application as an EAC chemotherapeutic agent.

TAK-441, a novel investigational smoothened antagonist, delays castration-resistant progression in prostate cancer by disrupting paracrine hedgehog signaling

Hedgehog (Hh) signaling is a highly conserved intercellular and intracellular communication mechanism that governs organogenesis and is dysregulated in cancers of numerous tissues, including prostate. Up-regulated expression of the Hh ligands, Sonic (Shh) and Desert (Dhh), has been reported in androgen-deprived and castration-resistant prostate cancer (CRPC). In a cohort of therapy naive, short- and long-term neoadjuvant hormone therapy-treated (NHT), and CRPC specimens, we observed elevated Dhh expression predominantly in long-term NHT specimens and elevated Shh expression predominantly in CRPC specimens. Together with previously demonstrated reciprocal signaling between Shh-producing prostate cancer (PCa) cells and urogenital mesenchymal fibroblasts, these results suggest that castration-induced Hh expression promotes CRPC progression through reciprocal paracrine signaling within the tumor microenvironment. We tested whether the orally available Smoothened (Smo) antagonist, TAK-441, could impair castration-resistant progression of LNCaP PCa xenografts by disrupting paracrine Hh signaling. Although TAK-441 or cyclopamine did not affect androgen withdrawal-induced Shh up-regulation or viability of LNCaP cells, castration-resistant progression of LNCaP xenografts was significantly delayed in animals treated with TAK-441. In TAK-441-treated xenografts, expression of murine orthologs of the Hh-activated genes, Gli1, Gli2 and Ptch1, was substantially suppressed, while expression of the corresponding human orthologs was unaffected. As androgen-deprived LNCaP cells up-regulate Shh expression, but are not sensitive to Smo antagonists, these studies indicate that TAK-441 leads to delayed castration-resistant progression of LNCaP xenografts by disrupting paracrine Hh signaling with the tumor stroma. Thus, paracrine Hh signaling may offer unique opportunities for prognostic biomarker development, drug targeting and therapeutic response monitoring of PCa progression.

Abstract 1624: Targeting the Hedgehog pathway to inhibit osteosarcoma growth through dual effects on tumor and microenvironment cells.

Abstract In addition to serving crucial roles in bone development, Hedgehog (Hh) signaling contributes to the development and progression of many cancers, making it an attractive candidate for treatment of bone-resident cancers. Recent data suggest that Hh-targeted agents exert pluripotent effects on host bone microenvironment cells through both cell-intrinsic and paracrine mechanisms, interrupting the ‘vicious cycle’ of tumor cell, osteoblast (OB), osteoclast (OC), and bone marrow stromal cell (BMSC) interactions in bone metastatic breast cancers. Here, reciprocal stimulation between tumor cells and bone cells enhance both tumor growth and bone pathology. Similarly, development of osteosarcoma (OS), the most common primary bone cancer, is strongly influenced by conditions within surrounding microenvironment providing additional points for therapeutic intervention. The 5-year survival rate for metastatic OS is under 30%, highlighting the need for novel and targeted treatments. We have demonstrated that mice deficient in the tumor suppressor ARF (p19ARF; p14ARF in humans) have enhanced rates of bone turnover, mimicking the adolescent growth period in which OS is prevalent. By crossing Arf-/- mice with those expressing Tax, an HTLV-1 oncogene that results in osteolytic tumors, we developed a model of high penetrant spontaneous OS that recapitulates many aspects of human disease. Here, suppression of bone turnover with the bisphosphonate zoledronic acid prevented the development of OS, suggesting that enhanced OC activity may stimulate OS growth. In agreement, we found that Tax+Arf-/- OS had increased RANKL-to-OPG ratios resulting in increased osteoclastogenic ability. Compared to normal osteoblasts and mesenchymal stem cell precursors, Tax+Arf-/- OS cells have increased expression of Hh pathway genes and exhibit increased susceptibility to Hh inhibitors (SMO antagonists). In particular, Tax+Arf-/- OS cells express high levels of the Hh ligands Sonic (SHH) and Indian (IHH), suggesting they may stimulate surrounding cells in a paracrine fashion. Notably, BMSC derived from non-tumor bearing Tax+Arf-/- mice also exhibit increased expression of pro-tumorigenic factors (including IL-6 and IGF), generating a fertile ‘soil’. SHH or conditioned media from Tax+Arf-/- OS cells enhanced OC activity and BMSC cell production of pro-tumorigenic growth factors. Furthermore, the increased OB and OC differentiation and activity present in Tax+Arf-/- cells could be abrogated with SMO inhibitors. We have established an OS cell line from Tax+Arf-/- mice (TAN) with the ability to form mineralized tumors upon intratibial injection. Using this model, we hypothesize that treatment with SMO antagonists will decrease OS growth due to both tumor cytotoxic effects and direct effects on host bone microenvironment cells that abrogate the pro-tumor microenvironment. Citation Format: Michelle Anne Hurchla, Katherine N. Weilbaecher. Targeting the Hedgehog pathway to inhibit osteosarcoma growth through dual effects on tumor and microenvironment cells. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1624. doi:10.1158/1538-7445.AM2013-1624

Abstract 4952: A novel smoothened antagonist, TAK-441, delays castration-resistant progression in prostate cancer by disrupting paracrine hedgehog signaling.

Abstract Hedgehog (Hh) signaling is a highly conserved inter- and intracellular communication mechanism that governs organogenesis and is dysregulated in cancers of numerous tissues, including prostate. Up-regulated expression of the Hh ligands, Sonic (Shh) and Desert (Dhh), has been reported in androgen-deprived and castration-resistant prostate cancer (CRPC). In a cohort of therapy naive, short- and long-term neoadjuvant hormone therapy-treated (NHT), and CRPC specimens, we observed elevated Dhh expression predominantly in long-term NHT specimens and elevated Shh expression predominantly in CRPC specimens. Together with previously demonstrated reciprocal signaling between Shh-producing prostate cancer (PCa) cells and urogenital mesenchymal fibroblasts, these results suggest that castration-induced Hh expression promotes CRPC progression through reciprocal paracrine signaling within the tumor microenvironment. We tested whether the orally available Smoothened (Smo) antagonist, TAK-441, could impair castration-resistant progression of LNCaP PCa xenografts by disrupting paracrine Hh signaling. While TAK-441 or cyclopamine did not affect androgen withdrawal-induced Shh up-regulation or viability of LNCaP cells, castration-resistant progression of LNCaP xenografts was significantly delayed in animals treated with TAK-441. In TAK-441-treated xenografts, expression of murine orthologues of the Hh-activated genes, Gli1, Gli2, and Ptch1, was substantially suppressed, while expression of the corresponding human orthologues was unaffected. Since androgen-deprived LNCaP cells up-regulate Shh expression, but are not sensitive to Smo antagonists, these studies indicate that TAK-441 leads to delayed castration-resistant progression of LNCaP xenografts by disrupting paracrine Hh signaling with the tumor stroma. Thus, paracrine Hh signaling may offer unique opportunities for prognostic biomarker development, drug targeting and therapeutic response monitoring of PCa progression. Citation Format: Mazyar Ghaffari, Naokazu Ibuki, Irene Iu, Mitali Pandey, Ladan Fazli, Masahide Kashiwagi, Hideaki Tojo, Osamu Nakanishi, Martin E. Gleave, Michael E. Cox. A novel smoothened antagonist, TAK-441, delays castration-resistant progression in prostate cancer by disrupting paracrine hedgehog signaling. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 4952. doi:10.1158/1538-7445.AM2013-4952

Abstract 3246: Pharmacologic targeting of the Hedgehog (HH) signal transduction pathway significantly suppresses growth of malignant pleural mesothelioma (MPM) and non-small cell lung cancer (NSCLC) cells in vitro.

Abstract OBJECTIVE. The HH signal transduction pathway plays crucial roles in organ morphogenesis and is active during embryonic development but quiescent in terminally differentiated cells. Binding of HH ligands to PTCH1 relieves its inhibitory activity on the pathway activator SMO leading to pathway activation and upregulation of target gene expression including the transcription factor Gli1 that serves as marker of pathway activation. It is reactivated in many solid cancers including NSCLC as we have previously demonstrated and proven to be the key oncogenic driver in tumors such as skin basal cell carcinoma. The aim of this study is to determine if HH pathway regulates cell growth and survival of MPM cells and to evaluate the efficacy of pathway blockade using SMO antagonists (SMO inhibitor GDC0449 - GDC or the antifungal drug itraconazole -ITRA) or Gli inhibitors (GANT61 or the anti-leukemia drug arsenic trioxide - ATO) in suppressing the viability of not only NSCLC but also MPM cells. METHODS. Expression of main components of HH pathway in 8 MPM cells was assessed by qRT-PCR. Suppression of HH/SMO-mediated signaling by these pathway antagonists was determined by LightII cells. Selective knockdown of SMO to inhibit HH signaling was achieved by siRNA in 3 MPM cells H2373, Gardner and H2452. Cell viability following treatments with GDC, ITRA, GANT61or ATO were evaluated in a panel of 8 MPM cells and 8 NSCLC cells using MTT assay. Apoptosis was determined by annexinV/PE staining and flow cytometry. RESULTS. All MPM cells, similar to previously demonstrated in NSCLC cells, express varying levels of HH ligands, PTCH1, SMO with readily detectable Gli1 observed in 7/8 of MPM cells by qRT-PCR. SMO siRNA mediate 2- to 3-fold reduction of SMO and also of Gli1 gene expression by qRT-PCR, indicating significant HH pathway blockade. This was associated with 40±6% to 70±8% reduction of cell viability (p<0.01 versus non-target siRNA controls). All 4 pathway antagonists completely blocked HH activation in LightII reporter cells. Treating MPM or NSCLC cells with HH inhibitors resulted in 1.5- to 4-fold reduction of Gli1 expression. GANT61, ATO, ITRA and to a lesser degree GDC significantly suppressed viability of all cancer cells at low microM concentrations. More importantly, ITRA, ATO, GANT61 induce significant apoptosis (ranging from 30% to 60%) in representative MPM or NSCLC cells. CONCLUSIONS. HH signaling is active in MPM and regulates cell viability. ATO and ITRA are as effective as the prototypic SMO inhibitor GDC and the Gli inhibitor GANT61 in suppressing HH signaling in MPM and NSCLC cells. Pharmaceuticals that are FDA-approved for other indications but recently found to have anti-HH activity such as ATO or ITRA may be repurposed to treat HH-dependent MPM or NSCLC cells. Citation Format: Min You, Javier Varona Santos, David J. Robbins, Niramol Savaraj, Dao M. Nguyen. Pharmacologic targeting of the Hedgehog (HH) signal transduction pathway significantly suppresses growth of malignant pleural mesothelioma (MPM) and non-small cell lung cancer (NSCLC) cells in vitro. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3246. doi:10.1158/1538-7445.AM2013-3246

Discovery, Molecular and Pharmacological Characterization of GSA-10, a Novel Small-Molecule Positive Modulator of Smoothened

Activation of the Smoothened (Smo) receptor mediates Hedgehog (Hh) signaling. Hh inhibitors are in clinical trials for cancer, and small-molecule Smo agonists may have therapeutic interests in regenerative medicine. Here, we have generated and validated a pharmacophoric model for Smo agonists and used this model for the virtual screening of a library of commercially available compounds. Among the 20 top-scoring ligands, we have identified and characterized a novel quinolinecarboxamide derivative, propyl 4-(1-hexyl-4-hydroxy-2-oxo-1,2-dihydroquinoline-3-carboxamido) benzoate, (GSA-10), as a Smo agonist. GSA-10 fits to the agonist pharmacophoric model with two hydrogen bond acceptor groups and four hydrophobic regions. Using pharmacological, biochemical, and molecular approaches, we provide compelling evidence that GSA-10 acts at Smo to promote the differentiation of multipotent mesenchymal progenitor cells into osteoblasts. However, this molecule does not display the hallmarks of reference Smo agonists. Remarkably, GSA-10 does not recognize the classic bodipy-cyclopamine binding site. Its effect on cell differentiation is inhibited by Smo antagonists, such as MRT-83, SANT-1, LDE225, and M25 in the nanomolar range, by GDC-0449 in the micromolar range, but not by cyclopamine and CUR61414. Thus, GSA-10 allows the pharmacological characterization of a novel Smo active site, which is notably not targeted to the primary cilium and strongly potentiated by forskolin and cholera toxin. GSA-10 belongs to a new class of Smo agonists and will be helpful for dissecting Hh mechanism of action, with important implications in physiology and in therapy.

SMO expression level correlates with overall survival in patients with malignant pleural mesothelioma

BackgroundMalignant mesothelioma is an aggressive, treatment-resistant tumor arising from mesothelium of pleura, peritoneum and pericardium. Despite current combined regimen, its prognosis remains dismal, calling for more effective targeted therapies. We investigated whether aberrant Hh activation may play a role in mesothelioma.MethodsSMO and SHH expression levels were analyzed in 46 mesothelioma tissue specimens with real-time RT-PCR, and correlation with survival was analyzed with univariate and multivariate Cox proportional hazards models, Kaplan-Meier survival curves, and the log-rank test. We also examined multiple mesothelioma cell lines for SMO expression and the effect of Hh inhibition by a specific SMO antagonist on cell proliferation by MTS assay.ResultsWe observed strong correlation between higher SMO and SHH expression levels with poorer overall survival. Remarkably, Hh inhibition by a specific SMO inhibitor significantly suppressed cell proliferation in the mesothelioma cell lines examined.ConclusionOur data strongly support that Hh signaling deregulation plays critical roles in proliferation of mesothelioma, and consistently exerts significant impact on prognosis of the disease. Therefore our findings revealed the hitherto unappreciated role of Hh activation in mesothelioma, and pinpointed Hh signaling antagonist as a potential new therapy against this devastating disease.

Macrocyclic Hedgehog Pathway Inhibitors: Optimization of Cellular Activity and Mode of Action Studies

Macrocyclic Hedgehog (Hh) pathway inhibitors have been discovered with improved potency and maximal inhibition relative to the previously reported macrocycle robotnikinin. Analogues were prepared using a modular and efficient build-couple-pair (BCP) approach, with a ring-closing metathesis step to form the macrocyclic ring. Varying the position of the macrocycle nitrogen and oxygen atoms provided inhibitors with improved activity in cellular assays; the most potent analogue was 29 (BRD-6851), with an IC50 of 0.4 μM against C3H10T1/2 cells undergoing Hh-induced activation, as measured by Gli1 transcription and alkaline phosphatase induction. Studies with Patched knockout (Ptch–/–) cells and competition studies with the Smoothened (Smo) agonists SAG and purmorphamine demonstrate that in contrast to robotnikinin, select analogues are Smo antagonists.

Small molecule inhibitors of Smoothened ciliary localization and ciliogenesis

Vertebrate Hedgehog (Hh) signals involved in development and some forms of cancer, such as basal cell carcinoma, are transduced by the primary cilium, a microtubular projection found on many cells. A critical step in vertebrate Hh signal transduction is the regulated movement of Smoothened (Smo), a seven-transmembrane protein, to the primary cilium. To identify small molecules that interfere with either the ciliary localization of Smo or ciliogenesis, we undertook a high-throughput, microscopy-based screen for compounds that alter the ciliary localization of YFP-tagged Smo. This screen identified 10 compounds that inhibit Hh pathway activity. Nine of these Smo antagonists (SA1-9) bind Smo, and one (SA10) does not. We also identified two compounds that inhibit ciliary biogenesis, which block microtubule polymerization or alter centrosome composition. Differential labeling of cell surface and intracellular Smo pools indicates that SA1-7 and 10 specifically inhibit trafficking of intracellular Smo to cilia. In contrast, SA8 and 9 recruit endogenous Smo to the cilium in some cell types. Despite these different mechanisms of action, all of the SAs inhibit activation of the Hh pathway by an oncogenic form of Smo, and abrogate the proliferation of basal cell carcinoma-like cancer cells. The SA compounds may provide alternative means of inhibiting pathogenic Hh signaling, and our study reveals that different pools of Smo move into cilia through distinct mechanisms.

Small molecule inhibitors of the hedgehog signaling pathway for the treatment of cancer

Over the past decade, the Hedgehog signaling pathway has attracted considerable interest because the pathway plays important roles in the tumorigenesis of several types of cancer as well as developmental processes. It has also been observed that Hedgehog signaling regulates the proliferation and self-renewal of cancer stem cells. A great number of Hedgehog pathway inhibitors have been discovered through small molecule screens and subsequent medicinal chemistry efforts. Among the inhibitors, several Smo antagonists have reached the clinical trial phase. It has been proved that the inhibition of Hedgehog signaling with Smo antagonists is beneficial to cancer patients with basal cell carcinoma and medulloblastoma. In this review, we provide an overview of Hedgehog pathway inhibitors with focusing on the preclinical and/or clinical efficacy and molecular mechanisms of these inhibitors.

Glucocorticoid Compounds Modify Smoothened Localization and Hedgehog Pathway Activity

The Hedgehog signaling pathway is linked to a variety of diseases, notably a range of cancers. The first generation of drug screens identified Smoothened (Smo), a membrane protein essential for signaling, as an attractive drug target. Smo localizes to the primary cilium upon pathway activation, and this transition is critical for the response to Hedgehog ligands. In a high content screen directly monitoring Smo distribution in Hedgehog-responsive cells, we identified different glucocorticoids as specific modulators of Smo ciliary accumulation. One class promoted Smo accumulation, conferring cellular hypersensitivity to Hedgehog stimulation. In contrast, a second class inhibited Smo ciliary localization and signaling activity by both wild-type Smo, and mutant forms of Smo, SmoM2, and SmoD473H, that are refractory to previously identified Smo antagonists. These findings point to the potential for developing glucocorticoid-based pharmacological modulation of Smo signaling to treat mutated drug-resistant forms of Smo, an emerging problem in long-term cancer therapy. They also raise a concern about potential crosstalk of glucocorticoid drugs in the Hedgehog pathway, if therapeutic administration exceeds levels associated with on-target transcriptional mechanisms of glucocorticoid action.

Smoothened Antagonists Reverse Taxane Resistance in Ovarian Cancer

The hedgehog pathway has been implicated in the formation and maintenance of a variety of malignancies, including ovarian cancer; however, it is unknown whether hedgehog signaling is involved in ovarian cancer chemoresistance. The goal of this study was to determine the effects of antagonizing the hedgehog receptor, Smoothened (Smo), on chemotherapy response in ovarian cancer. Expression of hedgehog pathway members was assessed in three pairs of parental and chemotherapy-resistant ovarian cancer cell lines (A2780ip2/A2780cp20, SKOV3ip1/SKOV3TRip2, HeyA8/HeyA8MDR) using quantitative PCR and Western blot analysis. Cell lines were exposed to increasing concentrations of two different Smo antagonists (cyclopamine, LDE225) alone and in combination with carboplatin or paclitaxel. Selective knockdown of Smo, Gli1, or Gli2 was achieved using siRNA constructs. Cell viability was assessed by MTT assay. A2780cp20 and SKOV3TRip2 orthotopic xenografts were treated with vehicle, LDE225, paclitaxel, or combination therapy. Chemoresistant cell lines showed higher expression (>2-fold, P < 0.05) of hedgehog signaling components compared with their respective parental lines. Smo antagonists sensitized chemotherapy-resistant cell lines to paclitaxel, but not to carboplatin. LDE225 treatment also increased sensitivity of ALDH-positive cells to paclitaxel. A2780cp20 and SKOV3TRip2 xenografts treated with combined LDE225 and paclitaxel had significantly less tumor burden than those treated with vehicle or either agent alone. Increased taxane sensitivity seems to be mediated by a decrease in P-glycoprotein (MDR1) expression. Selective knockdown of Smo, Gli1, or Gli2 all increased taxane sensitivity. Smo antagonists reverse taxane resistance in chemoresistant ovarian cancer models, suggesting combined anti-hedgehog and chemotherapies could provide a useful therapeutic strategy for ovarian cancer.

Abstract IA19: Small-molecule modulators of the Hedgehog signaling pathway

Abstract The Hedgehog (Hh) signaling pathway plays critical roles in embryonic patterning and tissue homeostasis, and its inappropriate activation can lead to basal cell carcinoma, medulloblastoma, and other cancers. Small molecules that modulate Hh signaling proteins can therefore be valuable probes of Hh pathway-dependent physiology and targeted therapies for Hh pathway-related diseases. While high-throughput screening campaigns in academia and industry have yielded several Hh pathway modulators that potently and selectively target the transmembrane protein Smoothened (Smo), there is a growing need for compounds that inhibit Hh target gene expression through other mechanisms. Such small molecules could provide new insights into the cellular processes that regulate Gli transcription factor function and possibly prevent or overcome the emergence of tumors that are resistant to Smo antagonists. Toward this goal, we have completed large-scale screens for Hh pathway inhibitors that act downstream of Smo, revealing several compounds that inhibit Gli-dependent transcription through distinct mechanisms of action. We have successfully determined the cellular target of one inhibitor from our screens, and mechanistic studies of other Gli antagonists are currently underway. Citation Format: James K. Chen. Small-molecule modulators of the Hedgehog signaling pathway [abstract]. In: Proceedings of the AACR Special Conference on Chemical Systems Biology: Assembling and Interrogating Computational Models of the Cancer Cell by Chemical Perturbations; 2012 Jun 27-30; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2012;72(13 Suppl):Abstract nr IA19.

A phase I/II study of LDE225, a smoothened (Smo) antagonist, in pediatric patients with recurrent medulloblastoma (MB) or other solid tumors.

9519 Background: Hedgehog (Hh) signaling is crucial in the development and homeostasis of many human organs and tissues. Aberrant Hh signaling is involved in tumorigenesis through promotion of cell proliferation, survival, and differentiation in wide range of human cancers, including approximately 30% of MBs. LDE225 is a potent and selective inhibitor of Smo, a key positive regulator of Hh signaling. The phase I is exploring the safety and pharmacokinetics of LDE225 in pediatric patients with advanced solid tumors that are potentially dependent on Hh signaling. Preliminary data from the ongoing phase I are presented. Methods: Dose-escalation was performed according to a Bayesian design starting at 372 mg/m2 of continuous once daily oral LDE225. Safety and preliminary efficacy of LDE225 at the maximum tolerated dose will be assessed in pediatric and adult patients with recurrent MB in a phase II expansion part. Pharmacokinetic profiles were performed at Day 1 and 21. Tumor samples were analyzed for Hh pathway activation status using a 5-gene Hh signature assay. Results: Thirty-three patients (24 MB, 3 rhabdomyoscarcoma [RMS], 3 osteosarcoma, and 1 each of neuroblastoma, gliomatosis and oligoastrocytoma) with a median age of 13 years (range, 4–17 y) have enrolled. Dose-limiting toxicity of Grade 4 creatine phosphokinase elevation occurred in 1 RMS patient out of 7 patients treated at 372 mg/m2. No dose-limiting toxicity was observed at 233 and 425 mg /m2. LDE225 at 233 and 372 mg/m2 was absorbed with a median Tmax of 2 h (range, 1–24 h). Systemic exposures were comparable with adults. Two MB patients achieved a confirmed complete response (CR) at doses of 372 and 425 mg/m2. Analysis of 14 available MB tumor samples using the 5-gene Hh signature assay showed that the 2 CR patients have Hh‑activated tumor. The remaining 12 tumor samples were from patients who did not achieve response and were determined to be Hh pathway non-activated. Conclusions: LDE225 is well tolerated in pediatric patients with advanced malignancies. Preliminary data show promising efficacy in medulloblastoma patients and support the use of the 5-gene Hh signature assay as a pre-selection tool in future trials.