Discovery of NVP-LDE225, a Potent and Selective Smoothened Antagonist

Hedgehog acyltransferase as a target in pancreatic ductal adenocarcinoma

Sonic Hedgehog (Shh) is abnormally expressed in pancreatic cancer and is associated with disease onset and progression. Inhibition of Shh signaling is thus an attractive clinical target for therapeutic intervention. Most efforts to block Shh signaling have focused on inhibitors of Smoothened, which target the canonical Shh signaling pathway. These approaches have met with limited success, in part due to development of resistance-conferring mutations and contributions from non-canonical signaling pathways. Here, we show that Hedgehog acyltransferase (Hhat), the enzyme responsible for the attachment of palmitate onto Shh, is a novel target for inhibition of Shh signaling in pancreatic cancer cells. Depletion of Hhat with lentivirally delivered small hairpin RNA decreased both anchorage-dependent and independent proliferation of human pancreatic cancer cells. In vivo, Hhat knockdown led to reduction of tumor growth in a mouse xenograft model of pancreatic cancer. RU-SKI 43, a small molecule inhibitor of Hhat recently developed by our group, reduced pancreatic cancer cell proliferation and Gli-1 activation through Smoothened-independent non-canonical signaling. In addition, RU-SKI 43 treatment inhibited two key proliferative pathways regulated by Akt and mTOR. This work demonstrates that Hhat has a critical role in pancreatic cancer and that a small molecule inhibitor of Hhat can successfully block pancreatic cancer cell proliferation. It also highlights the importance of developing optimized Hhat inhibitors to be used as therapeutics in pancreatic cancer, as well as in other malignancies characterized by Shh overexpression.

The chemistry and biological activity of heterocycle-fused quinolinone derivatives: A review

Among all heterocycles, the heterocycle-fused quinolinone scaffold is one of the privileged structures in drug discovery as heterocycle-fused quinolinone derivatives exhibit various biological activities allowing them to act as anti-inflammatory, anticancer, antidiabetic, and antipsychotic agents. This wide spectrum of biological activity has attracted a great deal of attention in the field of medicinal chemistry. In this review, we provide a comprehensive description of the biological and pharmacological properties of various heterocycle-fused quinolinone scaffolds and discuss the synthetic methods of some of their derivatives.

A five-gene hedgehog signature developed as a patient preselection tool for hedgehog inhibitor therapy in medulloblastoma

PURPOSE

Distinct molecular subgroups of medulloblastoma, including hedgehog (Hh) pathway-activated disease, have been reported. We identified and clinically validated a five-gene Hh signature assay that can be used to preselect patients with Hh pathway-activated medulloblastoma.

EXPERIMENTAL DESIGN

Gene characteristics of the Hh medulloblastoma subgroup were identified through published bioinformatic analyses. Thirty-two genes shown to be differentially expressed in fresh-frozen and formalin-fixed paraffin-embedded tumor samples and reproducibly analyzed by RT-PCR were measured in matched samples. These data formed the basis for building a multi-gene logistic regression model derived through elastic net methods from which the five-gene Hh signature emerged after multiple iterations. On the basis of signature gene expression levels, the model computed a propensity score to determine Hh activation using a threshold set a priori. The association between Hh activation status and tumor response to the Hh pathway inhibitor sonidegib (LDE225) was analyzed.

RESULTS

Five differentially expressed genes in medulloblastoma (GLI1, SPHK1, SHROOM2, PDLIM3, and OTX2) were found to associate with Hh pathway activation status. In an independent validation study, Hh activation status of 25 medulloblastoma samples showed 100% concordance between the five-gene signature and Affymetrix profiling. Further, in medulloblastoma samples from 50 patients treated with sonidegib, all 6 patients who responded were found to have Hh-activated tumors. Three patients with Hh-activated tumors had stable or progressive disease. No patients with Hh-nonactivated tumors responded.

CONCLUSIONS

This five-gene Hh signature can robustly identify Hh-activated medulloblastoma and may be used to preselect patients who might benefit from sonidegib treatment.

Hedgehog pathway blockade with the cancer drug LDE225 disrupts taste organs and taste sensation

Taste sensation on the anterior tongue requires chorda tympani nerve function and connections with continuously renewing taste receptor cells. However, it is unclear which signaling pathways regulate the receptor cells to maintain chorda tympani sensation. Hedgehog (HH) signaling controls cell proliferation and differentiation in numerous tissues and is active in taste papillae and taste buds. In contrast, uncontrolled HH signaling drives tumorigenesis, including the common skin cancer, basal cell carcinoma. Systemic HH pathway inhibitors (HPIs) lead to basal cell carcinoma regression, but these drugs cause severe taste disturbances. We tested the hypothesis that taste disruption by HPIs reflects a direct requirement for HH signaling in maintaining taste organs and gustatory sensation. In mice treated with the HPI LDE225 up to 28 days, HH-responding cells were lost in fungiform papilla epithelium, and papillae acquired a conical apex. Taste buds were either absent or severely reduced in size in more than 90% of aberrant papillae. Taste bud remnants expressed the taste cell marker keratin 8, and papillae retained expression of nerve markers, neurofilament and P2X3. Chorda tympani nerve responses to taste stimuli were markedly reduced or absent in LDE225-treated mice. Responses to touch were retained, however, whereas cold responses were retained after 16 days of treatment but lost after 28 days. These data identify a critical, modality-specific requirement for HH signaling in maintaining taste papillae, taste buds and neurophysiological taste function, supporting the proposition that taste disturbances in HPI-treated patients are an on-target response to HH pathway blockade in taste organs.

Survivin as a therapeutic target in Sonic hedgehog-driven medulloblastoma

Medulloblastoma (MB) is a highly malignant brain tumor that occurs primarily in children. Although surgery, radiation and high-dose chemotherapy have led to increased survival, many MB patients still die from their disease, and patients who survive suffer severe long-term side effects as a consequence of treatment. Thus, more effective and less toxic therapies for MB are critically important. Development of such therapies depends in part on identification of genes that are necessary for growth and survival of tumor cells. Survivin is an inhibitor of apoptosis protein that regulates cell cycle progression and resistance to apoptosis, is frequently expressed in human MB and when expressed at high levels predicts poor clinical outcome. Therefore, we hypothesized that Survivin may have a critical role in growth and survival of MB cells and that targeting it may enhance MB therapy. Here we show that Survivin is overexpressed in tumors from patched (Ptch) mutant mice, a model of Sonic hedgehog (SHH)-driven MB. Genetic deletion of survivin in Ptch mutant tumor cells significantly inhibits proliferation and causes cell cycle arrest. Treatment with small-molecule antagonists of Survivin impairs proliferation and survival of both murine and human MB cells. Finally, Survivin antagonists impede growth of MB cells in vivo. These studies highlight the importance of Survivin in SHH-driven MB, and suggest that it may represent a novel therapeutic target in patients with this disease.

Recent advances in the design of Hedgehog pathway inhibitors for the treatment of malignancies

INTRODUCTION

The Hedgehog (Hh) signaling pathway is known to be dysregulated in several forms of cancer. Hence, specifically targeting this signaling cascade is a valid and promising strategy for successful therapeutic intervention. Several components within the Hh pathway have been proven to be druggable; however, challenges in the discovery and development process for small molecules targeting this pathway have been identified.

AREAS COVERED

This review details both the current state and future potential of Hh pathway inhibitors as anticancer chemotherapeutics that target a variety of human malignancies.

EXPERT OPINION

The initial development of Hh pathway inhibitors focused on small-molecule antagonists of Smoothened, a transmembrane protein that is a key regulator of pathway signaling. More recently, efforts to identify and develop inhibitors of pathway signaling that function through alternate mechanisms have been increasing. However, none of these have advanced into clinical trials. Further, early evidence suggesting the broad application of Hh pathway inhibitors as a monotherapy in a wide range of human cancers has not been validated. The potential for Hh pathway inhibitors as combination therapy has demonstrated promising preclinical results. However, more research to identify rational drug combinations to fully explore the potential of this anticancer drug class is warranted.

Absorption, distribution, metabolism, and excretion (ADME) of ¹⁴C-sonidegib (LDE225) in healthy volunteers

PURPOSE

The absorption, distribution, metabolism, and excretion of the hedgehog pathway inhibitor sonidegib (LDE225) were determined in healthy male subjects.

METHODS

Six subjects received a single oral dose of 800 mg ¹⁴C-sonidegib (74 kBq, 2.0 µCi) under fasting conditions. Blood, plasma, urine, and fecal samples were collected predose, postdose in-house (days 1-22), and during 24-h visits (weekly, days 29-43; biweekly, days 57-99). Radioactivity was determined in all samples using accelerator mass spectrometry (AMS). Liquid chromatography-tandem mass spectrometry (LC-MS/MS) was used to determine concentrations of sonidegib and its main circulating metabolite in plasma. Metabolite profiles and structures were determined in pooled plasma, urine, and fecal samples using high-performance LC-AMS and LC-MS/MS, respectively.

RESULTS

A single dose of ¹⁴C-sonidegib was well tolerated in healthy subjects. Unchanged sonidegib and total radioactivity reached peak concentration in plasma by 2 and 3 h, respectively, and demonstrated similarly long half-lives of 319 and 331 h, respectively. Absorbed sonidegib (estimated 6-7 %) was extensively distributed, and the approximate terminal volume of distribution was 2,500 L. Unchanged sonidegib and a metabolite resulting from amide hydrolysis were the major circulating components (36.4 and 15.4 % of radioactivity area under the curve, respectively). Absorbed sonidegib was eliminated predominantly through oxidative metabolism of the morpholine part and amide hydrolysis. Unabsorbed sonidegib was excreted through the feces. Metabolites in excreta accounted for 4.49 % of the dose (1.20 % in urine, 3.29 % in feces). The recovery of radioactivity in urine and feces was essentially complete (95.3 ± 1.93 % of the dose in five subjects; 56.9 % of the dose in one subject with incomplete feces collection suspected).

CONCLUSIONS

Sonidegib exhibited low absorption, was extensively distributed, and was slowly metabolized. Elimination of absorbed sonidegib occurred largely by oxidative and hydrolytic metabolism.

An Efficient Synthesis of Erismodegib

A highly efficient synthesis of Erismodegib (LDE225) is described. The chlorine of 2-chloro-5-nitropyridine was displaced by 2,6-dimethylmorpholine and the nitro group reduced to give 3-amino-6-(2’,6'-dimethylmorpholino)pyridine. The Suzuki coupling of methyl 3-bromo-2-methylbenzoate with 4-trifluoromethoxy phenylboronic acid gave methyl-4'-(trifluormethoxy) biphenyl-3-carboxylate. These two fragments were coupled through amide bond formation to give Erismodegib. This synthesis procedure which proceeded in high yield did not require special conditions and is suitable for industrial production.

PTEN loss mitigates the response of medulloblastoma to Hedgehog pathway inhibition

Medulloblastoma is a cancer of the cerebellum, for which there is currently no approved targeted therapy. Recent transcriptomics approaches have demonstrated that medulloblastoma is composed of molecularly distinct subgroups, one of which is characterized by activation of the Hedgehog pathway, which in mouse models is sufficient to drive medulloblastoma development. There is thus considerable interest in targeting the Hedgehog pathway for therapeutic benefit in medulloblastoma, particularly given the recent approval of the Hedgehog pathway inhibitor vismodegib for metastatic and locally advanced basal cell carcinoma. Like other molecularly targeted therapies, however, there have been reports of acquired resistance to vismodegib, driven by secondary Hedgehog pathway mutations and potentially by activation of the phosphatidylinositol 3-kinase (PI3K) pathway. Given that acquired resistance to vismodegib may occur as a result of inappropriate PI3K pathway activation, we asked if loss of the PI3K pathway regulator, phosphatase and tensin homologue (Pten), which has been reported to occur in patients within the Hedgehog subgroup, would constitute a mechanism of innate resistance to vismodegib in Hedgehog-driven medulloblastoma. We find that Hedgehog pathway inhibition successfully restrains growth of Pten-deficient medulloblastoma in this mouse model, but does not drive tumor regression, as it does in Pten-wild-type medulloblastoma. Combined inhibition of the Hedgehog and PI3K pathways may lead to superior antitumor activity in PTEN-deficient medulloblastoma in the clinic.

Coordinate activation of Shh and PI3K signaling in PTEN-deficient glioblastoma: new therapeutic opportunities

In glioblastoma, phosphatidylinositol 3-kinase (PI3K) signaling is frequently activated by loss of the tumor suppressor phosphatase and tensin homolog (PTEN). However, it is not known whether inhibiting PI3K represents a selective and effective approach for treatment. We interrogated large databases and found that sonic hedgehog (SHH) signaling is activated in PTEN-deficient glioblastoma. We demonstrate that the SHH and PI3K pathways synergize to promote tumor growth and viability in human PTEN-deficient glioblastomas. A combination of PI3K and SHH signaling inhibitors not only suppressed the activation of both pathways but also abrogated S6 kinase (S6K) signaling. Accordingly, targeting both pathways simultaneously resulted in mitotic catastrophe and tumor apoptosis and markedly reduced the growth of PTEN-deficient glioblastomas in vitro and in vivo. The drugs tested here appear to be safe in humans; therefore, this combination may provide a new targeted treatment for glioblastoma.

Targeted therapy for advanced Basal-cell carcinoma: vismodegib and beyond

Basal-cell carcinoma is a commonly occurring skin malignancy that has the potential to progress into locally invasive or resistant disease, as well as spread distantly. Due to advances in the molecular understanding of the disease over the last two decades, it has been discovered that the Hedgehog pathway plays an important role in the pathogenesis of this disease and can be exploited as a treatment target. Several agents that inhibit the Hedgehog pathway have reached clinical studies and one drug, vismodegib, has recently been US Food and Drug Administration (FDA) approved based on clinical activity and tolerability in patients with advanced basal-cell carcinoma. This review will describe the clinical development of vismodegib, as well as the proper application of the drug in clinical practice. Other important clinical questions, such as mechanisms of resistance to vismodegib and the role of other Hedgehog pathway inhibitors currently in development will also be discussed.

Inhibitors of Hedgehog acyltransferase block Sonic Hedgehog signaling

Inhibition of Sonic hedgehog (Shh) signaling is of great clinical interest. Here we exploit Hedgehog acyltransferase (Hhat)-mediated Shh palmitoylation, a modification critical for Shh signaling, as a new target for Shh pathway inhibition. A target-oriented high-throughput screen was used to identify small-molecule inhibitors of Hhat. In cells, these Hhat inhibitors specifically block Shh palmitoylation and inhibit autocrine and paracrine Shh signaling.

Itraconazole and arsenic trioxide inhibit Hedgehog pathway activation and tumor growth associated with acquired resistance to smoothened antagonists

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.

Novel molecular targets for the treatment of gastroenteropancreatic endocrine tumors: answers and unsolved problems

As more knowledge on molecular alterations favoring carcinogenesis and spreading of gastroenteropancreatic endocrine tumors has become available, a number of targeted agents interfering with key growth and angiogenic pathways have been explored in preclinical and clinical studies. The mTOR inhibitor Everolimus, and the multi-target antiangiogenetic agent Sunitinib, have been shown to be effective and thus have been approved by the FDA for treatment of pancreatic endocrine tumors. However, there is little data on the primary resistance to targeted agents on these tumors. The goals of the present review are to elucidate the possible advantage of combined treatments in overcoming induced resistances, and to identify biomarkers able to predict clinical efficacy. Moreover, the role of interesting targets for which a strong biological rationale exists, and specific inhibitors are available, such as the Src Family Kinases and the Hedgehog Pathway, are discussed. There is now need for more preclinical studies on cell lines and animal models to provide a stronger preclinical background in this field, as well as clinical trials specifically comparing one targeted therapy with another or combining different targeted agents.

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.

Toward a systems-level understanding of the Hedgehog signaling pathway: defining the complex, robust, and fragile

The Hedgehog (Hh) signaling pathway plays a fundamental role in development and tissue homeostasis, governing cell proliferation and differentiation, as well as cell fate. Hh signaling is mediated by an intricate network of proteins that have positive and negative roles that work in concert to fine-tune signaling output. Using feedback loops, redundancy and subcellular compartmentalization, the temporal and spatial dynamics of Hh signaling have evolved to be complex and robust. Yet developmental defects and cancers that arise from perturbation of the Hh pathway reflect specific pathway fragilities. Importantly, these fragile nodes and edges present opportunities for the design of targeted therapies. Despite these significant advances, unconnected molecular links within the Hh pathway still remain, many of which revolve around the dependence of Hh signaling on the primary cilium, an antenna-like sensory organelle. A systems-level understanding of Hh signaling and of ciliary biology will comprehensively define all nodes and edges of the Hh signaling network and will help identify precise therapeutic targets.

Identification of a novel Smoothened antagonist that potently suppresses Hedgehog signaling

The Hedgehog signaling pathway plays an essential role in embryo development and adult tissue homeostasis, in regulating stem cells and is abnormally activated in many cancers. Given the importance of this signaling pathway, we developed a novel and versatile high-throughput, cell-based screening platform using confocal imaging, based on the role of β-arrestin in Hedgehog signal transduction, that can identify agonists or antagonist of the pathway by a simple change to the screening protocol. Here we report the use of this assay in the antagonist mode to identify novel antagonists of Smoothened, including a compound (A8) with low nanomolar activity against wild-type Smo also capable of binding the Smo point mutant D473H associated with clinical resistance in medulloblastoma. Our data validate this novel screening approach in the further development of A8 and related congeners to treat Hedgehog related diseases, including the treatment of basal cell carcinoma and medulloblastoma.

Design, synthesis, and structure-activity-relationship of phenyl imidazoles as potent Smoothened antagonists

Through scaffold morphing of a known Smoothened antagonist Antag691, a series of novel phenyl imidazole derivatives were developed. Structure-activity-relationship studies and lead optimization led to the discovery of potent, selective and orally bioavailable Smoothened antagonist 19 that is suitable for in vivo studies.

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.

Canonical and noncanonical Hedgehog pathway in the pathogenesis of multiple myeloma

The Hedgehog (Hh) pathway is required for cell-fate determination during the embryonic life, as well as cell growth and differentiation in the adult organism, where the inappropriate activation has been implicated in several cancers. Here we demonstrate that Hh signaling plays a significant role in growth and survival of multiple myeloma (MM) cells. We observed that CD138(+) MM cells express Hh genes and confirmed Smoothened (Smo)-dependent Hh signaling in MM using a novel synthetic Smo inhibitor, NVP-LDE225 (Novartis), which decreased MM cell viability by inducing specific down-regulation of Gli1 and Ptch1, hallmarks of Hh activity. In addition, we detected a nuclear localization of Gli1 in MM cells, which is completely abrogated by Forskolin, a Gli1-modulating compound, confirming Smo-independent mechanisms leading to Hh activation in MM. Finally, we identified that bone marrow stromal cells are a source of the Shh ligand, although they are resistant to the Hh inhibitor because of defective Smo expression and Ptch1 up-regulation. Further in vitro as well as in vivo studies showed antitumor efficacy of NVP-LDE225 in combination with bortezomib. Altogether, our data demonstrate activation of both canonical and noncanonical Hh pathway in MM, thus providing the rationale for testing Hh inhibitors in clinical trials to improve MM patient outcome.

Molecular pathways: the hedgehog signaling pathway in cancer

The Hedgehog (Hh) signaling pathway regulates embryonic development and may be aberrantly activated in a wide variety of human cancers. Efforts to target pathogenic Hh signaling have steadily progressed from the laboratory to the clinic, and the recent approval of the Hh pathway inhibitor vismodegib for patients with advanced basal cell carcinoma represents an important milestone. On the other hand, Hh pathway antagonists have failed to show significant clinical activity in other solid tumors. The reasons for these negative results are not precisely understood, but it is possible that the impact of Hh pathway inhibition has not been adequately measured by the clinical endpoints used thus far or that aberrancies in Hh signal transduction limits the activity of currently available pathway antagonists. Further basic and correlative studies to better understand Hh signaling in human tumors and validate putative antitumor mechanisms in the clinical setting may ultimately improve the success of Hh pathway inhibition to other tumor types.

Matching mice to malignancy: molecular subgroups and models of medulloblastoma

INTRODUCTION

Medulloblastoma, the largest group of embryonal brain tumors, has historically been classified into five variants based on histopathology. More recently, epigenetic and transcriptional analyses of primary tumors have subclassified medulloblastoma into four to six subgroups, most of which are incongruous with histopathological classification.

DISCUSSION

Improved stratification is required for prognosis and development of targeted treatment strategies, to maximize cure and minimize adverse effects. Several mouse models of medulloblastoma have contributed both to an improved understanding of progression and to developmental therapeutics. In this review, we summarize the classification of human medulloblastoma subtypes based on histopathology and molecular features. We describe existing genetically engineered mouse models, compare these to human disease, and discuss the utility of mouse models for developmental therapeutics. Just as accurate knowledge of the correct molecular subtype of medulloblastoma is critical to the development of targeted therapy in patients, we propose that accurate modeling of each subtype of medulloblastoma in mice will be necessary for preclinical evaluation and optimization of those targeted therapies.

Discovery of PF-04449913, a Potent and Orally Bioavailable Inhibitor of Smoothened

Inhibitors of the Hedgehog signaling pathway have generated a great deal of interest in the oncology area due to the mounting evidence of their potential to provide promising therapeutic options for patients. Herein, we describe the discovery strategy to overcome the issues inherent in lead structure 1 that resulted in the identification of Smoothened inhibitor 1-((2R,4R)-2-(1H-benzo[d]imidazol-2-yl)-1-methylpiperidin-4-yl)-3-(4-cyanophenyl)urea (PF-04449913, 26), which has been advanced to human clinical studies.

Hedgehog inhibition with the orally bioavailable Smo antagonist LDE225 represses tumor growth and prolongs survival in a transgenic mouse model of islet cell neoplasms

BACKGROUND

This study was designed to evaluate the role of the hedgehog pathway in tumor progression of murine islet cell tumors. Blockade of aberrant hedgehog activation has recently been proposed as a therapeutic target, but effects in models of islet cell tumors with a new orally bioavailable Smoothened (Smo) antagonist LDE225 have not been examined.

MATERIAL AND METHODS

To assess in vivo effects, transgenic Rip1Tag2 mice, which develop islet cell neoplasms, were treated with vehicle or LDE225 (80 mg/kg/d) from week 5 until death. The resected pancreata were evaluated macroscopically and microscopically by iummohistochemsistry. Quantitative real-time polymerase chain reaction was performed for hedgehog target genes with RNA from islet, isolated from treated and untreated Rip1Tag2 mice.

RESULTS

LDE225 significantly reduced tumor volume by 95% compared with untreated control mice. Hedgehog inhibition with LDE225 significantly prolonged median survival in the used transgenic mouse model (105 vs 116 days; P = 0.02). Quantitative real-time polymerase chain reaction for downstream hedgehog target genes demonstrated significant downregulation in the islet cell tumors of Rip1Tag2 mice treated with LDE225, confirming the ability to achieve effective pharmacologic levels of LDE225 within the desired tissue site, in vivo.

CONCLUSION

This is the first study to show that the orally bioavailable Smo antagonist LDE225 may provide a new option for therapy of islet cell neoplasms.

A crucial requirement for Hedgehog signaling in small cell lung cancer

Small-cell lung cancer (SCLC) is an aggressive neuroendocrine subtype of lung cancer for which there is no effective treatment. Using a mouse model in which deletion of Rb1 and Trp53 in the lung epithelium of adult mice induces SCLC, we found that the Hedgehog signaling pathway is activated in SCLC cells independently of the lung microenvironment. Constitutive activation of the Hedgehog signaling molecule Smoothened (Smo) promoted the clonogenicity of human SCLC in vitro and the initiation and progression of mouse SCLC in vivo. Reciprocally, deletion of Smo in Rb1 and Trp53-mutant lung epithelial cells strongly suppressed SCLC initiation and progression in mice. Furthermore, pharmacological blockade of Hedgehog signaling inhibited the growth of mouse and human SCLC, most notably following chemotherapy. These findings show a crucial cell-intrinsic role for Hedgehog signaling in the development and maintenance of SCLC and identify Hedgehog pathway inhibition as a therapeutic strategy to slow the progression of disease and delay cancer recurrence in individuals with SCLC.

Small molecule antagonists in distinct binding modes inhibit drug-resistant mutant of smoothened

Several small molecule antagonists for Smoothened (Smo) have been developed, and achieved promising preclinical efficacy in cancers that are dependent on Hedgehog (Hh) signaling. However, in a recent clinical study, a drug-resistant D473H SMO mutant was identified that is thought to be responsible for cancer relapse in a patient with medulloblastoma. Here, we report two Smo antagonists that bind to distinct sites, as compared to known antagonists and agonists, and inhibit both wild-type and mutant Smo. These findings provide an insight of the ligand-binding sites of Smo and a basis for the development of potential therapeutics for tumors with drug-resistant Smo mutations.

The controversial role of the Hedgehog pathway in normal and malignant hematopoiesis

Hedgehog (Hh) is a developmental signaling pathway in which Hh ligands bind Patched (Ptch), which relieves its inhibition of Smoothened (Smo), allowing the Gli family of transcription factors to translocate to the nucleus and activate Hh target genes. The role of Hh signaling in hematopoiesis is controversial and ill defined. Although some groups observed self-renewal defects with decreased replating and reduced efficiency of secondary murine transplants, other groups reported no hematopoietic phenotypes, which may be related to the timing of Hh abrogation. In malignant hematopoiesis, most attention has been focused on the role of Hh signaling in chronic myeloid leukemia (CML), considered by many to be a stem cell disorder that bears the constitutively active BCR-ABL tyrosine kinase. Despite the elimination of most leukemia cells through BCR-ABL inhibition, most patients remain PCR positive, suggesting that the putative CML stem cell may be resistant to kinase antagonism. Groups are now exploring the Hh pathway as an alternate pathway supporting CML stem cell survival. Knockdown or inhibition of Smo abrogates or delays the appearance of CML in several in vitro and in vivo models. These data have lead to clinical trials using BCR-ABL kinase and novel Smo inhibitors in combination.

Topical treatment of Basal cell carcinomas in nevoid Basal cell carcinoma syndrome with a smoothened inhibitor

Basal cell carcinoma (BCC) is a distinctive manifestation in nevoid basal cell carcinoma syndrome (NBCCS) patients. Both inherited and acquired mutations of patched 1 (PTCH1), a tumor-suppressor gene controlling the activity of Smoothened (SMO), are the primary cause of the constitutive activation of the Hedgehog (HH) pathway, leading to the emergence of BCCs in NBCCS. LDE225, a distinct, selective antagonist of SMO, showed potent inhibition of basaloid tumor nest formation and mediated regression of preformed basaloid tumors in organ cultures of skin derived from Ptch1 heterozygous knockout mice. In a double-blind, randomized, vehicle-controlled, intraindividual study, a total of 8 NBCCS patients presenting 27 BCCs were treated twice daily with 0.75% LDE225 cream or vehicle for 4 weeks. Application of 0.75% LDE225 cream was well tolerated and showed no skin irritation. Of 13 LDE225-treated BCCs, 3 showed a complete, 9 a partial, and only 1 no clinical response. Except for one partial response, the vehicle produced no clinical response in any of the 14 treated BCCs. Treatment with 0.75% LDE225 cream in NBCCS patients was very well tolerated and caused BCC regression, thus potentially offering an attractive therapeutic alternative to currently available therapies for this indication.JID JOURNAL CLUB ARTICLE: For questions, answers, and open discussion about this article, please go to http://www.nature.com/jid/journalclub.

Interfering with resistance to smoothened antagonists by inhibition of the PI3K pathway in medulloblastoma

The malignant brain cancer medulloblastoma is characterized by mutations in Hedgehog (Hh) signaling pathway genes, which lead to constitutive activation of the G protein (heterotrimeric guanosine triphosphate-binding protein)-coupled receptor Smoothened (Smo). The Smo antagonist NVP-LDE225 inhibits Hh signaling and induces tumor regression in animal models of medulloblastoma. However, evidence of resistance was observed during the course of treatment. Molecular analysis of resistant tumors revealed several resistance mechanisms. We noted chromosomal amplification of Gli2, a downstream effector of Hh signaling, and, more rarely, point mutations in Smo that led to reactivated Hh signaling and restored tumor growth. Analysis of pathway gene expression signatures also, unexpectedly, identified up-regulation of phosphatidylinositol 3-kinase (PI3K) signaling in resistant tumors as another potential mechanism of resistance. Probing the relevance of increased PI3K signaling, we demonstrated that addition of the PI3K inhibitor NVP-BKM120 or the dual PI3K-mTOR (mammalian target of rapamycin) inhibitor NVP-BEZ235 to the initial treatment with the Smo antagonist markedly delayed the development of resistance. Our findings may be useful in informing treatment strategies for medulloblastoma.

Frequent deregulations in the hedgehog signaling network and cross-talks with the epidermal growth factor receptor pathway involved in cancer progression and targeted therapies

The hedgehog (Hh)/glioma-associated oncogene (GLI) signaling network is among the most important and fascinating signal transduction systems that provide critical functions in the regulation of many developmental and physiological processes. The coordinated spatiotemporal interplay of the Hh ligands and other growth factors is necessary for the stringent control of the behavior of diverse types of tissue-resident stem/progenitor cells and their progenies. The activation of the Hh cascade might promote the tissue regeneration and repair after severe injury in numerous organs, insulin production in pancreatic beta-cells, and neovascularization. Consequently, the stimulation of the Hh pathway constitutes a potential therapeutic strategy to treat diverse human disorders, including severe tissue injuries; diabetes mellitus; and brain, skin, and cardiovascular disorders. In counterbalance, a deregulation of the Hh signaling network might lead to major tissular disorders and the development of a wide variety of aggressive and metastatic cancers. The target gene products induced through the persistent Hh activation can contribute to the self-renewal, survival, migration, and metastasis of cancer stem/progenitor cells and their progenies. Moreover, the pivotal role mediated through the Hh/GLI cascade during cancer progression also implicates the cooperation with other oncogenic products, such as mutated K-RAS and complex cross-talk with different growth factor pathways, including tyrosine kinase receptors, such as epidermal growth factor receptor (EGFR), Wnt/beta-catenin, and transforming growth factor-beta (TGF-beta)/TGF-beta receptors. Therefore, the molecular targeting of distinct deregulated gene products, including Hh and EGFR signaling components and other signaling elements that are frequently deregulated in highly tumorigenic cancer-initiating cells and their progenies, might constitute a potential therapeutic strategy to eradicate the total cancer cell mass. Of clinical interest is that these multitargeted approaches offer great promise as adjuvant treatments for improving the current antihormonal therapies, radiotherapies, and/or chemotherapies against locally advanced and metastatic cancers, thereby preventing disease relapse and the death of patients with cancer.

Loss of the tumor suppressor Snf5 leads to aberrant activation of the Hedgehog-Gli pathway

Aberrant activation of the Hedgehog (Hh) pathway can drive tumorigenesis. To investigate the mechanism by which glioma-associated oncogene family zinc finger-1 (GLI1), a crucial effector of Hh signaling, regulates Hh pathway activation, we searched for GLI1-interacting proteins. We report that the chromatin remodeling protein SNF5 (encoded by SMARCB1, hereafter called SNF5), which is inactivated in human malignant rhabdoid tumors (MRTs), interacts with GLI1. We show that Snf5 localizes to Gli1-regulated promoters and that loss of Snf5 leads to activation of the Hh-Gli pathway. Conversely, re-expression of SNF5 in MRT cells represses GLI1. Consistent with this, we show the presence of a Hh-Gli-activated gene expression profile in primary MRTs and show that GLI1 drives the growth of SNF5-deficient MRT cells in vitro and in vivo. Therefore, our studies reveal that SNF5 is a key mediator of Hh signaling and that aberrant activation of GLI1 is a previously undescribed targetable mechanism contributing to the growth of MRT cells.