Targeting the Hedgehog pathway in cancer

Structural and logical analysis of a comprehensive hedgehog signaling pathway to identify alternative drug targets for glioma, colon and pancreatic cancer

Hedgehog is an evolutionarily conserved developmental pathway, widely implicated in controlling various cellular responses such as cellular proliferation and stem cell renewal in human and other organisms, through external stimuli. Aberrant activation of this pathway in human adult stem cell line may cause different types of cancers. Hence, targeting this pathway in cancer therapy has become indispensable, but the non availability of detailed molecular interactions, complex regulations by extra- and intra-cellular proteins and cross talks with other pathways pose a serious challenge to get a coherent understanding of this signaling pathway for making therapeutic strategy. This motivated us to perform a computational study of the pathway and to identify probable drug targets. In this work, from available databases and literature, we reconstructed a complete hedgehog pathway which reports the largest number of molecules and interactions to date. Using recently developed computational techniques, we further performed structural and logical analysis of this pathway. In structural analysis, the connectivity and centrality parameters were calculated to identify the important proteins from the network. To capture the regulations of the molecules, we developed a master Boolean model of all the interactions between the proteins and created different cancer scenarios, such as Glioma, Colon and Pancreatic. We performed perturbation analysis on these cancer conditions to identify the important and minimal combinations of proteins that can be used as drug targets. From our study we observed the under expressions of various oncoproteins in Hedgehog pathway while perturbing at a time the combinations of the proteins GLI1, GLI2 and SMO in Glioma; SMO, HFU, ULK3 and RAS in Colon cancer; SMO, HFU, ULK3, RAS and ERK12 in Pancreatic cancer. This reconstructed Hedgehog signaling pathway and the computational analysis for identifying new combinatory drug targets will be useful for future in-vitro and in-vivo analysis to control different cancers.

Hypoxia and metastasis in an orthotopic cervix cancer xenograft model

BACKGROUND

Hypoxia can promote tumor metastasis by mechanisms that are believed to result from changes in gene expression. The current study examined the role of putative metastatic genes regulated by cyclic hypoxia in relation to metastasis formation in orthotopic models of cervix cancer.

METHODS

Orthotopic tumors derived from ME180 human cervix cancer cells or from early generation human cervix cancer xenografts were exposed to cyclic hypoxic conditions during growth in vivo and tumor growth and lymphnode metastases were monitored. Expression of the chemokine receptor CXCR4 and various genes in the Hedgehog (Hh) pathway were inhibited using genetic (inducible shRNA vs CXCR4) small molecule (AMD3100) or antibody (5E1) treatment (CXCR4 and Hh genes, respectively) during tumor growth.

RESULTS

As reported previously, exposure of tumor bearing mice to cyclic hypoxia caused a reduction of tumor growth but a large increase in metastasis. Inhibition of CXCR4 or Hh gene activity during tumor growth further reduced primary tumor size and reduced lymphatic metastasis to levels below those seen in control mice exposed to normoxic conditions.

CONCLUSION

Blocking CXCR4 or Hh gene expression are potential therapeutic pathways for improving cervix cancer treatment.

Hedgehog signaling in prostate cancer and its therapeutic implication

Activation of Hedgehog (Hh) signaling is implicated in the development and progression of several tumor types, including prostate cancer, which is still the most common non-skin malignancy and the third leading cause of cancer-related mortality in men in industrialized countries worldwide. Several studies have indicated that the Hh pathway plays a crucial role in the development as well as in the progression of this disease to more aggressive and even therapy-resistant disease states. Moreover, preclinical data have shown that inhibition of Hh signaling has the potential to reduce prostate cancer invasiveness and metastatic potential. Clinical trials investigating the benefit of Hh inhibitors in patients with prostate cancer have recently been initiated. However, acquired drug resistance has already been observed in other tumor types after long-term Hh inhibition. Therefore, combining Hh inhibitors with ionizing radiation, chemotherapy or other molecular targeted agents could represent an alternative therapeutic strategy. In this review, we will highlight the role of Hh signaling in the development and progression of prostate cancer and summarize the different therapeutic applications of Hedgehog inhibition.

LKB1 inhibits breast cancer partially through repressing the Hedgehog signaling pathway

Constitutive activation of the Hedgehog (Hh) signaling pathway has been implicated in the development of many human malignancies. Hh targets, such as Patched (PTCH), smoothened (SMO), Sonic hedgehog (SHH) and glioma-associated oncogene homologue 1 (GLI1), are markers of Hh signaling activation and expressed in most Hh-associated tumors. The protein kinase LKB1 has been shown to slow proliferation and induce cell-cycle arrest in many cell lines. In this study, we observed that activated LKB1 decreased the expression of factors related to Hh reporter activity in MDA-MB-231 breast cancer cells, including of SMO, SHH and GLI1. In contrast, LKB1 siRNA increased the expression of these target genes. The same results were shown to inhibit the Hh factors Sufu and Hip. Furthermore, we also observed negative correlation between LKB1 and glioma-associated oncogene homologue 1 (GLI1) in three breast cancer cell lines. Meanwhile, LKB1 siRNA rescued the inhibition of cell growth by 3-Keto-N-(aminoethyl-N'-aminocaproyldihydrocinnamoyl) cyclopamine (KAAD-cyclopamine), an antagonist of the Hh element SMO, which suggests that LKB1 acts as the downstream of SMO. In vivo, LKB1 siRNA increased tumor growth in the mammary fat pad, and the expression levels of Hh displayed similar results in vitro. Overexpression of the LKB1 protein in human breast cancers is associated with the expression of Hh. We found that breast carcinomas with detectable Hh had weak or undetectable expression of LKB1, whereas tumors that expressed high levels of LKB1 had undetectable Hh signaling. In this study, we find that LKB1 are negatively correlated with the expression of Hh related transcription factors. These findings suggest that LKB1 may inhibit tumorigenesis by regulating Hh signaling in certain cancers.

Discovery of small-molecule modulators of the Sonic Hedgehog pathway

The Hedgehog signaling pathway is involved in the development of multicellular organisms and, when deregulated, can contribute to certain cancers, among other diseases. The molecular characterization of the pathway, which has been enabled by small-molecule probes targeting its components, remains incomplete. Here, we report the discovery of two potent, small-molecule inhibitors of the Sonic Hedgehog (Shh) pathway, BRD50837 and BRD9526. Both compounds exhibit stereochemistry-based structure–activity relationships, a feature suggestive of a specific and selective interaction of the compounds with as-yet-unknown cellular target(s) and made possible by the strategy used to synthesize them as members of a stereochemically and skeletally diverse screening collection. The mechanism-of-action of these compounds in some ways shares similarities to that of cyclopamine, a commonly used pathway inhibitor. Yet, in other ways their mechanism-of-action is strikingly distinct. We hope that these novel compounds will be useful probes of this complex signaling pathway.

Toward personalized cancer nanomedicine - past, present, and future

Tumors are composed of highly proliferate, migratory, invasive, and therapy-evading cells. These characteristics are conferred by an enormously complex landscape of genomic, (epi-)genetic, and proteomic aberrations. Recent efforts to comprehensively catalogue these reversible and irreversible modifications have began to identify molecular mechanisms that contribute to cancer pathophysiology, serve as novel therapeutic targets, and may constitute biomarkers for early diagnosis and prediction of therapy responses. With constantly evolving technologies that will ultimately enable a complete survey of cancer genomes, the challenges for discovery cancer science and drug development are daunting. Bioinformatic and functional studies must differentiate cancer-driving and -contributing mutations from mere bystanders or 'noise', and have to delineate their molecular mechanisms of action as a function of collaborating oncogenic and tumor suppressive signatures. In addition, the translation of these genomic discoveries into meaningful clinical endpoints requires the development of co-extinction strategies to therapeutically target multiple cancer genes, to robustly deliver therapeutics to tumor sites, and to enable widespread dissemination of therapies within tumor tissue. In this perspective, I will describe the most current paradigms to study and validate cancer gene function. I will highlight advances in the area of nanotechnology, in particular, the development of RNA interference (RNAi)-based platforms to more effectively deliver therapeutic agents to tumor sites, and to modulate critical cancer genes that are difficult to target using conventional small-molecule- or antibody-based approaches. I will conclude with an outlook on the deluge of challenges that genomic and bioengineering sciences must overcome to make the long-awaited era of personalized nano-medicine a clinical reality for cancer patients.

Molecular-targeted agents combination therapy for cancer: developments and potentials

Although chemotherapy has advanced into the era of targeted drugs, the antitumor efficacies of current therapies are limited, most likely because of the high degree of cancer clonal heterogeneity, intratumor genetic heterogeneity and cell signal complexity. As shutdown of a single target does not necessarily eradicate the cancer, the use of combinations of molecular-targeted agents (MATs) has been proposed, and some pioneering research has been conducted to examine the efficacy of this strategy. In this article, the clinical and preclinical studies that are underway in an attempt to improve the anticancer efficacy of chemotherapies through combination strategies are summarized. Studies of combining cytotoxic agents with MATs, coinhibiting two or more targets in a single pathway or coinhibiting parallel or compensatory pathways as well as specific combinations will be introduced, and the antitumor potentials of each combination strategy will be evaluated.

The emerging mutational landscape of G proteins and G-protein-coupled receptors in cancer

Aberrant expression and activity of G proteins and G-protein-coupled receptors (GPCRs) are frequently associated with tumorigenesis. Deep sequencing studies show that 4.2% of tumours carry activating mutations in GNAS (encoding Gαs), and that oncogenic activating mutations in genes encoding Gαq family members (GNAQ or GNA11) are present in ~66% and ~6% of melanomas arising in the eye and skin, respectively. Furthermore, nearly 20% of human tumours harbour mutations in GPCRs. Many human cancer-associated viruses also express constitutively active viral GPCRs. These studies indicate that G proteins, GPCRs and their linked signalling circuitry represent novel therapeutic targets for cancer prevention and treatment.

Children's Oncology Group's 2013 blueprint for research: central nervous system tumors

In the US, approximately 2,500 children are diagnosed annually with brain tumors. Their survival ranges from >90% to <10%. For children with medulloblastoma, the most common malignant brain tumor, 5-year survival ranges from >80% (standard-risk) to 60% (high-risk). For those with high-grade gliomas (HGGs) including diffuse intrinsic pontine gliomas, 5-year survival remains <10%. Sixty-five percent patients with ependymoma are cured after surgery and radiation therapy depending on the degree of resection and histopathology of the tumor. Phase II trials for brain tumors will investigate agents that act on cMET, PDGFRA, or EZH2 in HGG, DIPG, or medulloblastoma, respectively. Phase III trials will explore risk-based therapy stratification guided by molecular and clinical traits of children with medulloblastoma or ependymoma.

Current therapeutic strategies and novel approaches in osteosarcoma

Osteosarcoma is the most frequent malignant primary bone tumor and a main cause of cancer-related death in children and adolescents. Although long-term survival in localized osteosarcoma has improved to about 60% during the 1960s and 1970s, long-term survival in both localized and metastatic osteosarcoma has stagnated in the past several decades. Thus, current conventional therapy consists of multi-agent chemotherapy, surgery and radiation, which is not fully adequate for osteosarcoma treatment. Innovative drugs and approaches are needed to further improve outcome in osteosarcoma patients. This review describes the current management of osteosarcoma as well as potential new therapies.

Comprehensive methylome analysis of ovarian tumors reveals hedgehog signaling pathway regulators as prognostic DNA methylation biomarkers

Women with advanced stage ovarian cancer (OC) have a five-year survival rate of less than 25%. OC progression is associated with accumulation of epigenetic alterations and aberrant DNA methylation in gene promoters acts as an inactivating ?hit? during OC initiation and progression. Abnormal DNA methylation in OC has been used to predict disease outcome and therapy response. To globally examine DNA methylation in OC, we used next-generation sequencing technology, MethylCap-sequencing, to screen 75 malignant and 26 normal or benign ovarian tissues. Differential DNA methylation regions (DMRs) were identified, and the Kaplan?Meier method and Cox proportional hazard model were used to correlate methylation with clinical endpoints. Functional role of specific genes identified by MethylCap-sequencing was examined in in vitro assays. We identified 577 DMRs that distinguished (p < 0.001) malignant from non-malignant ovarian tissues; of these, 63 DMRs correlated (p < 0.001) with poor progression free survival (PFS). Concordant hypermethylation and corresponding gene silencing of sonic hedgehog pathway members ZIC1 and ZIC4 in OC tumors was confirmed in a panel of OC cell lines, and ZIC1 and ZIC4 repression correlated with increased proliferation, migration and invasion. ZIC1 promoter hypermethylation correlated (p < 0.01) with poor PFS. In summary, we identified functional DNA methylation biomarkers significantly associated with clinical outcome in OC and suggest our comprehensive methylome analysis has significant translational potential for guiding the design of future clinical investigations targeting the OC epigenome. Methylation of ZIC1, a putative tumor suppressor, may be a novel determinant of OC outcome.

Hedgehog signaling pathway: the must, the maybe and the unknown

Lung cancer treatment consists from the basic chemotherapeutic drugs (e.g., platinum analogues) and from pharmaceuticals targeting the different genome of lung tumors (e.g., tyrosine kinase inhibitors). During the last years pharmaceuticals targeting the tumor mutations are approved for first line treatment since they have provided increased overall survival in comparison to standard chemotherapy treatment. Furthermore, due to the increased interest in unrevealing the mechanisms of cell mutation, tumor evolution and tumor cell maintenance the hedgehog pathway has been elicited. Along with Notch and Wnt these three pathways are responsible for progenitor cell development and pulmonary organogenesis. Inhibitors of this pathway have been discovered and their application in the clinical practice is being investigated. However, further understanding of the mechanisms of regulation is needed.

Targeting hedgehog-GLI-2 pathway in osteosarcoma

Osteosarcoma is the most common primary malignant tumor of bone. Patients with localized osteosarcoma are routinely treated with chemotherapy and surgery. However, many of these patients eventually relapse after these treatments. In such cases, there are limited treatment options for these patients and most will eventually die with metastatic disease. Therefore, it is imperative to identify better therapeutic strategies. Hedgehog-GLI is responsible for the development of vertebrate embryonic and tumorigenesis. Specifically, the transcription factor, GLI-2, plays a key role in development of normal prostate. Aberrant activation of GLI-2 is correlated with various malignancies. We observe that GLI-2 is highly expressed in osteosarcoma cell lines, and this correlates with poor clinical outcomes in patients. Knockdown of GLI-2 by siRNA decreases osteosarcoma cell proliferation and viability, which eventually induces cell death as revealed in both in 2D and 3D cultures. In addition, we notice that administration of GLI-2 siRNA can increase the sensitivity of osteosarcoma cells to chemotherapeutic drugs. These findings suggest GLI-2 is required for osteosarcoma cell proliferation and survival. GLI-2 may be exploited as a therapeutic target for the treatment of osteosarcoma patients.

Hedgehog signalling pathway in adult liver: a major new player in hepatocyte metabolism and zonation?

Metabolic Zonation, i.e. the heterogeneous distribution of different metabolic pathways in different zones of the lobules, forms the basis of proper function of the liver in metabolic homeostasis and its regulation. According to recent results, Metabolic Zonation is controlled by the Wnt/β-catenin signalling pathway. Here, we hypothesize that hedgehog signalling via Indian hedgehog ligands plays an equal share in this control although, up to now, hedgehog signalling is considered not to be active in healthy adult hepatocytes. We provide broad evidence taken mainly by analogy from other mature organs that hedgehog signalling in adult hepatocytes may particularly control liver lipid and cholesterol metabolism as well as certain aspects of hormone biosynthesis. Like Wnt/β-catenin signalling, it seems to act on a very low level forming a porto-central gradient in the lobules opposite to that of Wnt/β-catenin signalling with which it is interacting by mutual inhibition. Consequently, modulation of hedgehog signalling by endogenous and exogenous agents may considerably impact on liver lipid metabolism and beyond. If functioning improperly, it may possibly contribute to diseases like non-alcoholic fatty liver disease (NAFLD) and other diseases such as lipodystrophy.

Overexpression of Gli1 in cancer interstitial tissues predicts early relapse after radical operation of breast cancer

OBJECTIVE

To investigate whether Gli1 expression is important in relapse after radical operation of breast cancer.

METHODS

Using immunohistochemistry, Gli1 expression was analyzed in human primary breast cancer (n=284) and paracancerous tissues (n=20), and also in local lymph nodes (n=28) and metastatic lymph nodes (n=28).

RESULTS

Initial analysis of Gli1 expression in a small cohort of 20 breast tumors and their paracancerous tissues showed a tendency towards Gli1 overexpression in breast cancer tissues (P<0.001). Further, Gli1 expression in 284 breast cancer tissue samples was analyzed and a significant correlation was found between increased expression of nuclear Gli1 and unfavorable recurrence-free survival (RFS) (P<0.05). The nuclear expression of Gli1 in metastatic lymph nodes following relapse after radical operation was much higher than that in the local lymph nodes of primary carcinoma (P<0.05). Most interestingly, the expression of Gli1 was much higher in the interstitial tissues of the relapsed group than of the non-relapsed group (P<0.001).

CONCLUSIONS

Breast cancer shows a high prevalence of Gli1 expression, which is significantly correlated with aggressive features and unfavorable RFS. Nuclear Gli1 overexpression, especially in the interstitial tissues, signified early relapse after radical operation of breast cancer.

Decoding the phosphorylation code in Hedgehog signal transduction

Hedgehog (Hh) signaling plays pivotal roles in embryonic development and adult tissue homeostasis, and its deregulation leads to numerous human disorders including cancer. Binding of Hh to Patched (Ptc), a twelve-transmembrane protein, alleviates its inhibition of Smoothened (Smo), a seven-transmembrane protein related to G-protein-coupled receptors (GPCRs), leading to Smo phosphorylation and activation. Smo acts through intracellular signaling complexes to convert the latent transcription factor Cubitus interruptus (Ci)/Gli from a truncated repressor to a full-length activator, leading to derepression/activation of Hh target genes. Increasing evidence suggests that phosphorylation participates in almost every step in the signal relay from Smo to Ci/Gli, and that differential phosphorylation of several key pathway components may be crucial for translating the Hh morphogen gradient into graded pathway activities. In this review, we focus on the multifaceted roles that phosphorylation plays in Hh signal transduction, and discuss the conservation and difference between Drosophila and mammalian Hh signaling mechanisms.

Mutations in the hedgehog pathway genes SMO and PTCH1 in human gastric tumors

The causal role of the hedgehog pathway in cancer has been best documented in basal cell carcinoma of the skin. To assess potential DNA alterations of the hedgehog pathway in gastric cancer, we sequenced SMO and PTCH1 genes in a set of 39 gastric tumors. Tumors were classified by histology based on the Lauren classification and Sanger sequencing was performed to obtain full length coding sequences. Genomic instability was evident in these tumors as a number of silent or missense mutations were found. In addition to those that are potential germline polymorphisms, we found three SMO missense mutations, and one PTCH1 frameshift mutation that are novel and have not been documented in basal cell carcinoma. Mutations were found in both intestinal and diffuse type gastric tumors as well as in tumors that exhibit both intestinal and diffuse features. mRNA expression of hedgehog pathway genes was also examined and their levels do not indicate unequivocal higher pathway activity in tumors with mutations than those without. In summary, SMO and/or PTCH1 mutations are present at low frequency in different histologic subtypes of gastric tumors and these do not appear to be driver mutations.

Lung cancer-initiating cells: a novel target for cancer therapy

Lung cancer is a major public health problem causing more deaths than any other cancer. A better understanding of the biology of this disease and improvements in treatment are greatly needed. Increasing evidence supports the concept that a rare and specialized population of cancer cells, so-called cancer-initiating cells with stem cell-like characteristics, is responsible for tumor growth, maintenance, and recurrence. Cancer-initiating cells also exhibit characteristics that render them resistant to both radiation and chemotherapy, and therefore they are believed to play a role in treatment failure. This has led to the hypothesis that traditional therapies that indiscriminately kill tumor cells will not be as effective as therapies that selectively target cancer-initiating cells. Investigating putative cancer-initiating cells in lung cancer will greatly benefit the understanding of the origins of this disease and may lead to novel approaches to therapy by suggesting markers for use in either further isolating this population for study or for selectively targeting these cells. This review will discuss (1) lung cancer, (2) stem cells, and the role of cancer-initiating cells in tumorigenesis; (3) markers and functional characteristics associated with lung cancer-initiating cells; and (4) the potential to selectively target this subpopulation of tumor cells.

Hedgehog signaling pathway in ovarian cancer

Despite advances in surgical and chemotherapeutic treatment options, less than 50% of patients with advanced-stage ovarian cancer survive five years after initial diagnosis. In this regard, novel treatment approaches are warranted utilizing molecularly targeted therapies directed against particular components of specific signaling pathways which are required for tumor development and progression. One molecular pathway of interest is the hedgehog (Hh) signaling pathway. Activation of the Hh pathway has been observed in several cancer types, including ovarian cancer. This review highlights the crucial role of Hh signaling in the development and progression of ovarian cancer and might lead to a better understanding of the Hh signaling in ovarian tumorigenesis, thus encouraging the investigation of novel targeted therapies.

Microenvironment-evoked cell lineage conversion: Shifting the focus from internal reprogramming to external forcing

Seeking possible ways to create replacement cells for the faded ones with deficits in functionality or quantity inspires comprehensive needs for cell lineage conversion. To fulfill this promise, reprogramming and microenvironment direction have been used to manipulate abundant cell fates. We briefly describe the evolution and fundamental insights of these two major strategies applied for lineage specification, comment generally on their current limitations, and analyze the orchestral interplay between them. We also present several future directions and discuss the potential clinical uses. Based on the relatively slight safety and technical issues, we conclude that microenvironment-evoked cell lineage conversion, instead of reprogramming, will be the shifting focus in regenerative medicine.

Vismodegib: a promising drug in the treatment of basal cell carcinomas

Hedgehog pathway signaling is important for embryonic development; however, inappropriate reactivation of this pathway in adults has been linked to several forms of cancer. Vismodegib (Erivedge™), a first-in-class hedgehog pathway inhibitor, blocks the pathway by inhibiting the activity of the signaling protein SMO. Preclinical studies have provided promising indications of potential tumor-reducing activity in several cancers. Thus far, clinical pharmacology and Phase I studies have demonstrated the unique pharmacokinetic profile of vismodegib, its efficacy in certain types of tumors and a generally tolerable adverse-event profile. A pivotal Phase II clinical trial confirmed the favorable benefit:risk profile of vismodegib in advanced basal cell carcinoma.

Targeting the hedgehog pathway: role in cancer and clinical implications of its inhibition

The Hedgehog (Hh) pathway is a signaling cascade that is evolutionally highly conserved and plays an important role in embryonic pattern formation and stem cell response to tissue damage. Given the pivotal role the Hh pathway plays in embryonic development in terms of proliferation and differentiation, it is not surprising that it has also been implicated in tumorigenesis and tumor growth acceleration in a vast variety of malignancies. This article summarizes the mechanism of Hh pathway signal transduction, discusses the models of pathway activation, reviews the clinical data using Hh inhibitors, and discusses challenges to the development of pathway inhibitors.

The Hedgehog signal transduction network

Hedgehog (Hh) proteins regulate the development of a wide range of metazoan embryonic and adult structures, and disruption of Hh signaling pathways results in various human diseases. Here, we provide a comprehensive review of the signaling pathways regulated by Hh, consolidating data from a diverse array of organisms in a variety of scientific disciplines. Similar to the elucidation of many other signaling pathways, our knowledge of Hh signaling developed in a sequential manner centered on its earliest discoveries. Thus, our knowledge of Hh signaling has for the most part focused on elucidating the mechanism by which Hh regulates the Gli family of transcription factors, the so-called "canonical" Hh signaling pathway. However, in the past few years, numerous studies have shown that Hh proteins can also signal through Gli-independent mechanisms collectively referred to as "noncanonical" signaling pathways. Noncanonical Hh signaling is itself subdivided into two distinct signaling modules: (i) those not requiring Smoothened (Smo) and (ii) those downstream of Smo that do not require Gli transcription factors. Thus, Hh signaling is now proposed to occur through a variety of distinct context-dependent signaling modules that have the ability to crosstalk with one another to form an interacting, dynamic Hh signaling network.

Overlapping activities of TGF-β and Hedgehog signaling in cancer: therapeutic targets for cancer treatment

Recent advances in the field of cancer therapeutics come from the development of drugs that specifically recognize validated oncogenic or pro-metastatic targets. The latter may be mutated proteins with altered function, such as kinases that become constitutively active, or critical components of growth factor signaling pathways, whose deregulation leads to aberrant malignant cell proliferation and dissemination to metastatic sites. We herein focus on the description of the overlapping activities of two important developmental pathways often exacerbated in cancer, namely Transforming Growth Factor-β (TGF-β) and Hedgehog (HH) signaling, with a special emphasis on the unifying oncogenic role played by GLI1/2 transcription factors. The latter are the main effectors of the canonical HH pathway, yet are direct target genes of TGF-β/SMAD signal transduction. While tumor-suppressor in healthy and pre-malignant tissues, TGF-β is often expressed at high levels in tumors and contributes to tumor growth, escape from immune surveillance, invasion and metastasis. HH signaling regulates cell proliferation, differentiation and apoptosis, and aberrant HH signaling is found in a variety of cancers. We discuss the current knowledge on HH and TGF-β implication in cancer including cancer stem cell biology, as well as the current state, both successes and failures, of targeted therapeutics aimed at blocking either of these pathways in the pre-clinical and clinical settings.

A phase II, randomized, placebo-controlled study of vismodegib as maintenance therapy in patients with ovarian cancer in second or third complete remission

PURPOSE

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).

EXPERIMENTAL DESIGN

Patients with recurrent epithelial ovarian, fallopian tube, or primary peritoneal cancer in second or third CR were randomized 1:1 to vismodegib (GDC-0449; 150 mg daily) or placebo three to 14 weeks after completing chemotherapy. Treatment continued until radiographic progression or toxicity. The primary endpoint was investigator-assessed progression-free survival (PFS).

RESULTS

One hundred four patients were randomized to vismodegib (n = 52) or placebo (n = 52); median PFS was 7.5 months and 5.8 months, respectively [HR 0.79; 95% confidence interval (CI), 0.46-1.35]. The HR was 0.66 (95% CI, 0.36-1.20) for second CR patients (n = 84) and 1.79 (95% CI, 0.50-6.48) for third CR patients (n = 20). The most common adverse events in the vismodegib arm were dysgeusia/ageusia, muscle spasms, and alopecia. Grade 3/4 adverse events occurred in 12 patients (23.1%) with vismodegib and six (11.5%) with placebo. Hedgehog expression was detected in 13.5% of archival tissues.

CONCLUSIONS

In this study, the sought magnitude of increase in PFS was not achieved for vismodegib maintenance versus placebo in patients with ovarian cancer in second or third CR. The frequency of Hedgehog ligand expression was lower than expected.

The ciliary Evc/Evc2 complex interacts with Smo and controls Hedgehog pathway activity in chondrocytes by regulating Sufu/Gli3 dissociation and Gli3 trafficking in primary cilia

Hedgehog (Hh) signaling is involved in patterning and morphogenesis of most organs in the developing mammalian embryo. Despite many advances in understanding core components of the pathway, little is known about how the activity of the Hh pathway is adjusted in organ- and tissue-specific developmental processes. Mutations in EVC or EVC2 disrupt Hh signaling in tooth and bone development. Using mouse models, we show here that Evc and Evc2 are mutually required for localizing to primary cilia and also for maintaining their normal protein levels. Consistent with Evc and Evc2 functioning as a complex, the skeletal phenotypes in either single or double homozygous mutant mice are virtually indistinguishable. Smo translocation to the cilium was normal in Evc2-deficient chondrocytes following Hh activation with the Smo-agonist SAG. However, Gli3 recruitment to cilia tips was reduced and Sufu/Gli3 dissociation was impaired. Interestingly, we found Smo to co-precipitate with Evc/Evc2, indicating that in some cells Hh signaling requires direct interaction of Smo with the Evc/Evc2 complex. Expression of a dominantly acting Evc2 mutation previously identified in Weyer's acrodental dysostosis (Evc2Δ43) caused mislocalization of Evc/Evc2Δ43 within the cilium and also reproduced the Gli3-related molecular defects observed in Evc2(-/-) chondrocytes. Moreover, Evc silencing in Sufu(-/-) cells attenuated the output of the Hh pathway, suggesting that Evc/Evc2 also promote Hh signaling in the absence of Sufu. Together our data reveal that the Hh pathway involves Evc/Evc2-dependent modulations that are necessary for normal endochondral bone formation.

Plasma Shh levels reduced in pancreatic cancer patients

OBJECTIVES

Normally, sonic hedgehog (Shh) is expressed in the pancreas during fetal development and transiently after tissue injury. Although pancreatic cancers express Shh, it is not known if the protein is secreted into the blood and whether its plasma levels change with pancreatic transformation. The goal of this study was to develop an enzyme-linked immunosorbent assay to detect human Shh in blood and determine its levels in subjects with and without pancreatic cancer.

METHODS

A human Shh enzyme-linked immunosorbent assay was developed, and plasma Shh levels were measured in blood samples from healthy subjects and patients with pancreatitis or pancreatic cancer. The biological activity of plasma Shh was tested using NIH-3T3 cells.

RESULTS

The mean levels of Shh in human blood were lower in patients with pancreatitis and pancreatic cancer than in healthy subjects. Hematopoietic cells did not express Shh, suggesting that Shh is secreted into the bloodstream. Plasma fractions enriched with Shh did not induce Gli-1 messenger RNA, suggesting that the protein was not biologically active.

CONCLUSIONS

Shh is secreted from tissues and organs into the circulation, but its activity is blocked by plasma proteins. Reduced plasma levels were found in pancreatic cancer patients, but alone were not sufficient to predict pancreatic cancer.

Sonic hedgehog pathway expression in non-small cell lung cancer

OBJECTIVE

Activation of the hedgehog pathway is an important signaling mechanism crucial in embryogenesis and has strong links to carcinogenesis. This study investigates the expression of the Sonic hedgehog pathway molecules in non-small cell lung tumors as it relates to clinical outcome of various non-small cell lung cancers.

METHODS

A tissue microarray with 81 samples from 42 patients with various non-small cell lung cancer histologies was examined without the aid of laser microdissection. All samples were stained with antibodies directed against Sonic hedgehog, Ptch-1, Smoothened, and Gli-1.

RESULTS

Most of the tumor samples showed negative to weak expression of the pathway proteins (Sonic hedgehog, 38% negative to 20% weak; Ptch-1, 100% negative; Smoothened, 69% negative to 7% weak; Gli-1, 57% negative to 5% weak) compared with higher expression in normal lung epithelial cells.

CONCLUSION

The same pathway expression did not correlate with clinical outcome. While our results do not provide any indication that the pathway molecules are correlated to overall patient survival possibly due to the limited sample size, our study shows minimum overexpression of Sonic hedgehog pathway in non-small cell lung cancer and this did not correlate clinically with patient outcome.

Sonic hedgehog signaling pathway induces cell migration and invasion through focal adhesion kinase/AKT signaling-mediated activation of matrix metalloproteinase (MMP)-2 and MMP-9 in liver cancer

The aberrant activation of sonic hedgehog (SHH) pathway contributes to initiation and progression of various malignancies. However, the roles and underlying mechanisms of SHH signaling pathway in invasion and metastasis of liver cancer have not been well understood. In this study, we found that SHH signaling was activated and correlated with invasion and metastasis in hepatocellular carcinoma (HCC). Enhanced SHH signaling by recombinant human SHH N-terminal peptide (rSHH-N) promoted hepatoma cell adhesion, migration and invasion, whereas blockade of SHH signaling with SHH neutralizing antibody or cyclopamine suppressed hepatoma cell adhesion, migration and invasion. Furthermore, matrix metalloproteinase (MMP)-2 and MMP-9 expressions and activities were upregulated and downregulated by rSHH-N and SHH signaling inhibitor, respectively. The rSHH-N-mediated hepatoma cell migration and invasion was blocked by MMP-specific inhibitors or neutralizing antibodies to MMP-2 and MMP-9. In addition, phosphorylations of AKT and focal adhesion kinase (FAK) were increased and decreased by rSHH-N and SHH signaling inhibitor, respectively. Further investigations showed that activation of AKT and FAK were required for rSHH-N-mediated upregulation of MMP-2 and MMP-9, cell migration and invasion. Finally, we found that SHH protein expression was positively correlated with phosphorylatd FAK Tyr397, phosphorylatd AKT Ser473, MMP-2 and MMP-9 protein expressions in HCC samples. Taken together, our findings suggest that SHH pathway induces cell migration and invasion through FAK/AKT signaling-mediated MMP-2 and MMP-9 production and activation in liver cancer.

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.

Hedgehog signalling as an antagonist of ageing and its associated diseases

Hedgehog is an important morphogenic signal that directs pattern formation during embryogenesis, but its activity also remains present through adult life. It is now becoming increasingly clear that during the reproductive phase of life and beyond it continues to direct cell renewal (which is essential to combat the chronic environmental stress to which the body is constantly exposed) and counteracts vascular, osteolytic and sometimes oncological insults to the body. Conversely, down-regulation of hedgehog signalling is associated with ageing-related diseases such as type 2 diabetes, neurodegeneration, atherosclerosis and osteoporosis. Hence, in this essay we argue that hedgehog signalling is not only important at the start of life, but also constitutes an important anti-geriatric influence, and that enhanced understanding of its properties may contribute to developing rational strategies for healthy ageing and prevention of ageing-related diseases.

Micellar delivery of cyclopamine and gefitinib for treating pancreatic cancer

Hedgehog (Hh) and epidermal growth factor receptor (EGFR) signaling are involved in pancreatic cancer progression. Targeting these pathways simultaneously with cyclopamine (Hh inhibitor) and gefitinib (EGFR inhibitor) is a promising approach for treating pancreatic cancer. However, the major limitation for effective clinical translation of these molecules is their low aqueous solubility. We have previously demonstrated that methoxy polyethyleneglycol-b-poly(carbonate-co-lactic acid) {mPEG-b-P(CB-co-LA)} copolymer solubilizes hydrophobic anticancer drugs and has the potential to deliver to tumors by an enhanced permeability and retention (EPR) effect. In this study, using the nanoprecipitation method, cyclopamine and gefitinib were efficiently loaded into mPEG-b-P(CB-co-LA) micelles with encapsulation efficiencies of 94.4 and 88.6%, respectively. These micelles had a narrow particle size distribution with a mean particle size of 54.3 nm and a PDI of 0.14. Combination therapy showed a synergistic effect against L3.6pl cells but an additive effect against MIA PaCa-2 cells. Caspase 3/7 activity was also increased when this combination therapy was used, indicating apoptotic cell death. Gene and protein expression analysis indicated cross-talk between Hh and EGFR signaling. Furthermore, the combination decreased tumor growth rate in L3.6pl-derived xenograft mouse tumors. These data suggest the applicability of our micellar system to effectively load and deliver cyclopamine and gefitinib for combination chemotherapy.

Shh maintains dermal papilla identity and hair morphogenesis via a Noggin-Shh regulatory loop

During hair follicle morphogenesis, dermal papillae (DPs) function as mesenchymal signaling centers that cross-talk with overlying epithelium to regulate morphogenesis. While the DP regulates hair follicle formation, relatively little is known about the molecular basis of DP formation. The morphogen Sonic hedgehog (Shh) is known for regulating hair follicle epithelial growth, with excessive signaling resulting in basal cell carcinomas. Here, we investigate how dermal-specific Shh signaling contributes to DP formation and hair growth. Using a Cre-lox genetic model and RNAi in hair follicle reconstitution assays, we demonstrate that dermal Smoothened (Smo) loss of function results in the loss of the DP precursor, the dermal condensate, and a stage 2 hair follicle arrest phenotype reminiscent of Shh(-/-) skin. Surprisingly, dermal Smo does not regulate cell survival or epithelial proliferation. Rather, molecular screening and immunostaining studies reveal that dermal Shh signaling controls the expression of a subset of DP-specific signature genes. Using a hairpin/cDNA lentiviral system, we show that overexpression of the Shh-dependent gene Noggin, but not Sox2 or Sox18, can partially rescue the dermal Smo knockdown hair follicle phenotype by increasing the expression of epithelial Shh. Our findings suggest that dermal Shh signaling regulates specific DP signatures to maintain DP maturation while maintaining a reciprocal Shh-Noggin signaling loop to drive hair follicle morphogenesis.

Aberrant activation of hedgehog pathway in nasopharyngeal carcinoma

Nasopharyngeal carcinoma (NPC) is a very common head and neck cancer in southern china. Despite advances in surgical and chemotherapeutic approaches, its prognosis is still not promising. Hedgehog signaling pathway was reported to be involved in a number of cancers including head and neck. However, it remains unclear regarding the role of this pathway in NPC. By real-time PCR, we found Ptch1, Smo, and Gli-1 were expressed in all human nasopharyngeal epithelial tissues and cell lines. Compared with nasopharyngeal normal epithelial tissues, the mRNA expression level of Gli-1 was higher in carcinoma and nasopharyngitis (NPI) epithelial tissues. While compared with nasopharyngitis epithelia, the mRNA expression level of Ptch1 was lower in carcinoma epithelia and normal epithelia. The expressions of Smo mRNA were not significantly different among these epithelial tissues. Immunohistochemistry analysis revealed that the expression level of Gli-1 was higher in NPC than NPI. Thus, our data indicated that aberrant activation of hedgehog pathway in NPC. Furthermore, blocking the pathway with cyclopamine inhibited the proliferation of NPC epithelia cell lines. In addition, blockade of the pathway in three NPC cell lines with cyclopamine-induced tumor cell apoptosis. The transcription of hedgehog target genes also is inhibited by cyclopamine. These data suggested that hedgehog pathway may sustain nasopharyngeal tumor growth. Our data demonstrated that hedgehog signaling pathway was involved in NPC pathogenesis and might be a novel therapeutic target for NPC.

Hedgehog pathway regulators influence cervical cancer cell proliferation, survival and migration

Human papillomavirus (HPV) infection is considered to be a primary hit that causes cervical cancer. However, infection with this agent, although needed, is not sufficient for a cancer to develop. Additional cellular changes are required to complement the action of HPV, but the precise nature of these changes is not clear. Here, we studied the function of the Hedgehog (Hh) signaling pathway in cervical cancer. The Hh pathway can have a role in a number of cancers, including those of liver, lung and digestive tract. We found that components of the Hh pathway are expressed in several cervical cancer cell lines, indicating that there could exists an autocrine Hh signaling loop in these cells. Inhibition of Hh signaling reduces proliferation and survival of the cervical cancer cells and induces their apoptosis as seen by the up-regulation of the pro-apoptotic protein cleaved caspase 3. Our results indicate that Hh signaling is not induced directly by HPV-encoded proteins but rather that Hh-activating mutations are selected in cells initially immortalized by HPV. Sonic Hedgehog (Shh) ligand induces proliferation and promotes migration of the cervical cancer cells studied. Together, these results indicate pro-survival and protective roles of an activated Hh signaling pathway in cervical cancer-derived cells, and suggest that inhibition of this pathway may be a therapeutic option in fighting cervical cancer.

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.

Pathway-based classification of cancer subtypes

Background

Molecular markers based on gene expression profiles have been used in experimental and clinical settings to distinguish cancerous tumors in stage, grade, survival time, metastasis, and drug sensitivity. However, most significant gene markers are unstable (not reproducible) among data sets. We introduce a standardized method for representing cancer markers as 2-level hierarchical feature vectors, with a basic gene level as well as a second level of (more stable) pathway markers, for the purpose of discriminating cancer subtypes. This extends standard gene expression arrays with new pathway-level activation features obtained directly from off-the-shelf gene set enrichment algorithms such as GSEA. Such so-called pathway-based expression arrays are significantly more reproducible across datasets. Such reproducibility will be important for clinical usefulness of genomic markers, and augment currently accepted cancer classification protocols.

Results

The present method produced more stable (reproducible) pathway-based markers for discriminating breast cancer metastasis and ovarian cancer survival time. Between two datasets for breast cancer metastasis, the intersection of standard significant gene biomarkers totaled 7.47% of selected genes, compared to 17.65% using pathway-based markers; the corresponding percentages for ovarian cancer datasets were 20.65% and 33.33% respectively. Three pathways, consisting of Type_1_diabetes mellitus, Cytokine-cytokine_receptor_interaction and Hedgehog_signaling (all previously implicated in cancer), are enriched in both the ovarian long survival and breast non-metastasis groups. In addition, integrating pathway and gene information, we identified five (ID4, ANXA4, CXCL9, MYLK, FBXL7) and six (SQLE, E2F1, PTTG1, TSTA3, BUB1B, MAD2L1) known cancer genes significant for ovarian and breast cancer respectively.

Conclusions

Standardizing the analysis of genomic data in the process of cancer staging, classification and analysis is important as it has implications for both pre-clinical as well as clinical studies. The paradigm of diagnosis and prediction using pathway-based biomarkers as features can be an important part of the process of biomarker-based cancer analysis, and the resulting canonical (clinically reproducible) biomarkers can be important in standardizing genomic data. We expect that identification of such canonical biomarkers will improve clinical utility of high-throughput datasets for diagnostic and prognostic applications.

Reviewers

This article was reviewed by John McDonald (nominated by I. King Jordon), Eugene Koonin, Nathan Bowen (nominated by I. King Jordon), and Ekaterina Kotelnikova (nominated by Mikhail Gelfand).

Co-clustering phenome-genome for phenotype classification and disease gene discovery

Understanding the categorization of human diseases is critical for reliably identifying disease causal genes. Recently, genome-wide studies of abnormal chromosomal locations related to diseases have mapped >2000 phenotype–gene relations, which provide valuable information for classifying diseases and identifying candidate genes as drug targets. In this article, a regularized non-negative matrix tri-factorization (R-NMTF) algorithm is introduced to co-cluster phenotypes and genes, and simultaneously detect associations between the detected phenotype clusters and gene clusters. The R-NMTF algorithm factorizes the phenotype–gene association matrix under the prior knowledge from phenotype similarity network and protein–protein interaction network, supervised by the label information from known disease classes and biological pathways. In the experiments on disease phenotype–gene associations in OMIM and KEGG disease pathways, R-NMTF significantly improved the classification of disease phenotypes and disease pathway genes compared with support vector machines and Label Propagation in cross-validation on the annotated phenotypes and genes. The newly predicted phenotypes in each disease class are highly consistent with human phenotype ontology annotations. The roles of the new member genes in the disease pathways are examined and validated in the protein–protein interaction subnetworks. Extensive literature review also confirmed many new members of the disease classes and pathways as well as the predicted associations between disease phenotype classes and pathways.

Selective identification of hedgehog pathway antagonists by direct analysis of smoothened ciliary translocation

Hedgehog (Hh) signaling promotes tumorigenesis. The accumulation of the membrane protein Smoothened (Smo) within the primary cilium (PC) is a key event in Hh signal transduction, and many pharmacological inhibitors identified to date target Smo's actions. Smo ciliary translocation is inhibited by some pathway antagonists, while others promote ciliary accumulation, an outcome that can lead to a hypersensitive state on renewal of Hh signaling. To identify novel inhibitory compounds acting on the critical mechanistic transition of Smo accumulation, we established a high content screen to directly analyze Smo ciliary translocation. Screening thousands of compounds from annotated libraries of approved drugs and other agents, we identified several new classes of compounds that block Sonic hedgehog-driven Smo localization within the PC. Selective analysis was conducted on two classes of Smo antagonists. One of these, DY131, appears to inhibit Smo signaling through a common binding site shared by previously reported Smo agonists and antagonists. Antagonism by this class of compound is competed by high doses of Smo-binding agonists such as SAG and impaired by a mutation that generates a ligand-independent, oncogenic form of Smo (SmoM2). In contrast, a second antagonist of Smo accumulation within the PC, SMANT, was less sensitive to SAG-mediated competition and inhibited SmoM2 at concentrations similar to those that inhibit wild-type Smo. Our observations identify important differences among Hh antagonists and the potential for development of novel therapeutic approaches against mutant forms of Smo that are resistant to current therapeutic strategies.

Synthesis and characterization of Sant-75 derivatives as Hedgehog-pathway inhibitors

Sant-75 is a newly identified potent inhibitor of the hedgehog pathway. We designed a diversity-oriented synthesis program, and synthesized a series of Sant-75 analogues, which lays the foundation for further investigation of the structure–activity relationship of this important class of hedgehog-pathway inhibitors.