Th17 Cell-Derived Amphiregulin Promotes Colitis-Associated Intestinal Fibrosis Through Activation of mTOR and MEK in Intestinal Myofibroblasts.

BACKGROUND & AIMS: Intestinal fibrosis is a significant complication of Crohn's disease (CD). Gut microbiota reactive Th17 cells are crucial in the pathogenesis of CD; however, how Th17 cells induce intestinal fibrosis is still not completely understood. METHODS: In this study, T-cell transfer model with wild-type (WT) and Areg-/- Th17 cells and dextran sulfate sodium (DSS)-induced chronic colitis model in WT and Areg-/- mice were used. CD4+ T-cell expression of AREG was determined by quantitative reverse-transcriptase polymerase chain reaction and enzyme-linked immunosorbent assay. The effect of AREG on proliferation/migration/collagen expression in human intestinal myofibroblasts was determined. AREG expression was assessed in healthy controls and patients with CD with or without intestinal fibrosis. RESULTS: Although Th1 and Th17 cells induced intestinal inflammation at similar levels when transferred into Tcrßxδ-/- mice, Th17 cells induced more severe intestinal fibrosis. Th17 cells expressed higher levels of AREG than Th1 cells. Areg-/- mice developed less severe intestinal fibrosis compared with WT mice on DSS insults. Transfer of Areg-/- Th17 cells induced less severe fibrosis in Tcrßxδ-/- mice compared with WT Th17 cells. Interleukin (IL)6 and IL21 promoted AREG expression in Th17 cells by activating Stat3. Stat3 inhibitor suppressed Th17-induced intestinal fibrosis. AREG promoted human intestinal myofibroblast proliferation, motility, and collagen I expression, which was mediated by activating mammalian target of rapamycin and MEK. AREG expression was increased in intestinal CD4+ T cells in fibrotic sites compared with nonfibrotic sites from patients with CD. CONCLUSIONS: These findings reveal that Th17-derived AREG promotes intestinal fibrotic responses in experimental colitis and human patients with CD. Thereby, AREG might serve as a potential therapeutic target for fibrosis in CD.

Inhibition of MEK signaling prevents SARS-CoV2-induced lung damage and improves the survival of infected mice.

Coronavirus disease 2019 (COVID-19) is the illness caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Over 500 million confirmed cases of COVID-19 have been recorded, with six million deaths. Thus, reducing the COVID-19-related medical burden is an unmet need. Despite a vaccine that is successful in preventing COVID-19-caused death, effective medication to relieve COVID-19-associated symptoms and alleviate disease progression is still in high demand. In particular, one in three COVID-19 patients have signs of long COVID syndrome and are termed, long haulers. At present, there are no effective ways to treat long haulers. In this study, we determine the effectiveness of inhibiting mitogen-activated protein kinase (MEK) signaling in preventing SARS-CoV-2-induced lung damage in mice. We showed that phosphorylation of extracellular signal-regulated kinase, a marker for MEK activation, is high in SARS-CoV-2-infected lung tissues of mice and humans. We also showed that selumetinib, a specific inhibitor of the upstream MEK kinases, reduces cell proliferation, reduces lung damage following SARS-CoV-2 infection, and prolongs the survival of the infected mice. Selumetinib has been approved by the US Food and Drug Administration to treat cancer. Further analysis indicates that amphiregulin, an essential upstream molecule, was upregulated following SARS-CoV-2 infection. Our data suggest that MEK signaling activation represents a target for therapeutic intervention strategies against SARS-CoV-2-induced lung damage and that selumetinib may be repurposed to treat COVID-19.

Functional significance of Hippo/YAP signaling for drug resistance in colorectal cancer.

Colorectal cancer is a leading cause of cancer-related death worldwide. While early stage colorectal cancer can be removed by surgery, patients with advanced disease are treated by chemotherapy, with 5-Fluorouracil (5-FU) as a main ingredient. However, most patients with advanced colorectal cancer eventually succumb to the disease despite some responded initially. Thus, identifying molecular mechanisms responsible for drug resistance will help design novel strategies to treat colorectal cancer. In this study, we analyzed an acquired 5-FU resistant cell line, LoVo-R, and determined that elevated expression of YAP target genes is a major alteration in the 5-FU resistant cells. Hippo/YAP signaling, a pathway essential for cell polarity, is an important regulator for tissue homeostasis, organ size, and stem cells. We demonstrated that knockdown of YAP1 sensitized LoVo-R cells to 5-FU treatment in cultured cells and in mice. The relevance of our studies to colorectal cancer patients is reflected by our discovery that high expression of YAP target genes in the tumor was associated with an increased risk of cancer relapse and poor survival in a larger cohort of colorectal cancer patients who underwent 5-FU-related chemotherapy. Taken together, we demonstrate a critical role of YAP signaling for drug resistance in colorectal cancer.

Identifying therapeutic targets in gastric cancer: the current status and future direction.

Gastric cancer is the third leading cause of cancer-related death worldwide. Our basic understanding of gastric cancer biology falls behind that of many other cancer types. Current standard treatment options for gastric cancer have not changed for the last 20 years. Thus, there is an urgent need to establish novel strategies to treat this deadly cancer. Successful clinical trials with Gleevec in CML and gastrointestinal stromal tumors have set up an example for targeted therapy of cancer. In this review, we will summarize major progress in classification, therapeutic options of gastric cancer. We will also discuss molecular mechanisms for drug resistance in gastric cancer. In addition, we will attempt to propose potential future directions in gastric cancer biology and drug targets.

The Hedgehog pathway: role in cell differentiation, polarity and proliferation.

Hedgehog (Hh) is first described as a genetic mutation that has "spiked" phenotype in the cuticles of Drosophila in later 1970s. Since then, Hh signaling has been implicated in regulation of differentiation, proliferation, tissue polarity, stem cell population and carcinogenesis. The first link of Hh signaling to cancer was established through discovery of genetic mutations of Hh receptor gene PTCH1 being responsible for Gorlin syndrome in 1996. It was later shown that Hh signaling is associated with many types of cancer, including skin, leukemia, lung, brain and gastrointestinal cancers. Another important milestone for the Hh research field is the FDA approval for the clinical use of Hh inhibitor Erivedge/Vismodegib for treatment of locally advanced and metastatic basal cell carcinomas. However, recent clinical trials of Hh signaling inhibitors in pancreatic, colon and ovarian cancer all failed, indicating a real need for further understanding of Hh signaling in cancer. In this review, we will summarize recent progress in the Hh signaling mechanism and its role in human cancer.

A role for transcription factor STAT3 signaling in oncogene smoothened-driven carcinogenesis.

Activation of the Hedgehog (Hh) pathway is known to drive development of basal cell carcinoma and medulloblastomas and to associate with many other types of cancer, but the exact molecular mechanisms underlying the carcinogenesis process remain elusive. We discovered that skin tumors derived from epidermal expression of oncogenic Smo, SmoM2, have elevated levels of IL-11, IL-11Rα, and STAT3 phosphorylation at Tyr(705). The relevance of our data to human conditions was reflected by the fact that all human basal cell carcinomas examined have detectable STAT3 phosphorylation, mostly in keratinocytes. The functional relevance of STAT3 in Smo-mediated carcinogenesis was revealed by epidermal specific knockout of STAT3. We showed that removal of STAT3 from mouse epidermis dramatically reduced SmoM2-mediated cell proliferation, leading to a significant decrease in epidermal thickness and tumor development. We also observed a significant reduction of epidermal stem/progenitor cell population and cyclin D1 expression in mice with epidermis-specific knockout of STAT3. Our evidence indicates that STAT3 signaling activation may be mediated by the IL-11/IL-11Rα signaling axis. We showed that tumor development was reduced after induced expression of SmoM2 in IL-11Rα null mice. Similarly, neutralizing antibodies for IL-11 reduced the tumor size. In two Hh-responsive cell lines, ES14 and C3H10T1/2, we found that addition of Smo agonist purmorphamine is sufficient to induce STAT3 phosphorylation at Tyr(705), but this effect was abolished after IL-11Rα down-regulation by shRNAs. Taken together, our results support an important role of the IL-11Rα/STAT3 signaling axis for Hh signaling-mediated signaling and carcinogenesis.

Activation of the Hedgehog signaling pathway leads to fibrosis in aortic valves.

BACKGROUND: Fibrosis is a pathological wound healing process characterized by excessive extracellular matrix deposition, which interferes with normal organ function and contributes to ~ 45% of human mortality. Fibrosis develops in response to chronic injury in nearly all organs, but the a cascade of events leading to fibrosis remains unclear. While hedgehog (Hh) signaling activation has been associated with fibrosis in the lung, kidney, and skin, it is unknown whether hedgehog signaling activation is the cause or the consequence of fibrosis. We hypothesize that activation of hedgehog signaling is sufficient to drive fibrosis in mouse models. RESULTS: In this study, we provide direct evidence to show that activation of Hh signaling via expression of activated smoothened, SmoM2, is sufficient to induce fibrosis in the vasculature and aortic valves. We showed that activated SmoM2 -induced fibrosis is associated with abnormal function of aortic valves and heart. The relevance of this mouse model to human health is reflected in our findings that elevated GLI expression is detected in 6 out of 11 aortic valves from patients with fibrotic aortic valves. CONCLUSIONS: Our data show that activating hedgehog signaling is sufficient to drive fibrosis in mice, and this mouse model is relevant to human aortic valve stenosis.

Requirement of TGFbeta signaling for SMO-mediated carcinogenesis.

Hedgehog (Hh) signaling, via the key signal transducer Smoothened (SMO) and Gli transcription factors, is essential for embryonic development and carcinogenesis. At present, the molecular mechanism of Hh signaling-mediated carcinogenesis is not completely understood. Using a mouse model (K14cre/R26SmoM2) of SMO-mediated basal cell carcinoma development, we identified TGFß2 as a major Hh-regulated gene. TGFß2 expression was high in the keratinocytes, with activated TGFß signaling (indicated by elevated expression of phosphorylated SMAD2/3) detected in both tumor and stroma. The significance of TGFß signaling for SMO function was demonstrated in two assays. Down-regulation of TGFß2 expression prevented Hh signaling-dependent osteoblast differentiation and motor neuron differentiation. Furthermore, inhibition of TGFß signaling by TGFß receptor I inhibitor SD208 significantly reduced tumor area in K14cre/R26SmoM2 mice. Tumor shrinkage in mice was associated with an increased number of lymphocytes, suggesting an immune suppression role of TGFß signaling. The relevance of our results to human cancer is reflected by the fact that human basal cell carcinomas, which almost always harbor activated Hh signaling, have activated TGFß signaling, as indicated by high levels of phosphorylated SMAD2 and SMAD3 in tumor and stroma. Together, our data indicate that TGFß signaling is critical for Hh signaling-mediated carcinogenesis.

Active sonic hedgehog signaling between androgen independent human prostate cancer cells and normal/benign but not cancer-associated prostate stromal cells.

BACKGROUND: Sonic hedgehog (Shh) signaling plays a pivotal role in stromal-epithelial interaction during normal development but its role in tumor-stromal interaction during carcinogenic progression is less well defined. Since hormone refractory prostate cancer with bone metastasis is difficult to treat, it is crucial to investigate how androgen independent (AI) human prostate cancer cells communicate with their associated stroma. METHODS: Shh and its target transcription factor, Gli1 mRNA, were assessed by RT-PCR and/or quantitative RT-PCR in co-cultured cell recombinants comprised of AI C4-2 either with NPF (prostate fibroblasts from normal/benign prostate gland) or CPF (cancer-associated stromal fibroblasts) under Shh/cyclopamine (a hedgehog signaling inhibitor) treatment. Human bone marrow stromal (HS27A) cells were used as controls. In vivo investigation was performed by checking serum PSA and immunohistochemical staining for the apoptosis-associated M30 gene in mice bearing chimeric C4-2/NPF tumors. RESULTS: We found that (1) Shh has minimal growth-stimulating effects on prostate cancer cells, but it stimulated the growth of NPF but not CPF; (2) active Shh signaling was found between AI C4-2 cells and NPF but not CPF; and (3) osteonectin (ON) is a Gli1 target gene in NPF and not in CPF, and ON up-regulation in NPF can be blocked by cyclopamine CONCLUSIONS: Based on co-culture and chimeric tumor models, active Shh-mediated signaling was demonstrated between AI prostate cancer and NPF in a paracrine- and tumor progression-dependent manner. Our study suggests that drugs like cyclopamine that interfere with Shh signaling could be beneficial in preventing AI progression in prostate cancer cells.

Clinical implications of hedgehog signaling pathway inhibitors.

Hedgehog was first described in Drosophila melanogaster by the Nobel laureates Eric Wieschaus and Christiane Nüsslein-Volhard. The hedgehog (Hh) pathway is a major regulator of cell differentiation, proliferation, tissue polarity, stem cell maintenance, and carcinogenesis. The first link of Hh signaling to cancer was established through studies of a rare familial disease, Gorlin syndrome, in 1996. Follow-up studies revealed activation of this pathway in basal cell carcinoma, medulloblastoma and, leukemia as well as in gastrointestinal, lung, ovarian, breast, and prostate cancer. Targeted inhibition of Hh signaling is now believed to be effective in the treatment and prevention of human cancer. The discovery and synthesis of specific inhibitors for this pathway are even more exciting. In this review, we summarize major advances in the understanding of Hh signaling pathway activation in human cancer, mouse models for studying Hh-mediated carcinogenesis, the roles of Hh signaling in tumor development and metastasis, antagonists for Hh signaling and their clinical implications.

Tumor shrinkage by cyclopamine tartrate through inhibiting hedgehog signaling.

The link of hedgehog (Hh) signaling activation to human cancer and synthesis of a variety of Hh signaling inhibitors raise great expectation that inhibiting Hh signaling may be effective in human cancer treatment. Cyclopamine (Cyc), an alkaloid from the Veratrum plant, is a specific natural product inhibitor of the Hh pathway that acts by targeting smoothened (SMO) protein. However, its poor solubility, acid sensitivity, and weak potency relative to other Hh antagonists prevent the clinical development of Cyc as a therapeutic agent. Here, we report properties of cyclopamine tartrate salt (CycT) and its activities in Hh signaling-mediated cancer in vitro and in vivo. Unlike Cyc, CycT is water soluble (5-10 mg/mL). The median lethal dose (LD50) of CycT was 62.5 mg/kg body weight compared to 43.5 mg/kg for Cyc, and the plasma half-life (T1/2) of CycT was not significantly different from that of Cyc. We showed that CycT had a higher inhibitory activity for Hh signaling-dependent motor neuron differentiation than did Cyc (IC50 = 50 nmol/L for CycT vs. 300 nmol/L for Cyc). We also tested the antitumor effectiveness of these Hh inhibitors using two mouse models of basal cell carcinomas (K14cre:Ptch1(neo/neo) and K14cre:SmoM2(YFP)). After topical application of CycT or Cyc daily for 21 days, we found that all CycT-treated mice had tumor shrinkage and decreased expression of Hh target genes. Taken together, we found that CycT is an effective inhibitor of Hh signaling-mediated carcinogenesis.

The Role of the Hedgehog Pathway in Chemoresistance of Gastrointestinal Cancers.

The hedgehog pathway, which plays a significant role in embryonic development and stem cell regulation, is activated in gastrointestinal cancers. Chemotherapy is widely used in cancer treatment. However, chemoresistance becomes a substantial obstacle in cancer therapy. This review focuses on the recent advances in the hedgehog pathway's roles in drug resistance of gastrointestinal cancers and the novel drugs and strategies targeting hedgehog signaling.

Prognosis and Characterization of Immune Microenvironment in Acute Myeloid Leukemia Through Identification of an Autophagy-Related Signature.

Acute myeloid leukemia (AML) is one of the most common hematopoietic malignancies that has an unfavorable outcome and a high rate of relapse. Autophagy plays a vital role in the development of and therapeutic responses to leukemia. This study identifies a potential autophagy-related signature to monitor the prognoses of patients of AML. Transcriptomic profiles of AML patients (GSE37642) with the relevant clinical information were downloaded from Gene Expression Omnibus (GEO) as the training set while TCGA-AML and GSE12417 were used as validation cohorts. Univariate regression analyses and multivariate stepwise Cox regression analysis were respectively applied to identify the autophagy-related signature. The univariate Cox regression analysis identified 32 autophagy-related genes (ARGs) that were significantly associated with the overall survival (OS) of the patients, and were mainly rich in signaling pathways for autophagy, p53, AMPK, and TNF. A prognostic signature that comprised eight ARGs (BAG3, CALCOCO2, CAMKK2, CANX, DAPK1, P4HB, TSC2, and ULK1) and had good predictive capacity was established by LASSO-Cox stepwise regression analysis. High-risk patients were found to have significantly shorter OS than patients in low-risk group. The signature can be used as an independent prognostic predictor after adjusting for clinicopathological parameters, and was validated on two external AML sets. Differentially expressed genes analyzed in two groups were involved in inflammatory and immune signaling pathways. An analysis of tumor-infiltrating immune cells confirmed that high-risk patients had a strong immunosuppressive microenvironment. Potential druggable OS-related ARGs were then investigated through protein-drug interactions. This study provides a systematic analysis of ARGs and develops an OS-related prognostic predictor for AML patients. Further work is needed to verify its clinical utility and identify the underlying molecular mechanisms in AML.

A critical role of AREG for bleomycin-induced skin fibrosis.

We report our discovery of an important player in the development of skin fibrosis, a hallmark of scleroderma. Scleroderma is a fibrotic disease, affecting 70,000 to 150,000 Americans. Fibrosis is a pathological wound healing process that produces an excessive extracellular matrix to interfere with normal organ function. Fibrosis contributes to nearly half of human mortality. Scleroderma has heterogeneous phenotypes, unpredictable outcomes, no validated biomarkers, and no effective treatment. Thus, strategies to slow down scleroderma progression represent an urgent medical need. While a pathological wound healing process like fibrosis leaves scars and weakens organ function, oral mucosa wound healing is a scarless process. After re-analyses of gene expression datasets from oral mucosa wound healing and skin fibrosis, we discovered that several pathways constitutively activated in skin fibrosis are transiently induced during oral mucosa wound healing process, particularly the amphiregulin (Areg) gene. Areg expression is upregulated ~ 10 folds 24hrs after oral mucosa wound but reduced to the basal level 3 days later. During bleomycin-induced skin fibrosis, a commonly used mouse model for skin fibrosis, Areg is up-regulated throughout the fibrogenesis and is associated with elevated cell proliferation in the dermis. To demonstrate the role of Areg for skin fibrosis, we used mice with Areg knockout, and found that Areg deficiency essentially prevents bleomycin-induced skin fibrosis. We further determined that bleomycin-induced cell proliferation in the dermis was not observed in the Areg null mice. Furthermore, we found that inhibiting MEK, a downstream signaling effector of Areg, by selumetinib also effectively blocked bleomycin-based skin fibrosis model. Based on these results, we concluded that the Areg-EGFR-MEK signaling axis is critical for skin fibrosis development. Blocking this signaling axis may be effective in treating scleroderma.

Distinct transcriptomic landscapes of cutaneous basal cell carcinomas and squamous cell carcinomas.

The majority of non-melanoma skin cancer (NMSC) is cutaneous basal cell carcinoma (BCC) or squamous cell carcinoma (SCC), which are also called keratinocyte carcinomas, as both of them originate from keratinocytes. The incidence of keratinocyte carcinomas is over 5 million per year in the US, three-fold higher than the total incidence of all other types of cancer combined. While there are several reports on gene expression profiling of BCC and SCC, there are significant variations in the reported gene expression changes in different studies. One reason is that tumor-adjacent normal skin specimens were not included in many studies as matched controls. Furthermore, while numerous studies of skin stem cells in mouse models have been reported, their relevance to human skin cancer remains unknown. In this report, we analyzed gene expression profiles of paired specimens of keratinocyte carcinomas with their matched normal skin tissues as the control. Among several novel findings, we discovered a significant number of zinc finger encoding genes up-regulated in human BCC. In BCC, a novel link was found between hedgehog signaling, Wnt signaling, and the cilium. While the SCC cancer-stem-cell gene signature is shared between human and mouse SCCs, the hair follicle stem-cell signature of mice was not highly represented in human SCC. Differential gene expression (DEG) in human BCC shares gene signature with both bulge and epidermal stem cells. We have also determined that human BCCs and SCCs have distinct gene expression patterns, and some of them are not fully reflected in current mouse models.

Activation of hedgehog signaling is not a frequent event in ovarian cancers.

The hedgehog (Hh) signaling pathway regulates many processes of development and tissue homeostasis. Activation of hedgehog signaling has been reported in about 30% of human cancer including ovarian cancer. Inhibition of hedgehog signaling has been pursued as an effective strategy for cancer treatment including an ongoing phase II clinical trial in ovarian cancer. However, the rate of hedgehog signaling activation in ovarian cancer was reported differently by different groups. To predict the successful for future clinical trials of hedgehog signaling inhibitors in ovarian cancer, we assessed hedgehog pathway activation in 34 ovarian epithelial tumor specimens through analyses of target gene expression by in-situ hybridization, immunohistochemistry, RT-PCR and real-time PCR. In contrast to previous reports, we only detected a small proportion of ovarian cancers with hedgehog target gene expression, suggesting that identification of the tumors with activated hedgehog signaling activation will facilitate chemotherapy with hedgehog signaling inhibitors.

The role of GLI-SOX2 signaling axis for gemcitabine resistance in pancreatic cancer.

Pancreatic cancer, mostly pancreatic ductal adenocarcinomas (PDAC), is one of the most lethal cancers, with a dismal median survival around 8 months. PDAC is notoriously resistant to chemotherapy. Thus far, numerous attempts using novel targeted therapies and immunotherapies yielded limited clinical benefits for pancreatic cancer patients. It is hoped that delineating the molecular mechanisms underlying drug resistance in pancreatic cancer may provide novel therapeutic options. Using acquired gemcitabine resistant pancreatic cell lines, we revealed an important role of the GLI-SOX2 signaling axis for regulation of gemcitabine sensitivity in vitro and in animal models. Down-regulation of GLI transcriptional factors (GLI1 or GLI2), but not SMO signaling inhibition, reduces tumor sphere formation, a characteristics of tumor initiating cell (TIC). Down-regulation of GLI transcription factors also decreased expression of TIC marker CD24. Similarly, high SOX2 expression is associated with gemcitabine resistance whereas down-regulation of SOX2 sensitizes pancreatic cancer cells to gemcitabine treatment. We further revealed that elevated SOX2 expression is associated with an increase in GLI1 or GLI2 expression. Our ChIP assay revealed that GLI proteins are associated with a putative Gli binding site within the SOX2 promoter, suggesting a more direct regulation of SOX2 by GLI transcription factors. The relevance of our findings to human disease was revealed in human cancer specimens. We found that high SOX2 protein expression is associated with frequent tumor relapse and poor survival in stage II PDAC patients (all of them underwent gemcitabine treatment), indicating that reduced SOX2 expression or down-regulation of GLI transcription factors may be effective in sensitizing pancreatic cancer cells to gemcitabine treatment.

Hedgehog signaling pathway: development of antagonists for cancer therapy.

The hedgehog pathway, initially discovered in Drosophila by two Nobel laureates, Dr. Eric Wieschaus and Dr. Christiane Nüsslein-Volhard, is a major regulator for cell differentiation, tissue polarity, and cell proliferation. Studies from many laboratories--including ours--reveal activation of this pathway in most basal cell carcinomas and nearly one third of extracutaneous human cancers, including medulloblastomas and gastrointestinal and prostate cancers. Even more exciting is the discovery and synthesis of specific signaling antagonists for the hedgehog pathway, which have significant clinical implications in novel cancer therapeutics. This review discusses the current understanding of the hedgehog signaling pathway and its activation in human cancers. It also discusses putative and confirmed signaling antagonists and their perspectives in therapeutic applications.

Molecular biology of basal and squamous cell carcinomas.

Basal cell carcinomas and Squamous cell carcinomas are the two most common human cancers. The incidence of these two types of cancer is estimated to double within 20 years. Identification of the key molecular events is critical in helping us design novel strategies to treat and to prevent these cancers. For example, identification of hedgehog signaling activation has opened up many opportunities for targeted therapy and prevention of basal cell carcinomas. Significant progress has also been made in our understanding of squamous cell carcinomas of the skin. In this chapter, we will focus on major recent developments in our understanding of basal cell carcinomas and squamous cell carcinomas at the molecular levels and their clinical implications.

Implications of hedgehog signaling antagonists for cancer therapy.

The hedgehog (Hh) pathway, initially discovered in Drosophila by two Nobel laureates, Dr. Eric Wieschaus and Dr. Christiane Nusslein-Volhard, is a major regulator for cell differentiation, tissue polarity and cell proliferation. Studies from many laboratories, including ours, reveal activation of this pathway in most basal cell carcinomas and in approximately 30% of extracutaneous human cancers, including medulloblastomas, gastrointestinal, lung, breast and prostate cancers. Thus, it is believed that targeted inhibition of Hh signaling may be effective in treating and preventing many types of human cancers. Even more exciting is the discovery and synthesis of specific signaling antagonists for the Hh pathway, which have significant clinical implications in novel cancer therapeutics. This review discusses the major advances in the current understanding of Hh signaling activation in different types of human cancers, the molecular basis of Hh signaling activation, the major antagonists for Hh signaling inhibition and their potential clinical application in human cancer therapy.