The Hedgehog Signalling Pathway and its Role in Basal Cell Carcinoma

The hedgehog signalling pathway plays a vital role in Drosophila embryonic patterning and development. Hedgehog is a secreted protein, unrelated to classical growth factors, which seems to form concentration gradients across those tissues involved in pattern formation. Cloning of vertebrate homologues of hedgehog and other genes has illustrated the remarkable conservation of function of this pathway throughout evolution. The human homologue of patched, a receptor for the hedgehog protein, was cloned as the gene responsible for naevoid basal cell carcinoma syndrome (NBCCS/Gorlin Syndrome), an autosomal dominant condition in which patients suffer from multiple basal cell carcinomas and a wide spectrum of developmental abnormalities. Its role as a tumour suppressor gene in both NBCCS and sporadic basal cell carcinoma led to the suggestion that mutation or inactivation of human patched may be an essential step in development of basal cell carcinomas and other skin tumours. This review describes our current understanding of hedgehog signalling in Drosophila and vertebrates and its relation to the development of human basal cell carcinoma and other skin tumours, together with a discussion of future avenues of research into this critical and intriguing pathway.     

Complete and sustained response of adult medulloblastoma to first-line sonic hedgehog inhibition with vismodegib

Medulloblastoma is an aggressive primitive neuroectodermal tumor of the cerebellum that is rare in adults. Medulloblastomas fall into 4 prognostically significant molecular subgroups that are best defined by experimental gene expression profiles: the WNT pathway, sonic hedgehog (SHH) pathway, and subgroups 3 and 4 (non-SHH/WNT). Medulloblastoma of adults belong primarily to the SHH category. Vismodegib, an SHH-pathway inhibitor FDA-approved in 2012 for treatment of basal cell carcinoma, has been used successfully in the setting of chemorefractory medulloblastoma, but not as a first-line therapy. In this report, we describe a sustained response of an unresectable multifocal form of adult medulloblastoma to vismodegib. Molecular analysis in this case revealed mutations in TP53 and a cytogenetic abnormality, i17q, that is prevalent and most often associated with subgroup 4 rather than the SHH-activated form of medulloblastoma. Our findings indicate that vismodegib may also block alternate, non-canonical forms of downstream SHH pathway activation. These findings provide strong impetus for further investigation of vismodegib in clinical trials in the first-line setting for pediatric and adult forms of medulloblastoma.     

Paracrine sonic hedgehog signaling contributes significantly to acquired steroidogenesis in the prostate tumor microenvironment

Despite the substantial benefit of androgen deprivation therapy (ADT) for metastatic prostate cancer, patients often progress to castration‐resistant disease (CRPC) that is more difficult to treat. CRPC is associated with renewed androgen receptor activity in tumor cells and restoration of tumor androgen levels through acquired intratumoral steroidogenesis (AIS). Although prostate cancer (PCa) cells have been shown to have steroidogenic capability in vitro, we previously found that benign prostate stromal cells (PrSCs) can also synthesize testosterone (T) from an adrenal precursor, DHEA, when stimulated with a hedgehog (Hh) pathway agonist, SAG. Here, we show exposure of PrSCs to a different Smoothened (Smo) agonist, Ag1.5, or to conditioned medium from sonic hedgehog overexpressing LNCaP cells induces steroidogenic enzyme expression in PrSCs and significantly increases production of T and its precursor steroids in a Smo‐dependent manner from 22‐OH‐cholesterol substrate. Hh agonist‐/ligand‐treated PrSCs produced androgens at a rate similar to or greater than that of PCa cell lines. Likewise, primary bone marrow stromal cells became more steroidogenic and produced T under the influence of Smo agonist. Treatment of mice bearing LNCaP xenografts with a Smo antagonist, TAK‐441, delayed the onset of CRPC after castration and substantially reduced androgen levels in residual tumors. These outcomes support the idea that stromal cells in ADT‐treated primary or metastatic prostate tumors can contribute to AIS as a consequence of a paracrine Hh signaling microenvironment. As such, Smo antagonists may be useful for targeting prostate tumor stromal cell‐derived AIS and delaying the onset of CRPC after ADT.     

Targeted treatment for sonic hedgehog-dependent medulloblastoma

Novel treatment options, including targeted therapies, are needed for patients with medulloblastoma (MB), especially for those with high-risk or recurrent/relapsed disease. Four major molecular subgroups of MB have been identified, one of which is characterized by activation of the sonic hedgehog (SHH) pathway. Preclinical data suggest that inhibitors of the hedgehog (Hh) pathway could become valuable treatment options for patients with this subgroup of MB. Indeed, agents targeting the positive regulator of the pathway, smoothened (SMO), have demonstrated efficacy in a subset of patients with SHH MB. However, because of resistance and the presence of mutations downstream of SMO, not all patients with SHH MB respond to SMO inhibitors. The development of agents that target these resistance mechanisms and the potential for their combination with traditional chemotherapy and SHH inhibitors will be discussed. Due to its extensive molecular heterogeneity, the future of MB treatment is in personalized therapy, which may lead to improved efficacy and reduced toxicity. This will include the development of clinically available tests that can efficiently discern the SHH subgroup. The preliminary use of these tests in clinical trials is also discussed herein.     

De-regulation of the sonic hedgehog pathway in the InsGas mouse model of gastric carcinogenesis

This study investigated sonic hedgehog (Shh) signalling in gastric metaplasia in the insulin-gastrin (InsGas) hypergastrinaemic mouse +/- Helicobacter felis (H. felis) infection. Sonic hedgehog gene and protein expression was reduced in pre-metaplastic lesions from non-infected mice (90% gene reduction, P<0.01) compared to normal mucosa. Sonic hedgehog was reactivated in gastric metaplasia of H. felis-infected mice (3.5-fold increase, P<0.01) compared to pre-metaplastic lesions. Additionally, the Shh target gene, glioma-associated oncogene (Gli)-1, was significantly reduced in the gastric glands of InsGas mice (75% reduction, P<0.05) and reactivated with H. felis infection (P<0.05, base of glands, P<0.01 stroma of metaplastic glands). The ability of H. felis to activate the Shh pathway was investigated by measuring the effect of target cytokine, interleukin-8 (IL-8), on Shh expression in AGS and MGLVA1 cells, which was shown to induce Shh expression at physiological concentrations. H. felis induced the expression of NF-kappaB in inflammatory infiltrates in vivo, and the expression of the IL-8 mouse homologue, protein KC, in inflammatory infiltrates and metaplastic lesions. Sonic hedgehog pathway reactivation was paralleled with an increase in proliferation of metaplastic lesions (15.75 vs 4.39% in infected vs non-infected mice, respectively, P<0.001). Furthermore, Shh overexpression increased the growth rate of the gastric cancer cell line, AGS. The antiapoptotic protein, bcl-2, was expressed in the stroma of infected mice, along with a second Shh target gene, patched-1 (P=0.0001, stroma of metaplastic gland). This study provides evidence suggesting reactivation of Shh signalling from pre-metaplastic to advanced metaplastic lesions of the stomach and outlines the importance of the Shh pathway as a potential chemoprophylactic target for gastric carcinogenesis.     

Inhibition of the sonic hedgehog pathway by cyplopamine reduces the CD133+/CD15+ cell compartment and the in vitro tumorigenic capability of neuroblastoma cells

Sonic hedgehog (Hh) developmental pathway deregulation has been proven to play an essential role in several malignancies as neuroblastoma. We found that Hh signaling is active in neuroblastoma, as most pathway components, including GLI1, were expressed in cell lines and tumor samples. Furthermore, SHH ligand expression was found in cell lines and tumors, and GLI1 up-regulation was achieved in response to SHH treatment, suggesting an autocrine mechanism of aberrant activation. A decrease of proliferation and tumorigenic potential, as well as increased apoptosis and a dramatic decrease in the percentage of CD15+ cell population were produced upon Hh inhibition by cyclopamine.     

Locally advanced and metastatic basal cell carcinoma: molecular pathways,treatment options and new targeted therapies

The hedgehog (Hh) signaling pathway has been identified as important to normal embryonic development in living organisms and it is implicated in processes including cell proliferation, differentiation and tissue patterning. Aberrant Hh pathway has been involved in the pathogenesis and chemotherapy resistance of different solid and hematologic malignancies. Basal cell carcinoma (BCC) and medulloblastoma are two well-recognized cancers with mutations in components of the Hh pathway. Vismodegib has recently approved as the first inhibitor of one of the components of the Hh pathway (smoothened). This review attempts to provide current data on the molecular pathways involved in the development of BCC and the therapeutic options available for the treatment of locally advanced and metastatic BCC, and the new targeted therapies in development.     

Challenges and new horizons in the management of advanced basal cell carcinoma: a UK perspective

Basal cell carcinoma (BCC) is a common malignancy with a good prognosis in the majority of cases. However, some BCC patients develop a more advanced disease that poses significant management challenges. Such cases include locally advanced, recurrent or metastatic BCC, or tumours that occur in anatomical sites where surgical treatment would result in significant deformity. Until recently, treatment options for these patients have been limited, but increased understanding of the molecular basis of BCC has enabled potential therapies, such as hedgehog signalling pathway inhibitors, to be developed. A clear definition of advanced BCC as a distinct disease entity and formal management guidelines have not previously been published, presumably because of the rarity, heterogeneity and lack of treatment options available for the disease. Here we provide a UK perspective from a multidisciplinary group of experts involved in the treatment of complex cases of BCC, addressing the key challenges associated with the perceived definition and management of the disease. With new treatments on the horizon, we further propose a definition for advanced BCC that may be used as a guide for healthcare professionals involved in disease diagnosis and management.     

Loss of Trp53 promotes medulloblastoma development but not skin tumorigenesis in Sufu heterozygous mutant mice

Basal cell carcinoma of the skin typically carries genetic alterations in components of the hedgehog (HH) signaling pathway. Previously, we generated a knockout mouse with a loss-of-function mutation in suppressor of fused (Sufu), an essential repressor of the pathway downstream of Hh ligand cell surface reception. Mice heterozygous for the mutated Sufu allele develop a skin phenotype that includes lesions similar to basaloid follicular hamartomas. The purpose of the current study was to test the possibility that the simultaneous loss of the tumor suppressor gene, transformation related protein 53 (Trp53), would aggravate the Sufu skin phenotype since Trp53 loss is known to enhance the growth of other Hh-driven tumors. Consistent with previous reports, medulloblastomas and rhabdomyosarcomas developed in Sufu(+/-) ;Trp53(-/-) mice. However, the characteristic Sufu(+/-) skin phenotype was not altered in the absence of Trp53, and showed no changes in latency, multiplicity, cellular phenotype, or proliferative capacity of the basaloid lesions. This finding was both novel and intriguing and demonstrated a differential, tissue-specific sensitivity to Sufu and Trp53 tumor suppressor gene loss, which may be linked to developmental stage and the degree of proliferative activity in specific cell types.     

The hedgehog signalling pathway in tumorigenesis and development

The hedgehog signalling pathway is responsible for the embryonic patterning of a range of tissues, and it is now known that dysregulation of this pathway can result in the formation of several tumour types. This cascade is regulated at the cell surface by the opposing actions of the patched and smoothened molecules which together form a receptor complex for hedgehog. The discovery that inactivation of the human patched gene is responsible for familial and sporadic forms of basal cell carcinoma firmly established a role for dysregulation of hedgehog signalling in tumorigenesis. Other key members of this pathway have also been shown to be involved in tumour formation, as have more distal downstream targets of hedgehog signalling. Since it appears that tumorigenesis results from constitutive activation of hedgehog responsive genes, the identification of novel downstream targets of hedgehog signalling in given cell types is likely to increase our understanding of the molecular processes underlying tumour formation.     

音猬因子、Ptch1基因在胃癌中的表达及临床意义

目的:研究胃癌组织中音猬因子（Shh）、Patched1(Ptch1)基因的表达及意义。方法:采用反转录-聚合酶链反应(RT-PCR)和Westem blot检测98例胃癌组织和配对的癌旁组织中Shh、Ptch1 mRNA和蛋白的表达情况。结果:RT-PCR检测结果显示,Shh、Ptch1 mRNA在胃癌中相对表达量分别为0.687±0.057、0.594±0.046,在胃癌旁组织中分别为0.314±0.025、0.293±0.074（P＜0.05）。Western blot检测结果显示,Shh、Ptch1蛋白在胃癌中的相对表达量分别为0.525±0.057、0.481±0.046,在胃癌旁组织中分别为0.236±0.025、0.215±0.074。胃癌组织Shh、Ptch1 mRNA和蛋白平均表达水平高于癌旁组织,差异有统计学意义（P＜0.05）;Shh、Ptch1 mRNA和蛋白表达水平与胃癌的分化程度、TNM分期、浸润深度和淋巴结转移明显相关（P＜0.05）,与患者年龄、性别和肿瘤直径无明显相关（P＞0.05）。结论:胃癌组织中Shh、Ptch1蛋白呈高表达,Shh、Ptch1蛋白的高表达可能与胃癌的发生及发展有关。     

音猬因子、Smo基因在宫颈鳞状细胞癌中的表达及临床意义

目的:探讨音猬因子(Shh)、Smoothened(Smo)基因在宫颈鳞状细胞癌中的表达及意义.方法:采用反转录-聚合酶链反应(RT-PCR)和Westem blot检测76例宫颈鳞状细胞癌组织和42例正常宫颈组织中Shh、Smo mRNA和蛋白的表达情况.结果:RT-PCR检测结果显示,Shh、Smo mRNA在宫颈鳞状细胞癌中相对表达量分别为0.715±0.048、0.638±0.037,在正常宫颈组织中分别为0.341±0.072、0.311±0.051(P<0.05).Western blot检测结果显示,Shh、Smo蛋白在宫颈鳞状细胞癌中的相对表达量分别为0.568±0.013、0.521±0.056,在正常宫颈组织中分别为0.281±0.047、0.252±0.064(P<0.05).宫颈鳞状细胞癌组织Shh、Smo mRNA和蛋白平均表达水平高于正常宫颈组织,差异有统计学意义(P<0.05);Shh、Smo mRNA和蛋白表达水平与宫颈鳞状细胞癌的分化程度明显相关(P<0.05),与患者年龄、FIGO分期、侵犯血管和神经、淋巴结转移、远处转移无明显相关(P>0.05).结论:宫颈鳞状细胞癌组织中Shh、Smo蛋白呈高表达,Shh、Smo蛋白的高表达可能与宫颈鳞状细胞癌的发生、发展及转移关系密切.     

Betulinic acid induces apoptosis and inhibits hedgehog signalling in rhabdomyosarcoma

Background:

Rhabdomyosarcoma (RMS) is the most common soft-tissue sarcoma in childhood with the ability to resist apoptosis by the activation of survival promoting and anti-apoptotic proteins.

Methods:

Efficacy of the apoptosis-inducing agent betulinic acid (BA) was determined in RMS cell cultures and in vivo by measuring cell viability, survival, apoptosis, hedgehog signalling activity, and neovascularisation.

Results:

Betulinic acid had a strong cytotoxic effect on RMS cells in a dose-dependent manner. The BA treatment caused a massive induction of apoptosis mediated by the intrinsic mitochondrial pathway, which could be inhibited by the broad-range caspase inhibitor zVAD.fmk. Exposure of hedgehog-activated RMS-13 cells to BA resulted in a strong decrease in GLI1, GLI2, PTCH1, and IGF2 expression as well as hedgehog-responsive luciferase activity. Intraperitoneal injection of 20 mg BA per kg per day significantly retarded growth of RMS-13 xenografts in association with markedly higher counts of apoptotic cells and down-regulation of GLI1 expression compared with control tumours, while leaving microvascular density, cell proliferation, and myogenic differentiation unaffected.

Conclusion:

Our data show that induction of apoptosis and inhibition of hedgehog signalling are important features of the anti-tumourigenic effect of BA in RMS and advices this compound for the use in a multimodal therapy of this highly aggressive paediatric tumour.     

Activation of the hedgehog pathway in a subset of lung cancers

Activation of the hedgehog pathway is reported in lung cancer, but its frequency remains unknown. We examine activation of this pathway in lung cancers by in situ hybridization and immunohistochemstry, and find that less than 10% of the tumors have elevated hedgehog target gene expression. We further identify a cell line NCI-H209 and two primary tumors with no detectable Su(Fu), a negative regulator of the pathway. Ectopic expression of Su(Fu) in NCI-H209 cells down-regulates hedgehog target gene expression and leads to inhibition of cell proliferation. These data indicate that activation of the hedgehog pathway is activated through Shh over-expression or Su(Fu) inactivation in only a subset of lung cancers.