A paracrine requirement for hedgehog signalling in cancer

Glucose regulated protein 78: a critical link between tumor microenvironment and cancer hallmarks

Glucose regulated protein 78 (GRP78) has long been recognized as a molecular chaperone in the endoplasmic reticulum (ER) and can be induced by the ER stress response. Besides its location in the ER, GRP78 has been found to be present in cell plasma membrane, cytoplasm, mitochondria, nucleus as well as cellular secretions. GRP78 is implicated in tumor cell proliferation, apoptosis resistance, immune escape, metastasis and angiogenesis, and its elevated expression usually correlates with a variety of tumor microenvironmental stresses, including hypoxia, glucose deprivation, lactic acidosis and inflammatory response. GRP78 protein acts as a centrally located sensor of stress, which feels and adapts to the alteration in the tumor microenvironment. This article reviews the potential contributions of GRP78 to the acquisition of cancer hallmarks based on intervening in stress responses caused by tumor niche alterations. The paper also introduces several potential GRP78 relevant targeted therapies.

Genetic ablation of Cav1 differentially affects melanoma tumor growth and metastasis in mice: role of Cav1 in Shh heterotypic signaling and transendothelial migration

Both cell-autonomous and non-cell-autonomous factors contribute to tumor growth and metastasis of melanoma. The function of caveolin-1 (Cav1), a multifunctional scaffold protein known to modulate several biologic processes in both normal tissue and cancer, has been recently investigated in melanoma cancer cells, but its role in the melanoma microenvironment remains largely unexplored. Here, we show that orthotopic implantation of B16F10 melanoma cells in the skin of Cav1KO mice increases tumor growth, and co-injection of Cav1-deficient dermal fibroblasts with melanoma cells is sufficient to recapitulate the tumor phenotype observed in Cav1KO mice. Using indirect coculture experiments with fibroblasts and melanoma cells combined with cytokine analysis, we found that Cav1-deficient fibroblasts promoted the growth of melanoma cells via enhanced paracrine cytokine signaling. Specifically, Cav1-deficient fibroblasts displayed increased ShhN expression, which heterotypically enhanced the Shh signaling pathway in melanoma cells. In contrast to primary tumor growth, the ability of B16F10 melanoma cells to form lung metastases was significantly reduced in Cav1KO mice. This phenotype was associated mechanistically with the inability of melanoma cells to adhere to and to transmigrate through a monolayer of endothelial cells lacking Cav1. Together, our findings show that Cav1 may regulate different mechanisms during primary melanoma tumor growth and metastatic dissemination.

Bone marrow-derived proangiogenic cells in pancreatic cancer

Tumor-derived signals systemically induce an angiogenic switch that allows cancer cells to survive and grow. However, the vascular network in tumors is not well organized and fails to meet metabolic needs to maintain tissue homeostasis, resulting in significant hypoxia. Among various tumors, pancreatic ductal adenocarcinoma (PDAC) typically develops in an unusually disordered microenvironment, which contributes to its highly aggressive behavior. Since anti-vascular endothelial growth factor (VEGF) (Avastin) has failed to demonstrate a survival benefit in PDAC, we need to re-visit the basic biology of this disease and understand what makes it so refractory to the anti-angiogenic approaches that are clinically effective in other neoplasms. To address this issue, we specifically focused on the process of neovascularization where bone marrow-derived cells (BMDCs) play a role during pancreatic tumorigenesis. We have identified subsets of BMDCs that regulate key processes during development of the neovessels through paracrine Hedgehog signaling. Considering the importance of systemic responses occurring in tumor bearing hosts, we are currently using genetically engineered mice, which spontaneously develop PDAC, Pdx1-Cre;LSL-Kras(G12D);p53(lox/+) strain, to clarify critical events that can trigger aberrant angiogenesis in pancreatic cancer. These studies allow us to provide insights into the cellular and molecular mechanisms of pancreatic tumorigenesis and have an implication for the design of therapies against this difficult disease.

Hedgehog-Gli pathway activation during kidney fibrosis

The Hedgehog (Hh) signaling pathway regulates tissue patterning during development, including patterning and growth of limbs and face, but whether Hh signaling plays a role in adult kidney remains undefined. In this study, using a panel of hedgehog-reporter mice, we show that the two Hh ligands (Indian hedgehog and sonic hedgehog ligands) are expressed in tubular epithelial cells. We report that the Hh effectors (Gli1 and Gli2) are expressed exclusively in adjacent platelet-derived growth factor receptor-β-positive interstitial pericytes and perivascular fibroblasts, suggesting a paracrine signaling loop. In two models of renal fibrosis, Indian Hh ligand was upregulated with a dramatic activation of downstream Gli effector expression. Hh-responsive Gli1-positive interstitial cells underwent 11-fold proliferative expansion during fibrosis, and both Gli1- and Gli2-positive cells differentiated into α-smooth muscle actin-positive myofibroblasts. In the pericyte-like cell line 10T1/2, hedgehog ligand triggered cell proliferation, suggesting a possible role for this pathway in the regulation of cell cycle progression of myofibroblast progenitors during the development of renal fibrosis. The hedgehog antagonist IPI-926 abolished Gli1 induction in vivo but did not decrease kidney fibrosis. However, the transcriptional induction of Gli2 was unaffected by IPI-926, suggesting the existence of smoothened-independent Gli activation in this model. This study is the first detailed description of paracrine hedgehog signaling in adult kidney, which indicates a possible role for hedgehog-Gli signaling in fibrotic chronic kidney disease.

Hedgehog-EGFR cooperation response genes determine the oncogenic phenotype of basal cell carcinoma and tumour-initiating pancreatic cancer cells

Inhibition of Hedgehog (HH)/GLI signalling in cancer is a promising therapeutic approach. Interactions between HH/GLI and other oncogenic pathways affect the strength and tumourigenicity of HH/GLI. Cooperation of HH/GLI with epidermal growth factor receptor (EGFR) signalling promotes transformation and cancer cell proliferation in vitro. However, the in vivo relevance of HH-EGFR signal integration and the critical downstream mediators are largely undefined. In this report we show that genetic and pharmacologic inhibition of EGFR signalling reduces tumour growth in mouse models of HH/GLI driven basal cell carcinoma (BCC). We describe HH-EGFR cooperation response genes including SOX2, SOX9, JUN, CXCR4 and FGF19 that are synergistically activated by HH-EGFR signal integration and required for in vivo growth of BCC cells and tumour-initiating pancreatic cancer cells. The data validate EGFR signalling as drug target in HH/GLI driven cancers and shed light on the molecular processes controlled by HH-EGFR signal cooperation, providing new therapeutic strategies based on combined targeting of HH-EGFR signalling and selected downstream target genes.

In vitro and in vivo characterization of a novel Hedgehog signaling antagonist in human glioblastoma cell lines

Glioblastoma multiforme (GBM) is composed of heterogeneous and genetically different cells, which are highly invasive and motile. The standard chemotherapeutic agent, temozolomide, affects GBM cell proliferation but is generally unable to prevent tumor recurrence. Hedgehog pathway activation has been reported to be relevant in GBM and different pharmacological pathway modulators have been identified. We report that by growing a commercially available recurrent GBM cell line (DBTRG-05MG) without serum and in the presence of defined growth factors; we obtained a less differentiated cell population, growing in suspension as neurospheres, in which the Hedgehog pathway is activated. Furthermore, the expression profile of Hedgehog pathway components found in DBTRG-05MG neurospheres is similar to primary stem-like cells derived from recurrent GBM patients. We report the effect of our novel specific Smoothened receptor antagonist (SEN450) on neurosphere growing cells and compared its effect to that of well known benchmark compounds. Finally, we showed that SEN450 is both antiproliferative on its own and further reduces tumor volume after temozolomide pretreatment in a mouse xenograft model using DBTRG-05MG neurosphere cells. Altogether our data indicate that the Hedgehog pathway is not irreversibly switched off in adherent cells but can be reactivated when exposed to well-defined culture conditions, thus restoring the condition observed in primary tumor-derived material, and that pharmacological modulation of this pathway can have profound influences on tumor proliferation. Therefore, pharmacological inhibition of the Hedgehog pathway is a potentially useful therapeutic approach in GBM.

Aberrant signaling pathways in pancreatic cancer: a two compartment view

Pancreatic cancer is a devastating disease with historically limited success in treatment and a poor prognosis. Pancreatic cancer appears to have a progressive pathway of development, initiating from well-described pancreatic intraepithelial neoplasia lesions and concluding with invasive carcinoma. These early lesions have been shown to harbor-specific alterations in signaling pathways that remain throughout this tumorigenesis process. Meanwhile, new alterations occur during this process of disease progression to have a cumulative effect. This series of events not only impacts the epithelial cells comprising the tumor, but they may also affect the surrounding stromal cells. The result is the formation of complex signaling networks of communication between the tumor epithelial cell and the stromal cell compartments to promote a permissive and cooperative environment. This article highlights some of the most common pathway aberrations involved with this disease, and how these may subsequently affect one or both cellular compartments. Consequently, furthering our understanding of these pathways in terms of their function on the tumoral epithelial and stromal compartments may prove to be crucial to the development of targeted and more successful therapies in the future.

Specific inhibition of the transcription factor Ci by a cobalt(III) Schiff base-DNA conjugate

We describe the use of Co(III) Schiff base-DNA conjugates, a versatile class of research tools that target C2H2 transcription factors, to inhibit the Hedgehog (Hh) pathway. In developing mammalian embryos, Hh signaling is critical for the formation and development of many tissues and organs. Inappropriate activation of the Hedgehog (Hh) pathway has been implicated in a variety of cancers including medulloblastomas and basal cell carcinomas. It is well-known that Hh regulates the activity of the Gli family of C2H2 zinc finger transcription factors in mammals. In Drosophila the function of the Gli proteins is performed by a single transcription factor with an identical DNA binding consensus sequence, Cubitus Interruptus (Ci). We have demonstrated previously that conjugation of a specific 17 base-pair oligonucleotide to a Co(III) Schiff base complex results in a targeted inhibitor of the Snail family C2H2 zinc finger transcription factors. Modification of the oligonucleotide sequence in the Co(III) Schiff base-DNA conjugate to that of Ci's consensus sequence (Co(III)-Ci) generates an equally selective inhibitor of Ci. Co(III)-Ci irreversibly binds the Ci zinc finger domain and prevents it from binding DNA in vitro. In a Ci responsive tissue culture reporter gene assay, Co(III)-Ci reduces the transcriptional activity of Ci in a concentration dependent manner. In addition, injection of wild-type Drosophila embryos with Co(III)-Ci phenocopies a Ci loss of function phenotype, demonstrating effectiveness in vivo. This study provides evidence that Co(III) Schiff base-DNA conjugates are a versatile class of specific and potent tools for studying zinc finger domain proteins and have potential applications as customizable anticancer therapeutics.

RACK1 promotes non-small-cell lung cancer tumorigenicity through activating sonic hedgehog signaling pathway

Non-small-cell lung cancer (NSCLC) is a deadly disease due to lack of effective diagnosis biomarker and therapeutic target. Much effort has been made in defining gene defects in NSCLC, but its full molecular pathogenesis remains unexplored. Here, we found RACK1 (receptor of activated kinase 1) was elevated in most NSCLC, and its expression level correlated with key pathological characteristics including tumor differentiation, stage, and metastasis. In addition, RACK1 activated sonic hedgehog signaling pathway by interacting with and activating Smoothened to mediate Gli1-dependent transcription in NSCLC cells. And silencing RACK1 dramatically inhibited in vivo tumor growth and metastasis by blocking the sonic hedgehog signaling pathway. These results suggest that RACK1 represents a new promising diagnosis biomarker and therapeutic target for NSCLC.

Hedgehog signaling in myofibroblasts directly promotes prostate tumor cell growth

Despite strong evidence for the involvement of the stroma in Hedgehog signaling, little is known about the identity of the stromal cells and the signaling mechanisms that mediate the growth promoting effect of Hh signaling. We developed an in vitro co-culture model using microchannel technology to examine the effect of paracrine Hh signaling on proliferation of prostate cancer cells. We show here that activation of Hh signaling in myofibroblasts is sufficient to accelerate tumor cell growth. This effect was independent of any direct effect of Hh ligand on tumor cells or other cellular components of the tumor stroma. Further, the trophic effect of Hh pathway activation in myofibroblasts does not require collaboration of other elements of the stroma or direct physical interaction with the cancer cells. By isolating the tropic effect of Hh pathway activation in prostate stroma, we have taken the first step toward identifying cell-specific mechanisms that mediate the effect of paracrine Hh signaling on tumor growth.

Sonic hedgehog maintains survival and growth of chronic myeloid leukemia progenitor cells through β-catenin signaling

Sonic hedgehog (Shh) signaling plays an important role in many human cancers and cancer stem cells. Here we investigate the activity and functional role of Shh signaling in chronic myeloid leukemia (CML) and leukemia progenitor cells. Differential activation of Shh signaling was found in about 50% CML chronic phase samples, about 70% of CML accelerated phase samples, and >80% CML blast crisis phase samples. Deregulated activation of Shh signaling was observed in CD34(+) and c-kit(+) leukemia progenitor cells. Stimulation of Shh signaling with exogenous Shh peptide induced expansion of CD34(+) and c-kit(+) progenitor cells (p < 0.05), inversely, blocking the pathway with signal inhibitor induced cell apoptosis (p < 0.05). Low level of Shh protein was observed in CML bone marrow stromal cells, and CD34(+) progenitor cells are less sensitive to exogenous Shh peptide and more sensitive to cyclopamine than CD34(-) cells (p < 0.05), implying cell-autonomous activation of Shh signaling play a predominant role in progenitor cells. Coactivation of Shh and β-catenin signaling was found in CD34(+) and c-kit(+) progenitor cells. Administration of Shh-neutralizing antibody or Wnt3a-neutralizing antibody in c-kit(+) progenitor cells induced cell apoptosis; however, Wnt3a peptide could salvage cell apoptosis, while Shh peptide failed to revert anti-Wnt3a-induced cell apoptosis. C-MYC, GLI1, BCL-2, and P21 were also found to be downstream targets of Shh signaling, mediating apoptosis or G(2)/M cell cycle arrest of progenitor cells. Our results demonstrate that autoactivated Shh signaling provides survival and proliferative cues in CML progenitor cells through downstream β-catenin signaling, suggesting a novel therapeutic approach in CML.

Oncogenic Kras is required for both the initiation and maintenance of pancreatic cancer in mice

Pancreatic cancer is almost invariably associated with mutations in the KRAS gene, most commonly KRASG12D, that result in a dominant-active form of the KRAS GTPase. However, how KRAS mutations promote pancreatic carcinogenesis is not fully understood, and whether oncogenic KRAS is required for the maintenance of pancreatic cancer has not been established. To address these questions, we generated two mouse models of pancreatic tumorigenesis: mice transgenic for inducible KrasG12D, which allows for inducible, pancreas-specific, and reversible expression of the oncogenic KrasG12D, with or without inactivation of one allele of the tumor suppressor gene p53. Here, we report that, early in tumorigenesis, induction of oncogenic KrasG12D reversibly altered normal epithelial differentiation following tissue damage, leading to precancerous lesions. Inactivation of KrasG12D in established precursor lesions and during progression to cancer led to regression of the lesions, indicating that KrasG12D was required for tumor cell survival. Strikingly, during all stages of carcinogenesis, KrasG12D upregulated Hedgehog signaling, inflammatory pathways, and several pathways known to mediate paracrine interactions between epithelial cells and their surrounding microenvironment, thus promoting formation and maintenance of the fibroinflammatory stroma that plays a pivotal role in pancreatic cancer. Our data establish that epithelial KrasG12D influences multiple cell types to drive pancreatic tumorigenesis and is essential for tumor maintenance. They also strongly support the notion that inhibiting KrasG12D, or its downstream effectors, could provide a new approach for the treatment of pancreatic cancer.

Cooperative Hedgehog-EGFR signaling

It has been known for many years that cooperative interactions between oncogenes (e.g. RAS, MYC, BCL2) can fuel cancer growth (1-5), but the restricted druggability of many of those interacting cancer genes has hampered translation of combined targeting to medical cancer therapy. The identification and characterization of cooperative cancer signaling pathways amenable to medical therapy is therefore a crucial step towards the establishment of efficient targeted combination treatments urgently needed to improve cancer therapy. Here we review recent findings of our group and colleagues on the molecular mechanisms of cooperative Hedgehog/GLI and Epidermal Growth Factor Receptor (EGFR) signaling, two clinically relevant oncogenic pathways involved in the development of many human malignancies. We also discuss the possible implications of these findings for the design of a therapeutic regimen relying on combined targeting of key effectors of both pathways.

A new era for an ancient drug: arsenic trioxide and Hedgehog signaling

Arsenic has been used for ages as a therapeutic agent. Currently, it is an FDA approved drug to treat acute promyelocytic leukemia where it leads to degradation of the PML-RAR fusion protein. It has been shown to have various other targets in cells such as JNK, NFκB, thioredoxin reductase, and MAPK pathways. Most of its effects in cells have been through arsenic's ability to bind to thiol groups in cysteine residues. Recent evidence has shown that arsenic can inhibit the Hedgehog pathway by inhibiting GLI proteins. The proposed mechanism of action is through direct binding. Potential binding sites include the critical cysteine residues in GLI zinc finger domains. The role of the Hedgehog pathway has been implicated in many cancers such as basal cell carcinoma, medulloblastoma, Ewing sarcoma, and rhabdoid tumors. Current Hedgehog pathway inhibitors have been fraught with resistance issues and so arsenic trioxide may provide an alternative therapy when combined with these other inhibitors or after acquired resistance.

Hedgehog inhibition as an anti-cancer strategy

Dysregulated Hedgehog (Hh) signaling has been implicated in a growing number of human cancers. Although first identified as an important developmental signaling pathway crucial for cellular proliferation, differentiation, and migration during organogenesis in invertebrates, these fundamental processes have been co-opted in human cancers. Initial evidence for the Hh pathway in tumor biology comes from mutations of signaling pathway components in a hereditary cancer syndrome that typically results in basal-cell carcinoma and medulloblastoma. Subsequent analysis revealed that Hh pathway mutations are found in sporadic tumors as well as activated Hh signaling in several epithelial cancers independent of Hh pathway mutation status. Further, recent evidence has demonstrated paracrine Hh signaling within stromal cells of the tumor microenvironment with implications for drug delivery. Several Hh antagonists targeting the Hh receptor, Smoothened (SMO), have been developed and show efficacy in preclinical studies and early-stage clinical trials in humans. However, major issues with these small molecule compounds include rapid acquired resistance, potential developmental toxicities secondary to use in children, and limited efficacy in cancers driven by Hh signaling downstream of the SMO receptor.

Canonical and noncanonical Hedgehog/GLI signaling in hematological malignancies

The highly conserved Hedgehog/GLI signaling pathway regulates multiple aspects of embryonic development and plays a decisive role in tissue homeostasis and the hematopoietic system by controlling cell fate decisions, stem cell self-renewal, and activation. Loss of negative control of Hedgehog signaling contributes to tumor pathogenesis and progression. In the classical view of canonical Hedgehog signaling, Hedgehog ligand binding to its receptor Patched culminates in the activation of the key pathway activator Smoothened, followed by activation of the GLI transcription factors. Its essential function and druggability render Smoothened well suited to therapeutic intervention. However, recent evidence suggests a critical role of Smoothened-independent regulation of GLI activity by several other signaling pathways including the PI3K/AKT and RAS/RAF/MEK/ERK axes. In addition, the contribution of canonical Hedgehog signaling via Patched and Smoothened to normal and malignant hematopoiesis has been the subject of recent controversies. In this review, we discuss the current understanding and controversial findings of canonical and noncanonical GLI activation in hematological malignancies in light of the current therapeutic strategies targeting the Hedgehog pathway.

Hh-Gli signaling pathway activity in oral and oropharyngeal squamous cell carcinoma

BACKGROUND

The aim of this study was to examine the role of Hh-Gli signaling in oral and oropharyngeal squamous cell carcinoma (SCC). The role of this signaling pathway in SCC formation has not yet been elucidated.

METHODS

Sixty-four tissue and blood samples were collected from 60 patients with SCC, all tobacco and alcohol users. An additional six buccal mucosa tissue samples were collected from nonsmokers and nondrinkers as control tissue.

RESULTS

Hedgehog-Gli pathway components were associated with clinical and pathologic features. Broders' grade and N stage were associated with higher Ptch1 and lower Gli1 expression. Tumor stage was negatively associated with Smo expression, and tumor size was positively associated with p16 expression. Ptch1 and Shh were frequently detected in the surrounding stroma. Ptch1 was found to be correlated with p16 expression, as well as with survivin expression.

CONCLUSIONS

The signaling pathway is activated in SCC and inducible in vitro by Shh protein.

Aberrations and therapeutics involving the developmental pathway Hedgehog in pancreatic cancer

To conduct a systematic review of the role that the hedgehog signaling pathway has in pancreatic cancer tumorigenesis. A PubMed search from 2000 to 2010 and literature-based references were sourced. It was found that in 2009 a genetic analysis of pancreatic cancers discovered that a core set of 12 cellular signaling pathways including hedgehog were genetically altered in 67-100% of cases. Second, in vitro and in vivo studies of treatment with cyclopamine (a naturally occurring antagonist of the hedgehog signaling pathway component; Smoothened) have shown that inhibition of hedgehog can abrogate pancreatic cancer metastasis. Third, experimental evidence has demonstrated that sonic hedgehog (Shh) is correlated with desmoplasia in pancreatic cancer. This is important because targeting the Shh pathway potentially may facilitate chemotherapeutic drug delivery as pancreatic cancers tend to have a dense fibrotic stroma that extrinsically compressed the tumor vasculature leading to a hypoperfusing intratumoral circulation. It is probable that patients with locally advanced pancreatic cancer will derive the greatest benefit from treatment with Smoothened antagonists. Fourth, it has been found that ligand-dependent activation by hedgehog occurs in the tumor stromal microenvironment in pancreatic cancer, a paracrine effect on tumorigenesis. Finally, in pancreatic cancer, cells with the CD44+CD24+ESA+ immunophenotype select a population enriched for cancer initiating stem cells. Shh is increased 46-fold in CD44+CD24+ESA+ cells compared with normal pancreatic epithelial cells. Medications that destruct pancreatic cancer initiating stem cells are a potentially novel strategy in cancer treatment. In conclusion, aberrant hedgehog signaling occurs in pancreatic cancer tumorigenesis and therapeutics that target the transmembrane receptor Smoothened abrogate hedgehog signaling and may improve the outcomes of patients with pancreatic cancer.

Two distinct sites in sonic Hedgehog combine for heparan sulfate interactions and cell signaling functions

Hedgehog (Hh) proteins are morphogens that mediate many developmental processes. Hh signaling is significant for many aspects of embryonic development, whereas dysregulation of this pathway is associated with several types of cancer. Hh proteins require heparan sulfate proteoglycans (HSPGs) for their normal distribution and signaling activity. Here, we have used molecular modeling to examine the heparin-binding domain of sonic hedgehog (Shh). In biochemical and cell biological assays, the importance of specific residues of the putative heparin-binding domain for signaling was assessed. It was determined that key residues in human (h) Shh involved in heparin and HSPG syndecan-4 binding and biological activity included the well known cationic Cardin-Weintraub motif (lysines 32-38) but also a previously unidentified major role for lysine 178. The activity of Shh mutated in these residues was tested by quantitation of alkaline phosphatase activity in C3H10T1/2 cells differentiating into osteoblasts and hShh-inducible gene expression in PANC1 human pancreatic ductal adenocarcinoma cells. Mutated hShhs such as K37S/K38S, K178S, and particularly K37S/K38S/K178S that could not interact with heparin efficiently had reduced signaling activity compared with wild type hShh or a control mutation (K74S). In addition, the mutant hShh proteins supported reduced proliferation and invasion of PANC1 cells compared with control hShh proteins, following endogenous hShh depletion by RNAi knockdown. The data correlated with reduced Shh multimerization where the Lys-37/38 and/or Lys-178 mutations were examined. These studies provide a new insight into the functional roles of hShh interactions with HSPGs, which may allow targeting this aspect of hShh biology in, for example, pancreatic ductal adenocarcinoma.

Evaluation of vitamin D3 A-ring analogues as Hedgehog pathway inhibitors

A structure-activity relationship study focusing on the A-ring of vitamin D3 (VD3) was undertaken to elucidate its role in inhibiting the Hedgehog pathway and in mediating anti-cancer effects. Analogues resulting from simple functional group substitution at 3' position of VD3 were evaluated in a variety of biological assays to determine their ability to selectively inhibit Hh signaling. Moderately active Hh inhibitors that have insignificant binding affinity for VDR were identified; however, these compounds also activate the traditional VDR pathway, presumably due to metabolites produced in the cultured cells. Thus, further structural modifications to the VD3 scaffold are required to yield potent, selective Hh inhibitors.

Opposing roles of voltage-gated Ca2+ channels in neuronal control of regenerative patterning

There is intense interest in developing methods to regulate proliferation and differentiation of stem cells into neuronal fates for the purposes of regenerative medicine. One way to do this is through in vivo pharmacological engineering using small molecules. However, a key challenge is identification of relevant signaling pathways and therein druggable targets to manipulate stem cell behavior efficiently in vivo. Here, we use the planarian flatworm as a simple chemical-genetic screening model for nervous system regeneration to show that the isoquinoline drug praziquantel (PZQ) acts as a small molecule neurogenic to produce two-headed animals with integrated CNSs following regeneration. Characterization of the entire family of planarian voltage-operated Ca(2+) channel α subunits (Ca(v)α), followed by in vivo RNAi of specific Ca(v) subunits, revealed that PZQ subverted regeneration by activation of a specific voltage-gated Ca(2+) channel isoform (Ca(v)1A). PZQ-evoked Ca(2+) entry via Ca(v)1A served to inhibit neuronally derived Hedgehog signals, as evidenced by data showing that RNAi of Ca(v)1A prevented PZQ-evoked bipolarity, Ca(2+) entry, and decreases in wnt1 and wnt11-5 levels. Surprisingly, the action of PZQ was opposed by Ca(2+) influx through a closely related neuronal Ca(v) isoform (Ca(v)1B), establishing a novel interplay between specific Ca(v)1 channel isoforms, Ca(2+) entry, and neuronal Hedgehog signaling. These data map PZQ efficacy to specific neuronal Ca(v) complexes in vivo and underscore that both activators (Ca(v)1A) and inhibitors (Ca(v)1B) of Ca(2+) influx can act as small molecule neurogenics in vivo on account of the unique coupling of Ca(2+) channels to neuronally derived polarity cues.

Hedgehog signaling inhibition blocks growth of resistant tumors through effects on tumor microenvironment

Hedgehog (Hh) signaling is implicated in bone development and cellular transformation. Here we show that inhibition of Hh pathway activity inhibits tumor growth through effects on the microenvironment. Pharmacologic inhibition of the Hh effector Smoothened (Smo) increased trabecular bone in vivo and inhibited osteoclastogenesis in vitro. In addition, enhanced Hh signaling due to heterozygosity of the Hh inhibitory receptor Patched (Ptch1(+/-)) increased bone resorption, suggesting direct regulation of osteoclast (OC) activity by the Hh pathway. Ptch1(+/-) mice had increased bone metastatic and subcutaneous tumor growth, suggesting that increased Hh activation in host cells promoted tumor growth. Subcutaneous growth of Hh-resistant tumor cells was inhibited by LDE225, a novel orally bioavailable SMO antagonist, consistent with effects on tumor microenvironment. Knockdown of the Hh ligand Sonic Hh (SHH) in these cells decreased subcutaneous tumor growth and decreased stromal cell production of interleukin-6, indicating that tumor-derived Hh ligands stimulated tumor growth in a paracrine fashion. Together our findings show that inhibition of the Hh pathway can reduce tumor burden, regardless of tumor Hh responsiveness, through effects on tumor cells, OCs, and stromal cells within the tumor microenvironment. Hh may be a promising therapeutic target for solid cancers and bone metastases.

Pancreatic cancer: promise for personalised medicine?

Pancreatic cancer has an infaust prognosis and is the fourth commonest cause of cancer related death in men. Design of rational treatment has been hampered by lack of insight into the pathogenesis of the disease. Recently more insight has been gained into a number of crucial aspects of pancreatic carcinogenesis, in particular the cell types that can give rise to oncological transformation in the pancreas, different modes of interaction between transformed pancreatic cells and the stroma that fosters further disease progression, the need of the pancreatic tumour cells to overcome the pressure of immune surveillance and the various changes in intercellular biochemistry that tumour cells employ to both sustain chemoresistance and metastasis. Although still largely incomplete, this new knowledge opens novel avenues on more successful treatment of the disease through personalised medicine.

Notch1 regulates the expression of the multidrug resistance gene ABCC1/MRP1 in cultured cancer cells

Multidrug resistance (MDR) is a barrier to successful cancer chemotherapy. Although MDR is associated with overexpression of ATP-binding cassette (ABC) membrane transporters, mechanisms behind their up-regulation are not entirely understood. The cleaved form of the Notch1 protein, intracellular Notch1 (N1(IC)), is involved in transcriptional regulation of genes. To test whether Notch1 is involved in the expression of multidrug resistance-associated protein 1 (ABCC1/MRP1; herein referred to as ABCC1), we measured N1(IC) and presenilin 1 (PSEN1), the catalytic subunit of γ-secretase required for Notch activation. We observed higher levels of N1(IC) and PSEN1 proteins as well as higher activity of N1(IC) in ABCC1-expressing MDR MCF7/VP cells compared with parental MCF7/WT cells. Reducing N1(IC) levels in MCF7/VP cells with either a γ-secretase inhibitor or shRNA led to reduction of ABCC1. By contrast, ectopic expression of N1(IC) in MCF7/WT cells led to increased expression of ABCC1 and associated drug resistance, consistent with expression of this transporter. Inhibition of ABCC1 reversed drug resistance of N1(IC)-overexpressing stable cells. Using an ABCC1 promoter construct, we observed both its reduced transcriptional activity after blocking the generation of N1(IC) and its increased transcriptional activity in stable cells overexpressing N1(IC). ChIP and gel-shift assays revealed an interaction between a specific promoter region of ABCC1 and the N1(IC)-activated transcription factor CBF1, suggesting that the regulation of ABCC1 expression by Notch1 is mediated by CBF1. Indeed, deletion or site-directed mutagenesis of these CBF1 binding sites within the ABCC1 promoter region attenuated promoter-reporter activity. Overall, our results reveal a unique regulatory mechanism of ABCC1 expression.

Aberrant Hedgehog ligands induce progressive pancreatic fibrosis by paracrine activation of myofibroblasts and ductular cells in transgenic zebrafish

Hedgehog (Hh) signaling is frequently up-regulated in fibrogenic pancreatic diseases including chronic pancreatitis and pancreatic cancer. Although recent series suggest exclusive paracrine activation of stromal cells by Hh ligands from epithelial components, debates still exist on how Hh signaling works in pathologic conditions. To explore how Hh signaling affects the pancreas, we investigated transgenic phenotypes in zebrafish that over-express either Indian Hh or Sonic Hh along with green fluorescence protein (GFP) to enable real-time observation, or GFP alone as control, at the ptf1a domain. Transgenic embryos and zebrafish were serially followed for transgenic phenotypes, and investigated using quantitative reverse transcription-polymerase chain reaction (qRT-PCR), in situ hybridization, and immunohistochemistry. Over-expression of Ihh or Shh reveals virtually identical phenotypes. Hh induces morphologic changes in a developing pancreas without derangement in acinar differentiation. In older zebrafish, Hh induces progressive pancreatic fibrosis intermingled with proliferating ductular structures, which is accompanied by the destruction of the acinar structures. Both myofibroblasts and ductular are activated and proliferated by paracrine Hh signaling, showing restricted expression of Hh downstream components including Patched1 (Ptc1), Smoothened (Smo), and Gli1/2 in those Hh-responsive cells. Hh ligands induce matrix metalloproteinases (MMPs), especially MMP9 in all Hh-responsive cells, and transform growth factor-ß1 (TGFß1) only in ductular cells. Aberrant Hh over-expression, however, does not induce pancreatic tumors. On treatment with inhibitors, embryonic phenotypes are reversed by either cyclopamine or Hedgehog Primary Inhibitor-4 (HPI-4). Pancreatic fibrosis is only prevented by HPI-4. Our study provides strong evidence of Hh signaling which induces pancreatic fibrosis through paracrine activation of Hh-responsive cells in vivo. Induction of MMPs and TGFß1 by Hh signaling expands on the current understanding of how Hh signaling affects fibrosis and tumorigenesis. These transgenic models will be a valuable platform in exploring the mechanism of fibrogenic pancreatic diseases which are induced by Hh signaling activation.

Myofibroblast-derived PDGF-BB promotes Hedgehog survival signaling in cholangiocarcinoma cells

Cholangiocarcinoma (CCA) cells paradoxically express the death ligand, tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) and, therefore, are dependent upon potent survival signals to circumvent TRAIL cytotoxicity. CCAs are also highly desmoplastic cancers with a tumor microenvironment rich in myofibroblasts (MFBs). Herein, we examine a role for MFB-derived CCA survival signals. We employed human KMCH-1, KMBC, HuCCT-1, TFK-1, and Mz-ChA-1 CCA cells, as well as human primary hepatic stellate and myofibroblastic LX-2 cells, for these studies. In vivo experiments were conducted using a syngeneic rat orthotopic CCA model. Coculturing CCA cells with myofibroblastic human primary hepatic stellate cells or LX-2 cells significantly decreased TRAIL-induced apoptosis in CCA cells, a cytoprotective effect abrogated by neutralizing platelet-derived growth factor (PDGF)-BB antiserum. Cytoprotection by PDGF-BB was dependent upon Hedgehog (Hh) signaling, because it was abolished by the smoothened (SMO; the transducer of Hh signaling) inhibitor, cyclopamine. PDGF-BB induced cyclic adenosine monophosphate-dependent protein kinase-dependent trafficking of SMO to the plasma membrane, resulting in glioma-associated oncogene (GLI)2 nuclear translocation and activation of a consensus GLI reporter gene-based luciferase assay. A genome-wide messenger RNA expression analysis identified 67 target genes to be commonly up- (50 genes) or down-regulated (17 genes) by both Sonic hedgehog and PDGF-BB in a cyclopamine-dependent manner in CCA cells. Finally, in a rodent CCA in vivo model, cyclopamine administration increased apoptosis in CCA cells, resulting in tumor suppression.

CONCLUSIONS

MFB-derived PDGF-BB protects CCA cells from TRAIL cytotoxicity by a Hh-signaling-dependent process. These results have therapeutical implications for the treatment of human CCA.

Pancreatic cancer stem cell biology and its therapeutic implications

Pancreatic cancer remains one of the most difficult malignancies to treat. Significant developments in our understanding of pancreatic cancer biology have occurred over the past decade. One of the key advances has been the formulation of the cancer stem cell model of tumor growth and subsequent experimental proof of pancreatic cancer stem cell existence. Cancer stem cells contribute to pancreatic tumor growth and progression and are at least partially responsible for the relative resistance of the tumor to systemic chemotherapy and radiation. Significant questions remain about how the mutational profile of the tumor, the tumor microenvironment, and normal pancreatic developmental pathways contribute to pancreatic cancer stem cell biology. Answers to these questions will likely yield new therapeutic approaches for this deadly disease.

The hedgehog pathway conditions the bone microenvironment for osteolytic metastasis of breast cancer

The microenvironment at the site of tumor metastasis plays a key role in determining the fate of the metastasizing tumor cells. This ultimately has a direct impact on the progression of cancer. Bone is the preferred site of metastasis of breast cancer. Painful, debilitating osteolytic lesions are formed as a result of crosstalk between breast cancer cells and cells in the bone, predominantly the osteoblasts and osteoclasts. In this paper, we have discussed the temporal and spatial role of hedgehog (Hh) signaling in influencing the fate of metastatic breast cancer cells in bone. By virtue of its secreted ligands, the Hh pathway is capable of homotypic and heterotypic signaling and consequently altering the microenvironment in the bone. We also have put into perspective the therapeutic implications of using Hh inhibitors to prevent and/or treat bone metastases of breast cancer.

Mechanisms of Hedgehog signalling in cancer

The Hedgehog (Hh) pathway is a conserved signalling system essential for embryonic development and for the maintenance of self-renewal pathways in progenitor cells. Mutations that deregulate Hh signalling are directly implicated in basal cell carcinoma and medulloblastoma. The mechanisms of Hh pathway activation in cancers in which no pathway mutations have been identified are less clear, but of great translational significance. Small molecule inhibitors of the pathway, many of which are in early phase clinical trials, may shed further light on this question. Canonical Hh signalling promotes the expression of target genes through the Glioma-associated oncogene (GLI) transcription factors. There is now increasing evidence suggesting that 'non-canonical' Hh signalling mechanisms, some of which are independent of GLI-mediated transcription, may be important in cancer and development. The focus of this review is to summarise some of the known mechanisms of Hh signalling as well as its emerging role in cancer.

Inhibition of Hedgehog signaling antagonizes serous ovarian cancer growth in a primary xenograft model

Background

Recent evidence links aberrant activation of Hedgehog (Hh) signaling with the pathogenesis of several cancers including medulloblastoma, basal cell, small cell lung, pancreatic, prostate and ovarian. This investigation was designed to determine if inhibition of this pathway could inhibit serous ovarian cancer growth.

Methodology

We utilized an in vivo pre-clinical model of serous ovarian cancer to characterize the anti-tumor activity of Hh pathway inhibitors cyclopamine and a clinically applicable derivative, IPI-926. Primary human serous ovarian tumor tissue was used to generate tumor xenografts in mice that were subsequently treated with cyclopamine or IPI-926.

Principal Findings

Both compounds demonstrated significant anti-tumor activity as single agents. When IPI-926 was used in combination with paclitaxel and carboplatinum (T/C), no synergistic effect was observed, though sustained treatment with IPI-926 after cessation of T/C continued to suppress tumor growth. Hh pathway activity was analyzed by RT-PCR to assess changes in Gli1 transcript levels. A single dose of IPI-926 inhibited mouse stromal Gli1 transcript levels at 24 hours with unchanged human intra-tumor Gli1 levels. Chronic IPI-926 therapy for 21 days, however, inhibited Hh signaling in both mouse stromal and human tumor cells. Expression data from the micro-dissected stroma in human serous ovarian tumors confirmed the presence of Gli1 transcript and a significant association between elevated Gli1 transcript levels and worsened survival.

Conclusions/Significance

IPI-926 treatment inhibits serous tumor growth suggesting the Hh signaling pathway contributes to the pathogenesis of ovarian cancer and may hold promise as a novel therapeutic target, especially in the maintenance setting.

Hedgehog signaling and the Gli code in stem cells, cancer, and metastases

The Hedgehog (Hh)-Gli signaling pathway is an essential pathway involved in development and cancer. It controls the Gli code-the sum of all activator and repressor functions of the Gli transcription factors. Through the Gli code, and Gli1 in particular, it modulates the fate and behavior of stem and cancer stem cells, as well as tumor growth and survival in many human cancer types. It also affects recurrence and metastasis and is enhanced in advanced tumors, where it promotes an embryonic stem (ES) cell-like gene expression signature. A central component of this signature, Nanog, is critical for glioblastoma and cancer stem cell survival and expansion. Gli1 activity is also enhanced by several oncogenic proteins, including Ras, Myc, and Akt, and by loss of tumor suppressors, such as p53 and PTEN. The oncogenic load boosts Gli1 levels, which supports tumor progression, and promotes a critical threshold of Gli1 activity that allows cells to enter the metastatic transition. In colon cancers, this transition is defined by enhanced Hh-Gli and, surprisingly, by repressed Wnt-Tcf signaling. Together our data support a model in which the Gli code, and Gli1 in particular, acts as a key sensor that responds to both Hh signals and the oncogenic load. We hypothesize that, in turn, the Gli-regulated ES-like factors induce a reprogramming event in cancer stem cells that promotes high invasion, growth and/or metastasis. Targeting the Gli code, the autoregulatory Gli1-Nanog module and interacting partners and pathways thus offers new therapeutic possibilities.

GLI1 inhibition promotes epithelial-to-mesenchymal transition in pancreatic cancer cells

The Hedgehog (HH) pathway has been identified as an important deregulated signal transduction pathway in pancreatic ductal adenocarcinoma (PDAC), a cancer type characterized by a highly metastatic phenotype. In PDAC, the canonical HH pathway activity is restricted to the stromal compartment while HH signaling in the tumor cells is reduced as a consequence of constitutive KRAS activation. Here, we report that in the tumor compartment of PDAC the HH pathway effector transcription factor GLI1 regulates epithelial differentiation. RNAi-mediated knockdown of GLI1 abolished characteristics of epithelial differentiation, increased cell motility, and synergized with TGFβ to induce an epithelial-to-mesenchymal transition (EMT). Notably, EMT conversion in PDAC cells occurred in the absence of induction of SNAIL or SLUG, two canonical inducers of EMT in many other settings. Further mechanistic analysis revealed that GLI1 directly regulated the transcription of E-cadherin, a key determinant of epithelial tissue organization. Collectively, our findings identify GLI1 as an important positive regulator of epithelial differentiation, and they offer an explanation for how decreased levels of GLI1 are likely to contribute to the highly metastatic phenotype of PDAC.

Targeting the Hedgehog pathway in cancer

The Hedgehog (Hh) pathway is a major regulator of many fundamental processes in vertebrate embryonic development including stem cell maintenance, cell differentiation, tissue polarity and cell proliferation. Constitutive activation of the Hh pathway leading to tumorigenesis is seen in basal cell carcinomas and medulloblastoma. A variety of other human cancers, including brain, gastrointestinal, lung, breast and prostate cancers, also demonstrate inappropriate activation of this pathway. Paracrine Hh signaling from the tumor to the surrounding stroma was recently shown to promote tumorigenesis. This pathway has also been shown to regulate proliferation of cancer stem cells and to increase tumor invasiveness. Targeted inhibition of Hh signaling may be effective in the treatment and prevention of many types of human cancers. The discovery and synthesis of specific Hh pathway inhibitors have significant clinical implications in novel cancer therapeutics. Several synthetic Hh antagonists are now available, several of which are undergoing clinical evaluation. The orally available compound, GDC-0449, is the farthest along in clinical development. Initial clinical trials in basal cell carcinoma and treatment of select patients with medulloblastoma have shown good efficacy and safety. We review the molecular basis of Hh signaling, the current understanding of pathway activation in different types of human cancers and we discuss the clinical development of Hh pathway inhibitors in human cancer therapy.

Hedgehog signaling antagonist GDC-0449 (Vismodegib) inhibits pancreatic cancer stem cell characteristics: molecular mechanisms

Background

Recent evidence from in vitro and in vivo studies has demonstrated that aberrant reactivation of the Sonic Hedgehog (SHH) signaling pathway regulates genes that promote cellular proliferation in various human cancer stem cells (CSCs). Therefore, the chemotherapeutic agents that inhibit activation of Gli transcription factors have emerged as promising novel therapeutic drugs for pancreatic cancer. GDC-0449 (Vismodegib), orally administrable molecule belonging to the 2-arylpyridine class, inhibits SHH signaling pathway by blocking the activities of Smoothened. The objectives of this study were to examine the molecular mechanisms by which GDC-0449 regulates human pancreatic CSC characteristics in vitro.

Methodology/Principal Findings

GDC-0499 inhibited cell viability and induced apoptosis in three pancreatic cancer cell lines and pancreatic CSCs. This inhibitor also suppressed cell viability, Gli-DNA binding and transcriptional activities, and induced apoptosis through caspase-3 activation and PARP cleavage in pancreatic CSCs. GDC-0449-induced apoptosis in CSCs showed increased Fas expression and decreased expression of PDGFRα. Furthermore, Bcl-2 was down-regulated whereas TRAIL-R1/DR4 and TRAIL-R2/DR5 expression was increased following the treatment of CSCs with GDC-0449. Suppression of both Gli1 plus Gli2 by shRNA mimicked the changes in cell viability, spheroid formation, apoptosis and gene expression observed in GDC-0449-treated pancreatic CSCs. Thus, activated Gli genes repress DRs and Fas expressions, up-regulate the expressions of Bcl-2 and PDGFRα and facilitate cell survival.

Conclusions/Significance

These data suggest that GDC-0499 can be used for the management of pancreatic cancer by targeting pancreatic CSCs.

Multiple myeloma mesenchymal stem cells: characterization, origin, and tumor-promoting effects

Hematologic malignancies rely heavily on support from host cells through a number of well-documented mechanisms. Host cells, specifically mesenchymal stem cells (MSC), support tumor cell growth, metastasis, survival, bone marrow colonization, and evasion of the immune system. In multiple myeloma, similar to solid tumors, supporting cells have typically been considered healthy host cells. However, recent evidence reveals that many MSCs derived from patients with multiple myeloma (MM-MSC) show significant defects compared with MSCs from nondiseased donors (ND-MSC). These abnormalities range from differences in gene and protein expression to allelic abnormalities and can initiate after less than 1 day of coculture with myeloma cells or persist for months, perhaps years, after removal from myeloma influence. Alterations in MM-MSC function contribute to disease progression and provide new therapeutic targets. However, before the scientific community can capitalize on the distinctions between MM-MSCs and ND-MSCs, a number of confusions must be clarified, as we have done in this review, including the origin(s) of MM-MSCs, identification and characterization of MM-MSCs, and downstream effects and feedback circuits that support cancer progression. Further advances require more genetic analysis of MM-MSCs and disease models that accurately represent MSC-MM cell interactions.

Aberrant activation of the hedgehog signaling pathway in malignant hematological neoplasms

The hedgehog (HH) signaling pathway is a highly regulated signaling pathway that is important not only for embryonic development, tissue patterning, and organogenesis but also for tissue repair and the maintenance of stem cells in adult tissues. In the adult hematopoietic system, HH signaling regulates intrathymic T-cell development, and it is one of the survival signals provided by follicular dendritic cells to prevent apoptosis in germinal center B cells. HH signaling is required for primitive hematopoiesis; however, conflicting data have been reported regarding the role of the HH pathway in adult hematopoiesis. Inappropriate activation of the HH signaling pathway occurs in several human cancers, including hematological neoplasms. Emerging data demonstrate abnormal HH pathway activation in chronic lymphocytic leukemia/small lymphocytic lymphoma, plasma cell myeloma, mantle cell lymphoma, diffuse large B-cell lymphoma, ALK-positive anaplastic large cell lymphoma, chronic myelogenous leukemia, and acute leukemias. In these neoplasms, HH signaling promotes proliferation and survival, contributes to the maintenance of cancer stem cells, and enhances tolerance or resistance to chemotherapeutic agents. Here, we review current understanding of HH signaling, its role in the pathobiology of hematological malignancies, and its potential as a therapeutic target to treat malignant hematological neoplasms.

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

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

A polymeric nanoparticle encapsulated small-molecule inhibitor of Hedgehog signaling (NanoHHI) bypasses secondary mutational resistance to Smoothened antagonists

Aberrant activation of the hedgehog (Hh) signaling pathway is one of the most prevalent abnormalities in human cancer. Tumors with cell autonomous Hh activation (e.g., medulloblastomas) can acquire secondary mutations at the Smoothened (Smo) antagonist binding pocket, which render them refractory to conventional Hh inhibitors. A class of Hh pathway inhibitors (HPI) has been identified that block signaling downstream of Smo; one of these compounds, HPI-1, is a potent antagonist of the Hh transcription factor Gli1 and functions independent of upstream components in the pathway. Systemic administration of HPI-1 is challenging due to its minimal aqueous solubility and poor bioavailability. We engineered a polymeric nanoparticle from [poly(lactic-co-glycolic acid); (PLGA)] conjugated with polyethylene glycol (PEG), encapsulating HPI-1 (NanoHHI). NanoHHI particles have an average diameter of approximately 60 nm, forms uniform aqueous suspension, and improved systemic bioavailability compared with the parent compound. In contrast to the prototype targeted Smo antagonist, HhAntag (Genentech), NanoHHI markedly inhibits the growth of allografts derived from Ptch(-/+); Trp53(-/-) mouse medulloblastomas that harbor a Smo(D477G) binding site mutation (P < 0.001), which is accompanied by significant downregulation of mGli1 as well as bona fide Hh target genes (Akna, Cltb, and Olig2). Notably, NanoHHI combined with gemcitabine also significantly impedes the growth of orthotopic Pa03C pancreatic cancer xenografts that have a ligand-dependent, paracrine mechanism of Hh activation when compared with gemcitabine alone. No demonstrable hematologic or biochemical abnormalities were observed with NanoHHI administration. NanoHHI should be amenable to clinical translation in settings where tumors acquire mutational resistance to current Smo antagonists.

Hedgehog pathway signaling in cervical carcinoma and outcome after chemoradiation

BACKGROUND

Hedgehog (Hh) signaling was assessed in patients with primary cervical carcinoma who were receiving chemoradiation. Because the up-regulation of Hh has been reported in response to hypoxia, the authors examined associations between Hh gene expression and measurements of HP5 (the percentage of oxygen pressure readings in each tumor <5 mm Hg) and interstitial fluid pressure (IFP).

METHODS

Sonic hedgehog (SHH), Indian hedgehog (IHH), patched 1 and 2 (PTCH1 and PTCH2), smoothened (SMO), and glioma-associated oncogene family zinc finger 1 (Gli1) expression levels were determined using quantitative reverse transcriptase-polymerase chain reaction analysis on 85 frozen samples of primary cervical carcinoma and on 16 normal cervical samples. Clinicopathologic data were collected prospectively. Possible correlations between Hh expression and tumor hypoxia (HP5 and IFP) measured at the time of biopsy, the time to local recurrence, and disease-free survival (DFS) were examined.

RESULTS

At least 1 member of the Hh pathway was elevated in all but 1 tumor compared with normal tissue (P < .0001). Hh gene expression was heterogeneous with SHH, IHH, and GLI exhibiting bimodal distribution. Elevation of SHH expression (P = .04) and low SMO expression (P = .0007) were associated with HP5. The risk of local recurrence was associated with the up-regulation of SMO (hazard ratio [HR], 2.41; 95% confidence interval [CI], 1.00-5.82; P = .044), the up-regulation of >3 Hh genes (HR, 2.56; 95% CI, 1.09-6.00; P = .026), tumor size (HR, 1.41; 95% CI, 1.14-1.74; P = .0015), and lymph node-positive disease (HR, 2.82; 95% CI, 1.16-6.86; P = .022).

CONCLUSIONS

The proportion of tumors that expressed Hh genes in cervical cancer was very high. The current data support a role for the Hh pathway in repopulation after chemoradiation and suggest that SMO may be a valid therapeutic target. The authors concluded that further investigation into this pathway after radiation and Hh inhibition are warranted.

Hedgehog signaling and pancreatic tumor development

Numerous signaling pathways are misregulated in pancreatic ductal adenocarcinoma (PDAC), a highly malignant type of cancer. One of these is the Hedgehog (HH) pathway, which is normally involved in patterning processes in the developing embryo. Expression of the main ligand Sonic Hedgehog is an early event in carcinogenesis and correlates with the mutation of the KRAS oncogene, the cardinal molecular feature of pancreatic cancer. Recent data establish a functional role for HH signaling primarily in the tumor microenvironment, where it is involved in myofibroblast differentiation and the induction of stroma-derived growth promoting molecules. Given the protumorigenic functions of the abundant stromal desmoplasia typically associated with pancreatic cancer, targeting the HH pathway might prove beneficial in the treatment of the disease. First data using small molecule antagonists of HH signaling in mouse models of pancreatic cancer are promising and reveal a substantial, yet transient, effect on the myofibroblastic stroma. In this review, we try to give an outline on the current knowledge about HH signaling in pancreatic cancer including a perspective of using pharmacological inhibitors of this pathway in the clinic.

A crucial requirement for Hedgehog signaling in small cell lung cancer

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

Contribution of epithelial-to-mesenchymal transition and cancer stem cells to pancreatic cancer progression

Pancreatic adenocarcinoma remains among the most lethal of human malignancies. Overall 5-y survival is less than 5%, and only 20% of patients presenting with localized disease amenable to surgical resection. Even in patients who undergo resection, long-term survival remains extremely poor. A major contributor to the aggressiveness of multiple cancers, and pancreatic cancer in particular, is the process of epithelial-to-mesenchymal transition (EMT). This review highlights the growing evidence of EMT in pancreatic cancer progression, focusing on the contribution of EMT to the development of cancer stem cells and on interaction of EMT with other pathways central to cancer progression, such as Hedgehog signaling, the K-ras oncogene, and transforming growth factor-beta (TGF-β). We will also discuss EMT-targeting agents currently in development and in clinical trials that may help to reduce the morbidity and mortality associated with pancreatic cancer.

A global insight into a cancer transcriptional space using pancreatic data: importance, findings and flaws

Despite the increasing wealth of available data, the structure of cancer transcriptional space remains largely unknown. Analysis of this space would provide novel insights into the complexity of cancer, assess relative implications in complex biological processes and responses, evaluate the effectiveness of cancer models and help uncover vital facets of cancer biology not apparent from current small-scale studies. We conducted a comprehensive analysis of pancreatic cancer-expression space by integrating data from otherwise disparate studies. We found (i) a clear separation of profiles based on experimental type, with patient tissue samples, cell lines and xenograft models forming distinct groups; (ii) three subgroups within the normal samples adjacent to cancer showing disruptions to biofunctions previously linked to cancer; and (iii) that ectopic subcutaneous xenografts and cell line models do not effectively represent changes occurring in pancreatic cancer. All findings are available from our online resource for independent interrogation. Currently, the most comprehensive analysis of pancreatic cancer to date, our study primarily serves to highlight limitations inherent with a lack of raw data availability, insufficient clinical/histopathological information and ambiguous data processing. It stresses the importance of a global-systems approach to assess and maximise findings from expression profiling of malignant and non-malignant diseases.

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

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

Interactions between acute lymphoblastic leukemia and bone marrow stromal cells influence response to therapy

The cure rate for pediatric patients with B precursor acute lymphoblastic leukemia (pre-B ALL) is steadily improving, however relapses do occur despite initial response to therapy. To identify links between drug resistance and gene deregulation we used oligonucleotide microarray technology and determined in 184 pre-B ALL specimen genes differentially expressed compared to normal CD34(+) specimens. We identified 20 signature genes including CTGF, BMP-2, CXCR4 and IL7R, documented to regulate interactions in the bone marrow. We recorded remarkably similar levels of expression in three independent patient cohorts, and found distinct patterns in cytogenetically defined subgroups of pre-B ALL. The canonical pathways that were affected are involved in inter- and intra-cellular communication, regulating signaling within the microenvironment. We tested experimentally whether interaction with stromal cells conferred protection to four drugs used in current ALL therapy, and demonstrated that bone marrow stromal cells significantly influenced resistance to vincristine and cytosine arabinoside. Compounds designed to block the identified cellular interactions within the bone marrow microenvironment are expected to mobilise the leukemic cells and make them more accessible to contemporary antileukemic agents. The data provide novel insight into the pathobiology of ALL and indicate new therapeutic targets for patients with ALL.

Advances in pancreatic cancer

PURPOSE OF REVIEW

This review intends to describe recent studies on the interaction between pancreatic cancer cells and tumor stroma, and potential opportunities and limitations to therapeutically targeting the stroma.

RECENT FINDINGS

Pancreatic cancer is characterized by densely desmoplastic stroma. It is becoming increasingly clear that there are complex and mutually supportive interactions between cancer cells and the stroma. Specific signaling pathways exist between cancer cells and cancer-associated fibroblasts that contribute to hypoxic desmoplasia. Recent developments in therapeutic approaches to targeting the stroma have demonstrated potential for enhancing efficacy of cytotoxic therapies. However, the heterogeneity and genomic complexity between tumors has also become more evident based on recent findings. There is increasing evidence for hierarchy of cancer cells with identification of a subpopulation of cancer stem cells that are inherently resistant to traditional therapies.

SUMMARY

Targeting pancreatic cancer stroma is a novel therapeutic strategy that appears justified based on recent studies; however, continued focus is needed to develop more effective therapies against cells resistant to standard chemotherapy.

Akt1 interacts with epidermal growth factor receptors and hedgehog signaling to increase stem/transit amplifying cells in the embryonic mouse cortex

A subset of precursors in the embryonic mouse cortex and in neurospheres expresses a higher level of the serine/threonine kinase Akt1 than neighboring precursors. We reported previously that the functional significance of high Akt1 expression was enhanced Akt1 activity, resulting in an increase in survival, proliferation, and self-renewal of multipotent stem/transit amplifying cells. Akt1 can interact with a number of signaling pathways, but the extrinsic factors that are required for specific effects of elevated Akt1 expression have not been identified. In this study we addressed the contributions of signaling via epidermal growth factor (EGF) and hedgehog (Hh) receptors. In EGF receptor-null precursors or following transient inhibition of EGF receptor tyrosine kinase activity, elevating Akt1 by retroviral transduction could still increase survival and proliferation but could not increase self-renewal. We also found that elevated Akt1 expression induced the expression of EGF receptors (EGFRs) in wild-type precursors. Several extrinsic factors, including Shh, can induce EGFR expression by cortical precursors, and we found that elevating Akt1 allowed them to respond to a subthreshold concentration of Shh to induce EGFRs. In precursors that lack the Hh receptor smoothened, however, elevating Akt1 did not increase EGFR expression or self-renewal, though it could still stimulate proliferation. These findings suggest that a subset of precursors in the embryonic cortex that express an elevated level of Akt1 can respond to lower concentrations of Shh than neighboring precursors, resulting in an increase in their expression of EGFRs. Signaling via EGFRs is required for their self-renewal.

Prevalence of epithelial ovarian cancer stem cells correlates with recurrence in early-stage ovarian cancer

Epithelial ovarian cancer stem cells (EOC stem cells) have been associated with recurrence and chemoresistance. CD44 and CK18 are highly expressed in cancer stem cells and function as tools for their identification and characterization. We investigated the association between the number of CD44+ EOC stem cells in ovarian cancer tumors and progression-free survival. EOC stem cells exist as clusters located close to the stroma forming the cancer stem cell “niche”. 17.1% of the samples reveled high number of CD44+ EOC stem cells (>20% positive cells). In addition, the number of CD44+ EOC stem cells was significantly higher in patients with early-stage ovarian cancer (FIGO I/II), and it was associated with shorter progression-free survival (P = 0.026). This study suggests that quantification of the number of EOC stem cells in the tumor can be used as a predictor of disease and could be applied for treatment selection in early-stage ovarian cancer.