Treatment of medulloblastoma with hedgehog pathway inhibitor GDC-0449

Regulation of DNA damage following termination of Hedgehog (HH) survival signaling at the level of the GLI genes in human colon cancer

Transcriptional regulation of the Hedgehog (HH) signaling response is mediated by GLI genes (GLI1, GLI2) downstream of SMO, that are also activated by oncogenic signaling pathways. We have demonstrated the importance of targeting GLI downstream of SMO in the induction of cell death in human colon carcinoma cells. In HT29 cells inhibition of GLI1/GLI2 by the small molecule inhibitor GANT61 induced DNA double strand breaks (DSBs) and activation of ATM, MDC1 and NBS1; γH2AX and MDC1, NBS1 and MDC1 co-localized in nuclear foci. Early activation of ATM was decreased by 24 hr, when p-NBS1^Ser343, activated by ATM, was significantly reduced in cell extracts. Bound γH2AX was detected in isolated chromatin fractions or nuclei during DNA damage but not during DNA repair. MDC1 was tightly bound to chromatin at 32 hr as cells accumulated in early S-phase prior to becoming subG1, and during DNA repair. Limited binding of NBS1 was detected at all times during DNA damage but was strongly bound during DNA repair. Transient overexpression of NBS1 protected HT29 cells from GANT61-induced cell death, while knockdown of H2AX by H2AXshRNA delayed DNA damage signaling. Data demonstrate following GLI1/GLI2 inhibition: 1) induction of DNA damage in cells that are also resistant to SMO inhibitors, 2) dynamic interactions between γH2AX, MDC1 and NBS1 in single cell nuclei and in isolated chromatin fractions, 3) expression and chromatin binding properties of key mediator proteins that mark DNA damage or DNA repair, and 4) the importance of NBS1 in the DNA damage response mechanism.

Targeting Hedgehog signaling and understanding refractory response to treatment with Hedgehog pathway inhibitors

Hedgehog (Hh) signaling is a principal component of the morphogenetic code best known to direct pattern formation during embryogenesis. The Hh pathway remains active in adulthood however where it guides tissue regeneration and remodeling and Hh production in the niche plays an important role in maintaining stem cell compartment size. Deregulated Hh signaling activity is associated, depending on the context, with both cancer initiation and progression. Interestingly, the Hh pathway is remarkably druggable, raising hopes that inhibition of the pathway could support anticancer therapy. Indeed, a large body of preclinical data supports such an action, but promising clinical data are still limited to basal cell carcinoma (BSC) and medulloblastoma. Nevertheless cancer resistance against Hh targeting has already emerged as a major problem. Here we shall review the current situation with respect to targeting the Hh pathway in cancer in general and in chemotolerance in particular with a focus on the problems associated with the emergence of tumors resistant to treatment with inhibitors targeting the Hh receptor Smoothened (SMO).

Selective elimination of leukemia stem cells: hitting a moving target

Despite the widespread use of chemotherapeutic cytotoxic agents that eradicate proliferating cell populations, patients suffering from a wide variety of malignancies continue to relapse as a consequence of resistance to standard therapies. In hematologic malignancies, leukemia stem cells (LSCs) represent a malignant reservoir of disease that is believed to drive relapse and resistance to chemotherapy and tyrosine kinase inhibitor (TKIs). Major research efforts in recent years have been aimed at identifying and characterizing the LSC population in leukemias, such as chronic myeloid leukemia (CML), which represents an important paradigm for understanding the molecular evolution of cancer. However, the precise molecular mechanisms that promote LSC-mediated therapeutic recalcitrance have remained elusive. It has become clear that the LSC population evolves during disease progression, thus presenting a serious challenge for development of effective therapeutic strategies. Multiple reports have demonstrated that LSC initiation and propagation occurs as a result of aberrant activation of pro-survival and self-renewal pathways regulated by stem-cell related signaling molecules including β-catenin and Sonic Hedgehog (Shh). Enhanced survival in LSC protective microenvironments, such as the bone marrow niche, as well as acquired dormancy of cells in these niches, also contributes to LSC persistence. Key components of these cell-intrinsic and cell-extrinsic pathways provide novel potential targets for therapies aimed at eradicating this dynamic and therapeutically recalcitrant LSC population. Furthermore, combination strategies that exploit LSC have the potential to dramatically improve the quality and quantity of life for patients that are resistant to current therapies.

Implication of cancer stem cells in cancer drug development and drug delivery

Conventional therapy against cancer by chemotherapy and radiation therapy has proven successful at decreasing bulk tumor size when cancer is diagnosed early enough. These therapeutic approaches, however, often result in recurrence years later. A number of studies have begun to identify a subpopulation of tumor-initiating cells that may be critical to early tumorigenesis and subsequent recurrence. These cells have been termed cancer stem cells (CSCs) and have been demonstrated to have properties of self-renewal, differentiation into other tumor cell types, and enhanced drug resistance. Given the growing body of evidence that CSCs play a key role in tumor biology in many cancer types, it is important to take into account the properties of these cells when developing novel cancer drugs and designing enhanced methods of drug delivery. This review covers some of the mechanisms by which CSCs escape conventional therapy as well as the potential approaches to targeting CSCs that may be used during cancer drug development.

Small molecule inhibitors of Smoothened ciliary localization and ciliogenesis

Vertebrate Hedgehog (Hh) signals involved in development and some forms of cancer, such as basal cell carcinoma, are transduced by the primary cilium, a microtubular projection found on many cells. A critical step in vertebrate Hh signal transduction is the regulated movement of Smoothened (Smo), a seven-transmembrane protein, to the primary cilium. To identify small molecules that interfere with either the ciliary localization of Smo or ciliogenesis, we undertook a high-throughput, microscopy-based screen for compounds that alter the ciliary localization of YFP-tagged Smo. This screen identified 10 compounds that inhibit Hh pathway activity. Nine of these Smo antagonists (SA1-9) bind Smo, and one (SA10) does not. We also identified two compounds that inhibit ciliary biogenesis, which block microtubule polymerization or alter centrosome composition. Differential labeling of cell surface and intracellular Smo pools indicates that SA1-7 and 10 specifically inhibit trafficking of intracellular Smo to cilia. In contrast, SA8 and 9 recruit endogenous Smo to the cilium in some cell types. Despite these different mechanisms of action, all of the SAs inhibit activation of the Hh pathway by an oncogenic form of Smo, and abrogate the proliferation of basal cell carcinoma-like cancer cells. The SA compounds may provide alternative means of inhibiting pathogenic Hh signaling, and our study reveals that different pools of Smo move into cilia through distinct mechanisms.

Voltage-gated potassium channel EAG2 controls mitotic entry and tumor growth in medulloblastoma via regulating cell volume dynamics

Medulloblastoma (MB) is the most common pediatric CNS malignancy. We identify EAG2 as an overexpressed potassium channel in MBs across different molecular and histological subgroups. EAG2 knockdown not only impairs MB cell growth in vitro, but also reduces tumor burden in vivo and enhances survival in xenograft studies. Mechanistically, we demonstrate that EAG2 protein is confined intracellularly during interphase but is enriched in the plasma membrane during late G2 phase and mitosis. Disruption of EAG2 expression results in G2 arrest and mitotic catastrophe associated with failure of premitotic cytoplasmic condensation. While the tumor suppression function of EAG2 knockdown is independent of p53 activation, DNA damage checkpoint activation, or changes in the AKT pathway, this defective cell volume control is specifically associated with hyperactivation of the p38 MAPK pathway. Inhibition of the p38 pathway significantly rescues the growth defect and G2 arrest. Strikingly, ectopic membrane expression of EAG2 in cells at interphase results in cell volume reduction and mitotic-like morphology. Our study establishes the functional significance of EAG2 in promoting MB tumor progression via regulating cell volume dynamics, the perturbation of which activates the tumor suppressor p38 MAPK pathway, and provides clinical relevance for targeting this ion channel in human MBs.

The current state of targeted therapy in melanoma: this time it's personal

Treatment of metastatic melanoma has long been a challenge. Over the past 8 years significant advances have been made in understanding the genetic changes that drive melanoma development and progression. These studies have shown melanoma to be a heterogeneous group of tumors, driven by a diverse array of oncogenic mutations. There is now good evidence that activating mutations in the serine/threonine kinase BRAF and the receptor tyrosine kinase KIT constitute good therapeutic targets for restricted subgroups of melanoma. In this article, we discuss the genetics and etiology of cutaneous and noncutaneous melanoma and review some of the latest preclinical and clinical data on the new targeted therapy agents that are beginning to make an impact on the lives of melanoma patients.

Markers of survival and metastatic potential in childhood CNS primitive neuro-ectodermal brain tumours: an integrative genomic analysis

BACKGROUND

Childhood CNS primitive neuro-ectodermal brain tumours (PNETs) are very aggressive brain tumours for which the molecular features and best treatment approaches are unknown. We assessed a large cohort of these rare tumours to identify molecular markers to enhance clinical management of this disease.

METHODS

We obtained 142 primary hemispheric CNS PNET samples from 20 institutions in nine countries and examined transcriptional profiles for a subset of 51 samples and copy number profiles for a subset of 77 samples. We used clustering, gene, and pathway enrichment analyses to identify tumour subgroups and group-specific molecular markers, and applied immunohistochemical and gene-expression analyses to validate and assess the clinical significance of the subgroup markers.

FINDINGS

We identified three molecular subgroups of CNS PNETs that were distinguished by primitive neural (group 1), oligoneural (group 2), and mesenchymal lineage (group 3) gene-expression signatures with differential expression of cell-lineage markers LIN28 and OLIG2. Patients with group 1 tumours were most often female (male:female ratio 0·61 for group 1 vs 1·25 for group 2 and 1·63 for group 3; p=0·043 [group 1 vs groups 2 and 3]), youngest (median age at diagnosis 2·9 years [95% CI 2·4-5·2] for group 1 vs 7·9 years [6·0-9·7] for group 2 and 5·9 years [4·9-7·8] for group 3; p=0·005), and had poorest survival (median survival 0·8 years [95% CI 0·5-1·2] in group 1, 1·8 years [1·4-2·3] in group 2 and 4·3 years [0·8-7·8] in group 3; p=0·019). Patients with group 3 tumours had the highest incidence of metastases at diagnosis (no distant metastasis:metastasis ratio 0·90 for group 3 vs 2·80 for group 1 and 5·67 for group 2; p=0·037).

INTERPRETATION

LIN28 and OLIG2 are promising diagnostic and prognostic molecular markers for CNS PNET that warrant further assessment in prospective clinical trials.

FUNDING

Canadian Institute of Health Research, Brainchild/SickKids Foundation, and the Samantha Dickson Brain Tumour Trust.

The utility of hedgehog signaling pathway inhibition for cancer

The Hedgehog (Hh) signaling pathway has been implicated in tumor initiation and metastasis across different malignancies. Major mechanisms by which the Hh pathway is aberrantly activated can be attributed to mutations of members of Hh pathway or excessive/inappropriate expression of Hh pathway ligands. The Hh signaling pathway also affects the regulation of cancer stem cells, leading to their capabilities in tumor formation, disease progression, and metastasis. Preliminary results of early phase clinical trials of Hh inhibitors administered as monotherapy demonstrated promising results in patients with basal cell carcinoma and medulloblastoma, but clinically meaningful anticancer efficacy across other tumor types seems to be lacking. Additionally, cases of resistance have been already observed. Mutations of SMO, activation of Hh pathway components downstream to SMO, and upregulation of alternative signaling pathways are possible mechanisms of resistance development. Determination of effective Hh inhibitor-based combination regimens and development of correlative biomarkers relevant to this pathway should remain as clear priorities for future research.

Syndromes predisposing to pediatric central nervous system tumors: lessons learned and new promises

Central nervous system (CNS) neoplasms are a leading cause of morbidity and mortality among children with cancer. In contrast to adults, a genetic basis for brain tumors is relatively common in children. A child harboring a germline mutation in a cancer-related gene will be predisposed to develop CNS tumors. These cancer predisposition syndromes are rare but pose overwhelming clinical and psychosocial challenges to families and the treating team. Recent significant advances in our understanding of the biological processes that govern these genetic conditions combined with international efforts to define and treat clinical aspects of these tumors are transforming the lives of these individuals. In this article, we summarize recent progress made for each of the major CNS tumor syndromes. We discuss the biological and clinical relevance of such advances, and suggest a comprehensive approach to a child affected by a predisposition to brain tumors.

Update on molecular and genetic alterations in adult medulloblastoma

Medulloblastoma encompasses a group of aggressively growing cancers that arise either in the cerebellum or brain stem. They present primarily in children, with 80-85 % of medulloblastomas being diagnosed in patients of 16 years and younger. In adults, medulloblastomas are rare and account for less than 1 % of intracranial malignancies. Due to the low incidence of medulloblastoma in adults, the biology and genetics of adult medulloblastomas have long been poorly understood. Many centers therefore still treat adults either by radiotherapy only or by using glioblastoma protocols (both often noncurative), or with standard pediatric medulloblastoma regimes (often associated with dose-limiting toxicity).Current clinical staging systems discriminate between standard-risk or high-risk patients based on clinical and histological parameters. However, clinico-pathological features often fail to accurately predict treatment response. In children, molecularly defined risk assessment has become important to improve survival of high-risk patients and to decrease treatment-related toxicity and long-term sequelae in standard-risk patients. However, several recent studies have shown that adult and pediatric medulloblastomas are genetically distinct and may require different algorithms for molecular risk stratification. Moreover, four subtypes of medulloblastoma have been identified that appear at different frequencies in children and adults and that have a different prognostic impact depending on age. Molecular markers such as chromosome 10q and chromosome 17 statuses can be used for molecular risk stratification of adult medulloblastoma, but only in a subgroup-specific context. Here we present an overview of the current knowledge of the genomics of adult medulloblastoma and how these tumors differ from their pediatric counterparts.

Interactions between bone marrow stromal microenvironment and B-chronic lymphocytic leukemia cells: any role for Notch, Wnt and Hh signaling pathways?

B-cell chronic lymphocytic leukemia (CLL), which is the most common lymphoproliferative disorder, displays characteristics consistent with a defect in programmed cell death and exhibit prolonged survival of affected cells in vivo. When recovered from peripheral blood or lymphoid tissues of patients and cultured in vitro, CLL malignant cells rapidly undergo spontaneous apoptosis. CLL B-cells co-culture with different adherent cell types, collectively referred to as stromal cells, induces leukemia cell survival, migration, and drug resistance. In addition, such survival-promoting microenvironments can rescue leukemia cells from cytotoxic therapy, giving way to disease relapse. Quite surprisingly considering that many anti-cancer drugs, including γ-secretase inhibitors, Cyclopamine and Quercetin, were reported to block Notch, Wnt, and Hedgehog anti-apoptotic signaling pathways respectively, the link between the latter anti-apoptotic pathways and bone marrow stromal cells in CLL has been pointed out only recently. Data concerning the pathogenesis of CLL have been critically reviewed in regards to the growing body of evidence indicating deregulations of Notch, Wnt and Hedgehog anti-apoptotic signaling pathways in the stromal microenvironment of affected cells.

The hedgehog processing pathway is required for NSCLC growth and survival

Considerable interest has been generated from the results of recent clinical trials using smoothened (SMO) antagonists to inhibit the growth of hedgehog (HH) signaling-dependent tumors. This interest is tempered by the discovery of SMO mutations mediating resistance, underscoring the rationale for developing therapeutic strategies that interrupt HH signaling at levels distinct from those inhibiting SMO function. Here, we demonstrate that HH-dependent non-small cell lung carcinoma (NSCLC) growth is sensitive to blockade of the HH pathway upstream of SMO, at the level of HH ligand processing. Individually, the use of different lentivirally delivered shRNA constructs targeting two functionally distinct HH-processing proteins, skinny hedgehog (SKN) or dispatched-1 (DISP-1), in NSCLC cell lines produced similar decreases in cell proliferation and increased cell death. Further, providing either an exogenous source of processed HH or a SMO agonist reverses these effects. The attenuation of HH processing, by knocking down either of these gene products, also abrogated tumor growth in mouse xenografts. Finally, we extended these findings to primary clinical specimens, showing that SKN is frequently overexpressed in NSCLC and that higher DISP-1 expression is associated with an unfavorable clinical outcome. Our results show a critical role for HH processing in HH-dependent tumors, identifies two potential druggable targets in the HH pathway, and suggest that similar therapeutic strategies could be explored to treat patients harboring HH ligand-dependent cancers.

Molecular pathways: the hedgehog signaling pathway in cancer

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

Pediatric neuro-oncology: current status and future directions

Tumors of the central nervous system (CNS) are the most common solid malignancies in childhood and are the leading cause of cancer-related death in this age group. While an ongoing improvement in overall prognosis has been achieved in the last few decades, current therapeutic approaches still confer significant morbidities, especially for the very young. The traditional strategies of surgery, radiotherapy and conventional cytotoxic chemotherapy need to be further refined while newer approaches, including molecularly targeted agents, hold the promise of better responses, improved outcomes and reduced toxicities. This article discusses treatment standards, the focus of current clinical investigations and the future promise of novel, biologically based approaches for the most common pediatric CNS tumors: primitive neuroectodermal tumors including medulloblastomas, ependymomas and astrocytomas (both low-grade and high-grade glioma).

Hedgehog signaling: from the cuirass to the heart of pancreatic cancer

Exocrine pancreatic cancer is the fifth cause of cancer-related death in Europe and carries a very poor prognosis for all disease stages. To date no medical treatment has significantly increased patients' survival. One of the reasons for pancreatic cancer's chemoresistence is the complex tumor architecture: cancer cells are surrounded by a dense desmoplastic stroma that blocks drug delivery. Moreover, pancreatic cancer is characterized by a marked heterogeneity of cells, including cancer stem cells (CSCs) that act as tumor-initiating cells and hierarchically control the differentiated cancer cells. In particular, this subpopulation is resistant to classic cytotoxic therapies, and seems to be responsible for disease renewal. Hedgehog signaling (HH) is implicated in pancreatic gland development during embryogenesis and is reactivated during tumorigenesis and the maintenance of pancreatic cancer. Some studies demonstrated that the Hedgehog-secreted signaling proteins are overexpressed in both the stromal and CSCs pools, implying an abnormal activation of HH in the main compartment of pancreatic cancer. For this reason, the Hedgehog pathway could be an interesting target for clinical trials to increase drug concentration in neoplastic cells and hence deplete the stroma and directly kill tumor-initiating cells.

Vismodegib

Vismodegib (GDC-0449), an orally bioavailable small-molecule inhibitor of Hedgehog signaling, was recently approved by the U.S. Food and Drug Administration for the treatment of basal cell carcinoma that is either metastatic or locally advanced in patients who are not candidates for surgical resection or radiation. Given the absence of previously defined effective drug therapy for this disease, approval was granted primarily on the basis of outcome of a nonrandomized parallel cohort phase II study of 99 patients with advanced basal cell carcinoma, with a primary endpoint of objective response rate. Response rates of 30.3% and 42.9% were observed in metastatic and locally advanced cohorts in this study, respectively, associated with median progression-free survival in both cohorts of 9.5 months. Ongoing clinical investigations include evaluation of the potential efficacy of vismodegib in a variety of diseases and in combination with other agents. The mechanism of action, preclinical and clinical data, and potential utility in other disease contexts are reviewed here.

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

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

Hedgehog inhibitor decreases chemosensitivity to 5-fluorouracil and gemcitabine under hypoxic conditions in pancreatic cancer

Pancreatic cancer is one of the deadliest types of cancer. Previously, we showed that hypoxia increases invasiveness through upregulation of Smoothened (Smo) transcription in pancreatic ductal adenocarcinoma (PDAC) cells. Here, we first evaluated whether hypoxia-induced increase in Smo contributes to the proliferation of PDAC cells. We showed that Smo, but not Gli1, inhibition decreases proliferation significantly under hypoxic conditions. To further investigate the effects of Smo on PDAC growth, cell cycle analysis was carried out. Inhibition of Smo under hypoxia led to G(0) /G(1) arrest and decreased S phase. As 5-fluorouracil (5-FU) and gemcitabine, which are first-line drugs for pancreatic cancer, are sensitive to S phase, we then evaluated whether cyclopamine-induced decreased S phase under hypoxia affected the chemosensitivity of 5-FU and gemcitabine in PDAC cells. Cyclopamine treatment under hypoxia significantly decreased chemosensitivity to 5-FU and gemcitabine under hypoxia in both in vitro and in vivo models. In contrast, cis-diamminedichloroplatinum, which is cell cycle-independent, showed significant synergistic effects. These results suggest that hypoxia-induced increase of Smo directly contributes to the proliferation of PDAC cells through a hedgehog/Gli1-independent pathway, and that decreased S phase due to the use of Smo inhibitor under hypoxia leads to chemoresistance in S phase-sensitive anticancer drugs. Our results could be very important clinically because a clinical trial using Smo inhibitors and chemotherapy drugs will begin in the near future.

Targeting the Hedgehog signaling pathway for cancer therapy

INTRODUCTION

Hedgehog (Hh) signaling pathway plays key roles in embryonic development, formation and maintenance of cancer stem cells (CSCs) and acquisition of epithelial-to-mesenchymal transition (EMT). Since CSCs and EMT are important biological factors responsible for cancer cell invasion, metastasis, drug resistance and tumor recurrence, the Hh signaling pathway is believed to be an important target for cancer therapy.

AREAS COVERED

In recent years, small-molecule inhibitors of Hh signaling have been synthesized for cancer treatment. Clinical trials using these inhibitors are being conducted to determine their toxicity profiles and efficacies. In addition, nutraceuticals (such as isoflavones, curcumin, vitamin D, etc) have been shown to inhibit cancer growth through downregulation of Hh signaling.

EXPERT OPINION

Inhibition of Hh signaling is important for suppression of cancer growth, invasion, metastasis and recurrence in cancer therapy. However, targeting only one molecule in Hh signaling may not be sufficient to kill cancer cells because cancers show deregulation of multiple signals. Therefore, utilizing new technologies to determine alterations in Hh and other signals for individuals and designing combination strategies with small-molecule Hh inhibitors, nutraceuticals and other chemotherapeutics in targeted personalized therapy could have a significant effect on improving the overall survival of patients with cancers.

The clinical implications of medulloblastoma subgroups

Medulloblastoma, the most common malignant paediatric brain tumour, is currently diagnosed and stratified using a combination of clinical and demographic variables. Recent transcriptomic approaches have demonstrated that the histological entity known as medulloblastoma is comprised of multiple clinically and molecularly distinct subgroups. The current consensus is that four defined subgroups of medulloblastoma exist: WNT, SHH, Group 3, and Group 4. Each subgroup probably contains at least one additional level of hierarchy, with some evidence for multiple subtypes within each subgroup. The demographic and clinical differences between the subgroups present immediate and pressing questions to be addressed in the next round of clinical trials for patients with medulloblastoma. Many of the genetically defined targets for rational medulloblastoma therapies are unique to a given subgroup, suggesting the need for subgroup-specific trials of novel therapies. The development of practical, robust and widely accepted subgroup biomarkers that are amenable to the conditions of a prospective clinical trial is, therefore, an urgent need for the paediatric neuro-oncology community. In this Review, we discuss the clinical implications of molecular subgrouping in medulloblastoma, highlighting how these subgroups are transitioning from a research topic in the laboratory to a clinically relevant topic with important implications for patient care.

The mesenchymal tumor microenvironment: a drug-resistant niche

Drug and radiation resistance represent a challenge for most anticancer therapies. Diverse experimental approaches have provided evidence that the tumor-associated microenvironment constitutes both a protective shell that impedes drug or radiation access and a permissive or promotive microenvironment that encourages a nurturing cancer (i.e., cancer stem cell) niche where tumor cells overcome treatment- and cancer-induced stresses. Better understanding of the effects of the tumor microenvironment on cancer cells before, during and immediately after chemo- or radiotherapy is imperative to design new therapies aimed at targeting this tumor-protective niche. This review summarizes some of the known mesenchymal stromal effects that account for drug resistance, the main signal transduction pathways associated with this resistance and the therapeutic efforts directed to increase the success of current therapies. Special emphasis is given to environment-mediated drug resistance in general and to cell adhesion-mediated drug resistance in particular.

Inhibition of hedgehog signalling prevents experimental fibrosis and induces regression of established fibrosis

OBJECTIVES

Tissue fibrosis is a leading cause of death in patients with systemic sclerosis (SSc). Effective antifibrotic treatments are not available. Here, the authors investigated inhibition of hedgehog signalling by targeting Smoothened (Smo) as a novel antifibrotic approach.

METHODS

The activation status of the hedgehog pathway was assessed by immunohistochemistry for Gli transcription factors and by quantification of hedgehog target genes. Hedgehog signalling was inhibited by the selective inhibitor LDE223 and by small interfering RNA against Smo in the models of bleomycin-induced dermal fibrosis and in tight-skin-1 mice.

RESULTS

Hedgehog signalling is activated in SSc and in murine models of SSc. Inhibition of Smo either by LDE223 or by small interfering RNA prevented dermal thickening, myofibroblast differentiation and accumulation of collagen upon challenge with bleomycin. Targeting Smo also exerted potent antifibrotic effects in tight-skin-1 mice and did prevent progression of fibrosis and induced regression of pre-established fibrosis.

CONCLUSIONS

Inhibition of hedgehog signalling exerted potent antifibrotic effects in preclinical models of SSc in both preventive and therapeutic settings. These findings might have direct translational implications because inhibitors of Smo are already available and yielded promising results in initial clinical trials.

Hedgehog pathway inhibitor saridegib (IPI-926) increases lifespan in a mouse medulloblastoma model

The Sonic Hedgehog (Shh) pathway drives a subset of medulloblastomas, a malignant neuroectodermal brain cancer, and other cancers. Small-molecule Shh pathway inhibitors have induced tumor regression in mice and patients with medulloblastoma; however, drug resistance rapidly emerges, in some cases via de novo mutation of the drug target. Here we assess the response and resistance mechanisms to the natural product derivative saridegib in an aggressive Shh-driven mouse medulloblastoma model. In this model, saridegib treatment induced tumor reduction and significantly prolonged survival. Furthermore, the effect of saridegib on tumor-initiating capacity was demonstrated by reduced tumor incidence, slower growth, and spontaneous tumor regression that occurred in allografts generated from previously treated autochthonous medulloblastomas compared with those from untreated donors. Saridegib, a known P-glycoprotein (Pgp) substrate, induced Pgp activity in treated tumors, which likely contributed to emergence of drug resistance. Unlike other Smoothened (Smo) inhibitors, the drug resistance was neither mutation-dependent nor Gli2 amplification-dependent, and saridegib was found to be active in cells with the D473H point mutation that rendered them resistant to another Smo inhibitor, GDC-0449. The fivefold increase in lifespan in mice treated with saridegib as a single agent compares favorably with both targeted and cytotoxic therapies. The absence of genetic mutations that confer resistance distinguishes saridegib from other Smo inhibitors.

Molecular prescreening to select patient population in early clinical trials

The efficacy of targeted therapies in patient populations selected for treatment on the basis of the molecular features of their tumours is shifting the current focus of treatment to biomarker-driven clinical trials. Phase I trials provide an arena for early hypothesis testing, examining not only safety and toxicity, but also target engagement, biologically effective dosages, and the appropriate patient population. In this Perspectives article, we describe this new trend in early drug development, establishing the different approaches for building a pre-screening programme in an academic institution that is involved in early drug development. Our experience establishing the phase I programme at Vall d'Hebrón serves as an example of how these approaches can be integrated in ongoing trials, and we believe these considerations will help others to implement similar programmes in their institutions.

Subgroup-specific alternative splicing in medulloblastoma

Medulloblastoma comprises four distinct molecular variants: WNT, SHH, Group 3, and Group 4. We analyzed alternative splicing usage in 14 normal cerebellar samples and 103 medulloblastomas of known subgroup. Medulloblastoma samples have a statistically significant increase in alternative splicing as compared to normal fetal cerebella (2.3-times; P < 6.47E-8). Splicing patterns are distinct and specific between molecular subgroups. Unsupervised hierarchical clustering of alternative splicing events accurately assigns medulloblastomas to their correct subgroup. Subgroup-specific splicing and alternative promoter usage was most prevalent in Group 3 (19.4%) and SHH (16.2%) medulloblastomas, while observed less frequently in WNT (3.2%), and Group 4 (9.3%) tumors. Functional annotation of alternatively spliced genes reveals overrepresentation of genes important for neuronal development. Alternative splicing events in medulloblastoma may be regulated in part by the correlative expression of antisense transcripts, suggesting a possible mechanism affecting subgroup-specific alternative splicing. Our results identify additional candidate markers for medulloblastoma subgroup affiliation, further support the existence of distinct subgroups of the disease, and demonstrate an additional level of transcriptional heterogeneity between medulloblastoma subgroups.

Neurotoxicity of biologically targeted agents in pediatric cancer trials

Biologically targeted agents offer the promise of delivering specific anticancer effects while limiting damage to healthy tissue, including the central and peripheral nervous systems. During the past 5-10 years, these agents were examined in preclinical and adult clinical trials, and are used with increasing frequency in children with cancer. This review evaluates current knowledge about neurotoxicity from biologically targeted anticancer agents, particularly those in pediatric clinical trials. For each drug, neurotoxicity data are reviewed in adult (particularly studies of brain tumors) and pediatric studies when available. Overall, these agents are well tolerated, with few serious neurotoxic effects. Data from younger patients are limited, and more neurotoxicity may occur in the pediatric population because these agents target pathways that control not only tumorigenesis but also neural maturation. Further investigation is needed into long-term neurologic effects, particularly in children.

Promises and challenges of exhausting pediatric neural cancer stem cells

Cancer relapse is one of the major setbacks in pediatric oncology. Cancer stem cells (CSCs) have emerged as a major driving force governing tumor recurrence. CSCs are a small subpopulation of cells capable of regenerating a tumor and are resistant to conventional anticancer therapies. No CSC therapy has been approved by the US Food and Drug Administration. Because CSCs and normal stem cells share many characteristics, CSC-directed therapies have potential detrimental effects on normal stem cells, tissue maintenance, and development. Designing treatments that specifically target neural CSCs while allowing neural tissue stem cells to normally develop the brain is a major challenge in pediatric neuro-oncology. In recent years, better identification and characterization of neural CSCs, together with identifying differences between CSCs and normal neural stem cells, have been key factors in developing tailored therapeutics for these devastating diseases. This review focuses on the promises and challenges of pediatric neural CSC-directed therapies. We delineate the options currently in use to exhaust the ability of neural CSCs to self-renew. Finally, we suggest a comprehensive approach to combine anti-CSC therapies with other therapeutic approaches to prevent tumor recurrence.

Molecular subgroups of medulloblastoma: the current consensus

Medulloblastoma, a small blue cell malignancy of the cerebellum, is a major cause of morbidity and mortality in pediatric oncology. Current mechanisms for clinical prognostication and stratification include clinical factors (age, presence of metastases, and extent of resection) as well as histological subgrouping (classic, desmoplastic, and large cell/anaplastic histology). Transcriptional profiling studies of medulloblastoma cohorts from several research groups around the globe have suggested the existence of multiple distinct molecular subgroups that differ in their demographics, transcriptomes, somatic genetic events, and clinical outcomes. Variations in the number, composition, and nature of the subgroups between studies brought about a consensus conference in Boston in the fall of 2010. Discussants at the conference came to a consensus that the evidence supported the existence of four main subgroups of medulloblastoma (Wnt, Shh, Group 3, and Group 4). Participants outlined the demographic, transcriptional, genetic, and clinical differences between the four subgroups. While it is anticipated that the molecular classification of medulloblastoma will continue to evolve and diversify in the future as larger cohorts are studied at greater depth, herein we outline the current consensus nomenclature, and the differences between the medulloblastoma subgroups.

Matching mice to malignancy: molecular subgroups and models of medulloblastoma

INTRODUCTION

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

DISCUSSION

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

Ectopic overexpression of Sonic Hedgehog (Shh) induces stromal expansion and metaplasia in the adult murine pancreas

Ligand-dependent activation of the Hedgehog (Hh) signaling pathway has been implicated in both tumor initiation and metastasis of pancreatic ductal adenocarcinoma (PDAC). Prior studies in genetically engineered mouse models (GEMMs) have assessed the role of Hh signaling by cell autonomous expression of a constitutively active Gli2 within epithelial cells. On the contrary, aberrant pathway reactivation in the human exocrine pancreas occurs principally as a consequence of Sonic Hh ligand (Shh) overexpression from epithelial cells. To recapitulate the cognate pathophysiology of Hh signaling observed in the human pancreas, we examined GEMM where Hh ligand is conditionally overexpressed within the mature exocrine pancreas using a tamoxifen-inducible Elastase-Cre promoter (Ela-CreERT2;LSL-mShh). We also facilitated potential cell autonomous epithelial responsiveness to secreted Hh ligand by generating compound transgenic mice with concomitant expression of the Hh receptor Smoothened (Ela-CreERT2;LSL-mShh;LSL-mSmo). Of interest, none of these mice developed intraductal precursor lesions or PDAC during the follow-up period of up to 12 months after tamoxifen induction. Instead, all animals demonstrated marked expansion of stromal cells, consistent with the previously described epithelial-to-stromal paracrine Hh signaling. Hh responsiveness was mirrored by the expression of primary cilia within the expanded mesenchymal compartment and the absence within mature acinar cells. In the absence of cooperating mutations, Hh ligand overexpression in the mature exocrine pancreas is insufficient to induce neoplasia, even when epithelial cells coexpress the Smo receptor. This autochthonous model serves as a platform for studying epithelial stromal interactions in pancreatic carcinogenesis.

Pathways involved in Drosophila and human cancer development: the Notch, Hedgehog, Wingless, Runt, and Trithorax pathway

Animal models are established tools to study basic questions of biology in a systematic way. They have greatly facilitated our understanding of the mechanisms by which nature forms and maintains organisms. Much of the knowledge on molecular changes underlying the development of organisms originates from research in the fruit fly model Drosophila melanogaster. Vertebrate models including the mouse and zebrafish model, but also other animal models coming from different corners of the animal kingdom have shown that much of the basic machinery of development is essentially identical, not just in all vertebrates but in all major phyla of invertebrates too. Moreover, key elements of this machinery have been demonstrated to be involved in recurrent molecular abnormalities detected in tumor-tissue from patients, indicating their implication in the genesis of human cancer. Thus, research in this field has become a common topic for both biologists and hemato-oncologists. In this review, we summarize current knowledge on some of these key elements and molecular pathways such as Notch, Hedgehog, Wingless, Runt, and Trithorax that have been originally described and studied in animal models and which seem to play a major role in the pathophysiology and targeted management of human cancer.

Hedgehog pathway activation in human transitional cell carcinoma of the bladder

BACKGROUND

The Hedgehog (Hh) signalling pathway functions as an organiser in embryonic development. Recent studies have shown constitutive activation of this pathway in various malignancies, but its role in bladder cancer remains poorly studied.

METHODS

Expression levels of 31 genes and 9 microRNAs (miRNAs) involved in the Hh pathway were determined by quantitative real-time RT-PCR in 71 bladder tumour samples (21 muscle-invasive (MIBC) and 50 non-muscle-invasive (NMIBC) bladder cancers), as well as in 6 bladder cancer cell lines.

RESULTS

The SHH ligand gene and Gli-inducible target genes (FOXM1, IGF2, OSF2, H19, and SPP1) were overexpressed in tumour samples as compared with normal bladder tissue. SHH overexpression was found in 96% of NMIBC and 52% of MIBC samples, as well as in two bladder cancer cell lines. Altered expression of miRNAs supported their oncogene or tumour-suppressor gene status. In univariate analysis, high expression levels of PTCH2, miRNA-92A, miRNA-19A, and miRNA-20A were associated with poorer overall survival in MIBC (P=0.02, P=0.012, P=0.047, and P=0.036, respectively).

CONCLUSION

We observed constitutive activation of the Hh pathway in most NMIBC and about 50% of MIBC. We also found that some protein-coding genes and miRNAs involved in the Hh pathway may have prognostic value at the individual level.

Hedgehog pathway as a drug target: Smoothened inhibitors in development

Emerging laboratory and clinical investigations demonstrate that Hedgehog signaling (Hh) represents a novel therapeutic target in various human cancers. This conserved signaling pathway precisely regulates self-renewal and terminal differentiation in embryonic development, but is typically silenced in adult tissues, with reactivation usually only during tissue repair. Aberrant Hh pathway signaling has been implicated in the pathogenesis, self-renewal, and chemotherapy resistance of a growing number of solid and hematologic malignancies. Major components of the Hh pathway include the Hh ligands (Sonic, Desert, and Indian), the transmembrane receptor Patched, the signal transducer Smoothened (Smo), and transcription factors Gli1–3 which regulate the transcription of Hh target genes. Mutations in Hh pathway genes, increased Hh signaling in tumor stroma, and Hh overexpression in self-renewing cells (cancer stem cells) have been described, and these different modes of Hh signaling have implications for the design of Hh pathway inhibitors and their integration into conventional treatment regimens. Discovery of a naturally-occurring Smo inhibitor, cyclopamine, and the identification of Hh pathway mutations and over expression in cancer cells prompted the development of several cyclopamine derivatives. Encouraging laboratory and in vivo data has resulted in Phase I and II clinical trials of Smo inhibitors. In this review, we will discuss the current understanding of Hh pathway signaling in malignancy and Smo antagonists in development. Recent data with these agents shows that they are well-tolerated and may be effective for subsets of patients. Challenges remain for appropriate patient selection and the optimal combination and sequence of these targeted therapies into current treatment paradigms.

Biological and clinical relevance of stem cells in pancreatic adenocarcinoma

Cancer stem cells (CSC) have been identified in a growing number of human malignancies. CSC are functionally defined by their ability to self-renew and recapitulate tumors in the ectopic setting, and a growing number of studies have shown that they display other functional characteristics, such as invasion and drug resistance. These unique functional properties implicate a role for CSC in clinical consequences, such as initial tumor formation, relapse following treatment, metastasis, and resistance, suggesting they are a major factor in directing clinical outcomes. Pancreatic adenocarcinoma is a highly-aggressive disease with a propensity for early metastasis and drug resistance. Tumorigenic pancreatic cancer cells have been identified using the cell surface antigens CD44, CD24, and CD133, as well as the high expression of aldehyde dehydrogenase (ALDH). In vitro and in vivo studies have shown that ALDH- and CD133-expressing pancreatic CSC have a greater propensity for metastasis, and ALDH-expressing CSC have been shown to be resistant to conventional chemotherapy. In clinical samples from patients with resected pancreatic adenocarcinoma, the presence of ALDH-expressing CSC was associated with worse overall survival. The development of CSC-targeting therapies might be important in changing the clinical outcomes of patients with this disease, and others and we have begun to identify novel compounds that block CSC function. This review will discuss the biological and clinical relevance of CSC in pancreatic cancer, and will discuss novel therapeutic strategies to target them.

Latest advances and current challenges in the treatment of multiple myeloma

Effectively treating patients with multiple myeloma is challenging. The development of therapeutic regimens over the past decade that incorporate the proteasome inhibitor bortezomib and the immunomodulatory drugs thalidomide and lenalidomide has been the cornerstone of improving the outcome of patients with myeloma. Although these treatment regimens have improved patient survival, nearly all patients eventually relapse. Our improved understanding of the biology of the disease and the importance of the microenvironment has translated into ongoing work to help overcome the challenge of relapse. Several classes of agents including next-generation proteasome inhibitors, immunomodulatory agents, selective histone-deacetylase inhibitors, antibody and antitumor immunotherapy approaches are currently undergoing preclinical and clinical evaluation. This Review provides an update on the latest advances in the treatment of multiple myeloma. In particular, we focus on novel therapies including modulating protein homeostasis, kinases inhibitors, targeting accessory cells and cytokines, and immunomodulatory agents. A discussion of the challenges associated with these therapeutic approaches is also presented.

FISH and chips: the recipe for improved prognostication and outcomes for children with medulloblastoma

Rapidly evolving genomic technologies have permitted progressively detailed studies of medulloblastoma biology in recent years. These data have increased our understanding of the molecular pathogenesis of medulloblastoma, identified prognostic markers, and suggested future avenues for targeted therapy. Although current randomized trials are still stratified based largely on clinical variables, the use of molecular markers is approaching routine use in the clinic. In particular, integrated genomics has uncovered that medulloblastoma comprises four distinct molecular and clinical variants: WNT, sonic hedgehog (SHH), group 3, and group 4. Children with WNT medulloblastoma have improved survival, whereas those with group 3 medulloblastoma have a dismal prognosis. Additionally, integrated genomics has shown that adult medulloblastoma is molecularly and clinically distinct from the childhood variants. Prognostic and predictive markers identified by genomics should drive changes in stratification of treatment protocols for medulloblastoma patients on clinical trials once they can be demonstrated to be reliable, reproducible, and practical. Cases with excellent prognoses (WNT cases) should be considered for therapy de-escalation, whereas those with bleak prognoses (group 3 cases) should be prioritized for experimental therapy. In this review, we will summarize the genomic data published over the past decade and attempt to interpret its prognostic significance, relevance to the clinic, and use in upcoming clinical trials.

Hedgehog pathway and GLI1 isoforms in human cancer

The Hedgehog signaling pathway regulates normal cell growth and differentiation. When deregulated, the Hedgehog pathway leads to tumorigenesis and supports more aggressive phenotypes of human cancers, such as progression, metastasis, and therapeutic resistance. The glioma-associated oncogene homolog 1 (GLI1) family of zinc finger transcription factors is the nuclear mediator of the Hedgehog pathway that regulates genes essential for various stages of tumor development and progression. Consequently, several components of the Hedgehog pathway are major targets of cancer therapy, including GLI1 and smoothened. Although the GLI1 gene was initially identified as an amplified gene in glioblastoma, its amplification was found to be relatively rare. No somatic mutations have been reported in the GLI1 gene. Notably, two decades after the discovery of the GLI1 gene, the GLI1 transcript was recently found to undergo alternative splicing forming two shorter isoforms, an N-terminal deletion variant (GLI1ΔN) and a truncated GLI1 (tGLI1). These variants appear to have different patterns of tissue expression and functions. Most notably, the tGLI1 isoform behaves as a gain-of-function GLI1 that can induce expression of genes not regulated by GLI1 and promotes more aggressive cancer phenotypes. Therefore, this review will focus on the structural and functional differences between these isoforms, and also on their contributions to important cancer cell characteristics, including proliferation, motility, invasion, and angiogenesis.