Treatment of medulloblastoma with hedgehog pathway inhibitor GDC-0449

Recent advances in the design of Hedgehog pathway inhibitors for the treatment of malignancies

INTRODUCTION

The Hedgehog (Hh) signaling pathway is known to be dysregulated in several forms of cancer. Hence, specifically targeting this signaling cascade is a valid and promising strategy for successful therapeutic intervention. Several components within the Hh pathway have been proven to be druggable; however, challenges in the discovery and development process for small molecules targeting this pathway have been identified.

AREAS COVERED

This review details both the current state and future potential of Hh pathway inhibitors as anticancer chemotherapeutics that target a variety of human malignancies.

EXPERT OPINION

The initial development of Hh pathway inhibitors focused on small-molecule antagonists of Smoothened, a transmembrane protein that is a key regulator of pathway signaling. More recently, efforts to identify and develop inhibitors of pathway signaling that function through alternate mechanisms have been increasing. However, none of these have advanced into clinical trials. Further, early evidence suggesting the broad application of Hh pathway inhibitors as a monotherapy in a wide range of human cancers has not been validated. The potential for Hh pathway inhibitors as combination therapy has demonstrated promising preclinical results. However, more research to identify rational drug combinations to fully explore the potential of this anticancer drug class is warranted.

Phage display discovery of novel molecular targets in glioblastoma-initiating cells

Glioblastoma is the most common primary intrinsic brain tumor and remains incurable despite maximal therapy. Glioblastomas display cellular hierarchies with self-renewing glioma-initiating cells (GICs) at the apex. To discover new GIC targets, we used in vivo delivery of phage display technology to screen for molecules selectively binding GICs that may be amenable for targeting. Phage display leverages large, diverse peptide libraries to identify interactions with molecules in their native conformation. We delivered a bacteriophage peptide library intravenously to a glioblastoma xenograft in vivo then derived GICs. Phage peptides bound to GICs were analyzed for their corresponding proteins and ranked based on prognostic value, identifying VAV3, a Rho guanine exchange factor involved tumor invasion, and CD97 (cluster of differentiation marker 97), an adhesion G-protein-coupled-receptor upstream of Rho, as potentially enriched in GICs. We confirmed that both VAV3 and CD97 were preferentially expressed by tumor cells expressing GIC markers. VAV3 expression correlated with increased activity of its downstream mediator, Rac1 (ras-related C3 botulinum toxin substrate 1), in GICs. Furthermore, targeting VAV3 by ribonucleic acid interference decreased GIC growth, migration, invasion and in vivo tumorigenesis. As CD97 is a cell surface protein, CD97 selection enriched for sphere formation, a surrogate of self-renewal. In silico analysis demonstrated VAV3 and CD97 are highly expressed in tumors and inform poor survival and tumor grade, and more common with epidermal growth factor receptor mutations. Finally, a VAV3 peptide sequence identified on phage display specifically internalized into GICs. These results show a novel screening method for identifying oncogenic pathways preferentially activated within the tumor hierarchy, offering a new strategy for developing glioblastoma therapies.

FoxG1 interacts with Bmi1 to regulate self-renewal and tumorigenicity of medulloblastoma stem cells

Brain tumors represent the leading cause of childhood cancer mortality, of which medulloblastoma (MB) is the most frequent malignant tumor. Recent studies have demonstrated the presence of several MB molecular subgroups, each distinct in terms of prognosis and predicted therapeutic response. Groups 1 and 2 are characterized by relatively good clinical outcomes and activation of the Wnt and Shh pathways, respectively. In contrast, groups 3 and 4 ("non-Shh/Wnt MBs") are distinguished by metastatic disease, poor patient outcome, and lack a molecular pathway phenotype. Current gene expression platforms have not detected brain tumor-initiating cell (BTIC) self-renewal genes in groups 3 and 4 MBs as BTICs typically comprise a minority of tumor cells and may therefore go undetected on bulk tumor analyses. Since increasing BTIC frequency has been associated with increasing tumor aggressiveness and poor patient outcome, we investigated the subgroup-specific gene expression profile of candidate stem cell genes within 251 primary human MBs from four nonoverlapping MB transcriptional databases (Amsterdam, Memphis, Toronto, Boston) and 74 NanoString-subgrouped MBs (Vancouver). We assessed the functional relevance of two genes, FoxG1 and Bmi1, which were significantly enriched in non-Shh/Wnt MBs and showed these genes to mediate MB stem cell self-renewal and tumor initiation in mice. We also identified their transcriptional regulation through reciprocal promoter occupancy in CD15+ MB stem cells. Our work demonstrates the application of stem cell data gathered from genomic platforms to guide functional BTIC assays, which may then be used to develop novel BTIC self-renewal mechanisms amenable to therapeutic targeting.

Activation of liver X receptors inhibits hedgehog signaling, clonogenic growth, and self-renewal in multiple myeloma

The Hedgehog (Hh) signaling pathway is aberrantly activated in a wide variety of human cancers, and recent clinical studies have demonstrated that pathway inhibitors are effective in advanced basal cell carcinoma (BCC). The majority of these agents have been designed to target SMOOTHENED (SMO), a transmembrane regulator of Hh signaling, but subsequent mutations in SMO have been found to generate drug resistance. In other cancers, oncogenic events that bypass SMO may activate canonical Hh signaling, and SMO antagonists have not demonstrated significant activity in several diseases. Therefore, alternative strategies targeting the Hh pathway downstream of SMO may have clinical utility. Liver X receptors (LXR) regulate cholesterol and fatty acid homeostasis, and LXR activation can inhibit the Hh pathway in normal mouse embryonic fibroblasts. We examined the effects of LXR activation on Hh signaling in human multiple myeloma cells and found that LXR agonists inhibited Hh pathway activity and clonogenic tumor growth in vitro. LXR activation also inhibited putative multiple myeloma cancer stem cells in vivo leading to the loss of tumor initiating and self-renewal potential. Finally, Hh signaling was inhibited downstream of SMO, suggesting that LXR agonists may represent a novel strategy to target pathogenic Hh signaling as well as treat multiple myeloma.

Vismodegib for the treatment of basal cell carcinoma: results and implications of the ERIVANCE BCC trial

ABSTRACT: 

The need for effective treatment of patients with locally advanced or metastatic basal cell carcinoma (BCC), in conjunction with major advances in the elucidation of the molecular basis of this tumor has led to the advent of new targeted therapies – namely, hedgehog inhibitors. The rationale for their use in patients with advanced BCC is based on their inhibitory effect on the hedgehog pathway, which is aberrantly activated in BCCs due to mutations of its primary components, PTCH1 and SMO genes. Vismodegib (GDC-0449) is an orally bioavailable hedgehog pathway inhibitor that selectively inhibits SMO. The ERIVANCE BCC study is a Phase II, international, multicenter clinical trial evaluating the efficacy and safety of vismodegib 150 mg once daily in patients with locally advanced or metastatic BCC. Vismodegib has been approved for the treatment of adult patients with metastatic BCC, or with locally advanced BCC that has recurred following surgery or who are not candidates for surgery or radiation therapy. This article will outline the rationale, design and available results from the ERIVANCE BCC study and discuss the clinical implications of vismodegib in the management of patients with BCC. Challenges regarding vismodegib use include the recurrence of BCC after drug discontinuation, the development of acquired resistance, the dramatic efficacy in patients with Gorlin syndrome, and class-related drug toxicity. Ongoing clinical trials aim to explore the role of vismodegib in the neoadjuvant setting prior to surgery, the potential use of alternate dosing regimens in order to limit chronic adverse events, as well as the identification of patients with BCC that are more likely to respond to this targeted therapy based on genotypic and/or phenotypic characteristics.

Emerging drugs and combination strategies for basal cell carcinoma

INTRODUCTION

Basal cell carcinoma (BCC) is a malignancy that is driven by an activated Hedgehog (Hh) pathway. Smoothened inhibitors are a new promising treatment option for patients with locally advanced or metastatic BCC or basal cell nevus syndrome. But long-term data are still limited, the optimal treatment duration is not yet defined and there are already documented cases with acquired resistance.

AREAS COVERED

Treatment modalities with Hh inhibitors, side effects and potential pharmacological combination options are discussed. The current literature, including PubMed, Cochrane database and registered trials on ClinicalTrials.gov, was searched.

EXPERT OPINION

BCCs typically regress during therapy with Hh inhibitors. Muscle toxicity, dysgeusia and hair loss can be considered as on target adverse reactions. Muscle toxicity is the dose-limiting toxicity of sonidegib. It was not seen with vismodegib because of its high binding to plasma protein α-1-acid glycoprotein. Sonidegib is different and shows a clear dose-toxicity relationship, which allows to address the question of whether there is a dose dependency of regression rate, cure rate and progression-free survival. In addition, basic research has offered strategies to enhance efficacy by the combination with other molecules, such as EGFR inhibitors, MEK inhibitors or immunotherapy.

Structure-activity relationships for vitamin D3-based aromatic a-ring analogues as hedgehog pathway inhibitors

A structure-activity relationship study for a series of vitamin D3-based (VD3) analogues that incorporate aromatic A-ring mimics with varying functionality has provided key insight into scaffold features that result in potent, selective Hedgehog (Hh) pathway inhibition. Three analogue subclasses containing (1) a single substitution at the ortho or para position of the aromatic A-ring, (2) a heteroaryl or biaryl moiety, or (3) multiple substituents on the aromatic A-ring were prepared and evaluated. Aromatic A-ring mimics incorporating either single or multiple hydrophilic moieties on a six-membered ring inhibited the Hh pathway in both Hh-dependent mouse embryonic fibroblasts and cultured cancer cells (IC50 values 0.74-10 μM). Preliminary studies were conducted to probe the cellular mechanisms through which VD3 and 5, the most active analogue, inhibit Hh signaling. These studies suggested that the anti-Hh activity of VD3 is primarily attributed to the vitamin D receptor, whereas 5 affects Hh inhibition through a separate mechanism.

Inactivation of the transcription factor GLI1 accelerates pancreatic cancer progression

The role of GLI1 in pancreatic tumor initiation promoting the progression of preneoplastic lesions into tumors is well established. However, its function at later stages of pancreatic carcinogenesis remains poorly understood. To address this issue, we crossed the gli1 knock-out (GKO) animal with cre-dependent pancreatic activation of oncogenic kras concomitant with loss of the tumor suppressor tp53 (KPC). Interestingly, in this model, GLI1 played a tumor-protective function, where survival of GKO/KPC mice was reduced compared with KPC littermates. Both cohorts developed pancreatic cancer without significant histopathological differences in survival studies. However, analysis of mice using ultrasound-based imaging at earlier time points showed increased tumor burden in GKO/KPC mice. These animals have larger tumors, decreased body weight, increased lactate dehydrogenase production, and severe leukopenia. In vivo and in vitro expression studies identified FAS and FAS ligand (FASL) as potential mediators of this phenomenon. The FAS/FASL axis, an apoptotic inducer, plays a role in the progression of pancreatic cancer, where its expression is usually lost or significantly reduced in advanced stages of the disease. Chromatin immunoprecipitation and reporter assays identified FAS and FASL as direct targets of GLI1, whereas GKO/KPC mice showed lower levels of this ligand compared with KPC animals. Finally, decreased levels of apoptosis were detected in tumor tissue in the absence of GLI1 by TUNEL staining. Together, these findings define a novel pathway regulated by GLI1 controlling pancreatic tumor progression and provide a new theoretical framework to help with the design and analysis of trials targeting GLI1-related pathways.

NL-103, a novel dual-targeted inhibitor of histone deacetylases and hedgehog pathway, effectively overcomes vismodegib resistance conferred by Smo mutations

Misregulation of hedgehog (Hh) signaling has been implicated in the pathogenesis of basal cell carcinoma (BCC) and medulloblastoma. Vismodegib, an orally bioavailable Hh signal pathway inhibitor targeting Smo, has been approved for the treatment of advanced BCC. However, acquired drug resistance to vismodegib induced by point mutation in Smo is emerging as a major problem to vismodegib treatment. In this study, we designed and synthesized a novel chimeric compound NL-103, which comprises structural elements of Hh pathway inhibitor vismodegib, and histone deacetylase (HDAC) inhibitor vorinostat. NL-103 simultaneously and significantly inhibited both HDACs and Hh pathway. Importantly, NL-103, as well as vorinostat, effectively overcame vismodegib resistance induced by Smoothened point mutations. Moreover, NL-103 and vorinostat, but not vismodegib, significantly downregulated the expression of Gli2 which plays an important role in Hh pathway. These results indicate that HDAC inhibitory activity is essential for NL-103 to overcome vismodegib resistance and that dual inhibition of HDAC and Hh signaling pathway may be a rational strategy for overcoming vismodegib resistance. Our findings suggest that NL-103 may be a promising compound for clinical development as a more effective Hh pathway inhibitor.

Genome sequencing of SHH medulloblastoma predicts genotype-related response to smoothened inhibition

Smoothened (SMO) inhibitors recently entered clinical trials for sonic-hedgehog-driven medulloblastoma (SHH-MB). Clinical response is highly variable. To understand the mechanism(s) of primary resistance and identify pathways cooperating with aberrant SHH signaling, we sequenced and profiled a large cohort of SHH-MBs (n = 133). SHH pathway mutations involved PTCH1 (across all age groups), SUFU (infants, including germline), and SMO (adults). Children >3 years old harbored an excess of downstream MYCN and GLI2 amplifications and frequent TP53 mutations, often in the germline, all of which were rare in infants and adults. Functional assays in different SHH-MB xenograft models demonstrated that SHH-MBs harboring a PTCH1 mutation were responsive to SMO inhibition, whereas tumors harboring an SUFU mutation or MYCN amplification were primarily resistant.

Diagnostic application of high resolution single nucleotide polymorphism array analysis for children with brain tumors

Single nucleotide polymorphism (SNP) array analysis is currently used as a first tier test for pediatric brain tumors at The Children's Hospital of Philadelphia. The results from 100 consecutive patients are summarized in the present report. Eighty-seven percent of the tumors had at least one pathogenic copy number alteration. Nineteen of 56 low grade gliomas (LGGs) demonstrated a duplication in 7q34, which resulted in a KIAA1549-BRAF fusion. Chromosome band 7q34 deletions, which resulted in a FAM131B-BRAF fusion, were identified in one pilocytic astrocytoma (PA) and one dysembryoplastic neuroepithelial tumor (DNT). One ganglioglioma (GG) demonstrated a 6q23.3q26 deletion that was predicted to result in a MYB-QKI fusion. Gains of chromosomes 5, 6, 7, 11, and 20 were seen in a subset of LGGs. Monosomy 6, deletion of 9q and 10q, and an i(17)(q10) were each detected in the medulloblastomas (MBs). Deletions and regions of loss of heterozygosity that encompassed TP53, RB1, CDKN2A/B, CHEK2, NF1, and NF2 were identified in a variety of tumors, which led to a recommendation for germline testing. A BRAF p.Thr599dup or p.V600E mutation was identified by Sanger sequencing in one and five gliomas, respectively, and a somatic TP53 mutation was identified in a fibrillary astrocytoma. No TP53 hot-spot mutations were detected in the MBs. SNP array analysis of pediatric brain tumors can be combined with pathologic examination and molecular analyses to further refine diagnoses, offer more accurate prognostic assessments, and identify patients who should be referred for cancer risk assessment.

Local perspective on a rare brain tumour: adult medulloblastoma

BACKGROUND

Little contemporary data are available regarding Australian patterns of care in adult medulloblastoma. It is unclear whether treatment, extrapolated from paediatric protocols despite known differences between the two groups, results in comparable efficacy.

AIM

To perform a retrospective review of patterns of care in adult medulloblastoma, especially with respect to adjuvant chemotherapy, in Australian patients.

METHODS

All medulloblastoma patients aged 15 years or older at two neuro-oncology institutions were identified from January 1995-May 2011. Patients with supratentorial or peripheral tumours were excluded. Standardised data were extracted from each institution regarding symptoms, disease staging, treatments received, toxicities and survival outcomes.

RESULTS

Seventeen eligible patients were identified. Median age was 37 years (range 20-67 years). All had good performance status (Eastern Cooperative Oncology Group 0-1). There were 11 standard-risk de novo patients, three high-risk de novo patients and three patients with recurrent disease. Median overall survival (OS) had not been reached for standard-risk patients with median follow up of 58 months. The median OS for high-risk de novo patients was 21 months, while the median OS was 15 months for patients with recurrent disease. Treatment was well tolerated, with haematological toxicities being most common.

CONCLUSIONS

Combined modality therapy (surgery followed by postoperative radiotherapy and adjuvant chemotherapy) was well tolerated and associated with good outcomes in standard-risk de novo patients. High-risk and recurrent disease patients do extremely poorly regardless of treatment and better treatment strategies are needed in these patients.

Hedgehog signaling pathway is a potential therapeutic target for gallbladder cancer

Gallbladder cancer (GBC) is a particularly deadly type of cancer with a 5-year survival rate of only 10%. New effective therapeutic strategies are greatly needed. Recently, we have shown that Hedgehog (Hh) signaling is reactivated in various types of cancer and is a potential therapeutic target. However, little is known about the biological significance of Hh signaling in human GBC. In this study, we determined whether Hh signaling could be a therapeutic target in GBC. The Hh transcription factor Gli1 was detected in the nucleus of GBC cells but not in the nucleus of normal gallbladder cells. The expression levels of Sonic Hh (Shh) and Smoothened (Smo) in human GBC specimens (n = 37) were higher than those in normal gallbladder tissue. The addition of exogenous Shh ligand augmented the anchor-dependent and anchor-independent proliferation and invasiveness of GBC cells in vitro. In contrast, inhibiting the effector Smo decreased the anchor-dependent and anchor-independent proliferation. Furthermore, the suppression of Smo decreased GBC cell invasiveness through the inhibition of MMP-2 and MMP-9 expression and inhibited the epithelial–mesenchymal transition. In a xenograft model, tumor volume in Smo siRNA-transfected GBC cells was significantly lower than in control tumors. These results suggest that Hh signaling is elevated in GBC and may be involved in the acquisition of malignant phenotypes, and that Hh signaling may be a potential therapeutic target for GBC.

A phase I, multicenter, open-label, first-in-human, dose-escalation study of the oral smoothened inhibitor Sonidegib (LDE225) in patients with advanced solid tumors

PURPOSE

This phase I trial was undertaken to determine the maximum tolerated dose (MTD), dose-limiting toxicities (DLT), safety, tolerability, pharmacokinetics, pharmacodynamics, and preliminary antitumor activity of the novel smoothened inhibitor sonidegib (LDE225), a potent inhibitor of hedgehog signaling, in patients with advanced solid tumors.

EXPERIMENTAL DESIGN

Oral sonidegib was administered to 103 patients with advanced solid tumors, including medulloblastoma and basal cell carcinoma (BCC), at doses ranging from 100 to 3,000 mg daily and 250 to 750 mg twice daily, continuously, with a single-dose pharmacokinetics run-in period. Dose escalations were guided by a Bayesian logistic regression model. Safety, tolerability, efficacy, pharmacokinetics, and biomarkers in skin and tumor biopsies were assessed.

RESULTS

The MTDs of sonidegib were 800 mg daily and 250 mg twice daily. The main DLT of reversible grade 3/4 elevated serum creatine kinase (18% of patients) was observed at doses ≥ the MTD in an exposure-dependent manner. Common grade 1/2 adverse events included muscle spasm, myalgia, gastrointestinal toxicities, increased liver enzymes, fatigue, dysgeusia, and alopecia. Sonidegib exposure increased dose proportionally up to 400 mg daily, and displayed nonlinear pharmacokinetics at higher doses. Sonidegib exhibited exposure-dependent reduction in GLI1 mRNA expression. Tumor responses observed in patients with medulloblastoma and BCC were associated with evidence of hedgehog pathway activation.

CONCLUSIONS

Sonidegib has an acceptable safety profile in patients with advanced solid tumors and exhibits antitumor activity in advanced BCC and relapsed medulloblastoma, both of which are strongly associated with activated hedgehog pathway, as determined by gene expression.

All-trans-retinoic acid antagonizes the Hedgehog pathway by inducing patched

Male germ cell tumors (GCTs) are a model for a curable solid tumor. GCTs can differentiate into mature teratomas. Embryonal carcinomas (ECs) represent the stem cell compartment of GCTs and are the malignant counterpart to embryonic stem (ES) cells. GCTs and EC cells are useful to investigate differentiation therapy and chemotherapy response. This study explored mechanistic interactions between all-trans-retinoic acid (RA), which induces differentiation of EC and ES cells, and the Hedgehog (Hh) pathway, a regulator of self-renewal and proliferation. RA was found to induce mRNA and protein expression of Patched 1 (Ptch1), the Hh ligand receptor and negative regulator of this pathway. PTCH1 is also a target gene of Hh signaling through Smoothened (Smo) activation. Yet, this observed RA-mediated Ptch1 induction was independent of Smo. It occurred despite co-treatment with RA and Smo inhibitors. Retinoid induction of Ptch1 also occurred in other RA-responsive cancer cell lines and in normal ES cells. Notably, this enhanced Ptch1 expression was preceded by induction of the homeobox transcription factor Meis1, a direct RA target. Direct interaction between Meis1 and Ptch1 was confirmed using chromatin immunoprecipitation assays. To establish the translational relevance of this work, Ptch1 expression was shown to be deregulated in human ECs relative to mature teratoma and the normal seminiferous tubule. Taken together, these findings reveal a previously unrecognized mechanism through which RA can inhibit the Hh pathway via Ptch1 induction. Engaging this pathway is a new way to repress the Hh pathway that can be translated into the cancer clinic.

Open-label, exploratory phase II trial of oral itraconazole for the treatment of basal cell carcinoma

PURPOSE

Itraconazole, a US Food and Drug Administration-approved antifungal drug, inhibits the Hedgehog (HH) signaling pathway, a crucial driver of basal cell carcinoma (BCC) tumorigenesis, and reduces BCC growth in mice. We assessed the effect of itraconazole on the HH pathway and on tumor size in human BCC tumors.

PATIENTS AND METHODS

Patients with ≥ one BCC tumor > 4 mm in diameter were enrolled onto two cohorts to receive oral itraconazole 200 mg twice per day for 1 month (cohort A) or 100 mg twice per day for an average of 2.3 months (cohort B). The primary end point was change in biomarkers: Ki67 tumor proliferation and HH activity (GLI1 mRNA). Secondary end points included change in tumor size in a subset of patients with multiple tumors.

RESULTS

A total of 29 patients were enrolled, of whom 19 were treated with itraconazole. Itraconazole treatment was associated with two adverse events (grade 2 fatigue and grade 4 congestive heart failure). Itraconazole reduced cell proliferation by 45% (P = .04), HH pathway activity by 65% (P = .03), and reduced tumor area by 24% (95% CI, 18.2% to 30.0%). Of eight patients with multiple nonbiopsied tumors, four achieved partial response, and four had stable disease. Tumors from untreated control patients and from those previously treated with vismodegib showed no significant changes in proliferation or tumor size.

CONCLUSION

Itraconazole has anti-BCC activity in humans. These results provide the basis for larger trials of longer duration to measure the clinical efficacy of itraconazole, especially relative to other HH pathway inhibitors.

Arsenic trioxide inhibits tumor cell growth in malignant rhabdoid tumors in vitro and in vivo by targeting overexpressed Gli1

Rhabdoid tumors are highly aggressive tumors occurring in infants and very young children. Despite multimodal and intensive therapy prognosis remains poor. Molecular analyses have uncovered several deregulated pathways, among them the CDK4/6-Rb-, the WNT- and the Sonic hedgehog (SHH) pathways. The SHH pathway is activated in rhabdoid tumors by GLI1 overexpression. Here, we demonstrate that arsenic trioxide (ATO) inhibits tumor cell growth of malignant rhabdoid tumors in vitro and in a mouse xenograft model by suppressing Gli1. Our data uncover ATO as a promising therapeutic approach to improve prognosis for rhabdoid tumor patients.

Molecularly targeted therapies for nonmelanoma skin cancers

Over the past two decades, advances in the fields of cancer genetics and molecular biology have elucidated molecular pathways that cause numerous cutaneous malignancies. This in turn has spurred the rational design of molecularly targeted therapies. In this review, we discuss the molecular pathways critical to the development of nonmelanoma skin cancers and the novel pharmacologic agents that target them. Included is a review of vismodegib for basal cell carcinoma, cetuximab for squamous cell carcinomas, imatinib for dermatofibrosarcoma protuberans, and sirolimus for Kaposi's sarcoma.

Chromosomal and genetic imbalances in Chinese patients with rhabdomyosarcoma detected by high-resolution array comparative genomic hybridization

Rhabdomyosarcoma (RMS) is the most common soft-tissue sarcoma in children. Although associations between ARMS tumorigenesis and PAX3, PAX7, and FKHR are well recognized, the complete genetic etiology underlying RMS pathogenesis and progression remains unclear. Chromosomal copy number variations (CNVs) and the involved genes may play important roles in the pathogenesis and progression of human malignancies. Using high-resolution array comparative genomic hybridization (aCGH), we examined 20 formalin-fixed, paraffin-embedded (FFPE) RMS tumors to explore the involvement of the relevant chromosomal regions with resident genes in RMS tumorigenesis. In RMS, frequent gains were identified on chromosome regions 12q13.3-q14.1, 12q24.31, 17q25.1, 1q21.1, and 7q11.23, whereas frequent losses were observed on chromosome regions 5q13.2, 14q32.33, and 15q11.2. Amplifications were observed on chromosome regions 9p13.3, 12q13.3-q14.1, 12q15, and 16p13.11, whereas deletions were detected on chromosome regions 1p36.33, 1p13.1, 2q11.1, 5q13.2, 8p23.1, 9p24.3, and 16p11.2. Frequent gains were detected in GLI1, GEFT, OS9, and CDK4 (12q13.3-q14.1), being 60% in embryonal rhabdomyosarcoma (ERMS) and 66.67% in alveolar rhabdomyosarcoma (ARMS), respectively. However, frequent losses were detected in IGHG1, IGHM, IGHG3, and IGHG4 (14q32.33), being 70% in ERMS and 55.56% in and ARMS, respectively. Frequent gains were detected in TYROBP, HCST, LRFN3, and ALKBH6 (19q13.12) in ERMS but not in ARMS. The frequency of TYROBP, HCST, LRFN3, and ALKBH6 gains is significantly different in ERMS versus ARMS (P=0.011). The results suggest that novel TYROBP, HCST, LRFN3, and ALKBH6 genes may play important roles in ERMS. The technique used is a feasible approach for array comparative genomic hybridization analysis in archival tumor samples.

Synthesis and biological evaluation of novel benzamide derivatives as potent smoothened antagonists

A series of novel benzamide derivatives were prepared and evaluated using cell-based measurements. Among these compounds, 10f significantly inhibited Hedgehog signaling and showed equivalent or more potency than GDC-0449 in different tests. Furthermore, compound 10f potently inhibited the proliferation of Daoy, a medulloblastoma cell line that is reported to be resistant to GDC-0449, which indicated a promising prospect in the treatment of Hedgehog signaling pathway related cancer in clinical trial.

Hedgehog-GLI signaling inhibition suppresses tumor growth in squamous lung cancer

PURPOSE

Lung squamous cell carcinoma (LSCC) currently lacks effective targeted therapies. Previous studies reported overexpression of Hedgehog (HH)-GLI signaling components in LSCC. However, they addressed neither the tumor heterogeneity nor the requirement for HH-GLI signaling. Here, we investigated the role of HH-GLI signaling in LSCC, and studied the therapeutic potential of HH-GLI suppression.

EXPERIMENTAL DESIGN

Gene expression datasets of two independent LSCC patient cohorts were analyzed to study the activation of HH-GLI signaling. Four human LSCC cell lines were examined for HH-GLI signaling components. Cell proliferation and apoptosis were assayed in these cells after blocking the HH-GLI pathway by lentiviral-shRNA knockdown or small-molecule inhibitors. Xenografts in immunodeficient mice were used to determine the in vivo efficacy of GLI inhibitor GANT61.

RESULTS

In both cohorts, activation of HH-GLI signaling was significantly associated with the classical subtype of LSCC. In cell lines, genetic knockdown of Smoothened (SMO) produced minor effects on cell survival, whereas GLI2 knockdown significantly reduced proliferation and induced extensive apoptosis. Consistently, the SMO inhibitor GDC-0449 resulted in limited cytotoxicity in LSCC cells, whereas the GLI inhibitor GANT61 was very effective. Importantly, GANT61 demonstrated specific in vivo antitumor activity in xenograft models of GLI(+) cell lines.

CONCLUSION

Our studies demonstrate an important role for GLI2 in LSCC, and suggest GLI inhibition as a novel and potent strategy to treat a subset of patients with LSCC.

Overcoming resistance to Sonic Hedgehog inhibition by targeting p90 ribosomal S6 kinase in pediatric medulloblastoma

BACKGROUND

Molecular subtyping has allowed for the beginning of personalized treatment in children suffering from medulloblastoma (MB). However, resistance inevitably emerges against these therapies, particularly in the Sonic Hedgehog (SHH) subtype. We found that children with SHH subtype have the worst outcome underscoring the need to identify new therapeutic targets.

PROCEDURE

High content screening of a 129 compound library identified agents that inhibited SHH MB growth. Lead molecular target levels, p90 ribosomal S6 kinase (RSK) were characterized by immunoblotting and qRT-PCR. Comparisons were made to human neural stem cells (hNSC). Impact of inhibiting RSK with the small molecule BI-D1870 or siRNA was assessed in growth assays (monolayer, neurosphere, and soft agar). NanoString was used to detect RSK in a cohort of 66 patients with MB. To determine BI-D1870 pharmacokinetics/pharmacodynamics, 100 mg/kg was I.P. injected into mice and tissues were collected at various time points.

RESULTS

Daoy, ONS76, UW228, and UW426 MB cells were exquisitely sensitive to BI-D1870 but unresponsive to SHH inhibitors. Anti-tumor growth corresponded with inactivation of RSK in MB cells. BI-D1870 had no effect on hNSCs. Inhibiting RSK with siRNA or BI-D1870 suppressed growth, induced apoptosis, and sensitized cells to SHH agents. Notably, RSK expression is correlated with SHH patients. In mice, BI-D1870 was well-tolerated and crossed the blood-brain barrier (BBB).

CONCLUSIONS

RSK inhibitors are promising because they target RSK which is correlated with SHH patients as well as cause high levels of apoptosis to only MB cells. Importantly, BI-D1870 crosses the BBB, acting as a scaffold for development of more long-lived RSK inhibitors.

Vismodegib: a review

In January 2012, vismodegib (Erivedge, manufactured by Genentech) became the first selective inhibitor of the Hedgehog signaling pathway to be approved by the US Food and Drug Administration for the treatment of locally advanced and metastatic basal cell carcinoma. The drug selectively binds to Smoothened, a 7-helix transmembrane receptor, thereby inhibiting activation of transcription factors of the glioma-associated oncogene family and suppressing tumor proliferation and growth. Studies published to date have assessed the efficacy of vismodegib according to clinical and radiologic outcomes but little information is available on the molecular mechanisms underpinning the proven clinical efficacy of the drug. This review will cover recent data on the Hedgehog signaling pathway and data from clinical trials with vismodegib in the treatment of basal cell carcinoma, and will consider its use in other types of tumor.

Molecular pathways: response and resistance to BRAF and MEK inhibitors in BRAF(V600E) tumors

The RAS-RAF-MEK (MAP-ERK kinase)-ERK (extracellular signal-regulated kinase) pathway plays a central role in driving proliferation, survival, and metastasis signals in tumor cells, and the prevalence of oncogenic mutations in RAS and BRAF and upstream nodes makes this pathway the focus of significant oncology drug development efforts. This focus has been justified by the recent success of BRAF and MEK inhibitors in prolonging the lives of patients with BRAF(V600E/K)-mutant melanoma. Although it is disappointing that cures are relatively rare, this should not detract from the value of these agents to patients with cancer and the opportunity they provide in allowing us to gain a deeper understanding of drug response and resistance. These insights have already provided the basis for the evaluation of alternative dosing regimens and combination therapies in patients with melanoma.

Fact or fiction--identifying the elusive multiple myeloma stem cell

Multiple Myeloma (MM) is a debilitating disease of proliferating and malignant plasma cells that is currently incurable. The ability of monoclonal recurrence of disease suggests it might arise from a stem cell-like population capable of self-renewal. The difficulty to isolate the cancer stem-like cell in MM has introduced confusion toward this hypothesis. However, recent evidence has suggested that MM originates from the B cell lineage with memory-B cell like features, allowing for self-renewal of the progenitor-like status and differentiation to a monoclonal plasma cell population. Furthermore, this tumor-initiating cell uses signaling pathways and microenvironment similar to the hematopoietic stem cell, though hijacking these mechanisms to create and favor a more tumorigenic environment. The bone marrow niche allows for pertinent evasion, either through avoiding immunosurveillance or through direct interaction with the stroma, inducing quiescence and thus drug resistance. Understanding the interaction of the MM stem cell to the microenvironment and the mechanisms utilized by various stem cell-like populations to allow persistence and therapy-resistance can enable for better targeting of this cell population and potential eradication of the disease.

The rationale for targeted therapies in medulloblastoma

Medulloblastoma (MB) is the most frequent malignant brain tumor in children. Patients with MB who are classified as having high-risk disease or those with recurrent disease respond poorly to current therapies and have an increased risk of MB-related mortality. Preclinical studies and molecular profiling of MB tumors have revealed upregulation or activation of several key signaling pathways such as the sonic hedgehog and WNT pathways. Although the exact mechanisms underlying MB tumorigenesis remain poorly understood, inhibiting these key pathways with molecularly targeted therapies represents an important approach to improving MB outcomes. Several molecularly targeted therapies are already under clinical investigation in MB patients. We discuss current preclinical and clinical data, as well as data from clinical trials of targeted therapies that are either ongoing or in development for MB.

Structural basis of SUFU-GLI interaction in human Hedgehog signalling regulation

Hedgehog signalling plays a fundamental role in the control of metazoan development, cell proliferation and differentiation, as highlighted by the fact that its deregulation is associated with the development of many human tumours. SUFU is an essential intracellular negative regulator of mammalian Hedgehog signalling and acts by binding and modulating the activity of GLI transcription factors. Despite its central importance, little is known about SUFU regulation and the nature of SUFU-GLI interaction. Here, the crystal and small-angle X-ray scattering structures of full-length human SUFU and its complex with the key SYGHL motif conserved in all GLIs are reported. It is demonstrated that GLI binding is associated with major conformational changes in SUFU, including an intrinsically disordered loop that is also crucial for pathway activation. These findings reveal the structure of the SUFU-GLI interface and suggest a mechanism for an essential regulatory step in Hedgehog signalling, offering possibilities for the development of novel pathway modulators and therapeutics.

Nanomedicines of Hedgehog inhibitor and PPAR-γ agonist for treating liver fibrosis

PURPOSE

Hedgehog (Hh) and peroxisome proliferator-activated receptor gamma (PPAR-γ) are major signaling pathways involved in the pathogenesis of liver fibrosis. Since Hh inhibitor, vismodegib (GDC) and PPAR-γ agonist, rosiglitazone (RSG) have poor water solubility, our objective was to formulate biodegradable polymeric nanoparticles encapsulating GDC and RSG for treating liver fibrosis.

METHODS

Methoxy-polyethylene-glycol-b-poly(carbonate-co-lactide) [mPEG-b-p(CB-co-LA)] was synthesized and characterized using (1)H NMR. Nanoparticles were prepared using this polymer by emulsification/solvent evaporation method to encapsulate GDC and RSG either alone or in combination. Nanoparticles were characterized for particle size, drug loading, drug release, and anti-fibrotic efficacy after tail vein injection into common bile duct ligated (CBDL) fibrotic rats.

RESULTS

mPEG-b-p(CB-co-LA) copolymer has molecular weight of 30,000 Da as determined by (1)H NMR. Nanoparticles were monodisperse with a mean particle size of 120-130 nm. Drug loading was 5% and 2% w/w for GDC and RSG, respectively. Nanoparticles carrying both GDC and RSG were formulated at half of their individual drug loading. Systemic administration of drug loaded nanoparticles protected liver injury in CBDL rats by suppressing the activation of hepatic stellate cells, and decreasing inflammatory cytokines.

CONCLUSION

Polymeric nanoparticles for co-delivery of Hh inhibitor and PPAR-γ agonist have the potential to treat liver fibrosis by intervening complex fibrotic cascade.

Lkb1/Stk11 regulation of mTOR signaling controls the transition of chondrocyte fates and suppresses skeletal tumor formation

Liver kinase b1 (Lkb1) protein kinase activity regulates cell growth and cell polarity. Here, we show Lkb1 is essential for maintaining a balance between mitotic and postmitotic cell fates in development of the mammalian skeleton. In this process, Lkb1 activity controls the progression of mitotic chondrocytes to a mature, postmitotic hypertrophic fate. Loss of this Lkb1-dependent switch leads to a dramatic expansion of immature chondrocytes and formation of enchondroma-like tumors. Pathway analysis points to a mammalian target of rapamycin complex 1-dependent mechanism that can be partially suppressed by rapamycin treatment. These findings highlight a critical requirement for integration of mammalian target of rapamycin activity into developmental decision-making during mammalian skeletogenesis.

Hedgehog pathway agonism: therapeutic potential and small-molecule development

The Hedgehog (Hh) pathway is a developmental signaling pathway that plays multiple roles during embryonic development and in adult tissues. Constitutive Hh signaling has been linked to the development and progression of several forms of cancer, and the application of small-molecule pathway inhibitors as anticancer chemotherapeutics is well studied and clearly defined. Activation of the Hh pathway as a therapeutic strategy for a variety of degenerative or ischemic disorders has also been proposed; however, the development of small-molecule Hh agonists has received less attention. The goal of this review is to highlight the recent evidence supporting the therapeutic potential of Hh pathway activators and to provide a comprehensive overview of small-molecule pathway agonists.

Unraveling the therapeutic potential of the Hedgehog pathway in cancer

Major progress has been made in recent years in the development of Hedgehog (Hh) pathway inhibitors for the treatment of patients with cancer. Promising clinical trial results have been obtained in cancers that harbor activating mutations of the Hh pathway, such as basal cell carcinoma and medulloblastoma. However, for many cancers, in which Hh ligand overexpression is thought to drive tumor growth, results have been disappointing. Here we review the preclinical data that continue to shape our understanding of the Hh pathway in tumorigenesis and the emerging clinical experience with smoothened inhibitors.

A gene signature based method for identifying subtypes and subtype-specific drivers in cancer with an application to medulloblastoma

BACKGROUND

Subtypes are widely found in cancer. They are characterized with different behaviors in clinical and molecular profiles, such as survival rates, gene signature and copy number aberrations (CNAs). While cancer is generally believed to have been caused by genetic aberrations, the number of such events is tremendous in the cancer tissue and only a small subset of them may be tumorigenic. On the other hand, gene expression signature of a subtype represents residuals of the subtype-specific cancer mechanisms. Using high-throughput data to link these factors to define subtype boundaries and identify subtype-specific drivers, is a promising yet largely unexplored topic.

RESULTS

We report a systematic method to automate the identification of cancer subtypes and candidate drivers. Specifically, we propose an iterative algorithm that alternates between gene expression clustering and gene signature selection. We applied the method to datasets of the pediatric cerebellar tumor medulloblastoma (MB). The subtyping algorithm consistently converges on multiple datasets of medulloblastoma, and the converged signatures and copy number landscapes are also found to be highly reproducible across the datasets. Based on the identified subtypes, we developed a PCA-based approach for subtype-specific identification of cancer drivers. The top-ranked driver candidates are found to be enriched with known pathways in certain subtypes of MB. This might reveal new understandings for these subtypes.

CONCLUSIONS

Our study indicates that subtype-signature defines the subtype boundaries, characterizes the subtype-specific processes and can be used to prioritize signature-related drivers.

Preferential activation of the hedgehog pathway by epigenetic modulations in HPV negative HNSCC identified with meta-pathway analysis

Head and neck squamous cell carcinoma (HNSCC) is largely divided into two groups based on their etiology, human papillomavirus (HPV)-positive and –negative. Global DNA methylation changes are known to drive oncogene and tumor suppressor expression in primary HNSCC of both types. However, significant heterogeneity in DNA methylation within the groups results in different transcriptional profiles and clinical outcomes. We applied a meta-pathway analysis to link gene expression changes to DNA methylation in distinguishing HNSCC subtypes. This approach isolated specific epigenetic changes controlling expression in HPV− HNSCC that distinguish it from HPV+ HNSCC. Analysis of genes identified Hedgehog pathway activation specific to HPV− HNSCC. We confirmed that GLI1, the primary Hedgehog target, showed higher expression in tumors compared to normal samples with HPV− tumors having the highest GLI1 expression, suggesting that increased expression of GLI1 is a potential driver in HPV− HNSCC. Our algorithm for integration of DNA methylation and gene expression can infer biologically significant molecular pathways that may be exploited as therapeutics targets. Our results suggest that therapeutics targeting the Hedgehog pathway may be of benefit in HPV− HNSCC. Similar integrative analysis of high-throughput coupled DNA methylation and expression datasets may yield novel insights into deregulated pathways in other cancers.

Genome variation and personalized cancer medicine

Genomic variation, through effects on gene structure and expression, plays an important role in understanding disease predisposition, biology and clinical response to therapy. Transforming this knowledge into clinically relevant information that tailors interventions to an individual's specific genetic, physical, social and environmental profile is challenging. To illustrate how research initiatives at preclinical phases of development are attempting to address clinically important issues in oncology, six clinical problems related to cancers of the colon, prostate, breast, pancreas and brain (medulloblastoma) as well as metastatic disease of different origins are described. A unifying theme across applications is that healthy individuals previously indistinguishable in regards to cancer risk and patients with cancer previously categorized as similar with regard to prognosis or drug response are being stratified into more refined subgroups with different clinical profiles. Effective matching of a broad range of tests with more tailored strategies for prevention and/or treatment will require well-designed clinical studies to evaluate benefits and costs.

Sleeping Beauty mutagenesis in a mouse medulloblastoma model defines networks that discriminate between human molecular subgroups

The Sleeping Beauty (SB) transposon mutagenesis screen is a powerful tool to facilitate the discovery of cancer genes that drive tumorigenesis in mouse models. In this study, we sought to identify genes that functionally cooperate with sonic hedgehog signaling to initiate medulloblastoma (MB), a tumor of the cerebellum. By combining SB mutagenesis with Patched1 heterozygous mice (Ptch1(lacZ/+)), we observed an increased frequency of MB and decreased tumor-free survival compared with Ptch1(lacZ/+) controls. From an analysis of 85 tumors, we identified 77 common insertion sites that map to 56 genes potentially driving increased tumorigenesis. The common insertion site genes identified in the mutagenesis screen were mapped to human orthologs, which were used to select probes and corresponding expression data from an independent set of previously described human MB samples, and surprisingly were capable of accurately clustering known molecular subgroups of MB, thereby defining common regulatory networks underlying all forms of MB irrespective of subgroup. We performed a network analysis to discover the likely mechanisms of action of subnetworks and used an in vivo model to confirm a role for a highly ranked candidate gene, Nfia, in promoting MB formation. Our analysis implicates candidate cancer genes in the deregulation of apoptosis and translational elongation, and reveals a strong signature of transcriptional regulation that will have broad impact on expression programs in MB. These networks provide functional insights into the complex biology of human MB and identify potential avenues for intervention common to all clinical subgroups.

Enhancing radiation therapy for patients with glioblastoma

Radiation therapy has been the foundation of therapy following maximal surgical resection in patients with newly diagnosed glioblastoma for decades and the primary therapy for unresected tumors. Using the standard approach with radiation and temozolomide, however, outcomes are poor, and glioblastoma remains an incurable disease with the majority of recurrences and progression within the radiation treatment field. As such, there is much interest in elucidating the mechanisms of resistance to radiation therapy and in developing novel approaches to overcoming this treatment resistance.