Treatment of medulloblastoma with hedgehog pathway inhibitor GDC-0449

PTEN loss mitigates the response of medulloblastoma to Hedgehog pathway inhibition

Medulloblastoma is a cancer of the cerebellum, for which there is currently no approved targeted therapy. Recent transcriptomics approaches have demonstrated that medulloblastoma is composed of molecularly distinct subgroups, one of which is characterized by activation of the Hedgehog pathway, which in mouse models is sufficient to drive medulloblastoma development. There is thus considerable interest in targeting the Hedgehog pathway for therapeutic benefit in medulloblastoma, particularly given the recent approval of the Hedgehog pathway inhibitor vismodegib for metastatic and locally advanced basal cell carcinoma. Like other molecularly targeted therapies, however, there have been reports of acquired resistance to vismodegib, driven by secondary Hedgehog pathway mutations and potentially by activation of the phosphatidylinositol 3-kinase (PI3K) pathway. Given that acquired resistance to vismodegib may occur as a result of inappropriate PI3K pathway activation, we asked if loss of the PI3K pathway regulator, phosphatase and tensin homologue (Pten), which has been reported to occur in patients within the Hedgehog subgroup, would constitute a mechanism of innate resistance to vismodegib in Hedgehog-driven medulloblastoma. We find that Hedgehog pathway inhibition successfully restrains growth of Pten-deficient medulloblastoma in this mouse model, but does not drive tumor regression, as it does in Pten-wild-type medulloblastoma. Combined inhibition of the Hedgehog and PI3K pathways may lead to superior antitumor activity in PTEN-deficient medulloblastoma in the clinic.

The adolescent and young adult with cancer: state of the art--brain tumor

The management of adolescents and young adults with brain tumors, which consist of many different histologic subtypes, continues to be a challenge. Better outcome with a decrease of the side effects of the disease and therapy and improvement of quality of life has been demonstrated in recent decades for some tumors. Significant differences in survival and cure are also observed between adult and pediatric tumors of the same histologic grade. Genetic, developmental, and environmental factors likely influence the type of tumor and response observed, even though no clear pathologic features differentiate these lesions among children, adolescents, and adults. Similarly, treatment strategies are not identical among these populations; most patients receive surgery, followed by radiation therapy and multiagent chemotherapy. Advances in understanding the biology underlying the distribution of tumors in adolescents and young adults may influence the development of prospective trials. A more individualized view of these tumors will likely influence stratification of patients in future studies as well as selection for targeted agents. Accordingly, outcomes may improve and long-term morbidities may decrease.

Silencing of the miR-17~92 cluster family inhibits medulloblastoma progression

Medulloblastoma, originating in the cerebellum, is the most common malignant brain tumor in children. Medulloblastoma consists of four major groups where constitutive activation of the Sonic Hedgehog (SHH) signaling pathway is a hallmark of one group. Mouse and human SHH medulloblastomas exhibit increased expression of microRNAs encoded by the miR-17~92 and miR-106b~25 clusters compared with granule progenitors and postmitotic granule neurons. Here, we assessed the therapeutic potential of 8-mer seed-targeting locked nucleic acid (LNA)-modified anti-miR oligonucleotides, termed tiny LNAs, that inhibit microRNA seed families expressed by miR-17~92 and miR-106b~25 in two mouse models of SHH medulloblastomas. We found that tumor cells (medulloblastoma cells) passively took up 8-mer LNA-anti-miRs and specifically inhibited targeted microRNA seed-sharing family members. Inhibition of miR-17 and miR-19a seed families by anti-miR-17 and anti-miR-19, respectively, resulted in diminished tumor cell proliferation in vitro. Treatment of mice with systemic delivery of anti-miR-17 and anti-miR-19 reduced tumor growth in flank and brain allografts in vivo and prolonged the survival of mice with intracranial transplants, suggesting that inhibition of the miR-17~92 cluster family by 8-mer LNA-anti-miRs might be considered for the treatment of SHH medulloblastomas.

Vismodegib: an inhibitor of the Hedgehog signaling pathway in the treatment of basal cell carcinoma

OBJECTIVE

To review vismodegib, the first Food and Drug Administration (FDA)-approved Hedgehog (Hh) signaling pathway inhibitor, in the treatment of advanced basal cell carcinoma (BCC).

DATA SOURCES

MEDLINE and PubMed were searched using the terms vismodegib, GDC-0449, RG3616, and basal cell carcinoma for relevant clinical trials through September 2013. The FDA Web site, the National Clinical Trials registry, and abstracts from the American Society of Clinical Oncology (ASCO) were also evaluated to identify unpublished data and future clinical trials.

STUDY SELECTION/DATA EXTRACTION

All identified clinical and preclinical studies published in the English language were assessed, including selected references from the bibliographies of articles.

DATA SYNTHESIS

Activation of the Hh signaling pathway is well documented in BCC. Vismodegib is a small-molecule inhibitor of Hh signaling that acts by antagonizing the protein Smoothened (SMO), thereby preventing downstream transcriptional activation of genes involved in cell proliferation and survival. Vismodegib was approved by the FDA in January 2012 for the treatment of recurrent, locally advanced BCC (laBCC), or metastatic BCC (mBCC) for which surgery or radiation cannot be utilized. A pivotal phase 2 trial evaluating 104 patients demonstrated that treatment with vismodegib, 150 mg orally once daily, resulted in a 30% and 43% objective response rate in patients with mBCC and laBCC, respectively. The most common adverse effects from vismodegib were mild to moderate and included muscle spasms, dysgeusia, decreased weight, fatigue, alopecia, and diarrhea. However, clinical studies noted a high incidence of discontinuation of therapy by patients for reasons other than disease progression.

CONCLUSIONS

The approval of vismodegib represents the only targeted, prospectively studied treatment option for patients with advanced BCC. Further research assessing the utility of vismodegib in the treatment of other malignancies and the development of resistance patterns will more clearly define the role of Hedgehog inhibition in the broader scheme of oncological disorders.

Targeting sonic hedgehog-associated medulloblastoma through inhibition of Aurora and Polo-like kinases

Medulloblastoma is the most common malignant brain tumor in children. Although aggressive surgery, radiation, and chemotherapy have improved outcomes, survivors suffer severe long-term side effects, and many patients still succumb to their disease. For patients whose tumors are driven by mutations in the sonic hedgehog (SHH) pathway, SHH antagonists offer some hope. However, many SHH-associated medulloblastomas do not respond to these drugs, and those that do may develop resistance. Therefore, more effective treatment strategies are needed for both SHH and non-SHH-associated medulloblastoma. One such strategy involves targeting the cells that are critical for maintaining tumor growth, known as tumor-propagating cells (TPC). We previously identified a population of TPCs in tumors from patched mutant mice, a model for SHH-dependent medulloblastoma. These cells express the surface antigen CD15/SSEA-1 and have elevated levels of genes associated with the G2-M phases of the cell cycle. Here, we show that CD15(+) cells progress more rapidly through the cell cycle than CD15(-) cells and contain an increased proportion of cells in G2-M, suggesting that they might be vulnerable to inhibitors of this phase. Indeed, exposure of tumor cells to inhibitors of Aurora kinase (Aurk) and Polo-like kinases (Plk), key regulators of G2-M, induces cell-cycle arrest, apoptosis, and enhanced sensitivity to conventional chemotherapy. Moreover, treatment of tumor-bearing mice with these agents significantly inhibits tumor progression. Importantly, cells from human patient-derived medulloblastoma xenografts are also sensitive to Aurk and Plk inhibitors. Our findings suggest that targeting G2-M regulators may represent a novel approach for treatment of human medulloblastoma.

G-protein coupled receptor expression patterns delineate medulloblastoma subgroups

Background

Medulloblastoma is the most common malignant brain tumor in children. Genetic profiling has identified four principle tumor subgroups; each subgroup is characterized by different initiating mutations, genetic and clinical profiles, and prognoses. The two most well-defined subgroups are caused by overactive signaling in the WNT and SHH mitogenic pathways; less is understood about Groups 3 and 4 medulloblastoma. Identification of tumor subgroup using molecular classification is set to become an important component of medulloblastoma diagnosis and staging, and will likely guide therapeutic options. However, thus far, few druggable targets have emerged. G-protein coupled receptors (GPCRs) possess characteristics that make them ideal targets for molecular imaging and therapeutics; drugs targeting GPCRs account for 30-40% of all current pharmaceuticals. While expression patterns of many proteins in human medulloblastoma subgroups have been discerned, the expression pattern of GPCRs in medulloblastoma has not been investigated. We hypothesized that analysis of GPCR expression would identify clear subsets of medulloblastoma and suggest distinct GPCRs that might serve as molecular targets for both imaging and therapy.

Results

Our study found that medulloblastoma tumors fall into distinct clusters based solely on GPCR expression patterns. Normal cerebellum clustered separately from the tumor samples. Further, two of the tumor clusters correspond with high fidelity to the WNT and SHH subgroups of medulloblastoma. Distinct over-expressed GPCRs emerge; for example, LGR5 and GPR64 are significantly and uniquely over-expressed in the WNT subgroup of tumors, while PTGER4 is over-expressed in the SHH subgroup. Uniquely under-expressed GPCRs were also observed. Our key findings were independently validated using a large international dataset.

Conclusions

Our results identify GPCRs with potential to act as imaging and therapeutic targets. Elucidating tumorigenic pathways is a secondary benefit to identifying differential GPCR expression patterns in medulloblastoma tumors.

Targeting hedgehog signaling in cancer: research and clinical developments

Since its first description in Drosophila by Drs Nusslein-Volhard and Wieschaus in 1980, hedgehog (Hh) signaling has been implicated in regulation of cell differentiation, proliferation, tissue polarity, stem cell maintenance, and carcinogenesis. The first link of Hh signaling to cancer was established through studies of Gorlin syndrome in 1996 by two independent teams. Later, it was shown that Hh signaling may be involved in many types of cancer, including skin, leukemia, lung, brain, and gastrointestinal cancers. In early 2012, the US Food and Drug Administration approved the clinical use of Hh inhibitor Erivedge/vismodegib for treatment of locally advanced and metastatic basal cell carcinomas. With further investigation, it is possible to see more clinical applications of Hh signaling inhibitors. In this review, we will summarize major advances in the last 3 years in our understanding of Hh signaling activation in human cancer, and recent developments in preclinical and clinical studies using Hh signaling inhibitors.

Rhabdoid tumors: clinical approaches and molecular targets for innovative therapy

Rhabdoid tumors are rare but highly aggressive tumors with a predilection for infants and young children. The majority of these tumors harbor biallelic mutations in SMARCB1/INI1/hSNF5. Rather rare cases with mutations in other SWI/SNF core members such as BRG1 are on record. Rhabdoid tumors have only recently been registered and treated according to specifically designed treatment recommendations and in the framework of clinical trials. Within the last decade, prognosis has improved significantly but at least 50% of patients still relapse and subsequently almost inevitably succumb to their disease. This review summarizes past and current clinical approaches and presents an overview of the rationales for targeted therapy with potential for future clinical treatment trials for rhabdoid tumors.

Molecular neuro-oncology in clinical practice: a new horizon

Primary brain tumours are heterogeneous in histology, genetics, and outcome. Although WHO's classification of tumours of the CNS has greatly helped to standardise diagnostic criteria worldwide, it does not consider the substantial progress that has been made in the molecular classification of many brain tumours. Recent practice-changing clinical trials have defined a role for routine assessment of MGMT promoter methylation in glioblastomas in elderly people, and 1p and 19q codeletions in anaplastic oligodendroglial tumours. Moreover, large-scale molecular profiling approaches have identified new mutations in gliomas, affecting IDH1, IDH2, H3F3, ATRX, and CIC, which has allowed subclassification of gliomas into distinct molecular subgroups with characteristic features of age, localisation, and outcome. However, these molecular approaches cannot yet predict patients' benefit from therapeutic interventions. Similarly, transcriptome-based classification of medulloblastoma has delineated four variants that might now be candidate diseases in which to explore novel targeted agents.

Phase I study of vismodegib in children with recurrent or refractory medulloblastoma: a pediatric brain tumor consortium study

PURPOSE

To investigate the safety, dose-limiting toxicities, and pharmacokinetics of the smoothened inhibitor vismodegib in children with refractory or relapsed medulloblastoma.

EXPERIMENTAL DESIGN

Initially, vismodegib was administered daily at 85 mg/m(2) and escalated to 170 mg/m(2). The study was then revised to investigate a flat-dosing schedule of 150 mg for patients with small body surface area (BSA, 0.67-1.32 m(2)) or 300 mg for those who were larger (BSA, 1.33-2.20 m(2)). Pharmacokinetics were performed during the first course of therapy, and the right knees of all patients were imaged to monitor bone toxicity. Immunohistochemical analysis was done to identify patients with Sonic Hedgehog (SHH)-subtype medulloblastoma.

RESULTS

Thirteen eligible patients were enrolled in the initial study: 6 received 85 mg/m(2) vismodegib, and 7 received 170 mg/m(2). Twenty eligible patients were enrolled in the flat-dosing part of the study: 10 at each dosage level. Three dose-limiting toxicities were observed, but no drug-related bone toxicity was documented. The median (range) vismodegib penetration in the cerebrospinal fluid (CSF) was 0.53 (0.26-0.78), when expressed as a ratio of the concentration of vismodegib in the CSF to that of the unbound drug in plasma. Antitumor activity was seen in 1 of 3 patients with SHH-subtype disease whose tumors were evaluable, and in none of the patients in the other subgroups.

CONCLUSIONS

Vismodegib was well tolerated in children with recurrent or refractory medulloblastoma; only two dose-limiting toxicities were observed with flat dosing. The recommended phase II study dose is 150 or 300 mg, depending on the patient's BSA. Clin Cancer Res; 19(22); 6305-12. ©2013 AACR.

Current and future directions for Phase II trials in high-grade glioma

Despite surgery, radiation and chemotherapy, the prognosis for high-grade glioma (HGG) is poor. Our understanding of the molecular pathways involved in gliomagenesis and progression has increased in recent years, leading to the development of novel agents that specifically target these pathways. Results from most single-agent trials have been modest at best, however. Despite the initial success of antiangiogenesis agents in HGG, the clinical benefit is short-lived and most patients eventually progress. Several novel agents, multi-targeted agents and combination therapies are now in clinical trials for HGG and several more strategies are being pursued.

PCAF ubiquitin ligase activity inhibits Hedgehog/Gli1 signaling in p53-dependent response to genotoxic stress

The Hedgehog (Hh) signaling regulates tissue development, and its aberrant activation is a leading cause of malignancies, including medulloblastoma (Mb). Hh-dependent tumorigenesis often occurs in synergy with other mechanisms, such as loss of p53, the master regulator of the DNA damage response. To date, little is known about mechanisms connecting DNA-damaging events to morphogen-dependent processes. Here, we show that genotoxic stress triggers a cascade of signals, culminating with inhibition of the activity of Gli1, the final transcriptional effector of Hh signaling. This inhibition is dependent on the p53-mediated elevation of the acetyltransferase p300/CBP-associated factor (PCAF). Notably, we identify PCAF as a novel E3 ubiquitin ligase of Gli1. Indeed PCAF, but not a mutant with a deletion of its ubiquitination domain, represses Hh signaling in response to DNA damage by promoting Gli1 ubiquitination and its proteasome-dependent degradation. Restoring Gli1 levels rescues the growth arrest and apoptosis effect triggered by genotoxic drugs. Consistently, DNA-damaging agents fail to inhibit Gli1 activity in the absence of either p53 or PCAF. Finally, Mb samples from p53-null mice display low levels of PCAF and upregulation of Gli1 in vivo, suggesting PCAF as potential therapeutic target in Hh-dependent tumors. Together, our data define a mechanism of inactivation of a morphogenic signaling in response to genotoxic stress and unveil a p53/PCAF/Gli1 circuitry centered on PCAF that limits Gli1-enhanced mitogenic and prosurvival response.

Hedgehog pathway modulation by multiple lipid binding sites on the smoothened effector of signal response

Hedgehog (Hh) signaling during development and in postembryonic tissues requires activation of the 7TM oncoprotein Smoothened (Smo) by mechanisms that may involve endogenous lipidic modulators. Exogenous Smo ligands previously identified include the plant sterol cyclopamine (and its therapeutically useful synthetic mimics) and hydroxylated cholesterol derivatives (oxysterols); Smo is also highly sensitive to cellular sterol levels. The relationships between these effects are unclear because the relevant Smo structural determinants are unknown. We identify the conserved extracellular cysteine-rich domain (CRD) as the site of action for oxysterols on Smo, involving residues structurally analogous to those contacting the Wnt lipid adduct in the homologous Frizzled CRD; this modulatory effect is distinct from that of cyclopamine mimics, from Hh-mediated regulation, and from the permissive action of cellular sterol pools. These results imply that Hh pathway activity is sensitive to lipid binding at several Smo sites, suggesting mechanisms for tuning by multiple physiological inputs.

Inhibition of Hedgehog signaling in the gastrointestinal tract: targeting the cancer microenvironment

This review summarizes emerging information regarding the Hedgehog (Hh) signaling pathway during neoplastic transformation in the gastrointestinal tract. Although there is a role for the well-established canonical pathway in which Hedgehog ligands interact with their receptor Patched, there is sufficient evidence that downstream components of the Hh pathway, e.g., Gli1, are hijacked by non-Hh signaling pathways to promote the conversion of the epithelium to dysplasia and carcinoma. We review the canonical pathway and involvement of primary cilia, and then focus on current evidence for Hh signaling in luminal bowel cancers as well as accessory organs, i.e., liver, pancreas and biliary ducts. We conclude that targeting the Hh pathway with small molecules, nutriceuticals and other mechanisms will likely require a combination of inhibitors that target Gli transcription factors in addition to canonical modulators such as Smoothened.

Neuronal differentiation associated with Gli3 expression predicts favorable outcome for patients with medulloblastoma

Medulloblastoma (MB) is a malignant cerebellar tumor arising in children, and its ontogenesis is regulated by Sonic Hedgehog (Shh) signaling. No data are available regarding the correlation between expression of Gli3, a protein lying downstream of Shh, and neuronal differentiation of MB cells, or the prognostic significance of these features. We re-evaluated the histopathological features of surgical specimens of MB taken from 32 patients, and defined 15 of them as MB with neuronal differentiation (ND), three as MB with both glial and neuronal differentiation (GD), and 14 as differentiation-free (DF) MB. Gli3-immunoreactivity (IR) was evident as a clear circular stain outlining the nuclei of the tumor cells. The difference in the frequency of IR between the ND+GD (94.4%) and DF (0%) groups was significant (P < 0.001). The tumor cells with ND showed IR for both Gli3 and neuronal nuclei. Ultrastructurally, Gli3-IR was observed at the nuclear membrane. The overall survival and event-free survival rates of the patients in the ND group were significantly higher than those in the other groups. The expression profile of Gli3 is of considerable significance, and the association of ND with this feature may be prognostically favorable in patients with MB.

Structural and logical analysis of a comprehensive hedgehog signaling pathway to identify alternative drug targets for glioma, colon and pancreatic cancer

Hedgehog is an evolutionarily conserved developmental pathway, widely implicated in controlling various cellular responses such as cellular proliferation and stem cell renewal in human and other organisms, through external stimuli. Aberrant activation of this pathway in human adult stem cell line may cause different types of cancers. Hence, targeting this pathway in cancer therapy has become indispensable, but the non availability of detailed molecular interactions, complex regulations by extra- and intra-cellular proteins and cross talks with other pathways pose a serious challenge to get a coherent understanding of this signaling pathway for making therapeutic strategy. This motivated us to perform a computational study of the pathway and to identify probable drug targets. In this work, from available databases and literature, we reconstructed a complete hedgehog pathway which reports the largest number of molecules and interactions to date. Using recently developed computational techniques, we further performed structural and logical analysis of this pathway. In structural analysis, the connectivity and centrality parameters were calculated to identify the important proteins from the network. To capture the regulations of the molecules, we developed a master Boolean model of all the interactions between the proteins and created different cancer scenarios, such as Glioma, Colon and Pancreatic. We performed perturbation analysis on these cancer conditions to identify the important and minimal combinations of proteins that can be used as drug targets. From our study we observed the under expressions of various oncoproteins in Hedgehog pathway while perturbing at a time the combinations of the proteins GLI1, GLI2 and SMO in Glioma; SMO, HFU, ULK3 and RAS in Colon cancer; SMO, HFU, ULK3, RAS and ERK12 in Pancreatic cancer. This reconstructed Hedgehog signaling pathway and the computational analysis for identifying new combinatory drug targets will be useful for future in-vitro and in-vivo analysis to control different cancers.

Management of recurrent medulloblastoma in adult patients: a systematic review and recommendations

Medulloblastoma accounts for almost one-third of pediatric central nervous system (CNS) cancers, but is very rare in the adult population. As a result, adult patients with medulloblastoma are often treated according to therapies developed for children with similarly staged disease at diagnosis, based on the assumption that adult and pediatric tumors have similar properties. The purpose of this review was to summarize the evidence and to make recommendations for the management of recurrent disease in adult patients with medulloblastoma. We conducted a systematic literature search to find publications addressing treatment of recurrent medulloblastoma in adults. Current treatment strategies for adult patients with relapsed medulloblastoma are based on the results of retrospective case series and published consensus recommendations, and include maximal safe re-resection where possible, combined with chemotherapy and/or re-irradiation. We describe the results of 13 publications involving 66 adult patients treated with high-dose chemotherapy (HDCT) plus stem cell transplantation for recurrent medulloblastoma. HDCT with stem cell transplantation may be a treatment option for a small proportion of adult patients who are unlikely to benefit from conventional chemotherapy and who are fit and have their disease recurrence contained within the CNS. Potential cases in which stem cell transplantation is being considered should be discussed at a multidisciplinary tumor board which includes involvement by hematologic oncologists and transplant specialists.

Arsenic trioxide prevents osteosarcoma growth by inhibition of GLI transcription via DNA damage accumulation

The Hedgehog pathway is activated in various types of malignancies. We previously reported that inhibition of SMO or GLI prevents osteosarcoma growth in vitro and in vivo. Recently, it has been reported that arsenic trioxide (ATO) inhibits cancer growth by blocking GLI transcription. In this study, we analyzed the function of ATO in the pathogenesis of osteosarcoma. Real-time PCR showed that ATO decreased the expression of Hedgehog target genes, including PTCH1, GLI1, and GLI2, in human osteosarcoma cell lines. WST-1 assay and colony formation assay revealed that ATO prevented osteosarcoma growth. These findings show that ATO prevents GLI transcription and osteosarcoma growth in vitro. Flow cytometric analysis showed that ATO promoted apoptotic cell death. Comet assay showed that ATO treatment increased accumulation of DNA damage. Western blot analysis showed that ATO treatment increased the expression of γH2AX, cleaved PARP, and cleaved caspase-3. In addition, ATO treatment decreased the expression of Bcl-2 and Bcl-xL. These findings suggest that ATO treatment promoted apoptotic cell death caused by accumulation of DNA damage. In contrast, Sonic Hedgehog treatment decreased the expression of γH2AX induced by cisplatin treatment. ATO re-induced the accumulation of DNA damage attenuated by Sonic Hedgehog treatment. These findings suggest that ATO inhibits the activation of Hedgehog signaling and promotes apoptotic cell death in osteosarcoma cells by accumulation of DNA damage. Finally, examination of mouse xenograft models showed that ATO administration prevented the growth of osteosarcoma in nude mice. Because ATO is an FDA-approved drug for treatment of leukemia, our findings suggest that ATO is a new therapeutic option for treatment of patients with osteosarcoma.

Hedgehog signaling in prostate cancer and its therapeutic implication

Activation of Hedgehog (Hh) signaling is implicated in the development and progression of several tumor types, including prostate cancer, which is still the most common non-skin malignancy and the third leading cause of cancer-related mortality in men in industrialized countries worldwide. Several studies have indicated that the Hh pathway plays a crucial role in the development as well as in the progression of this disease to more aggressive and even therapy-resistant disease states. Moreover, preclinical data have shown that inhibition of Hh signaling has the potential to reduce prostate cancer invasiveness and metastatic potential. Clinical trials investigating the benefit of Hh inhibitors in patients with prostate cancer have recently been initiated. However, acquired drug resistance has already been observed in other tumor types after long-term Hh inhibition. Therefore, combining Hh inhibitors with ionizing radiation, chemotherapy or other molecular targeted agents could represent an alternative therapeutic strategy. In this review, we will highlight the role of Hh signaling in the development and progression of prostate cancer and summarize the different therapeutic applications of Hedgehog inhibition.

Brain tumor stem cells: Molecular characteristics and their impact on therapy

Glioblastoma (GBM) is the most prevalent primary brain tumor and ranks among the most lethal of human cancers with conventional therapy offering only palliation. Great strides have been made in understanding brain cancer genetics and modeling these tumors with new targeted therapies being tested, but these advances have not translated into substantially improved patient outcomes. Multiple chemotherapeutic agents, including temozolomide, the first-line treatment for glioblastoma, have been developed to kill cancer cells. However, the response to temozolomide in GBM is modest. Radiation is also moderately effective but this approach is plagued by limitations due to collateral radiation damage to healthy brain tissue and development of radioresistance. Therapeutic resistance is attributed at least in part to a cell population within the tumor that possesses stem-like characteristics and tumor propagating capabilities, referred to as cancer stem cells. Within GBM, the intratumoral heterogeneity is derived from a combination of regional genetic variance and a cellular hierarchy often regulated by distinct cancer stem cell niches, most notably perivascular and hypoxic regions. With the recent emergence as a key player in tumor biology, cancer stem cells have symbiotic relationships with the tumor microenvironment, oncogenic signaling pathways, and epigenetic modifications. The origins of cancer stem cells and their contributions to brain tumor growth and therapeutic resistance are under active investigation with novel anti-cancer stem cell therapies offering potential new hope for this lethal disease.

The histone deacetylase inhibitor SAHA acts in synergism with fenretinide and doxorubicin to control growth of rhabdoid tumor cells

BACKGROUND

Rhabdoid tumors are highly aggressive malignancies affecting infants and very young children. In many instances these tumors are resistant to conventional type chemotherapy necessitating alternative approaches.

METHODS

Proliferation assays (MTT), apoptosis (propidium iodide/annexin V) and cell cycle analysis (DAPI), RNA expression microarrays and western blots were used to identify synergism of the HDAC (histone deacetylase) inhibitor SAHA with fenretinide, tamoxifen and doxorubicin in rhabdoidtumor cell lines.

RESULTS

HDAC1 and HDAC2 are overexpressed in primary rhabdoid tumors and rhabdoid tumor cell lines. Targeting HDACs in rhabdoid tumors induces cell cycle arrest and apoptosis. On the other hand HDAC inhibition induces deregulated gene programs (MYCC-, RB program and the stem cell program) in rhabdoid tumors. These programs are in general associated with cell cycle progression. Targeting these activated pro-proliferative genes by combined approaches of HDAC-inhibitors plus fenretinide, which inhibits cyclinD1, exhibit strong synergistic effects on induction of apoptosis. Furthermore, HDAC inhibition sensitizes rhabdoid tumor cell lines to cell death induced by chemotherapy.

CONCLUSION

Our data demonstrate that HDAC inhibitor treatment in combination with fenretinide or conventional chemotherapy is a promising tool for the treatment of chemoresistant rhabdoid tumors.

Daily dosing of vismodegib to steady state does not prolong the QTc interval in healthy volunteers

INTRODUCTION

Vismodegib was assessed as being of low risk for QT interval prolongation based on prior nonclinical and clinical experience. A dedicated study was conducted to further assess the potential for vismodegib to prolong the QTc interval.

METHODS AND RESULTS

Given the nonlinear pharmacokinetics of vismodegib, a thorough QTc study as is typically designed was not possible, and an innovative design was employed. This dedicated QTc study was powered to exclude a 20-millisecond change from the baseline QTc interval. The subjects were administered daily oral 150 mg of vismodegib for 7 days, or a single dose of 400 mg of moxifloxacin, with corresponding matching placebos. The upper limits of the 90% confidence intervals for the difference in ΔQTcF between vismodegib and placebo at steady state were <20 milliseconds at all timepoints with a maximum of 10 milliseconds at 12 hours postdose. Exposure-response analysis yielded an estimated slope equal to 0.11 ms/μM, which was not statistically significant. After a single dose of moxifloxacin was administered, the lower limits of the 90% confidence interval of the difference in ΔQTcF between moxifloxacin and placebo were >5 milliseconds from 1-12 hours postdose, thereby establishing assay sensitivity.

CONCLUSIONS

There was no effect of vismodegib on the QTc interval when dosed daily at 150 mg to steady state.

Advanced basal cell carcinoma of the skin: targeting the hedgehog pathway

PURPOSE OF REVIEW

This article provides an update on basal cell carcinoma (BCC), with a focus on the advanced BCC (aBCC), and the recent progress with targeted hedgehog signaling pathway inhibition for treatment of aBCC.

RECENT FINDINGS

The hedgehog signaling pathway is aberrantly activated in most BCC tumors providing an attractive therapeutic target in this cancer. Recently developed targeted hedgehog pathway inhibitors have demonstrated remarkable efficacy in the treatment of aBCC and the first oral hedgehog pathway inhibitor vismodegib was granted the US Food and Drug Administration (FDA) approval. Toxicities of the current hedgehog pathway inhibitors are mostly mild to moderate, but with prolonged treatment can pose a therapeutic challenge.

SUMMARY

Hedgehog pathway inhibition is a novel and powerful approach for treatment of aBCC. Current research efforts aim to enhance the activity and minimize toxicity of this promising new therapy.

Children's Oncology Group's 2013 blueprint for research: central nervous system tumors

In the US, approximately 2,500 children are diagnosed annually with brain tumors. Their survival ranges from >90% to <10%. For children with medulloblastoma, the most common malignant brain tumor, 5-year survival ranges from >80% (standard-risk) to 60% (high-risk). For those with high-grade gliomas (HGGs) including diffuse intrinsic pontine gliomas, 5-year survival remains <10%. Sixty-five percent patients with ependymoma are cured after surgery and radiation therapy depending on the degree of resection and histopathology of the tumor. Phase II trials for brain tumors will investigate agents that act on cMET, PDGFRA, or EZH2 in HGG, DIPG, or medulloblastoma, respectively. Phase III trials will explore risk-based therapy stratification guided by molecular and clinical traits of children with medulloblastoma or ependymoma.

The Hedgehog inhibitor cyclopamine impairs the benefits of immunotherapy with activated T and NK lymphocytes derived from patients with advanced cancer

Hedgehog (Hh) signaling is activated in various types of cancer and contributes to the progression, proliferation, and invasiveness of cancer cells. Many Hh inhibitors are undergoing clinical trial and show promise as anticancer drugs. Hh signaling is also induced in the activated T and NK (TNK) lymphocytes that are used in immunotherapy. Activated TNK lymphocyte therapy is anticipated to work well within a tumor's hypoxic environment. However, most studies on the immunobiological functions of activated TNK lymphocytes have been conducted on healthy donor samples, under normoxic conditions. In the present study, we evaluated the effects of Hh inhibition and oxygen concentrations on the function of activated TNK lymphocytes derived from patients with advanced cancer. Proliferation, migration, surface NKG2D expression, and cytotoxicity were all significantly inhibited, and IFN-γ secretion was significantly increased upon Hh inhibitor treatment of activated TNK lymphocytes under hypoxic conditions in vitro. Tumors from mice injected with cyclopamine-treated activated TNK lymphocytes showed a significant increase in tumor size and had fewer apoptotic cells compared with the tumors in mice injected with control activated TNK lymphocytes. These results suggest that Hh signaling plays a pivotal role in activated TNK lymphocyte cell function. Combination therapy using Hh inhibitors and activated TNK lymphocytes derived from patients with advanced cancer may not be advantageous.

Tumor prognostic factors and the challenge of developing predictive factors

Histopathologic classification has been widely used to type and grade primary brain tumors. However, the diverse behavior of primary brain tumors has made prognostic determinations based purely on clinical and histopathologic variables difficult. Recent advances in the molecular genetics of brain tumors have helped to explain the witnessed heterogeneity regarding response to treatment, time to progression, and overall survival. Additionally, there has been interest in identifying predictive factors to help direct patients to therapeutic interventions specific to their tumor and patient biology. Further identification of both prognostic and predictive biomarkers will make possible better patient stratification and individualization of treatment.

The KDM1A histone demethylase is a promising new target for the epigenetic therapy of medulloblastoma

Background

Medulloblastoma is a leading cause of childhood cancer-related deaths. Current aggressive treatments frequently lead to cognitive and neurological disabilities in survivors. Novel targeted therapies are required to improve outcome in high-risk medulloblastoma patients and quality of life of survivors. Targeting enzymes controlling epigenetic alterations is a promising approach recently bolstered by the identification of mutations in histone demethylating enzymes in medulloblastoma sequencing efforts. Hypomethylation of lysine 4 in histone 3 (H3K4) is also associated with a dismal prognosis for medulloblastoma patients. Functional characterization of important epigenetic key regulators is urgently needed.

Results

We examined the role of the H3K4 modifying enzyme, KDM1A, in medulloblastoma, an enzyme also associated with malignant progression in the closely related tumor, neuroblastoma. Re-analysis of gene expression data and immunohistochemistry of tissue microarrays of human medulloblastomas showed strong KDM1A overexpression in the majority of tumors throughout all molecular subgroups. Interestingly, KDM1A knockdown in medulloblastoma cell lines not only induced apoptosis and suppressed proliferation, but also impaired migratory capacity. Further analyses revealed bone morphogenetic protein 2 (BMP2) as a major KDM1A target gene. BMP2 is known to be involved in development and differentiation of granule neuron precursor cells (GNCPs), one potential cell of origin for medulloblastoma. Treating medulloblastoma cells with the specific KDM1A inhibitor, NCL-1, significantly inhibited growth in vitro.

Conclusion

We provide the first evidence that a histone demethylase is functionally involved in the regulation of the malignant phenotype of medulloblastoma cells, and lay a foundation for future evaluation of KDM1A-inihibiting therapies in combating medulloblastoma.

Current therapeutic strategies and novel approaches in osteosarcoma

Osteosarcoma is the most frequent malignant primary bone tumor and a main cause of cancer-related death in children and adolescents. Although long-term survival in localized osteosarcoma has improved to about 60% during the 1960s and 1970s, long-term survival in both localized and metastatic osteosarcoma has stagnated in the past several decades. Thus, current conventional therapy consists of multi-agent chemotherapy, surgery and radiation, which is not fully adequate for osteosarcoma treatment. Innovative drugs and approaches are needed to further improve outcome in osteosarcoma patients. This review describes the current management of osteosarcoma as well as potential new therapies.

The Hedgehog inhibitor suppresses the function of monocyte-derived dendritic cells from patients with advanced cancer under hypoxia

Immunotherapy using monocyte derived dendritic cells (Mo-DCs) from cancer patients has been developed; however, the Mo-DCs regularly studied have been derived from non-cancer bearing donors or mice, and evaluated in normoxic conditions. In the present study, we investigated the effects of Hedgehog (Hh) inhibitors which are being developed as molecular target drugs for cancer on the functions of Mo-DCs derived from patients with advanced cancer when cultured in a tumor-like hypoxic environment. Mo-DC induction, migration, chemotaxis, phagocytosis, maturation, IL-12 p40 or p70 secretion and the allogeneic lymphocyte stimulation activity of Mo-DCs from patients with advanced cancer were all significantly inhibited by the Hh inhibitor, cyclopamine under hypoxic conditions. Our results suggest that Hh signaling plays an important role in the maintenance and function of Mo-DCs derived from patients with advanced cancer when cultured under hypoxic conditions.

Targeting Gli transcription activation by small molecule suppresses tumor growth

Targeted inhibition of Hedgehog signaling at the cell membrane has been associated with anti-cancer activity in preclinical and early clinical studies. Hedgehog signaling involves activation of Gli transcription factors that can also be induced by alternative pathways. In this study we identified an interaction between Gli proteins and a transcription co-activator TAF9, and validated its functional relevance in regulating Gli transactivation. We also describe a novel, synthetic small molecule, FN1-8, that efficiently interferes with Gli/TAF9 interaction and down-regulate Gli/TAF9 dependent transcriptional activity. More importantly, FN1-8 suppresses cancer cell proliferation in vitro and inhibits tumor growth in vivo. Our results suggest that blocking Gli transactivation, a key control point of multiple oncogenic pathways, may be an effective anti-cancer strategy.

Medulloblastoma biology in the post-genomic era

Medulloblastomas, the most common malignant pediatric brain tumors, are comprised of four molecularly distinct subtypes. However, treatment has yet to exploit these molecular vulnerabilities. Three recent studies sequenced a total of 310 primary tumors and identified that two of the four medulloblastoma subtypes are concomitantly associated with subtype-specific mutations as previously characterized. In contrast, the overwhelming majority of mutations occurred only once in the entire cohort and just 12 genes were recurrently mutated with statistical significance. Perturbations in epigenetic regulation are emerging as a unifying theme in cancer and similarly recurring mutations in epigenetic mechanisms were distributed across all subtypes in medulloblastoma. Designing targeted therapies to such a molecularly diverse disease in the post-genomic era presents new challenges. This will require novel methods to link these nonrecurrent mutations into pathways, and preclinical models that faithfully recapitulate patient driver events. Presently, medulloblastoma reinforces epigenetic mechanisms as a tantalizing therapeutic target in cancers.

Genomic Medicine Frontier in Human Solid Tumors: Prospects and Challenges

Recent discoveries of genomic alterations that underlie and promote the malignant phenotype, together with an expanded repertoire of targeted agents, have provided many opportunities to conduct hypothesis-driven clinical trials. The ability to profile each unique cancer for actionable aberrations by using high-throughput technologies in a cost-effective way provides unprecedented opportunities for using matched therapies in a selected patient population. The major challenges are to integrate and make biologic sense of the substantial genomic data derived from multiple platforms. We define two different approaches for the analysis, interpretation, and clinical applicability of genomic data: (1) the genomically stratified model originates from the “one test-one drug” paradigm and is currently being expanded with an upfront multicategorical approach following recent advances in multiplexed genotyping platforms; and (2) the comprehensive assessment model is based on whole-genome, -exome, and -transcriptome data and allows identification of novel drivers and subsequent therapies in the experimental setting. Tumor heterogeneity and evolution of the diverse populations of cancer cells during cancer progression, influenced by the effects of systemic treatments, will need to be addressed in the new scenario of early drug development. Logistical issues related to prescreening strategies and trial allocation, in addition to concerns in the economic and ethical domains, must be taken into consideration. Here we present a historical view of how increased understanding of cancer genomics has been translated to the clinic and discuss the prospects and challenges for further implementation of a personalized treatment strategy for human solid tumors.

Future of Clinical Genomics in Pediatric Oncology

The somatic genomic alterations in pediatric cancers to some extent overlap with those seen in adult cancers, but the exact distribution throughout the genome and the types and frequency of alterations differ. The ultimate goal of genomic research in children, as with adults, is translation to the clinic to achieve more accurate diagnosis, more precise risk stratification, and more effective, less toxic therapy. The genomic features of pediatric malignancies and pediatric-specific issues in clinical investigation may make translating genomic discoveries to the clinic more difficult. However, through large-scale molecular profiling of pediatric tumors, continued coordinated efforts to evaluate novel therapies in the pediatric population, thoughtful phase II and III trial design, and continued drug development, genomically based therapies will become more common in the pediatric oncology clinic in the future.

The dawn of hedgehog inhibitors: Vismodegib

Cancer, one of the leading causes of death worldwide is estimated to increase to approximately 13.1 million by 2030. This has amplified the research in oncology towards the exploration of novel targets. Recently there has been lots of interest regarding the hedgehog (Hh) pathway, which plays a significant role in the development of organs and tissues during embryonic and postnatal periods. In a normal person, the Hh signaling pathway is under inhibition and gets activated upon the binding of Hh ligand to a transmembrane receptor called Patched (PTCH1) thus allowing the transmembrane protein, smoothened (SMO) to transfer signals through various proteins. One of the newer drugs namely vismodegib involves the inhibition of Hh pathway and has shown promising results in the treatment of advanced basal-cell carcinoma as well as medulloblastoma. It has been granted approval by US Food and Drug Administration's (US FDA) priority review program on January 30, 2012 for the treatment of advanced basal-cell carcinoma. The drug is also being evaluated in malignancies like medulloblastoma, pancreatic cancer, multiple myeloma, chondrosarcoma and prostate cancer. Moreover various Hh inhibitors namely LDE 225, saridegib, BMS 833923, LEQ 506, PF- 04449913 and TAK-441 are also undergoing phase I and II trials for different neoplasms. Hence this review will describe briefly the Hh pathway and the novel drug vismodegib.

TAK-441, a novel investigational smoothened antagonist, delays castration-resistant progression in prostate cancer by disrupting paracrine hedgehog signaling

Hedgehog (Hh) signaling is a highly conserved intercellular and intracellular communication mechanism that governs organogenesis and is dysregulated in cancers of numerous tissues, including prostate. Up-regulated expression of the Hh ligands, Sonic (Shh) and Desert (Dhh), has been reported in androgen-deprived and castration-resistant prostate cancer (CRPC). In a cohort of therapy naive, short- and long-term neoadjuvant hormone therapy-treated (NHT), and CRPC specimens, we observed elevated Dhh expression predominantly in long-term NHT specimens and elevated Shh expression predominantly in CRPC specimens. Together with previously demonstrated reciprocal signaling between Shh-producing prostate cancer (PCa) cells and urogenital mesenchymal fibroblasts, these results suggest that castration-induced Hh expression promotes CRPC progression through reciprocal paracrine signaling within the tumor microenvironment. We tested whether the orally available Smoothened (Smo) antagonist, TAK-441, could impair castration-resistant progression of LNCaP PCa xenografts by disrupting paracrine Hh signaling. Although TAK-441 or cyclopamine did not affect androgen withdrawal-induced Shh up-regulation or viability of LNCaP cells, castration-resistant progression of LNCaP xenografts was significantly delayed in animals treated with TAK-441. In TAK-441-treated xenografts, expression of murine orthologs of the Hh-activated genes, Gli1, Gli2 and Ptch1, was substantially suppressed, while expression of the corresponding human orthologs was unaffected. As androgen-deprived LNCaP cells up-regulate Shh expression, but are not sensitive to Smo antagonists, these studies indicate that TAK-441 leads to delayed castration-resistant progression of LNCaP xenografts by disrupting paracrine Hh signaling with the tumor stroma. Thus, paracrine Hh signaling may offer unique opportunities for prognostic biomarker development, drug targeting and therapeutic response monitoring of PCa progression.

Hypoxia triggers hedgehog-mediated tumor-stromal interactions in pancreatic cancer

Pancreatic cancer is characterized by a desmoplastic reaction that creates a dense fibroinflammatory microenvironment, promoting hypoxia and limiting cancer drug delivery due to decreased blood perfusion. Here, we describe a novel tumor-stroma interaction that may help explain the prevalence of desmoplasia in this cancer. Specifically, we found that activation of hypoxia-inducible factor-1α (HIF-1α) by tumor hypoxia strongly activates secretion of the sonic hedgehog (SHH) ligand by cancer cells, which in turn causes stromal fibroblasts to increase fibrous tissue deposition. In support of this finding, elevated levels of HIF-1α and SHH in pancreatic tumors were determined to be markers of decreased patient survival. Repeated cycles of hypoxia and desmoplasia amplified each other in a feed forward loop that made tumors more aggressive and resistant to therapy. This loop could be blocked by HIF-1α inhibition, which was sufficient to block SHH production and hedgehog signaling. Taken together, our findings suggest that increased HIF-1α produced by hypoxic tumors triggers the desmoplasic reaction in pancreatic cancer, which is then amplified by a feed forward loop involving cycles of decreased blood flow and increased hypoxia. Our findings strengthen the rationale for testing HIF inhibitors and may therefore represent a novel therapeutic option for pancreatic cancer.

Prolonged inhibition of glioblastoma xenograft initiation and clonogenic growth following in vivo Notch blockade

PURPOSE

To examine the effects of clinically relevant pharmacologic Notch inhibition on glioblastoma xenografts.

EXPERIMENTAL DESIGN

Murine orthotopic xenografts generated from temozolomide-sensitive and -resistant glioblastoma neurosphere lines were treated with the γ-secretase inhibitor MRK003. Tumor growth was tracked by weekly imaging, and the effects on animal survival and tumor proliferation were assessed, along with the expression of Notch targets, stem cell, and differentiation markers, and the biology of neurospheres isolated from previously treated xenografts and controls.

RESULTS

Weekly MRK003 therapy resulted in significant reductions in growth as measured by imaging, as well as prolongation of survival. Microscopic examination confirmed a statistically significant reduction in cross-sectional tumor area and mitotic index in a MRK003-treated cohort as compared with controls. Expression of multiple Notch targets was reduced in the xenografts, along with neural stem/progenitor cell markers, whereas glial differentiation was induced. Neurospheres derived from MRK003-treated xenografts exhibited reduced clonogenicity and formed less aggressive secondary xenografts. Neurospheres isolated from treated xenografts remained sensitive to MRK003, suggesting that therapeutic resistance does not rapidly arise during in vivo Notch blockade.

CONCLUSIONS

Weekly oral delivery of MRK003 results in significant in vivo inhibition of Notch pathway activity, tumor growth, stem cell marker expression, and clonogenicity, providing preclinical support for the use of such compounds in patients with malignant brain tumors. Some of these effects can persist for some time after in vivo therapy is complete.

Targeting placental growth factor/neuropilin 1 pathway inhibits growth and spread of medulloblastoma

Medulloblastoma is the most common pediatric malignant brain tumor. Although current therapies improve survival, these regimens are highly toxic and are associated with significant morbidity. Here, we report that placental growth factor (PlGF) is expressed in the majority of medulloblastomas, independent of their subtype. Moreover, high expression of PlGF receptor neuropilin 1 (Nrp1) correlates with poor overall survival in patients. We demonstrate that PlGF and Nrp1 are required for the growth and spread of medulloblastoma: PlGF/Nrp1 blockade results in direct antitumor effects in vivo, resulting in medulloblastoma regression, decreased metastasis, and increased mouse survival. We reveal that PlGF is produced in the cerebellar stroma via tumor-derived Sonic hedgehog (Shh) and show that PlGF acts through Nrp1-and not vascular endothelial growth factor receptor 1-to promote tumor cell survival. This critical tumor-stroma interaction-mediated by Shh, PlGF, and Nrp1 across medulloblastoma subtypes-supports the development of therapies targeting PlGF/Nrp1 pathway.

Pharmacokinetics and pharmacodynamics of sunitinib for the treatment of advanced pancreatic neuroendocrine tumors

INTRODUCTION

Despite being the second most common malignancy of the pancreas, pancreatic neuroendocrine tumors (PNET) have long been understudied due to their low incidence and heterogeneous clinical presentation. Emerging data from a Phase III trial demonstrates improved progression-free survival of patients with advanced PNET on treatment with sunitinib .

AREAS COVERED

This article reviews the role of sunitinib, a multitargeted tyrosine kinase inhibitor with potent antiangiogenic and antitumor effects, in the clinical management of PNET. Furthermore, the authors also discuss the pharmacokinetics and pharmacodynamics as well as other clinically relevant aspects regarding sunitinib.

EXPERT OPINION

A recent Phase III clinical trial of sunitinib demonstrated significant improvement of progression-free survival in patients with advanced or metastatic well-differentiated PNET that led to its approval in several countries, including Europe and United States. This marks a significant step forward in the clinical management of this disease and spurs hopes to further improve overall survival in this once difficult-to-treat set of patients in the coming years. Fields of future interest will include evaluation of combinatorial regimens, including conventional cytotoxic agents as well as additional targeted drugs in order to overcome resistance to sunitinib.

Drugging Hedgehog: signaling the pathway to translation

First discovered in Drosophila, the Hedgehog signaling pathway controls a wide range of developmental processes and is implicated in a variety of cancers. The success of a screen for chemical modulators of this pathway, published in 2002, opened a new chapter in the quest to translate the results of basic developmental biology research into therapeutic applications. Small molecule pathway agonists are now used to program stem cells, whilst antagonists are proving effective as anti-cancer therapies.

Menin epigenetically represses Hedgehog signaling in MEN1 tumor syndrome

Multiple endocrine neoplasia type 1 (MEN1) is an inherited tumor syndrome that includes susceptibility to pancreatic islet tumors. This syndrome results from mutations in the MEN1 gene, encoding menin. Although menin acts as an oncogenic cofactor for mixed lineage leukemia (MLL) fusion protein-mediated histone H3 lysine 4 methylation, the precise basis for how menin suppresses gene expression and proliferation of pancreatic beta cells remains poorly understood. Here, we show that menin ablation enhances Hedgehog signaling, a proproliferative and oncogenic pathway, in murine pancreatic islets. Menin directly interacts with protein arginine methyltransferase 5 (PRMT5), a negative regulator of gene transcription. Menin recruits PRMT5 to the promoter of the Gas1 gene, a crucial factor for binding of Sonic Hedgehog (Shh) ligand to its receptor PTCH1 and subsequent activation of the Hedgehog signaling pathway, increases repressive histone arginine symmetric dimethylation (H4R3m2s), and suppresses Gas1 expression. Notably, MEN1 disease-related menin mutants have reduced binding to PRMT5, and fail to impart the repressive H4R3m2s mark at the Gas1 promoter, resulting in its elevated expression. Pharmacologic inhibition of Hedgehog signaling significantly reduces proliferation of insulinoma cells, and expression of Hedgehog signaling targets including Ptch1, in MEN1 tumors of mice. These findings uncover a novel link between menin and Hedgehog signaling whereby menin/PRMT5 epigenetically suppresses Hedgehog signaling, revealing it as a target for treating MEN1 tumors.

Transcriptional regulation of serine/threonine protein kinase (AKT) genes by glioma-associated oncogene homolog 1

Aberrant activation of Hedgehog signaling has been described in a growing number of cancers, including malignant lymphomas. Here, we report that canonical Hedgehog signaling modulates the transcriptional expression of AKT genes and that AKT1 is a direct transcriptional target of GLI1. We identified two putative binding sites for GLI1 in the AKT1 promoter region and confirmed their functionality using chromatin immunoprecipitation, luciferase reporter, and site-directed mutagenesis assays. Moreover, we provide evidence that GLI1 contributes to the survival of diffuse large B-cell lymphoma (DLBCL) cells and that this effect occurs in part through promotion of the transcription of AKT genes. This finding is of interest as constitutive activation of AKT has been described in DLBCL, but causative factors that explain AKT expression in this lymphoma type are not completely known. In summary, we demonstrated the existence of a novel cross-talk at the transcriptional level between Hedgehog signaling and AKT with biological significance in DLBCL.

The unfolded protein response selectively targets active smoothened mutants

The Hedgehog signaling pathway, an essential regulator of developmental patterning, has been implicated in playing causative and survival roles in a range of human cancers. The signal-transducing component of the pathway, Smoothened, has revealed itself to be an efficacious therapeutic target in combating oncogenic signaling. However, therapeutic challenges remain in cases where tumors acquire resistance to Smoothened antagonists, and also in cases where signaling is driven by active Smoothened mutants that exhibit reduced sensitivity to these compounds. We previously demonstrated that active Smoothened mutants are subjected to prolonged endoplasmic reticulum (ER) retention, likely due to their mutations triggering conformation shifts that are detected by ER quality control. We attempted to exploit this biology and demonstrate that deregulated Hedgehog signaling driven by active Smoothened mutants is specifically attenuated by ER stressors that induce the unfolded protein response (UPR). Upon UPR induction, active Smoothened mutants are targeted by ER-associated degradation, resulting in attenuation of inappropriate pathway activity. Accordingly, we found that the UPR agonist thapsigargin attenuated mutant Smoothened-induced phenotypes in vivo in Drosophila melanogaster. Wild-type Smoothened and physiological Hedgehog patterning were not affected, suggesting that UPR modulation may provide a novel therapeutic window to be evaluated for targeting active Smoothened mutants in disease.

The Hedgehog signalling pathway in breast development, carcinogenesis and cancer therapy

Despite the progress achieved in breast cancer screening and therapeutic innovations, the basal-like subtype of breast cancer (BLBC) still represents a particular clinical challenge. In order to make an impact on survival in this type of aggressive breast cancer, new targeted therapeutic agents are urgently needed. Aberrant activation of the Hedgehog (Hh) signalling pathway has been unambiguously tied to cancer development and progression in a variety of solid malignancies, and the recent approval of vismodegib, an orally bioavailable small-molecule inhibitor of Smoothened, validates Hh signalling as a valuable therapeutic target. A number of recent publications have highlighted a role for Hh signalling in breast cancer models and clinical specimens. Interestingly, Hh ligand overexpression is associated with the BLBC phenotype and a poor outcome in terms of metastasis and breast cancer-related death. In this review, we provide a comprehensive overview of the canonical Hh signalling pathway in mammals, highlight its roles in mammary gland development and breast carcinogenesis and discuss its potential therapeutic value in BLBC.