Brent A. Orr

Vismodegib Exerts Targeted Efficacy Against Recurrent Sonic Hedgehog–Subgroup Medulloblastoma: Results From Phase II Pediatric Brain Tumor Consortium Studies PBTC-025B and PBTC-032

PURPOSE Two phase II studies assessed the efficacy of vismodegib, a sonic hedgehog (SHH) pathway inhibitor that binds smoothened (SMO), in pediatric and adult recurrent medulloblastoma (MB). PATIENTS AND METHODS Adult patients enrolled onto PBTC-025B and pediatric patients enrolled onto PBTC-032 were treated with vismodegib (150 to 300 mg/d). Protocol-defined response, which had to be sustained for 8 weeks, was confirmed by central neuroimaging review. Molecular tests to identify patterns of response and insensitivity were performed when tissue was available. RESULTS A total of 31 patients were enrolled onto PBTC-025B, and 12 were enrolled onto PBTC-032. Three patients in PBTC-025B and one in PBTC-032, all with SHH-subgroup MB (SHH-MB), exhibited protocol-defined responses. Progression-free survival (PFS) was longer in those with SHH-MB than in those with non-SHH-MB, and prolonged disease stabilization occurred in 41% of patient cases of SHH-MB. Among those with SHH-MB, loss of heterozygosity of PTCH1 was associated with prolonged PFS, and diffuse staining of P53 was associated with reduced PFS. Whole-exome sequencing identified mutations in SHH genes downstream from SMO in four of four tissue samples from nonresponders and upstream of SMO in two of four patients with favorable responses. CONCLUSION Vismodegib exhibits activity against adult recurrent SHH-MB but not against recurrent non-SHH-MB. Inadequate accrual of pediatric patients precluded conclusions in this population. Molecular analyses support the hypothesis that SMO inhibitor activity depends on the genomic aberrations within the tumor. Such inhibitors should be advanced in SHH-MB studies; however, molecular and genomic work remains imperative to identify target populations that will truly benefit.

Decreased 5-hydroxymethylcytosine is associated with neural progenitor phenotype in normal brain and shorter survival in malignant glioma.

Epigenetic modification of DNA by cytosine methylation to produce 5-methylcytosine (5mC) has become well-recognized as an important epigenetic process in human health and disease. Recently, further modification of 5mC by the ten eleven translocated (TET) family of enzymes to produce 5-hydroxymethylcytosine (5hmC) has been described. In the present study, we used immunohistochemistry to evaluate the distribution of 5hmC in human brain during different periods of development and in a large series of gliomas (n = 225). We found that during development, 5hmC levels are high in more differentiated compartments like the fetal cortex, but low in the periventricular progenitor cell regions. In adults, we found 5hmC levels to be highest in the cortex, but present in all intrinsic cell types in the brain including stromal elements. In brain tumors, 5hmC levels were high in low grade tumors and reduced in malignant glioma, but did not exhibit any correlation with IDH1 mutation status. Additionally, we identified a significant relationship between low levels of 5hmC and reduced survival in malignant glioma. This observation was further supported by in silico analysis showing differential expression of genes involved in 5hmC homeostasis in aggressive subsets of glioblastoma. Finally, we show that several genes involved in regulating the levels of 5hmC are also prognostic in malignant glioma. These findings suggest that 5hmC regulation in malignant glioma may represent an important determinant of tumor differentiation and aggressive behavior, as well as a potential therapeutic target.

Activation of canonical WNT/β-catenin signaling enhances in vitro motility of glioblastoma cells by activation of ZEB1 and other activators of epithelial-to-mesenchymal transition

Here we show that activation of the canonical WNT/β-catenin pathway increases the expression of stem cell genes and promotes the migratory and invasive capacity of glioblastoma. Modulation of WNT signaling alters the expression of epithelial-to-mesenchymal transition activators, suggesting a role of this process in the regulation of glioma motility. Using immunohistochemistry in patient-derived glioblastoma samples we showed higher numbers of cells with intranuclear signal for β-catenin in the infiltrating edge of tumor compared to central tumor parenchyma. These findings suggest that canonical WNT/β-catenin pathway is a critical regulator of GBM invasion and may represent a potential therapeutic target.

Active medulloblastoma enhancers reveal subgroup-specific cellular origins

Medulloblastoma is a highly malignant paediatric brain tumour, often inflicting devastating consequences on the developing child. Genomic studies have revealed four distinct molecular subgroups with divergent biology and clinical behaviour. An understanding of the regulatory circuitry governing the transcriptional landscapes of medulloblastoma subgroups, and how this relates to their respective developmental origins, is lacking. Here, using H3K27ac and BRD4 chromatin immunoprecipitation followed by sequencing (ChIP-seq) coupled with tissue-matched DNA methylation and transcriptome data, we describe the active cis-regulatory landscape across 28 primary medulloblastoma specimens. Analysis of differentially regulated enhancers and super-enhancers reinforced inter-subgroup heterogeneity and revealed novel, clinically relevant insights into medulloblastoma biology. Computational reconstruction of core regulatory circuitry identified a master set of transcription factors, validated by ChIP-seq, that is responsible for subgroup divergence, and implicates candidate cells of origin for Group 4. Our integrated analysis of enhancer elements in a large series of primary tumour samples reveals insights into cis-regulatory architecture, unrecognized dependencies, and cellular origins.

Long Interspersed Element-1 Protein Expression Is a Hallmark of Many Human Cancers

Cancers comprise a heterogeneous group of human diseases. Unifying characteristics include unchecked abilities of tumor cells to proliferate and spread anatomically, and the presence of clonal advantageous genetic changes. However, universal and highly specific tumor markers are unknown. Herein, we report widespread long interspersed element-1 (LINE-1) repeat expression in human cancers. We show that nearly half of all human cancers are immunoreactive for a LINE-1-encoded protein. LINE-1 protein expression is a common feature of many types of high-grade malignant cancers, is rarely detected in early stages of tumorigenesis, and is absent from normal somatic tissues. Studies have shown that LINE-1 contributes to genetic changes in cancers, with somatic LINE-1 insertions seen in selected types of human cancers, particularly colon cancer. We sought to correlate this observation with expression of the LINE-1-encoded protein, open reading frame 1 protein, and found that LINE-1 open reading frame 1 protein is a surprisingly broad, yet highly tumor-specific, antigen.

Yes-Associated Protein 1 Is Widely Expressed in Human Brain Tumors and Promotes Glioblastoma Growth

The hippo pathway and its downstream mediator yes-associated protein 1 (YAP1) regulate mammalian organ size in part through modulating progenitor cell numbers. YAP1 has also been implicated as an oncogene in multiple human cancers. Currently, little is known about the expression of YAP1 either in normal human brain tissue or in central nervous system neoplasms. We used immunohistochemistry to evaluate nuclear YAP1 expression in the fetal and normal adult human brains and in 264 brain tumors. YAP1 was expressed infetal and adult brain regions known to harbor neural progenitor cells, but there was little YAP1 immunoreactivity in the adult cerebral cortex. YAP1 protein was also readily detected in the nuclei ofhuman brain tumors. In medulloblastoma, the expression varied between histologic subtypes and was most prominent in nodular/desmoplastic tumors. In gliomas, it was frequently expressed in infiltrating astrocytomas and oligodendrogliomas but rarely in pilocytic astrocytomas. Using a loss-of-function approach, we show thatYAP1 promoted growth of glioblastoma cell lines in vitro. High levels of YAP1 messenger RNA expression were associated with aggressive molecular subsets of glioblastoma and with a nonsignificanttrend toward reduced mean survival in human astrocytoma patients. These findings suggest that YAP1 may play an important rolein normal human brain development and that it could represent a new target in human brain tumors.

Molecular and morphologic correlates of the alternative lengthening of telomeres phenotype in high-grade astrocytomas

Recent studies suggest that the telomere maintenance mechanism known as alternative lengthening of telomeres (ALT) is relatively more common in specific glioma subsets and strongly associated with ATRX mutations. We retrospectively examined 116 high‐grade astrocytomas (32 pediatric glioblastomas, 65 adult glioblastomas, 19 anaplastic astrocytomas) with known ALT status using tissue microarrays to identify associations with molecular and phenotypic features. Immunohistochemistry was performed using antibodies against ATRX, DAXX, p53 and IDH1R132H mutant protein. EGFR amplification was evaluated by fluorescence in situ hybridization (FISH). Almost half of fibrillary and gemistocytic astrocytomas (44%) demonstrated ALT. Conversely all gliosarcomas (n = 4), epithelioid (n = 2), giant cell (n = 2) and adult small cell astrocytomas (n = 7) were ALT negative. The ALT phenotype was positively correlated with the presence of round cells (P = 0.002), microcysts (P < 0.0002), IDH1 mutant protein (P < 0.0001), ATRX protein loss (P < 0.0001), strong P53 immunostaining (P < 0.0001) and absence of EGFR amplification (P = 0.004). There was no significant correlation with DAXX expression. We conclude that ALT represents a specific phenotype in high‐grade astrocytomas with distinctive pathologic and molecular features. Future studies are required to clarify the clinical and biological significance of ALT in high‐grade astrocytomas.

Striatal neuronal loss correlates with clinical motor impairment in Huntington's disease

Huntingtons disease (HD) is characterized clinically by chorea, motor impairment, psychiatric manifestations, and dementia. Atrophy of the striatum is the neuropathological hallmark of HD, and previous studies have suggested that striatal atrophy correlates more closely with motor impairment than with chorea. Motor impairment, as measured by motor impairment score, correlates with functional disability in HD patients, but chorea does not. In this study, we investigated the relation between neuronal loss and these motor features. We conducted neuropathological and stereologic assessments of neurons in putamen and subthalamic nuclei in HD patients and age‐matched controls. In putamen, we estimated the total number and volume of medium spiny neurons labeled with dopamine‐ and cAMP‐regulated phosphoprotein 32 kDa (DARPP‐32). In subthalamic nuclei, we estimated the total number of neurons on hematoxylin & eosin/luxol fast blue stains. In putamen of HD, immunohistochemistry showed DARPP‐32 neuronal atrophy with extensive disruption of neurites and neuropil; stereologic studies found significant decreases in both the number and size of DARPP‐32 neurons; we also detected a significant reduction of overall putamen volume in HD patients, compared to controls. In subthalamic nuclei, there was a mild, but significant, neuronal loss in the HD group. The loss of neurons in putamen and subthalamic nuclei as well as putaminal atrophy were significantly correlated with severity of motor impairment, but not with chorea. Our findings suggest that neuronal loss and atrophy in striatum and neuronal loss in subthalamic nuclei contribute specifically to the motor impairment of HD, but not to chorea.

Alisertib is active as single agent in recurrent atypical teratoid rhabdoid tumors in 4 children

BACKGROUND Aurora Kinase A (AURKA) encodes a protein that regulates the formation and stability of the mitotic spindle and is highly active in atypical teratoid rhabdoid tumors (ATRT) through loss of the INI1 tumor suppressor gene. Alisertib (MLN8237) inhibits AURKA in vitro and in vivo. Given the strong preclinical data supporting the use of alisertib for ATRT patients, we sought and obtained permission to use alisertib in single patient treatment plans for 4 recurrent pediatric ATRT patients. METHODS Patients with recurrent or progressive ATRT received alisertib 80 mg/m(2) by mouth once daily for 7 days of a 21-day treatment cycle. Disease evaluation (MRI of brain and spine and lumbar puncture) was done after 2 cycles of alisertib and every 2-3 cycles thereafter for as long as the patients remained free from tumor progression. RESULTS Four patients with median age of 2.5 years (range, 1.39-4.87 y) at diagnosis received alisertib 80 mg/m(2) by mouth once daily for 7 days of a 21-day treatment cycle, and all 4 patients had disease stabilization and/or regression after 3 cycles of alisertib therapy. Two patients continued to have stable disease regression for 1 and 2 years, respectively, on therapy. CONCLUSIONS Single-agent alisertib produced marked and durable regression in disease burden, as detected by brain and spine MRI and by evaluation of spinal fluid cytology. Alisertib has moderate but manageable toxicities, and its chronic administration appears feasible in this pediatric population. These novel data support the incorporation of alisertib in future therapeutic trials for children with ATRT.

ZEB1 Promotes Invasion in Human Fetal Neural Stem Cells and Hypoxic Glioma Neurospheres.

Diffuse spread through brain parenchyma and the presence of hypoxic foci rimmed by neoplastic cells are two cardinal features of glioblastoma, and low oxygen is thought to drive movement of malignant gliomas in the core of the lesions. Transcription factors associated with epithelial‐to‐mesenchymal transition (EMT) have been linked to this invasion, and we found that hypoxia increased in vitro invasion up to fourfold in glioblastoma neurosphere lines and induced the expression of ZEB1. Immunohistochemical assessment of 295 surgical specimens consisting of various types of pediatric and adult brain cancers showed that ZEB1 expression was significantly higher in infiltrative lesions than less invasive tumors such as pilocytic astrocytoma and ependymoma. ZEB1 protein was also present in human fetal periventricular stem and progenitor cells and ZEB1 inhibition impaired migration of in vitro propagated human neural stem cells. The induction of ZEB1 protein in hypoxic glioblastoma neurospheres could be partially blocked by the HIF1alpha inhibitor digoxin. Targeting ZEB1 blocked hypoxia‐augmented invasion of glioblastoma cells in addition to slowing them in normoxia. These data support the role for ZEB1 in invasive and high‐grade brain tumors and suggest its key role in promoting invasion in the hypoxic tumor core as well as in the periphery.