Subset Of Human Medulloblastomas Research Articles

PDTM-19. MYC AND FAK/SRC COMBINATION TREATMENT OF FOXR2-HIGH BRAIN TUMORS

Abstract Brain tumors are the leading cause of cancer-related deaths in children. To identify novel therapeutic targets in two types of pediatric brain tumors, medulloblastoma (MB) and central nervous system primitive neuroectodermal tumors (CNS-PNETs), we performed a Sleeping Beauty transposon mutagenesis screen in mice. In doing this, we identified FOXR2 (Forkhead box R2) as a candidate oncogene in MB. FOXR2 is expressed at high levels in a subset of human MB and increased FOXR2 expression drives MB formation in mice. FOXR2 has been implicated as an oncogene in several cancers of neural original, including CNS-PNET, adult and pediatric high-grade glioma, and malignant peripheral nerve sheath tumors. We have also found that FOXR2 is upregulated in non-MYCN amplified high-risk neuroblastoma. Therefore, we propose that FOXR2 represents a strong candidate for targeted therapy across multiple brain tumor entities. We have uncovered a dual role of FOXR2 in stabilization of CMYC protein and activation of the FAK/SRC signaling pathway. We are working to further define the mechanism of FOXR2-mediated MYC stabilization and FAK/SRC activation. We plan to treat FOXR2-high tumors with combinations of drugs effective against tumors with high MYC, FAK, or SRC in clinical development. Inhibitors or combinations of that score well in vitro will be used to treat mice with orthotopically injected FOXR2-high tumor cells (MB, neuroblastoma, and glioma). In addition, we are working to construct mouse models of FOXR2-driven neural tumors for use in drug testing. We hypothesize that FOXR2-high tumors will be sensitive to MYC and FAK/SRC inhibitor combination therapy, establishing FOXR2 as a molecular marker for treatment success of MYC and FAK/SRC inhibitors in patients.

MTOR pathway as a potential target in a subset of human medulloblastoma.

As mammalian Target of Rapamycin (mTOR) plays role in protein synthesis and metabolism, mTOR pathway activation is involved in the pathogenesis of several types of tumors. Our aim was to elucidate its role in medulloblastoma in terms of prognosis and as a therapeutic target. Members of activated mTOR complex 1 (mTORC1) pathway, phospho-mTOR (p-mTOR) and phospho-S6 (p-S6) were examined by immunohistochemistry in formalin fixed paraffin embedded samples of 40 patients with medulloblastoma, and results were compared to clinical features and survival of patients. In proliferation assays, Daoy and UW228-2 medulloblastoma cell lines were tested by rapamycin, an mTORC1 inhibitor, and NVP-BEZ235, a dual mTOR and phosphatidylinositol 3-kinase (PI3K) inhibitor, each in monotherapy and in combination with cytostatic drugs (cisplatin, etoposide). Components of mTORC1 and mTORC2 complexes were also examined in these cell lines. Neither presence of p-mTOR (32.5 %) nor p-S6 (32.5 %) correlated with age, gender or histological subtype. In 22.5 % of cases simultaneous expression of p-mTOR and p-S6 was shown. Kaplan-Meier analysis showed inferior survival of patients expressing both marker proteins, but it was not statistically significant, probably due to low case number. UW228-2 cells had greater sensitivity to mTOR inhibitors, possibly due to its higher mTORC1 specific protein expression levels, compared to Daoy cells. In both cell lines antiproliferative effect of cytostatic drugs was significantly enhanced by mTOR inhibitors (p < 0.05). Based on our in vitro and clinicopathological studies mTOR inhibitors may have a role in the future treatment of a subset of patients with medulloblastoma.

Abstract 1431: A novel tumor-suppressor role of MyoD, a muscle differentiation factor, in mouse models of medulloblastoma

Abstract Medulloblastoma, an embryonal tumor of the cerebellum, is the most common pediatric brain cancer. For decades, it has been known that a small subset of medulloblastomas present with myogenic differentiation. However, the mechanistic basis and significance of this biological anomaly remain to be determined. We have identified hitherto unknown expression of muscle differentiation factor, MyoD in cerebellar tumors from mouse models of medulloblastoma as well as in a subset of human medulloblastomas. At a cellular level, MyoD is expressed in mitotically active cells and intriguingly, in mouse tumors does not activate its canonical targets involved in the muscle differentiation program. To understand the functional consequence of this finding in medulloblastoma genesis, we have conducted genetic studies to assess tumor formation in the SmoA1 and SmoA2 medulloblastoma models, on a MyoD-deficient background. We demonstrate that MyoD acts as a haploinsufficient tumor suppressor as the MyoD wt/-; SmoA1 and MyoD wt/-; SmoA2 mice have an accelerated onset of tumors compared to MyoD wt/wt; SmoA1 or MyoD wt/wt; SmoA2 mice respectively. Our findings suggest that the expression of MyoD might be an oncogene-induced compensatory response in the cerebellum to suppress tumor growth by restoring balance between proliferation and differentiation, similar to the role of some other bHLH transcription factors. Harnessing this latent tumor suppressor network to induce differentiation or cell cycle arrest holds promise for future therapeutic interventions. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 1431. doi:1538-7445.AM2012-1431

Severe Alterations of Cerebellar Cortical Development after Constitutive Activation of Wnt Signaling in Granule Neuron Precursors

The Wnt/β-catenin signaling pathway plays crucial roles in early hindbrain formation, and its constitutive activity is associated with a subset of human medulloblastoma, a malignant childhood tumor of the posterior fossa. However, the precise function of Wnt/β-catenin signaling during cerebellar development is still elusive. We generated Math1-cre::Apc(Fl/Fl) mice with a conditional knockout for the Adenomatosis polyposis coli (Apc) gene that displayed a constitutive activity of Wnt/β-catenin signaling in cerebellar granule neuron precursors. Such mice showed normal survival without any tumor formation but had a significantly smaller cerebellum with a complete disruption of its cortical histoarchitecture. The activation of the Wnt/β-catenin signaling pathway resulted in a severely inhibited proliferation and premature differentiation of cerebellar granule neuron precursors in vitro and in vivo. Mutant mice hardly developed an internal granular layer, and layering of Purkinje neurons was disorganized. Clinically, these mice presented with significantly impaired motor coordination and ataxia. In summary, we conclude that cerebellar granule neurons essentially require appropriate levels of Wnt signaling to balance their proliferation and differentiation.

Abstract 2485: The Hippo downstream effector YAP promotes survival, radiation resistance and chromosome instability in medulloblastoma

Abstract Medulloblastoma, the most common solid pediatric tumor, originates in the cerebellum during postnatal development. It is postulated that cerebellar granule neuron precursors (CGNPs) are cells-of-origin for certain classes of medulloblastomas. CGNPs require the mitogen/morphogen Shh to proliferate. We identified YAP as a new Shh target that promotes CGNP proliferation. YAP is a transcriptional co-activator negatively regulated by the Hippo pathway, a signaling cascade involved in organ size regulation and cell contact inhibition. We found YAP to be highly expressed in human and mouse Shh-driven medulloblastomas. Moreover, YAP was strikingly amplified in a subset of human medulloblastomas. YAP was localized to the peri-vascular niche where cancer stem cells have recently been described to reside in brain tumors. When we irradiated medulloblastoma-bearing mice, most of the cells in the tumor underwent apoptosis 6 hours after radiation. However, cells expressing YAP were resistant to radiation-induced apoptosis. These radiation-resistant cells have been described to have the ability to re-populate the tumor. In concordance with this, mouse medulloblastoma cells over-expressing YAP and injected in P0-P4 pups grow faster than those overexpressing GFP and give rise to more aggressive tumors. In vitro, YAP-overexpressing CGNPs and medulloblastoma cells produce higher levels of IGF2, which activates Akt and promotes their survival. 24 hours after radiation, YAP-overexpressing cells contain more damaged DNA; however, they skip the G2/M checkpoint and don't arrest despite the damage in their DNA. Our results indicate that YAP promotes both chromosome instability and survival of medulloblastoma cells, thus is a new attractive potential target for medulloblastoma therapies. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 2485. doi:10.1158/1538-7445.AM2011-2485

Abstract LB-385: The Hippo pathway component YAP1 promotes cerebellar precursor survival after irradiation and can accelerate medulloblastoma onset

Abstract Medulloblastoma is the most common malignant solid tumor in children. These tumors arise in the developing cerebellum, a region of the brain that undergoes rapid expansion after birth. Current treatments for medulloblastoma include radiation, surgery and chemotherapy, all of which are associated with devastating physical and mental side effects in long-term survivors. Recently, cells within medulloblastomas that survive radiation treatment and can repopulate the tumors post-radiation have been identified. These cells reside in regions adjacent to blood vessels, and their post-radiation survival is promoted by PI3 kinase pathway activity. Ideal medulloblastoma therapies will attack the tumors and eliminate the tumor re-initiating cells but spare the rest of the brain. We have recently published that the oncogenic transcriptional co-activator YAP1, which is negatively regulated by the Hippo pathway, is up regulated and amplified in a subset of human medulloblastomas with aberrant Sonic hedgehog (Shh) signaling. YAP1 is found in cells of the perivascular niche, where proposed tumor-repopulating cells reside. Post-irradiation, YAP1 was found in newly-growing tumor cells. We report here that YAP1 is actively involved in survival post-irradiation. CGNPs that over-express YAP1 in vitro proliferate more and present less apoptosis after irradiation than those over-expressing GFP. Among YAP1 target genes in CGNPs we found Securin, which, apart from its known role in mitosis, it has been shown to have roles in survival after DNA damage. We also found Securin highly expressed in human and mouse medulloblastomas. Moreover, injection of YAP 1 over-expressing medulloblastoma cells in postnatal day 4 wild type mice accelerate medulloblastoma onset compared to GFP over-expressing cells. These findings implicate YAP1 as a new Shh effector that may be targeted by medulloblastoma therapies aimed at eliminating medulloblastoma recurrence. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr LB-385.

02-P018 Cerebellar stem cells act as medulloblastoma initiating cells in a mouse model and a neural stem cell signature characterises a subset of human medulloblastoma

02-P018 Cerebellar stem cells act as medulloblastoma initiating cells in a mouse model and a neural stem cell signature characterises a subset of human medulloblastoma

Identification of CD15 as a Marker for Tumor-Propagating Cells in a Mouse Model of Medulloblastoma

The growth of many cancers depends on self-renewing cells called cancer stem cells or tumor-propagating cells (TPCs). In human brain tumors, cells expressing the stem cell marker CD133 have been implicated as TPCs. Here we show that tumors from a model of medulloblastoma, the Patched mutant mouse, are propagated not by CD133(+) cells but by cells expressing the progenitor markers Math1 and CD15/SSEA-1. These cells have a distinct expression profile that suggests increased proliferative capacity and decreased tendency to undergo apoptosis and differentiation. CD15 is also found in a subset of human medulloblastomas, and tumors expressing genes similar to those found in murine CD15(+) cells have a poorer prognosis. Thus, CD15 may represent an important marker for TPCs in medulloblastoma.