The developmental stage of the medulloblastoma cell-of-origin restricts Hedgehog pathway usage and drug sensitivity

Sonic hedgehog (SHH) medulloblastoma originates from the cerebellar granule neuron progenitor (CGNP) lineage, which depends on Hedgehog signaling for its perinatal expansion. Whereas SHH tumors exhibit overall deregulation of this pathway, they also show patient age-specific aberrations. To investigate whether the developmental stage of the CGNP can account for these age-specific lesions, we analyzed developing murine CGNP transcriptomes and observed highly dynamic gene expression as a function of age. Cross-species comparison with human SHH medulloblastoma showed partial maintenance of these expression patterns, and highlighted low primary cilium expression as hallmark of infant medulloblastoma and early embryonic CGNPs. This coincided with reduced responsiveness to upstream SHH pathway component Smoothened, whereas sensitivity to downstream components SUFU and GLI family proteins was retained. Together, these findings can explain the preference for SUFU mutations in infant medulloblastoma and suggest that drugs targeting the downstream SHH pathway will be most appropriate for infant patients.

Summary: There is a relationship between the age of the medulloblastoma patient and the developmental age of the tumor cell-of-origin, and this influences the SHH pathway signaling route used by the tumor.

Identification of Two Protein-Signaling States Delineating Transcriptionally Heterogeneous Human Medulloblastoma

The brain cancer medulloblastoma consists of different transcriptional subgroups. To characterize medulloblastoma at the phosphoprotein-signaling level, we performed high-throughput peptide phosphorylation profiling on a large cohort of SHH (Sonic Hedgehog), group 3, and group 4 medulloblastomas. We identified two major protein-signaling profiles. One profile was associated with rapid death post-recurrence and resembled MYC-like signaling for which MYC lesions are sufficient but not necessary. The second profile showed enrichment for DNA damage, as well as apoptotic and neuronal signaling. Integrative analysis demonstrated that heterogeneous transcriptional input converges on these protein-signaling profiles: all SHH and a subset of group 3 patients exhibited the MYC-like protein-signaling profile; the majority of the other group 3 subset and group 4 patients displayed the DNA damage/apoptotic/neuronal signaling profile. Functional analysis of enriched pathways highlighted cell-cycle progression and protein synthesis as therapeutic targets for MYC-like medulloblastoma.

Abstract 5826: Essential role for cyclic-AMP responsive element binding protein 1 (CREB1) phosphorylation in the survival of medulloblastoma patients

Prognosis for recurrent medulloblastoma patients is extremely poor, with a median survival of 26.8 months. Treatment options for recurrent medulloblastoma patients are limited and ineffective due to resistance to chemotherapeutic agents and radiotherapy. Therefore, more research is required to address the high mortality of medulloblastoma patients that have therapy-resistant medulloblastoma. In a previous, study, we showed that cyclic-AMP responsive element binding protein (CREB1) was highly phosphorylated in primary medulloblastoma specimens. CREB is an important transcription factor involved in cerebellar cell proliferation and survival. In various cancers types, the expression of CREB is associated with prognosis. Untill now, CREB expression and its relation with overall survival has not been studied in medulloblastoma patients. In this study, we determined CREB phosphorylation levels and mRNA levels of CREB and its transcriptional co-activators CREBBP and EP300 using peptide phosphorylation and gene expression arrays in a cohort of 50 pediatric medulloblastoma patients. Furthermore, we performed shRNA-mediated knockdown of CREB, CREBBP and EP300 mRNA levels in medulloblastoma cell line DAOY. Knockdown was confirmed by means of qRT-PCR and western blotting. Next, cell viability assays were used to investigate the effect of chemotherapeutic reagents (etoposide and/or cisplatin) on cell viability in CREB, CREBBP or EP300 knockdown cells or in combination with a small molecule CREB inhibitor (KG-501).Low CREB phosphorylation levels in combination with low CREBBP and EP300 mRNA levels was significantly associated with poor overall survival (p=0.0001) with a median survival of 11.7 months in medulloblastoma patients. High CREB phosphorylation in combination with high CREBBP and EP300 mRNA levels was associated with a favourable prognosis (5 year-overall survival: 91%). Supervised clustering of gene expression data based upon low versus high CREB phosphorylation and CREBBP/EP300 mRNA levels and subsequent gene ontology analysis showed significant enrichment of genes associated with cerebellar and neuronal differentiation and development. Furthermore, knockdown with shCREB.3, shCBP.1-2 or shEP300A completely rescued DAOY cells from the etoposide-induced decrease in cell viability that was observed in the scrambled control. Similarly, addition of the CREB inhibitor KG-501 (2μM) completely rescued DAOY cells from the etoposide-induced decrease in cell viability and partially rescued DAOY cells from the cisplatin-induced decrease in cell viability.Together, these findings support an important role for CREB in neuronal differentiation, chemosensitivity and in the overall survival of pediatric medulloblastoma patients.

Citation Format: Walderik W. Zomerman, Sabine L. Plasschaert, Frank J. Scherpen, Harm Jan J. Lourens, Geesina C. Huizinga, Eelco W. Hoving, Wilfred F. den Dunnen, Sophia Bruggeman, Eveline S.J.M. de Bont. Essential role for cyclic-AMP responsive element binding protein 1 (CREB1) phosphorylation in the survival of medulloblastoma patients [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5826. doi:10.1158/1538-7445.AM2017-5826

Exogenous HGF Bypasses the Effects of ErbB Inhibition on Tumor Cell Viability in Medulloblastoma Cell Lines

Recent clinical trials investigating receptor tyrosine kinase (RTK) inhibitors showed a limited clinical response in medulloblastoma. The present study investigated the role of micro-environmental growth factors expressed in the brain, such as HGF and EGF, in relation to the effects of hepatocyte growth factor receptor (MET) and epidermal growth factor receptor family (ErbB1-4) inhibition in medulloblastoma cell lines. Medulloblastoma cell lines were treated with tyrosine kinase inhibitors crizotinib or canertinib, targeting MET and ErbB1-4, respectively. Upon treatment, cells were stimulated with VEGF-A, PDGF-AB, HGF, FGF-2 or EGF. Subsequently, we measured cell viability and expression levels of growth factors and downstream signaling proteins. Addition of HGF or EGF phosphorylated MET or EGFR, respectively, and demonstrated phosphorylation of Akt and ERK1/2 as well as increased tumor cell viability. Crizotinib and canertinib both inhibited cell viability and phosphorylation of Akt and ERK1/2. Specifically targeting MET using shRNA’s resulted in decreased cell viability. Interestingly, addition of HGF to canertinib significantly enhanced cell viability as well as phosphorylation of Akt and ERK1/2. The HGF-induced bypass of canertinib was reversed by addition of crizotinib. HGF protein was hardly released by medulloblastoma cells itself. Addition of canertinib did not affect RTK cell surface or growth factor expression levels. This manuscript points to the bypassing capacity of exogenous HGF in medulloblastoma cell lines. It might be of great interest to anticipate on these results in developing novel clinical trials with a combination of MET and EGFR inhibitors in medulloblastoma.

Abstract 4025: Exogenous HGF bypasses ErbB inhibition on tumor cell viability in medulloblastoma cell lines

Recent clinical trials investigating receptor tyrosine kinase (RTK) inhibitors showed limited clinical responses in medulloblastoma. An emerging concept is the role of the tumor microenvironment in bypassing targeted therapies by producing ligands that can compensate for the drug-inhibited RTK via alternative routes of pathway activation. The aim of this study is to investigate the role of well-known CNS expressed growth factors in relation to the effects of hepatocyte growth factor receptor (MET) and epidermal growth factor receptor family (EGFR, ErbB2-4) inhibition on tumor cell viability and downstream signaling in medulloblastoma cell lines.

Five different medulloblastoma cell lines (DAOY, RES256, UW402, UW426, and UW473) were treated with crizotinib or canertinib, targeting MET or EGFR, ErbB2-4, respectively. Upon treatment, cells were stimulated with the CNS expressed growth factor VEGF-A PDGF-AB, HGF, FGF-2 or EGF basic. Subsequently, a cell viability assay was used to measure cell viability upon growth factor stimulation, compared to non-growth factor stimulated cells. Expression levels of respective receptor tyrosine kinases (RTK’s) and growth factors were analyzed using flow cytometry and human growth factor antibody arrays. Phosphorylation status of RTK's and downstream signaling effectors was visualized using western blot analysis and human phospho-kinase antibody arrays.

We observed high MET and EGFR cell surface expression levels. Addition of HGF or EGF phosphorylated MET or EGFR, respectively, and resulted in downstream phosphorylation of Akt and ERK1/2 as well as increased tumor cell viability. Whereas crizotinib and canertinib inhibited cell viability and phosphorylation of Akt and ERK1/2, addition of HGF to canertinib significantly enhanced cell viability and phosphorylation of Akt and ERK1/2. The HGF induced bypass of canertinib was reversed by the addition of crizotinib. HGF protein was hardly released by medulloblastoma cell lines. This suggests that MET activation is mainly dependent on paracrine HGF contribution. In conclusion, these data point to the bypassing capacity of well-known CNS expressed paracrine growth factors (e.g. HGF) in medulloblastoma cell lines and provides a potential explanation for the limited clinical response of single RTK inhibitors in medulloblastoma clinical trials. It might be of great interest to anticipate on these results in developing novel clinical trials with a combination of tyrosine kinase inhibitors, targeting for example MET and EGFR in medulloblastoma.

Citation Format: Walderik W. Zomerman, Sabine LA Plasschaert, Sander H. Diks, Harm-Jan Lourens, Tiny Meeuwsen-de Boer, Eelco W. Hoving, Wilfred FA den Dunnen, Eveline SJM de Bont. Exogenous HGF bypasses ErbB inhibition on tumor cell viability in medulloblastoma cell lines. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 4025. doi:10.1158/1538-7445.AM2015-4025

Growth-factor-driven rescue to receptor tyrosine kinase (RTK) inhibitors through Akt and Erk phosphorylation in pediatric low grade astrocytoma and ependymoma

Up to now, several clinical studies have been started investigating the relevance of receptor tyrosine kinase (RTK) inhibitors upon progression free survival in various pediatric brain tumors. However, single targeted kinase inhibition failed, possibly due to tumor resistance mechanisms. The present study will extend our previous observations that vascular endothelial growth factor receptor (VEGFR)-2, platelet derived growth factor receptor (PDGFR)β, Src, the epidermal growth factor receptor (ErbB) family, and hepatocyte growth factor receptor (HGFR/cMet) are potentially drugable targets in pediatric low grade astrocytoma and ependymoma with investigations concerning growth-factor-driven rescue. This was investigated in pediatric low grade astrocytoma and ependymoma cell lines treated with receptor tyrosine kinase (RTK) inhibitors e.g. sorafenib, dasatinib, canertinib and crizotinib. Flow cytometry analyses showed high percentage of cells expressing VEGFR-1, fibroblast growth factor receptor (FGFR)-1, ErbB1/EGFR, HGFR and recepteur d’origine nantais (RON) (respectively 52-77%, 34-51%, 63-90%, 83-98%, 65-95%). Their respective inhibitors induced decrease of cell viability, measured with WST-1 cell viability assays. At least this was partially due to increased apoptotic levels measured by Annexin V/Propidium Iodide apoptosis assays. EGF, HGF and FGF, which are normally expressed in brain (tumor) tissue, showed to be effective rescue inducing growth factors resulting in increased cell survival especially during treatment with dasatinib (complete rescue) or sorafenib (partial rescue). Growth-factor-driven rescue was less prominent when canertinib or crizotinib were used. Rescue was underscored by significantly activating downstream Akt and/or Erk phosphorylation and increased tumor cell migration. Combination treatment showed to be able to overcome the growth-factor-driven rescue. In conclusion, our study highlights the extensive importance of environmentally present growth factors in developing tumor escape towards RTK inhibitors in pediatric low grade astrocytoma and ependymoma. It is of great interest to anticipate upon these results for the design of new therapeutic trials with RTK inhibitors in these pediatric brain tumors.

Abstract B10: HGF enhances tumor cell survival in canertinib-treated medulloblastoma cell lines

Medulloblastoma is the most common malignant pediatric brain tumor. Unfortunately, conventional therapies have led to long-term side effects in the majority of survivors. Therefore, novel therapies inhibiting specific target molecules seem promising. However, the efficacy of these novel drug treatments targeting specific tyrosine kinases is often hampered, leading to tumor recurrence within several months of treatment. The aim of this study is to examine whether various growth factors, present in the tumor micro-environment, are able to influence the viability of medulloblastoma cell lines during tyrosine kinase inhibitor (TKI) treatment, providing a possible explanation for the recurrence of the tumor.

To test this hypothesis, five different medulloblastoma cell lines (DAOY, RES256, UW402, UW426, and UW473) were treated with the tyrosine kinase inhibitor canertinib or crizotinib, targeting the Epidermal Growth Factor Receptor (EGFR) and MET-receptor, respectively. Upon treatment, cells were stimulated with the growth factor HGF, EGF, FGF, VEGF or PDGF. Subsequently, a cell viability assay was used to measure cell survival upon growth factor stimulation, compared to non-growth factor stimulated cells. Expression levels of respective receptor tyrosine kinases (RTK's) were analyzed using flow cytometry and phosphorylation status was visualized using western blot analysis. Effects on downstream signaling effectors were examined using western blot analysis and human phospho-kinase arrays.

The cell viability assays showed increased cell viability upon HGF stimulation in canertinib treated medulloblastoma cell lines. The respective RTK's, MET and EGFR, were highly expressed on the cell surface of all medulloblastoma cell lines. Furthermore, western blotting and phospho-kinase arrays showed that HGF and EGF were able to phosphorylate their respective RTK's and activate downstream signaling effectors. As expected from the cell survival results, stimulation with HGF during canertinib treatment led to re-activation of downstream signaling effectors Akt and/or ERK1/2. Surprisingly, stimulation with EGF during crizotinib treatment also led to downstream re-activation but did not however, lead to an increase in overall tumor cell survival. Enhanced tumor cell survival due to HGF during canertinib treatment could be reversed by combined treatment with a low additional dose of the MET-inhibitor crizotinib. This decrease in cell viability during combined treatment with crizotinib was also mirrored by the inhibition of downstream signaling effectors.

In this study we show that the availability of HGF can lead to enhanced tumor cell survival and re-activation of downstream signaling effectors in canertinib treated medulloblastoma cell lines. This redundancy in RTK-activation by alternative RTK-ligands might provide a possible explanation for the recurrence of the tumor. Therefore, a combined treatment with tyrosine kinase inhibitors, targeting for example MET and EGFR, would be rational in the treatment of medulloblastoma.

Citation Format: Walderik W. Zomerman, Sabine L.A. Plasschaert, Sander H. Diks, Harm Jan Lourens, Eelco W. Hoving, Wilfred F.A. den Dunnen, Eveline S.J.M. de Bont. HGF enhances tumor cell survival in canertinib-treated medulloblastoma cell lines. [abstract]. In: Proceedings of the AACR Special Conference on Pediatric Cancer at the Crossroads: Translating Discovery into Improved Outcomes; Nov 3-6, 2013; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2013;74(20 Suppl):Abstract nr B10.