Cross-species analysis of SHH medulloblastoma models reveals significant inhibitory effects of trametinib on tumor progression

Sonic Hedgehog (SHH) medulloblastomas (MBs) exhibit an intermediate prognosis and extensive intertumoral heterogeneity. While SHH pathway antagonists are effective in post-pubertal patients, younger patients exhibit significant side effects, and tumors that harbor mutations in downstream SHH pathway genes will be drug resistant. Thus, novel targeted therapies are needed. Here, we performed preclinical testing of the potent MEK inhibitor (MEKi) trametinib on tumor properties across 2 human and 3 mouse SHH MB models in vitro and in 3 orthotopic MB xenograft models in vivo. Trametinib significantly reduces tumorsphere size, stem/progenitor cell proliferation, viability, and migration. RNA-sequencing on human and mouse trametinib treated cells corroborated these findings with decreased expression of cell cycle, stem cell pathways and SHH-pathway related genes concomitant with increases in genes associated with cell death and ciliopathies. Importantly, trametinib also decreases tumor growth and increases survival in vivo. Cell cycle related E2F target gene sets are significantly enriched for genes that are commonly downregulated in both trametinib treated tumorspheres and primary xenografts. However, IL6/JAK STAT3 and TNFα/NFκB signaling gene sets are specifically upregulated following trametinib treatment in vivo indicative of compensatory molecular changes following long-term MEK inhibition. Our study reveals a novel role for trametinib in effectively attenuating SHH MB tumor progression and warrants further investigation of this potent MEK1/2 inhibitor either alone or in combination with other targeted therapies for the treatment of SHH MB exhibiting elevated MAPK pathway activity.

Metabolism-based targeting of MYC via MPC-SOD2 axis-mediated oxidation promotes cellular differentiation in group 3 medulloblastoma

Group 3 medulloblastoma (G3 MB) carries the worst prognosis of all MB subgroups. MYC oncoprotein is elevated in G3 MB tumors; however, the mechanisms that support MYC abundance remain unclear. Using metabolic and mechanistic profiling, we pinpoint a role for mitochondrial metabolism in regulating MYC. Complex-I inhibition decreases MYC abundance in G3 MB, attenuates the expression of MYC-downstream targets, induces differentiation, and prolongs male animal survival. Mechanistically, complex-I inhibition increases inactivating acetylation of antioxidant enzyme SOD2 at K68 and K122, triggering the accumulation of mitochondrial reactive oxygen species that promotes MYC oxidation and degradation in a mitochondrial pyruvate carrier (MPC)-dependent manner. MPC inhibition blocks the acetylation of SOD2 and oxidation of MYC, restoring MYC abundance and self-renewal capacity in G3 MB cells following complex-I inhibition. Identification of this MPC-SOD2 signaling axis reveals a role for metabolism in regulating MYC protein abundance that has clinical implications for treating G3 MB.

Failure of human rhombic lip differentiation underlies medulloblastoma formation

Medulloblastoma (MB) comprises a group of heterogeneous paediatric embryonal neoplasms of the hindbrain with strong links to early development of the hindbrain^1-4. Mutations that activate Sonic hedgehog signalling lead to Sonic hedgehog MB in the upper rhombic lip (RL) granule cell lineage^5-8. By contrast, mutations that activate WNT signalling lead to WNT MB in the lower RL^9,10. However, little is known about the more commonly occurring group 4 (G4) MB, which is thought to arise in the unipolar brush cell lineage^3,4. Here we demonstrate that somatic mutations that cause G4 MB converge on the core binding factor alpha (CBFA) complex and mutually exclusive alterations that affect CBFA2T2, CBFA2T3, PRDM6, UTX and OTX2. CBFA2T2 is expressed early in the progenitor cells of the cerebellar RL subventricular zone in Homo sapiens, and G4 MB transcriptionally resembles these progenitors but are stalled in developmental time. Knockdown of OTX2 in model systems relieves this differentiation blockade, which allows MB cells to spontaneously proceed along normal developmental differentiation trajectories. The specific nature of the split human RL, which is destined to generate most of the neurons in the human brain, and its high level of susceptible EOMES⁺KI67⁺ unipolar brush cell progenitor cells probably predisposes our species to the development of G4 MB.

SNO 2020 diversity survey: defining demographics, racial biases, career success metrics and a path forward for the field of neuro-oncology

BACKGROUND

Neuro-oncology has grown tremendously since 2010, marked by increasing society membership, specialized clinical expertise, and new journals. Yet, modest improvement in racial/ethnic diversity amongst clinical trial participants, researchers and clinicians led us to conduct a survey to identify opportunities to enhance diversity and inclusiveness amongst neuro-oncology professionals.

METHODS

In summer 2020, the Women and Diversity Committee of the Society for Neuro-Oncology (SNO) distributed an anonymous online survey to members and affiliates including European Association of Neuro-Oncology (EANO), Asian Society for Neuro-Oncology (ASNO), Society for Neuro-Oncology Latin America (SNOLA) and Society for Neuro-Oncology Sub-Saharan Africa (SNOSSA). The survey captured personal and professional characteristics, biases, effective mentorship qualities, career service metrics and suggested field/society changes. Results were analyzed by geography, profession, age, racial/ethnic and sexual identity. Standard descriptive statistics characterized the study population.

RESULTS

The 386 respondents were predominantly female (58%) with a median age range of 40-49 years (31%), White (65%), and SNO members (97%). Most worked in North America (77%) in a research profession (67%). A majority of White respondents reported never experiencing biases (64%), while the majority of non-White respondents reported unconscious biases/microaggressions, followed by a lack of/limited mentorship. Qualitative assessments showcased that personal/professional success metrics were linked to needed improvements in diversity and inclusion efforts within the neuro-oncology field.

CONCLUSIONS

The prevalence of racial/ethnic biases and poor mentorship rates amongst underrepresented groups in neuro-oncology is high and potentially linked to the limited diverse representation amongst members and affiliates. These findings warrant a swift implementation of equity and inclusion practices within the neuro-oncology field.

From sorting to sequencing in the molecular era: the evolution of the cancer stem cell model in medulloblastoma

The cancer stem cell (CSC) model posits that tumors contain subpopulations that display defining features of normal stem cells including self-renewal capacity and differentiation. Tumor cells exhibiting these features are now considered to be responsible for tumor propagation and drug resistance in a wide variety of cancers. Therefore, the identification of robust CSC markers and characterization of CSC-specific molecular signatures may lead to the identification of novel therapeutics that selectively abolish this clinically relevant cell population while preserving normal tissue. Brain tumor researchers have been at the forefront of the CSC field. From initial in vitro cell sorting experiments to the sophisticated bioinformatic technologies that now exquisitely resolve primary brain tumors at a single-cell level, recent glioma and medulloblastoma (MB) studies have integrated developmental state with genomic and transcriptome data to identify the spectrum of cell types that may drive tumor progression. This review will examine the last two decades of CSC studies in the field. Seminal discoveries, emerging controversies, and outstanding questions will be covered with a particular focus on MB, the most common malignant primary brain tumor in children.

Embryonic Stem Cell Models of Human Brain Tumors

Utilization of human embryonic stem cells (hESCs) as a model system to study highly malignant pediatric cancers has led to significant insight into the molecular mechanisms governing tumor progression and has revealed novel therapeutic targets for these devastating diseases. Here, we describe a method for generating heterogeneous populations of neural precursors from both normal and neoplastic hESCs and the subsequent injection of neoplastic human embryonic neural cells (hENs) into intracerebellar or intracranial xenograft models. Histopathologically, neural tumors derived from neoplastic hENs exhibit features similar to more aggressive medulloblastoma, the most common malignant primary pediatric brain tumor. In this chapter, we will outline the detailed methods for culturing normal and neoplastic neural precursor cells in both adherent and tumorsphere format and the full characterization of the brain tumors generated from these cells in non-obese diabetic severe combined immunodeficiency (NOD SCID) mice.

CD271+ Cells Are Diagnostic and Prognostic and Exhibit Elevated MAPK Activity in SHH Medulloblastoma

The extensive heterogeneity both between and within the medulloblastoma subgroups underscores a critical need for variant-specific biomarkers and therapeutic strategies. We previously identified a role for the CD271/p75 neurotrophin receptor (p75NTR) in regulating stem/progenitor cells in the SHH medulloblastoma subgroup. Here, we demonstrate the utility of CD271 as a novel diagnostic and prognostic marker for SHH medulloblastoma using IHC analysis and transcriptome data across 763 primary tumors. RNA sequencing of CD271⁺ and CD271^- cells revealed molecularly distinct, coexisting cellular subsets, both in vitro and in vivo MAPK/ERK signaling was upregulated in the CD271⁺ population, and inhibiting this pathway reduced endogenous CD271 levels, stem/progenitor cell proliferation, and cell survival as well as cell migration in vitro Treatment with the MEK inhibitor selumetinib extended survival and reduced CD271 levels in vivo, whereas, treatment with vismodegib, a well-known smoothened (SMO) inhibitor currently in clinical trials for the treatment of recurrent SHH medulloblastoma, had no significant effect in our models. Our study demonstrates the clinical utility of CD271 as both a diagnostic and prognostic tool for SHH medulloblastoma tumors and reveals a novel role for MEK inhibitors in targeting CD271⁺ SHH medulloblastoma cells.Significance: This study identifies CD271 as a specific and novel biomarker of SHH-type medulloblastoma and that targeting CD271⁺ cells through MEK inhibition represents a novel therapeutic strategy for the treatment of SHH medulloblastoma. Cancer Res; 78(16); 4745-59. ©2018 AACR.

Characterization of a novel OTX2-driven stem cell program in Group 3 and Group 4 medulloblastoma

Medulloblastoma (MB) is the most common malignant primary pediatric brain cancer. Among the most aggressive subtypes, Group 3 and Group 4 originate from stem/progenitor cells, frequently metastasize, and often display the worst prognosis, yet we know the least about the molecular mechanisms driving their progression. Here, we show that the transcription factor orthodenticle homeobox 2 (OTX2) promotes self-renewal while inhibiting differentiation in vitro and increases tumor initiation from MB stem/progenitor cells in vivo. To determine how OTX2 contributes to these processes, we employed complementary bioinformatic approaches to characterize the OTX2 regulatory network and identified novel relationships between OTX2 and genes associated with neuronal differentiation and axon guidance signaling in Group 3 and Group 4 MB stem/progenitor cells. In particular, OTX2 levels were negatively correlated with semaphorin (SEMA) signaling, as expression of 9 SEMA pathway genes is upregulated following OTX2 knockdown with some being potential direct OTX2 targets. Importantly, this negative correlation was also observed in patient samples, with lower expression of SEMA4D associated with poor outcome specifically in Group 4 tumors. Functional proof-of-principle studies demonstrated that increased levels of select SEMA pathway genes are associated with decreased self-renewal and growth in vitro and in vivo and that RHO signaling, known to mediate the effects of SEMA genes, is contributing to the OTX2 KD phenotype. Our study provides mechanistic insight into the networks controlled by OTX2 in MB stem/progenitor cells and reveals novel roles for axon guidance genes and their downstream effectors as putative tumor suppressors in MB.

Novel glycolipid agents for killing cisplatin-resistant human epithelial ovarian cancer cells

Background

Chemotherapy resistance is one of the major factors contributing to mortality from human epithelial ovarian cancer (EOC). Identifying drugs that can effectively kill chemotherapy-resistant EOC cells would be a major advance in reducing mortality. Glycosylated antitumour ether lipids (GAELs) are synthetic glycolipids that are cytotoxic to a wide range of cancer cells. They appear to induce cancer cell death in an apoptosis-independent manner.

Methods

Herein, the effectiveness of two GAELs, GLN and MO-101, in killing chemotherapy-sensitive and –resistant EOC cells lines and primary cell samples was tested using monolayer, non-adherent aggregate, and non-adherent spheroid cultures.

Results

Our results show that EOC cells exhibit a differential sensitivity to the GAELs. Strikingly, both GAELs are capable of inducing EOC cell death in chemotherapy-sensitive and –resistant cells grown as monolayer or non-adherent cultures. Mechanistic studies provide evidence that apoptotic-cell death (caspase activation) contributes to, but is not completely responsible for, GAEL-induced cell killing in the A2780-cp EOC cell line, but not primary EOC cell samples.

Conclusions

Studies using primary EOC cell samples supports previously published work showing a GAEL-induced caspase-independent mechanism of death. GAELs hold promise for development as novel compounds to combat EOC mortality due to chemotherapy resistance.

Electronic supplementary material

The online version of this article (doi:10.1186/s13046-017-0538-9) contains supplementary material, which is available to authorized users.

Characterization of novel biomarkers in selecting for subtype specific medulloblastoma phenotypes

Major research efforts have focused on defining cell surface marker profiles for characterization and selection of brain tumor stem/progenitor cells. Medulloblastoma is the most common primary malignant pediatric brain cancer and consists of 4 molecular subgroups: WNT, SHH, Group 3 and Group 4. Given the heterogeneity within and between medulloblastoma variants, surface marker profiles may be subtype-specific. Here, we employed a high throughput flow cytometry screen to identify differentially expressed cell surface markers in self-renewing vs. non-self-renewing SHH medulloblastoma cells. The top 25 markers were reduced to 4, CD271/p75NTR/NGFR, CD106/VCAM1, EGFR and CD171/NCAM-L1, by evaluating transcript levels in SHH tumors relative to samples representing the other variants. However, only CD271/p75NTR/NGFR and CD171/NCAM-L1 maintain differential expression between variants at the protein level. Functional characterization of CD271, a low affinity neurotrophin receptor, in cell lines and primary cultures suggested that CD271 selects for lower self-renewing progenitors or stem cells. Moreover, CD271 levels were negatively correlated with expression of SHH pathway genes. Our study reveals a novel role for CD271 in SHH medulloblastoma and suggests that targeting CD271 pathways could lead to the design of more selective therapies that lessen the broad impact of current treatments on developing nervous systems.

Differential cellular responses induced by dorsomorphin and LDN-193189 in chemotherapy-sensitive and chemotherapy-resistant human epithelial ovarian cancer cells

Inherent or acquired drug resistance is a major contributor to epithelial ovarian cancer (EOC) mortality. Novel drugs or drug combinations that produce EOC cell death or resensitize drug resistant cells to standard chemotherapy may improve patient treatment. After conducting drug tolerability studies for the multikinase inhibitors dorsomorphin (DM) and it is structural analogue LDN-193189 (LDN), these drugs were tested in a mouse intraperitoneal xenograft model of EOC. DM significantly increased survival, whereas LDN showed a trend toward increased survival. In vitro experiments using cisplatin (CP)-resistant EOC cell lines, A2780-cp or SKOV3, we determined that pretreatment or cotreatment with DM or LDN resensitized cells to the killing effect of CP or carboplatin (CB). DM was capable of blocking EOC cell cycle and migration, whereas LDN produced a less pronounced effect on cell cycle and no effect on migration. Subsequent analyses using primary human EOC cell samples or additional established EOC cells lines showed that DM or LDN induced a dose-dependent autophagic or cell death response, respectively. DM induced a characteristic morphological change with the appearance of numerous LC3B-containing acidic vacuoles and an increase in LC3BII levels. This was coincident with a decrease in cell growth and the altered cell cycle consistent with DM-induced cytostasis. By contrast, LDN produced a caspase 3-independent, reactive oxygen species-dependent cell death. Overall, DM and LDN possess drug characteristics suitable for adjuvant agents used to treat chemotherapy-sensitive and -resistant EOC.

In vivo generation of neural tumors from neoplastic pluripotent stem cells models early human pediatric brain tumor formation

Recent studies have identified gene signatures in malignant tumors that are associated with human embryonic stem cells, suggesting a molecular relationship between aggressive cancers and pluripotency. Here, we characterize neural precursors (NPs) derived from transformed human embryonic stem cells (N-t-hESCs) that exhibit neoplastic features of human brain tumors. NPs derived from t-hESCs have enhanced cell proliferation and an inability to mature toward the astrocytic lineage, compared with progeny derived from normal human embryonic stem cells (N-hESCs) independent of adherent or neurosphere outgrowth. Intracranial transplantation of NPs derived from N-t-hESCs and N-hESCs into NOD SCID mice revealed development of neuroectoderm tumors exclusively from the N-t-hESCs NPs and not from normal N-hESCs. These tumors infiltrated the ventricles and the cerebellum of recipient mice and displayed morphological, phenotypic, and molecular features associated with classic medulloblastoma including retention of a pluripotent signature. Importantly, N-t-hESCs did not exhibit cytogenetic changes associated with medulloblastoma, suggesting that aberrant cellular and molecular properties precede the acquisition of karyotypic changes thus underscoring the value of this model system of human medulloblastoma. Our study demonstrates that NPs from a starting population of neoplastic human pluripotent parent cells possess brain tumor-initiating cell capacity, thereby providing a model system to investigate initiation and progression of primitive human neural cancers that are difficult to assess using somatic sources.

Evidence for the transmission of neoplastic properties from transformed to normal human stem cells

The in vivo relationship between human tumor cells and interacting normal cells in their local environment is poorly understood. Here, using a uniquely developed in vitro co-culture system for human embryonic stem cells (hESCs), we examined the interactions between transformed and normal human stem cells. Co-culture of transformed-hESCs (t-hESCs) with normal hESCs led to enhanced self-renewal and niche independence in normal hESCs. Global gene expression analysis of normal hESCs after timed exposure to t-hESCs indicated a transition of the molecular network controlling the hESC state, which included epigenetic changes, towards neoplastic features. These included enhanced pluripotent marker expression and a differentiation blockade as major hallmark changes. Functional studies revealed a loss in normal terminal differentiation programs for both hematopoiesis and neural lineages after normal stem cell co-culture with transformed variants. This transmission of neoplastic properties from t-hESCs to normal hESCs was dependent on direct cell-cell contact. Our study indicates that normal human stem cells can co-opt neoplastic cancer stem cell properties, raising the possibility that assimilation of healthy cells towards neoplastic behavior maybe a contributing feature of sustained tumorigenesis in vivo.

Pluripotent transcription factors possess distinct roles in normal versus transformed human stem cells

Background

Cancer and normal stem cells (SCs) share proliferative properties of self-renewal and expression of key transcription factors (TFs). Despite similar TF identities, the functional role of specific TFs responsible for retaining SC state has yet to be examined in cancer.

Methodology/Principal Findings

Here, we compare the role of Oct4 and Nanog, two-core pluripotent TFs, in transformed (t-hPSCs), and normal human pluripotent stem cells (hPSCs). Unlike normal SCs, self-renewal and survival of t-hPSCs were found to be independent of Oct4. In contrast, t-hPSCs exhibit hypersensitivity to reduction in Nanog and demonstrate complete loss of self-renewal coupled with apoptosis. Dual and sequential knockdown of Oct4 and Nanog revealed that sensitivity of t-hPSCs to Nanog was Oct4 dependent.

Conclusions/Significance

Our study indicates a bifurcation for the role of two-core SC and cancer related TFs in self-renewal and survival processes. We suggest that the divergent roles of these TFs establish a paradigm to develop novel therapeutics towards selective destruction of aggressive tumors harboring cancer stem cells (CSCs) with similar molecular signatures.

Pluripotent human stem cell lines: what we can learn about cancer initiation

Although the cancer stem cell (CSC) hypothesis has become an attractive model to account for tumor recurrence, failure to define a cell of origin has created the need to explore alternative models for cancer initiation and maintenance. Recent studies have linked an embryonic stem cell (ESC)-like gene signature with poorly defined high-grade tumors. Here, we review advances in the ESC field with an emphasis on how human pluripotent stem cells (hPSCs) can be used to define early tumorigenic events, including potential miRNA and epigenetic targets, as well as proto-oncogene and tumor suppressor networks that might facilitate hierarchal transformation. These studies allow for investigation of cancer initiation in a manner that cannot be achieved using primary tumors, where only retrospective evaluation of CSC development is possible. By comparing transformed hPSCs with their normal counterparts, we hope to develop novel cell-specific therapies that selectively target CSCs.

Inhibition of medulloblastoma cell invasion by Slit

Invasion of brain tumor cells has made primary malignant brain neoplasms among the most recalcitrant to therapeutic strategies. We tested whether the secreted protein Slit2, which guides the projection of axons and developing neurons, could modulate brain tumor cell invasion. Slit2 inhibited the invasion of medulloblastoma cells in a variety of in vitro models. The effect of Slit2 was inhibited by the Robo ectodomain. Time-lapse videomicroscopy indicated that Slit2 reduced medulloblastoma invasion rate without affecting cell direction or proliferation. Both medulloblastoma and glioma tumors express Robo1 and Slit2, but only medulloblastoma invasion is inhibited by recombinant Slit2 protein. Downregulation of activated Cdc42 may contribute to this differential response. Our findings reinforce the concept that neurodevelopmental cues such as Slit2 may provide insights into brain tumor invasion.

Isolation of a natural inhibitor of human malignant glial cell invasion: inter alpha-trypsin inhibitor heavy chain 2

Malignant central nervous system (CNS) tumors, such as glioblastoma multiforme, invade the brain and disrupt normal tissue architecture, making complete surgical removal virtually impossible. Here, we have developed and optimized a purification strategy to isolate and identify natural inhibitors of glioma cell invasion in a three-dimensional collagen type I matrix. Inter alpha-trypsin inhibitor heavy chain 2 (ITI H2) was identified from the most inhibitory fractions and its presence was confirmed both as a single protein and in a bikunin-bound form. Stable overexpression in U251 glioma cells validated ITI H2's strong inhibition of human glioma cell invasion together with significant inhibition of cell proliferation and promotion of cell-cell adhesion. Analysis of primary human brain tumors showed significantly higher levels of ITI H2 in normal brain and low-grade tumors compared with high-grade gliomas, indicating an inverse correlation with malignancy. The phosphatidylinositol 3-kinase/Akt signaling cascade seemed to be one of the pathways involved in the effect of ITI H2 on U251 cells. These findings suggest that reduction of ITI H2 expression correlates with brain tumor progression and that targeting factors responsible for its loss or restoring the ITI supply exogenously may serve as potential therapeutic strategies for a variety of CNS tumors.