Dual MAPK Inhibition Triggers Pro-inflammatory Signals and Sensitizes BRAF Glioma to T Cell-Mediated Checkpoint Therapy.

BRAF pediatric low-grade gliomas frequently transform into high-grade gliomas (HGG) and poorly respond to chemotherapy, resulting in high mortality. Although combined BRAF and MEK inhibition (BRAFi+MEKi) outperforms chemotherapy, ∼70% of BRAF HGG patients are therapy resistant and undergo unbridled tumor progression. BRAF glioma have an immune-rich microenvironment suggesting that they could be responsive to immunotherapy but effects of BRAFi+MEKi on anti-tumor immunity are unclear.

BRAF V600E in a preclinical model of pleomorphic Xanthoastrocytoma: Analysis of the tumor microenvironment and immune cell infiltration dynamics .

Low-grade glioma (LGG) is the most common brain tumor affecting pediatric patients (pLGG) and BRAF mutations constitute the most frequent genetic alterations. Within the spectrum of pLGGs, approximately 70%-80% of pediatric patients diagnosed with transforming pleomorphic xanthoastrocytoma (PXA) harbor the BRAF V600E mutation. However, the impact of glioma BRAF V600E cell regulation of tumor-infiltrating immune cells and their contribution to tumor progression remains unclear.

Successes and challenges in modeling heterogeneous BRAF mutated central nervous system neoplasms.

Central nervous system (CNS) neoplasms are difficult to treat due to their sensitive location. Over the past two decades, the availability of patient tumor materials facilitated large scale genomic and epigenomic profiling studies, which have resulted in detailed insights into the molecular underpinnings of CNS tumorigenesis. Based on results from these studies, CNS tumors have high molecular and cellular intra-tumoral and inter-tumoral heterogeneity.

LGL1 binds to Integrin β1 and inhibits downstream signaling to promote epithelial branching in the mammary gland.

Branching morphogenesis is a fundamental process by which organs in invertebrates and vertebrates form branches to expand their surface areas. The current dogma holds that directional cell migration determines where a new branch forms and thus patterns branching. Here, we asked whether mouse Lgl1, a homolog of the Drosophila tumor suppressor Lgl, regulates epithelial polarity in the mammary gland.

A pilot precision medicine trial for children with diffuse intrinsic pontine glioma-PNOC003: A report from the Pacific Pediatric Neuro-Oncology Consortium.

This clinical trial evaluated whether whole exome sequencing (WES) and RNA sequencing (RNAseq) of paired normal and tumor tissues could be incorporated into a personalized treatment plan for newly diagnosed patients (<25 years of age) with diffuse intrinsic pontine glioma (DIPG). Additionally, whole genome sequencing (WGS) was compared to WES to determine if WGS would further inform treatment decisions, and whether circulating tumor DNA (ctDNA) could detect the H3K27M mutation to allow assessment of therapy response. Patients were selected across three Pacific Pediatric Neuro-Oncology Consortium member institutions between September 2014 and January 2016.

Lgl1 controls NG2 endocytic pathway to regulate oligodendrocyte differentiation and asymmetric cell division and gliomagenesis.

Oligodendrocyte progenitor cells (OPC) undergo asymmetric cell division (ACD) to generate one OPC and one differentiating oligodendrocyte (OL) progeny. Loss of pro-mitotic proteoglycan and OPC marker NG2 in the OL progeny is the earliest immunophenotypic change of unknown mechanism that indicates differentiation commitment. Here, we report that expression of the mouse homolog of Drosophila tumor suppressor Lethal giant larvae 1 (Lgl1) is induced during OL differentiation.

Impaired neural stem cell expansion and hypersensitivity to epileptic seizures in mice lacking the EGFR in the brain.

Mice lacking the epidermal growth factor receptor (EGFR) develop an early postnatal degeneration of the frontal cortex and olfactory bulbs and show increased cortical astrocyte apoptosis. The poor health and early lethality of EGFR mice prevented the analysis of mechanisms responsible for the neurodegeneration and function of the EGFR in the adult brain. Here, we show that postnatal EGFR-deficient neural stem cells are impaired in their self-renewal potential and lack clonal expansion capacity in vitro.

Regulation of Asymmetric Cell Division in Mammalian Neural Stem and Cancer Precursor Cells.

Stem and progenitor cells are characterized by their abilities to self-renew and produce differentiated progeny. The balance between self-renewal and differentiation is achieved through control of cell division mode, which can be either asymmetric or symmetric. Failure to properly control cell division mode may result in premature depletion of the stem/progenitor cell pool or abnormal growth and impaired differentiation.

BRAF Status in Personalizing Treatment Approaches for Pediatric Gliomas.

Purpose: Alteration of the BRAF/MEK/MAPK pathway is the hallmark of pediatric low-grade gliomas (PLGGs), and mTOR activation has been documented in the majority of these tumors. We investigated combinations of MEK1/2, BRAF and mTOR inhibitors in gliomas carrying specific genetic alterations of the MAPK pathway.

Experimental Design: We used human glioma lines containing BRAF (adult high-grade: AM-38, DBTRG, PLGG: BT40), or wild-type BRAF (pediatric high-grade: SF188, SF9427, SF8628) and isogenic systems of KIAA1549:BRAF-expressing NIH/3T3 cells and BRAF-expressing murine brain cells.

Concurrent MEK targeted therapy prevents MAPK pathway reactivation during BRAFV600E targeted inhibition in a novel syngeneic murine glioma model.

Inhibitors of BRAFV600E kinase are currently under investigations in preclinical and clinical studies involving BRAFV600E glioma. Studies demonstrated clinical response to such individualized therapy in the majority of patients whereas in some patients tumors continue to grow despite treatment. To study resistance mechanisms, which include feedback activation of mitogen-activated protein kinase (MAPK) signaling in melanoma, we developed a luciferase-modified cell line (2341luc) from a BrafV600E mutant and Cdkn2a- deficient murine high-grade glioma, and analyzed its molecular responses to BRAFV600E- and MAPK kinase (MEK)-targeted inhibition.

Pan-cancer analysis of the extent and consequences of intratumor heterogeneity.

Intratumor heterogeneity (ITH) drives neoplastic progression and therapeutic resistance. We used the bioinformatics tools 'expanding ploidy and allele frequency on nested subpopulations' (EXPANDS) and PyClone to detect clones that are present at a ≥10% frequency in 1,165 exome sequences from tumors in The Cancer Genome Atlas. 86% of tumors across 12 cancer types had at least two clones.

Targeting a Plk1-Controlled Polarity Checkpoint in Therapy-Resistant Glioblastoma-Propagating Cells.

The treatment of glioblastoma (GBM) remains challenging in part due to the presence of stem-like tumor-propagating cells that are resistant to standard therapies consisting of radiation and temozolomide. Among the novel and targeted agents under evaluation for the treatment of GBM are BRAF/MAPK inhibitors, but their effects on tumor-propagating cells are unclear. Here, we characterized the behaviors of CD133(+) tumor-propagating cells isolated from primary GBM cell lines.

Numerical chromosomal instability mediates susceptibility to radiation treatment.

The exquisite sensitivity of mitotic cancer cells to ionizing radiation (IR) underlies an important rationale for the widely used fractionated radiation therapy. However, the mechanism for this cell cycle-dependent vulnerability is unknown. Here we show that treatment with IR leads to mitotic chromosome segregation errors in vivo and long-lasting aneuploidy in tumour-derived cell lines.

ASYMMETRIC CELL DIVISION: IMPLICATIONS FOR GLIOMA DEVELOPMENT AND TREATMENT.

Glioma is a heterogeneous disease process with differential histology and treatment response. It was previously thought that the histological features of glial tumors indicated their cell of origin. However, the discovery of continuous neuro-gliogenesis in the normal adult brain and the identification of brain tumor stem cells within glioma have led to the hypothesis that these brain tumors originate from multipotent neural stem or progenitor cells, which primarily divide asymmetrically during the postnatal period.

Pharmacologic inhibition of histone demethylation as a therapy for pediatric brainstem glioma.

Pediatric brainstem gliomas often harbor oncogenic K27M mutation of histone H3.3. Here we show that GSKJ4 pharmacologic inhibition of K27 demethylase JMJD3 increases cellular H3K27 methylation in K27M tumor cells and demonstrate potent antitumor activity both in vitro against K27M cells and in vivo against K27M xenografts.

Heterogeneously expressed fezf2 patterns gradient Notch activity in balancing the quiescence, proliferation, and differentiation of adult neural stem cells.

Balancing quiescence, self-renewal, and differentiation in adult stem cells is critical for tissue homeostasis. The underlying mechanisms, however, remain incompletely understood. Here we identify Fezf2 as a novel regulator of fate balance in adult zebrafish dorsal telencephalic neural stem cells (NSCs).

A microRNA-operated switch of asymmetric-to-symmetric cancer stem cell divisions.

Defective asymmetric cell divisions of stem and progenitor cells are associated with tumorigenesis by a largely unknown mechanism. A signalling axis involving Snail, microRNA-146a and Numb is now shown to regulate the switch between symmetric and asymmetric cell division in colorectal cancer stem cells.

EXPANDS: expanding ploidy and allele frequency on nested subpopulations.

Motivation: Several cancer types consist of multiple genetically and phenotypically distinct subpopulations. The underlying mechanism for this intra-tumoral heterogeneity can be explained by the clonal evolution model, whereby growth advantageous mutations cause the expansion of cancer cell subclones. The recurrent phenotype of many cancers may be a consequence of these coexisting subpopulations responding unequally to therapies.

Asymmetric cell division of stem and progenitor cells during homeostasis and cancer.

Stem and progenitor cells are characterized by their ability to self-renew and produce differentiated progeny. A fine balance between these processes is achieved through controlled asymmetric divisions and is necessary to generate cellular diversity during development and to maintain adult tissue homeostasis. Disruption of this balance may result in premature depletion of the stem/progenitor cell pool, or abnormal growth.

Proteoglycans and their roles in brain cancer.

Glioblastoma, a malignant brain cancer, is characterized by abnormal activation of receptor tyrosine kinase signalling pathways and a poor prognosis. Extracellular proteoglycans, including heparan sulfate and chondroitin sulfate, play critical roles in the regulation of cell signalling and migration via interactions with extracellular ligands, growth factor receptors and extracellular matrix components, as well as intracellular enzymes and structural proteins. In cancer, proteoglycans help drive multiple oncogenic pathways in tumour cells and promote critical tumour-microenvironment interactions.

Cooperative interactions of BRAFV600E kinase and CDKN2A locus deficiency in pediatric malignant astrocytoma as a basis for rational therapy.

Although malignant astrocytomas are a leading cause of cancer-related death in children, rational therapeutic strategies are lacking. We previously identified activating mutations of v-raf murine sarcoma viral oncogene homolog B1 (BRAF) (BRAF(T1799A) encoding BRAF(V600E)) in association with homozygous cyclin-dependent kinase inhibitor 2A (CDKN2A, encoding p14ARF and p16Ink4a) deletions in pediatric infiltrative astrocytomas. Here we report that BRAF(V600E) expression in neural progenitors (NPs) is insufficient for tumorigenesis and increases NP cellular differentiation as well as apoptosis.

Asymmetry-defective oligodendrocyte progenitors are glioma precursors.

Postnatal oligodendrocyte progenitor cells (OPC) self-renew, generate mature oligodendrocytes, and are a cellular origin of oligodendrogliomas. We show that the proteoglycan NG2 segregates asymmetrically during mitosis to generate OPC cells of distinct fate. NG2 is required for asymmetric segregation of EGFR to the NG2(+) progeny, which consequently activates EGFR and undergoes EGF-dependent proliferation and self-renewal.

Dronc caspase exerts a non-apoptotic function to restrain phospho-Numb-induced ectopic neuroblast formation in Drosophila.

Drosophila neuroblasts have served as a model to understand how the balance of stem cell self-renewal versus differentiation is achieved. Drosophila Numb protein regulates this process through its preferential segregation into the differentiating daughter cell. How Numb restricts the proliferation and self-renewal potentials of the recipient cell remains enigmatic.