Suppression of autophagy impedes glioblastoma development and induces senescence

The function of macroautophagy/autophagy during tumor initiation or in established tumors can be highly distinct and context-dependent. To investigate the role of autophagy in gliomagenesis, we utilized a KRAS-driven glioblastoma mouse model in which autophagy is specifically disrupted via RNAi against Atg7, Atg13 or Ulk1. Inhibition of autophagy strongly reduced glioblastoma development, demonstrating its critical role in promoting tumor formation. Further supporting this finding is the observation that tumors originating from Atg7-shRNA injections escaped the knockdown effect and thereby still underwent functional autophagy. In vitro, autophagy inhibition suppressed the capacity of KRAS-expressing glial cells to form oncogenic colonies or to survive low serum conditions. Molecular analyses revealed that autophagy-inhibited glial cells were unable to maintain active growth signaling under growth-restrictive conditions and were prone to undergo senescence. Overall, these results demonstrate that autophagy is crucial for glioma initiation and growth, and is a promising therapeutic target for glioblastoma treatment

Snail regulates BMP and TGFβ pathways to control the differentiation status of glioma-initiating cells

Glioblastoma multiforme is a brain malignancy characterized by high heterogeneity, invasiveness, and resistance to current therapies, attributes related to the occurrence of glioma stem cells (GSCs). Transforming growth factor β (TGFβ) promotes self-renewal and bone morphogenetic protein (BMP) induces differentiation of GSCs. BMP7 induces the transcription factor Snail to promote astrocytic differentiation in GSCs and suppress tumor growth in vivo. We demonstrate that Snail represses stemness in GSCs. Snail interacts with SMAD signaling mediators, generates a positive feedback loop of BMP signaling and transcriptionally represses the TGFB1 gene, decreasing TGFβ1 signaling activity. Exogenous TGFβ1 counteracts Snail function in vitro, and in vivo promotes proliferation and re-expression of Nestin, confirming the importance of TGFB1 gene repression by Snail. In conclusion, novel insight highlights mechanisms whereby Snail differentially regulates the activity of the opposing BMP and TGFβ pathways, thus promoting an astrocytic fate switch and repressing stemness in GSCs

A Patient-Derived Cell Atlas Informs Precision Targeting of Glioblastoma

Glioblastoma (GBM) is a malignant brain tumor with few therapeutic options. The disease presents with a complex spectrum of genomic aberrations, but the pharmacological consequences of these aberrations are partly unknown. Here, we report an integrated pharmacogenomic analysis of 100 patient-derived GBM cell cultures from the human glioma cell culture (HGCC) cohort. Exploring 1,544 drugs, we find that GBM has two main pharmacological subgroups, marked by differential response to proteasome inhibitors and mutually exclusive aberrations in TP53 and CDKN2A/B. We confirm this trend in cell and in xenotransplantation models, and identify both Bcl-2 family inhibitors and p53 activators as potentiators of proteasome inhibitors in GBM cells, We can further predict the responses of individual cell cultures to several existing drug classes, presenting opportunities for drug repurposing and design of stratified trials. Our functionally profiled biobank provides a valuable resource for the discovery of new treatments for GBM.Patrik Johansson, Cecilia Krona and Soumi Kundu share first authorship</p

Histidine-Rich Glycoprotein Can Prevent Development of Mouse Experimental Glioblastoma

Extensive angiogenesis, formation of new capillaries from pre-existing blood vessels, is an important feature of malignant glioma. Several antiangiogenic drugs targeting vascular endothelial growth factor (VEGF) or its receptors are currently in clinical trials as therapy for high-grade glioma and bevacizumab was recently approved by the FDA for treatment of recurrent glioblastoma. However, the modest efficacy of these drugs and emerging problems with anti-VEGF treatment resistance welcome the development of alternative antiangiogenic therapies. One potential candidate is histidine-rich glycoprotein (HRG), a plasma protein with antiangiogenic properties that can inhibit endothelial cell adhesion and migration. We have used the RCAS/TV-A mouse model for gliomas to investigate the effect of HRG on brain tumor development. Tumors were induced with platelet-derived growth factor-B (PDGF-B), in the presence or absence of HRG. We found that HRG had little effect on tumor incidence but could significantly inhibit the development of malignant glioma and completely prevent the occurrence of grade IV tumors (glioblastoma)

On the origin of glioma

Glioma is the most frequent primary brain tumor of adults that has a presumably glial origin. Although our knowledge regarding molecular mechanisms and signaling pathways involved in gliomagenesis has increased immensely during the past decade, high-grade glioma remains a lethal disease with dismal prognosis. The failure of current therapies has to a large extent been ascribed the functional heterogeneity of glioma cells. One reason for this heterogeneity is most certainly the large number of variations in genetic alterations that can be found in high-grade gliomas. Another factor that may influence glioma heterogeneity could be the cell type from which the glioma is initiated. The cell of origin for glioma is still undefined, and additional knowledge about this issue may prove critical for a more complete understanding of glioma biology. Based on information from patients, developmental biology, and experimental glioma models, the most putative target cells include astrocytes, neural stem cells, and oligodendrocyte precursor cells, which are all discussed in more detail in this article. Animal modeling of glioma suggests that these three cell types have the capability to be the origin of glioma, and we have reason to believe that, depending on the initiating cell type, prognosis and response to therapy may be significantly different. Thus, it is essential to explore further the role of cellular origin in glioma

PDGF in gliomas: more than just a growth factor?

Platelet-derived growth factor B (PDGF-B) is a growth factor promoting and regulating cell migration, proliferation, and differentiation, involved in both developmental processes and in maintaining tissue homeostasis under strict regulation. What are the implications of prolonged or uncontrolled growth factor signaling in vivo, and when does a growth factor such as PDGF-B become an oncogene? Under experimental conditions, PDGF-B induces proliferation and causes tumor induction. It is not known whether these tumors are strictly a PDGF-B-driven proliferation of cells or associated with secondary genetic events such as acquired mutations or methylation-mediated gene silencing promoting neoplasia. If PDGF-B-driven tumorigenesis was only cellular proliferation, associated changes in gene expression would thus be correlated with proliferation and not associated with secondary events involved in tumorigenesis and neoplastic transformation such as cycle delay, DNA damage response, and cell death. Changes in gene expression might be expected to be reversible, as is PDGF-B-driven proliferation under normal circumstances. Since PDGF signaling is involved in oligodendrocyte progenitor cell differentiation and maintenance, it is likely that PDGF-B stimulates proliferation of a pool of cells with that phenotype, and inhibition of PDGF-B signaling would result in reduced expression of oligodendrocyte-associated genes. More importantly, inhibition of PDGF signaling would be expected to result in reversion of genes induced by PDGF-B accompanied by a decrease in proliferation. However, if PDGF-B-driven tumorigenesis is more than simply a proliferation of cells, inhibition of PDGF signaling may not reverse gene expression or halt proliferation. These fundamental questions concerning PDGF-B as a potential oncogene have not been resolved

Non-Invasive Detection of a Small Number of Bioluminescent Cancer Cells In Vivo

Early detection of tumors can significantly improve the outcome of tumor treatment. One of the most frequently asked questions in cancer imaging is how many cells can be detected non-invasively in a live animal. Although many factors limit such detection, increasing the light emission from cells is one of the most effective ways of overcoming these limitations. Here, we describe development and utilization of a lentiviral vector containing enhanced firefly luciferase (luc2) gene. The resulting single cell clones of the mouse mammary gland tumor (4T1-luc2) showed stable light emission in the range of 10,000 photons/sec/cell. In some cases individual 4T1-luc2 cells inserted under the skin of a nu/nu mouse could be detected non-invasively using a cooled CCD camera in some cases. In addition, we showed that only few cells are needed to develop tumors in these mice and tumor progression can be monitored right after the cells are implanted. Significantly higher luciferase activity in these cells allowed us to detect micrometastases in both, syngeneic Balb/c and nu/nu mice

Recruited Cells Can Become Transformed and Overtake PDGF-Induced Murine Gliomas In Vivo during Tumor Progression

Gliomas are thought to form by clonal expansion from a single cell-of-origin, and progression-associated mutations to occur in its progeny cells. Glioma progression is associated with elevated growth factor signaling and loss of function of tumor suppressors Ink4a, Arf and Pten. Yet, gliomas are cellularly heterogeneous; they recruit and trap normal cells during infiltration.We performed lineage tracing in a retrovirally mediated, molecularly and histologically accurate mouse model of hPDGFb-driven gliomagenesis. We were able to distinguish cells in the tumor that were derived from the cell-of-origin from those that were not. Phenotypic, tumorigenic and expression analyses were performed on both populations of these cells. Here we show that during progression of hPDGFb-induced murine gliomas, tumor suppressor loss can expand the recruited cell population not derived from the cell-of-origin within glioma microenvironment to dominate regions of the tumor, with essentially no contribution from the progeny of glioma cell-of-origin. Moreover, the recruited cells can give rise to gliomas upon transplantation and passaging, acquire polysomal expression profiles and genetic aberrations typically present in glioma cells rather than normal progenitors, aid progeny cells in glioma initiation upon transplantation, and become independent of PDGFR signaling.These results indicate that non-cell-of-origin derived cells within glioma environment in the mouse can be corrupted to become bona fide tumor, and deviate from the generally established view of gliomagenesis

Autocrine PDGF stimulation in malignancies

Platelet-derived growth factor (PDGF) isoforms are important mitogens for different types of mesenchymal cells, which have important functions during the embryonal development and in the adult during wound healing and tissue homeostasis. In tumors, PDGF isoforms are often over-expressed and contribute to the growth of both normal and malignant cells. This review focuses on tumors expressing PDGF isoforms together with their tyrosine kinase receptors, thus resulting in autocrine stimulation of growth and survival. Patients with such tumors could benefit from treatment with inhibitors of either PDGF or PDGF receptors