Widespread resetting of DNA methylation in glioblastoma-initiating cells suppresses malignant cellular behavior in a lineage-dependent manner

Abstract

Epigenetic changes are frequently observed in cancer. However, their role in establishing or sustaining the malignant state has been difficult to determine due to the lack of experimental tools that enable resetting of epigenetic abnormalities. To address this, we applied induced pluripotent stem cell (iPSC) reprogramming techniques to invoke widespread epigenetic resetting of glioblastoma (GBM)-derived neural stem (GNS) cells. GBM iPSCs (GiPSCs) were subsequently redifferentiated to the neural lineage to assess the impact of cancerspecific epigenetic abnormalities on tumorigenicity. GiPSCs and their differentiating derivatives display widespread resetting of common GBM-associated changes, such as DNA hypermethylation of promoter regions of the cell motility regulator TES (testis-derived transcript), the tumor suppressor cyclin-dependent kinase inhibitor 1C (CDKN1C; p57KIP2), and many polycomb-repressive complex 2 (PRC2) target genes (e.g., SFRP2). Surprisingly, despite such global epigenetic reconfiguration, GiPSC-derived neural progenitors remained highly malignant upon xenotransplantation. Only when GiPSCs were directed to nonneural cell types did we observe sustained expression of reactivated tumor suppressors and reduced infiltrative behavior. These data suggest that imposing an epigenome associated with an alternative developmental lineage can suppress malignant behavior. However, in the context of the neural lineage, widespread resetting of GBM-associated epigenetic abnormalities is not sufficient to override the cancer genome.

Multiplexed RNAi therapy against brain tumor-initiating cells via lipopolymeric nanoparticle infusion delays glioblastoma progression

“…The concept that forced differentiation abolishes the malignant epigenetic programs underlying tumorigenesis was strengthened further, thanks to efforts in the field of leukemia (58), by the global reset of the epigenetic states to override the tumor genome (59). Although a single factor [e.g., bone morphogenic protein 4 (BMP4) (60)] is capable of inducing BTIC differentiation, complex signaling mixtures, such as serum (61), or a chromatin regulator complex, such as PRC2 (62), demonstrate gradual and at times reversible epigenetic override of the malignant gene circuits of BTICs.…”

Convection enhanced delivery of panobinostat (LBH589)-loaded pluronic nano-micelles prolongs survival in the F98 rat glioma model

“…Patient-derived glioma stem cell lines, G144 and G26 were obtained as a kind gift from Dr Colin Watts (University of Cambridge, Cambridge, UK) and Dr Steven Pollard (University of Edinburgh, Edinburgh, UK) and cultured following instructions from the host laboratories. 34,35 Primary hippocampal cell culture Neuronal cultures were obtained from the hippocampus of 18-day-old Wistar rat embryos as previously described. 36 Cells were counted and plated on poly-d-lysine-coated 10 mm coverslips (Sigma-Aldrich, Dorset, UK) at a density of 75,000 cells per coverslip.…”

Using induced pluripotent stem cells as a tool for modelling carcinogenesis

“…Generation of iPSCs from other cancer types is necessary to develop relevant in vitro models for carcinogenesis. [73] , 2013 CML iPSCs from CML cell lines and primary patient samples Carette et al [70] , 2010 Kumano et al [72] , 2012 JML Derived iPSCs from 2 JML patients Gandre-Babbe et al [75] , 2013 Gastrointestinal cancer Generated iPSCs from multiple GI cancer cell lines Miyoshi et al [69] , 2010 Glioblastoma iPSCs generated from glioblastoma-derived neural stem cells Stricker et al [76] , 2014; Stricker et al [77] , 2013…”

“…However, lineage specificity may remain due to incomplete reprogramming and can also be induced by differentiation. For example, in iPSCs derived from glioblastomas both lineage and cancer associated methylation marks were reset however during differentiation along the neural lineage cells maintained their malignant phenotype [76,77] .…”