Glioblastoma (GBM) is the most common adult primary brain tumor, and the 5-year survival rate is less than 5%. GBM malignancy is driven in part by a population of GBM stem-like cells (GSCs) that exhibit indefinite self-renewal capacity, multipotent differentiation, expression of neural stem cell markers, and resistance to conventional treatments. GSCs are enriched in specialized niche microenvironments that regulate stem phenotypes and support GSC radioresistance. Therefore, identifying GSC-niche interactions that regulate stem phenotypes may present a unique target for disrupting the maintenance and persistence of this treatment resistant population. In this work, we engineered 3D scaffolds from temperature responsive poly(N-isopropylacrylamide-co-Jeffamine M-1000® acrylamide), or PNJ copolymers, as a platform for enriching stem-specific phenotypes in two molecularly distinct human patient-derived GSC cell lines. Notably, we observed that, compared to conventional neurosphere cultures, PNJ cultured GSCs maintained multipotency and exhibited enhanced self-renewal capacity. Concurrent increases in expression of proteins known to regulate self-renewal, invasion, and stem maintenance in GSCs (NESTIN, EGFR, CD44) suggest that PNJ scaffolds effectively enrich the GSC population. We further observed that PNJ cultured GSCs exhibited increased resistance to radiation treatment compared to GSCs cultured in standard neurosphere conditions. GSC radioresistance is supported in vivo by niche microenvironments, and this remains a significant barrier to effectively treating these highly tumorigenic cells. Taken in sum, these data indicate that the microenvironment created by synthetic PNJ scaffolds models niche enrichment of GSCs in patient-derived GBM cell lines, and presents tissue engineering opportunities for studying clinically important behaviors such as radioresistance in vitro.

Glioblastoma (GBM) is characterized by an aberrant yet druggable epigenetic landscape. One major family of epigenetic regulators, the histone deacetylases (HDACs), are considered promising therapeutic targets for GBM due to their repressive influences on transcription. Although HDACs share redundant functions and common substrates, the unique isoform-specific roles of different HDACs in GBM remain unclear. In neural stem cells, HDAC2 is the indispensable deacetylase to ensure normal brain development and survival in the absence of HDAC1. Surprisingly, we find that HDAC1 is the essential class I deacetylase in glioma stem cells, and its loss is not compensated for by HDAC2. Using cell-based and biochemical assays, transcriptomic analyses, and patient-derived xenograft models, we find that knockdown of HDAC1 alone has profound effects on the glioma stem cell phenotype in a p53-dependent manner. We demonstrate marked suppression in tumor growth upon targeting of HDAC1 and identify compensatory pathways that provide insights into combination therapies for GBM. Our study highlights the importance of HDAC1 in GBM and the need to develop isoform-specific drugs.

OLIG2 is a central nervous system-specific transcription factor that is expressed in almost all diffuse gliomas. It is also one of the key core transcription factors that can reprogram differentiated glioma cells to highly tumorigenic glioma stem-like cells (GSCs). We have previously shown that expression of OLIG2 is critical for glioma growth both in a genetically relevant mouse model as well as in patient-derived xenograft models. Our work suggests that a small molecule inhibitor of OLIG2 could serve as a highly targeted therapy for high-grade glioma; however, transcription factors are generally very difficult to target because their interactions with DNA and co-regulatory proteins involve large and complex surface area contacts. Our laboratory has shown that OLIG2 functions are regulated through interactions with distinct co-regulator proteins in normal neural stem cells. However, there are currently no reports on interactors that promote the proto-oncogenic functions of OLIG2 in malignant glioma. In this study, we employed two independent proteomics screens identify tumor-specific, druggable OLIG2 co-regulators as possible surrogate targets to suppress OLIG2 function in glioma. These screens led to the identification of a novel OLIG2 partner protein: Histone Deacetylase 1 (HDAC1). We confirmed that this interaction occurs in both murine and human glioma models. Although HDACs are ubiquitously expressed and are known to be functionally redundant, we show that ablation of HDAC1 alone significantly decreases the stemness and proliferation capacity of patient-derived GSCs in a p53-dependent manner, while having a minimal impact on normal human neural stem cells and astrocytes. Furthermore, we demonstrate that knockdown of HDAC1, in combination with ionizing radiation treatment, significantly alters the growth pattern of intracranial tumors in vivo. We demonstrate that HDAC1 function is critical for GSC growth and provide a strong rationale for targeting the OLIG2-HDAC1 interaction in malignant glioma.

Glioblastoma (GBM) brain tumors contain a subpopulation of self-renewing multipotent Glioblastoma stem-like cells (GSCs) that are believed to drive the near inevitable recurrence of GBM. We previously engineered temperature responsive...