Authors:
Sheila Mansouri, Carlos Velasquez, Shirin Karimi, Farshad Nassiri, Yasin Mamatjan, Olivia Singh, Julie Metcalf, Mira Li, Suganth Suppiah, Alireza Mansouri, Alireza Mansouri, Kenneth Aldape, Gelareh Zadeh
Abstract:
High cellularity and poorly organized tumour vasculature in high-grade gliomas leads to insufficient blood supply, hypoxic areas, and ultimately to the formation of necrosis. Thus, hypoxia is a hallmark of malignant glioma microenvironment and it is associated with aggressive tumor behavior such as growth, progression, and resistance to chemo-radiation. Current pathologic markers are insufficient to identify patients that may benefit from specific treatments. We therefore, hypothesized that underlying epigenetic alterations confer therapeutic r (...)
High cellularity and poorly organized tumour vasculature in high-grade gliomas leads to insufficient blood supply, hypoxic areas, and ultimately to the formation of necrosis. Thus, hypoxia is a hallmark of malignant glioma microenvironment and it is associated with aggressive tumor behavior such as growth, progression, and resistance to chemo-radiation. Current pathologic markers are insufficient to identify patients that may benefit from specific treatments. We therefore, hypothesized that underlying epigenetic alterations confer therapeutic resistance under hypoxic conditions. Twenty five GBM patients were consented and treated with pimonidazole (PIMO) 16–18 hours prior to surgery. Tumor sections were subjected to immunohistochemical analysis using antibodies against PIMO and other hypoxia markers such HIF1a and CAIX. Samples were subjected to laser capture microdissection followed by DNA isolation and DNA methylation profiling using the Illumina Human Methylation EPIC Array. Data was analyzed using minfi and conumee packages in Bioconductor, together with appropriate biostatistics tools. PIMO score was determined to range from 10–60% and positively correlated with other hypoxia markers such as CA IX and HIF1a (p4,000) were hypomethylated. Gene set enrichment analysis (GSEA) indicated that the majority of these CpGs are associated with genes involved in signalling cascades and oncogenic processes, including WNT and NOTCH. These were compared to DNA methylation profiles of glioma stem cells exposed to transient hypoxia and extensive overlap was found in proportion of hypomethylated CpG sites and cellular processes that were altered. These findings were correlated with complementary RNA expression data from RNA sequencing to establish the biological relevance of changes in DNA methylation profiles under hypoxia in GBM.
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