144 - GTP Cyclohydrolase I in Tumor Initiating Cell Maintenance and Glioblastoma Growth: Functions and Mechanisms

Abstract

Glioblastoma (GBM), or grade IV astrocytoma, is a deadly disease due in part to the high degree of intratumoral heterogeneity that contributes to treatment failures. One cellular subset enriched for the capacity to propagate tumor growth and promote therapeutic resistance is brain tumor initiating cells (BTICs). The aim of the study was to define the roles of GTP cyclohydrolase 1 (GCH1) in regulation of BTIC phenotypes via reactive species. We examined GCH1 mRNA and protein expression in patient-derived xenografts, clinical samples and glioma gene expression datasets. GCH1 levels were modulated using lentiviral expression systems, and effects on cell growth, self-renewal, reactive species production and in vitro animal survival were determined. We found that GCH1 RNA and protein expression were increased in BTICs in comparison to non-BTICs, but that GCH1 was not exclusive to the BTIC fraction. Indeed, GCH1 was elevated in GBM in comparison to normal brain. Overexpression of GCH1 in GBM cells increased cell growth in vitro and decreased survival in an intracranial GBM mouse model. In contrast, GCH1 knockdown with short hairpin RNA in GBM cells led to growth inhibition in vitro as well as increased survival in animal models. Mechanistically, GCH1 increased CD44 expression and was critical for controlling reactive species balance, including suppressing reactive oxygen species production. In silico analyses demonstrated that higher GCH1 levels in glioma patients correlate with higher glioma grade, recurrence and worse survival. Together, our data suggest that upregulation of GCH1 in BTICs promotes tumor maintenance and is a key regulator of reactive oxygen species in GBM.