Abstract
Given that glioma stem cells (GSCs) play a critical role in the initiation and chemoresistance in glioblastoma multiforme (GBM), targeting GSCs is an attractive strategy to treat GBM. Utilizing an anti-cancer compound library, we identified R406, the active metabolite of a FDA-approved Syk inhibitor for immune thrombocytopenia (ITP), with remarkable cytotoxicity against GSCs but not normal neural stem cells. R406 significantly inhibited neurosphere formation and triggered apoptosis in GSCs. R406 induced a metabolic shift from glycolysis to oxidative phosphorylation (OXPHOS) and subsequently production of excess ROS in GSCs. R406 also diminished tumor growth and efficiently sensitized gliomas to temozolomide in GSC-initiating xenograft mouse models. Mechanistically, the anti-GSC effect of R406 was due to the disruption of Syk/PI3K signaling in Syk-positive GSCs and PI3K/Akt pathway in Syk-negative GSCs respectively. Overall, these findings not only identify R406 as a promising GSC-targeting agent but also reveal the important role of Syk and PI3K pathways in the regulation of energy metabolism in GSCs.
Highlights
Glioblastoma multiforme (GBM) is one of the most lethal cancers in adults[1]
We identified R406, which is the active metabolite of a FDA-approved Spleen tyrosine kinase (Syk) inhibitor for immune thrombocytopenia (ITP), to effectively reverse glycolysis and trigger apoptosis in glioma stem cells (GSCs)
By using Seahorse Bioscience extracellular flux analyzer, we found a significant increase in the basal and maximal oxygen consumption rate (OCR) in GSCs after 24- and 48-hour incubation of R406 compared with the control (Fig. 3a), indicating the enhanced oxidative phosphorylation (OXPHOS)
Summary
Conventional treatments including maximal neurosurgical resection, chemoradiation followed by adjuvant chemotherapy with temozolomide (TMZ), and recently emerging tumor treating fields (TTF), offer limited survival benefits. The prognosis still remains dismal for GBM patients, with the overall survival of approximately 21 months[2]. Numerous studies have reported the existence of cellular hierarchy in GBM. Namely Warburg effect, is a hallmark of gliomas, by which glioma cells metabolize glucose into lactate for energy generation even under normoxic condition[6]. Glycolysis is critical for the maintenance of GSCs. It has been reported that GSCs are enriched in a hypoxic niche and preferentially rely on glycolysis[9,10]. Reverse of Warburg effect efficiently drives the differentiation of CSCs into non-stem cells and delays tumor
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