Chemical approaches towards elucidating glioblastoma biology

Glioblastoma multiforme (GBM) is the most aggressive, infiltrative brain cancer. Tumour recurrence is common and accounts for the poor 5-year survival rates of GBM (<10%). The ability to re-grow the tumour after surgical removal of the tumour bulk has been attributed to cells with stem cell-like phenotypes, termed glioma stem cells (GSCs). Identification of molecular GSC vulnerabilities targetable by therapeutic agents is urgently required. In this context, I examined the potential anti-GSC effect of KHS101, an experimental compound that induces differentiation in neural progenitor cells in vitro and in vivo. Interestingly, in patient-derived GSCs, KHS101 selectively reduced viability. KHS101 cytotoxicity was associated with a vacuolisation/autophagy phenotype, and loss of clonogenicity of GSCs. Consistently, KHS101 significantly reduced xenograft tumour growth and invasion and prolonged survival of mice bearing GSC-derived tumours. Analysis of the mechanism of action of KHS101 indicated the disruption of oxidative phosphorylation leading to metabolic exhaustion of GSCs.
To go beyond the possibilities of single agent treatment, I explored the potential of a combination therapy integrating oncolytic virotherapy with coxsackievirus A21 (CVA21). Targeting of tumour cells by CVA21 requires surface expression of Intercellular Adhesion Molecule-1 (ICAM-1), which is a limiting factor in GBM tumours. Notably, genetic manipulation of GSCs showed that expression of ICAM-1 is sufficient to increase susceptibility to CVA21. To identify ICAM-1 inducing compounds, I carried out a focused combination compound screen for the induction of ICAM1 expression in GSCs. From a panel of 23 compounds, I identified combined retinoic acid (RA) and KHS101 as an efficient ICAM1 mRNA up-regulation treatment. RA/KHS101 also significantly increased surface expression of ICAM-1 protein on GSCs. Notably, RA/KHS101-induced ICAM-1 expression rendered GSCs vulnerable to CVA21-mediated oncolysis in vitro. Hence, a combination of pharmacological treatment and oncolytic virotherapy could complement available chemo-/radiotherapy by eliminating the GSC population and thus preventing tumour recurrence.