DDIS-04. INTERFERON-β SENSITIZES HUMAN GLIOBLASTOMA CELLS TO THE CYCLIN-DEPENDENT KINASE INHIBITOR, TG02

Abstract

Abstract Novel treatments for glioblastoma, the most common malignant primary brain tumor, are urgently needed. Type I interferons (IFN) are natural cytokines primarily involved in defense against viral infections, but may also play a role in the control of cancer, notably in the suppression of the cancer stem cell phenotype. TG02 is a novel orally available cyclin-dependent kinase 9 inhibitor which induces glioma cell apoptosis without profound caspase activation and is currently being explored in early clinical trials in newly diagnosed and recurrent glioblastoma. Here we used human glioma-initiating cell line models to explore whether IFN-β modulate the anti-glioma activity of TG02. Pre-exposure to IFN-β sensitized human glioma models to a variable extent to subsequent exposure to TG02. Combination treatment was associated with increased DEVD-amc cleaving activity that was blocked by BCL2. However, BCL2 did not protect from the synergistic effects of IFN and TG02 on glioma cell growth, furthermore, although IFN strongly induced pro-apoptotic XIAP-associated factor (XAF) expression, disrupting XAF expression did not abrogate the synergy with TG02 either. Consistent with that, caspase 3 gene silencing did not abrogate effects of TG02 or IFN-β alone or in combination. Finally, we observed that IFN-β may indeed modulate the effects of TG02 up-stream in the signaling cascade since inhibition of RNA polymerase II phosphorylation, a direct readout of TG02 pharmacodynamic activity, was facilitated in glioma cells pre-exposed to IFN-β. In summary, these data suggest that type I IFN may be combined with TG02 to limit glioblastoma growth but the well characterized effects of IFN and TG02 on apoptotic signaling are dispensable for synergistic control of tumor growth. Instead, exploring how IFN signaling primes glioma cells for TG02-mediated direct target inhibition may help to design novel, more effective pharmacological approaches to glioblastoma.