The Interference of Notch1 target Hes1 affects cell growth, differentiation and invasiveness of glioblastoma stem cells through modulation of multiple oncogenic targets

The invasive and lethal nature of Glioblastoma multiforme (GBM) necessitatesthe continuous identification of molecular targets and search of efficacious therapiesto inhibit GBM growth. The GBM resistance to chemotherapy and radiation it isattributed to the existence of a rare fraction of cancer stem cells (CSC) that wehave identified within the tumor core and in peritumor tissue of GBM. Since Notch1pathway is a potential therapeutic target in brain cancer, earlier we highlightedthat pharmacological inhibition of Notch1 signalling by ?-secretase inhibitor-X(GSI-X), reduced cell growth of some c-CSC than to their respective p-CSC, butproduced negligible effects on cell cycle distribution, apoptosis and cell invasion.In the current study, we assessed the effects of Hes1-targeted shRNA, a Notch1gene target, specifically on GBM CSC refractory to GSI-X. Depletion of Hes1 proteininduces major changes in cell morphology, cell growth rate and in the invasive abilityof shHes1-CSC in response to growth factor EGF. shHes1-CSC show a decrease ofthe stemness marker Nestin concurrently to a marked increase of neuronal markerMAP2 compared to pLKO.1-CSC. Those effects correlated with repression of EGFRprotein and modulation of Stat3 phosphorylation at Y705 and S727 residues. In thelast decade Stat3 has gained attention as therapeutic target in cancer but there isnot yet any approved Stat3-based glioma therapy. Herein, we report that exposureto a Stat3/5 inhibitor, induced apoptosis either in shHes1-CSC or control cells. Takentogether, Hes1 seems to be a favorable target but not sufficient itself to target GBMefficaciously, therefore a possible pharmacological intervention should provide forthe use of anti-Stat3/5 drugs either alone or in combination regimen.