gms | German Medical Science

Objective: Glioblastoma multiforme (GBM) is a highly aggressive brain tumour, characterized by massive neovascularisation and intense therapy resistance. Dll4-Notch signaling is vascular specific. Activation of this signaling has been found in various tumours and associated with the resistance to anti-VEGF therapy. Blockage of Dll4-Notch signaling inhibits tumour growth by promoting non-productive vessels in animals. The aims of the present study were to address whether Notch signaling is deregulated in GBM and furthermore to explore the angiogenic function of this signaling.

Method: 26 primary GBM patients were enrolled to study the expression of Notch signaling core-components by RT²-PCR, Western blot and immunostaining. The vascular pattern and vessel density were analysed after immunostaing with laminin on GBM sections. The angiogenic function of Notch signaling was further investigated in endothelial culture by means of biologically modifying the activation status of Notch signaling.

Results: The mRNA and protein expression of the core-components of Notch signaling was significantly upregulated in a subset of GBM, concomitantly accompanied by an increased VEGF expression and activation of Akt and Erk1,2 pathways. Activation of Notch signaling was correlated to a functional (classic) vascular pattern and to a low vascular density (VD) in GBM. Immunostaining revealed an intensive immunoreactivity of DLL4 and Notch1 in the endothelium of the tumour vessels. Treatment of cells with recombinant human Dll4 (rhDll4) upregulated Dll4 expression, activated Notch signaling and subsequently inhibited endothelial angiogenesis, whereas inhibition of Notch signaling by DAPT, an inhibitor of Notch signaling, stimulated VEGF-mediated hyper-angiogenic phenotype.

Conclusions: Activation of Notch signaling is implicated in a subset of GBM and associated with the better perfused vascular pattern despite a lower vascular density in GBM tissue. The crucial role of Notch-signaling in regulating endothelial angiogenesis identified from an in vitro study supported the current concept of anti-Notch signaling in tumour therapy. Moreover, the access to the activation status of Notch signaling seems to be particularly important for GBM with resistance to anti-VEGF therapy, which would warrant a personalized application of anti-Notch therapy in combination with anti-VEGF therapy in GBM.