As we had found that an RGD-peptide blocks the interaction of integrin αvβ3 on ECs with L1CAM on CSCs, we examined the effects of administration of the cyclic-RGD-peptide in an established orthotopic mouse model of GBM on the distance of Sox2-positive tumor cells from ECs and integrin αvβ3-mediated signaling in the ECs. Here, L1CAM is linked to glioblastoma.