Design and characterization of a CXCR4-retargeted and sTRAILarmed oncolytic HSV-1 to attack Glioblastoma stem-like cells (GSCs)

Virotherapy is one of the techniques that has been highlighted as a promising new therapeutic approach against cancer. Oncolytic Herpes simplex virus (oHSV) has been shown to have potent oncolytic effects against tumour cells and tumour microenvironment.
Glioblastoma (GBM) is the most aggressive primary brain tumour in adults, and patients have a poor prognosis mainly due to recurrences. It has been shown that GBM cells can escape the tumour mass and invade healthy parenchyma. This migration is mediated by a CXCL12/CXCR4 pathway. These CXCR4+ cells share characteristics with stem cells and are considered as GBM stem-like cells (GSC) partly responsible of the recurrences. They appear therefore, as a target for oncolytic virus therapy. We have created a retargeted and armed oHSV. The glycoprotein D has been modified by inserting a nanobody specific to human CXCR4 to selectively target GSCs, and the virus has been armed with a soluble form of TRAIL to induce the extrinsic apoptosis pathway under the control of nestin promoter. Infection of U87MG or U87MG CXCR4+ with the retargeted oHSV showed a viral replication only in cells over-expressing CXCR4, indicating an efficient retargeting. The analysis of the arming in U87MG CXCR4+ infected cells showed more apoptosis with the sTRAIL-armed virus. Further evaluation on human patient-derived glioblastoma cells cultured as tumourospheres was
done, showing a correlation between CXCR4 expression and viral infection. Finally, an in vivo orthotopic xenograft model with U87MG CXCR4+ cells demonstrates the ability of this retargeted and armed virus to significantly reduce the tumour volume and increase survival. In the future, improving the arming strategy and the validation of the retargeting safety by the creation of a nanobody that recognise human and murine CXCR4 will be
addressed.