2641 - Impact of Angiopoietin-2 on glioblastoma response to combined chemo-radiotherapy

Background

Glioblastoma (GB) are brain tumors with a poor prognosis despite multimodal treatment combining resection, chemotherapy (CT) and radiotherapy (RT). The rich vascularization of these tumors led to the introduction of anti-angiogenic therapy with most efforts focused on the vascular endothelial growth factor (VEGF). However, the angiopoietins (Ang) have emerged as alternative regulators of angiogenesis. In particular, in GB, Ang2 is up-regulated and stimulates tumor angiogenesis in concert with VEGF but also activates pro-angiogenic functions of macrophages. However, Ang2 functions are context-dependent. Therefore, we sought to elucidate the involvement of Ang2 in the interaction of glioma response to CT and RT, both therapeutic modalities known to alter tumor angiogenesis and inflammation.

Methods

To recapitulate high levels of Ang2 in GB patients, Ang2 was overexpressed in murine glioma cells (GL261-Ang2). Effects of Ang2 were studied on an orthotopic syngenic model of GB (GL261 cells) in response to combined CT/RT. C57bl/6 mice were co-treated with temozolomide (TMZ 10 mg/kg; i.p.) and brain tumors were irradiated with X-rays (4 Gy) at 7, 9 and 11 days post-cell injection. The tumor growth and its microenvironment were followed by MRI and immunohistology analyses.

Results

We showed that, in this model, the chronic overexpression of Ang2 does not modify tumor progression, but leads to a decrease in vessel density (-39±10%, p < 0.001) and to an increase in CD68+ inflammatory cells (+24±8%, p < 0.05), compared with the control tumor group (GL261). Interestingly, when combined with CT/RT, the overexpression of Ang2 in the tumor induces a robust delay in tumor recurrence (>3 months) compared with treated GL261 tumors (18±3 days). In vitro, no difference in the chemo-radiosensitivity of GL261 and GL261-Ang2 cells was noticed, suggesting a paracrine effect of Ang2 on the tumor microenvironment. Accordingly, we showed that Ang2 sensitizes the tumor vasculature to CT/RT and sustains inflammatory cells in the tumor microenvironment until 3 months post-treatment.

Conclusions

These results suggest that Ang2 might influence the therapeutic response of GB by acting on angiogenesis and inflammation.

Clinical trial identification

Editorial acknowledgement

Legal entity responsible for the study

E. Petit.

Funding

This study was funded by the Région Normandie, the Centre National de la Recherche Scientifique (CNRS), the Université de Caen Normandie (UNICAEN), the European Union-Fonds Européen de Développement Régional (FEDER), ARCHADE, HABIONOR European project, la Fédération pour la Recherche sur le Cerveau par l’opération Rotary «Espoir en tête » (FRC), EdNBise 497 - Normandie Université.

Disclosure

All authors have declared no conflicts of interest.