OS3.1 Differential impact of Ang-2 VEGF-A and dual Ang-2/VEGF-A blocking on the efficacy of radio- and chemotherapy in a glioblastoma model

摘要

High levels of pro-angiogenic factors like VEGF-A and angiopoietin-2 (Ang-2) in the microenvironment of brain tumors lead to an abnormal structure, organization and function of the tumor vasculature. It is of interest whether inhibition of Ang-2 or even dual inhibition of both major angiogenic factors is more efficient in glioma therapy, particularly with respect to vascular normalization. In this context, the ideal combination regimen with chemotherapy and/or radiotherapy is still unclear today. Here, we used an orthotopic glioblastoma model to compare dual blocking of Ang-2 and VEGF-A by a bispecific antibody vs. monospecific Ang-2 and VEGF-A blocking. In addition, we evaluated combinations of both antiangiogenic antibodies with either chemotherapy or radiation therapy.The best parameter to describe vascular normalization was the microvascular blood flow velocity: Both the control and the anti-Ang-2 antibody led to a strong reduction of this parameter in all treatment modalities. Anti-VEGF-A and anti-Ang-2/VEGF-A treatment schedules showed differential effects, depending on the combination cytotoxic therapy: while VEGF-A blockade led to an increased blood flow velocity only in combination with radiotherapy, anti-Ang-2/VEGF-A treatment was effective both in monotherapy and in combination with chemotherapy.To describe vascular changes longitudinally, different parameters (vascular diameter, total vessel length, vascular volume/ surface, number of branches, branch length/ tortuosity, lacunarity and the Hausdorff dimension which describes the degree of complexity) were determined.Anti-VEGF-A therapy as a monotherapy or in combination with temozolomide showed an impact on vascular volume in comparison to the control and anti-Ang-2 treatment schedules (p<0.05). However, combination of anti-Ang-2/VEGF-A alone as well as in combination with temozolomide or radiotherapy presented with the highest impact on total vascular volume.In the case of tumor diameter, no significant differences were observed for the monotherapies. For combination with chemotherapy, reduced tumor growth was measured only for dual anti-Ang-2/VEGF-A antibody (p=0.04 at D9, p=0.05 at D12), whereas the other antibodies did not slow down tumor growth significantly. If combined with radiotherapy, anti-VEGF-A showed no variations to the control arm. Unexpectedly, the combination of radiotherapy with anti-Ang-2/VEGF-A (p=0.01 at D15), and even more with anti-Ang-2 (p=0.04 at D9, p= 0.008 at D12, p=0.003 at D15) lead to an increased tumor diameter.In conclusion, vascular normalization was most effectively achieved by dual targeting of Ang-2 and VEGF-A, which resulted in improved response to chemotherapy, but attenuated effectiveness of radiotherapy. These findings are important for the development of novel antiangiogenic strategies, and planning of future clinical trials in glioblastoma.