Targeting invasive and angiogenic mechanisms in human glioblastoma

The aim of our project is to identify mechanisms of invasion and angiogenesis of malignant brain tumors and also find a combination therapy to target both mechanisms simultaneously. In the project period we have found 1. that EGFR wild-type receptor activates invasion of brain tumor cells (published in Acta neuropathologica 2013) 2. a way to culture EGFR amplified cells in vitro (published in Plos one 2013) 3. that a mutated EGFR named EGFRvIII induces angiogenesis; furthermore, the mutation is heterogenously distributed in patient GBMs (manuscript submitted) 4. that Src mediates angiogenesis downstream of EGFRvIII (manuscript submitted) 5. We used an anti-EGFR antibody to target invasion and an anti-VEGF antibody to target angiogenesis. The double treatment showed an effect on tumor growth and invasion, while single EGFR treatment only reduced invasion. Single VEGF treatment did not have an effect. We are currently investigating the molecular mechanisms behind the treatment effect.

The major survival strategies of many tumors in general and human malignant brain tumors in particular are invasion and angiogenesis. To investigate and therapeutically target these features, we have developed a new animal model in our lab, which in contr ast to cell-line based model systems shows both, invasion and angiogenesis. In our recent work, we have defined the EGFR/Src pathway as the main driver of tumor invasion and shown that its action is independent of tumor angiogenesis. By blocking EGFR func tion using a dominant-negative EGFR mutant, tumors switched from invasion to angiogenesis. This can explain therapy resistance of human glioblastoma to EGFR inhibitors. In a second approach, we blocked angiogenesis by using the clinically approved anti- V EGF antibody bevacizumab. Tumor angiogenesis was efficiently blocked, however, tumors escaped treatment by switching to invasive growth. Thus, to efficiently target tumor growth, both angiogenesis and invasion have to be suppresssed simultaneously. The a im of the present project is 1.to functionally verify that Src is acting as the main driver of tumor invasion downstream of EGFR. We will block Src activation in invasive tumors by using a dominant negative mutant and the small molecule inhibitor Dasatin ib. In angiogenic tumors, we will overexpress a constituively active Src mutant to analyze whether tumors can switch to invasive growth 2.to block angiogenesis and invasion simultaneously by using anti-VEGF antibodies and dominant negative constructs/sma ll molecule inhibitors of EGFR/Src. By analyzing tumor growth, angiogenesis and invasion as well as downstream signalling pathways we will determine whether this strategy is promising for future therapeutic application in the clinic. Importantly, we wil l also analyze potential escape mechanisms on the molecular level to identify whether tumor cells might use other signalling pathways which might lead to therapy resistance.