Glioblastoma multiforme (GBM) is the most malignant brain tumor. Despite recent therapeutic improvements, the median overall survival remains poor. Due to its high grade of vascularity, GBM is an ideal candidate for anti-angiogenic therapy. In 2009, US Food and Drug Administration granted accelerated approval for Bevacizumab, a humanized monoclonal antibody directed against VEGF-A, for patients with recurrent disease. Its use in newly diagnosed GBM is currently being evaluated. In the recurrent setting, Bevacizumab provides a transient improvement in PFS that unfortunately does not translate into increased OS. In fact, most tumors become resistant to Bevacizumab and patients invariably experience tumor regrowth. Moreover, a large number of recurrent tumors display an infiltrative and invasive phenotype, thus leading to extremely aggressive tumor growth. Understanding the molecular mechanisms underlying ‘invasive resistance’ to Bevacizumab represents a key step towards the development of improved therapeutic strategies for GBM. We hypothesized that Bevacizumab-induced tumor hypoxia could be responsible for the activation of pro-invasive pathways. We tested this hypothesis using different human GBM cell lines, both in vitro and in orthotopic mouse models of GBM. In vitro, hypoxia promoted increased expression of MET, the high affinity receptor for Hepatocyte Growth Factor(HGF), in all GBM cells analyzed. Increased MET expression resulted in higher sensitivity to HGF stimulation and in enhanced invasiveness. Higher MET levels were not due to transcriptional activation of c-met, but rather to post-transcriptional redistribution of the MET protein from the cytoplasm to the plasma membrane. In vivo, Bevacizumab did marginally improve survival of mice implanted orthotopically with human GBM tumors, but exacerbated tumor hypoxia and resulted in MET activation. Histological analysis of Bevacizumab-treated tumors revealed a highly invasive and infiltrative phenotype. Combined treatment with Bevacizumab and JNJ-38877605, a highly selective, orally available small molecule MET tyrosine kinase inhibitor, significantly prolonged mouse survival compared to both placebo and Bevacizumab alone. Histological examination showed no infiltrative phenotype in the combined treatment arm. Treatment with JNJ-38877605 alone also improved mouse survival in both tumors displaying HGF-MET autocrine stimulation (implanted in nude mice) and in tumors requiring paracrine HGF stimulation (implanted in human HGF knock-in SCID mice). These results unveil a new mechanism by which GBM may become resistant to Bevacizumab, generating proof-of-concept for conducting clinical trials using angiogenesis inhibitors in combination with MET inhibitors.

Citation Format: Manuela Cazzanti, Paolo Michieli. Inhibition of MET overcomes invasive resistance to Bevacizumab and prolongs survival in orthotopic mouse models of glioblastoma multiforme. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 3726. doi:10.1158/1538-7445.AM2014-3726