Abstract 1610: Serial treatment-transplant xenograft model of Bevacizumab-resistance reveals temporal induction of markers associated with disease progression.

Proceedings: AACR 104th Annual Meeting 2013; Apr 6-10, 2013; Washington, DC INTRODUCTION: Acquired resistance threatens the potential of anti-angiogenic therapy. Xenograft models of acquired anti-angiogenic therapy resistance are lacking and often fail to reflect changes human tumors acquire during prolonged serial treatment with anti-angiogenic therapy because of the significantly shorter lifespan of tumor-bearing mice. To create a xenograft model of bevacizumab-resistant GBM allowing temporal definition of changes during resistance to VEGF blockade, we created a model whereby serially passaged xenografts were continually exposed to bevacizumab versus IgG control antibody over 5 generations in vivo. METHODS: We treated 5 subcutaneous U87 glioma cell line-derived xenografts with bevacizumab or IgG, explanted the least responsive xenograft and reimplanted it subcutaneously, then repeated this pattern of treatment followed by explantation and reimplantation of the least responsive xenograft for 4 more generations, generating 5 generations of U87-IgG and U87-BevR xenografts. Western blot assessed temporal changes. RESULTS: Subcutaneous fifth generation U87-BevR were unresponsive to bevacizumab versus IgG (P=0.8). Bevacizumab caused U87-IgG to regress (P<0.05) while U87BevR grew exponentially during bevacizumab treatment (P=0.6). Intracranial U87-BevR xenografts were bevacizumab unresponsive (P=0.1), while intracranial U87-IgG xenografts responded to bevacizumab (P=0.006). Intracranial U87-BevR xenografts also exhibited further discontinuous invasion, higher percent of invading tumor cells 10 μm from a vessel, and more invasive islands (P<0.05). U87-BevR xenografts expressed 9-fold more c-Met protein than U87-IgG xenografts after one generation, an effect sustained through all 5 generations. U87-BevR exhibited 6-fold more phosphorylated c-Met, a change not occurring until the fifth generation. U87-BevR exhibited 9-fold more phosphorylated STAT3 and 8-fold more VEGFR2 than U87-IgG through all 5 generations. U87-BevR exhibited 5-8-fold more alpha5beta1 integrin than U87-IgG cells, a disparity peaking during the third generation before resolving during generations 4-5. CONCLUSIONS: Our novel model of acquired anti-angiogenic therapy resistance showed that acquired resistance increases parenchymal and perivascular invasion with some changes (increased c-Met, VEGFR2, and phosphorylated STAT3) occurring early and lasting throughout resistance, while other changes like alpha5beta1 integrin upregulation peaked later and decreased over time. The ability of this model to replicate prolonged anti-angiogenic therapy duration seen in patients should generate a molecular profile of anti-angiogenic therapy resistance, and should define which resistance-associated changes are driver versus passenger alterations. Citation Format: Arman Jahangiri, Michael De Lay, W. Shawn Carbonell, Liane Miller, Manish K. Aghi. Serial treatment-transplant xenograft model of Bevacizumab-resistance reveals temporal induction of markers associated with disease progression. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1610. doi:10.1158/1538-7445.AM2013-1610