Abstract 4322: Efficacy of Sym004, a novel anti-EGFR antibody mixture, against EGFRvIII positive glioblastoma xenografts.

Abstract

Abstract INTRODUCTION Glioblastoma (GBM) is the most common intracranial cancer in adults but despite recent advances in therapy the overall survival remains about 20 months. The epidermal growth factor receptor variant III (EGFRvIII) is a truncated, constitutively active, and highly oncogenic form of the EGFR expressed on approximately 30% of GBMs. Sym004 is a recombinant IgG1 antibody mixture consisting of two antibodies against domain III of the epidermal growth factor receptor (EGFR). Like anti-EGFR monoclonal antibodies, Sym004 inhibits cancer cell growth and survival by blocking ligand-binding and receptor signaling. However, unlike the monoclonal antibodies, Sym004 induces a rapid and efficient internalization and degradation of the EGFR. Here, we examine whether the more efficient removal of the EGFR and the constitutive active EGFRvIII by Sym004 would translate into increased tumor growth inhibition of EGFRvIII GBM xenografts. METHODS Both subcutaneous (sc) and intracranial (ic) adult brain tumor xenografts were grown in athymic BALB/c mice. After tumor size reached 200-500 mm3 subcutaneously or 3 days after intracranial implantation, groups of 10 mice were randomly treated with either drug vehicle, Sym004 (50 mg/kg) or cetuximab (50 mg/kg) IP twice weekly for 5 weeks. Tumor responses for sc xenografts were assessed by tumor growth delay and regression and for ic xenografts by difference in median survival. Xenograft lines utilized for this study expressed either primarily EGFR wildtype (D-54 MG) or mutant EGFRvIII (D-270 MG and D-317 MG). RESULTS AND DISCUSSION The sc results for D-54 MG did not demonstrate statistically significant growth delays for either Sym004 or cetuximab. In sc EGFRvIII models, however, Sym004 produced statistically significant (p<0.001) growth delays of 7.8 and 76.5 days and outperformed cetuximab by 4.6 and 71.9 days in D-270 MG and D-317 MG, respectively. Intracranially, Sym004 produced statistically significant (p<0.001) increases in survival of 39% and 163% and outperformed cetuximab by 27% and 115% in D-270 MG and D-317 MG, respectively. We speculate that the superior effect of the Sym004 antibody mixture compared to the monoclonal antibody cetuximab in the EGFRvIII models is due to a more efficient internalization and degradation - and thereby shutdown - of the constitutively active EGFRvIII. Histological examination of the receptor status in the tumors following treatment is ongoing. CONCLUSIONS The novel strategy to target EGFR demonstrates the significant anti-tumor activity of Sym004 against adult glioblastoma xenografts that express EGFRvIII. These results warrant further exploration of Sym004 in clinical trials for the treatment of EGFRvIII positive brain tumors. Funding for these studies was provided by Symphogen and the Tisch Preclinical Therapy Screening Program Citation Format: Stephen T. Keir, Martin A. Roskoski, Michael Kragh, Mikkel W. Pederson, Helle J. Jacobsen, Ivan D. Horak, Henry S. Friedman, Darell D. Bigner. Efficacy of Sym004, a novel anti-EGFR antibody mixture, against EGFRvIII positive glioblastoma xenografts. [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 4322. doi:10.1158/1538-7445.AM2013-4322