Abstract 3797: Validation of a novel antibody against fibulin-3 for targeted therapy of glioblastoma

Glioblastomas (GBM) are highly invasive brain tumors that resist cytotoxic and antiangiogenic therapies, resulting in a high rate of recurrence. Fibulin-3 is an extracellular matrix protein secreted by GBM cells but absent from normal brain. This protein activates Notch signaling to promote tumor invasion and resistance to apoptosis. Conditional knockdown of fibulin-3 reduces GBM growth, invasion and vascularization, thus extending survival. Here we report the initial validation of a function-blocking antibody against this unique GBM target. We first identified the Notch-activating motif of fibulin-3 and developed an immunizing peptide against a key sequence within this motif. A monoclonal antibody generated against this peptide (mAb428.2) showed high affinity for fibulin-3 (Kd 5 nM) and no cross-reactivity against highly homologous fibulin-4 or -5. Antibody mAb428.2 detected fibulin-3 in the stroma and capillaries of human GBM without cross-reactivity against normal brain. The antibody (50-250 μg/ml) blocked the activation of Notch induced by fibulin-3 in GBM cells and caused GBM cell cytotoxicity but had no effects on astrocytes or HEK293 cells. Treatment of mice carrying subcutaneous GBM stem-cell (GSC) derived tumors with mAb428.2 (30 mg/kg IV, q24h x 8 days) resulted in tumor slowdown and extended median survival (47% and 64% in two different GSC models). mAb428.2-treated tumors showed decreased BrdU uptake and increased inflammatory reaction in the tumor stroma (macrophage infiltration and cytokine levels). Mice bearing intracranial tumors did not respond to mAb428.2 when delivered by IV or IP routes, likely due to the inability of the antibody to cross the blood brain barrier. This deficiency was overcome by direct intraparenchymal delivery of the mAb428.2 using chronic infusion (0.3 mg of mAb in 200 μl delivered at 1 μl/h over 7d), which resulted in a 26% increase in median survival. These encouraging results suggest that targeted reagents against fibulin-3 may be of clinical importance for novel combination therapies against GBM.

Citation Format: Mohan Sobhana Nandhu, Prajna Behera, Vivek Bhaskaran, Ennio Antonio Chiocca, Mariano S. Viapiano. Validation of a novel antibody against fibulin-3 for targeted therapy of glioblastoma. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 3797.