Abstract 5089: Combined treatment of trebananib (AMG 386) with panitumumab in preclinical tumor models.

Proceedings: AACR 104th Annual Meeting 2013; Apr 6-10, 2013; Washington, DC Introduction: Cancer therapies that combine agents directly targeting tumor cells with those impacting the tumor stroma hold the promise of improving patient outcomes. In this preclinical study, we examined the effects of inhibiting both EGF signaling in human tumor cells and angiopoietin signaling in the murine stroma. Using tumor xenograft models, we tested a treatment combination of panitumumab, a fully human monoclonal antibody against human EGF receptor, and trebananib, an investigational peptide-Fc fusion protein that prevents binding of angiopoietins 1 and 2 to their receptor, Tie2. We assessed the effect of this combination on tumor growth and explored mechanisms of enhanced efficacy. Methods: Athymic nude mice were injected SC in the right flank with either 1x107 A431 (human epidermoid carcinoma) or 5x106 DLD-1 (colon adenocarcinoma) cells. When tumors were ∼ 200 mm3, 20 μg panitumumab IP and/or 70 μg trebananib SC were given twice weekly. Controls were isotype antibody or human Fc. In mechanism of action studies, DLD-1 tumors (∼ 300‐400 mm3) received 2 treatments over 5 days before harvest and processing for paraffin sectioning. To examine endothelial cell proliferation, treated tumors were enzyme-digested and stained with anti-CD31, anti-CD45, and anti-BrdU antibodies. The percentage of BrdU-positive tumor-associated endothelial cells (CD31high/CD45neg) was determined by flow cytometry. Results: In both tumor models, combined treatment with panitumumab and trebananib resulted in significantly greater tumor growth inhibition (p≤0.014) than treatment with either single agent alone. All treatments were well tolerated; no significant weight loss was observed. Mechanistic studies revealed that combination treatment did not alter the single-agent activity of either treatment: histological analyses showed a significant reduction in estimated blood vessel area within viable tumor after treatment with either trebananib (p=0.0006) or panitumumab (p=0.012) alone; this reduction was not affected by combination treatment. Similarly, BrdU incorporation assays demonstrated that single-agent panitumumab significantly impaired tumor cell proliferation (p=0.0003), whereas single-agent trebananib significantly reduced endothelial cell proliferation (p<0.0001). Combined treatment did not change the effects on cell proliferation seen with either single agent alone. Conclusions: This study demonstrates that combined treatment with agents targeting EGF signaling in the tumor and angiopoietin signaling in the stroma results in significantly enhanced antitumor activity. Neither agent appears to impact the biochemical activities of the other, but instead gives rise to an orthogonal enhancement of antitumor activities. These findings support further clinical testing of agents that target the tumor stroma in combination with direct tumor-targeting therapies. Citation Format: James V. Bready, Paula Kaplan-Lefko, Jodi Moriguchi, Marc Payton, Stephen Kaufman, Jonathan Oliner, Robert Radinsky, Angela Coxon. Combined treatment of trebananib (AMG 386) with panitumumab in preclinical tumor models. [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 5089. doi:10.1158/1538-7445.AM2013-5089