Abstract 2329: Anti-tumor efficacy of Dll4 blockade in combination with sunitinib or aflibercept in primary human renal cell carcinoma models (2012)

Abstract Background: The Notch ligand Delta-like 4 (Dll4) is highly expressed in vascular endothelium and has been shown to play a pivotal role in regulating tumor angiogenesis, particularly angiogenic sprouting. Blockade of the Dll4-Notch pathway leads to an excessive production of aberrant non-functional tumor vascular structures and is associated with reduced tumor growth. REGN1035, an antibody that selectively binds and blocks murine Dll4, has demonstrated potent inhibition of tumor growth in a broad spectrum of xenograft models. The aim of this study was to assess the effect of REGN1035 alone and in combination with anti-VEGF therapy in two preclinical models of primary RCC. We hypothesized that combining REGN1035 with sunitinib or the VEGF blocker aflibercept would provide greater anti-tumor and anti-angiogenesis efficacy compared to single agent treatments. Methods: Two human RCC models isolated from skin metastases from a patient with sporadic ccRCC (RP-01) and a patient with hereditary ccRCC (RP-02), respectively, were bilaterally implanted subcutaneously into the flank area of three sets of 32 SCID mice (8 mice/group). When tumor volume reached ∼ 25 mm2, mice were treated with vehicle (human Fc control protein, 4.89 mg/kg, 1x/wk, s.q.), REGN1035 (5 mg/kg, 1x/wk, s.q.), sunitinib (40 mg/kg, 5x/wk, oral gavage), aflibercept (10 mg/kg, 2x/wk, s.q.) or REGN1035 plus sunitinib or aflibercept. Tumor growth was assessed with serial caliper measurements. Once tumor volume of vehicle mice reached 200 mm2, mice were sacrificed and tumor tissue was excised and analyzed. Results: In the RP-01 and RP-02 models, sunitinib and REGN1035 induced 60-69% and 71-81% inhibition (p &amp;lt; .01 vs. control), respectively, while the combination group showed 89-114% inhibition (p &amp;lt; .001 vs. single agents), respectively. No overt signs of toxicity (i.e., weight loss, diarrhea) were observed in any of the experimental groups. Similar results were observed by combining the VEGF blocker aflibercept with REGN1035. HIF-1α and HIF-2α protein levels in the tumor were both found to be downregulated in the combination treated mice, as compared to the single agent treated mice as monitored by Western blotting analysis. A reduction in microvessel density, as measured by CD31 and VEGF immunohistochemistry, was observed in the sunitinib treated group, whereas an increase in abnormal vascular structures was seen in the REGN1035 group. Summary: Overall, the data demonstrate that combination therapy with REGN1035 and sunitinib or aflibercept resulted in significant anti-tumor efficacy including tumor regression in primary human RCC xenografts and highlights the potential therapeutic application of combined VEGF and Dll4 blockade for the treatment of RCC. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2329. doi:1538-7445.AM2012-2329