Abstract 5429: The combination of Apo2L/Trail and a death receptor 5 agonist antibody leads to enhanced antitumor activity in mouse syngeneic tumor models
Authors: Sullivan Timothy , Branstetter Daniel , Holland Pamela , Bush Tammy L. 
Published: May 2015

Abstract
Background: Death receptor-5 (DR5, TR2, TRAIL-R2) is a death domain-containing receptor that induces an apoptosis signaling cascade when engaged by Apo2L/TRAIL or a DR5 agonist antibody1. Many tumor cell lines express DR5 and are sensitive to DR5 agonists2. Despite pre-clinical efficacy, several DR5 agonists have failed to advance beyond phase II clinical trials due to poor clinical efficacy. Strong synergystic activity was observed with the combination of Apo2L/TRAIL and AMG655 (DR5 agonist antibody) pre-clinically in vitro and in vivo (manuscript submitted). Although Apo2L/TRAIL and AMG655 were well tolerated in clinical trials when delivered as single agents3, the efficacy and safety profile of combining Apo2L/TRAIL and AMG655 has not been investigated.
Objective: To determine a therapeutic index for Apo2L/TRAIL + DR5 agonist antibody combination treatment in mouse syngeneic tumor cell lines and xenograft models.
Results: To evaluate both efficacy and tolerability, we utilized a mouse monoclonal antibody, MD5-1, that recognizes the mouse DR5 (mDR5) receptor. In vitro, treatment with Apo2L/TRAIL + MD5-1 enhanced cell killing in multiple mouse tumor lines, which all expressed mDR5 at similar levels. In vivo, we observed marked anti-tumor activity after treatment with Apo2L/TRAIL at 5 mg/kg for 5 days per week and MD5-1 at 1ug/mouse for 2 days per week. In the Renca model, Apo2L/TRAIL + MD5-1 treatment resulted in enhanced efficacy compared to either single agent (&gt; 92% inhibition; p &lt;0.0001); whereas, in the LLC1 model, an involution of the tumor tissue was observed following Apo2L/TRAIL + MD5-1 administration. On day three after treatment was initiated, a macroscopic observation of the tumors displayed a hemorrhagic appearance in both the Renca and LLC1 models. Histological analysis revealed that tumor cells, as well as, tumor-associated vasculature were positive for activated caspase 3/7 after treatment with Apo2L/TRAIL + MD5-1. Strong expression of mDR5 on both tumor cells and associated vasculature were detected, but not on vasculature in other tissues. In follow up studies, we demonstrated anti-tumor activity in a dose-dependent manner with lower doses of Apo2L/TRAIL + MD5-1 treatment. However, at higher doses, Apo2L/TRAIL + MD5-1 treatment resulted in body weight loss associated with diarrhea, dehydration, and scruffy coat. Histological analysis indicated minimal to severe apoptosis/degeneration/necrosis in the epithelium of tissues, predominantly in the gastrointestinal tract, which expressed the highest levels of mDR5.
Conclusion: Our preclinical findings provide evidence that a therapeutic index can be achieved for Apo2L/TRAIL in combination with a DR5 agonist antibody and may be an effective strategy for cancer therapy.
Citation Format: Timothy Sullivan, Daniel Branstetter, Pamela Holland, Tammy L. Bush. The combination of Apo2L/Trail and a death receptor 5 agonist antibody leads to enhanced antitumor activity in mouse syngeneic tumor models. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 5429. doi:10.1158/1538-7445.AM2014-5429