4867

Tumor necrosis factor Related Apoptosis Inducing Ligand (TRAIL) Receptor-2 (TR-2) is a member of the tumor necrosis factor family of receptors and can transduce an apoptotic signal following TRAIL stimulation. Agonistic TR-2 antibodies can mimic the effect of TRAIL, triggering the death of ligand sensitive cells. AMG 655 is a fully human monoclonal agonistic antibody (IgG1) directed against human TR-2 and is currently in clinical development. Binding of AMG 655 to TR-2 can activate intracellular caspases and induce apoptosis in a variety of transformed human cell lines in vitro. The anti-tumor potential of AMG 655 was confirmed in vivo using Colo 205 (colon), H2122 (lung), and MiaPaCa2 (pancreatic) tumor xenograft models. AMG 655 inhibited the growth of tumor xenografts in a dose-dependent manner and at higher doses induced the regression of established tumor xenografts. The mechanism of action of AMG 655 was explored in established Colo 205 tumor xenografts using immunohistochemistry (IHC) and laser scanning cytometry. Apoptosis was evaluated by IHC staining for activated caspases and cellular proliferation was evaluated by IHC staining for BrdU. Activated caspases were induced in a dose- and time-dependent manner. Activated caspase-3 was transiently induced following a single dose of AMG 655, peaking approximately 12 hours post-treatment and returning to baseline levels by approximately 96 hours. Transient induction of activated caspase-8 occurred prior to the induction of activated caspase-3 and peaked at approximately 6 hours following treatment. In addition to activation of caspases in the extrinsic pathway, activated caspase-9 was also transiently increased indicating that AMG 655 also activates the intrinsic apoptotic pathway. Tumor cell proliferation did not change in vivo following treatment with AMG 655. Concurrent with apoptotic induction in the tumor, elevated levels of activated caspase-3 and M30 (a cytokeratin 18 neoepitope generated by apoptosis) were also detected in the serum of tumor bearing mice following treatment with AMG 655. Consistent with the rapid activation of caspases in the tumor xenograft, peak levels of activated caspase-3 and M30 were detected in the serum approximately 24 hours after treatment with AMG 655. Thus AMG 655 induces rapid apoptosis in tumors followed by subsequent detection of markers of apoptosis in the serum. These data demonstrate potent anti-tumor activity of AMG 655 both in vitro and in vivo via induction of caspase-mediated apoptosis. These data support the clinical development of AMG 655.

98th AACR Annual Meeting-- Apr 14-18, 2007; Los Angeles, CA