Jennifer Joy Kordich

Conatumumab, a fully human agonist antibody to death receptor 5, induces apoptosis via caspase activation in multiple tumor types

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) binds to death receptors 4 and 5 (DR4, DR5) to transduce apoptotic signals. Conatumumab (AMG 655) is an investigational, fully human monoclonal agonist antibody (IgG1) to human DR5, which induces apoptosis via caspase activation. In this study, we demonstrate that conatumumab binds to DR5, activating intracellular caspases in vitro in the presence of a cross-linker. We also show that conatumumab has activity in vivo and inhibits tumor growth in colon (Colo205 and HCT-15), lung (H2122), and pancreatic (MiaPaCa2/T2) xenograft models. Conatumumab also enhances the anti-tumor activity of chemotherapeutics in vivo. Caspase activation in Colo205 tumors is dose-dependent and correlated with serum concentrations of conatumumab. We demonstrate for the first time that increases in serum caspase-3/7 activity and levels of M30 (neoepitope of caspase-cleaved cytokeratin-18) are linked to activation of the extrinsic apoptotic pathway using conatumumab in a preclinical model. These data suggest that conatumumab has potential as a therapeutic agent for treating patients with multiple tumor types, and that serum caspase-3/7 and M30 levels may serve as biomarkers of conatumumab activity.

In Vivo Regulation of TGF-β by R-Ras2 Revealed through Loss of the RasGAP Protein NF1

Ras superfamily proteins participate in TGF-β-mediated developmental pathways that promote either tumor suppression or progression. However, the specific Ras proteins, which integrate in vivo with TGF-β signaling pathways, are unknown. As a general approach to this question, we activated all Ras proteins in vivo by genetic deletion of the RasGAP protein Nf1 and examined mice doubly deficient in a Ras protein to determine its requirement in formation of TGF-β-dependent neurofibromas that arise in Nf1-deficient mice. Animals lacking Nf1 and the Ras-related protein R-Ras2/TC21 displayed a delay in formation of neurofibromas but an acceleration in formation of brain tumors and sarcomas. Loss of R-Ras2 was associated with elevated expression of TGF-β in Nf1-deficient Schwann cell precursors, blockade of a Nf1/TGFβRII/AKT-dependent autocrine survival loop in tumor precursor cells, and decreased precursor cell numbers. Furthermore, the increase in size of sarcomas from xenografts doubly deficient in these genes was also found to be TGF-β-dependent, in this case resulting from cell nonautonomous effects on endothelial cells and myofibroblasts. Extending these findings in clinical specimens, we documented an increase in TGF-β ligands and an absence of TGF-β receptor II in malignant peripheral nerve sheath tumors, which correspond to tumors in the Nf1-deficient mouse model. Together, our findings reveal R-Ras2 as a critical regulator of TGF-β signaling in vivo.