Application of pharmacodynamic assays in a phase Ia trial of Apo2L/TRAIL in patients with advanced tumors

3535 Background: Recombinant human (rh) Apo2L/TRAIL is a dual pro-poptotic receptor agonist (PARA) that induces apoptosis by binding to pro-apoptotic receptors DR4 and DR5, which recruit a death inducing signaling complex upon ligand binding. This results in activation of the effector caspase 3/7, that subsequently cleaves intracellular substrates to execute cellular apoptosis. A Phase1a trial is underway to evaluate the safety and tolerability of rhApo2L/TRAIL in patients with advanced tumors. The aim of this study was to develop and validate high-throughput pharmacodynamic assays to monitor rhApo2L/TRAIL activity in easily accessible patient samples such as serum. Methods: To monitor rhApo2L/TRAIL activity in patients, we optimized assays to measure the release of the apoptotic markers caspase 3/7, cytokeratin 18 (CK18), and genomic DNA (gDNA) in serum. Serum caspase 3/7 levels were monitored using the Caspase Glo kit, which generates a luminescent signal upon cleavage of a caspase 3/7 substrate; cleava...