Redox-Active Agents for Pancreatic Cancer

DESCRIPTION (provided by applicant): The goal of this proposal is to characterize and develop a new class of redox-active small molecules for the treatment of pancreatic cancer (PC), for which no new drugs have been approved since 1997. Imexon is a non-myelosuppressive aziridine-containing small molecule which is currently finishing a phase I trial in patients with advanced cancer. In myeloma cells the drug has previously been shown to produce reactive oxygen species (ROS) and apoptosis via activation of intrinsic pathway caspases. New mechanism of action studies in human pancreatic cancer cells show that ROS are generated at pharmacologically achievable drug concentrations. A threshold of 200uM must be achieved in pancreatic cells before inducing a G2 arrest and apoptosis. A new target has been identified in PC cells, ribonucleotide reductase, (RNR), which may explain the marked synergy for the combination of gemcitabine (GEM), and imexon (now being explored in a separate phase I clinical trial). There are three specific aims proposed in this application: (1) characterize the mechanism of action of imexon and three related cyanoziridine-containing analogs (CCA) in human PC cells, (2) determine the biochemical mechanism of the marked synergy between imexon and GEM, including detailed studies of GEM metabolic pathways, and (3) evaluate the pharmacodynamic dose-response relationship for imexon in patients receiving imexon and gemcitabine for advanced pancreatic cancer. PD endpoints include response, grade 3/4 toxicities and plasma thiol levels measured by a validated HPLC assay. The methods will utilize molecular assays to determine the drug's effects on redox proteins, and GEM metabolic pathways, as well as modified Hill equations for the PD effects in the clinical trial. The GEM- imexon interaction will be further characterized in scid mice bearing human PC tumors and in transgenic mice with Cre-modulated Kras mutations (KrasG12D) and tumor suppressor (Ink4a/Arf) knockouts. Overall, this project seeks to provide patients with advanced pancreatic cancer a new option for treatment, involving a novel class of agents targeted to the disregulated redox environment found in pancreatic cancer cells. The underlying clinical trial is underway and has already produced objective evidence of efficacy for this drug combination.