Copper as a target for prostate cancer therapeutics: copper-ionophore pharmacology and altering systemic copper distribution

// Delphine Denoyer 1 , Helen B. Pearson 2, 3 , Sharnel A.S. Clatworthy 1 , Zoe M. Smith 4 , Paul S. Francis 4 , Roxana M. Llanos 1 , Irene Volitakis 5 , Wayne A. Phillips 2, 3 , Peter M. Meggyesy 1 , Shashank Masaldan 1 , Michael A. Cater 1, 6 1 Centre for Cellular and Molecular Biology, School of Life and Environmental Sciences, Deakin University, Burwood, Victoria, Australia 2 Research Division, Peter MacCallum Cancer Centre, East Melbourne, Victoria, Australia 3 Sir Peter MacCallum Department of Oncology, the University of Melbourne, Parkville, Victoria, Australia 4 Centre for Chemistry and Biotechnology, School of Life and Environmental Sciences, Deakin University, Waurn Ponds, Victoria, Australia 5 The Florey Institute of Neuroscience and Mental Health, the University of Melbourne, Parkville, Victoria, Australia 6 Department of Pathology, the University of Melbourne, Parkville, Victoria, Australia Correspondence to: Michael A. Cater, email: mcater@deakin.edu.au , mcater@unimelb.edu.au Keywords: copper, ionophore, prostate cancer, Atp7b, TRAMP Received: March 09, 2016 Accepted: April 26, 2016 Published: May 09, 2016 ABSTRACT Copper-ionophores that elevate intracellular bioavailable copper display significant therapeutic utility against prostate cancer cells in vitro and in TRAMP (Transgenic Adenocarcinoma of Mouse Prostate) mice. However, the pharmacological basis for their anticancer activity remains unclear, despite impending clinical trails. Herein we show that intracellular copper levels in prostate cancer, evaluated in vitro and across disease progression in TRAMP mice, were not correlative with copper-ionophore activity and mirrored the normal levels observed in patient prostatectomy tissues (Gleason Score 7 & 9). TRAMP adenocarcinoma cells harbored markedly elevated oxidative stress and diminished glutathione (GSH)-mediated antioxidant capacity, which together conferred selective sensitivity to prooxidant ionophoric copper. Copper-ionophore treatments [Cu II (gtsm), disulfiram & clioquinol] generated toxic levels of reactive oxygen species (ROS) in TRAMP adenocarcinoma cells, but not in normal mouse prostate epithelial cells (PrECs). Our results provide a basis for the pharmacological activity of copper-ionophores and suggest they are amendable for treatment of patients with prostate cancer. Additionally, recent in vitro and mouse xenograft studies have suggested an increased copper requirement by prostate cancer cells. We demonstrated that prostate adenocarcinoma development in TRAMP mice requires a functional supply of copper and is significantly impeded by altered systemic copper distribution. The presence of a mutant copper-transporting Atp7b protein (tx mutation: A4066G/Met1356Val) in TRAMP mice changed copper-integration into serum and caused a remarkable reduction in prostate cancer burden (64% reduction) and disease severity (grade), abrogating adenocarcinoma development. Implications for current clinical trials are discussed.