RESEARCH PAPER The Role of the Transition Metal Copper and the Ionophore A23187 in the Development of Irinophore C™ Nilesh Patankar & Malathi Anantha & Euan Ramsay & Dawn Waterhouse & Marcel Bally Received: 27 September 2010 / Accepted: 29 November 2010 / Published online: 23 December 2010 # Springer Science+Business Media, LLC 2010 ABSTRACT Purpose A liposomal irinotecan formulation referred to as Irinophore C relies on the ability of copper to complex irinotecan within the liposome. It is currently being evaluated for critical drug-loading parameters. Studies presented here were designed to determine the optimum copper concentra- tion required for the effective encapsulation and retention of irinotecan into liposomes. Methods Distearoylphosphatidylcholine/cholesterol lipo- somes were formulated using buffers containing various copper or manganese concentrations, and irinotecan loading was determined in the presence and absence of divalent metal ionophore A23187. The rate and extent of irinotecan encapsulation and the rate of irinotecan release from the liposomes were assessed. The amount of copper retained inside liposomes following irinotecan loading and the effect of copper on membrane permeability were determined. Results Efficient (>98%) irinotecan loading was achieved using encapsulated copper concentrations of 50 mM. However, irinotecan release was copper concentration dependent, with a minimum 300 mM concentration required for optimal drug retention. The presence of copper increased liposomal mem- brane permeability. Conclusion Results explain why irinotecan loading rates are enhanced in the presence of formulations prepared with copper, and we speculate that the Irinophore C formulation exhibits improved drug retention, due to generation of a complex between copper and irinotecan. KEY WORDS copper . ionophore . irinotecan . liposomes INTRODUCTION The success of clinically approved liposomal formulations of anthracyclines (1,2), such as Caelyx, have highlighted the potential of liposomal nanoparticle (LNP) formulations to improve the therapeutic activity of selected anticancer drugs. However, the clinical development of preclinically promising LNP formulations has proven challenging. This is due to several reasons, including rising interest in molecularly targeted drugs designed to correct aberrant signaling pathways uniquely expressed in cancer cells as well as the fact that preclinical data obtained with optimized LNP formulations has not effectively predicted activities in patients. We are now pursuing clinical N. Patankar : D. Waterhouse : M. Bally Faculty of Pharmaceutical Sciences, University of British Columbia Vancouver, British Columbia V6T1Z3, Canada N. Patankar (*) : M. Anantha : E. Ramsay : D. Waterhouse : M. Bally Experimental Therapeutics, B C Cancer Agency 675 W 10th Avenue Vancouver, British Columbia V5Z 1L3, Canada e-mail: npatankar@gmail.com M. Bally Department of Pathology & Laboratory Medicine University of British Columbia Vancouver, British Columbia V6T 2B5, Canada E. Ramsay : M. Bally Centre for Drug Research and Development Vancouver, British Columbia V6T 1Z4, Canada Pharm Res (2011) 28:848–857 DOI 10.1007/s11095-010-0340-2