Abstract 4319: A novel tool to study apoptosis in living mice (2010)

Abstract INTRODUCTION. The limitations of cellular models and xenograft for the identification of anti-neoplastic drugs are well known. The purpose of our study is to test the validity of a novel methodology to identify apoptotic cells in living mice genetically modified or pharmacologically treated to develop cancer. METHODS AND RESULTS. The method presented here relies on the combined use of reporter mice engineered to express the luciferase gene ubiquitously (1-2) and modified luciferase substrates (Glo technology) where a pro-luciferin (VivoGlo Caspase-3/7) is converted into a luminogenic substrate only in the presence of the apoptotic enzymes Caspase-3/7 (3-4). The novel methodology was tested by inducing liver apoptosis in luciferase reporter mice by a single i.p. injection of D-galactosamine (D-GalN; 800mg/kg) and Lipopolysaccharide (LPS; 100μg/kg) shown to increase the number of apoptotic cells in the liver of 5-10 fold compared to vehicle-treated animals (5); 6 hours after LPS/D-GalN or vehicle administration, mice were treated i.p. with increasing doses (17-150mg/kg) of the VivoGlo Caspase-3/7 substrate (Z-DEVD-Aminoluciferin, Sodium Salt) and subjected to the bioluminescence in vivo imaging procedure. The in vivo imaging data obtained clearly show a dose-dependent increase of photon emission in the hepatic area of mice treated with D-GalN/LPS. No photon emission was observed in organs not affected by the apoptotic treatment. A complete analysis of pro-apoptotic effects induced by the treatment was carried out by ex vivo imaging acquisition of photon emission in several dissected tissues. This investigation confirmed that light emission observed in vivo was produced selectively by liver and adipose tissues. Finally, the presence of increased apoptotic cells in liver was also confirmed by western blot analysis and Caspase-3/7 enzymatic activity assay carried out on protein extracts. CONCLUSIONS. The present study, by showing the power of modified luciferin substrates to label apoptotic cells in living animals, provides an important advancement over current imaging methodologies based on fluorescence, nuclear or magnetic resonance including: virtually null background, high sensitivity and simple instrumentation needed for the in vivo imaging measurement of the Caspase-3/7 activity. The present application carried out in reporter mice genetically engineered to develop specific cancers will open the way to novel, more predictive approaches for the study of anti-cancer treatments that will enable, for the first time, to measure drug efficacy in space and time providing relevant information to be rapidly translated to human therapy. REFERENCES 1- Maggi et al. Trends Pharmacol Sci. 2004. 2- Maggi A and Ciana P Nat Rev Drug Discov. 2005. 3- Meisenheimer PL et al. Promega Notes 2008. 4- Kizaka-Kondoh S et al. Clin Cancer Res. 2009. 5- Nakama T et al. Hepatology. 2001. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4319.