Comparison of Drug Distribution Images from Whole-Body Thin Tissue Sections Obtained Using Desorption Electrospray Ionization Tandem Mass Spectrometry and Autoradiography Vilmos Kertesz,* ,† Gary J. Van Berkel, † Marissa Vavrek, ‡ Kenneth A. Koeplinger, ‡ Bradley B. Schneider, § and Thomas R. Covey § Organic and Biological Mass Spectrometry Group, Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-6131, Drug Metabolism and Pharmacokinetics, Merck Research Laboratories, West Point, Pennsylvania 19486-0004, and MDS Analytical Technologies, Concord, Ontario, L4K 4V8, Canada Desorption electrospray ionization tandem mass spectrom- etry (DESI-MS/MS) and whole-body autoradiography (WBA) were used for chemical imaging of whole-body thin tissue sections of mice intravenously dosed with propranolol (7.5 mg/kg). DESI-MS/MS imaging utilized selected reaction monitoring detection performed on an AB/MDS SCIEX 4000 QTRAP mass spectrometer equipped with a prototype extended length particle discriminator interface. Propranolol images of the tissue sections using DESI-MS/MS were obtained at surface scan rates of 0.1, 0.5, 2, and 7 mm/s. Although signal decreased with increasing scan rate, useful whole-body images for propranolol were obtained from the tissues even at 7 mm/s, which required just 79 min of analysis time. Attempts to detect and image the distribution of the known propranolol metabolites were unsuccessful. Regions of the tissue sections showing the most radioactivity from WBA sections were excised and analyzed by high- performance liquid chromatography (HPLC) with radio- chemical detection to determine relative levels of propra- nolol and metabolites present. Comparison of the DESI-MS/ MS signal for propranolol and the radioactivity attributed to propranolol from WBA sections indicated nominal agree- ment between the two techniques for the amount of propra- nolol in the brain, lung, and liver. Data from the kidney showed an unexplained disparity between the two tech- niques. The results of this study show the feasibility of using DESI-MS/MS to obtain useful chemical images of a drug in whole-body thin tissue sections following drug administra- tion at a pharmacologically relevant level. Further optimiza- tion to improve sensitivity and enable detection of the drug metabolites will be among the requirements necessary to move DESI-MS/MS chemical imaging forward as a practical tool in drug discovery. At the present time, whole-body autoradiography (WBA) using radiolabeled drugs is a standard method for quantitative chemical imaging of the distribution of a drug and its metabolites in thin tissue sections. 1,2 However, there are three main drawbacks to this technique that limit its utility. First, WBA requires a radio- labeled drug for the imaging experiment. Second, this approach does not provide molecular structure information. Thus, metabo- lites either cannot be distinguished from the parent drug or are not detected if the radiolabel is lost in a metabolic process. And third, development of a WBA image can require a 4-7 day exposure time depending on the radiolabel utilized. Information acquired by mass spectrometry compliments WBA because it can provide information about the particular molecular form of the drug-related material in the tissue. Mass spectrometry- based tissue imaging is generally label-free and can provide chemical images in 24 h or less. Multiple mass spectrometry-based surface sampling/ionization and chemical imaging techniques are currently being investigated for thin tissue section analysis and drug discovery applications. 3 These techniques include, among others, secondary ion mass spectrometry (SIMS) and matrix- assisted laser desorption ionization mass spectrometry (MALDI-MS). 4,5 The latter technique has been particularly suc- cessful for the analysis of endogenous large-mass biomolecules such as proteins. 6,7 MALDI-MS is also now being used for the analysis of drugs and their associated metabolites in tissues. 8,9 Newer atmospheric pressure surface sampling/ionization tech- niques like electrospray-assisted laser desorption ionization (EL- DI), 10 atmospheric pressure (AP)-MALDI-MS, 11,12 laser ablation * Corresponding author. Phone: 865-574-4878. Fax: 865-576-8559. E-mail: kerteszv@ornl.gov. † Oak Ridge National Laboratory. ‡ Merck Research Laboratories. § MDS Analytical Technologies. (1) Solon, E. 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