The 8th Mass Spectrometry CVG Annual Symposium - Full Day Event!!!
Presentation No. 7 - High-Field MALDI FTMS for Direct Pre-Clinical Imaging of Drug Distribution and Metabolism
Katherine A. Kellersberger1; Michael L. Easterling1; Santosh Kesari2; Claire M. Sauvageot2; Jeffrey N. Agar3; Nathalie Y.R. Agar4
1Bruker Daltonics, Inc., Billerica , MA; 2Dana Farber Cancer Institute, Harvard Med. School, Boston, MA; 3Brandeis University, Waltham, MA; 4Harvard Medical School, Neurosurgery, Boston, MA
Novel Aspect: Direct assessment of drug distribution, metabolism, and blood-brain barrier crossing in animal xenografts using a MALDI-FTMS-based platform for preclinical imaging.
Introduction: Mass spectrometry imaging (MSI) has proven to be a powerful technique for the direct analysis of chemical species in tissue. The combination of spectral and spatial information derived from MALDI-MS experiments provides a workflow which does not rely on labeling strategies. Instead only mass based information is used for selectivity, facilitating both targeted and non-targeted analysis. As the spectral figures-of-merit associated with the MS detector used for molecular imaging increase, so does the confidence in elemental assignment of small molecules. In this work, we show the advantages of using MALDI-FTMS for drug and metabolite imaging of anti-cancer targeted therapy administered at therapeutic levels in mice with brain tumor xenografts.
Methods: Two swiss male nu/nu mice of 12 weeks of age were administered therapeutic doses of erlotinib by oral gavage. Both animals were sacrificed up to 4 hours later. The brain, kidneys, and liver from both animals were dissected immediately and flash frozen in liquid nitrogen. Frozen mouse organs were sectioned using a Microm HM525 cryostat from Mikron Instruments Inc, and thaw mounted on indium tin oxide (ITO) coated glass slides. Samples were matrix coated with DHB using piezoelectric nebulization of the matrix solution. Mass spectrometry was performed on an ApexUltra 12.0 T FTMS consisting of a hybrid Qh front-end and dual stage ion funnel source equipped for both MALDI and ESI.
Results: Using an in-situ xenobiotic assay by MALDI-FTMS imaging, erlotinib was detected directly from brain, liver, and kidney tissue sections. In the liver section, the drug as well as 6 of the known first- and second-generation metabolites were spatially resolved in the tissue and identified using the high mass accuracy of the detector. Metabolites were also identified in kidney and brain sections, in some cases localized to tumor regions. The high resolving power associated with the FTMS experiment (>150,000) allowed discrimination between isobaric peaks from the tissue matrix and the low-level metabolites, as shown for two of the identified species. Furthermore, the ability to visualize heme provides a means to evaluate the ability of the drug to cross the blood-brain barrier, which can be a considerable limiting factor in the development of effective brain tumor treatment.
