Spatial Quantitation of Drugs in tissues using Liquid Extraction Surface Analysis Mass Spectrometry Imaging

Abstract

Liquid extraction surface analysis mass spectrometry imaging (LESA-MSI) has been shown to be an effective tissue profiling and imaging technique, producing robust and reliable qualitative distribution images of an analyte or analytes in tissue sections. Here, we expand the use of LESA-MSI beyond qualitative analysis to a quantitative analytical technique by employing a mimetic tissue model previously shown to be applicable for MALDI-MSI quantitation. Liver homogenate was used to generate a viable and molecularly relevant control matrix for spiked drug standards which can be frozen, sectioned and subsequently analyzed for the generation of calibration curves to quantify unknown tissue section samples. The effects of extraction solvent composition, tissue thickness and solvent/tissue contact time were explored prior to any quantitative studies in order to optimize the LESA-MSI method across several different chemical entities. The use of a internal standard to normalize regional differences in ionization response across tissue sections was also investigated. Data are presented comparing quantitative results generated by LESA-MSI to LC-MS/MS. Subsequent analysis of adjacent tissue sections using DESI-MSI is also reported.

METASPACE: A community-populated knowledge base of spatial metabolomes in health and disease

“…As of January 2019, 101 datasets were publicly shared by seven pharma companies ( link to all datasets ). As a case study, we explored a published dataset which was originally used for spatial quantitation of drugs in a rat liver 14 ( dataset link , Figure 5). Using METASPACE, we reproduced the original results 14 showing erlotinib in the liver of the cassette-dosed animals and olanzapine in both the cassette-and discrete-dosed animals.…”

“…As a case study, we explored a published dataset which was originally used for spatial quantitation of drugs in a rat liver 14 ( dataset link , Figure 5). Using METASPACE, we reproduced the original results 14 showing erlotinib in the liver of the cassette-dosed animals and olanzapine in both the cassette-and discrete-dosed animals. Moreover, when searching for metabolites of olanzapine from the DrugBank database 18 (Figure 5b), we discovered metabolites of olanzapine (isomeric 7-hydroxyolanzapine and 2-hydroxymethylolanzapine as well as 4'-N-desmethylolanzapine) which were not reported in the original publication ( Figure 5c).…”

“…Recent advances in surface sampling, mass spectrometry, and bioinformatics made imaging MS a technique of choice for spatial metabolomics in a variety of biomedical and pharmacological applications [7][8][9][10] . Imaging MS has a near-single-cell spatial resolution of 1.4 μm on a commercial instrumentation 11 , the throughput to analyze a tissue section in minutes 12 , high specificity when using high-mass-resolution 13 , sensitivity to detect small molecules at physiological micromolar concentrations 14 , and capacity to detect various classes of molecules including amino acids, central carbon metabolism intermediates, free fatty acids, various lipids, and neurotransmitters 15 . Until recently, the progress and applications of imaging MS were hampered by the lack of algorithms for metabolite identification, namely for associating ion peaks and images with their corresponding molecules.…”

Fabrication of homogenous three‐dimensional biomimetic tissue for mass spectrometry imaging

“…With respect to drugs or other exogenous analytes, “on‐tissue” or “under‐tissue” micropipetting strategies are also difficult to accurately reflect the similar drug status within native tissue, where desorption/ionization is being processed under the complicated suppression by cells and extracellular matrix (ECM). Apart from parallel cryo‐sections, tissue homogenate is another type of surrogate used for representing the analyte's surrounding environment . Compared with standard‐spiked native tissue sections, analytes have much more in‐depth incorporation and uniform distribution .…”

“…Apart from parallel cryo-sections, tissue homogenate is another type of surrogate used for representing the analyte's surrounding environment. [26][27][28][29][30][31][32][33] Compared with standard-spiked native tissue sections, analytes have much more in-depth incorporation and uniform distribution. 34,35 Unfortunately, cells can seldomly survive under this violent homogenization process, 35 whereas the existence of cells should also contribute as the real impact factor for the analyte's desorption/ionization.…”