Abstract
Recent advances in matrix-assisted laser desorption/ionization (MALDI) mass spectrometry have enabled whole cell-MALDI mass spectrometry biotyping of drug-treated cultured cells for rapid monitoring of known abundant pharmacodynamic protein markers such as polyacetylated histones. In contrast, generic and automated analytical workflows for discovery of such pharmacodynamic markers, in particular lipid markers, and their use in cellular tests of drug-like compounds are still lacking. Here, we introduce such a workflow and demonstrate its utility for cellular drug-response monitoring of BCR-ABL tyrosine kinase inhibitors in K562 leukemia cells: First, low-molecular mass features indicating drug responses are computationally extracted from groups of MALDI-TOF mass spectra. Then, the lipids/metabolites corresponding to these features are identified by MALDI-Fourier transformation mass spectrometry. To demonstrate utility of the method, we identify the potassium adduct of phosphatidylcholine PC(36:1) as well as heme B, a marker for erythroid differentiation, as markers for a label-free MALDI MS-based test of cellular responses to BCR-ABL inhibitors. Taken together, these results suggest that MALDI-TOF mass spectrometry of lipids and other low molecular mass metabolites could support cell-based drug profiling.
Highlights
Since the first description of species-specific small-molecule mass spectrometry (MS) fingerprints obtained by whole cell measurements of bacteria in 19751, matrix-assisted laser desorption/ionization (MALDI) MS fingerprinting has been established as an important tool in environmental microbiology and for clinical identification of pathogenic bacteria[2,3,4]
Whereas applications of MALDI-TOF MS-based lipid/metabolite fingerprinting of mammalian cell extracts have been described in several fields including bioprocess engineering[10], to date few studies describe MALDI-TOF MS lipid/metabolite fingerprinting of non-extracted mammalian cells
Few WC-MALDI-TOF MS biotyping-based workflows with potential utility as drug profiling tests have been established, most of which are based on the analysis of protein fingerprints[7,8]
Summary
Since the first description of species-specific small-molecule mass spectrometry (MS) fingerprints obtained by whole cell measurements of bacteria in 19751, matrix-assisted laser desorption/ionization (MALDI) MS fingerprinting ( referred to as biotyping) has been established as an important tool in environmental microbiology and for clinical identification of pathogenic bacteria[2,3,4]. Drug profiling based on whole cell(WC-) MALDI-TOF MS protein biotyping workflows using either known abundant protein markers such as polyacetylated histone H4 or defined sets of m/z values corresponding to uncharacterized proteins have been established[7,8]. Generic workflows for development of label-free WC-MALDI-TOF MS cellular tests that utilize small molecule lipid/metabolite markers for determination of IC50 values have not been described yet. We present a new computational WC-MALDI-TOF MS workflow that automatically extracts low mass m/z features that indicate lipid/metabolite concentration-responses in cultured cells. The corresponding lipids/ metabolites are elucidated by MALDI-Fourier transform ion cyclotron resonance (FTICR) MS As an example, this workflow was applied for determination of IC50 values for the anti-leukemia drug imatinib and other BCR-Abl tyrosine kinase inhibitors in the chronic myelogenous leukemia (CML) cell line K562. We identified the potassium adduct of the phosphatidyl choline PC(36:1), and heme B, a marker for erythroid redifferentiation of CML cells, as markers of BCR-ABL potency that could be used for IC50 determination
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