Quantitative imaging of chemical composition in single cells by secondary ion mass spectrometry: cisplatin affects calcium stores in renal epithelial cells

Innovation in drug toxicology: Application of mass spectrometry imaging technology

Mass spectrometry imaging (MSI) is a powerful molecular imaging technology that can obtain qualitative, quantitative, and location information by simultaneously detecting and mapping endogenous or exogenous molecules in biological tissue slices without specific chemical labeling or complex sample pretreatment. This article reviews the progress made in MSI and its application in drug toxicology research, including the tissue distribution of toxic drugs and their metabolites, the target organs (liver, kidney, lung, eye, and central nervous system) of toxic drugs, the discovery of toxicity-associated biomarkers, and explanations of the mechanisms of drug toxicity when MSI is combined with the cutting-edge omics methodologies. The unique advantages and broad prospects of this technology have been fully demonstrated to further promote its wider use in the field of pharmaceutical toxicology.

Analysis of the intracellular localization of amiodarone using live single-cell mass spectrometry

Amiodarone is a well-known antiarrhythmic drug with side effects including phospholipidosis. However, it is not clear how amiodarone and its metabolites are localized in the cell. In the present study, the localization of amiodarone in the cytosol, vacuoles, and lipid droplets of a single HepG2 human hepatocellular carcinoma cell was determined directly using live single-cell mass spectrometry. The cytosol, vacuoles, and lipid droplets of a single HepG2 cell treated with amiodarone were separately captured using a nano-spray tip under a fluorescence microscope after visualizing the lipid droplets using a fluorescent probe. This assay showed a linearity in the measurement of amiodarone levels with R² values of 0.9996 and 0.9998 in the cell lysates and serum, respectively. The peak intensities of amiodarone and its metabolites in lipid droplets and vacuoles were significantly higher than those in the cytosol, while those in lipid droplets were higher than those in vacuoles. Amiodarone metabolites were detected in both lipid droplets and the cytosol. Live single-cell mass spectrometry combined with fluorescence imaging demonstrated clear localization of amiodarone and its metabolites in lipid droplets separately from the vacuole. This assay system combined with fluorescence imaging could be useful for investigating the intracellular localization of various drugs and their metabolites.

[Pt(O,O'-acac)(γ-acac)(DMS)]: Alternative Strategies to Overcome Cisplatin-Induced Side Effects and Resistance in T98G Glioma Cells

Cisplatin (CDDP) is one of the most effective chemotherapeutic agents, used for the treatment of diverse tumors, including neuroblastoma and glioblastoma. CDDP induces cell death through different apoptotic pathways. Despite its clinical benefits, CDDP causes several side effects and drug resistance.[Pt(O,O'-acac)(γ-acac)(DMS)], namely PtAcacDMS, a new platinum(II) complex containing two acetylacetonate (acac) and a dimethylsulphide (DMS) in the coordination sphere of metal, has been recently synthesized and showed 100 times higher cytotoxicity than CDDP. Additionally, PtAcacDMS was associated to a decreased neurotoxicity in developing rat central nervous system, also displaying great antitumor and antiangiogenic activity both in vivo and in vitro. Thus, based on the knowledge that several chemotherapeutics induce cancer cell death through an aberrant increase in [Ca2+]i, in the present in vitro study we compared CDDP and PtAcacDMS effects on apoptosis and intracellular Ca2+ dynamics in human glioblastoma T98G cells, applying a battery of complementary techniques, i.e., flow cytometry, immunocytochemistry, electron microscopy, Western blotting, qRT-PCR, and epifluorescent Ca2+ imaging. The results confirmed that (i) platinum compounds may induce cell death through an aberrant increase in [Ca2+]i and (ii) PtAcacDMS exerted stronger cytotoxic effect than CDDP, associated to a larger increase in resting [Ca2+]i. These findings corroborate the use of PtAcacDMS as a promising approach to improve Pt-based chemotherapy against gliomas, either by inducing a chemosensitization or reducing chemoresistance in cell lineages resilient to CDDP treatment.

Nano-scale imaging of dual stable isotope labeled oxaliplatin in human colon cancer cells reveals the nucleolus as a putative node for therapeutic effect

Oxaliplatin shows a superior clinical activity in colorectal cancer compared to cisplatin. Nevertheless, the knowledge about its cellular distribution and the mechanisms responsible for the different range of oxaliplatin-responsive tumors is far from complete. In this study, we combined highly sensitive element specific and isotope selective imaging by nanometer-scale secondary ion mass spectrometry (NanoSIMS) with transmission electron microscopy to investigate the subcellular accumulation of oxaliplatin in three human colon cancer cell lines (SW480, HCT116 wt, HCT116 OxR). Oxaliplatin bearing dual stable isotope labeled moieties, i.e. 2H-labeled diaminocyclohexane (DACH) and 13C-labeled oxalate, were applied for comparative analysis of the subcellular distribution patterns of the central metal and the ligands. In all the investigated cell lines, oxaliplatin was found to have a pronounced tendency for cytoplasmic aggregation in single membrane bound organelles, presumably related to various stages of the endocytic pathway. Moreover, nuclear structures, heterochromatin and in particular nucleoli, were affected by platinum-drug exposure. In order to explore the consequences of oxaliplatin resistance, subcellular drug distribution patterns were investigated in a pair of isogenic malignant cell lines with distinct levels of drug sensitivity (HCT116 wt and HCT116 OxR, the latter with acquired resistance to oxaliplatin). The subcellular platinum distribution was found to be similar in both cell lines, with only slightly higher accumulation in the sensitive HCT116 wt cells which is inconsistent with the resistance factor of more than 20-fold. Instead, the isotopic analysis revealed a disproportionally high accumulation of the oxalate ligand in the resistant cell line.

Antitumour and Toxicity Evaluation of a Ru(II)-Cyclopentadienyl Complex in a Prostate Cancer Model by Imaging Tools

BACKGROUND

Ruthenium complexes have been extensively investigated for their prospective value as alternatives to cisplatin. Recently, we reported the in vitro anticancer properties of a family of organometallic ruthenium( II)-cyclopentadienyl complexes and have explored their mechanism of action.

OBJECTIVE

The purpose of this study was to evaluate the in vivo antitumour efficacy and toxicity of one of these Ru(II) compounds, [RuCp(mTPPMSNa)(2,2'-bipy)][CF3SO2] (TM85) which displayed an interesting spectrum of activity against several cancer cells.

METHODS

Studies to assess the antitumour activity and toxicity were performed in a metastatic prostate (PC3) mice model using ICP-MS, nuclear microscopy, elemental analysis and Transmission Electron Microscopy (TEM).

RESULTS

TM85 showed low systemic toxicity but no significant tumour reduction, when administered at tolerated dose (20mg/kg) over 10 days. Ru was mainly retained in the liver and less in kidneys, with low accumulation in tumour. Increased bilirubin levels, anomalous Ca and Fe concentrations in liver and mitochondria alterations were indicative of liver injury. The hepatotoxicity observed was less severe than that of cisplatin and no nephrotoxicity was found.

CONCLUSION

Under the experimental conditions of this study, TM85 is less toxic than cisplatin, induces similar tumour reduction and avoids the formation of metastatic foci. No renal toxicity was observed by the analysis of creatinine levels and the effective renal plasma flow by 99mTc-MAG3 clearance. Hence, it can be considered a valuable compound for further studies in the field of Ru-based anticancer drugs.

Beyond the H&E: Advanced Technologies for in situ Tissue Biomarker Imaging

For decades, histopathology with routine hematoxylin and eosin staining has been and remains the gold standard for reaching a morphologic diagnosis in tissue samples from humans and veterinary species. However, within the past decade, there has been exponential growth in advanced techniques for in situ tissue biomarker imaging that bridge the divide between anatomic and molecular pathology. It is now possible to simultaneously observe localization and expression magnitude of multiple protein, nucleic acid, and molecular targets in tissue sections and apply machine learning to synthesize vast, image-derived datasets. As these technologies become more sophisticated and widely available, a team-science approach involving subspecialists with medical, engineering, and physics backgrounds is critical to upholding quality and validity in studies generating these data. The purpose of this manuscript is to detail the scientific premise, tools and training, quality control, and data collection and analysis considerations needed for the most prominent advanced imaging technologies currently applied in tissue sections: immunofluorescence, in situ hybridization, laser capture microdissection, matrix-assisted laser desorption ionization imaging mass spectrometry, and spectroscopic/optical methods. We conclude with a brief overview of future directions for ex vivo and in vivo imaging techniques.

Single-Cell Mass Spectrometry Reveals Changes in Lipid and Metabolite Expression in RAW 264.7 Cells upon Lipopolysaccharide Stimulation

It has been widely recognized that individual cells that exist within a large population of cells, even if they are genetically identical, can have divergent molecular makeups resulting from a variety of factors, including local environmental factors and stochastic processes within each cell. Presently, numerous approaches have been described that permit the resolution of these single-cell expression differences for RNA and protein; however, relatively few techniques exist for the study of lipids and metabolites in this manner. This study presents a methodology for the analysis of metabolite and lipid expression at the level of a single cell through the use of imaging mass spectrometry on a high-performance Fourier transform ion cyclotron resonance mass spectrometer. This report provides a detailed description of the overall experimental approach, including sample preparation as well as the data acquisition and analysis strategy for single cells. Applying this approach to the study of cultured RAW264.7 cells, we demonstrate that this method can be used to study the variation in molecular expression with cell populations and is sensitive to alterations in that expression that occurs upon lipopolysaccharide stimulation. Graphical Abstract.

Failure of Elevating Calcium Induces Oxidative Stress Tolerance and Imparts Cisplatin Resistance in Ovarian Cancer Cells

Cisplatin is a commonly used chemotherapeutic drug, used for the treatment of malignant ovarian cancer, but acquired resistance limits its application. There is therefore an overwhelming need to understand the mechanism of cisplatin resistance in ovarian cancer, that is, ovarian cancer cells are insensitive to cisplatin treatment. Here, we show that failure of elevating calcium and oxidative stress tolerance play key roles in cisplatin resistance in ovarian cancer cell lines. Cisplatin induces an increase in oxidative stress and alters intracellular Ca(2+) concentration, including cytosolic and mitochondrial Ca(2+) in cisplatin-sensitive SKOV3 cells, but not in cisplatin-resistant SKOV3/DDP cells. Cisplatin induces mitochondrial damage and triggers the mitochondrial apoptotic pathway in cisplatin-sensitive SKOV3 cells, but rarely in cisplatin-resistant SKOV3/DDP cells. Inhibition of calcium signaling attenuates cisplatin-induced oxidative stress and intracellular Ca(2+) overload in cisplatin-sensitive SKOV3 cells. Moreover, in vivo xenograft models of nude mouse, cisplatin significantly reduced the growth rates of tumors originating from SKOV3 cells, but not that of SKOV3/DDP cells. Collectively, our data indicate that failure of calcium up-regulation mediates cisplatin resistance by alleviating oxidative stress in ovarian cancer cells. Our results highlight potential therapeutic strategies to improve cisplatin resistance.

Bioanalytics in Quantitive (Bio)imaging/Mapping of Metallic Elements in Biological Samples

The aim of this article is to describe selected analytical techniques and their applications in the quantitative mapping/(bio)imaging of metals in biological samples. This work presents the advantages and disadvantages as well as the appropriate methods of scope for research. Distribution of metals in biological samples is currently one of the most important issues in physiology, toxicology, pharmacology, and other disciplines where functional information about the distribution of metals is essential. This issue is a subject of research in (bio)imaging/mapping studies, which use a variety of analytical techniques for the identification and determination of metallic elements. Increased interest in analytical techniques enabling the (bio)imaging of metals in a variety of biological material has been observed more recently. Measuring the distribution of trace metals in tissues after a drug dose or ingestion of poison-containing metals allows for the studying of pathomechanisms and the pathophysiology of various diseases and disorders related to the management of metals in human and animal systems.

Imaging mass spectrometry: Instrumentation, applications, and combination with other visualization techniques

Imaging Mass Spectrometry (IMS) is strengthening its position as a valuable analytical tool. It has unique ability to identify structures and to unravel molecular changes that occur in the precisely defined part of the sample. These unique features open new possibilities in the field of various aspects of biological research. In this review we briefly discuss the main imaging mass spectrometry techniques, as well as the nature of biological samples and molecules, which might be analyzed by such methodology. Moreover, a novel approach, where different analytical techniques might be combined with the results of IMS study, is emphasized and discussed. With such a fast development of IMS and related methods, we can foresee the promising future of this technique.

Development and validation of TOF-SIMS and CLSM imaging method for cytotoxicity study of ZnO nanoparticles in HaCaT cells

Zinc oxide nanoparticles (ZnO NPs) exhibit novel physiochemical properties and have found increasing use in sunscreen products and cosmetics. The potential toxicity is of increasing concern due to their close association with human skin. A time-of-flight secondary ion mass spectrometry (TOF-SIMS) and confocal laser scanning microscopy (CLSM) imaging method was developed and validated for rapid and sensitive cytotoxicity study of ZnO NPs using human skin equivalent HaCaT cells as a model system. Assorted material, chemical, and toxicological analysis methods were used to confirm their shape, size, crystalline structure, and aggregation properties as well as dissolution behavior and effect on HaCaT cell viability in the presence of various concentrations of ZnO NPs in aqueous media. Comparative and correlative analyses of aforementioned results with TOF-SIMS and CLSM imaging results exhibit reasonable and acceptable outcome. A marked drop in survival rate was observed with 50μg/ml ZnO NPs. The CLSM images reveal the absorption and localization of ZnO NPs in cytoplasm and nuclei. The TOF-SIMS images demonstrate elevated levels of intracellular ZnO concentration and associated Zn concentration-dependent (40)Ca/(39)K ratio, presumably caused by the dissolution behavior of ZnO NPs. Additional validation by using stable isotope-labeled (68)ZnO NPs as tracers under the same experimental conditions yields similar cytotoxicity effect. The imaging results demonstrate spatially-resolved cytotoxicity relationship between intracellular ZnO NPs, (40)Ca/(39)K ratio, phosphocholine fragments, and glutathione fragments. The trend of change in TOF-SIMS spectra and images of ZnO NPs treated HaCaT cells demonstrate the possible mode of actions by ZnO NP involves cell membrane disruption, cytotoxic response, and ROS mediated apoptosis.

Quantitative evaluation of boron neutron capture therapy (BNCT) drugs for boron delivery and retention at subcellular-scale resolution in human glioblastoma cells with imaging secondary ion mass spectrometry (SIMS)

Boron neutron capture therapy (BNCT) of cancer depends on the selective delivery of a sufficient number of boron-10 ((10)B) atoms to individual tumour cells. Cell killing results from the (10)B (n, α)(7) Li neutron capture and fission reactions that occur if a sufficient number of (10)B atoms are localized in the tumour cells. Intranuclear (10)B localization enhances the efficiency of cell killing via damage to the DNA. The net cellular content of (10)B atoms reflects both bound and free pools of boron in individual tumour cells. The assessment of these pools, delivered by a boron delivery agent, currently cannot be made at subcellular-scale resolution by clinically applicable techniques such as positron emission tomography and magnetic resonance imaging. In this study, a secondary ion mass spectrometry based imaging instrument, a CAMECA IMS 3f ion microscope, capable of 500 nm spatial resolution was employed. Cryogenically prepared cultured human T98G glioblastoma cells were evaluated for boron uptake and retention of two delivery agents. The first, L-p-boronophenylalanine (BPA), has been used clinically for BNCT of high-grade gliomas, recurrent tumours of the head and neck region and melanomas. The second, a boron analogue of an unnatural amino acid, 1-amino-3-borono-cyclopentanecarboxylic acid (cis-ABCPC), has been studied in rodent glioma and melanoma models by quantification of boron in the nucleus and cytoplasm of individual tumour cells. The bound and free pools of boron were assessed by exposure of cells to boron-free nutrient medium. Both BPA and cis-ABCPC delivered almost 70% of the pool of boron in the free or loosely bound form to the nucleus and cytoplasm of human glioblastoma cells. This free pool of boron could be easily mobilized out of the cell and was in some sort of equilibrium with extracellular boron. In the case of BPA, the intracellular free pool of boron also was affected by the presence of phenylalanine in the nutrient medium. This suggests that it might be advantageous if patients were placed on a low phenylalanine diet prior to the initiation of BNCT. Since BPA currently is used clinically for BNCT, our observations may have direct relevance to future clinical studies utilizing this agent and provides support for individualized treatment planning regimens rather than the use of fixed BPA infusion protocols.

NanoSIMS multi-element imaging reveals internalisation and nucleolar targeting for a highly-charged polynuclear platinum compound

Simultaneous multi-element imaging using NanoSIMS (nano-scale secondary ion mass spectrometry), exploiting the novel combination of (195)Pt and (15)N in platinum-am(m)ine antitumour drugs, provides information on the internalisation and subcellular localisation of both metal and ligands, and allows identification of ligand exchange.

Biodistribution and subcellular localization of an unnatural boron-containing amino acid (cis-ABCPC) by imaging secondary ion mass spectrometry for neutron capture therapy of melanomas and gliomas

The development of new boron-delivery agents is a high priority for improving the effectiveness of boron neutron capture therapy. In the present study, 1-amino-3-borono-cyclopentanecarboxylic acid (cis-ABCPC) as a mixture of its L- and D- enantiomers was evaluated in vivo using the B16 melanoma model for the human tumor and the F98 rat glioma as a model for human gliomas. A secondary ion mass spectrometry (SIMS) based imaging instrument, CAMECA IMS 3F SIMS Ion Microscope, was used for quantitative imaging of boron at 500 nm spatial resolution. Both in vivo and in vitro studies in melanoma models demonstrated that boron was localized in the cytoplasm and nuclei with some cell-to-cell variability. Uptake of cis-ABCPC in B16 cells was time dependent with a 7.5:1 partitioning ratio of boron between cell nuclei and the nutrient medium after 4 hrs. incubation. Furthermore, cis-ABCPC delivered boron to cells in all phases of the cell cycle, including S-phase. In vivo SIMS studies using the F98 rat glioma model revealed an 8:1 boron partitioning ratio between the main tumor mass and normal brain tissue with a 5:1 ratio between infiltrating tumor cells and contiguous normal brain. Since cis-ABCPC is water soluble and can cross the blood-brain-barrier via the L-type amino acid transporters (LAT), it may accumulate preferentially in infiltrating tumor cells in normal brain due to up-regulation of LAT in high grade gliomas. Once trapped inside the tumor cell, cis-ABCPC cannot be metabolized and remains either in a free pool or bound to cell matrix components. The significant improvement in boron uptake by both the main tumor mass and infiltrating tumor cells compared to those reported in animal and clinical studies of p-boronophenylalanine strongly suggest that cis-ABCPC has the potential to become a novel new boron delivery agent for neutron capture therapy of gliomas and melanomas.

Quantitative mass spectrometry imaging of propranolol and olanzapine using tissue extinction calculation as normalization factor

In order to quantify small molecules at the early stage of drug discovery, we developed a quantitation approach based on mass spectrometry imaging (MSI) using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) without the use of a labeled compound. We describe a method intended to respond to the main challenges encountered in quantification through MALDI imaging dedicated to whole-body or single heterogeneous organ samples (brain, eye, liver). These include the high dependence of the detected signal on the matrix deposition, the MALDI ionization yield of specific target molecules, and lastly, the ion suppression effect on the tissue. To address these challenges, we based our approach on the use of a normalization factor called the TEC (Tissue Extinction Coefficient). This factor takes into account the ion suppression effect that is both tissue- and drug-specific. Through this protocol, the amount of drug per gram of tissue was determined, which in turn, was compared with other analytical techniques such as Liquid Chromatography-Mass spectrometry (LC-MS/MS).

Mass spectrometry imaging and profiling of single cells

Mass spectrometry imaging and profiling of individual cells and subcellular structures provide unique analytical capabilities for biological and biomedical research, including determination of the biochemical heterogeneity of cellular populations and intracellular localization of pharmaceuticals. Two mass spectrometry technologies-secondary ion mass spectrometry (SIMS) and matrix assisted laser desorption/ionization mass spectrometry (MALDI MS)-are most often used in micro-bioanalytical investigations. Recent advances in ion probe technologies have increased the dynamic range and sensitivity of analyte detection by SIMS, allowing two- and three-dimensional localization of analytes in a variety of cells. SIMS operating in the mass spectrometry imaging (MSI) mode can routinely reach spatial resolutions at the submicron level; therefore, it is frequently used in studies of the chemical composition of subcellular structures. MALDI MS offers a large mass range and high sensitivity of analyte detection. It has been successfully applied in a variety of single-cell and organelle profiling studies. Innovative instrumentation such as scanning microprobe MALDI and mass microscope spectrometers enables new subcellular MSI measurements. Other approaches for MS-based chemical imaging and profiling include those based on near-field laser ablation and inductively-coupled plasma MS analysis, which offer complementary capabilities for subcellular chemical imaging and profiling.

MALDI mass spectrometry imaging of neuronal cell cultures

Mass spectrometry imaging (MSI) provides the ability to detect and identify a broad range of analytes and their spatial distributions from a variety of sample types, including tissue sections. Here we describe an approach for probing neuropeptides from sparse cell cultures using matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) MSI--at single cell spatial resolution-in both MS and tandem MS modes. Cultures of Aplysia californica neurons are grown on an array of glass beads embedded in a stretchable layer of Parafilm M. As the membrane is stretched, the beads/neurons are separated physically and the separated beads/neurons analyzed via MALDI TOF MS. Compared with direct MS imaging of samples, the stretching procedure enhances analyte extraction and incorporation into the MALDI matrix, with negligible analyte spread between separated beads. MALDI tandem MSI using the stretched imaging approach yields localization maps of both parent and fragment ions from Aplysia pedal peptide, thereby confirming peptide identification. This methodology represents a flexible platform for MSI investigation of a variety of cell cultures, including functioning neuronal networks.

Boronated unnatural cyclic amino acids as potential delivery agents for neutron capture therapy

Boron delivery characteristics of cis and trans isomers of a boronated unnatural amino acid, 1-amino-3-boronocyclopentanecarboxylic acid (ABCPC) were tested in the B16 mouse model for human melanoma. Both ABCPC isomers delivered comparable boron to B16 melanoma tumor cells as L-p-boronophenylalanine (BPA). Secondary ion mass spectrometry (SIMS) analysis revealed the presence of boron throughout the tumor from these compounds, and a near homogeneous distribution between the nucleus and cytoplasm of B16 cells grown in vitro. These encouraging observations support further studies of these new boron carriers in BNCT.

A quantitation method for mass spectrometry imaging

A new quantitation method for mass spectrometry imaging (MSI) with matrix-assisted laser desorption/ionization (MALDI) has been developed. In this method, drug concentrations were determined by tissue homogenization of five 10 µm tissue sections adjacent to those analyzed by MSI. Drug levels in tissue extracts were measured by liquid chromatography coupled to tandem mass spectrometry (LC/MS/MS). The integrated MSI response was correlated to the LC/MS/MS drug concentrations to determine the amount of drug detected per MSI ion count. The study reported here evaluates olanzapine in liver tissue. Tissue samples containing a range of concentrations were created from liver harvested from rats administered a single dose of olanzapine at 0, 1, 4, 8, 16, 30, or 100 mg/kg. The liver samples were then analyzed by MALDI-MSI and LC/MS/MS. The MALDI-MSI and LC/MS/MS correlation was determined for tissue concentrations of ~300 to 60,000 ng/g and yielded a linear relationship over two orders of magnitude (R(2) = 0.9792). From this correlation, a conversion factor of 6.3 ± 0.23 fg/ion count was used to quantitate MSI responses at the pixel level (100 µm). The details of the method, its importance in pharmaceutical analysis, and the considerations necessary when implementing it are presented.