Differences in cisplatin distribution in sensitive and resistant ovarian cancer cells: a TEM/NanoSIMS study

Genetic polymorphisms as potential pharmacogenetic biomarkers for platinum-based chemotherapy in non-small cell lung cancer

Platinum-based chemotherapy (PBC) is a widely used treatment for various solid tumors, including non-small cell lung cancer (NSCLC). However, its efficacy is often compromised by the emergence of drug resistance in patients. There is growing evidence that genetic variations may influence the susceptibility of NSCLC patients to develop resistance to PBC. Here, we provide a comprehensive overview of the mechanisms underlying platinum drug resistance and highlight the important role that genetic polymorphisms play in this process. This paper discussed the genetic variants that regulate DNA repair, cellular movement, drug transport, metabolic processing, and immune response, with a focus on their effects on response to PBC. The potential applications of these genetic polymorphisms as predictive indicators in clinical practice are explored, as are the challenges associated with their implementation.

Investigations of cellular copper metabolism in ovarian cancer cells using a ratiometric fluorescent copper dye

Imbalances in metal homeostasis have been implicated in the progression and drug response of cancer cells. Understanding these changes will enable identification of new treatment regimes and precision medicine approaches to cancer treatment. In particular, there has been considerable interest in the interplay between copper homeostasis and response to platinum-based chemotherapeutic agents. Here, we have studied differences in the Cu uptake and distributions in the ovarian cancer cell line, A2780, and its cisplatin resistant form, A2780.CisR, by measuring total Cu content and the bioavailable Cu pool. Atomic absorption spectroscopy (AAS) revealed a lower total Cu uptake in A2780.CisR compared to A2780 cells. Conversely, live-cell confocal microscopy studies with the ratiometric Cu(I)-sensitive fluorescent dye, InCCu1, revealed higher relative cellular content of labile Cu in A2780.CisR cells compared with A2780 cells. These results demonstrate that Cu trafficking, homeostasis and speciation are different in the Pt-sensitive and resistant cells and may be associated with the predominance of different phenotypes for A2780 (epithelial) and A2780.CisR (mesenchymal) cells.

Quantitative subcellular acyl-CoA analysis reveals distinct nuclear metabolism and isoleucine-dependent histone propionylation

Quantitative subcellular metabolomic measurements can explain the roles of metabolites in cellular processes but are subject to multiple confounding factors. We developed stable isotope labeling of essential nutrients in cell culture-subcellular fractionation (SILEC-SF), which uses isotope-labeled internal standard controls that are present throughout fractionation and processing to quantify acyl-coenzyme A (acyl-CoA) thioesters in subcellular compartments by liquid chromatography-mass spectrometry. We tested SILEC-SF in a range of sample types and examined the compartmentalized responses to oxygen tension, cellular differentiation, and nutrient availability. Application of SILEC-SF to the challenging analysis of the nuclear compartment revealed a nuclear acyl-CoA profile distinct from that of the cytosol, with notable nuclear enrichment of propionyl-CoA. Using isotope tracing, we identified the branched chain amino acid isoleucine as a major metabolic source of nuclear propionyl-CoA and histone propionylation, thus revealing a new mechanism of crosstalk between metabolism and the epigenome.

Beyond Single-Cell Analysis of Metallodrugs by ICP-MS: Targeting Cellular Substructures

Platinum compounds such as cisplatin (cisPt) embody the backbone of combination chemotherapy protocols against advanced lung cancer. However, their efficacy is primarily limited by inherent or acquired platinum resistance, the origin of which has not been fully elucidated yet, although of paramount interest. Using single cell inductively coupled plasma mass spectrometry (SC-ICP-MS), this study quantifies cisPt in single cancer cells and for the first time in isolated nuclei. A comparison of cisPt uptake was performed between a wild type (wt) cancer cell line and related resistant sublines. In both, resistant cells, wt cells, and their nuclei, cisPt uptake was measured at different incubation times. A lower amount of cisPt was found in resistant cell lines and their nuclei compared to wt cells. Moreover, the abundance of internalized cisPt decreased with increasing resistance. Interestingly, concentrations of cisPt found within the nuclei were higher than compared to cellular concentrations. Here, we show, that SC-ICP-MS allows precise and accurate quantification of metallodrugs in both single cells and cell organelles such as nuclei. These findings pave the way for future applications investigating the potency and efficacy of novel metallodrugs developed for cancer treatment.

Subcellular localization of biomolecules and drug distribution by high-definition ion beam imaging

Simultaneous visualization of the relationship between multiple biomolecules and their ligands or small molecules at the nanometer scale in cells will enable greater understanding of how biological processes operate. We present here high-definition multiplex ion beam imaging (HD-MIBI), a secondary ion mass spectrometry approach capable of high-parameter imaging in 3D of targeted biological entities and exogenously added structurally-unmodified small molecules. With this technology, the atomic constituents of the biomolecules themselves can be used in our system as the “tag” and we demonstrate measurements down to ~30 nm lateral resolution. We correlated the subcellular localization of the chemotherapy drug cisplatin simultaneously with five subnuclear structures. Cisplatin was preferentially enriched in nuclear speckles and excluded from closed-chromatin regions, indicative of a role for cisplatin in active regions of chromatin. Unexpectedly, cells surviving multi-drug treatment with cisplatin and the BET inhibitor JQ1 demonstrated near total cisplatin exclusion from the nucleus, suggesting that selective subcellular drug relocalization may modulate resistance to this important chemotherapeutic treatment. Multiplexed high-resolution imaging techniques, such as HD-MIBI, will enable studies of biomolecules and drug distributions in biologically relevant subcellular microenvironments by visualizing the processes themselves in concert, rather than inferring mechanism through surrogate analyses.

Multiplexed ion beam imaging can provide subcellular localisation information but with limited resolution. Here the authors report an ion beam imaging method with nanoscale resolution which they use to assess the subcellular distribution of cisplatin.

Characterization of a hyaluronic acid and folic acid-based hydrogel for cisplatin delivery: Antineoplastic effect in human ovarian cancer cells in vitro

We successfully prepared and characterized a hyaluronic acid- and folic acid-based hydrogel for the delivery of cisplatin (GEL-CIS) with the aim to induce specific and efficient incorporation of CIS into ovarian cancer (OC) cells, improve its antineoplastic effect and avoid CIS-resistance. The slow and controlled release of the drug from the polymeric network and its swelling degree at physiologic pH suggested its suitability for CIS delivery in OC. We compared here the effects of pure CIS to that of GEL-CIS on human OC cell lines, either wild type or CIS-resistant, in basal conditions and in the presence of macrophage-derived conditioned medium, mimicking the action of tumor-associated macrophages in vivo. GEL-CIS inhibited OC cell growth and migration more efficiently than pure CIS and modulated the expression of proteins involved in the Epithelial Mesenchymal Transition, a process playing a key role in OC metastatic spread and resistance to CIS.

Pt-ttpy, a G-quadruplex binding platinum complex, induces telomere dysfunction and G-rich regions DNA damage

Pt-ttpy (tolyl terpyridin-Pt complex) covalently binds to G-quadruplex (G4) structures in vitro and to telomeres in cellulo via its Pt moiety. Here, we identified its targets in the human genome, in comparison to Pt-tpy, its derivative without G4 affinity, and cisplatin. Pt-ttpy, but not Pt-tpy, induces the release of the shelterin protein TRF2 from telomeres concomitantly to the formation of DNA damage foci at telomeres but also at other chromosomal locations. γ-H2AX chromatin immunoprecipitation (ChIP-seq) after treatment with Pt-ttpy or cisplatin revealed accumulation in G- and A-rich tandemly repeated sequences, but not particularly in potential G4 forming sequences. Collectively, Pt-ttpy presents dual targeting efficiency on DNA, by inducing telomere dysfunction and genomic DNA damage at specific loci.

Enhanced Laterally Resolved ToF-SIMS and AFM Imaging of the Electrically Conductive Structures in Cable Bacteria

Cable bacteria are electroactive bacteria that form a long, linear chain of ridged cylindrical cells. These filamentous bacteria conduct centimeter-scale long-range electron transport through parallel, interconnected conductive pathways of which the detailed chemical and electrical properties are still unclear. Here, we combine time-of-flight secondary-ion mass spectrometry (ToF-SIMS) and atomic force microscopy (AFM) to investigate the structure and composition of this naturally occurring electrical network. The enhanced lateral resolution achieved allows differentiation between the cell body and the cell-cell junctions that contain a conspicuous cartwheel structure. Three ToF-SIMS modes were compared in the study of so-called fiber sheaths (i.e., the cell material that remains after the removal of cytoplasm and membranes, and which embeds the electrical network). Among these, fast imaging delayed extraction (FI-DE) was found to balance lateral and mass resolution, thus yielding the following multiple benefits in the study of structure-composition relations in cable bacteria: (i) it enables the separate study of the cell body and cell-cell junctions; (ii) by combining FI-DE with in situ AFM, the depth of Ni-containing protein-key in the electrical transport-is determined with greater precision; and (iii) this combination prevents contamination, which is possible when using an ex situ AFM. Our results imply that the interconnects in extracted fiber sheaths are either damaged during extraction, or that their composition is different from fibers, or both. From a more general analytical perspective, the proposed methodology of ToF-SIMS in the FI-DE mode combined with in situ AFM holds great promise for studying the chemical structure of other biological systems.

Tracking the cargo of extracellular symbionts into host tissues with correlated electron microscopy and nanoscale secondary ion mass spectrometry imaging

Extracellular bacterial symbionts communicate biochemically with their hosts to establish niches that foster the partnership. Using quantitative ion microprobe isotopic imaging (nanoscale secondary ion mass spectrometry [NanoSIMS]), we surveyed localization of ¹⁵ N-labelled molecules produced by the bacterium Vibrio fischeri within the cells of the symbiotic organ of its host, the Hawaiian bobtail squid, and compared that with either labelled non-specific species or amino acids. In all cases, two areas of the organ's epithelia were significantly more ¹⁵ N enriched: (a) surface ciliated cells, where environmental symbionts are recruited, and (b) the organ's crypts, where the symbiont population resides in the host. Label enrichment in all cases was strongest inside host cell nuclei, preferentially in the euchromatin regions and the nucleoli. This permissiveness demonstrated that uptake of biomolecules is a general mechanism of the epithelia, but the specific responses to V. fischeri cells recruited to the organ's surface are due to some property exclusive to this species. Similarly, in the organ's deeper crypts, the host responds to common bacterial products that only the specific symbiont can present in that location. The application of NanoSIMS allows the discovery of such distinct modes of downstream signalling dependent on location within the host and provides a unique opportunity to study the microbiogeographical patterns of symbiotic dialogue.

Spatially Resolved Mass Spectrometry at the Single Cell: Recent Innovations in Proteomics and Metabolomics

Biological systems are composed of heterogeneous populations of cells that intercommunicate to form a functional living tissue. Biological function varies greatly across populations of cells, as each single cell has a unique transcriptome, proteome, and metabolome that translates to functional differences within single species and across kingdoms. Over the past decade, substantial advancements in our ability to characterize omic profiles on a single cell level have occurred, including in multiple spectroscopic and mass spectrometry (MS)-based techniques. Of these technologies, spatially resolved mass spectrometry approaches, including mass spectrometry imaging (MSI), have shown the most progress for single cell proteomics and metabolomics. For example, reporter-based methods using heavy metal tags have allowed for targeted MS investigation of the proteome at the subcellular level, and development of technologies such as laser ablation electrospray ionization mass spectrometry (LAESI-MS) now mean that dynamic metabolomics can be performed in situ. In this Perspective, we showcase advancements in single cell spatial metabolomics and proteomics over the past decade and highlight important aspects related to high-throughput screening, data analysis, and more which are vital to the success of achieving proteomic and metabolomic profiling at the single cell scale. Finally, using this broad literature summary, we provide a perspective on how the next decade may unfold in the area of single cell MS-based proteomics and metabolomics.

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.

Dual-mode imaging of copper transporter 1 in HepG2 cells by hyphenating confocal laser scanning microscopy with laser ablation ICPMS

Copper transporter 1 (CTR1) is a transport protein involved in copper and cisplatin uptake. The visualization of cellular CTR1 migration and its redistribution is highly important in copper/cisplatin exposure/transport. However, to the best of our knowledge, this is a highly challenging task. Herein, a dual-mode imaging strategy for CTR1 is developed by hyphenating confocal laser scanning microscopy (CLSM) and laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS) with a fluorescent/elemental bifunctional tag conjugated with anti-CTR1 antibody. The tag consists of rhodamine B and zirconium metal-organic frameworks (Zr-MOF) for CLSM fluorescence imaging and LA-ICPMS element imaging for a same group of HepG2 cells in a designated visual zone. This dual-mode imaging strategy facilitates visualization of CTR1 migration and meanwhile provides information of CTR1 redistribution in HepG2 cells by uptake of divalent copper or cisplatin. The present dual-mode imaging strategy provides in-depth information for the elucidation of CTR1 involved biological processes. Graphical abstract.

Copper Complexes with 1,10-Phenanthroline Derivatives: Underlying Factors Affecting Their Cytotoxicity

The interpretation of in vitro cytotoxicity data of Cu(II)-1,10-phenanthroline (phen) complexes normally does not take into account the speciation that complexes undergo in cell incubation media and its implications in cellular uptake and mechanisms of action. We synthesize and test the activity of several distinct Cu(II)-phen compounds; up to 24 h of incubation, the cytotoxic activity differs for the Cu complexes and the corresponding free ligands, but for longer incubation times (e.g., 72 h), all compounds display similar activity. Combining the use of several spectroscopic, spectrometric, and electrochemical techniques, the speciation of Cu-phen compounds in cell incubation media is evaluated, indicating that the originally added complex almost totally decomposed and that Cu(II) and phen are mainly bound to bovine serum albumin. Several methods are used to disclose relationships between structure, activity, speciation in incubation media, cellular uptake, distribution of Cu in cells, and cytotoxicity. Contrary to what is reported in most studies, we conclude that interaction with cell components and cell death involves the separate action of Cu ions and phen molecules, not [Cu(phen)_n] species. This conclusion should similarly apply to many other Cu-ligand systems reported to date.

Natural compound Tan-I enhances the efficacy of Paclitaxel chemotherapy in ovarian cancer

Background

Paclitaxel is a widely used clinical first line chemotherapy drug for ovarian carcinoma. Tanshinone I (Tan-I) is one of the vital fat-soluble components, which derived from Chinese herbal medicine, Salvia miltiorrhiza Bunge. Herein, we evaluated whether Tan-I could enhance the efficacy of ovarian cancer to chemotherapy of Paclitaxel.

Methods

Ovarian cancer cells A2780 and ID-8 were exposed with Tan-I (4.8 µg/mL), Paclitaxel (0.1 µg/mL), or Tan-I combination with Paclitaxel for 24 hours. The cell proliferation was analyzed by CCK8 and EdU staining. Cell apoptosis was analyzed by the TUNEL assay and flow cytometry. The protein levels were determined by western blot. Cell migration was analyzed by Transwell and wound healing. Cell senescence was analyzed by senescence-associated b-galactosidase staining. Antitumor activity was analyzed by a subcutaneous tumor xenograft model of human ovarian cancer in nude mice. The protein expression and apoptosis level of tumor tissues were analyzed by immunohistochemistry and TUNEL staining.

Results

Tan-I treatment significantly elevated the Paclitaxel-cause reduction of A2780 and ID-8 cell proliferation and cell migration. Tan-I combination with Paclitaxel promotes apoptosis of cancer cells by promoting Bax expression and Bcl-2 expression. Besides, Tan-I treatment can notably increase Paclitaxel-inducing cell senescence by promoting DNA damage and senescence-associated proteins such as p21 and p16. Furthermore, the result of the transplanted tumor model indicated that Tan-I combination with Paclitaxel could inhibit tumor growth in vivo by inhibiting cell proliferation and inducing cell apoptosis.

Conclusions

Natural compound Tan-I enhances the efficacy of ovarian cancer to Paclitaxel chemotherapy. The results will help to supply the potential clinical use of ovarian carcinoma cells.

Subcellular Mass Spectrometry Imaging and Absolute Quantitative Analysis across Organelles

Mass spectrometry imaging is a field that promises to become a mainstream bioanalysis technology by allowing the combination of single-cell imaging and subcellular quantitative analysis. The frontier of single-cell imaging has advanced to the point where it is now possible to compare the chemical contents of individual organelles in terms of raw or normalized ion signal. However, to realize the full potential of this technology, it is necessary to move beyond this concept of relative quantification. Here we present a nanoSIMS imaging method that directly measures the absolute concentration of an organelle-associated, isotopically labeled, pro-drug directly from a mass spectrometry image. This is validated with a recently developed nanoelectrochemistry method for single organelles. We establish a limit of detection based on the number of isotopic labels used and the volume of the organelle of interest, also offering this calculation as a web application. This approach allows subcellular quantification of drugs and metabolites, an overarching and previously unmet goal in cell science and pharmaceutical development.

Subcellular Localization of Copper-Cellular Bioimaging with Focus on Neurological Disorders

As an essential trace element, copper plays a pivotal role in physiological body functions. In fact, dysregulated copper homeostasis has been clearly linked to neurological disorders including Wilson and Alzheimer’s disease. Such neurodegenerative diseases are associated with progressive loss of neurons and thus impaired brain functions. However, the underlying mechanisms are not fully understood. Characterization of the element species and their subcellular localization is of great importance to uncover cellular mechanisms. Recent research activities focus on the question of how copper contributes to the pathological findings. Cellular bioimaging of copper is an essential key to accomplish this objective. Besides information on the spatial distribution and chemical properties of copper, other essential trace elements can be localized in parallel. Highly sensitive and high spatial resolution techniques such as LA-ICP-MS, TEM-EDS, S-XRF and NanoSIMS are required for elemental mapping on subcellular level. This review summarizes state-of-the-art techniques in the field of bioimaging. Their strengths and limitations will be discussed with particular focus on potential applications for the elucidation of copper-related diseases. Based on such investigations, further information on cellular processes and mechanisms can be derived under physiological and pathological conditions. Bioimaging studies might enable the clarification of the role of copper in the context of neurodegenerative diseases and provide an important basis to develop therapeutic strategies for reduction or even prevention of copper-related disorders and their pathological consequences.

Effect of sample preparation techniques upon single cell chemical imaging: A practical comparison between synchrotron radiation based X-ray fluorescence (SR-XRF) and Nanoscopic Secondary Ion Mass Spectrometry (nano-SIMS)

Analytical capabilities of Nanoscopic Secondary Ion Mass Spectrometry (nano-SIMS) and Synchrotron Radiation based X-ray Fluorescence (SR nano-XRF) techniques were compared for nanochemical imaging of polymorphonuclear human neutrophils (PMNs). PMNs were high pressure frozen (HPF), cryo-substituted, embedded in Spurr's resin and cut in thin sections (500 nm and 2 μm for both techniques resp.) Nano-SIMS enabled nanoscale mapping of isotopes of C, N, O, P and S, while SR based nano-XRF enabled trace level imaging of metals like Ca, Mn, Fe, Ni, Cu and Zn at a resolution of approx. 50 nm. The obtained elemental distributions were compared with those of whole, cryofrozen PMNs measured at the newly developed ID16A nano-imaging beamline at the European Synchrotron Radiation Facility (ESRF) in Grenoble, France. Similarities were observed for elements more tightly bound to the cell structure such as phosphorus and sulphur, while differences for mobile ions such as chlorine and potassium were more pronounced. Due to the observed elemental redistribution of mobile ions such as potassium and chlorine, elemental analysis of high pressure frozen (HPF), cryo-substituted and imbedded cells should be interpreted critically. Although decreasing analytical sensitivity occurs due to the presence of ice, analysis of cryofrozen cells - close to their native state - remains the golden standard. In general, we found nanoscale secondary ion mass spectrometry (nano-SIMS) and synchrotron radiation based nanoscopic X-ray fluorescence (SR nano-XRF) to be two supplementary alternatives for nanochemical imaging of single cells at the nanoscale.

Infrared nanospectroscopic mapping of a single metaphase chromosome

The integrity of the chromatin structure is essential to every process occurring within eukaryotic nuclei. However, there are no reliable tools to decipher the molecular composition of metaphase chromosomes. Here, we have applied infrared nanospectroscopy (AFM-IR) to demonstrate molecular difference between eu- and heterochromatin and generate infrared maps of single metaphase chromosomes revealing detailed information on their molecular composition, with nanometric lateral spatial resolution. AFM-IR coupled with principal component analysis has confirmed that chromosome areas containing euchromatin and heterochromatin are distinguishable based on differences in the degree of methylation. AFM-IR distribution of eu- and heterochromatin was compared to standard fluorescent staining. We demonstrate the ability of our methodology to locate spatially the presence of anticancer drug sites in metaphase chromosomes and cellular nuclei. We show that the anticancer 'rule breaker' platinum compound [Pt[N(p-HC6F4)CH2]2py2] preferentially binds to heterochromatin, forming localized discrete foci due to condensation of DNA interacting with the drug. Given the importance of DNA methylation in the development of nearly all types of cancer, there is potential for infrared nanospectroscopy to be used to detect gene expression/suppression sites in the whole genome and to become an early screening tool for malignancy.

An Antitumor Bis(N-Heterocyclic Carbene)Platinum(II) Complex That Engages Asparagine Synthetase as an Anticancer Target

New anticancer platinum(II) compounds with distinctive modes of action are appealing alternatives to combat the drug resistance and improve the efficacy of clinically used platinum chemotherapy. Herein, we describe a rare example of an antitumor Pt^II complex targeting a tumor-associated protein, rather than DNA, under cellular conditions. Complex [(bis-NHC)Pt(bt)]PF₆ (1 a; Hbt=1-(3-hydroxybenzo[b]thiophen-2-yl)ethanone) overcomes cisplatin resistance in cancer cells and displays significant tumor growth inhibition in mice with higher tolerable doses compared to cisplatin. The cellular Pt species shows little association with DNA, and localizes in the cytoplasm as revealed by nanoscale secondary ion mass spectrometry. An unbiased thermal proteome profiling experiment identified asparagine synthetase (ASNS) as a molecular target of 1 a. Accordingly, 1 a treatment reduced the cellular asparagine levels and inhibited cancer cell proliferation, which could be reversed by asparagine supplementation. A bis-NHC-ligated Pt species generated from the hydrolysis of 1 a forms adducts with thiols and appears to target an active-site cysteine of ASNS.

Recent advances in single-cell analysis by mass spectrometry

Cells are the most basic structural units that play vital roles in the functioning of living organisms. Analysis of the chemical composition and content of a single cell plays a vital role in ensuring precise investigations of cellular metabolism, and is a crucial aspect of lipidomic and proteomic studies. In addition, structural knowledge provides a better understanding of cell behavior as well as the cellular and subcellular mechanisms. However, single-cell analysis can be very challenging due to the very small size of each cell as well as the large variety and extremely low concentrations of substances found in individual cells. On account of its high sensitivity and selectivity, mass spectrometry holds great promise as an effective technique for single-cell analysis. Numerous mass spectrometric techniques have been developed to elucidate the molecular profiles at the cellular level, including electrospray ionization mass spectrometry (ESI-MS), secondary ion mass spectrometry (SIMS), laser-based mass spectrometry and inductively coupled plasma mass spectrometry (ICP-MS). In this review, the recent advances in single-cell analysis by mass spectrometry are summarized. The strategies of different ionization modes to achieve single-cell analysis are classified and discussed in detail.

ColorEM: analytical electron microscopy for element-guided identification and imaging of the building blocks of life

Nanometer-scale identification of multiple targets is crucial to understand how biomolecules regulate life. Markers, or probes, of specific biomolecules help to visualize and to identify. Electron microscopy (EM), the highest resolution imaging modality, provides ultrastructural information where several subcellular structures can be readily identified. For precise tagging of (macro)molecules, electron-dense probes, distinguishable in gray-scale EM, are being used. However, practically these genetically-encoded or immune-targeted probes are limited to three targets. In correlated microscopy, fluorescent signals are overlaid on the EM image, but typically without the nanometer-scale resolution and limited to visualization of few targets. Recently, analytical methods have become more sensitive, which has led to a renewed interest to explore these for imaging of elements and molecules in cells and tissues in EM. Here, we present the current state of nanoscale imaging of cells and tissues using energy dispersive X-ray analysis (EDX), electron energy loss spectroscopy (EELS), cathodoluminescence (CL), and touch upon secondary ion mass spectroscopy at the nanoscale (NanoSIMS). ColorEM is the term encompassing these analytical techniques the results of which are then displayed as false-color at the EM scale. We highlight how ColorEM will become a strong analytical nano-imaging tool in life science microscopy.

Redox-responsive cisplatin nanogels for anticancer drug delivery

Inspired by cisplatin's deactivation by glutathione (GSH) in cancer, a GSH responsive nanogel loaded with doxorubicin (Dox) was prepared using hyaluronan as a matrix and cisplatin as a crosslinker. The elevated GSH depletes the cisplatin crosslinker in the nanogel, enhances Dox release and boosts cytotoxicity, thus providing a new GSH responsive platform to reverse cisplatin resistance.

High resolution imaging and 3D analysis of Ag nanoparticles in cells with ToF-SIMS and delayed extraction

Within this study, the authors use human mesenchymal stem cells incubated with silver nanoparticles (AgNPs) as a model system to systematically investigate the advantages and drawbacks of the fast imaging delayed extraction mode for two-dimensional and three-dimensional (3D) analyses at the cellular level. The authors compare the delayed extraction mode with commonly employed measurement modes in terms of mass and lateral resolution, intensity, and dose density. Using the delayed extraction mode for single cell analysis, a high mass resolution up to 4000 at m/z = 184.08 combined with a lateral resolution up to 360 nm is achieved. Furthermore, the authors perform 3D analyses with Ar-clusters (10 keV) and O₂⁺ (500 eV) as sputter species, combined with Bi₃⁺ and delayed extraction for analysis. Cell compartments like the nucleus are visualized in 3D, whereas no realistic 3D reconstruction of intracellular AgNP is possible due to the different sputter rates of inorganic and organic cell materials. Furthermore, the authors show that the sputter yield of Ag increases with the decreasing Ar-cluster size, which might be an approach to converge the different sputter rates.