Scott D. Tanner

Single-Cell Mass Cytometry of Differential Immune and Drug Responses Across a Human Hematopoietic Continuum

Simultaneous measurement of more than 30 properties in individual human cells is used to characterize signaling in the immune system. Flow cytometry is an essential tool for dissecting the functional complexity of hematopoiesis. We used single-cell “mass cytometry” to examine healthy human bone marrow, measuring 34 parameters simultaneously in single cells (binding of 31 antibodies, viability, DNA content, and relative cell size). The signaling behavior of cell subsets spanning a defined hematopoietic hierarchy was monitored with 18 simultaneous markers of functional signaling states perturbed by a set of ex vivo stimuli and inhibitors. The data set allowed for an algorithmically driven assembly of related cell types defined by surface antigen expression, providing a superimposable map of cell signaling responses in combination with drug inhibition. Visualized in this manner, the analysis revealed previously unappreciated instances of both precise signaling responses that were bounded within conventionally defined cell subsets and more continuous phosphorylation responses that crossed cell population boundaries in unexpected manners yet tracked closely with cellular phenotype. Collectively, such single-cell analyses provide system-wide views of immune signaling in healthy human hematopoiesis, against which drug action and disease can be compared for mechanistic studies and pharmacologic intervention.

Highly multiparametric analysis by mass cytometry.

This review paper describes a new technology, mass cytometry, that addresses applications typically run by flow cytometer analyzers, but extends the capability to highly multiparametric analysis. The detection technology is based on atomic mass spectrometry. It offers quantitation, specificity and dynamic range of mass spectrometry in a format that is familiar to flow cytometry practitioners. The mass cytometer does not require compensation, allowing the application of statistical techniques; this has been impossible given the constraints of fluorescence noise with traditional cytometry instruments. Instead of colors the mass cytometer reads the stable isotope tags attached to antibodies using metal-chelating labeling reagents. Because there are many available stable isotopes, and the mass spectrometer provides exquisite resolution between detection channels, many parameters can be measured as easily as one. For example, in a single tube the technique allows for the ready detection and characterization of the major cell subsets in blood or bone marrow. Here we describe mass cytometric immunophenotyping of human leukemia cell lines and leukemia patient samples, differential cell analysis of normal peripheral and umbilical cord blood; intracellular protein identification and metal-encoded bead arrays.

Flow cytometer with mass spectrometer detection for massively multiplexed single-cell biomarker assay

This paper describes the development and application of new metal-tagging reagents and a novel mass spectrometer (MS) detector for a flow cytometer that enables highly multiplexed measurement of many biomarkers in individual cells. A new class of tagging reagents, based on an acrylic polymer backbone that incorporates a reproducible number of lanthanide elements, has been developed. When linked to antibodies that specifically recognize target proteins of interest, determination of the tag elements is diagnostic for the presence and quantification of the antigen. The use of enriched stable isotope tags provides the opportunity for multiparametric assay. The new instrument uses inductively coupled plasma (ICP) to vaporize, atomize, and ionize individual cells that have been probed using the metal-labeled antibodies. The elemental composition, specifically of the metal tags, is recorded simultaneously using a time-of-flight (TOF)-MS that has been specifically designed for high-speed analysis during the short transient corresponding to the individual cell event. The detector provides for well-resolved atomic fingerprints of many elemental and isotopic tags, with little overlap of neighboring signals (high abundance sensitivity) and wide dynamic range both for a single antigen and between antigens.

An introduction to mass cytometry: fundamentals and applications.

Mass cytometry addresses the analytical challenges of polychromatic flow cytometry by using metal atoms as tags rather than fluorophores and atomic mass spectrometry as the detector rather than photon optics. The many available enriched stable isotopes of the transition elements can provide up to 100 distinguishable reporting tags, which can be measured simultaneously because of the essential independence of detection provided by the mass spectrometer. We discuss the adaptation of traditional inductively coupled plasma mass spectrometry to cytometry applications. We focus on the generation of cytometry-compatible data and on approaches to unsupervised multivariate clustering analysis. Finally, we provide a high-level review of some recent benchmark reports that highlight the potential for massively multi-parameter mass cytometry.

Element-tagged immunoassay with ICP-MS detection : Evaluation and comparison to conventional immunoassays

We have investigated the possibility of using element-tagged antibodies for protein detection and quantification in microplate format using Inductively Coupled Plasma Mass Spectrometry (ICP-MS), and compared the results to conventional immunoassays, such as Enzyme-Linked Immunosorbent Assay (ELISA) and Western blotting. The technique was further employed to detect low levels and measure DNA-binding activity of transcription factor p53 in leukemia cell lysates through its interaction with immobilized oligonucleotides and recognition by element-tagged antibodies. The advantages of ICP-MS detection for routine performance of immunoassays include increased sensitivity, wide dynamic range, minimal interference from complex matrices, and high throughput. Our approach advances the ICP-MS technology and demonstrates its applicability to proteomic studies through the use of antibodies directly labeled with polymer tags bearing multiple atoms of lanthanides. Development of this novel methodology will enable fast and quantitative identification of multiple analytes in a single well.

Human CD4+ lymphocytes for antigen quantification: Characterization using conventional flow cytometry and mass cytometry

To transform the linear fluorescence intensity scale obtained with fluorescent microspheres to an antibody bound per cell (ABC) scale, a biological cell reference material is needed. Optimally, this material should have a reproducible and tight ABC value for the expression of a known clinical reference biomarker. In this study, we characterized commercially available cryopreserved peripheral blood mononuclear cells (PBMCs) and two lyophilized PBMC preparations, Cyto‐Trol and PBMC–National Institute for Biological Standard and Control (NIBSC) relative to freshly prepared PBMC and whole blood samples. It was found that the ABC values for CD4 expression on cryopreserved PBMC were consistent with those of freshly obtained PBMC and whole blood samples. By comparison, the ABC value for CD4 expression on Cyto‐Trol is lower and the value on PBMC–NIBSC is much lower than those of freshly prepared cell samples using both conventional flow cytometry and CyTOF™ mass cytometry. By performing simultaneous surface and intracellular staining measurements on these two cell samples, we found that both cell membranes are mostly intact. Moreover, CD4+ cell diameters from both lyophilized cell preparations are smaller than those of PBMC and whole blood. This could result in steric interference in antibody binding to the lyophilized cells. Further investigation of the fixation effect on the detected CD4 expression suggests that the very low ABC value obtained for CD4+ cells from lyophilized PBMC–NIBSC is largely due to paraformaldehyde fixation; this significantly decreases available antibody binding sites. This study provides confirmation that the results obtained from the newly developed mass cytometry are directly comparable to the results from conventional flow cytometry when both methods are standardized using the same ABC approach. Published 2012 Wiley Periodicals, Inc.

Single-cell mass cytometry reveals intracellular survival/proliferative signaling in FLT3-ITD-mutated AML stem/progenitor cells.

Understanding the unique phenotypes and complex signaling pathways of leukemia stem cells (LSCs) will provide insights and druggable targets that can be used to eradicate acute myeloid leukemia (AML). Current work on AML LSCs is limited by the number of parameters that conventional flow cytometry (FCM) can analyze because of cell autofluorescence and fluorescent dye spectral overlap. Single‐cell mass cytometry (CyTOF) substitutes rare earth elements for fluorophores to label antibodies, which allows measurements of up to 120 parameters in single cells without correction for spectral overlap. The aim of this study was the evaluation of intracellular signaling in antigen‐defined stem/progenitor cell subsets in primary AML. CyTOF and conventional FCM yielded comparable results on LSC phenotypes defined by CD45, CD34, CD38, CD123, and CD99. Intracellular phosphoprotein responses to ex vivo cell signaling inhibitors and cytokine stimulation were assessed in myeloid leukemia cell lines and one primary AML sample. CyTOF and conventional FCM results were confirmed by western blotting. In the primary AML sample, we investigated the cell responses to ex vivo stimulation with stem cell factor and BEZ235‐induced inhibition of PI3K and identified activation patterns in multiple PI3K downstream signaling pathways including p‐4EBP1, p‐AKT, and p‐S6, particularly in CD34+ subsets. We evaluated multiple signaling pathways in antigen‐defined subpopulations in primary AML cells with FLT3‐ITD mutations. The data demonstrated the heterogeneity of cell phenotype distribution and distinct patterns of signaling activation across AML samples and between AML and normal samples. The mTOR targets p‐4EBP1 and p‐S6 were exclusively found in FLT3‐ITD stem/progenitor cells, but not in their normal counterparts, suggesting both as novel targets in FLT3 mutated AML. Our data suggest that CyTOF can identify functional signaling pathways in antigen‐defined subpopulations in primary AML, which may provide a rationale for designing therapeutics targeting LSC‐enriched cell populations.

Messenger RNA Detection in Leukemia Cell lines by Novel Metal-Tagged in situ Hybridization using Inductively Coupled Plasma Mass Spectrometry

Conventional gene expression profiling relies on using fluorescent detection of hybridized probes. Physical characteristics of fluorophores impose limitations on achieving a highly multiplex gene analysis of single cells. Our work demonstrates the feasibility of using metal-tagged in situ hybridization for mRNA detection by inductively coupled plasma mass spectrometry (ICP-MS). ICP-MS as an analytical detector has a number of unique and relevant properties: 1) metals and their stable isotopes generate non-overlapping distinct signals that can be detected simultaneously; 2) these signals can be measured over a wide dynamic range; 3) ICP-MS is quantitative and very sensitive. We used commercial antibodies conjugated to europium (Eu) and gold together with biotinylated oligonucleotide probes reacted with terbium-labeled streptavidin to demonstrate simultaneous mRNA and protein detection by ICP-MS in leukemia cells.Urokinase-type plasminogen activator (uPA) is associated with cancer recurrence where the most evidence comes from studies in breast cancer. According to the European Organization for Research and Treatment of Cancer, uPA is considered one of the most prominent biomarkers for cancer recurrence and therefore new agents are needed to inhibit it. Whether uPA is also expressed in pediatric cancers is yet unknown. If it is then uPA inhibitors might also help children with recurrent cancers. In this study, we addressed whether the integrin-linked kinase inhibitor (ILK), QLT0267, could suppress uPA. We previously showed that uPA expression is maximally inhibited when both the Akt and MAP kinase pathways were blocked which we anticipated can be achieved via QLT0267. In MDA-MB-231 breast cancer cells, QLT0267 blocked signaling through Akt and MAP kinase with a correlative decrease in uPA protein and mRNA, which corresponded to an inhibition of c-Jun phosphorylation. Consistent with these findings, cellular invasion was inhibited with either QLT0267 or with small interfering RNA against ILK. We then questioned whether uPA was commonly expressed in childhood sarcomas and if QLT0267 might be effective in this setting. We determined for the first time that uPA was highly expressed in rhabdomyosarcomas (RMS), but not Ewings sarcomas by screening cell lines (n = 31) and patient samples (n = 200) using Affymetrix microarrays. In alveolar RMS (ARMS) cell lines, QLT0267 blocked cell signaling, uPA production, invasion and ultimately survival. We concluded that QLT0267 blocks the production of uPA providing a new target for the management of recurrent cancers.There is a growing body of literature suggesting that signaling based therapy might be a potential approach for medullary thyroid cancer (MTC). In this review we focus on the tumor suppressor role of Notch1 and Raf-1 signaling in MTC. Interestingly these two pathways are minimally active or absent in these tumors and activation of Notch1 and Raf-1 significantly reduces tumor growth in vitro. Therefore, identification of compounds that induce these pathways could be a potential strategy to treat patients with MTC.In the last two decades there has been considerable progress in our understanding of the role of sphingolipids in controlling signal transduction processes, particularly in the mechanisms leading to regulation of cell growth and death. Ceramide is a well-characterized sphingolipid metabolite and second messenger that can be produced by cancer cells in response to a variety of stimuli, including therapeutic drugs, leading to cell cycle arrest and apoptosis. Although this is a promising aspect when thinking of treating cancer, it should be borne in mind that ceramide production may not always be a growth inhibitory or pro-apoptotic signal. In fact, ceramide can be readily converted to sphingosine 1-phosphate (S1P) by the concerted actions of ceramidases and sphingosine kinases, or to ceramide 1-phosphate (C1P) by the action of ceramide kinase. In general, S1P and C1P have opposing effects to ceramide, acting as pro-survival or mitogenic signals in most cell types. This review will address our current understanding of the many roles of ceramide, S1P and C1P in the regulation of cell growth and survival with special emphasis to the emerging role of these molecules and their metabolizing enzymes in controlling tumor progression and metastasis.The Y-box Binding Protein-1 (YB-1) is a highly conserved oncogenic transcription/translation factor that is expressed in cancers affecting adults and children. It is now believed that YB-1 plays a causal role in the development of cancer given recent work showing that its expression drives the tumorigenesis in the mammary gland. In human breast cancers, YB-1 is associated with rapidly proliferating tumors that are highly aggressive. Moreover, expression of YB-1 promotes the growth of breast cancer cell lines both in monolayer and anchorage independent conditions. The involvement of YB-1 in breast cancer pathogenesis has made it a putative therapeutic target; however, the mechanism(s) that regulate YB-1 are poorly understood. This review first describes the oncogenic properties of YB-1 in cancer. It also highlights the importance of YB-1 in hardwiring signal transduction pathways to the regulation of genes involved in the development of cancer.Specific combinations of transcription-factor binding sites in the promoter regions of genes regulate gene expression, and thus key functional processes in cells. Analysis of such promoter regions in specific functional contexts can be used to delineate novel disease-associated genes based on shared phenotypic properties. The aim of this study was to utilize promoter analysis to predict cell proliferation-associated genes and to test this method in colon cancer cell lines. We used freely-available bioinformatic techniques to identify cell-proliferation-associated genes expressed in colon cancer, extract a shared promoter module, and identify novel genes that also contain this module in the human genome. An EGRF/ETSF promoter module was identified as prevalent in proliferation-associated genes from a colon cancer cDNA library. We detected 30 other genes, from the known promoters of the human genome, which contained this proliferation-associated module. This group included known proliferation-associated genes, such as HERG1 and MCM7, and a number of genes not previously implicated in cell proliferation in cancer, such as TSPAN3, Necdin and APLP2. Suppression of TSPAN3 and APLP2 by siRNA was performed and confirmed by RT-PCR. Inhibition of these genes significantly inhibited cell proliferation in colon cancer cell lines. This study demonstrates that promoter analysis can be used to identify novel cancer-associated genes based on shared functional processes.Background: Potassium bromate (KBrO3), used in both the food and cosmetics industry, and a drinking water disinfection by-product, is a nephrotoxic compound and rodent carcinogen. To gain insight into the carcinogenic mechanism of action and provide possible biomarkers of KBrO3 exposure, the gene expression in kidneys from chronically exposed male F344 rats was investigated. Methods: Male F344 rats were exposed to KBrO3 in drinking water for 52 and 100 wk. Kidneys were removed, frozen, and stored at −80°C, then used for Affymetrix microarray analysis. Gene expression patterns were examined using a non-carcinogenic (20 ppm) and carcinogenic dose (400 ppm) at 52 wk, and compared to 100 wk high dose (400 ppm) and adenoma gene expression. Results: Statistical analysis revealed 144, 224, 43, and 994 genes out of 15866 from the 52 wk low, 52 wk high, 100 wk high, and adenomas respectively, were differentially expressed when compared to control kidneys. Gene ontology classification of the 52 wk high dose showed alterations of gene transcripts involved in oxidative stress, lipid metabolism, kidney function/ion transport, and cellular function. In a comparison of kidney development gene expression, alterations were seen in the adenomas but not in the 52 wk bromate-treated kidneys. However, the normal kidney from the high dose group resembled the adenoma expression pattern with early kidney development genes being up-regulated and adult phase genes being down-regulated. Moreover, eight genes were identified which could serve as biomarkers of carcinogenic exposure to bromate. The most promising of these was Pendrin, or Slc26a4, a solute carrier of chloride and iodide active in the kidney, thyroid, and inner ear. All these tissues are targets of KBrO3 toxicity. Expression array results were verified with quantitative real-time rtPCR. Conclusions: These data demonstrate that the 400 ppm carcinogenic dose of KBrO3 showed marked gene expression differences from the 20 ppm non-carcinogenic dose. Comparison of kidney development gene expression showed that the adenoma patterns were more characteristic of embryonic than adult kidneys, and that the normal kidney from the high dose group resembled the adenoma-like gene expression pattern. Taken together, the analysis from this study identifies potential biomarkers of exposure and illuminates a possible carcinogenic mode of action for KBrO3.Chronic eosinophilic leukemia is a clonal disease characterized by hypereosinophilia and eosinophilia-related pathologic manifestations. Recently, the fusion gene FIP1L1/PDGFRA was found in the long arm of chromosome 4 and its expression has been shown to be associated with development of a clinical hypereosinophilic syndrome (HES) in a significant proportion of patients. FIP1L1/PDGFRα, the product of the gene FIP1L1/PDGFRA, is a constitutively activated tyrosine kinase and can be inhibited by imatinib mesylate. Several investigations have tried to dissect the mechanism of leukemogenesis and signaling induced by FIP1L1/PDGFRα in cell lines, primary human eosinophils and in murine myeloproliferative models. In this review, we analyzed the current knowledge on the relationship between FIP1L1/PDGFRα-induced signaling and eosinophil proliferation, survival and activation, specially focusing on its possible role in the modulation of cytokine and chemoattractant signaling pathways.The increasing number of proteomic and DNA-microarray studies is continually providing a steady acquisition of data on the molecular abnormalities associated with human tumors. Rapid translation of this accumulating biological information into better diagnostics and more effective cancer therapeutics in the clinic depends on the use of robust function-testing strategies. Such strategies should allow identification of molecular lesions that are essential for the maintenance of the transformed phenotype and enable validation of potential drug-targets. The tetracycline regulated gene expression/ suppression systems (Tet-systems) developed and optimized by bioengineers over recent years seem to be very well suited for the function-testing purposes in cancer research. We review the history and latest improvements in Tet-technology in the context of functional oncogenomics.Multiple lines of evidence implicate over-expression and activation of the androgen receptor (AR) in the progression of prostate cancer (PC) to androgen-independence (AI) and resistance to therapy. The mechanisms leading to AR over-expression are not fully understood but binding of Sp1 to specific Sp1-binding sites in the AR promoter and 5′-untranslated region (5′-UTR) was shown to up-regulate AR transcription. In this work, we further characterized the role of Sp1 in the control of AR transcription and explored its potential as a therapeutic target in androgen-dependent (AD) and independent (AI) LNCaP cells. We identified a pair of new Sp1-binding site in the 5′-UTR of AR which we named ARSp1-3. ARSp1-3 binds Sp1 with higher affinity than other known Sp1-binding sites in the promoter/5′-UTR and in transfection experiments, the ARSp1-3 reporter showed higher transcriptional activity in AI than in AD cells. Treatment of these cells with nanomolar concentrations of Mithramycin inhibited binding of Sp1 to its binding sites in the promoter/5′-UTR of the AR gene but more specifically the binding of ARSp1-3 while other regulatory elements of the AR promoter were not affected. Inhibition of Sp1 binding by Mithramycin decreased the AR transcription and transactivation of PSA reporter constructs. At the lowest concentrations, Mithramycin decreased endogenous AR protein and proliferation of AD and AI LNCaP cells. The combinations of Mithramycin with either paclitaxel or bicalutamide were highly synergistic. Conclusion: Sp1 binding induces AR transcription in LNCaP cells. The higher affinity of ARSp1-3 for Sp1 may support higher AR mRNA levels in AI than AD LNCaP cells. Mithramycin is a potent and specific inhibitor of Sp1 and AR transcription with potential, at very low concentrations, to enhance the efficacy of hormones or taxane based therapy in patients with recurrent or androgen-independent progression that sustain AR expression.Many tumor markers for bladder cancer have been evaluated for use in detecting and monitoring bladder cancers tissue specimens, bladder washes, and urine specimens. However, none of the biomarkers reported to date has shown sufficient sensitivity and specificity to detect the entire spectrum of bladder cancers in routine clinical practice. The limited value of the established prognostic markers demands analysis of new molecular parameters having the potential to predict the prognosis of bladder cancer patients, particularly, the high-risk patients at risk of cancer progression and recurrence. Abnormal methylation of CpG islands can efficiently repress transcription of the associated gene in a manner akin to mutations and deletions. Several tumor suppressor genes correlated with bladder cancer contain CpG islands in their promoters. Markers for aberrant methylation may be a potential gateway for monitoring bladder cancer. Hypermethylation of several gene promoters was detected in urine sediment DNA from bladder cancer patients. Detection of DNA methylation in voided urine is feasible and noninvasive. Methylation is an important molecular mechanism in the development of bladder cancer and could be used as a prognostic and diagnostic marker. Aberrant patterns of epigenetic modification could, in the near future, be crucial indicators in cancer diagnosis, prognosis, and may additionally be good targets for developing novel therapies while maintaining quality of life.In 1911 Peyton Rous described a transmissible agent that could induce sarcoma in chicken, this was later identifi ed as a virus and named Rous Sarcoma Virus (Rous, 1911). Identifi cation of the viral tyrosine kinase v-Src and its cellular counterpart c-Src (later in the text referred as Src), introduced the concept of proto-oncogene which has had a signifi cant impact on the progress of our knowledge of carcinogenesis (Martin, 2001). Since its description, Src has been implicated in a variety of malignancies (Frame, 2002) including prostate cancer (Chang et al. 2007), which is the most commonly diagnosed cancer in men and the second leading cause of cancer-related death in men in the U.K. and U.S. (Jemal et al. 2007). The Src-family kinases (SFK) comprises of nine members including Src, Fyn, Yes, Blk, Yrk, Fgr, Hck, Lck and Lyn; Src, Fyn and Yes being ubiquitously expressed in all cells while other kinases are tissue specifi c. Apart from Src, two other family members, Fgr (Edwards et al. 2003) and Lyn (Goldenberg-Furmanov et al. 2004) have been implicated in prostate cancer. All SFK members share similar structure; each protein consists of four Src homology (SH) domains and a unique amino-terminal domain. High resolution crystallographic analysis of Src revealed the complex nature of structural changes involved in switching between active and inactive state. Src can be locked in an inactive conformation when its negative regulatory tail is phosphorylated at tyrosine Y530 by c-terminal Src kinase (Csk). However, when Src becomes autophosphorylated at tyrosine Y419, which is located in the kinase domain, the protein unfolds assuming its catalytically active conformation. Apart from being a tyrosine kinase, Src may function as a scaffolding molecule being an adaptor for other intracellular proteins that in turn can activate Src by the release of its intramolecular bonds. Another mechanism of Src activation, called peripheral targeting, involves translocation of inactive Src, which is located in the perinuclear region, to the cell periphery where Src becomes attached to the inner surface of cell membrane by its myristoylation fragment (Frame, 2002).Src interacts with a wide variety of proteins including receptor tyrosine kinases, G-protein coupled receptors, steroid receptors, integrins, other non-receptor protein kinases etc., which is re fl ected in the multiplicity of resulting cellular biological events (Thomas and Brugge, 1997). Crosstalk between Src and the components of PI3K (phosphatidylinositol 3-kinase) and MAPK (mitogen activated protein kinase) pathways may affect tumor cell proliferation and apoptosis while involvement in focal adhesion complexes, especially FAK (focal adhesion kinase), paxillin and p130CAS (p130 Crk-associate sub-strate) plays an important part in promoting cell adhesion, migration and invasion (Summy and Gallick, 2006). Considering its unique position at the crossroads of the intracellular signaling networks, Src has become an attractive target in the search of novel prostate cancer therapies (McCarty, 2004).The oncogene MCTS1, discovered as an amplified product in a subset of T-cell lymphoma lines, has been implicated in cell cycle progression and conferring a growth advantage in lymphomas and breast cancer. Recent research shows that it modulates the MAPK pathway and acts as a translational activator both in vivo and in vitro. In breast cancer cells, expression of MCTS1 confers aggressive properties and inhibits apoptosis. This article will review these data and its implications on our understanding of cancer.

Single-cell measurement of the uptake, intratumoral distribution and cell cycle effects of cisplatin using mass cytometry

Although of fundamental importance to the treatment of cancer patients, the quantitative study of drug distribution and action in vivo at the single cell level is challenging. We used the recently‐developed technique of mass cytometry to measure cisplatin uptake into individual tumor cells (Pt atoms/cell), combined with measurement of the rate of IdU incorporation into DNA (I127 atoms/cell/min) and tumor hypoxia identified by the 2‐nitroimidazole EF5 in cisplatin‐treated BxPC‐3 and ME‐180 xenografts. Pt levels of 105 to 106 atoms/cell were obtained following a single cisplatin treatment using clinically relevant doses. Cisplatin caused cell cycle arrest in a dose‐ and time‐dependent manner that paralleled effects in vitro, and it readily penetrated into hypoxic tumor regions. Similar levels of Pt/cell were found in xenografts treated with oxaliplatin. Mass cytometry offers the unique capability to study the cellular uptake and anticancer effects of platinum‐containing drugs at the single cell level in animal models, and it has the potential for application to samples obtained from cancer patients during treatment.

High precision rhenium and platinum isotope dilution analyses by plasma ionisation multicollector mass spectrometry

The platinum group elements (PGE; Os, Ir, Ru, Rh, Pt, Pd) and rhenium, which is considered with the PGEs due to its similar chemical behaviour, are powerful tools for understanding several fundamental aspects of the origin and evolution of the Earth such as core segregation, late accretion histories, 1 2 and core-mantle exchange. 4 Abundance measurements for the PGE are useful geochemical tracers in a variety of terrestrial and extraterrestrial materials. 5 6 7 8 In addition the ability to accurately analyze Pt at very low levels is being applied to studies of cancer therapy drugs 9 10 and environmental studies. The information obtained from abundance measurements of the PGE and Re, can be complemented by two geologically important isotopic decay schemes;