Inverted Transflection Spectroscopy of Live Cells Using Metallic Grating on Elevated Nanopillars

Water absorption of mid-infrared (MIR) radiation severely limits the options for vibrational spectroscopy of the analytes-including live biological cells-that must be probed in aqueous environments. While internal reflection elements, such as attenuated total reflection prisms and metasurfaces, partially overcome this limitation, such devices have their own limitations: ATR prisms are difficult to integrate with multiwell cell culture workflows, while metasurfaces suffer from a limited spectral range and small penetration depth into analytes. In this work, we introduce an alternative live cell biosensing platform based on metallic nanogratings fabricated on top of elevated dielectric pillars. For the MIR wavelengths that are significantly longer than the grating period, reflection-based spectroscopy enables broadband sensing of the analytes inside the trenches separating the dielectric pillars. Because the depth of the analyte twice-traversed by the MIR light excludes the highly absorbing thick water layer above the grating, we refer to the technique as inverted transflection spectroscopy (ITS). The analytic power of ITS is established by measuring a wide range of protein concentrations in solution, with the limit of detection in the single-digit mg mL-1. The ability of ITS to interrogate live cells that naturally wrap themselves around the grating is used to characterize their adhesion kinetic.

VIBRANT: spectral profiling for single-cell drug responses

High-content cell profiling has proven invaluable for single-cell phenotyping in response to chemical perturbations. However, methods with improved throughput, information content and affordability are still needed. We present a new high-content spectral profiling method named vibrational painting (VIBRANT), integrating mid-infrared vibrational imaging, multiplexed vibrational probes and an optimized data analysis pipeline for measuring single-cell drug responses. Three infrared-active vibrational probes were designed to measure distinct essential metabolic activities in human cancer cells. More than 20,000 single-cell drug responses were collected, corresponding to 23 drug treatments. The resulting spectral profile is highly sensitive to phenotypic changes under drug perturbation. Using this property, we built a machine learning classifier to accurately predict drug mechanism of action at single-cell level with minimal batch effects. We further designed an algorithm to discover drug candidates with new mechanisms of action and evaluate drug combinations. Overall, VIBRANT has demonstrated great potential across multiple areas of phenotypic screening.

Inverted transflection spectroscopy of live cells using metallic grating on elevated nanopillars

Water absorption of mid-infrared (MIR) radiation severely limits the options for vibrational spectroscopy of the analytes - including live biological cells - that must be probed in aqueous environments. While internal reflection elements, such as attenuated total reflection prisms and metasurfaces, partially overcome this limitation, such devices have their own limitations: high cost, incompatibility with standard cell culture workflows, limited spectral range, and small penetration depth into the analyte. In this work, we introduce an alternative live cell biosensing platform based on metallic nanogratings fabricated atop elevated dielectric pillars. For the MIR wavelengths that are significantly longer than the grating period, reflection-based spectroscopy enables broadband sensing of the analytes inside the trenches separating the dielectric pillars. Because the depth of the analyte twice-traversed by the MIR light excludes the highly absorbing thick water layer above the grating, we refer to the technique as Inverted Transflection Spectroscopy (ITS). We demonstrate the analytic power of ITS by measuring protein concentrations in solution. The ability of ITS to interrogate live cells that naturally wrap themselves around the grating is also exploited to characterize their adhesion kinetics.

Synchrotron radiation-based Fourier transform infrared microspectroscopy investigation of WRL68 cells treated with doxorubicin

Doxorubicin is an effective chemotherapeutic agent applied in a wide variety of cancers. Despite its potent anticancer activity towards cancer cells, doxorubicin is also toxic to noncancerous cells. Therefore, doxorubicin can cause serious side effects in various organs, especially when dose escalation is required for patients with advanced disease. The liver is the major detoxification organ that metabolizes drugs, and hepatotoxicity is one of the most common adverse effects of doxorubicin administration. However, the exact mechanisms of doxorubicin-induced hepatotoxicity have not been clearly identified, and how doxorubicin treatment affects the biomolecular contents of normal human hepatocytes has rarely been studied. Synchrotron radiation-based Fourier transform infrared (SR-FTIR) microspectroscopy is a state-of-the-art analytical technique for characterizing the biomolecules present in cells. In this research, the biomolecular alterations of doxorubicin-treated normal human hepatocytes compared to untreated control cells were investigated at the single-cell level by combining SR-FTIR microspectroscopy with the Cell Counting Kit-8 (CCK-8) assay and flow cytometry. WRL68 human normal embryonic liver cells, which have been shown to be very promising for assessing the cytotoxicity of toxic compounds and investigating hepato-toxicology, were used in this research. Principal component analysis (PCA) and orthogonal partial least squares-discriminant analysis (OPLS-DA) were used to further analyse the biomolecular contents of WRL68 cells. The order of lipid acyl chains and protein α-helix structures in doxorubicin-treated WRL68 cells was found to be distinctly changed, while the nucleic acids were altered relatively less. No alteration in the carbohydrate content was distinguishable after doxorubicin treatment. These results provide more comprehensive information about the biomolecular changes in hepatocytes induced by doxorubicin treatment and help to elucidate the mechanism of doxorubicin-induced hepatotoxicity. This research also proves that SR-FTIR microspectroscopy, combined with PCA and OPLS-DA, is a promising approach for investigating drug-cell interaction systems.

Identification of Neoadjuvant Chemotherapy Response in Muscle-Invasive Bladder Cancer by Fourier-Transform Infrared Micro-Imaging

Simple Summary

Assessing the tumor response to chemotherapy is a paramount predictive step to improve patient care. Infrared spectroscopy probes the chemical composition of samples, and in combination with statistical multivariate processing, presents the capacity to highlight subtle molecular alterations associated with malignancy characteristics. Microscopic infrared imaging of tissue samples reveals spectral heterogeneity within histological structures, providing a new approach to characterize tumoral heterogeneity. We have taken advantage of the analytical capabilities of mid-infrared spectral imaging to implement a classification model to predict the response of a tumor to chemotherapy. Our development was demonstrated in muscle-invasive bladder cancer (MIBC) by comparing samples from responders and non-responders to neoadjuvant chemotherapy.

Abstract

Background: Neoadjuvant chemotherapy (NAC) improves survival in responder patients. However, for non-responders, the treatment represents an ineffective exposure to chemotherapy and its potential adverse events. Predicting the response to treatment is a major issue in the therapeutic management of patients, particularly for patients with muscle-invasive bladder cancer. Methods: Tissue samples of trans-urethral resection of bladder tumor collected at the diagnosis time, were analyzed by mid-infrared imaging. A sequence of spectral data processing was implemented for automatic recognition of informative pixels and scoring each pixel according to a continuous scale (from 0 to 10) associated with the response to NAC. The ground truth status of the responder or non-responder was based on histopathological examination of the samples. Results: Although the TMA spots of tumors appeared histologically homogeneous, the infrared approach highlighted spectral heterogeneity. Both the quantification of this heterogeneity and the scoring of the NAC response at the pixel level were used to construct sensitivity and specificity maps from which decision criteria can be extracted to classify cancerous samples. Conclusions: This proof-of-concept appears as the first to evaluate the potential of the mid-infrared approach for the prediction of response to neoadjuvant chemotherapy in MIBC tissues.

Analysis of Fixed and Live Single Cells Using Optical Photothermal Infrared with Concomitant Raman Spectroscopy

This paper reports the first use of a novel completely optically based photothermal method (O-PTIR) for obtaining infrared spectra of both fixed and living cells using a quantum cascade laser (QCL) and optical parametric oscillator (OPO) laser as excitation sources, thus enabling all biologically relevant vibrations to be analyzed at submicron spatial resolution. In addition, infrared data acquisition is combined with concomitant Raman spectra from exactly the same excitation location, meaning the full vibrational profile of the cell can be obtained. The pancreatic cancer cell line MIA PaCa-2 and the breast cancer cell line MDA-MB-231 are used as model cells to demonstrate the capabilities of the new instrumentation. These combined modalities can be used to analyze subcellular structures in both fixed and, more importantly, live cells under aqueous conditions. We show that the protein secondary structure and lipid-rich bodies can be identified on the submicron scale.

Single-cell infrared phenomics: phenotypic screening with infrared microspectroscopy

We conceptually demonstrate single-cell infrared phenomics as a novel strategy of phenotypic screening with infrared microspectroscopy. Based on this development, the cancer cell HepG2 glycocalyx was first identified as a potential target of protopanaxadiol, an herbal medicine. These findings provide a powerful tool to accurately evaluate the cell stress response and to largely expand the phenotypic screening toolkit for drug discovery.

Detection of macromolecular inversion-induced structural changes in osteosarcoma cells by FTIR microspectroscopy

Fourier transform infrared (FTIR) microspectroscopy provides a biochemical fingerprint of the cells. In this study, chemical changes in 143B osteosarcoma cells were investigated using FTIR analysis of cancer cells after their treatment with polymeric invertible micellar assemblies (IMAs) and curcumin-loaded IMAs and compared with untreated osteosarcoma cells. A comprehensive principal component analysis (PCA) was applied to analyze the FTIR results and confirm noticeable changes in cell surface chemical structures in the fingerprint regions of 1480-900 cm^-1. The performed clustering shows visible differences for all investigated groups of cancer cells. It is demonstrated that a combination of FTIR microspectroscopy with PCA can be an efficient approach in determining interactions of osteosarcoma cells and drug-loaded polymer micellar assemblies. Graphical abstract.

Identifying the Responses from the Estrogen Receptor-Expressed MCF7 Cells Treated in Anticancer Drugs of Different Modes of Action Using Live-Cell FTIR Spectroscopy

Recently, we have shown that changes in Fourier transform infrared (FTIR) spectra of living MDA-MB-231 cells (a triple negative cell line) upon exposure to anticancer drugs reflect the changes in the cellular compositions which are correlated to the modes of action of drugs. In the present study, MCF7 cells (an estrogen receptor expressing breast cancer cell line) were exposed to three anticancer drugs belonging to two well-characterized anticancer classes: selective estrogen receptor modulators (SERMs) and DNA-intercalating agent. First, we evaluated if the changes in the spectrum of cells are according to the modes of action of drugs and the characteristics of the MCF7 cell line in the same way as the MDA-MB-231 cell. Living MCF7 cells were treated in the three drugs at half maximal inhibitory concentration (IC50), and the difference spectra were analyzed using principal component analysis (PCA). The results demonstrated clear separation between tamoxifen/toremifene (SERM)-treated cells from the doxorubicin (DNA-intercalator)-treated and untreated cells (control). Tamoxifen and toremifene induced similar spectral changes in the cellular compositions of MCF7 cells and lead to the clustering of these two drugs in the same quadrant of the principal component 1 (PC1) versus PC2 score plots. The separation is mostly attributed to their similar modes of actions. However, doxorubicin-treated MCF7 cells highlighted spectral changes that mainly occur in bands at 1085 and 1200-1240 cm^-1, which could be associated with the DNA-intercalation effects of the drug. Second, the pairwise PCA at various individual time points was employed to investigate whether the spectral changes of MCF7 and MDA-MB-231 cells in response to the IC50 of tamoxifen/toremifene and doxorubicin are dependent on the characteristics of the cell lines. The estrogen-expressing MCF7 cells demonstrated significant differences in response to the SERMs in comparison to the triple negative MDA-MB-231 cells, suggesting that different modes of action have taken place in the two tested cell lines. In contrast, the doxorubicin-treated MDA-MB-231 and MCF7 cells show similar changes in 1150-950 cm^-1, which indicates that the DNA intercalation effect of doxorubicin is found in both cell lines. The results have demonstrated that live-cell FTIR analysis is sensitive to the different modes of action from the same drugs on cells with different characteristics.

Live single cell analysis using synchrotron FTIR microspectroscopy: development of a simple dynamic flow system for prolonged sample viability

Synchrotron radiation Fourier transform infrared microspectroscopy (SR-microFTIR) of live biological cells has the potential to provide far greater biochemical and morphological detail than equivalent studies using dehydrated, chemically-fixed single cells. Attempts to measure live cells using microFTIR are complicated by the aqueous environment required and corresponding strong infrared absorbance by water. There is also the additional problem of the limited lifetime of the cells outside of their preferred culture environment. In this work, we outline simple, cost-effective modifications to a commercially available liquid sample holder to perform single live cell analysis under an IR microscope and demonstrate cell viability up to at least 24 hours. A study using this system in which live cells have been measured at increasing temperature has shown spectral changes in protein bands attributed to α-β transition, consistent with other published work, and proves the ability to simultaneously induce and measure biochemical changes. An additional study of deuterated palmitic acid (D31-PA) uptake at different timepoints has made use of over 200 individual IR spectra collected over ∼4 hours, taking advantage of the ability to maintain viable cell samples for longer periods of time in the measurement environment, and therefore acquire greatly increased numbers of spectra without compromising on spectral quality. Further developments of this system are planned to widen the range of possible experiments, and incorporate more complex studies, including drug-cell interaction.

Towards identifying the mode of action of drugs using live-cell FTIR spectroscopy

Fourier transform infrared spectroscopy (FTIR) has been shown to be a promising tool for identifying the mode of action of drugs.

The Impact of Antioxidants from the Diet on Breast Cancer Cells Monitored by Raman Microspectroscopy

Background:

The impact of the ubiquitous dietary phenolic compound p-coumaric acid on human breast cancer cells was assessed, through a multidisciplinary approach: Combined biological assays for cytotoxicity evaluation and biochemical profiling by Raman microspectroscopic analysis in cells. </P><P> Methods: Para-coumaric acid was shown to exert in vitro chemoprotective and antitumor activities, depending on the concentration and cell line probed: a significant anti-invasive ability was detected for the triple-negative MDA-MB-231 cells, while a high pro-oxidant effect was found for the estrogen- dependent MCF-7 cells. A striking cell selectivity was obtained, with a more noticeable outcome on the triple-negative MDA-MB-231 cell line.

Results:

The main impact on the cellular biochemical profile was verified to be on proteins and lipids, thus justifying the compound´s anti-invasive effect and chemoprotective ability.

Conclusion:

p-Coumaric acid was thus shown to be a promising chemoprotective/chemotherapeutic agent, particularly against the low prognosis triple-negative human breast adenocarcinoma.

HTS-FTIR spectroscopy allows the classification of polyphenols according to their differential effects on the MDA-MB-231 breast cancer cell line

Breast cancer is a major public health issue among women in the world. Meanwhile new anticancer treatments struggle more and more to be accepted in the pharmaceutical market and research costs still increase. There is therefore a need to find new treatments and new screening methods to test them more quickly and efficiently. Among natural compounds, an increasing interest has been given to polyphenols as they can take action at the different stages of carcinogenesis, from tumour initiation to metastasis formation, by disturbing multiple cellular signalling pathways. They constitute one of the largest groups of plant metabolites and more than 8000 compounds have already been identified based on their chemical structure. Traditionally in pharmacology, new anticancer drugs are first evaluated for their potential to inhibit the proliferation of cancer cell lines. Numerous potential drugs are discarded at this stage even though they could show interesting modes of action. In turn, there is an increasing demand for more systemic approaches in order to obtain a global and accurate insight into the biochemical processes mediated by drugs. Recently, FTIR spectroscopy was demonstrated to be an innovative tool to obtain a unique fingerprint of the effects of anticancer drugs on cells in culture. While this spectral technique appears to have a definite potential to sort drugs according to their spectral fingerprints, characteristic of the metabolic modifications induced, the present challenge remains to evaluate the drug-induced spectral changes in cancer cells on a larger scale. This article presents the results obtained for a 24 h-exposure of the breast cancer cell line MDA-MB-231 to 15 compounds belonging to different classes of polyphenols using FTIR spectroscopy connected to a high throughput screening extension. Through unsupervised and supervised statistical analyses (PCA, MANOVA, Student's t-tests and HCA), a distinction between polyphenol treatments and controls could be well established.

Increased optical pathlength through aqueous media for the infrared microanalysis of live cells

The study of live cells using Fourier transform infrared spectroscopy (FTIR) and FTIR microspectroscopy (FT-IRMS) intrinsically yields more information about cell metabolism than comparable experiments using dried or chemically fixed samples. There are, however, a number of barriers to obtaining high-quality vibrational spectra of live cells, including correction for the significant contributions of water bands to the spectra, and the physical stresses placed upon cells by compression in short pathlength sample holders. In this study, we present a water correction method that is able to result in good-quality cell spectra from water layers of 10 and 12 μm and demonstrate that sufficient biological detail is retained to separate spectra of live cells based upon their exposure to different novel anti-cancer agents. The IR brilliance of a synchrotron radiation (SR) source overcomes the problem of the strong water absorption and provides cell spectra with good signal-to-noise ratio for further analysis. Supervised multivariate analysis (MVA) and investigation of average spectra have shown significant separation between control cells and cells treated with the DNA cross-linker PL63 on the basis of phosphate and DNA-related signatures. Meanwhile, the same control cells can be significantly distinguished from cells treated with the protein kinase inhibitor YA1 based on changes in the amide II region. Each of these separations can be linked directly to the known biochemical mode of action of each agent.

Gene expression data and FTIR spectra provide a similar phenotypic description of breast cancer cell lines in 2D and 3D cultures

Gene expression patterns and FTIR spectral data are strongly correlated. Both identified the genotypes and phenotypes of breast cancer cell lines.

ATR-FTIR spectroscopy shows changes in ovarian cancer cells after incubation with novel organoamidoplatinum(ii) complexes

ATR-FTIR spectroscopy has been applied to compare the effect of new organoamidoplatinum(ii) complexes with cisplatin on cells from a cisplatin-sensitive and a cisplatin-resistant ovarian cancer cell line.

Microfluidic approaches to synchrotron radiation-based Fourier transform infrared (SR-FTIR) spectral microscopy of living biosystems

A long-standing desire in biological and biomedical sciences is to be able to probe cellular chemistry as biological processes are happening inside living cells. Synchrotron radiation-based Fourier transform infrared (SR-FTIR) spectral microscopy is a label-free and nondestructive analytical technique that can provide spatiotemporal distributions and relative abundances of biomolecules of a specimen by their characteristic vibrational modes. Despite great progress in recent years, SR-FTIR imaging of living biological systems remains challenging because of the demanding requirements on environmental control and strong infrared absorption of water. To meet this challenge, microfluidic devices have emerged as a method to control the water thickness while providing a hospitable environment to measure cellular processes and responses over many hours or days. This paper will provide an overview of microfluidic device development for SR-FTIR imaging of living biological systems, provide contrast between the various techniques including closed and open-channel designs, and discuss future directions of development within this area. Even as the fundamental science and technological demonstrations develop, other ongoing issues must be addressed; for example, choosing applications whose experimental requirements closely match device capabilities, and developing strategies to efficiently complete the cycle of development. These will require imagination, ingenuity and collaboration.

Raman microspectroscopy for probing the impact of a dietary antioxidant on human breast cancer cells

Breast cancer is the second most common type of cancer worldwide and the most frequent among women, being the fifth cause of death from neoplastic disease. Since this is an oxidative-stress related neoplasia, it is largely preventable. A dietary isoflavone abundant in soybean - daidzein - is currently being investigated owing to its chemopreventive and/or chemotherapeutic properties towards the human MDA-MB-231 (metastatic, estrogen-unresponsive) and MCF-7 (estrogen-responsive) breast cancer cell lines. Biological assays for evaluation of antitumour and anti-invasive activities were combined with state-of-the-art vibrational microspectroscopy techniques. At 50 and 100 μM concentrations and 48 h incubation time, daidzein was found to induce a marked decrease in cell viability (ca. 50%) for MDA-MB-231 and MCF-7 cells (respectively ca. 50% and 42%) and 40% inhibition of cell migration. MicroRaman analysis of fixed cells upon exposure to this isoflavone unveiled its metabolic impact on both cell lines. Multivariate data analysis (unsupervised PCA) led to a clear discrimination between the control and DAID-exposed cells, with distinctive effects on their biochemical profile, particularly regarding DNA, lipids and protein components, in a cell-dependent way. This is the first reported study on the impact of dietary antioxidants on cancer cells by microRaman techniques.

Fundamental developments in infrared spectroscopic imaging for biomedical applications

Infrared chemical imaging is a rapidly emerging field with new advances in instrumentation, data acquisition and data analysis. These developments have had significant impact in biomedical applications and numerous studies have now shown that this technology offers great promise for the improved diagnosis of the diseased state. Relying on purely biochemical signatures rather than contrast from exogenous dyes and stains, infrared chemical imaging has the potential to revolutionise histopathology for improved disease diagnosis. In this review we discuss the recent advances in infrared spectroscopic imaging specifically related to spectral histopathology (SHP) and consider the current state of the field. Finally we consider the practical application of SHP for disease diagnosis and consider potential barriers to clinical translation highlighting current directions and the future outlook.

Comparison of transmission and transflectance mode FTIR imaging of biological tissue

FTIR microscopy is a powerful technique which has become popular due to its ability to provide complementary information during histopathological assessment of biomedical tissue samples. Recently however, questions have been raised on the suitability of the transflection mode of operation for clinical diagnosis due to the so called Electric Field Standing Wave (EFSW) effect. In this paper we compare chemical images measured in transmission and transflection from prostate tissue obtained from five different patients, and discuss the variability of the spectra acquired with each sampling modality. We find that spectra obtained in transflection undergo a non-linear distortion, i.e. non-linear variations in absorption band strength across the spectra, and that there are significant differences in spectra measured from the same area of tissue depending on the mode of operation. Principal Component Analysis (PCA) is used to highlight that poorer discrimination between benign and cancerous tissue is obtained in transflection mode. In addition we show that use of second derivatives, while qualitatively improves spectral discrimination, does not completely alleviate the underlying problem.

Label-free phenotyping of peripheral blood lymphocytes by infrared imaging

It is now widely accepted that the immune microenvironment of tumors and more precisely Tumor Infiltrating Lymphocytes (TIL) play an important role in cancer development and outcome. TILs are considered to be important prognostic and predictive factors based on a growing body of clinical evidence; however, their presence at the tumor site is not currently assessed routinely. FTIR (Fourier transform infrared) imaging has proven it has value in studying a range of tumors, particularly for characterizing tumor cells. Currently, very little is known about the potential for FTIR imaging to characterize TIL. The present proof of concept study investigates the ability of FTIR imaging to identify the principal lymphocyte subpopulations present in human peripheral blood (PB). A negative cell isolation method was employed to select pure, label-free, helper T cells (CD4(+)), cytotoxic T cells (CD8(+)) and B cells (CD19(+)) from six healthy donors PB by Fluorescence Activated Cell Sorting (FACS). Cells were centrifuged onto Barium Fluoride windows and ten infrared images were recorded for each lymphocyte subpopulation from all six donors. After spectral pre-treatment, statistical analyses were performed. Unsupervised Principal Component Analyses (PCA) revealed that in the absence of donor variability, CD4(+) T cells, CD8(+) T cells and B cells each display distinct IR spectral features. Supervised Partial Least Square Discriminant Analyses (PLS-DA) demonstrated that the differences between the three lymphocyte subpopulations are reflected in their IR spectra, permitting their individual identification even when significant donor variability is present. Our results also show that a distinct spectral signature is associated with antibody binding. To our knowledge this is the first study reporting that FTIR imaging can effectively identify T and B lymphocytes and differentiate helper T cells from cytotoxic T cells. This proof of concept study demonstrates that FTIR imaging is a reliable tool for the identification of lymphocyte subpopulations and has the potential for use in characterizing TIL.

FTIR spectral signature of anticancer drugs. Can drug mode of action be identified?

Infrared spectroscopy has brought invaluable information about proteins and about the mechanism of action of enzymes. These achievements are difficult to transpose to living organisms as all biological molecules absorb in the mid infrared, with usually a high degree of overlap. Deciphering the contribution of each enzyme is therefore almost impossible. On the other hand, small changes in the infrared spectra of cells induced by environmental conditions or drugs may provide an accurate signature of the metabolic shift experienced by the cell as a response to a change in the growth medium. The present paper aims at reviewing the contribution of infrared spectroscopy to the description of small chemical changes that occur in cells when they are exposed to a drug. In particular, this review will focus on cancer cells and anti-cancer drugs. Results accumulated so far tend to demonstrate that infrared spectroscopy could be a very accurate descriptor of the mode of action of anticancer drugs. If confirmed, such a segmentation of potential drugs according to their "mode of action" will be invaluable for the discovery of new therapeutic molecules. This article is part of a Special Issue entitled: Physiological Enzymology and Protein Functions.

Vibrational spectroscopic methods for cytology and cellular research

The use of vibrational spectroscopy, FTIR and Raman, for cytology and cellular research has the potential to revolutionise the approach to cellular analysis. Vibrational spectroscopy is non-destructive, simple to operate and provides direct information. Importantly it does not require expensive exogenous labels that may affect the chemistry of the cell under analysis. In addition, the advent of spectroscopic microscopes provides the ability to image cells and acquire spectra with a subcellular resolution. This introductory review focuses on recent developments within this fast paced field and highlights potential for the future use of FTIR and Raman spectroscopy. We particularly focus on the development of live cell research and the new technologies and methodologies that have enabled this.

Direct determination of phosphatase activity from physiological substrates in cells

A direct and continuous approach to determine simultaneously protein and phosphate concentrations in cells and kinetics of phosphate release from physiological substrates by cells without any labeling has been developed. Among the enzymes having a phosphatase activity, tissue non-specific alkaline phosphatase (TNAP) performs indispensable, multiple functions in humans. It is expressed in numerous tissues with high levels detected in bones, liver and neurons. It is absolutely required for bone mineralization and also necessary for neurotransmitter synthesis. We provided the proof of concept that infrared spectroscopy is a reliable assay to determine a phosphatase activity in the osteoblasts. For the first time, an overall specific phosphatase activity in cells was determined in a single step by measuring simultaneously protein and substrate concentrations. We found specific activities in osteoblast like cells amounting to 116 ± 13 nmol min(-1) mg(-1) for PPi, to 56 ± 11 nmol min(-1) mg(-1) for AMP, to 79 ± 23 nmol min(-1) mg(-1) for beta-glycerophosphate and to 73 ± 15 nmol min(-1) mg(-1) for 1-alpha-D glucose phosphate. The assay was also effective to monitor phosphatase activity in primary osteoblasts and in matrix vesicles. The use of levamisole--a TNAP inhibitor--served to demonstrate that a part of the phosphatase activity originated from this enzyme. An IC50 value of 1.16 ± 0.03 mM was obtained for the inhibition of phosphatase activity of levamisole in osteoblast like cells. The infrared assay could be extended to determine any type of phosphatase activity in other cells. It may serve as a metabolomic tool to monitor an overall phosphatase activity including acid phosphatases or other related enzymes.

Cellular injury evidenced by impedance technology and infrared microspectroscopy

Fourier Transform Infrared (FTIR) spectroscopy is finding increasing biological application, for example in the analysis of diseased tissues and cells, cell cycle studies and investigating the mechanisms of action of anticancer drugs. Cancer treatment studies routinely define the types of cell-drug responses as either total cell destruction by the drug (all cells die), moderate damage (cell deterioration where some cells survive) or reversible cell cycle arrest (cytostasis). In this study the loss of viability and related chemical stress experienced by cells treated with the medicinal plant, Plectranthus ciliatus, was investigated using real time cell electronic sensing (RT-CES) technology and FTIR microspectroscopy. The use of plants as medicines is well established and ethnobotany has proven that crude extracts can serve as treatments against various ailments. The aim of this study was to determine whether FTIR microspectroscopy would successfully distinguish between different types of cellular injury induced by a potentially anticancerous plant extract. Cervical adenocarcinoma (HeLa) cells were treated with a crude extract of Pciliatus and cells monitored using RT-CES to characterize the type of cellular responses induced. Cell populations were then investigated using FTIR microspectroscopy and statistically analysed using One-way Analysis of Variance (ANOVA) and Principal Component Analysis (PCA). The plant extract and a cancer drug control (actinomycin D) induced concentration dependent cellular responses ranging from nontoxic, cytostatic or cytotoxic. Thirteen spectral peaks (915cm(-)(1), 933cm(-)(1), 989cm(-)(1), 1192cm(-)(1), 1369cm(-)(1), 1437cm(-)(1), 1450cm(-)(1), 1546cm(-)(1), 1634cm(-)(1), 1679cm(-)(1) 1772cm(-)(1), 2874cm(-)(1) and 2962cm(-)(1)) associated with cytotoxicity were significantly (p value<0.05, one way ANOVA, Tukey test, Bonferroni) altered, while two of the bands were also indicative of early stress related responses. In PCA, poor separation between nontoxic and cytostatic responses was evident while clear separation was linked to cytotoxicity. RT-CES detected morphological changes as indicators of cell injury and could distinguish between viable, cytostatic and cytotoxic responses. FTIR microspectroscopy confirmed that cytostatic cells were viable and could still recover while also describing early cellular stress related responses on a molecular level.

Characterising cytotoxic agent action as a function of the cell cycle using fourier transform infrared microspectroscopy

Infrared spectral signatures of drug–cell interaction, suggest that both the stages of proliferation and the degree of apoptosis need to be taken into account to elucidate the fine biochemical details of the immediate cellular response to the drug.

Enhanced FTIR bench-top imaging of single biological cells

A new optical system has recently been developed that enables infrared images to be obtained with a pixel resolution of 1 micron on a bench-top instrument using a thermal source.

High throughput absorbance spectra of cancerous cells: a microscopic investigation of spectral artifacts

Infrared spectra of cell smears change in shape with cell density.

Fourier transform infrared microspectroscopy monitoring of 5-fluorouracil-induced apoptosis in SW620 colon cancer cells

Colon cancer is associated with a high incidence and a poor prognosis. The aim of the present study was to determine whether Fourier transform infrared (FTIR) microspectroscopy can be used to monitor the chemotherapy drug-induced apoptosis of SW620 colon cancer cells. The 50% inhibitory concentration (IC₅₀) of 5-fluorouracil (5-FU), the main chemotherapeutic agent used for the treatment of colorectal cancer, was determined as the inhibition of growth of the SW620 cells using an MTT assay. Cell starvation and 5-FU treatment synergized to arrest the cells in the G1 and S phases of the cell cycle. FTIR combined with fluorescence activated cell sorting (FACS) analysis were used to analyze the SW620 cells following treatment with 5-FU for 12, 24 and 48 h. The apoptotic cells had several spectral characteristics. The relative peak intensity ratio (I₁₇₄₀/I₁₄₆₀) was significantly increased (P<0.05), the I₁₇₄₀/I₁₄₆₀ ratio, associated with a band of amino acid residues at 1,410 cm⁻¹ was significantly increased at the early and late phases of cell death (P<0.05), the peaks at 1,240 cm⁻¹ increased in wave number, a band at 1,040 cm⁻¹, associated with polysaccharides, appeared at 24 and 48 h and then moved to a higher wave number and the I₁₀₄₀/I₁₄₆₀ ratio increased at the late stage of apoptosis. These results demonstrated that FTIR can be used as a label-free technique to monitor cancer cell apoptosis and to understand the spectral fingerprints of apoptotic cells. This suggested that FTIR spectral features have potential as a powerful tool to monitor cancer cell apoptosis.

Rapid and sensitive screening of 17β-estradiol estrogenicity using Fourier transform infrared imaging spectroscopy (FT-IRIS)

It is important to develop rapid and sensitive screening assays to assess the biological effects of emerging contaminants. In this contribution, the ability to determine the molecular level effects of 17β-estradiol on single MCF-7 cells using Fourier transform infrared imaging spectroscopy (FT-IRIS) was investigated. The use of FT-IRIS enabled subcellular imaging of the cells and determination of a dose dependent response in mucin concentration at 24 and 48 h of incubation. The 48 h increase in mucin was comparable to increases in cellular proliferation (Pearson R = 0.978). The EC50 values for the E-screen and FT-IRIS assays were 2.29 and 2.56 ppt, respectively, indicating that the molecular changes, which are observed at the single cell level using FT-IRIS, are reflective of physiological changes that are observed as the cell population responds to 17ß-estradiol. The FT-IRIS method, when combined with principal component analysis, enabled differentiation and grouping of cells exposed to varying concentrations of 17ß-estradiol. The FT-IRIS method shows potential to be used as a rapid and sensitive screening technique for the detection of biological responses to different emerging contaminants in relevant cells or tissues.

Highlighting a need to distinguish cell cycle signatures from cellular responses to chemotherapeutics in SR-FTIR spectroscopy

Previous research has seen difficulties in establishing clear discrimination by principal component analysis (PCA) between drug-treated cells analysed by single point SR-FTIR spectroscopy, relative to multisampling cell monolayers by conventional FTIR. It is suggested that the issue arises due to signal mixing between cellular-response signatures and cell cycle phase contributions in individual cells. Consequently, chemometric distinction of cell spectra treated with multiple drugs is difficult even with supervised methods. In an effort to separate cell cycle chemistry from cellular response chemistry in the spectra, renal carcinoma cells were stained with propidium iodide and fluorescent-activated cell sorted (FACS) after exposure to a number of chemotherapeutic compounds; 5-fluorouracil (5FU) and a set of novel gold-based experimental compounds. The cell spectra were analysed separately by PCA in G(1), S or G(2)/M phase. The mode of action of established drug 5FU, known to disrupt S phase, was confirmed by FACS analysis. The chemical signature of 5FU-treated cells discriminated against both the control and gold-compound (KF0101)-treated cell spectra, suggesting a different mode of action due to a difference in cellular response.

FTIR spectral signature of anticancer drug effects on PC-3 cancer cells: is there any influence of the cell cycle?

FTIR spectroscopy was recently demonstrated to be a useful tool to obtain a unique fingerprint of several anticancer drugs. While cell responses to anticancer drugs are related to their "mode of action", it is obvious that some of the drugs used in the previous studies affect the cell cycle. For example, antimicrotubules disable the mitotic apparatus by disrupting the formation or the depolymerisation of microtubules. Cells are thus mostly blocked in the G2/M phase. On the other hand, it has been suggested that the changes observed in the cell spectra due to treatments could be related to the cell cycle. The aim of the present study is to examine this hypothesis and to investigate whether spectral variations induced by a treatment reflect the cell cycle behaviour or the metabolic perturbations induced by the drug. To answer this question, a method was developed that allows an unambiguous identification of the cell cycle phase for each individual cell. This method is based on the superimposition of three types of images: visible, infrared and propidium iodide fluorescence images. Propidium iodide intercalates the bases of the DNA. As the DNA amount in a cell is correlated with the cell cycle phase, the exact phase of each individual cell could be identified. On IR images, mean spectra corresponding to single cells were calculated and associated with the cycle stage defined using fluorescence images. Statistical analyses were applied on these IR spectra, first in order to compare spectra of cells from different stages of the cycle and second, to investigate to what extent the modifications related to the cell cycle contribute to the spectral variations due to paclitaxel treatment. Results demonstrate that the FTIR cell cycle signature is very small with respect to the changes induced by paclitaxel.

The action of all-trans-retinoic acid (ATRA) and synthetic retinoid analogues (EC19 and EC23) on human pluripotent stem cells differentiation investigated using single cell infrared microspectroscopy

All trans-retinoic acid (ATRA) is widely used to direct the differentiation of cultured stem cells. When exposed to the pluripotent human embryonal carcinoma (EC) stem cell line, TERA2.cl.SP12, ATRA induces ectoderm differentiation and the formation of neuronal cell types. We have previously generated synthetic analogues of retinoic acid (EC23 and EC19) which also induce the differentiation of EC cells. Even though EC23 and EC19 have similar chemical structures, they have differing biochemical effects in terms of EC cell differentiation. EC23 induces neuronal differentiation in a manner similar to ATRA, whereas EC19 directs the cells to form epithelial-like derivatives. Previous MALDI-TOF MS analysis examined the response of TERA2.cl.SP12 cells after exposure to ATRA, EC23 and EC19 and further demonstrated the similarly in the effect of ATRA and EC23 activity whilst responses to EC19 were very different. In this study, we show that Fourier Transform Infrared Micro-Spectroscopy (FT-IRMS) coupled with appropriate scatter correction and multivariate analysis can be used as an effective tool to further investigate the differentiation of human pluripotent stem cells and monitor the alternative affects different retinoid compounds have on the induction of differentiation. FT-IRMS detected differences between cell populations as early as 3 days of compound treatment. Populations of cells treated with different retinoid compounds could easily be distinguished from one another during the early stages of cell differentiation. These data demonstrate that FT-IRMS technology can be used as a sensitive screening technique to monitor the status of the stem cell phenotype and progression of differentiation along alternative pathways in response to different compounds.

Substrate contributions in micro-ATR of thin samples: implications for analysis of cells, tissue and biological fluids

Low-e microscope slides are a common substrate for biological samples. Typically they are used for transflection infrared microspectroscopy but increasingly they are also being used for micro-ATR experiments since it is assumed that the FTIR-ATR absorbance spectra of cells and tissue on low-e substrates will not contain any spectral contributions from the substrate materials. This, in part, is due to the expectation that all the infrared light will be reflected at the highly reflective surface. At low sample thicknesses, however (e.g. less than 2 μm) the electric field does indeed penetrate through the substrate layers and undergoes absorption, from the glass supporting layer making up the majority of the slide. In this paper we show experimental evidence of the substrate contributions in ATR spectra and also a theoretical model giving insight into the spectral contributions of the substrate as a function of sample thickness.

The effect of optical substrates on micro-FTIR analysis of single mammalian cells

The study of individual cells with infrared (IR) microspectroscopy often requires living cells to be cultured directly onto a suitable substrate. The surface effect of the specific substrates on the cell growth—viability and associated biochemistry—as well as on the IR analysis—spectral interference and optical artifacts—is all too often ignored. Using the IR beamline, MIRIAM (Diamond Light Source, UK), we show the importance of the substrate used for IR absorption spectroscopy by analyzing two different cell lines cultured on a range of seven optical substrates in both transmission and reflection modes. First, cell viability measurements are made to determine the preferable substrates for normal cell growth. Successively, synchrotron radiation IR microspectroscopy is performed on the two cell lines to determine any genuine biochemically induced changes or optical effect in the spectra due to the different substrates. Multivariate analysis of spectral data is applied on each cell line to visualize the spectral changes. The results confirm the advantage of transmission measurements over reflection due to the absence of a strong optical standing wave artifact which amplifies the absorbance spectrum in the high wavenumber regions with respect to low wavenumbers in the mid-IR range. The transmission spectra reveal interference from a more subtle but significant optical artifact related to the reflection losses of the different substrate materials. This means that, for comparative studies of cell biochemistry by IR microspectroscopy, it is crucial that all samples are measured on the same substrate type.

Figure

Cell separation by PCA due to the refractive index of the substrate used, revealing transmission artifact.

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The inherent problem of transflection-mode infrared spectroscopic microscopy and the ramifications for biomedical single point and imaging applications

Transflection-mode FTIR spectroscopy has become a popular method of measuring spectra from biomedical and other samples due to the relative low cost of substrates compared to transmission windows, and a higher absorbance due to a double pass through the same sample approximately doubling the effective path length. In this publication we state an optical description of samples on multilayer low-e reflective substrates. Using this model we are able to explain in detail the so-called electric-field standing wave effect and rationalise the non-linear change in absorbance with sample thickness. The ramifications of this non-linear change, for imaging and classification systems, where a model is built from tissue sectioned at a particular thickness and compared with tissue of a different thickness are discussed. We show that spectra can be distorted such that classification fails leading to inaccurate tissue segmentation which may have subsequent implications for disease diagnostics applications.

Basis of a FTIR spectroscopy methodology for automated evaluation of Akt kinase inhibitor on leukemic cell lines used as model

The PI3K/Akt-signaling pathway, associated with cancer development and disease progression, is recognized to be an anti-tumor drug target that could present important therapeutic benefit. However, no targeted Akt medicines have been commercialized yet, reflecting that drug selection procedures requires significant improvement from early research to clinical trials. Thus, new methods permitting both the evaluation of cytotoxic and proliferation inhibition effect on cancer cells but also to provide a global fingerprint of the drug action mechanism of new Akt inhibitor candidates are of major interest. Because it can detect very subtle molecular changes and could provide a global fingerprint of drug effects on cells, Fourier-transform infrared (FTIR) spectroscopy appears to be a promising method to develop new time- and cost-saving tools for chemical library screening improvements. In this study, we combine FTIR spectroscopy, advanced chemometrics analysis and cross-validation by standard biological assays to establish a basis of a mid-throughput methodology for rapid and automated assessment of cell response to Akt inhibitors and quantitative evaluation of their anti-proliferative effects. Our results shows that our methodology is able (1) to detect cell response to an Akt inhibitor exposure even for very low doses, (2) to provide biochemical information of interest about its effects on the cell metabolism, lipidome, and proteome, (3) to predict accurately resulting cell proliferation inhibition rate. Thus, further based on a large spectral data base, our methodology could contribute to facilitate preliminary screening of chemical libraries and improving the selection procedure of drug candidates in laboratory routine.

Concentration-dependent effects of carbon nanoparticles in gram-negative bacteria determined by infrared spectroscopy with multivariate analysis

With increasing production of carbon nanoparticles (CNPs), environmental release of these entities becomes an ever-greater inevitability. However, many questions remain regarding their impact on soil microorganisms. This study examined the effects of long or short multiwalled carbon nanotubes (MWCNTs), C60 fullerene and fullerene soot in Gram-negative bacteria. Attenuated total reflection Fourier-transform infrared (ATR-FTIR) spectroscopy was applied to derive signature spectral fingerprints of effects. A concentration-dependent response in spectral alterations was observed for each nanoparticle type. Long or short MWCNTs and fullerene soot gave rise to similar alterations to lipids, Amide II and DNA. The extent of alteration varies with nanoparticle size, with smaller short MWCNTs resulting in greater toxicity than long MWCNTs. Fullerene soot was the least toxic. C60 results in the most distinct and largest overall alterations, notably in extensive protein alteration. This work demonstrates a novel approach for assaying and discriminating the effects of CNPs in target systems.

Synchrotron Radiation Spectroscopic Techniques as Tools for the Medicinal Chemist: Microprobe X-Ray Fluorescence Imaging, X-Ray Absorption Spectroscopy, and Infrared Microspectroscopy

This review updates the recent advances and applications of three prominent synchrotron radiation techniques, microprobe X-ray fluorescence spectroscopy/imaging, X-ray absorption spectroscopy, and infrared microspectroscopy, and highlights how these tools are useful to the medicinal chemist. A brief description of the principles of the techniques is given with emphasis on the advantages of using synchrotron radiation-based instrumentation rather than instruments using typical laboratory radiation sources. This review focuses on several recent applications of these techniques to solve inorganic medicinal chemistry problems, focusing on studies of cellular uptake, distribution, and biotransformation of established and potential therapeutic agents. The importance of using these synchrotron-based techniques to assist the development of, or validate the chemistry behind, drug design is discussed.

Applications of Infrared and Raman Microspectroscopy of Cells and Tissue in Medical Diagnostics: Present Status and Future Promises

This paper summarizes the progress achieved over the past fifteen years in applying vibrational (Raman and IR) spectroscopy to problems of medical diagnostics and cellular biology. During this time, a number of research groups have verified the enormous information content of vibrational spectra; in fact, genomic, proteomic, and metabolomic information can be deduced by decoding the observed vibrational spectra. This decoding process is aided enormously by the availability of high-power computer workstations and advanced algorithms for data analysis. Furthermore, commercial instrumentation for the fast collection of both Raman and infrared microspectral data has rendered practical the collection of images based solely on spectral data. The progress in the field has been manifested by a steady increase in the number and quality of publications submitted by established and new research groups in vibrational biological and biomedical arenas.

Label-free characterization of cancer-activated fibroblasts using infrared spectroscopic imaging

Glandular tumors arising in epithelial cells comprise the majority of solid human cancers. Glands are supported by stroma, which is activated in the proximity of a tumor. Activated stroma is often characterized by the molecular expression of α-smooth muscle actin (α-SMA) within fibroblasts. However, the precise spatial and temporal evolution of chemical changes in fibroblasts upon epithelial tumor signaling is poorly understood. Here we report a label-free method to characterize fibroblast changes by using Fourier transform infrared spectroscopic imaging and comparing spectra with α-SMA expression in primary normal human fibroblasts. We recorded the fibroblast activation process by spectroscopic imaging using increasingly tissue-like conditions: 1), stimulation with the growth factor TGFβ1; 2), coculture with MCF-7 human breast cancerous epithelial cells in Transwell coculture; and 3), coculture with MCF-7 in three-dimensional cell culture. Finally, we compared the spectral signatures of stromal transformation with normal and malignant human breast tissue biopsies. The results indicate that this approach reveals temporally complex spectral changes and thus provides a richer assessment than simple molecular imaging based on α-SMA expression. Some changes are conserved across culture conditions and in human tissue, providing a label-free method to monitor stromal transformations.