Auranofin sensitizes breast cancer cells to paclitaxel chemotherapy by disturbing the cellular redox system

The intrinsic redox status of cancer cells limits the efficacy of chemotherapeutic drugs. Auranofin, a Food and Drug Administration-approved gold-containing compound, documented with effective pharmacokinetics and safety profiles in humans, has recently been repurposed for anticancer activity. This study examined the paclitaxel-sensitizing effect of auranofin by targeting redox balance in the MDA-MB-231 and MCF-7 breast cancer cell lines. Auranofin treatment depletes the activities of superoxide dismutase, catalase, and glutathione peroxidase and alters the redox ratio in the breast cancer cell lines. Furthermore, it has been noticed that auranofin augmented paclitaxel-mediated cytotoxicity in a concentration-dependent manner in both MDA-MB-231 and MCF-7 cell lines. Moreover, auranofin increased the levels of intracellular reactive oxygen species (observed using 2, 7-diacetyl dichlorofluorescein diacetate staining) and subsequently altered the mitochondrial membrane potential (rhodamine-123 staining) in a concentration-dependent manner. Further, the expression of apoptotic marker p21 was found to be higher in auranofin plus paclitaxel-treated breast cancer cells compared to paclitaxel-alone treatment. Thus, the present results illustrate the chemosensitizing property of auranofin in MDA-MB-231 and MCF-7 breast cancer cell lines via oxidative metabolism. Therefore, auranofin could be considered a chemosensitizing agent during cancer chemotherapy.

Development of an optical fiber-based redox monitoring system for tissue metabolism

An optical redox ratio can potentially be used to report on the dynamics of cell and tissue metabolism and define altered metabolic conditions for different pathologies. While there are methods to measure the optical redox ratio, they are not particularly suited to real-time in situ or in vivo analysis. Here, we have developed a fiber-optic system to measure redox ratios in cells and tissues and two mathematical models to enable real-time, in vivo redox measurements. The optical redox ratios in tissue explants are correlated directly with endogenous NADH/FAD fluorescence emissions. We apply the mathematical models to the two-photon microscopy data and show consistent results. We also used our fiber-optic system to measure redox in different tissues and show consistent results between the two models, hence demonstrating proof-of-principle. This innovative redox monitoring system will have practical applications for defining different metabolic disease states.

Identifying metastatic ability of prostate cancer cell lines using native fluorescence spectroscopy and machine learning methods

Metastasis is the leading cause of mortalities in cancer patients due to the spreading of cancer cells to various organs. Detecting cancer and identifying its metastatic potential at the early stage is important. This may be achieved based on the quantification of the key biomolecular components within tissues and cells using recent optical spectroscopic techniques. The aim of this study was to develop a noninvasive label-free optical biopsy technique to retrieve the characteristic molecular information for detecting different metastatic potentials of prostate cancer cells. Herein we report using native fluorescence (NFL) spectroscopy along with machine learning (ML) to differentiate prostate cancer cells with different metastatic abilities. The ML algorithms including principal component analysis (PCA) and nonnegative matrix factorization (NMF) were used for dimension reduction and feature detection. The characteristic component spectra were used to identify the key biomolecules that are correlated with metastatic potentials. The relative concentrations of the molecular spectral components were retrieved and used to classify the cancer cells with different metastatic potentials. A multi-class classification was performed using support vector machines (SVMs). The NFL spectral data were collected from three prostate cancer cell lines with different levels of metastatic potentials. The key biomolecules in the prostate cancer cells were identified to be tryptophan, reduced nicotinamide adenine dinucleotide (NADH) and hypothetically lactate as well. The cancer cells with different metastatic potentials were classified with high accuracy using the relative concentrations of the key molecular components. The results suggest that the changes in the relative concentrations of these key fluorophores retrieved from NFL spectra may present potential criteria for detecting prostate cancer cells of different metastatic abilities.

Combined noninvasive metabolic and spindle imaging as potential tools for embryo and oocyte assessment

STUDY QUESTION

Is the combined use of fluorescence lifetime imaging microscopy (FLIM)-based metabolic imaging and second harmonic generation (SHG) spindle imaging a feasible and safe approach for noninvasive embryo assessment?

SUMMARY ANSWER

Metabolic imaging can sensitively detect meaningful metabolic changes in embryos, SHG produces high-quality images of spindles and the methods do not significantly impair embryo viability.

WHAT IS KNOWN ALREADY

Proper metabolism is essential for embryo viability. Metabolic imaging is a well-tested method for measuring metabolism of cells and tissues, but it is unclear if it is sensitive enough and safe enough for use in embryo assessment.

STUDY DESIGN, SIZE, DURATION

This study consisted of time-course experiments and control versus treatment experiments. We monitored the metabolism of 25 mouse oocytes with a noninvasive metabolic imaging system while exposing them to oxamate (cytoplasmic lactate dehydrogenase inhibitor) and rotenone (mitochondrial oxidative phosphorylation inhibitor) in series. Mouse embryos (n = 39) were measured every 2 h from the one-cell stage to blastocyst in order to characterize metabolic changes occurring during pre-implantation development. To assess the safety of FLIM illumination, n = 144 illuminated embryos were implanted into n = 12 mice, and n = 108 nonilluminated embryos were implanted into n = 9 mice.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Experiments were performed in mouse embryos and oocytes. Samples were monitored with noninvasive, FLIM-based metabolic imaging of nicotinamide adenine dinucleotide (NADH) and flavin adenine dinucleotide (FAD) autofluorescence. Between NADH cytoplasm, NADH mitochondria and FAD mitochondria, a single metabolic measurement produces up to 12 quantitative parameters for characterizing the metabolic state of an embryo. For safety experiments, live birth rates and pup weights (mean ± SEM) were used as endpoints. For all test conditions, the level of significance was set at P < 0.05.

MAIN RESULTS AND THE ROLE OF CHANCE

Measured FLIM parameters were highly sensitive to metabolic changes due to both metabolic perturbations and embryo development. For oocytes, metabolic parameter values were compared before and after exposure to oxamate and rotenone. The metabolic measurements provided a basis for complete separation of the data sets. For embryos, metabolic parameter values were compared between the first division and morula stages, morula and blastocyst and first division and blastocyst. The metabolic measurements again completely separated the data sets. Exposure of embryos to excessive illumination dosages (24 measurements) had no significant effect on live birth rate (5.1 ± 0.94 pups/mouse for illuminated group; 5.7 ± 1.74 pups/mouse for control group) or pup weights (1.88 ± 0.10 g for illuminated group; 1.89 ± 0.11 g for control group).

LIMITATIONS, REASONS FOR CAUTION

The study was performed using a mouse model, so conclusions concerning sensitivity and safety may not generalize to human embryos. A limitation of the live birth data is also that although cages were routinely monitored, we could not preclude that some runt pups may have been eaten.

WIDER IMPLICATIONS OF THE FINDINGS

Promising proof-of-concept results demonstrate that FLIM with SHG provide detailed biological information that may be valuable for the assessment of embryo and oocyte quality. Live birth experiments support the method's safety, arguing for further studies of the clinical utility of these techniques.

STUDY FUNDING/COMPETING INTEREST(S)

Supported by the Blavatnik Biomedical Accelerator Grant at Harvard University and by the Harvard Catalyst/The Harvard Clinical and Translational Science Center (National Institutes of Health Award UL1 TR001102), by NSF grants DMR-0820484 and PFI-TT-1827309 and by NIH grant R01HD092550-01. T.S. was supported by a National Science Foundation Postdoctoral Research Fellowship in Biology grant (1308878). S.F. and S.A. were supported by NSF MRSEC DMR-1420382. Becker and Hickl GmbH sponsored the research with the loaning of equipment for FLIM. T.S. and D.N. are cofounders and shareholders of LuminOva, Inc., and co-hold patents (US20150346100A1 and US20170039415A1) for metabolic imaging methods. D.S. is on the scientific advisory board for Cooper Surgical and has stock options with LuminOva, Inc.

Single-cell redox states analyzed by fluorescence lifetime metrics and tryptophan FRET interaction with NAD(P)H

Redox changes in live HeLa cervical cancer cells after doxorubicin treatment can either be analyzed by a novel fluorescence lifetime microscopy (FLIM)-based redox ratio NAD(P)H-a2%/FAD-a1%, called fluorescence lifetime redox ratio or one of its components (NAD(P)H-a2%), which is actually driving that ratio and offering a simpler and alternative metric and are both compared. Auto-fluorescent NAD(P)H, FAD lifetime is acquired by 2- photon excitation and Tryptophan by 3-photon, at 4 time points after treatment up to 60 min demonstrating early drug response to doxorubicin. Identical Fields-of-view (FoV) at each interval allows single-cell analysis, showing heterogeneous responses to treatment, largely based on their initial control redox state. Based on a discrete ROI selection method, mitochondrial OXPHOS and cytosolic glycolysis are discriminated. Furthermore, putative FRET interaction and energy transfer between tryptophan residue carrying enzymes and NAD(P)H correlate with NAD(P)H-a2%, as does the NADPH/NADH ratio, highlighting a multi-parametric assay to track metabolic changes in live specimens. © 2019 International Society for Advancement of Cytometry.

Increased nicotinamide adenine dinucleotide pool promotes colon cancer progression by suppressing reactive oxygen species level

Nicotinamide adenine dinucleotide (NAD) exists in an oxidized form (NAD⁺) and a reduced form (NADH). NAD⁺ plays crucial roles in cancer metabolism, including in cellular signaling, energy production and redox regulation. However, it remains unclear whether NAD(H) pool size (NAD⁺ and NADH) could be used as biomarker for colon cancer progression. Here, we showed that the NAD(H) pool size and NAD⁺/NADH ratio both increased during colorectal cancer (CRC) progression due to activation of the NAD⁺ salvage pathway mediated by nicotinamide phosphoribosyltransferase (NAMPT). The NAMPT expression was upregulated in adenoma and adenocarcinoma tissues from CRC patients. The NADH fluorescence intensity measured by two‐photon excitation fluorescence (TPEF) microscopy was consistently increased in CRC cell lines, azoxymethane/dextran sodium sulfate (AOM/DSS)‐induced CRC tissues and tumor tissues from CRC patients. The increases in the NAD(H) pool inhibited the accumulation of excessive reactive oxygen species (ROS) levels and FK866, a specific inhibitor of NAMPT, treatment decreased the CRC nodule size by increasing ROS levels in AOM/DSS mice. Collectively, our results suggest that NAMPT‐mediated upregulation of the NAD(H) pool protects cancer cells against detrimental oxidative stress and that detecting NADH fluorescence by TPEF microscopy could be a potential method for monitoring CRC progression.

Combined reflectance spectroscopy and coherent light backscattering measurement differentiate cervical cancer from normal epithelial tissue in a xenograft mouse model

Cervical cancer is a type of slow-growing cancer associated with high mortality rates. Early detection can enable lifesaving early intervention. Current cervical premalignant lesion detection methods suffer from both high miss rates and excessive referrals for unnecessary biopsies. Herein, coherent light backscatter and modifications in reflected white-light spectra were measured to specifically discriminate between cervical tumors and normal squamous epithelial tissues resected from a mouse xenograft model. The combined measurements resulted in 92% sensitivity and 93% specificity in discrimination between the two tissues. These methods can be used to develop a noninvasive portable optical probe for sensitive and objective detection of precancer and cancer epithelial lesions in the cervix and other accessible epithelial tissues.

Label-free dynamic segmentation and morphological analysis of subcellular optical scatterers

Imaging without fluorescent protein labels or dyes presents significant advantages for studying living cells without confounding staining artifacts and with minimal sample preparation. Here, we combine label-free optical scatter imaging with digital segmentation and processing to create dynamic subcellular masks, which highlight significantly scattering objects within the cells' cytoplasms. The technique is tested by quantifying organelle morphology and redistribution during cell injury induced by calcium overload. Objects within the subcellular mask are first analyzed individually. We show that the objects' aspect ratio and degree of orientation ("orientedness") decrease in response to calcium overload, while they remain unchanged in untreated control cells. These changes are concurrent with mitochondrial fission and rounding observed by fluorescence, and are consistent with our previously published data demonstrating scattering changes associated with mitochondrial rounding during calcium injury. In addition, we show that the magnitude of the textural features associated with the spatial distribution of the masked objects' orientedness values, changes by more than 30% in the calcium-treated cells compared with no change or changes of less than 10% in untreated controls, reflecting dynamic changes in the overall spatial distribution and arrangement of subcellular scatterers in response to injury. Taken together, our results suggest that our method successfully provides label-free morphological signatures associated with cellular injury. Thus, we propose that dynamically segmenting and analyzing the morphology and organizational patterns of subcellular scatterers as a function of time can be utilized to quantify changes in a given cellular condition or state.

Protein-bound NAD(P)H Lifetime is Sensitive to Multiple Fates of Glucose Carbon

While NAD(P)H fluorescence lifetime imaging (FLIM) can detect changes in flux through the TCA cycle and electron transport chain (ETC), it remains unclear whether NAD(P)H FLIM is sensitive to other potential fates of glucose. Glucose carbon can be diverted from mitochondria by the pentose phosphate pathway (via glucose 6-phosphate dehydrogenase, G6PDH), lactate production (via lactate dehydrogenase, LDH), and rejection of carbon from the TCA cycle (via pyruvate dehydrogenase kinase, PDK), all of which can be upregulated in cancer cells. Here, we demonstrate that multiphoton NAD(P)H FLIM can be used to quantify the relative concentrations of recombinant LDH and malate dehydrogenase (MDH) in solution. In multiple epithelial cell lines, NAD(P)H FLIM was also sensitive to inhibition of LDH and PDK, as well as the directionality of LDH in cells forced to use pyruvate versus lactate as fuel sources. Among the parameters measurable by FLIM, only the lifetime of protein-bound NAD(P)H (τ₂) was sensitive to these changes, in contrast to the optical redox ratio, mean NAD(P)H lifetime, free NAD(P)H lifetime, or the relative amount of free and protein-bound NAD(P)H. NAD(P)H τ₂ offers the ability to non-invasively quantify diversions of carbon away from the TCA cycle/ETC, which may support mechanisms of drug resistance.

Investigation of Mitochondrial Metabolic Response to Doxorubicin in Prostate Cancer Cells: An NADH, FAD and Tryptophan FLIM Assay

Prostate cancer (PCa) is one of the leading cancers in men in the USA. Lack of experimental tools that predict therapy response is one of the limitations of current therapeutic regimens. Mitochondrial dysfunctions including defective oxidative phosphorylation (OXPHOS) in cancer inhibit apoptosis by modulating ROS production and cellular signaling. Thus, correction of mitochondrial dysfunction and induction of apoptosis are promising strategies in cancer treatment. We have used Fluorescence Lifetime Imaging Microscopy (FLIM) to quantify mitochondrial metabolic response in PCa cells by tracking auto-fluorescent NAD(P)H, FAD and tryptophan (Trp) lifetimes and their enzyme-bound fractions as markers, before and after treatment with anti-cancer drug doxorubicin. A 3-channel FLIM assay and quantitative analysis of these markers for cellular metabolism show in response to doxorubicin, NAD(P)H mean fluorescence lifetime (τ_m) and enzyme-bound (a₂%) fraction increased, FAD enzyme-bound (a₁%) fraction was decreased, NAD(P)H-a₂%/FAD-a₁% FLIM-based redox ratio and ROS increased, followed by induction of apoptosis. For the first time, a FRET assay in PCa cells shows Trp-quenching due to Trp-NAD(P)H interactions, correlating energy transfer efficiencies (E%) vs NAD(P)H-a₂%/FAD-a₁% as sensitive parameters in predicting drug response. Applying this FLIM assay as early predictor of drug response would meet one of the important goals in cancer treatment.

NMR Metabolomics Show Evidence for Mitochondrial Oxidative Stress in a Mouse Model of Polycystic Ovary Syndrome

Polycystic ovary syndrome (PCOS) is associated with metabolic and endocrine disorders in women of reproductive age. The etiology of PCOS is still unknown. Mice prenatally treated with glucocorticoids exhibit metabolic disturbances that are similar to those seen in women with PCOS. We used an untargeted nuclear magnetic resonance (NMR)-based metabolomics approach to understand the metabolic changes occurring in the plasma and kidney over time in female glucocorticoid-treated (GC-treated) mice. There are significant changes in plasma amino acid levels (valine, tyrosine, and proline) and their intermediates (2-hydroxybutyrate, 4-aminobutyrate, and taurine), whereas in kidneys, the TCA cycle metabolism (citrate, fumarate, and succinate) and the pentose phosphate (PP) pathway products (inosine and uracil) are significantly altered (p < 0.05) from 8 to 16 weeks of age. Levels of NADH, NAD(+), NAD(+)/NADH, and NADH redox in kidneys indicate increased mitochondrial oxidative stress from 8 to 16 weeks in GC-treated mice. These results indicate that altered metabolic substrates in the plasma and kidneys of treated mice are associated with altered amino acid metabolism, increased cytoplasmic PP, and increased mitochondrial activity, leading to a more oxidized state. This study identifies biomarkers associated with metabolic dysfunction in kidney mitochondria of a prenatal gluococorticoid-treated mouse model of PCOS that may be used as early predictive biomarkers of oxidative stress in the PCOS metabolic disorder in women.

Detection of urinary bladder cancer cells using redox ratio and double excitation wavelengths autofluorescence

The optical redox ratio as a measure of cellular metabolism is determined by an altered ratio between endogenous fluorophores NADH and flavin adenine dinucleotide (FAD). Although reported for other cancer sites, differences in optical redox ratio between cancerous and normal urothelial cells have not previously been reported. Here, we report a method for the detection of cellular metabolic states using flow cytometry based on autofluorescence, and a statistically significant increase in the redox ratio of bladder cancer cells compared to healthy controls. Urinary bladder cancer and normal healthy urothelial cell lines were cultured and redox overview was assessed using flow cytometry. Further localisation of fluorescence in the same cells was carried out using confocal microscopy. Multiple experiments show correlation between cell type and redox ratio, clearly differentiating between healthy cells and cancer cells. Based on our preliminary results, therefore, we believe that this data contributes to current understanding of bladder tissue fluorescence and can inform the design of endoscopic probes. This approach also has significant potential as a diagnostic tool for discrimination of cancer cells among shed urothelial cells in voided urine, and could lay the groundwork for an automated system for population screening for bladder cancer.

Quantitative optical imaging of primary tumor organoid metabolism predicts drug response in breast cancer

There is a need for technologies to predict the efficacy of cancer treatment in individual patients. Here, we show that optical metabolic imaging of organoids derived from primary tumors can predict the therapeutic response of xenografts and measure antitumor drug responses in human tumor-derived organoids. Optical metabolic imaging quantifies the fluorescence intensity and lifetime of NADH and FAD, coenzymes of metabolism. As early as 24 hours after treatment with clinically relevant anticancer drugs, the optical metabolic imaging index of responsive organoids decreased (P < 0.001) and was further reduced when effective therapies were combined (P < 5 × 10(-6)), with no change in drug-resistant organoids. Drug response in xenograft-derived organoids was validated with tumor growth measurements in vivo and staining for proliferation and apoptosis. Heterogeneous cellular responses to drug treatment were also resolved in organoids. Optical metabolic imaging shows potential as a high-throughput screen to test the efficacy of a panel of drugs to select optimal drug combinations. Cancer Res; 74(18); 5184-94. ©2014 AACR.

Extraction of intrinsic fluorescence from single fiber fluorescence measurements on a turbid medium: experimental validation

The detailed mechanisms associated with the influence of scattering and absorption properties on the fluorescence intensity sampled by a single optical fiber have recently been elucidated based on Monte Carlo simulated data. Here we develop an experimental single fiber fluorescence (SFF) spectroscopy setup and validate the Monte Carlo data and semi-empirical model equation that describes the SFF signal as a function of scattering. We present a calibration procedure that corrects the SFF signal for all system-related, wavelength dependent transmission efficiencies to yield an absolute value of intrinsic fluorescence. The validity of the Monte Carlo data and semi-empirical model is demonstrated using a set of fluorescent phantoms with varying concentrations of Intralipid to vary the scattering properties, yielding a wide range of reduced scattering coefficients (μ's = 0-7 mm (-1)). We also introduce a small modification to the model to account for the case of μ's = 0 mm (-1) and show its relation to the experimental, simulated and theoretically calculated value of SFF intensity in the absence of scattering. Finally, we show that our method is also accurate in the presence of absorbers by performing measurements on phantoms containing red blood cells and correcting for their absorption properties.

Riboflavin carrier protein-targeted fluorescent USPIO for the assessment of vascular metabolism in tumors

Riboflavin (Rf) and its metabolic analogs flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD) are essential for normal cellular growth and function. Their intracellular transport is regulated by the riboflavin carrier protein (RCP), which has been shown to be over-expressed by metabolically active cancer cells. Therefore, FAD-decorated ultrasmall superparamagnetic iron oxide nanoparticles (FAD USPIO) were developed as the first carrier-protein-targeted molecular MR agents for visualizing tumor metabolism. FAD USPIO were synthesized using an adsorptive, fluorescent and non-polymeric coating method, and their physicochemical properties were characterized using TEM, SEM, FTIR, MRI and fluorescence spectroscopy. In vitro analyses showed the biocompatibility of FAD USPIO, and confirmed that they were strongly and specifically taken up by cancer (LnCap) and endothelial (HUVEC) cells. In vivo molecular MRI together with subsequent histological validation finally demonstrated that FAD USPIO efficiently accumulate in tumors and tumor blood vessels, indicating that RCP-targeted diagnostic nanoparticles are interesting new materials for the assessment of vascular metabolism in tumors.

Optical imaging using endogenous contrast to assess metabolic state

Optical microscopic imaging offers opportunities to perform noninvasive assessments of numerous parameters associated with the biochemistry, morphology, and functional state of biological samples. For example, it is possible to detect the endogenous fluorescence from a small number of important biomolecules, including NADH and FAD, which are two coenzymes involved in key metabolic pathways such as glycolysis, the Krebs cycle, and oxidative phosphorylation. Here, we review different imaging approaches to isolate the fluorescence from these chromophores in two- and three-dimensional samples and discuss the origins and potential interpretation of the observed signals in terms of cell metabolic status. Finally, we discuss the challenges and limitations of these approaches, as well as important research directions that we expect will evolve in the near future.

Assessing the contribution of cell body and intracellular organelles to the backward light scattering

We report a method of assessing the contribution of whole cell body and its nucleus to the clinically most relevant backward light scattering. We first construct an experimental system that can measure forward scattering and use the system to precisely extract the optical properties of a specimen such as the refractive index contrast, size distribution, and their density. A system that can simultaneously detect the backscattered light is installed to collect the backscattering for the same specimen. By comparing the measured backscattering spectrum with that estimated from the parameters determined by the forward scattering experiment, the contribution of cell body and nucleus to the backward light scattering is quantitatively assessed. For the HeLa cells in suspension, we found that the cell body contributes less than 10% and cell nucleus on the order of 0.1% to the total backscattering signal. Quantitative determination of the origin of backscattered light may help design a system that aims for detecting particular structure of biological tissues.

Optical imaging of metabolism in HER2 overexpressing breast cancer cells

The optical redox ratio (fluorescence intensity of NADH divided by that of FAD), was acquired for a panel of breast cancer cell lines to investigate how overexpression of human epidermal growth factor receptor 2 (HER2) affects tumor cell metabolism, and how tumor metabolism may be altered in response to clinically used HER2-targeted therapies. Confocal fluorescence microscopy was used to acquire NADH and FAD auto-fluorescent images. The optical redox ratio was highest in cells overexpressing HER2 and lowest in triple negative breast cancer (TNBC) cells, which lack HER2, progesterone receptor, and estrogen receptor (ER). The redox ratio in ER-positive/HER2-negative cells was higher than what was seen in TNBC cells, but lower than that in HER2 overexpressing cells. Importantly, inhibition of HER2 using trastuzumab significantly reduced the redox ratio in HER2 overexpressing cells. Furthermore, the combinatorial inhibition of HER2 and ER decreased the redox ratio in ER+/HER2+ breast cancer cells to a greater extent than inhibition of either receptor alone. Interestingly, trastuzumab had little impact upon the redox ratio in a cell line selected for acquired resistance to trastuzumab. Taken together, these data indicate that the optical redox ratio measures changes in tumor metabolism that reflect the oncogenic effects of HER2 activity within the cell, as well as the response of the cell to therapeutic inhibition of HER2. Therefore, optical redox imaging holds the promise of measuring response and resistance to receptor-targeted breast cancer therapies in real time, which could potentially impact clinical decisions and improve patient outcome.

Assessment of cell viability in three-dimensional scaffolds using cellular auto-fluorescence

After assessing cell viability (CV), tissue-engineered constructs are often discarded, as current CV assays commonly require specific (fluorescent) dyes to stain cells and may need scaffold/tissue digestion before quantifying the live and dead cells. Here, we demonstrate and evaluate how cellular auto-fluorescence can be exploited to facilitate a noninvasive CV estimation in three-dimensional scaffolds using two advanced microscopy methods. Mixtures of live and dead C2C12 myoblasts (0%, 25%, 50%, 75%, and 100% live cells) were prepared, and CV was determined before seeding cells into collagen carriers using the trypan blue (TB) assay. Cell-seeded collagen gels ([CSCGs], n=5/cell mixture) were produced by mixing collagen solution with the live/dead cell mixtures (7×10(6) cells/mL). After polymerization, two-photon microscopy (TPM) and confocal microscopy images of the CSCG were acquired (n=30 images/CSCG). It was found that live and dead cells systematically emit auto-fluorescent light with different spectral characteristics. Viable cells showed predominantly blue fluorescence with a peak emission around 470 nm, whereas dead cells appeared to mainly emit green fluorescent light with a peak intensity around 560 nm. For TPM, live and dead cells were distinguished spectrally. For confocal images, the intensity ratio of images taken with band-pass filters was used to distinguish live from dead cells. CV values obtained with both TPM and confocal imaging did not significantly differ from those acquired with the established TB method. In comparison to TPM, confocal microscopy was found to be less accurate in assessing the exact CV in constructs containing mostly live or dead cells. In summary, monitoring cellular auto-fluorescence using advanced microscopy techniques allows CV assessment requiring no additional dyes and/or scaffold digestion and, thus, may be especially suitable for tissue-engineering studies where CV is measured at multiple time points.

Automated biochemical, morphological, and organizational assessment of precancerous changes from endogenous two-photon fluorescence images

Background

Multi-photon fluorescence microscopy techniques allow for non-invasive interrogation of live samples in their native environment. These methods are particularly appealing for identifying pre-cancers because they are sensitive to the early changes that occur on the microscopic scale and can provide additional information not available using conventional screening techniques.

Methodology/Principal Findings

In this study, we developed novel automated approaches, which can be employed for the real-time analysis of two-photon fluorescence images, to non-invasively discriminate between normal and pre-cancerous/HPV-immortalized engineered tissues by concurrently assessing metabolic activity, morphology, organization, and keratin localization. Specifically, we found that the metabolic activity was significantly enhanced and more uniform throughout the depths of the HPV-immortalized epithelia, based on our extraction of the NADH and FAD fluorescence contributions. Furthermore, we were able to separate the keratin contribution from metabolic enzymes to improve the redox estimates and to use the keratin localization as a means to discriminate between tissue types. To assess morphology and organization, Fourier-based, power spectral density (PSD) approaches were employed. The nuclear size distribution throughout the epithelial depths was quantified by evaluating the variance of the corresponding spatial frequencies, which was found to be greater in the normal tissue compared to the HPV-immortalized tissues. The PSD was also used to calculate the Hurst parameter to identify the level of organization in the tissues, assuming a fractal model for the fluorescence intensity fluctuations within a field. We found the range of organization was greater in the normal tissue and closely related to the level of differentiation.

Conclusions/Significance

A wealth of complementary morphological, biochemical and organizational tissue parameters can be extracted from high resolution images that are acquired based entirely on endogenous sources of contrast. They are promising diagnostic parameters for the non-invasive identification of early cancerous changes and could improve significantly diagnosis and treatment for numerous patients.

Confocal backscattering spectroscopy for leukemic and normal blood cell discrimination

Leukemia is the most common pediatric cancer and leading cause of cancer related deaths in children. Improvements in the assessment of leukemic cells have the potential to influence not only the diagnosis of leukemia, but also the risk assessment of patients during the course of the treatment, both of which are important for improving the cure rate for this disease. In this study, we report on the design and performance of a confocal laser based system built to collect backscattered light over a range of 26° at 405, 488, and 633 nm to discriminate leukemic cells from normal red blood cells (RBC) and white blood cells (WBC). The design of the system is based on the spectral differences observed from spectroscopy measurements with a similar system designed with a white light source. Significant differences are observed in the intensity and wavelength dependence of leukemic cells from normal RBC and WBC. Specifically, the distinct light scattering of RBC is due to hemoglobin absorption, allowing for its discrimination from leukemic cells, mononuclear, and polymorphonuclear WBC particularly at certain wavelengths. Meanwhile, the high scattering intensities of polymorphonuclear WBC reflect the intracellular complexity of these cells in comparison to the leukemic or normal lymphocytes. Additionally, the detected light scattering spectra for leukemic cells are consistently steeper in comparison to normal WBC, which we attributed to differences in the fractal organization of intracellular scatterers. Based on our findings, the system has potential applications in the detection and quantification of leukemic cells in blood either in vivo or in vitro, using microfluidic-based systems, for disease monitoring.

Confocal backscattering-based detection of leukemic cells in flowing blood samples

The prognostic value of assessing minimal residual disease (MRD) in leukemia has been established with advancements in flow cytometry and PCR. Nonetheless, these techniques are limited by high equipment costs, complex, and costly cell processing and the need for highly trained personnel. Here, we demonstrate the potential of exploiting differences in the relative intensities of backscattered light at three wavelengths to detect the presence of leukemic cells in samples containing varying mixtures of white blood cells (WBCs) and leukemic cells flowing through microfluidic channels. Using 405, 488, and 633 nm illumination, we identify distinct light scattering intensity distributions for Nalm-6 leukemic cells, normal mononuclear (PBMC) and polymorphonuclear (PMN) white blood cells and red blood cells. We exploit these differences to develop cell classification algorithms, whose performance is evaluated based on simultaneous acquisition of light scattering and fluorescence flow cytometry data. When this algorithm is used prospectively for the analysis of samples consisting of mixtures of PBMCs and leukemic cells, we achieve an average specificity and sensitivity of leukemic cell detection of 99.6 and 45.2%, respectively. When we consider samples that include leukemic cells along with PMNs and PBMCs, which can be acquired using a simple red blood cell lysis step following venipuncture, the specificity and sensitivity of the approach decreases to 91.6 and 39.5%, respectively. On the basis of the performance of these algorithms, we estimate that 42 or 71 μL of blood would be adequate to confirm the presence of leukemia at an 80% power level in samples containing 0.01% leukemia to either PBMCs or PBMCs and PMNs, respectively. Therefore, light scattering-based flow cytometry in a microfluidic platform could provide a low cost, highly portable, minimally invasive approach for detection and monitoring of leukemic patients. This could offer significant improvements especially for pediatric patients and for patients in developing countries.

Noninvasive identification of subcellular organization and nuclear morphology features associated with leukemic cells using light-scattering spectroscopy

Leukemia is the most common and deadly cancer among children and one of the most prevalent cancers among adults. Improvements in its diagnosis and monitoring of leukemic patients could have a significant impact in their long-term treatment. We demonstrate that light-scattering spectroscopy (LSS)-based approaches could serve as a tool to achieve this goal. Specifically, we characterize the light scattering properties of leukemic (NALM-6) cells and compare them to those of normal lymphocytes and granulocytes in the 440-710 nm range, over ±4 deg about the exact backscattering direction. We find that the LSS spectra are well described by an inverse power-law wavelength dependence, with a power exponent insensitive to the scattering angle but significantly higher for leukemic cells than for normal leukocytes. This is consistent with differences in the subcellular morphology of these cells, detected in differential interference contrast images. Furthermore, the residual light-scattering signal, extracted after subtracting the inverse power-law fit from the data, can be analyzed assuming a Gaussian distribution of spherical scatterers using Mie theory. This analysis yields scatterer sizes that are consistent with the diameters of cell nuclei and allows the detection of the larger nuclei of NALM-6 cells compared to those of lymphocytes and granulocytes.

Compact point-detection fluorescence spectroscopy system for quantifying intrinsic fluorescence redox ratio in brain cancer diagnostics

We report the development of a compact point-detection fluorescence spectroscopy system and two data analysis methods to quantify the intrinsic fluorescence redox ratio and diagnose brain cancer in an orthotopic brain tumor rat model. Our system employs one compact cw diode laser (407 nm) to excite two primary endogenous fluorophores, reduced nicotinamide adenine dinucleotide, and flavin adenine dinucleotide. The spectra were first analyzed using a spectral filtering modulation method developed previously to derive the intrinsic fluorescence redox ratio, which has the advantages of insensitivity to optical coupling and rapid data acquisition and analysis. This method represents a convenient and rapid alternative for achieving intrinsic fluorescence-based redox measurements as compared to those complicated model-based methods. It is worth noting that the method can also extract total hemoglobin concentration at the same time but only if the emission path length of fluorescence light, which depends on the illumination and collection geometry of the optical probe, is long enough so that the effect of absorption on fluorescence intensity due to hemoglobin is significant. Then a multivariate method was used to statistically classify normal tissues and tumors. Although the first method offers quantitative tissue metabolism information, the second method provides high overall classification accuracy. The two methods provide complementary capabilities for understanding cancer development and noninvasively diagnosing brain cancer. The results of our study suggest that this portable system can be potentially used to demarcate the elusive boundary between a brain tumor and the surrounding normal tissue during surgical resection.

Intrinsic optical biomarkers associated with the invasive potential of tumor cells in engineered tissue models

This report assesses the ability of intrinsic two-photon excited fluorescence (TPEF) and second harmonic generation (SHG) imaging to characterize features associated with the motility and invasive potential of epithelial tumor cells engineered in tissues. Distinct patterns of organization are found both within the cells and the matrix that depend on the adhesive properties of the cells as well as factors attributed to adjacent fibroblasts. TPEF images are analyzed using automated algorithms that reveal unique features in subcellular organization and cell spacing that correlate with the invasive potential. We expect that such features have significant diagnostic potential for basic in vitro studies that aim to improve our understanding of cancer development or response to treatments, and, ultimately can be applied in prognostic evaluation.

Microscopic imaging and spectroscopy with scattered light

Optical contrast based on elastic scattering interactions between light and matter can be used to probe cellular structure, cellular dynamics, and image tissue architecture. The quantitative nature and high sensitivity of light scattering signals to subtle alterations in tissue morphology, as well as the ability to visualize unstained tissue in vivo, has recently generated significant interest in optical-scatter-based biosensing and imaging. Here we review the fundamental methodologies used to acquire and interpret optical scatter data. We report on recent findings in this field and present current advances in optical scatter techniques and computational methods. Cellular and tissue data enabled by current advances in optical scatter spectroscopy and imaging stand to impact a variety of biomedical applications including clinical tissue diagnosis, in vivo imaging, drug discovery, and basic cell biology.

Optical redox ratio differentiates breast cancer cell lines based on estrogen receptor status

Autofluorescence spectroscopy is a powerful imaging technique that exploits endogenous fluorophores. The endogenous fluorophores NADH and flavin adenine dinucleotide (FAD) are two of the principal electron donors and acceptors in cellular metabolism, respectively. The optical oxidation-reduction (redox) ratio is a measure of cellular metabolism and can be determined by the ratio of NADH/FAD. We hypothesized that there would be a significant difference in the optical redox ratio of normal mammary epithelial cells compared with breast tumor cell lines and that estrogen receptor (ER)-positive cells would have a higher redox ratio than ER-negative cells. To test our hypothesis, the optical redox ratio was determined by collecting the fluorescence emission for NADH and FAD via confocal microscopy. We observed a statistically significant increase in the optical redox ratio of cancer compared with normal cell lines (P < 0.05). Additionally, we observed a statistically significant increase in the optical redox ratio of ER(+) breast cancer cell lines. The level of ESR1 expression, determined by real-time PCR, directly correlated with the optical redox ratio (Pearson's correlation coefficient = 0.8122, P = 0.0024). Furthermore, treatment with tamoxifen and ICI 182,870 statistically decreased the optical redox ratio of only ER(+) breast cancer cell lines. The results of this study raise the important possibility that fluorescence spectroscopy can be used to identify subtypes of breast cancer based on receptor status, monitor response to therapy, or potentially predict response to therapy. This source of optical contrast could be a potentially useful tool for drug screening in preclinical models.

Investigating the spectral characteristics of backscattering from heterogeneous spherical nuclei using broadband finite-difference time-domain simulations

Reflectance spectra measured from epithelial tissue have been used to extract size distribution and refractive index of cell nuclei for noninvasive detection of precancerous changes. Despite many in vitro and in vivo experimental results, the underlying mechanism of sizing nuclei based on modeling nuclei as homogeneous spheres and fitting the measured data with Mie theory has not been fully explored. We describe the implementation of a three-dimensional finite-difference time-domain (FDTD) simulation tool using a Gaussian pulse as the light source to investigate the wavelength-dependent characteristics of backscattered light from a nuclear model consisting of a nucleolus and clumps of chromatin embedded in homogeneous nucleoplasm. The results show that small-sized heterogeneities within the nuclei generate about five times higher backscattering than homogeneous spheres. More interestingly, backscattering spectra from heterogeneous spherical nuclei show periodic oscillations similar to those from homogeneous spheres, leading to high accuracy of estimating the nuclear diameter by comparison with Mie theory. In addition to the application in light scattering spectroscopy, the reported FDTD method could be adapted to study the relations between measured spectral data and nuclear structures in other optical imaging and spectroscopic techniques for in vivo diagnosis.

In vivo native fluorescence spectroscopy and nicotinamide adinine dinucleotide/flavin adenine dinucleotide reduction and oxidation states of oral submucous fibrosis for chemopreventive drug monitoring

Native fluorescence spectroscopy has shown potential to characterize and diagnose oral malignancy. We aim at extending the native fluorescence spectroscopy technique to characterize normal and oral submucous fibrosis (OSF) patients under pre- and post-treated conditions, and verify whether this method could also be considered in the monitoring of therapeutic prognosis noninvasively. In this study, 28 normal subjects and 28 clinically proven cases of OSF in the age group of 20 to 40 years are diagnosed using native fluorescence spectroscopy. The OSF patients are given dexamethasone sodium phosphate and hyaluronidase twice a week for 6 weeks, and the therapeutic response is monitored using fluorescence spectroscopy. The fluorescence emission spectra of normal and OSF cases of both pre- and post-treated conditions are recorded in the wavelength region of 350 to 600 nm at an excitation wavelength of 330 nm. The statistical significance is verified using discriminant analysis. The oxidation-reduction ratio of the tissue is also calculated using the fluorescence emission intensities of flavin adenine dinucleotide and nicotinamide adinine dinucleotide at 530 and 440 nm, respectively, and they are compared with conventional physical clinical examinations. This study suggests that native fluorescence spectroscopy could also be extended to OSF diagnosis and therapeutic prognosis.

Assessing light scattering of intracellular organelles in single intact living cells

This report presents a model-independent method of assessing contributions to the light scattering from individual organelles in single intact cells. We first measure the 3D index map of a living cell, and then modify the map in such a way so as to eliminate contrast due to a particular intracellular organelle. By calculating and comparing the light scattering distributions calculated from the original and modified index maps using the Rytov approximation, we extract the light scattering contribution from the particular organelle of interest. The relative contributions of the nucleus and nucleolus to the scattering of the entire cell are thus determined, and the applicability of the homogeneous spherical model to non-spherical and heterogeneous organelles in forward scattering is evaluated.

Optical spectroscopy and imaging for the noninvasive evaluation of engineered tissues

Optical spectroscopy and imaging approaches offer the potential to noninvasively assess different aspects of the cellular, extracellular matrix, and scaffold components of engineered tissues. In addition, the combination of multiple imaging modalities within a single instrument is highly feasible, allowing acquisition of complementary information related to the structure, organization, biochemistry, and physiology of the sample. The ability to characterize and monitor the dynamic interactions that take place as engineered tissues develop promises to enhance our understanding of the interdependence of processes that ultimately leads to functional tissue outcomes. It is expected that this information will impact significantly upon our abilities to optimize the design of biomaterial scaffolds, bioreactors, and cell systems. Here, we review the principles and performance characteristics of the main methodologies that have been exploited thus far, and we present examples of corresponding tissue engineering studies.

Confocal light scattering spectroscopic imaging system for in situ tissue characterization

We report on the design and construction of a confocal light scattering spectroscopic imaging system aimed ultimately to conduct depth-resolved characterization of biological tissues. The confocal sectioning ability of the system is demonstrated using a two-layer sample consisting of a 200 microm thick cancer cell layer on top of a scattering layer doped with a green absorber. The measurement results demonstrate that distinct light scattering signals can be isolated from each layer with an axial and a lateral resolution of 30 and 27 microm, respectively. Such a system is expected to have significant applications in the areas of tissue engineering and disease diagnostics and monitoring.

Two-photon autofluorescence microscopy of multicolor excitation

We developed a two-photon autofluorescence lifetime imaging system with excitations selected from the supercontinuum generated from a photonic crystal fiber. The system excites multiple endogenous fluorophores, such as nicotinamide adenine dinucleotide (NADH) and tryptophan, simultaneously and produces coregistered two-photon autofluorescence images of a biological sample. The technology provides a unique approach to investigate the cellular metabolic activity and protein expression in cells that are potentially important for noninvasive precancer diagnostics. We demonstrated that by taking the tryptophan fluorescence as a reference the ratio of NADH to the tryptophan signal serves as a sensitive indicator of cellular metabolism. The ratio can also clearly differentiate normal cells from cancer cells. The tryptophan fluorescence lifetime images of cells shows that the lifetime of tryptophan fluorescence, varying over a wide range, may be highly dependent on the expression and structure of the protein that tryptophan is packed in.

Measuring mucosal blood supply in vivo with a polarization-gating probe

There has been significant interest in developing depth-selective optical interrogation of biological tissue in general and of superficial (e.g., mucosal) tissue in particular. We report an in vivo polarization-gating fiber-optic probe that obtains backscattering spectroscopic measurements from a range of near-surface depths (100-200 microm). The design and testing was performed with polarized light Monte Carlo simulations and in tissue model experiments. We used the probe to investigate mucosal changes in early carcinogenesis. Measurements performed in the colonic mucosa of 125 human subjects provide the first in vivo evidence that mucosal blood supply is increased early in carcinogenesis, not only in precancerous adenomatous lesions, but also in the histologically normal-appearing tissue surrounding these lesions. This effect was primarily limited to the mucosal microcirculation and was not present in the larger blood vessels located deeper in colonic tissue.

Optical imaging for cervical cancer detection: solutions for a continuing global problem

Cervical cancer is the leading cause of cancer death for women in developing countries. Optical technologies can improve the accuracy and availability of cervical cancer screening. For example, battery-powered digital cameras can obtain multi-spectral images of the entire cervix, highlighting suspicious areas, and high-resolution optical technologies can further interrogate such areas, providing in vivo diagnosis with high sensitivity and specificity. In addition, targeted contrast agents can highlight changes in biomarkers of cervical neoplasia. Such advances should provide a much needed global approach to cervical cancer prevention.