Cell health and stress readouts are critical indicators of altered or impaired function in normal and diseased states of cells, and work has been underway to develop improved small molecule sensor dyes compatible with traditional imaging and High Content Analysis (HCA) interrogation of apoptotic and mitochondrial stress pathways. The CellEvent™ Caspase Green dye effectively reports caspase activation, but suffers complications in assay configuration when attempting to multiplex with the Green Fluorescent Protein (GFP), calcein, or other 488 laser line tools in fluorescence microscopy. Here, we describe the testing and functional characterization of a new candidate molecule for measuring apoptosis in living cells. Our sensor is comprised of a fluorogenic reporter dye that is liberated from a DEVD peptide substrate by caspase activation, but operates in the Texas Red, 590nm excitation band, with an emission peak near 610 nm, permitting easy multiplex with GFP or calcein stained neurons in both traditional and HCA microscopy configurations. Similarly, mitochondrial superoxide accompanying cell stress is probed in microscopy with the MitoSOX™ Red Mitochondrial Superoxide Indicator dye, which localizes to mitochondria and reports superoxide generation, ignoring other Reactive Oxygen Species (ROS) and Reactive Nitrogen Species (RNS). This dye has an unusually long Stokes’ shift, requiring specialized microscopy and HCA filters that excite at 405nm, and capture emission at 610nm for specific superoxide detection. This unconventional spectroscopic profile prevents the dye’s use on many imaging platforms and promotes phototoxicity. To this end, our team has produced a dye with the same level of specificity for superoxide that will operate in one of the traditional fluorescence microscopy channels. Our candidate dye, here named MitoSOX™ Green Mitochondrial Superoxide Indicator also localizes to mitochondria of live cells and selectively reports superoxide generation, while ignoring other ROS and RNS species in ex vivo testing. With an Excitation/Emission profile in the GFP/FITC microscopy channel, a series of comparative studies in immortalized and neural cells are shown, highlighting photostability, specificity and signal amplitude from the dye. These reagents are research use only, not for diagnostic purposes Citation Format: Bhaskar S. Mandavilli, Daniel Beacham, Yi Zhen Hu, Jongtae Yang, Aimei Chen. New generation of fluorescent probes for cell-based measurements of caspase activation and mitochondrial superoxide. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 4781.

Oxysterols, oxidized derivatives of cholesterol found in LDL and atherosclerotic plaques, trigger several biological responses involved in the initiation and progression of atherosclerosis. Endothelial dysfunction, which occurs when vascular homeostasis is altered, plays a key role in the pathogenesis of several metabolic diseases. The contribution of endoplasmic reticulum (ER) stress to endothelial disfunction is a relatively recent area of investigation. There is a well-established link between LDL oxidation and ER stress but the role played by specific products of lipid oxidation into this interaction is still to be defined. The present study shows that secosterol-B (SEC-B), 3β-hydroxy-5β-hydroxy-B-norcholestane-6βcarboxaldehyde, a cholesterol autoxidation product recently identified in the atherosclerotic plaque, is able to induce ER stress in HUVEC cells, as revealed by significant expansion and change of structure.At low doses, i.e. 1 and 5 μM, cells try to cope with this stress by activating autophagy and the ubiquitin proteasome system in the attempt to restore ER function. However, at higher doses, i.e. 20 μM, cell apoptosis occurs in a pathway that involves early phosphorylation of eIF2α and NF-kB activation, suggesting that the adaptive program fails and the cell activates the apoptotic program. These findings provide additional insight about the role of oxysterols in endothelial dysfunction and its potential involvement in atherosclerotic pathophysiology.

3-dimensional tumor spheroids provide biochemical conditions that closely resemble the tumor microenvironment in an intact organism. Noninvasive approaches such as fluorescence microscopy and high content analysis are highly advantageous as they allow for the study of these 3-dimensional systems. Here we investigate the penetration and potency of natural killer cells, cytotoxic T cells, and antibody‐drug conjugates in three‐dimensional models of breast and lung cancer. Unstimulated T cells produced minimal cytotoxicity, similar to untreated spheroids. Activated T cells penetrated and produced significant cytotoxicity throughout cancer spheroids. SKBR3 breast cancer cells form a compact, viable spheroid. Addition of NK cells leads to moderate cytotoxicity, while addition of NK cells and trastuzumab results in substantial cytotoxicity and degradation of spheroid structure. Trastuzumab labeled with iFL pHrodo Red becomes brightly fluorescent following specific endosomal internalization into breast cancer cells, but minimal toxicity is observed. Trastuzumab conjugated with both iFL pHrodo Red and MMAE internalizes into cells and results in cell killing. Fluorescence microscopy combined with novel cell and antibody labeling methods permits investigation of the penetration and potency of natural killer cells, cytotoxic T cells, and antibody‐drug conjugates in three‐dimensional solid tumor models.Citation Format: Bhaskar S. Mandavilli, Chris Langsdorf, Aimei Chen, Yi-Zhen Hu, Marcy Wickett, Scott T. Clark. Evaluating cellular cytotoxicity and potency of antibody-drug conjugates within 3-dimensional tumor models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 123.

Automated quantitative fluorescence microscopy, also known as high content imaging (HCI), is a rapidly growing analytical approach in cell biology. Because automated image analysis relies heavily on robust demarcation of cells and subcellular regions, reliable methods for labeling cells is a critical component of the HCI workflow. Labeling of cells for image segmentation is typically performed with fluorescent probes that bind DNA for nuclear-based cell demarcation or with those which react with proteins for image analysis based on whole cell staining. These reagents, along with instrument and software settings, play an important role in the successful segmentation of cells in a population for automated and quantitative image analysis. In this chapter, we describe standard procedures for labeling and image segmentation in both live and fixed cell samples. The chapter will also provide troubleshooting guidelines for some of the common problems associated with these aspects of HCI.

Immunoglobulin antibodies contribute to a broad range of research assays and also provide the foundation for a diverse variety of biopharmaceutical agents. Here we describe the use of bio-orthogonal click chemistry reactions to synthesize several common antibody-based structures and demonstrate their use in cell-based applications. First, defined antibody-fluorophore conjugates were synthesized, characterized and functionally tested in receptor occupancy and antibody internalization assays. Next, a double conjugation strategy was employed to synthesize antibody drug conjugates which become brightly fluorescent upon endocytosis. ADC uptake and targeted cell killing were demonstrated using cell line and spheroid models. Then bispecific antibodies were constructed using a click chemistry reaction to create tetravalent heterodimeric antibodies. Structure and function of these bispecific constructs are demonstrated in cell-free and flow cytometry assays.

High content imaging-based cell cycle analysis allows multiplexing of various parameters including DNA content, DNA synthesis, cell proliferation, and other cell cycle markers such as phosho-histone H3. 5'-Ethynyl-2'-deoxyuridine (EdU) incorporation is a thymidine analog that provides a sensitive method for the detection of DNA synthesis in proliferating cells that is a more convenient method than the traditional BrdU detection by antibody. Caspase 3 is activated in programmed cell death induced by both intrinsic (mitochondrial) and extrinsic factors (death ligand). Cell cycle and apoptosis are common parameters studied in the phenotypic analysis of compound toxicity and anti-cancer drugs. In this chapter, we describe methods for the detection of s-phase cell cycle progression by EdU incorporation, and caspase 3 activation using the CellEvent caspase 3/7 detection reagent.

Hypoxia is a condition where low levels of oxygen levels are present (1% to 2% O2). Hypoxia play a wide role in physiological and pathological conditions, from developmental angiogenesis to tumor progression and evasion. Hypoxia also modulates a number of immune functions from promoting inflammation to suppressing adaptive immunity. The current method for detecting hypoxic cells relies on an immunochemical approach. Pimonidazole react with peptide thiols in hypoxic cells and the resulting adduct is detected with an anti-pimonidazole antibody. To increase the availability of hypoxia detection reagents, we have developed a rhodamine-based hypoxia reagent (HR) for live cells. Using Jurkat leukemia cells incubated in hypoxic or normoxic conditions and stained with HR, we were able to clearly distinguish hypoxic cells from normoxic cells on a flow cytometer. We were also able to resolve cells incubated at differing levels of O2 (10%, 5% and 2.5% O2). To demonstrate that HR is compatible with other reagents, hypoxic cells were co-stained with a viability dye (SYTOX Red), a dye retained in intact mitochondria (TMRM) and with staining for a marker of apoptosis (annexin V). The results show that hypoxic cells excluded the dead cells dye while retaining TMRM, and were negative for annexin V staining at early time points. As expected, prolong incubation at hypoxia resulted in dead and apoptotic cells as evident in an increase in dead cells staining, a loss of mitochondrial integrity and an increase in annexin V+ cells. In summary, we present a sensitive reagent for detecting hypoxic cells without the need for cellular fixation and permeablization, while retaining it usage with other live cell flow cytometry detection reagents.

Macroautophagy, hereafter referred to as autophagy, is a predominately pro-survival catabolic process responsible for the degradation of long-lived or aggregated proteins, invading microorganisms and damaged or redundant intracellular organelles. Removal of these entities is achieved through encompassment of the target by the autophagosome and subsequent delivery to the lysosome. The use of fluorescence microscopy is a common method to investigate autophagy through monitoring the spatial and temporal recruitment both of autophagosomal markers and cargo to the autophagosome. In this section, we will discuss the use of high content imaging (HCI) and analysis in the study of autophagy with reference to commonly used markers of autophagosomal formation.

High content screening (HCS)-based multiparametric measurements are very useful in early toxicity testing and safety assessment during drug development, and useful in evaluating the impact from new food supplements and environmental toxicants. Mitochondrial membrane potential, plasma membrane permeability, oxidative stress, phosphoplipidosis, and steatosis are a few of the important markers routinely studied for the assessment of drug-induced liver injury and toxicity. Mitochondrial dysfunction leads to oxidative stress and cell death. Liver injury from drug-induced phospholipidosis and steatosis is routinely studied in hepatotoxicity investigations to determine the risk factors and fate of drugs or chemical compounds as some drugs can lead to defects in lipid metabolism and accumulation of lipids in lysosomes. In this chapter, we describe fluorescent reagents and the protocols for the measurement of various parameters such as mitochondrial membrane potential, plasma membrane permeability, oxidative stress, phospholipidosis, and steatosis using high content imaging-based methodologies and instrumentation.

Abstract Hypoxia is an important phenomenon in many physiological processes and involved in many human diseases including cancer. Inflammation can lead to significant hypoxia in tissues. The study of hypoxia has been complicated with the lack of proper instrumentation to induce hypoxia in cells and image cells under hypoxic conditions. Here, we describe a live cell-based method to conveniently measure hypoxia using a new Image-iT® Hypoxia Probe and a specialized microscope incubator which can control oxygen concentrations down to 1%, The Image-iT® Hypoxia Probe is an oxygen sensing fluorescent probe, is quenched with increasing oxygen concentrations, and has excitation and emission peaks of 483 and 616 nm respectively. The probe is sensitive to varying concentrations of oxygen and can detect as low as 1% O2 concentrations in cells. Imaging of cells with the Image-iT® Hypoxia Probe in the incubator prevents re-oxygenation of cells and gives more precise measurement of hypoxia in cells, allowing for reversible and dynamic measurements of hypoxia in cells. Using this system, we measured hypoxia in several cell lines including A549, HeLa and U-2 OS. The Image-iT® Hypoxia Probe is also very good at detecting hypoxia in 3D tumor spheroids generated using different methods. The new hypoxia probe gives good signal to noise with more than 3-fold changes at 5% O2 levels with robust statistics. The Image-iT® Hypoxia Probe provides a good system for precise, robust and reproducible measurements of hypoxia in cells. Citation Format: Bhaskar S. Mandavilli, Michael O'Grady. Intracellular detection of hypoxia in live cells. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 3007. doi:10.1158/1538-7445.AM2015-3007

Mitophagy is a specialized form of autophagy that removes damaged mitochondria, thereby maintaining efficient cellular metabolism and reducing cellular stress caused by aberrant oxidative bursts. Deficits in mitophagy underlie several diseases, and a substantial body of research has elucidated key steps in the pathways that lead to and execute autophagic clearance of mitochondria. Many of these studies employ fluorescence microscopy to visualize mitochondrial morphology, mass, and functional state. Studies in this area also examine colocalization/recruitment of accessory factors, components of the autophagic machinery and signaling molecules to mitochondria. In this review, we provide a brief summary of the current understanding about the processes involved in mitophagy followed by a discussion of probes commonly employed and important considerations of the methodologies to study and analyze mitophagy using fluorescence microscopy. Representative data, where appropriate, are provided to highlight the use of key probes to monitor mitophagy. The review will conclude with a consideration of new possibilities for mitophagy research and a discussion of recently developed technologies for this emerging area of cell biology.

Cell death can occur through multiple pathways, such as apoptosis, autophagy, and necrosis. Although necessary for proper growth and development, dysregulation of apoptosis has been associated with a variety of diseases including cancer and neurodegenerative disorders. Increased oxidative stress has also been associated with these diseases and has been shown to lead to cell death. Cell death can occur through a single pathway, or in concert involving multiple pathways. The goal of this study was to utilize multi‐parametric fluorescence microscopy to examine temporal characteristics of cell death after induction by various agonists. Using a fluorogenic caspase substrate in combination with a probe for oxidative stress, we observed that increased oxidative stress was followed by caspase activation after induction by several agonists. By simultaneously examining multiple parameters over time we were able to define the temporal progression of apoptosis relative to the onset of oxidative stress. Moreover, we were able to further characterize the mechanism of cell death by discriminating between cells which were apoptotic (active caspase‐3/7), autophagic (LC3B‐postive autophagosomes), or both. This multi‐parametric approach provided detailed information at the cellular level so that correlations and temporal resolution could be determined between oxidative stress and cell death mechanisms.

Abstract Oxidative stress plays an important role in the progression of several diseases including inflammation, atherosclerosis, aging and age-related degenerative disorders. Reactive oxygen species damage membrane bound lipids resulting in lipid peroxidation-derived protein modifications. Cell-based measurements of oxidative stress, lipid peroxidation and protein carbonylation by traditional fluorescence microscopy provide a powerful platform to quantitate oxidative stress and lipid peroxidation. Here, we used three different approaches to measure oxidative stress and lipid peroxidation in cells by fluorescence microscopy. 1) Two new fluorogenic probes, CellROX™ Orange and CellROX ™ Green Reagents to measure oxidative stress in cells, 2) Image-iT® Lipid Peroxidation Kit for a ratiometric determination of lipid peroxidation in live cells 3) Click-iT® Lipid Peroxidation Imaging Kit, a click chemistry-based approach which utilizes incorporation of an alkyne-modified unsaturated fatty acid analog, linoleamide, into the cellular membranes. The resulting oxidation products, like 9, 12-dioxo-10(E) dodecenoic acid (DODE) can readily modify proteins and these modifications were readily detected in fixed cells by the copper-catalyzed click reaction using fluorescent azides. Using these approaches, we measured oxidative stress and lipid peroxidation caused by several oxidants in cells. Increases in oxidative stress, lipid peroxidation, and protein modifications were assessed by high content imaging and analysis as well as traditional fluorescence microscopy. In the models tested, at least 2-3 fold increases were observed compared to controls was and responses were successfully inhibited by antioxidants. The three strategies described here provide powerful new tools for the assessment of oxidative stress in cells and convey distinct advantages over existing cell-based methods. Citation Format: Bhaskar S. Mandavilli, Robert Aggeler. Cell-based analysis of oxidative stress, lipid peroxidation and lipid peroxidation-derived protein modifications using fluorescence microscopy. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 512. doi:10.1158/1538-7445.AM2014-512