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Measurement of Compound-Induced Cytotoxicity with Roche's xCELLigence Real-Time Cell Analysis System
Viability and cytotoxicity assays are routinely used to determine how various treatments potentially perturb cell homeostasis leading to decreased viability and increased cytotoxicity. Many agents used for cancer therapeutics modulate the intricate balance between cell proliferation and cell death. The ultimate aim of cancer therapy is to reduce or eliminate cancerous cells in the body, thus shifting the balance by either increasing cell death or decreasing cell proliferation.
In a recent study (1) of Ning Ke and Yama Abassi of ACEA Bioscience in San Diego, Roche's (SIX: RO, ROG; OTCQX: RHHBY) xCELLigence System had been used for studying cell viability and cell death when testing various cytotoxic compounds. Realtime impedancebased cell analyzers, such as the RTCA SP Instrument and E-Plate 96, could identify the onset of cytotoxicity using continuous impedancebased monitoring of cell viability, pinpointing when maximal effects occur. Furthermore, the instrument identified the best time point, i.e., when CI values are at their lowest, for conducting functional endpoint assays that examine cell fate transitions, such as apoptosis and cell cycling, in greater detail. The xCELLigence System also proved to be suitable for identifying culture wells with inappropriate cell numbers at the beginning of the assay, thus minimizing the role of cell seeding and culture plate edge artifacts during data analysis.
Cell death occurs through a spectrum of distinct morphological and biochemical pathways culminating in apoptosis, necrosis and autophagy. It is important to understand the different modes of cell death mediated by cytotoxic agents to decipher the mechanisms of drug action and identify significant side effects. The direct effect of compound treatment on cell death is often transient and difficult to capture using standard endpoint assays. For example, apoptosis occurs only during a short window of time, often within just hours, and is frequently followed by secondary necrotic events. It is therefore crucial to conduct relevant assays, measuring either cell viability or cell death, at the optimal experimental time points. Considering that the kinetics of cell killing is likely to be different for different compounds, it is important to monitor cell viability and toxicity continuously, to pinpoint the optimal time points for conducting endpoint assays and to gain the necessary mechanistic information.
The xCELLigence System allows for realtime, labelfree and dynamic monitoring of cellular phenotypic changes by measuring electrical impedance. The system measures impedance using interdigitated microelectrodes integrated into the bottom of each well of the tissue culture E-Plates 96. Impedance measurements are displayed as Cell Index (CI) values, providing quantitative information about the biological status of the cells, including cell number, cell viability and cell morphology. Impedancebased monitoring of cell viability correlates to cell number and MTTbased readout. The kinetic aspect of impedancebased cell viability measurements provides the necessary temporal information, for instance, when compounds of interest are used to induce cytotoxic effects. In particular, the xCELLigence System is ideal for pinpointing optimum time points, i.e., when cytotoxic compounds achieve their maximum effect, as indicated by the lowest CI values in cytotoxicity and cell death assays.
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