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Rationale for the real-time and dynamic cell death assays using propidium iodide.

ABSTRACT: We have recently reported an innovative approach to use charged fluorochromes such as propidium iodide (PI) in the real-time, dynamic cell viability assays. This study was designed to provide a mechanistic rationale for the kinetic assays using cell permeability markers. Uptake of PI by live cells, effect on the cell cycle, long-term proliferation capacity, DNA damage response, and pharmacologic interactions with anticancer drugs were studied using both laser scanning microscopy and laser scanning cytometry. Exposure of human carcinomic alveolar basal epithelial A549 cells in cultures to 1.5 or 7.5 microM of PI for 24 h had minimal effect on cell cycle progression including DNA replication as measured by incorporation of 5'-ethynyl-2-deoxyuridine (EdU) detected by the "click chemistry" approach and measured by laser scanning cytometry. A modest reduction, from 44 to 40% or 33%, in frequency of DNA replicating cells was seen after 48 h at 1.5 or 7.5 microM concentration of PI. There was no evidence of increased phosphorylation of histone gammaH2AX in cells growing in the presence of 1.5 or 7.5 microM of PI for up to 48 h. Confocal image analysis of HeLa and NIH 3T3 mouse embryonic fibroblasts growing in the presence of PI showed granular distribution in cell cytoplasm suggesting PI accumulation in endosomes and progressive increase in fluorescence of nucleoli reflecting PI binding to nucleolar RNA. The overall responses of cells to cytotoxic agents were also not affected by the growth in the presence PI. Our data lend further support to the notion that PI can be effectively used in real-time, kinetic viability assays.

SUBMITTER: Zhao H

PROVIDER: S-EPMC3646415 | biostudies-literature | 2010 Apr

REPOSITORIES: biostudies-literature

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Rationale for the real-time and dynamic cell death assays using propidium iodide.

Zhao Hong H Oczos Jadwiga J Janowski Pawel P Trembecka Dominika D Dobrucki Jurek J Darzynkiewicz Zbigniew Z Wlodkowic Donald D

Cytometry. Part A : the journal of the International Society for Analytical Cytology 20100401 4

We have recently reported an innovative approach to use charged fluorochromes such as propidium iodide (PI) in the real-time, dynamic cell viability assays. This study was designed to provide a mechanistic rationale for the kinetic assays using cell permeability markers. Uptake of PI by live cells, effect on the cell cycle, long-term proliferation capacity, DNA damage response, and pharmacologic interactions with anticancer drugs were studied using both laser scanning microscopy and laser scanni ...[more]

PMID: 20131407

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Project description:A growing understanding of the molecular interactions between immune effector cells and target tumor cells, coupled with refined gene therapy approaches, are giving rise to novel cancer immunotherapeutics with remarkable efficacy in the clinic against both solid and liquid tumors. While immunotherapy holds tremendous promise for treatment of certain cancers, significant challenges remain in the clinical translation to many other types of cancers and also in minimizing adverse effects. Therefore, there is an urgent need for functional potency assays, in vitro and in vivo, that could model the complex interaction of immune cells with tumor cells and can be used to rapidly test the efficacy of different immunotherapy approaches, whether it is small molecule, biologics, cell therapies or combinations thereof. Herein we report the development of an xCELLigence real-time cytolytic in vitro potency assay that uses cellular impedance to continuously monitor the viability of target tumor cells while they are being subjected to different types of treatments. Specialized microtiter plates containing integrated gold microelectrodes enable the number, size, and surface attachment strength of adherent target tumor cells to be selectively monitored within a heterogeneous mixture that includes effector cells, antibodies, small molecules, etc. Through surface-tethering approach, the killing of liquid cancers can also be monitored. Using NK92 effector cells as example, results from RTCA potency assay are very well correlated with end point data from image-based assays as well as flow cytometry. Several effector cells, i.e., PBMC, NK, CAR-T were tested and validated as well as biological molecules such as Bi-specific T cell Engagers (BiTEs) targeting the EpCAM protein expressed on tumor cells and blocking antibodies against the immune checkpoint inhibitor PD-1. Using the specifically designed xCELLigence immunotherapy software, quantitative parameters such as KT50 (the amount of time it takes to kill 50% of the target tumor cells) and % cytolysis are calculated and used for comparing the relative efficacy of different reagents. In summary, our results demonstrate the xCELLigence platform to be well suited for potency assays, providing quantitative assessment with high reproducibility and a greatly simplified work flow.

Project description:BACKGROUND: Cell viability and motility comprise ubiquitous mechanisms involved in a variety of (patho)biological processes including cancer. We report a technical comparative analysis of the novel impedance-based xCELLigence Real-Time Cell Analysis detection platform, with conventional label-based endpoint methods, hereby indicating performance characteristics and correlating dynamic observations of cell proliferation, cytotoxicity, migration and invasion on cancer cells in highly standardized experimental conditions. METHODOLOGY/PRINCIPAL FINDINGS: Dynamic high-resolution assessments of proliferation, cytotoxicity and migration were performed using xCELLigence technology on the MDA-MB-231 (breast cancer) and A549 (lung cancer) cell lines. Proliferation kinetics were compared with the Sulforhodamine B (SRB) assay in a series of four cell concentrations, yielding fair to good correlations (Spearman's Rho 0.688 to 0.964). Cytotoxic action by paclitaxel (0-100 nM) correlated well with SRB (Rho>0.95) with similar IC(50) values. Reference cell migration experiments were performed using Transwell plates and correlated by pixel area calculation of crystal violet-stained membranes (Rho 0.90) and optical density (OD) measurement of extracted dye (Rho>0.95). Invasion was observed on MDA-MB-231 cells alone using Matrigel-coated Transwells as standard reference method and correlated by OD reading for two Matrigel densities (Rho>0.95). Variance component analysis revealed increased variances associated with impedance-based detection of migration and invasion, potentially caused by the sensitive nature of this method. CONCLUSIONS/SIGNIFICANCE: The xCELLigence RTCA technology provides an accurate platform for non-invasive detection of cell viability and motility. The strong correlations with conventional methods imply a similar observation of cell behavior and interchangeability with other systems, illustrated by the highly correlating kinetic invasion profiles on different platforms applying only adapted matrix surface densities. The increased sensitivity however implies standardized experimental conditions to minimize technical-induced variance.

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Rationale for the real-time and dynamic cell death assays using propidium iodide.

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Rationale for the real-time and dynamic cell death assays using propidium iodide.

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