Cell Proliferation Assays

Cell proliferation assays are valuable tools with a wide range of applications in cell biology and drug-discovery research. They are commonly used to assess normal cell heath and are essential for evaluating the antiproliferative potency and compound toxicity of novel chemotherapeutic agents. AAT Bioquest offers several strategies for assessing cell proliferation based on tracking generations of cell division or monitoring critical parameters of cell health, including metabolic activity, DNA synthesis, or ATP concentration. Select from a broad range of traditional colorimetric reagents for determining cell proliferation, in particular tetrazolium salts, and several highly sensitive fluorescent-based assays for flow cytometry, imaging, and microplate applications.

Selecting the Right Cell Proliferation Assay

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The most accurate method for assaying cell proliferation is to measure newly synthesized DNA via BrdU (5-bromo-2'-deoxyuridine) incorporation during DNA replication. Although highly accurate and reproducible, this method can be rather tedious as subsequent detection with fluorescent anti-BrdU antibodies is necessary to measure proliferation. Alternatively, cell proliferation can be assessed more rapidly by measuring the rate of metabolic activity with WST, resazurin, or cellular esterase cleaved dyes or tracking generations of cell division with CytoTell™ dyes or CFSE. Ultimately, selecting the cell proliferation assay best suited for your purpose depends mainly upon cell type, research protocol, and the action mechanism you wish to study. The following table provides an overview of the types of cell proliferation assays available.

DNA Synthesis Cell Proliferation Assays

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Measuring newly synthesized DNA in situ is the most reliable and precise method for identifying proliferating cells. One way to accomplish this involves incorporating the thymidine analog, BrdU (17030), into newly replicated DNA during the S phase of the cell cycle. Proliferating BrdU-labeled cells can then be measured using fluorescently labeled anti-BrdU antibodies. BrdU staining is suitable for various applications, including IHC, ICC, and ELISA, and is amenable to staining with other biomarkers of interest in flow cytometry. We offer fluorescent conjugates of the mouse monoclonal anti-BrdU antibody clone Bu20a labeled with PE (V103305) and unlabeled mouse monoclonal anti-BrdU antibody clone Bu20a (V103300) and clone MoBu-1 (V103295) that can be labeled with our brightest and most photostable iFluor® dyes.

Bucculite™ XdU Cell Proliferation Assays

Unlike BrdU assays, Bucculite™ XdU Cell Proliferation Assays do not rely on antibodies to quantify nascent DNA, nor do they require DNA denaturation needed to facilitate antibody detection of BrdU-labeled nucleosides. Rather, Bucculite™ XdU Cell Proliferation Assays use a proprietary mixture of alkyne-containing thymidine analogs, XdU, that is incorporated into newly synthesized DNA.

Because of the mild reaction conditions, Bucculite™ XdU Cell Proliferation Assays preserve cell morphology, antigen-binding sites, and sample integrity, affording the user an opportunity for multiplexing analysis with cell cycle dyes, antibodies against cell surface markers, and fluorescent proteins. After XdU incorporation, the reaction and subsequent wash steps can be completed in less than 60 minutes, and nascent DNA can be quantified using standard imaging systems or a flow-cytometer. Also available are environmentally safe copper-free Bucculite™ FdU Cell Proliferation Assays in green, red, and deep red fluorescence. These kits utilize our patent Buccutite™ labeling chemistry to facilitate the detection of newly synthesized DNA in actively proliferating cells.

Dye Dilution Assays for Cell Proliferation

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CFSE and CytoTell™ indicators are fluorescent tracking dyes useful for monitoring cell proliferation in living cells by flow cytometry. As cells divide, the fluorescent dye is uniformly distributed between daughter cells, resulting in the progressive halving of fluorescence intensity with each successive generation. These proliferation dyes can be used to track cell proliferation long-term both in vitro and in vivo for several generations.

Proliferation Assay Using CFSE

CFSE (Carboxyfluorescein diacetate, succinimidyl ester, 22022) and ReadiUse™ CFSE (22028) are cell-permeable green fluorescent proliferation indicators that emit a fluorescence signal at 517 nm when excited by the 488 nm argon-ion laser. Both dyes passively diffuse across uncompromised cell membranes, whereby enzyme reactions with intracellular esterases cleave acetate groups from CFSE to yield an amine-reactive carboxyfluorescein, SE that covalently binds to proteins within the cell. While CFSE remains widely used as a green fluorescent proliferation indicator excited at 498 nm, it is, however, not without caveats. CFSE is highly toxic to cells, susceptible to dye leakage, and is known to spill over into the PE and PE-Texas Red channels.

CytoTell™ Proliferation Indicators

CytoTell™ dyes are a series of cell-permeable fluorescent tracers designed to monitor cell proliferation in living cells without any of the drawbacks of CFSE. Upon passive diffusion across cell membranes, CytoTell™ dyes are hydrolyzed by intracellular esterases to yield highly fluorescent amine-reactive or thiol-reactive dyes that irreversibly bind to amine or thiol groups on intracellular proteins. Cytotoxicity is minimal, and the dyes are well-retained within cells through several generations of division. Visualize up to 9 generations using CytoTell™ UltraGreen (22240). CytoTell™ dyes are available in 7 different fluorescence emission colors offering greater flexibility in multicolor analysis. They may be fixed and permeabilized to analyze intracellular targets using standard formaldehyde-containing fixatives and saponin-based permeabilization buffers.

Metabolic Assays for Cell Proliferation

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Metabolic indicators, such as tetrazolium salts and resazurin, measure the cellular reduction potential in metabolically active cells to evaluate proliferation. Following reduction, these substrates yield bright colorimetric products that can be measured using a spectrophotometer or microplate reader in low- or high-throughput configurations. Reduced resazurin can also be measured using a fluorescence microplate reader.

Proliferation Assay Using Tetrazolium Salts

The four types of tetrazolium salts used to measure proliferation are MTT, MTS, XTT, and WST-8. Reduction of MTT is the most common, however, for most commercial MTT assays, solubilization of the purple formazan product in DMSO or isopropanol is required before quantification. The convenient Cell Meter™ Colorimetric MTT Cell Proliferation Kit (22768) simplifies the task of counting cells to an easy mix and read format without the need for solubilization. The concentration of formazan determined by optical density at 560 nm is directly proportional to the number of live cells. Among the other tetrazolium salts, the water-soluble WST-8 offers the highest sensitivity. Reduction of WST-8 by cellular dehydrogenases yields water-soluble orange formazan crystals that do not require solubilization prior to quantification. The concentration of formazan product can be determined by measuring absorbance at 460 nm and is proportional to the number of living cells. The Cell Meter™ Colorimetric WST-8 Cell Quantification Kit provides a sensitive assay with exceptional linearity of up to ~10⁶ cells per well. No pre-mixing of components is required, as the WST-8 substrate is conveniently provided in a solution that can be directly added to the cells. Each kit provides sufficient reagents for either ~1000 (22770) or ~5000 tests (22771) using a standard 96-well microplate. WST-8 is also available as a stand-alone reagent in 25 mg (15705), 100 mg (15706), and 1 g (15707) unit sizes supplied as 50 mM aqueous solutions.

Proliferation Assay Using Resazurin

Like the aforementioned tetrazolium salts, the oxidation-reduction indicator resazurin (15700) can be useful for quantifying cell proliferation. Following reduction, the blue non-fluorescent resazurin yields a pink-colored and highly fluorescent resorufin product that is compatible with both fluorescence and absorbance microplate readers. The fluorescent or colorimetric signal is proportional to the number of living cells in the sample. Resazurin has been reported to be successfully used in a wide range of cell types, including bacteria, yeast, fungi, protozoa, and cultured mammalian cells.

ATP Assays for Cell Proliferation

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ATP, which is present in all metabolically active cells and virtually non-existent in dead cells, is a suitable biomarker for identifying viable cells. Assays for quantifying ATP have been used to determine cell proliferation and cytotoxicity in both bacterial and mammalian cells and for detecting low-level bacterial contamination in samples such as water, soil, and blood. While several detection methods can be used, researchers commonly choose luciferin-luciferase bioluminescence-based ATP assays to measure cell proliferation due to its higher sensitivity. The PhosphoWorks™ Luminometric ATP Assay Kits provide a simple and homogeneous method for measuring ATP using firefly luciferase and its substrate luciferin. In the presence of Mg²⁺, firefly luciferase catalyzes the reaction of luciferin, ATP, and O₂ to produce light at ~560 nm that can be detected using a luminometer. The concentration of ATP present is proportional to the number of viable cells in the sample. Also available is a PhosphoWorks™ Colorimetric ATP Assay Kit (21617) and a PhosphoWorks™ Fluorimetric ATP Assay Kit (21620) that can detect ~3 µM or ~0.4 µM of ATP in a 100 µL reaction volume, respectively.