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Comparison of Three Different Methods for Determining Cell Proliferation in Breast Cancer Cell Lines
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A simple high-content cell cycle assay reveals frequent discrepancies between cell number and ATP and MTS
Grace Ka Yan Chan1, Tracy L Kleinheinz, David Peterson
1Department of Biochemical and Cellular Pharmacology, Genentech, Inc South, San Francisco, California, United States of America.
Abstract:
In order to efficiently characterize both antiproliferative potency and mechanism of action of small molecules targeting the cell cycle, we developed a high-throughput image-based assay to determine cell number and cell cycle phase distribution. Using this we profiled the effects of experimental and approved anti-cancer agents with a range mechanisms of action on a set of cell lines, comparing direct cell counting versus two metabolism-based cell viability/proliferation assay formats, ATP-dependent bioluminescence, MTS (3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium) reduction, and a whole-well DNA-binding dye fluorescence assay. We show that, depending on compound mechanisms of action, the metabolism-based proxy assays are frequently prone to 1) significant underestimation of compound potency and efficacy, and 2) non-monotonic dose-response curves due to concentration-dependent phenotypic 'switching'. In particular, potency and efficacy of DNA synthesis-targeting agents such as gemcitabine and etoposide could be profoundly underestimated by ATP and MTS-reduction assays. In the same image-based assay we showed that drug-induced increases in ATP content were associated with increased cell size and proportionate increases in mitochondrial content and respiratory flux concomitant with cell cycle arrest. Therefore, differences in compound mechanism of action and cell line-specific responses can yield significantly misleading results when using ATP or tetrazolium-reduction assays as a proxy for cell number when screening compounds for antiproliferative activity or profiling panels of cell lines for drug sensitivity.
Insights
Metabolism-based assays can underestimate anti-cancer drug potency and efficacy by misinterpreting cell cycle arrest as proliferation. A high-throughput image-based assay accurately measures cell number and cell cycle phase for reliable drug screening.
Area of Science:
- Cell Biology
- Pharmacology
- Drug Discovery
Background:
- Accurate characterization of antiproliferative potency and mechanism of action is crucial for small molecule drug development targeting the cell cycle.
- Existing metabolism-based assays (ATP-dependent bioluminescence, MTS reduction) are commonly used but may not accurately reflect cell number and proliferation.
- Understanding assay limitations is essential for reliable drug screening and sensitivity profiling.
Purpose of the Study:
- To develop and validate a high-throughput image-based assay for precise measurement of cell number and cell cycle phase distribution.
- To compare the performance of the image-based assay against traditional metabolism-based assays for profiling anti-cancer agents.
- To investigate the impact of compound mechanism of action on assay results and identify potential sources of error.
Main Methods:
- Development of a high-throughput image-based assay to determine cell number and cell cycle phase distribution.
- Profiling of experimental and approved anti-cancer agents across various cell lines using the developed assay.
- Comparative analysis of direct cell counting, ATP-dependent bioluminescence, MTS reduction, and DNA-binding dye fluorescence assays.
Main Results:
- Metabolism-based assays frequently underestimate compound potency and efficacy, particularly for DNA synthesis inhibitors like gemcitabine and etoposide.
- Concentration-dependent phenotypic 'switching' in metabolism-based assays can lead to non-monotonic dose-response curves.
- Drug-induced increases in ATP content correlated with cell cycle arrest, increased cell size, and mitochondrial content, not necessarily proliferation.
Conclusions:
- High-throughput image-based assays provide a more accurate assessment of antiproliferative activity and mechanism of action compared to metabolism-based assays.
- Metabolism-based assays can yield misleading results due to variations in compound mechanism and cell line-specific responses.
- The developed image-based assay is a valuable tool for reliable drug screening and sensitivity profiling in cancer research.
