title: A simple high-content cell cycle assay reveals frequent discrepancies between cell number and ATP and MTS proliferation assays.
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.
authors.affiliation: Department of Biochemical and Cellular Pharmacology, Genentech, Inc South, San Francisco, California, United States of America.
authors.forename: Grace Ka Yan
authors.initials: GK
authors.lastname: Chan
authors.forename: Tracy L
authors.initials: TL
authors.lastname: Kleinheinz
authors.forename: David
authors.initials: D
authors.lastname: Peterson
authors.forename: John G
authors.initials: JG
authors.lastname: Moffat
mesh_terms: D000255:Adenosine Triphosphate; D000970:Antineoplastic Agents / Q000494:pharmacology*; D002452:Cell Count / Q000379:methods*; D002453:Cell Cycle / Q000187:drug effects* / Q000502:physiology; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects*; D004305:Dose-Response Relationship, Drug; D055808:Drug Discovery / Q000379:methods*; D057166:High-Throughput Screening Assays / Q000379:methods*; D006801:Humans; D008163:Luminescent Measurements; D013778:Tetrazolium Salts
chemical_list: D000970:Antineoplastic Agents; D013778:Tetrazolium Salts; D000255:Adenosine Triphosphate