The Resazurin Reduction Assay Can Distinguish Cytotoxic from Cytostatic Compounds in Spheroid Screening Assays.
Spheroid-based cellular screening approaches represent a highly physiologic experimental setup to identify novel anticancer drugs and an innovative preclinical model to reduce the high failure rate of anticancer compounds in clinical trials. The resazurin reduction (RR) assay, known as the alamarBlue or CellTiter-Blue assay, is frequently used to determine cell viability/proliferation capacity in eukaryotic cells. Whether this assay is applicable to assess viability in multicellular spheroids has not been evaluated. We analyzed the RR assay to measure cytotoxic and/or cytostatic responses in tumor cell spheroids compared with conventional 2D cultures. We found that tight cell-cell interactions in compact spheroids hamper resazurin uptake and its subsequent reduction to resorufin, leading to lowered reduction activity in relation to the actual cellular health/cell number. Treatment with staurosporine disrupted close cell-cell contacts, which increased resazurin reduction compared with untreated controls. Loss of tight junctions by trypsinization or addition of EGTA or EDTA restored high resazurin reduction rates in untreated spheroids. In conclusion, the RR assay is unsuited to quantitatively measure cellular health/cell number in compact spheroids. However, it can be used to distinguish between cytotoxic versus cytostatic compounds in spheroids. Restoration of the correlation of cell viability/number to resazurin reduction capacity can be achieved by disruption of tight junctions.
Institute of Medical Genetics, Medical University of Vienna, Vienna, Austria.
Angelika
A
Walzl
Institute of Medical Genetics, Medical University of Vienna, Vienna, Austria Center of Biomedical Technology, Donau Universität Krems, Krems, Austria.
Christine
C
Unger
Institute of Medical Genetics, Medical University of Vienna, Vienna, Austria Center of Biomedical Technology, Donau Universität Krems, Krems, Austria.
Nina
N
Kramer
Institute of Medical Genetics, Medical University of Vienna, Vienna, Austria.
Daniela
D
Unterleuthner
Institute of Medical Genetics, Medical University of Vienna, Vienna, Austria.
Martin
M
Scherzer
Institute of Medical Genetics, Medical University of Vienna, Vienna, Austria.
Markus
M
Hengstschläger
Center of Biomedical Technology, Donau Universität Krems, Krems, Austria.
Dagmar
D
Schwanzer-Pfeiffer
Institute of Medical Genetics, Medical University of Vienna, Vienna, Austria helmut.dolznig@meduniwien.ac.at.
Helmut
H
Dolznig
D000970:Antineoplastic Agents / Q000737:chemistry*; D017209:Apoptosis; D001681:Biological Assay; D002450:Cell Communication; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D002470:Cell Survival; D004354:Drug Screening Assays, Antitumor / Q000379:methods*; D004492:Edetic Acid / Q000737:chemistry; D004533:Egtazic Acid / Q000737:chemistry; D019073:HT29 Cells; D006801:Humans; D018613:Microscopy, Confocal; D009369:Neoplasms / Q000188:drug therapy*; D010078:Oxazines / Q000737:chemistry*; D018874:Spheroids, Cellular; D019311:Staurosporine / Q000737:chemistry; D014966:Xanthenes / Q000737:chemistry*
D000970:Antineoplastic Agents; D010078:Oxazines; D014966:Xanthenes; C005843:resazurin; D004533:Egtazic Acid; D004492:Edetic Acid; D019311:Staurosporine
3D cell culture; cellular screening; rezazurin to resorufin reduction assay; spheroid