title: The MTT assay underestimates the growth inhibitory effects of interferons.
abstract: The growth inhibitory effects of interferons, IFN-alpha and IFN-gamma on human lung cancer cell lines were studied using both a tetrazolium (MTT) colorimetric assay and direct cell counting. Significant discrepancies between the two assays were observed, the MTT assay consistently underestimating the growth inhibitory effects of the IFNs. There was no direct chemical effect of the IFNs on the tetrazolium reduction process. IFN treated cells showed increased cell size compared with control cells, although there was little or no change in cell cycle distribution. Mitochondrial activity was 30-50% greater in IFN-gamma treated cells (COR-L23) than the controls. Reduced formazan production per cell was observed in medium which had supported cell growth for several days. Differential 'medium conditioning' led to a difference in formazan production per cell between IFN and control cells and this was the major basis of the observed discrepancy. This discrepancy was not due to the differences in the glucose concentrations between these media. However, differences in pH between the media proved to be the major contributory factor of the discrepancy.
authors.affiliation: Medical Research Council Clinical Oncology, Cambridge, UK.
authors.forename: S A
authors.initials: SA
authors.lastname: Jabbar
authors.forename: P R
authors.initials: PR
authors.lastname: Twentyman
authors.forename: J V
authors.initials: JV
authors.lastname: Watson
mesh_terms: D002452:Cell Count; D002460:Cell Line; D003124:Colorimetry / Q000379:methods*; D004396:Coloring Agents; D003470:Culture Media; D005562:Formazans / Q000032:analysis; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007370:Interferon Type I / Q000627:therapeutic use*; D008175:Lung Neoplasms / Q000473:pathology / Q000628:therapy*; D011971:Receptors, Immunologic; D017471:Receptors, Interferon; D013778:Tetrazolium Salts; D013844:Thiazoles; D014407:Tumor Cells, Cultured / Q000473:pathology
chemical_list: D004396:Coloring Agents; D003470:Culture Media; D005562:Formazans; D007370:Interferon Type I; D011971:Receptors, Immunologic; D017471:Receptors, Interferon; D013778:Tetrazolium Salts; D013844:Thiazoles; C022616:thiazolyl blue