The TdT‐mediated dUTP Nick End Labeling Assay Precisely Assesses the DNA Damage in Human Tumor Xenografts

Cultured HL‐60, HeLa S3 and WiDr cells grown in male BALB/c nu/nu mice were studied by conventional and field‐inversion DNA gel electrophoresis (FIGE), as well as by means of cytomorphological approaches, including TdT‐mediated dUTP nick end labeling (TUNEL) assay. Chemosensitivity tests revealed HL‐60 to be sensitive to vindesine (VDS), and HeLa S3 and WiDr to mitomycin C (MMC). Although VDS‐treated HL‐60 exhibited condensation of chromatin and a DNA ladder, MMC‐exposed HL‐60 cells showed apoptotic figures without typical DNA ladders. With MMC‐treated WiDr cells, neither DNA ladders nor apoptotic figures were observed. Cells characterized by chromatin condensation were TUNEL‐positive in both treated and untreated cases with the exception of the MMC‐treated WiDr case, in which many TUNEL‐positive cells were observed without cytomorphological changes. On FIGE, DNA fragments of approximately 50, 300 and 400 kbp were detected in groups treated with both effective and ineffective drugs, as well as in untreated controls. Furthermore, change of the time parameters in FIGE resulted in different sizes (550 and 850 kbp) of DNA fragments. These findings indicate that i) cell death is not always detectable in terms of apoptotic figures or DNA oligonucleosomal fragmentation, ii) only the TUNEL assay is a reliable tool to detect DNA damage and, iii) FIGE does not provide accurate size profiles of macromolecular DNA fragments.