Exposure-time dependency of KP1019 and KP1339 cytotoxicity. Pulsing experiments were performed in KB-3-1 cells by replacing a KP1019- and b KP1339-containing test mediums after 1, 2, and 3 h with fresh culture medium. Following a total experimental time of 72 h, cell vitality was determined by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assays. The values given are means and standard deviations (SD) of three independent experiments in triplicate