Induction of apoptosis by the COX-2-selective NSAID NS-398 in colorectal carcinoma cells. (A) N-398 induces apoptosis in HT-29 cells. HT-29 cells were treated with 0 μ M (vehicle only), 50 μ M or 75 μ M NS-398. At 72 and 96 h, both attached and floating cells were harvested and counted and floating cell yields were calculated as a percentage of total cell yields. Floating cell yield data are means±s.e.m. of three independent repeat experiments carried out in triplicate. Apoptotic morphology of floating cells was confirmed by acridine orange staining (as in Elder et al, 1997). (B) Floating cells show the absence of intact PARP and the presence of cleaved PARP, a biochemical marker of apoptosis. HT-29 cells were treated with 0 μ M (vehicle) or 75 μ M NS-398 for 96 h. Lysates from 2 × 106 attached and floating cells were analysed by Western blotting for PARP expression and cleavage.