Induction of apoptosis (programmed cell death) in tumour cell lines by widely diverging stimuli.

( a ) S. cerevisiae was grown for 24 h in the presence of various octenidine concentrations and in the absence (0) or presence ( m ) of ethidium bromide (10 pglml) and assayed for petite mutants. Growth conditions and petite assay were as described by Meyer & Whittaker 161. ( 6 ) S. cerevisiue was grown in the presence of ethidium bromide (10 pglml). Octenidine (0.5 pg/ml) was added after 1 h (+), 2 h (0) and 4 h ( A ) . A control culture ( x ) had no octenidine addition. Samples were assayed at intervals for petite mutants. Growth conditions and petite assay were as described by Meyer & Whittaker 161. b relative to cytochrome c. The latter effect would bc expected if octenidine acted either as an inhibitor of mitochondrial protein synthesis or as a petite mutagen. In contrast, pirtenidine showed no evidence of an effect on cytochrome synthesis. The possibility that octenidine might act to induce the formation of petite mutants in S. cerevisiue was investigated. Peiite mutants have suffered loss or gross deletion of their mitochondrial DNA [5] and are consequently incapable of mitochondrial protein synthesis. Fig. 1( a ) shows that octenidine does increase the level of petite mutants in a culture in a dose-dependent fashion. The level of petite mutants observed, however, was insufficient to account for the diminution of respiration induced by this drug. The potent petire mutagen ethidium bromide gives 100"/0 petite mutants after 24 h incubation at 10 pg/ml. Rather surprisingly octenidine diminishes the petite mutagenic effect of ethidium bromide in a dose-dependent manner (Fig. 1 u), so much so that, at an octenidine concentration of 0.5 pg/ml the mutant level achieved is hardly affected by the presence or absence of ethidium bromide. Fig. 1( h ) shows that octenidine, added at various times during the course of ethidium bromide mutagenesis, appeared to cause immediate inhibition of mutagenesis. In contrast to these observations, pirtenidine neither induced petite mutation nor antagonized ethidium bromide induction of petite mutants. It seems likely from these observations that pirtenidine has a direct effect on the mitochondria1 electron transport system. It is probable that octenidine also shows this effect. In addition, possibly because of its bifunctional nature, octenidine interferes with mitochondria1 assembly causing petire mutation and diminished cytochrome synthesis. I t is possible that the inhibitory effect of octenidine on ethidium bromide mutagenesis might relate to the requirement for ATP for efficient mutagenesis by ethidium bromide I 71.