Differential effects of tri-n-butylstannyl benzoates on induction of apoptosis in K562 and MCF-7 cells

Tributyltin compounds have been shown to induce apoptosis by causing extracellular Ca2+ influx and generating reactive oxygen species (ROS). Several organotin compounds were reported to have differential cytotoxicity on various human cell lines depending on the length of the alkyl chain. In this report, the cytotoxic effects of three tri-n-butylstannyl (halo)benzoate compounds-tri-n-butylstannyl benzoate (TBSB), tri-n-butylstannyl-2,6-difluorobenzoate (TBSDFB) and tri-n-butylstannyl-2-iodobenzoate (TBSIB)-were studied on lymphocytic cells of human leukemic K562 lineage and epithelial cells of human breast cancer MCF-7 cells lineage. K562 cells were found to be more sensitive to these compounds than MCF-7 cells. Although the induction of apoptosis by the above compounds in K562 cells resulted from the extracellular Ca2+ influx and the generation of ROS, the initial amount of extracellular Ca2+ influx was greater in TBSB-treated K562 cells than the cells treated with either TBSDFB or TBSIB. Similarly, DNA fragmentation by endonucleases was observed as an early event in TBSB-treated K562 cells, which might be correlated with the initially greater extracellular Ca2+ influx. In contrast, MCF-7 cells were found to undergo apoptosis mainly because of the generation of ROS. The present results suggest that the differential effects of tributyltin compounds on induction of apoptosis in K562 and MCF-7 cells are largely attributable to the extent of extracellular Ca2+ influx.