Developing polyamine conjugates having the potential of transporting naphthalimide selectively into tumor cells is attractive. However, the evaluation of their cytotoxic mechanism has not been comprehensive. This study focused on the effects of mononaphthalimide spermidine (MNISpd) conjugate on apoptosis induction and the relationship between MNISpd-induced apoptosis and reactive oxygen species (ROS) in HeLa cells. Our findings indicated that 9 µM MNISpd induced apoptosis in HeLa cells during a 48-h period. MNISpd induced apoptosis in HeLa cells following cytochrome c release, elevation of caspase 3/9 activity, apoptosis-inducing factor (AIF) translocation and up-/down-regulation of Bax/Bcl-2 protein expression, respectively, and these effects were completely antagonized by pre-incubation with 10 mM NAC for 2 h. MNISpd induced significant ROS accumulation following up-regulation of polyamine oxidase (PAO) activity and complex variations in glutathione levels. It is concluded that MNISpd-induced apoptosis is related to intrinsic caspase-dependent and AIF-mediated caspase-independent apoptosis pathways in HeLa cells. MNISpd-induced apoptosis correlates to MNISpd-induced ROS production resulting from GSH (reduced form of glutathione) pool depletion, and PAO is likely to be the source of ROS.

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