Apoptosis induced by sonodynamic treatment by protoporphyrin IX on MDA-MB-231 cells

Sonodynamic therapy (SDT) is a promising modality for cancer treatment, involving the synergistic interaction of ultrasound and some chemical compounds termed as sono-sensitizers. It has been found that SDT can lead to apoptotic cell death because of the induction of direct sonochemical and subsequent redox reactions. However, the detailed mechanisms are not clear. This study was to identify the cytotoxic effects of ultrasound-activated protoporphyrin IX (PpIX) on MDA-MB-231 cells. The fluorescence microscope was used to detect the sub-cellular localization of PpIX. Several distinct sonochemical effects were found after SDT treatment, including the decrease of cell viability, generation of intracellular ROS, the loss of mitochondrial membrane potential. The activation of some special apoptosis-associated proteins [Caspase-9, Caspase-3 and polypeptide poly (ADP-robose) polymerase] was evaluated by western blotting. The results show that PpIX mediated SDT (PpIX-SDT) treatment could obviously inhibit the proliferation of MDA-MB-231 cells, and which was significantly reduced by the pan-Caspase inhibitor z-VAD-fmk and the reactive oxygen species (ROS) scavenger N-acetylcysteine (NAC). Further, SDT induced a conspicuous loss of mitochondrial membrane potential (MMP) and a mass of ROS accumulation in MDA-MB-231 cells at 1 h post-treatment and the SDT-treated cells showed obvious Caspase-3 and Caspase-9 activation, and PARP cleavage at 6 h after treatment. And, the general apoptosis marker-Caspase-3 activation-was also greatly relieved by NAC. These findings primarily indicate a Caspase-depended apoptosis could be induced by PpIX-SDT in MDA-MB-231 cells, and the intracellular ROS was involved during the apoptotic process.

► The ultrasonically induced cytotoxicity of MDA-MB-231 cells was significantly enhanced by PpIX.
► Mitochondria may be the main target of SDT because PpIX co-localized well with MTG in MDA-MB-231.
► SDT could induce apoptotic cell death of MDA-MB-231 cells, and which might be Caspase dependent.
► Intracellular ROS was involved in SDT-induced cytotoxic effect in MDA-MB-231 cells.