Comparison between sonodynamic and photodynamic effect on MDA-MB-231 cells

•Both PDT and SDT exhibit cytotoxicity on MDA-MB-231 cells.•Synergistic damage of PDT and SDT are due to the mitochondria damage, excessive intracellular ROS generation and the MMP loss.•Cell membrane is an important target in SDT, but not in PDT on MDA-MB-231 cells.

Photodynamic therapy (PDT) and sonodynamic therapy (SDT) are therapeutic modalities for tumors. In this study we investigated the combined cytotoxic effect of 0.36 W/cm2 and 0.72 W/cm2 ultrasound with various Ce6 concentrations (1, 2, 5, 10 μg/ml), and that of 1 μg/ml Ce6 with different laser light dose (650 nm; 10.4 mW/cm2; 0.3, 0.6, 1.2 and 2.5 J/cm2) on MDA-MB-231 cells. Both high reactive oxygen species (ROS) production and a decline in mitochondrial membrane potential (MMP) were detected with high Ce6 concentrations (5 and 10 μg/ml) combined with 0.72 W/cm2 ultrasound and 1.2, 2.5 J/cm2 laser light with 1 μg/ml Ce6. In addition, cell membrane integrity was evaluated by using propidium iodide (PI), revealing membrane damage was aggravated with the increasing ultrasound intensity, but no significant difference on cell membrane integrity could be observed after PDT treatment. These results suggest ROS may play an important role both in SDT and PDT. Besides, mitochondria may be an initial target in PDT while SDT can cause multi-site damages in MDA-MB-231 cells.