Apoptosis of ovarian cancer cells induced by methylene blue-mediated sonodynamic action

Objective: The present study aims to investigate apoptosis of ovarian cancer cells induced by methylene blue (MB)-mediated sonodynamic therapy (SDT). Methods: The MB concentration was kept constant at 100 mu M and ovarian cancer HO-8910 cells were exposed to ultrasound therapy for 5 s with an intensity of 0.46 W/cm(2). The cytotoxicity was investigated 24 h after MB-mediated sonodynamic action. Apoptosis was analyzed using a flow cytometer with Annexin V-FITC and propidium iodine (PI) staining as well as fluorescence microscopy with Hoechst 33258 staining. Intracellular reactive oxygen species (ROS) level was measured by flow cytometer with 2,7-dichlorodihydrofluorescein diacetate (DCFH-DA) staining. Results: The cytotoxicity of MB-mediated SDT on HO-8910 cells after MB-mediated SDT was significantly higher than those of other treatments including ultrasound alone, MB alone and sham treatment. Flow cytometric analysis showed a significant increase in the early and late apoptotic cell populations by MB-mediated SDT of HO-8910 cells. Nuclear condensation and increased ROS levels were also found in HO-8910 cells treated by MB-mediated SDT. Conclusions: Our findings demonstrated that MB-mediated sonodynamic action significantly induced apoptosis of HO-8910 cells and an increase in intracellular ROS level. This indicates that apoptosis is an important mechanism of cell death induced by MB-mediated SDT. Thus, MB-mediated SDT might be a potential therapeutic strategy for combating ovarian cancer. (C) 2010 Elsevier B.V. All rights reserved.