Involvement of caspase 8 in apoptosis induced by ultrasound-activated hematoporphyrin in sarcoma 180 cells in vitro

Objective. Sonodynamic therapy (SDT), a novel and promising cancer therapy that uses a combination of ultrasound and hematoporphyrin, can induce apoptosis in some cancer cells. However, the mechanism(s) of SDT-induced cell apoptosis is not well understood. This study investigated SDT-induced apoptosis in sarcoma 180 cells. Methods. Cell suspension were treated by 1.75-MHz continuous focused ultrasound in the presence of hematoporphyrin for 3 minutes, and apoptosis was assessed by flow cytometry, scanning electron microscopy, terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate-biotin nick end labeling, confocal microscopy, and apoptosis-related protein analysis. Results. DNA breaks, apoptotic bodies, and cleaved poly (adenosine triphosphate-ribose) polymerase were observed 1 hour after SDT By using laser-scanning confocal microscopy, we found that the Fas-associated death domain and caspase 8 translocated from the cytoplasm to the plasma membrane. Activities of caspase 8 and caspase 3 were detected by an immunohistochemical assay The results suggested that SDT led to activation of caspase 8, which in turn activated downstream caspase 3. In addition, Z-Ile-Glu-Thr-Asp-fluoromethylketone, a specific inhibitor for caspase 8, was used to confirm the effect of caspase 8 in apoptosis. Conclusions. Our data primarily show that SDT can induce apoptosis in sarcoma 180 cells in vitro, and caspase 8 may play an important role in SDT-induced apoptosis.