Purpose: To elucidate the underlying events in Chlorin e6 (Ce6)-mediated sonodynamic therapy (SDT) (Ce6-SDT)-induced apoptosis of human leukemia cell line U937.
Materials and methods: The viability of cells was determined by 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltertrazolium bromide tetrazolium (MTT) test. Apoptosis was analyzed using a flow cytometer as well as fluorescence microscopy with 4'-6-Diamidino-2-Phenylindole (DAPI) staining. Western blotting was used to analyze the expression of caspase-3, poly ADP- ribose polymerase (PARP) and mitogen-activated protein kinase (MAPK).
Results: Several distinct sonochemical effects were found after SDT treatment. The participation of MAPK signals in SDT which caused U937 cell damage was specifically examined and the inhibition of p38 MAPK and Jun-N-terminal kinase (JNK) both apparently exerted a negative effect on SDT-induced cell death, while extracellular signal-regulating kinase (ERK1/2) inhibition enhanced SDT-induced cell death. The intracellular reactive oxygen species (ROS) was significantly enhanced by SDT, and pre-treatment with ROS scavenger N-acetylcysteine (NAC) partially alleviated SDT-induced cell viability loss, DNA fragmentation, mitochondria membrane potential (MMP) dissipation, caspase-3 activation, but interestingly MAPK activation was not affected much by NAC.
Conclusions: In the present paper, cell apoptosis of U937 cells was markedly enhanced after Ce6-SDT. Meanwhile, p38 MAPK, JNK and ERK were all differently activated in this process. One possible explanation for the induced cell apoptosis could be the increased ROS generation in Ce6-SDT.