Hypocrellin B Enhance Low-intensity Ultrasound Killing Nasopharyngeal Carcinoma Cells

Background: Nasopharyngeal carcinoma (NPC) is one of most common cancers in southern China. Recent therapeutic modalities have some shortcomings and serious side-effects. There is an urgent need to explore novel therapeutic strategies for improving clinical outcomes. Photodynamic therapy (PDT) is an alternative strategy in the management of malignant tumor. PDT destroys tumor cells dependent on photodynamic action of photosensitizers which can selectivity retention in actively proliferating tissues activated by light at the specific wavelength. The poor penetration of light in the biological tissues is the main limitation to clinical application of PDT. Recent studies showed that ultrasound could efficiently activate some sensitizers to produce sonodynamic action, namely, sonodynamic therapy (SDT). Many sensitizers used in current SDT research are primarily photosensitizers for example porphyrin. Hypocrellin B (HB), a newly prospective photosensitizer and a natural pigment from the traditional Chinese herb. In the present study, we have explored whether hypocrellin B(HB) could enhance the ultrasound-induced cell death of nasopharyngeal carcinoma cells as tumor model cells in vitro. Our aims are to explore a novel sonosensitizer and a new therapeutic method to treat nasopharyngeal carcinoma.Material/Methods: To investigate a novel sonosensitizer and explore a potential therapeutic modality , the poorly differentiated CNE2 cell line was chosen as tumor model cells for various assay after ultrasound exposure (1.7MHz.0.65W/cm2) and HB. The cytotoxicity of ultrasound (1.7MHz.0.65W/cm2) and HB on the CNE2 cells was measured using CCK-8 colormetric assay. Light microscope was used to observe the morphological changes of the treated CNE2 cells. Apoptosis was evaluated using flow cytometry with annexin V-FITC and propidium iodine staining and nuclear staining with Hoechst 33258. The mitochondrial membrane potential (Δψm) was monitored using confocal laser-scanning microscopy (CLSM) with rhodamine 123 staining. Transmission electron microscopy (TEM) was performed to observe ultrastructural changes.Result: No significant dark cytotoxicity of hypocrellin B in the CNE2 cells was observed at the concentration of 2.5 uM in this study. With the same ultrasound sonification time, the death rate of the CNE2 cells induced by ultrasound was significantly higher in the presence of hypocrellin B than in the absence of it. The early and late apoptotic rates after ultrasound sonification in the presence of hypocrellin B (2.5 uM) significantly increased to 18.61%. Significant changes of the mean fluorescence intensity in theΔψm for the CNE2 cells after ultrasound and HB treatment together, in which collapse of theΔψm was observed. After treatment with ultrasound and HB together, the mitochondria of the cells were damaged more seriously, obviously swollen mitochondria and mitochondria in which cristae almost completely disappeared were observed, indicating that ultrasound radiation in the presence of HB substantially damaged the mitochondrial structure.Conclusion: Our results demonstated that HB could significantly enhance the cell death induced by low-intensity ultrasound. Hypocrellin B is a novel sonosensitizer and hypocrellinB-mediated sonodynamic therapy is a potential therapeutic modality in the management of malignant tumors.