Sonodynamically induced apoptosis with porfimer sodium in HL-60 cells was investigated. HL-60 cells were exposed to ultrasound for up to 3 min in the presence and absence of porfimer sodium. After the exposure, sonodynamically induced apoptosis was assessed according to morphologic changes, DNA fragmentation and caspase-3 activation. The cells treated with 50 μg/ml porfimer sodium and ultrasound clearly showed membrane blebbing and cell shrinkage, whereas no significant morphologic change was observed in the cells exposed to either ultrasound alone or porfimer sodium alone. DNA ladder formation was observed in the cells treated with ultrasound in the presence of porfimer sodium. Activation of caspase-3 was also observed after the treatment with ultrasound and porfimer sodium. Both sonodynamically induced apoptosis and caspase-3 activation were significantly suppressed by histidine. These results indicate that combination treatment with ultrasound and porfimer sodium induced apoptosis in HL-60 cells. Significant reduction by histidine in both sonodynamically induced apoptosis and caspase-3 activation suggests that some ultrasonically generated active species, deactivatable by histidine, are the major mediators to induce the observed apoptosis.
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