High-intensity focused ultrasound induced apoptosis with caspase3, 8, and 9/6 activation in rat hepatoma.

Abstract

The purpose of the present study is to investigate anticancer efficacy and apoptosis confirmed by caspase under several exposure conditions of high-intensity focused ultrasound (HIFU). Twenty-five rats with KDH-8 hepatoma were treated by HIFU at several acoustic energies to evaluate treatment efficacy. Apoptosis was examined by terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) and Hoechst 33258 staining, and caspase3, 8, and 9/6 activity was respectively assayed. The KDH-8 subcutaneous tumors were reduced by HIFU, and these rats survived longer than the nontreatment rats (P<0.01). The minimal threshold of HIFU energy was 30W×1.0s for tumor control and long-term survival. The tumors exposed to HIFU exhibited marked apoptotic features under conditions of less than 10W×1.0s. In cultured KDH-8 cells, apoptosis was caused at less than 30W×1.0s (P<0.01), and more was induced as the energy went down. Caspase3, 8, and 9/6 were more activated at low energy under 10W×1.0s (P<0.01), and caspase8, which is death receptor dependent, was significantly more activated than caspase9/6, which is mitochondria dependent (P<0.01). HIFU-induced apoptosis invivo and invitro is one of the mechanisms for tumor control and is mediated by caspase3, 8, and 9/6. The significantly greater activation of caspase8 than of caspase9/6 suggests that the apoptosis pathway induced by HIFU might be more mitochondria dependent than death receptor dependent. However, further examination will be needed.