Low-Intensity Ultrasound Combined with Microbubbles Inhibit the Viability of Breast Cancer Cells through Activating Autophagy and Apoptosis

Abstract: Autophagy and apoptosis are the key factors resulting in the cell death of breast cancer， and the therapeutic effect of low-intensity ultrasound (LPUS) combined with microbubbles (MBs) on tumor cells has aroused increasing attention. However， the effect of LPUS-MBs on autophagy and apoptosis in breast cancer cells remains unclear. In the present study， human breast cancer MDA-MB-231 cells were cultured and treated with 1 MHz LPUS with 0.5 W/cm2 combined with MBs for 60 s. Acridine orange (AO) staining， transmission electron microscopy (TEM) and GFP-LC3 transfection were used to analyze the number of autophagosomes. The protein levels of microtubule associated protein 1 light chain 3-II (LC3-II)， ATG5 and SQSTM1(sequestosome 1)/p62 determined by Western blot reflected the level of autophagy. Annexin V/PI， DAPI staining and caspase-3 indicated the apoptosis of MDA-MB-231 cells. ATG5 siRNA transfection was employed to inhibit autophagy， and Z-VAD-FMK to inhibit apoptosis. The results showed that LPUS-MBs significantly enhanced the protein level of LC3-II and ATG5， but inhibited SQSTM1/p62 level (P<0.05). The result of TEM and GFP-LC3 assay found the increased number of autophagosomes in the LPUS-MBs-treated MDA-MB-231 cells. Furthermore， LPUS-MBs increased the level of caspase-3 and the percentage of apoptosis. Inhibition of autophagy and apoptosis attenuated the inhibitory effect of LPUS-MBs on cell viability (P<0.05). These results indicated that LPUS-MBs inhibited the cell viability by activating autophagy and apoptosis.

CSTR: 32200.14.cjcb.2017.08.0006