Enhanced antitumor effects of low-frequency ultrasound and microbubbles in combination with simvastatin by downregulating caveolin-1 in prostatic DU145 cells

Abstract

Advanced prostate cancer is difficult to treat due to androgen resistance, its deep location and blood tumor barriers. Low-frequency ultrasound (LFU) has potential clinical applications in the treatment of prostate cancer due to its strong penetrability and high sensitivity towards tumor cells. Simvastatin has often been administered as a preventive agent in prostate tumors. The aim of the present study was to investigate the enhanced effects of LFU and microbubbles in combination with simvastatin, in inhibiting cell viability and promoting apoptosis of androgen-independent prostatic DU145 cells. Cultured DU145 cells were divided into six groups based on the combination of treatments as follows: Control, LFU, LFU and microbubbles (LFUM), simvastatin, LFU and simvastatin, LFUM and simvastatin. The cells were treated by LFU (80 kHz) continuously for 30 sec with an ultrasound intensity of 0.45 W/cm2 and a microbubble density of 20%. Simvastatin was added 30 h prior to the ultrasound exposure. The results indicated that cell viability was marginally reduced in the LFU and simvastatin alone treatment groups compared with the control 24 h following ultrasound exposure. The combination of LFU, with microbubbles or simvastatin, potentiated the growth inhibition; the greatest inhibition was observed in the cells that were subject to treatment with LFUM and simvastatin in combination. Furthermore, this inhibitory effect was enhanced in a time-dependent manner. For cell apoptosis, a low dose of simvastatin had no apparent affect on the DU145 cells, while LFU marginally promoted cell apoptosis. Microbubbles or simvastatin increased the apoptosis rate of the DU145 cells, however, the combination of LFUM and simvastatin induced a strong synergistic effect on cell apoptosis. Western blotting analysis demonstrated a high expression level of caveolin-1 in resting DU145 cells. LFUM or combined LFU and simvastatin resulted in a greater reduction in the expression compared with the control group (P<0.05). The expression of caveolin-1 was lowest in the LFUM combined with simvastatin treatment group. The expression of phospho-Akt (p-Akt) was consistent with caveolin-1, with the lowest expression levels of p-Akt observed in the cells that were treated with the combination of LFUM and simvastatin. The results indicate that LFUM in combination with simvastatin may additively or synergistically inhibit cell viability and induce apoptosis of DU145 cells by downregulating caveolin-1 and p-Akt protein expression.

Clinical study of ultrasound and microbubbles for enhancing chemotherapeutic sensitivity of malignant tumors in digestive system

“…The role of the sonoporation effect in targeted drug release and gene therapy has been demonstrated in animal experiments ( 42 - 44 ). This technique is a promising approach for increasing drug and gene delivery efficiency ( 38 , 45 - 47 ). The primary objective of this study was to explore the safety of ultrasound combined with microbubbles in enhancing the chemotherapeutic sensitivity of malignant tumors in the digestive system.…”

Low‑frequency ultrasound and microbubbles combined with simvastatin promote the apoptosis of MCF‑7 cells by affecting the LATS1/YAP/RHAMM pathway

“…The biological influence of LFU and microbubbles on cancer cells is dependent on the microbubble density, ultrasound intensity and irradiation time ( 34 , 35 ). Generally, a pilot experiment should be prepared to debug the optimized ultrasound parameters, so as to induce cell apoptosis to the maximum extent ( 36 , 37 ).…”

Upregulation of Beclin-1 expression in DU-145 cells following low-frequency ultrasound irradiation combined with microbubbles

“…Tabuchi et al (23) observed that 193 genes were downregulated and 201 were upregulated in tumor cells following irradiation by low-frequency ultrasound. These genes are associated with cell growth, proliferation, apoptosis, movement, polymorphism and death (24).…”