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.
Highlights
Prostate cancer is the second leading cause of cancer‐associated mortality in males in the USA [1]
The results demonstrated that cell viability was marginally reduced in the Low‐frequency ultrasound (LFU) (96.3±4.7%) or the simvastatin (95.1±7.1%) group compared with the control (100%) at 24 h following ultrasound exposure
These results indicated that the LFU and microbubbles (LFUM) or LFU and simvastatin‐treated cells exhibited improved growth inhibition compared with LFU or simvastatin alone
Summary
Prostate cancer is the second leading cause of cancer‐associated mortality in males in the USA [1]. The incidence of prostate cancer in China, which is gradually becoming an aging society, has been increasing by 9.2% each year from 2001 to 2010 according to statistics released by the Beijing Bureau of Health [2]. There are no therapeutic options that will effectively cure patients with AIPC or HRPC. A number of studies have demonstrated that caveolin‐1 is overexpressed and that its upregulation is positively correlated with cell proliferation and progression in AIPC or HRPC [4,5]. Caveolin‐1 is, a biomarker and therapeutic target for prostate carcinomas
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