Selective clinical ultrasound signals mediate differential gene transfer and expression in two human prostate cancer cell lines: LnCap and PC-3

Low intensity ultrasound signals, similar to that employed in clinical therapy, are found to mediate differential gene transfer and expression of the Green Fluorescence Protein (GFP) reporter in two human prostate cancer cell lines, LnCap and PC-3. Cell suspensions in the presence or in the absence of GFP (44.5 nM) were treated at 37°C under a standing wave condition. Cells were exposed to either continuous wave, 932.7 kHz ultrasound, or to several independent bursts, each burst comprising a 20% duty cycle (932.7 kHz) sine wave. The burst 'repetition' frequency was varied from 10 Hz to 10 kHz in several different experiments and each treatment received a net identical ultrasound energy exposure. Transient GFP expression levels in viable cells were monitored by flow cytometry. The findings revealed a strong ultrasound tone-burst frequency dependence on the transfection efficiencies. Interestingly, the ultrasound signal parameters which are routinely employed in clinical therapy did not yield any statistically significant enhancement in transfection efficiency relative to their sham counterparts.