Evaluation of antitumor effects following tumor necrosis factor-α gene delivery using nanobubbles and ultrasound.

The antitumor effects of tumor necrosis factor (TNF-α) were evaluated following transfection of TNF-α plasmid DNA into solid mouse tumors using the nanobubbles (NBs) and ultrasound (US) gene delivery system. Murine breast carcinoma (EMT6) cells expressing luciferase (1 × 10(6) cells) were injected intradermally into the flanks of 6-7-week-old male SCID mice on day 0. Ten microliters of TNF-α (5 μg/μL) or TNF-α mock plasmid DNA (5 μg/μL) with/without NBs (15 μL) and saline was injected intratumorally in a total volume of 30 μL, and tumors were exposed to US (frequency, 1 MHz; intensity, 3.0 W/cm(2); duty cycle, 20%; number of pulses, 200; and exposure time, 60 s) on days 2, 4, 7, and 9. Changes in tumor size were measured with an in vivo bioluminescent imaging system and a mechanical caliper. Changes in tumor vessel area were quantified using contrast-enhanced US imaging with Sonazoid and a high frequency US imaging system (40 MHz) and immunohistochemistry (CD31). At the mRNA level, expression of TNF-α, caspase-3, and p53 were quantified using real-time quantitative RT-PCR. At the protein level, expression of caspase-3 and p53 were confirmed by immunohistochemistry. We show that repeated TNF-α gene delivery using NBs and US can lead to the local production of TNF-α. This results in antitumor effects, including activation of p53-dependent apoptosis, decrease in tumor vessel density, and suppression of tumor size. In this study, we showed the effectiveness of using NBs and US for TNF-α gene delivery into tumor cells.