Synergistic effects of ultrasound-activated microbubbles and doxorubicin on short-term survival of mouse mammary tumor cells

The primary focus of this paper is to quantify the therapeutic synergism when combining ultrasound, ultrasound contrast agents (UCAs) and doxorubicin for breast cancer treatment using an in vitro experimental configuration with mouse mammary tumor (4T1) cells. The 4T1 cells were grown in 96 well plates and allowed to grow to 90% confluency. A 1-MHz focused (f/3) single-element transducer was usedtoexpose the microbubbles(MBs) (Definity) with ultrasound near the surface of the cells. After the ultrasound exposure, different doses of doxorubicin were added and incubated for 24 hours at 37°C, 100% humidity and 5% CO₂. The efficacies of the drug only and ultrasound-activated MBs combined with drug therapiestokill cells were then quantified by analyzing the cell viability after 24 hours of treatment using the MTT Cell Proliferation Assay. The combined therapy resulted in 60±5.9% officell viability compared to 82±4.5% when only doxorubicin was used. The cell viability was 72±5.8% when only ultrasound-activated MBs were used with a similar acoustic pressure condition. No significant increase in cell death was observed for higher concentrations of doxorubicin whereas higher peak negative pressure of the ultrasound wave resulted in increased cell death.