Intracellular uptake of DOX released from ultrasound-triggered GdSL3. MFI was determined by flow cytometry analysis. GdSL3-1, GdSL3-2, and GdSL3-3 were irradiated by 20-kHz ultrasound for 2 min at intensity levels of 14.8, 27.8, and 63.5 W/cm2, respectively. GdSL3, free DOX, and Doxil® were not irradiated with ultrasound. Mean and S.D. are shown (n = 3) (asterisk, two asterisks, and three asterisks denote p < 0.1, Student's t test).