Passive targeting study of nanoscale lipid ultrasound contrast agents on tumors

Objective To tested the passive targeting of nanobubbles penetrating tumor vascular endothelial cells gap.Methods Twenty female BALB/c nude mice subcutaneously bearing human ovary cancer SKOV3 were devided into two groups:group A (ultrasound imaging) and group B (frozen sections:B1 and B2).DiI labled nanobubbles and microbubbles were prepared and adjusted into the same concentrations.Group A:Microbubbles and nanobubbles of 35 μl were injected into the tail vein of every mouse respectively (1.5 h interval).Ultrasound imaging were acquired.Group B:Nanobubbles and microbubbles of 10 μl were injected into the tail vein of mice in Group B1 and Group B2 respectively.Heart perfusion by PBS or 0.9％ normal saline was carried out 1.5 h after bubbles injection to clear the free bubbles in blood circulation.And the tumor and muscle of right lower limb were immediately cut off for frozen slices (3 μm),which were stained by Hoechst 33342 to mark the nucleus.Images were obtained with a confocal microscope.Results In vivo ultrasound imaging,the time to peak and clearance time of nanobubbles were longer than those of microbubbles,whereas the intensity of enhancement was lower than microbubbles.Frozen sections showed:with the confocal laser scanning microscopy imaging,quite a number of DiI-labeled nanobubbles existed in the intercellular space of SKOV3 tumor,whereas there were few nanobubbles in skeletal muscle sections.In the control,rare DiI-labeled microbubbles were observed in tumors and skeletal muscle.Conclusions Self-made lipid nanobubbles were small enough to pass through the tumor vascular endothelial gap,namely achieve the tumor passive targeting. Key words: Ultrasonography ;  Microbubbles ;  Nanotechnology