ABSTRACT
The drug-loaded ultrasound (US) contrast nanoparticles, which can effectively accumulate in the tumor to penetrate into its deep section, were prepared. After being heated or under the near infrared (NIR) light irradiation, the size of nanoparticles would transform from nanometer-scale to micrometer-scale in vitro, which can vastly enhance the effect of US imaging. We evaluated the size changes of the nanoparticles in vitro, investigating their effect in ultrasound imaging and distribution in vivo. Liposomes containing hydrophobic modified hollow gold nanospheres (HAuNS), doxorubicin (DOX) and perfluorohexane (PFH), which were referred to DOX and HAuNS loaded PFH liposome (DHPL), were prepared by thin film evaporation and ultrasonic technique. The morphology and size of DHPL were measured by transmission electron microscopy and particle size analyzer with dynamic light scattering (DLS) method. The agar gel pore model was used to investigate the enhanced effect of nanoparticles in vitro US imaging under the NIR light irradiation. The biodistribution of DHPL in 4T1 tumor-bearing mice after intravenous injection was measured by the in vivo imaging system. The DHPL were spherical at a particle size of 302 ±5 nm and polydispersity index of 0.195 ±0.018. The HAuNS loaded on phospholipid membrane was observed in transmission electron microscope (TEM) image. Under the NIR light irradiation (1 or 2 W·cm-2), the temperature of the solution containing the DHPL (0.2, 0.04, 0.02 g·L-1 in terms of HAuNS) rose rapidly. And a certain amount of micrometer-sized particles could be detected by the particle size analyzer when the temperature of the analyzer was raised to 52℃. The abundant microbubbles, which would enhance the effect of US imaging, were detected by ultrasonic diagnostic apparatus when the nanoparticles were irradiated by NIR light in the in vitro US imaging experiment. The in vivo distribution experiment showed that the DHPL could effectively accumulate in the tumor due to the enhanced permeability and retention effect (EPR effect) of the tumor. In this study, we successfully made a nanometer-micrometer reversible nanoparticles that can accumulate inside the tumor to provide a feasible scheme for US imaging in the tumor site and the combinational photothermal-chemotheraphy simultaneously.