Abstract
We proposed an innovative strategy of developing the multifunctional cell-based cancer theranostic systems by employing the tumor-homing macrophages （RAW 267.4） as a vehicle capable of simultaneously carrying doxorubicin （DOX）-loaded polymeric vesicles and polymer bubbles to the target cells and releasing the therapeutic payload via the focused ultrasound treatment. The lipid-containing copolymers, poly（acrylic acid-co-distearin acrylate） （poly（AAc-co-DSA））, with DSA content of 15 and 25 mol% were used respectively as the materials to fabricate the nano-scaled polymer vesicles and polymer bubbles. The results of flow cytometry and confocal laser scanning microscopy clearly demonstrate that the drug-loaded vesicles and polymer bubbles can be effectively engulfed into macrophages via phagocytosis. Taking advantage of the dense lipid-rich membrane structure, the DOX-encapsulated polymeric vesicles after being internalized by macrophages strongly prevent the drug from leakage, thereby allowing the high activity and viability of macrophages at least for 24 h. Moreover, the polymer bubbles within the macrophages still exhibit the long-term profound ultrasound imaging contrast. Interestingly enough, through the focused ultrasound-triggered disruption of polymer bubbles, the generated inertial cavitation most likely impairs the structure of DOX-loaded vesicles, thus facilitating the drug liberation. The in vitro cytotoxicity data further confirm that while being subjected to focused ultrasound treatment and then incubated with either TRAMP-C1 or HeLa cells, the payload-containing macrophages displayed a pronounced anticancer efficacy to inhibit cell proliferation. On the other hand, we found that bone-marrow derived monocytes also served as a carrier for delivery of drug-loaded vesicles and polymer bubbles to tumor sites similar to the above macrophages（RAW 267.4）. It is noteworthy that these monocytes carrying both drug-loaded vesicles and polymer bubbles exhibit better capability of migrating toward tumor cells in the simulated tumoral environment medium than those under the serum concentration gradient conditions. This demonstrates that they still retain tumor-homing nature and can be exploited as a promising candidate for the active delivery of therapeutics and imaging contrast agents.