Ultrasound triggered drug release from 10-hydroxycamptothecin-loaded phospholipid microbubbles for targeted tumor therapy in mice.

Ultrasound targeted microbubble destruction (UTMD) was one of the most promising strategies to enhance drug delivery in cancer therapy. Microbubbles (MBs) serve as a vehicle to carry anti-tumor drugs and locally release them when exposed to therapeutic ultrasound, resulting in drug accumulation in tumor tissues and enhanced anti-tumor effect. However the ultrasound triggered drug delivery system has been seriously limited due to the poor loading capacity of MBs. Here we present a new strategy to overcome the low drug payload of MBs for ultrasound guided drug delivery. In this study, we developed a novel microbubble carrying 10-HCPT which only needs a particularly low single dose of injection (4-6 mg) for tumor therapy in clinical application, therefore, the required high dosing of drug loaded MBs for ultrasound mediated drug delivery is not necessary. We subsequently investigated the combination of ultrasound application with HLMs to achieve therapeutic effect on tumor at a feasible dose of MBs. HLMs were manufactured with a high drug encapsulation and loading content and simultaneously maintained the acoustic properties as an ultrasound contrast agent. After that, tumor-bearing mice were routinely and non-invasively administered with HLMs through the tail vein and were then exposed to ultrasound, resulting in a remarkable drug accumulation in tumor tissues and a significant increase in tumor inhibition rate (70.6%) compared with HLMs alone (47.8%) as well as commercial HCPT injection (49.4). In conclusion, HLMs are expected to improve the therapeutic efficacy of MBs and are worthy of further study for UTMD mediated drug delivery.