Abstract
Targeted delivery of immunosuppressants to allografts can increase the concentrations of drugs in pathological tissues, improve therapeutic effects and reduce unfavorable side effects. Therefore, we synthesized FK506-loaded microbubbles (FK506-MBs) for site-specific release of FK506 into transplanted hearts by the ultrasound-targeted microbubble destruction (UTMD) technique. The average particle size of FK506-MBs was 1.65 ± 0.32 μm and they had high drug loading and encapsulation efficiency. The in vivo drug concentration in transplanted hearts that were treated with FK506-MBs plus UTMD was about 1.64-fold higher than that in grafts that received free FK506 at the same dosage. The degree of graft rejection in the FK506-MB plus UTMD group was lower than those of other groups. Both infiltration of T cells and secretion of inflammatory cytokines were significantly reduced in the FK506-MB plus UTMD group. More importantly, the mean survival time of the grafts was significantly longer (16.00 ± 0.89 day) than those of the PBS group (6.66 ± 1.36 day) and the FK506 group (12.83 ± 1.17 day). In addition, we also found that the concentration of FK506 in whole blood was lower in the FK506-MB plus UTMD group than that in the FK506 group, which would be beneficial for reducing the side effects. Hence, our results showed that combining FK506-MBs with UTMD was an effective strategy to deliver FK506 to transplanted hearts, which can increase the local drug concentration and enhance its efficacy on rejection. Ultrasound-targeted drug release is safe and radiation-free, with great potential for clinical transformation, and could also be extended to the treatment of other graft rejection cases, such as liver transplantation, kidney transplantation and so on.