Micelles of methoxy poly(ethylene glycol)-poly(epsilon-caprolactone) as a novel drug delivery vehicle for tacrolimus.

As a traditional immunosuppressive drug, tacrolimus showed the potency in treating ulcerative colitis. In this study, a novel drug delivery vehicle achieved by self-assembly was applied to tacrolimus. During the preparation, amphiphilic copolymer MPEG-PCL was chosen to form the unique core-shell structure, and tacrolimus was loaded into the hydrophobic core due to its great hydrophobicity. After several relevant tests, MPEG-PCL (2000-2000) was selected to be the most suitable and safest copolymer for drug carrier. For the tacrolimus loaded MPEG-PCL (2000-2000) micelles, the mean particle size and drug entrapment efficiency were ca. 25 +/- 5 nm and 98.47 +/- 0.43% respectively. The micelles could be stored for quite a long time even at room temperature after freeze-drying, and the freeze-drying process didn't affect the monodispersity of micelles. Transmission electron microscope (TEM) image emerged the spherical shape of micelles. Both Differential Scanning Calorimetric (DSC) and X-ray Diffractometer (XRD) assays demonstrated that tacrolimus was relatively completely incorporated into the core-shell structure. In vitro release profiles showed the apparent sustained release behavior compared with tacrolimus solution. Above all, animal treatment showed the most satisfactory therapeutic effect of tacrolimus loaded micelles, which means the micelles possess the ability to treat ulcerative colitis induced by dextran sulfate sodium (DSS) in mice. Therefore, micelles of MPEG-PCL could be a very promising novel vehicle for tacrolimus.