Mitoxantrone- and Folate-TPGS2k Conjugate Hybrid Micellar Aggregates To Circumvent Toxicity and Enhance Efficiency for Breast Cancer Therapy.

Mitoxantrone (MTO) is a potent drug used to treat breast cancer; however, efforts to expand its clinical applicability have been restricted because of its high risk for cardiotoxicity. In this study, we successfully conjugated MTO or folic acid (FA) to a synthesized D-α-tocopheryl polyethylene glycol 2000 succinate (TPGS2k), herein, shortened to MCT and FCT, respectively. The two produced conjugates could self-assemble to form MCT micelles or MCT/FCT mixed micelles (FMCT) aiming to lower systemic toxicity, enhance entrapment efficiency, and provide a platform for targeted delivery. Moreover, these micellar materials showed a significantly low CMC and could be used to load MTO. The diameters of MTO-loaded micelles (MTO-MCT and MTO-FMCT) were less than 100 nm with a negative zeta potential. We further characterized the pH-responsive drug release of MTO-MCT and MTO-FMCT and then assessed their cellular uptake and antitumor efficacy in human breast cancer cell lines (MCF-7) via confocal microscopy, flow cytometry, and cytotoxicity studies. All the results revealed that both MTO-MCT and MTO-FMCT increased drug loading and entrapment efficiency and possessed sufficient pH-sensitive release. Additionally, MTO-FMCT displayed an improved uptake through folate-mediated endocytosis, resulting in a higher cytotoxic effect on MCF-7 cells compared with that of MTO-MCT. Meanwhile, both MTO-MCT and MTO-FMCT exhibited a low toxicity on hCMEC/D3 normal cells. More importantly, pharmacokinetic study demonstrated that, in comparison with free MTO injection, MTO-MCT and MTO-FMCT, respectively, achieved half-lives 11.5 and 13 times longer and a 9.7- and 5.8-fold increase in AUC. In vivo, both MTO-MCT and MTO-FMCT formulations significantly prolonged the survival time of MCF-7 tumor-bearing mice and had a better efficacy/toxicity ratio. Promisingly, MTO-FMCT micelles remarkably increased MTO accumulation in tumors in vivo, induced higher tumor cell apoptosis, and showed lower toxicity toward major organs. These results imply that MTO-FMCT may be used as a potential drug delivery system for breast cancer targeted therapy.