Targeted Delivery of Doxorubicin by Folic Acid-Decorated Dual Functional Nanocarrier

Doxorubicin (DOX) is one of the most commonly used antineoplastic agents, but its clinical application is oftentimes coupled with severe side effects. Selective delivery of DOX to tumors via nanosized drug carrier represents an attractive approach to this problem. Previously, we developed a dual functional nanomicellar carrier, PEG_5K-embelin₂ (PEG_5K-EB₂), which was able to deliver paclitaxel (PTX) selectively to tumors and to achieve an enhanced therapeutic effect. In the present study, we examined the utility of PEG_5K-EB₂ to deliver DOX to tumors. In addition, folic acid (FA) was coupled to the surface of the PEG_5K-EB₂ micelles (FA-PEG_5K-EB₂) to further improve the selective targetability of the system. DOX-loaded PEG_5K-EB₂ micelles were uniformly spherical particles with a diameter of approximately 20 nm. Incorporation of FA had minimal effect on the size of the particles. The DOX loading efficiency was as high as 91.7% and 93.5% for PEG_5K-EB₂ and FA-PEG_5K-EB₂, respectively. DOX formulated in PEG_5K-EB₂ micelles (with or without FA decoration) demonstrated sustained kinetics of DOX release compared to free DOX. FA-PEG_5K-EB₂ significantly facilitated the intracellular uptake of DOX over free DOX and PEGylated liposomal DOX (Doxil) in breast cancer cells, 4T1.2, and drug resistant cells, NCI/ADR-RES. P-gp ATPase assay showed that PEG_5K-EB₂ significantly inhibited the function of the P-gp efflux pump. The maximum tolerated dose of DOX-loaded PEG_5K-EB₂ micelles was 15 mg/kg in mice, which was 1.5-fold greater than that for free DOX. Pharmacokinetics (PK) and biodistribution studies showed that both types of DOX-loaded micelles, especially FA-PEG_5K-EB₂, were able to significantly prolong the blood circulation time of DOX and facilitate its preferential accumulation at the tumor tissue. Finally, DOX/PEG_5K-EB₂ mixed micelles demonstrated significantly enhanced tumor growth inhibitory effect with minimal toxicity in comparison to free DOX and Doxil and the antitumor activity was further enhanced after the decoration by folic acid. Our data suggest that FA-PEG_5K-EB₂ micelles represent a promising DOX delivery system that warrants more study in the future.