Folate-functionalized polymeric micelles for tumor targeted delivery of a potent multidrug-resistance modulator...

To overcome multidrug resistance (MDR) existing in tumor chemotherapy, polymeric micelles encoded with folic acid on the micelle surface were prepared with the encapsulation of a potent MDR modulator, FG020326. The micelles were fabricated from diblock copolymers of poly(ethylene glycol) (PEG) and biodegradable poly(epsilon-caprolactone) (PCL) with folate attached to the distal ends of PEG chains. The folate-conjugated copolymers, folate-PEG-PCL, were synthesized by multistep chemical reactions. First, allyl-terminated copolymer (allyl-PEG-PCL) was synthesized through a ring-opening polymerization of epsilon-caprolactone in bulk employing monoallyl-PEG as a macroinitiator. Second, the allyl terminal groups of copolymers were converted into primary amino groups by a radical addition reaction, followed by conjugation of the carboxylic group of folic acid. In vitro studies at 37 degrees C demonstrated that FG020326 release from micelles at pH 5.0 was faster than that at pH 7.4. Cytotoxicity studies with MTT assays indicated that folate-functionalized and FG020326-loaded micelles resensitized the cells approximately five times more than their folate-free counterparts (p < 0.01) in human KB(v200) cells treated with vincristine (VCR). The in vitro Rhodamine 123 efflux experiment using MDR KB(v200) cells revealed that when cells were pretreated with folate-attached and FG020326-loaded micelles, the P-glycoprotein (P-gp) drug efflux function was significantly inhibited.