Multifunctional pH-disintegrable micellar nanoparticles of asymmetrically functionalized β-cyclodextrin-based star copolymer covalently conjugated with doxorubicin and DOTA-Gd moieties.

We report on a novel type of multifunctional pH-disintegrable micellar nanoparticles fabricated from asymmetrically functionalized β-cyclodextrin (β-CD) based star copolymers covalently conjugated with doxorubicin (DOX), folic acid (FA), and DOTA-Gd moieties for integrated cancer cell-targeted drug delivery and magnetic resonance (MR) imaging contrast enhancement. Asymmetrically functionalized β-CD, (N(3))(7)-CD-(Br)(14), which possesses 7 azide functionalities and 14 α-bromopropionate moieties in the upper and lower rim of rigid toroidal β-CD core, respectively, was synthesized at first. The subsequent atom transfer radical polymerization (ATRP) of N-(2-hydroxypropyl) methacrylamide (HPMA), conjugation with DOX and FA, and click reaction with alkynyl-(DOTA-Gd) complex afforded (DOTA-Gd)(7)-CD-(PHPMA-FA-DOX)(14) star copolymer comprising of 7 DOTA-Gd complex moieties and 14 PHPMA arms covalently anchored with DOX and FA via acid-labile carbamate linkages and ester bonds, respectively. The covalent conjugation with ∼13 DOX molecules onto PHPMA arms per star copolymer (∼14 wt% loading content) endows the initially hydrophilic one with amphiphilicity, leading to the self-assembly into micellar nanoparticles of several tens of nanometers in aqueous solution at pH 7.4. In vitro DOX release profile from micellar nanoparticles is highly pH-dependent, and over a time period of 42 h, cumulative releases of ∼10%, 53%, and 89% conjugated DOX at pH 7.4, 5.0, and 4.0, respectively, were observed. Most importantly, the pH-modulated release of conjugated DOX from micellar nanoparticles is accompanied with the micelle disintegration due to the loss of amphiphilicity of the star copolymer scaffold. In vitro cell viability assays revealed that (DOTA-Gd)(7)-CD-(PHPMA(15))(14) star copolymer is almost non-cytotoxic up to a concentration of 0.5 g/L, whereas DOX-conjugated micellar nanoparticles of (DOTA-Gd)(7)-CD-(PHPMA-FA-DOX)(14) can effectively enter and kill HeLa cells at a concentration higher than ∼80 mg/L. In vitro MR imaging experiments indicated a considerably enhanced T(1) relaxivity (r(1) = 11.4 s(-1) mM(-1)) for micellar nanoparticles compared to that for the small molecule counterpart, alkynyl-DOTA-Gd (r(1) = 3.1 s(-1) mM(-1)). In vivo MR imaging assay in rats revealed considerable accumulation of micellar nanoparticles within rat liver and kidney and prominent positive contrast enhancement. The integrated design of diagnostic and therapeutic functions of multifunctional pH-disintegrable micellar nanoparticles augurs well for their practical applications in the field of image-guided cancer chemotherapy.