Design And Synthesis Of Environment-Responsive Reversibly Crosslinked Drug Carriers

Nanosized particles formed by self-assembly of amphiphilic copolymer are one of most ideal nano-carriers for hydrophobic antitumor drugs. However, these nano-carriers after in vivo administration may subject to dissociation and premature drug release due to extensive dilution and interactions with biomolecules, resulting in diminished tumor-targetability. Their stability may be enhanced by cross-linking. It should be noted, nevertheless, that stably crosslinked nano-carriers though arriving at the disease site may not be able to efficiently release drug, leading to low drug efficacy.In this thesis, four novel types of amphiphilic "intelligent" nano-carriers for triggered release of anti-cancer drugs including doxorubicin (DOX) and paclitaxel (PTX) were designed and evaluated in vitro. The stability of these nano-carriers was markedly enhanced through cross-linking. However, because the crosslinker can be reversed under the reductive environments encountered in cancer cells or mildly acidic environments in endosome, drugs are efficiently released inside cells, resulting in safe and efficient drug delivery. The thesis includes following four parts:Part I:Disulfide-crosslinked dextran nanoparticles were designed for triggered release of doxorubicin, an antitumor drug. The crosslinked nanoparticles were stable against large volume dilution and concentrated salt condition. In vitro release studies showed reduction-responsive release of doxorubicin. For example, only 10% DOX was released from dextran-lipoic acid with a substitution degree (DS), after 11 hours in 10 mM PB. However,90% DOX was released in 11 hours in the presence of 10 mM DTT (mimicking the intracelullar reductive environment) under otherwise the same conditions. MTT assays displayed that DOX loaded crosslinked nanoparticles had a similar drug efficacy to the non-crosslinked counterparts. The intracellular trafficking of DOX in HeLa cells using confocal laser scanning microscopy (CLSM) revealed that DOX-loaded crosslinked nanoparticles efficiently delivered and released DOX into the cell nucleus. These novel nano-vehicles yet simple display unprecedented multi-functionalities, such as biocompatibility, degradability, high drug loading and efficient drug release inside cells, which render them superb for tumor-targeted delivery of anticancer drugs.Part II:Crosslinked nanoparticles were prepared from polyvinyl alcohol-lipoic acid derivatives. These crosslinked nanoparticles showed enhanced stability. The release studies revealed reduction-sensitive DOX release from DOX-loaded crosslinked nanoparticles. The intracellular release of DOX from the crosslinked nanoparticles followed by CLSM using Hela cells showed that DOX-loaded crosslinked nanoparticles efficiently delivered and released DOX into the cells. Toxicity studies demonstrated that DOX loaded crosslinked nanoparticles had a similar drug efficacy to the non-crosslinked counterparts.Part III:Micelles based on poly(ε-caprolactone)-polyethylenimine-poly(ethylene glycol) (PCL-PEI-PEG) copolymers were prepared and crosslinked at the interface using 3,3'-dithiodipropionic acid (DTDPA) as a crosslinker under aqueous conditions. The resulting crosslinked micelles had improved stability The DOX release from DTDPA crosslinked PCL-PEI-PEG2 micelles was less than 20% in 12 h. However, in the presence of 10 mM DTT under otherwise the same conditions., DOX was released nearly quantitatively in 12 h CLSM observations showed fast endosomal escape and rapid de-crosslinking of micelles in the cytoplasm, resulting in efficient intracellular DOX release.Part IV:cis-aconitic acid anhydride(CAA) crosslinked PCL-PEI-PEG micelles were prepared and used for triggered release of paclitaxel. CAA-crosslinked micelles were stable against large volume dilution and physical salt condition. The in vitro release studies revealed that PTX release from CAA crosslinked PCL-PEI-PEG2 micelles were pH-dependant.