Preparation, Characterization And Application Of Environment-responsive Polymeric Nano-drug Carriers

With the rapid development of material science, biomedicine and clinical medicine, drug nano-carriers have received widespread attention as they can effectively load the active drug molecules in to the matrix, protect the drug activity and improve the drug bioavailability. Among drug nano-carriers, polymeric drug nano-carriers possess many advantages as good biocompatibility and stability, easy functionalization by surface modification, and drug controlled release, thus changing the drug distribution in the body and pharmacokinetic, improving the drug bioavailability, and reducing the side effects of drugs.As tumor tissues have some characteristics such as the ability to grow fast, enhanced permeability and retention effect(EPR) for nanoparticles, and different microenvironment from normal tissues, in addition to biocompatibility and high loading/encapsulation of desired drug molecules, the ideal anti-tumor drug delivery system has to achieve effective controlled release as zero or low premature release of drug molecules in blood circulation while rapid and complete release of drug molecules when reaching targeted sites. Environment-responsive polymeric nano-carriers not only have excellent biocompatibility and high capacity of loading drug molecules but also effectively control drug release by responding to the stimulus (pH, temperature, redox and so on) in the tumor microenvironment. Therefore, three novel types of environment-responsive polymeric nano-carriers were synthesized and their drug loading capacity and drug controlled release behavior were investigated. In summary, this dissertation includes three parts as follows:(1) Acid-degradable polyketal PCADK was synthesized by the acetal exchange reaction between 2,2-dimethoxypropane and 1,4-cyclohexanedimethanol, and based on the above synthetic method, polyketal PK3 was synthesized by copolymerizing 13.3 mol% hydrophilic 1,5-pentanediol to improve polymer hydrophilicity. Polyketal PK3 was used as drug carrier due to the better hydrophilicity and proper hydrolysis rate, and doxorubicin hydrochloride and paclitaxel was respectively encapsulated into the polymer through modified (W/O/W) double emulsion method and (O/W) single emulsion method. The results demonstrated that the drug loading content and encapsulation efficiency depended on the mass ratio of drug and polymer. In comparison to hydrophilic doxorubicin hydrochloride (DOX), hydrophobic paclitaxel (PTX) was entrapped into polyketal PK3 more effectively due to its hydrophobic character and the single emulsion method of preparing drug-loaded nanoparticles. The in vitro release behaviors of the DOX-loaded and PTX-loaded nanoparticles exhibited that both DOX and PTX release were pH-dependent, and the release rate was much faster in acid environment than that in neutral environment. The cytotoxicity assay indicated that blank PK3 nanoparticles were biocompatible and suitable as drug vehicles, while PK3 nanoparticles encapsulating DOX or PTX could efficiently kill the tumor cells.(2) Poly(vinylcaprolactam)(PVCL)-based degradable P(VCL-s-s-MAA)-PEG nanogels with PEGMA-rich corona were prepared as drug nano-carrier via precipitation polymerization, where N,N-bis(acryloyl) cystamine (BAC) served as cross-linker, methacrylic acid (MAA) and PEG methyl ether methacrylate (PEGMA) acted as comonomers. The synthetic P(VCL-s-s-MAA)-PEG nanogels with excellent stability had distinct temperature sensitivity as largely observed in the case of PVCL-based particles and their volume phase transition temperature (VPTT) could be accurately adjusted by changing MAA content and ambient pH. In the presence of reducing agent glutathione (GSH) or dithiothreitol (DTT), the nanogels could be degraded into individual short linear polymer chains by the cleavage of the disulfide linkages coming from the cross-linker BAC. The nanogels could effectively encapsulate DOX inside and presented stimuli-triggered drug release that more drug was released as the pH was lowered, and 95% of DOX was released when in reducing environment with 10 mM GSH. The results of the cytotoxicity assays further demonstrated that the blank P(VCL-s-s-MAA)-PEG nanogels were non-toxic to normal cells and DOX-loaded nanogels presented efficient anti-tumor activity to HeLa cells.(3) Ketal-containing 2,2-dimethacroyloxy-l-ethoxypropane (DMAEP) was synthesized and used as cross-linker to prepare poly(vinylcaprolactam)(PVCL)-based acid-degradable nanogels P(VCL-ketal-HPMA), where precipitation polymerization was adopted and N-(2-hydroxypropyl)methacrylamide (HPMA) acted as comonomer. The prepared P(VCL-ketal-HPMA) nanogels had distinct temperature sensitivity that the nanogels got collapsed with increasing temperature and the VPTT could be accurately regulated by changing the mass ratio of HPMA ang VCL. Besides, P(VCL-ketal-HPMA) nanogels presented pH response that they could remain stable in neutral condition while dissolve into short linear polymers in acid environment due to the cleavage of ketal cross-linking units. The nanogels could effectively encapsulate DOX inside and presented pH-dependent drug release profiles. In comparison to the DOX-loaded non-degradable P(VCL-cross-HPMA) nanogels which were cross-linked with N,N’-methylene bisacrylamide(MBA), DOX-loaded-P(VCL-ketal-HPMA) nanogels exhibited more effective drug controlled release behavior that 13% of DOX was released in simulated blood circulation (pH 7.4), while a rapid and complete drug release (96%) was triggered in an acidic environment such as in lysosomes, much more than that released from non-degradable nanogels. The results of the cytotoxicity assays demonstrated that the blank P(VCL-ketal-HPMA) nanogels were very biocompatible due to the PHPMA in the nanogels, while compared to the DOX-loaded non-degradable nanogels, DOX-loaded P(VCL-ketal-HPMA) nanogels presented more efficient anti-tumor activity to HeLa cells.