Synthesis And Characterization Of Reducing Sensitive Camptothecin Polymer Prodrugs

Camptothecin(CPT) is a kind of alkaloids with anti-cancer activity which has therapeutic effect to a wide variety of tumors such as liver cancer, colorectal cancer, lung cancer and leukemia. However, the development of CPT as a therapeutic agent has been severely hampered by its poor aqueous solubility, which can lead to rapid blood clearance and unpredictable efficacy following intravenous administration. Polyphosphoesters(PPES) are appealing for potential biological applications because of their good biocompatibility and biodegradability, as well as the structural versatility. Dextran is a kind of natural polysaccharide, possess good biocompatibility, water solubility, biodegradability and extensive sources, have broad application in drug delivery system. To end this, this paper designed and synthesized a kind of camptothecin derivatives containing disulfide bond and azide group, and then the camptothecin derivatives was conjugated to polyphosphate or dextran by click reaction. The chemical structure and biological applications of resulting polymeric prodrug were studied.The work is mainly divided into the following two parts:1. Synthesis and characterization of a polyphosphoester-conjugated camptothecin prodrug with disulfide linkage for potent reduction-triggered drug deliveryA reduction-cleavable camptothecin(CPT) prodrug was developed with one releasable disulfide carbonate linker built between CPT and polyphosphoester backbone, resulting in disruption of the micellar structure and rapid release of CPT parent drug under the intracellular reducing milieu. The polymeric prodrug, abbreviated as(PBYP-g-ss-CPT)-b-PEEP, was synthesized via a combination of ring-opening polymerization(ROP) and Cu(I)-catalyzed azide-alkyne cycloaddition(CuAAC) “click” reaction. The chemical structures of the intermediate polymers and polymeric prodrug have been fully characterized by 1H NMR and FT-IR analyses, while the molecular weights and molecular weight distributions were measured by gel permeation chromatography(GPC). The self-assembly behaviors were investigated by a fluorescence probe method, dynamic light scattering(DLS) and transmission electron microscopy(TEM) analyses. The resulting CPT conjugates formed well-defined nanoparticles in an aqueous solution with a diameter of 140-152 nm. The DLS results indicated that they were relatively stable in neutral pH media, but could be degraded under reductive microenvironments. The in vitro drug release studies showed that drug released from CPT prodrug nanoparticles was in a GSH-dependent manner. A methyl thiazolyl tetrazolium(MTT) assay demonstrated that the polyphosphoester backbone possess low cytotoxicity against L929 cells and HepG2 cells cells, and the CPT prodrug nanoparticles could efficiently prohibit the growth of HepG2 cells. In addition, the intracellular uptake of prodrug nanoparticles could efficiently deliver and release CPT into HepG2 cells revealed by a live cell imaging system.2. Synthesis and characterization of a dextran-conjugated camptothecin prodrug with disulfide linkage for potent reduction-triggered drug deliveryThe chemical structures of the intermediate polymers and polymeric prodrug(Dex-g-ss-CPT)have been fully characterized by 1H NMR and FT-IR analyses. The self-assembly behaviors were investigated by a fluorescence probe method, dynamic light scattering(DLS) and transmission electron microscopy(TEM) analyses. The resulting CPT conjugates formed well-defined nanoparticles in an aqueous solution. The in vitro drug release studies showed that drug released from CPT prodrug nanoparticles was in a GSH-dependent manner. A methyl thiazolyl tetrazolium(MTT) assay demonstrated that the polyphosphoester backbone possess low cytotoxicity against L929 cells and HepG2 cells cells, and the CPT prodrug nanoparticles could efficiently prohibit the growth of HepG2 cells.