Study On The Anticancer Efficacy Of Antitumor Drug Loaded Polymeric Nanomaterials

Drug delivery systems based on polymeric nanoparticles have attracted great interest since 1990s, accompanied by the birth of nanotechnology and the development of biocompatible polymeric materials. It has been reported that besides the abilities to increase drug solubility, improve stability and achieve controlled release, which may be brought about by conventional drug delivery systems, polymeric nanoparticulate drug carriers also have the power to greatly alter drug biodistribution, reduce systemic toxicity and enhance drug potency. In addition, it is widely known that nanoparticles are the vehicles beneficial for "passive" tumor targeting owing to the enhanced permeability and retention (EPR) effect caused by the disorganized vascularization, defective vascular architecture of tumors and lack of lymphatic drainage, which can be taken advantage to effectively improve the concentration of drug in tumor tissues after systemic administration.However, it is also found that some potential barriers that hinder the deep permeation of drug-loaded nanoparticles through tumor tissue after their successfully reaching the tumor via EPR effect. These include the abnormal tumor vessels, high interstitial fluid pressure and complex extracellular matrix (ECM). Hence, drug-loaded nanoparticles cannot efficiently penetrate tumor tissue to reach all of the viable cells. However, most researches have focused on the antitumor efficacy or in vivo imaging of the nanoparticles. There have been few published studies on the penetration of polymeric nanoparticles in solid tumors, although it is critical for the effectiveness of tumor chemotherapy.In experimental tumor models, intratumoral administration of drug-loaded nanoparticles has been found to be an alterative method for cancer treatment in addition to limiting systemic exposure. Unfortunately, after debulking surgery as the initial primary treatment for major ovarian or gastrointestinal cancers, the residual tumors peritoneally disseminated can hardly be observed, and it is difficult to inject nanoparticle solution into so many metastatic tumors with small sizes. Moreover, the weak ability to efficiently penetrate the tumor and affect cells distant from the injection site also limits therapeutic efficacy of nanoparticles.With the above-mentioned problems in mind, the following original work has been carried out in this thesis:(1) We chose cationic natural biomacromolecule gelatin (GEL) and an anionic monomer acrylic acid (AA) as reactants and successfully prepared gelatin-poly(acrylic acid) (GEL-PAA) nanospheres by initiating the polymerization of AA in GEL aqueous solution. The GEL-PAA nanospheres were found to be well-dispersed, size controllable and stable in aqueous medium. After the nanospheres were cross-linked by adding cross-linker, glutaraldehyde, their stability in basic or high salt concentration solutions could be notably enhanced.(2) Cisplatin (CDDP)-loaded GEL-PAA nanoparticles were successfully synthesized by polymer-metal complex formation of CDDP with carboxylic groups in aqueous solution. The obtained nanoparticles had a spherical shape with a mean size of about 100nm and satisfactory drug loading content and encapsulation efficiency were achieved. The nanospheres exhibited a continuous release of the entrapped CDDP in vitro and showed relatively high kinetic stability, keeping their size for 10 days in phosphate buffered saline (PBS). In vitro cytotoxicity study revealed that CDDP-loaded nanoparticles had similar cytotoxicity to free CDDP after 48 h co-incubation, while the empty GEL-PAA nanoparticles are no cytotoxicity at the normal concentration and show good biocompatibility. Furthermore, NIRF dye or radioactive nuclide were modified in the CDDP-loaded nanoparticles, respectively, to evaluate their tumor targeting ability and in vivo biodistribution in tumor-bearing mice after intravenous (i.v.) administration. We found that our nanoparticles show remarkable EPR effect, leading to high tumor uptake, and the ones that are not accumulated into tumors can be easily cleared out from the body. It was also demonstrated that the nanoparticle formulation was superior in anticancer effect in vivo than free CDDP on murine hepatic H22 tumor-bearing mice model through systemic administration.(3) We have investigated the effect of a trans-tissue drug delivery system for peritumoral chemotherapy on tumor suppression. We incorporated CDDP-loaded GEL-PAA nanoparticles into the physically cross-linked gelatin hydrogel, aiming to obtain a nanoparticle-encapsulated matrix (jelly) which can be surgically implanted and plastered on the tumor mass. The implantation of jelly on tumor tissue shows more superior efficacy in impeding tumor growth and prolonging the lifetime of mice than that of intravenous injection of CDDP-loaded nanoparticles in a murine hepatoma H22 cancer model, due to much higher concentration and retention of CDDP in tumor as well as greatly increased tumor-to-normal organ CDDP uptake ratios.(4) To investigate the penetration of CDDP-loaded GEL-PAA nanoparticles through tumor tissue, we injected biotin labeled and CDDP-loaded nanoparticles into subcutaneous H22 tumor-bearing mice via the tail vein. The results suggested that a lot of nanoparticles can be located in or around the blood vessels at 4 h post-injection (p.i.), whereas they are able to be located not only around the blood vessels but also within a distance of about 20μm from the blood vessels at 24 h p.i., demonstrating that the nanoparticles have the ability to penetrate further away from the blood vessels and affect more viable cancer cells as the time elapsed. Moreover, the results of nanoparticles penetration in tumors via jelly formulation clearly reveal that not only do the drug-loaded nanoparticles permeate the tumor tissue by diffusion, but also they are able to penetrate the tumor deeply through leaky tumor vasculature.(5) We successfully synthesized well-defined GEL-PAA nanorods by storing the solution of GEL-PAA nanospheres with a size of 35 nm at 4℃. The results demonstrated that GEL-PAA nanorods were formed with one-dimensional growth of nanospheres through the triple helix re-formation of gelatin. In addition, using anionic azo dye methyl orange (MO) as template, gelatin nanotubes were successfully prepared. Next, CDDP was loaded into the nanotubes through the interaction between the platinum of CDDP and the carboxylic group of the nanotubes. In vitro cytotoxicity was investigated to assess the antitumor effect of the CDDP-loaded nanotubes.