Design And Synthesis Of The Smart Theranostic System For Tumor Imaging And Targeted Therapy Based On Polyaspartic Derivative

The scientific researchers in the world are all facing an important research topicof cancer diagnosis and therapy. With the full cooperation of all the scientific researchfield, especially the chemistry, biology and medical science, there is a continuousimprovement and development for cancer diagnosis and therapy. In recent years,nanotechnology is gradually becoming a new pathway for cancer diagnosis andtherapy. In this paper, various polymeric delivery system based on polyaspartic acidderivatives were prepared for delivering anti-cancer drug or imaging agent.The amphiphilic entipede-like polymer poly(succinimide)-grafted-p(ethyleneglycol)-dodecylamine (PSI-g-PEG-DDA) was successfully synthesized. Through theself assembling process of the polymer, polymer encapsulated the superparamagneticiron oxides (SPIOs) for preparing a new imaging contrast. The particle size andmorphology of the system was characterized. The result of mice magnetic responseimaging (MRI) in vivo showed that this new type of system caused a greatenhancement effect on T2magnetic resonance and long half-life in the circulation.A biodegradable and biocompatible polymeric micelle system to solubilize ADRand release this anticancer agent in a pH-dependent manner was prepared. To achievethe purpose above, the pH-responsive amphiphilic centipede-like polymer conjugatep(aspartate)-graft-p(ethylene glycol)-dodecylamine-hydrazone-adriamycin(PASP-g-PEG-DDA-Hyd-ADR) was successfully synthesized. Adriamycin (ADR)was conjugated to the polymer backbone through an acid-labile hydrazone bond. Theproduct was found to form spherical micelles in aqueous media because of itsamphiphilic nature with average particle size of25nm measured by dynamic lightscattering (DLS) and AFM imaging. Drug release curve pointed out the content ofreleased ADR gradually increased with the pH decreasing and that almost no ADRwas released at normal human condition (pH7.4). This result showed the micelles can stably preserve drugs under physiological conditions (pH7.4) and selectivelyrelease them by sensing the intracellular pH decrease in endosomes and lysosomes(pH4-6). MTT assay showed the cytotoxicity to HepG2decreased compared withfree ADR and that the conjugate kept the antitumor activity of free ADR. Remarkably,CLSM revealed that the localized fluorescence is dot-shaped within the cytoplasm,suggesting the presence of the micelles trapped in vesicular entities after2h. Thetime-dependent increase in fluorescence intensity, which was also observed by flowcytometry, indicated the polymer-drug micelles were uptaken by the cancer cellsthrough endocytosis process.A pH-responsive anticancer drug polymer conjugate p(aspartate)-graft-p(ethyleneglycol)-dodecylamine-hydrazone-(adriamycin-levulinic acid) was synthesized as aMRI-visible and pH-sensitive drug delivery system. Being pH-sensitive, theanticancer drug ADR are stable in the polymeric micelles at neutral pH, resemblingthe physiological environment, whereas they released rapidly in acidicendosomal/lysosomal compartments of tumor cells for cancer therapy with theacid-linker breaking. For the purporse of MR imaging, the hydrophobicsuperparamagnetic iron oxide nanoparticles (SPIONs) were encapsulated inside thecore of the micelles. In order to identify the specific liver cancer tumors moreefficiently, Anti-vascular endothelial growth factor (anti-VEGF) was modified to themicelles. The stability studies showed that all the conjugate@IO have excellentsolubility and stability in stimulate biological media, suggesting that they have longercirculation time. Drug release studies in vitro showed that the ADR release from thepH-sensitive polymeric micelles was significantly faster at pH5.0than at of pH7.4.MTT assay showed that all the conjugate@IO exhibit low cytotoxicity and highantitumor activities against HepG2cells. Furthermore, the anti-VEGF-conjugate@IOshowed a high spin-spin (T2) relaxivity. In vivo MRI experiments on tumor-bearingmice demonstrated that the anti-VEGF-conjugate@IO achieved an appreciableaccumulation into tumor, suggesting their potential utility as tumor-selective MRIcontrast agents.A smart drug delivery system is prepared by citraconylated polyaspartic acid(PASP) derivate-drug conjugate. The conjugate contains two pH-sensitive groups: citraconic amide and hydrazone linker. Citraconic amide group can enhance tumortherapy efficiency by the extracellular pH-sensitive charge-conversion property.Hydrazone linker between polymer and drug can cleave efficiently in the intracellularpH environment. The resulting conjugate shows dual-pH sensitive properties:extracellular pH-triggered enhanced tumor targeting and intracellular pH-triggereddrug release. The results of physicochemical properties, intracellular location andcytotoxicity of conjugate micelles demonstrates that this novel smart drug deliverysystem can enhance intracellular delivery of drug at a low pH and then release drugrapidly.We also reported a novel gadolinium chelate surface conjugated superparamagneticiron oxide (SPIO) nanomicelles. In our design, Gd-DTPA conjguated with the folicacid (FA) targeting polyaspatric derivative (PASPD) coating surface of SPIOnanoparticles (IO-PASPD). The morphology of the Gd-DTPA-IO-PASPD wasuniform spherical with an average particle size of50nm measured by dynamic lightscattering (DLS) and TEM imaging. The stablity results showed that theFA-Gd-DTPA-IO-PASPD can stably preserve IO under physiological conditions (pH7.4). An MTT assay showed that the cytotoxicity of FA-Gd-DTPA-IO-PASPDagainst hepatoma carcinoma (HepG2) cells was no significant after24h incubation.MRI in vitro and in vivo were also imaged and characterized. In summary,FA-Gd-DTPA-IO-PASPD could achieve T1-weighted and T2-weighted MR imagingstimultaneously and lengthen the half life time.In summary, we prepare various polymeric delivery system based on polyasparticacid derivatives for achieving the expectant goal. Those delivery system all havespecial characteristics and application.