Design And Bioapplication Of Functional Polymer Carriers Besed On Acylhydrazone Bond

With the development of polymer chemistry and physics, functional polymer materials become more and more important. Functional polymers refer to the synthesis or nature polymers which have special functions like chemical activity, smart responsibility, conductivity, biocompatibility, catalytic activity, pharmacological properties, selectivity, and so on. Recently, functional polymers have drawn great attention in biological field, espectially for biosensors, drug delivery system and bio-image. In this dissertation, based on the requirements from biology, a series of functional polymers with distinct structures and functions have been successfully designed and applied for biosensors, drug delivery and multifunctional theranostics. This dissertation is divided into four major sections, and the details and key conclusions are described as follows:1. Construction and bioapplication of acylhydrazone-connected tri-block copolymer micelles based on poly(ε-caprolactone)-a-poly(ethylene glycol)-a-poly(ε-caprolactone)Smart amphiphilic polymer micelles have been widely used for drug delivery carriers. The structure of the macromolecules and the ratio of hydrophilic/hydrophobic segment will significant affect the drug loading efficiency, drug release profile and antitumor effect. Here, we reported a series of acylhydrazone-connected tri-block amphiphilic copolymers(PCL-a-PEG-a-PCL) and investigated their application in stimuli-responsive drug delivery systems. The length of hydrophobic PCL segment in PCL-a-PEG-a-PCL was controlled through changing the ratio of ε-caprolactone(ε-CL) and hydroxyethyl terminal with acylhydrazone-linked poly(ethylene glycol), which induced the size change of self-assembled micelles. Hydrolysis results and drug release profile of different PCL-a-PEG-a-PCL in various phosphate buffers indicated the relationship between the length of hydrophobic segments and disassembly of micelles. The cytotoxicity against NIH/3T3 normal cells evaluated via MTT assay showed that PCL-a-PEG-a-PCL exhibited good cytocompatibility. In addition, anti-cancer effect against He La cell showed that doxorubicin(DOX) loaded PCL-a-PEG-a-PCL micelles had a relative high in vitro therapeutic effect compared to free DOX and the antitumor effect was highly related to the ratio of hydrophilic/hydrophobic segments.2. Construction and application of pH-triggered cleavable hyperbranched polyacylhydrazone for drug deliveryPolymeric drug carriers with high stability during long circulation, triggered drug release and degradation after they reached the target tissue are particularly interesting in drug delivery system. Here, a novel pH-triggered backbone pH-cleavable hyperbranched polyacylhydrazone(HPAH) was successfully prepared and used for drug delivery carriers. As a water soluble hyperbranched polymer with a large amount of hydrazine group, HPAH was grafted with DOX to form polymer-drug conjugates. The obtained HPAH-DOX conjugates could self-assemble into polymeric micelles with an average diameter of 20 nm, due to the amphiphilicity of HPAH-DOX. According to the previous literatures, micelles within 20-200 nm have the EPR effect during the long circulation. 2D DOSY NMR degradation experiments demonstrated that HPAH was stable in neutral conditions while cleavable in acidic environments. According to MTT assay, it demonstrated that HPAH, monomers, and degradation products had good cytocompatibility to NIH/3T3 cell line. Both flow cytometry and confocal laser scanning microscopy(CLSM) confirmed the faster cellular uptake of HPAH-DOX than free DOX. In vitro anti-cancer results showed that the HPAH-DOX could inhibit the growth of He La cells. Thus, we expect HPAH can be further investigated in drug delivery system and become a promising drug delivery carrier.3. Construction and application of a pH-sensitive nanoreactor via a double-hydrophilic multiarm hyperbranched polymerSmart biosensor requires that the system can fast response to the change of environment. Here, a double-hydrophilic multiarm hyperbranched polymer with a hyperbranched poly(amidoamine)(HPAMAM) core and many poly(ethylene glycol) monomethyl ether(MPEG) arms connected by pH-sensitive acylhydrazone bonds(HPAMAM-g-MPEG) was successfully prepared. Benefiting from the cationic dendritic core and PEGylation shell, the double-hydrophilic multiarm hyperbranched polymer was used as a nanoreactor for Cd S quantum dots(Cd S QDs) synthesis in aqueous solution. The obtained HPAMAM-g-MPEG and Cd S/HPAMAM-g-MPEG nanocomposites not only had good water solubility and biocompatibility, but also pH sensitivity. Fluorescence spectroscopy investigations confirmed that the acylhydrazone linkage between the dendritic core and linear arms was readily broken under acidic condition(pH < 5.5). When MPEG arms departed from the HPAMAM core, the fluorescence intensity of Cd S/HPAMAM-g-MPEG nanocomposites greatly increased. As we know that pH gradient widely exists in different organs and subcellular organelle. In vitro cell experiment showed that the fluorescence of cells incubated with Cd S/HPAMAM-g-MPEG nanocomposites increased with time. Such pH-responsive behavior of Cd S/HPAMAM-g-MPEG nanocomposites was utilized as an exploration of a novel fluorescence probe in an acidic lysosome exemplified by COS-7 cells.4. Multifunctional pH-sensitive superparamagnetic iron-oxide nanocomposites for targeted theranosticTheranostic is defined as a material that combines the modalities of therapy and diagnostic imaging. The ultimate goal of the theranostic is to decrease the expense and complication of diagnosis and medical clinic. It also gains the ability to monitor the diseased tissue and drug efficacy. Here, a multifunctional pH-sensitive superparamagnetic iron-oxide(SPIO) nanocomposite system was developed for simultaneous tumor magnetic resonance imaging(MRI) and therapy. Small-size SPIO nanoparticles were chemically bonded with antitumor drug, DOX, and biocompatible poly(ethylene glycol)(PEG) through pH-sensitive acylhydrazone linkages, resulting in the formation of water soluble SPIO nanocomposites with magnetic targeting and pH-sensitive properties. Under an acidic environment, the DOX was quickly released from the SPIO nanocomposites due to the cleavage of pH-sensitive acylhydrazone linkages. With the help of magnetic field, the DOX-conjugated SPIO nanocomposites showed higher cellular uptake and better antitumor effect, compared to free DOX. Both in vitro and in vivo MRI results showed these SPIO nanocomposites illustrated high resolution in MRI diagnosis.