A nonionic and water-soluble polyphosphoester, poly(2-hydroxyethyl propylene phosphate) (PPE3), wassynthesized by chlorination of poly(4-methyl-2-oxo-2-hydro-1,3,2-dioxaphospholane), followed by esterificationwith 2-benzyloxyethanol and deprotection of the hydroxyl group by catalytic hydrogenation in thepresence of Pd-C. PPE3 degraded rapidly in PBS 7.4 at 37℃. The cytotoxicity and tissue compatibilityassays suggested good biocompatibility of PPE3 in vitro and in vivo. The expression of pVR1255 Lucplasmid in mouse muscle after intramuscular (i.m.) injection of DNA formulated with PPE3 solution insaline was enhanced up to 4-fold compared with that of naked DNA. These results suggest the potential ofthis polyphosphoester for naked DNA-based gene therapy. The advantages of this polymer design includethe biodegradability of the polyphosphoester and its structural versatility, which allows the fine-tuning ofthe physicochemical properties to optimize the enhancement of gene expression in muscle.

Poly(amidoamine)s with pendant primary amine (polymer 1a-1c) were evaluated as in vitro non-viralgene delivery vectors for bone marrow stromal cells (BMSCs). The cytotoxicity of these poly(amidoamine)s, measured by MTT assay, increased with increasing length of side chain, however, they were lesstoxic than branched polyethylenimine (PEI) 25 kDa. Using pGL-3 and pEGFP-C1 as luciferase gene andgreen fluorescent protein (GFP) gene, among all polycations including polymer 1a-1c and PEI, polymer1b at optimal N/P ratio showed highest luciferase expression (1.92×108 RLU/mg protein) as well aspercentage of cells expressing GFP (29.01±2.33%). For all polycations, intracellular trafficking of Cy3-labelled plasmid DNA (pDNA) was similar. Fluorescent particles attached to cell membrane at 0.5h afteradding the polycation/DNA complexes, aggregated in cytoplasm after 2h, and then stayed around theperinuclear region after 4h. pDNA nuclear localization appeared at 4h post-transfection, but much morepDNA entered into nucleus at 24h. At high N/P ratio, polymer 1a-1c could deliver pDNA into 70-80% ofBMSCs after 24h transfection, however, labelled pDNA was observed in only 4-25% of cells at the sametime. Compared to PEI, polymer 1b showed comparable or even higher percentage of pDNA uptake andnuclear localization. We concluded that poly(amidoamine)s with pendant primary amine, especiallypolymer 1b, are new kind of promising candidates of less toxic and highly efficient non-viral genedelivery vectors for BMSCs.

An amphiphilic diblock copolymer of poly(acrylic acid-b-DL-lactide) (PAAc-b-PDLLA) was synthesized byring-opening polymerization of DL-lactide initiated by hydroxyl-terminated polyacrylic acid (PAAc-OH).The critical micelle concentration (CMC) of PAAc-b-PDLLA in aqueous solution, determined by fluorescencespectroscopy using pyrene as a probe, was found about 80 mg L_1. A solution of PAAc-b-PDLLA intetrahydrofuran (THF) was dialyzed against pure water to form pH-responsive micelles. Transmissionelectron microscopy (TEM) measurement showed that the micelles exhibited regular sphericalmorphology and the diameters of particles were in the range from 40 to 90 nm. The micelles were stableat a pH above 3 or at an ionic strength below 1.0, however, they aggregated and precipitated in thesolutions when further decreasing pH or increasing ionic strength. Prednisone acetate, as a modelhydrophobic drug, was loaded into the polymeric micelles. In vitro release of prednisone acetate frompolymeric micelles showed that the release kinetics was strongly pH-dependent. Hydrophobic drugdisplayed "burst" release at pH 7.4, while only a small part of loaded drug released at pH 1.4. Thisprovides a new choice to design delivery system for the gastrointestinal tract (GI tract), where the pHenvironment is strongly acidic in stomach and basic in intestine. The cytotoxicity measurement by MTTassay indicated that PAAc-b-PDLLA was low toxic in HeLa cells with an IC50 value of 2.8 mg mL_1, whichsuggests that PAAc-b-PDLLA could be used as a safe candidate for pH-responsive drug delivery.

Three poly(beta-aminoester)s with pendant primary amines were synthesized by Michael addition of N-Boc-protected diamine to 1,4-butanedioldiacrylate, followed by removal of N-Boc-protective group under anhydrous acidic conditions. The degradation rate of poly(beta-aminoester)s with pendant primary amines is dependant on their side-chain structures and pH value of incubation buffer. The degradation in basicenvironments is much faster than in acidic environments. The degradation of poly(beta-aminoester) with pendant primary amine involves intramolecular/intermolecular amidation and hydrolytic degradation. Under physiological conditions, the intramolecular/intermolecular amidation ofpoly(beta-aminoester) plays an important role in the polymer degradation. Polymers 1ae1c show significant buffer capacity at pH 4e10. Thecytotoxicity of polymer 1a is much higher than that of polymers 1b and 1c.

Polyamidoamine dendrimers using inositol as a core were designed, synthesized andcharacterized. The electrostatics interaction of PAMAM dendrimer with DNA causes the condensationof DNA to form DNA/dendrimer complexes. The sizes of complexes prepared from dendrimerG6 and pRE Luc at N/P ratio 10︰1 range from 80 to 300nm. Dendrimers G3 G6 are able toefficiently deliver pRE Luc and pSV-gal gene into HeLa and HEK 293 cells. The transfectionefficiencies of G5 and G6 are much higher than that of poly L-lysine (PLL) and comparable to that ofthe commercial branched polyethylenimine (PEI, Mw 25000), whereas the cytoctoxicities of G5 andG6 are lower than that of PLL.