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Diblock copolymers (MPEG-b-PCLs) of poly(ε-caprolactone) (PCL) and monomethoxyl poly(ethylene glycol) (MPEG) were synthesized by the conventional ring-opening polymerization of ε-caprolactone using MPEG as a macroinitiator. The monohydroxy-bearing diblock copolymers were reacted first with maleic anhydride and then with N-hydroxysuccinimide (NHS) to yield activated succinimidyl carbonate derivatives that are reactive with the primary amino group. Subsequently, a new class of biodegradable amphiphilic copolymer (hy-PEI-g-PCL-b-PEG) was prepared by grafting the activated PCL-b-PEG onto the hyperbranched poly(ethylene imine) (hy-PEI). Thermal properties of bulk graft copolymers were investigated using differential scanning calorimetry and thermogravimetric analysis. Depending on their compositions, these polymers are completely soluble in water or form micelles of tens to hundreds of nanometers in size in the studied concentration range, as revealed by surface tension and dynamic light scattering measurements of copolymer solutions. Complexation of plasmid DNA (pDNA) with various copolymers was investigated to achieve particles of ca. 200 nm diameter (N/P = 7). Copolymer composition was found to affect significantly the gene transfection efficiency of polyplexes. In general, low graft density and high molecular weight of PEI blocks favor high gene transfection efficiency. All DNA/copolymer complexes (N/P = 7) showed a much lower ξ-potential (i.e., neutral or negative) than the DNA/PEI25 kDa complex (21 mV), indicating lower toxicity of copolymer-based complexes. Lower cytotoxicity of DNA/copolymer complexes was also demonstrated by the viability of cells in the transfection experiments. These results indicate that these ternary copolymers are promising candidates for gene delivery, featuring good biocompatibility, potential biodegradability, and relatively high gene transfection efficiency. Their neutral surface charge offers potential for intravenous administration.

Soluble supramolecular inclusion complexes were formed by threading alpha-cyclodextrin (alpha-CD) molecules over poly(ethylene glycol) (PEG) and poly(epsilon-caprolactone) (PCL) chains of ternary block copolymers of PEG, PCL and polyethylenimine (PEI). Characteristic shifts of PCL absorptions in FTIR, (1)H NMR and UV spectra strongly suggest that alpha-CD is threaded over PEG and PCL blocks. Due to the reduced hydrophobic interaction between PCL blocks, the resulting supramolecular complexes displayed a dramatically increased solubility, in comparison with the ternary block copolymers. Their ability to complex DNA was almost as efficient as that of branched PEI 25 kDa, as shown in the ethidium bromide fluorescence quenching experiments. Resulting DNA polyplexes displayed a size of around 200 nm and a neutral surface charge. Microscopy studies in 3T3 fibroblasts revealed an efficient cellular uptake. Transfection efficiencies of inclusion complexes were in the same order of magnitude as PEI. In contrast to PEI a 100x lower toxicity was observed by MTT-assay, allowing the administration of nitrogen-to-phosphate ratios of up to 20. These new gene delivery systems merit further characterization under in vivo conditions.