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To improve the transfection efficiency of nonviral vector, we synthesized the starburst polyamidoamine dendrimer conjugates with alpha-, beta-, and gamma-cyclodextrins (CDE conjugates), expecting the synergistic effect of dendrimer and cyclodextrins (CyDs). The (1)H NMR spectroscopic data indicated that alpha-, beta-, and gamma-CyDs are covalently bound to dendrimer in a molar ratio of 1:1. The agarose gel electrophoretic studies revealed that CDE conjugates formed the complexes with plasmid DNA (pDNA) and protected the degradation of pDNA by DNase I in the same manner as dendrimer. CDE conjugates showed a potent luciferase gene expression, especially in the dendrimer conjugate with alpha-CyD (alpha-CDE conjugate) which provided the greatest transfection activity (approximately 100 times higher than those of dendrimer alone and of the physical mixture of dendrimer and alpha-CyD) in NIH3T3 and RAW264.7 cells. In addition, the gene transfer activity of alpha-CDE conjugate was superior to that of Lipofectin. The enhancing gene transfer effect of alpha-CDE conjugate may be attributable to not only increasing the cellular association, but also changing the intracellular trafficking of pDNA. These findings suggest that alpha-CDE conjugate could be a new preferable nonviral vector of pDNA.

The purpose of the present study is to optimize the structure of the polyamidoamine starburst dendrimer (dendrimer) conjugate with alpha-cyclodextrin (alpha-CDE conjugate) as a nonviral vector. alpha-CDE conjugates of dendrimer (generation 3, G3) with various average degrees of substitution (DS) of alpha-CyD of 1.1, 2.4, and 5.4 were prepared. alpha-CDE conjugates formed the complexes with pDNA, resulting in a change of the particle sizes of pDNA complexes, but the distinction of physicochemical properties among their vector/pDNA complexes was only very slight. The membrane-disruptive ability of alpha-CDE conjugates on liposomes encapsulating calcein and their cytotoxicity to NIH3T3 and HepG2 increased with an increase in the DS value of alpha-CyD. In vitro gene transfer activity of alpha-CDE conjugates in both NIH3T3 and HepG2 cells augmented as the charge ratio (vector/pDNA) increased, and the activity of alpha-CDE conjugate (DS 2.4) was the highest at higher charge ratios among dendrimer (G3), the three alpha-CDE conjugates, and TransFast. After intravenous administration of pDNA complexes in mice, alpha-CDE conjugate (DS 2.4) delivered pDNA more efficiently in spleen, liver, and kidney, compared with dendrimer and other alpha-CDE conjugates (DS 1.1 and 5.4). The potential use of alpha-CDE conjugate (G3, DS 2.4) could be expected as a nonviral vector in vitro and in vivo, and these data may be useful for design of alpha-CyD conjugates with other nonviral vectors.

To improve gene transfer activity of a new nonviral vector, a polyamidoamine dendrimer (G2) conjugate with alpha-cyclodextrin (alpha-CDE conjugate (G2)), we prepared alpha-CDE conjugates with dendrimer having different generations (G3 and G4), and their gene transfer activities were compared with those of alpha-CDE conjugate (G2) and TransFast, a novel transfection reagent. alpha-CDE conjugates (G2, G3, and G4) formed the complexes with pDNA, changing the zeta-potential and particle size of pDNA complexes and the protection of pDNA from DNase I in a charge ratio-dependent manner, although their differences at higher charge ratios (vector/pDNA) were small. The gene transfer activity of alpha-CDE conjugates (G2, G3, and G4) was higher than that of the corresponding dendrimer alone in NIH3T3 and RAW264.7 cells. Of these CDE conjugates, alpha-CDE conjugate (G3) had a superior gene transfer activity which was comparable to that of TransFast in NIH3T3 cells. The intracellular distribution of pDNA after application of the pDNA complex with alpha-CDE conjugate (G3) to NIH3T3 cells was different from that with dendrimer alone (G3), although the cellular association of pDNA was almost comparable among all vectors. alpha-CDE conjugate (G3) strongly interacted with a fluorescence probe, 2-(p-toluidinyl)-naphthalene-6-sulfonate (TNS), suggesting that the conjugate possesses the inclusion ability with biomembrane constituents such as phospholipids after transfection. These results suggest that alpha-CDE conjugates, particularly the G3 conjugate, could be novel nonviral gene transfer agents.

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