Polyamidoamine (PAMAM) dendrimer represents one of the most efficient polymeric gene carriers. To investigate the effect of the core structure and generation of dendrimers on the complex formation and transfection efficiency, a series of PAMAM dendrimers with a trimesyl core (DT) at different generations (DT4 to DT8) were developed as gene carriers and compared with the PAMAM dendrimers derived from pentaerythritol (DP) and inositol (DI). The minimal generation number of DTs at which the dendrimer has enough amino group density to effectively condense DNA was higher (generation 6) than those of DPs and DIs (generation 5). DTs of generation 6 or higher condensed DNA into complexes with an average diameter ranging from 100 to 300 nm, but the 4th and 5th generations of DT (DT4 and DT5) formed only a severe aggregate with DNA. Interestingly, the DT6/pDNA complex was determined to be much smaller (100-300 nm) than those prepared with DP5 or DI5 (>600 nm) at N/P ratios higher than 15. The optimal generation numbers at which the dendrimers showed the highest transgene expression in COS-7 cells were 5 for DPs and DIs but 6 for DTs. The DT6/pDNAcomplex with smaller size mediated higher transgene expression in COS-7 cells than those prepared with DP5 or DI5. The in vitro transfection efficiency of the DT dendrimers as evaluated in HeLa cells, COS-7 cells, and primary hepatocytes decreased in the order of DT6 > DT7 > DT8 > DT5 > DT4. The transfection mediated by DT6 was significantly inhibited by bafilomycin A1. The acid-base titration curve for DT6 showed high buffer capacity in the pH range from 5.5 to 6.4 (pK(a) approximately 6). This permits dendrimers to buffer the pH change in the endosomal compartment. However, the transfection efficiency mediated by DT6 decreased significantly in the presence of serum in both HeLa cells and COS-7 cells. The cytotoxicity of DTs evaluated in HeLa cells using the 3-{4,5-dimethylthiazol-2-yl}-2,5-diphenyltetrazolium bromide assay showed a trend of increasing toxicity with the polymer generations. The LD50 values of DT4 through DT8 were 628, 236, 79, 82, and 77 microg/mL, respectively, which were higher than that of poly(ethyleneimide) (18 microg/mL) and poly(L-lysine) (28 microg/mL) in the same assay. With a lower cytotoxicity and versatility for chemical conjugation, these PAMAM dendrimers with a DT core warrant further investigation for nonviral gene delivery.

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Cationic polyaspartamides including poly‐α,β‐[N′‐(2‐aminoethy1)‐L‐aspartamide] (PAEA), poly‐α,β‐[N′‐(4‐aminobutyl)‐L‐aspartamide] (PABA), poly‐α,β‐[N′‐(6‐aminohexyl)‐L‐aspartamide] (PAHA), poly‐α,β‐[N′‐(5‐amino‐3‐azapentyl)‐L‐aspartamide] (PAAPA) and poly‐α,β‐[N′‐(8‐amino‐3,6‐diazaoctyl)‐L‐aspartamide] (PADAOA) were synthesized from polysuccinimide. Their properties were evaluated by 1H NMR, IR, GPC, fluorescence measurement and in vitro cytotoxicity assays. The molecular weights per primary amine charge group of PAEA(1) (Mn=2229), PAAPA and PADAOA are 212, 279, and 226. Polyaspartamides including PAEA(1), PAAPA, PADAOA and low molecular weight PAHA are markedly less toxic than poly(ethyleneimine) and poly(L‐lysine), however, PABA and higher molecular weight PAHA are slightly less toxic than poly(L‐lysine). Cell cytotoxicity of PAHA was seen to decrease with increasing molecular weight of PAHA, due to water solubility reduction. The negatively charged plasmid DNA has been found to be completely neutralized and complexed by the cationic polyaspartamides at an N/P ratio of 5:1 to 10:1, forming self‐assembled polyplexes via ionic interactions. These polyaspartamide/DNA complexes possess stable zeta potentials and mean particle diameters of about 180 nm for PAEA (1)/DNA and PAAPA/DNA complexes and 280 nm for PADAOA/DNA complexes.