Potential use of folate-polyethylene glycol (PEG)-appended dendrimer (G3) conjugate with α-cyclodextrin as DNA carriers to tumor cells

We previously reported that polyamidoamine STARBURST dendrimer (generation 3, G3) (dendrimer) conjugate with alpha-cyclodextrin (alpha-CyD) having an average degree of substitution of 2.4 of alpha-CyD (alpha-CDE) provided remarkable aspects as novel carriers for DNA and small-interfering RNA. To develop novel alpha-CDE derivatives with tumor cell specificity, we prepared folate-appended alpha-CDEs (Fol-alpha-CDEs) and folate-polyethylene glycol (PEG)-appended alpha-CDEs (Fol-P alpha Cs) with the various degrees of substitution of folate (DSF), and evaluated in vitro and in vivo gene transfer activity, cytotoxicity, cellular association and physicochemical properties. In vitro gene transfer activity of Fol-alpha-CDEs (G3, DSF 2, 5 or 7) was lower than that of alpha-CDE (G3) in KB cells, folate receptor (FR)-overexpressing cancer cells. Of the three Fol-P alpha Cs (G3, DSF 2, 5 or 7), Fol-P alpha C (G3, DSF 5) had the highest gene transfer activity in KB cells. The activity of Fol-P alpha C (G3, DSF 5) was significantly higher than that of alpha-CDE (G3) in KB cells, but not in A549 cells, FR-negative cells. Negligible cytotoxicity of the plasmid DNA (pDNA) complex with Fol-P alpha C (G3, DSF 5) was observed in KB cells or A549 cells up to a charge ratio of 100/1 (carrier/pDNA). The cellular association of the pDNA complex with Fol-P alpha C (G3, DSF 5) could be mediated by FR on KB cells, resulting in its efficient cellular uptake. Fol-P alpha C (G3, DSF 5) had a higher binding affinity with folate-binding protein than alpha-CDE (G3), although the physicochemical properties of pDNA complex with Fol-P alpha C (G3, DSF 5) were almost comparable to that with alpha-CDE (G3), although the onset charge ratio and the compaction ability of Fol-P alpha C (G3, DSF 5) were slightly different. Fol-P alpha C (G3, DSF 5) tended to show a higher gene transfer activity than alpha-CDE (G3) 12 h after intratumoral administration in mice. These results suggest that Fol-P alpha C (G3, DSF 5), not Fol-alpha-CDEs, could be potentially used as a FR-overexpressing cancer cell-selective DNA carrier.