Folate-PEG-Appended Dendrimer Conjugate with α-Cyclodextrin as a Novel Cancer Cell-Selective siRNA Delivery Carrier

We previously reported that of the various Polyamidoamine (PAMAM) STARBURST dendrimer (generation 3, G3) (dendrimer) conjugates with cyclodextrins (CyDs), the dendrimer (G3) conjugate with alpha-CyD having an average degree of substitution of 2.4 (alpha-CDE (G3)) has the greatest potential for a novel carrier for siRNA in vitro and in vivo. To improve the siRNA transfer activity and the lack of target specificity of alpha-CDE (G3), we prepared folate-polyethylene glycol (PEG)-appended alpha-CDEs (G3) (Fol-P alpha Cs) with various degrees of substitution of folate (DSF) and evaluated their siRNA transfer activity to folate receptor (FR)-overexpressing cancer cells in vitro and in vivo. Of the three Fol-P alpha C (G3, DSF 2, 4 and 7), Fol-P alpha C (G3, DSF 4) had the highest siRNA transfer activity in KB cells (FR-positive). Fol-P alpha C (G3, DSF 4) was endocytosed into KB cells through FR. No cytotoxicity of the siRNA complex with Fol-P alpha C (G3, DSF 4) was observed in KB cells (FR-positive) or A549 cells (FR-negative) up to the charge ratio of 100/1 (carrier/siRNA). In addition, the siRNA complex with Fol-P alpha C (G3, DSF 4) showed neither interferon response nor inflammatory response. Importantly, the siRNA complex with Fol-P alpha C (G3, DSF 4) tended to show the in vivo RNAi effects after intratumoral injection and intravenous injection in tumor cells-bearing mice. The FITC-labeled siRNA and TRITC-labeled Fol-P alpha C (G3, DSF 4) were actually accumulated in tumor tissues after intravenous injection in the mice. In conclusion, the present results suggest that Fol-P alpha C (G3, DSF 4) could potentially be used as a FR-overexpressing cancer cell-selective siRNA delivery carrier in vitro and in vivo.