Effects of structure of β-cyclodextrin-containing polymers on gene delivery

Linear cationic beta -cyclodextrin-based polymers (beta CDPs) are capable of forming polyplexes with nucleic acids and transfecting cultured cells. The beta CDPs are synthesized by the condensation of a diamino-cyclodextrin monomer A with a diimidate comonomer B. In this paper, the effects of polymer structure on polyplex formation, in vitro transfection efficiency and toxicity are elucidated. By comparison of the beta CDPs to polyamidines lacking cyclodextrins, the inclusion of a cyclodextrin moiety in the comonomer A units reduces the IC(50)s of the polymer by up to 3 orders of magnitude. The spacing between the cationic amidine groups is also important. Different polymers with 4, 5, 6, 7, 8, and 10 methylene units (beta CDP4, 5, 6, 7, 8, and 10) in the comonomer B molecule are synthesized. Transfection efficiency is dependent on comonomer B length with up to 20-fold difference between polymers. Optimum transfection is achieved with the beta CDP6 polymer. In vitro toxicity varied by 1 order of magnitude and the lowest toxicity is observed with beta CDP8. The LD40 of the beta CDP6 to mice is 200 mg/kg, making this polymer a promising agent for in vivo gene delivery applications.