Structural effects of carbohydrate-containing polycations on gene delivery. 2. Charge center type.

Recent polycation structure-gene delivery studies reveal that subtle changes in the molecular structure of polycations have substantial influences on DNA-binding and condensation and on in vitro toxicity and gene delivery efficiency. In Part 1 of this structure-property study using carbohydrate-containing polycations (1), it is demonstrated that as the amidine charge center is removed further from the carbohydrate unit within the polycation structure, the toxicity increases. Inclusion of larger carbohydrate species within the polycation backbone also reduces the toxicity. Here, the effect that polycation charge center type has on toxicity and gene delivery efficiency is investigated. A series of quaternary ammonium polycations containing N,N,N',N'-tetramethyl-1,6-hexanediamine, d-trehalose, and beta-cyclodextrin are synthesized in order to elucidate the effects of charge center type (by comparison to the data given in Part 1) on gene delivery. In all cases, it is found that the quaternary ammonium analogues exhibit lower gene expression values and similar toxicities to their amidine analogues. Additionally, transfection experiments conducted in the presence of chloroquine reveal increased gene expression from quaternary ammonium containing polycations and not from their amidine analogues.