Effect of cationic cholesterol derivatives on gene transfer and protein kinase C activity

Four different cationic derivatives of cholesterol were synthesized which contain either a tertiary or a quaternary amino head group, with and without a succinyl spacer-arm. Their ability to inhibit protein kinase C (PKC) activity was measured in a detergent mixed micellar solution. Derivatives containing a quaternary amino head group were effective inhibitors (Ki approx. 12 and 59 microM) of PKC and derivatives containing a tertiary amino head group were approx. 4-20-fold less inhibitory. Liposomes containing an equimolar mixture of dioleoylphosphatidylethanolamine (DOPE) and a cationic cholesterol derivative were tested for the DNA-mediated transfection activity in mouse L929 cells. Highest activity was found with the derivative with low PKC inhibitory activity and with a succinyl spacer-arm. The transfection activity of this tertiary amine derivative, N,N-dimethylethylenediaminyl succinyl cholesterol was dependent on DOPE as a helper lipid; liposomes containing dioleoylphosphatidylcholine and this derivative had little activity. The transfection protocol of this new cationic liposome reagent was optimized with respect to the ratio of liposome/DNA, dose of the complex and time of incubation with cells. Several adherent cell lines could be efficiently transfected with this liposome reagent without any apparent cytotoxicity. However, the transfection activity was strongly inhibited by the presence of serum components.