Patent ID: 7112337

Claim:
A composition for administration of a nucleic acid, comprising: (a) liposomes comprised of (i) a lipid having the formula where each of R 1 and R 2 is an alkyl or alkenyl chain having between 8-24 carbon atoms, and each of R 1 or R 2 are independently selected; n=0-20; L is selected from the group consisting of (1) —X—(C═O)—Y—[[CH 2 —]], (2) —X—(C═O)—, and (3) —X—[[CH 2 —]], where X and Y are independently selected from oxygen, NH and a direct bond; Z is a weakly basic moiety that has a pk of less than 7.4 and greater than about 4.0; and (ii) a compound having the general structure: wherein R 3 is a hydrophilic polymer comprising a linkage for attachment to the dithiobenzyl moiety; R 4 is selected from the group consisting of H, alkyl and aryl; R 5 is selected from the group consisting of O(C═O)R 7 , S(C═O)R 7 , and O(C═S)R 7 ; R 7 comprises an amine-containing lipid; and R 6 is selected from the group consisting of H, alkyl and aryl; and where orientation of CH 2 —R 5 is selected from the ortho position and the para position; and (b) a nucleic acid associated with said liposomes.