DOTMA

A DNA-transfection protocol has been developed that makes use of a synthetic cationic lipid, N-[1-(2,3-dioleyloxy)propyl]-N,N,N-trimethylammonium chloride (DOTMA). Small unilamellar liposomes containing DOTMA interact spontaneously with DNA to form lipid-DNA complexes with 100% entrapment of the DNA, DOTMA facilitates fusion of the complex with the plasma membrane of tissue culture cells, resulting in both uptake and expression of the DNA. The technique is simple, highly reproducible, and effective for both transient and stable expression of transfected DNA. Depending upon the cell line, lipofection is from 5- to greater than 100-fold more effective than either the calcium phosphate or the DEAE-dextran transfection technique.

The crystal structures of chelates formed between each stable paramagnetic lanthanide ion and the octadentate polyamino carboxylate ligand DOTMA are described. A total of 23 individual chelates structures were obtained; in each chelate the coordination geometry around the metal ion is best described as a twisted square antiprism (torsion angle -25.0°--31.4°). Despite the uniformity of the general coordination geometry provided by the DOTMA ligand, there is a considerable variation in the hydration state of each chelate. The early Ln3+chelates are associated with a single inner sphere water molecule; the Ln-OH2interaction is remarkable for being very long. After a clear break at gadolinium, the number of chelates in the unit cell that have a water molecule interacting with the Ln3+decreases linearly until at Tm3+no water is found to interact with the metal ion. The Ln-OH2distance observed in the chelates of the later Ln3+ions are also extremely long and increase as the ions contract (2.550-2.732 Å). No clear break between hydrated and dehydrated chelates is observed; rather this series of chelates appear to represent a continuum of hydration states in which the ligand gradually closes around the metal ion as its ionic radius decreases (with decreased hydration) and the metal drops down into the coordination cage.

Eleven structural analogues of two known cationic lipids, N-[1-(2, 3-dioleyloxy)propyl]-N,N,N-trimethylammonium chloride (DOTMA) and N-[1-(2,3-dioleoyloxy)propyl]-N,N,N-trimethylammonium chloride (DOTAP) were synthesized and utilized to evaluate the structural characteristics of DOTMA for its high intravenous transfection activity. Using a CMV-driven expression system and luciferase gene as a reporter, the transfection activity of these analogues was evaluated in mice using tail vein injection. Results concerning the structure-activity relationship with regard to the influence of the backbone, relative position between head group and the hydrophobic chains on the backbone, linkage bonds, as well as the composition of the aliphatic chains revealed that cationic lipids which give a higher in vivo transfection activity share the following structural characteristics: (1) cationic head group and its neighboring aliphatic chain being in a 1,2-relationship on the backbone; (2) ether bond for bridging the aliphatic chains to the backbone; and (3) paired oleyl chains as the hydrophobic anchor. Cationic lipids without these structural features had lower in vivo transfection activity. These structural characteristics, however, did not significantly influence their in vitro transfection activity. The contribution that cationic lipids make to the overall in vivo transfection activity is likely to be determined by the structure of DNA/lipid complexes and by the outcome of the interaction between the DNA/lipid complexes and blood components upon intravenous administration.