Aspects of nonviral gene therapy: correlation of molecular parameters with lipoplex structure and transfection efficacy in pyridinium-based cationic lipids

Abstract

This study seeks correlations between the molecular structures of cationic and neutral lipids, the lipid phase behavior of the mixed-lipid lipoplexes they form with plasmid DNA, and the transfection efficacy of the lipoplexes. Synthetic cationic pyridinium lipids were co-formulated (1:1) with the cationic lipid 1,2-dimyristoyl-sn-glycero-3-ethylphosphocholine (EPC), and these lipids were co-formulated (3:2) with the neutral lipids 1,2-dioleoyl-sn-glycero-3-phosphatidylethanolamine (DOPE) or cholesterol. All lipoplex formulations exhibited plasmid DNA binding and a level of protection from DNase I degradation. Composition-dependent transfection (beta-galactosidase and GFP) and cytotoxicity was observed in Chinese hamster ovarian-K1 cells. The most active formulations containing the pyridinium lipids were less cytotoxic but of comparable activity to a Lipofectamine 2000™ control. Molecular structure parameters and partition coefficients were calculated for all lipids using fragment additive methods. The derived shape parameter values correctly correlated with observed hexagonal lipid phase behavior of lipoplexes as derived from small-angle X-ray scattering experiments. A transfection index applicable to hexagonal phase lipoplexes derived from calculated parameters of the lipid mixture (partition coefficient, shape parameter, lipoplex packing) produced a direct correlation with transfection efficiency.

Keywords: 1,2-dimyristoyl-sn-glycero-3-ethylphosphocholine; 1,2-dioleoyl-sn-glycero-3-phosphatidylethanolamine; 3,5-bis((hexadec-15-en-1-yloxy)carbonyl)-1-methylpyridin-1-ium; 3,5-bis((hexadecyloxy)carbonyl)-1-methylpyridin-1-ium; AI; CHO-K1; CR; Cationic lipids; Chinese hamster ovarian (K1) cells; Chol; DNA transfer; DOPE; Di16:0; Di16:1; EPC; GFP; Gene therapy.; HGS; LDS; LI; Lipoplex formulation; Pyridinium-based lipids; QSAR; Quantitative structure–activity relationship; R; S; S(+), S(mix); SAXS; Shape parameter; TI; V(C), V(lip), V(mix); a(0); amphipathic index; charge ratio of cationic lipid N to anionic DNA P; cholesterol; critical chain length of the hydrocarbon portion of a lipid, overall length of the lipid including the head group; f(lat), f(cyl); filling factors of the lattice and cylinder unit cell, see equation 6; green fluorescent protein; headgroup size; l(c), l(lip); lipid head group area; lipid shape parameter, see equation 2; lipofection index, see equation 1; lipophilic domain size; logP(sub); molar amount of lipid in the experiment with respect to the unit cell; mole weighted average value of S for cationic lipids or mixed lipids; n(exp); n(lat), n(cyl); octanol-water partition coefficient, subscript indicates mole weighted average value of mixed lipids (mix), cationic lipids (+), or neutral lipids (0); optimum molar amount of a lipid to fill the unit cell of a hexagonal lattice or a cylinder outside of the volume occupied by DNA; pDNA; partial molar volume of the hydrocarbon portion of a lipid, the overall lipid molecule including a counterion if required, mole weighted average value of a mixture; plasmid DNA; ratio of cationic lipid to neutral lipid; small-angle X-ray scattering; transfection index computed according to equations 3 to 6; β-gal; β-galactosidase.