A microsphere-lipoplex (microplex) vector for targeted gene therapy of cancer. I. Construction and in vitro evaluation

Plasmid DNA binding to cationic liposomes and the ability to bind these liposomes, both with and without complexed plasmid DNA, to cation exchange microspheres were examined, The two plasmids tested were pCMV-CAT and pRcCMV-p53. Commercial Lipofectin, Lipofectace, Lipofectamine, and three formulation ratios of dimethyldioctadecyl ammonium bromide (DDAB):phosphatidylcholine and DDAB:dioleoylphosphatidyl ethanolamine liposomes were evaluated. The binding of empty liposomes onto microspheres increased and the release from microspheres decreased with increasing ratio of cationic:neutral lipid. Of all liposomes, Lipofectamine bound the most copy numbers of both plasmids. The amount of plasmid bound on the laboratory-formulated liposomes increased as the ratio of cationic:neutral lipid was increased. The amount of plasmid hound to the formulated liposomes was not affected by the type of neutral lipid used. On average, in terms of copy numbers, binding with pCMV-CAT was 1.38-fold higher than pRcCMV-p53, However, microspheres bound 1.7-fold more copy numbers of liposomal-complexed-pRcCMV-p53 plasmid compared to complexed pCMV-CAT, In the release studies, even in the terminal wash, at least 6 x 10(8) copies of complexed plasmids were released, with additional plasmids being held in reserve, Examination of the applicability of such a combination vehicle for in vivo gene targeting to solid tumors is warranted.