Tomoko Ito, Masazumi Eriguchi and Yoshiyuki Koyama
Effect of pDNA Complex Particle Size on Gene Expression: Difference between In Vitro and In Vivo Experiments
We have developed a novel gene-transfection system comprising very small (70-150 nm) plasmid/polyethyleneimine/hyaluronan (HA) ternary complexes having negative surface charge, and reduced nonspecific interactions with bio-components. They showed high in vivo gene expression efficiency. However, in in vitro transfection experiments, such small ternary complexes often demonstrated rather much lower gene expression than the conventional DNA/ polycation complex. In this study, we investigated the influence of the complex particle size on gene expression efficiency, focusing on the difference between in vitro and in vivo transfection. Size of the DNA complex particles strongly depended on the concentration of the mixing solutions, and the higher concentration resulted in the larger particles. As for the in vitro transfection, DNA/ polyethyleneimine binary complexes could readily be bound to the cells through the electrostatic attractions, regardless of their size. Smaller binary complexes particles showed higher gene expression than the larger ones, likely due to their high internalization efficiency. On the other hand, small DNA/polyethyleneimine/HA ternary complexes having negative surface charge kept dispersing in the medium away from the cells, and demonstrated lower in vitro gene transfection efficiency than larger ones. In regards to in vivo transfection after intravenous injection, only small ternary complexes showed high gene expression, because reduced nonspecific interactions and small size of the complex particles are required to be distributed in the body, and accumulated in tumor. The superiority and inferiority of the vectors for in vivo transfection cannot be always correctly predicted by the results of in vitro transfection.
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