DNA delivery

Two main challenges are involved in transferring genes into cells without using viral vectors, to avoid potential antigenic effects. The first is presenting the DNA in such a way that cells can take it up. This requires balancing the negative charge usually found on DNA with a cationic compound so it can be attracted to negatively charged cells. The second obstacle is ensuring that the largest practicable amount of DNA is presented to each individual cell to maximize the efficiency of the uptake process. This is difficult to do without using a large excess of the DNA complex, most of which may be wasted or might inundate the cells, threatening viability.

In a recent paper, researchers at Northwestern University (Evanston, IL) have reported on a new method for solving both problems at once by the use of “surface-tethered DNA complexes”.

Tatiana Segura and Lonnie Shea reported that they could take advantage of the phenomenon whereby DNA released from a polymeric substrate or scaffolding shows enhanced gene transfer (Bioconjug. Chem. 2002, 13, 621–629). They designed a system for gene delivery that combines the benefits of polymeric attachment with an improved proximity to the cells to be transformed. The two created cationic polymer–DNA complexes using polylysine (with a degree of polymerization of 19 or 150) and plasmid DNA coding for the reporter gene beta -galactosidase.

Taking advantage of the powerful affinity between biotin and avidin, Segura and Shea used biotinylated polylysine to create DNA complexes that could be tethered to surfaces that were coated with neutravidin (nonglycosylated avidin). Because the cells that were used— HEK293T (from human kidney cells) and NIH/3T3 (from mice)—grew along the surfaces, they were directly exposed to the tethered complexes and were easily transformed. Transfection was a direct function of surface DNA quantities and the number of tethers attaching to the complex. And, as determined by colorimetric assay, up to 100-fold greater transformation was observed using tethering compared with traditional bulk delivery methods.

MARK S. LESNEY

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