PHILADELPHIA – Coating DNA with a topical steroid might make for more effective therapeutic gene delivery, according to bioengineers at the University of Pennsylvania. The researchers have shown that a common anti-inflammatory steroid, wrapped around a strand of DNA, can prevent the immune responses commonly associated with gene-transfer techniques.
Studies of the technique, performed in animal models, are presented in the Feb. 15 issue of the journal Gene Therapy, available online now.
"The steroid coating not only allows the gene to be taken up into a cell more easily, but the steroid itself also prevents the sort of inflammatory immune response seen in gene transfer therapy," said Scott Diamond, senior author and professor of bioengineering at Penn and associate director of Penn's Institute for Medicine and Engineering. "The concept paves the way to coupling therapeutic gene delivery with a pharamacological agent, an approach that mitigates some of the drawbacks to the gene-delivery techniques in use now."
Currently there are two basic approaches to delivering therapeutic genes: nonviral and viral. Injecting a subject with pure DNA is possible, but a DNA molecule, by itself, has inherent trouble in entering cells. Viral carriers can serve as delivery vehicles for DNA, literally infecting cells with new genes. Both methods, however, are associated with the creation of inflammatory immune responses that reduces the action of the therapeutic gene.
DNA is a large and negatively charged molecule, which is the source of the stumbling point in getting cells to take up DNA. To counter the negative charge of DNA, Diamond and his colleagues took a common steroid, dexamethasone, and made it "sticky" by adding a nitrogen-rich, postively charged tail. This tail provides the glue that attaches the steroid to the naked DNA.
"The steroid is a fatty lipid so, in essense, we have greased up DNA for cellular uptake," Diamond said, "plus the cells get a big dose of steroid."
According to Diamond, the chemistry involved in manufacturing this new steroid vehicle is a fairly straightforward, one-step process that is simple compared to creating viral gene-therapy vectors. "But this is more than just 'gene therapy on steroids,'" Diamond said. "The dexmethasone not only eased inflammation in an animal model, but, as our study showed, actually allowed the cells to use the foreign DNA more effectively."
In addition, corticosteroids can suppress the major inflammatory cytokines created by the immune response after gene delivery. According to studies in cell culture and animal models, the steroid-coated DNA showed lower initial inflammation and greater expression of the gene over time. The results have encouraged the researchers to continue studies and to envision broader application of the technique toward diseases that might also benefit from gene-transfer therapy.
"In humans, especially in inflamatory diseases, a steroid coating would greatly enhance the chances of successful gene transfer" Diamond said. "As an alternative, I could foresee the use of this coating technique to tailor therapies by choosing drugs that would amplify the benefit of a particular therapeutic gene."
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