Credit: © 2008 ACS

Making effective drugs is not easy. The first problem is finding a drug that works. Once you have one, the next challenge is to get the drug to where it is needed in the body. Hydrogels — water-insoluble networks of polymer chains — are potential candidates for carrying drugs, but the next and possibly most important step is to release the drug at the desired location.

Now, Weihong Tan and co-workers from the University of Florida, Gainesville have produced1 a hydrogel in which the crosslinking is controlled by DNA aptamers — short single-stranded pieces of DNA that bind to specific target molecules. The researchers made water-soluble polymers with two different short DNA strands attached to them. A linker molecule was also prepared that contains three DNA sequences: two complementary to those attached to the polymers, and the other an aptamer segment. When the polymer and linker combine, a gel is formed that can absorb drugs. The linker molecule can be engineered so that the aptamer overlaps with one of the complementary binding sequences. Thus the presence of a target molecule, which binds more strongly to the aptamer than to the pendant DNA strands, disrupts the crosslinking, causing the gel to dissolve and release its cargo.

Aptamers exist for a broad range of target molecules, including several cancer biomarkers. This presents the possibility that the same hydrogel system can be used to deliver a number of different drugs, simply by using linkers that incorporate different aptamers