Long chains of DNA make up our chromosomes and collectively contain the genetic information needed for our cells to function. However, we can synthesize DNA molecules in the laboratory and put them to use in other ways. Tiny chains of DNA that fold up into variety of 3-dimensional shapes that recognize and bind to a whole host of biological molecules are called aptamers. Because aptamers can target and bind to specific biological molecules within a complex mixture of molecules they are being developed as so-called “affinity reagents” that allow researchers to isolate and study targeted molecules. Large collections of aptamers are generated randomly and are screened for their interactions with target molecules. The aptamers that bind to the target molecule are selected for multiple rounds of testing until only the aptamers best able to recognize and bind to the target molecule survive the increasingly rigorous screening conditions. Dr. Soh, a Protein Capture Reagents Program grantee, and colleagues have developed a method called Quantitative Parallel Aptamer Selection System (QPASS) that enables them to test thousands of selected aptamers simultaneously. QPASS also reduces the number of rounds of screening necessary to find the aptamers that bind best. The increased efficiency in identifying aptamers that bind tightly to specific molecules could make aptamers a feasible and economical reagent for biomedical researchers who wish to isolate and study specific molecules in the future.
QPASS could also make aptamers a useful tool in creating new medical devices. Dr. Soh and his research team developed a sensor that uses aptamers to recognize specific drug molecules. The sensor continuously measures the amount of drug molecules in the bloodstream by recording an electrical signal when aptamers bind to drug molecules. Monitoring this signal over time informed the researchers how much drug was present at any time during of the course of the experiment.
The hope is that aptamers will be a less expensive and more efficient alternative to antibody molecules in research and medical practice. Antibodies are used every day in many diagnostic assays and as therapeutic agents when a certain target biological molecule needs to be recognized. However, antibodies are very complex molecules that are expensive to produce, and difficult to reproduce exactly from batch to batch. Aptamers are relatively straightforward to produce, and once an optimal aptamer has been found, it can be reproduced indefinitely with little or no variation from batch to batch.
Image information: Green drug molecules in the blood bind purple apatmers attached to the sensor. Image source: Ferguson et al. Sci Transl Med 5, 213ra165 (2013). Reprinted with permission from AAAS.
Science published a brief free-access article and video describing the sensor at:
Cho M, Soo Oh S, Nie J, Stewart R, Eisenstein M, Chambers J, Marth JD, Walker F, Thomson JA, Soh HT. Quantitative selection and parallel characterization of aptamers. PNAS, Nov 12, 2013; 110(46): 18460-5. PMID: 24167271.
Drug Sensor Reference:
Ferguson BS, Hoggarth DA, Maliniak D, Ploense K, White RJ, Woodward N, Hsieh K, Bonham AJ, Eisenstein M, Kippin TE, Plaxco KW, Soh HT. Real-time, aptamer-based tracking of circulating therapeutic agents in living animals. Science Translational Medicine. Nov 27, 2013; 5(213): 213ra165. PMID: 24285484.