Telomerase, an enzyme that prevents chromosomes from shortening when they divide, is widely suspected of playing a key role in making cancer cells immortal. Though researchers have developed a variety of methods for measuring the activity of this enzyme, none of these methods have proved suitable for use in diagnostic assays for cancer or in efforts to develop drugs that block telomerase activity.
Chad Mirkin of Northwestern University and his research team have developed a new type of nanoparticle-based assay that appears to be both accurate and sensitive enough for clinical use. The assay system consists of gold nanoparticles coated with short stretches of DNA that can serve as a substrate for telomerase. When a sample containing this enzyme is mixed with these nanoparticles, telomerase binds to the DNA sequences and begins adding repeated stretches of six specific nucleotides to the end of the DNA. After a short time, the investigators wash off any telomerase and then add magnetic micro particles coated with a piece of oligonucleotide that is complementary to the sequence added by telomerase. The coated magnetic micro particles bind to any elongated DNA and enable the researchers to separate those complexes from the rest of the gold nanoparticles by using a magnetic field. Next, the DNA sequences are removed from the gold nanoparticles and are detected using a silver development process and automated reader known as the biobarcode assay.
Using this assay, the investigators were able to reliably detect telomerase activity in as few as 10 to 1,000 tumor cells grown in culture. This will help to develop telomerase inhibitors as anticancer agents.