Gene analysis at the patient's bedside
The desktop device, recently approved by the US Food and Drug Administration (FDA), will eventually allow pharmacogenomic testing – the analysis of a patient's genetic information to select optimal treatment methods - to be put on stream. The device, called Verigene, was created by specialists of the recently appeared Nanosphere company, based in Northbrook (Illinois). It allows you to analyze the genome of the patient's blood cells within a few hours and identify genetic modifications that affect the effectiveness of certain drugs.
The reaction of different people to medications can be very different due to the individual characteristics of the enzymes that break them down. Pharmacogenomic testing in the selection of antitumor drugs has already found wide application in oncological practice, but other drugs, including painkillers, as well as drugs for the treatment of HIV and epilepsy, the effectiveness of which strongly depends on the genetic characteristics of the body, are still prescribed almost at random. The technology that allows identifying the necessary genetic variations in patients has been developed for several years, but it is time-consuming and expensive. To carry it out, the doctor must send a sample of the patient's saliva or blood to a certified laboratory, where DNA will be isolated from it, amplified using a polymerase chain reaction and analyzed. The whole process can take from several days to several weeks, which in some cases is absolutely unacceptable.
A good example is the anticoagulant warfarin, often prescribed for the prevention of thrombosis. The metabolism of this drug in different people proceeds differently, so doctors should carefully monitor whether their patients suffer from bleeding. In 2007, the FDA made a note in the labeling of the drug that there are two specific genetic variants that affect the metabolism of the drug, however, for the reasons described above, pharmacogenomic testing before prescribing warfarin has not yet been widely used.
The test developed by Nanosphere will allow this analysis to be carried out within 1-2 hours. To do this, the patient's blood sample will need to be inserted into a disposable cartridge, inside which DNA is isolated from blood leukocytes and fixed on a glass plate inside the cartridge. The plastic cartridge case contains a system of microfluidic chambers with reagents. When the cartridge is inserted into the device in various chambers with the help of mechanical valves and air pressure, the reagents are mixed, which triggers the necessary chemical reactions.
The figures show a Verigene equipment kit and a cartridge. The round chambers visible in the image are filled with reagents that ensure the flow of various chemical reactions during the analysis.
First, with the help of magnetic beads, white blood cells are released from the blood, which are destroyed by ultrasound, releasing DNA fragments. All excess fragments of cells are washed out, and the resulting suspension of DNA fragments is driven along the surface of the glass plate. In this case, the target DNA fragments interact with the nucleotide sequences attached to the glass surface, complementary to the genes of the studied enzymes. After that, gold nanoparticles with a diameter of 13 nanometers are attached to the free ends of the attached DNA fragments. Each nanoparticle is coated with a layer of silver, which increases the diameter to half a micron and makes it easy to register the light reflected by the particles.
The company's specialists are also working on pharmacogenomic tests to determine the feasibility of using Plavix, a drug that prevents blood clotting, which is prescribed to patients with implanted cardiac stents. In the body, this drug turns into an active form under the action of an enzyme, which, according to the results of a recent study, is represented by a low-active form in 30% of Caucasians. Currently, in the USA, the identification of such patients is also possible only by sending a sample to a centralized laboratory, and doctors are very interested in speeding up the process of obtaining results.
In addition to the Verigene device presented by Nanosphere, several other microfluidic devices for genetic testing "at the patient's bedside" are currently under development. Verigene, which received FDA approval in October this year, can be equipped with various modules designed for various types of testing, including modules for the diagnosis of genetic pathologies, pharmacogenomic testing, identification of viral genomes and markers of various diseases. Depending on the configuration, the cost of the device varies from 40,000 to 80,000 US dollars.
Evgeniya Ryabtseva
Portal "Eternal youth" http://vechnayamolodost.ru based on the materials of TechnologyReview: Gene-Testing Machine for Doctors.
08.12.2009