NEC Corporation and NEC Solution Innovators today announced the successful development of artificial DNA aptamers (*1) that bind to the novel coronavirus(SARS-CoV-2). This breakthrough stems from the NEC Group’s efforts to promote spatial monitoring business using aptamers, including the development of new biosensing systems, such as measuring equipment that can monitor spaces where various viruses, including SARS-CoV-2 and influenza viruses, are present.
Overview of Aptamers
SARS-CoV-2 enters into human cells when the spike protein,Receptor-Binding Domain (*2, RBD), on the surface of the virus binds to the ACE2 receptors (*3) on the surface of human cells.
The aptamer developed by NEC Solution Innovatorstargets RBD, which is the keyto infection,then traps the virus by recognizing the three-dimensional structure of the RBD and binding very strongly to it (*4, a dissociation constant indicating the strength of the binding between molecules is less than 1nM). This aptamer uses a new modified base called Base appended Base (*5, Patent No. 6763551), which was developedby NEC Solution Innovators and Gunma University from 2014-2017 supported by a grant for“Adaptable and Seamless Technology Transfer Program through Target-driven R&D”(A-STEP) from the Japan Science and Technology Agency(JST).
Three variants of SARS-CoV-2, including the original strain (WK521 Wuhan strain) and twomutant strains (TY7-501 Brazilian and QK002 UK strains) are being studied by academic laboratories in collaboration with the NEC Group. The binding assessment tests with aptamers were conducted in a biosafety level 3 (*6, BSL3) laboratory, which is allowed to handle SARS-CoV-2.
Binding assessment tests were conducted using the Direct ELAA method (*7), in which viruses were adsorbed onto plates and detected with enzyme-labeled aptamers. As a result, a strong binding of aptamers to SARS-CoV-2 was observed in all three strains.
Future Prospects
NEC is developing ameasuring device that enables spatial monitoring of SARS-CoV-2 by combining MSSs (*8, Membrane-type Surface Stress Sensor)and an aptamer that binds to SARS-CoV-2. This measuring device is designed to be used in spaces where people gather and spend time in close proximity, such as public facilities, restaurants, lodging facilities, event venues and offices. In fiscal 2021, NEC expects to provide a prototype of a fixed-type spatial monitoring measuring device for companies, universities and other research institutions that perform virus measurement and other measures. In addition, in fiscal 2022, NEC aims to provide a biosensing system that can be used for space monitoring and as an embedded device for equipment such as air conditioners.
The NEC Group is developing next-generation biosensors using an aptamer that can be stably produced in large quantities. The aptamer, which binds strongly to SARS-CoV-2, was found to have a weak inhibitory effect on infection against TMPRSS2 expressing Vero E6 cells derived from African green monkey kidney epithelial cells (*9), which are highly susceptible toSARS-CoV-2 infection.
“Going forward,through joint research in fiscal 2021, theNEC Group will accelerate the development of aptamers with stronger ability to inhibit infection, which will facilitatethe aptamers’ potential as an antiviral drug,” said Yutaka Ukegawa, Senior Vice President, NEC Corporation. “These initiatives are in line with the NEC Group’s aim to achieve NEC Safer Cities, which utilize state-of-the-art ICT and biotechnology in support of vibrant communities,” he added.
(*1) Aptamer:
A nucleic acid (DNA or RNA) that recognizes and specifically binds to the conformation of a particular target molecule, such as a virus or protein. It can be artificially created SELEX technology that searches for sequences that bind strongly to a test target.
(*2) Receptor Binding Domain(RBD)
SARS-CoV-2 spike glycoprotein (S protein) recognizes and binds to ACE2(angiotensin-converting enzyme 2) expressed on cells. RBDs refer to domains containing ACE2 binding sites on the S protein.
(*3) ACE2 receptor:
ACE2(Angiotensin-converting enzyme 2) is an important receptor in the human body that contributes to elevated blood pressure by vasoconstriction and hormonal secretion. On the other hand, it has been reported that the human coronaviruses SARS-CoV and SARS-CoV-2 enter cells by adhering to ACE2, making them host receptors.
(*4) Dissociation constants and units:
In chemistry, biochemistry, and pharmacology, the dissociation constant (Kd value) is estimated by measuring the off rate (dissociation) and on rate (association) between ligand and analyte. The smaller Kd value indicates thestronger interaction of ligand and analyte.In general, the range of Kd value for the protein-protein interaction is between micro- and nano-molar.
(*5) Patent No. 6763551:
New modified bases that add additional bases to native DNA bases to enhance DNA reactivity and structural diversity
(*6) Biosafety level:
Rating of laboratories/facilities that handle microorganisms/pathogens such as bacteria and viruses based on guidelines established by the World Health Organization (WHO).
(*7) Direct ELAA (Enzyme-Linked Aptamer Assay)
A methodto detect enzymatic activity in which a target protein or virus to be detected is adsorbed on a plate, and an enzyme such as horseradish peroxidase (HRP) or alkaline phosphatase is added to an aptamer.
(*8) MSS sensor:
A highly sensitive nanomechanical sensor that utilizes electric read-out based on piezoresistors, is capable of measuring/analyzing scents and odors and can be used for many other applications.
(*9) TMPRSS2 expressing Vero E6 cells:
The Vero cells that stably express TMPRSS2 and playan important role inSARS-CoV-2 entering into a cell bythe cleavage of the spike glycoprotein.