Aptamer
Encyclopedia
Aptamers are oligonucleic acid
or peptide
molecules that bind to a specific target molecule. Aptamers are usually created by selecting them from a large random sequence
pool, but natural aptamers also exist in riboswitch
es. Aptamers can be used for both basic research and clinical purposes as macromolecular drugs. Aptamers can be combined with ribozyme
s to self-cleave in the presence of their target molecule. These compound molecules have additional research, industrial and clinical applications.
More specifically, aptamers can be classified as:
species that have been engineered through repeated rounds of in vitro selection
or equivalently, SELEX (systematic evolution of ligands by exponential enrichment
) to bind to various molecular targets such as small molecules, proteins, nucleic acids, and even cells, tissues and organisms. Aptamers are useful in biotechnological
and therapeutic applications as they offer molecular recognition properties that rival that of the commonly used biomolecule, antibodies
. In addition to their discriminate recognition, aptamers offer advantages over antibodies as they can be engineered completely in a test tube, are readily produced by chemical synthesis, possess desirable storage properties, and elicit little or no immunogenicity
in therapeutic applications.
In 1990, two labs independently developed the technique of selection: the Gold lab, using the term SELEX for their process of selecting RNA ligands
against T4 DNA polymerase
; and the Szostak lab, coining the term in vitro selection, selecting RNA ligands against various organic dyes. The Szostak lab also coined the term aptamer (from the Latin, aptus, meaning ‘to fit’) for these nucleic acid-based ligands. Two years later, the Szostak lab and Gilead Sciences
, independent of one another, used in vitro selection schemes to evolve single stranded DNA ligands for organic dyes and human coagulant, thrombin, respectively. There does not appear to be any systematic differences between RNA and DNA aptamers, save the greater intrinsic chemical stability of DNA.
Interestingly enough, the notion of selection in vitro was actually preceded twenty-plus years prior when Sol Spiegelman
used a Qbeta replication system as a way to evolve a self-replicating molecule. In addition, a year before the publishing of in vitro selection and SELEX, Gerald Joyce
used a system that he termed ‘directed evolution’ to alter the cleavage activity of a ribozyme.
Since the discovery of aptamers, many researchers have used aptamer selection as a means for application and discovery. In 2001, the process of in vitro selection was automated by the Ellington lab at the University of Texas at Austin
, and at SomaLogic, Inc (Boulder, CO), reducing the duration of a selection experiment from six weeks to three days.
While the process of artificial engineering of nucleic acid ligands is highly interesting to biology and biotechnology, the notion of aptamers in the natural world had yet to be uncovered until 2002 when two groups led by Ronald Breaker and Evgeny Nudler discovered a nucleic acid-based genetic regulatory element called a riboswitch that possesses similar molecular recognition properties to the artificially made aptamers. In addition to the discovery of a new mode of genetic regulation, this adds further credence to the notion of an ‘RNA World
,’ a postulated stage in time in the origins of life on Earth.
Lately, a concept of smart aptamers, and smart ligands
in general, has been introduced. It describes aptamers that are selected with pre-defined equilibrium (
), rate (
, 
) constants and thermodynamic (ΔH, ΔS) parameters of aptamer-target interaction. Kinetic capillary electrophoresis
is the technology used for the selection of smart aptamers. It obtains aptamers in a few rounds of selection.
Recent developments in aptamer-based therapeutics have been rewarded in the form of the first aptamer-based drug approved by the U.S. Food and Drug Administration
(FDA) in treatment for age-related macular degeneration (AMD), called Macugen offered by OSI Pharmaceuticals
. In addition, Cambridge, MA - based Archemix (http://www.archemix.com) is leading the development of aptamers as a new class of directed therapeutics for the prevention and treatment of chronic and acute diseases. ARC1779, its lead proprietary candidate, is a potent, selective, first-in-class antagonist of von Willebrand Factor
(vWF). ARC1779 is being evaluated in patients diagnosed with acute coronary syndrome
(ACS) who are undergoing percutaneous coronary intervention
(PCI). Phase I testing for ARC1779 was initiated in December 2006, and a Phase 2 study in ACS is planned to begin by the end of 2007.
Non-modified aptamers are cleared rapidly from the bloodstream, with a half-life of minutes to hours, mainly due to nuclease
degradation and clearance from the body by the kidneys, a result of the aptamer's inherently low molecular weight. Unmodified aptamer applications currently focus on treating transient conditions such as blood clotting, or treating organs such as the eye where local delivery is possible. This rapid clearance can be an advantage in applications such as in vivo diagnostic imaging. An example is a tenascin-binding aptamer under development by Schering AG for cancer imaging. Several modifications, such as 2'-fluorine-substituted pyrimidines, polyethylene glycol
(PEG) linkage, etc. (both of which are used in Macugen, an FDA-approved aptamer) are available to scientists with which to increase the serum half-life
of aptamers easily to the day or even week time scale.
Another approach to increase the nuclease resistance of aptamers is to use a Spiegelmer
.
In addition to the development of aptamer-based therapeutics, many researchers such as the Ellington lab and independently another company SomaLogic (Boulder, CO) have been developing diagnostic techniques for aptamer based plasma protein profiling called aptamer plasma proteomics. This technology will enable future multi-biomarker protein measurements that can aid diagnostic distinction of disease versus healthy states. Somalogic aptamers to HER2 and EGFR membrane proteins have also been demonstrated to work in the context of rapid frozen tissue intraoperative diagnostic pathology applications.
As a resource for all in vitro selection and SELEX experiments, the Ellington lab has developed the Aptamer Database cataloging all published experiments. This is found at http://aptamer.icmb.utexas.edu/.
s inside cells. They consist of a variable peptide loop attached at both ends to a protein scaffold. This double structural constraint greatly increases the binding affinity of the peptide aptamer to levels comparable to an antibody's (nanomolar range).
The variable loop length is typically composed of ten to twenty amino acid
s, and the scaffold may be any protein which has good solubility
and compacity properties. Currently, the bacterial protein Thioredoxin
-A is the most used scaffold protein, the variable loop being inserted within the reducing active site, which is a -Cys-Gly-Pro-Cys- loop in the wild protein, the two Cysteine
s lateral chains being able to form a disulfide bridge.
Peptide aptamer selection can be made using different systems, but the most used is currently the yeast
two-hybrid system.
Selection of Ligand Regulated Peptide Aptamers (LiRPAs) has been demonstrated. By displaying 7 amino acid peptides from a novel scaffold protein
based on the trimeric FKBP-rapamycin-FRB structure, interaction between the randomized peptide and target molecule can be controlled by the small molecule Rapamycin or non-immunosuppressive analogs.
Peptide aptamer can also be selected from combinatorial peptide libraries constructed by phage dsiplay and other surface display technologies such as mRNA display
, ribosome display
, bacterial display
and yeast display
. These experimental procedures are also known as biopanning
s. Among peptides obtained from biopannings, mimotope
s can be considered as a kind of peptide aptamers. All the peptides panned from combinatorial peptide libraries have been stored in a special database with the name MimoDB, which is freely available at http://immunet.cn/mimodb.
identification of biomarkers. The important feature of the AptaBiD technology is that it produces synthetic affinity probes (aptamers) simultaneously with biomarker discovery. In AptaBiD, aptamers are developed for cell surface biomarkers in their native state and conformation. In addition to facilitating biomarker identification, such aptamers can be directly used for cell isolation, cell visualization, and tracking cells in vivo. They can also be used to modulate activities of cell receptors and deliver different agents (e.g., siRNA
and drugs) into the cells.
Oligonucleotide
An oligonucleotide is a short nucleic acid polymer, typically with fifty or fewer bases. Although they can be formed by bond cleavage of longer segments, they are now more commonly synthesized, in a sequence-specific manner, from individual nucleoside phosphoramidites...
or peptide
Peptide
Peptides are short polymers of amino acid monomers linked by peptide bonds. They are distinguished from proteins on the basis of size, typically containing less than 50 monomer units. The shortest peptides are dipeptides, consisting of two amino acids joined by a single peptide bond...
molecules that bind to a specific target molecule. Aptamers are usually created by selecting them from a large random sequence
Sequencing
In genetics and biochemistry, sequencing means to determine the primary structure of an unbranched biopolymer...
pool, but natural aptamers also exist in riboswitch
Riboswitch
In molecular biology, a riboswitch is a part of an mRNA molecule that can directly bind a small target molecule, and whose binding of the target affects the gene's activity. Thus, an mRNA that contains a riboswitch is directly involved in regulating its own activity, in response to the...
es. Aptamers can be used for both basic research and clinical purposes as macromolecular drugs. Aptamers can be combined with ribozyme
Ribozyme
A ribozyme is an RNA molecule with a well defined tertiary structure that enables it to catalyze a chemical reaction. Ribozyme means ribonucleic acid enzyme. It may also be called an RNA enzyme or catalytic RNA. Many natural ribozymes catalyze either the hydrolysis of one of their own...
s to self-cleave in the presence of their target molecule. These compound molecules have additional research, industrial and clinical applications.
More specifically, aptamers can be classified as:
- DNA or RNA aptamers. They consist of (usually short) strands of oligonucleotides.
- PeptidePeptidePeptides are short polymers of amino acid monomers linked by peptide bonds. They are distinguished from proteins on the basis of size, typically containing less than 50 monomer units. The shortest peptides are dipeptides, consisting of two amino acids joined by a single peptide bond...
aptamers. They consist of a short variable peptide domain, attached at both ends to a protein scaffold.
Nucleic Acid aptamers
Nucleic acid aptamers are nucleic acidNucleic acid
Nucleic acids are biological molecules essential for life, and include DNA and RNA . Together with proteins, nucleic acids make up the most important macromolecules; each is found in abundance in all living things, where they function in encoding, transmitting and expressing genetic information...
species that have been engineered through repeated rounds of in vitro selection
Selection
In the context of evolution, certain traits or alleles of genes segregating within a population may be subject to selection. Under selection, individuals with advantageous or "adaptive" traits tend to be more successful than their peers reproductively—meaning they contribute more offspring to the...
or equivalently, SELEX (systematic evolution of ligands by exponential enrichment
Systematic Evolution of Ligands by Exponential Enrichment
SELEX , also referred to as in vitro selection or in vitro evolution, is a combinatorial chemistry technique in molecular biology for producing oligonucleotides of either single-stranded DNA or RNA that specifically bind to a target ligand or ligands....
) to bind to various molecular targets such as small molecules, proteins, nucleic acids, and even cells, tissues and organisms. Aptamers are useful in biotechnological
Biotechnology
Biotechnology is a field of applied biology that involves the use of living organisms and bioprocesses in engineering, technology, medicine and other fields requiring bioproducts. Biotechnology also utilizes these products for manufacturing purpose...
and therapeutic applications as they offer molecular recognition properties that rival that of the commonly used biomolecule, antibodies
Antibody
An antibody, also known as an immunoglobulin, is a large Y-shaped protein used by the immune system to identify and neutralize foreign objects such as bacteria and viruses. The antibody recognizes a unique part of the foreign target, termed an antigen...
. In addition to their discriminate recognition, aptamers offer advantages over antibodies as they can be engineered completely in a test tube, are readily produced by chemical synthesis, possess desirable storage properties, and elicit little or no immunogenicity
Immunogenicity
Immunogenicity is the ability of a particular substance, such as an antigen or epitope, to provoke an immune response in the body of a human or animal.- Immunogenicity :The ability to induce humoral and/or cell-mediated immune responses....
in therapeutic applications.
In 1990, two labs independently developed the technique of selection: the Gold lab, using the term SELEX for their process of selecting RNA ligands
Ligand (biochemistry)
In biochemistry and pharmacology, a ligand is a substance that forms a complex with a biomolecule to serve a biological purpose. In a narrower sense, it is a signal triggering molecule, binding to a site on a target protein.The binding occurs by intermolecular forces, such as ionic bonds, hydrogen...
against T4 DNA polymerase
DNA polymerase
A DNA polymerase is an enzyme that helps catalyze in the polymerization of deoxyribonucleotides into a DNA strand. DNA polymerases are best known for their feedback role in DNA replication, in which the polymerase "reads" an intact DNA strand as a template and uses it to synthesize the new strand....
; and the Szostak lab, coining the term in vitro selection, selecting RNA ligands against various organic dyes. The Szostak lab also coined the term aptamer (from the Latin, aptus, meaning ‘to fit’) for these nucleic acid-based ligands. Two years later, the Szostak lab and Gilead Sciences
Gilead Sciences
Gilead Sciences is a biopharmaceutical company that discovers, develops and commercializes therapeutics. For many years since the company was founded, the company concentrated primarily on antiviral drugs to treat patients infected with HIV, hepatitis B or influenza. In 2006, Gilead acquired two...
, independent of one another, used in vitro selection schemes to evolve single stranded DNA ligands for organic dyes and human coagulant, thrombin, respectively. There does not appear to be any systematic differences between RNA and DNA aptamers, save the greater intrinsic chemical stability of DNA.
Interestingly enough, the notion of selection in vitro was actually preceded twenty-plus years prior when Sol Spiegelman
Sol Spiegelman
Sol Spiegelman was an American molecular biologist. He developed the technique of nucleic acid hybridization, which helped to lay the groundwork for advances in recombinant DNA technology....
used a Qbeta replication system as a way to evolve a self-replicating molecule. In addition, a year before the publishing of in vitro selection and SELEX, Gerald Joyce
Gerald Joyce
Gerald Francis Joyce is a professor and researcher at The Scripps Research Institute, best known for his work on in vitro evolution of catalytic RNA molecules and the origins of life....
used a system that he termed ‘directed evolution’ to alter the cleavage activity of a ribozyme.
Since the discovery of aptamers, many researchers have used aptamer selection as a means for application and discovery. In 2001, the process of in vitro selection was automated by the Ellington lab at the University of Texas at Austin
University of Texas at Austin
The University of Texas at Austin is a state research university located in Austin, Texas, USA, and is the flagship institution of the The University of Texas System. Founded in 1883, its campus is located approximately from the Texas State Capitol in Austin...
, and at SomaLogic, Inc (Boulder, CO), reducing the duration of a selection experiment from six weeks to three days.
While the process of artificial engineering of nucleic acid ligands is highly interesting to biology and biotechnology, the notion of aptamers in the natural world had yet to be uncovered until 2002 when two groups led by Ronald Breaker and Evgeny Nudler discovered a nucleic acid-based genetic regulatory element called a riboswitch that possesses similar molecular recognition properties to the artificially made aptamers. In addition to the discovery of a new mode of genetic regulation, this adds further credence to the notion of an ‘RNA World
RNA world hypothesis
The RNA world hypothesis proposes that life based on ribonucleic acid pre-dates the current world of life based on deoxyribonucleic acid , RNA and proteins. RNA is able both to store genetic information, like DNA, and to catalyze chemical reactions, like an enzyme protein...
,’ a postulated stage in time in the origins of life on Earth.
Lately, a concept of smart aptamers, and smart ligands
Smart ligands
Smart ligands are affinity ligands selected with pre-defined equilibrium , kinetic and thermodynamic parameters of biomolecular interaction....
in general, has been introduced. It describes aptamers that are selected with pre-defined equilibrium (
), rate ( , ) constants and thermodynamic (ΔH, ΔS) parameters of aptamer-target interaction. Kinetic capillary electrophoresisKinetic capillary electrophoresis
Kinetic capillary electrophoresis or KCE is capillary electrophoresis of molecules that interact during electrophoresis. KCE was introduced and developed by Professor Sergey Krylov and his research group at York University, Toronto, Canada...
is the technology used for the selection of smart aptamers. It obtains aptamers in a few rounds of selection.
Recent developments in aptamer-based therapeutics have been rewarded in the form of the first aptamer-based drug approved by the U.S. Food and Drug Administration
Food and Drug Administration
The Food and Drug Administration is an agency of the United States Department of Health and Human Services, one of the United States federal executive departments...
(FDA) in treatment for age-related macular degeneration (AMD), called Macugen offered by OSI Pharmaceuticals
OSI Pharmaceuticals
OSI Pharmaceuticals, Inc. is an American pharmaceutical company based in Long Island, New York with facilities in Colorado, New Jersey and the United Kingdom. OSI specializes in the discovery and development of molecular targeted therapies, and was listed in the NASDAQ Biotechnology Index...
. In addition, Cambridge, MA - based Archemix (http://www.archemix.com) is leading the development of aptamers as a new class of directed therapeutics for the prevention and treatment of chronic and acute diseases. ARC1779, its lead proprietary candidate, is a potent, selective, first-in-class antagonist of von Willebrand Factor
Von Willebrand factor
von Willebrand factor is a blood glycoprotein involved in hemostasis. It is deficient or defective in von Willebrand disease and is involved in a large number of other diseases, including thrombotic thrombocytopenic purpura, Heyde's syndrome, and possibly hemolytic-uremic syndrome...
(vWF). ARC1779 is being evaluated in patients diagnosed with acute coronary syndrome
Acute coronary syndrome
Acute coronary syndrome is usually one of three diseases involving the coronary arteries: ST elevation myocardial infarction , non ST elevation myocardial infarction , or unstable angina ....
(ACS) who are undergoing percutaneous coronary intervention
Percutaneous coronary intervention
Percutaneous coronary intervention , commonly known as coronary angioplasty or simply angioplasty, is one therapeutic procedure used to treat the stenotic coronary arteries of the heart found in coronary heart disease. These stenotic segments are due to the build up of cholesterol-laden plaques...
(PCI). Phase I testing for ARC1779 was initiated in December 2006, and a Phase 2 study in ACS is planned to begin by the end of 2007.
Non-modified aptamers are cleared rapidly from the bloodstream, with a half-life of minutes to hours, mainly due to nuclease
Nuclease
A nuclease is an enzyme capable of cleaving the phosphodiester bonds between the nucleotide subunits of nucleic acids. Older publications may use terms such as "polynucleotidase" or "nucleodepolymerase"....
degradation and clearance from the body by the kidneys, a result of the aptamer's inherently low molecular weight. Unmodified aptamer applications currently focus on treating transient conditions such as blood clotting, or treating organs such as the eye where local delivery is possible. This rapid clearance can be an advantage in applications such as in vivo diagnostic imaging. An example is a tenascin-binding aptamer under development by Schering AG for cancer imaging. Several modifications, such as 2'-fluorine-substituted pyrimidines, polyethylene glycol
Polyethylene glycol
Polyethylene glycol is a polyether compound with many applications from industrial manufacturing to medicine. It has also been known as polyethylene oxide or polyoxyethylene , depending on its molecular weight, and under the tradename Carbowax.-Available forms:PEG, PEO, or POE refers to an...
(PEG) linkage, etc. (both of which are used in Macugen, an FDA-approved aptamer) are available to scientists with which to increase the serum half-life
Half-life
Half-life, abbreviated t½, is the period of time it takes for the amount of a substance undergoing decay to decrease by half. The name was originally used to describe a characteristic of unstable atoms , but it may apply to any quantity which follows a set-rate decay.The original term, dating to...
of aptamers easily to the day or even week time scale.
Another approach to increase the nuclease resistance of aptamers is to use a Spiegelmer
Spiegelmer
Spiegelmers are ribonucleic acid -like molecules built from the unnatural L- ribonucleotides. They are artificial oligonucleotides and their name is derived from the fact that they are stereochemically mirror images of natural oligonucleotides. Spiegelmers are a form of aptamers...
.
In addition to the development of aptamer-based therapeutics, many researchers such as the Ellington lab and independently another company SomaLogic (Boulder, CO) have been developing diagnostic techniques for aptamer based plasma protein profiling called aptamer plasma proteomics. This technology will enable future multi-biomarker protein measurements that can aid diagnostic distinction of disease versus healthy states. Somalogic aptamers to HER2 and EGFR membrane proteins have also been demonstrated to work in the context of rapid frozen tissue intraoperative diagnostic pathology applications.
As a resource for all in vitro selection and SELEX experiments, the Ellington lab has developed the Aptamer Database cataloging all published experiments. This is found at http://aptamer.icmb.utexas.edu/.
Peptide aptamers
Peptide aptamers are proteins that are designed to interfere with other protein interactionProtein-protein interaction
Protein–protein interactions occur when two or more proteins bind together, often to carry out their biological function. Many of the most important molecular processes in the cell such as DNA replication are carried out by large molecular machines that are built from a large number of protein...
s inside cells. They consist of a variable peptide loop attached at both ends to a protein scaffold. This double structural constraint greatly increases the binding affinity of the peptide aptamer to levels comparable to an antibody's (nanomolar range).
The variable loop length is typically composed of ten to twenty amino acid
Amino acid
Amino acids are molecules containing an amine group, a carboxylic acid group and a side-chain that varies between different amino acids. The key elements of an amino acid are carbon, hydrogen, oxygen, and nitrogen...
s, and the scaffold may be any protein which has good solubility
Solubility
Solubility is the property of a solid, liquid, or gaseous chemical substance called solute to dissolve in a solid, liquid, or gaseous solvent to form a homogeneous solution of the solute in the solvent. The solubility of a substance fundamentally depends on the used solvent as well as on...
and compacity properties. Currently, the bacterial protein Thioredoxin
Thioredoxin
Thioredoxin is a class of small redox proteins known to be present in all organisms. It plays a role in many important biological processes. In humans, it is encoded by the TXN gene. Loss-of-function mutation of either of the two human thioredoxin genes is lethal at the four-cell stage of the...
-A is the most used scaffold protein, the variable loop being inserted within the reducing active site, which is a -Cys-Gly-Pro-Cys- loop in the wild protein, the two Cysteine
Cysteine
Cysteine is an α-amino acid with the chemical formula HO2CCHCH2SH. It is a non-essential amino acid, which means that it is biosynthesized in humans. Its codons are UGU and UGC. The side chain on cysteine is thiol, which is polar and thus cysteine is usually classified as a hydrophilic amino acid...
s lateral chains being able to form a disulfide bridge.
Peptide aptamer selection can be made using different systems, but the most used is currently the yeast
Yeast
Yeasts are eukaryotic micro-organisms classified in the kingdom Fungi, with 1,500 species currently described estimated to be only 1% of all fungal species. Most reproduce asexually by mitosis, and many do so by an asymmetric division process called budding...
two-hybrid system.
Selection of Ligand Regulated Peptide Aptamers (LiRPAs) has been demonstrated. By displaying 7 amino acid peptides from a novel scaffold protein
Scaffold protein
In biology, scaffold proteins are crucial regulators of many key signaling pathways. Although scaffolds are not strictly defined in function, they are known to interact and/or bind with multiple members of a signaling pathway, tethering them into complexes...
based on the trimeric FKBP-rapamycin-FRB structure, interaction between the randomized peptide and target molecule can be controlled by the small molecule Rapamycin or non-immunosuppressive analogs.
Peptide aptamer can also be selected from combinatorial peptide libraries constructed by phage dsiplay and other surface display technologies such as mRNA display
MRNA display
mRNA display is a display technique used for in vitro protein, and/or peptide evolution to create molecules that can bind to a desired target. The process results in translated peptides or proteins that are associated with their mRNA progenitor via a puromycin linkage. The complex then binds to...
, ribosome display
Ribosome display
Ribosome display is a technique used to perform in vitro protein evolution to create proteins that can bind to a desired ligand. The process results in translated proteins that are associated with their mRNA progenitor which is used, as a complex, to bind to an immobilized ligand in a selection step...
, bacterial display
Bacterial display
Bacterial display is a protein engineering technique used for in vitro protein evolution...
and yeast display
Yeast display
Yeast display is a technique used in the field of protein engineering. The yeast display technique was first published by the laboratory of Professor K. Dane Wittrup. The technology was sold to Abbott Laboratories in 2001....
. These experimental procedures are also known as biopanning
Biopanning
Biopanning is an affinity selection technique which selects for peptides that bind to a given target . All peptide sequences obtained from biopanning using combinatorial peptide libraries have been stored in a special database with the name MimoDB , which is freely available...
s. Among peptides obtained from biopannings, mimotope
Mimotope
A mimotope is a macromolecule, often a peptide, which mimics the structure of an epitope. Because of this property it causes an antibody response similar to the one elicited by the epitope. An antibody for a given epitope antigen will recognize a mimotope which mimics that epitope. Mimotopes are...
s can be considered as a kind of peptide aptamers. All the peptides panned from combinatorial peptide libraries have been stored in a special database with the name MimoDB, which is freely available at http://immunet.cn/mimodb.
AptaBiD
AptaBiD or Aptamer-Facilitated Biomarker Discovery is a technology for biomarker discovery. AptaBiD is based on multi-round generation of an aptamer or a pool of aptamers for differential molecular targets on the cells which facilitates exponential detection of biomarkers. It involves three major stages: (i) differential multi-round selection of aptamers for biomarker of target cells; (ii) aptamer-based isolation of biomarkers from target cells; and (iii) mass spectrometryMass spectrometry
Mass spectrometry is an analytical technique that measures the mass-to-charge ratio of charged particles.It is used for determining masses of particles, for determining the elemental composition of a sample or molecule, and for elucidating the chemical structures of molecules, such as peptides and...
identification of biomarkers. The important feature of the AptaBiD technology is that it produces synthetic affinity probes (aptamers) simultaneously with biomarker discovery. In AptaBiD, aptamers are developed for cell surface biomarkers in their native state and conformation. In addition to facilitating biomarker identification, such aptamers can be directly used for cell isolation, cell visualization, and tracking cells in vivo. They can also be used to modulate activities of cell receptors and deliver different agents (e.g., siRNA
Small interfering RNA
Small interfering RNA , sometimes known as short interfering RNA or silencing RNA, is a class of double-stranded RNA molecules, 20-25 nucleotides in length, that play a variety of roles in biology. The most notable role of siRNA is its involvement in the RNA interference pathway, where it...
and drugs) into the cells.