Aptamers

What are aptamers?

Aptamers are short, single-stranded molecules of nucleic acid, most often DNA or RNA, that span between 20 and 100 bases. These molecules are generated by the Systematic Evolution of Ligands by Exponential Enrichment (SELEX) process, and these molecules are extremely specific and have affinity for the target molecules. They fold into complex three-dimensional forms - loops, stems, and hairpins - and so can be selectively recognised and bound to a wide range of substrates, including proteins, small molecules, and even cells.

Figure 1. A schematic presentation of SELEX, aptamer folding and its binding with a final target protein. The aptamer folds into a specific three-dimensional structure and binds with a target molecule which results in the formation of a target-aptamer complex^[1].

How to make aptamers?

Aptamers are synthesized mostly through the Systematic Evolutionary Ligand by Exponential Enrichment (SELEEX) method, a screening procedure for highly specific and high-affinity aptamers from randomly generated oligonucleotide libraries, first developed by Gold and Szostak in 1990.

In SELEX, a library of DNA or RNA with lots of random sequences is first made and then continuously loaded with aptamers that will bind to specific molecules (i.e., proteins, small molecules, metal ions, etc.). with multiple screening and amplification rounds. The screening process usually includes the following steps:

a. Construction of random sequence library: Generate an oligonucleotide library containing a large number of random sequences by chemical synthesis.

b. Target molecule binding screening: mix the oligonucleotide library with the target molecule and isolate the oligonucleotides that can bind the target molecule by affinity purification method.

c. PCR amplification: PCR amplification is performed on the bound oligonucleotides to increase their concentration.

d. Repeat screening: The binding affinity and specificity of the aptamer to the target molecule are gradually improved through multiple rounds of screening and amplification.

In recent years, SELEX technology has also been highly optimized - for example, the cellular SELEX method, which leverages cells as a screen to make sure the aptamer recognises the natural conformation of cell surface proteins. Also, strategies are also based on computer simulation and machine learning to overcome the constraints of conventional SELEX procedures.

Aptamers can be synthesized without SELEX technology through other techniques such as solid-phase phosphoramidite chemical standard synthesis and chemical synthesis with modified nucleotides or non-natural nucleotides. All of these methods have benefits, e.g., modified nucleotides may increase stability and specificity of the aptamer.

Figure 2. Selection step within one cycle of cell-SELEX. A library of single-stranded sequences is incubated with target cells. After the washing program, negative selection is performed to remove non-specifically bound sequences. Subsequently, the resulting sequences are PCR amplified before proceeding to the next cycle^[1].

Aptamers vs. Antibodies

There are many advantages of aptamers over the old-school antibodies in diagnosis and treatment. Their benefits include:

• Quick Screening: Aptamer screenings with SELEX will happen in a matter of days or weeks, compared to months of antibody development.
• Better Specificity: Aptamers can be designed in vitro without unwanted immunogenicity and toxicity.
• Small Molecular Size: They are smaller than the normal size, which means that they penetrate tissues much more effectively and target them more efficiently, especially in high tumor burden.
• Very Low Immunogenicity: Aptamers are not immunogenic and so can be used multiple times without creating unwanted immune responses.
• Easy to Modify: Aptamers can be chemically modified to increase stability, bioavailability, and functionalization for multimodality therapy.
• Thermal and Chemical Stability: These antibodies are very stable under different conditions, which makes them better to store and provide long-lasting performance than temperature-sensitive antibodies.

What are aptamers used for?

Diagnostics

Aptamers are widely used as molecular recognition elements in biosensors and diagnostic assays, detecting biomarkers with high sensitivity.

Therapeutics

• Aptamer-Drug Conjugates (ApDCs): These conjugates deliver therapeutic agents directly to target sites, maximizing efficacy while minimizing off-target effects. Examples include triptolide ApDCs and camptothecin ApDCs.
• Immunotherapy: Aptamers can modulate immune responses by activating co-stimulatory receptors or blocking immune checkpoint inhibitors.
• Drug Delivery Systems: The integration of aptamers with nanomaterials, such as liposomes and nanoparticles, facilitates precise drug delivery to cancer cells. Notable studies highlight the use of MUC1 and PSMA-targeting aptamers in reducing adverse effects and enhancing treatment outcomes.

Cancer Treatment

• Aptamers targeting specific cancer biomarkers, such as AS1411 for nucleolin, are undergoing clinical trials for hard-to-treat malignancies
• Glycan-targeting aptamers for tumor-associated carbohydrate antigens (TACAs) represent a promising avenue for diagnostics and therapeutic interventions.

Aptamers Development at Alfa Chemistry

Alfa Chemistry produces and customises the best quality aptamers. With the most powerful SELEX technology and the world's most powerful synthesis platforms, Alfa Chemistry guarantees aptamer products to exceed scientific standards.

• Target selection.
• Sequence design of aptamers.
• Synthesis and chemical modification of aptamers.
• Screening of aptamers (SELEX technology)
• Delivery system selection or development of aptamers.
• Nonclinical evaluation of aptamers.
• Scale-up of aptamers.

Aptamers are transforming diagnostics, therapies, and drug delivery through unparalleled specificity, flexibility, and stability. Alfa Chemistry, through a complete suite of aptamer products and services, advances innovative research and development, enabling researchers to reach the next generation in healthcare and biotechnology.

Our products and services are for research use only and cannot be used for any clinical purposes.

Online Inquiry

* Name

Phone

* Email

* Services & Products of Interest Aptamers

Project Description

* Verification Code

Submit