Active Drug Targeting by Aptamers

CD Bioparticles offers custom services for nanocarriers which have targeting ligands. Aptamers have been widely explored as targeting ligand in the past three decades to deliver therapeutic as well as diagnostic agents in biomedical research due to its unique chemical features and biological functions. Our experienced scientists have created a comprehensive platform to design the aptamers for drug delivery system upon request.

Introduction to Aptamers Used in Active Targeting

Aptamers are a special class of nucleic acid molecules (DNA or RNA) which can form unique three-dimensional structures capable of specifically binding (with higher affinity) to molecular targets including small molecules, proteins, nucleic acids, and other cellular targets. Aptamer-conjugated nanoparticles have significant potential as drug-delivery carriers because they not only have all the advantages of antibodies, but also with unique attributes, such as thermal stability, low cost, and unlimited applications. In contrast to antibodies, aptamers have a small size, are easy to synthesize, show high stability in vivo, and possess good solubility in different solvents. At the molecular level, aptamers bind to its target site through non-covalent interactions. Aptamers bind to these specific targets because of electrostatic interactions, hydrophobic interactions, and their complementary shapes. Aptamers are useful in biotechnological and therapeutic applications as they offer molecular recognition properties the commonly used biomolecule, antibodies. In addition to their discriminate recognition and readily produced by chemical synthesis, aptamers offer advantages over antibodies as they can be engineered completely in a test tube, possess desirable storage properties, and elicit little or no immunogenicity in therapeutic applications. Various high throughput processes such as SELEX (Systematic Evolution of Ligands by Exponential Amplification) and other in vitro selection techniques are used to isolate aptamers with high affinity, and screen and evaluate aptamers against potential targets from combinatorial oligonucleotide libraries. Furthermore, several types of in vitro selection processes could apply with SELEX, including nitrocellulose membrane filtration, affinity chromatography, magnetic bead, and capillary electrophoresis-based selection methods for aptamer separation. Numerous analytical techniques, such as electrochemical, colorimetric, optical, and mass-sensitive methods, can be utilized to detect targets to confirm its targeting capability. Finally, an optimal aptamer will be selected as a targeting ligand for a drug delivery system.

Key Features of the Aptamers

• Targeted-release nanocarriers can protect healthy tissues from toxic drugs and decrease the side-effects by releasing in target tissues.
• It is possible to synthesize aptamers with a specific functional moiety, such as a carboxylate, amino, sulfhydryl or aldehyde, at only one end of the nucleic acid aptamer. This ensures and greatly facilitates site-specific conjugation and prevents the formation of heterogeneous mixtures.
• Aptamers are typically non-immunogenic.
• Aptamers are non-toxic and modifiable for stability in circulation.
• Aptamers can be selected in vitro and in vivo, and be repeatedly and reversibly denatured.
• Aptamers are not dependent on animals or their immune responses, aptamers can be selected against weakly immunogenic targets and toxins.
• Aptamers are much smaller than antibodies and can form compact structures, allowing them to bind clefts, binding sites, and enzymatic active sites, which is difficult, for antibodies to achieve.

Figure 1. Schematic illustration of aptamer binding to its biomarker. (Sun, H., et al. Molecular Therapy-Nucleic Acids, 2014, 3, e182.)

Aptamers Technology Applications

It has been shown that aptamers result in increased targeting specificity and more efficient drug delivery to tumor cells. Hence, they are more suitable for the development of novel clinical applications. Aptamer technology has been widely investigated in various biomedical fields for biomarker discovery, in vitro diagnosis, in vivo imaging, and targeted therapy.

• Aptamers that bind to internalized cell surface receptors have been exploited to deliver drugs and a variety of other cargo into cells.
• Aptamers can efficiently and safely deliver siRNAs into specific cells for the therapeutic use of the siRNAs to be effective.
• Aptamers have an innate ability to bind to any molecule they're targeted at, including cancer cells and bacteria. Bound to a target, aptamers inhibit its activity. So aptamers are not only a drug-targeting method, but it is also a therapeutic drug in itself.

Our Aptamers Services

CD Bioparticles is specialized in the development of drug targeting strategy and customizing nanoparticles for drug delivery and targeting utilizing our core technologies. With our high-quality products and services, the efficacy of your drug delivery can be tremendously improved by nucleic acid aptamers.

Our team can provide service from aptamer library construction to aptamer-mediated drug delivery system characterization. We are proficient in designing and modifying copolymer, liposome, metal, and virus-like nanoparticles with aptamers. In addition to common nanoparticles, hydrogels, silica, quantum dots (QD), and single-walled carbon nanotubes are also available for aptamer-mediated delivery of targeted therapeutics. In addition, particle properties such as component molecular weight, surface charges and charge density, solubility, and hydrophobicity could be designed and engineered at your will.

Quotations and Ordering

References:
1. Bertrand N, Wu J, Xu X, Kamaly N, Farokhzad OC. Cancer nanotechnology: the impact of passive and active targeting in the era of modern cancer biology. Advanced drug delivery reviews, 2014, 66, 2-5.
2. Sun, H., Zhu, X., Lu, P.Y., Rosato, R.R., Tan, W. and Zu, Y. Oligonucleotide aptamers: new tools for targeted cancer therapy. Molecular Therapy-Nucleic Acids, 2014, 3, e182.
3. Shangguan, D., Li, Y., Tang, Z., Cao, Z.C., Chen, H.W., Mallikaratchy, P., Sefah, K., Yang, C.J. and Tan, W. Aptamers evolved from live cells as effective molecular probes for cancer study. Proceedings of the National Academy of Sciences, 2006, 103(32), 11838-11843.
4. Nimjee, S. M., Rusconi, C. P., & Sullenger, B. A. Aptamers: an emerging class of therapeutics. Annu. Rev. Med., 2005, 56, 555-583.
5. Kyung-Mi S., et al. Aptamers and Their Biological Applications. Sensors. 2012, 12: 612-631.