Application of aptamers in diagnostics, drug-delivery and imaging

Abstract

Aptamers are small, single-stranded oligonucleotides (DNA or RNA) that bind to their target with high specificity and affinity. Although aptamers are analogous to antibodies for a wide range of target recognition and variety of applications, they have significant advantages over antibodies. Since aptamers have recently emerged as a class of biomolecules with an application in a wide array of fields, we need to summarize the latest developments herein. In this review we will discuss about the latest developments in using aptamers in diagnostics, drug delivery and imaging. We begin with diagnostics, discussing the application of aptamers for the detection of infective agents itself, antigens/ toxins (bacteria), biomarkers (cancer), or a combination. The ease of conjugation and labelling of aptamers makes them a potential tool for diagnostics. Also, due to the reduced off-target effects of aptamers, their use as a potential drug delivery tool is emerging rapidly. Hence, we discuss their use in targeted delivery in conjugation with siRNAs, nanoparticles, liposomes, drugs and antibodies. Finally, we discuss about the conjugation strategies applicable for RNA and DNA aptamers for imaging. Their stability and self-assembly after heating makes them superior over protein-based binding molecules in terms of labelling and conjugation strategies.

Aptamers for Targeted Delivery: Current Challenges and Future Opportunities

“…Aptamers have been used to functionalize liposomes to increase their bioavailability through targeted delivery (Figure 1) [4]. Since aptamers are negatively charged it is easier to pack them with cationic liposomes.…”

“…Aptamers are selected from a pool of random single-stranded DNA/RNA oligonucleotide library (>10 15 random sequences) by iterative rounds of selection and amplification by SELEX method as shown in Figure 2 [4]. Therapeutic aptamers have been developed against cell surface targets [62] as well as for delivery of therapeutic conjugates into the cells, i.e., for internalization [3].…”

“…All these properties make aptamers as suitable candidates for therapeutic use, particularly targeted nano-delivery. Several aptamers have already been selected against cell surface targets for targeted delivery of therapeutic payload for different diseases, e.g., cancer and human immunodeficiency virus (HIV) infected cells [4]. Table 1 lists the common differences between antibodies and aptamers.…”

G-quadruplex-based aptamers against protein targets in therapy and diagnostics

“…These aptasensors can be generally divided into two classes: "labeled" and "label-free" sensors [170]. The most recent developments in the use of aptamers in diagnostics and imaging have been recently reviewed by Neerathilingam et al, who have discussed in detail the applications of aptamers for the detection of infective agents, antigens/ toxins (bacteria) and biomarkers (cancer) [171].…”

Potentiometric Aptasensing of Vibrio alginolyticus Based on DNA Nanostructure-Modified Magnetic Beads

“…Since aptamers have high specificities and binding affinities to their targets, they have been widely used to develop a variety of electrochemical biosensors for the detection of small molecules, metal ions, and proteins [11,12,13,14,15]. Nowadays, aptamers have also been used for the detection of bacteria based on their high specificity bindings to proteins either on the cell surfaces or inside the cells [16,17,18,19]. Various electrochemical aptasensors using different transduction modes such as amperometry, impedimetry, and potentiometry have been developed [20,21,22].…”