Abstract
G-quadruplexes constitute a unique class of nucleic acid structures formed by G-rich oligonucleotides of DNA- or RNA-type. Depending on their chemical nature, loops length, and localization in the sequence or structure molecularity, G-quadruplexes are highly polymorphic structures showing various folding topologies. They may be formed in the human genome where they are believed to play a pivotal role in the regulation of multiple biological processes such as replication, transcription, and translation. Thus, natural G-quadruplex structures became prospective targets for disease treatment. The fast development of systematic evolution of ligands by exponential enrichment (SELEX) technologies provided a number of G-rich aptamers revealing the potential of G-quadruplex structures as a promising molecular tool targeted toward various biologically important ligands. Because of their high stability, increased cellular uptake, ease of chemical modification, minor production costs, and convenient storage, G-rich aptamers became interesting therapeutic and diagnostic alternatives to antibodies. In this review, we describe the recent advances in the development of G-quadruplex based aptamers by focusing on the therapeutic and diagnostic potential of this exceptional class of nucleic acid structures.
Highlights
Aptamers are small DNA- or RNA-based oligonucleotides which are typically produced by the systematic evolution of ligands by exponential enrichment (SELEX) technology
The T40214 aptamer is 2nt longer than T40231 and has two G-quartets in the center and three C-G loop domains: two at the bottom and one at the top (Figure 2E); T40231 has two G-quartets with three T-G loops: two at the bottom and one at the top (Figure 2F). These aptamers significantly suppress the growth of human non-small cell lung cancer (NSCLC) tumors in vivo by selectively inhibiting the activation of Stat3 and its downstream proteins such as Bcl-2, Bcl-xL, Mcl-1, survivin, VEGF, Cyclin D1, and c-myc
The Stat3 protein is a signal transducer and activator of transcription and is involved in cellular differentiation, proliferation, and apoptosis. These results demonstrate that Stat3 is an important molecular target for NSCLC therapy [89]
Summary
Aptamers are small DNA- or RNA-based oligonucleotides which are typically produced by the systematic evolution of ligands by exponential enrichment (SELEX) technology. Several modified SELEX methods have been set up to decrease the selection time and enhance the hit rates One of such method is negative SELEX, where after three selection cycles, the library is incubated with chromatography columns as negative selection and the non-specific binding sequences are removed from each pool [4]. In another approach, named counter SELEX, an extra step, using structurally similar targets, is introduced for incubation with aptamers to effectively discriminate non-specific oligonucleotides [4]. We summarize the recent developments and applications of G-rich aptamers in therapy, drug delivery, and diagnostics
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