Aptamers used for molecular imaging and theranostics - recent developments

Abstract

Aptamers are single stranded oligonucleotides that fold into three dimensional structures and are able to recognize a variety of molecular targets. Due to the similarity to antibodies with regards to specificity and affinity and their chemical versatility, aptamers are increasingly used to create targeted probes for in vivo molecular imaging and therapy. Hence, aptamer-based probes have been utilized in practically all major imaging modalities such as nuclear imaging, magnetic resonance imaging, x-ray computed tomography, echography and fluorescence imaging, as well as newer modalities such as surface enhanced Raman spectroscopy. Aside from targeting, aptamers have been used for the creation of sensors that allow the localized detection of cellular markers such as ATP in vivo . This review focuses on in vivo studies of aptamer-based probes for imaging and theranostics since the comprehensive overview by Bouvier-Müller and Ducongé in 2018.

Toehold-Exchange-Based Activation of Aptamer Switches Enables High Thermal Robustness and Programmability

“…Molecular switches that undergo conformational changes upon target binding are naturally evolved machinery to regulate diverse biological functions . For example, riboswitches are widely adopted by living organisms to control gene expressions in response to environmental stimuli. , Inspired by nature, chemists and synthetic biologists have developed intense research interests to create artificial chemically activated switches that can be used to mimic processes in living systems and further expand their functionality for uses in biosensing, imaging, , therapeutics, , and beyond. , In this regard, aptamers are ideal functional molecules to develop artificial molecular switches because they not only are synthetic binders with high affinity and selectivity but can also be readily engineered via Watson–Crick base pairing. To be a molecular switch, an aptamer must be selected or engineered so that it shifts reversibly and controllably between an inactive “off” and a binding-competent “on” state, which is often achieved by caging an aptamer in a metastable inter- or intramolecular duplex motif (Figure a) …”

“…1 For example, riboswitches are widely adopted by living organisms to control gene expressions in response to environmental stimuli. 2,3 Inspired by nature, chemists and synthetic biologists have developed intense research interests to create artificial chemically activated switches that can be used to mimic processes in living systems and further expand their functionality for uses in biosensing, 4 imaging, 5,6 therapeutics, 7,8 and beyond. 9,10 In this regard, aptamers are ideal functional molecules to develop artificial molecular switches because they not only are synthetic binders with high affinity and selectivity but can also be readily engineered via Watson−Crick base pairing.…”

Aptamers Enhance Oncolytic Viruses’ Antitumor Efficacy

“…Moreover, by loading such a bifunctional aptamer (EPCAM-TfR) with doxorubicin (DOX), it is possible to transcytose the endothelial cells of the BBB and deliver a payload for the treatment of EPCAM-positive brain metastases [ 59 ]. Aptamers have great potential for use as theranostic—diagnostic and therapeutic—tools due to their ability to diffuse through the entire tumor area in the intracranial cavity [ 60 ]. It is possible to design aptamers targeting specific cell surface biomarkers with high affinity and specificity by a combinatorial SELEX procedure [ 61 , 62 ].…”

Quantitative Evaluation of a Multimodal Aptamer-Targeted Long-Circulating Polymer for Tumor Targeting

“…Aptamers are short single-stranded oligonucleotides that are able to bind to a variety of molecular targets. In recent years, aptamers have been increasingly used as targeting moieties for nanomaterials for diagnostic and therapeutic purposes. , One of the best described DNA aptamers is arguably sgc8, which was selected against CCRF-CEM cells using cell-SELEX . Tyrosine-protein kinase-like 7 (PTK7), also known as colon carcinoma kinase 4 (CCK4), has been identified as the molecular target of sgc8 .…”