Molecular Imaging with Nucleic Acid Aptamers

Abstract

With many desirable properties such as ease of synthesis, small size, lack of immunogenicity, and versatile chemistry, aptamers represent a class of targeting ligands that possess tremendous potential in molecular imaging applications. Non-invasive imaging of various disease markers with aptamer-based probes has many potential clinical applications such as lesion detection, patient stratification, treatment monitoring, etc. In this review, we will summarize the current status of molecular imaging with aptamer-based probes. First, fluorescence imaging will be described which include both direct targeting and activatable probes. Next, we discuss molecular magnetic resonance imaging and targeted ultrasound investigations using aptamer-based agents. Radionuclide-based imaging techniques (single-photon emission computed tomography and positron emission tomography) will be summarized as well. In addition, aptamers have also been labeled with various tags for computed tomography, surface plasmon resonance, dark-field light scattering microscopy, transmission electron microscopy, and surface-enhanced Raman spectroscopy imaging. Among all molecular imaging modalities, no single modality is perfect and sufficient to obtain all the necessary information for a particular question. Thus, a multimodality probe has also been constructed for concurrent fluorescence, gamma camera, and magnetic resonance imaging in vivo. Although the future of aptamer-based molecular imaging is becoming increasingly bright and many proof-of-principle studies have already been reported, much future effort needs to be directed towards the development of clinically translatable aptamer-based imaging agents which will eventually benefit patients.

Development and Characterization of a ssDNA-based Aptamer that Selectively Targets Epithelial Carcinoma Cells

“…For example, imaging of various diseases could be performed on the bases of targeting specific molecular markers, where aptamers offer unmatched capabilities. As such, these highly specific molecular aptamer probes could be used for detection of lesions, stratification of patients for clinical studies, evaluation of new drug toxicities and biodistribution, and treatment monitoring, among others [40][41][42][43].…”

Current Progress of Aptamer-Based Molecular Imaging

“…Aptamers’ small size and ability to target a wide range of molecules make them excellent molecular imaging probes for cellular imaging. Aptamer-based imaging probes can be formulated either by directly linking them to fluorescent molecules or by conjugating aptamers to nanoparticle-based optical probes (8). These aptamer-based molecular imaging probes have been used to image biomarkers and cellular proteins such as integrins, prostate-specific membrane antigen (PSMA), and nucleolin.…”

“…The very first report of an aptamer-based imaging probe was a radiolabeled ( 99m Tc) aptamer targeted against human neutrophil elastase to identify sites of inflammation (8). When compared with a radiolabeled IgG, the aptamer probe achieved a higher target-to-background ratio (4-fold) than that of IgG (3-fold).…”

Selection of Peptidoglycan-Specific Aptamers for Bacterial Cells Identification

“…They are minimally immunogenic, inexpensive, simple to chemically modify, easy to synthesize, have a small size which allows better tissue penetration, and possess increased temperature stability over antibodies. Aptamers have a wide variety of targets ranging from small organic molecules to complex protein or even whole intact cells; they can be labeled with different radioisotopes and are emerging as a new class of molecules for radiopharmaceuticals development [9,10]. Studies using aptamers for inflammation, thrombus, and tumor imaging have been published [11].…”