Radiolabeling of Nucleic Acid Aptamers for Highly Sensitive Disease-Specific Molecular Imaging

Nucleic Acid Drugs in Radiotherapy

Radiotherapy remains a cornerstone of cancer treatment, using high-energy radiation to induce DNA damage in tumor cells, leading to cell death. However, its efficacy is often hindered by challenges such as radiation resistance and side effects. As a powerful class of functional molecules, nucleic acid drugs (NADs) present a promising solution to these limitations. Engineered to target key pathways like DNA repair and tumor hypoxia, NADs can enhance radiotherapy sensitivity. NADs can also serve as delivery vehicles for radiotherapy agents such as radionuclides, improving targeting accuracy and minimizing side effects. This review explores the role of NADs in optimizing radiotherapy, highlighting their mechanisms, clinical applications, and synergies with radiotherapy, ultimately offering a promising strategy for improving patient outcomes in cancer therapy.

Preclinical Evaluation of a PSMA Aptamer-Based Bifunctional PET and Fluorescent Probe

Prostate cancer is the most prevalent malignant tumor affecting male individuals worldwide. The accurate early detection of prostate cancer is crucial to preventing unnecessary diagnosis and subsequent excessive treatment. Prostate-specific membrane antigen (PSMA) has emerged as a promising biomarker for the diagnosis of prostate cancer. In this study, a dual-modality imaging probe utilizing aptamer technology was developed for positron emission tomography/near-infrared fluorescence (PET/NIRF) imaging, and the specificity and sensitivity of the probe toward PSMA were evaluated both in vitro and in vivo. The probe precursor NOTA-PSMA-Cy5 was synthesized via automated solid-phase oligonucleotide synthesis. Subsequently, the PET/NIRF dual-modality probe [68Ga]Ga-NOTA-PSMA-Cy5 was successfully prepared and exhibited favorable fluorescence properties and stability in vitro. The binding specificity of [68Ga]Ga-NOTA-PSMA-Cy5 to PSMA was assessed through flow cytometry, fluorescence imaging, and cellular uptake experiments in LNCaP cells and PC-3 cells. In vivo PET/NIRF imaging studies demonstrated the sensitive and specific binding of [68Ga]Ga-NOTA-PSMA-Cy5 to PSMA. Overall, the PET/NIRF dual-modality probe [68Ga]Ga-NOTA-PSMA-Cy5 shows promise for the diagnosis of prostate cancer and for the fluorescence-guided identification of PSMA-positive cancer lesions during surgical procedures.

Novel Aptamer Strategies in Combating Bacterial Infections: From Diagnostics to Therapeutics

Bacterial infections and antimicrobial resistance are posing substantial difficulties to the worldwide healthcare system. The constraints of conventional diagnostic and therapeutic approaches in dealing with continuously changing infections highlight the necessity for innovative solutions. Aptamers, which are synthetic oligonucleotide ligands with a high degree of specificity and affinity, have demonstrated significant promise in the field of bacterial infection management. This review examines the use of aptamers in the diagnosis and therapy of bacterial infections. The scope of this study includes the utilization of aptasensors and imaging technologies, with a particular focus on their ability to detect conditions at an early stage. Aptamers have shown exceptional effectiveness in suppressing bacterial proliferation and halting the development of biofilms in therapeutic settings. In addition, they possess the capacity to regulate immune responses and serve as carriers in nanomaterial-based techniques, including radiation and photodynamic therapy. We also explore potential solutions to the challenges faced by aptamers, such as nuclease degradation and in vivo instability, to broaden the range of applications for aptamers to combat bacterial infections.

Construction of test strips for lung cancer detection based on aptamers

Lung cancer is the most common malignancy worldwide. Early diagnosis helps to reduce mortality and improve survival. Aptamers are widely used in cancer screening because of their high specificity, good stability and low cost. In this study, using the specific aptamer of lung cancer serum, the sandwich method colloidal gold test strip was prepared by isothermal amplification technique and the principle of nucleic acid hybridisation for the early diagnosis of lung cancer. The results showed that the test strip was positive in 8 patients with lung cancer, which was consistent with the actual cases. The test strip can accurately identify lung cancer patients. The concentration range of nucleic acid detection is 1 × 10-4 - 7 × 10-4 mol/L, and the detection limit is 0.67 mM. The test strip detection method has low cost and simple operation, and provides a reference for the development of home portable tumor early detection.

RNA nanostructures for targeted drug delivery and imaging

The RNA molecule plays a pivotal role in many biological processes by relaying genetic information, regulating gene expression, and serving as molecular machines and catalyzers. This inherent versatility of RNA has fueled significant advancements in the field of RNA nanotechnology, driving the engineering of complex nanoscale architectures toward biomedical applications, including targeted drug delivery and bioimaging. RNA polymers, serving as building blocks, offer programmability and predictability of Watson-Crick base pairing, as well as non-canonical base pairing, for the construction of nanostructures with high precision and stoichiometry. Leveraging the ease of chemical modifications to protect the RNA from degradation, researchers have developed highly functional and biocompatible RNA architectures and integrated them into preclinical studies for the delivery of payloads and imaging agents. This review offers an educational introduction to the use of RNA as a biopolymer in the design of multifunctional nanostructures applied to targeted delivery in vivo, summarizing physical and biological barriers along with strategies to overcome them. Furthermore, we highlight the most recent progress in the development of both small and larger RNA nanostructures, with a particular focus on imaging reagents and targeted cancer therapeutics in pre-clinical models and provide insights into the prospects of this rapidly evolving field.

Advantages of Material Biofunctionalization Using Nucleic Acid Aptamers in Tissue Engineering and Regenerative Medicine

Material engineering is a fundamental issue in the applications of materials in the medical field. One of the aspects of material engineering is incorporating recognition sites on the surface of biomaterials, which plays an essential role in increasing the efficiency of tissue engineering scaffolds in various aspects. The application of peptides and antibodies to establish the recognition and adhesion sites has limitations, such as fragility and instability under physical and chemical processes. Therefore, synthetic ligands such as nucleic acid aptamers have received much attention for easy synthesis, minimal immunogenicity, high specificity, and stability under processing. Due to the effective role of these ligands in increasing the efficiency of engineered constructs in this study, the advantages of nucleic acid aptamers in tissue engineering will be reviewed. Aptamer-functionalized biomaterials can attract endogenous stem cells to wounded areas and organize their actions to facilitate tissue regeneration. This approach harnesses the body's inherent regeneration potential to treat many diseases. Also, increased efficacy in controlled release, slow and targeted drug delivery are important issues in drug delivery for tissue engineering approaches which can be achieved by incorporating aptamers in drug delivery systems. Aptamer-functionalized scaffolds have very applications, such as diagnosis of cancer, hematological infections, narcotics, heavy metals, toxins, controlled release from the scaffolds, and in vivo cell tracing. Aptasensors, as a result of many advantages over other traditional assay methods, can replace older methods. Furthermore, their unique targeting mechanism also targets compounds with no particular receptors. Targeting cell homing, local and targeted drug delivery, cell adhesion efficacy, cytocompatibility and bioactivity of scaffolds, aptamer-based biosensor, and aptamer-functionalized scaffolds are the topics that will be examined in this review study.

Recent Advances in Bioorthogonal Click Chemistry for Enhanced PET and SPECT Radiochemistry

Due to their high reaction rate and reliable selectivity, bioorthogonal click reactions have been extensively investigated in numerous research fields, such as nanotechnology, drug delivery, molecular imaging, and targeted therapy. Previous reviews on bioorthogonal click chemistry for radiochemistry mainly focus on ¹⁸F-labeling protocols employed to produce radiotracers and radiopharmaceuticals. In fact, besides fluorine-18, other radionuclides such as gallium-68, iodine-125, and technetium-99m are also used in the field of bioorthogonal click chemistry. Herein, to provide a more comprehensive perspective, we provide a summary of recent advances in radiotracers prepared using bioorthogonal click reactions, including small molecules, peptides, proteins, antibodies, and nucleic acids as well as nanoparticles based on these radionuclides. The combination of pretargeting with imaging modalities or nanoparticles, as well as the clinical translations study, are also discussed to illustrate the effects and potential of bioorthogonal click chemistry for radiopharmaceuticals.

Radiochemical Synthesis of 4-[18F]FluorobenzylAzide and Its Conjugation with EGFR-Specific Aptamers

Central nervous system tumors related to gliomas are of neuroectodermal origin and cover about 30% of all primary brain tumors. Glioma is not susceptible to any therapy and surgical attack remains one of the main approaches to its treatment. Preoperative tumor imaging methods, such as positron emission tomography (PET), are currently used to distinguish malignant tissue to increase the accuracy of glioma removal. However, PET is lacking a specific visualization of cells possessing certain molecular markers. Here, we report an application of aptamers to enhancing specificity in imaging tumor cells bearing the epidermal growth factor receptor (EGFR). Glioblastoma is characterized by increased EGFR expression, as well as mutations of this receptor associated with active division, migration, and adhesion of tumor cells. Since 2021, EGFR has been included into the WHO classification of gliomas as a molecular genetic marker. To obtain conjugates of aptamers GR20 and GOL1-specific to EGFR, a 4-[¹⁸F]fluorobenzylazide radiotracer was used as a synthon. For the production of the synthon, a method of automatic synthesis on an Eckert & Ziegler research module was adapted and modified using spirocyclic iodonium ylide as a precursor. Conjugation of 4-[¹⁸F]fluorobenzylazide and alkyne-modified aptamers was carried out using Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC) with/without the TBTA ligand. As a result, it was possible to obtain ¹⁸F-labelled conjugates with 97% radiochemical purity for [¹⁸F]FB-GR20 and 98% for [¹⁸F]FB-GOL1. The obtained conjugates can be used for further studies in PET analysis on model animals with grafted glioblastoma.

Nucleic Acids as Biotools at the Interface between Chemistry and Nanomedicine in the COVID-19 Era

The recent development of mRNA vaccines against the SARS-CoV-2 infection has turned the spotlight on the potential of nucleic acids as innovative prophylactic agents and as diagnostic and therapeutic tools. Until now, their use has been severely limited by their reduced half-life in the biological environment and the difficulties related to their transport to target cells. These limiting aspects can now be overcome by resorting to chemical modifications in the drug and using appropriate nanocarriers, respectively. Oligonucleotides can interact with complementary sequences of nucleic acid targets, forming stable complexes and determining their loss of function. An alternative strategy uses nucleic acid aptamers that, like the antibodies, bind to specific proteins to modulate their activity. In this review, the authors will examine the recent literature on nucleic acids-based strategies in the COVID-19 era, focusing the attention on their applications for the prophylaxis of COVID-19, but also on antisense- and aptamer-based strategies directed to the diagnosis and therapy of the coronavirus pandemic.

Ovarian cancer and KiSS-1 gene expression: A consideration of the use of Kisspeptin plus Kisspeptin aptamers in diagnostics and therapy

Gynaecological cancers continue to present a significant health burden upon the health of the global female population. This deficit is most prominent with ovarian cancer which possesses the lowest survival rate compared to all other cancers occurring within this anatomical region, with an annual UK-mortality of 7,300. The poor tolerability and selectively of the treatment options that are currently available is likely to have contributed to this high mortality rate thus, demonstrating the need for the development of enhanced therapeutic approaches. Aptamer technology would involve the engineering of specifically sequenced oligonucleotide chains, which bind to macromolecular targets with a high degree of affinity and selectively. Recent in-vitro studies conducted upon the clinical utility of this technique have supported its superiority in targeting individual therapeutic drug targets compared to various other targeting moieties currently within therapeutic use such as, monoclonal antibodies. For this reason, the employment of this technique is likely to be favourable in reducing the incidence of non-specific, chemotherapy-associated adverse effects. Kisspeptin is a naturally expressed polypeptide with an established role in the development of the reproductive system and other proposed roles in influencing the ability of ovarian cancer growths to exhibit the metastasis hallmark. This distinctive feature would indicate the potential for the manipulation of this pathway through the application of aptamer structures in developing a novel prophylactic strategy and improve the long-term outcome for ovarian cancer patients.

Diagnostics and Therapeutics in Targeting HER2 Breast Cancer: A Novel Approach

Breast cancer is one of the most commonly occurring cancers in women globally and is the primary cause of cancer mortality in females. BC is highly heterogeneous with various phenotypic expressions. The overexpression of HER2 is responsible for 15-30% of all invasive BC and is strongly associated with malignant behaviours, poor prognosis and decline in overall survival. Molecular imaging offers advantages over conventional imaging modalities, as it provides more sensitive and specific detection of tumours, as these techniques measure the biological and physiological processes at the cellular level to visualise the disease. Early detection and diagnosis of BC is crucial to improving clinical outcomes and prognosis. While HER2-specific antibodies and nanobodies may improve the sensitivity and specificity of molecular imaging, the radioisotope conjugation process may interfere with and may compromise their binding functionalities. Aptamers are single-stranded oligonucleotides capable of targeting biomarkers with remarkable binding specificity and affinity. Aptamers can be functionalised with radioisotopes without compromising target specificity. The attachment of different radioisotopes can determine the aptamer's functionality in the treatment of HER2(+) BC. Several HER2 aptamers and investigations of them have been described and evaluated in this paper. We also provide recommendations for future studies with HER2 aptamers to target HER2(+) BC.

Machine learning guided aptamer refinement and discovery

Aptamers are single-stranded nucleic acid ligands that bind to target molecules with high affinity and specificity. They are typically discovered by searching large libraries for sequences with desirable binding properties. These libraries, however, are practically constrained to a fraction of the theoretical sequence space. Machine learning provides an opportunity to intelligently navigate this space to identify high-performing aptamers. Here, we propose an approach that employs particle display (PD) to partition a library of aptamers by affinity, and uses such data to train machine learning models to predict affinity in silico. Our model predicted high-affinity DNA aptamers from experimental candidates at a rate 11-fold higher than random perturbation and generated novel, high-affinity aptamers at a greater rate than observed by PD alone. Our approach also facilitated the design of truncated aptamers 70% shorter and with higher binding affinity (1.5 nM) than the best experimental candidate. This work demonstrates how combining machine learning and physical approaches can be used to expedite the discovery of better diagnostic and therapeutic agents.

Current aptamer discovery approaches are unable to probe the complete space of possible sequences. Here, the authors use machine learning to facilitate the development of DNA aptamers with improved binding affinities, and truncate them without significantly compromising binding affinity.

In Vivo Production of RNA Aptamers and Nanoparticles: Problems and Prospects

RNA aptamers are becoming increasingly attractive due to their superior properties. This review discusses the early stages of aptamer research, the main developments in this area, and the latest technologies being developed. The review also highlights the advantages of RNA aptamers in comparison to antibodies, considering the great potential of RNA aptamers and their applications in the near future. In addition, it is shown how RNA aptamers can form endless 3-D structures, giving rise to various structural and functional possibilities. Special attention is paid to the Mango, Spinach and Broccoli fluorescent RNA aptamers, and the advantages of split RNA aptamers are discussed. The review focuses on the importance of creating a platform for the synthesis of RNA nanoparticles in vivo and examines yeast, namely Saccharomyces cerevisiae, as a potential model organism for the production of RNA nanoparticles on a large scale.

Aptamer-based technology for radionuclide targeted imaging and therapy: a promising weapon against cancer

INTRODUCTION

aptamers are short artificial, single-strand oligonucleotide sequences (DNA, RNA or modified RNA), capable of binding to biological molecules with high affinity and specificity. Due to their relatively low cost of production and scarce immunogenicity, many efforts have been made to produce aptamers directed against specific molecular targets, such as receptors or transporters overexpressed by malignancies.

AREAS COVERED

the technological approaches for generating aptamers are reviewed. Furthermore, the applications of radiolabeled aptamers for the in vivo imaging of several oncological biomarkers through single photon emission computed tomography (SPECT) or positron emission tomography (PET), are covered. Lastly, targeted therapy based on the utilization of aptamers labeled with radionuclides emitting beta particles is discussed, with particular emphasis to the oncological perspectives.

EXPERT OPINION

The main limitation of radiolabeled aptamers is represented by their in vivo sensitivity to endogenous nuclease, so that several strategies have been developed to increase the stability of these compounds. Although the applications of aptamers are still in a preliminary and pre-clinical phase, it is reasonable to hypothesize that this technology will play a major role for personalized medicine in the next years.

Aptamers, the Nucleic Acid Antibodies, in Cancer Therapy

The arrival of the monoclonal antibody (mAb) technology in the 1970s brought with it the hope of conquering cancers to the medical community. However, mAbs, on the whole, did not achieve the expected wonder in cancer therapy although they do have demonstrated successfulness in the treatment of a few types of cancers. In 1990, another technology of making biomolecules capable of specific binding appeared. This technique, systematic evolution of ligands by exponential enrichment (SELEX), can make aptamers, single-stranded DNAs or RNAs that bind targets with high specificity and affinity. Aptamers have some advantages over mAbs in therapeutic uses particularly because they have little or no immunogenicity, which means the feasibility of repeated use and fewer side effects. In this review, the general properties of the aptamer, the advantages and limitations of aptamers, the principle and procedure of aptamer production with SELEX, particularly the undergoing studies in aptamers for cancer therapy, and selected anticancer aptamers that have entered clinical trials or are under active investigations are summarized.

Aptamers as Versatile Ligands for Biomedical and Pharmaceutical Applications

Aptamers are a class of targeting ligands that bind exclusively to biomarkers of interest. Aptamers have been identified as candidates for the construction of various smart systems for therapy, diagnosis, bioimaging, and drug delivery due to their high target affinity and specificity. Aptamers are accounted as chemical antibodies that can be readily linked to drugs, sensors, signal enhancers, or nanocarriers for functionalization. Use of aptamer-guided medications, especially nanomedicines, has resulted in encouraging outcomes compared to those use of aptamer-free counterparts. This article reviews recent advances in the use of aptamers as targeting ligands for various biomedical and pharmaceutical purposes. Special interests focus on aptamer-based theranostics, biosensing, bioimaging, drug potentiation, and targeted drug delivery.

Predicting Future Prospects of Aptamers in Field-Effect Transistor Biosensors

Aptamers, in sensing technology, are famous for their role as receptors in versatile applications due to their high specificity and selectivity to a wide range of targets including proteins, small molecules, oligonucleotides, metal ions, viruses, and cells. The outburst of field-effect transistors provides a label-free detection and ultra-sensitive technique with significantly improved results in terms of detection of substances. However, their combination in this field is challenged by several factors. Recent advances in the discovery of aptamers and studies of Field-Effect Transistor (FET) aptasensors overcome these limitations and potentially expand the dominance of aptamers in the biosensor market.

Evaluation of the specific uptake of radiolabeled Staphylococcus aureus aptamers in the infectious foci

The specific uptake of ^99mTc radiolabeled Staphylococcus aureus aptamers in the infectious foci was evaluated by scintigraphic imaging of infection-bearing mice. The radiotracer uptake was inhibited by non-radiolabeled aptamers in a competition assay. In addition, when a different number of bacterial cells was used to infect mice an increase in the target/non-target ratios of images correlated with the increase of CFU per gram of tissue was verified. These results confirmed that ^99mTc-aptamers were specific to bacterial focus and the level of uptake was dependent on the number of bacterial cells.

A simple time-resolved fluorescence assay for quantitative determination of DOTA chelator

DOTA (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetate) is one of the preeminent metal chelator applied for diagnostic and therapeutic purposes, however to date there is no versatile and reliable nonradioisotopic method for its precise determination. In this technical note, we present a novel and sensitive fluorimetric assay for quantitative determination of DOTA based on the luminescence quenching of the highly luminescent europium ions complex with trioctyl phosphine oxide and naphthoyl trifluoroacetone sensitizing activators. The assay is carried out in two simple steps and enables the determination of DOTA in the nanomolar range providing a superior tool compared to commonly applied spectrophotometric assay with Arsenazo-III reagent.

Updates on Aptamer Research

For many years, different probing techniques have mainly relied on antibodies for molecular recognition. However, with the discovery of aptamers, this has changed. The science community is currently considering using aptamers in molecular targeting studies because of the many potential advantages they have over traditional antibodies. Some of these possible advantages are their specificity, higher binding affinity, better target discrimination, minimized batch-to-batch variation, and reduced side effects. Overall, these characteristics of aptamers have attracted scholars to use them as molecular probes in place of antibodies, with some aptamer-based targeting products being now available in the market. The present review is aimed at discussing the potential of aptamers as probes in molecular biology and in super-resolution microscopy.