Selection and characterization of novel DNA aptamer against colorectal carcinoma Caco-2 cells

Development of a highly sensitive immunoassay based on pentameric nanobodies for carcinoembryonic antigen detection

BACKGROUND

Carcinoembryonic antigen-related cell adhesion molecule 5 (CEACAM-5) is a well-characterized biomarker for the clinical diagnosis of various cancers. Nanobodies, considered the smallest antibody fragments with intact antigen-binding capacity, have gained significant attention in disease diagnosis and therapy. Due to their peculiar properties, nanobodies have become promising alternative diagnostic reagents in immunoassay. However, nanobodies-based immunoassay is still hindered by small molecular size and low antigen capture efficacy. Therefore, there is a pressing need to develop novel nanobody-based immunoassays with superior performance.

RESULTS

A novel pentameric nanobodies-based immunoassay (PNIA) was developed with enhanced sensitivity and specificity for CEACAM-5 detection. The binding epitopes of three anti-CEACAM-5 nanobodies (Nb1, Nb2 and Nb3) were analyzed. To enhance the capture and detection efficacy of CEACAM-5 in the immunoassay, we engineered bispecific nanobodies (Nb1-Nb2-rFc) as the capture antibody, and developed the FITC-labeled pentameric nanobodies (Nb3-VT1B) as the detection antibody. The binding affinities of Nb1-Nb2-rFc (1.746 × 10-10) and Nb3-VT1B (1.279 × 10-11) were significantly higher than those of unmodified nanobodies (Nb1-rFc, 4.063 × 10-9; Nb2-rFc, 2.136 × 10-8; Nb3, 3.357 × 10-9). The PNIA showed a linear range of 0.625-160 ng mL-1 with a correlation coefficient R2 of 0.9985, and a limit of detection of 0.52 ng mL-1, which was 24-fold lower than the immunoassay using monomeric nanobody. The PNIA was validated with the spiked human serum. The average recoveries ranged from 91.8% to 102% and the coefficients of variation ranged from 0.026% to 0.082%.

SIGNIFICANCE AND NOVELTY

The advantages of nanobodies offer a promising alternative to conventional antibodies in disease diagnosis. The novel PNIA demonstrated superior sensitivity and high specificity for the detection of CEACAM-5 antigen. This bispecific or multivalent nanobody design will provide some new insights into the design of immunoassays for clinical diagnosis.

Re-endothelialization of Decellularized Scaffolds With Endothelial Progenitor Cell Capturing Aptamer: A New Strategy for Tissue-Engineered Heart Valve

Tissue-engineered heart valve (TEHV) is a promising alternative to current heart valve substitute. Decellularized porcine aortic heart valves (DAVs) are the most common scaffolds of TEHV. Hard to endothelialization is one of the disadvantages of DAVs. Therefore, we aimed to immobilize endothelial progenitor cell (EPC)-aptamer onto DAVs for accelerating endothelialization. In this study, three groups of scaffolds were constructed: DAVs, aptamer-immobilized DAVs (aptamer-DAVs), and glutaraldehyde crosslinked DAVs (GA-DAVs). The results of flow cytometry revealed that EPC-aptamer was specific to EPCs and was immobilized onto DAVs. Cells adhesion experiments demonstrated that EPCs adhered more tightly onto aptamer-DAVs group than other two groups of scaffolds. And cell proliferation assay indicated that EPCs seeded onto aptamer-DAVs group grew faster than DAVs group and GA-DAVs group. Moreover, dynamic capture experiment in flow conditions revealed that the number of EPCs captured by aptamer-DAVs group was more than other two groups. In conclusion, aptamer-DAVs could specifically promote adhesion and proliferation of EPCs and had ability to capture EPCs in simulated flow condition. This could promote re-endothelialization of scaffolds.

Tools and techniques for the discovery of therapeutic aptamers: recent advances

INTRODUCTION

The pursuit of novel therapeutic agents for serious diseases such as cancer has been a global endeavor. Aptamers characteristic of high affinity, programmability, low immunogenicity, and rapid permeability hold great promise for the treatment of diseases. Yet obtaining the approval for therapeutic aptamers remains challenging. Consequently, researchers are increasingly devoted to exploring innovative strategies and technologies to advance the development of these therapeutic aptamers.

AREAS COVERED

The authors provide a comprehensive summary of the recent progress of the SELEX (Systematic Evolution of Ligands by EXponential enrichment) technique, and how the integration of modern tools has facilitated the identification of therapeutic aptamers. Additionally, the engineering of aptamers to enhance their functional attributes, such as inhibiting and targeting, is discussed, demonstrating the potential to broaden their scope of utility.

EXPERT OPINION

The grand potential of aptamers and the insufficient development of relevant drugs have spurred countless efforts for stimulating their discovery and application in the therapeutic field. While SELEX techniques have undergone significant developments with the aid of advanced analysis instruments and ingeniously updated aptameric engineering strategies, several challenges still impede their clinical translation. A key challenge lies in the insufficient understanding of binding conformation and susceptibility to degradation under physiological conditions. Despite the hurdles, our opinion is optimistic. With continued progress in overcoming these obstacles, the widespread utilization of aptamers for clinical therapy is envisioned to become a reality soon.

Aptamers Targeting Membrane Proteins for Sensor and Diagnostic Applications

Many biological processes (physiological or pathological) are relevant to membrane proteins (MPs), which account for almost 30% of the total of human proteins. As such, MPs can serve as predictive molecular biomarkers for disease diagnosis and prognosis. Indeed, cell surface MPs are an important class of attractive targets of the currently prescribed therapeutic drugs and diagnostic molecules used in disease detection. The oligonucleotides known as aptamers can be selected against a particular target with high affinity and selectivity by iterative rounds of in vitro library evolution, known as Systematic Evolution of Ligands by EXponential Enrichment (SELEX). As an alternative to antibodies, aptamers offer unique features like thermal stability, low-cost, reuse, ease of chemical modification, and compatibility with various detection techniques. Particularly, immobilized-aptamer sensing platforms have been under investigation for diagnostics and have demonstrated significant value compared to other analytical techniques. These "aptasensors" can be classified into several types based on their working principle, which are commonly electrochemical, optical, or mass-sensitive. In this review, we review the studies on aptamer-based MP-sensing technologies for diagnostic applications and have included new methodological variations undertaken in recent years.

Aptamer-Based Detection of Circulating Targets for Precision Medicine

The past decade has witnessed ongoing progress in precision medicine to improve human health. As an emerging diagnostic technique, liquid biopsy can provide real-time, comprehensive, dynamic physiological and pathological information in a noninvasive manner, opening a new window for precision medicine. Liquid biopsy depends on the sensitive and reliable detection of circulating targets (e.g., cells, extracellular vesicles, proteins, microRNAs) from body fluids, the performance of which is largely governed by recognition ligands. Aptamers are single-stranded functional oligonucleotides, capable of folding into unique tertiary structures to bind to their targets with superior specificity and affinity. Their mature evolution procedure, facile modification, and affinity regulation, as well as versatile structural design and engineering, make aptamers ideal recognition ligands for liquid biopsy. In this review, we present a broad overview of aptamer-based liquid biopsy techniques for precision medicine. We begin with recent advances in aptamer selection, followed by a summary of state-of-the-art strategies for multivalent aptamer assembly and aptamer interface modification. We will further describe aptamer-based micro-/nanoisolation platforms, aptamer-enabled release methods, and aptamer-assisted signal amplification and detection strategies. Finally, we present our perspectives regarding the opportunities and challenges of aptamer-based liquid biopsy for precision medicine.

Advances of aptamers screened by Cell-SELEX in selection procedure, cancer diagnostics and therapeutics

Aptamers are a class of short artificial single-stranded oligo(deoxy) nucleotides that can bind to different targets, which generated by Systematic Evolution of Ligands by Exponential Enrichment (SELEX). Due to excellent selectivity and high affinity to targets, aptamers hold considerable potential as molecular probe in diverse applications ranging from ensuring food safety, monitoring environment, disease diagnosis to therapy. This review highlights recent development and challenges about aptamers screened by Cell-SELEX, and its application about cancer diagnostics and therapeutics. Advances about some operation methods such as seperation method and culture method in aptamers selection procedure were summarized in this paper. Some common challenges and technological difficulties such as nonspecific binding and biostability were discussed. Up to now, the recent endeavors about cancer diagnostic and therapeutic applications of aptamers are summarized and expatiated. Most of aptamers screened by Cell-SELEX took tumor cells as target cells, and such aptamers have been assembled to various aptasensor for cancer diagnosis. Aptamers conjugated various drugs or nanomaterials are functioned for cancer target therapy to improve drugs delivery efficiency and reduce side effects. Furthermore, the duplexed aptamer is discussed to be applied for cancer cells detection and some conflicts of theories about duplexed aptamer designs are analyzed.

Cell-SELEX, an Effective Way to the Discovery of Biomarkers and Unexpected Molecular Events

Cell-SELEX can not only generate aptamers for specific cell isolation/detection, diagnosis, and therapy, but also lead to the discovery of biomarkers and unexpected molecular events. However, most cell-SELEX research is concentrated on aptamer generation and applications. In this progress report, recent research progress with cell-SELEX in terms of the discovery of biomarkers and unexpected molecular events is highlighted. In particular, the key technical challenges for cell-SELEX-based biomarker discovery, namely, the methods for identification and validation of target proteins of aptamers, are discussed in detail. Finally, the prospects of the applications of cell-SELEX in this field now and in the near future are described. It is expected that this report will attract attention to the benefit of cell-SELEX and provide a practical reference for biomedical researchers.

Recent Advances in Aptamer Discovery and Applications

Aptamers are short, single-stranded DNA, RNA, or synthetic XNA molecules that can be developed with high affinity and specificity to interact with any desired targets. They have been widely used in facilitating discoveries in basic research, ensuring food safety and monitoring the environment. Furthermore, aptamers play promising roles as clinical diagnostics and therapeutic agents. This review provides update on the recent advances in this rapidly progressing field of research with particular emphasis on generation of aptamers and their applications in biosensing, biotechnology and medicine. The limitations and future directions of aptamers in target specific delivery and real-time detection are also discussed.

Novel insights into the role of aptamers in the fight against cancer

PURPOSE

Aptamers are a class of single-stranded nucleic acid (DNA or RNA) oligonucleotides that are screened in vitro by a technique called systematic evolution of ligands by exponential enrichment (SELEX). They have stable three-dimensional structures that can bind to various targets with high affinity and specificity. Due to distinct properties such as easy synthesis, high stability, small size, low toxicity and immunogenicity, they have been largely studied as anticancer agents/tools. Consequently, aptamers are starting to play important roles in disease prevention, diagnosis and therapy. This review focuses on studies that evaluated the effect of aptamers on various aspects of cancer therapy. It also provides novel and unique insights into the role of aptamers on the fight against cancer.

METHODS

We reviewed literatures about the role of aptamers against cancer from PUBMED databases in this article.

RESULTS

Here, we summarized the role of aptamers on the fight against cancer in a unique point of view. Meanwhile, we presented novel ideas such as aptamer-pool-drug conjugates for the treatment of refractory cancers.

CONCLUSIONS

Aptamers and antibodies should form a "coalition" against cancers to maximize their advantages and minimize disadvantages.