Angiogenin-mediated photosensitizer-aptamer conjugate for photodynamic therapy

Aptamers as Diagnostic and Therapeutic Agents for Aging and Age-Related Diseases

In the 21st century, the demographic shift toward an aging population has posed a significant challenge, particularly with respect to age-related diseases, which constitute a major threat to human health. Accordingly, the detection, prevention, and treatment of aging and age-related diseases have become critical issues, and the introduction of novel molecular recognition elements, called aptamers, has been considered. Aptamers, a class of oligonucleotides, can bind to target molecules with high specificity. In addition, aptamers exhibit superior stability, biocompatibility, and applicability, rendering them promising tools for the diagnosis and treatment of human diseases. In this paper, we present a comprehensive overview of aptamers, systematic evolution of ligands by exponential enrichment (SELEX), biomarkers associated with aging, as well as aptamer-based diagnostic and therapeutic platforms. Finally, the limitations associated with predicting and preventing age-related conditions are discussed, along with potential solutions based on advanced technologies and theoretical approaches.

Recent progress in the engineering of multifunctional colloidal nanoparticles for enhanced photodynamic therapy and bioimaging

This up-to-date review summarizes the design and current fabrication strategies that have been employed in the area of mono- and multifunctional colloidal nanoparticles - nanocarriers well suited for photodynamic therapy (PDT) and diagnostic purposes. Rationally engineered photosensitizer (PS)-loaded nanoparticles may be achieved via either noncovalent (i.e., self-aggregation, interfacial deposition, interfacial polymerization, or core-shell entrapment along with physical adsorption) or covalent (chemical immobilization or conjugation) processes. These PS loading approaches should provide chemical and physical stability to PS payloads. Their hydrophilic surfaces, capable of appreciable surface interactions with biological systems, can be further modified using functional groups (stealth effect) to achieve prolonged circulation in the body after administration and/or grafted by targeting agents (such as ligands, which bind to specific receptors uniquely expressed on the cell surface) or stimuli (e.g., pH, temperature, and light)-responsive moieties to improve their action and targeting efficiency. These attempts may in principle permit efficacious PDT, combination therapies, molecular diagnosis, and - in the case of nanotheranostics - simultaneous monitoring and treatment. Nanophotosensitizers (nano-PSs) should possess appropriate morphologies, sizes, unimodal distributions and surface processes to be successfully delivered to the place of action after systemic administration and should be accumulated in certain tumors by passive and/or active targeting. Additionally, physically facilitating drug delivery systems emerge as a promising approach to enhancing drug delivery, especially for the non-invasive treatment of deep-seated malignant tissues. Recent advances in nano-PSs are scrutinized, with an emphasis on design principles, via the promising use of colloid chemistry and nanotechnology.

Zn phthalocyanine conjugation to H2-ul aptamer for HER2-targeted breast cancer photodynamic therapy: Design, optimization and properties

Tetrasulfonated Zn phthalocyanine was conjugated to a ssDNA aptamer moiety to produce a HER2 targeted photosensitizer. The tetraconjugate obtained was subjected to purification and the monoconjugate was successfully isolated, purified and characterized. This monoconjugate retained the ability to bind to HER2 as well as the potency to generate singlet oxygen.

Aptamers: active targeting ligands for cancer diagnosis and therapy

Aptamers, including DNA, RNA and peptide aptamers, are a group of promising recognition units that can specifically bind to target molecules and cells. Due to their excellent specificity and high affinity to targets, aptamers have attracted great attention in various fields in which selective recognition units are required. They have been used in biosensing, drug delivery, disease diagnosis and therapy (especially for cancer treatment). In this review, we summarized recent applications of DNA and RNA aptamers in cancer theranostics. The specific binding ability of aptamers to cancer-related markers and cancer cells ensured their high performance for early diagnosis of cancer. Meanwhile, the efficient targeting ability of aptamers to cancer cells and tissues provided a promising way to deliver imaging agents and drugs for cancer imaging and therapy. Furthermore, with the development of nanoscience and nanotechnology, the conjugation of aptamers with functional nanomaterials paved an exciting way for the fabrication of theranostic agents for different types of cancers, which might be a powerful tool for cancer treatment.

Aptamer-mediated indirect quantum dot labeling and fluorescent imaging of target proteins in living cells

Protein labeling for dynamic living cell imaging plays a significant role in basic biological research, as well as in clinical diagnostics and therapeutics. We have developed a novel strategy in which the dynamic visualization of proteins within living cells is achieved by using aptamers as mediators for indirect protein labeling of quantum dots (QDs). With this strategy, the target protein angiogenin was successfully labeled with fluorescent QDs in a minor intactness model, which was mediated by the aptamer AL6-B. Subsequent living cell imaging analyses indicated that the QDs nanoprobes were selectively bound to human umbilical vein endothelial cells, gradually internalized into the cytoplasm, and mostly localized in the lysosome organelle, indicating that the labeled protein retained high activity. Compared with traditional direct protein labeling methods, the proposed aptamer-mediated strategy is simple, inexpensive, and provides a highly selective, stable, and intact labeling platform that has shown great promise for future biomedical labeling and intracellular protein dynamic analyses.

Nucleic acid aptamer-mediated drug delivery for targeted cancer therapy

Aptamers are emerging as promising therapeutic agents and recognition elements. In particular, cell-SELEX (systematic evolution of ligands by exponential enrichment) allows in vitro selection of aptamers selective to whole cells without prior knowledge of the molecular signatures on the cell surface. The advantage of aptamers is their high affinitiy and binding specificity towards the target. This Minireview focuses on single-stranded (ss) oligonucleotide (DNA or RNA)-based aptamers as cancer therapeutics/theranostics. Specifically, aptamer-nanomaterial conjugates, aptamer-drug conjugates, targeted phototherapy and targeted biotherapy are covered in detail. In reviewing the literature, the potential of aptamers as delivery systems for therapeutic and imaging applications in cancer is clear, however, major challenges remain to be resolved, such as the poorly understood pharmacokinetics, toxicity and off-target effects, before they can be fully exploited in a clinical setting.

Nucleic Acid aptamers: new methods for selection, stabilization, and application in biomedical science

The adoption of oligonucleotide aptamer is well on the rise, serving an ever increasing demand for versatility in biomedical field. Through the SELEX (Systematic Evolution of Ligands by EXponential enrichment), aptamer that can bind to specific target with high affinity and specificity can be obtained. Aptamers are single-stranded nucleic acid molecules that can fold into complex threedimensional structures, forming binding pockets and clefts for the specific recognition and tight binding of any given molecular target. Recently, aptamers have attracted much attention because they not only have all of the advantages of antibodies, but also have unique merits such as thermal stability, ease of synthesis, reversibility, and little immunogenicity. The advent of novel technologies is revolutionizing aptamer applications. Aptamers can be easily modified by various chemical reactions to introduce functional groups and/or nucleotide extensions. They can also be conjugated to therapeutic molecules such as drugs, drug containing carriers, toxins, or photosensitizers. Here, we discuss new SELEX strategies and stabilization methods as well as applications in drug delivery and molecular imaging.

Functionalized silica nanoparticles: a platform for fluorescence imaging at the cell and small animal levels

Going in vivo, including living cells and the whole body, is very important for gaining a better understanding of the mystery of life and requires specialized imaging techniques. The diversity, composition, and temporal-spatial variation of life activities from cells to the whole body require the analysis techniques to be fast-response, noninvasive, highly sensitive, and stable, in situ and in real-time. Functionalized nanoparticle-based fluorescence imaging techniques have the potential to meet such needs through real-time and noninvasive visualization of biological events in vivo. Functionalized silica nanoparticles (SiNPs) doped with fluorescent dyes appear to be an ideal and flexible platform for developing fluorescence imaging techniques used in living cells and the whole body. We can select and incorporate different dyes inside the silica matrix either noncovalently or covalently. These form the functionalized hybrid SiNPs, which support multiplex labeling and ratiometric sensing in living systems. Since the silica matrix protects dyes from outside quenching and degrading factors, this enhances the photostability and biocompatibility of the SiNP-based probes. This makes them ideal for real-time and long-time tracking. One nanoparticle can encapsulate large numbers of dye molecules, which amplifies their optical signal and temporal-spatial resolution response. Integrating fluorescent dye-doped SiNPs with targeting ligands using various surface modification techniques can greatly improve selective recognition. Along with the endocytosis, functionalized SiNPs can be efficiently internalized into cells for noninvasive localization, assessment, and monitoring. These unique characteristics of functionalized SiNPs substantially support their applications in fluorescence imaging in vivo. In this Account, we summarize our efforts to develop functionalized dye-doped SiNPs for fluorescence imaging at the cell and small animal levels. We first discuss how to design and construct various functionalized dye-doped SiNPs. Then we describe their properties and imaging applications in cell surface receptor recognition, intracellular labeling, tracking, sensing, and controlled release. Additionally, we have demonstrated the promising application of dye-doped SiNPs as contrast imaging agents for in vivo fluorescence imaging in small animals. We expect these functionalized dye-doped SiNPs to open new opportunities for biological and medical research and applications.

Engineering a cell-surface aptamer circuit for targeted and amplified photodynamic cancer therapy

Photodynamic therapy is one of the most promising and noninvasive methods for clinical treatment of different malignant diseases. Here, we present a novel strategy of designing an aptamer-based DNA nanocircuit capable of selective recognition of cancer cells, controllable activation of photosensitizers, and amplification of photodynamic therapeutic effect. The aptamers can selectively recognize target cancer cells and bind to the specific proteins on cell membranes. Then the overhanging catalyst sequence on the aptamer can trigger a toehold-mediated catalytic strand displacement to activate the photosensitizer and achieve amplified therapeutic effect. The specific binding-induced activation allows the DNA circuit to distinguish diseased cells from healthy cells, reducing damage to nearby healthy cells. Moreover, the catalytic amplification reaction will only take place close to the target cancer cells, resulting in a high local concentration of singlet oxygen to selectively kill the target cells. The principle employed in this study demonstrated the feasibility of assembling a DNA circuit on cell membranes and could further broaden the utility of DNA circuits for applications in biology, biotechnology, and biomedicine.

A review of therapeutic aptamer conjugates with emphasis on new approaches

The potential to emulate or enhance antibodies with nucleic acid aptamers while lowering costs has prompted development of new aptamer-protein, siRNA, drug, and nanoparticle conjugates. Specific focal points of this review discuss DNA aptamers covalently bound at their 3' ends to various proteins for enhanced stability and greater pharmacokinetic lifetimes in vivo. The proteins can include Fc tails of IgG for opsonization, and the first component of complement (C1q) to trigger complement-mediated lysis of antibiotic-resistant Gram negative bacteria, cancer cells and possibly some parasites during vulnerable stages. In addition, the 3' protein adduct may be a biotoxin, enzyme, or may simply be human serum albumin (HSA) or a drug known to bind HSA, thereby retarding kidney and other organ clearance and inhibiting serum exonucleases. In this review, the author summarizes existing therapeutic aptamer conjugate categories and describes his patented concept for PCR-based amplification of double-stranded aptamers followed by covalent attachment of proteins or other agents to the chemically vulnerable overhanging 3' adenine added by Taq polymerase. PCR amplification of aptamers could dramatically lower the current $2,000/gram cost of parallel chemical oligonucleotide synthesis, thereby enabling mass production of aptamer-3'-protein or drug conjugates to better compete against expensive humanized monoclonal antibodies.

Application of near-infrared dyes for tumor imaging, photothermal, and photodynamic therapies

Near-infrared (NIR) dyes, small organic molecules that function in the NIR region, have received increasing attention in recent years as diagnostic and therapeutic agents in the field of tumor research. They have been demonstrated great successes in imaging and treating tumors both in vitro and in vivo. And their different applications in clinical practices have made rapid gains. This review primarily focuses on the progress of the application of NIR dyes in tumor imaging and therapy. In particular, advances in the use of different NIR dyes in tumor-specific imaging, photothermal, and photodynamic therapies are discussed. Limitations and prospects associated with NIR dyes in diagnostic and therapeutic application are also reviewed.