Aptamer-targeted cell-specific RNA interference

Identification of Major Capsid Protein as a Potential Biomarker of Grouper Iridovirus-Infected Cells Using Aptamers Selected by SELEX

Biomarkers have important roles in disease pathogenesis, and serve as important disease indicators for developing novel diagnostic and therapeutic approaches. Grouper iridovirus is a nucleocytoplasmic DNA virus, which not only causes great economic losses in mariculture but also seriously threatens the global biodiversity. However, a lack of biomarkers has limited the progress in clarifying iridovirus pathogenesis. Here, we report novel molecular probes, aptamers, for specific identification of biomarkers in grouper iridovirus-infected cells. Aptamers are selected by SELEX, which is a completely different approach from conventional antibody-based methods for biomarkers discovery. Aptamer-based technology is the unique efficient selection for cell-specific target molecules, and helps find out new biomarkers without the knowledge of characteristics of proteins expressed on virus-infected cell surface. With the implementation of a two-step strategy (aptamer selection and biomarker discovery), combined with mass spectrometry, grouper iridovirus major capsid protein was ultimately identified as a potential biomarker of aptamer Q5 for grouper iridovirus infection. The specific interactions of aptamer Q5 and MCP were experimentally validated by several assays, including EMSA, co-localization of fluorescence by LSCM, binding competition tests, and siRNA silencing tests by flow cytometry. This aptamer-based method for biomarkers discovery developed with grouper iridovirus-infected cells could be applicable to other types of virus infection, markedly improve our studies of biomarker discovery and virus pathogenesis, and further facilitate the development of diagnostic tools and therapeutic approaches to treat virus infection.

The study of genes and signal transduction pathways involved in mustard lung injury: A gene therapy approach

Sulfur mustard (SM) is a destructive and harmful chemical agent for the eyes, skin and lungs that causes short-term and long-term lesions and was widely used in Iraq war against Iran (1980-1988). SM causes DNA damages, oxidative stress, and Inflammation. Considering the similarities between SM and COPD (Chronic Obstructive Pulmonary Disease) pathogens and limited available treatments, a novel therapeutic approach is not developed. Gene therapy is a novel therapeutic approach that uses genetic engineering science in treatment of most diseases including chronic obstructive pulmonary disease. In this review, attempts to presenting a comprehensive study of mustard lung and introducing the genes therapy involved in chronic obstructive pulmonary disease and emphasizing the pathways and genes involved in the pathology and pathogenesis of sulfur Mustard. It seems that, given the high potential of gene therapy and the fact that this experimental technique is a candidate for the treatment of pulmonary diseases, further study of genes, vectors and gene transfer systems can draw a very positive perspective of gene therapy in near future.

Current Aspects of siRNA Bioconjugate for In Vitro and In Vivo Delivery

Studies on siRNA delivery have seen intense growth in the past decades since siRNA has emerged as a new class of gene therapeutics for the treatment of various diseases. siRNA bioconjugate, as one of the major delivery strategies, offers the potential to enhance and broaden pharmacological properties of siRNA, while minimizing the heterogeneity and stability-correlated toxicology. This review summarizes the recent developments of siRNA bioconjugate, including the conjugation with antibody, peptide, aptamer, small chemical, lipidoid, cell-penetrating peptide polymer, and nanoparticle. These siRNA bioconjugate, either administrated alone or formulated with other agents, could significantly improve pharmacokinetic behavior, enhance the biological half-life, and increase the targetability while maintaining sufficient gene silencing activity, with a concomitant improvement of the therapeutic outcomes and diminishment of adverse effects. This review emphasizes the delivery application of these siRNA bioconjugates, especially the conjugation strategy that control the integrity, stability and release of siRNA bioconjugates. The limitations conferred by these conjugation strategies have also been covered.

Characterization of ssDNA aptamers specifically directed against Trachinotus ovatus NNV (GTONNV)-infected cells with antiviral activities

Nervous necrosis virus (NNV), is one of the most fatal viruses in marine fish aquaculture, and is capable of infecting over 50 different fish species. Trachinotus ovatus NNV (GTONNV) was isolated from diseased golden pompano. This T. ovatus strain was isolated from Guangxi, China. Single-stranded DNA (ssDNA) aptamers with high specificity for GTONNV-infected T. ovatus cerebellum cells (TOCC) were produced by Systematic Evolution of Ligands by Exponential Enrichment (SELEX). The characterization of these aptamers was performed using flow cytometry and laser scanning confocal microscopy. The selected aptamers showed significant specificity for GTONNV-infected cells. Based on MFOLD prediction, aptamers formed distinct stem-loop structures that could form the basis for the aptamers' specific binding to their cellular targets. Protease treatment results revealed that the target molecules for aptamers TNA1, TNA4 and TNA19 within GTONNV-infected cells may be membrane proteins that were trypsin-sensitive. Specific endocytosis of aptamer TNA1, TNA4 and TNA19 into GTONNV-infected cells was also shown. The selected aptamers demonstrated antiviral effects against GTONNV both in vitro and in vivo. This is the first time that aptamers targeting GTONNV-infected T. ovatus cells have been selected and characterized. These aptamers hold promise as rapid diagnostic reagents or targeted therapeutic drugs against GTONNV.

Aptamer chemistry

Aptamers are single-stranded DNA or RNA molecules capable of tightly binding to specific targets. These functional nucleic acids are obtained by an in vitro Darwinian evolution method coined SELEX (Systematic Evolution of Ligands by EXponential enrichment). Compared to their proteinaceous counterparts, aptamers offer a number of advantages including a low immunogenicity, a relative ease of large-scale synthesis at affordable costs with little or no batch-to-batch variation, physical stability, and facile chemical modification. These alluring properties have propelled aptamers into the forefront of numerous practical applications such as the development of therapeutic and diagnostic agents as well as the construction of biosensing platforms. However, commercial success of aptamers still proceeds at a weak pace. The main factors responsible for this delay are the susceptibility of aptamers to degradation by nucleases, their rapid renal filtration, suboptimal thermal stability, and the lack of functional group diversity. Here, we describe the different chemical methods available to mitigate these shortcomings. Particularly, we describe the chemical post-SELEX processing of aptamers to include functional groups as well as the inclusion of modified nucleoside triphosphates into the SELEX protocol. These methods will be illustrated with successful examples of chemically modified aptamers used as drug delivery systems, in therapeutic applications, and as biosensing devices.

Targeted siRNA delivery using aptamer-siRNA chimeras and aptamer-conjugated nanoparticles

The sequence-specific gene-silencing ability of small interfering RNA (siRNA) has been exploited as a new therapeutic approach for the treatment of a variety of diseases. However, efficient and safe delivery of siRNA into target cells is still a challenge in the clinical development of siRNA-based therapeutics. Recently, nucleic acid-based aptamers that target cell surface proteins have emerged as a new class of targeting moieties due to their high specificity and avidity. To date, various aptamer-mediated siRNA delivery systems have been developed to enhance the RNA interference (RNAi) efficacy of siRNA via targeted delivery. In this review, we summarize recent advances in developing aptamer-mediated siRNA delivery systems for RNAi therapeutics, mainly aptamer-siRNA chimeras and aptamer-functionalized nanocarriers incorporating siRNA, with a focus on their molecular designs and formulations. In addition, the challenges and engineering strategies of aptamer-mediated siRNA delivery systems for clinical translation are discussed. This article is categorized under: Biology-Inspired Nanomaterials > Nucleic Acid-Based Structures Therapeutic Approaches and Drug Discovery > Nanomedicine for Oncologic Disease.

Bispecific therapeutic aptamers for targeted therapy of cancer: a review on cellular perspective

Aptamers (Aps), as short single-strand nucleic acids, can bind to their corresponding molecular targets with the high affinity and specificity. In comparison with the monoclonal antibodies (mAbs) and peptides, unique physicochemical and biological characteristics of Aps make them excellent targeting agents for different types of cancer molecular markers (CMMs). Much attention has been paid to the Ap-based multifunctional chimeric and therapeutic systems, which provide promising outcomes in the targeted therapy of various formidable diseases, including malignancies. In the Ap-based chimeric systems, a targeting Ap is conjugated to another therapeutic molecule (e.g., siRNA/miRNA, Ap, toxins, chemotherapeutic agents, DNAzyme/ribozymes) with a capability of binding to a specific cell surface receptor at the desired target site. Having been engineered as multifunctional nanosystems (NSs), Ap-based hybrid scaffolds can be used to concurrently target multiple markers/pathways in cancerous cells, causing drastic inhibitory effects on the growth and the progression of tumor cells. Multi/bispecific Aps composed of two/more Aps provide a versatile tool for the optimal and active targeting of cell surface receptor(s) with markedly high affinity and avidity. Targeting the optimum activity of key receptors and dominant signaling pathways in the activation of immunity, the multi/bispecific Ap-based therapeutics can also be used to enhance the antitumor activity of the immune system. Further, the bispecific systems can be designed to induce cytotoxicity in a heterogeneous population of cancer cells with different CMMs. In this review, we provide some important insights into the construction and applications of the Ap-based chimeric NSs and discuss the multifunctional Ap chimera and their effects on the signaling pathways in cancer.

Strategies for improving the specificity of siRNAs for enhanced therapeutic potential

INTRODUCTION

RNA interference has become a tool of choice in the development of drugs in various therapeutic areas of Post Transcriptional Gene Silencing (PTGS). The critical element in developing successful RNAi therapeutics lies in designing small interfering RNA (siRNA) using an efficient algorithm satisfying the designing criteria. Further, translation of siRNA from bench-side to bedside needs an efficient delivery system and/or chemical modification. Areas covered: This review emphasizes the importance of dicer, the criteria for efficient siRNA design, the currently available algorithms and strategies to overcome off-target effects, immune stimulatory effects and endosomal trap. Expert opinion: Specificity and stability are the primary concerns for siRNA therapeutics. The design criteria and algorithms should be chosen rationally to have a siRNA sequence that binds to the corresponding mRNA as it happens in the Watson and Crick base pairing. However, it must evade a few more hurdles (Endocytosis, Serum stability etc.) to be functional in the cytosol.

Receptor-targeted aptamer-siRNA conjugate-directed transcriptional regulation of HIV-1

Gene-based therapies represent a promising therapeutic paradigm for the treatment of HIV-1, as they have the potential to maintain sustained viral inhibition with reduced treatment interventions. Such an option may represent a long-term treatment alternative to highly active antiretroviral therapy.

Methods: We previously described a therapeutic approach, referred to as transcriptional gene silencing (TGS), whereby small noncoding RNAs directly inhibit the transcriptional activity of HIV-1 by targeting sites within the viral promoter, specifically the 5' long terminal repeat (LTR). TGS differs from traditional RNA interference (RNAi) in that it is characterized by concomitant silent-state epigenetic marks on histones and DNA. To deliver TGS-inducing RNAs, we developed functional RNA conjugates based on the previously reported dual function of the gp120 (A-1) aptamer conjugated to 27-mer Dicer-substrate anti-HIV-1 siRNA (dsiRNA), LTR-362.

Results: We demonstrate here that high levels of processed guide RNAs localize to the nucleus in infected T lymphoblastoid CEM cell line and primary human CD4+ T-cells. Treatment of the aptamer-siRNA conjugates induced TGS with an ~10-fold suppression of viral p24 levels as measured at day 12 post infection. To explore the silencing efficacy of aptamer-siRNA conjugates in vivo, HIV-1-infected humanized NOD/SCID/IL2 rγ^null mice (hu-NSG) were treated with the aptamer-siRNA conjugates. Systemic delivery of the A-1-stick-LTR-362 27-mer siRNA conjugates suppressed HIV-1 infection and protected CD4+ T cell levels in viremia hu-NSG mice.

Principle conclusions: Collectively these data suggest that the gp120 aptamer-dsiRNA conjugate design is suitable for systemic delivery of small RNAs that can be used to suppress HIV-1.

Selection and Identification of Skeletal-Muscle-Targeted RNA Aptamers

Oligonucleotide gene therapy has shown great promise for the treatment of muscular dystrophies. Nevertheless, the selective delivery to affected muscles has shown to be challenging because of their high representation in the body and the high complexity of their cell membranes. Current trials show loss of therapeutic molecules to non-target tissues leading to lower target efficacy. Therefore, strategies that increase uptake efficiency would be particularly compelling. To address this need, we applied a cell-internalization SELEX (Systematic Evolution of Ligands by Exponential Enrichment) approach and identified a skeletal muscle-specific RNA aptamer. A01B RNA aptamer preferentially internalizes in skeletal muscle cells and exhibits decreased affinity for off-target cells. Moreover, this in vitro selected aptamer retained its functionality in vivo, suggesting a potential new approach for targeting skeletal muscles. Ultimately, this will aid in the development of targeted oligonucleotide therapies against muscular dystrophies.

Aptamer-miRNA-212 Conjugate Sensitizes NSCLC Cells to TRAIL

TNF-related apoptosis-inducing ligand (TRAIL) is a promising antitumor agent for its remarkable ability to selectively induce apoptosis in cancer cells, without affecting the viability of healthy bystander cells. The TRAIL tumor suppressor pathway is deregulated in many human malignancies including lung cancer. In human non-small cell lung cancer (NSCLC) cells, sensitization to TRAIL therapy can be restored by increasing the expression levels of the tumor suppressor microRNA-212 (miR-212) leading to inhibition of the anti-apoptotic protein PED/PEA-15 implicated in treatment resistance. In this study, we exploited a previously described RNA aptamer inhibitor of the tyrosine kinase receptor Axl (GL21.T) expressed on lung cancer cells, as a means to deliver miR-212 into human NSCLC cells expressing Axl. We demonstrate efficient delivery of miR-212 following conjugation of the miR to GL21.T (GL21.T-miR212 chimera). We show that the chimera downregulates PED and restores TRAIL-mediate cytotoxicity in cancer cells. Importantly, treatment of Axl+ lung cancer cells with the chimera resulted in (i) an increase in caspase activation and (ii) a reduction of cell viability in combination with TRAIL therapy. In conclusion, we demonstrate that the GL21.T-miR212 chimera can be employed as an adjuvant to TRAIL therapy for the treatment of lung cancer.

Methods for assembling B-cell lymphoma specific and internalizing aptamer-siRNA nanoparticles via the sticky bridge

Structured functional RNA entities, including aptamers and siRNAs, have amazing versatility in structure and function. These molecules can serve as powerful, attractive building blocks for the bottom-up assembly of complex nanostructures. Here, we describe novel cell-type specific and internalizing B-cell activating factor receptor (BAFF-R) aptamer-siRNA delivery systems for B-cell lymphoma therapy, in which both the aptamer and the Dicer substrate siRNA (DsiRNA) portions are conjugated through a "sticky bridge." The BAFF-R is overexpressed on the surface of B-cell malignancies, allowing binding and internalization of the aptamer-stick-siRNA nanoparticles. STAT3 siRNAs are encapsulated within the nanoparticles delivered by the BAFF-R aptamers and are localized to the cytoplasm, resulting in robust gene silencing of STAT3 mRNAs in a variety of B-cell lines. Moreover, these nanoparticles do not induce cell proliferation and apoptosis. Collectively, aptamer-mediated delivery strategies provide a toolset to become a more widely used therapeutic modality for the treatment of diseases.

Smart functional nucleic acid chimeras: enabling tissue specific RNA targeting therapy

A major obstacle for effective utilization of therapeutic oligonucleotides such as siRNA, antisense, antimiRs etc. is to deliver them specifically to the target tissues. Toward this goal, nucleic acid aptamers are re-emerging as a prominent class of biomolecules capable of delivering target specific therapy and therapeutic monitoring by various molecular imaging modalities. This class of short oligonucleotide ligands with high affinity and specificity are selected from a large nucleic acid pool against a molecular target of choice. Poor cellular uptake of therapeutic oligonucleotides impedes gene-targeting efficacy in vitro and in vivo. In contrast, aptamer-oligonucleotide chimeras have shown the capacity to deliver siRNA, antimiRs, small molecule drugs etc. toward various targets and showed very promising results in various studies on different diseases models. However, to further improve the bio-stability of such chimeric conjugates, it is important to introduce chemically-modified nucleic acid analogs. In this review, we highlight the applications of nucleic acid aptamers for target specific delivery of therapeutic oligonucleotides.

Building a chimera of aptamer–antisense oligonucleotide for silencing galectin-1 gene

Galectin-1 is closely related with immune systems, and its overexpression may cause tumor metastasis.

EpCAM Aptamer-mediated Survivin Silencing Sensitized Cancer Stem Cells to Doxorubicin in a Breast Cancer Model

Understanding the molecular basis of drug resistance and utilising this information to overcome chemoresistance remains a key challenge in oncology. Here we report that survivin, a key protein implicated in drug resistance, is overexpressed in cancer stem cell pool of doxorubicin-resistant breast cancer cells. Moreover, by utilising an active targeting system consisting of an RNA aptamer targeted against the epithelial cell adhesion molecule and a Dicer substrate survivin siRNA, we could deliver a high dose of the siRNA to cancer stem cells in xenograft tumours. Importantly, silencing of survivin with this aptamer-siRNA chimera in cancer stem cell population led to the reversal of chemoresistance, such that combined treatment with low dose of doxorubicin inhibited stemness, eliminated cancer stem cells via apoptosis, suppressed tumour growth, and prolonged survival in mice bearing chemoresistant tumours. This strategy for in vivo cancer stem cell targeting has wide application for future effective silencing of anti-death genes and in fact any dysregulated genes involved in chemoresistance and tumour relapse.

Aptamer-Dendrimer Bioconjugates for Targeted Delivery of miR-34a Expressing Plasmid and Antitumor Effects in Non-Small Cell Lung Cancer Cells

Metastasis and drug resistance are major barriers for the treatment of non-small cell lung cancer (NSCLC). To explore new therapeutic options, we successfully encapsulated MicroRNA-34a (miR-34a), a potent endogenous tumor suppressor in NSCLC into S6 aptamer-conjugated dendrimer to form lung cancer-targeted gene delivery nanoparticles (PAM-Ap/pMiR-34a NPs). PAM-Ap/pMiR-34a NPs had a diameter of 100-200 nm and Zeta potential of ~30 mV at applied N/P ratio. The aptamer conjugation significantly improved cellular uptake as well as gene transfection efficiency of PAM-Ap/pMiR-34a NPs in cultured NSCLC cells. We showed that PAM-Ap/pMiR-34a NPs enhanced the regulation of targeted genes, BCL-2 and p53 in vitro. In addition, we revealed PAM-Ap/pMiR-34a NPs significantly inhibited cell growth, migration, invasion and induced apoptosis of lung cancer cells compared with non-targeted NPs. The method provided a novel therapeutic strategy for the experimental treatment of NSCLC.

EpCAM Aptamer-siRNA Chimera Targets and Regress Epithelial Cancer

Epithelial cell adhesion molecule (EpCAM), a cancer stem cell (CSC) marker is over expressed in epithelial cancers and in retinoblastoma (RB). We fabricated an EpCAM targeting aptamer-siRNA chimera and investigated its anti-tumor property and EpCAM intracellular domain (EpICD) mediated signaling in epithelial cancer. The anti-tumor efficacy of EpCAM aptamer-siEpCAM chimera (EpApt-siEp) was evaluated by qPCR, northern and Western blotting in WERI-Rb1- RB cell line, primary RB tumor cells and in MCF7- breast cancer cell line. Anti-tumor activity of EpApt-siEp was studied in vivo using epithelial cancer (MCF7) mice xenograft model. The mechanism and pathways involved in the anti-tumor activity was further studied using protein arrays and qPCR. EpApt-siEp chimera was processed in vitro by dicer enzyme. Treatment of the WERI-Rb1 and MCF7 cells with EpApt-siEp revealed statistically significant down regulation of EpCAM expression (P<0.005) and concomitant reduction in cellular proliferation. In primary RB cells cultured from RB tumors, EpApt-siEp silenced EpCAM, significantly inhibited (P<0.01) cell proliferation and induced cytotoxicity. Knockdown of EpICD expressed in RB primary tumors led to repression of pluripotency markers, SOX2, OCT4, NANOG, and CD133. In vivo studies showed complete tumor growth regression without any toxicity in animals (P<0.001) and tumor tissues showed significant downregulation (P<0.05) of EpCAM, MRP1, ABCG2, stathmin, survivin and upregulation of ATM (P<0.05) leading to apoptosis by intrinsic pathway with minor alteration in cytokines. Our results revealed that EpApt-siEp potentially eradicated EpCAM positive cancer cells through CSC marker suppression and apoptosis, while sparing normal EpCAM negative adjacent cells.

RNAi-mediated knockdown of INHBB increases apoptosis and inhibits steroidogenesis in mouse granulosa cells

Inhibins are members of the TGFβ superfamily and act as suppressors of follicle stimulating hormone (FSH) secretion from pituitary glands via a negative feedback mechanism to regulate folliculogenesis. In this study, the INHBB gene was knocked down by three RNAi-Ready pSIREN-RetroQ-ZsGreen vector- mediated recombinant plasmids to explore the effects of INHBB silencing on granulosa cell (GC) cell cycle, apoptosis and steroid production in vitro. Quantitative real-time polymerase chain reaction, Western blot, flow cytometry and ELISA were performed to evaluate the role of INHBB in the mouse GC cell cycle, apoptosis and steroid production in vitro. The results showed that the relative mRNA and protein expression of INHBB in mouse GCs can be significantly reduced by RNAi with pshRNA-B1, pshRNA-B2 and pshRNA-B3 plasmids, with pshRNA-B3 having the best knockdown efficiency. Downregulation of the expression of INHBB significantly arrests cells in the G1 phase of the cell cycle and increases the apoptosis rate in GCs. This was further confirmed by downregulation of the protein expressions of Cyclin D1, Cyclin E and Bcl2, while the protein expression of Bax was upregulated. In addition, specific downregulation of INHBB markedly decreased the concentration of estradiol and progesterone, which was further validated by the decrease in the mRNA levels of CYP19A1and CYP11A1. These findings suggest that inhibin βB is important in the regulation of apoptosis and cell cycle progression in granulosa cells. Furthermore, the inhibin βB subunit has a role in the regulation of steroid hormone biosynthesis. Evidence is accumulating to support the concept that inhibin βB is physiologically essential for early folliculogenesis in the mouse.

A Universal Aptamer Chimera for the Delivery of Functional microRNA-126

microRNAs (miRs) regulate vascular diseases such as atherosclerosis and cancer. miR-126 is important for endothelial cell signaling and promotes angiogenesis, protects against atherosclerosis, and reduces breast cancer cell growth and metastasis. The overexpression of miR-126, therefore, may be an attractive therapeutic strategy for the treatment of cardiovascular disease or cancer. Here we report a novel strategy to deliver miR-126 to endothelial and breast cancer cells. We tested three different strategies to deliver miR-126 by linking the miR to an aptamer for the ubiquitously expressed transferrin receptor (transferrin receptor aptamer, TRA). Linking the precursor of miR-126 (pre-miR-126) to the TRA by annealing of a complementary stick led to efficient uptake and processing of miR-126, resulting in the delivery of 1.6×10(6)±0.3×10(6) copies miR-126-3p per ng RNA in human endothelial cells and 7.4×10(5)±2×10(5) copies miR-126-3p per ng in MCF7 breast cancer cells. The functionality of the active TRA-miR-126 chimera was further demonstrated by showing that the chimera represses the known miR-126 target VCAM-1 and improved endothelial cell sprouting in a spheroid assay. Moreover, the TRA-miR-126 chimera reduced proliferation and paracrine endothelial cell recruitment of breast cancer cells to a similar extent as miR-126-3p mimics introduced by conventional liposome-based transfection. Together, this data demonstrates that pre-miR-126 can be delivered by a non-specific aptamer to exert biological functions in two different cell models. The use of the TRA-miR-126 chimera or the combination of the delivery strategy with other endothelial or tumor specific aptamers may provide an interesting therapeutic option to treat vascular disease or cancers.

Aptamers as a novel tool for diagnostics and therapy

Aptamers are short single-stranded DNA or RNA oligonucleotides that are capable of binding small molecules, proteins, or nucleotides with high specificity. They show a stable conformation and high binding affinity for their target molecules. There are numerous applications for aptamers in biotechnology, molecular diagnostics and targeted therapy of diseases. Their production is cheap, and they generally display lower immunogenicity than monoclonal antibodies. In the present review, we give an introduction to the preparation of aptamers and provide examples for their use in biotechnology, diagnostics and therapy of diseases.

Protein and oligonucleotide delivery systems for vaginal microbicides against viral STIs

Intravaginal delivery offers an effective option for localized, targeted, and potent microbicide delivery. However, an understanding of the physiological factors that impact intravaginal delivery must be considered to develop the next generation of microbicides. In this review, a comprehensive discussion of the opportunities and challenges of intravaginal delivery are highlighted, in the context of the intravaginal environment and currently utilized dosage forms. After a subsequent discussion of the stages of microbicide development, the intravaginal delivery of proteins and oligonucleotides is addressed, with specific application to HSV and HIV. Future directions may include the integration of more targeted delivery modalities to virus and host cells, in addition to the use of biological agents to affect specific genes and proteins involved in infection. More versatile and multipurpose solutions are envisioned that integrate new biologicals and materials into potentially synergistic combinations to achieve these goals.

Study on the prostate cancer-targeting mechanism of aptamer-modified nanoparticles and their potential anticancer effect in vivo

Ligand-mediated prostate cancer (PCa)-targeting gene delivery is one of the focuses of research in recent years. Our previous study reported the successful preparation of aptamer-modified nanoparticles (APT-NPs) in our laboratory and demonstrated their PCa-targeting ability in vitro. However, the mechanism underlying this PCa-targeting effect and their anticancer ability in vivo have not yet been elucidated. The objective of this study was to assess the feasibility of using APT-NPs to deliver micro RNA (miRNA) systemically to PCa cells, to testify their tumor-targeting efficiency, and to observe their biodistribution after systemic administration to a xenograft mouse model of PCa. In addition, the effect of APT depletion and endocytosis inhibitors on cellular uptake was also evaluated quantitatively in LNCaP cells to explore the internalization mechanism of APT-NPs. Finally, blood chemistry, and renal and liver function parameters were measured in the xenograft mouse model of PCa to see whether APT-NPs had any demonstrable toxicity in mice in vivo. The results showed that APT-NPs prolonged the survival duration of the PCa tumor-bearing mice as compared with the unmodified NPs. In addition, they had a potential PCa-targeting effect in vivo. In conclusion, this research provides a prototype for the safe and efficient delivery of miRNA expression vectors to PCa cells, which may prove useful for preclinical and clinical studies on the treatment of PCa.

Aptamer-mediated selective delivery of short RNA therapeutics in cancer cells

RNA interference (RNAi) is an important biological process that ultimately leads to suppression of gene expression. Activators of RNAi are typically small interfering RNAs (siRNA) and microRNAs (miRNA) that offer considerable therapeutic potnetial. However, a major obstacle to take these these molecules to the clinic is the absence of safe and reliable means for their specific delivery to target cells. In this regard, a highly promising class of molecules is represented by nucleic acid aptamers. These are short, structured, single-stranded RNAs or DNAs oligonucleotides that, by binding with high specificity to target molecules, provide high affinity ligands and potential antagonists of disease-associated proteins. Further, because of the high binding specificity, aptamers represent a powerful tool for the selective delivery of therapeutic cargos, including mi/siRNAs, chemotherapeutics, toxins and nanoparticles to cancer cells or tissues, thus potentially increasing the efficacy of a given therapy as well as reducing toxicity. In this review, we will focus on recent advances in the field of aptamer-mediated mi/siRNA delivery, discussing their potential and challenges in cancer therapy.

Aptamer technology for tracking cells' status & function

In fields such as cancer biology and regenerative medicine, obtaining information regarding cell bio-distribution, tropism, status, and other cellular functions are highly desired. Understanding cancer behaviors including metastasis is important for developing effective cancer treatments, while assessing the fate of therapeutic cells following implantation is critical to validate the efficacy and efficiency of the therapy. For visualization purposes with medical imaging modalities (e.g. magnetic resonance imaging), cells can be labeled with contrast agents (e.g. iron-oxide nanoparticles), which allows their identification from the surrounding environment. Despite the success of revealing cell biodistribution in vivo, most of the existing agents do not provide information about the status and functions of cells following transplantation. The emergence of aptamers, single-stranded RNA or DNA oligonucleotides of 15 to 60 bases in length, is a promising solution to address this need. When aptamers bind specifically to their cognate molecules, they undergo conformational changes which can be transduced into a change of imaging contrast (e.g. optical, magnetic resonance). Thus by monitoring this signal change, researchers can obtain information about the expression of the target molecules (e.g. mRNA, surface markers, cell metabolites), which offer clues regarding cell status/function in a non-invasive manner. In this review, we summarize recent efforts to utilize aptamers as biosensors for monitoring the status and function of transplanted cells. We focus on cancer cell tracking for cancer study, stem cell tracking for regenerative medicine, and immune cell (e.g. dendritic cells) tracking for immune therapy.

Aptamer technology for tracking cells' status & function

In fields such as cancer biology and regenerative medicine, obtaining information regarding cell bio-distribution, tropism, status, and other cellular functions are highly desired. Understanding cancer behaviors including metastasis is important for developing effective cancer treatments, while assessing the fate of therapeutic cells following implantation is critical to validate the efficacy and efficiency of the therapy. For visualization purposes with medical imaging modalities (e.g. magnetic resonance imaging), cells can be labeled with contrast agents (e.g. iron-oxide nanoparticles), which allows their identification from the surrounding environment. Despite the success of revealing cell biodistribution in vivo, most of the existing agents do not provide information about the status and functions of cells following transplantation. The emergence of aptamers, single-stranded RNA or DNA oligonucleotides of 15 to 60 bases in length, is a promising solution to address this need. When aptamers bind specifically to their cognate molecules, they undergo conformational changes which can be transduced into a change of imaging contrast (e.g. optical, magnetic resonance). Thus by monitoring this signal change, researchers can obtain information about the expression of the target molecules (e.g. mRNA, surface markers, cell metabolites), which offer clues regarding cell status/function in a non-invasive manner. In this review, we summarize recent efforts to utilize aptamers as biosensors for monitoring the status and function of transplanted cells. We focus on cancer cell tracking for cancer study, stem cell tracking for regenerative medicine, and immune cell (e.g. dendritic cells) tracking for immune therapy.

Design and evaluation of thioalkylated mannose-modified dendrimer (G3)/α-cyclodextrin conjugates as antigen-presenting cell-selective siRNA carriers

To design and evaluate the potential use of thioalkylated mannose-modified dendrimer (generation 3; G3) conjugates with α-cyclodextrin (Man-S-α-CDE (G3)) as novel antigen-presenting cell (APC)-selective siRNA carriers, we investigated the RNAi effects of siRNA complexes with Man-S-α-CDEs (G3). Man-S-α-CDE (G3, average degree of substitution of mannose (DSM) 4)/siRNA complex had the potent RNAi effects in both NR8383 cells, a rat alveolar macrophage cell line, and JAWSII cells, a mouse dendritic cell line, through adequate physicochemical properties, mannose receptor (MR)-mediated cellular uptake, and efficient phagosomal escape of the siRNA complex. In addition, cytotoxic activities of the siRNA complexes with α-CDE (G3, DS2) and Man-S-α-CDE (G3, DSM4) were almost negligible up to a charge ratio of 100 (carrier/siRNA). Taken together, these results suggest that Man-S-α-CDE (G3, DSM4) has the potential for a novel APC-selective siRNA carrier.

Selection of DNA aptamers against epidermal growth factor receptor with high affinity and specificity

Epidermal growth factor receptor (EGFR/HER1/c-ErbB1), is overexpressed in many solid cancers, such as epidermoid carcinomas, malignant gliomas, etc. EGFR plays roles in proliferation, invasion, angiogenesis and metastasis of malignant cancer cells and is the ideal antigen for clinical applications in cancer detection, imaging and therapy. Aptamers, the output of the systematic evolution of ligands by exponential enrichment (SELEX), are DNA/RNA oligonucleotides which can bind protein and other substances with specificity. RNA aptamers are undesirable due to their instability and high cost of production. Conversely, DNA aptamers have aroused researcher's attention because they are easily synthesized, stable, selective, have high binding affinity and are cost-effective to produce. In this study, we have successfully identified DNA aptamers with high binding affinity and selectivity to EGFR. The aptamer named TuTu22 with Kd 56±7.3nM was chosen from the identified DNA aptamers for further study. Flow cytometry analysis results indicated that the TuTu22 aptamer was able to specifically recognize a variety of cancer cells expressing EGFR but did not bind to the EGFR-negative cells. With all of the aforementioned advantages, the DNA aptamers reported here against cancer biomarker EGFR will facilitate the development of novel targeted cancer detection, imaging and therapy.

Aptamers as both drugs and drug-carriers

Aptamers are short nucleic acid oligos. They may serve as both drugs and drug-carriers. Their use as diagnostic tools is also evident. They can be generated using various experimental, theoretical, and computational techniques. The systematic evolution of ligands by exponential enrichment which uses iterative screening of nucleic acid libraries is a popular experimental technique. Theory inspired methodology entropy-based seed-and-grow strategy that designs aptamer templates to bind specifically to targets is another one. Aptamers are predicted to be highly useful in producing general drugs and theranostic drugs occasionally for certain diseases like cancer, Alzheimer's disease, and so on. They bind to various targets like lipids, nucleic acids, proteins, small organic compounds, and even entire organisms. Aptamers may also serve as drug-carriers or nanoparticles helping drugs to get released in specific target regions. Due to better target specific physical binding properties aptamers cause less off-target toxicity effects. Therefore, search for aptamer based drugs, drug-carriers, and even diagnostic tools is expanding fast. The biophysical properties in relation to the target specific binding phenomena of aptamers, energetics behind the aptamer transport of drugs, and the consequent biological implications will be discussed. This review will open up avenues leading to novel drug discovery and drug delivery.

Isolation and characterization of a new class of DNA aptamers specific binding to Singapore grouper iridovirus (SGIV) with antiviral activities

The Singapore grouper iridovirus (SGIV), a member of the genus Ranavirus, is a major viral pathogen that has caused heavy economic losses to the grouper aquaculture industry in China and Southeast Asia. No efficient method of controlling SGIV outbreaks is currently available. Systematic evolution of ligands by exponential enrichment (SELEX) is now widely used for the in vitro selection of artificial ssDNA or RNA ligands, known as aptamers, which bind to targets through their stable three-dimensional structures. In our current study, we generated ssDNA aptamers against the SGIV, and evaluated their ability to block SGIV infection in cultured fish cells and cultured fish in vivo. The anti-SGIV DNA aptamers, LMB-761, LMB-764, LMB-748, LMB-439, LMB-755, and LMB-767, were selected from a pool of oligonucleotides randomly generated using a SELEX iterative method. The analysis of the secondary structure of the aptamers revealed that they all formed similar stem-loop structures. Electrophoretic mobility shift assays showed that the aptamers bound SGIV specifically, as evidenced by a lack cross-reactivity with the soft shell turtle iridovirus. The aptamers produced no cytotoxic effects in cultured grouper spleen cells (GS). Assessment of cytopathic effects (CPE) and viral titer assays showed that LMB-761, LMB-764, LMB-748, LMB-755, and LMB-767 significantly inhibited SGIV infection in GS cells. The in vivo experiments showed that LMB-761 and LMB-764 reduced SGIV-related mortality, and no negative effects were observed in orange-spotted grouper, Epinephelus coioides, indicating that these DNA aptamers may be suitable antiviral candidates for controlling SGIV infections in fish reared in marine aquaculture facilities.

Aptamers targeting rabies virus-infected cells inhibit street rabies virus in vivo

Rabies is a viral infection of the CNS that is almost always fatal once symptoms occur. No effective treatment of the disease is available and novel antiviral strategies are urgently required. Street rabies viruses are field isolates known to be highly neurotropic. Aptamers are single-stranded oligonucleotides that bind their targets with high affinity and specificity and thus have potential for use in diagnostic and therapeutic applications. In this study, we demonstrate that the aptamers FO24 and FO21, which target RABV-infected cells, can significantly protect mice from a lethal dose of the street rabies virus FJ strain in vivo. Groups receiving preexposure prophylaxis had higher survival rates than the groups receiving postexposure prophylaxis. When mice were inoculated with aptamers (4 nmol) for 24h by intracranial or intramuscular injection prior to intramuscular inoculation with the FJ strain, approximately 60% of the mice survived. These results indicate that the FO21 and FO24 aptamers may be used to develop preventative antiviral therapy against rabies disease.

High Specific DNAzyme-Aptamer Sensor for Salmonella paratyphi A Using Single-Walled Nanotubes-Based Dual Fluorescence-Spectrophotometric Methods

In this work, single-stranded DNA aptamers that are highly specific to enterotoxigenic Salmonella paratyphi A were obtained from an enriched oligonucleotide pool using Systematic Evolution of Ligands by Exponential Enrichment (SELEX) to target the flagellin protein. The selected aptamers were confirmed to have high sensitivity and specificity to the flagellin. In addition, a probe (P0) containing the DNAzyme and fluorescein isothiocyanate-labeled aptamer3 sequences was employed as a dual probe for observing fluorescence and absorbance changes. The flagellin demonstrated low detection limits of 5 ng/mL by fluorescence and 20 ng/mL by spectrophotometry. Moreover, milk samples spiked with Salmonella paratyphi A were also detected, with the low detection limits increasing to 10(5) CFU/mL by fluorescence and 10(6)CFU/mL by spectrophotometry. The combination of fluorescence and spectrophotometry offers a specific, rapid, and sensitive way for detecting Salmonella paratyphi A and has potential for detecting other pathogens in food.

Synergistic inhibition of lung cancer cell invasion, tumor growth and angiogenesis using aptamer-siRNA chimeras

Early metastasis is one of the major causes of mortality among patient with lung cancer. The process of tumor metastasis involves a cascade of events, including epithelial-mesenchymal transition, tumor cell migration and invasion, and angiogenesis. To specifically suppress tumor invasion and angiogenesis, two nucleolin aptamer-siRNA chimeras (aptNCL-SLUGsiR and aptNCL-NRP1siR) were used to block key signaling pathways involved in lung cancer metastasis that are pivotal to metastatic tumor cells but not to normal cells under ordinary physiologic conditions. Through nucleolin-mediated endocytosis, the aptNCL-siRNA chimeras specifically and significantly knocked down the expressions of SLUG and NRP1 in nucleolin-expressing cancer cells. Furthermore, simultaneous suppression of SLUG and NRP1 expressions by the chimeras synergistically retarded cancer cell motility and invasive ability. The synergistic effect was also observed in a xenograft mouse model, wherein the combined treatment using two chimeras suppressed tumor growth, the invasiveness, circulating tumor cell amount, and angiogenesis in tumor tissue without affecting liver and kidney functions. This study demonstrates that combined treatment of aptNCL-SLUGsiR and aptNCL-NRP1siR can synergistically suppress lung cancer cell invasion, tumor growth and angiogenesis by cancer-specific targeting combined with gene-specific silencing.

Current progress on aptamer-targeted oligonucleotide therapeutics

Exploiting the power of the RNAi pathway through the use of therapeutic siRNA drugs has remarkable potential for treating a vast array of human disease conditions. However, difficulties in delivery of these and similar nucleic acid-based pharmacological agents to appropriate organs or tissues, remains a major impediment to their broad clinical application. Synthetic nucleic acid ligands (aptamers) have emerged as effective delivery vehicles for therapeutic oligonucleotides, including siRNAs. In this review, we summarize recent attractive developments in creatively employing cell-internalizing aptamers to deliver therapeutic oligonucleotides (e.g., siRNAs, miRNAs, anti-miRs and antisense oligos) to target cells. We also discuss advancements in aptamer-siRNA chimera technology, as well as, aptamer-functionalized nanoparticles for siRNA delivery. In addition, the challenges and future prospects of aptamer-targeted oligonucleotide drugs for clinical translation are further highlighted.

Selection of an aptamer against rabies virus: a new class of molecules with antiviral activity

Rabies is a fatal central nervous system (CNS) disease caused by the neurotropic rabies virus (RABV). The therapeutic management of RABV infections is still problematic, and novel antiviral strategies are urgently required. We established the RVG-BHK-21 cell line, which expresses RABV glycoprotein on the cell surface, to select aptamers. Through 28 iterative rounds of selection, single-stranded DNA (ssDNA) aptamers were generated by exponential enrichment (SELEX). A virus titer assay and a real-time quantitative reverse transcription PCR (qRT-PCR) assay revealed that four aptamers could inhibit the replication of RABV in cultured baby hamster kidney (BHK)-21 cells. However, the aptamers did not inhibit the replication of other virus, e.g., canine distemper virus (CDV) and canine parvovirus (CPV). In addition, the GE54 aptamer was found to effectively protect mice against lethal RABV challenge. After inoculation with aptamers for 24h or 48h, followed by inoculation with CVS-11, approximately 25-33% of the mice survived. In summary, we selected aptamers that could significantly protect from a lethal dose of RABV in vitro and in vivo.

Nanoparticle-Based Delivery of RNAi Therapeutics: Progress and Challenges

RNA interference (RNAi) is an evolutionarily conserved, endogenous process for post-transcriptional regulation of gene expression. Although RNAi therapeutics have recently progressed through the pipeline toward clinical trials, the application of these as ideal, clinical therapeutics requires the development of safe and effective delivery systems. Inspired by the immense progress with nanotechnology in drug delivery, efforts have been dedicated to the development of nanoparticle-based RNAi delivery systems. For example, a precisely engineered, multifunctional nanocarrier with combined passive and active targeting capabilities may address the delivery challenges for the widespread use of RNAi as a therapy. Therefore, in this review, we introduce the major hurdles in achieving efficient RNAi delivery and discuss the current advances in applying nanotechnology-based delivery systems to overcome the delivery hurdles of RNAi therapeutics. In particular, some representative examples of nanoparticle-based delivery formulations for targeted RNAi therapeutics are highlighted.

Aptamer-based therapeutics: new approaches to combat human viral diseases

Viruses replicate inside the cells of an organism and continuously evolve to contend with an ever-changing environment. Many life-threatening diseases, such as AIDS, SARS, hepatitis and some cancers, are caused by viruses. Because viruses have small genome sizes and high mutability, there is currently a lack of and an urgent need for effective treatment for many viral pathogens. One approach that has recently received much attention is aptamer-based therapeutics. Aptamer technology has high target specificity and versatility, i.e., any viral proteins could potentially be targeted. Consequently, new aptamer-based therapeutics have the potential to lead a revolution in the development of anti-infective drugs. Additionally, aptamers can potentially bind any targets and any pathogen that is theoretically amenable to rapid targeting, making aptamers invaluable tools for treating a wide range of diseases. This review will provide a broad, comprehensive overview of viral therapies that use aptamers. The aptamer selection process will be described, followed by an explanation of the potential for treating virus infection by aptamers. Recent progress and prospective use of aptamers against a large variety of human viruses, such as HIV-1, HCV, HBV, SCoV, Rabies virus, HPV, HSV and influenza virus, with particular focus on clinical development of aptamers will also be described. Finally, we will discuss the challenges of advancing antiviral aptamer therapeutics and prospects for future success.

Use of oligonucleotide aptamer ligands to modulate the function of immune receptors

The paucity of costimulation at the tumor site compromises the ability of tumor-specific T cells to eliminate the tumor. The recent U.S. Food and Drug Administration approval of ipilumimab, an antibody that blocks the inhibitory action of CTLA-4, and clinical trials targeting 4-1BB and PD-1 or PD-L1, have underscored the therapeutic potential of using immunomodulatory antibodies to stimulate protective immunity in human patients. Nonetheless, systemic administration of immunomodulatory antibodies has been associated with dose-limiting autoimmune pathologies, conceivably reflecting also the activation of resident autoreactive T cells. Arguably, targeting immunomodulatory ligands to the disseminated tumor lesions of the patient would reduce such drug-associated toxicities. We have recently developed a new class of inhibitory (CTLA-4) and agonistic (4-1BB and OX-40) ligands composed of short oligonucleotide (ODN) aptamers that exhibited bioactivities comparable or superior to that of antibodies. To reduce toxicity, the immunomodulatory aptamers were targeted to the tumor by conjugation to a second aptamer that bound to a product expressed on the surface of the tumor cell, the targeting aptamer, generating a bispecific aptamer conjugate analogous to bispecific antibodies. In a proof-of-concept study in mice, we have shown that an agonistic 4-1BB-binding aptamer conjugated to a prostate-specific membrane antigen (PSMA)-binding aptamer led to the inhibition of PSMA-expressing tumors, was more effective than, and synergized with, vaccination, and exhibited a superior therapeutic index compared with nontargeted costimulation with 4-1BB antibodies or 4-1BB aptamers. The cell-free chemically synthesized ODN aptamers offer significant advantages over antibodies in terms of synthesis, cost, as well as conjugation chemistry needed to generate bispecific ligand fusions.

Oligonucleotide conjugates for therapeutic applications

Insufficient pharmacokinetic properties and poor cellular uptake are the main hurdles for successful therapeutic development of oligonucleotide agents. The covalent attachment of various ligands designed to influence the biodistribution and cellular uptake or for targeting specific tissues is an attractive possibility to advance therapeutic applications and to expand development options. In contrast to advanced formulations, which often consist of multiple reagents and are sensitive to a variety of preparation conditions, oligonucleotide conjugates are defined molecules, enabling structure-based analytics and quality control techniques. This review gives an overview of current developments of oligonucleotide conjugates for therapeutic applications. Attached ligands comprise peptides, proteins, carbohydrates, aptamers and small molecules, including cholesterol, tocopherol and folic acid. Important linkage types and conjugation methods are summarized. The distinct ligands directly influence biochemical parameters, uptake mechanisms and pharmacokinetic properties.

Cardiovascular RNA Interference Therapy

Understanding of the roles of noncoding RNAs (ncRNAs) within complex organisms has fundamentally changed. It is increasingly possible to use ncRNAs as diagnostic and therapeutic tools in medicine. Regarding disease pathogenesis, it has become evident that confinement to the analysis of protein-coding regions of the human genome is insufficient because ncRNA variants have been associated with important human diseases. Thus, inclusion of noncoding genomic elements in pathogenetic studies and their consideration as therapeutic targets is warranted. We consider aspects of the evolutionary and discovery history of ncRNAs, as far as they are relevant for the identification and selection of ncRNAs with likely therapeutic potential. Novel therapeutic strategies are based on ncRNAs, and we discuss here RNA interference as a highly versatile tool for gene silencing. RNA interference-mediating RNAs are small, but only parts of a far larger spectrum encompassing ncRNAs up to many kilobasepairs in size. We discuss therapeutic options in cardiovascular medicine offered by ncRNAs and key issues to be solved before clinical translation. Convergence of multiple technical advances is highlighted as a prerequisite for the translational progress achieved in recent years. Regarding safety, we review properties of RNA therapeutics, which may immunologically distinguish them from their endogenous counterparts, all of which underwent sophisticated evolutionary adaptation to specific biological contexts. Although our understanding of the noncoding human genome is only fragmentary to date, it is already feasible to develop RNA interference against a rapidly broadening spectrum of therapeutic targets and to translate this to the clinical setting under certain restrictions.

A new nucleic acid-based agent inhibits cytotoxic T lymphocyte-mediated immune disorders

BACKGROUND

Stevens-Johnson syndrome (SJS), toxic epidermal necrolysis (TEN), and graft-versus-host disease (GVHD) are distinct immune reactions elicited by drugs or allogeneic antigens; however, they share a pathomechanism with the activation of cytotoxic T lymphocytes (CTLs). CTLs produce cytotoxic proteins, cytokines, chemokines, or immune alarmins, such as granulysin (GNLY), leading to the extensive tissue damage and systemic inflammation seen in patients with SJS/TEN or GVHD. Currently, there is no effective therapeutic agent specific for CTL-mediated immune disorders.

OBJECTIVES

By targeting GNLY(+) CTLs, we aimed to develop a nucleic acid-based agent consisting of an anti-CD8 aptamer with GNLY small interfering RNA (siRNA).

METHODS

We performed systematic evolution of ligands using exponential enrichment to select and identify effective anti-CD8 aptamers. We developed an aptamer-siRNA chimera using a "sticky bridge" method by conjugating the aptamer with siRNA. We analyzed the inhibitory effects of the aptamer-siRNA chimera on CTL responses in patients with SJS/TEN or GVHD.

RESULTS

We identified a novel DNA aptamer (CD8AP17s) targeting CTLs. This aptamer could be specifically internalized into human CTLs. We generated the CD8AP17s aptamer-GNLY siRNA chimera, which showed a greater than 79% inhibitory effect on the production of GNLY by drug/alloantigen-activated T cells. The CD8AP17s aptamer-GNLY siRNA chimera decreased cytotoxicity in in vitro models of both SJS/TEN (elicited by drug-specific antigen) and GVHD (elicited by allogeneic antigens).

CONCLUSIONS

Our results identified a new nucleic acid-based agent (CD8 aptamer-GNLY siRNA chimera) that can significantly inhibit CTL-mediated drug hypersensitivity, such as that seen in patients with SJS/TEN, as well as the alloreactivity seen in patients with GVHD. This study provides a novel therapeutic strategy for CTL-mediated immune disorders.

Aptamers: molecules of great potential

Aptamers emerged over 20 years ago as a class of nucleic acids able to recognize specific targets. Today, aptamer-related studies constitute a large and important field of biotechnology. Functional oligonucleotides have proved to be a versatile tool in biomedical research due to the ease of synthesis, a wide range of potentially recognized molecular targets and the simplicity of selection. Similarly to antibodies, aptamers can be used to detect or isolate specific molecules, as well as to act as targeting and therapeutic agents. In this review we present different approaches to aptamer application in nanobiotechnology, diagnostics and medicine.

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.

Dual functional BAFF receptor aptamers inhibit ligand-induced proliferation and deliver siRNAs to NHL cells

The B-cell–activating factor (BAFF)-receptor (BAFF-R) is restrictedly expressed on B-cells and is often overexpressed in B-cell malignancies, such as non-Hodgkin’s lymphoma. On binding to its ligand BAFF, proliferation and cell survival are increased, enabling cancer cells to proliferate faster than normal B-cells. Nucleic acid aptamers can bind to target ligands with high specificity and affinity and may offer therapeutic advantages over antibody-based approaches. In this study, we isolated several 2′-F–modified RNA aptamers targeting the B-cell–specific BAFF-R with nanomolar affinity using in vitro SELEX technology. The aptamers efficiently bound to BAFF-R on the surface of B-cells, blocked BAFF-mediated B-cell proliferation and were internalized into B-cells. Furthermore, chimeric molecules between the BAFF-R aptamer and small interfering RNAs (siRNAs) were specifically delivered to BAFF-R expressing cells with a similar efficiency as the aptamer alone. We demonstrate that a signal transducer and activator of transcription 3 (STAT3) siRNA delivered by the BAFF-R aptamer was processed by Dicer and efficiently reduced levels of target mRNA and protein in Jeko-1 and Z138 human B-cell lines. Collectively, our results demonstrate that the dual-functional BAFF-R aptamer–siRNA conjugates are able to deliver siRNAs and block ligand mediated processes, suggesting it might be a promising combinatorial therapeutic agent for B-cell malignancies.