Current progress on aptamer-targeted oligonucleotide therapeutics

Bridging biological samples to functional nucleic acid biosensor applications: current enzymatic-based strategies for single-stranded DNA generation

The escalating threat of emerging diseases, often stemming from contaminants and lethal pathogens, has precipitated a heightened demand for sophisticated diagnostic tools. Within this landscape, the functional nucleic acid (FNA) biosensor, harnessing the power of single-stranded DNA (ssDNA), has emerged as a preeminent choice for target analyte detection. However, the dependence on ssDNA has raised difficulties in realizing it in biological samples. Therefore, the production of high-quality ssDNA from biological samples is critical. This review aims to discuss strategies for generating ssDNA from biological samples for integration into biosensors. Several innovative strategies for ssDNA generation have been deployed, encompassing techniques, such as asymmetric PCR, Exonuclease-PCR, isothermal amplification, biotin-streptavidin PCR, transcription-reverse transcription, ssDNA overhang generation, and urea denaturation PAGE. These approaches have been seamlessly integrated with biosensors for biological sample analysis, ushering in a new era of disease detection and monitoring. This amalgamation of ssDNA generation techniques with biosensing applications holds significant promise, not only in improving the speed and accuracy of diagnostic processes but also in fortifying the global response to deadly diseases, thereby underlining the pivotal role of cutting-edge biotechnology in public health and disease prevention.

Overcoming biological barriers by virus-like drug particles for drug delivery

Virus-like particles (VLPs) have natural structural antigens similar to those found in viruses, making them valuable in vaccine immunization. Furthermore, VLPs have demonstrated significant potential in drug delivery, and emerged as promising vectors for transporting chemical drug, genetic drug, peptide/protein, and even nanoparticle drug. With virus-like permeability and strong retention, they can effectively target specific organs, tissues or cells, facilitating efficient intracellular drug release. Further modifications allow VLPs to transfer across various physiological barriers, thus acting the purpose of efficient drug delivery and accurate therapy. This article provides an overview of VLPs, covering their structural classifications, deliverable drugs, potential physiological barriers in drug delivery, strategies for overcoming these barriers, and future prospects.

The emerging roles of long non-coding RNA in host immune response and intracellular bacterial infections

The long non-coding RNAs (lncRNAs) are evolutionarily conserved classes of non-coding regulatory transcripts of > 200 nucleotides in length. They modulate several transcriptional and post-transcriptional events in the organism. Depending on their cellular localization and interactions, they regulate chromatin function and assembly; and alter the stability and translation of cytoplasmic mRNAs. Although their proposed range of functionality remains controversial, there is increasing research evidence that lncRNAs play a regulatory role in the activation, differentiation and development of immune signaling cascades; microbiome development; and in diseases such as neuronal and cardiovascular disorders; cancer; and pathogenic infections. This review discusses the functional roles of different lncRNAs in regulation of host immune responses, signaling pathways during host-microbe interaction and infection caused by obligate intracellular bacterial pathogens. The study of lncRNAs is assuming significance as it could be exploited for development of alternative therapeutic strategies for the treatment of severe and chronic pathogenic infections caused by Mycobacterium, Chlamydia and Rickettsia infections, as well as commensal colonization. Finally, this review summarizes the translational potential of lncRNA research in development of diagnostic and prognostic tools for human diseases.

Targeted delivery of doxorubicin and therapeutic FOXM1 aptamer to tumor cells using gold nanoparticles modified with AS1411 and ATP aptamers

Objectives

A targeted delivery platform was prepared to co-deliver both doxorubicin (Dox) as an anticancer drug and FOXM1 aptamer as a therapeutic substance to breast cancer cells (4T1 and MCF-7) to reduce Dox side effects and increase its therapeutic efficacy. The targeted system (AuNPs-AFPA) consisted of FOXM1 aptamer, AS1411 aptamer (targeting oligonucleotide), ATP aptamer, and gold nanoparticles (AuNPs) as a carrier.

Materials and Methods

AuNPs were synthesized by reduction of HAuCl4. Next, after pegylation of ATP aptamer, FOXM1 aptamer-PEGylated ATP aptamer conjugate (FPA) was prepared. Then, the AS1411 aptamer and FPA were exposed to the AuNPs surface through their thiol groups. Subsequently, Dox was loaded into the complex to form a targeted therapeutic complex.

Results

The data of the MTT assay displayed that the targeted complex could remarkably reduce cell viability rate in target cells due to the overexpression of nucleolin on their cell membranes compared to nontarget cells, showing the targeting ability of AuNPs-AFPA-Dox. The in vivo antitumor effect confirmed that AuNPs-AFPA-Dox was capable of remarkably diminishing tumor growth relative to the free Dox in mice bearing 4T1 tumor cells.

Conclusion

The results confirmed that the targeted system improved the therapeutic effect by loading high amounts of Dox alongside the presence of the therapeutic effect of FOXM1 aptamer. Finally, it can be concluded that AuNPs-AFPA-Dox by enhancing antitumor effectiveness and reducing toxicity toward non-target cells, can be used potentially as an effective strategy for the treatment of breast cancer.

Nanoparticle-mediated selective Sfrp-1 silencing enhances bone density in osteoporotic mice

Osteoporosis (OP) is characterized by a loss in bone mass and mineral density. The stimulation of the canonical Wnt/β-catenin pathway has been reported to promote bone formation, this pathway is controlled by several regulators as secreted frizzled-related protein-1 (Sfrp-1), antagonist of the pathway. Thus, Sfrp-1 silencing therapies could be suitable for enhancing bone growth. However, the systemic stimulation of Wnt/β-catenin has been correlated with side effects. This work hypothesizes the administration of lipid-polymer NPs (LPNPs) functionalized with a MSC specific aptamer (Apt) and carrying a SFRP1 silencing GapmeR, could favor bone formation in OP with minimal undesired effects. Suitable SFRP1 GapmeR-loaded Apt-LPNPs (Apt-LPNPs-SFRP1) were administered in osteoporotic mice and their biodistribution, toxicity and bone induction capacity were evaluated. The aptamer functionalization of the NPs modified their biodistribution profile showing a four-fold increase in the bone accumulation and a ten-fold decrease in the hepatic accumulation compared to naked LPNPs. Moreover, the histological evaluation revealed evident changes in bone structure observing a more compact trabecular bone and a cortical bone thickness increase in the Apt-LPNPs-SFRP1 treated mice with no toxic effects. Therefore, these LPNPs showed suitable properties and biodistribution profiles leading to an enhancement on the bone density of osteoporotic mice.

Synthesis and Exon-Skipping Properties of a 3'-Ursodeoxycholic Acid-Conjugated Oligonucleotide Targeting DMD Pre-mRNA: Pre-Synthetic versus Post-Synthetic Approach

Steric blocking antisense oligonucleotides (ASO) are promising tools for splice modulation such as exon-skipping, although their therapeutic effect may be compromised by insufficient delivery. To address this issue, we investigated the synthesis of a 20-mer 2'-OMe PS oligonucleotide conjugated at 3'-end with ursodeoxycholic acid (UDCA) involved in the targeting of human DMD exon 51, by exploiting both a pre-synthetic and a solution phase approach. The two approaches have been compared. Both strategies successfully provided the desired ASO 51 3'-UDC in good yield and purity. It should be pointed out that the pre-synthetic approach insured better yields and proved to be more cost-effective. The exon skipping efficiency of the conjugated oligonucleotide was evaluated in myogenic cell lines and compared to that of unconjugated one: a better performance was determined for ASO 51 3'-UDC with an average 9.5-fold increase with respect to ASO 51.

Immunotherapy and Gene Therapy for Oncoviruses Infections: A Review

Immunotherapy has been shown to be highly effective in some types of cancer caused by viruses. Gene therapy involves insertion or modification of a therapeutic gene, to correct for inappropriate gene products that cause/may cause diseases. Both these types of therapy have been used as alternative ways to avoid cancers caused by oncoviruses. In this review, we summarize recent studies on immunotherapy and gene therapy including the topics of oncolytic immunotherapy, immune checkpoint inhibitors, gene replacement, antisense oligonucleotides, RNA interference, clustered regularly interspaced short palindromic repeats Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)-based gene editing, transcription activator-like effector nucleases (TALENs) and custom treatment for Epstein-Barr virus, human T-lymphotropic virus 1, hepatitis B virus, human papillomavirus, hepatitis C virus, herpesvirus associated with Kaposi's sarcoma, Merkel cell polyomavirus, and cytomegalovirus.

Advances in siRNA delivery strategies for the treatment of MDR cancer

RNA interference (RNAi) represents a promising therapeutic method that uses siRNA for cancer treatment. Although the RNAi technique has been increasingly used for clinical trials, systemic siRNA delivery into targeted cells is still challenging. The barriers impeding siRNA therapeutics delivery and impacting the treatment outcome must overcome with negligible systemic toxicity for a desirable and successful delivery of siRNA to MDR cancer cells. Nano delivery strategies have been investigated for nanocarrier functionalization, cancer immunotherapy and cancer targeting. Lipid nanoparticles (LNPs), dynamic polyconjugates (DPC™), GalNAc-siRNA conjugates, exosome and RBC systems have shown potential for efficient delivery of siRNA to cancer cells. Delivery of siRNA to tumor cells, immune cells to regulate T cell functions for immunotherapy are promising approaches.

Viral Mimicry as a Design Template for Nucleic Acid Nanocarriers

Therapeutic nucleic acids hold immense potential in combating undruggable, gene-based diseases owing to their high programmability and relative ease of synthesis. While the delivery of this class of therapeutics has successfully entered the clinical setting, extrahepatic targeting, endosomal escape efficiency, and subcellular localization. On the other hand, viruses serve as natural carriers of nucleic acids and have acquired a plethora of structures and mechanisms that confer remarkable transfection efficiency. Thus, understanding the structure and mechanism of viruses can guide the design of synthetic nucleic acid vectors. This review revisits relevant structural and mechanistic features of viruses as design considerations for efficient nucleic acid delivery systems. This article explores how viral ligand display and a metastable structure are central to the molecular mechanisms of attachment, entry, and viral genome release. For comparison, accounted for are details on the design and intracellular fate of existing nucleic acid carriers and nanostructures that share similar and essential features to viruses. The review, thus, highlights unifying themes of viruses and nucleic acid delivery systems such as genome protection, target specificity, and controlled release. Sophisticated viral mechanisms that are yet to be exploited in oligonucleotide delivery are also identified as they could further the development of next-generation nonviral nucleic acid vectors.

Assessing the capacity for mental manipulation in patients with statically-determined mild cognitive impairment using digital technology

Aims: Prior research employing a standard backward digit span test has been successful in operationally defining neurocognitive constructs associated with the Fuster’s model of executive attention. The current research sought to test if similar behavior could be obtained using a cross-modal mental manipulation test. Methods: Memory clinic patients were studied. Using Jak-Bondi criteria, 24 patients were classified with mild cognitive impairment (MCI), and 33 memory clinic patients did not meet criteria for MCI (i.e. non-MCI). All patients were assessed with the digital version of the WRAML-2 Symbolic Working Memory Test-Part 1, a cross-modal mental manipulation task where patients hear digits, but respond by touching digits from lowest to highest on an answer key. Only 4 and 5-span trials were analyzed. Using an iPad, all test stimuli were played; and, all responses were obtained with a touch key. Only correct trials were analyzed. Average time to complete trials and latency for each digit was recorded. Results: Groups did not differ when average time to complete 4-span trials was calculated. MCI patients displayed slower latency, or required more time to re-order the 1st and 3rd digits. Regression analyses, primarily involving initial and latter response latencies, were associated with better, but different underlying neuropsychological abilities. Almost no 5-span analyses were significant. Conclusions: This cross-modal test paradigm found no difference for total average time. MCI patients generated slower 1st and 3rd response latency, suggesting differences in time allocation to achieve correct serial order recall. Moreover, different neuropsychological abilities were associated with different time-based test components. These data extend prior findings using a standard backward digit span test. Differences in time epochs are consistent with constructs underlying the model of executive attention and help explain mental manipulation deficits in MCI. These latency measures could constitute neurocognitive biomarkers that track emergent disease.

Aptamers and antibodies: rivals or allies in cancer targeted therapy?

The goal of an efficacious cancer therapy is to specifically target diseased cells at high accuracy while sparing normal, healthy cells. Over the past three decades, immunotherapy, based on the use of monoclonal antibodies (mAbs) directed against tumor-associated antigens, to inhibit their oncogenic function, or against immune checkpoints, to modulate specific T cell responses against cancer, has proven to be an important strategy for cancer therapy. Nevertheless, the number of mAbs approved for clinical use is still limited because of significant drawbacks to their applicability. Oligonucleotide aptamers, similarly to antibodies, form high-affinity bonds with their specific protein targets, thus representing an effective tool for active cancer targeting. Compared to antibodies, aptamers’ use as therapeutic agents benefits from their low size, low/no immunogenicity, simple synthesis and design flexibility for improving efficacy and stability. This review intends to highlight recently emerged applications of aptamers as recognition elements, from biomarker discovery to targeted drug delivery and targeted treatment, showing aptamers’ potential to work in conjunction with antibodies for attacking cancer from multiple flanks.

Gene regulation by long non-coding RNAs and its biological functions

Evidence accumulated over the past decade shows that long non-coding RNAs (lncRNAs) are widely expressed and have key roles in gene regulation. Recent studies have begun to unravel how the biogenesis of lncRNAs is distinct from that of mRNAs and is linked with their specific subcellular localizations and functions. Depending on their localization and their specific interactions with DNA, RNA and proteins, lncRNAs can modulate chromatin function, regulate the assembly and function of membraneless nuclear bodies, alter the stability and translation of cytoplasmic mRNAs and interfere with signalling pathways. Many of these functions ultimately affect gene expression in diverse biological and physiopathological contexts, such as in neuronal disorders, immune responses and cancer. Tissue-specific and condition-specific expression patterns suggest that lncRNAs are potential biomarkers and provide a rationale to target them clinically. In this Review, we discuss the mechanisms of lncRNA biogenesis, localization and functions in transcriptional, post-transcriptional and other modes of gene regulation, and their potential therapeutic applications.

RNA Drugs and RNA Targets for Small Molecules: Principles, Progress, and Challenges

RNA-based therapies, including RNA molecules as drugs and RNA-targeted small molecules, offer unique opportunities to expand the range of therapeutic targets. Various forms of RNAs may be used to selectively act on proteins, transcripts, and genes that cannot be targeted by conventional small molecules or proteins. Although development of RNA drugs faces unparalleled challenges, many strategies have been developed to improve RNA metabolic stability and intracellular delivery. A number of RNA drugs have been approved for medical use, including aptamers (e.g., pegaptanib) that mechanistically act on protein target and small interfering RNAs (e.g., patisiran and givosiran) and antisense oligonucleotides (e.g., inotersen and golodirsen) that directly interfere with RNA targets. Furthermore, guide RNAs are essential components of novel gene editing modalities, and mRNA therapeutics are under development for protein replacement therapy or vaccination, including those against unprecedented severe acute respiratory syndrome coronavirus pandemic. Moreover, functional RNAs or RNA motifs are highly structured to form binding pockets or clefts that are accessible by small molecules. Many natural, semisynthetic, or synthetic antibiotics (e.g., aminoglycosides, tetracyclines, macrolides, oxazolidinones, and phenicols) can directly bind to ribosomal RNAs to achieve the inhibition of bacterial infections. Therefore, there is growing interest in developing RNA-targeted small-molecule drugs amenable to oral administration, and some (e.g., risdiplam and branaplam) have entered clinical trials. Here, we review the pharmacology of novel RNA drugs and RNA-targeted small-molecule medications, with a focus on recent progresses and strategies. Challenges in the development of novel druggable RNA entities and identification of viable RNA targets and selective small-molecule binders are discussed. SIGNIFICANCE STATEMENT: With the understanding of RNA functions and critical roles in diseases, as well as the development of RNA-related technologies, there is growing interest in developing novel RNA-based therapeutics. This comprehensive review presents pharmacology of both RNA drugs and RNA-targeted small-molecule medications, focusing on novel mechanisms of action, the most recent progress, and existing challenges.

Addiction to protein kinase Cɩ due to PRKCI gene amplification can be exploited for an aptamer-based targeted therapy in ovarian cancer

PRKCI, the gene for protein kinase Cι (PKCι), is frequently amplified in ovarian cancer and recent studies have shown that PKCι participates in ovary tumorigenesis. However, it is unknown whether PKCι is differentially involved in the growth/survival between PRKCI-amplified and non-amplified ovarian cancer cells. In this study, we analyzed ovarian cancer patient dataset and revealed that PRKCI is the only PKC family member significantly amplified in ovarian cancer and PRKCI amplification is associated with higher PKCι expression. Using a panel of ovarian cancer cell lines, we found that abundance of PKCι is generally associated with PRKCI amplification. Interestingly, silencing PKCι led to apoptosis in PRKCI-amplified ovarian cancer cells but not in those without PRKCI amplification, thus indicating an oncogenic addiction to PKCɩ in PRKCI-amplified cells. Since small-molecule inhibitors characterized to selectively block atypical PKCs did not offer selectivity nor sensitivity in PRKCI-amplified ovarian cancer cells and were even cytotoxic to non-cancerous ovary surface or fallopian tube epithelial cells, we designed an EpCAM aptamer-PKCι siRNA chimera (EpCAM-siPKCι aptamer). EpCAM-siPKCι aptamer not only effectively induced apoptosis of PRKCI-amplified ovarian cancer cells but also greatly deterred intraperitoneal tumor development in xenograft mouse model. This study has demonstrated a precision medicine-based strategy to target a subset of ovarian cancer that contains PRKCI amplification and shown that the EpCAM aptamer-delivered PKCι siRNA may be used to suppress such tumors.

Silencing RORγt in Human CD4+ T cells with CD30 aptamer-RORγt shRNA Chimera

Targeting specific T cell subtypes and intervening in their function are emerging a critical strategy for treatment of autoimmune diseases. Here we report that an RNA CD30 aptamer was utilized to deliver short hairpin RNA (shRNA) to CD30+ T cells to target retinoic acid receptor-related orphan receptor gamma t (RORγt), leading to impaired expression of RORγt and suppression of IL-17A and IL-17F. A DNA template consisting of CD30 aptamer and RORγt shRNA sequences was synthesized and was transcribed CD30 aptamer-RORγt shRNA chimera (CD30-AshR-RORγt). Insertion of 2'-F-dCTP and 2'-FdUTP was incorporated during CD30-AshR-RORγt transcription to increase its resistance to RNase. CD30-AshR-RORγt was specifically up-taken by CD30+ Karpas 299 cells, but not by Jurkat cells which lack CD30. It was also up-taken by activated, CD30 expressing human CD4+T cells, but not by resting CD4+ T cells. The RORγt shRNA moiety of CD30-AshR-RORγt chimera was cleaved and released by Dicers. Then, CD30-AshR-RORγt suppressed RORγt gene expression in Karpas 299 cells and activated human CD4+ T cells. Consistently, silence of Th17 cell differentiation and IL-17A and IL-17F synthesis with CD30-AshR-RORγt was demonstrated in activated human CD4+ T cells from healthy donors and RA patients. CD30-AshR-negative control chimera and prostate specific membrane antigen (PSMA)-AshR-RORγt had no significant impact on the expression of RORγt or IL-17A and IL-17F. These data present a novel strategy for shRNA delivery using CD30 RNA aptamers to down-regulate CD30+ Th17 cells and can be developed as a targeted therapy for treating Th17 cell mediated conditions.

Axl-Targeted Delivery of the Oncosuppressor miR-137 in Non-small-Cell Lung Cancer

Non-small-cell lung cancer (NSCLC) accounts for 85%–90% of all cases of lung cancer that is the most deadly type of cancer. Despite advances in chemotherapy and radiotherapy, severe side effects and frequent drug resistance limit the success of the treatments, and the identification of new therapeutic options still represents a crucial challenge. Here, we provide the evidence for the therapeutic potential of an aptamer-microRNA (miR) complex (AmiC) composed by an aptamer (GL21.T), able to bind and antagonize the oncogenic receptor Axl, and the miR-137, downregulated in lung cancer and involved in cell survival and proliferation. We found that, when applied to Axl-expressing NSCLC cancer cells, the complex is effectively internalized, increasing miR cellular levels and downregulating miR targets. Most importantly, the complex combines the inhibitory function of the GL21.T aptamer and miR-137, leading to a negative impact on NSCLC migration and growth. The described AmiC thus represents a promising tool for the development of new therapeutic approaches for NSCLC.

Aptamers: an emerging class of bioaffinity ligands in bioactive peptide applications

The food and health applications of bioactive peptides have grown remarkably in the past few decades. Current elucidations have shown that bioactive peptides have unique structural arrangement of amino acids, conferring distinct functionalities, and molecular affinity characteristics. However, whereas interest in the biological potency of bioactive peptides has grown, cost-effective techniques for monitoring the structural changes in these peptides and how these changes affect the biological properties have not grown at the same rate. Due to the high binding affinity of aptamers for other biomolecules, they have a huge potential for use in tracking the structural, conformational, and compositional changes in bioactive peptides. This review provides an overview of bioactive peptides and their essential structure-activity relationship. The review further highlights on the types and methods of synthesis of aptamers before the discussion of the prospects, merits, and challenges in the use of aptamers for bioaffinity interactions with bioactive peptides.

RNA inhibitors of nuclear proteins responsible for multiple organ dysfunction syndrome

The development of multiple organ dysfunction syndrome (MODS) following infection or tissue injury is associated with increased patient morbidity and mortality. Extensive cellular injury results in the release of nuclear proteins, of which histones are the most abundant, into the circulation. Circulating histones are implicated as essential mediators of MODS. Available anti-histone therapies have failed in clinical trials due to off-target effects such as bleeding and toxicity. Here, we describe a therapeutic strategy for MODS based on the neutralization of histones by chemically stabilized nucleic acid bio-drugs (aptamers). Systematic evolution of ligands by exponential enrichment technology identified aptamers that selectively bind those histones responsible for MODS and do not bind to serum proteins. We demonstrate the efficacy of histone-specific aptamers in human cells and in a murine model of MODS. These aptamers could have a significant therapeutic benefit in the treatment of multiple diverse clinical conditions associated with MODS.

Nucleic Acid-Based Therapeutics for Pulmonary Diseases

Nucleic acid-based therapeutics present huge potential in the treatment of pulmonary diseases ranging from lung cancer to asthma and chronic pulmonary diseases, which are often fatal and widely prevalent. The susceptibility of nucleic acids to degradation and the complex structure of lungs retard the effective pulmonary delivery of nucleic acid drug. To overcome these barriers, different strategies have been exploited to increase the delivery efficiency using chemically synthesized nucleic acids, vector encapsulation, proper formulation, and administration route. However, several limitations regarding off-target effects and immune stimulation of nucleic acid drugs hamper their translation into the clinical practice. Therefore, their successful clinical application will ultimately rely on well-developed carriers and methods to ensure safety and efficacy. In this review, we provide a comprehensive overview of the nucleic acid application for pulmonary diseases, covering action mechanism of the nucleic acid drugs, the novel delivery systems, and the current formulation for the administration to lungs. The latest advances of nucleic acid drugs under clinical evaluation to treat pulmonary disorders will also be detailed.

Identification and Characterization of DNA Aptamers Specific for Phosphorylation Epitopes of Tau Protein

Tau proteins are proteins that stabilize microtubules, but their hyperphosphorylation can result in the formation of protein aggregates and, over time, neurodegeneration. This phenomenon, termed tauopathy, is pathologically involved in several neurodegenerative disorders. DNA aptamers are single-stranded oligonucleotides capable of specific binding to target molecules. Using tau epitopes predisposed for phosphorylation, we identified six distinct aptamers that bind to tau at two phosphorylatable epitopes (Thr-231 and Ser-202) and to full-length Tau441 proteins with nanomolar affinity. In addition, several of these aptamers also inhibit tau phosphorylation (IT4, IT5, IT6) and tau oligomerization (IT3, IT4, IT5, IT6). This is the first report to identify tau epitope-specific aptamers. Such tau aptamers can be used to detect tau in biofluids and uncover the mechanism of tauopathy. They can be further developed into novel therapeutic agents in mitigating tauopathy-associated neurodegenerative disorders.

Tapping the RNA world for therapeutics

A recent revolution in RNA biology has led to the identification of new RNA classes with unanticipated functions, new types of RNA modifications, an unexpected multiplicity of alternative transcripts and widespread transcription of extragenic regions. This development in basic RNA biology has spawned a corresponding revolution in RNA-based strategies to generate new types of therapeutics. Here, I review RNA-based drug design and discuss barriers to broader applications and possible ways to overcome them. Because they target nucleic acids rather than proteins, RNA-based drugs promise to greatly extend the domain of 'druggable' targets beyond what can be achieved with small molecules and biologics.

Design and Preparation of Aptamer-siRNA Chimeras (AsiCs) for Targeted Cancer Therapy

Conjugation of cell-internalizing DNA or RNA aptamers to tumor-suppressing siRNAs represents a novel promising approach for cancer therapy. Here we describe how to employ RNA aptamers that bind to cell surface receptors as carriers for cell-targeted siRNA (or miRNA) delivery. This protocol was optimized to improve the efficiency of the aptamer-siRNA/miRNA conjugates and facilitate its implementation in most molecular biology labs. The single working steps include (1) outlining the optimal sequences of the RNA strands bearing the aptamer and siRNA sequence, for which further (2) a dsDNA template is synthesized and then (3) transcribed into an RNA that will be (4) folded and annealed to a chemically synthesized siRNA complementary strand. Moreover, we reference recent examples and advances in the aptamer delivery field.

Oligonucleotide aptamers against tyrosine kinase receptors: Prospect for anticancer applications

Transmembrane receptor tyrosine kinases (RTKs) play crucial roles in cancer cell proliferation, survival, migration and differentiation. Area of intense research is searching for effective anticancer therapies targeting these receptors and, to date, several monoclonal antibodies and small-molecule tyrosine kinase inhibitors have entered the clinic. However, some of these drugs show limited efficacy and give rise to acquired resistance. Emerging highly selective compounds for anticancer therapy are oligonucleotide aptamers that interact with their targets by recognizing a specific three-dimensional structure. Because of their nucleic acid nature, the rational design of advanced strategies to manipulate aptamers for both diagnostic and therapeutic applications is greatly simplified over antibodies. In this manuscript, we will provide a comprehensive overview of oligonucleotide aptamers as next generation strategies to efficiently target RTKs in human cancers.

Potentiating tumor immunity using aptamer-targeted RNAi to render CD8+ T cells resistant to TGFβ inhibition

TGFβ secreted by tumor cells and/or tumor infiltrating stromal cells is a key mediator of tumor growth and immune suppression at the tumor site. Nonetheless, clinical trials in cancer patients targeting the TGFβ pathway exhibited at best a modest therapeutic benefit. A likely reason, a common limitation of many cancer drugs, is that the physiologic roles of TGFβ in tissue homeostasis, angiogenesis, and immune regulation precluded the dose escalation necessary to achieve a profound clinical response. Murine studies have suggested that countering immune suppressive effects of TGFβ may be sufficient to inhibit tumor growth. Here we describe an approach to render vaccine-activated CD8⁺ T cells transiently resistant to TGFβ inhibition using an siRNA against Smad4 to inhibit a key step in the canonical TGFβ signaling pathway. The siRNA was targeted to vaccine activated CD8⁺ T cells in the mouse by conjugation to a 4-1BB binding oligonucleotide (ODN) aptamer ligand (4-1BB-Smad4 conjugate). In vitro the 4-1BB-Smad4 conjugate rendered T cells partially resistant to TGFβ inhibition, and treatment of tumor bearing mice with systemically administered 4-1BB-Smad4 conjugate enhanced vaccine- and irradiation-induced antitumor immunity. Limiting the inhibitory effects of TGFβ to tumor-specific T cells will not interfere with its multiple physiologic roles and hence reduce the risk of toxicity.

The potential of antisense oligonucleotide therapies for inherited childhood lung diseases

Antisense oligonucleotides are an emerging therapeutic option to treat diseases with known genetic origin. In the age of personalised medicines, antisense oligonucleotides can sometimes be designed to target and bypass or overcome a patient's genetic mutation, in particular those lesions that compromise normal pre-mRNA processing. Antisense oligonucleotides can alter gene expression through a variety of mechanisms as determined by the chemistry and antisense oligomer design. Through targeting the pre-mRNA, antisense oligonucleotides can alter splicing and induce a specific spliceoform or disrupt the reading frame, target an RNA transcript for degradation through RNaseH activation, block ribosome initiation of protein translation or disrupt miRNA function. The recent accelerated approval of eteplirsen (renamed Exondys 51™) by the Food and Drug Administration, for the treatment of Duchenne muscular dystrophy, and nusinersen, for the treatment of spinal muscular atrophy, herald a new and exciting era in splice-switching antisense oligonucleotide applications to treat inherited diseases. This review considers the potential of antisense oligonucleotides to treat inherited lung diseases of childhood with a focus on cystic fibrosis and disorders of surfactant protein metabolism.

Nucleic Acid Aptamers: Emerging Applications in Medical Imaging, Nanotechnology, Neurosciences, and Drug Delivery

Recent progresses in organic chemistry and molecular biology have allowed the emergence of numerous new applications of nucleic acids that markedly deviate from their natural functions. Particularly, DNA and RNA molecules-coined aptamers-can be brought to bind to specific targets with high affinity and selectivity. While aptamers are mainly applied as biosensors, diagnostic agents, tools in proteomics and biotechnology, and as targeted therapeutics, these chemical antibodies slowly begin to be used in other fields. Herein, we review recent progress on the use of aptamers in the construction of smart DNA origami objects and MRI and PET imaging agents. We also describe advances in the use of aptamers in the field of neurosciences (with a particular emphasis on the treatment of neurodegenerative diseases) and as drug delivery systems. Lastly, the use of chemical modifications, modified nucleoside triphosphate particularly, to enhance the binding and stability of aptamers is highlighted.

Aptamers as Valuable Molecular Tools in Neurosciences

Aptamers are short nucleic acids that interact with a variety of targets with high affinity and specificity. They have been shown to inhibit biological functions of cognate target proteins, and they are identifiable by an in vitro selection process, also termed SELEX (Systematic Evolution of Ligands by EXponential enrichment). Being nucleic acids, aptamers can be synthesized chemically or enzymatically. The latter renders RNA aptamers compatible with the cell's own transcription machinery and, thus, expressable inside cells. The synthesis of aptamers by chemical approaches opens up the possibility of producing aptamers on a large scale and enables a straightforward access to introduce modifications in a site-specific manner (e.g., fluorophores or photo-labile groups). These characteristics make aptamers broadly applicable (e.g., as an analytical, diagnostic, or separation tool). In this TechSight, we provide a brief overview on aptamer technology and the potential of aptamers as valuable research tools in neurosciences.

Depth-Profiling the Nuclease Stability and the Gene Silencing Efficacy of Brush-Architectured Poly(ethylene glycol)-DNA Conjugates

PEGylation of an oligonucleotide using a brush polymer can improve its biopharmaceutical characteristics, including enzymatic stability and biodistribution. Herein, we quantitatively explore the nuclease accessibility of the nucleic acid as a function of "depth" toward the backbone of the brush polymer. It is found that protein accessibility decreases as the nucleotide is located closer to the backbone. Thus, by moving the conjugation point from the terminus of the nucleic acid strand to an internal position, much smaller brushes can be used to achieve the same level of steric shielding. This finding also makes it possible to assess antisense gene regulation efficiency of these brush-DNA conjugates as a function of their nuclease stability.

Aptamer-siRNA Chimeras: Discovery, Progress, and Future Prospects

Synthetic nucleic acid ligands (aptamers) have emerged as effective delivery tools for many therapeutic oligonucleotide-based drugs, including small interfering RNAs (siRNAs). In this review, we summarize recent progress in the aptamer selection technology that has made possible the identification of cell-specific, cell-internalizing aptamers for the cell-targeted delivery of therapeutic oligonucleotides. In addition, we review the original, proof-of-concept aptamer-siRNA delivery studies and discuss recent advances in aptamer-siRNA conjugate designs for applications ranging from cancer therapy to the development of targeted antivirals. Challenges and prospects of aptamer-targeted siRNA drugs for clinical development are further highlighted.

Screening of specific nucleic acid aptamers binding tumor markers in the serum of the lung cancer patients and identification of their activities

Lung cancer is by far the leading cause of cancer death in the world. Despite the improvements in diagnostic methods, the status of early detection was not achieved. So, a new diagnostic method is needed. The aim of this study is to obtain the highly specific nucleic acid aptamers with strong affinity to tumor markers in the serum of the lung cancer patients for targeting the serum. Aptamers specifically binding to tumor markers in the serum of the lung cancer patients were screened from the random single-stranded DNA library with agarose beads as supports and the serum as a target by target-substituting subtractive SELEX technique and real-time quantitative polymerase chain reaction technique. Subsequently, the secondary single-stranded DNA library obtained by 10 rounds of screening was amplified to double-stranded DNA, followed by high-throughput genome sequence analysis to screen aptamers with specific affinity to tumor markers in the serum of the lung cancer patients. Finally, six aptamers obtained by 10 rounds of screening were identified with high specific affinity to tumor markers in the serum of the lung cancer patients. Compared with other five aptamers, the aptamer 43 was identified both with the highest specificity to bind target molecule and without any obvious affinity to non-specific proteins. The screened aptamers have relatively high specificity to combine tumor markers in the serum of the lung cancer patients, which provides breakthrough points for early diagnosis and treatment of lung cancer.

Simultaneous targeting of CD44 and EpCAM with a bispecific aptamer effectively inhibits intraperitoneal ovarian cancer growth

CD44 and EpCAM play crucial roles in intraperitoneal ovarian cancer development. In this study, we developed an RNA-based bispecific CD44-EpCAM aptamer that is capable of blocking CD44 and EpCAM simultaneously by fusing single CD44 and EpCAM aptamers with a double stranded RNA adaptor. With the aid of a panel of ovarian cancer cell lines, we found that bispecific CD44-EpCAM aptamer was much more effective than either single CD44 or EpCAM aptamer in the ability to inhibit cell growth and to induce apoptosis. When these aptamers were tested in intraperitoneal ovarian cancer xenograft model, bispecific CD44-EpCAM aptamer suppressed intraperitoneal tumor outgrowth much more significantly than single CD44 and EpCAM aptamer either alone or in combination. The enhanced efficacy of bispecific CD44-EpCAM aptamer is most likely to be attributed to its increased circulation time over the single aptamers. Moreover, we showed that bispecific CD44-EpCAM aptamer exhibited no toxicity to the host and was unable to trigger innate immunogenicity. Our study suggests that bispecific CD44-EpCAM aptamer may represent a promising therapeutic agent against advanced ovarian cancer.

PSMA redirects cell survival signaling from the MAPK to the PI3K-AKT pathways to promote the progression of prostate cancer

Increased abundance of the prostate-specific membrane antigen (PSMA) on prostate epithelium is a hallmark of advanced metastatic prostate cancer (PCa) and correlates negatively with prognosis. However, direct evidence that PSMA functionally contributes to PCa progression remains elusive. We generated mice bearing PSMA-positive or PSMA-negative PCa by crossing PSMA-deficient mice with transgenic PCa (TRAMP) models, enabling direct assessment of PCa incidence and progression in the presence or absence of PSMA. Compared with PSMA-positive tumors, PSMA-negative tumors were smaller, lower-grade, and more apoptotic with fewer blood vessels, consistent with the recognized proangiogenic function of PSMA. Relative to PSMA-positive tumors, tumors lacking PSMA had less than half the abundance of type 1 insulin-like growth factor receptor (IGF-1R), less activity in the survival pathway mediated by PI3K-AKT signaling, and more activity in the proliferative pathway mediated by MAPK-ERK1/2 signaling. Biochemically, PSMA interacted with the scaffolding protein RACK1, disrupting signaling between the β₁ integrin and IGF-1R complex to the MAPK pathway, enabling activation of the AKT pathway instead. Manipulation of PSMA abundance in PCa cell lines recapitulated this signaling pathway switch. Analysis of published databases indicated that IGF-1R abundance, cell proliferation, and expression of transcripts for antiapoptotic markers positively correlated with PSMA abundance in patients, suggesting that this switch may be relevant to human PCa. Our findings suggest that increase in PSMA in prostate tumors contributes to progression by altering normal signal transduction pathways to drive PCa progression and that enhanced signaling through the IGF-1R/β₁ integrin axis may occur in other tumors.

Aptamer-Conjugated Calcium Phosphate Nanoparticles for Reducing Diabetes Risk via Retinol Binding Protein 4 Inhibition

OBJECTIVES

Inhibition of the binding of retinol to its carrier, retinol binding protein 4, is a new strategy for treating type 2 diabetes; for this purpose, we have provided an aptamer-functionalized multishell calcium phosphate nanoparticle.

METHODS

First, calcium phosphate nanoparticles were synthesized and conjugated to the aptamer. The cytotoxicity of nanoparticles releases the process of aptamer from nanoparticles and their inhibition function of binding retinol to retinol binding protein 4.

RESULTS

After synthesizing and characterizing the multishell calcium phosphate nanoparticles and observing the noncytotoxicity of conjugate, the optimum time (48 hours) and the pH (7.4) for releasing the aptamer from the nanoparticles was determined. The half-maximum inhibitory concentration (IC₅₀) value for inhibition of retinol binding to retinol binding protein 4 was 210 femtomolar (fmol).

CONCLUSIONS

The results revealed that the aptamer could prevent connection between retinol and retinol binding protein 4 at a very low IC₅₀ value (210 fmol) compared to other reported inhibitors. It seems that this aptamer could be used as an efficient candidate not only for decreasing the insulin resistance in type 2 diabetes, but also for inhibiting the other retinol binding protein 4-related diseases.

Targeted si-RNA with liposomes and exosomes (extracellular vesicles): How to unlock the potential

The concept of RNA interference therapeutics has been initiated 18 years ago, and the main bottleneck for translation of the technology into therapeutic products remains the delivery of functional RNA molecules into the cell cytoplasm. In the present review article after an introduction about the theoretical basis of RNAi therapy and the main challenges encountered for its realization, an overview of the different types of delivery systems or carriers, used as potential systems to overcome RNAi delivery issues, will be provided. Characteristic examples or results obtained with the most promising systems will be discussed. Focus will be given mostly on the applications of liposomes or other types of lipid carriers, such as exosomes, towards improved delivery of RNAi to therapeutic targets. Finally the approach of integrating the advantages of these two vesicular systems, liposomes and exosomes, as a potential solution to realize RNAi therapy, will be proposed.

Aptamers for CD Antigens: From Cell Profiling to Activity Modulation

Nucleic acid-based aptamers are considered to be a promising alternative to antibodies because of their strong and specific binding to diverse targets, fast and inexpensive chemical synthesis, and easy labeling with a fluorescent dye or therapeutic agent. Cluster of differentiation (CD) proteins are among the most popular antigens for aptamers on the cell surface. These anti-CD aptamers could be used in cell biology and biomedicine, from simple cell phenotyping by flow cytometry or fluorescent microscopy to diagnosis and treatment of HIV/AIDS to cancer and immune therapies. The unique feature of aptamers is that they can act simultaneously as an agonist and antagonist of CD receptors depending on a degree of aptamer oligomerization. Aptamers can also deliver small interfering RNA to silence vital genes in CD-positive cells. In this review, we summarize nucleic acid sequences of anti-CD aptamers and their use, which have been validated in multiple studies.

Intracellular Expression of PAI-1 Specific Aptamers Alters Breast Cancer Cell Migration, Invasion and Angiogenesis

Plasminogen activator inhibitor-1 (PAI-1) is elevated in various cancers, where it has been shown to effect cell migration and invasion and angiogenesis. While, PAI-1 is a secreted protein, its intercellular levels are increased in cancer cells. Consequently, intracellular PAI-1 could contribute to cancer progression. While various small molecule inhibitors of PAI-1 are currently being investigated, none specifically target intracellular PAI-1. A class of inhibitors, termed aptamers, has been used effectively in several clinical applications. We previously generated RNA aptamers that target PAI-1 and demonstrated their ability to inhibit extracellular PAI-1. In the current study we explored the effect of these aptamers on intracellular PAI-1. We transiently transfected the PAI-1 specific aptamers into both MDA-MB-231 human breast cancer cells, and human umbilical vein endothelial cells (HUVECs) and studied their effects on cell migration, invasion and angiogenesis. Aptamer expressing MDA-MB-231 cells exhibited a decrease in cell migration and invasion. Additionally, intracellular PAI-1 and urokinase plasminogen activator (uPA) protein levels decreased, while the PAI-1/uPA complex increased. Moreover, a significant decrease in endothelial tube formation in HUVECs transfected with the aptamers was observed. In contrast, conditioned media from aptamer transfected MDA-MB-231 cells displayed a slight pro-angiogenic effect. Collectively, our study shows that expressing functional aptamers inside breast and endothelial cells is feasible and may exhibit therapeutic potential.

Sense-antisense gene-pairs in breast cancer and associated pathological pathways

More than 30% of human protein-coding genes form hereditary complex genome architectures composed of sense-antisense (SA) gene pairs (SAGPs) transcribing their RNAs from both strands of a given locus. Such architectures represent important novel components of genome complexity contributing to gene expression deregulation in cancer cells. Therefore, the architectures might be involved in cancer pathways and, in turn, be used for novel drug targets discovery. However, the global roles of SAGPs in cancer pathways has not been studied. Here we investigated SAGPs associated with breast cancer (BC)-related pathways using systems biology, prognostic survival and experimental methods. Gene expression analysis identified 73 BC-relevant SAGPs that are highly correlated in BC. Survival modelling and metadata analysis of the 1161 BC patients allowed us to develop a novel patient prognostic grouping method selecting the 12 survival-significant SAGPs. The qRT-PCR-validated 12-SAGP prognostic signature reproducibly stratified BC patients into low- and high-risk prognostic subgroups. The 1381 SAGP-defined differentially expressed genes common across three studied cohorts were identified. The functional enrichment analysis of these genes revealed the GABPA gene network, including BC-relevant SAGPs, specific gene sets involved in cell cycle, spliceosomal and proteasomal pathways. The co-regulatory function of GABPA in BC cells was supported using siRNA knockdown studies. Thus, we demonstrated SAGPs as the synergistically functional genome architectures interconnected with cancer-related pathways and associated with BC patient clinical outcomes. Taken together, SAGPs represent an important component of genome complexity which can be used to identify novel aspects of coordinated pathological gene networks in cancers.

High throughput sequencing analysis of RNA libraries reveals the influences of initial library and PCR methods on SELEX efficiency

The systemic evolution of ligands by exponential enrichment (SELEX) technique is a powerful and effective aptamer-selection procedure. However, modifications to the process can dramatically improve selection efficiency and aptamer performance. For example, droplet digital PCR (ddPCR) has been recently incorporated into SELEX selection protocols to putatively reduce the propagation of byproducts and avoid selection bias that result from differences in PCR efficiency of sequences within the random library. However, a detailed, parallel comparison of the efficacy of conventional solution PCR versus the ddPCR modification in the RNA aptamer-selection process is needed to understand effects on overall SELEX performance. In the present study, we took advantage of powerful high throughput sequencing technology and bioinformatics analysis coupled with SELEX (HT-SELEX) to thoroughly investigate the effects of initial library and PCR methods in the RNA aptamer identification. Our analysis revealed that distinct “biased sequences” and nucleotide composition existed in the initial, unselected libraries purchased from two different manufacturers and that the fate of the “biased sequences” was target-dependent during selection. Our comparison of solution PCR- and ddPCR-driven HT-SELEX demonstrated that PCR method affected not only the nucleotide composition of the enriched sequences, but also the overall SELEX efficiency and aptamer efficacy.

Cellular Delivery of RNA Nanoparticles

RNA nanostructures can be programmed to exhibit defined sizes, shapes and stoichiometries from naturally occurring or de novo designed RNA motifs. These constructs can be used as scaffolds to attach functional moieties, such as ligand binding motifs or gene expression regulators, for nanobiology applications. This review is focused on four areas of importance to RNA nanotechnology: the types of RNAs of particular interest for nanobiology, the assembly of RNA nanoconstructs, the challenges of cellular delivery of RNAs in vivo, and the delivery carriers that aid in the matter. The available strategies for the design of nucleic acid nanostructures, as well as for formulation of their carriers, make RNA nanotechnology an important tool in both basic research and applied biomedical science.

Strategies of targeting the extracellular domain of RON tyrosine kinase receptor for cancer therapy and drug delivery

PURPOSE

Cancer is one of the most important life-threatening diseases in the world. The current efforts to combat cancer are being focused on molecular-targeted therapies. The main purpose of such approaches is based on targeting cancer cell-specific molecules to minimize toxicity for the normal cells. RON (Recepteur d'Origine Nantais) tyrosine kinase receptor is one of the promising targets in cancer-targeted therapy and drug delivery.

METHODS

In this review, we will summarize the available agents against extracellular domain of RON with potential antitumor activities.

RESULTS

The presented antibodies and antibody drug conjugates against RON in this review showed wide spectrum of in vitro and in vivo antitumor activities promising the hope for them entering the clinical trials.

CONCLUSION

Due to critical role of extracellular domain of RON in receptor activation, the development of therapeutic agents against this region could lead to fruitful outcome in cancer therapy.

Co-targeting EGFR and survivin with a bivalent aptamer-dual siRNA chimera effectively suppresses prostate cancer

Current targeted therapies using small kinase inhibitors and antibodies have limited efficacy in treating prostate cancer (PCa), a leading cause of cancer death in American men. We have developed a novel strategy by engineering an RNA-based aptamer-siRNA chimera, in which a bivalent aptamer specifically binds prostate-specific membrane antigen (PSMA) via an antibody-like structure to promote siRNA internalization in PCa cells, and two siRNAs specific to EGFR and survivin are fused between two aptamers. The chimera is able to inhibit EGFR and survivin simultaneously and induce apoptosis effectively in vitro and in vivo. In the C4-2 PCa xenograft model, the treatment with the chimera significantly suppresses tumor growth and angiogenesis. The inhibition of angiogenesis is mediated by an EGFR-HIF1α-VEGF-dependent mechanism. Our results support that the bivalent aptamer-driven delivery of two siRNAs could be a new combination therapeutic strategy to effectively inhibit multiple and conventionally "undruggable" targets.

Exploring the binding of d(GGGT)4 to the HIV-1 integrase: An approach to investigate G-quadruplex aptamer/target protein interactions

The aptamer d(GGGT)4 (T30923 or T30695) forms a 5'-5' dimer of two stacked parallel G-quadruplexes, each characterized by three G-tetrads and three single-thymidine reversed-chain loops. This aptamer has been reported to exhibit anti-HIV activity by targeting the HIV integrase, a viral enzyme responsible for the integration of viral DNA into the host-cell genome. However, information concerning the aptamer/target interaction is still rather limited. In this communication we report microscale thermophoresis investigations on the interaction between the HIV-1 integrase and d(GGGT)4 aptamer analogues containing abasic sites singly replacing thymidines in the original sequence. This approach has allowed the identification of which part of the aptamer G-quadruplex structure is mainly involved in the interaction with the protein.

The delivery of therapeutic oligonucleotides

The oligonucleotide therapeutics field has seen remarkable progress over the last few years with the approval of the first antisense drug and with promising developments in late stage clinical trials using siRNA or splice switching oligonucleotides. However, effective delivery of oligonucleotides to their intracellular sites of action remains a major issue. This review will describe the biological basis of oligonucleotide delivery including the nature of various tissue barriers and the mechanisms of cellular uptake and intracellular trafficking of oligonucleotides. It will then examine a variety of current approaches for enhancing the delivery of oligonucleotides. This includes molecular scale targeted ligand-oligonucleotide conjugates, lipid- and polymer-based nanoparticles, antibody conjugates and small molecules that improve oligonucleotide delivery. The merits and liabilities of these approaches will be discussed in the context of the underlying basic biology.

Status and Prospects of Aptamers as Drug Components

The unique properties of nucleic acid aptamers and their suitability to therapeutic applications have attracted the attention of researchers for more than 2 decades. Aptamers exhibit significant advantages relative to antibody-based therapeutics and can serve dual roles as either the therapeutic agent itself or a targeting modality. Despite this intense research interest, aptamers have been slow to reach the clinic, partly due to practical limitations that can be overcome by rational chemical modifications and ingenious aptamer selection approaches. This review highlights the latest efforts to use aptamers in therapeutic applications, the key properties of aptamers that can be exploited, the aptamers that are currently in clinical trials, as well as speculation on the future of aptamers in the field of nanomedicine.

Structural computational modeling of RNA aptamers

RNA aptamers represent an emerging class of biologics that can be easily adapted for personalized and precision medicine. Several therapeutic aptamers with desirable binding and functional properties have been developed and evaluated in preclinical studies over the past 25years. However, for the majority of these aptamers, their clinical potential has yet to be realized. A significant hurdle to the clinical adoption of this novel class of biologicals is the limited information on their secondary and tertiary structure. Knowledge of the RNA's structure would greatly facilitate and expedite the post-selection optimization steps required for translation, including truncation (to reduce costs of manufacturing), chemical modification (to enhance stability and improve safety) and chemical conjugation (to improve drug properties for combinatorial therapy). Here we describe a structural computational modeling methodology that when coupled to a standard functional assay, can be used to determine key sequence and structural motifs of an RNA aptamer. We applied this methodology to enable the truncation of an aptamer to prostate specific membrane antigen (PSMA) with great potential for targeted therapy that had failed previous truncation attempts. This methodology can be easily applied to optimize other aptamers with therapeutic potential.

Ex Vivo and In Vivo Imaging and Biodistribution of Aptamers Targeting the Human Matrix MetalloProtease-9 in Melanomas

The human Matrix MetalloProtease-9 (hMMP-9) is overexpressed in tumors where it promotes the release of cancer cells thus contributing to tumor metastasis. We raised aptamers against hMMP-9, which constitutes a validated marker of malignant tumors, in order to design probes for imaging tumors in human beings. A chemically modified RNA aptamer (F3B), fully resistant to nucleases was previously described. This compound was subsequently used for the preparation of F3B-Cy5, F3B-S-acetylmercaptoacetyltriglycine (MAG) and F3B-DOTA. The binding properties of these derivatives were determined by surface plasmon resonance and electrophoretic mobility shift assay. Optical fluorescence imaging confirmed the binding to hMMP-9 in A375 melanoma bearing mice. Quantitative biodistribution studies were performed at 30 min, 1h and 2 h post injection of 99mTc-MAG-aptamer and 111In-DOTA-F3B. 99mTc radiolabeled aptamer specifically detected hMMP-9 in A375 melanoma tumors but accumulation in digestive tract was very high. Following i.v. injection of 111In-DOTA-F3B, high level of radioactivity was observed in kidneys and bladder but digestive tract uptake was very limited. Tumor uptake was significantly (student t test, p<0.05) higher for 111In-DOTA-F3B with 2.0%ID/g than for the 111In-DOTA-control oligonucleotide (0.7%ID/g) with tumor to muscle ratio of 4.0. Such difference in tumor accumulation has been confirmed by ex vivo scintigraphic images performed at 1h post injection and by autoradiography, which revealed the overexpression of hMMP-9 in sections of human melanomas. These results demonstrate that F3B aptamer is of interest for detecting hMMP-9 in melanoma tumor.