Triplex-forming Oligonucleotides Research Articles

Unraveling DNA Triplex Assembly: Mass Spectrometric Investigation of Modified Triplex Forming Oligonucleotides for Enhanced Gene Targeting.

Deoxyribonucleic acid triplexes have potential roles in a range of biological processes involving gene and transcriptional regulation. A major challenge in exploiting the formation of these higher-order structures to target genes in vivo is their low stability, which is dependent on many factors including the length and composition of bases in the sequence. Here, different DNA base modifications have been explored, primarily using native mass spectrometry, in efforts to enable stronger binding between the triplex forming oligonucleotide (TFO) and duplex target sites. These modifications can also be used to overcome pyrimidine interruptions in the duplex sequence in promoter regions of genomes, to expand triplex target sequences for antigene therapies. Using model sequences with a single pyrimidine interruption, triplex forming oligonucleotides containing locked nucleic acid base modifications were shown to have a higher triplex binding propensity than DNA-only and dSpacer-containing TFOs. However, the triplex forming ability of these systems was limited by the competitive formation of multiple higher order assemblies. Triplex forming sequences that correspond to specific gene targets from the Pseudomonas aeruginosa genome were also investigated, with LNA-containing TFOs the only variant able to form triplex using these sequences. This work indicates the advantages of utilizing synthetically modified TFOs to form triplex assemblies in vivo for potential therapeutic applications and highlights the advantages of native mass spectrometry for the study of their formation.

Comparison of classical Machine Learning-based algorithms to predict Triplex Forming Oligonucleotides

Machine learning algorithms can be utilized to tackle genomic challenges in biological systems, such as identifying therapeutic targets for drug development and searching for effective treatments for chronic diseases like cancer. Triplex-forming oligonucleotides (TFOs) can recognize specific sites in the major groove of duplex DNA sequences, aiding in the identification of therapeutic targets via computational methods. This study aims to compare the performance of five classical machine learning algorithms—Support Vector Machine (SVM), k-Nearest Neighbours (kNN), Decision Tree (DT), Random Forest (RF), and eXtreme Gradient Boosting (XGBoost)—in classifying single-stranded DNA into TFOs. Three datasets were created from an oligo library targeting the supF gene, developed by Kaufmann et al., and used to train the algorithms. The classifiers were optimized through hyperparameter tuning and their performance was evaluated using accuracy, precision, recall, and F1-score metrics. SVM and kNN achieved less than 90 % accuracy, while DT, RF, and XGBoost, which used tree-based methods, attained over 90 % accuracy. The XGBoost model showed the best performance with over 96 % accuracy in classifying single-stranded DNA into TFOs. This study demonstrates that supervised machine learning techniques are effective for accurately classifying single-stranded DNA into TFOs.

The Development of Non-natural Type Nucleoside to Stabilize Triplex DNA Formation against CG and TA Inversion Site.

Based on the sequence-specific recognition of target duplex DNA by triplexforming oligonucleotides (TFOs) at the major groove side, the antigene strategy has been exploited as a gene-targeting tool with considerable attention. Triplex DNA is formed via the specific base triplets by the Hoogsteen or reverse Hoogsteen hydrogen bond interaction between TFOs and the homo-purine strand from the target duplex DNA, leading to the established sequence-specificity. However, the presence of inversion sites, which are known as non-natural nucleosides that can form satisfactory interactions with 2'- deoxythymidine (dT) and 2'-deoxycytidine (dC) in TA and CG base pairs in the target homo-purine DNA sequences, drastically restricts the formation of classically stable base triplets and even the triplex DNA. Therefore, the design of non-natural type nucleosides, which can effectively recognize CG or/and TA inversion sites with satisfactory selectivity, should be of great significance to expanding the triplex-forming sequence. Here, this review mainly provides a comprehensive review of the current development of novel nonnatural nucleosides to recognize CG or/and TA inversion sites in triplex DNA formation against double-strand DNA (dsDNA).

Introducing Triplex Forming Oligonucleotide into Loop-Mediated Isothermal Amplification for Developing a Lateral Flow Biosensor for Streptococci Detection.

Loop-mediated isothermal amplification (LAMP) technology is extensively utilized for the detection of infectious diseases owing to its rapid processing and high sensitivity. Nevertheless, conventional LAMP signaling methods frequently suffer from a lack of sequence specificity. This study integrates a triplex-forming oligonucleotide (TFO) probe into the LAMP process to enhance sequence specificity. This TFO-LAMP technique was applied for the detection of Group B Streptococcus (GBS). The TFO probe is designed to recognize a specific DNA sequence, termed the TFO targeting sequence (TTS), within the amplified product, facilitating detection via fluorescent instrumentation or lateral flow biosensors. A screening method was developed to identify TFO sequences with high affinity to integrate TFO into LAMP, subsequently incorporating a selected TTS into an LAMP primer. In the TFO-LAMP assay, a FAM-labeled TFO is added to target the TTS. This TFO can be captured by an anti-FAM antibody on lateral flow test strips, thus creating a nucleic acid testing biosensor. The efficacy of the TFO-LAMP assay was confirmed through experiments with specimens spiked with varying concentrations of GBS, demonstrating 85% sensitivity at 300 copies and 100% sensitivity at 30,000 copies. In conclusion, this study has successfully developed a TFO-LAMP technology that offers applicability in lateral flow biosensors and potentially other biosensor platforms.

Functionalizing DNA Origami by Triplex-Directed Site-Specific Photo-Cross-Linking.

Here, we present a cross-linking approach to covalently functionalize and stabilize DNA origami structures in a one-pot reaction. Our strategy involves adding nucleotide sequences to adjacent staple strands, so that, upon assembly of the origami structure, the extensions form short hairpin duplexes targetable by psoralen-labeled triplex-forming oligonucleotides bearing other functional groups (pso-TFOs). Subsequent irradiation with UVA light generates psoralen adducts with one or both hairpin staples leading to site-specific attachment of the pso-TFO (and attached group) to the origami with ca. 80% efficiency. Bis-adduct formation between strands in proximal hairpins further tethers the TFO to the structure and generates "superstaples" that improve the structural integrity of the functionalized complex. We show that directing cross-linking to regions outside of the origami core dramatically reduces sensitivity of the structures to thermal denaturation and disassembly by T7 RNA polymerase. We also show that the underlying duplex regions of the origami core are digested by DNase I and thus remain accessible to read-out by DNA-binding proteins. Our strategy is scalable and cost-effective, as it works with existing DNA origami structures, does not require scaffold redesign, and can be achieved with just one psoralen-modified oligonucleotide.

TTSBBC: triplex target site biomarkers and barcodes in cancer.

The technology of triplex-forming oligonucleotides (TFOs) provides an approach to manipulate genes at the DNA level. TFOs bind to specific sites on genomic DNA, creating a unique intermolecular triple-helix DNA structure through Hoogsteen hydrogen bonding. This targeting by TFOs is site-specific and the locations TFOs bind are referred to as TFO target sites (TTS). Triplexes have been observed to selectively influence gene expression, homologous recombination, mutations, protein binding, and DNA damage. These sites typically feature a poly-purine sequence in duplex DNA, and the characteristics of these TTS sequences greatly influence the formation of the triplex. We introduce TTSBBC, a novel analysis and visualization platform designed to explore features of TTS sequences to enable users to design and validate TTSs. The web server can be freely accessed at https://kowalski-labapps.dellmed.utexas.edu/TTSBBC/.

Site-Selective Photo-Crosslinking of Stilbene Pairs in a DNA Duplex Mediated by Ruthenium Photocatalyst.

We herein report a method for site-selective photo-crosslinking of a DNA duplex. A stilbene pair was introduced into a DNA duplex and a ruthenium complex was conjugated with a triplex-forming oligonucleotide. We demonstrated that [2+2] photocycloaddition of the stilbene pair occurred upon irradiation with visible light when the ruthenium complex was in close proximity due to triplex formation. No reaction occurred when the ruthenium complex was not in proximity to the stilbene pair. The wavelength of visible light used was of lower energy than the wavelength of UV light necessary for direct excitation of stilbene. Quantum chemical calculation indicated that ruthenium complex catalyzed the photocycloaddition via triplet-triplet energy transfer. Site selectivity of this photo-crosslinking system was evaluated using a DNA duplex bearing two stilbene pairs as a substrate; we showed that the site of crosslinking was precisely regulated by the sequence of the oligonucleotide linked to the ruthenium complex. Since this method does not require orthogonal photoresponsive molecules, it will be useful in construction of complex photoresponsive DNA circuits, nanodevices and biological tools.

Modular Synthesis of Methyl-Substituted Novel Psoralen N-Hydroxysuccinimide Esters and Evaluation of DNA Photocrosslinking Properties of the Corresponding Triplex-Forming Oligonucleotide Conjugates

AbstractPsoralen-conjugated triplex-forming oligonucleotides (Ps-TFOs) have been used to induce DNA mutations or to suppress gene expression through the formation of crosslinked products with DNA in a sequence-specific manner. Psoralen can crosslink with DNA at its furan-ring and/or pyrone-ring side, yielding either a monoadduct or diadduct (interstrand crosslinking) product. The differences in the crosslinked structures of Ps-TFOs with the target DNAs are closely related to the changes in the biological outcomes induced by the Ps-TFOs. However, only a few reports have discussed the photocrosslinking properties of Ps-TFOs. The photocrosslinking properties of Ps-TFOs with structurally diverse psoralen derivatives remain elusive. Herein, we report the modular synthesis of novel methyl-substituted psoralen N-hydroxysuccinimide (NHS) esters. By using these esters, the effect of the methyl substituent of psoralen on the photocrosslinking of the corresponding Ps-TFOs was examined. The amount of the diadduct product was significantly reduced in the presence of methyl substituents at the C-3 and C-4 positions, while the total amount of photocrosslinking product was maintained. This work demonstrates the possibility of controlling the crosslinked product of Ps-TFOs by introducing methyl groups into psoralen: this ability to manipulate the product is an important factor in the biological applications of Ps-TFOs.

Development of an Artificial Nucleic Acid Skeleton Allowing for Unnatural-Type Triplex DNA Formation with Duplex DNA Having a TA Inversion Site.

Triplex DNA formation has generated much interest as a genomic targeting tool that directly targets duplex DNA. However, fundamental limitations in the base pairs of target duplex DNA sequences that can form stable triplex DNA have limited the application. Recently, we have reported on the recognition of CG and 5mCG base pairs by artificial nucleic acid derivatives with a 2'-deoxynebularine skeleton. Therefore, we attempted to explore the basic skeleton that is important for the development of new artificial nucleic acids allowing for the recognition of TA base pairs. In this study, we focused on a benzimidazole skeleton and introduced a hydroxyl group to enable one-point hydrogen bonding. We have synthesized artificial nucleoside analogues with hydroxyl group on the benzimidazole and incorporated their amidite derivatives into triplex forming oligonucleotides (TFOs). The gel shift assay was performed to evaluate the triplex DNA formation ability of synthesized TFOs, and TFOs containing hydroxybenzimidazole were successfully recognized TA base pairs for all four different sequences. Moreover, compared to the results for the TFOs containing benzimidazole, which suggested hydrogen bonding formation at the hydroxyl group. Therefore, hydroxybenzimidazole would be an important artificial nucleic acid skeleton for TA base pair recognition.

Adaptive DNA amplification of synthetic gene circuit opens a way to overcome cancer chemoresistance.

Drug resistance continues to impede the success of cancer treatments, creating a need for experimental model systems that are broad, yet simple, to allow the identification of mechanisms and novel countermeasures applicable to many cancer types. To address these needs, we investigated a set of engineered mammalian cell lines with synthetic gene circuits integrated into their genome that evolved resistance to Puromycin. We identified DNA amplification as the mechanism underlying drug resistance in 4 out of 6 replicate populations. Triplex-forming oligonucleotide (TFO) treatment combined with Puromycin could efficiently suppress the growth of cell populations with DNA amplification. Similar observations in human cancer cell lines suggest that TFOs could be broadly applicable to mitigate drug resistance, one of the major difficulties in treating cancer.

Recent Advancements in Development and Therapeutic Applications of Genome-Targeting Triplex-Forming Oligonucleotides and Peptide Nucleic Acids.

Recent developments in artificial nucleic acid and drug delivery systems present possibilities for the symbiotic engineering of therapeutic oligonucleotides, such as antisense oligonucleotides (ASOs) and small interfering ribonucleic acids (siRNAs). Employing these technologies, triplex-forming oligonucleotides (TFOs) or peptide nucleic acids (PNAs) can be applied to the development of symbiotic genome-targeting tools as well as a new class of oligonucleotide drugs, which offer conceptual advantages over antisense as the antigene target generally comprises two gene copies per cell rather than multiple copies of mRNA that are being continually transcribed. Further, genome editing by TFOs or PNAs induces permanent changes in the pathological genes, thus facilitating the complete cure of diseases. Nuclease-based gene-editing tools, such as zinc fingers, CRISPR-Cas9, and TALENs, are being explored for therapeutic applications, although their potential off-target, cytotoxic, and/or immunogenic effects may hinder their in vivo applications. Therefore, this review is aimed at describing the ongoing progress in TFO and PNA technologies, which can be symbiotic genome-targeting tools that will cause a near-future paradigm shift in drug development.

Post-Synthetic Modification of Triplex-Forming Oligonucleotides Containing 2-Aminoethyl-2'-Deoxynebularine Derivatives.

This article describes the detailed synthetic protocol for the preparation of oligonucleotides containing 2-guanidinoethyl-2'-deoxynebularine and 2-ureidoethyl-2'-deoxynebularine nucleoside derivatives. These derivatives are obtained by a post-synthetic modification of triplex-forming oligonucleotides (TFOs) containing 2-aminoethyl-2'-deoxynebularine, which is useful for forming stable triplex DNA with duplex DNA sequences containing 5m CG and CG interrupting sites. The hydroxyl groups of the sugar moiety of commercially available 2'-deoxyguanosine are acetyl-protected, the 6-position is chlorinated and reduced to give a 2-substituted nebularine derivative, and then the sugar moiety is deprotected. The hydroxyl groups of the sugar moiety are silyl-protected and the amino group at the 2-position is iodinated before being coupled with diethyl malonate. The ethyl ester is reduced and the resulting alcohol converted to an amino group for protection. The compound is then converted to a phosphoramidite unit and incorporated into a TFO. Subsequent modification of the aminoethyl group on the TFO completes the synthesis of the oligonucleotides containing 2-guanidinoethyl-2'-deoxynebularine and 2-ureidoethyl-2'-deoxynebularine. © 2023 Wiley Periodicals LLC. Basic Protocol 1: Preparation of the phosphoramidite unit of the 2-aminoethyl-2'-deoxynebularine derivative (14) Basic Protocol 2: Post-synthetic modification of oligonucleotides containing 2-aminoethyl-2'-deoxynebularine derivatives Basic Protocol 3: Determination of the triplex-forming ability of oligonucleotides containing 2-aminoethyl-2'-deoxynebularine derivatives.

Development and Crosslinking Properties of Psoralen-Conjugated Triplex-Forming Oligonucleotides as Antigene Tools Targeting Genome DNA.

Psoralen-conjugated triplex-forming oligonucleotides (Ps-TFOs) have been utilized for genome editing and anti-gene experiments for over thirty years. However, the research on Ps-TFOs employing artificial nucleotides is still limited, and their photo-crosslinking properties have not been thoroughly investigated in relation to biological activities. In this study, we extensively examined the photo-crosslinking properties of Ps-TFOs to provide fundamental insights for future Ps-TFO design. We developed novel Ps-TFOs containing 2'-O,4'-C-methylene-bridged nucleic acids (Ps-LNA-mixmer) and investigated their photo-crosslinking properties using stable cell lines that express firefly luciferase constitutively to evaluate the anti-gene activities of Ps-LNA-mixmer. As a result, Ps-LNA-mixmer successfully demonstrated suppression activity, and we presented the first-ever correlation between photo-crosslinking properties and their activities. Our findings also indicate that the photo-crosslinking process is insufficient under cell irradiation conditions (365 nm, 2 mW/cm2 , 60 min). Therefore, our results highlight the need to develop new psoralen derivatives that are more reactive under cell irradiation conditions.

TFOFinder: Python program for identifying purine-only double-stranded stretches in the predicted secondary structure(s) of RNA targets.

Nucleic acid probes are valuable tools in biology and chemistry and are indispensable for PCR amplification of DNA, RNA quantification and visualization, and downregulation of gene expression. Recently, triplex-forming oligonucleotides (TFO) have received increased attention due to their improved selectivity and sensitivity in recognizing purine-rich double-stranded RNA regions at physiological pH by incorporating backbone and base modifications. For example, triplex-forming peptide nucleic acid (PNA) oligomers have been used for imaging a structured RNA in cells and inhibiting influenza A replication. Although a handful of programs are available to identify triplex target sites (TTS) in DNA, none are available that find such regions in structured RNAs. Here, we describe TFOFinder, a Python program that facilitates the identification of intramolecular purine-only RNA duplexes that are amenable to forming parallel triple helices (pyrimidine/purine/pyrimidine) and the design of the corresponding TFO(s). We performed genome- and transcriptome-wide analyses of TTS in Drosophila melanogaster and found that only 0.3% (123) of total unique transcripts (35,642) show the potential of forming 12-purine long triplex forming sites that contain at least one guanine. Using minimization algorithms, we predicted the secondary structure(s) of these transcripts, and using TFOFinder, we found that 97 (79%) of the identified 123 transcripts are predicted to fold to form at least one TTS for parallel triple helix formation. The number of transcripts with potential purine TTS increases when the strict search conditions are relaxed by decreasing the length of the probe or by allowing up to two pyrimidine inversions or 1-nucleotide bulge in the target site. These results are encouraging for the use of modified triplex forming probes for live imaging of endogenous structured RNA targets, such as pre-miRNAs, and inhibition of target-specific translation and viral replication.

Environmentally Controlled Oscillator with Triplex Guided Displacement of DNA Duplexes.

The use of DNA triplex association is advantageous for the reconfiguration of dynamic DNA nanostructures through pH alteration and can provide environmental control for both structural changes and molecular signaling. The combination of pH-induced triplex-forming oligonucleotide (TFOs) binding with toehold-mediated strand displacement has recently garnered significant attention in the field of structural DNA nanotechnology. While most previous studies use single-stranded DNA to displace or replace TFOs within the triplex, here we demonstrate that pH alteration allows a DNA duplex, with a toehold assistance, to displace TFOs from the components of another DNA duplex. We examined the dependence of this process on toehold length and show that the pH changes allow for cyclic oscillations between two molecular formations. We implemented the duplex/triplex design onto the surface of 2D DNA origami in the form outlining binary digits 0 or 1 and verified the oscillatory conformational changes between the two formations with atomic force microscopy.

Folding Double-Stranded DNA into Designed Shapes with Triplex-Forming Oligonucleotides.

The compaction and organization of genomic DNA is a central mechanism in eukaryotic cells, but engineered architectural control over double-stranded DNA (dsDNA) is notably challenging. Here, long dsDNA templates are folded into designed shapes via triplex-mediated self-assembly. Triplex-forming oligonucleotides (TFOs) bind purines in dsDNA via normal or reverse Hoogsteen interactions. In the triplex origami methodology, these non-canonical interactions are programmed to compact dsDNA (linear or plasmid) into well-defined objects, which demonstrate a variety of structural features: hollow and raster-filled, single- and multi-layered, with custom curvatures and geometries, and featuring lattice-free, square-, or honeycomb-pleated internal arrangements. Surprisingly, the length of integrated and free-standing dsDNA loops can be modulated with near-perfect efficiency; from hundreds down to only six bp (2nm). The inherent rigidity of dsDNA promotes structural robustness and non-periodic structures of almost 25.000nt are therefore formed with fewer unique starting materials, compared to other DNA-based self-assembly methods. Densely triplexed structures also resist degradation by DNase I. Triplex-mediated dsDNA folding is methodologically straightforward and orthogonal to Watson-Crick-based methods. Moreover, it enables unprecedented spatial control over dsDNA templates. This article is protected by copyright. All rights reserved.

Abstract 3895: New potential mechanism of mnx1-as1 in the regulation of the carboplatin chemoresistant phenotype in ovarian cancer cell lines

Abstract Introduction: Ovarian cancer (OC) is one of the most lethal diseases in the female population worldwide, being considered by 2020 the eighth most common type of cancer and the eighth cause of cancer death in that population. The most widely used chemotherapy treatment is based on the application of platinum based drugs, carboplatin (CBDCA) being one of the most common, in combination with taxanes and cisplatin. Unfortunately, a high percentage of the population relapses shortly after chemotherapy treatment, presenting a drug resistant phenotype. This phenotype reduces overall survival in patients with OC. In this context, various mechanisms have been investigated to understand and study these chemoresistant phenotypes. In the last decade, lncRNAs have been identified in multiple biological processes, including the development of drug-resistant phenotypes in malignant tumors, however, little is known about their role in carboplatin resistance in OC. This study seeks to characterize the effect of lncRNA expression on the chemoresistant phenotype and its potential molecular mechanism involved. Materials and Methods: Ovarian cancer cell lines corresponding to: A2780-R-CBDCA, A2780-P, UCI-101, OVCAR3 and SKOV3 were used. Drug susceptibility assays were performed using MTT. Relative expression was performed via RTqPCR. RNAseq was performed on a CBDCA resistance model in vitro using the Illumina HiSeq 4000 platform. Gene Ontology (GO) was analyzed using ClueGO. Gene set enrichment analysis (GSEA) was performed to define enriched biological pathways. Triplexator was used to predict the triplex forming oligonucleotides (TFO) and triplex target sites (TTS) that may be involved in the formation of RNA-DNA triplexes. Results: RNAseq analysis showed 156 differentially expressed protein coding genes (DEGs). The most enriched and deregulated signaling pathway was Wnt/β-catenin. In this context, several regulators of this pathway were found to be altered, including sFRP1, sFRP4, PCDHB6, CTNNA2, DACT1, PCDHB6, WNT3A, and CER1. In addition, 17 lncRNAs involved in CDBCA resistance were found to be deregulated. In this sense, MNX1-AS1 showed high levels of expression in CBDCA resistant cell lines. Interestingly, it has been shown that MNX1-AS1 has the ability to form a triplex with the PCDHB6 gene, which is a tumor suppressor gene and whose expression was found to be decreased in CBDCA resistant cell lines. Conclusions: Our results indicate that MNX1-AS1 expression could contribute to the modulation of platinum drug resistance through regulation of PCDHB6 expression via triplexes formation in OC. This finding could explain a new mechanism in CBDCA resistance in OC. Citation Format: Tamara Alejandra Viscarra Alvarez, Kurt Leopoldo Buchegger Mena, Daniela Inés León Garrido, Carmen Gloria Ili Gangas, Jorge Sapunar Zenteno, Marcela Berrios Flores, Ramón Silva Pezoa, Sindy Paola Cabarca Barreto, Priscilla Brebi Mieville. New potential mechanism of mnx1-as1 in the regulation of the carboplatin chemoresistant phenotype in ovarian cancer cell lines. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 3895.

The Formation and Displacement of Ordered DNA Triplexes in Self-Assembled Three-Dimensional DNA Crystals.

Reconfigurable structures engineered through DNA hybridization and self-assembly offer both structural and dynamic applications in nanotechnology. Here, we have demonstrated that strand displacement of triplex-forming oligonucleotides (TFOs) can be translated to a robust macroscopic DNA crystal by coloring the crystals with covalently attached fluorescent dyes. We show that three different types of triplex strand displacement are feasible within the DNA crystals and the bound TFOs can be removed and/or replaced by (a) changing the pH from 5 to 7, (b) the addition of the Watson-Crick complement to a TFO containing a short toehold, and (c) the addition of a longer TFO that uses the duplex edge as a toehold. We have also proved by X-ray diffraction that the structure of the crystals remains as designed in the presence of the TFOs.

Inhibition of transcription and antiproliferative effects in a cancer cell line using antigene oligonucleotides containing artificial nucleoside analogues.

Antigene methods are promising novel therapeutic approaches to suppress abnormal gene expression. One of these methods inhibits transcription by forming triplex DNA against duplex DNA. However, by using natural-type triplex-forming oligonucleotides (TFOs), stable triplex formation is limited to homopurine and homopyrimidine strands in targeted duplex DNA. We recently developed artificial nucleoside analogues with the ability to recognize CG and TA inversion sites. We successfully formed stable unnatural-type triplex DNA for duplex DNA containing a CG base pair and extended the target sequence using TFOs containing 2-amino-3-methylpyridinyl pseudo-dC (3MeAP-ΨdC). Therefore, this present study investigated triplex-forming regions and synthesized antigene TFOs containing 3MeAP-ΨdC. Some of the synthesized antigene TFOs reduced transcription products and inhibited cell proliferation in several types of cultured cancer cells. The antigene effects of antigene TFOs containing artificial nucleic acids were markedly stronger than those of natural-type TFOs, and these results clearly demonstrated the usefulness of incorporating artificial nucleic acids within TFOs.

Triplex-forming oligonucleotides as an anti-gene technique for cancer therapy.

Triplex-forming oligonucleotides (TFOs) can bind to the major groove of double-stranded DNA with high specificity and affinity and inhibit gene expression. Triplex-forming oligonucleotides have gained prominence because of their potential applications in antigene therapy. In particular, the target specificity of triplex-forming oligonucleotides combined with their ability to suppress oncogene expression has driven their development as anti-cancer agents. So far, triplex-forming oligonucleotides have not been used for clinical treatment and seem to be gradually snubbed in recent years. But triplex-forming oligonucleotides still represent an approach to down-regulate the expression of the target gene and a carrier of active substances. Therefore, in the present review, we will introduce the characteristics of triplex-forming oligonucleotides and their anti-cancer research progress. Then, we will discuss the challenges in their application.