Targeting 24 bp within Telomere Repeat Sequences with Tandem Tetramer Pyrrole–Imidazole Polyamide Probes

Structural Studies of a Complex of a CAG/CTG Repeat Sequence-Specific Binding Molecule and A-A-Mismatch-Containing DNA

Triplet repeat diseases are caused by the abnormal elongation of repeated sequences comprising three bases. In particular, the elongation of CAG/CTG repeat sequences is thought to result in conditions such as Huntington's disease and myotonic dystrophy type 1. Although the causes of these diseases are known, fundamental treatments have not been established, and specific drugs are expected to be developed. Pyrrole imidazole polyamide (PIP) is a class of molecules that binds to the minor groove of the DNA duplex in a sequence-specific manner; because of this property, it shows promise in drug discovery applications. Earlier, it was reported that PIP designed to bind CAG/CTG repeat sequences suppresses the genes that cause triplet repeat diseases. In this study, we performed an X-ray crystal structure analysis of a complex of double-stranded DNA containing A-A mismatched base pairs and a cyclic-PIP that binds specifically to CAG/CTG sequences. Furthermore, the validity and characteristics of this structure were analyzed using in silico molecular modeling, ab initio energy calculations, gel electrophoresis, and surface plasmon resonance. With our direct observation using atomic force microscopy and DNA origami, we revealed that the PIP caused structural changes in the DNA strands carrying the expanded CAG/CTG repeat. Overall, our study provides new insight into PIP from a structural perspective.

Nucleic acid-based small molecules as targeted transcription therapeutics for immunoregulation

Transcription therapy is an emerging approach that centers on identifying the factors associated with the malfunctioning gene transcription machinery that causes diseases and controlling them with designer agents. Until now, the primary research focus in therapeutic gene modulation has been on small-molecule drugs that target epigenetic enzymes and critical signaling pathways. However, nucleic acid-based small molecules have gained popularity in recent years for their amenability to be pre-designed and realize operative control over the dynamic transcription machinery that governs how the immune system responds to diseases. Pyrrole-imidazole polyamides (PIPs) are well-established DNA-based small-molecule gene regulators that overcome the limitations of their conventional counterparts owing to their sequence-targeted specificity, versatile regulatory efficiency, and biocompatibility. Here, we emphasize the rational design of PIPs, their functional mechanisms, and their potential as targeted transcription therapeutics for disease treatment by regulating the immune response. Furthermore, we also discuss the challenges and foresight of this approach in personalized immunotherapy in precision medicine.

A cyclic pyrrole-imidazole polyamide reduces pathogenic RNA in CAG/CTG triplet repeat neurological disease models

Expansion of CAG and CTG (CWG) triplet repeats causes several inherited neurological diseases. The CWG repeat diseases are thought to involve complex pathogenic mechanisms through expanded CWG repeat-derived RNAs in a noncoding region and polypeptides in a coding region, respectively. However, an effective therapeutic approach has not been established for the CWG repeat diseases. Here, we show that a CWG repeat DNA-targeting compound, cyclic pyrrole-imidazole polyamide (CWG-cPIP), suppressed the pathogenesis of coding and noncoding CWG repeat diseases. CWG-cPIP bound to the hairpin form of mismatched CWG DNA, interfering with transcription elongation by RNA polymerase through a preferential activity toward repeat-expanded DNA. We found that CWG-cPIP selectively inhibited pathogenic mRNA transcripts from expanded CWG repeats, reducing CUG RNA foci and polyglutamine accumulation in cells from patients with myotonic dystrophy type 1 (DM1) and Huntington's disease (HD). Treatment with CWG-cPIP ameliorated behavioral deficits in adeno-associated virus-mediated CWG repeat-expressing mice and in a genetic mouse model of HD, without cytotoxicity or off-target effects. Together, we present a candidate compound that targets expanded CWG repeat DNA independently of its genomic location and reduces both pathogenic RNA and protein levels. CWG-cPIP may be used for the treatment of CWG repeat diseases and improvement of clinical outcomes.

Sequence-specific DNA labelling for fluorescence microscopy

The preservation of nucleus structure during microscopy imaging is a top priority for understanding chromatin organization, genome dynamics, and gene expression regulation. In this review, we summarize the sequence-specific DNA labelling methods that can be used for imaging in fixed and/or living cells without harsh treatment and DNA denaturation: (i) hairpin polyamides, (ii) triplex-forming oligonucleotides, (iii) dCas9 proteins, (iv) transcription activator-like effectors (TALEs) and (v) DNA methyltransferases (MTases). All these techniques are capable of identifying repetitive DNA loci and robust probes are available for telomeres and centromeres, but visualizing single-copy sequences is still challenging. In our futuristic vision, we see gradual replacement of the historically important fluorescence in situ hybridization (FISH) by less invasive and non-destructive methods compatible with live cell imaging. Combined with super-resolution fluorescence microscopy, these methods will open the possibility to look into unperturbed structure and dynamics of chromatin in living cells, tissues and whole organisms.

In silico study of HASDI (high-affinity selective DNA intercalator) as a new agent capable of highly selective recognition of the DNA sequence

Cancer as an acquired genetic disease is based on changes both in the genome itself and in transcription processes. Accordingly, it is at the DNA level that it makes sense to search for and design agents capable of effective and selective anticancer action. In this study, we used an iterative approach based on a molecular dynamics simulation to design a highly selective DNA-intercalating agent called HASDI. To confirm its selective affinity to DNA, we conducted two simulation experiments: HASDI in a complex with a DNA fragment of the EBNA1 gene (it targets 16 nucleotide pairs of this gene) and HASDI in a complex with a random DNA fragment of the KCNH2 gene. The molecular dynamics simulation was carried out in the GROMACS 2019 package. The binding energy was calculated by gmx_MMPBSA 1.5.2. The further analysis was performed using the built-in utilities of GROMACS, gmx_MMPBSA and also XMGRACE and Pymol 1.8. As a result, we determined that the EBNA1-50nt/HASDI complex was stable throughout the whole simulation trajectory. HASDI, due to the presence of a linker modified depending on a specific pair of nitrogenous bases, formed an average of 32 hydrogen bonds with a sequence of 16 nucleotide pairs. Phenazine rings were stably intercalated every 2 base pairs. The root-mean-square deviation of HASDI in such a complex fluctuated around the value of 6.5 Å and had no tendency to increase. The calculated value of the binding free energy was - 235.3 ± 7.77 kcal/mol. The KCNH2-50nt/HASDI complex, as an example of the intercalation of the designed structure into a random part of the human genome, maintained the stability of its position at a level comparable to the EBNA1-50nt/HASDI complex. The phenazine rings were constantly intercalated in their original positions, and the root-mean-square deviation fluctuated around one value, although it had a tendency to chaotic changes. At the same time, this complex was characterized by 17-19 hydrogen bonds, on average, and the binding free energy was - 193.47 ± 14.09 kcal/mol. Moreover, the DNA duplex had local single-nucleotide melting in the region of the 4th linker. According to a significant decrease in the number of hydrogen bonds, a decrease in energy gain, as well as a decrease in the stability of the DNA duplex characteristic of the KCNH2-50nt/HASDI complex compared to the target EBNA1-50nt/HASDI complex, the molecule we designed can be considered a potentially selective DNA polyintercalating agent capable of relatively accurate recognition of 16 base pairs.

Serine-γPNA, Invader probes, and chimeras thereof: three probe chemistries that enable sequence-unrestricted recognition of double-stranded DNA

Three probe chemistries are evaluated with respect to thermal denaturation temperatures, UV-Vis and fluorescence characteristics, recognition of complementary and mismatched DNA hairpin targets, and recognition of chromosomal DNA targets in the context of non-denaturing fluorescence in situ hybridization (nd-FISH) experiments: (i) serine-γPNAs (SγPNAs), i.e., single-stranded peptide nucleic acid (PNA) probes that are modified at the γ-position with (R)-hydroxymethyl moieties, (ii) Invader probes, i.e., DNA duplexes modified with +1 interstrand zippers of 2'-O-(pyren-1-yl)methyl-RNA monomers, a molecular arrangement that results in a violation of the neighbor exclusion principle, and (iii) double-stranded chimeric SγPNAs:Invader probes, i.e., duplexes between complementary SγPNA and Invader strands, which are destabilized due to the poor compatibility between intercalators and PNA:DNA duplexes. Invader probes resulted in efficient, highly specific, albeit comparatively slow recognition of the model DNA hairpin targets. Recognition was equally efficient and faster with the single-stranded SγPNA probes but far less specific, whilst the double-stranded chimeric SγPNAs:Invader probes displayed recognition characteristics that were intermediate of the parent probes. All three probe chemistries demonstrated the capacity to target chromosomal DNA in nd-FISH experiments, with Invader probes resulting in the most favorable and consistent characteristics (signals in >90% of interphase nuclei against a low background and no signal in negative control experiments). These probe chemistries constitute valuable additions to the molecular toolbox needed for DNA-targeting applications.

Telomere-specific chromatin capture using a pyrrole-imidazole polyamide probe for the identification of proteins and non-coding RNAs

Background

Knowing chromatin components at a DNA regulatory element at any given time is essential for understanding how the element works during cellular proliferation, differentiation and development. A region-specific chromatin purification is an invaluable approach to dissecting the comprehensive chromatin composition at a particular region. Several methods (e.g., PICh, enChIP, CAPTURE and CLASP) have been developed for isolating and analyzing chromatin components. However, all of them have some shortcomings in identifying non-coding RNA associated with DNA regulatory elements.

Results

We have developed a new approach for affinity purification of specific chromatin segments employing an N-methyl pyrrole (P)-N-methylimidazole (I) (PI) polyamide probe, which binds to a specific sequence in double-stranded DNA via Watson–Crick base pairing as a minor groove binder. This new technique is called proteomics and RNA-omics of isolated chromatin segments (PI-PRICh). Using PI-PRICh to isolate mouse and human telomeric components, we found enrichments of shelterin proteins, the well-known telomerase RNA component (TERC) and telomeric repeat-containing RNA (TERRA). When PI-PRICh was performed for alternative lengthening of telomere (ALT) cells with highly recombinogenic telomeres, in addition to the conventional telomeric chromatin, we obtained chromatin regions containing telomeric repeat insertions scattered in the genome and their associated RNAs.

Conclusion

PI-PRICh reproducibly identified both the protein and RNA components of telomeric chromatin when targeting telomere repeats. PI polyamide is a promising alternative to simultaneously isolate associated proteins and RNAs of sequence-specific chromatin regions under native conditions, allowing better understanding of chromatin organization and functions within the cell.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13072-021-00421-8.

Sequence-Specific Control of Mitochondrial Gene Transcription Using Programmable Synthetic Gene Switches Called MITO-PIPs

Mitochondria possess multiple copies of mitochondrial DNA (mtDNA) that encode 37 genes and their transcription and replication get controlled by unique molecular codes different from that in the nuclear DNA. The mtDNA has been gaining increased attention as one of the critical therapeutic targets as mutations in them impair the function of mitochondria and cause mitochondrial diseases like MELAS. In this chapter, we describe artificial control of mitochondrial transcription based on mtDNA sequence information with a new type of compounds termed MITO-PIPs, which encompasses two domains: pyrrole-imidazole polyamide as DNA recognition domain and mitochondrial penetrating peptide as the mitochondria-targeting domain. Because MITO-PIPs are amenable to tunability, they can be expanded as a synthetic strategy to modulate mitochondrial gene(s) on demand.

Chemical Approaches to the Development of Artificial Transcription Factors Based on Pyrrole-Imidazole Polyamides

To maintain the functions of living organisms, cells have developed complex gene regulatory networks. Transcription factors have a central role in spatiotemporal control of gene expression and this has motivated us to develop artificial transcription factors that mimic their function. We found that three functions could be mimicked by applying our chemical approaches: i) efficient delivery into organelles that contain target DNA, ii) specific DNA binding to the target genomic region, and iii) regulation of gene expression by interaction with other transcription coregulators. We chose pyrrole-imidazole polyamides (PIPs), sequence-selective DNA binding molecules, as DNA binding domains, and have achieved each of the required functions by introducing other functional moieties. The developed artificial transcription factors have potential as chemical tools that can be used to artificially modulate gene expression to enable cell fate control and to correct abnormal gene regulation for therapeutic purposes.

A Near-Infrared Fluorogenic Pyrrole-Imidazole Polyamide Probe for Live-Cell Imaging of Telomeres

Telomeres are closely associated with cellular senescence and cancer. Although some techniques have been developed to label telomeres in living cells for study of telomere dynamics, few biocompatible near-infrared probes based on synthetic molecules have been reported. In this study, we developed a near-infrared fluorogenic pyrrole-imidazole polyamide probe (SiR-TTet59B) to visualize telomeres by conjugating a silicon-rhodamine (SiR) fluorophore with a tandem tetramer pyrrole-imidazole polyamide targeting 24 bp in the telomeric double-stranded (ds) DNA. SiR-TTet59B was almost nonfluorescent in water but increased its fluorescence dramatically on binding to telomeric dsDNA. Using a peptide-based delivery reagent, we demonstrated the specific and effective visualization of telomeres in living U2OS cells. Moreover, SiR-TTet59B could be used to observe the dynamic movements of telomeres during interphase and mitosis. This simple imaging method using a synthetic near-infrared probe could be a powerful tool for studies of telomeres and for diagnosis.

X-ray Crystal Structure of a Cyclic-PIP-DNA Complex in the Reverse-Binding Orientation

Elucidation of the details of the associating mode is one of the major concerns for the precise design of DNA-binding molecules that are used for gene regulation. Pyrrole-imidazole polyamide (PIP) is a well-established synthetic DNA-binding molecule that has sequence-specificity for duplex DNA. By the design of the sequence of pyrrole, imidazole, and other synthetic units, PIP is bound to the target DNA sequence selectively. Here, we report the X-ray crystal structure of newly synthesized chiral cyclic PIP (cPIP) complexed with DNA at 1.5 Å resolution and reveal that cPIP binds in the reverse orientation in the DNA minor groove. Analysis of the crystal structure revealed that the positions of the hydrogen bonds between the bases and the pyrrole-imidazole moieties of cPIP were similar for both forward- and reverse-binding orientations and that the distortion of the B-form DNA structure caused by cPIP binding was also similar for both orientations. We further found that new hydrogen bonds formed between the amino groups on the γ-turn units and DNA at both ends of the cPIP molecule. Additionally, by comparing the reverse PIP orientation with the forward orientation, we could clarify that the cause of the preference toward the reverse orientation in the S-form cPIP as used in this study is the overall conformation of the cPIP-DNA complex, particularly the configuration of hydrogen bonds. These results thus provide an explanation for the different stereoselectivity of cPIP binding in the minor groove.

The Road Not Taken with Pyrrole-Imidazole Polyamides: Off-Target Effects and Genomic Binding

The high sequence specificity of minor groove-binding N-methylpyrrole-N-methylimidazole polyamides have made significant advances in cancer and disease biology, yet there have been few comprehensive reports on their off-target effects, most likely as a consequence of the lack of available tools in evaluating genomic binding, an essential aspect that has gone seriously underexplored. Compared to other N-heterocycles, the off-target effects of these polyamides and their specificity for the DNA minor groove and primary base pair recognition require the development of new analytical methods, which are missing in the field today. This review aims to highlight the current progress in deciphering the off-target effects of these N-heterocyclic molecules and suggests new ways that next-generating sequencing can be used in addressing off-target effects.

Head-to-head comparison of LNA, MPγPNA, INA and Invader probes targeting mixed-sequence double-stranded DNA

Four probe chemistries are characterized and compared with respect to thermal denaturation temperatures (Tms), thermodynamic parameters associated with duplex formation, and recognition of mixed-sequence double-stranded (ds) DNA targets: (i) oligodeoxyribonucleotides (ONs) modified with Locked Nucleic Acid (LNA) monomers, (ii) MPγPNAs, i.e., single-stranded peptide nucleic acid (PNA) probes that are functionalized at the γ-position with (R)-diethylene glycol (mini-PEG, MP) moieties, (iii) Invader probes, i.e., DNA duplexes modified with +1 interstrand zipper arrangements of 2'-O-(pyren-1-yl)methyl-RNA monomers, and (iv) intercalating nucleic acids (INAs), i.e., DNA duplexes with opposing insertions of 1-O-(1-pyrenylmethyl)glycerol bulges. Invader and INA probes, which are designed to violate the nearest-neighbor exclusion principle, denature readily, whereas the individual probe strands display exceptionally high affinity towards complementary DNA (cDNA) as indicated by increases in Tms of up to 8 °C per modification. Optimized Invader and INA probes enable efficient and highly specific recognition of mixed-sequence dsDNA targets with self-complementary regions (C50 = 30-50 nM), whereas recognition is less efficient with LNA-modified ONs and fully modified MPγPNAs due to lower cDNA affinity (LNA) and a proclivity for dimerization (LNA and MPγPNA). A Cy3-labeled Invader probe is shown to stain telomeric DNA of individual chromosomes in metaphasic spreads under non-denaturing conditions with excellent specificity.

Control of Forward/Reverse Orientation Preference of Cyclic Pyrrole-Imidazole Polyamides

Pyrrole-imidazole polyamides (PIPs) bind to predetermined double-stranded DNA sequences and selectively target a large variety of DNA sequences. Although the forward-binding (5'-3'/N-C) orientation, in which the N-terminus of PIPs faces the 5'-terminus of DNAs, is considered to be the main binding manner of PIPs, a reverse-binding (5'-3'/C-N) orientation, in which the C-terminus of PIPs faces the 3'-terminus of DNAs, sometimes causes unintended binding. Here, we synthesized optical or structural isomers of previously reported cyclic PIPs (cPIPs), which differ in the position of the amino groups in the γ-turn units, and we investigated their binding affinities both in the forward- and reverse-binding orientation. We show that cPIPs with (R)-α-amino-γ-turn units prefer the forward orientation as do hairpin PIPs. More importantly, we document for the first time the remarkable reverse-binding preference of cPIPs with (S)-α-amino-γ-turns. These results indicate that the orientation preference of cPIPs can be controlled by the position of the amino groups on the γ-turn units, which may markedly increase the number of DNA sequences that can be targeted by PIPs.

TAMRA-polypyrrole for A/T sequence visualization on DNA molecules

Fluorophore-linked, sequence-specific DNA binding reagents can visualize sequence information on a large DNA molecule. In this paper, we synthesized newly designed TAMRA-linked polypyrrole to visualize adenine and thymine base pairs. A fluorescent image of the stained DNA molecule generates an intensity profile based on A/T frequency, revealing a characteristic sequence composition pattern. Computer-aided comparison of this intensity pattern with the genome sequence allowed us to determine the DNA sequence on a visualized DNA molecule from possible intensity profile pattern candidates for a given genome. Moreover, TAMRA-polypyrrole offers robust advantages for single DNA molecule detection: no fluorophore-mediated photocleavage and no structural deformation, since it exhibits a sequence-specific pattern alone without the use of intercalating dyes such as YOYO-1. Accordingly, we were able to identify genomic DNA fragments from Escherichia coli cells by aligning them to the genomic A/T frequency map based on TAMRA-polypyrrole-generated intensity profiles. Furthermore, we showed band and interband patterns of polytene chromosomal DNA stained with TAMRA-polypyrrole because it prefers to bind AT base pairs.

Structural basis of DNA duplex distortion induced by thiazole-containing hairpin polyamides

This manuscript reports the molecular basis for double-stranded DNA (dsDNA) binding of hairpin polyamides incorporating a 5-alkyl thiazole (Nt) unit. Hairpin polyamides containing an N-terminal Nt unit induce higher melting stabilisation of target dsDNA sequences relative to an archetypical hairpin polyamide incorporating an N-terminal imidazole (Im) unit. However, modification of the N-terminus from Im to Nt-building blocks results in an increase in dsDNA binding affinity but lower G-selectivity. A general G-selectivity trend is observed for Nt-containing polyamide analogues. G-selectivity increases as the steric bulk in the Nt 5-position increases. Solution-based NMR structural studies reveal differences in the modulation of the target DNA duplex of Nt-containing hairpin polyamides relative to the Im-containing archetype. A structural hallmark of an Nt polyamide•dsDNA complex is a more significant degree of major groove compression of the target dsDNA sequence relative to the Im-containing hairpin polyamide.

Therapeutic gene regulation using pyrrole-imidazole polyamides

Recent innovations in cutting-edge sequencing platforms have allowed the rapid identification of genes associated with communicable, noncommunicable and rare diseases. Exploitation of this collected biological information has facilitated the development of nonviral gene therapy strategies and the design of several proteins capable of editing specific DNA sequences for disease control. Small molecule-based targeted therapeutic approaches have gained increasing attention because of their suggested clinical benefits, ease of control and lower costs. Pyrrole-imidazole polyamides (PIPs) are a major class of DNA minor groove-binding small molecules that can be predesigned to recognize specific DNA sequences. This programmability of PIPs allows the on-demand design of artificial genetic switches and fluorescent probes. In this review, we detail the progress in the development of PIP-based designer ligands and their prospects as advanced DNA-based small-molecule drugs for therapeutic gene modulation.

Cyclic Naphthalene Diimide Dimer with a Strengthened Ability to Stabilize Dimeric G-Quadruplex

A new type of dimeric cyclic naphthalene diimide derivatives (cNDI-dimers) carrying varied linker length were designed and synthesized to recognize dimeric G-quadruplex structures. All of the cNDI-dimers exhibited a high preference for recognizing G-quadruplex structures, and significantly enhanced the thermal stability of the dimeric G-quadruplex structure over the cNDI monomer by increasing the melting temperature by more than 23 °C, which indicated the strengthened ability of cNDI dimers for stabilizing dimeric G-quadruplex. cNDI dimers also showed a stronger ability to inhibit telomerase activity and stop telomere DNA elongation than cNDI monomer, which showed an improved anticancer potentiality for further therapeutic application.

Submolecular dissection reveals strong and specific binding of polyamide-pyridostatin conjugates to human telomere interface

To modulate biological functions, G-quadruplexes in genome are often non-specifically targeted by small molecules. Here, specificity is increased by targeting both G-quadruplex and its flanking duplex DNA in a naturally occurring dsDNA-ssDNA telomere interface using polyamide (PA) and pyridostatin (PDS) conjugates (PA-PDS). We innovated a single-molecule assay in which dissociation constant (Kd) of the conjugate can be separately evaluated from the binding of either PA or PDS. We found Kd of 0.8 nM for PA-PDS, which is much lower than PDS (Kd ∼ 450 nM) or PA (Kd ∼ 35 nM). Functional assays further indicated that the PA-PDS conjugate stopped the replication of a DNA polymerase more efficiently than PA or PDS. Our results not only established a new method to dissect multivalent binding into actions of individual monovalent components, they also demonstrated a strong and specific G-quadruplex targeting strategy by conjugating highly specific duplex-binding molecules with potent quadruplex ligands.

Structural and Kinetic Profiling of Allosteric Modulation of Duplex DNA Induced by DNA-Binding Polyamide Analogues

A combined structural and quantitative biophysical profile of the DNA binding affinity, kinetics and sequence-selectivity of hairpin polyamide analogues is described. DNA duplexes containing either target polyamide binding sites or mismatch sequences are immobilized on a microelectrode surface. Quantitation of the DNA binding profile of polyamides containing N-terminal 1-alkylimidazole (Im) units exhibit picomolar binding affinities for their target sequences, whereas 5-alkylthiazole (Nt) units are an order of magnitude lower (low nanomolar). Comparative NMR structural analyses of the polyamide series shows that the steric bulk distal to the DNA-binding face of the hairpin iPr-Nt polyamide plays an influential role in the allosteric modulation of the overall DNA duplex structure. This combined kinetic and structural study provides a foundation to develop next-generation hairpin designs where the DNA-binding profile of polyamides is reconciled with their physicochemical properties.

Cascaded Electrochemiluminescence Signal Amplifier for the Detection of Telomerase Activity from Tumor Cells and Tissues

Telomerase is closely linked to the physiological transformation of tumor cells and is commonly overexpressed in most types of tumor cells. Therefore, telomerase has become a potential biomarker for the process of tumorigenesis, progression, prognosis and metastasis. Thus, it is important to develop a simple, accurate and reliable method for detecting telomerase activity. As a high signal-to-noise ratio mode, electrochemiluminescence (ECL) has been widely applied in the field of biomedical analysis. Here, our objective was to construct an improved ECL signal amplifier for the detection of telomerase activity. Methods: A cascaded ECL signal amplifier was constructed to detect telomerase activity with high selectivity via controllable construction of a lysine-based dendric Ru(bpy)₃ ²⁺ polymer (DRP). The sensitivity, specificity and performance index were simultaneously evaluated by standard substance and cell and tissue samples. Results: With this cascaded ECL signal amplifier, high sensitivities of 100, 50, and 100 cells for three tumor cell lines (A549, MCF7 and HepG2 cell lines) were simultaneously achieved, and desirable specificity was also obtained. Furthermore, the excellent performance of this platform was also demonstrated in the detection of telomerase in tumor cells and tissues. Conclusion: This cascaded ECL signal amplifier has the potential to be a technological innovation in the field of telomerase activity detection.

DNA-Binding Properties of New Fluorescent AzaHx Amides: Methoxypyridylazabenzimidazolepyrroleimidazole/pyrrole

DNA minor groove binding polyamides have been extensively developed to control abnormal gene expression. The establishment of novel, inherently fluorescent 2-(p-anisyl)benzimidazole (Hx) amides has provided an alternative path for studying DNA binding in cells by direct observation of cell localization. Because of the 2:1 antiparallel stacking homodimer binding mode of these molecules to DNA, modification of Hx amides to 2-(p-anisyl)-4-azabenzimidazole (AzaHx) amides has successfully extended the DNA-recognition repertoire from central CG [recognized by Hx-I (I=N-methylimidazole)] to central GC [recognized by AzaHx-P (P=N-methylpyrrole)] recognition. For potential targeting of two consecutive GG bases, modification of the AzaHx moiety to 2- and 3-pyridyl-aza-benzimidazole (Pyr-AzaHx) moieties was explored. The newly designed molecules are also small-sized, fluorescent amides with the Pyr-AzaHx moiety connected to two conventional five-membered heterocycles. Complementary biophysical methods were performed to investigate the DNA-binding properties of these molecules. The results showed that neither 3-Pyr-AzaHx nor 2-Pyr-AzaHx was able to mimic I-I=N-methylimidazole-N-methylimidazole to target GG dinucleotides specifically. Rather, 3-Pyr-AzaHx was found to function like AzaHx, f-I (f=formamide), or P-I as an antiparallel stacked dimer. 3-Pyr-AzaHx-PI (2) binds 5'-ACGCGT'-3' with improved binding affinity and high sequence specificity in comparison to its parent molecule AzaHx-PI (1). However, 2-Pyr-AzaHx is detrimental to DNA binding because of an unfavorable steric clash upon stacking in the minor groove.

Region-specific alteration of histone modification by LSD1 inhibitor conjugated with pyrrole-imidazole polyamide

Epigenome regulates gene expression to determine cell fate, and accumulation of epigenomic aberrations leads to diseases, including cancer. NCD38 inhibits lysine-specific demethylase-1 (LSD1), a histone demethylase targeting H3K4me1 and H3K4me2, but not H3K4me3. In this study, we conjugated NCD38 with a potent small molecule called pyrrole (Py) imidazole (Im) polyamide, to analyze whether targets of the inhibitor could be regulated in a sequence-specific manner. We synthesized two conjugates using β-Ala (β) as a linker, i.e., NCD38-β-β-Py-Py-Py-Py (NCD38-β2P4) recognizing WWWWWW sequence, and NCD38-β-β-Py-Im-Py-Py (NCD38-β2PIPP) recognizing WWCGWW sequence. When RKO cells were treated with NCD38, H3K4me2 levels increased in 103 regions with significant activation of nearby genes (P = 0.03), whereas H3K4me3 levels were not obviously increased. H3K27ac levels were also increased in 458 regions with significant activation of nearby genes (P = 3 × 10-10), and these activated regions frequently included GC-rich sequences, but less frequently included AT-rich sequences (P < 1 × 10-15) or WWCGWW sequences (P = 2 × 10-13). When treated with NCD38-β2P4, 234 regions showed increased H3K27ac levels with significant activation of nearby genes (P = 2 × 10-11), including significantly fewer GC-rich sequences (P < 1 × 10-15) and significantly more AT-rich sequences (P < 1 × 10-15) compared with NCD38 treatment. When treated with NCD38-β2PIPP, 82 regions showed increased H3K27ac levels, including significantly fewer GC-rich sequences (P = 1 × 10-11) and fewer AT-rich sequences (P = 0.005), but significantly more WWCGWW sequences (P = 0.0001) compared with NCD38 treatment. These indicated that target regions of epigenomic inhibitors could be modified in a sequence-specific manner and that conjugation of Py-Im polyamides may be useful for this purpose.

An overview of recent advances in duplex DNA recognition by small molecules

As the carrier of genetic information, the DNA double helix interacts with many natural ligands during the cell cycle, and is amenable to such intervention in diseases such as cancer biogenesis. Proteins bind DNA in a site-specific manner, not only distinguishing between the geometry of the major and minor grooves, but also by making close contacts with individual bases within the local helix architecture. Over the last four decades, much research has been reported on the development of small non-natural ligands as therapeutics to either block, or in some cases, mimic a DNA–protein interaction of interest. This review presents the latest findings in the pursuit of novel synthetic DNA binders. This article provides recent coverage of major strategies (such as groove recognition, intercalation and cross-linking) adopted in the duplex DNA recognition by small molecules, with an emphasis on major works of the past few years.

Sequence-specific DNA binding Pyrrole-imidazole polyamides and their applications

Pyrrole-imidazole polyamides (Py-Im polyamides) are cell-permeable compounds that bind to the minor groove of double-stranded DNA in a sequence-specific manner without causing denaturation of the DNA. These compounds can be used to control gene expression and to stain specific sequences in cells. Here, we review the history, structural variations, and functional investigations of Py-Im polyamides.