High-throughput platform assay technology for the discovery of pre-microrna-selective small molecule probes

An ECD and NMR/DP4+ Computational Pipeline for Structure Revision and Elucidation of Diphenazine-Based Natural Products

Discovery and structure elucidation of natural products available in infinitesimally small quantities are recognized challenge. This challenge is epitomized by the diphenazine class of molecules that contain three bridged stereocenters, several conformations, ring fusions, and multiple spatially isolated phenols. Because empirical NMR and spatial analyses using ROESY/NOESY were unsuccessful in tackling these challenges, we developed a computational pipeline to determine the relative and absolute configurations and phenol positions of diphenazines as inhibitors of eukaryotic translation initiation factor 4E (eIF4E) protein-protein interactions. In this pipeline, we incorporated ECD and GIAO NMR calculations coupled with a DP4+ probability measure, enabling the structure revision of phenazinolin D (4), izumiphenazine A (5), and baraphenazine G (7) and the structure characterization of two new diphenazines, baraphenazine H (3) and izumiphenazine E (6). Importantly, through these efforts, we demonstrate the feasibility of NMR/DP4+ analysis for the determination of phenol positions in phenazine-based molecules, further expanding the limits of computational methods for the structure elucidation of complex natural products.

Trading places: Peptide and small molecule alternatives to oligonucleotide-based modulation of microRNA expression

It is well established that microRNA (miRNA) dysregulation is involved in the development and progression of various diseases, especially cancer. Emerging evidence suggests that small molecule and peptide agents can interfere with miRNA disease pathways. Despite this, very little is known about structural features that drive drug-miRNA interactions and subsequent inhibition. In this review, we highlight the advances made in the development of small molecule and peptide inhibitors of miRNA processing. Specifically, we attempt to draw attention to peptide features that may be critical for interaction with the miRNA secondary structure to regulate miRNA expression. We hope that this review will help to establish peptides as exciting miRNA expression modulators and will contribute towards the development of the first miRNA-targeting peptide therapy.

RiPCA: An Assay for the Detection of RNA-Protein Interactions in Live Cells

Increasing interest in studying and modulating the interactions between RNAs and their RNA-binding proteins has indicated the need for enabling technologies. Existing means of detecting RNA-protein interactions (RPIs) are often limited to biochemical or post-lysis methods or cell-based methods that require the addition of an RNA-based affinity tag, such as the MS2 hairpin, precluding them from use in detecting small or highly processed RNAs. Taking advantage of bioorthogonal chemistry- and split-luciferase-based technologies, we developed an assay for the detection of RPIs in live cells. This article details the protocol and design considerations for RiPCA, or RNA interaction with Protein-mediated Complementation Assay. © 2022 Wiley Periodicals LLC.

Systematically Studying the Effect of Small Molecules Interacting with RNA in Cellular and Preclinical Models

The interrogation and manipulation of biological systems by small molecules is a powerful approach in chemical biology. Ideal compounds selectively engage a target and mediate a downstream phenotypic response. Although historically small molecule drug discovery has focused on proteins and enzymes, targeting RNA is an attractive therapeutic alternative, as many disease-causing or -associated RNAs have been identified through genome-wide association studies. As the field of RNA chemical biology emerges, the systematic evaluation of target validation and modulation of target-associated pathways is of paramount importance. In this Review, through an examination of case studies, we outline the experimental characterization, including methods and tools, to evaluate comprehensively the impact of small molecules that target RNA on cellular phenotype.

Speeding drug discovery targeting RNAs: An iterative "RNA selection-compounds screening cycle" for exploring RNA-small molecule pairs

RNA is an emerging target of next-generation drug development. Recently, new small molecules targeting RNAs were discovered by several pharmaceutical companies. Methods have been reported to identify small molecules targeting a specific RNA sequence and structural motif, however, because of diverse sequence and structural motifs potentially present in the druggable functional RNAs, large sets of structure-activity relationships (SARs) information of small molecule - RNA interactions will be required for the acceleration and efficient startup of the discovery programs toward unprecedented RNA targets. Here we describe our iterative RNA selection and compounds screening to accumulate rich information about small molecules - RNA interaction. The RNAs that selectively bind to the initial molecular target, compound 1 from our in-house chemical library (JT-library), was isolated using in vitro selection technique from a hairpin-structured RNA library mimicking precursor microRNA (pre-miRNA). Then, we engineered pre-let-7f-2 to create its mutant that can bind to compound 1 by embedding the in vitro selected RNA motif for compound 1 in the hairpin loop region. The obtained mutant pre-let-7f-2-loop-mt was used as a target for screening 316 analogs of compound 1. A surface plasmon resonance (SPR) -based screening was performed against pre-let-7f-2-loop-mt-immobilized sensor surface and we obtained four compounds that can bind to the RNA. Among these four compounds, three compounds showed higher affinity to pre-let-7f-2-loop-mt than the parental compound 1, which suggests the feasibility of our strategy for gathering the SAR information on small molecule - RNA interactions. We demonstrated only one cycle of RNA selection and compounds screening in the present study, but can continue this cycle with the selected molecule to gain new RNAs and even new RNA motifs and gather much SAR information with improved accuracy.

A live-cell assay for the detection of pre-microRNA-protein interactions

Recent efforts in genome-wide sequencing and proteomics have revealed the fundamental roles that RNA-binding proteins (RBPs) play in the life cycle and function of coding and non-coding RNAs. While these methodologies provide a systems-level view of the networking of RNA and proteins, approaches to enable the cellular validation of discovered interactions are lacking. Leveraging the power of bioorthogonal chemistry- and split-luciferase-based assay technologies, we have devised a conceptually new assay for the live-cell detection of RNA-protein interactions (RPIs), RNA interaction with Protein-mediated Complementation Assay, or RiPCA. As proof-of-concept, we utilized the interaction of the pre-microRNA, pre-let-7, with its binding partner, Lin28. Using this system, we have demonstrated the selective detection of the pre-let-7-Lin28 RPI in both the cytoplasm and nucleus. Furthermore, we determined that this technology can be used to discern relative affinities for specific sequences as well as of individual RNA binding domains. Thus, RiPCA has the potential to serve as a useful tool in supporting the investigation of cellular RPIs.

Frameworks for targeting RNA with small molecules

Since the characterization of mRNA in 1961, our understanding of the roles of RNA molecules has significantly grown. Beyond serving as a link between DNA and proteins, RNA molecules play direct effector roles by binding to various ligands, including proteins, DNA, other RNAs, and metabolites. Through these interactions, RNAs mediate cellular processes such as the regulation of gene transcription and the enhancement or inhibition of protein activity. As a result, the misregulation of RNA molecules is often associated with disease phenotypes, and RNA molecules have been increasingly recognized as potential targets for drug development efforts, which in the past had focused primarily on proteins. Although both small molecule-based and oligonucleotide-based therapies have been pursued in efforts to target RNA, small-molecule modalities are often favored owing to several advantages including greater oral bioavailability. In this review, we discuss three general frameworks (sets of premises and hypotheses) that, in our view, have so far dominated the discovery of small-molecule ligands for RNA. We highlight the unique merits of each framework as well as the pitfalls associated with exclusive focus of ligand discovery efforts within only one framework. Finally, we propose that RNA ligand discovery can benefit from using progress made within these three frameworks to move toward a paradigm that formulates RNA-targeting questions at the level of RNA structural subclasses.

Template-guided selection of RNA ligands using imine-based dynamic combinatorial chemistry

This study establishes the applicability of imine-based dynamic combinatorial chemistry to discover non-covalent ligands for RNA targets. We elucidate properties underlying the reactivity of arylamines and demonstrate target-guided amplification of tight binders in an amiloride-based dynamic library.

High-Throughput Amenable MALDI-MS Detection of RNA and DNA with On-Surface Analyte Enrichment Using Fluorous Partitioning

High-throughput matrix-assisted laser desorption/ionization mass spectrometry (HT-MALDI-MS) has garnered considerable attention within the drug discovery industry as an information-rich alternative to assays using light-based detection methods. To date, these efforts have been primarily focused on assays using protein or peptide substrates. Methods for RNA or DNA analysis by HT-MALDI-MS have not been extensively reported due to the challenges associated with MALDI-MS of oligonucleotides, including the propensity to form multiple salt adducts, low ionization potential, and ease of fragmentation. The objective of this work was to develop a platform suitable for HT-MS analysis of RNA and DNA substrates that overcomes these hurdles by combining on-surface sample preparation with soft ionization. This has been accomplished through the selective immobilization of fluorous-tagged oligonucleotides on a fluorous-modified MS target plate, followed by on-surface enrichment, matrix addition, and direct laser desorption/ionization, a process dubbed fluorous HT-MS (F-HT-MS). The work has resulted in methods by which RNA and DNA substrates can be detected at nanomolar concentrations from a typical assay buffer system using procedures that are amenable to full automation. The protocols were applied to an miRNA biogenesis assay, demonstrating its potential for RNA processes and thereby filling a prominent gap in RNA drug discovery: the paucity of in vitro functional assays.

Progress toward the development of the small molecule equivalent of small interfering RNA

Given that many small molecules could bind to structured regions at sites that will not affect function, approaches that trigger degradation of RNA could provide a general way to affect biology. Indeed, targeted RNA degradation is an effective strategy to selectively and potently modulate biology. We describe several approaches to endow small molecules with the power to cleave RNAs. Central to these strategies is Inforna, which designs small molecules targeting RNA from human genome sequence. Inforna deduces the uniqueness of a druggable pocket, enables generation of hypotheses about functionality of the pocket, and defines on- and off-targets to drive compound optimization. RNA-binding compounds are then converted into cleavers that degrade the target directly or recruit an endogenous nuclease to do so. Cleaving compounds have significantly contributed to understanding and manipulating biological functions. Yet, there is much to be learned about how to affect human RNA biology with small molecules.

Catalytic Knockdown of miR-21 by Artificial Ribonuclease: Biological Performance in Tumor Model

Control of the expression of oncogenic small non-coding RNAs, notably microRNAs (miRNAs), is an attractive therapeutic approach. We report a design platform for catalytic knockdown of miRNA targets with artificial, sequence-specific ribonucleases. miRNases comprise a peptide [(LeuArg)₂Gly]₂ capable of RNA cleavage conjugated to the miRNA-targeted oligodeoxyribonucleotide, which becomes nuclease-resistant within the conjugate design, without resort to chemically modified nucleotides. Our data presented here showed for the first time a truly catalytic character of our miR-21-miRNase and its ability to cleave miR-21 in a multiple catalytic turnover mode. We demonstrate that miRNase targeted to miR-21 (miR-21-miRNase) knocked down malignant behavior of tumor cells, including induction of apoptosis, inhibition of cell invasiveness, and retardation of tumor growth, which persisted on transplantation into mice of tumor cells treated once with miR-21-miRNase. Crucially, we discover that the high biological activity of miR-21-miRNase can be directly related not only to its truly catalytic sequence-specific cleavage of miRNA but also to its ability to recruit the non-sequence specific RNase H found in most cells to elevate catalytic turnover further. miR-21-miRNase worked synergistically even with low levels of RNase H. Estimated degradation in the presence of RNase H exceeded 10³ miRNA target molecules per hour for each miR-21-miRNase molecule, which provides the potency to minimize delivery requirements to a few molecules per cell. In contrast to the comparatively high doses required for the simple steric block of antisense oligonucleotides, truly catalytic inactivation of miRNA offers more effective, irreversible, and persistent suppression of many copy target sequences. miRNase design can be readily adapted to target other pathogenic microRNAs overexpressed in many disease states.

Click Chemistry-Mediated Complementation Assay for RNA-Protein Interactions

Click chemistry-based assays are a growing class of biochemical assay for facilitating the discovery of modulators of important biological processes. To date, most have relied on the use of immobilized biomolecules, which increases the cost of the assay and decreases throughput because of the necessary washing steps. To overcome these challenges, we have developed a click chemistry-mediated complementation assay that retains many of the advantages of the previous technology, including catalytic signal amplification for assay robustness and applicability to full-length biomolecules, but that can be performed in a homogeneous format. As demonstration of this methodology, we have developed a new high-throughput screening method for RNA-protein interactions using the interaction of Lin28 with the pre-microRNA, prelet-7, as a model.

The Natural Product Butylcycloheptyl Prodiginine Binds Pre-miR-21, Inhibits Dicer-Mediated Processing of Pre-miR-21, and Blocks Cellular Proliferation

Identification of RNA-interacting pharmacophores could provide chemical probes and, potentially, small molecules for RNA-based therapeutics. Using a high-throughput differential scanning fluorimetry assay, we identified small-molecule natural products with the capacity to bind the discrete stem-looped structure of pre-miR-21. The most potent compound identified was a prodiginine-type compound, butylcycloheptyl prodiginine (bPGN), with the ability to inhibit Dicer-mediated processing of pre-miR-21 in vitro and in cells. Time-dependent RT-qPCR, western blot, and transcriptomic analyses showed modulation of miR-21 expression and its target genes such as PDCD4 and PTEN upon treatment with bPGN, supporting on-target inhibition. Consequently, inhibition of cellular proliferation in HCT-116 colorectal cancer cells was also observed when treated with bPGN. The discovery that bPGN can bind and modulate the expression of regulatory RNAs such as miR-21 helps set the stage for further development of this class of natural product as a molecular probe or therapeutic agent against miRNA-dependent diseases.

miRNA inhibition by proximity-enabled Dicer inactivation

microRNAs (miRNAs) are considered as master regulators of biological processes. Dysregulation of miRNA expression has been implicated in many human diseases. Driven by the key biological roles and the therapeutic potential, developing methods for miRNA regulation has become an intense research area. Due to favorable pharmacological properties, small molecule-based miRNA inhibition emerges as a promising strategy and significant progresses have been made. However, it remains challenging to regulate miRNA using small molecules because of the inherent difficulty in RNA targeting and inhibition. Herein we outline the workflow of generating bifunctional small molecule inhibitors blocking miRNA biogenesis through proximity-enabled inactivation of Dicer, an enzyme required for the processing of precursor miRNA (pre-miRNA) into mature miRNA. By conjugating a weak Dicer inhibitor with a pre-miRNA binder, the inhibitor can be delivered to the Dicer processing site associated with the targeted pre-miRNA, and as a result inhibiting Dicer-mediated pre-miRNA processing. This protocol can be applicable in producing bifunctional inhibitors for different miRNAs.

Tetracyclines as Inhibitors of Pre-microRNA Maturation: A Disconnection between RNA Binding and Inhibition

In a high-throughput screening campaign, we recently discovered the rRNA-binding tetracyclines, methacycline and meclocycline, as inhibitors of Dicer-mediated processing of microRNAs. Herein, we describe our biophysical and biochemical characterization of these compounds. Interestingly, although direct, albeit weak, binding to the pre-microRNA hairpins was observed, the inhibitory activity of these compounds was not due to RNA binding. Through additional biochemical and chemical studies, we revealed that metal chelation likely plays a principle role in their mechanism of inhibition. By exploring the activity of other known RNA-binding scaffolds, we identified additional disconnections between direct RNA interaction and inhibition of Dicer processing. Thus, the results presented within provide a valuable case study in the complexities of targeting RNA with small molecules, particularly with weak binding and potentially promiscuous scaffolds.

RFSMMA: A New Computational Model to Identify and Prioritize Potential Small Molecule-MiRNA Associations

More and more studies found that many complex human diseases occur accompanied by aberrant expression of microRNAs (miRNAs). Small molecule (SM) drugs have been utilized to treat complex human diseases by affecting the expression of miRNAs. Several computational methods were proposed to infer underlying associations between SMs and miRNAs. In our study, we proposed a new calculation model of random forest based small molecule-miRNA association prediction (RFSMMA) which was based on the known SM-miRNA associations in the SM2miR database. RFSMMA utilized the similarity of SMs and miRNAs as features to represent SM-miRNA pairs and further implemented the machine learning algorithm of random forest to train training samples and obtain a prediction model. In RFSMMA, integrating multiple kinds of similarity can avoid the bias of single similarity and choosing more reliable features from original features can represent SM-miRNA pairs more accurately. We carried out cross validations to assess predictive accuracy of RFSMMA. As a result, RFSMMA acquired AUCs of 0.9854, 0.9839, 0.7052, and 0.9917 ± 0.0008 under global leave-one-out cross validation (LOOCV), miRNA-fixed local LOOCV, SM-fixed local LOOCV, and 5-fold cross validation, respectively, under data set 1. Based on data set 2, RFSMMA obtained AUCs of 0.8456, 0.8463, 0.6653, and 0.8389 ± 0.0033 under four cross validations according to the order mentioned above. In addition, we implemented a case study on three common SMs, namely, 5-fluorouracil, 17β-estradiol, and 5-aza-2'-deoxycytidine. Among the top 50 associated miRNAs of these three SMs predicted by RFSMMA, 31, 32, and 28 miRNAs were verified, respectively. Therefore, RFSMMA is shown to be an effective and reliable tool for identifying underlying SM-miRNA associations.

A click chemistry assay to identify natural product ligands for pre-microRNAs

Despite the great diversity of structure and function and relevance to human health, RNA remains an underexploited area of drug discovery. A major bottleneck toward this goal has been the identification of probes and drug leads that are specific for select RNAs and methods that will facilitate such discovery efforts. Our laboratory has recently developed an innovative approach for assaying RNA-small molecule interactions, catalytic enzyme-linked click chemistry assay or cat-ELCCA, which is a functional assay that takes advantage of the power of catalytic signal amplification combined with the selectivity and bioorthogonality of click chemistry. Importantly, through application of this platform assay technology to the challenging problem of identifying selective inhibitors of pre-microRNA maturation, we identified natural products as a potential source of such compounds. Herein we describe this methodology in addition to the downstream pipeline toward the discovery of natural product ligands for pre-microRNAs. Through cat-ELCCA, our goal is to discover novel ligands to facilitate our investigation of RNA recognition by small molecules.

Small molecules that target group II introns are potent antifungal agents

Specific RNA structures control numerous metabolic processes that impact human health, and yet efforts to target RNA structures de novo have been limited. In eukaryotes, the self-splicing group II intron is a mitochondrial RNA tertiary structure that is absent in vertebrates but essential for respiration in plants, fungi and yeast. Here we show that this RNA can be targeted through a process of high-throughput in vitro screening, SAR and lead optimization, resulting in high-affinity compounds that specifically inhibit group IIB intron splicing in vitro and in vivo and lack toxicity in human cells. The compounds are potent growth inhibitors of the pathogen Candida parapsilosis, displaying antifungal activity comparable to that of amphotericin B. These studies demonstrate that RNA tertiary structures can be successfully targeted de novo, resulting in pharmacologically valuable compounds.

cat-ELCCA: catalyzing drug discovery through click chemistry

Click chemistry has emerged as a powerful tool in our arsenal for unlocking new biology. This includes its utility in both chemical biology and drug discovery. An emerging application of click chemistry is in the development of biochemical assays for high-throughput screening to identify new chemical probes and drug leads. This Feature Article will discuss the advancements in click chemistry that were necessary for the development of a new class of biochemical assay, catalytic enzyme-linked click chemistry assay or cat-ELCCA. Inspired by enzyme immunoassays, cat-ELCCA was designed as a click chemistry-based amplification assay where bioorthogonally-tagged analytes and enzymes are used in place of the enzyme-linked secondary antibodies used in immunoassays. The result is a robust assay format with demonstrated applicability in several important areas of biology and drug discovery, including post-translational modifications, pre-microRNA maturation, and protein-protein and RNA-protein interactions. Through the use of cat-ELCCA and other related click chemistry-based assays, new chemical probes for interrogating promising drug targets have been discovered. These examples will be discussed, in addition to a future outlook on the impact of this approach in probe and drug discovery.

Expansion of cat-ELCCA for the Discovery of Small Molecule Inhibitors of the Pre-let-7-Lin28 RNA-Protein Interaction

Dysregulation of microRNA (miRNA) expression has been linked to many human diseases; however, because of the challenges associated with RNA-targeted drug discovery, additional approaches are needed for probing miRNA biology. The emerging regulatory role of miRNA-binding proteins in miRNA maturation presents such an alternative strategy. Exploiting our laboratory’s click chemistry-based high-throughput screening (HTS) technology, catalytic enzyme-linked click chemistry assay or cat-ELCCA, we have designed a modular method by which to discover new chemical tools for manipulating pre-miRNA–miRNA–binding protein interactions. Using the pre-let-7d–Lin28 interaction as proof-of-concept, the results presented demonstrate how HTS using cat-ELCCA can enable the discovery of small molecules targeting RNA–protein interactions.

Covalent Strategies for Targeting Messenger and Non-Coding RNAs: An Updated Review on siRNA, miRNA and antimiR Conjugates

Oligonucleotide-based therapy has become an alternative to classical approaches in the search of novel therapeutics involving gene-related diseases. Several mechanisms have been described in which demonstrate the pivotal role of oligonucleotide for modulating gene expression. Antisense oligonucleotides (ASOs) and more recently siRNAs and miRNAs have made important contributions either in reducing aberrant protein levels by sequence-specific targeting messenger RNAs (mRNAs) or restoring the anomalous levels of non-coding RNAs (ncRNAs) that are involved in a good number of diseases including cancer. In addition to formulation approaches which have contributed to accelerate the presence of ASOs, siRNAs and miRNAs in clinical trials; the covalent linkage between non-viral vectors and nucleic acids has also added value and opened new perspectives to the development of promising nucleic acid-based therapeutics. This review article is mainly focused on the strategies carried out for covalently modifying siRNA and miRNA molecules. Examples involving cell-penetrating peptides (CPPs), carbohydrates, polymers, lipids and aptamers are discussed for the synthesis of siRNA conjugates whereas in the case of miRNA-based drugs, this review article makes special emphasis in using antagomiRs, locked nucleic acids (LNAs), peptide nucleic acids (PNAs) as well as nanoparticles. The biomedical applications of siRNA and miRNA conjugates are also discussed.

Development of Novel Therapeutic Agents by Inhibition of Oncogenic MicroRNAs

MicroRNAs (miRs, miRNAs) are regulatory small noncoding RNAs, with their roles already confirmed to be important for post-transcriptional regulation of gene expression affecting cell physiology and disease development. Upregulation of a cancer-causing miRNA, known as oncogenic miRNA, has been found in many types of cancers and, therefore, represents a potential new class of targets for therapeutic inhibition. Several strategies have been developed in recent years to inhibit oncogenic miRNAs. Among them is a direct approach that targets mature oncogenic miRNA with an antisense sequence known as antimiR, which could be an oligonucleotide or miRNA sponge. In contrast, an indirect approach is to block the biogenesis of miRNA by genome editing using the CRISPR/Cas9 system or a small molecule inhibitor. The development of these inhibitors is straightforward but involves significant scientific and therapeutic challenges that need to be resolved. In this review, we summarize recent relevant studies on the development of miRNA inhibitors against cancer.

High-Throughput Chemical Probing of Full-Length Protein-Protein Interactions

Human biology is regulated by a complex network of protein-protein interactions (PPIs), and disruption of this network has been implicated in many diseases. However, the targeting of PPIs remains a challenging area for chemical probe and drug discovery. Although many methodologies have been put forth to facilitate these efforts, new technologies are still needed. Current biochemical assays for PPIs are typically limited to motif-domain and domain-domain interactions, and assays that will enable the screening of full-length protein systems, which are more biologically relevant, are sparse. To overcome this barrier, we have developed a new assay technology, "PPI catalytic enzyme-linked click chemistry assay" or PPI cat-ELCCA, which utilizes click chemistry to afford catalytic signal amplification. To validate this approach, we have applied PPI cat-ELCCA to the eIF4E-4E-BP1  and eIF4E-eIF4G PPIs, key regulators of cap-dependent mRNA translation. Using these examples, we have demonstrated that PPI cat-ELCCA is amenable to full-length proteins, large (>200 kDa) and small (∼12 kDa), and is readily adaptable to automated high-throughput screening. Thus, PPI cat-ELCCA represents a powerful new tool in the toolbox of assays available to scientists interested in the targeting of disease-relevant PPIs.

Development and Implementation of an HTS-Compatible Assay for the Discovery of Selective Small-Molecule Ligands for Pre-microRNAs

microRNAs (miRNAs) are small gene regulatory RNAs, and their expression has been found to be dysregulated in a number of human diseases. To facilitate the discovery of small molecules capable of selectively modulating the activity of a specific miRNA, we have utilized new high-throughput screening technology targeting Dicer-mediated pre-miRNA maturation. Pilot screening of ~50,000 small molecules and ~33,000 natural product extract libraries against pre-miR-21 processing indicated the potential of our assay for this goal, yielding a campaign Z' factor of 0.52 and an average plate signal-to-background (S/B) ratio of 13. Using two-dimensional screening against a second pre-miRNA, pre-let-7d, we evaluated the selectivity of confirmed hits. The results presented demonstrate how high-throughput screening can be used to identify selective small molecules for a target RNA.

Discovery of Inhibitors of MicroRNA-21 Processing Using Small Molecule Microarrays

The identification of small molecules that bind to and perturb the function of microRNAs is an attractive approach for the treatment for microRNA-associated pathologies. However, there are only a few small molecules known to interact directly with microRNAs. Here, we report the use of a small molecule microarray (SMM) screening approach to identify low molecular weight compounds that directly bind to a pre-miR-21 hairpin. Compounds identified using this approach exhibit good affinity for the RNA (ranging from 0.8-2.0 μM) and are not composed of a polycationic scaffold. Several of the highest affinity compounds inhibit Dicer-mediated processing, while in-line probing experiments indicate that the compounds bind to the apical loop of the hairpin, proximal to the Dicer site. This work provides evidence that small molecules can be developed to bind directly to and inhibit miR-21.

A click chemistry-based microRNA maturation assay optimized for high-throughput screening

Catalytic enzyme-linked click-chemistry assays (cat-ELCCA) are an emerging class of biochemical assay. Herein we report on expanding the toolkit of cat-ELCCA to include the kinetically superior inverse-electron demand Diels-Alder (IEDDA) reaction. The result is a technology with improved sensitivity and reproducibility, enabling automated high-throughput screening.

Small-molecule approaches toward the targeting of oncogenic miRNAs: roadmap for the discovery of RNA modulators

miRNAs are a recently discovered class of small noncoding RNAs implicated in the regulation of gene expression. The deregulation of miRNAs levels has been linked to the development of various cancers where oncogenic miRNAs are overexpressed and tumor suppressor miRNAs are underexpressed. Here we report the three main strategies developed in order to discover small-molecule drugs able to selectively interfere with oncogenic miRNAs: the high throughput screening of large libraries of compounds, the focused screening of small libraries of molecules that are known to be able to interact with RNA thus being supposed modulators of miRNAs pathway and the design of small molecules based on the secondary structure of targeted RNA and/or three-dimensional structure of enzymes involved in miRNAs pathway.

Small molecules targeting microRNA for cancer therapy: Promises and obstacles

Aberrant expression of miRNAs is critically implicated in cancer initiation and progression. Therapeutic approaches focused on regulating miRNAs are therefore a promising approach for treating cancer. Antisense oligonucleotides, miRNA sponges, and CRISPR/Cas9 genome editing systems are being investigated as tools for regulating miRNAs. Despite the accruing insights in the use of these tools, delivery concerns have mitigated clinical application of such systems. In contrast, little attention has been given to the potential of small molecules to modulate miRNA expression for cancer therapy. In these years, many researches proved that small molecules targeting cancer-related miRNAs might have greater potential for cancer treatment. Small molecules targeting cancer related miRNAs showed significantly promising results in different cancer models. However, there are still several obstacles hindering the progress and clinical application in this area. This review discusses the development, mechanisms and application of small molecules for modulating oncogenic miRNAs (oncomiRs). Attention has also been given to screening technologies and perspectives aimed to facilitate clinical translation for small molecule-based miRNA therapeutics.