Tankyrase 1 Inhibitors with Drug-like Properties Identified by Screening a DNA-Encoded Chemical Library

Carbohydrate-DNA Conjugation Enabled by Glycosyl Radicals Generated from Glycosyl Sulfinates

Herein, we report a method that enables the synthesis of carbohydrate-DNA conjugates by radical addition. Key to the success is the use of readily available, bench-stable, and unprotected glycosyl sulfinates as precursors to glycosyl radicals. The redox neutral reaction proceeds under mild and simple conditions and tolerates a broad substrate scope. A small library of carbohydrate-DNA conjugates was prepared.

Privileged heterocycles for DNA-encoded library design and hit-to-lead optimization

It is well known that heterocyclic compounds play a key role in improving drug activity, target selectivity, physicochemical properties as well as reducing toxicity. In this review, we summarized the representative heterocyclic structures involved in hit compounds which were obtained from DNA-encoded library from 2013 to 2021. In some examples, the state of the art in heterocycle-based DEL synthesis and hit-to-lead optimization are highlighted. We hope that more and more novel heterocycle-based DEL toolboxes and in-depth pharmaceutical research on these lead compounds can be developed to accelerate the discovery of new drugs.

Combining pharmacophore models derived from DNA-encoded chemical libraries with structure-based exploration to predict Tankyrase 1 inhibitors

DNA-encoded chemical libraries (DECLs) interrogate the interactions of a target of interest with vast numbers of molecules. DECLs hence provide abundant information about the chemical ligand space for therapeutic targets, and there is considerable interest in methods for exploiting DECL screening data to predict novel ligands. Here we introduce one such approach and demonstrate its feasibility using the cancer-related poly-(ADP-ribose)transferase tankyrase 1 (TNKS1) as a model target. First, DECL affinity selections resulted in structurally diverse TNKS1 inhibitors with high potency including compound 2 with an IC50 value of 0.8 nM. Additionally, TNKS1 hits from four DECLs were translated into pharmacophore models, which were exploited in combination with docking-based screening to identify TNKS1 ligand candidates in databases of commercially available compounds. This computational strategy afforded TNKS1 inhibitors that are outside the chemical space covered by the DECLs and yielded the drug-like lead compound 12 with an IC50 value of 22 nM. The study further provided insights in the reliability of screening data and the effect of library design on hit compounds. In particular, the study revealed that while in general DECL screening data are in good agreement with off-DNA ligand binding, unpredictable interactions of the DNA-attachment linker with the target protein contribute to the noise in the affinity selection data.

DNA-Compatible Suzuki-Miyaura Cross-Coupling Reaction of Aryl Iodides With (Hetero)Aryl Boronic Acids for DNA-Encoded Libraries

An efficient method for the C-C bond formation via water soluble Na2PdCl4/sSPhos mediated Suzuki-Miyaura cross-coupling reaction of DNA-conjugated aryl iodide with (het)aryl boronic acids has been developed. This reaction proceeds at 37°C in water and acetonitrile (4:1) system. We also demonstrated that numerous aromatic and heteroaromatic boronic acids of different electronic natures, and harboring various functional groups, were highly compatible providing the desired coupling products in good to excellent yields. This DNA-compatible Suzuki-Miyaura cross-coupling reaction has strong potential to construct DNA-Encoded Libraries (DELs) in the context of drug discovery.

Photoredox Deaminative Alkylation in DNA-Encoded Library Synthesis

Herein, we report an on-DNA photoredox-mediated deaminative alkylation method for diversifying DNA-tagged acrylamide substrate with amine-derived radicals. The radicals can be conveniently generated from sterically hindered primary amines, and the deaminative alkylation can tolerate a broad array of radical precursors. Furthermore, the methodology is applicable to Boc-protected diamines, free amino acids, and aryl halides, which bear functional groups enabling additional rounds of diversification. The method is believed to offer a high potential for constructing DNA-encoded libraries, as was demonstrated by the production of a mock library in a 2 × 3 matrix format and confirmation of DNA stability by UPLC-MS and qPCR experiments.

Small-Molecule Inhibitors of Tankyrases as Prospective Therapeutics for Cancer

Tankyrases are multifunctional poly(adenosine diphosphate-ribose) polymerases that regulate diverse biological processes including telomere maintenance and cellular signaling. These processes are often implicated in a number of human diseases, with cancer being the most prevalent example. Accordingly, tankyrase inhibitors have gained increasing attention as potential therapeutics. Since the discovery of XAV939 and IWR-1 as the first tankyrase inhibitors over two decades ago, tankyrase-targeted drug discovery has made significant progress. This review starts with an introduction of tankyrases, with emphasis placed on their cancer-related functions. Small-molecule inhibitors of tankyrases are subsequently delineated based on their distinct modes of binding to the enzymes. In addition to inhibitors that compete with oxidized nicotinamide adenine dinucleotide (NAD⁺) for binding to the catalytic domain of tankyrases, non-NAD⁺-competitive inhibitors are detailed. This is followed by a description of three clinically trialled tankyrase inhibitors. To conclude, some of challenges and prospects in developing tankyrase-targeted cancer therapies are discussed.

High-power screening (HPS) empowered by DNA-encoded libraries

The world is totally dependent on medications. As science progresses, new, better, and cheaper drugs are needed more than ever. The pharmaceutical industry has been predominantly dependent on high-throughput screening (HTS) for the past three decades. Considering that the discovery rate has been relatively constant, can one hope for a much-needed sudden trend uptick? DNA-encoded libraries (DELs) and similar technologies, that have several orders of magnitude more screening power than HTS, and that we propose to group together under the umbrella term of high-power screening (HPS), are very well positioned to do exactly that. HPS also offers novel screening options such as parallel screening, ex vivo and in vivo screening, as well as a new path to druggable alternatives such as proteolysis targeting chimeras (PROTACs). Altogether, HPS unlocks novel powerful drug discovery avenues.

DNA-Encoded Chemical Libraries: A Comprehensive Review with Succesful Stories and Future Challenges

DNA-encoded chemical libraries (DELs) represent a versatile and powerful technology platform for the discovery of small-molecule ligands to protein targets of biological and pharmaceutical interest. DELs are collections of molecules, individually coupled to distinctive DNA tags serving as amplifiable identification barcodes. Thanks to advances in DNA-compatible reactions, selection methodologies, next-generation sequencing, and data analysis, DEL technology allows the construction and screening of libraries of unprecedented size, which has led to the discovery of highly potent ligands, some of which have progressed to clinical trials. In this Review, we present an overview of diverse approaches for the generation and screening of DEL molecular repertoires. Recent success stories are described, detailing how novel ligands were isolated from DEL screening campaigns and were further optimized by medicinal chemistry. The goal of the Review is to capture some of the most recent developments in the field, while also elaborating on future challenges to further improve DEL technology as a therapeutic discovery platform.

Large screening of DNA-compatible reaction conditions for Suzuki and Sonogashira cross-coupling reactions and for reverse amide bond formation

Progress in DNA-encoded chemical library synthesis and screening crucially relies on the availability of DNA-compatible reactions, which proceed with high yields and excellent purity for a large number of possible building blocks. In the past, experimental conditions have been presented for the execution of Suzuki and Sonogashira cross-coupling reactions on-DNA. In this article, our aim was to optimize Suzuki and Sonogashira reactions, comparing our results to previously published procedures. We have tested the performance of improved conditions using 606 building blocks (including boronic acids, pinacol boranes and terminal alkynes), achieving >70% conversion for 84% of the tested molecules. Moreover, we describe efficient experimental conditions for the on-DNA synthesis of amide bonds, starting from DNA derivatives carrying a carboxylic acid moiety and 300 primary, secondary and aromatic amines, as amide bonds are frequently found in DNA-encoded chemical libraries thanks to their excellent DNA compatibility.

Cholesterol-Modified Oligonucleotides as Internal Reaction Controls during DNA-Encoded Chemical Library Synthesis

We report two cholesterol-modified oligonucleotides for use as internal controls for on-DNA reactions during the pooled stages of a DNA-encoded chemical library (DECL) synthesis. As these cholesterol-tagged oligonucleotides are chromatographically separable from normal DECL intermediates, they can be directly monitored by mass spectrometry to track reaction progression within a complex pool of DNA. We observed similar product conversions for reactions on substrates linked to a standard DECL DNA headpiece, to the cholesterol-modified oligonucleotides, and to the cholesterol-modified oligonucleotides while in the presence of pooled DECL synthetic intermediates-validating their use as a representative control. We also highlight an example from a DECL production in which the use of the cholesterol-modified oligonucleotides provided quality control information that guided synthetic decisions. We conclude that the use of cholesterol-modified oligonucleotides as a regular control will significantly improve the quality of DECL productions.

Developments in Photoredox-Mediated Alkylation for DNA-Encoded Libraries

Recently, DNA-encoded library (DEL) technology has emerged as an innovative screening modality for the rapid discovery of therapeutic candidates in pharmaceutical settings. This platform enables a cost-effective, time-efficient, and large-scale assembly and interrogation of billions of small organic ligands against a biological target in a single experiment. An outstanding challenge in DEL synthesis is the necessity for water-compatible transformations under ambient conditions. To access uncharted chemical space, the adoption of photoredox catalysis in DELs, including Ni-catalyzed manifolds and radical/polar crossover reactions, has enabled the construction of novel structural scaffolds through regulated odd-electron intermediates. Herein, a critical discussion of the validation of photoredox-mediated alkylation in DEL environments is presented. Current synthetic gaps are highlighted and opportunities for further development are speculated upon.

Considerations for Achieving Maximized DNA Recovery in Solid-Phase DNA-Encoded Library Synthesis

DNA-encoded library (DEL) technology enables rapid, economical synthesis, and exploration of novel chemical space. Reaction development for DEL synthesis has recently accelerated in pace with a specific emphasis on ensuring that the reaction does not compromise the integrity of the encoding DNA. However, the factors that contribute to a reaction's "DNA compatibility" remain relatively unknown. We investigated several solid-phase reactions and encoding conditions and determined their impact on DNA compatibility. Conditions that minimized the accessibility of reactive groups on the DNA encoding tag (switching solvent, low temperature, double-stranded encoding tag) significantly improved compatibility. We showcased this approach in the multistep synthesis of an acyldepsipeptide (ADEP1) fragment, which preserved 73% of DNA for a >100-fold improvement over canonical conditions. These results are particularly encouraging in the context of multistep reaction sequences to access natural product-like scaffolds and more broadly underscore the importance of reconciling the biophysical properties and reactivity of DNA with chemistry development to yield high-quality libraries of those scaffolds.

Exploring Aldol Reactions on DNA and Applications to Produce Diverse Structures: An Example of Expanding Chemical Space of DNA-Encoded Compounds by Diversity-Oriented Synthesis

A DNA-encoded chemical library (DECL) is built with combinatorial chemistry, which works by bringing chemical fragments together to generate diverse structures. However, chemical diversity of DNA-encoded chemical libraries is often limited by DNA compatible synthetic reactions. This report shows a conceptual strategy to expand chemical space of DNA-encoded chemical libraries by incorporation of diversity-oriented synthesis in DECL synthesis. We developed Aldol reactions on DNA in a combinatorial way. After obtaining DNA-tagged α, β-unsaturated ketones which represent important chemical intermediates, many distinct structures with skeletal diversities are achieved by diversity-oriented synthesis.

A Single-Stranded DNA-Encoded Chemical Library Based on a Stereoisomeric Scaffold Enables Ligand Discovery by Modular Assembly of Building Blocks

A versatile and Lipinski-compliant DNA-encoded library (DEL), comprising 366 600 glutamic acid derivatives coupled to oligonucleotides serving as amplifiable identification barcodes is designed, constructed, and characterized. The GB-DEL library, constructed in single-stranded DNA format, allows de novo identification of specific binders against several pharmaceutically relevant proteins. Moreover, hybridization of the single-stranded DEL with a set of known protein ligands of low to medium affinity coupled to a complementary DNA strand results in self-assembled selectable chemical structures, leading to the identification of affinity-matured compounds.

Insights of tankyrases: A novel target for drug discovery

Tankyrases are the group of enzymes belonging to a class of Poly (ADP-ribose) polymerase (PARP) recently named ADP-ribosyltransferase (ARTD). The two isoforms of tankyrase i.e. tankyrase1 (TNKS1) and tankyrase2 (TNKS2) were abundantly expressed in various biological functions in telomere regulation, Wnt/β-catenin signaling pathway, viral replication, endogenous hormone regulation, glucose transport, cherubism disease, erectile dysfunction, and apoptosis. The structural analysis, mechanistic information, in vitro and in vivo studies led identification and development of several classes of tankyrase inhibitors under clinical phases. In the nutshell, this review will drive future research on tankyrase as it enlighten the structural and functional features of TNKS 1 and TNKS 2, different classes of inhibitors with their structure-activity relationship studies, molecular modeling studies, as well as past, current and future perspective of the different class of tankyrase inhibitors.

Denoising DNA Encoded Library Screens with Sparse Learning

DNA-encoded libraries (DELs) are large, pooled collections of compounds in which every library member is attached to a stretch of DNA encoding its complete synthetic history. DEL-based hit discovery involves affinity selection of the library against a protein of interest, whereby compounds retained by the target are subsequently identified by next-generation sequencing of the corresponding DNA tags. When analyzing the resulting data, one typically assumes that sequencing output (i.e., read counts) is proportional to the binding affinity of a given compound, thus enabling hit prioritization and elucidation of any underlying structure-activity relationships (SAR). This assumption, though, tends to be severely confounded by a number of factors, including variable reaction yields, presence of incomplete products masquerading as their intended counterparts, and sequencing noise. In practice, these confounders are often ignored, potentially contributing to low hit validation rates, and universally leading to loss of valuable information. To address this issue, we have developed a method for comprehensively denoising DEL selection outputs. Our method, dubbed "deldenoiser", is based on sparse learning and leverages inputs that are commonly available within a DEL generation and screening workflow. Using simulated and publicly available DEL affinity selection data, we show that "deldenoiser" is not only able to recover and rank true binders much more robustly than read count-based approaches but also that it yields scores, which accurately capture the underlying SAR. The proposed method can, thus, be of significant utility in hit prioritization following DEL screens.

A B2(OH)4-Mediated Synthesis of 2-Substituted Indazolone and Its Application in a DNA-Encoded Library

Indazolone cores are among the most common structural components in medicinal chemistry and can be found in many biologically active molecules. In this report, a mild and efficient approach to 2-substituted indazolones via B₂(OH)₄-mediated reductive N-N bond formation is developed. This strategy features mild conditions, no request for a metal catalyst, and a wide scope for both aliphatic and aromatic amines. Meanwhile, this method was further successfully applied on DNA to construct indazolone cores for a DNA-encoded library. This will enable the production of a very attractive indazolone-cored library from simple amines and scaffolds, which will provide considerable diversity.

Comparative evaluation of DNA-encoded chemical selections performed using DNA in single-stranded or double-stranded format

DNA-encoded chemical libraries (DEL) are increasingly being used for the discovery and optimization of small organic ligands to proteins of biological or pharmaceutical interest. The DNA fragments, that serve as amplifiable identification barcodes for individual compounds in the library, are typically used in double-stranded DNA format. To the best of our knowledge, a direct comparison of DEL selections featuring DNA in either single- or double-stranded DNA format has not yet been reported. In this article, we describe a comparative evaluation of selections with two DEL libraries (named GB-DEL and NF-DEL), based on different chemical designs and produced in both single- and double-stranded DNA format. The libraries were selected in identical conditions against multiple protein targets, revealing comparable and reproducible fingerprints for both types of DNA formats. Surprisingly, selections performed with single-stranded DNA barcodes exhibited improved enrichment factors compared to double-stranded DNA. Using high-affinity ligands to carbonic anhydrase IX as benchmarks for selection performance, we observed an improved selectivity for the NF-DEL library (on average 2-fold higher enrichment factors) in favor of single-stranded DNA. The enrichment factors were even higher for the GB-DEL selections (approximately 5-fold), compared to the same library in double-stranded DNA format. Collectively, these results indicate that DEL libraries can conveniently be synthesized and screened in both single- and double-stranded DNA format, but single-stranded DNA barcodes typically yield enhanced enrichment factors.

An overview of DNA-encoded libraries: A versatile tool for drug discovery

DNA-encoded libraries (DELs) are collections of small molecules covalently attached to amplifiable DNA tags carrying unique information about the structure of each library member. A combinatorial approach is used to construct the libraries with iterative DNA encoding steps, facilitating tracking of the synthetic history of the attached compounds by DNA sequencing. Various screening protocols have been developed which allow protein target binders to be selected out of pools containing up to billions of different small molecules. The versatile methodology has allowed identification of numerous biologically active compounds and is now increasingly being adopted as a tool for lead discovery campaigns and identification of chemical probes. A great focus in recent years has been on developing DNA compatible chemistries that expand the structural diversity of the small molecule library members in DELs. This chapter provides an overview of the challenges and accomplishments in DEL technology, reviewing the technological aspects of producing and screening DELs with a perspective on opportunities, limitations, and future directions.

Critical Evaluation of Photo-cross-linking Parameters for the Implementation of Efficient DNA-Encoded Chemical Library Selections

The growing importance of DNA-encoded chemical libraries (DECLs) as tools for the discovery of protein binders has sparked an interest for the development of efficient screening methodologies, capable of discriminating between high- and medium-affinity ligands. Here, we present a systematic investigation of selection methodologies, featuring a library displayed on single-stranded DNA, which could be hybridized to a complementary oligonucleotide carrying a diazirine photoreactive group. Model experiments, performed using ligands of different affinity to carbonic anhydrase IX, revealed a recovery of preferential binders up to 10%, which was mainly limited by the highly reactive nature of carbene intermediates generated during the photo-cross-linking process. Ligands featuring acetazolamide or p-phenylsulfonamide exhibited a higher recovery compared to their counterparts based on 3-sulfamoyl benzoic acid, which had a lower affinity toward the target. A systematic evaluation of experimental parameters revealed conditions that were ideally suited for library screening, which were used for the screening of a combinatorial DECL library, featuring 669 240 combinations of two sets of building blocks. Compared to conventional affinity capture procedures on protein immobilized on solid supports, photo-cross-linking provided a better discrimination of low-affinity CAIX ligands over the background signal and therefore can be used as a tandem methodology with the affinity capture procedures.

DNA-Encoded Library Screening as Core Platform Technology in Drug Discovery: Its Synthetic Method Development and Applications in DEL Synthesis

DNA-encoded library technology (DELT) was introduced to our medicinal chemistry society more than 20 years ago. The application of DELT in the development of clinical candidates has been actively reported in the literature recently. A few representative examples include RIP1K inhibitors for inflammatory diseases and sEH inhibitors for endothelial dysfunction or abnormal tissue repair, among many others. Here, the authors would like to recall the recent developments in on-DNA synthetic methodologies for DEL construction and to analyze recent examples in the literature of DELT-based drug development efforts pursued in both the academic and industrial sectors. With this perspective, we hope to provide a useful summary of recent DELT-based drug discovery research and to discuss the future scope of DELT in medicinal chemistry.

Multifunctional Building Blocks Compatible with Photoredox-Mediated Alkylation for DNA-Encoded Library Synthesis

DNA-encoded library (DEL) technology has emerged as a novel interrogation modality for ligand discovery in the pharmaceutical industry. Given the increasing demand for a higher proportion of C(sp3)-hybridized centers in DEL platforms, a photoredox-mediated cross-coupling and defluorinative alkylation process is introduced using commercially available alkyl bromides and structurally diverse α-silylamines. Notably, no protecting group strategies for amines are necessary for the incorporation of a variety of amino-acid-based organosilanes, providing crucial branching points for further derivatization.

Chemical composition of DNA-encoded libraries, past present and future

DNA-encoded libraries represent an exciting and powerful modality for high-throughput screening. In this article, we highlight recent important advances in this field and also suggest some important directions that would make the technology even more powerful.

EU-OPENSCREEN: A Novel Collaborative Approach to Facilitate Chemical Biology

Compound screening in biological assays and subsequent optimization of hits is indispensable for the development of new molecular research tools and drug candidates. To facilitate such discoveries, the European Research Infrastructure EU-OPENSCREEN was founded recently with the support of its member countries and the European Commission. Its distributed character harnesses complementary knowledge, expertise, and instrumentation in the discipline of chemical biology from 20 European partners, and its open working model ensures that academia and industry can readily access EU-OPENSCREEN's compound collection, equipment, and generated data. To demonstrate the power of this collaborative approach, this perspective article highlights recent projects from EU-OPENSCREEN partner institutions. These studies yielded (1) 2-aminoquinazolin-4(3 H)-ones as potential lead structures for new antimalarial drugs, (2) a novel lipodepsipeptide specifically inducing apoptosis in cells deficient for the pVHL tumor suppressor, (3) small-molecule-based ROCK inhibitors that induce definitive endoderm formation and can potentially be used for regenerative medicine, (4) potential pharmacological chaperones for inborn errors of metabolism and a familiar form of acute myeloid leukemia (AML), and (5) novel tankyrase inhibitors that entered a lead-to-candidate program. Collectively, these findings highlight the benefits of small-molecule screening, the plethora of assay designs, and the close connection between screening and medicinal chemistry within EU-OPENSCREEN.

A DNA-Encoded Library of Chemical Compounds Based on Common Scaffolding Structures Reveals the Impact of Ligand Geometry on Protein Recognition

A DNA-encoded chemical library (DECL) with 1.2 million compounds was synthesized by combinatorial reaction of seven central scaffolds with two sets of 343×492 building blocks. Library screening by affinity capture revealed that for some target proteins, the chemical nature of building blocks dominated the selection results, whereas for other proteins, the central scaffold also crucially contributed to ligand affinity. Molecules based on a 3,5-bis(aminomethyl)benzoic acid core structure were found to bind human serum albumin with a Kd value of 6 nm, while compounds with the same substituents on an equidistant but flexible l-lysine scaffold showed 140-fold lower affinity. A 18 nm tankyrase-1 binder featured l-lysine as linking moiety, while molecules based on d-Lysine or (2S,4S)-amino-l-proline showed no detectable binding to the target. This work suggests that central scaffolds which predispose the orientation of chemical building blocks toward the protein target may enhance the screening productivity of encoded libraries.

DNA-Encoded Chemical Libraries: A Selection System Based on Endowing Organic Compounds with Amplifiable Information

The discovery of organic ligands that bind specifically to proteins is a central problem in chemistry, biology, and the biomedical sciences. The encoding of individual organic molecules with distinctive DNA tags, serving as amplifiable identification bar codes, allows the construction and screening of combinatorial libraries of unprecedented size, thus facilitating the discovery of ligands to many different protein targets. Fundamentally, one links powers of genetics and chemical synthesis. After the initial description of DNA-encoded chemical libraries in 1992, several experimental embodiments of the technology have been reduced to practice. This review provides a historical account of important milestones in the development of DNA-encoded chemical libraries, a survey of relevant ongoing research activities, and a glimpse into the future.

Randomness in DNA Encoded Library Selection Data Can Be Modeled for More Reliable Enrichment Calculation

DNA Encoded Libraries (DELs) use unique DNA sequences to tag each chemical warhead within a library mixture to enable deconvolution following affinity selection against a target protein. With next-generation sequencing, millions to billions of sequences can be read and counted to report binding events. This unprecedented capability has enabled researchers to synthesize and analyze numerically large chemical libraries. Despite the common perception that each library member undergoes a miniaturized affinity assay, selections with higher complexity libraries often produce results that are difficult to rank order. In this study, we aimed to understand the robustness of DEL selection by examining the sequencing readouts of warheads and chemotype families among a large number of experimentally repeated selections. The results revealed that (1) the output of DEL selection is intrinsically noisy but can be reliably modeled by the Poisson distribution, and (2) Poisson noise is the dominating noise at low copy counts and can be estimated even from a single experiment. We also discuss the shortcomings of data analyses based on directly using copy counts and their linear transformations, and propose a framework that incorporates proper normalization and confidence interval calculation to help researchers better understand DEL data.

Regulation of Wnt/β-catenin signalling by tankyrase-dependent poly(ADP-ribosyl)ation and scaffolding

The Wnt/β-catenin signalling pathway is pivotal for stem cell function and the control of cellular differentiation, both during embryonic development and tissue homeostasis in adults. Its activity is carefully controlled through the concerted interactions of concentration-limited pathway components and a wide range of post-translational modifications, including phosphorylation, ubiquitylation, sumoylation, poly(ADP-ribosyl)ation (PARylation) and acetylation. Regulation of Wnt/β-catenin signalling by PARylation was discovered relatively recently. The PARP tankyrase PARylates AXIN1/2, an essential central scaffolding protein in the β-catenin destruction complex, and targets it for degradation, thereby fine-tuning the responsiveness of cells to the Wnt signal. The past few years have not only seen much progress in our understanding of the molecular mechanisms by which PARylation controls the pathway but also witnessed the successful development of tankyrase inhibitors as tool compounds and promising agents for the therapy of Wnt-dependent dysfunctions, including colorectal cancer. Recent work has hinted at more complex roles of tankyrase in Wnt/β-catenin signalling as well as challenges and opportunities in the development of tankyrase inhibitors. Here we review some of the latest advances in our understanding of tankyrase function in the pathway and efforts to modulate tankyrase activity to re-tune Wnt/β-catenin signalling in colorectal cancer cells.

LINKED ARTICLES

This article is part of a themed section on WNT Signalling: Mechanisms and Therapeutic Opportunities. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v174.24/issuetoc.

Combinatorial chemistry in drug discovery

Several combinatorial methods have been developed to create focused or diverse chemical libraries with a wide range of linear or macrocyclic chemical molecules: peptides, non-peptide oligomers, peptidomimetics, small-molecules, and natural product-like organic molecules. Each combinatorial approach has its own unique high-throughput screening and encoding strategy. In this article, we provide a brief overview of combinatorial chemistry in drug discovery with emphasis on recently developed new technologies for design, synthesis, screening and decoding of combinatorial library. Examples of successful application of combinatorial chemistry in hit discovery and lead optimization are given. The limitations and strengths of combinatorial chemistry are also briefly discussed. We are now in a better position to truly leverage the power of combinatorial technologies for the discovery and development of next-generation drugs.

Stability of Oligonucleotide-Small Molecule Conjugates to DNA-Deprotection Conditions

Oligonucleotide conjugates of small molecules are widely used in chemical biology and have found increasing interest in the context of DNA-encoded chemical libraries for drug discovery. Attachment of molecules to DNA bound to the solid support is an attractive small-molecule conjugation method that permits the use of organic solvents, rigorous reaction conditions, and simple workup. However, the conjugated structures must be resistant to the harsh DNA deprotection/cleavage conditions and the stabilities of building blocks under various deprotection conditions are mostly unexplored. In the present study, we analyzed the stability of 131 structurally diverse fragments that contain amides and amide-like elements during DNA deprotection protocols. Structural features susceptible to decomposition in DNA deprotection conditions were identified and a protocol that enabled the synthesis of DNA conjugates with labile fragments on solid support was identified.

Discovery of a Potent BTK Inhibitor with a Novel Binding Mode by Using Parallel Selections with a DNA-Encoded Chemical Library

We have identified and characterized novel potent inhibitors of Bruton's tyrosine kinase (BTK) from a single DNA-encoded library of over 110 million compounds by using multiple parallel selection conditions, including variation in target concentration and addition of known binders to provide competition information. Distinct binding profiles were observed by comparing enrichments of library building block combinations under these conditions; one enriched only at high concentrations of BTK and was competitive with ATP, and another enriched at both high and low concentrations of BTK and was not competitive with ATP. A compound representing the latter profile showed low nanomolar potency in biochemical and cellular BTK assays. Results from kinetic mechanism of action studies were consistent with the selection profiles. Analysis of the co-crystal structure of the most potent compound demonstrated a novel binding mode that revealed a new pocket in BTK. Our results demonstrate that profile-based selection strategies using DNA-encoded libraries form the basis of a new methodology to rapidly identify small molecule inhibitors with novel binding modes to clinically relevant targets.

DNA-encoded chemistry: enabling the deeper sampling of chemical space

DNA-encoded chemical library technologies are increasingly being adopted in drug discovery for hit and lead generation. DNA-encoded chemistry enables the exploration of chemical spaces four to five orders of magnitude more deeply than is achievable by traditional high-throughput screening methods. Operation of this technology requires developing a range of capabilities including aqueous synthetic chemistry, building block acquisition, oligonucleotide conjugation, large-scale molecular biological transformations, selection methodologies, PCR, sequencing, sequence data analysis and the analysis of large chemistry spaces. This Review provides an overview of the development and applications of DNA-encoded chemistry, highlighting the challenges and future directions for the use of this technology.

Recent advances on the encoding and selection methods of DNA-encoded chemical library

DNA-encoded chemical library (DEL) has emerged as a powerful and versatile tool for ligand discovery in chemical biology research and in drug discovery. Encoding and selection methods are two of the most important technological aspects of DEL that can dictate the performance and utilities of DELs. In this digest, we have summarized recent advances on the encoding and selection strategies of DEL and also discussed the latest developments on DNA-encoded dynamic library, a new frontier in DEL research.

DNA-encoded chemical libraries: foundations and applications in lead discovery

DNA-encoded chemical libraries have emerged as a powerful tool for hit identification in the pharmaceutical industry and in academia. Similar to biological display techniques (such as phage display technology), DNA-encoded chemical libraries contain a link between the displayed chemical building block and an amplifiable genetic barcode on DNA. Using routine procedures, libraries containing millions to billions of compounds can be easily produced within a few weeks. The resulting compound libraries are screened in a single test tube against proteins of pharmaceutical interest and hits can be identified by PCR amplification of DNA barcodes and subsequent high-throughput sequencing.

Automated screening for small organic ligands using DNA-encoded chemical libraries

DNA-encoded chemical libraries (DECLs) are collections of organic compounds that are individually linked to different oligonucleotides, serving as amplifiable identification barcodes. As all compounds in the library can be identified by their DNA tags, they can be mixed and used in affinity-capture experiments on target proteins of interest. In this protocol, we describe the screening process that allows the identification of the few binding molecules within the multiplicity of library members. First, the automated affinity selection process physically isolates binding library members. Second, the DNA codes of the isolated binders are PCR-amplified and subjected to high-throughput DNA sequencing. Third, the obtained sequencing data are evaluated using a C++ program and the results are displayed using MATLAB software. The resulting selection fingerprints facilitate the discrimination of binding from nonbinding library members. The described procedures allow the identification of small organic ligands to biological targets from a DECL within 10 d.