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[Image: see text] DNA-encoded library (DEL) technology is a powerful platform for hit identification in academia and the pharmaceutical industry. When conducting off-DNA resynthesis hit confirmation after affinity selection, PCR/sequencing, and data analysis, one typically assumes a “one-to-one” relationship between the DNA tag and the chemical structure of the attached small-molecule it encodes. Because library synthesis often yields a mixture, this approximation increases the risk of overlooking positive discoveries and valuable information. To address this issue, we apply a library synthesis “recipe” strategy for on-DNA resynthesis using a cleavable linker, followed by direct affinity selection mass spectrometry (AS-MS) evaluation and identification of binder(s) from the released small-molecule mixture. We validate and showcase this approach employing the receptor-interacting-protein kinase 2 (RIP2) DEL campaign. We also designed and developed two cleavable linkers to enable this method, a photocleavable linker (nitrophenyl-based) and acid-labile linker (tetrahydropyranyl ether). The strategy provides an effective means of hit identification and rapid determination of key active component(s) of the mixture.

DNA-encoded library technology (ELT) is a cutting-edge enabling technology platform for drug discovery. Here we describe how to design and synthesize a macrocyclic DNA-encoded library; how to perform selection, sequencing, and data analysis to identify potential active peptides; and how to synthesize off-DNA peptides to confirm activity. This approach provides an effective tool for pharmaceutical research based on peptides.

DNA-encoded libraries (DELs) have been broadly applied to identify chemical probes for target validation and lead discovery. To date, the main application of the DEL platform has been the identification of reversible ligands using multiple rounds of affinity selection. Irreversible (covalent) inhibition offers a unique mechanism of action for drug discovery research. In this study, we report a developing method of identifying irreversible (covalent) ligands from DELs. The new method was validated by using 3C protease (3CP) and on-DNA irreversible tool compounds (rupintrivir derivatives) spiked into a library at the same concentration as individual members of that library. After affinity selections against 3CP, the irreversible tool compounds were specifically enriched compared with the library members. In addition, we compared two immobilization methods and concluded that microscale columns packed with the appropriate affinity resin gave higher tool compound recovery than magnetic beads.

Nature Communications 8: Article number: 16081 (2017); Published: 17 July 2017, Updated: 13 July 2018 The original version of this Article omitted the following from the Acknowledgements: ‘We thank Robert Kirkpatrick for implementing the high throughput protein design strategy that enabled screeningand triage of essential A.

To identify novel antivirals to the hepatitis C virus (HCV) NS4B protein, we utilized encoded library technology (ELT), which enables purified proteins not amenable to standard biochemical screening methods to be tested against large combinatorial libraries in a short period of time. We tested NS4B against several DNA-encoded combinatorial libraries (DEL) and identified a single DEL feature that was subsequently progressed to off-DNA synthesis. The most active of the initial synthesized compounds had 50% inhibitory concentrations (IC 50 s) of 50 to 130 nM in a NS4B radioligand binding assay and 300 to 500 nM in an HCV replicon assay. Chemical optimization yielded compounds with potencies as low as 20 nM in an HCV genotype 1b replicon assay, 500 nM against genotype 1a, and 5 μM against genotype 2a. Through testing against other genotypes and genotype 2a-1b chimeric replicons and from resistance passage using the genotype 1b replicon, we confirmed that these compounds were acting on the proposed first transmembrane region of NS4B. A single sequence change (F98L) was identified as responsible for resistance, and it was thought to largely explain the relative lack of potency of this series against genotype 2a. Unlike other published series that appear to interact with this region, we did not observe sensitivity to amino acid substitutions at positions 94 and 105. The discovery of this novel compound series highlights ELT as a valuable approach for identifying direct-acting antivirals to nonenzymatic targets.

In the search of PI3K p110α wild type and H1047R mutant selective small molecule leads, an encoded library technology (ELT) campaign against the desired target proteins was performed which led to the discovery of a selective chemotype for PI3K isoforms from a three-cycle DNA encoded library. An X-ray crystal structure of a representative inhibitor from this chemotype demonstrated a unique binding mode in the p110α protein.

The inhibition of protein-protein interactions remains a challenge for traditional small molecule drug discovery. Here we describe the use of DNA-encoded library technology for the discovery of small molecules that are potent inhibitors of the interaction between lymphocyte function-associated antigen 1 and its ligand intercellular adhesion molecule 1. A DNA-encoded library with a potential complexity of 4.1 billion compounds was exposed to the I-domain of the target protein and the bound ligands were affinity selected, yielding an enriched small-molecule hit family. Compounds representing this family were synthesized without their DNA encoding moiety and found to inhibit the lymphocyte function-associated antigen 1/intercellular adhesion molecule-1 interaction with submicromolar potency in both ELISA and cell adhesion assays. Re-synthesized compounds conjugated to DNA or a fluorophore were demonstrated to bind to cells expressing the target protein.

The sirtuins SIRT1, SIRT2, and SIRT3 are NAD(+) dependent deacetylases that are considered potential targets for metabolic, inflammatory, oncologic, and neurodegenerative disorders. Encoded library technology (ELT) was used to affinity screen a 1.2 million heterocycle enriched library of DNA encoded small molecules, which identified pan-inhibitors of SIRT1/2/3 with nanomolar potency (e.g., 11c: IC50 = 3.6, 2.7, and 4.0 nM for SIRT1, SIRT2, and SIRT3, respectively). Subsequent SAR studies to improve physiochemical properties identified the potent drug like analogues 28 and 31. Crystallographic studies of 11c, 28, and 31 bound in the SIRT3 active site revealed that the common carboxamide binds in the nicotinamide C-pocket and the aliphatic portions of the inhibitors extend through the substrate channel, explaining the observable SAR. These pan SIRT1/2/3 inhibitors, representing a novel chemotype, are significantly more potent than currently available inhibitors, which makes them valuable tools for sirtuin research.

The identification and prioritization of chemically tractable therapeutic targets is a significant challenge in the discovery of new medicines. We have developed a novel method that rapidly screens multiple proteins in parallel using DNA-encoded library technology (ELT). Initial efforts were focused on the efficient discovery of antibacterial leads against 119 targets from Acinetobacter baumannii and Staphylococcus aureus. The success of this effort led to the hypothesis that the relative number of ELT binders alone could be used to assess the ligandability of large sets of proteins. This concept was further explored by screening 42 targets from Mycobacterium tuberculosis. Active chemical series for six targets from our initial effort as well as three chemotypes for DHFR from M. tuberculosis are reported. The findings demonstrate that parallel ELT selections can be used to assess ligandability and highlight opportunities for successful lead and tool discovery., Encoded Library Technology (ELT) has streamlined the identification of chemical ligands for protein targets in drug discovery. Here, the authors optimize the ELT approach to screen multiple proteins in parallel and identify promising targets and antibacterial compounds for S. aureus, A. baumannii and M. tuberculosis.

PAD4 has been strongly implicated in the pathogenesis of autoimmune, cardiovascular and oncological diseases through clinical genetics and gene disruption in mice. New selective PAD4 inhibitors binding a calcium-deficient form of the PAD4 enzyme have validated the critical enzymatic role of human and mouse PAD4 in both histone citrullination and neutrophil extracellular trap formation for, to our knowledge, the first time. The therapeutic potential of PAD4 inhibitors can now be explored. Published version

Inhibition of methionine aminopeptidase-2 (MetAP2) represents a novel approach to antiangiogenic therapy. We describe the synthesis and activity of fumagillin analogues that address the pharmacokinetic and safety liabilities of earlier candidates in this compound class. Two-step elaboration of fumagillol with amines yielded a diverse series of carbamates at C6 of the cyclohexane spiroepoxide. The most potent of these compounds exhibited subnanomolar inhibition of cell proliferation in HUVEC and BAEC assays. Although a range of functionalities were tolerated at this position, alpha-trisubstituted amines possessed markedly decreased inhibitory activity, and this could be rationalized by modeling based on the known fumagillin-MetAP2 crystal structure. The lead compound resulting from these studies, (3R,4S,5S,6R)-5-methoxy-4-((2R,3R)-2-methyl-3-(3-methylbut-2-enyl)oxiran-2-yl)-1-oxaspiro[2.5]octan-6-yl (R)-1-amino-3-methyl-1-oxobutan-2-ylcarbamate, (PPI-2458), demonstrated an improved pharmacokinetic profile relative to the earlier clinical candidate TNP-470, and has advanced into phase I clinical studies in non-Hodgkin's lymphoma and solid cancers.

Biochemical combinatorial techniques such as phage display, RNA display and oligonucleotide aptamers have proven to be reliable methods for generation of ligands to protein targets. Adapting these techniques to small synthetic molecules has been a long-sought goal. We report the synthesis and interrogation of an 800-million-member DNA-encoded library in which small molecules are covalently attached to an encoding oligonucleotide. The library was assembled by a combination of chemical and enzymatic synthesis, and interrogated by affinity selection. We describe methods for the selection and deconvolution of the chemical display library, and the discovery of inhibitors for two enzymes: Aurora A kinase and p38 MAP kinase.

The physical properties of a DNA:RNA hybrid sequence d(CCAACGTTGG)*(CCAACGUUGG) with modifications at the C2'-positions of the DNA strand by 2'-O-methyl (OMe) and 2'-S-methyl (SMe) groups are studied using computational techniques. Molecular dynamics simu-lations of SMe_DNA:RNA, OMe_DNA:RNA and standard DNA:RNA hybrids in explicit water indicate that the nature of the C2'-substituent has a significant influence on the macromolecular conformation. While the RNA strand in all duplexes maintains a strong preference for C3'-endo sugar puckering, the DNA strand shows considerable variation in this parameter depending on the nature of the C2'-substituent. In general, the preference for C3'-endo puckering follows the following trend: OMe_DNA>DNA>SMe_DNA. These results are further corroborated using ab initio methods. Both gas phase and implicit solvation calculations show the C2'-OMe group stabilizes the C3'-endo conformation while the less electronegative SMe group stabilizes the C2'-endo conformation when compared to the standard nucleoside. The macromolecular conformation of these nucleic acids also follows an analogous trend with the degree of A-form character decreasing as OMe_DNA:RNA>DNA:RNA>SMe_DNA:RNA. A structural analysis of these complexes is performed and compared with experimental melting point temper-atures to explain the structural basis to improved binding affinity across this series. Finally, a possible correlation between RNase H activity and conformational changes within the minor groove of these complexes is hypothesized.

The metalloprotease ADAMTS-5 is considered a potential target for the treatment of osteoarthritis. To identify selective inhibitors of ADAMTS-5, we employed encoded library technology (ELT), which enables affinity selection of small molecule binders from complex mixtures by DNA tagging. Selection of ADAMTS-5 against a four-billion member ELT library led to a novel inhibitor scaffold not containing a classical zinc-binding functionality. One exemplar, (R)-N-((1-(4-(but-3-en-1-ylamino)-6-(((2-(thiophen-2-yl)thiazol-4-yl)methyl)amino)-1,3,5-triazin-2-yl)pyrrolidin-2-yl)methyl)-4-propylbenzenesulfonamide (8), inhibited ADAMTS-5 with IC(50) = 30 nM, showing50-fold selectivity against ADAMTS-4 and1000-fold selectivity against ADAMTS-1, ADAMTS-13, MMP-13, and TACE. Extensive SAR studies showed that potency and physicochemical properties of the scaffold could be further improved. Furthermore, in a human osteoarthritis cartilage explant study, compounds 8 and 15f inhibited aggrecanase-mediated (374)ARGS neoepitope release from aggrecan and glycosaminoglycan in response to IL-1β/OSM stimulation. This study provides the first small molecule evidence for the critical role of ADAMTS-5 in human cartilage degradation.

We have initiated a program to develop promising drug candidate leads using a new drug discovery paradigm based on three-dimensional RNA-structure-based computational screening of about 200,000 commercially available compounds for binding to selected RNA targets. As our first endeavor, we are using the three-dimensional structure of portions of the HIV-1 genome. Candidate lead compounds we seek are water-soluble, nonpeptide, nonnucleotide organic compounds generally with molecular weight less than 500 daltons. Structural studies of complexes formed with potential leads and their RNA targets should eventually yield insight into features governing affinity and specificity. The promising leads identified by virtual screening are tested for inhibition in functional assays. Leads will be selected for further development via computational and experimental combinatorial chemistry.

BACE-1 (beta-site amyloid precursor protein cleaving enzyme), a prominent target in Alzheimer's disease drug discovery efforts, was surveyed using Tethering technology to discover small molecule fragment ligands that bind to the enzyme active site. Screens of a library of >15000 thiol-containing fragments versus a panel of BACE-1 active site cysteine mutants under redox-controlled conditions revealed several novel amine-containing fragments that could be selectively captured by subsets of the tethering sites. For one such hit class, defined by a central aminobenzylpiperidine (ABP) moiety, X-ray crystal structures of BACE mutant-disulfide conjugates revealed that the fragment bound by engaging both catalytic aspartates with hydrogen bonds. The affinities of ABP fragments were improved by structure-guided chemistry, first for conjugation as thiol-containing fragments and then for stand-alone, noncovalent inhibition of wild-type (WT) BACE-1 activity. Crystallography confirmed that the inhibitors bound in exactly the same mode as the disulfide-conjugated fragments that were originally selected from the screen. The ABP ligands represent a new type of nonpeptidic BACE-1 inhibitor motif that has not been described in the aspartyl protease literature and may serve as a starting point for the development of BACE-1-directed Alzheimer's disease therapeutics.

HIV-1 TAR RNA functions critically in viral replication by binding the transactivating regulatory protein Tat. We recently identified several compounds that experimentally inhibit the Tat-TAR interaction completely at a 100 nM concentration. We used computational screening of the 181,000-compound Available Chemicals Directory against the three-dimensional structure of TAR [1]. Here we report the NMR-derived structure of TAR complexed with acetylpromazine. This structure represents a new class of compounds with good bioavailability and low toxicity that bind with high affinity to TAR. NMR data unambiguously show that acetylpromazine binds only to the unique 5′ bulge site to which the Tat protein binds. Specificity and affinity of binding are conferred primarily by a network of base stacking and hydrophobic interactions. Acetylpromazine alters the structure of free TAR less than Tat peptides and neomycin do.

The structure and physical properties of 2'-sugar substituted O -(2-methoxyethyl) (MOE) nucleic acids have been studied using molecular dynamics simulations. Nanosecond simulations on the duplex MOE[CCAACGTTGG]-r[CCAACGUUGG] in aqueous solution have been carried out using the particle mesh Ewald method. Parameters for the simulation have been developed from ab initio calculations on dimethoxyethyl fragments in a manner consistent with the AMBER 4.1 force field database. The simulated duplex is compared with the crystal structure of the self-complementary duplex d[GCGTATMOEACGC]2, which contains a single modification in each strand. Structural details from each sequence have been analyzed to rationalize the stability imparted by substitution with 2'- O -(2-methoxyethyl) side chains. Both duplexes have an A-form structure, as indicated by several parameters, most notably a C3' endo sugar pucker in all residues. The simulated structure maintains a stable A-form geometry throughout the duration of the simulation with an average RMS deviation of 2.0 A from the starting A-form structure. The presence of the 2' substitution appears to lock the sugars in the C3' endo conformation, causing the duplex to adopt a stable A-form geometry. The side chains themselves have a fairly rigid geometry with trans , trans , gauche +/- and trans rotations about the C2'-O2', O2'-CA', CA'-CB' and CB'-OC' bonds respectively.

Nat. Chem. Biol. 5, 647–654 (2009); published online 2 August 2009; corrected after print 17 September 2009 In the version of this article initially published, the IC50 values in the table in Figure 3c were listed as nM instead of μM. The error has been corrected in the HTML and PDF versions of the article.

There has been little prior effort to discover new drugs on the basis of a unique RNA structure. Binding of the viral transactivator Tat to the 5′ bulge of the transactivation response (TAR) element is necessary for HIV-1 replication, so TAR RNA is a superb target. A computational approach was developed to screen a large chemical library for binding to a three-dimensional RNA structure. Scoring function development, flexible ligand docking, and limited target flexibility were essential. From the ranked list of compounds predicted to bind TAR, 43 were assayed for inhibition of the Tat-TAR interaction via electrophoretic mobility shift assays. Eleven compounds (between 0.1 and 1 μM) inhibited the Tat-TAR interaction, and some inhibited Tat transactivation in cells. NMR spectra verified specific binding to the 5′ bulge and no interaction with other regions of TAR.