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DNA-encoded library (DEL) technology has become a prominent screening platform in drug discovery owing to the capacity to screen billions or trillions of compounds in a single experiment. Although numerous successes with DEL technology have been reported, we are unaware of a rigorous examination of the many different variables that can influence a screen's success. Herein, we explore the impact of variable sample sequencing depth on the detection of tool compounds with known affinities toward a given target while simultaneously probing the effect of initial compound input. Our sequencing data confirm reports that high-affinity compounds can be discovered directly from a DEL screen, but we demonstrate that a mismatch between selection output and sequencing quantity can obscure useful ligands. Our results highlight the importance of selection coverage in grasping the entire picture of a DEL screen where the signal of a weak or underrepresented ligand may be suppressed by the inherent noise of a selection. These potential missed ligands may be critical to the success or failure of a drug discovery program.

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.

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.

To identify BCATm inhibitors suitable for in vivo study, Encoded Library Technology (ELT) was used to affinity screen a 117 million member benzimidazole based DNA encoded library, which identified an inhibitor series with both biochemical and cellular activities. Subsequent SAR studies led to the discovery of a highly potent and selective compound, 1-(3-(5-bromothiophene-2-carboxamido)cyclohexyl)-N-methyl-2-(pyridin-2-yl)-1H-benzo[d]imidazole-5-carboxamide (8b) with much improved PK properties. X-ray structure revealed that 8b binds to the active site of BACTm in a unique mode via multiple H-bond and van der Waals interactions. After oral administration, 8b raised mouse blood levels of all three branched chain amino acids as a consequence of BCATm inhibition.

As a potential target for obesity, human BCATm was screened against more than 14 billion DNA encoded compounds of distinct scaffolds followed by off-DNA synthesis and activity confirmation. As a consequence, several series of BCATm inhibitors were discovered. One representative compound (R)-3-((1-(5-bromothiophene-2-carbonyl)pyrrolidin-3-yl)oxy)-N-methyl-2′-(methylsulfonamido)-[1,1′-biphenyl]-4-carboxamide (15e) from a novel compound library synthesized via on-DNA Suzuki–Miyaura cross-coupling showed BCATm inhibitory activity with IC50 = 2.0 μM. A protein crystal structure of 15e revealed that it binds to BCATm within the catalytic site adjacent to the PLP cofactor. The identification of this novel inhibitor series plus the establishment of a BCATm protein structure provided a good starting point for future structure-based discovery of BCATm inhibitors.

SCH-C (SCH 351125) is a small-molecule antagonist of the human immunodeficiency virus type 1(HIV-1) coreceptor CCR5. It has in vitro activity against R5 viruses with 50% inhibitory concentrations ranging from 1.0 to 30.9 nM. We have studied anti-HIV-1 interactions of SCH-C with other antiretroviral agents in vitro. Synergistic interactions were seen with nucleoside reverse transcriptase inhibitors (zidovudine and lamivudine), nonnucleoside reverse transcriptase inhibitors (efavirenz), and protease inhibitors (indinavir) at all inhibitory concentrations evaluated. We have also studied antiviral interactions between the HIV-1 fusion inhibitor T-20 and SCH-C against a panel of R5 HIV-1 isolates. We found synergistic interactions against all the viruses tested, some of which harbored resistance mutations to reverse transcriptase and protease inhibitors. Anti-HIV-1 synergy was also observed between SCH-C and another R5 virus inhibitor, aminooxypentane-RANTES. These findings suggest that SCH-C may be a useful anti-HIV drug in combination regimens and that a combination of chemokine coreceptor/fusion inhibitors may be useful in the treatment of multidrug-resistant viruses.

Attachment and entry of HIV-1 into CD4 cells involve a series of events in which different viral envelope proteins interact with specific cell receptors, culminating in fusion of viral and cell membranes. AMD-3100 is a small molecule inhibitor of HIV-1 attachment to the CXCR4 chemokine receptor, and T-20 is a synthetic peptide corresponding to a region of HIV-1 gp41 that blocks fusion to cell membranes. To evaluate the interaction between agents acting at two different steps of the entry process, we conducted in vitro studies of the combination of T-20 and AMD-3100 against an X4 HIV-1 isolate. Single drugs or multiply diluted fixed ratio combinations of drugs were added to peripheral blood mononuclear cells infected with a clinical isolate, 14aPre. Drug interactions were evaluated using the median-effect principle and the combination index technique. The 50% inhibitory concentration (IC50) for T-20 was 0.10 microg/ml and for AMD-3100 was 0.19 microg/ml. Synergy was observed between T-20 and AMD-3100 and this increased with higher inhibitory concentrations, with combination indices ranging from 0.62 at IC50 to 0.02 at IC95. Whether these synergistic interactions translate into clinical benefit will need to be addressed in the context of clinical trials.

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.