Targeting tuberculosis using structure-guided fragment-based drug design.
Drug Discov Today. 2016 Oct 11;:
Authors: Mendes V, Blundell TL
Fragment-based drug discovery is now widely used in academia and industry to obtain small molecule inhibitors for a given target and is established for many fields of research including antimicrobials and oncology. Many molecules derived from fragment-based approaches are already in clinical trials and two - vemurafenib and venetoclax - are on the market, but the approach has been used sparsely in the tuberculosis field. Here, we describe the progress of our group and others, and examine the most recent successes and challenges in developing compounds with antimycobacterial activity.
PMID: 27742535 [PubMed - as supplied by publisher]
Developing Antagonists for the Met-HGF/SF Protein-Protein Interaction Using a Fragment-Based Approach.
Mol Cancer Ther. 2016 Jan;15(1):3-14
Authors: Winter A, Sigurdardottir AG, DiCara D, Valenti G, Blundell TL, Gherardi E
In many cancers, aberrant activation of the Met receptor tyrosine kinase leads to dissociation of cells from the primary tumor, causing metastasis. Accordingly, Met is a high-profile target for the development of cancer therapies, and progress has been made through development of small molecule kinase inhibitors and antibodies. However, both approaches pose significant challenges with respect to either target specificity (kinase inhibitors) or the cost involved in treating large patient cohorts (antibodies). Here, we use a fragment-based approach in order to target the protein-protein interaction (PPI) between the α-chain of hepatocyte growth factor/scatter factor (HGF/SF; the NK1 fragment) and its high-affinity binding site located on the Met Sema domain. Surface plasmon resonance was used for initial fragment library screening and hits were developed into larger compounds using substructure (similarity) searches. We identified compounds able to interfere with NK1 binding to Met, disrupt Met signaling, and inhibit tumorsphere generation and cell migration. Using molecular docking, we concluded that some of these compounds inhibit the PPI directly, whereas others act indirectly. Our results indicate that chemical fragments can efficiently target the HGF/SF-Met interface and may be used as building blocks for generating biologically active lead compounds. This strategy may have broad application for the development of a new class of Met inhibitors, namely receptor antagonists, and in general for the development of small molecule PPI inhibitors of key therapeutic targets when structural information is not available.
PMID: 26712116 [PubMed - indexed for MEDLINE]
Different DNA End Configurations Dictate Which NHEJ Components are Most Important for Joining Efficiency.
J Biol Chem. 2016 Oct 4;:
Authors: Chang HH, Watanabe G, Gerodimos CA, Ochi T, Blundell TL, Jackson SP, Lieber MR
The nonhomologous DNA end-joining (NHEJ) pathway is a key mechanism for repairing double-stranded DNA (dsDNA) breaks that occur often in eukaryotic cells. In the simplest model, these breaks are first recognized by Ku, which then interacts with other NHEJ proteins to improve their affinity at DNA ends. These include DNA-PKcs and Artemis for trimming the DNA ends; DNA polymerase μ and λ to add nucleotides; and the DNA ligase IV complex to ligate the ends with the additional factors, XRCC4 (X-ray repair cross-complementing protein 4), XLF (XRCC4-like factor/Cernunos), and PAXX (Paralog of XRCC4 and XLF). In vivo studies have demonstrated the degrees of importance of these NHEJ proteins in the mechanism of repair of dsDNA breaks, but interpretations can be confounded by other cellular processes. In vitro studies with NHEJ proteins have been performed to evaluate the nucleolytic resection, polymerization, and ligation steps but a complete system has been elusive. Here we have developed an NHEJ reconstitution system that includes the nuclease, polymerase, and ligase components to evaluate relative NHEJ efficiency and analyze ligated junctional sequences for various types of DNA ends, including blunt, 5' overhangs, and 3' overhangs. We find that different dsDNA end structures have differential dependence on these enzymatic components. The dependence of some end joining on only Ku and XRCC4:DNA ligase IV allows us to formulate a physical model that incorporates nuclease and polymerase components as needed.
PMID: 27703001 [PubMed - as supplied by publisher]
The Inosine Monophosphate Dehydrogenase, GuaB2, Is a Vulnerable New Bactericidal Drug Target for Tuberculosis.
ACS Infect Dis. 2016 Sep 8;
Authors: Singh V, Donini S, Pacitto A, Sala C, Hartkoorn RC, Dhar N, Keri G, Ascher DB, Mondésert G, Vocat A, Lupien A, Sommer R, Vermet H, Lagrange S, Buechler J, Warner DF, McKinney JD, Pato J, Cole ST, Blundell TL, Rizzi M, Mizrahi V
VCC234718, a molecule with growth inhibitory activity against Mycobacterium tuberculosis (Mtb), was identified by phenotypic screening of a 15344-compound library. Sequencing of a VCC234718-resistant mutant identified a Y487C substitution in the inosine monophosphate dehydrogenase, GuaB2, which was subsequently validated to be the primary molecular target of VCC234718 in Mtb. VCC234718 inhibits Mtb GuaB2 with a Ki of 100 nM and is uncompetitive with respect to IMP and NAD(+). This compound binds at the NAD(+) site, after IMP has bound, and makes direct interactions with IMP; therefore, the inhibitor is by definition uncompetitive. VCC234718 forms strong pi interactions with the Y487 residue side chain from the adjacent protomer in the tetramer, explaining the resistance-conferring mutation. In addition to sensitizing Mtb to VCC234718, depletion of GuaB2 was bactericidal in Mtb in vitro and in macrophages. When supplied at a high concentration (≥125 μM), guanine alleviated the toxicity of VCC234718 treatment or GuaB2 depletion via purine salvage. However, transcriptional silencing of guaB2 prevented Mtb from establishing an infection in mice, confirming that Mtb has limited access to guanine in this animal model. Together, these data provide compelling validation of GuaB2 as a new tuberculosis drug target.
PMID: 27726334 [PubMed - as supplied by publisher]
Engineering archeal surrogate systems for the development of protein-protein interaction inhibitors against human RAD51.
J Mol Biol. 2016 Oct 7;:
Authors: Moschetti T, Sharpe T, Fischer G, Marsh ME, Ng H, Morgan M, Scott D, Blundell TL, Venkitaraman A, Skidmore J, Abell C, Hyvönen M
Protein-protein interactions (PPIs) are increasingly important targets for drug discovery. Efficient fragment-based drug discovery approaches to tackle PPIs are often stymied by difficulties in the production of stable, unliganded target proteins. Here, we report an approach that exploits protein engineering to 'humanise' thermophilic archeal surrogate proteins as targets for small molecule inhibitor discovery, and exemplify this approach in the development of inhibitors against the PPI between the recombinase RAD51 and tumour suppressor BRCA2. As human RAD51 has proved impossible to produce in a form that is compatible with the requirements of fragment-based drug discovery, we have developed a surrogate protein system using RadA from Pyrococcus furiosus. Using a monomerised RadA as our starting point, we have adopted two parallel and mutually instructive approaches to mimic the human enzyme: firstly by mutating RadA to increase sequence identity with RAD51 in the BRC repeat binding sites, and secondly by generating a chimeric archaeal-human protein. Both approaches generate proteins that interact with a BRC4 repeat with affinity and stoichiometry comparable to human RAD51. Stepwise humanisation has also allowed us to elucidate the determinants of RAD51 binding to BRC repeats and the contributions of key interacting residues to this interaction. These surrogate proteins have enabled the development of biochemical and biophysical assays in our ongoing fragment-based small molecule inhibitor programme and they have allowed us to determine hundreds of liganded structures in support of our structure-guided design process, demonstrating the feasibility and advantages of using archeal surrogates to overcome difficulties in handling human proteins.
PMID: 27725183 [PubMed - as supplied by publisher]
Structure of Mycobacterium thermoresistibile GlgE defines novel conformational states that contribute to the catalytic mechanism.
Sci Rep. 2015 Nov 30;5:17144
Authors: Mendes V, Blaszczyk M, Maranha A, Empadinhas N, Blundell TL
GlgE, an enzyme of the pathway that converts trehalose to α-glucans, is essential for Mycobacterium tuberculosis. Inhibition of GlgE, which transfers maltose from a maltose-1-phosphate donor to α-glucan/maltooligosaccharide chain acceptor, leads to a toxic accumulation of maltose-1-phosphate that culminates in cellular death. Here we describe the first high-resolution mycobacterial GlgE structure from Mycobacterium thermoresistibile at 1.96 Å. We show that the structure resembles that of M. tuberculosis and Streptomyces coelicolor GlgEs, reported before, with each protomer in the homodimer comprising five domains. However, in M. thermoresistibile GlgE we observe several conformational states of the S domain and provide evidence that its high flexibility is important for enzyme activity. The structures here reported shed further light on the interactions between the N-terminal domains and the catalytic domains of opposing chains and how they contribute to the catalytic reaction. Importantly this work identifies a useful surrogate system to aid the development of GlgE inhibitors against opportunistic and pathogenic mycobacteria.
PMID: 26616850 [PubMed - indexed for MEDLINE]
Essential but not vulnerable: indazole sulfonamides targeting inosine monophosphate dehydrogenase as potential leads against Mycobacterium tuberculosis.
ACS Infect Dis. 2016 Oct 5;:
Authors: Park Y, Pacitto A, Bayliss T, Cleghorn LA, Wang Z, Hartman T, Arora K, Ioerger TR, Sacchettini J, Rizzi M, Donini S, Blundell TL, Ascher DB, Rhee KY, Breda A, Zhou N, Dartois V, Jonnala SR, Via LE, Mizrahi V, Epemolu O, Stojanovski L, Simeons FR, Osuna-Cabello M, Ellis L, MacKenzie CJ, Smith AR, Davis SH, Murugesan D, Buchanan KI, Turner PA, Huggett M, Zuccotto F, Rebollo-Lopez MJ, Lafuente-Monasterio MJ, Sanz O, Santos Diaz G, Lelièvre J, Ballell L, Selenski C, Axtman M, Ghidelli-Disse S, Pflaumer H, Boesche M, Drewes G, Freiberg G, Kurnick MD, Srikumaran M, Kempf DJ, Green SR, Ray PC, Read KD, Wyatt PG, Barry Rd CE, Boshoff HI
A potent, non-cytotoxic indazole sulfonamide was identified by high-throughput screening of >100,000 synthetic compounds for activity against Mycobacterium tuberculosis (Mtb). This non-cytotoxic compound did not directly inhibit cell wall biogenesis but triggered a slow lysis of Mtb cells as measured by release of intracellular green fluorescent protein (GFP). Isolation of resistant mutants followed by whole-genome sequencing showed an unusual gene amplification of a 40 gene region spanning Rv3371 to Rv3411c and in one case a potential promoter mutation upstream of guaB2 (Rv3411c) encoding inosine monophosphate dehydrogenase (IMPDH). Subsequent biochemical validation confirmed direct inhibition of IMPDH by an uncompetitive mode of inhibition and growth inhibition could be rescued by supplementation with guanine, a bypass mechanism for the IMPDH pathway. Beads containing immobilized indazole sulfonamides specifically interacted with IMPDH in cell lysates. X-ray crystallography of the IMPDH-IMP-inhibitor complex revealed that the primary interactions of these compounds with IMPDH were direct pi-pi interactions with the IMP substrate. Advanced lead compounds in this series with acceptable pharmacokinetic properties failed to show efficacy in acute or chronic murine models of tuberculosis (TB). Time-kill experiments in vitro suggest that sustained exposure to drug concentrations above MIC for 24 hours were required for a cidal effect, levels that have been difficult to achieve in vivo. Direct measurement of guanine levels in resected lung tissue from tuberculosis infected animals and patients revealed 0.5-2 mM concentrations in caseum and normal lung tissue. The high lesional levels of guanine and the slow lytic, growth-rate dependent, effect of IMPDH inhibition pose challenges to developing drugs against this target for use in treating TB.
PMID: 27704782 [PubMed - as supplied by publisher]
Optimization of Inhibitors of Mycobacterium tuberculosis Pantothenate Synthetase Based on Group Efficiency Analysis.
ChemMedChem. 2016 Jan 5;11(1):38-42
Authors: Hung AW, Silvestre HL, Wen S, George GP, Boland J, Blundell TL, Ciulli A, Abell C
Ligand efficiency has proven to be a valuable concept for optimization of leads in the early stages of drug design. Taking this one step further, group efficiency (GE) evaluates the binding efficiency of each appendage of a molecule, further fine-tuning the drug design process. Here, GE analysis is used to systematically improve the potency of inhibitors of Mycobacterium tuberculosis pantothenate synthetase, an important target in tuberculosis therapy. Binding efficiencies were found to be distributed unevenly within a lead molecule derived using a fragment-based approach. Substitution of the less efficient parts of the molecule allowed systematic development of more potent compounds. This method of dissecting and analyzing different groups within a molecule offers a rational and general way of carrying out lead optimization, with potential broad application within drug discovery.
PMID: 26486566 [PubMed - indexed for MEDLINE]