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Rhinoviruses are the pathogens most often responsible for the common cold, and are a frequent cause of exacerbations in asthma, chronic obstructive pulmonary disease and cystic fibrosis. Here we report discovery of IMP-1088, a picomolar dual inhibitor of the human N-myristoyltransferases NMT1 and NMT2, and use it to demonstrate that pharmacological inhibition of host cell N-myristoylation rapidly and completely prevents rhinoviral replication without inducing cytotoxicity. Identification of cooperative binding between weak-binding fragments led to rapid inhibitor optimization through fragment reconstruction, structure-guided fragment linking, and conformational control over linker geometry. We show that inhibition of co-translational myristoylation of a specific virus-encoded protein (VP0) by IMP-1088 potently blocks a key step in viral capsid assembly, delivering low nanomolar antiviral activity against multiple rhinovirus strains, poliovirus and foot-and-mouth disease virus, and protection of cells against virus-induced killing, highlighting the potential of host myristoylation as a drug target in picornaviral infections.

Inhibition of N-myristoyltransferase has been validated pre-clinically as a target for the treatment of fungal and trypanosome infections, using species-specific inhibitors. In order to identify inhibitors of protozoan NMTs, we chose to screen a diverse subset of the Pfizer corporate collection against Plasmodium falciparum and Leishmania donovani NMTs. Primary screening hits against either enzyme were tested for selectivity over both human NMT isoforms (Hs1 and Hs2) and for broad-spectrum anti-protozoan activity against the NMT from Trypanosoma brucei. Analysis of the screening results has shown that structure-activity relationships (SAR) for Leishmania NMT are divergent from all other NMTs tested, a finding not predicted by sequence similarity calculations, resulting in the identification of four novel series of Leishmania-selective NMT inhibitors. We found a strong overlap between the SARs for Plasmodium NMT and both human NMTs, suggesting that achieving an appropriate selectivity profile will be more challenging. However, we did discover two novel series with selectivity for Plasmodium NMT over the other NMT orthologues in this study, and an additional two structurally distinct series with selectivity over Leishmania NMT. We believe that release of results from this study into the public domain will accelerate the discovery of NMT inhibitors to treat malaria and leishmaniasis. Our screening initiative is another example of how a tripartite partnership involving pharmaceutical industries, academic institutions and governmental/non-governmental organisations such as Medical Research Council and Wellcome Trust can stimulate research for neglected diseases.

Summary The attachment of myristate to the N-terminal glycine of certain proteins is largely a co-translational modification catalyzed by N-myristoyltransferase (NMT), and involved in protein membrane-localization. Pathogen NMT is a validated therapeutic target in numerous infectious diseases including malaria. In Plasmodium falciparum , NMT substrates are important in essential processes including parasite gliding motility and host cell invasion. Here, we generated parasites resistant to a particular NMT inhibitor series and show that resistance in an in vitro parasite growth assay is mediated by a single amino acid substitution in the NMT substrate-binding pocket. The basis of resistance was validated and analyzed with a structure-guided approach using crystallography, in combination with enzyme activity, stability, and surface plasmon resonance assays, allowing identification of another inhibitor series unaffected by this substitution. We suggest that resistance studies incorporated early in the drug development process help selection of drug combinations to impede rapid evolution of parasite resistance.

Crystal structures of N-myristoyltransferase with four distinct Leishmania-selective small-molecule inhibitors identify key binding-site residues and suggest strategies to design compounds with increased affinity.

Inhibitors of LeishmaniaN-myristoyltransferase (NMT), a potential target for the treatment of leishmaniasis, obtained from a high-throughput screen, were resynthesized to validate activity. Crystal structures bound to Leishmania major NMT were obtained, and the active diastereoisomer of one of the inhibitors was identified. On the basis of structural insights, enzyme inhibition was increased 40-fold through hybridization of two distinct binding modes, resulting in novel, highly potent Leishmania donovani NMT inhibitors with good selectivity over the human enzyme.

SUMMARY 12 13Infections caused by protozoan parasites are among the most widespread and intractable transmissible 14 diseases affecting the developing world, with malaria and leishmaniasis being most costly in terms of 15 morbidity and mortality. Although new drugs are urgently required against both diseases in the face of 16 ever-rising resistance to frontline therapies, very few candidates passing through development 17 pipelines possess a known and novel mode of action. Set in the context of drugs currently in use and 18 under development, we present the evidence for N-myristoyltransferase (NMT), an enzyme that N-19 terminally lipidates a wide range of specific target proteins through post-translational modification, as 20 a potential drug target in malaria and the leishmaniases. We discuss the limitations of current 21 knowledge regarding the downstream targets of this enzyme in protozoa, and our recent progress 22 towards potent cell-active NMT inhibitors against the most clinically-relevant species of parasite. 23Finally, we outline the next steps required in terms of both tools to understand N-myristoylation in 24 protozoan parasites, and the generation of potential development candidates based on the output of 25 our recently-reported high-throughput screens. 26 INTRODUCTION 27Malaria 28 Malaria is a disease caused by infection of a human host with protozoan parasites of the genus 29Plasmodium, and is a devastating global health issue with approximately 200 million cases and 30 1 million deaths in 2010 alone (Murray et al. 2012). The complex life cycle of malaria parasites 31 spreads across two hosts and five host tissues whilst undergoing at least ten distinct morphological 32 transitions (Sturm et al. 2006; Mackinnon and Marsh 2010). Replication of parasites and subsequent 33 rupture of erythrocytes in the intra-erythrocytic stages are responsible for the clinical symptoms of 34 malaria, and the majority of drugs target these asexual (human-host) stages of the life cycle. Some 35 species of malaria, most notably Plasmodium vivax, can exist in a latent liver hypnozoite form that 36 can cause relapse even after clearance of bloodstream parasites (Derbyshire et al. 2012; Rodrigues et 37 al. 2012). Of the five relevant species of human parasite, the vast majority of deaths occur from P. 38 falciparum infections, which is the typical cause of severe malaria (Claessens et al. 2012). This has 39 led to the majority of drug discovery efforts focussing on P. falciparum, typically at the expense of 40 other species. Although the demand for new P. falciparum drugs is in no doubt, P. vivax is 41 responsible for the majority of worldwide malaria endemicity (Price et al. 2009; WHO 2011). 42However, difficulties culturing the parasite (Udomsangpetch et al. 2007) For the latter half of the 20 th century, antimalarial drug discovery was a success story for natural 47 product-inspired therapies, by far the most widely used of which are chloroquine (Loeb et al. 1946) 48 and artemisinin (Miller and Su 2011). 49Chlo...

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