Setting Our Sights on Infectious Diseases.

In May 2019, the Wellcome Centre for Anti-Infectives Research (WCAIR) at the University of Dundee, UK, held an international conference with the aim of discussing some key questions around discovering new medicines for infectious diseases and a particular focus on diseases affecting Low and Middle Income Countries. There is an urgent need for new drugs to treat most infectious diseases. We were keen to see if there were lessons that we could learn across different disease areas and between the preclinical and clinical phases with the aim of exploring how we can improve and speed up the drug discovery, translational, and clinical development processes. We started with an introductory session on the current situation and then worked backward from clinical development to combination therapy, pharmacokinetic/pharmacodynamic (PK/PD) studies, drug discovery pathways, and new starting points and targets. This Viewpoint aims to capture some of the learnings.

Preclinical candidate for the treatment of visceral leishmaniasis that acts through proteasome inhibition.

Visceral leishmaniasis (VL), caused by the protozoan parasites Leishmania donovani and Leishmania infantum, is one of the major parasitic diseases worldwide. There is an urgent need for new drugs to treat VL, because current therapies are unfit for purpose in a resource-poor setting. Here, we describe the development of a preclinical drug candidate, GSK3494245/DDD01305143/compound 8, with potential to treat this neglected tropical disease. The compound series was discovered by repurposing hits from a screen against the related parasite Trypanosoma cruzi Subsequent optimization of the chemical series resulted in the development of a potent cidal compound with activity against a range of clinically relevant L. donovani and L. infantum isolates. Compound 8 demonstrates promising pharmacokinetic properties and impressive in vivo efficacy in our mouse model of infection comparable with those of the current oral antileishmanial miltefosine. Detailed mode of action studies confirm that this compound acts principally by inhibition of the chymotrypsin-like activity catalyzed by the ß5 subunit of the L. donovani proteasome. High-resolution cryo-EM structures of apo and compound 8-bound Leishmania tarentolae 20S proteasome reveal a previously undiscovered inhibitor site that lies between the ß4 and ß5 proteasome subunits. This induced pocket exploits ß4 residues that are divergent between humans and kinetoplastid parasites and is consistent with all of our experimental and mutagenesis data. As a result of these comprehensive studies and due to a favorable developability and safety profile, compound 8 is being advanced toward human clinical trials.

The identification of isoprenoids that bind in the intersubunit cavity of Escherichia coli 2C-methyl-D-erythritol-2,4-cyclodiphosphate synthase by complementary biophysical methods.

The discovery of a distinct metabolic pathway, the non-mevalonate or 1-deoxy-D-xylulose-5-phosphate (DOXP) pathway for isoprenoid precursor biosynthesis, in eubacteria and apicomplexan parasites has revealed a new set of potential drug targets. The emphasis of research on this pathway has been on delineating the intermediates and the biochemical and structural characterization of component enzymes. Two new monoclinic crystal forms of recombinant Escherichia coli 2C-methyl-D-erythritol-2,4-cyclodiphosphate (MECP) synthase cocrystallized with (i) CMP and (ii) CMP and MECP show well defined electron density at the subunit interface suggestive of an isoprenoid-like ligand. 31P NMR analysis of the recombinant protein sample indicates the presence of bound diphosphate species and electrospray mass spectrometry identifies a mixture of isopentenyl diphosphate (and/or dimethylallyl diphosphate), geranyl diphosphate and farnesyl diphosphate in an approximate ratio of 1:4:2. The most prevalent species, geranyl diphosphate, was successfully modelled into the electron density, revealing the important protein-ligand interactions that stabilize binding of the isoprenoid. The observation that MECP synthase binds three metabolites that are produced by enzymes two, three and four stages downstream in isoprenoid biosynthesis suggests that feedback regulation of the non-mevalonate pathway is possible.