Selective Inhibitors of Protozoan Protein N-myristoyltransferases as Starting Points for Tropical Disease Medicinal Chemistry Programs

Abstract

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.

Acylation in trypanosomatids: an essential process and potential drug target

“…The major difference in T. brucei and L. major enzymes compared to other NMTS is the presence of additional positively charged residues in the binding cavity [84]. Although the L. donovani enzyme lacks the extra charged residues in the binding cavity, there is no structural overlap in this region between LdNMTs and either human or other protozoan NMTs, suggesting that any inhibitors of L. donovani NMTs will be selective [85]. …”

“…In addition, DD85646 is active against TcNMT, but is only effective against T. cruzi in culture at 1000x concentrations compared to T. brucei [87]. A screen performed on L. donovani identified a number of compounds that showed activity against LdNMT, with no detectable activity against human NMTs or TbNMT [85]. Interestingly, these compounds appear to bind to a region of the binding pocket distinct from other previously characterized NMT inhibitors, suggesting it may be possible to exploit multiple compound classes to target NMTs [85].…”

“…A screen performed on L. donovani identified a number of compounds that showed activity against LdNMT, with no detectable activity against human NMTs or TbNMT [85]. Interestingly, these compounds appear to bind to a region of the binding pocket distinct from other previously characterized NMT inhibitors, suggesting it may be possible to exploit multiple compound classes to target NMTs [85]. Although DD85646 is an effective NMT inhibitor against bloodstream form T. brucei in a mouse model, further optimization is required to enable central nervous system penetration.…”

Structure-guided optimization of quinoline inhibitors of Plasmodium N-myristoyltransferase

“…Later, novel families of NMT inhibitors were identified by high throughput screening (HTS) efforts 7,18–20. A selection of different chemotypes are under active development against NMT for numerous indications (Fig.…”

In Vitro and In Vivo Activities of 2-Aminopyrazines and 2-Aminopyridines in Experimental Models of Human African Trypanosomiasis

“…Brand et al have described the first T. brucei N-myrisoyl transferase (TbNMT) inhibitor DDD85646 and its related analogs as potent inhibitors of bloodstream-borne T. brucei proliferation (22). In addition, TbNMT has been extensively validated as a relevant target for the development of trypanosomiasis therapy in a number of models of HAT (9,23).…”