The work began with the screening of a library of 700,000 small molecules for inhibitors of 'Trypanosoma brucei' growth (a phenotypic screen). The resulting set of 1035 hit compounds was reviewed by ...a team of medicinal chemists, leading to the nomination of 17 chemically distinct scaffolds for further investigation. The first triage step was the assessment for brain permeability (looking for brain levels at least 20% of plasma levels) in order to optimize the chances of developing candidates for treating late-stage human African trypanosomiasis. Eleven scaffolds subsequently underwent hit-to-lead optimization using standard medicinal chemistry approaches. Over a period of six years in an academic setting, 1539 analogs to the 11 scaffoldswere synthesized. Eight scaffoldswere discontinued either due to insufficient improvement in antiparasitic activity (5), poor pharmacokinetic properties (2), or a slow(static) antiparasitic activity (1). Three scaffoldswere optimized to the point of curing the acute and/or chronic 'T. brucei' infection model in mice. The progress was accomplished without knowledge of the mechanism of action (MOA) for the compounds, although the MOA has been discovered in the interim for one compound series. Studies on the safety and toxicity of the compounds are planned to help select candidates for potential clinical development. This research demonstrates the power of the phenotypic drug discovery approach for neglected tropical diseases.
A high throughput screening and subsequent hit validation identified compound 1 as an inhibitor of Trypanosoma brucei parasite growth. Extensive structure–activity relationship optimization based on ...antiparasitic activity led to the highly potent compounds, 1-(4-fluorobenzyl)-3-(4-dimethylamino-3-chlorophenyl)-2-thiohydantoin (68) and 1-(2-chloro-4-fluorobenzyl)-3-(4-dimethylamino-3-methoxyphenyl)-2-thiohydantoin (76), with a T. brucei EC50 of 3 and 2 nM, respectively. This represents >100-fold improvement in potency compared to compound 1. In vivo efficacy experiments of 68 and 76 in an acute mouse model of Human African Trypanosomiasis showed a 100% cure rate after 4 days of oral treatment at 50 mg/kg twice per day.
A screening hit 1 against Trypanosoma brucei methionyl-tRNA synthetase was optimized using a structure-guided approach. The optimization led to the identification of two novel series of potent ...inhibitors, the cyclic linker and linear linker series. Compounds of both series were potent in a T. brucei growth inhibition assay while showing low toxicity to mammalian cells. The best compound of each series, 16 and 31, exhibited EC50s of 39 and 22 nM, respectively. Compounds 16 and 31 also exhibited promising PK properties after oral dosing in mice. Moreover, compound 31 had moderately good brain permeability, with a brain/plasma ratio of 0.27 at 60 min after IP injection. This study provides new lead compounds for arriving at new treatments of human African trypanosomiasis (HAT).
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•Structure-based design was used to optimize a HTS hit against T. brucei MetRS.•Two series of inhibitors were designed and synthesized targeting T. brucei MetRS.•Best compounds in both series have EC50 of <50 nM against parasites.•Crystallography study confirms inhibitor binding modes as designed.•The two best inhibitors have oral bioavailability; one has good brain permeability.
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Pyridyl benzamide 2 is a potent inhibitor of Trypanosoma cruzi, but not other protozoan parasites, and had a selectivity-index of ≥10. The initial structure–activity relationship ...(SAR) indicates that benzamide and sulfonamide functional groups, and N-methylpiperazine and sterically unhindered 3-pyridyl substructures are required for high activity against T. cruzi. Compound 2 and its active analogs had low to moderate metabolic stabilities in human and mouse liver microsomes.
Mycobacterium avium complex (MAC) infections, generally viewed as opportunistic infections, often trigger an evaluation for an underlying immunodeficiency disorder. However, MAC infections can occur ...in patients who presumably are immunocompetent, particularly in those with an underlying structural lung disease. T-cell immunity plays a critical role in controlling MAC infection. We presented a case of lymphopenia, which complicated the clinical course of a pulmonary MAC infection in a patient who was negative for human immunodeficiency virus.
As part of a structural genomics initiative, 1000 open reading frames from
Plasmodium falciparum, the causative agent of the most deadly form of malaria, were tested in an
E. coli protein expression ...system. Three hundred and thirty-seven of these targets were observed to express, although typically the protein was insoluble. Sixty-three of the targets provided soluble protein in yields ranging from 0.9 to 406.6
mg from one liter of rich media. Higher molecular weight, greater protein disorder (segmental analysis, SEG), more basic isoelectric point (pI), and a lack of homology to
E. coli proteins were all highly and independently correlated with difficulties in expression. Surprisingly, codon usage and the percentage of adenosines and thymidines (%AT) did not appear to play a significant role. Of those proteins which expressed, high pI and a hypothetical annotation were both strongly and independently correlated with insolubility. The overwhelmingly important role of pI in both expression and solubility appears to be a surprising and fundamental issue in the heterologous expression of
P. falciparum proteins in
E. coli. Twelve targets which did not express in
E. coli from the native gene sequence were codon-optimized through whole gene synthesis, resulting in the (insoluble) expression of three of these proteins. Seventeen targets which were expressed insolubly in
E. coli were moved into a baculovirus/
Sf-21 system, resulting in the soluble expression of one protein at a high level and six others at a low level. A variety of factors conspire to make the heterologous expression of
P. falciparum proteins challenging, and these observations lay the groundwork for a rational approach to prioritizing and, ultimately, eliminating these impediments.
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Potent inhibitors of Trypanosoma brucei methionyl-tRNA synthetase were previously designed using a structure-guided approach. Compounds 1 and 2 were the most active compounds in the ...cyclic and linear linker series, respectively. To further improve cellular potency, SAR investigation of a binding fragment targeting the “enlarged methionine pocket” (EMP) was performed. The optimization led to the identification of a 6,8-dichloro-tetrahydroquinoline ring as a favorable fragment to bind the EMP. Replacement of 3,5-dichloro-benzyl group (the EMP binding fragment) of inhibitor 2 using this tetrahydroquinoline fragment resulted in compound 13, that exhibited an EC50 of 4nM.
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