ABSTRACT
Recent development of benzoxaborole-based chemistry gave rise to a collection of compounds with great potential in targeting diverse infectious diseases, including human African Trypanosomiasis (HAT), a devastating neglected tropical disease. However, further medicinal development is largely restricted by a lack of insight into mechanism of action (MoA) in pathogenic kinetoplastids. We adopted a multidisciplinary approach, combining a high-throughput forward genetic screen with functional group focused chemical biological, structural biology and biochemical analyses, to tackle the complex MoAs of benzoxaboroles in Trypanosoma brucei. We describe an oxidative enzymatic pathway composed of host semicarbazide-sensitive amine oxidase and a trypanosomal aldehyde dehydrogenase TbALDH3. Two sequential reactions through this pathway serve as the key underlying mechanism for activating a series of 4-aminomethylphenoxy-benzoxaboroles as potent trypanocides; the methylamine parental compounds as pro-drugs are transformed first into intermediate aldehyde metabolites, and further into the carboxylate metabolites as effective forms. Moreover, comparative biochemical and crystallographic analyses elucidated the catalytic specificity of TbALDH3 towards the benzaldehyde benzoxaborole metabolites as xenogeneic substrates. Overall, this work proposes a novel drug activation mechanism dependent on both host and parasite metabolism of primary amine containing molecules, which contributes a new perspective to our understanding of the benzoxaborole MoA, and could be further exploited to improve the therapeutic index of antimicrobial compounds.
Subject(s)
Aldehyde Dehydrogenase/metabolism , Amine Oxidase (Copper-Containing)/metabolism , Boron Compounds/metabolism , Models, Biological , Prodrugs/metabolism , Trypanocidal Agents/metabolism , Trypanosoma brucei brucei/enzymology , Activation, Metabolic , Aldehyde Dehydrogenase/antagonists & inhibitors , Aldehyde Dehydrogenase/chemistry , Aldehyde Dehydrogenase/genetics , Aldehyde Oxidoreductases/antagonists & inhibitors , Aldehyde Oxidoreductases/chemistry , Aldehyde Oxidoreductases/genetics , Aldehyde Oxidoreductases/metabolism , Amine Oxidase (Copper-Containing)/antagonists & inhibitors , Amine Oxidase (Copper-Containing)/chemistry , Amine Oxidase (Copper-Containing)/genetics , Amino Acid Substitution , Animals , Boron Compounds/chemistry , Boron Compounds/pharmacology , Drug Resistance , High-Throughput Screening Assays , Humans , Molecular Structure , Mutation , Phylogeny , Prodrugs/chemistry , Prodrugs/pharmacology , Protein Interaction Domains and Motifs , RNA Interference , Rats , Recombinant Fusion Proteins/chemistry , Recombinant Fusion Proteins/metabolism , Recombinant Proteins/chemistry , Recombinant Proteins/metabolism , Structure-Activity Relationship , Trypanocidal Agents/chemistry , Trypanocidal Agents/pharmacology , Trypanosoma brucei brucei/drug effects , Trypanosoma brucei brucei/physiologyABSTRACT
African trypanosomiasis, caused by the proto zoal pathogen Trypanosoma brucei (T. brucei), is one of the most neglected tropical diseases that are in great need of new drugs. We report the design and synthesis of T. brucei leucyl-tRNA synthetase (TbLeuRS) inhibitors and their structure--activity relationship. Benzoxaborole was used as the core structure and C(6) was modified to achieve improved affinity based on docking results that showed further binding space at this position. Indeed, compounds with C(7) substitutions showed diminished activity due to clash with the eukaryote specific I4ae helix while substitutions at C(6) gave enhanced affinity. TbLeuRS inhibitors with IC(50) as low as 1.6 µM were discovered, and the structure-activity relationship was discussed. The most potent enzyme inhibitors also showed excellent T. brucei parasite growth inhibition activity. This is the first time that TbLeuRS inhibitors are reported, and this study suggests that leucyl-tRNA synthetase (LeuRS) could be a potential target for antiparasitic drug development.
Subject(s)
Boronic Acids/chemical synthesis , Leucine-tRNA Ligase/antagonists & inhibitors , Trypanocidal Agents/chemical synthesis , Trypanosoma brucei brucei/drug effects , Animals , Boronic Acids/chemistry , Boronic Acids/pharmacology , Cell Line , Drug Design , Mice , Models, Molecular , Stereoisomerism , Structure-Activity Relationship , Trypanocidal Agents/chemistry , Trypanocidal Agents/pharmacology , Trypanosoma brucei brucei/enzymology , Trypanosoma brucei brucei/growth & developmentABSTRACT
Onychomycosis is a fungal infection of the fingernails and toenails that results in thickening, discoloration, splitting of the nails and lifting of the nail from the nail bed. The disease is caused by dermatophytes and has a high incidence within the general population, especially among older individuals. Present treatment options include both oral and topical drugs, with oral therapies giving better outcomes; however, neither of these treatment options provides high cure rates that are durable. The difficulty in treating onychomycosis results from the deep-seated nature of the infection within the nail unit (nail plate, nail bed and surrounding tissue) and the inability of drugs to effectively reach all sites. Ongoing drug development activities have focused on novel delivery technologies to facilitate penetration of existing antifungal drugs through the nail plate and on the discovery of inherently penetrable antifungals. AN-2690 represents an oxaborole antifungal that is designed to penetrate the nail plate and is showing promising results in clinical trials.
