Multi-Target Antitubercular Drugs

DprE1 Inhibitors: Enduring Aspirations for Future Antituberculosis Drug Discovery

DprE1 is a crucial enzyme involved in the cell wall synthesis of Mycobacterium tuberculosis and a promising target for antituberculosis drug development. However, its unique structural characteristics for ligand binding and association with DprE2 make developing new clinical compounds challenging. This review provides an in-depth analysis of the structural requirements for both covalent and non-covalent inhibitors, their 2D and 3D binding patterns, as well as their biological activity data in vitro and in vivo, including pharmacokinetic information. We also introduce a protein quality score (PQS) and an active-site map of the DprE1 enzyme to help medicinal chemists better understand DprE1 inhibition and develop new and effective anti-TB drugs. Furthermore, we examine the resistance mechanisms associated with DprE1 inhibitors to understand future developments due to resistance emergence. This comprehensive review offers insight into the DprE1 active site, including protein-binding maps, PQS, and graphical representations of known inhibitors, making it a valuable resource for medicinal chemists working on future antitubercular compounds.

A d-Phenylalanine-Benzoxazole Derivative Reveals the Role of the Essential Enzyme Rv3603c in the Pantothenate Biosynthetic Pathway of Mycobacterium tuberculosis

New drugs and new targets are urgently needed to treat tuberculosis. We discovered that d-phenylalanine-benzoxazole Q112 displays potent antibacterial activity against Mycobacterium tuberculosis (Mtb) in multiple media and in macrophage infections. A metabolomic profiling indicates that Q112 has a unique mechanism of action. Q112 perturbs the essential pantothenate/coenzyme A biosynthetic pathway, depleting pantoate while increasing ketopantoate, as would be expected if ketopantoate reductase (KPR) were inhibited. We searched for alternative KPRs, since the enzyme annotated as PanE KPR is not essential in Mtb. The ketol-acid reductoisomerase IlvC catalyzes the KPR reaction in the close Mtb relative Corynebacterium glutamicum, but Mtb IlvC does not display KPR activity. We identified the essential protein Rv3603c as an orthologue of PanG KPR and demonstrated that a purified recombinant Rv3603c has KPR activity. Q112 inhibits Rv3603c, explaining the metabolomic changes. Surprisingly, pantothenate does not rescue Q112-treated bacteria, indicating that Q112 has an additional target(s). Q112-resistant strains contain loss-of-function mutations in the twin arginine translocase TatABC, further underscoring Q112's unique mechanism of action. Loss of TatABC causes a severe fitness deficit attributed to changes in nutrient uptake, suggesting that Q112 resistance may derive from a decrease in uptake.

Synthesis, Characterization, and Biological Evaluation of Novel 7-Oxo-7H-thiazolo[3,2-b]-1,2,4-triazine-2-carboxylic Acid Derivatives

A series of novel 7-oxo-7H-thiazolo[3,2-b]-1,2,4-triazine-2-carboxylic acid derivatives was synthesized in good yields by a multi-step procedure that included the generation of the S-alkylated derivatives from 6-substituted arylmethyl-3-mercapto-1,2,4-triazin-5-ones with ethyl 2-chloroacetoacetate, intramolecular cyclization with microwave irradiation, hydrolysis and amidation. All of the target compounds were fully characterized through ¹H-NMR, ¹³C-NMR and HRMS spectra. The intramolecular cyclization occurred regioselectively at the N2-position of 1,2,4-triazine ring, which was confirmed by compound 3e using single-crystal X-ray diffraction analysis. The antibacterial and antitubercular activities of the target compounds were evaluated. Compared with Ciprofloxacin and Rifampicin, compounds 5d, 5f and 5g containing the terminal amide fragment exhibited broad spectrum antibacterial activity, and carboxylic acid derivatives or its corresponding ethyl esters had less effect on antibacterial properties. The most potent compound 5f also displayed excellent in vitro antitubercular activity against Mycobacterium smegmatis (minimum inhibitory concentration (MIC) = 50 μg/mL) and better growth inhibition activity of leucyl-tRNA synthetase (78.24 ± 4.05% at 15 μg/mL).

Multitargeting Compounds: A Promising Strategy to Overcome Multi-Drug Resistant Tuberculosis

Tuberculosis is still an urgent global health problem, mainly due to the spread of multi-drug resistant M. tuberculosis strains, which lead to the need of new more efficient drugs. A strategy to overcome the problem of the resistance insurgence could be the polypharmacology approach, to develop single molecules that act on different targets. Polypharmacology could have features that make it an approach more effective than the classical polypharmacy, in which different drugs with high affinity for one target are taken together. Firstly, for a compound that has multiple targets, the probability of development of resistance should be considerably reduced. Moreover, such compounds should have higher efficacy, and could show synergic effects. Lastly, the use of a single molecule should be conceivably associated with a lower risk of side effects, and problems of drug–drug interaction. Indeed, the multitargeting approach for the development of novel antitubercular drugs have gained great interest in recent years. This review article aims to provide an overview of the most recent and promising multitargeting antitubercular drug candidates.

A Repurposing Approach for Uncovering the Anti-Tubercular Activity of FDA-Approved Drugs with Potential Multi-Targeting Profiles

Tuberculosis (TB) is one of the top 10 causes of death worldwide. This scenario is further complicated by the insurgence of multidrug-resistant (MDR) and extensively drug-resistant (XDR) TB. The identification of appropriate drugs with multi-target affinity profiles is considered to be a widely accepted strategy to overcome the rapid development of resistance. The aim of this study was to discover Food and Drug Administration (FDA)-approved drugs possessing antimycobacterial activity, potentially coupled to an effective multi-target profile. An integrated screening platform was implemented based on computational procedures (high-throughput docking techniques on the target enzymes peptide deformylase and Zmp1) and in vitro phenotypic screening assays using two models to evaluate the activity of the selected drugs against Mycobacterium tuberculosis (Mtb), namely, growth of Mtb H37Rv and of two clinical isolates in axenic media, and infection of peripheral blood mononuclear cells with Mtb. Starting from over 3000 FDA-approved drugs, we selected 29 marketed drugs for submission to biological evaluation. Out of 29 drugs selected, 20 showed antimycobacterial activity. Further characterization suggested that five drugs possessed promising profiles for further studies. Following a repurposing strategy, by combining computational and biological efforts, we identified marketed drugs with relevant antimycobacterial profiles.