Shawn Chen

New anti-tuberculosis (TB) drugs with novel modes of action are in great demand due to the complex treatment regimens as well as the rising number of multidrug-resistant TB cases. We recently re-evaluated a few 2,5,6-trisubstituted benzimidazole derivatives (SBZ) previously demonstrated to have potent antitubercular activity. These compounds displayed favorable MICs and significantly reduced bacterial counts in an acute mouse infection model. Although this antitubercular lead series was initially reported to inhibit mycobacterial cell division, our findings suggest that its primary activity likely involves other cellular targets. By using bacterial cytological profiling, we observed that SBZ-treated Mycobacterium tuberculosis cells exhibit cell wall-damaging phenotypes resembling those caused by known cell wall biosynthesis inhibitors, such as AU1235 and SQ109, that mostly target the membrane protein large 3 (MmpL3). Whole-cell assays further supported the findings by showing activation of the iniBAC operon and accumulation of intracellular ATP. The antitubercular activity of SBZs was tested against engineered mycobacterial strains that have the transcriptionally regulated mmpL3 gene expression, confirming that SBZs engage the MmpL3 target in the cell. Strains with mutations in mmpL3 exhibited either low- or high-level resistance to the SBZs. A molecule docking model is proposed, based on a high-resolution crystal structure of MmpL3, which could be useful in reconciling the inhibition mechanism and suggesting a further development of MmpL3 inhibitor starting with the SBZ scaffold.

Tuberculosis (TB) remains a leading global health threat, with over 10 million new cases and 1.25 million deaths reported in 2023. Current TB therapies rely on a limited drug repertoire and prolonged treatment courses that have changed little in four decades. Here, we present GenVS-TBDB, a target-aware AI-generated and virtual-screened small-molecule database, which expands the chemical space against Mycobacterium tuberculosis (M.tb) essential proteins. We first identified 460 probable small-molecule binding pockets across 377 essential M.tb proteins by integrating multiple sources. Then, by leveraging the target-aware molecule generative model, over 1.2 million novel small molecules tailored to these pockets were produced. The key physicochemical properties were computed for all compounds to ensure medicinal chemistry tractability. These compounds were also evaluated using molecular docking and anti-TB specific graph neural network model, yielding binding propensity ranking and whole-cell activity prioritization for each target. To substantiate the integrated AI-driven workflow for anti-TB discovery, 30 compounds were obtained, including 22 AI-designed molecules synthesized de novo and 8 commercially available analogs. In validation, 2 synthesized compounds demonstrated significant thermal stabilization of FtsZ, confirming target engagement. 6 compounds exhibited cellular inhibition below 50 µM, the most potent at 12 µM. Furthermore, GDI-11785 showed binding to the cell wall biosynthesis pathway with 35 µM cellular activity, establishing a promising starting point for tuberculosis drug discovery. Our findings contribute a significant library of bioactive molecules which may hasten the preliminary phase of tuberculosis drug discovery. The GenVS-TBDB small library is publicly accessible and can be downloaded freely at https://datascience.ghddi.org/database/view .

The caseinolytic protease complex ClpP1P2 is crucial for protein homeostasis in mycobacteria and stress response and virulence of the pathogens. Its role as a potential drug target for combating tuberculosis (TB) has just begun to be substantiated in drug discovery research. We conducted a biochemical screening targeting the ClpP1P2 using a library of compounds phenotypically active against Mycobacterium tuberculosis (Mtb). The screening identified a phenyl ester compound GDI‐5755, inhibiting the growth of Mtb and M. bovis BCG, the model organism of mycobacteria. GDI‐5755 covalently modified the active‐site serine residue of ClpP1, rendering the peptidase inactive, which was delineated through protein mass spectrometry and kinetic analyses. GDI‐5755 exerted antibacterial activity by inhibiting ClpP1P2 in the bacteria, which could be demonstrated through a minimum inhibitory concentration (MIC) shift assay with a clpP1 CRISPRi knockdown (clpP1‐KD) mutant GH189. The knockdown also remarkably heightened the mutant's sensitivity to ethionamide and meropenem, but not to many other TB drugs. On the other hand, a comparative proteomic analysis of wild‐type cells exposed to GDI‐5755 revealed the dysregulated proteome, specifically showing changes in the expression levels of multiple TB drug targets, including EthA, Ldt_Mt2, and PanD. Subsequent evaluation confirmed the synergistic activity of GDI‐5755 when combined with the TB drugs to inhibit mycobacterial growth. Our findings indicate that small‐molecule inhibitors targeting ClpP1P2, when used alongside existing TB medications, could represent novel therapeutic strategies.

Pleuromutilins are a group of antibiotics derived from the naturally occurring compound. The recent approval of lefamulin for both intravenous and oral doses in humans to treat community-acquired bacterial pneumonia has prompted investigations in modifying the structure to broaden the antibacterial spectrum, enhance the activity, and improve the pharmacokinetic properties. AN11251 is a C(14)-functionalized pleuromutilin with a boron-containing heterocycle substructure. It was demonstrated to be an anti-Wolbachia agent with therapeutic potential for Onchocerciasis and lymphatic filariasis. Here, the in vitro and in vivo PK parameters of AN11251 were measured including PPB, intrinsic clearance, half-life, systemic clearance, and volume of distribution. The results indicate that the benzoxaborole-modified pleuromutilin possesses good ADME and PK properties. AN11251 has potent activities against the Gram-positive bacterial pathogens tested, including various drug-resistant strains, and against the slow-growing mycobacterial species. Finally, we employed PK/PD modeling to predict the human dose for treatment of disease caused by Wolbachia, Gram-positive bacteria, or Mycobacterium tuberculosis, which might facilitate the further development of AN11251.

ATP provides energy in the biosynthesis of cellular metabolites as well as regulates protein functions through phosphorylation. Many ATP-dependent enzymes are antibacterial and anticancer targets including human kinases acted on by most of the successful drugs. In search of new chemotherapeutics for tuberculosis (TB), we screened repurposing compounds against the essential glutamine synthase (GlnA1) of Mycobacterium tuberculosis (Mtb) and identified linsitinib, a clinical-stage drug originally targeting kinase IGF1R/IR as a potent GlnA1 inhibitor. Linsitinib has direct antimycobacterial activity. Biochemical, molecular modeling, and target engagement analyses revealed the inhibition is ATP-competitive and specific in Mtb. Linsitinib also improves autophagy flux in both Mtb-infected and uninfected THP1 macrophages, as demonstrated by the decreased p-mTOR and p62 and the increased lipid-bound LC3B-II and autophagosome forming puncta. Linsitinib-mediated autophagy reduces intracellular growth of wild-type and isoniazid-resistant Mtb alone or in combination with bedaquiline. We have demonstrated that an IGF-IR/IR inhibitor can potentially be used to treat TB. Our study reinforces the concept of targeting ATP-dependent enzymes for novel anti-TB therapy.

Indolmycin (IND) is a microbial natural product that selectively inhibits bacterial tryptophanyl-tRNA synthetase (TrpRS). The tryptophan biosynthesis pathway was recently shown to be an important target for developing new antibacterial agents against Mycobacterium tuberculosis (Mtb). We investigated the antibacterial activity of IND against several mycobacterial model strains. A TrpRS biochemical assay was developed to analyze a library of synthetic IND analogues. The 4″-methylated IND compound, Y-13, showed improved anti-Mtb activity with a minimum inhibitory concentration (MIC) of 1.88 μM (∼0.5 μg/mL). The MIC increased significantly when overexpression of TrpRS was induced in the genetically engineered surrogate M. bovis BCG. The cocrystal structure of Mtb TrpRS complexed with IND and ATP has revealed that the amino acid pocket is in a state between the open form of apo protein and the closed complex with the reaction intermediate. In whole-cell-based experiments, we studied the combination effect of Y-13 paired with different antibacterial agents. We evaluated the killing kinetics, the frequency of resistance to INDs, and the mode of resistance of IND-resistant mycobacteria by genome sequencing. The synergistic interaction of Y-13 with the TrpE allosteric inhibitor, indole propionic acid, suggests that prospective IND analogues could shut down tryptophan biosynthesis and protein biosynthesis in pathogens, leading to a new class of antibiotics. Finally, we discuss a strategy to expand the genome mining of antibiotic-producing microbes specifically for antimycobacterial development.

Mycobacteria tuberculosis (Mtb) remains the deadliest pathogenic bacteria worldwide. The search for new antibiotics to treat drug-sensitive as well as drug-resistant tuberculosis has become a priority. The essential enzyme phenylalanyl-tRNA synthetase (PheRS) is an antibacterial drug target because of the large differences between bacterial and human PheRS counterparts. In a high-throughput screening of 2148 bioactive compounds, PF-3845, which is a known inhibitor of human fatty acid amide hydrolase (FAAH), was identified inhibiting Mtb PheRS at K _i ∼0.73 ± 0.055 µM. The inhibition mechanism was studied with enzyme kinetics, protein structural modelling and crystallography, in comparison to a PheRS inhibitor of the noted phenyl-thiazolylurea-sulfonamide class. The 2.3-Å crystal structure of Mtb PheRS in complex with PF-3845 revealed its novel binding mode, in which a trifluoromethyl-pyridinylphenyl group occupies the Phe pocket while a piperidine-piperazine urea group binds into the ATP pocket through an interaction network enforced by a sulfate ion. It represents the first non-nucleoside bi-substrate competitive inhibitor of bacterial PheRS. PF-3845 inhibits the in vitro growth of Mtb H37Rv at ∼24 µM, and the potency of PF-3845 increased against Mtb pheS-FDAS, suggesting on target activity in mycobacterial whole cells. PF-3845 does not inhibit human cytoplasmic or mitochondrial PheRSs in biochemical assay, which can be explained from the crystal structures. Further elaboration of the piperidine-piperazine urea moiety by medicinal chemistry effort will produce potential antibacterial lead with improved selectivity on the cellular level.

Development of effective antimicrobial agents continues to be a great challenge, particularly due to the increasing resistance of superbugs and frequent hospital breakouts. There is an urgent need for more potent and safer antibiotics with novel scaffolds. As historically many commercial drugs were derived from natural products, discovery of antimicrobial agents from complex natural product structures still holds a great promise. Herein, we report the total synthesis of natural albomycins δ₁ (1a), δ₂ (1b), and ε (1c), which validates the structures of these peptidylnucleoside compounds and allows for synthetic access to bioactive albomycin analogs. The efficient synthesis of albomycins enables extensive evaluations of these natural products against model bacteria and clinical pathogens. Albomycin δ₂ has the potential to be developed into an antibacterial drug to treat Streptococcus pneumoniae and Staphylococcus aureus infections.