Biology subjects

Ostrer, L.

Publications and source records attributed to Ostrer, L..

4 recordsLinked to original sources

bioRxiv2025

Structure-Guided Development of a Potent BioA Inhibitor ValidatesBiotin Synthesis Inhibition as a Therapeutic Strategy forTuberculosis

Conditionally essential pathways - such as the biotin biosynthesis - represent promising targets for new antibiotics. However, the chemical interrogation of the biotin pathway with an orally effective lead remains elusive, and the preclinical development of biotin inhibitors for mycobacterial infections in vivo is challenging due to the unusually high concentration of biotin in standard mouse models. Structure-guided optimization was applied to develop the first oral lead targeting aminotransferase BioA, a key enzyme in bacterial biotin biosynthesis, resulting in C48, a picomolar inhibitor displaying sub-micromolar MICs against Mycobacterium tuberculosis (Mtb). Mechanism of action was confirmed by biochemical, structural, and genetic studies. C48 demonstrated favorable pharmacokinetics and excellent oral bioavailability resulting in over 39,000-fold improved exposure. We next developed an easy-to-operate, low-biotin mouse model that recapitulates human biotin physiology. C48 significantly reduced Mtb burden in this low-biotin mouse model, providing the first in vivo proof-of-concept for targeting biotin biosynthesis in Mtb.

microbiology↗

bioRxiv2024

Thiol Stress Fuels Pyrazinamide Action Against Mycobacterium tuberculosis

Pyrazinamide (PZA) is a cornerstone of first-line antitubercular drug therapy and is unique in its ability to kill nongrowing populations of Mycobacterium tuberculosis through disruption of coenzyme A synthesis. Unlike other drugs, PZA action is conditional and requires potentiation by host-relevant environmental stressors, such as low pH and nutrient limitation. Despite its pivotal role in tuberculosis therapy, the durability of this crucial drug is challenged by the emergent spread of drug-resistance. To advance drug discovery efforts, we characterized the activity of a more potent PZA analog, morphazinamide (MZA). Here, we demonstrate that like PZA, MZA acts in part through impairment of coenzyme A synthesis. Unexpectedly, we find that, in contrast to PZA, MZA does not require potentiation and maintains bactericidal activity against PZA-resistant strains due to an additional mechanism involving aldehyde release. Further, we find that the principal mechanism for resistance to the aldehyde component is through promoter mutations that increase expression of the mycothiol oxidoreductase MscR. Our findings reveal a dual action synergistic mechanism of MZA that results in a faster kill rate and a higher barrier to resistance. These observations provide new insights for discovery of improved therapeutic approaches for addressing the growing problem of drug-resistant tuberculosis. Significance StatementPyrazinamide is the only antitubercular drug of its kind, capable of targeting persistent Mycobacterium tuberculosis through disruption of the coenzyme A biosynthetic pathway. With the emergent spread of drug-resistant tuberculosis, it is imperative to identify more effective next-generation drugs. In this study, we characterized the mechanism of action of a more potent analog of pyrazinamide, morphazinamide. We demonstrate that like pyrazinamide, morphazinamide impairs coenzyme A metabolism. In contrast to pyrazinamide, we find that morphazinamide has an additional aldehyde-dependent mechanism that mediates potent bactericidal activity against both pyrazinamide-susceptible and pyrazinamide-resistant strains of M. tuberculosis. These findings open up new opportunities for the development of next-generation antitubercular drugs to tackle the increasing challenge of drug-resistant tuberculosis.

microbiology↗

bioRxiv2024

α-Aminooxyacetic acid derivatives acting as pro-drugs against Mycobacterium tuberculosis

Tuberculosis (TB), a significant cause of mortality globally, continues to claim 1.5 million lives each year. Despite recent advances in TB management, the emergence of multidrug-resistant strains of TB is exacerbating the treatment of TB. Therefore, there is an immediate necessity to uncover new anti-TB compounds with unprecedented targets. This study introduces novel antimycobacterial molecules that are based on -aminooxyacetic acid core structures. The lead compounds KSK-104 and KSK-106 displayed potent sub-micromolar antibacterial activity against Mycobacterium tuberculosis H37Rv and XDR clinical isolates, while exhibiting virtually no cytotoxicity against various human cells. Complementation experiments following whole genome sequencing of spontaneously resistant mutants generated against these bactericidal compounds suggested that they are pro-drugs that are intracellularly hydrolyzed by one or both of two specific amidohydrolases, Rv0552 and AmiC. Furthermore, proteomic and transcriptomic analyses of stressed cells and genetic interaction mapping employing transposon insertion sequencing suggest a "dirty drug" mechanism that involves the simultaneous attack of the various drug cleavage products on multiple intracellular targets. Our results suggest a primary role of the pyridoxal 5-phosphate (PLP) synthesis and salvage pathway and/or PLP-dependent enzymes, the oxidative stress network, and the largely uncharacterized Rv3092c-Rv3095 gene cluster in the mode of action.

microbiology↗

bioRxiv2020

Identification and characterization of pleiotropic high-persistence mutations in the beta subunit of the bacterial RNA polymerase

Individual bacteria can escape killing by bactericidal antibiotics by becoming dormant. Such cells, also known as persisters, naturally occur in bacterial populations at a low frequency. Here we present the finding that antibiotic-resistance mutations in the rpoB gene, encoding the beta subunit of RNA polymerase, increase the frequency of persisters by orders of magnitude. Furthermore, we show that: i) the persistent state depends on the (p)ppGpp transcriptional program and not on (p)ppGpp itself; ii) the high persistence (hip) is associated with increased populational heterogeneity in transcription; iii) indole overproduction, caused by transcriptional changes in the hip mutants, explains 50-80% of the hip phenotype. We report that the analogous rpoB mutations occur frequently in clinical isolates of Acinetobacter baumannii, Mycobacterium tuberculosis and Staphylococcus aureus, and we demonstrate that one of those rpoB mutations causes high persistence in MRSA. We also show that the RpoB-associated hip phenotype can be reversed by inhibiting protein synthesis. ImportancePersistence is an inevitable consequence of antibiotic usage. Although persistence is not a genetically heritable trait, here we demonstrate for the first time that antibiotic resistance, which is heritable, can promote persistence formation. Our finding that resistance to one antibiotic, rifampicin, can boost persistence to other antibiotics, such as ciprofloxacin and ampicillin, may help explain why certain chronic infections are particularly recalcitrant to antibiotic therapies. Out results also emphasize the need to assess the effects of combination antibiotic therapies on persistence.

microbiology↗