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Isoniazid (INH) inhibits mycolic acid synthesis in Mycobacterium tuberculosis (Mtb) and is a cornerstone of treatment regimens against this deadly pathogen. However, over 10% of Mtb infections are INH-resistant. The compound C10 can sensitize clinically relevant INH-resistant mutants to killing by INH. Thus, understanding the mechanism of action for C10 could aid in designing new strategies for circumventing drug resistance. We find that C10 treatment reroutes carbon flux toward valine, drawing carbon away from gluconeogenesis and the TCA cycle. As a result, C10 decreases cell envelope capsule thickness and blocks an accumulation of peptidoglycan precursors that occurs in response to INH treatment in an INH-resistant Mtb katG mutant. In this altered metabolic state induced by C10, INH treatment of the INH-resistant Mtb katG mutant inhibits peptidoglycan synthesis, precipitating collapse of cell envelope integrity. Pyruvate supplementation relieves the C10-induced requirement for carbon flux toward valine, enhancing carbon assimilation into cell envelope precursors and restoring resistance to INH. In addition, we identify the formation of isoniazid-pyruvate in INH-treated katGW328LMtb, where pyruvate sequesters INH, lowering the concentration of INH available to inhibit Mtb. Together, our findings reveal a bactericidal activity for INH in Mtb that can function in INH-resistant mutants independently of INH-mediated inhibition of mycolic acid synthesis. This activity for INH can be elicited by shifting carbon flux toward valine and away from cell envelope precursor synthesis, highlighting a metabolic vulnerability that can be exploited to kill INH-resistant Mtb.

Apical hook development is an ideal model for studying differential growth in plants and is controlled by complex phytohormonal crosstalk, with auxin being the major player. Here, we identified a bioactive small molecule that decelerates apical hook opening in Arabidopsis thaliana. Our genetic studies suggest that this molecule enhances or maintains the auxin maximum found in the inner hook side and requires certain auxin signaling components to modulate apical hook opening. Using biochemical approaches, we then revealed the WD40 repeat scaffold protein RECEPTOR FOR ACTIVATED C KINASE 1A (RACK1A) as a direct target of this compound. We present data in support of RACK1A playing a positive role in apical hook opening by activating specific auxin signaling mechanisms and negatively regulating the differential auxin response gradient across the hook, thereby adjusting differential cell growth, an essential process for organ structure and function in plants.

We have developed GmPcides from a peptidomimetic dihydrothiazolo ring-fused 2-pyridone scaffold that has antimicrobial activities against a broad spectrum of Gram-positive pathogens. Here, we examine the treatment efficacy of GmPcides using skin and soft tissue infection (SSTI) and biofilm formation models by Streptococcus pyogenes. Screening our compound library for minimal inhibitory (MIC) and minimal bactericidal (MBC) concentrations identified GmPcide PS757 as highly active against S. pyogenes. Treatment of S. pyogenes biofilm with PS757 revealed robust efficacy against all phases of biofilm formation by preventing initial biofilm development, ceasing biofilm maturation and eradicating mature biofilm. In a murine model of S. pyogenes SSTI, subcutaneous delivery of PS757 resulted in reduced levels of tissue damage, decreased bacterial burdens, and accelerated rates of wound healing, which were associated with down-regulation of key virulence factors, including M protein and the SpeB cysteine protease. These data demonstrate that GmPcides show considerable promise for treating S. pyogenes infections.

Of the approximately 10 million cases of Mycobacterium tuberculosis (Mtb) infections each year, over 10% are resistant to the frontline antibiotic isoniazid (INH). INH resistance is predominantly caused by mutations that decrease the activity of the bacterial enzyme KatG, which mediates the conversion of the pro-drug INH to its active form INH-NAD. We previously discovered an inhibitor of Mtb respiration, C10, that enhances the bactericidal activity of INH, prevents the emergence of INH-resistant mutants, and re-sensitizes a collection of INH-resistant mutants to INH through an unknown mechanism. To investigate the mechanism of action of C10, we exploited the toxicity of high concentrations of C10 to select for resistant mutants. We discovered two mutations that confer resistance to the disruption of energy metabolism and allow for the growth of Mtb in high C10 concentrations, indicating that growth inhibition by C10 is associated with inhibition of respiration. Using these mutants as well as direct inhibitors of the Mtb electron transport chain, we provide evidence that inhibition of energy metabolism by C10 is neither sufficient nor necessary to potentiate killing by INH. Instead, we find that C10 acts downstream of INH-NAD synthesis, causing Mtb to become particularly sensitive to inhibition of the INH-NAD target, InhA, without changing the concentration of INH-NAD or the activity of InhA, the two predominant mechanisms of potentiating INH. Our studies revealed that there exists a vulnerability in Mtb that can be exploited to render Mtb sensitive to otherwise subinhibitory concentrations of InhA inhibitor. IMPORTANCE Isoniazid (INH) is a critical frontline antibiotic to treat Mycobacterium tuberculosis (Mtb) infections. INH efficacy is limited by its suboptimal penetration of the Mtb-containing lesion and by the prevalence of clinical INH resistance. We previously discovered a compound, C10, that enhances the bactericidal activity of INH, prevents the emergence of INH-resistant mutants, and re-sensitizes a set of INH-resistant mutants to INH. Resistance is typically mediated by katG mutations that decrease the activation of INH, which is required for INH to inhibit the essential enzyme InhA. Our current work demonstrates that C10 re-sensitizes INH-resistant katG-hypomorphs without enhancing the activation of INH. We furthermore show that C10 causes Mtb to become particularly vulnerable to InhA inhibition without compromising InhA activity on its own. Therefore, C10 represents a novel strategy to curtail the development of INH resistance and to sensitize Mtb to sub-lethal doses of INH, such as those achieved at the infection site.

Numerous challenges hinder the development of neuroprotective treatments for Parkinson's disease, with a regularly identified issue being the lack of clinically relevant animal models. Viral vector overexpression of α-synuclein is widely considered the most relevant model; however, this has been limited by high variability and inconsistency. One potential method of optimisation is pairing it with a secondary insult such as FN075, a synthetic molecule demonstrated to accelerate α-synucleinopathy. Thus, the aim of this study was to investigate if sequential infusion of adeno-associated virus (AAV)-α-synuclein and FN075 into the rat brain can replicate α-synucleinopathy, nigrostriatal pathology and motor dysfunction associated with Parkinson's disease. Rats received a unilateral injection of AAV-α-synuclein (or AAV-green fluorescent protein) into two sites in the substantia nigra, followed 4 weeks later by unilateral injection of FN075 (or vehicle) into the striatum. Animals underwent behavioural testing every 4 weeks until sacrifice at 20 weeks, followed by immunohistochemistry assessment post-mortem. As anticipated, AAV-α-synuclein led to extensive overexpression of human α-synuclein throughout the nigrostriatal pathway, as well as elevated levels of phosphorylated and aggregated forms of the protein. However, the sequential administration of FN075 into the striatum did not exacerbate any of the α-synuclein pathology. Furthermore, despite the extensive α-synuclein pathology, neither administration of AAV-α-synuclein nor FN075, alone or in combination, was sufficient to induce dopaminergic degeneration or motor deficits. In conclusion, this approach did not replicate the key characteristics of Parkinson's disease, and further studies are required to create more representational models for testing of novel compounds and treatments for Parkinson's disease.

We have developed an Ir(PPy)3 photoredox-catalyzed cross-coupling reaction that allows installation of quinoxalinones at the C7 position of thiazolino ring-fused 2-pyridones (TRPs) under mild conditions. The methodology tolerates various substituted quinoxalinones and biologically relevant substituents on the C8 position of the TRP. The TRP scaffold has large potential in the development of lead compounds, and while the coupled products are interesting from a drug-development perspective, the methodology will be useful for developing more potent and drug-like TRP-based candidates.

A selective [4 + 2] cycloaddition reaction of thiazolo-2-pyridones with arynes has been demonstrated. The developed protocol allows rapid access to highly functionalized, structurally complex thiazolo-fused bridged isoquinolones in high yields, which are susceptible to further late-stage functionalization.

Listeria monocytogenes is a facultative Gram-positive bacterium that causes listeriosis, a severe foodborne disease. We previously discovered that ring-fused 2-pyridone compounds can decrease virulence factor expression in Listeria by binding and inactivating the PrfA virulence activator. In this study, we tested PS900, a highly substituted 2-pyridone that was recently discovered to be bactericidal to other Gram-positive pathogenic bacteria, such as Staphylococcus aureus and Enterococcus faecalis. We show that PS900 can interact with PrfA and reduce the expression of virulence factors. Unlike previous ring-fused 2-pyridones shown to inactivate PrfA, PS900 had an additional antibacterial activity and was found to potentiate sensitivity toward cholic acid. Two PS900-tolerant mutants able to grow in the presence of PS900 carried mutations in the brtA gene, encoding the BrtA repressor. In wild-type (WT) bacteria, cholic acid binds and inactivates BrtA, thereby alleviating the expression of the multidrug transporter MdrT. Interestingly, we found that PS900 also binds to BrtA and that this interaction causes BrtA to dissociate from its binding site in front of the mdrT gene. In addition, we observed that PS900 potentiated the effect of different osmolytes. We suggest that the increased potency of cholic acid and osmolytes to kill bacteria in the presence of PS900 is due to the ability of the latter to inhibit general efflux, through a yet-unknown mechanism. Our data indicate that thiazolino 2-pyridones constitute an attractive scaffold when designing new types of antibacterial agents.

IMPORTANCE: Bacteria resistant to one or several antibiotics are a very large problem, threatening not only treatment of infections but also surgery and cancer treatments. Thus, new types of antibacterial drugs are desperately needed. In this work, we show that a new generation of substituted ring-fused 2-pyridones not only inhibit Listeria monocytogenes virulence gene expression, presumably by inactivating the PrfA virulence regulator, but also potentiate the bactericidal effects of cholic acid and different osmolytes. We identified a multidrug repressor as a second target of 2-pyridones. The repressor–2-pyridone interaction displaces the repressor from DNA, thus increasing the expression of a multidrug transporter. In addition, our data suggest that the new class of ring-fused 2-pyridones are efficient efflux inhibitors, possibly explaining why the simultaneous addition of 2-pyridones together with cholic acid or osmolytes is detrimental for the bacterium. This work proves conclusively that 2-pyridones constitute a promising scaffold to build on for future antibacterial drug design.

Mycobacterium tuberculosis (Mtb) drug resistance poses an alarming threat to global tuberculosis control. We previously reported that C10, a ring-fused thiazolo-2-pyridone, inhibits Mtb respiration, blocks biofilm formation, and restores the activity of the antibiotic isoniazid (INH) in INH-resistant Mtb isolates. This discovery revealed a new strategy to address INH resistance. Expanding upon this strategy, we identified C10 analogues with improved potency and drug-like properties. By exploring three heterocycle spacers (oxadiazole, 1,2,3-triazole, and isoxazole) on the ring-fused thiazolo-2-pyridone scaffold, we identified two novel isoxazoles, 17h and 17j. 17h and 17j inhibited Mtb respiration and biofilm formation more potently with a broader therapeutic window, were better potentiators of INH-mediated inhibition of an INH-resistant Mtb mutant, and more effectively inhibited intracellular Mtb replication than C10. The (−)17j enantiomer showed further enhanced activity compared to its enantiomer and the 17j racemic mixture. Our potent second-generation C10 analogues offer promise for therapeutic development against drug-resistant Mtb.

Virulence factors enable pathogenic bacteria to infect host cells, establish infection, and contribute to disease progressions. In Gram-positive pathogens such as Staphylococcus aureus (Sa) and Enterococcus faecalis (Ef), the pleiotropic transcription factor CodY plays a key role in integrating metabolism and virulence factor expression. However, to date, the structural mechanisms of CodY activation and DNA recognition are not understood. Here, we report the crystal structures of CodY from Sa and Ef in their ligand-free form and their ligand-bound form complexed with DNA. Binding of the ligands - branched chain amino acids and GTP - induces conformational changes in the form of helical shifts that propagate to the homodimer interface and reorient the linker helices and DNA binding domains. DNA binding is mediated by a non-canonical recognition mechanism dictated by DNA shape readout. Furthermore, two CodY dimers bind to two overlapping binding sites in a highly cooperative manner facilitated by cross-dimer interactions and minor groove deformation. Our structural and biochemical data explain how CodY can bind a wide range of substrates, a hallmark of many pleiotropic transcription factors. These data contribute to a better understanding of the mechanisms underlying virulence activation in important human pathogens.