Ethionamide

Prodrug Activation and Enzymatic Pathways

Ethionamide's efficacy stems from its transformation into a reactive species. This enzymatic conversion is primarily mediated by a specific mycobacterial monooxygenase.

The primary enzyme responsible for the bioactivation of this compound in M. tuberculosis is the flavin adenine dinucleotide (FAD)-containing monooxygenase, EthA (Rv3854c) wikipedia.orgfrontiersin.orgpatsnap.comuniprot.orgmdpi.comasm.orgdrugbank.comresearchgate.netresearchgate.netselleckchem.comnih.gov. This enzyme catalyzes the initial oxidative steps required for this compound to reach its active form. The expression of the ethA gene is regulated by EthR, a transcriptional repressor wikipedia.orgfrontiersin.orgresearchgate.net.

EthA has been characterized as a Baeyer-Villiger monooxygenase (BVMO) frontiersin.orguniprot.orgasm.orgnih.govmdpi.com. BVMOs are a class of enzymes known for their ability to catalyze the insertion of an oxygen atom adjacent to a carbonyl group, typically converting ketones to esters or lactones. In the context of this compound, EthA facilitates oxidative modifications of the thiocarbamide structure. EthA is an NADPH-specific, FAD-containing monooxygenase capable of performing Baeyer-Villiger oxidation reactions asm.org.

A key step in the bioactivation of this compound by EthA is the formation of the this compound S-oxide metabolite uniprot.orgresearchgate.netselleckchem.comrsc.orgscispace.comnih.govacs.orgsemanticscholar.orgoup.comebi.ac.ukebi.ac.ukuni.lu. This S-oxide derivative is considered to retain significant antituberculosis activity, and in some studies, it has been shown to have considerably better activity than the parent drug researchgate.netselleckchem.comscispace.comnih.govsemanticscholar.orgoup.comebi.ac.ukebi.ac.uk. Further oxidation of the S-oxide can occur, potentially leading to less active or inactive metabolites scispace.comacs.org. Studies using biomimetic oxidation systems have also demonstrated the formation of the S-oxide intermediate rsc.orgacs.org.

While EthA is the primary activator, evidence suggests the existence of alternative pathways for this compound bioactivation in M. tuberculosis that are independent of the ethA/R locus frontiersin.org. Another mycobacterial Baeyer-Villiger monooxygenase, MymA (Rv3083), has been reported to also play a role in activating this compound frontiersin.orgmdpi.comnih.govnih.gov. Loss-of-function mutations in mymA can result in increased resistance to this compound, suggesting its contribution to the activation process frontiersin.orgmdpi.comnih.gov. Furthermore, a cryptic alternative bioactivation pathway involving a bicistronic divergent operon (rv0077c-rv0078) with homologies to the ethA/R locus has been reported, although direct cross-talk between these regulons has not been demonstrated frontiersin.org.

The mycothiol biosynthesis pathway, involving genes such as mshA, mshB, and mshC, and its end product, mycothiol (MSH), have also been implicated in this compound bioactivation frontiersin.orgmdpi.comresearchgate.net. Mycothiol is a low-molecular-weight thiol unique to actinomycetes, including mycobacteria, and serves a function analogous to glutathione in other organisms. While the detailed molecular mechanisms remain to be fully elucidated, studies suggest that mycothiol or components of its biosynthesis pathway contribute to the activation of this compound frontiersin.orgmdpi.comresearchgate.net. Given that EthA has been shown to oxidize this compound into a sulfenic acid metabolite, it is hypothesized that this compound metabolites could react with mycothiol in a manner similar to the reaction of thiacetazone metabolites with glutathione frontiersin.org.

Formation of S-oxide Metabolite

Target Inhibition and Cellular Effects in Mycobacterium tuberculosis

The activated form of this compound exerts its effects by inhibiting key enzymes and interfering with vital synthetic pathways in M. tuberculosis. patsnap.com

Intracellular Accumulation and Molecular Sorting of Metabolites

The bioactivation of this compound is coupled with a precise molecular sorting mechanism of its metabolites within the mycobacterial cell. Studies using high-resolution magic angle spinning-NMR (HRMAS-NMR) have provided insights into the distribution of ETH-derived compounds. frontiersin.orgoup.comoup.com

Genetic Mutations Conferring Resistance

Genetic alterations are the main cause of ethionamide resistance. asm.org These mutations can lead to reduced activation of the drug or modifications in the target enzyme, diminishing the drug's inhibitory effect.

Efflux Pump Induction and its Role in Resistance

Efflux pumps are membrane proteins that actively transport drugs out of the bacterial cell, thereby reducing the intracellular drug concentration and contributing to drug resistance. nih.govplos.org While the primary mechanisms of ETH resistance involve mutations in activating enzymes or the drug target, the induction or overexpression of efflux pumps can also play a role. nih.govnih.gov Increased efflux pump activity can lead to a lower intracellular accumulation of this compound, potentially contributing to a resistant phenotype or facilitating the selection of strains with higher-level resistance mutations. plos.org Research suggests that efflux pump induction can be an early step in the development of drug resistance in M. tuberculosis, including resistance to this compound. plos.orgoup.com

Genotypic vs. Phenotypic Drug Susceptibility Testing

Drug susceptibility testing (DST) is essential for guiding the treatment of tuberculosis. Phenotypic DST, which determines the ability of bacteria to grow in the presence of a drug, is considered the reference standard for most anti-TB compounds. nih.govwho.int However, phenotypic DST can be slow and requires specialized infrastructure. who.int Genotypic DST, which identifies mutations known to confer resistance, offers a faster alternative. who.int For this compound, the correlation between genotypic and phenotypic resistance can be complex and not always perfect. mdpi.comnih.gov Studies have shown discrepancies between genotypic and phenotypic results for ETH, with some isolates exhibiting resistance-associated mutations but appearing phenotypically susceptible, and vice versa. nih.govnih.gov This highlights that while genotypic methods are valuable for detecting known resistance mutations, they may not capture all mechanisms of resistance, and phenotypic testing remains important for a complete assessment of ETH susceptibility. asm.orgnih.gov

Table: Concordance between Phenotypic and Genotypic DST for this compound

Acquired Drug Resistance (ADR) Development

Acquired drug resistance (ADR) to this compound develops primarily through the accumulation of genetic mutations in M. tuberculosis during treatment. asm.orgasm.orgmdpi.com Exposure to subinhibitory concentrations of the drug, often due to poor adherence or inadequate treatment regimens, can select for spontaneous mutations that confer resistance. nih.gov The most common mutations associated with ETH resistance occur in the ethA gene, leading to reduced activation of the prodrug. nih.govasm.orgnih.gov Mutations in the inhA gene or its promoter region, which is the target of activated ETH, also contribute significantly to resistance, often resulting in cross-resistance with isoniazid. nih.govnih.govasm.orgnih.gov Other genes, such as ethR (a repressor of ethA), ndh, and mshA, have also been implicated in the development of acquired resistance. asm.orgasm.orgnih.gov The development of ADR is a major challenge in TB treatment, necessitating the use of combination therapy to prevent the emergence of resistant strains. nih.gov

Population Pharmacokinetic Modeling

Population pharmacokinetic modeling of Ethionamide has been employed to describe the drug's behavior in various patient populations, including adults and children with tuberculosis. researchgate.netnih.govasm.orgasm.orgresearchgate.net These models typically utilize a one-compartment structure with first-order absorption and elimination, often incorporating a lag time before absorption begins. researchgate.netnih.govasm.orgresearchgate.net

Pharmacodynamic Parameters and Therapeutic Targets

This compound's action can be bacteriostatic or bactericidal depending on the concentration achieved at the infection site and the susceptibility of the organism. drugbank.comasm.org It is thought to work by inhibiting the synthesis of mycolic acids, essential components of the bacterial cell wall, similar to isoniazid. drugbank.comwikipedia.org Specifically, the activated form is thought to inhibit InhA, an enoyl reductase from Mycobacterium tuberculosis. drugbank.comwikipedia.org

Pharmacodynamic studies aim to link this compound exposure to its antimicrobial effect. Key pharmacodynamic parameters include the ratio of the area under the concentration-time curve to the minimum inhibitory concentration (AUC/MIC) and the ratio of the peak concentration to the minimum inhibitory concentration (Cmax/MIC), as well as the time the concentration remains above the MIC (Time > MIC). tandfonline.com

Studies have sought to define optimal PK/PD targets for this compound. An AUC0-24/MIC ratio greater than 56.2 has been identified as a potential target exposure for achieving maximal kill and suppressing acquired drug resistance in a hollow fiber system model of tuberculosis. nih.govresearchgate.net For the fAUC0-24/MIC target of 10, simulations have shown that at least 1,500 mg per day may be needed for ≥90% target attainment at an MIC of ≤1 mg/liter. asm.org The target Cmax range has been suggested as 2.5-5 μg/mL, which is within the minimum inhibitory concentration (MIC) range. nih.gov The average MIC for Mycobacterium tuberculosis is reported to be 0.6 - 2.5 µg/mL, with most susceptible organisms inhibited by 10 µg/mL or less. inchem.org

Research indicates that this compound MIC is a significant predictor of the time to sputum conversion in patients with multidrug-resistant tuberculosis. researchgate.net A linear negative relationship between this compound Sensititre MIC and time to sputum conversion has been observed up to an MIC of 2.5 mg/L, beyond which patients with MDR-TB were more likely to fail combination therapy. nih.govresearchgate.net Suboptimal this compound exposures have been linked to efflux pump-mediated acquired drug resistance. nih.govresearchgate.net

Pharmacokinetic Parameters of this compound

Pharmacodynamic Targets of this compound

Preclinical Pharmacokinetic/Pharmacodynamic Studies

Preclinical PK/PD studies are essential for understanding the relationship between this compound exposure and its effect on M. tuberculosis before clinical trials. These studies often utilize in vitro models and animal models to simulate human-like drug exposures and evaluate antimicrobial activity and resistance development diva-portal.org.

Pharmacokinetic Interactions with Co-Administered Drugs

This compound is typically administered as part of a combination regimen for tuberculosis, and its pharmacokinetics can be influenced by co-administered drugs. Several interactions have been reported.

This compound has been found to temporarily increase serum concentrations of isoniazid wikipedia.orgrxlist.com. Co-administration with isoniazid can lead to increased this compound exposure, with one study reporting a 44% increase in AUC₀–₂₄ when isoniazid was co-administered asm.org. The mechanism for this interaction is not fully understood, though both drugs are structurally similar asm.org. This interaction could potentially increase the risk of this compound-associated toxicities asm.org.

Concomitant use of this compound with cycloserine has been associated with an increased risk of adverse effects, including seizures wikipedia.orgrxlist.comdrugbank.com. Special care is advised when these two drugs are included in the same treatment regimen rxlist.com.

High rates of hepatotoxicity have been reported when this compound is taken with rifampicin wikipedia.org. This compound may also potentiate the adverse effects of other antituberculous drugs administered concurrently wikipedia.orgrxlist.com.

Excessive alcohol consumption should be avoided during this compound therapy, as it has been reported to provoke a psychotic reaction wikipedia.orgrxlist.comdrugbank.com.

Other potential interactions include a decreased therapeutic efficacy of thyroid medications (such as Liothyronine, Liotrix, Methimazole, Propylthiouracil, Thyroid, porcine, Tiratricol, Thyrotropin alfa) when used with this compound drugbank.com. This compound may also decrease the serum concentration of magnesium drugbank.com. The risk or severity of methemoglobinemia may be increased when this compound is combined with certain drugs like meloxicam, mepivacaine, propoxycaine, ropivacaine, and tetracaine drugbank.com. The therapeutic efficacy of certain vaccines, such as the Typhoid vaccine, may be decreased by this compound drugbank.com.

Preclinical studies in mice have also investigated pharmacokinetic interactions. For example, co-administration of oral this compound with d-cycloserine resulted in a decrease in this compound's plasma half-life and a reduction in its AUC, suggesting an interaction that affects this compound exposure nih.gov.

Pediatric Pharmacokinetics

Limited information is available on the pharmacokinetics of this compound in children, and current pediatric doses have often been extrapolated from weight-based adult doses. researchgate.netnih.govdiva-portal.orgasm.orgresearchgate.net Studies have aimed to characterize this compound pharmacokinetics in pediatric populations to inform more appropriate dosing strategies.

Population pharmacokinetic studies in children with tuberculosis have utilized nonlinear mixed-effects modeling to estimate pharmacokinetic parameters. researchgate.netnih.govdiva-portal.orgasm.org A one-compartment model with transit absorption and first-order elimination has been found to best describe this compound pharmacokinetics in children. researchgate.netnih.govdiva-portal.orgasm.org

Allometric scaling of clearance and volume of distribution with body weight, along with maturation of clearance and absorption, improved the model fit in pediatric populations. researchgate.netnih.govdiva-portal.orgasm.org Typical values for clearance and volume of distribution in children have been estimated. researchgate.netnih.govdiva-portal.orgasm.org

Younger children have been observed to have lower this compound concentrations compared to older children receiving the same milligram-per-kilogram dose. researchgate.net Age has been shown to correlate significantly with the AUC in children. researchgate.net Maturation of clearance is predicted to reach 50% within 2 months after birth and over 95% maturity at about 2 years of age. nih.gov

HIV co-infection in children has been associated with lower this compound exposure. nih.govresearchgate.net Rifampin co-treatment in children was found to increase this compound clearance. nih.gov

Studies have highlighted the need for pediatric dosing schemes based on more robust evidence to improve antituberculosis treatment in children, especially in small children. researchgate.netnih.govdiva-portal.org

Design and Synthesis of Novel Ethionamide Analogs

The design and synthesis of novel this compound analogs involve modifying the core structure of this compound to explore the impact of these changes on biological activity. This includes the creation of hybrid molecules linking the this compound structure to other pharmacophores known for antimycobacterial activity, such as imidazoles and benzimidazoles. Synthetic strategies often involve multi-step chemical pathways to introduce various substituents and structural motifs. For example, a two-step chemical pathway has been developed for the efficient synthesis of eighteen this compound analogues to study their bioactivation. The synthesis of 1,2,4-oxadiazole derivatives as potential antitubercular agents has also been explored, with various substituents introduced to the core structure.

Structural Modifications and Impact on Antimycobacterial Activity

Structural modifications to this compound and its analogs can significantly impact their antimycobacterial activity. Studies have investigated the effect of altering functional groups, introducing different ring systems, and modifying linker regions.

EthR Inhibitors as this compound Boosters

EthR inhibitors represent a promising strategy to enhance the efficacy of this compound by increasing its bioactivation within M. tuberculosis.

Molecular Docking and Computational Studies of Derivatives

Molecular docking and computational studies play a significant role in the design and evaluation of this compound derivatives and boosters. These in silico methods help in understanding the binding interactions between potential drug candidates and their biological targets, such as EthR and InhA. nih.govnih.gov

Computational tools are used to predict the binding modes and affinities of this compound derivatives and EthR inhibitors. nih.govacs.org Rigid receptor docking and other computational approaches have been applied to explore novel chemotypes that bind to the lipophilic ligand site of EthR. nih.gov These studies can sometimes yield multiple predicted binding orientations for a single compound within the EthR binding site. nih.govacs.org For instance, the EthR binding site is described as highly lipophilic with key asparagine residues (Asn 176 and Asn 179) that can be involved in hydrogen bonding and anchoring ligands, potentially leading to different binding modes. nih.govacs.org

Molecular docking studies have been conducted on various this compound derivatives, including imidazole and benzimidazole linked analogs, to evaluate their potential as inhibitors of InhA. nih.govresearchgate.net These studies aim to confirm experimental findings regarding the inhibitory action of these derivatives. nih.govresearchgate.net Computational analyses can also provide insights into the ADMET (Absorption, Distribution, Metabolism, Excretion, and Toxicity) properties and drug-likeness of designed compounds. nih.govresearchgate.netinnovareacademics.in

Table 2: Molecular Docking Studies of this compound Derivatives

Computational methods are also applied to understand the impact of mutations in Mycobacterium tuberculosis on drug resistance, including mutations in ethR that affect this compound susceptibility. frontiersin.org Modeling studies can help identify key residues involved in ligand binding and the effects of mutations on these interactions. frontiersin.org

Impact of Oxidized Methionine on this compound Degradation and Inactive Metabolite Formation

This compound undergoes metabolism in the organism, leading to the formation of its active form. However, certain metabolic pathways can result in the loss of its activity through the formation of inactive metabolites. researchgate.netrsc.org Research has shown that the presence of oxidized methionine in cells can influence the degradation of this compound, leading to the appearance of an inactive metabolite. researchgate.netrsc.orgresearchgate.netx-mol.comtiedejatutkimus.fi

This degradation process, influenced by oxidized methionine, results in an inactive metabolite that can be detected using analytical techniques such as HPLC and mass spectrometry. researchgate.netrsc.org Furthermore, the extent of this process increases with the degree of methionine oxidation. researchgate.netrsc.org

The oxidation of methionine residues in proteins to methionine sulfoxide (MetO) can occur due to reactive oxygen species (ROS). researchgate.net While methionine oxidation can be reversed by methionine sulfoxide reductase enzymes, its presence can impact this compound's metabolic fate. researchgate.net

Understanding the influence of oxidized methionine on this compound degradation is important for a better understanding of this compound's metabolism in living organisms. rsc.org This knowledge could potentially aid in the design of new drugs or this compound boosters aimed at combating multidrug-resistant tuberculosis by mitigating the formation of inactive metabolites. rsc.org

Table 3: Impact of Oxidized Methionine

The proposed mechanism for this compound activation involves its oxidation to S-oxide this compound. rsc.org This intermediate can then undergo further reactions, potentially leading to the formation of both the active ETH-NAD adduct and various inactive metabolites. rsc.org The influence of factors like oxidized methionine on these pathways can shift the balance towards inactive metabolite formation, impacting the drug's efficacy.

Development of Novel Ethionamide Analogues and Boosters

Research is actively pursuing the development of novel this compound analogues and boosters to improve its activity and overcome resistance. This compound boosters are designed to enhance the bioactivation of this compound, potentially allowing for lower, less toxic doses while maintaining or increasing efficacy. bioworld.comeuropa.eu These boosters often target bacterial transcriptional regulators, such as EthR, which represses the expression of the activating enzyme EthA. nih.govresearchgate.netacs.orgnih.gov By inhibiting EthR, the expression of EthA is increased, leading to greater conversion of this compound to its active form. nih.gov

Studies have identified new chemical series displaying the ability to potentiate this compound and counteract resistance linked to EthA mutations. bioworld.com For instance, BVL-GSK-098 (alpibectir) is a promising compound identified as an this compound booster. bioworld.com Preclinical studies with BVL-GSK-098 have been completed, and a Phase I trial showed it was generally safe and well tolerated in healthy volunteers. bioworld.combioversys.com A Phase IIa study is underway to compare this compound alone and in combination with BVL-GSK-098 in patients with drug-susceptible pulmonary TB. bioworld.comwho.int This combination aims to increase the level of this compound bioactivation, reduce the required dose, and potentially revert pre-existing clinical resistance. europa.eu

The development of EthR inhibitors has involved extensive structure-activity relationship (SAR) studies. researchgate.netacs.org Compounds like BDM31343 and BDM41906 have been identified as potent EthR inhibitors capable of boosting this compound activity in vitro and in vivo. researchgate.netacs.org

Beyond boosters, this compound analogues are also being investigated for potential new applications. For example, some this compound analogues have shown potent inhibition of tyrosinase, an enzyme involved in melanin biosynthesis, suggesting potential uses beyond tuberculosis treatment. researchgate.net

Strategies to Overcome this compound Resistance

This compound resistance in Mycobacterium tuberculosis primarily arises from mutations affecting its activation and target. The main enzyme responsible for this compound activation is EthA, and mutations in the ethA gene are a common mechanism of resistance. bioworld.commdpi.comasm.org Resistance can also be mediated by mutations in ethR, the repressor of ethA, or in inhA, the gene encoding the target enzyme enoyl-ACP reductase. mdpi.comasm.org

Strategies to overcome this compound resistance include the use of this compound boosters, as discussed above, which can increase the levels of the active drug even in the presence of some resistance mechanisms. bioworld.comeuropa.eu Another approach involves understanding the complex interplay of mutations that lead to resistance. Studies using whole-genome and transcriptome analysis are helping to identify novel transcription-mediated mechanisms of resistance, such as specific promoter mutations that reduce ethA expression. asm.org Further research is needed to clarify the extent to which individual mutations contribute to resistance and how they interact. asm.org

The mechanism of resistance to this compound is still not fully understood in all cases, with a percentage of resistant clinical isolates showing no mutations in the commonly implicated genes like ethA, ethR, or inhA. mdpi.comasm.org This highlights the need for further research to uncover additional resistance mechanisms. asm.org

Repurposing and Re-evaluating Old Drugs in Combination with this compound

Repurposing existing drugs in combination with this compound is a strategy to develop new treatment regimens, particularly for drug-resistant tuberculosis. nih.govexplorationpub.com This approach offers advantages as the safety profiles of these older drugs are generally well-established. nih.govmdpi.com

This compound is often used as a component in regimens for MDR-TB. asm.orgnih.gov Re-evaluating its use in combination with other existing or repurposed drugs could lead to more effective and potentially shorter treatment courses. For example, combinations of this compound with other second-line drugs like levofloxacin, cycloserine, pyrazinamide, and ethambutol are used in current regimens for drug-resistant TB. pensoft.net

Research is needed to optimize the dosing and duration of this compound when used in combination therapies. nih.gov Exploring combinations with drugs that have different mechanisms of action could help overcome resistance and improve treatment outcomes. The potential for combining this compound with folate-targeting drugs is also being explored. nih.gov

Advanced Drug Delivery Systems (e.g., Nanoparticles for Sustained Release)

Advanced drug delivery systems, particularly nanoparticle-based formulations, are being investigated to improve the efficacy and reduce the limitations of this compound, such as the need for frequent dosing and potential gastrointestinal intolerance. tandfonline.commdpi.comnih.gov Nanoparticles can offer sustained release of the drug, potentially reducing dosing frequency and improving patient compliance. tandfonline.comresearchgate.netfrontiersin.orgjpmer.com

Studies have demonstrated that this compound-loaded nanoparticles, such as those made from poly(DL-lactide-co-glycolide) (PLGA), can provide sustained release of this compound for several days in plasma and tissues in animal models. tandfonline.comresearchgate.netfrontiersin.orgjpmer.com For instance, orally administered this compound-loaded PLGA nanoparticles showed sustained release for 6 days in plasma compared to 6 hours for free this compound, and the drug was detected in organs like the lung, liver, and spleen for up to 5-7 days. tandfonline.comresearchgate.netfrontiersin.org These formulations can also help maintain drug levels above the minimum inhibitory concentration (MIC) for extended periods. tandfonline.comjpmer.com

Pulmonary delivery of this compound using nanoparticles is also being explored to target the drug directly to the site of infection in the lungs. mdpi.comresearchgate.net This approach could potentially enhance drug efficacy and reduce systemic exposure. mdpi.comresearchgate.net Other nanoparticle systems, such as niosomes, are also being investigated for this compound delivery with the aim of prolonging its presence in the bloodstream and improving therapeutic efficacy. researchgate.net

Pharmacogenomics and Personalized Medicine Approaches

Pharmacogenomics and personalized medicine approaches hold potential for optimizing this compound treatment. Understanding how genetic variations in both the host and the Mycobacterium tuberculosis pathogen influence this compound metabolism, transport, and efficacy could help tailor treatment regimens to individual patients. mdpi.com

Genomic profiling of M. tuberculosis isolates can identify resistance-conferring mutations, which can inform the choice of drugs and the likelihood of success with this compound-containing regimens. mdpi.comasm.orgasm.org Rapid genotypic tests for M. tuberculosis mutations are recommended to be integrated into clinical trials. nih.gov

While the provided search results did not yield specific research findings on host pharmacogenomics related to this compound, the general principle of personalized medicine in TB treatment, leveraging genomic profiling of both the pathogen and the host, is highlighted as a promising area for optimizing treatment regimens and minimizing drug resistance. mdpi.com

Integration of Artificial Intelligence and Machine Learning in Drug Discovery and Optimization

Artificial intelligence (AI) and machine learning (ML) are increasingly being integrated into drug discovery and optimization processes, including for tuberculosis drugs like this compound. researchgate.netslideshare.netresearchgate.net These technologies can analyze vast datasets to identify potential drug candidates, design new compounds, and predict their efficacy and properties. slideshare.netresearchgate.net

In the context of this compound, AI and ML can be applied to various aspects of research:

Identification of Novel Analogues and Boosters: AI/ML algorithms can screen large chemical libraries to identify compounds with desired properties, such as enhanced activity against resistant strains or the ability to boost this compound's effect by targeting EthR or other pathways. slideshare.netresearchgate.net

Prediction of Resistance Mechanisms: ML models can be trained on genomic and phenotypic data of M. tuberculosis isolates to predict this compound resistance based on genetic profiles. plos.org Studies have used ML systems to predict minimum inhibitory concentrations (MIC) for this compound and other anti-TB drugs from sequencing data. plos.org

Optimization of Drug Combinations: AI can help identify optimal drug combinations with this compound by analyzing data on drug interactions and efficacy in different M. tuberculosis strains.

Pharmacokinetic and Pharmacodynamic Modeling: ML can be used to build models that predict the pharmacokinetic and pharmacodynamic behavior of this compound and its formulations, aiding in the design of improved drug delivery systems.

ML models have shown promising accuracy in predicting MIC for this compound from sequencing data, although performance can vary for resistant isolates. plos.org The application of AI/ML in predicting in vivo efficacy of small molecules against M. tuberculosis is also being explored. acs.org

Addressing Unclear Mechanisms and Unidentified Metabolites

Despite decades of use, certain aspects of this compound's mechanism of action and metabolism remain unclear, particularly the precise nature of the active form and the role of various metabolites. mdpi.comresearchgate.netscispace.comoup.comnih.govnih.govfrontiersin.org this compound is a prodrug activated primarily by EthA, leading to the formation of an S-oxide metabolite. scispace.comnih.gov However, the exact downstream activated species that inhibits InhA is still debated. mdpi.comnih.gov

Research using techniques like high-resolution magic angle spinning-NMR (HRMAS-NMR) in living mycobacterial cells has provided insights into this compound metabolism. scispace.comoup.comnih.gov These studies suggest that while metabolites like the S-oxide and 4-pyridylmethanol are found outside the bacteria, a distinct, still unidentified metabolite, referred to as ETH, is the only this compound derivative detected within the bacterial cell and is considered the prime candidate for the active compound. oup.comnih.govfrontiersin.org ETH appears to accumulate intracellularly and is unable to cross the bacterial envelope. nih.gov

Further research is crucial to fully characterize the structure and activity of ETH* and other unidentified polar metabolites. oup.comnih.gov Understanding the precise activation pathway and the role of different enzymes and cellular components, including mycothiol, in this compound metabolism is essential for developing strategies to improve its efficacy and overcome resistance. mdpi.comscispace.comfrontiersin.org The complexity of this compound resistance mechanisms, with a percentage of resistant isolates lacking mutations in known resistance genes, also underscores the need to identify novel mechanisms and factors involved. mdpi.comasm.org

Improving in vitro and ex vivo Models for Drug Evaluation

Improving the predictive capacity and throughput of in vitro and ex vivo models is a critical area of future research for evaluating this compound and potential this compound-based therapies. Current in vitro drug susceptibility testing (DST) methods for this compound face challenges, including the drug's thermolability and the narrow range between the minimum inhibitory concentration (MIC) and the therapeutic index, which can complicate the distinction between susceptible and resistant isolates. nih.gov The reproducibility of DST for this compound is reported to be around 80%. nih.gov Furthermore, in vitro results sometimes show poor correlation with clinical outcomes. nih.gov

Research is ongoing to refine existing methods and develop new models that better mimic the complex environment of Mycobacterium tuberculosis infection in the host. Standardized critical concentrations for this compound have been established for various assays, such as the MGIT 960 system, where a critical concentration of 5 µg/ml is used. nih.govbasicmedicalkey.com However, phenotypic methods for testing this compound are not perfectly correlated, and isolates with an MIC of 5 mg/L are considered to have intermediate resistance. researchgate.net Studies comparing different phenotypic DST methods have observed poor correlation. researchgate.net

Dynamic in vitro models, such as the hollow fiber system model of tuberculosis (HFS-TB), are being utilized to study the pharmacokinetics/pharmacodynamics (PK/PD) of this compound. oup.com These models can simulate drug concentration variations over time, which is a crucial factor in vivo but is not captured by conventional static in vitro models. mdpi.com HFS-TB studies have been performed to identify the optimal 0-24 hour area under the concentration-time curve (AUC₀-₂₄) to MIC ratios for maximal kill and resistance suppression. oup.com

Ex vivo models, particularly those using infected host cells like macrophages, are valuable for evaluating the intracellular activity of this compound and potential this compound boosters. researchgate.netnih.gov These models can provide insights into how host cells affect the drug's availability and efficacy against intracellular bacteria. nih.gov For instance, studies have used Mycobacterium tuberculosis-infected macrophages to investigate the potency of compounds designed to boost this compound activity by inhibiting the transcriptional repressor EthR. researchgate.netnih.gov EthR controls the expression of EthA, the monooxygenase responsible for activating this compound. nih.govacs.orgrcsb.orgacs.org Inhibitors of EthR can enhance this compound's bioactivation and increase its potency. researchgate.netnih.govacs.org

Developing in vitro granuloma models is another area of research aimed at testing drug candidates against both dormant and active mycobacteria, which can exist within the hypoxic environment of granulomas in human infection. mdpi.com These models offer a more controlled and less expensive alternative to in vivo models for evaluating drug activity against different bacterial states. mdpi.com

Efforts are also focused on developing high-throughput screening platforms, including those that can directly screen for Mycobacterium tuberculosis inhibitors in infected macrophages. tandfonline.com The use of non-infectious, fast-growing mycobacteria like Mycobacterium aurum, which has an InhA homologue similar to Mycobacterium tuberculosis, is being explored as a model for early-stage high-throughput antituberculosis drug screening. nih.gov Studies have shown that susceptibility to isoniazid/ethionamide is altered in genetically modified M. aurum mutants with altered InhA expression, supporting its potential as a screening model. nih.gov

Furthermore, research into novel drug delivery systems, such as this compound-loaded nanoparticles, is being evaluated using in vivo drug disposition studies in animal models. tandfonline.com These studies assess the pharmacokinetic profile and tissue distribution of the drug delivered via nanoparticles, aiming to improve efficacy and potentially reduce the required dose. tandfonline.com

The development and refinement of these diverse in vitro and ex vivo models, alongside advanced techniques like microcalorimetry for DST and surface plasmon resonance (SPR) to study protein interactions, are crucial for a more accurate and efficient evaluation of this compound and new drug candidates in the fight against tuberculosis. mdpi.commdpi.com

Illustrative Data from Research Findings:

Research investigating EthR inhibitors as this compound boosters has demonstrated their potential to enhance this compound activity in ex vivo models. For example, studies using Mycobacterium tuberculosis-infected macrophages have shown that certain EthR inhibitors can boost this compound activity. researchgate.netnih.gov

Studies using the hollow fiber system model have generated PK/PD targets for this compound. For instance, specific AUC₀-₂₄/MIC ratios were identified as targets for achieving maximal kill and suppressing acquired drug resistance in this model. oup.com

Note: Specific numerical values for the AUC₀-₂₄/MIC ratios were presented in the context of experimental results in the source oup.com but require careful interpretation within the full study context. The table above is illustrative.

Research on nanoparticle delivery systems has shown altered pharmacokinetic profiles compared to free this compound. For example, this compound-loaded nanoparticles demonstrated a prolonged drug release profile in mice compared to free this compound. tandfonline.com

Note: This data is based on observed trends and reported durations in the source tandfonline.com.

These examples highlight the use of various models to generate data informing the understanding and potential improvement of this compound's efficacy.

Q. How do researchers address conflicting hypotheses about this compound’s synergy with other antimycobacterials?

• Methodological Answer : Perform checkerboard assays to quantify fractional inhibitory concentration indices (FICIs). Use isobolograms to classify interactions (synergistic, additive, antagonistic). Validate findings in macrophage infection models to assess physiological relevance .