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Mycobacterium tuberculosis (Mtb) aspartate decarboxylase PanD is required for biosynthesis of the essential cofactor coenzyme A and targeted by the first line drug pyrazinamide (PZA). PZA is a prodrug that is converted by a bacterial amidase into its bioactive form pyrazinoic acid (POA). Employing structure-function analyses we previously identified POA-based inhibitors of Mtb PanD showing much improved inhibitory activity against the enzyme. Here, we performed the first structure-function studies on PanD encoded by the non-tuberculous mycobacterial lung pathogen Mycobacterium abscessus (Mab), shedding light on the differences and similarities of Mab and Mtb PanD. Solution X-ray scattering data provided the solution structure of the entire tetrameric Mab PanD, which in comparison to the structure of the derived C-terminal trun-cated Mab PanD1-114 mutant, revealed the orientation of the four flexible C-termini relative to the catalytic core. Enzymatic studies of Mab PanD1-114 explored the essentiality of the C-terminus for catalysis. A library of recombinant Mab PanD mutants based on structural information and PZA/POA resistant PanD mutations in Mtb, illuminated critical residues involved in the substrate tunnel and enzymatic activity. Using our library of POA analogs, we identified (3-(1-naphthamido)pyrazine-2-car-boxylic acid) (analog 2) as the first potent inhibitor of Mab PanD. The inhibitor shows mainly electrostatic- and hydrogen bonding interaction with the target enzyme as explored by isothermal titration calorimetry and confirmed by docking studies. The observed unfavorable entropy indicates that significant conformational changes are involved in the binding process of analog 2 to Mab PanD. In contrast to PZA and POA, which are whole-cell inactive, analog 2 exerts appreciable antibacterial activity against the three subspecies of Mab. Ministry of Education (MOE) National Research Foundation (NRF) Submitted/Accepted version Research reported in this publication is supported by the National Institute of Allergy and Infectious Diseases of the National Institutes of Health under Award Numbers 2R01AI106398-05 (T.D., (T.D., (T.D., C.A.,C.A., G.G.) G.G.) . The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health. The studies are also supported by the National Research Founda-tion (NRF) Singapore, NRF Competitive Research Programme (CRP), Grant Award Number NRF–CRP18–2017–01 (G.G., T.D.), and the Singapore Ministry of Education (MOE) Academic Research Fund Tier 1 (RG107/20) to G.G.

Pyrazinoic acid or pyrazine-2-carboxylic acid (PA), due to its nitrogenous heteroaromatic ring, can be explored as an anticancer agent. Here, a series of twenty novels PA derivatives have been synthesized and characterized using IR, NMR, and mass spectrums. Their cytotoxic activity was evaluated against three different cancer cell lines, including lung (A549), breast (MCF-7), and colon (HT-29). P16, the most potent compound, showed moderate cytotoxicity with IC50 of 6.11 μM, 10.64 μM, and 14.92 μM, against the A549, MCF-7, and HT-29 cell lines, respectively. Furthermore, the effect of this compound against MRC5 as a non-tumoral lung cell line, exhibited a selectivity index of 9.02. The apoptotic induction activity of P16 was also performed on the A549 cell line. The results showed that as the concentration of the compound increases (from 3 to 6 μM), the percentage of induction of apoptosis increases from 8.54% to 72.4%. Electrophoretic gel mobility shift assays showed that P16 was also able to ROS induce DNA cleavage in the presents of H2O2 (1.0 mM) in dose-dependent manner. Molecular docking was also applied to anticipate the binding locations and the binding of the synthesized compound with Bcl-2 apoptosis regulator and DNA as their proposed targets.

The influence of the zinc(II) starting material in the nucleophilic addition of piperidine (abbreviated as pipe) to acetonitrile to form amidine, piperidinoacetamidine (pipeam), was assessed. Thus, zinc(II) oxide, zinc(II) chloride or zinc(II) acetate were reacted with picolinic acid or pyrazinoic acid, piperidine and acetonitrile. The acid was used as a source of an N,O-donor ligand. The reactions with picolinic acid (picH) gave pipeamH[Zn(pic)3]·0.5H2O (1), an amidinium salt of a homoleptic complex [Zn(pic)3]–. The same product was obtained when [Zn(pic)(picH)Cl], an already known picolinate complex, was reacted under similar conditions. The chloride-containing mixtures produced another amidine compound, (pipeamH)Cl. The reactions with pyrazinoic acid (pyrazH) gave pipeamH[Zn(pyraz)3] (3), the amidinium salt of a homoleptic complex [Zn(pyraz)3]–. The acetate-containing mixture yielded acetamidinium acetate. The latter product indicates the presence of ammonia in the reaction. Notably, no amidine species was isolated when the coordinatively saturated pyrazinoate complex, [Zn(pyraz)2]n (2), was reacted with piperidine and acetonitrile. A detailed structural characterization of the new compounds and a discussion of their formation are presented.

Background: Resistance to the critical first line anti-tubercular drug, Pyrazinamide, is a significant obstacle to achieving the global end to tuberculosis targets. Approximately 50% of multidrug- resistant tuberculosis and over 90% of extensively drug-resistant tuberculosis strains are also Pyrazinamide resistant. Pyrazinamide is a pro-drug that reduces the duration of tuberculosis therapy time by 9-12 months, while used as an anti-biotic in the 1st- & 2nd-line tuberculosis treatment regimens. Pyrazinamidase is an enzyme encoded by pncA gene, which is responsible for the amide hydrolysis of pyrazinamide into active pyrazinoic acid. Pyrazinoic acid can inhibit trans-translation by binding to ribosomal protein S1 and competing with tmRNA, the natural cofactor of ribosomal protein S1. Although pncA mutations have been commonly associated with pyrazinamide resistance, a small number of resistance cases have been associated with mutations in ribosomal protein S1. Ribosomal protein S1was recently identified as a possible target of pyrazinamide based on its binding activity to pyrazinoic acid and the capacity to inhibit trans-translation. Objective: Despite the critical role played by pyrazinamide, its mechanisms of action are not yet fully understood. Therefore, this study is an effort to explore the resistance mechanism toward pyrazinamide drug in Mycobacterium (M.) tuberculosis. Methods: An extensive molecular dynamics simulation was performed using the AMBER software package. We mutated residues of the binding site (i.e., F307A, F310A, and R357A) in the RpsA S1 domain to address the drug-resistant mechanism of RpsA in complex that might be responsible for pyrazinamide resistance. : Moreover, it is challenging to collect the drug mutant to combine the complex of a protein by single- crystal X-ray diffraction. Thus, the total three structures were prepared by inducing mutations in the wild-type protein using PyMol. Results: The dynamic results revealed that a mutation in the binding pocket produced pyrazinamide resistance due to the specificity of these residues in binding pockets, which resulted in the scarcity of hydrophobic and hydrogen bonding interaction with pyrazinoic acid, increasing the CAdistance between the binding pocket residues as compared to wild type RpsA that led to structural instability. Conclusion: The overall dynamic results will provide useful information behind the drug resistance mechanism to manage tuberculosis and also helps in better management for future drug resistance.

Graphical abstract, Pyrazinamide (PZA) is a component of first-line drugs, active against latent Mycobacterium tuberculosis (MTB) isolates. The prodrug is activated into the active form, pyrazinoic acid (POA) via pncA gene-encoded pyrazinamidase (PZase). Mutations in pncA have been reported, most commonly responsible for PZA-resistance in more than 70% of the resistant cases. In our previous study, we detected many mutations in PZase among PZA-resistance MTB isolates including A46V, H71Y, and D129N. The current study was aimed to investigate the molecular mechanism of PZA-resistance behind mutants (MTs) A46V, H71Y, and D129N in comparison with the wild type (WT) through molecular dynamic (MD) simulation. MTB positive samples were subjected to PZA drug susceptibility testing (DST) against critical concentration (100ug/ml). The resistant samples were subjected to pncA sequencing. Thirty-six various mutations have been observed in the coding region of pncA of PZA-resistant isolates (GenBank accession No. MH461111) including A46V, H71Y, and D129N. The post-simulation analysis revealed a significant variation in MTs structural dynamics as compared to the WT. Root means square deviations (RMSD) and Root means square fluctuation (RMSF) has been found in variation between WT and MTs. Folding effect and pocket volume were altered in MTs when compared with WT. Geometric matching supports the effect of mutation A46V, H71Y, and D129N on PZase structure that may have an insight effect on PZase dynamics, making them vulnerable to convert pro-PZA into active form, POA. In conclusion, the current analyses will provide useful information behind PZA-resistance for better management of drug-resistant TB.

Pyrazinamide, a first-line antibiotic used against Mycobacterium tuberculosis, has been shown to act in a pH-dependent manner in vitro. Why pyrazinamide, an antitubercle prodrug discovered more than 65 years ago, exhibits this pH-dependent activity was unclear. Upon entering mycobacterial cells, pyrazinamide is deamidated to pyrazinoate by an enzymatic process and exists in an acid-base equilibrium with pyrazinoic acid. Thus, the effects of total pyrazinoic acid (pyrazinoic acid + pyrazinoate) on M. tuberculosis growth, pH homeostasis, and proton motive force over a range of pH values found in host tissues were investigated. Although M. tuberculosis was able to maintain pH homeostasis over an external pH range of 7.0 to 5.5, total pyrazinoic acid induced growth inhibition increased as culture medium pH was decreased from 7.3 to 6.4. Consistent with growth inhibition, total pyrazinoic acid increased both acidification of the bacterial cytoplasm and dissipation of membrane potential as the environmental pH decreased when added to the bacterial suspensions. The results suggest pyrazinoic acid is the active form of the drug, which acts as an uncoupler of proton motive force, likely a protonophore, providing a mechanistic explanation for the pH dependence of the drug activity.

Pyrazinamidase (PZase) is a member of Fe-dependent amidohydrolases that activates pyrazinamide (PZA) into active pyrazinoic acid (POA). PZA, a nicotinamide analogue, is an essential first-line drug...

As part of the quest for new gold drugs, we have explored the efficacy of three gold complexes derived from the tuberculosis drug pyrazinamide (PZA), namely, the gold(I) complex [Au(PPh3)(PZA)]OTf (1, OTf = trifluoromethanesulfonate) and two gold(III) complexes [Au(PZA)Cl2] (2) and [Au(PZO)Cl2] (3, PZO = pyrazinoic acid, the metabolic product of PZA) against two mycobacteria, Mycobacterium tuberculosis and Mycobacterium smegmatis. Only complex 1 with the {Au(PPh3)}+ moiety exhibits significant bactericidal activity against both strains. In the presence of thiols, 1 gives rise to free PZA and {Au(PPh3)}-thiol polymeric species. A combination of PZA and the {Au(PPh3)}-thiol polymeric species appears to lead to enhanced efficacy of 1 against M. tuberculosis.

Pyrazinamide (PZA) is the only first-line antitubercular drug active against latent Mycobacterium tuberculosis (Mtb). It is activated to pyrazinoic acid by the pncA-encoded pyrazinamidase enzyme (PZase). Despite the emergence of PZA drug resistance, the underlying mechanisms of resistance remain unclear. This study investigated part of these mechanisms by modelling a PZA-bound wild type and 82 mutant PZase structures before applying molecular dynamics (MD) with an accurate Fe2+ cofactor coordination geometry. After observing nanosecond-scale PZA unbinding from several PZase mutants, an algorithm was developed to systematically detect ligand release via centre of mass distances (COM) and ligand average speed calculations, before applying the statistically guided network analysis (SGNA) method to investigate conserved protein motions associated with ligand unbinding. Ligand and cofactor perspectives were also investigated. A conserved pair of lid-destabilising motions was found. These consisted of (1) antiparallel lid and side flap motions; (2) the contractions of a flanking region within the same flap and residue 74 towards the core. Mutations affecting the hinge residues (H51 and H71), nearby residues or L19 were found to destabilise the lid. Additionally, other metal binding site (MBS) mutations delocalised the Fe2+ cofactor, also facilitating lid opening. In the early stages of unbinding, a wider variety of PZA poses were observed, suggesting multiple exit pathways. These findings provide insights into the late events preceding PZA unbinding, which we found to occur in some resistant PZase mutants. Further, the algorithm developed here to identify unbinding events coupled with SGNA can be applicable to other similar problems.

Drug–drug and drug–nutraceutical multicomponent solids of an antipsychotic drug olanzapine (OLN) are prepared using mechanochemistry. Drug molecules, viz., nateglinide (NAT) and pyrazinoic acid (PZO) as well as nutraceuticals, namely, 2,4,6-trihydroxybenzoic acid (246THBA), gallic acid (GA) and sinapic acid (SPA) are used as coformers in this study. After neat grinding (NG), incomplete conversion (partially amorphous) was observed, whereas liquid-assisted grinding (LAG) resulted in the formation of coamorphous OLN–NAT and crystalline salts/salt hydrates of OLN with rest of the coformers, which were characterized using a combination of techniques, including single crystal X-ray diffraction. The OLN–NAT coamorphous salt has a potential scope for development as a combination drug in order to suppress the increase in the blood sugar level, a common side-effect observed during the monotherapy of psychiatric patients using OLN. The equilibrium solubility study shows a substantial enhancement in the solubility of olanzapinium pyrazinoate compared to that of the pure base.

Pyrazinamide (PZA) is one of the essential anti-mycobacterium drugs, active against non-replicating Mycobacterium tuberculosis (MTB) isolates. PZA is converted into its active state, called pyrazinoic acid (POA), by action of pncA encoding pyrazinamidase (PZase). In the majority of PZA-resistance isolates, pncA harbored mutations in the coding region. In our recent report, we detected a number of novel variants in PZA-resistance (PZAR) MTB isolates, whose resistance mechanisms were yet to be determined. Here we performed several analyses to unveil the PZAR mechanism of R123P, T76P, G150A, and H71R mutants (MTs) through molecular dynamics (MD) simulations. In brief, culture positive MTB isolates were subjected to PZA susceptibility tests using the WHO recommended concentration of PZA (100 μg ml−1). The PZAR samples were screened for mutations in pncA along sensitive isolates through polymerase chain reactions and sequencing. A large number of variants (GeneBank accession no. MH461111), including R123P, T76P, G150A, and H71R, have been spotted in more than 70% of isolates. However, the mechanism of PZAR for mutants (MTs) R123P, T76P, G150A, and H71R was unknown. For the MTs and native PZase structures (WT), thermodynamic properties were compared using molecular dynamics simulations for 100 ns. The MTs structural activity was compared to the WT. Folding effect and pocket volume variations have been detected when comparing between WT and MTs. Geometric matching further confirmed the effect of R123P, T76P, G150A, and H71R mutations on PZase dynamics, making them vulnerable for activating the pro-drug into POA. This study offers a better understanding for management of PZAR TB. The results may be used as alternative diagnostic tools to infer PZA resistance at a structural dynamics level.

Tuberculosis (TB) remains a leading cause of infectious disease-related mortality and morbidity. Pyrazinamide (PZA) is a critical component of the first-line TB treatment regimen because of its sterilizing activity against non-replicating Mycobacterium tuberculosis (Mtb), but its mechanism of action has remained enigmatic. PZA is a prodrug converted by pyrazinamidase encoded by pncA within Mtb to the active moiety, pyrazinoic acid (POA) and PZA resistance is caused by loss-of-function mutations to pyrazinamidase. We have recently shown that POA induces targeted protein degradation of the enzyme PanD, a crucial component of the coenzyme A biosynthetic pathway essential in Mtb. Based on the newly identified mechanism of action of POA, along with the crystal structure of PanD bound to POA, we designed several POA analogs using structure for interpretation to improve potency and overcome PZA resistance. We prepared and tested ring and carboxylic acid bioisosteres as well as 3, 5, 6 substitutions on the ring to study the structure activity relationships of the POA scaffold. All the analogs were evaluated for their whole cell antimycobacterial activity, and a few representative molecules were evaluated for their binding affinity, towards PanD, through isothermal titration calorimetry. We report that analogs with ring and carboxylic acid bioisosteres did not significantly enhance the antimicrobial activity, whereas the alkylamino-group substitutions at the 3 and 5 position of POA were found to be up to 5 to 10-fold more potent than POA. Further development and mechanistic analysis of these analogs may lead to a next generation POA analog for treating TB. Ministry of Education (MOE) Research reported in this work was supported by the National Institute of Allergy and Infectious Diseases of the National Institutes of Health under Award Number R01 AI106398 and the Singapore Ministry of Education (MoE) Academic Research Fund Tier 1 (RG107/20).

Human cytosolic prolyl-tRNA synthetase (HcProRS) catalyses the formation of the prolyl-tRNAPro, playing an important role in protein synthesis. Inhibition of HcProRS activity has been shown to have potential benefits in the treatment of fibrosis, autoimmune diseases and cancer. Recently, potent pyrazinamide-based inhibitors were identified by a high-throughput screening (HTS) method, but no further elaboration was reported. The pyrazinamide core is a bioactive fragment found in numerous clinically validated drugs and has been subjected to various modifications. Therefore, we applied a virtual screening protocol to our in-house library of pyrazinamide-containing small molecules, searching for potential novel HcProRS inhibitors. We identified a series of 3-benzylaminopyrazine-2-carboxamide derivatives as positive hits. Five of them were confirmed by a thermal shift assay (TSA) with the best compounds 3b and 3c showing EC50 values of 3.77 and 7.34 µM, respectively, in the presence of 1 mM of proline (Pro) and 3.45 µM enzyme concentration. Co-crystal structures of HcProRS in complex with these compounds and Pro confirmed the initial docking studies and show how the Pro facilitates binding of the ligands that compete with ATP substrate. Modelling 3b into other human class II aminoacyl-tRNA synthetases (aaRSs) indicated that the subtle differences in the ATP binding site of these enzymes likely contribute to its potential selective binding of HcProRS. Taken together, this study successfully identified novel HcProRS binders from our anti-tuberculosis in-house compound library, displaying opportunities for repurposing old drug candidates for new applications such as therapeutics in HcProRS-related diseases. ispartof: INTERNATIONAL JOURNAL OF MOLECULAR SCIENCES vol:22 issue:15 ispartof: location:Switzerland status: published

Pyrazinamide (PZA), a crucial component of anti-TB therapy, is a prodrug. PZA interacts with PncA protein to be converted into its functional form i.e. pyrazinoic acid (POA). It has unique feature to kill dormant tubercle bacilli of acidic environment. Although significance of pH environment in PZA activation has been investigated in several of previous studies, insight into the significant atomistic variations in the interaction pattern of PZA with PncA, at different pH environments, are still required to be explored. On the other hand, continuously emerging PncA mutants, associated with PZA resistance, have also become a serious threat for global TB control program. Therefore, the current study was designed to understand the role of pH environment in the PZA activation and to explore the PZA resistance mechanism in various PncA mutants. The study included various in silico experiments like molecular docking, MD simulation, binding free energy estimation, PCA and FEL. In our study, we have found pH-3 and pH-5 environment as a highly significant environment for PZA activation. It was found that protonation or deprotonation of PZA activation site (PAS) residues, majorly K48, D56, K96 and E107, resulted in rearrangement of the PAS according to the pH conditions. It has also been observed that positioning of PZA binding near to Fe2+ and residues of catalytic triad (i.e. D8, K96 and C138) also play a very crucial role in the activation of PZA. The overall insight from the current study may help to develop new therapeutics against PncA mutated PZA resistance. Communicated by Ramaswamy H. Sarma

Pyrazinamide (PZA) is an important component of first-line anti-tuberculosis (anti-TB) drugs. The anti-TB agent is activated into an active form, pyrazinoic acid (POA), by Mycobacterium tuberculosi...

Tuberculosis is an infectious disease, affecting mostly lungs, that is still considered a health global problem as it causes millions of deaths worldwide. Current treatment is effective, however, associated with severe adverse effects due to the high doses of each anti-tuberculosis drug daily administrated by oral therapy. For the first time, a pyrazinoic acid biodegradable nanoconjugate was synthesized and developed for pulmonary administration in an attempt to reduce the administered doses by achieving a high drug payload and controlled release at the target site. The conjugate was synthesized by coupling pyrazinoic acid on carboxylic groups of poly(malic acid), which is a biodegradable and biocompatible polymer, and posteriorly self-assembled into nanoconjugates. Characterization confirmed the formation of nanometric, spherical and negatively charged pyrazinoic acid nanoconjugate (NC-PA). NC-PA was stable for 60 days at 4 and 37 ºC and able to deliver PA in a sustained release manner over time. On macrophages, they exhibited no cell toxicity for a wide range of concentrations (from 1 to 100 µg/mL), demonstrating the safety of NC-PA. In addition, the nanoconjugate was efficiently taken up by RAW 264.7 cells over 6 hours reaching a maximum value after 3h of incubation. In conclusion, innovative nanoconjugates are a promising alternative to deliver drugs directly to the lungs and contributing to improving tuberculosis therapy.

The pro-drug pyrazinamide is hydrolyzed to pyrazinoic acid (POA) in its use for the treatment of tuberculosis. As a molecule with bactericidal activity, POA binds to the C-terminal S1 domain of ribosomal protein S1 from Mycobacterium tuberculosis (MtRpsACTD_S1) to inhibit trans-translation. Trans-translation is a critical component of protein synthesis quality control, and is mediated by transfer-messenger RNA. Here, we have determined the solution structure of MtRpsACTD_S1(280–368), and analyzed its structural dynamics by NMR spectroscopy. The solution structure of MtRpsACTD_S1(280–368) mainly consists of five anti-parallel β strands, two α helices, and two 310 helices. Backbone dynamics reveals that the overall structure of MtRpsACTD_S1(280–368) is rigid, but segment L326–V333 undergoes large amplitude fluctuations on picosecond to nanosecond time scales. In addition, residues V321, H322, V331 and D335 with large Rex values exhibit significant chemical or conformational exchange on microsecond to millisecond time scale. Titration of the truncated MtRpsACTD_S1(280–368) with POA shows similar characteristics to titration of MtRpsACTD_S1(280–438) with POA. In addition, diverse length fragments of MtRpsACTD_S1 show various HN resonance signals, and we find that the interaction of MtRpsA(369–481) with MtRpsACTD_S1(280–368) [Kd = (4.25 ± 0.15) mM] is responsible for the structural difference between MtRpsACTD_S1(280–368) and MtRpsACTD_S1. This work may shed light on the underlying molecular mechanism of MtRpsACTD recognizing and binding POA or mRNA, as well as the detailed mechanism of interactions between MtRpsACTD_S1(280–368) and the additional C-terminal MtRpsA(369–481).

Toxic metabolites (N-acetylisoniazid, pyrazinoic acid, and desacetylrifampicin) of first-line anti-tuberculosis drugs (ethambutol, pyrazinamide, rifampicin, and isoniazid) are identified by liquid chromatography–mass spectrometry, which is important in selecting the required dosages of these drugs for the maximum therapeutic effects and the reduction of side effects. Characteristic chromatographic profiles of blood plasma samples from donors with pulmonary tuberculosis (“pathology”) and a clinically healthy group (“norm”) are obtained and processed by principal component analysis and the k-nearest neighbor method. A perspective of this approach for obtaining of additional diagnostic criteria for pulmonary tuberculosis is shown.

Resistance to key first-line drugs is a major hurdle to achieve the global end tuberculosis (TB) targets. A prodrug, pyrazinamide (PZA) is the only drug, effective in latent TB, recommended in drug resistance and susceptible Mycobacterium tuberculosis (MTB) isolates. The prodrug conversion into active form, pyrazinoic acid (POA), required the activity of pncA gene encoded pyrazinamidase (PZase). Although pncA mutations have been commonly associated with PZA resistance but a small number of resistance cases have been associated with mutationss in RpsA protein. Here in this study a total of 69 PZA resistance isolates have been sequenced for pncA mutations. However, samples that were found PZA resistant but pncA wild type (pncAWT), have been sequenced for rpsA and panD genes mutation. We repeated a drug susceptibility testing according to the WHO guidelines on 18 pncAWT MTB isolates. The rpsA and panD genes were sequenced. Out of total 69 PZA resistant isolates, 51 harbored 36 mutations in pncA gene (GeneBank Accession No. MH46111) while, fifteen different mutations including seven novel, were detected in the fourth S1 domain of RpsA known as C-terminal (MtRpsACTD) end. We did not detect any mutations in panD gene. Among the rpsA mutations, we investigated the molecular mechanism of resistance behind mutations, D342N, D343N, A344P, and I351F, present in the MtRpsACTD through molecular dynamic simulations (MD). WT showed a good drug binding affinity as compared to mutants (MTs), D342N, D343N, A344P, and I351F. Binding pocket volume, stability, and fluctuations have been altered whereas the total energy, protein folding, and geometric shape analysis further explored a significant variation between WT and MTs. In conclusion, mutations in MtRpsACTD might be involved to alter the RpsA activity, resulting in drug resistance. Such molecular mechanism behind resistance may provide a better insight into the resistance mechanism to achieve the global TB control targets.

In this work, we present a simple, two-stage method for the preparation of new and efficient antimicrobial hybrid systems, based on isoniazid and pyrazine-2-carbohydrazide tuberculostatic agents covalently linked to graphene oxide. In the first step, the carboxyl groups of graphene oxide are activated by transforming them into the corresponding acid chloride groups, which, in the second step, will react with the amino groups of the two drugs. Pyrazine-2-carbohydrazide was obtained from pyrazinoic acid and hydrazine hydrate and was confirmed by nuclear magnetic resonance spectroscopy. The materials have been characterized by elemental analysis, infrared spectroscopy, Raman spectroscopy, scanning electron microscopy, and X-ray photoelectron spectroscopy. Their antimicrobial activity was tested on mycobacterial (Mycobacterium terrae), as well as on Gram-negative bacteria (Escherichia coli ATCC 25922, Pseudomonas aeruginosa ATCC 27853), Gram-positive bacteria (Staphylococcus aureus ATCC 6538, Staphylococcus aureus ATCC 25923) and fungal (Candida albicans ATCC 10231), in planktonic and biofilm growth state. The biocompatibility of the tested compounds was assessed in vitro by live-dead fluorescence staining and flow cytometry. The results of this study have shown that the functionalization of graphene oxide with isoniazid and pyrazine-2-carbohydrazide both enhanced the anti-mycobacterial activity of the respective drugs and extended their antimicrobial spectrum towards other microbial strains, in planktonic and biofilm growth state, showing a promising potential for mitigating the impact of antimicrobial resistance and the deleterious effects of microbial biofilms. At the active tuberculostatic concentrations, the tested compounds exhibit very low cytotoxicity and do not interfere with the cellular cycle of Hep-2 cells. The flow cytometry and live/dead fluorescence staining proved that the tested compounds exhibit a microbicidal effect through induction of cellular lesions, consecutive to membrane depolarization.

Pyrazinamide (PZA) is an essential first line antitubercular drug, which plays a crucial role in tuberculosis treatment. The PZA, which is considered as a pro-drug needs an enzyme of mycobacterial pyrazinamidase (PZase) for its conversion into an active form pyrazinoic acid. Further, this active form of PZA inhibits the ribosomal proteins S1, which facilitates the transfer-mRNA complex formation throughout the translation. The spontaneous mutations in RpsA have been found to be associated with PZA drug resistance. However, the drug resistance mechanism is still unclear. Furthermore, there is no such information available about the structural dynamics of RpsA protein because of mutations that confer Pyrazinoic acid resistance. Moreover, a total of 18 clinical PZA-resistant isolates were investigated and found to be pncAWT, which allowed exploration of the resistance mechanism of RpsA in the mutated state. Samples were repeated for the drug susceptibility testing followed by RpsA gene sequencing. A total of 11 clinical isolates harbored a total of 15 mutations. Almost half of the total strains (7/15) were observed to be in the conserved region of RpsA and known as Mycobacterium tuberculosis C-terminal domain. In the current study, (2/7) mutation T370P (mutant 1) and W403G (mutant 2) were explored to ensure the RpsA resistance mechanism through essential dynamics simulation. The essential dynamics study results revealed that the distal loop mutations drastically altered the conformation of RpsA both in the absence (-) and presence (+) of pyrazinoic acid drug for two reasons: (1) dramatic alteration or reduction in the binding pattern of pyrazinoic acid with active site residues observed and (2) a clear image of the opening and closing switching mechanism was seen upon the distal site mutation on nearby 310-helixes beside the pyrazinoic acid binding site. This switch was found to consistently remain closed only in wild type systems, while it was open in the mutant systems. We called such distance impact an "allosteric effect." The overall mechanistic investigations will provide useful information behind drug resistance for better understanding to manage tuberculosis.

Background Pyrazinamide (PZA) is an important component of first-line drugs because of its distinctive capability to kill subpopulations of persistent Mycobacterium tuberculosis (MTB). The prodrug (PZA) is converted to its active form, pyrazinoic acid (POA) by MTB pncA-encoded pyrazinamidase (PZase). Mutation in pncA is the most common and primary cause of PZA resistance. The aim of the present study was to explore the molecular characterization of PZA resistance in a Pashtun-dominated region of Khyber Pakhtunkhwa, Pakistan. Methods We performed drug susceptibility testing (DST) on 753 culture-positive isolates collected from the Provincial Tuberculosis Control Program Khyber Pakhtunkhwa using the BACTEC MGIT 960 PZA method. In addition, the pncA gene was sequenced in PZA-resistant isolates, and PZA susceptibility testing results were used to determine the sensitivity and specificity of pncA gene mutations. Results A total of 69 isolates were PZA resistant (14.8%). Mutations were investigated in 69 resistant, 26 susceptible and one H37Rv isolates by sequencing. Thirty-six different mutations were identified in PZA-resistant isolates, with fifteen mutations, including 194_203delCCTCGTCGTG and 317_318delTC, that have not been reported in TBDRM and GMTV Databases and previous studies. Mutations Lys96Thr and Ser179Gly were found in the maximum number of isolates (n = 4 each). We did not detect mutations in sensitive isolates, except for the synonymous mutation 195C > T (Ser65Ser). The sensitivity and specificity of the pncA sequencing method were 79.31% (95% CI, 69.29 to 87.25%) and 86.67% (95% CI, 69.28 to 96.24%). Conclusion Mutations in the pncA gene in circulating isolates of geographically distinct regions, especially in high-burden countries, should be investigated for better control and management of drug-resistant TB. Molecular methods for the investigation of PZA resistance are better than DST.

Pyrazinamide (PZA) is the first-line drug commonly used in treating Mycobacterium tuberculosis (Mtb) infections and reduces treatment time by 33%. This prodrug is activated and converted to an active form, Pyrazinoic acid (POA), by Pyrazinamidase (PZase) enzyme. Mtb resistance to PZA is the outcome of mutations frequently reported in pncA, rpsA, and panD genes. Among the mentioned genes, pncA mutations contribute to 72–99% of the total resistance to PZA. Thus, considering the vital importance of this gene in PZA resistance, its frequent mutations (D49N, Y64S, W68G, and F94A) were investigated through in-depth computational techniques to put conclusions that might be useful for new scaffolds design or structure optimization to improve the efficacy of the available drugs. Mutants and wild type PZase were used in extensive and long-run molecular dynamics simulations in triplicate to disclose the resistance mechanism induced by the above-mentioned point mutations. Our analysis suggests that these mutations alter the internal dynamics of PZase and hinder the correct orientation of PZA to the enzyme. Consequently, the PZA has a low binding energy score with the mutants compared with the wild type PZase. These mutations were also reported to affect the binding of Fe2+ ion and its coordinated residues. Conformational dynamics also revealed that β-strand two is flipped, which is significant in Fe2+ binding. MM-GBSA analysis confirmed that these mutations significantly decreased the binding of PZA. In conclusion, these mutations cause conformation alterations and deformities that lead to PZA resistance.

Pyrazinamide (PZA) is a widely used antitubercular chemotherapeutic. Typically, PZA resistance (PZA-R) emerges in Mycobacterium tuberculosis strains with existing resistance to isoniazid and rifampin (i.e., multidrug resistance [MDR]) and is conferred by loss-of-function pncA mutations that inhibit conversion to its active form, pyrazinoic acid (POA). PZA-R departing from this canonical scenario is poorly understood. Here, we genotyped pncA and purported alternative PZA-R genes (panD, rpsA, and clpC1) with long-read sequencing of 19 phenotypically PZA-monoresistant isolates collected in Sweden and compared their phylogenetic and genomic characteristics to a large set of MDR PZA-R (MDRPZA-R) isolates. We report the first association of ClpC1 mutations with PZA-R in clinical isolates, in the ClpC1 promoter (clpC1p−138) and the N terminus of ClpC1 (ClpC1Val63Ala). Mutations have emerged in both these regions under POA selection in vitro, and the N-terminal region of ClpC1 has been implicated further, through its POA-dependent efficacy in PanD proteolysis. ClpC1Val63Ala mutants spanned 4 Indo-Oceanic sublineages. Indo-Oceanic isolates invariably harbored ClpC1Val63Ala and were starkly overrepresented (odds ratio [OR] = 22.2, P < 0.00001) among PZA-monoresistant isolates (11/19) compared to MDRPZA-R isolates (5/80). The genetic basis of Indo-Oceanic isolates’ overrepresentation in PZA-monoresistant tuberculosis (TB) remains undetermined, but substantial circumstantial evidence suggests that ClpC1Val63Ala confers low-level PZA resistance. Our findings highlight ClpC1 as potentially clinically relevant for PZA-R and reinforce the importance of genetic background in the trajectory of resistance development.