Pharmacokinetic Considerations for Optimizing Inhaled Spray-Dried Pyrazinoic Acid Formulations

Tuberculosis (TB), caused by Mycobacterium tuberculosis (Mtb), remains a leading cause of death with 1.6 million deaths worldwide reported in 2021. Oral pyrazinamide (PZA) is an integral part of anti-TB regimens, but its prolonged use has the potential to drive the development of PZA-resistant Mtb. PZA is converted to the active moiety pyrazinoic acid (POA) by the Mtb pyrazinamidase encoded by pncA, and mutations in pncA are associated with the majority of PZA resistance. Conventional oral and parenteral therapies may result in subtherapeutic exposure in the lung; hence, direct pulmonary administration of POA may provide an approach to rescue PZA efficacy for treating pncA-mutant PZA-resistant Mtb. The objectives of the current study were to (i) develop novel dry powder POA formulations, (ii) assess their feasibility for pulmonary delivery using physicochemical characterization, (iii) evaluate their pharmacokinetics (PK) in the guinea pig model, and (iv) develop a mechanism-based pharmacokinetic model (MBM) using in vivo PK data to select a formulation providing adequate exposure in epithelial lining fluid (ELF) and lung tissue. We developed three POA formulations for pulmonary delivery and characterized their PK in plasma, ELF, and lung tissue following passive inhalation in guinea pigs. Additionally, the PK of POA following oral, intravenous, and intratracheal administration was characterized in guinea pigs. The MBM was used to simultaneously model PK data following administration of POA and its formulations via the different routes. The MBM described POA PK well in plasma, ELF, and lung tissue. Physicochemical analyses and MBM predictions suggested that POA maltodextrin was the best among the three formulations and an excellent candidate for further development as it has: (i) the highest ELF-to-plasma exposure ratio (203) and lung tissue-to-plasma exposure ratio (30.4) compared with POA maltodextrin and leucine (75.7/16.2) and POA leucine salt (64.2/19.3) and (ii) the highest concentration in ELF (CmaxELF: 171 nM) within 15.5 min, correlating with a fast transfer into ELF after pulmonary administration (KPM: 22.6 1/h). The data from the guinea pig allowed scaling, using the MBM to a human dose of POA maltodextrin powder demonstrating the potential feasibility of an inhaled product.

Structural and Mechanistic Insights into Mycobacterium abscessus Aspartate Decarboxylase PanD and a Pyrazinoic Acid-Derived Inhibitor

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 nontuberculous 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 truncated 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 analogues, we identified (3-(1-naphthamido)pyrazine-2-carboxylic acid) (analogue 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 analogue 2 to Mab PanD. In contrast to PZA and POA, which are whole-cell inactive, analogue 2 exerts appreciable antibacterial activity against the three subspecies of Mab.

Design, Synthesis, Anti-microbial and Molecular Docking Studies of Novel 5-Pyrazyl-2-Sulfanyl-1, 3, 4-Oxadiazole Derivatives

BACKGROUND

Chemical modification of Oxadiazole may lead to a potent therapeutic agent. A series of novel 5-pyrazyl-2-sulfanyl-1, 3, 4-oxadiazole derivatives (5ag) have been synthesised utilising pyrazinoic acid as a precursor. The new oxadiazole compounds were docked against potential targets and evaluated for antibacterial and antitubercular activity.

METHODS

The 5-pyrazyl-2-substituted sulfanyl-1, 3,4-oxadiazole derivatives (5a-g) were synthesized from the crucial intermediate 2-sulfanyl-5-pyrazyl-1, 3,4-oxadiazole (4), which was prepared by treating the 2-pyrazyl hydrazide with CS2 and pyridine. IR, ¹HNMR, ¹³C, MS and elemental analyses were used to confirm the chemical structures.

RESULTS

Antimicrobial activity was determined for each synthesized compound. Additionally, compounds were evaluated for antitubercular activity against the Mycobacterium Tuberculosis H37Rv strain. Compounds 5c, 5g, and 5a had a favourable antibacterial profile, while 5c and 5g (MIC = 25 g/ml) demonstrated potential antitubercular activity when compared to the other produced compounds. Molecular docking experiments using V-Life Science MDS 4.6 supplemented the biological data.

CONCLUSION

Each compound has been tested for antibacterial and antitubercular action against a variety of microorganism strains and exhibits considerable activity. Additionally, molecular docking analysis confirmed the experimental results by describing improved interaction patterns.

Factors Affecting the Pharmacokinetics of Pyrazinamide and Its Metabolites in Patients Coinfected with HIV and Implications for Individualized Dosing

Pyrazinamide is a first-line drug used in the treatment of tuberculosis. High exposure to pyrazinamide and its metabolites may result in hepatotoxicity, whereas low exposure to pyrazinamide has been correlated with treatment failure of first-line antitubercular therapy. The aim of this study was to describe the pharmacokinetics and metabolism of pyrazinamide in patients coinfected with tuberculosis and HIV. We further aimed to identify demographic and clinical factors which affect the pharmacokinetics of pyrazinamide and its metabolites in order to suggest individualized dosing regimens. Plasma concentrations of pyrazinamide, pyrazinoic acid, and 5-hydroxypyrazinamide from 63 Rwandan patients coinfected with tuberculosis and HIV were determined by liquid chromatography-tandem mass spectrometry followed by nonlinear mixed-effects modeling. Females had a close to 50% higher relative pyrazinamide bioavailability compared to males. The distribution volumes of pyrazinamide and both metabolites were lower in patients on concomitant efavirenz-based HIV therapy. Furthermore, there was a linear relationship between serum creatinine and oral clearance of pyrazinoic acid. Simulations indicated that increasing doses from 25 mg/kg of body weight to 35 mg/kg and 50 mg/kg in females and males, respectively, would result in adequate exposure with regard to suggested thresholds and increase probability of target attainment to >0.9 for a MIC of 25 mg/liter. Further, lowering the dose by 40% in patients with high serum creatinine would prevent accumulation of toxic metabolites. Individualized dosing is proposed to decrease variability in exposure to pyrazinamide and its metabolites. Reducing the variability in exposure may lower the risk of treatment failure and resistance development.

Structural insights of catalytic mechanism in mutant pyrazinamidase of Mycobacterium tuberculosis

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 used in Mycobacterium tuberculosis (Mtb) treatment. The active form of PZA, POA, is toxic and potently inhibits the growth of latent Mtb, which makes it possible to shorten the conventional 9-month tuberculosis treatment to 6 months. In this study, an extensive molecular dynamics simulation was carried out to the study the resistance mechanism offered by the three mutations Q10P and D12A and G97D. Our results showed that two regions Gln10-His43, Phe50-Gly75 are profoundly affected by these mutations. Among the three mutations, Q10P and D12A mutations strongly disturb the communication among the catalytic triad (Asp8, Lys98 and Cys138). The oxyanion hole is formed between the backbone nitrogen atoms of A134 and C138 which stabilizes the hydroxyl anion of nicotinamide. The D12A mutation greatly disturbs the oxyanion hole formation followed by the Q10P and G97D. Our results also showed that these mutations destabilize the interaction between Fe²⁺ ion and Asp49, His51, His57 and His71. The binding pocket analysis showed that these mutations increase the cavity volume, which results in loose binding of PZA. MMGBSA analyzes have shown that these mutations reduce the binding affinity to the PZA drug. Our results may provide useful information for the design of new and effective PZase inhibitors based on structural information of WT and mutant PZases.Communicated by Ramaswamy H. Sarma.

Metallochaperones Are Needed for Mycobacterium tuberculosis and Escherichia coli Nicotinamidase-Pyrazinamidase Activity

Tuberculosis is an infectious disease caused by the bacterium Mycobacterium tuberculosis and remains one of the major causes of disease and death worldwide. Pyrazinamide is a key drug used in the treatment of tuberculosis, yet its mechanism of action is not fully understood, and testing strains of M. tuberculosis for pyrazinamide resistance is not easy with the tools that are presently available. The significance of the present research is that a metallochaperone-like protein may be crucial to pyrazinamide’s mechanisms of action and of resistance. This may support the development of improved tools to detect pyrazinamide resistance, which would have significant implications for the clinical management of patients with tuberculosis: drug regimens that are appropriately tailored to the resistance profile of a patient’s individual strain lead to better clinical outcomes, reduced onward transmission of infection, and reduction of the development of resistant strains that are more challenging and expensive to treat.

Mycobacterium tuberculosis nicotinamidase-pyrazinamidase (PZAse) is a metalloenzyme that catalyzes conversion of nicotinamide-pyrazinamide to nicotinic acid-pyrazinoic acid. This study investigated whether a metallochaperone is required for optimal PZAse activity. M. tuberculosis and Escherichia coli PZAses (PZAse-MT and PZAse-EC, respectively) were inactivated by metal depletion (giving PZAse-MT–Apo and PZAse-EC–Apo). Reactivation with the E. coli metallochaperone ZnuA or Rv2059 (the M. tuberculosis analog) was measured. This was repeated following proteolytic and thermal treatment of ZnuA and Rv2059. The CDC1551 M. tuberculosis reference strain had the Rv2059 coding gene knocked out, and PZA susceptibility and the pyrazinoic acid (POA) efflux rate were measured. ZnuA (200 μM) achieved 65% PZAse-EC–Apo reactivation. Rv2059 (1 μM) and ZnuA (1 μM) achieved 69% and 34.3% PZAse-MT–Apo reactivation, respectively. Proteolytic treatment of ZnuA and Rv2059 and application of three (but not one) thermal shocks to ZnuA significantly reduced the capacity to reactivate PZAse-MT–Apo. An M. tuberculosis Rv2059 knockout strain was Wayne positive and susceptible to PZA and did not have a significantly different POA efflux rate than the reference strain, although a trend toward a lower efflux rate was observed after knockout. The metallochaperone Rv2059 restored the activity of metal-depleted PZAse in vitro. Although Rv2059 is important in vitro, it seems to have a smaller effect on PZA susceptibility in vivo. It may be important to mechanisms of action and resistance to pyrazinamide in M. tuberculosis. Further studies are needed for confirmation.

IMPORTANCE Tuberculosis is an infectious disease caused by the bacterium Mycobacterium tuberculosis and remains one of the major causes of disease and death worldwide. Pyrazinamide is a key drug used in the treatment of tuberculosis, yet its mechanism of action is not fully understood, and testing strains of M. tuberculosis for pyrazinamide resistance is not easy with the tools that are presently available. The significance of the present research is that a metallochaperone-like protein may be crucial to pyrazinamide’s mechanisms of action and of resistance. This may support the development of improved tools to detect pyrazinamide resistance, which would have significant implications for the clinical management of patients with tuberculosis: drug regimens that are appropriately tailored to the resistance profile of a patient’s individual strain lead to better clinical outcomes, reduced onward transmission of infection, and reduction of the development of resistant strains that are more challenging and expensive to treat.

Design and Characterization of Inulin Conjugate for Improved Intracellular and Targeted Delivery of Pyrazinoic Acid to Monocytes

The propensity of monocytes to migrate into sites of mycobacterium tuberculosis (TB) infection and then become infected themselves makes them potential targets for delivery of drugs intracellularly to the tubercle bacilli reservoir. Conventional TB drugs are less effective because of poor intracellular delivery to this bacterial sanctuary. This study highlights the potential of using semicrystalline delta inulin particles that are readily internalised by monocytes for a monocyte-based drug delivery system. Pyrazinoic acid was successfully attached covalently to the delta inulin particles via a labile linker. The formation of new conjugate and amide bond was confirmed using zeta potential, Proton Nuclear Magnetic Resonance (¹HNMR) and Fourier transform infrared spectroscopy (FTIR). Scanning electron microscopy (SEM) confirmed that no significant change in size after conjugation which is an important parameter for monocyte targeting. Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) were used to establish the change in thermal properties. The analysis of in-vitro release demonstrated pH-triggered drug cleavage off the delta inulin particles that followed a first-order kinetic process. The efficient targeting ability of the conjugate for RAW 264.7 monocytic cells was supported by cellular uptake studies. Overall, our finding confirmed that semicrystalline delta inulin particles (MPI) can be modified covalently with drugs and such conjugates allow intracellular drug delivery and uptake into monocytes, making this system potentially useful for the treatment of TB.

Pyrazinamide drug resistance in RpsA mutant (∆438A) of Mycobacterium tuberculosis: Dynamics of essential motions and free-energy landscape analysis

Pyrazinamide is an essential first-line antitubercular drug which plays pivotal role in tuberculosis treatment. It is a prodrug that requires amide hydrolysis by mycobacterial pyrazinamidase enzyme for conversion into pyrazinoic acid (POA). POA is known to target ribosomal protein S1 (RpsA), aspartate decarboxylase (PanD), and some other mycobacterial proteins. Spontaneous chromosomal mutations in RpsA have been reported for phenotypic resistance against pyrazinamide. We have constructed and validated 3D models of the native and Δ438A mutant form of RpsA protein. RpsA protein variants were then docked to POA and long range molecular dynamics simulations were carried out. Per residue binding free-energy calculations, free-energy landscape analysis, and essential dynamics analysis were performed to outline the mechanism underlying the high-level PZA resistance conferred by the most frequently occurring deletion mutant of RpsA. Our study revealed the conformational modulation of POA binding site due to the disruptive collective modes of motions and increased conformational flexibility in the mutant than the native form. Residue wise MMPBSA decomposition and protein-drug interaction pattern revealed the difference of energetically favorable binding site in the wild-type (WT) protein in comparison with the mutant. Analysis of size and shape of minimal energy landscape area delineated higher stability of the WT complex than the mutant form. Our study provides mechanistic insights into pyrazinamide resistance in Δ438A RpsA mutant, and the results arising out of this study will pave way for design of novel and effective inhibitors targeting the resistant strains of Mycobacterium tuberculosis.

MODS-Wayne, a Colorimetric Adaptation of the Microscopic-Observation Drug Susceptibility (MODS) Assay for Detection of Mycobacterium tuberculosis Pyrazinamide Resistance from Sputum Samples

Although pyrazinamide (PZA) is a key component of first- and second-line tuberculosis treatment regimens, there is no gold standard to determine PZA resistance. Approximately 50% of multidrug-resistant tuberculosis (MDR-TB) and over 90% of extensively drug-resistant tuberculosis (XDR-TB) strains are also PZA resistant.

Although pyrazinamide (PZA) is a key component of first- and second-line tuberculosis treatment regimens, there is no gold standard to determine PZA resistance. Approximately 50% of multidrug-resistant tuberculosis (MDR-TB) and over 90% of extensively drug-resistant tuberculosis (XDR-TB) strains are also PZA resistant. pncA sequencing is the endorsed test to evaluate PZA susceptibility. However, molecular methods have limitations for their wide application. In this study, we standardized and evaluated a new method, MODS-Wayne, to determine PZA resistance. MODS-Wayne is based on the detection of pyrazinoic acid, the hydrolysis product of PZA, directly in the supernatant of sputum cultures by detecting a color change following the addition of 10% ferrous ammonium sulfate. Using a PZA concentration of 800 µg/ml, sensitivity and specificity were evaluated at three different periods of incubation (reading 1, reading 2, and reading 3) using a composite reference standard (MGIT-PZA, pncA sequencing, and the classic Wayne test). MODS-Wayne was able to detect PZA resistance, with a sensitivity and specificity of 92.7% and 99.3%, respectively, at reading 3. MODS-Wayne had an agreement of 93.8% and a kappa index of 0.79 compared to the classic Wayne test, an agreement of 95.3% and kappa index of 0.86 compared to MGIT-PZA, and an agreement of 96.9% and kappa index of 0.90 compared to pncA sequencing. In conclusion, MODS-Wayne is a simple, fast, accurate, and inexpensive approach to detect PZA resistance, making this an attractive assay especially for low-resource countries, where TB is a major public health problem.

Crystal structure of a 1:1 salt of 4-amino-benzoic acid (vitamin B10) with pyrazinoic acid

The title 1:1 salt, C7H8NO2 +·C5H3N2O2 - (systematic name: 4-carb-oxy-anilinium pyrazine-2-carboxyl-ate), was synthesized successfully by slow evaporation of a saturated solution from water-ethanol (1:1 v/v) mixture and characterized by X-ray diffraction (SCXRD, PXRD) and calorimetry (DSC). The crystal structure of the salt was solved and refined at 150 and 293 K. The salt crystallizes with one mol-ecule of 4-amino-benzoic acid (PABA) and one mol-ecule of pyrazinoic acid (POA) in the asymmetric unit. In the crystal, the PABA and POA mol-ecules are associated via COOH⋯Narom heterosynthons, which are connected by N-H⋯O hydrogen bonds, creating zigzag chains. The chains are further linked by N-H⋯O hydrogen bonds and π-π stacking inter-actions along the b axis [centroid-to-centroid distances = 3.7377 (13) and 3.8034 (13) Å at 150 and 293 K, respectively] to form a layered three-dimensional structure.

Pyrazinoic Acid Inhibits Mycobacterial Coenzyme A Biosynthesis by Binding to Aspartate Decarboxylase PanD

Previously, we showed that a major in vitro and in vivo mechanism of resistance to pyrazinoic acid (POA), the bioactive component of the critical tuberculosis (TB) prodrug pyrazinamide (PZA), involves missense mutations in the aspartate decarboxylase PanD, an enzyme required for coenzyme A biosynthesis. What is the mechanism of action of POA? Upon demonstrating that treatment of M. bovis BCG with POA resulted in a depletion of intracellular coenzyme A and confirming that this POA-mediated depletion is prevented by either missense mutations in PanD or exogenous supplementation of pantothenate, we hypothesized that POA binds to PanD and that this binding blocks the biosynthetic pathway. Here, we confirm both hypotheses. First, metabolomic analyses showed that POA treatment resulted in a reduction of the concentrations of all coenzyme A precursors downstream of the PanD-mediated catalytic step. Second, using isothermal titration calorimetry, we established that POA, but not its prodrug PZA, binds to PanD. Binding was abolished for mutant PanD proteins. Taken together, these findings support a mechanism of action of POA in which the bioactive component of PZA inhibits coenzyme A biosynthesis via binding to aspartate decarboxylase PanD. Together with previous works, these results establish PanD as a genetically, metabolically, and biophysically validated target of PZA.

Ureidopyrazine Derivatives: Synthesis and Biological Evaluation as Anti-Infectives and Abiotic Elicitors

Tuberculosis (TB) caused by Mycobacterium tuberculosis (Mtb) has become a frequently deadly infection due to increasing antimicrobial resistance. This serious issue has driven efforts worldwide to discover new drugs effective against Mtb. One research area is the synthesis and evaluation of pyrazinamide derivatives as potential anti-TB drugs. In this paper we report the synthesis and biological evaluations of a series of ureidopyrazines. Compounds were synthesized by reacting alkyl/aryl isocyanates with aminopyrazine or with propyl 5-aminopyrazine-2-carboxylate. Reactions were performed in pressurized vials using a CEM Discover microwave reactor with a focused field. Purity and chemical structures of products were assessed, and the final compounds were tested in vitro for their antimycobacterial, antibacterial, and antifungal activities. Propyl 5-(3-phenylureido)pyrazine-2-carboxylate (compound 4, MIC_Mtb = 1.56 μg/mL, 5.19 μM) and propyl 5-(3-(4-methoxyphenyl)ureido)pyrazine-2-carboxylate (compound 6, MIC_Mtb = 6.25 μg/mL, 18.91 μM) had high antimycobacterial activity against Mtb H37Rv with no in vitro cytotoxicity on HepG2 cell line. Therefore 4 and 6 are suitable for further structural modifications that might improve their biological activity and physicochemical properties. Based on the structural similarity to 1-(2-chloropyridin-4-yl)-3-phenylurea, a known plant growth regulator, two selected compounds were evaluated for similar activity as abiotic elicitors.

Design, Synthesis, Antimycobacterial Evaluation, and In Silico Studies of 3-(Phenylcarbamoyl)-pyrazine-2-carboxylic Acids

Pyrazinamide, the first-line antitubercular drug, has been regarded the basic component of tuberculosis treatment for over sixty years. Researchers have investigated its effect on Mycobacterium tuberculosis for this long time, and as a result, new potential targets of pyrazinamide or its active form, pyrazinoic acid, have been found. We have designed and prepared 3-(phenyl-carbamoyl)pyrazine-2-carboxylic acids as more lipophilic derivatives of pyrazinoic acid. We also prepared methyl and propyl derivatives as prodrugs with further increased lipophilicity. Antimycobacterial, antibacterial and antifungal growth inhibiting activity was investigated in all prepared compounds. 3-[(4-Nitrophenyl)carbamoyl]pyrazine-2-carboxylic acid (16) exerted high antimycobacterial activity against Mycobacterium tuberculosis H37Rv with MIC = 1.56 μg·mL⁻¹ (5 μM). Propyl 3-{[4-(trifluoromethyl)phenyl]carbamoyl}pyrazine-2-carboxylate (18a) showed also high antimycobacterial activity against Mycobacterium tuberculosis H37Rv with MIC = 3.13 μg·mL⁻¹. In vitro cytotoxicity of the active compounds was investigated and no significant cytotoxic effect was observed. Based to structural similarity to known inhibitors of decaprenylphosphoryl-β-d-ribose oxidase, DprE1, we performed molecular docking of the prepared acids to DprE1. These in silico experiments indicate that modification of the linker connecting aromatic parts of molecule does not have any negative influence on the binding.

In Vivo-Selected Pyrazinoic Acid-Resistant Mycobacterium tuberculosis Strains Harbor Missense Mutations in the Aspartate Decarboxylase PanD and the Unfoldase ClpC1

Through mutant selection on agar containing pyrazinoic acid (POA), the bioactive form of the prodrug pyrazinamide (PZA), we recently showed that missense mutations in the aspartate decarboxylase PanD and the unfoldase ClpC1, and loss-of-function mutation of polyketide synthases Mas and PpsA-E involved in phthiocerol dimycocerosate synthesis, cause resistance to POA and PZA in Mycobacterium tuberculosis. Here we first asked whether these in vitro-selected POA/PZA-resistant mutants are attenuated in vivo, to potentially explain the lack of evidence of these mutations among PZA-resistant clinical isolates. Infection of mice with panD, clpC1, and mas/ppsA-E mutants showed that whereas growth of clpC1 and mas/ppsA-E mutants was attenuated, the panD mutant grew as well as the wild-type. To determine whether these resistance mechanisms can emerge within the host, mice infected with wild-type M. tuberculosis were treated with POA, and POA-resistant colonies were confirmed for PZA and POA resistance. Genome sequencing revealed that 82 and 18% of the strains contained missense mutations in panD and clpC1, respectively. Consistent with their lower fitness and POA resistance level, independent mas/ppsA-E mutants were not found. In conclusion, we show that the POA/PZA resistance mechanisms due to panD and clpC1 missense mutations are recapitulated in vivo. Whereas the representative clpC1 mutant was attenuated for growth in the mouse infection model, providing a possible explanation for their absence among clinical isolates, the growth kinetics of the representative panD mutant was unaffected. Why POA/PZA resistance-conferring panD mutations are observed in POA-treated mice but not yet among clinical strains isolated from PZA-treated patients remains to be determined.

Pyrazinoic Acid Inhibits a Bifunctional Enzyme in Mycobacterium tuberculosis

Pyrazinamide (PZA), an indispensable component of modern tuberculosis treatment, acts as a key sterilizing drug. While the mechanism of activation of this prodrug into pyrazinoic acid (POA) by Mycobacterium tuberculosis has been extensively studied, not all molecular determinants that confer resistance to this mysterious drug have been identified. Here, we report how a new PZA resistance determinant, the Asp67Asn substitution in Rv2783, confers M. tuberculosis resistance to PZA. Expression of the mutant allele but not the wild-type allele in M. tuberculosis recapitulates the PZA resistance observed in clinical isolates. In addition to catalyzing the metabolism of RNA and single-stranded DNA, Rv2783 also metabolized ppGpp, an important signal transducer involved in the stringent response in bacteria. All catalytic activities of the wild-type Rv2783 but not the mutant were significantly inhibited by POA. These results, which indicate that Rv2783 is a target of PZA, provide new insight into the molecular mechanism of the sterilizing activity of this drug and a basis for improving the molecular diagnosis of PZA resistance and developing evolved PZA derivatives to enhance its antituberculosis activity.

Ameliorative effects of pyrazinoic acid against oxidative and metabolic stress manifested in rats with dimethylhydrazine induced colonic carcinoma

Pyrazinoic acid (PA) is structurally similar to nicotinic acid which acts on G-protein-coupled receptor (GPR109A). GPR109A expresses in colonic and intestinal epithelial sites, and involves in DNA methylation and cellular apoptosis. Therefore, it may be assumed that PA has similar action like nicotinic acid and may be effective against colorectal carcinoma (CRC). CRC was produced via subcutaneous injection of dimethylhydrazine (DMH) at 40 mg/kg body weight once in a week for 4 weeks. After that, PA was administered orally at 2 doses of 10 and 25 mg/kg daily for 15 d to observe the antiproliferative effect. Various physiologic, oxidative stress, molecular parameters, histopathology, RT-PCR and NMR based metabolomics were performed to evaluate the antiproliferative potential of PA. Our results collectively suggested that PA reduced body weight, tumor volume and incidence no. to normal. It restored various oxidative stress parameters and normalized IL-2, IL-6, and COX-2 as compared with carcinogen control. In molecular level, overexpressed IL-6 and COX-2 genes became normal after PA administration. Again, normal tissue architecture was prominent after PA administration. Score plots of PLS-DA models exhibited that PA treated groups were significantly different from CRC group. We found that CRC rat sera have increased levels of acetate, glutamine, o-acetyl-glycoprotein, succinate, citrulline, choline, o-acetyl choline, tryptophan, glycerol, creatinine, lactate, citrate and decreased levels of 3-hydroxy butyrate, dimethyl amine, glucose, maltose, myoinositol. Further the PA therapy has ameliorated the CRC-induced metabolic alterations, signifying its antiproliferative properties. In conclusion, our study provided the evidence that PA demonstrated good antiproliferative effect on DMH induced CRC and thus demonstrated the potential of PA as a useful drug for future anticancer therapy.

Pyrazinamide Resistance Is Caused by Two Distinct Mechanisms: Prevention of Coenzyme A Depletion and Loss of Virulence Factor Synthesis

Pyrazinamide (PZA) is a critical component of first- and second-line treatments of tuberculosis (TB), yet its mechanism of action largely remains an enigma. We carried out a genetic screen to isolate Mycobacterium bovis BCG mutants resistant to pyrazinoic acid (POA), the bioactive derivative of PZA, followed by whole genome sequencing of 26 POA resistant strains. Rather than finding mutations in the proposed candidate targets fatty acid synthase I and ribosomal protein S1, we found resistance conferring mutations in two pathways: missense mutations in aspartate decarboxylase panD, involved in the synthesis of the essential acyl carrier coenzyme A (CoA), and frameshift mutations in the vitro nonessential polyketide synthase genes mas and ppsA-E, involved in the synthesis of the virulence factor phthiocerol dimycocerosate (PDIM). Probing for cross resistance to two structural analogs of POA, nicotinic acid and benzoic acid, showed that the analogs share the PDIM- but not the CoA-related mechanism of action with POA. We demonstrated that POA depletes CoA in wild-type bacteria, which is prevented by mutations in panD. Sequencing 10 POA-resistant Mycobacterium tuberculosis H37Rv isolates confirmed the presence of at least 2 distinct mechanisms of resistance to the drug. The emergence of resistance through the loss of a virulence factor in vitro may explain the lack of clear molecular patterns in PZA-resistant clinical isolates, other than mutations in the prodrug-converting enzyme. The apparent interference of POA with virulence pathways may contribute to the drug's excellent in vivo efficacy compared to its modest in vitro potency.

Inhaled Pyrazinoic Acid Esters for the Treatment of Tuberculosis

PURPOSE

Analog development of existing drugs and direct drug delivery to the lungs by inhalation as treatments for multiple and extensively drug resistant (MDR and XDR) tuberculosis (TB) represent new therapeutic strategies. Pyrazinamide (PZA) is critical to drug sensitive TB therapy and is included in regimens for MDR TB. However, PZA-resistant Mycobacterium tuberculosis (Mtb) strains threaten its use. Pyrazinoic acid esters (PAEs) are PZA analogs effective against Mtb in vitro, including against the most common PZA resistant strains. However, PAEs require testing for TB efficacy in animal models.

METHODS

PAEs were delivered daily as aqueous dispersions from a vibrating mesh nebulizer to Mtb infected guinea pigs for 4 weeks in a regimen including orally administered first-line TB drugs.

RESULTS

PAEs tested as a supplement to oral therapy significantly reduced the organ bacterial burden in comparison to infected, untreated control animals. Thus, PAE aerosol therapy is a potentially significant addition to the regimen for PZA resistant MDR-TB and XDR-TB treatment. Interestingly, low dose oral PZA treatment combined with standard therapy also reduced bacterial burden. This observation may be important for PZA susceptible disease treatment.

CONCLUSION

The present study justifies further evaluation of PZA analogs and their lung delivery to treat TB.

Host-Mediated Bioactivation of Pyrazinamide: Implications for Efficacy, Resistance, and Therapeutic Alternatives

Pyrazinamide has played a critical role in shortening therapy against drug-sensitive, drug-resistant, active, and latent tuberculosis (TB). Despite widespread recognition of its therapeutic importance, the sterilizing properties of this 60-year-old drug remain an enigma given its rather poor activity in vitro. Here we revisit longstanding paradigms and offer pharmacokinetic explanations for the apparent disconnect between in vitro activity and clinical impact. We show substantial host-mediated conversion of prodrug pyrazinamide (PZA) to the active form, pyrazinoic acid (POA), in TB patients and in animal models. We demonstrate favorable penetration of this pool of circulating POA from plasma into lung tissue and granulomas, where the pathogen resides. In standardized growth inhibition experiments, we show that POA exhibits superior in vitro potency compared to PZA, indicating that the vascular supply of host-derived POA may contribute to the in vivo efficacy of PZA, thereby reducing the apparent discrepancy between in vitro and in vivo activity. However, the results also raise the possibility that subinhibitory concentrations of POA generated by the host could fuel the emergence of resistance to both PZA and POA. In contrast to widespread expectations, we demonstrate good oral bioavailability and exposure in preclinical species in pharmacokinetic studies of oral POA. Baseline exposure of oral POA can be further increased by the xanthine oxidase inhibitor and approved gout drug allopurinol. These promising results pave the way for clinical investigations of oral POA as a therapeutic alternative or an add-on to overcome PZA resistance and salvage this essential TB drug.