Translating basic science insight into public health action for multidrug- and extensively drug-resistant tuberculosis

Crystal structure of the polyketide cyclase from Mycobacterium tuberculosis

About 40% of proteins are classified as conserved hypothetical proteins in Mycobacterium tuberculosis (TB). Identification and characterization of these proteins are beneficial to understand the pathogenesis of TB and exploiting novel drugs for TB treatments. The polyketide cyclase, a protein from M. tuberculosis ( MtPC) has been annotated as a hypothetical protein in Uniprot database. Sequence analysis shows that the MtPC belongs to the NTF2-like superfamily proteins with diverse functions. Here, we determined the crystal structure of MtPC at a resolution of 2.4 Å and measured backbone relaxation parameters for the MtPC protein. MtPC exists as a dimer in solution, and each subunit contains a six-stranded mixed β-sheet and three α helixes which are arranged in the order α1-α2-β1-β2-α3-β3-β4-β5-β6. The NMR dynamics analysis showed that the overall structure of MtPC is highly rigid on ps-ns time scales. Furthermore, we predicted the potential function of MtPC based on the crystal structure. Our results lay the basis for further exploiting and mechanistically understanding the biological functions of MtPC.

Effect of Disease State on the Pharmacokinetics of Bedaquiline in Renal-Impaired and Diabetic Rats

Bedaquiline (TMC-207) is a key anti-tubercular drug to fight against multidrug resistance tuberculosis. Little information is available till date on the impact of any disease state toward its pharmacokinetic behavior. The present research work aimed to investigate the effect of renal impairment and diabetes mellitus on the oral pharmacokinetics of bedaquiline in the rat model. Renal impairment and diabetes mellitus were induced in the Wistar rat model separately using cisplatin and streptozotocin, respectively, and thereafter, an oral pharmacokinetic study of bedaquiline was carried out in the individual disease models as well as in the normal rat model. Pharmacokinetic parameters of bedaquiline were not altered markedly in cisplatin-induced renal-impaired rats compared to normal rats except an area under the curve (AUC) for plasma concentration of bedaquiline in the experimental time frame (AUC_0-t ) reduced to 3477 ± 228 from 4984 ± 1174 ng h/mL, respectively. Maximum plasma concentrations of bedaquiline (259 ± 77 ng/mL), AUC_0-t (3112 ± 1046 ng h/mL), and AUC_0-∞ (3673 ± 1493 ng h/mL) were significantly reduced along with an increase in the clearance of bedaquiline (3.1 ± 1.1 L/h/kg) in the case of streptozotocin-induced diabetic rats compared to respective pharmacokinetic parameters of bedaquiline (482 ± 170 ng/mL, 4984 ± 1174 ng h/mL, and 6137 ± 1542 ng h/mL) in the normal rats. Preclinical findings suggest that dose adjustment of bedaquiline is required in the diabetes mellitus condition to prevent the therapeutic failure of bedaquiline treatment, but clinical exploration is needed to establish the fact. It is the first report for the consequence of renal impairment and diabetes mellitus on the pharmacokinetics of bedaquiline in the preclinical model.

Cytokine and Chemokine Concentrations as Biomarkers of Feline Mycobacteriosis

Mycobacteriosis is an emerging zoonotic disease of domestic cats and timely, accurate diagnosis is currently challenging. To identify differential cytokine/chemokine concentrations in serum/plasma of cats, which could be diagnostic biomarkers of infection we analysed plasma/serum from 116 mycobacteria-infected cats, 16 healthy controls and six cats hospitalised for unrelated reasons was analysed using the Milliplex MAP Feline Cytokine Magnetic Bead multiplex assay. Three cytokines; sFAS, IL-13 and IL-4 were reduced while seven; GM-CSF, IL-2, PDGF-BB, IL-8, KC, RANTES and TNF-α were elevated in mycobacteria-infected cats compared to healthy controls. However, IL-8 and KC concentrations were not significantly different from cats hospitalised for other reasons. Elevations in TNF-α and PDGF-BB may have potential to identify M. bovis and M. microti infected cats specifically while GM-CSF, IL-2 and FLT3L were increased in MTBC infected cats. This study demonstrates potential use of feline tuberculosis as a spontaneously occurring model of this significant human disease. Cytokine profiling has clear diagnostic potential for mycobacteriosis of cats and could be used discriminate tuberculous from non-tuberculous disease to rapidly inform on zoonotic risk. Future work should focus on the in-field utility of these findings to establish diagnostic sensitivity and specificity of these markers.

Overview of the Development of DprE1 Inhibitors for Combating the Menace of Tuberculosis

Decaprenylphosphoryl-β-d-ribose 2'-epimerase (DprE1), a vital enzyme for cell wall synthesis, plays a crucial role in the formation of lipoarabinomannan and arabinogalactan. It was first reported as a druggable target on the basis of inhibitors discovered in high throughput screening of a drug library. Since then, inhibitors with different types of chemical scaffolds have been reported for their activity against this enzyme. Formation of a covalent or noncovalent bond by the interacting ligand with the enzyme causes loss of its catalytic activity which ultimately leads to the death of the mycobacterium. This Perspective describes various DprE1 inhibitors as anti-TB agents reported to date.

Totally drug-resistant tuberculosis and adjunct therapies

The first cases of totally drug-resistant (TDR) tuberculosis (TB) were reported in Italy 10 years ago; more recently, cases have also been reported in Iran, India and South Africa. Although there is no consensus on terminology, it is most commonly described as 'resistance to all first- and second-line drugs used to treat TB'. Mycobacterium tuberculosis (M.tb) acquires drug resistance mutations in a sequential fashion under suboptimal drug pressure due to monotherapy, inadequate dosing, treatment interruptions and drug interactions. The treatment of TDR-TB includes antibiotics with disputed or minimal effectiveness against M.tb, and the fatality rate is high. Comorbidities such as diabetes and infection with human immunodeficiency virus further impact on TB treatment options and survival rates. Several new drug candidates with novel modes of action are under late-stage clinical evaluation (e.g., delamanid, bedaquiline, SQ109 and sutezolid). 'Repurposed' antibiotics have also recently been included in the treatment of extensively drug resistant TB. However, because of mutations in M.tb, drugs will not provide a cure for TB in the long term. Adjunct TB therapies, including therapeutic vaccines, vitamin supplementation and/or repurposing of drugs targeting biologically and clinically relevant molecular pathways, may achieve better clinical outcomes in combination with standard chemotherapy. Here, we review broader perspectives of drug resistance in TB and potential adjunct treatment options.

Novel on-line column extraction apparatus coupled with binary peak focusing for high-performance liquid chromatography determination of rifampicin in human plasma: a strategy for therapeutic drug monitoring

In order to develop a method that is completely suitable for the routine therapeutic drug monitoring, a sensitive and fully automated on-line column extraction apparatus in combination with high-performance liquid chromatography allowing binary peak focusing was developed and validated for the determination of rifampicin in human plasma. Rifapentine was used as an internal standard. The analytical cycle started with the injection of 100 μL of the sample pretreated by protein precipitation in a Venusil SCX extraction column. After the elution, the analytes were transferred and concentrated in an Xtimate C18 trap column. Finally, the trapped analytes were separated by an Xtimate C18 analytical column and were analyzed by an ultraviolet detector at 336 nm. With this new strategy, continuous on-line analysis of the compounds was successfully performed. The method showed excellent performance for the analysis of rifampicin in plasma samples, including calibration curve linearity (All r were larger than 0.9996), sensitivity (lowest limit of quantification was 0.12 μg/mL), method accuracy (within 6.6% in terms of relative error), and precision (relative standard deviations of intra- and interday precision were less than 7.8%). These results demonstrated that the simple, reliable, and automatic method based on on-line column extraction and binary peak focusing is a promising approach for therapeutic drug monitoring in complex biomatrix samples.

Progress in tuberculosis vaccine development and host-directed therapies--a state of the art review

Tuberculosis continues to kill 1·4 million people annually. During the past 5 years, an alarming increase in the number of patients with multidrug-resistant tuberculosis and extensively drug-resistant tuberculosis has been noted, particularly in eastern Europe, Asia, and southern Africa. Treatment outcomes with available treatment regimens for drug-resistant tuberculosis are poor. Although substantial progress in drug development for tuberculosis has been made, scientific progress towards development of interventions for prevention and improvement of drug treatment outcomes have lagged behind. Innovative interventions are therefore needed to combat the growing pandemic of multidrug-resistant and extensively drug-resistant tuberculosis. Novel adjunct treatments are needed to accomplish improved cure rates for multidrug-resistant and extensively drug-resistant tuberculosis. A novel, safe, widely applicable, and more effective vaccine against tuberculosis is also desperately sought to achieve disease control. The quest to develop a universally protective vaccine for tuberculosis continues. So far, research and development of tuberculosis vaccines has resulted in almost 20 candidates at different stages of the clinical trial pipeline. Host-directed therapies are now being developed to refocus the anti-Mycobacterium tuberculosis-directed immune responses towards the host; a strategy that could be especially beneficial for patients with multidrug-resistant tuberculosis or extensively drug-resistant tuberculosis. As we are running short of canonical tuberculosis drugs, more attention should be given to host-directed preventive and therapeutic intervention measures.

Synthetic modifications of the immunomodulating peptide thymopentin to confer anti-mycobacterial activity

Effective global control of tuberculosis (TB) is increasingly threatened by the convergence of multidrug-resistant TB and the human immunodeficiency virus (HIV) infection. TB/HIV coinfections exert a tremendous burden on the host's immune system, and this has prompted the clinical use of immunomodulators to enhance host defences as an alternative therapeutic strategy. In this study, we modified the clinically used synthetic immunomodulatory pentapeptide, thymopentin (TP-5, RKDVY), with six arginine residues (RR-6, RRRRRR) at the N- and C-termini to obtain the cationic peptides, RR-11 (RKDVYRRRRRR-NH₂) and RY-11 (RRRRRRRKDVY-NH₂), respectively. The arginine residues conferred anti-mycobacterial activity to TP-5 in the peptides as shown by effective minimum inhibitory concentrations of 125 mg/L and killing efficiencies of >99.99% against both rifampicin-susceptible and -resistant Mycobacterium smegmatis. The immunomodulatory action of the peptides remained unaffected as shown by their ability to stimulate TNF-α production in RAW 264.7 mouse macrophage cells. A distinct change in surface morphology after peptide treatment was observed in scanning electron micrographs, while confocal microscopy and dye leakage studies suggested bacterial membrane disruption by the modified peptides. The modified peptides were non-toxic and did not cause hemolysis of rat red blood cells up to a concentration of 2000 mg/L. Moreover, RY-11 showed synergism with rifampicin and reduced the effective concentration of rifampicin, while preventing the induction of rifampicin resistance. The synthetic peptides may have a potential application in both immunocompetent and immunocompromised TB patients.

The DprE1 enzyme, one of the most vulnerable targets of Mycobacterium tuberculosis

The re-emergence of tuberculosis in recent years led the World Health Organization (WHO) to launch the Stop TB Strategy program. Beside repurposing the existing drugs and exploring novel molecular combinations, an essential step to face the burden of tuberculosis will be to develop new drugs by identifying vulnerable bacterial targets. Recent studies have focused on decaprenylphosphoryl-D-ribose oxidase (DprE1) of Mycobacterium tuberculosis, an essential enzyme involved in cell wall metabolism, for which new promising molecules have proved efficacy as antitubercular agents. This review summarizes the state of the art concerning DprE1 in terms of structure, enzymatic activity and inhibitors. This enzyme is emerging as one of the most vulnerable target in M. tuberculosis.