Current Affairs, Future Perspectives of Tuberculosis and Antitubercular Agents

Insights into development of Decaprenyl-phosphoryl-β-D-ribose 2'-epimerase (DprE1) inhibitors as antitubercular agents: A state of the art review

Mycobacterium tuberculosis is a causative agent for the world threatening infectious disease known as tuberculosis. M. tuberculosis is also referred as Koch's bacillus as it was first defined by Robert Koch in 1821. In the entire history of M. tuberculosis infection, several different targets were identified and explored with a hope of effective therapeutic treatment against tuberculosis. Drug-resistant tuberculosis is the major obstacle for researchers and letting them fail continuously to discover new drug candidates. Among the numerous antitubercular targets, Decaprenyl-phosphoryl-β-D-ribose-2'-epimerase (DprE1) is novel target identified in the year 2009. The present article portrays insights of DprE1 enzyme in all the aspects i.e., identification, structural elucidation to designing strategies and synthesis of potential drug candidates to combat resistant strains. Along with the synthesis and biological activity of novel compounds, structure-activity relationship (SAR) data is given to help medicinal chemists and researchers working in this area for the development of new inhibitors to fight against M. tuberculosis. DprE1 is new ray of hope for antitubercular treatment. No single drug candidate (DprE1 inhibitor) has passed clinical trial yet and hence it nullifies the risk of development of resistance or mutations at specific residues. Researchers working in this area have to design and come up with new potent candidates with less dose, no toxicity to combat this deadly infection. This review emphasized on year wise systematic development and progress of DprE1 inhibitors.

Tapping into the antitubercular potential of 2,5-dimethylpyrroles: A structure-activity relationship interrogation

An exploration of the chemical space around a 2,5-dimethylpyrrole scaffold of antitubercular hit compound 1 has led to the identification of new derivatives active against Mycobacterium tuberculosis and multidrug-resistant clinical isolates. Analogues incorporating a cyclohexanemethyl group on the methyleneamine side chain at C3 of the pyrrole core, including 5n and 5q, exhibited potent inhibitory effects against the M. tuberculosis strains, substantiating the essentiality of the moiety to their antimycobacterial activity. In addition, selected derivatives showed promising cytotoxicity profiles against human pulmonary fibroblasts and/or murine macrophages, proved to be effective in inhibiting the growth of intracellular mycobacteria, and elicited either bactericidal effects, or bacteriostatic activity comparable to 1. Computational studies revealed that the new compounds bind to the putative target, MmpL3, in a manner similar to that of known inhibitors BM212 and SQ109.

Structural Rigidification of N-Aryl-pyrroles into Indoles Active against Intracellular and Drug-Resistant Mycobacteria

A series of indolyl-3-methyleneamines incorporating lipophilic side chains were designed through a structural rigidification approach and synthesized for investigation as new chemical entities against Mycobacterium tuberculosis (Mtb). The screening led to the identification of a 6-chloroindole analogue 7j bearing an N-octyl chain and a cycloheptyl moiety, which displayed potent in vitro activity against laboratory and clinical Mtb strains, including a pre-extensively drug-resistant (pre-XDR) isolate. 7j also demonstrated a marked ability to restrict the intracellular growth of Mtb in murine macrophages. Further assays geared toward mechanism of action elucidation have thus far ruled out the involvement of various known promiscuous targets, thereby suggesting that the new indole 7j may inhibit Mtb via a unique mechanism.

Advances in the application of 1,2,4-triazole-containing hybrids as anti-tuberculosis agents

Tuberculosis is a deadly communicable disease caused by the bacillus Mycobacterium tuberculosis (MTB), and pulmonary tuberculosis accounts for over 80% of the total cases. The 1,2,4-triazole is a privileged structure in the discovery of new drugs, and its derivatives act on various targets in MTB. In particular, 1,2,4-triazole hybrids can not only exert dual or multiple antitubercular mechanisms of action but also have the potential to enhance efficacy and reduce side effects. The present work aims to summarize the current status of 1,2,4-triazole hybrids as potential antitubercular agents, covering articles published between 2010 and 2020, to aid the further rational design of novel potential drug candidates endowed with higher efficacy, better compliance and fewer side effects.

Triazole-containing hybrids with anti-Mycobacterium tuberculosis potential - Part I: 1,2,3-Triazole

Tuberculosis regimens currently applied in clinical practice require months of multidrug therapy, which imposes a major challenge of patient compliance and drug resistance development. Moreover, because of the increasing emergence of hard-to-treat tuberculosis, this disease continues to be a significant threat to the human population. 1,2,3-triazole as a privileged structure has been widely used as an effective template for drug discovery, and 1,2,3-triazole-containing hybrids that can simultaneously act on dual or multiple targets in Mycobacterium tuberculosis have the potential to circumvent drug resistance, enhance efficacy, reduce side effects and improve pharmacokinetic as well as pharmacodynamic profiles. Thus, 1,2,3-triazole-containing hybrids are useful scaffolds for the development of antitubercular agents. This review aims to highlight recent advances of 1,2,3-triazole-containing hybrids with potential activity against various forms of M. tuberculosis, covering articles published between 2015 and 2020. The structure-activity relationship and the mechanism of action are also discussed to facilitate further rational design of more effective drug candidates.

In vitro and in vivo antitubercular activity of benzothiazinone-loaded human serum albumin nanocarriers designed for inhalation

The aim of this study was to investigate the potential of human serum albumin (HSA) as a solubilising agent/drug delivery vehicle for pulmonary administration of antimycobacterial benzothiazinone (BTZ) compounds. The solubility of four novel BTZ compounds (IR 20, IF 274, FG 2, AR 112) was enhanced 2 to 140-fold by incubation with albumin (0.38-134 μg/mL). Tryptophan 213 residue quenching studies indicated moderate binding strength to Sudlow's site I. Nanoparticle manufacture achieved 37-60% encapsulation efficiency in HSA particles (169 nm, zeta potential -31 mV). Drug release was triggered by proteases with >50% released in 4 h. The antimycobacterial activity of IR 20 and FG 2 loaded in HSA nanoparticles was enhanced compared to DMSO/phosphate buffered saline (PBS) or albumin/PBS solutions in an in vitro M. tuberculosis-infected macrophage model. Intranasal instillation was used to achieve pulmonary delivery daily over 10 days to M. tuberculosis infected mice for FG2 HSA nanoparticles (0.4 mg/kg), FG 2 DMSO/saline (0.4 and 8 mg/kg) and a reference compound, BTZ043, DMSO/saline (0.4 and 8 mg/kg). A lower lung M. tuberculosis burden was apparent for all BTZ cohorts, but only significant for BTZ043 at both doses. In conclusion, mechanisms of HSA nanoparticle loading and release of BTZ compounds were demonstrated, enhanced antimycobacterial activity of the nanoparticle formulations was demonstrated in a biorelevant in vitro bioassay and the effectiveness of BTZ by pulmonary delivery in vivo was established with pilot evidence for effectiveness when delivered by HSA nanoparticles. Finally, the feasibility of developing an inhaled nanoparticle-in-microparticle powder formulation was ascertained.

A Protein Complex from Human Milk Enhances the Activity of Antibiotics and Drugs against Mycobacterium tuberculosis

Mycobacterium tuberculosis, the causative agent of human tuberculosis (TB), has surpassed HIV/AIDS as the leading cause of death from a single infectious agent. The increasing occurrence of drug-resistant strains has become a major challenge for health care systems and, in some cases, has rendered TB untreatable. However, the development of new TB drugs has been plagued with high failure rates and costs. Alternative strategies to increase the efficacy of current TB treatment regimens include host-directed therapies or agents that make M. tuberculosis more susceptible to existing TB drugs. In this study, we show that HAMLET, an α-lactalbumin-oleic acid complex derived from human milk, has bactericidal activity against M. tuberculosis HAMLET consists of a micellar oleic acid core surrounded by a shell of partially denatured α-lactalbumin molecules and unloads oleic acid into cells upon contact with lipid membranes. At sublethal concentrations, HAMLET potentiated a remarkably broad array of TB drugs and antibiotics against M. tuberculosis For example, the minimal inhibitory concentrations of rifampin, bedaquiline, delamanid, and clarithromycin were decreased by 8- to 16-fold. HAMLET also killed M. tuberculosis and enhanced the efficacy of TB drugs inside macrophages, a natural habitat of M. tuberculosis Previous studies showed that HAMLET is stable after oral delivery in mice and nontoxic in humans and that it is possible to package hydrophobic compounds in the oleic acid core of HAMLET to increase their solubility and metabolic stability. The potential of HAMLET and other liprotides as drug delivery and sensitization agents in TB chemotherapy is discussed here.

Poor treatment outcomes and its determinants among tuberculosis patients in selected health facilities in East Wollega, Western Ethiopia

BACKGROUND

Although it is a preventable and treatable disease, tuberculosis remains a major medical and public health problem throughout the world. The control and elimination of tuberculosis is currently challenged by the development and spread of antituberculosis drug resistance. The resistance is often correlated to the absence of properly implemented control measures that lead to poor treatment outcomes. Therefore, the aim of the current study was to assess poor treatment outcomes and its determinants among tuberculosis patients in selected health facilities in East Wollega zone, Western Ethiopia.

METHOD

A five-year retrospective cross-sectional study design was employed. Data were collected from patients' medical record from January to March 2017. Data were entered and analyzed using SPSS version 20. Descriptive statistics were used to generate and summarize frequencies. Univariate and multivariate logistic regression analysis were used to associate the potential determinants of poor treatment outcomes.

RESULTS

From 995 patients with documented treatment outcomes, 58.9% were males with a mean age of 31.9±16.3 years and 58% lived in rural areas. Majorities of cases (95.7%) were newly treated ones. Nearly half of the cases had extrapulmonary tuberculosis and 6.8% were co-infected with HIV. Nearly three-quarter of patients had completed their treatment while 17.2%, 2.9%, 4.8%, 0.4% patients were cured, defaulted, died, and failed, respectively. The overall treatment success rate was 91.9%. Being treated in Anger Gute health center (adjusted odds ratio (AOR): 2.27; 95% confidence interval (CI): 1.18-4.38); male (AOR: 1.81; 95% CI: 1.06-3.10); lived in rural areas (AOR: 1.73; 95% CI: 1.02-2.91); previously treated (AOR: 2.72; 95% CI: 1.16-6.39) and unknown HIV status (AOR: 4.56; 95% CI: 1.98-10.50) were determinants of poor treatment outcomes.

CONCLUSION

The current treatment success rate was exceeded the recommended target. However, special attention and strict follow up is required for tuberculosis patients with high risk of unsuccessful treatment outcomes including male, rural resident, previously treated and unknown in HIV status patients throughout their treatment periods.