Expanding the squaramide library as mycobacterial ATP synthase inhibitors: Innovative synthetic pathway and biological evaluation

Mycobacterial ATP synthase is a validated therapeutic target for combating drug-resistant tuberculosis. Inhibition of this enzyme has been featured as an efficient strategy for the development of new antimycobacterial agents against drug-resistant pathogens. In this study, we synthesised and explored two distinct series of squaric acid analogues designed to inhibit mycobacterial ATP synthase. Among the extensive array of compounds investigated, members of the phenyl-substituted sub-library emerged as primary hits. To gain deeper insights into their mechanisms of action, we conducted advanced biological studies, focusing on the compounds displaying a direct binding of a nitrogen heteroatom to the phenyl ring, resulting in the highest potency. Our investigations into spontaneous mutants led to the validation of a single point mutation within the atpB gene (Rv1304), responsible for encoding the ATP synthase subunit a. This genetic alteration sheds light on the molecular basis of resistance to squaramides. Furthermore, we explored the possibility of synergy between squaramides and the reference drug clofazimine using a checkerboard assay, highlighting the promising avenue for enhancing the effectiveness of existing treatments through combined therapeutic approaches. This study contributes to the expansion of investigating squaramides as promising drug candidates in the ongoing battle against drug-resistant tuberculosis.

Distribution of multi-drug resistant tuberculosis in Ekiti and Ondo states, Nigeria

Background

Tuberculosis (TB), caused by Mycobacterium tuberculosis (MTB), is one of the top infectious killer diseases in the world. The emergence of drug-resistant MTB strains has thrown challenges in controlling TB worldwide. This study investigated the prevalence of drug-resistant tuberculosis in the states of Nigeria and the risk factors that can increase the incidence of tuberculosis.

Methods

The study is a cross-sectional epidemiological research carried out in the six senatorial districts of Ekiti and Ondo states, Nigeria, between February 2019 and January 2020. A structured questionnaire was administered to 1203 respondents for socio-demographic information, and sputum samples were collected from them for TB investigation. GeneXpert technique was used to diagnose TB from the sputum samples, followed by bacterial isolation using Löweinstein-Jensen medium and antibiotic susceptibility testing.

Results

Prevalence of TB in the two states combined was 15 ​%; with 13.8 ​% for Ekiti state and 16.1 ​% for Ondo State. The distribution of TB in the senatorial districts was such that: Ondo South ​> ​Ekiti Central ​> ​Ekiti South ​> ​Ondo North ​> ​Ekiti North ​> ​Ondo Central. The risk factors identified for TB prevalence in two states were gender, male ​> ​female (OR ​= ​0.548, p ​= ​0.004); overcrowding (OR ​= ​0.733, p ​= ​0.026); room size (OR ​= ​0.580, p ​= ​0.002); smoking (OR ​= ​0.682, p ​= ​0.019) and dry and dusty season (OR ​= ​0.468, p ​= ​0.005). The prevalence of MDR-TB in Ekiti and Ondo States were 1.2 ​% and 1.3 ​% respectively. The identified risk factors for MDR were education (OR ​= ​0.739, p ​= ​0.017), age (OR ​= ​0.846, p ​= ​0.048), religion (OR ​= ​1.95, p ​= ​0.0003), family income (OR ​= ​1.76, p ​= ​0.008), previous TB treatment (OR ​= ​3.64, p ​= ​0.004), smoking (OR ​= ​1.33, p ​= ​0.035) and HIV status (OR ​= ​1.85, p ​= ​0.006). Rifampicin monoresistant was reported in 6.7 ​% of the rifampicin-resistant strains, while 93.3 ​% were rifampicin polyresistant strains. Two (13.3 ​%) of the MDR-TB strains were resistant to all the 3 first-line antimycobacterial agents. All the Rifampicin-resistant TB strains were susceptible to the aminoglycosides (Amikacin, Capreomycin and Kanamycin), also with high susceptibility to the fluoroquinilones: Moxifloxacin (100 ​%) and Levofloxacin (86.7 ​%). Sixteen (94.1 ​%) of the 17 Rifampicin-susceptible strains were susceptible to all the eight antibiotics tested, while one (5.9 ​%) was susceptible to Rifampicin and Isoniazid but resistant to the rest antibiotics. Conclusion: The study showed that there is high prevalence of TB and MDR-TB in Ekiti and Ondo States Nigeria, hence, to meet the SDG Target 3.3 of ending TB epidemic by 2030, culturing and antibiotic susceptibility testing should be carried out on every TB-positive sputum and the patients treated accordingly.

Mesoporous silica nanoparticles containing silver as novel antimycobacterial agents against Mycobacterium tuberculosis

Tuberculosis remains today a major public health issue with a total of 9 million new cases and 2 million deaths annually. The lack of an effective vaccine and the increasing emergence of new strains of Mycobacterium tuberculosis (Mtb) highly resistant to antibiotics, anticipate a complicated scenario in the near future. The use of nanoparticles features as an alternative to antibiotics in tackling this problem due to their potential effectiveness in resistant bacterial strains. In this context, silver nanoparticles have demonstrated high bactericidal efficacy, although their use is limited by their relatively high toxicity, which calls for the design of nanocarriers that allow silver based nanoparticles to be safely delivered to the target cells or tissues. In this work mesoporous silica nanoparticles are used as carriers of silver based nanoparticles as antimycobacterial agent against Mtb. Two different synthetic approaches have been used to afford, on the one hand, a 2D hexagonal mesoporous silica nanosystem which contains silver bromide nanoparticles distributed all through the silica network and, on the other hand, a core@shell nanosystem with metallic silver nanoparticles as core and mesoporous silica shell in a radial mesoporous rearrangement. Both materials have demonstrated good antimycobacterial capacity in in vitro test using Mtb, being lower the minimum inhibitory concentration for the nanosystem which contains silver bromide. Therefore, the interaction of this material with the mycobacterial cell has been studied by cryo-electron microscopy, establishing a direct connection between the antimycobactericidal effect observed and the damage induced in the cell envelope.

Medicinal plants used in the treatment of tuberculosis - Ethnobotanical and ethnopharmacological approaches

Tuberculosis is a highly infectious disease declared a global health emergency by the World Health Organization, with approximately one third of the world's population being latently infected with Mycobacterium tuberculosis. Tuberculosis treatment consists in an intensive phase and a continuation phase. Unfortunately, the appearance of multi drug-resistant tuberculosis, mainly due to low adherence to prescribed therapies or inefficient healthcare structures, requires at least 20 months of treatment with second-line, more toxic and less efficient drugs, i.e., capreomycin, kanamycin, amikacin and fluoroquinolones. Therefore, there exists an urgent need for discovery and development of new drugs to reduce the global burden of this disease, including the multi-drug-resistant tuberculosis. To this end, many plant species, as well as marine organisms and fungi have been and continue to be used in various traditional healing systems around the world to treat tuberculosis, thus representing a nearly unlimited source of active ingredients. Besides their antimycobacterial activity, natural products can be useful in adjuvant therapy to improve the efficacy of conventional antimycobacterial therapies, to decrease their adverse effects and to reverse mycobacterial multi-drug resistance due to the genetic plasticity and environmental adaptability of Mycobacterium. However, even if some natural products have still been investigated in preclinical and clinical studies, the validation of their efficacy and safety as antituberculosis agents is far from being reached, and, therefore, according to an evidence-based approach, more high-level randomized clinical trials are urgently needed.

Discovery of novel isatin-based thiosemicarbazones: synthesis, antibacterial, antifungal, and antimycobacterial screening

Background and purpose:

A group of thiosemicarbazones were prepared and their structures were confirmed by spectroscopic methods such as IR and H-NMR, mass spectrometry and also analytical method like elemental analysis. The synthesized semicarbazones were then assessed for their inhibitory activity against bacterial strains including Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, Staphylococcus epidermidis, Bacillus cereus, Salmonella species, Enterobacter faecalis, methicillin-resistant Staphylococcus aureus, and fungi such as Candida albicans and Aspergillus niger.

Experimental approach:

The schiff bases of isatin (2a-j) were prepared by a condensation reaction between thiosemicarbazide and substituted N-aryl isatins leading to the desired thiosemicarbazones with exquisite purity.

Findings / Results:

The results disclosed that all compounds have noticeable inhibitory activity. Compounds 2a, 2b, 2c, 2g, and 2h were among the most potent derivatives against Gram negative bacteria and fungi. Besides, the activity of theses compounds were tested against Mycobacterium bovis bacillus Calmette-Guerin (M. bovis BCG). The antimycobacterial activity indicated compounds 2e and 2j are highly active against M. bovis BCG (minimum inhibitory concentration < 3.9 μg/mL). Among fluorinated structures, compounds 2a and 2j showed the best activities against M. bovis BCG.

Conclusion and implications:

To sum up, amongst the 10 synthesized compounds, fluorinated derivatives exhibited remarkable activities against both gram negative strains and candida albicans microorganism. Therefore, they should be considered as a clue for further modifications in next investigations. Furthermore, inserting a small/medium size halogen atom with electron-withdrawing and lipophilic properties increases anti- salmonella activity of these compounds and moreover 2-halogenated semithiocarbazones presented promising antimycobacterial activity.

RETRACTED: Medicinal plants used in the treatment of tuberculosis - Ethnobotanical and ethnopharmacological approaches

Tuberculosis is a highly infectious disease declared a global health emergency by the World Health Organization, with approximately one third of the world's population being latently infected with Mycobacterium tuberculosis. Tuberculosis treatment consists in an intensive phase and a continuation phase. Unfortunately, the appearance of multi drug-resistant tuberculosis, mainly due to low adherence to prescribed therapies or inefficient healthcare structures, requires at least 20months of treatment with second-line, more toxic and less efficient drugs, i.e., capreomycin, kanamycin, amikacin and fluoroquinolones. Therefore, there exists an urgent need for discovery and development of new drugs to reduce the global burden of this disease, including the multi-drug-resistant tuberculosis. To this end, many plant species, as well as marine organisms and fungi have been and continue to be used in various traditional healing systems around the world to treat tuberculosis, thus representing a nearly unlimited source of active ingredients. Besides their antimycobacterial activity, natural products can be useful in adjuvant therapy to improve the efficacy of conventional antimycobacterial therapies, to decrease their adverse effects and to reverse mycobacterial multi-drug resistance due to the genetic plasticity and environmental adaptability of Mycobacterium. However, even if some natural products have still been investigated in preclinical and clinical studies, the validation of their efficacy and safety as antituberculosis agents is far from being reached, and, therefore, according to an evidence-based approach, more high-level randomized clinical trials are urgently needed.

Antimycobacterial and cytotoxicity activity of microcystins

BACKGROUND

The present work aimed to evaluate the antimycobacterial activity and cytotoxicity of Microcystis aeruginosa toxins, the MC-LR variant and purified extract of [D-Leu(1)] microcystin-LR.

METHODS

The antimicrobial activity of M. aeruginosa extract and microcystin was evaluated by resazurin microtiter assay against Mycobacterium tuberculosis, M. terrae, M. chelonae and M. kansasii. The cytotoxicity assay was performed by trypan blue exclusion against the HTC cell line.

RESULTS

Antimicrobial activity was observed in the hexanic extract of M. aeruginosa (RST 9501 strain) against M. tuberculosis, including sensitive and resistant strains with minimal inhibitory concentrations (MIC) between 1.93 μM and 0.06 μM. The high activity of M. aeruginosa hexanic extract could be attributed to the major presence of the toxins MC-LR and [D-Leu(1)] MC-LR that showed activity at MIC between 53 and 0.42 μM against tested mycobacterial strains. Even at the highest concentration tested, no toxicity of M. aeruginosa extracts was identified against HTC cells.

CONCLUSIONS

These preliminary results suggest that [D-Leu(1)] MC-LR is a promising candidate for the development of a new antimycobacterial agent.

In-silico Metabolome Target Analysis Towards PanC-based Antimycobacterial Agent Discovery

Mycobacterium tuberculosis, the main cause of tuberculosis (TB), has still remained a global health crisis especially in developing countries. Tuberculosis treatment is a laborious and lengthy process with high risk of noncompliance, cytotoxicity adverse events and drug resistance in patient. Recently, there has been an alarming rise of drug resistant in TB. In this regard, it is an unmet need to develop novel antitubercular medicines that target new or more effective biochemical pathways to prevent drug resistant Mycobacterium. Integrated study of metabolic pathways through in-silico approach played a key role in antimycobacterial design process in this study. Our results suggest that pantothenate synthetase (PanC), anthranilate phosphoribosyl transferase (TrpD) and 3-isopropylmalate dehydratase (LeuD) might be appropriate drug targets. In the next step, in-silico ligand analysis was used for more detailed study of chemical tractability of targets. This was helpful to identify pantothenate synthetase (PanC, Rv3602c) as the best target for antimycobacterial design procedure. Virtual library screening on the best ligand of PanC was then performed for inhibitory ligand design. At the end, five chemical intermediates showed significant inhibition of Mycobacterium bovis with good selectivity indices (SI) ≥10 according to Tuberculosis Antimicrobial Acquisition & Coordinating Facility of US criteria for antimycobacterial screening programs.

Synthesis of novel isothiazolopyridines and their in vitro evaluation against Mycobacterium and Propionibacterium acnes

In this paper we describe synthesis, structures and some physicochemical properties of 20 isothiazolopyridines 8-13 substituted differently into an isothiazole ring as well as their in vitro antibacterial assays against Mycobacterium tuberculosis H37Rv, Mycobacterium fortuitum PCM 672 and Propionibacterium acnes PCM 2400. Compound 13a was found to be the most active derivative against M. tuberculosis H37Rv, demonstrating 100% growth inhibition of microorganisms in the primary screen (minimum inhibitory concentration [MIC] 6.25μg/mL). Nineteen of the prepared compounds were evaluated against M. fortuitum PCM 672 and P. acnes PCM 2400 and only compounds 9 and 12d exhibited excellent activity against individual strains of microorganisms with MIC90 <1μg/mL. The inhibitory action of the remaining isothiazolopyridines towards the tested strains of the microorganism was low, absent, or a non-linear correlation prohibited accurate determination of MIC values. Unexpectedly, seven of the remaining isothiazolopyridines tested against M. fortuitum and P. acnes stimulated growth of the microorganisms in the range 10-50% or even more (10b) under experimental conditions.

LC-MS based assay to measure intracellular compound levels in Mycobacterium smegmatis: linking compound levels to cellular potency

Dihydrofolate reductase (DHFR) plays a central role in maintaining cellular pool of tetrahydrofolic acid, a cofactor necessary for DNA, RNA and protein synthesis. The clinical validation of DHFR as antibacterial target was established by the success of trimethoprim (TMP). DHFR is also an attractive target for identifying anti-tuberculosis molecules however, due to observed weak cellular potency, no DHFR inhibitors have been developed as drugs so far. TMP and its analogs have poor cellular potency on Mycobacterium tuberculosis and Mycobacterium smegmatis cells. We found a mutant strain of M. smegmatis, mc²155 to be sensitive to TMP whereas wild type strain was not inhibited by TMP. We utilized this system to probe if poor or lack of activity of TMP is a consequence of poor intracellular compound levels. An LC-MS based method was developed for measuring TMP and rifampicin (RIF) in M. smegmatis. Using the assay, equivalent RIF levels were observed in both strains however, TMP was detected only in mc²155 cells, hence proving a positive correlation between potency and compound levels. To the best of our knowledge this is the first time LC-MS method has been used to measure compound levels in mycobacterial cells. We propose it to be a valuable tool to understand the lack of potency or resistance mechanisms in antimycobacterial drug development.