Tone Tønjum

Myxin and iodinin are phenazines known for antileukemic- and antimicrobial effects. Herein, we synthesized carbamate derivatives from an iodinin regioisomer and assessed their cytotoxicity in vitro toward leukemic and tubercular cells, as well as non-cancerous NRK and H9c2 cells, and evaluated their in vivo toxicity in zebrafish larvae. Myxin’ s antileukemic potency of 1.4 μM IC50 (MOLM-13 cells) was outperformed by several carbamate derivatives, including a methylsulfonyl-imidazolidinone analog (21) showing IC50 of 0.26 μM. The analogs showed large variation in cytotoxic selectivity toward MOLM-13 over normal cells, and in zebrafish larvae toxicity. An imidazolidinone derivative (22) was identified to be particularly favorable, combining high antileukemic- and antitubercular potency with low cytotoxicity to non-cancerous cells and undetected zebrafish toxicity at 200 μM. Furthermore, this derivative was less prone to liver metabolism than myxin. The findings establish carbamate functionalization as a promising strategy for developing new antileukemic and antitubercular phenazines.

Isoniazid (isonicotinic acid hydrazide, INH) is a key drug used to treat tuberculosis (TB), which continues to be the world’s most lethal infectious disease. Nevertheless, the efficacy of INH has diminished because of the emergence of Mycobacterium tuberculosis (Mtb) strains that are resistant to INH. Our goal in this study was to modify INH to reduce this significant resistance chemically. We synthesized INH-based hydrazones (IP1–IP13) through the reaction of INH with in-house obtained benzaldehydes carrying a piperidine or piperazine ring in refluxing ethanol. Upon confirmation of their proposed structures by various spectral techniques, IP1–IP13 were evaluated for their antimycobacterial capacity against Mtb H37Rv strain and INH-resistant clinical isolates with katG and inhA mutations using the Microplate Alamar Blue Assay (MABA). The compounds were additionally tested for their cytotoxicity. The obtained data indicated that the compounds with moderately increased lipophilicity compared to INH (IP7–IP13) were promising antitubercular drug candidates, exhibiting drug-like properties and negligible cytotoxicity. Out of these, IP11 (N′-(4-(4-cyclohexylpiperazin-1-yl)benzylidene)isonicotinohydrazide) emerged as the most promising derivative, demonstrating the lowest MIC values against all Mtb strains tested. Subsequently, the target molecules were evaluated for their capacity to inhibit enoyl acyl carrier protein reductase (InhA), the main target enzyme of INH. Except for IP11 demonstrating 81% InhA inhibition at a concentration of 50 μM, direct InhA inhibition was shown not to be the primary mechanism responsible for the antitubercular activity of the compounds. The binding mechanism of IP11 to InhA was analyzed through molecular docking and molecular dynamics simulations. Altogether, our research identified a novel approach to modify INH to address the challenges posed by the rising prevalence of drug-resistant Mtb strains.

Tuberculosis (TB) remains a major global health challenge, underscoring the urgent need for new therapeutic options. In this study, a series of salicylidenehydrazine derivatives were synthesized and characterized using spectroscopic techniques. Their antimycobacterial activity was assessed against Mycobacterium tuberculosis H37Rv. Among the 35 synthesized compounds, nine demonstrated significant inhibitory activity, with MIC values ranging from 0.78 to 50 μM. These active molecules were further evaluated against clinical isoniazid‐resistant (bearing inhA promoter and/or katG mutations) and multidrug‐resistant (MDR) M. tuberculosis strains. A particularly potent compound derived from 2‐bromo‐4‐nitrosalicylaldehyde exhibited an MIC of 0.78 μM against H37Rv and demonstrated low MIC values of 6.25, 1.56, and 1.56 μM against the inhA + , katG + , and MDR strains, respectively. Molecular docking studies were also conducted to investigate the interaction of active compounds with the target enzyme InhA. Overall, the results indicate that salicylidenehydrazine derivatives represent promising lead structures for the development of new anti‐TB agents effective against both drug‐sensitive and drug‐resistant M. tuberculosis strains.

Background: Human macrophages generate antimicrobial reactive nitrogen species in response to infection by Mycobacterium tuberculosis (Mtb). Exposure to these redox‐reactive compounds induces stress response in Mtb, which can affect posttranslational modifications (PTM). Methods: Here, we present the global analysis of the PTM acylation of Mtb proteins in response to a sublethal dose of nitrosative stress in the form of nitric oxide (NO) using label free quantification. Results: A total of 6437 acylation events were identified on 1496 Mtb proteins, and O‐acylation accounted for 92.2% of the events identified, while 7.8% were N‐acylation events. About 22% of the sites identified were found to be acylated by more than one acyl‐group. Furthermore, the abundance of each acyl‐group decreased as their molecular weight increased. Quantitative PTM analysis revealed differential abundance of acylation in proteins involved in stress response, iron ion homeostasis, growth, energy metabolism, and antimicrobial resistance (AMR) induced by nitrosative stress over time. Conclusions: The results reveal a potential role of Mtb protein acylation in the bacterial stress responses and AMR. To our knowledge, this is the first report on global O‐acylation profile of Mtb in response to NO. This will significantly improve our understanding of the changes in Mtb acylation under nitrosative stress, highly relevant for global health.

Mycobacterium abscessus (M. abscessus) is a multidrug-resistant nontuberculous mycobacterium (NTM) that is responsible for a wide spectrum of infections in humans. The lack of effective bactericidal drugs and the formation of biofilm make its clinical treatment very difficult. The FDA-approved drug library containing 3048 marketed and pharmacopeial drugs or compounds was screened at 20 μM against M. abscessus type strain 19977 in 7H9 medium, and 62 hits with potential antimicrobial activity against M. abscessus were identified. Among them, bithionol, a clinically approved antiparasitic agent, showed excellent antibacterial activity and inhibited the growth of three different subtypes of M. abscessus from 0.625 μM to 2.5 μM. We confirmed the bactericidal activity of bithionol by the MBC/MIC ratio being ≤4 and the time–kill curve study and also electron microscopy study. Interestingly, it was found that at 128 μg/mL, bithionol could completely eliminate biofilms after 48h, demonstrating an outstanding antibiofilm capability compared to commonly used antibiotics. Additionally, bithionol could eliminate 99.9% of biofilm bacteria at 64 μg/mL, 99% at 32 μg/mL, and 90% at 16 μg/mL. Therefore, bithionol may be a potential candidate for the treatment of M. abscessus infections due to its significant antimicrobial and antibiofilm activities.

Serotonergic toxicity due to MAO enzyme inhibition is a significant concern when using linezolid to treat MDR-TB. To address this issue, we designed linezolid bioisosteres with a modified acetamidomethyl side chain at the C-5 position of the oxazolidine ring to balance activity and reduce toxicity. Among these bioisosteres, R7 emerged as a promising candidate, demonstrating greater effectiveness against M. tuberculosis (Mtb) H₃₇Rv cells with an MIC of 2.01 μM compared to linezolid (MIC = 2.31 μM). Bioisostere R7 also exhibited remarkable activity (MIC₅₀) against drug-resistant Mtb clinical isolates, with values of 0.14 μM (INH^R, inhA+), 0.53 μM (INH^R, katG+), 0.24 μM (RIF^R, rpoB+), and 0.92 μM (INH^R INH^R, MDR). Importantly, it was >6.52 times less toxic as compared to the linezolid toward the MAO-A and >64 times toward the MAO-B enzyme, signifying a substantial improvement in its drug safety profile.

This study reports the synthesis and evaluation of a series of new pyridazin-3-ones with furan moieties 5a?j and 6a?f, to test for their antimycobacterial and antifungal activities. The structures of the target compounds were confirmed by elemental analysis and spectroscopic techniques (IR, mass, 1H-and 13C-NMR). Amongst the compounds tested, 5e, 5g, 5i and 6e exhibited highest activity against Mycobacterium tuberculosis, while 5h, 6d and 6f showed moderate in vitro antifungal activities against Candida albicans and Candida parapsilosis.