Synthesis and biological evaluation of 3,4-dihydro-1H-[1,4] oxazepino [6,5,4-hi] indol-1-ones and 4,6-dihydrooxepino [5,4,3-cd] indol-1(3H)-ones as Mycobacterium tuberculosis inhibitors.

This study focuses on the synthesis of 1,7- and 3,4-indole-fused lactones via a simple and efficient reaction sequence. The functionalization of these "oxazepino-indole" and "oxepino-indole" tricycles is carried out by palladium catalysed CC coupling, nucleophilic substitution or 1,3-dipolar cycloaddition. The evaluation of their activity against Mycobacterium tuberculosis shows that the "oxazepino-indole" structure is a new inhibitor of M. tuberculosis growth in vitro.

Biological and Biochemical Evaluation of Isatin-Isoniazid Hybrids as Bactericidal Candidates against Mycobacterium tuberculosis.

Tuberculosis remains a leading cause of mortality among infectious diseases worldwide, prompting the need to discover new drugs to fight this disease. We report here the design, synthesis, and antimycobacterial activity of isatin-mono/bis-isoniazid hybrids. Most of the compounds exhibited very high activity against Mycobacterium tuberculosis, with MICs in the range of 0.195 to 0.39 µg/ml, and exerted a more potent bactericidal effect than the standard antitubercular drug isoniazid (INH). Importantly, these compounds were found to be well tolerated at high doses (>200 µg/ml) on Vero kidney cells, leading to high selectivity indices. Two of the most promising hybrids were evaluated for activity in THP-1 macrophages infected with M. tuberculosis, among which compound 11e was found to be slightly more effective than INH. Overexpression of InhA along with cross-resistance determination of the most potent compounds, selection of resistant mutants, and biochemical analysis, allowed us to decipher their mode of action. These compounds effectively inhibited mycolic acid biosynthesis and required KatG to exert their biological effects. Collectively, this suggests that the synthesized isatin-INH hybrids are promising antitubercular molecules for further evaluation in preclinical settings.

Rifabutin Is Bactericidal against Intracellular and Extracellular Forms of Mycobacterium abscessus.

Mycobacterium abscessus is increasingly recognized as an emerging opportunistic pathogen causing severe lung diseases. As it is intrinsically resistant to most conventional antibiotics, there is an unmet medical need for effective treatments. Repurposing of clinically validated pharmaceuticals represents an attractive option for the development of chemotherapeutic alternatives against M. abscessus infections. In this context, rifabutin (RFB) has been shown to be active against M. abscessus and has raised renewed interest in using rifamycins for the treatment of M. abscessus pulmonary diseases. Here, we compared the in vitro and in vivo activity of RFB against the smooth and rough variants of M. abscessus, differing in their susceptibility profiles to several drugs and physiopathologial characteristics. While the activity of RFB is greater against rough strains than in smooth strains in vitro, suggesting a role of the glycopeptidolipid layer in susceptibility to RFB, both variants were equally susceptible to RFB inside human macrophages. RFB treatment also led to a reduction in the number and size of intracellular and extracellular mycobacterial cords. Furthermore, RFB was highly effective in a zebrafish model of infection and protected the infected larvae from M. abscessus-induced killing. This was corroborated by a significant reduction in the overall bacterial burden, as well as decreased numbers of abscesses and cords, two major pathophysiological traits in infected zebrafish. This study indicates that RFB is active against M. abscessus both in vitro and in vivo, further supporting its potential usefulness as part of combination regimens targeting this difficult-to-treat mycobacterium.

Synthesis and evaluation of heterocycle structures as potential inhibitors of Mycobacterium tuberculosis UGM.

In this study, we screen three heterocyclic structures as potential inhibitors of UDP-galactopyranose mutase (UGM), an enzyme involved in the biosynthesis of the cell wall of Mycobacterium tuberculosis. In order to understand the binding mode, docking simulations are performed on the best inhibitors. Their activity on Mycobacterium tuberculosis is also evaluated. This study made it possible to highlight an "oxazepino-indole" structure as a new inhibitor of UGM and of M. tuberculosis growth in vitro.

Efficacy of Bedaquiline, Alone or in Combination with Imipenem, against Mycobacterium abscessus in C3HeB/FeJ Mice.

Mycobacterium abscessus lung infections remain difficult to treat. Recent studies have recognized the power of new combinations of antibiotics, such as bedaquiline and imipenem, although in vitro data have questioned this combination. We report that the efficacy of bedaquiline-imipenem combination treatment relies essentially on the activity of bedaquiline in a C3HeB/FeJ mice model of infection with a rough variant of M. abscessus The addition of imipenem contributed to clearing the infection in the spleen.

Synergistic Interactions of Indole-2-Carboxamides and ß-Lactam Antibiotics against Mycobacterium abscessus.

New drugs or therapeutic combinations are urgently needed against Mycobacterium abscessus Previously, we demonstrated the potent activity of indole-2-carboxamides 6 and 12 against M. abscessus We show here that these compounds act synergistically with imipenem and cefoxitin in vitro and increase the bactericidal activity of the ß-lactams against M. abscessus In addition, compound 12 also displays synergism with imipenem and cefoxitin within infected macrophages. The clinical potential of these new drug combinations requires further evaluation.

Active Benzimidazole Derivatives Targeting the MmpL3 Transporter in Mycobacterium abscessus.

The prevalence of pulmonary infections due to nontuberculous mycobacteria such as Mycobacterium abscessus has been increasing and surpassing tuberculosis (TB) in some industrialized countries. Because of intrinsic resistance to most antibiotics that drastically limits conventional chemotherapeutic treatment options, new anti-M. abscessus therapeutics are urgently needed against this emerging pathogen. Extensive screening of a library of benzimidazole derivatives that were previously shown to be active against Mycobacterium tuberculosis led to the identification of a lead compound exhibiting very potent in vitro activity against a wide panel of M. abscessus clinical strains. Designated EJMCh-6, this compound, a 2-(2-cyclohexylethyl)-5,6-dimethyl-1H-benzo[d]imidazole), also exerted very strong activity against intramacrophage-residing M. abscessus. Moreover, the treatment of infected zebrafish embryos with EJMCh-6 was correlated with significantly increased embryo survival and a decrease in the bacterial burden as compared to those for untreated fish. Insights into the mechanism of action were inferred from the generation of spontaneous benzimidazole-resistant strains and the identification of a large set of missense mutations in MmpL3, the mycolic acid transporter in mycobacteria. Overexpression of the mutated mmpL3 alleles in a susceptible M. abscessus strain was associated with high resistance levels to EJMCh-6 and to other known MmpL3 inhibitors. Mapping the mutations conferring resistance on an MmpL3 three-dimensional homology model defined a potential EJMCh-6-binding cavity. These data emphasize a yet unexploited chemical structure class against M. abscessus with promising translational development for the treatment of M. abscessus lung diseases.

Verapamil Improves the Activity of Bedaquiline against Mycobacterium abscessus In Vitro and in Macrophages.

Due to intrinsic multidrug resistance, pulmonary infections with Mycobacterium abscessus are extremely difficult to treat. Previously, we demonstrated that bedaquiline is highly effective against Mycobacterium abscessus both in vitro and in vivo Here, we report that verapamil improves the efficacy of bedaquiline activity against M. abscessus clinical isolates and low-level resistant strains, both in vitro and in macrophages. Verapamil may have clinical potential as adjunctive therapy provided that sufficiently high doses can be safely achieved.