Rv0579 Is Involved in the Resistance to the TP053 Antitubercular Prodrug

Expanding the knowledge around antitubercular 5-(2-aminothiazol-4-yl)isoxazole-3-carboxamides: Hit-to-lead optimization and release of a novel antitubercular chemotype via scaffold derivatization

Tuberculosis is one of the deadliest infectious diseases in the world, and the increased number of multidrug-resistant and extensively drug-resistant strains is a reason for concern. We have previously reported a series of substituted 5-(2-aminothiazol-4-yl)isoxazole-3-carboxamides with growth inhibitory activity against Mycobacterium tuberculosis strains and low propensity to be substrate of efflux pumps. Encouraged by these preliminary results, we have undertaken a medicinal chemistry campaign to determine the metabolic fate of these compounds and to delineate a reliable body of Structure-Activity Relationships. Keeping intact the (thiazol-4-yl)isoxazole-3-carboxamide core, as it is deemed to be the pharmacophore of the molecule, we have extensively explored the structural modifications able to confer good activity and avoid rapid clearance. Also, a small set of analogues based on isostere manipulation of the 2-aminothiazole were prepared and tested, with the aim to disclose novel antitubercular chemotypes. These studies, combined, were instrumental in designing improved compounds such as 42g and 42l, escaping metabolic degradation by human liver microsomes and, at the same time, maintaining good antitubercular activity against both drug-susceptible and drug-resistant strains.

A New Benzothiazolthiazolidine Derivative, 11726172, Is Active In Vitro, In Vivo, and against Nonreplicating Cells of Mycobacterium tuberculosis

Tuberculosis (TB) still poses a global menace as one of the deadliest infectious diseases. A quarter of the human population is indeed latently infected with Mycobacterium tuberculosis. People with latent infection have a 5 to 10% lifetime risk of becoming ill with TB, representing a reservoir for TB active infection. This is a worrisome problem to overcome in the case of relapse; unfortunately, few drugs are effective against nonreplicating M. tuberculosis cells. Novel strategies to combat TB, including its latent form, are urgently needed. In response to the lack of new effective drugs and after screening about 500 original chemical molecules, we selected a compound, 11726172, that is endowed with potent antitubercular activity against M. tuberculosis both in vitro and in vivo and importantly also against dormant nonculturable bacilli. We also investigated the mechanism of action of 11726172 by applying a multidisciplinary approach, including transcriptomic, labeled metabolomic, biochemical, and microbiological procedures. Our results represent an important step forward in the development of a new antitubercular compound with a novel mechanism of action active against latent bacilli. IMPORTANCE The discontinuation of TB services due to COVID-19 causes concern about a future resurgence of TB, also considering that latent infection affects a high number of people worldwide. To combat this situation, the identification of antitubercular compounds targeting Mycobacterium tuberculosis through novel mechanisms of action is necessary. These compounds should be active against not only replicating bacteria cells but also nonreplicating cells to limit the reservoir of latently infected people on which the bacterium can rely to spread after reactivation.

Thieno[2,3-d]pyrimidine-Core Compounds Show Activity Against Clinically Relevant Gram-Positive Bacteria

Thieno[2,3- d ]pyrimidines represent a novel antibacterial prodrug scaffold, previously identified through a screening campaign against Mycobacterium tuberculosis in which the formation of highly antimycobacterial metabolites catalyzed by the nitroreductase Mrx2 is suggested to be the relevant killing mechanism. As analogical activation pathways may also be employed in other prokaryotes, in this work we explored general antibacterial effects of this compound class. Through exploration of the chemical space by different synthetic strategies, 51 novel derivatives were generated, biologically evaluated and thus enabled initial conclusions about structure-activity-relationships. Remarkably, anti-Gram-positive activity can be well modulated, particularly towards Staphylococci (MRSA) and even slightly against some Gram-negative strains. The two most promising hit compounds showed good pharmacokinetic properties in vitro as well as acceptable toxicity in HeLa cells qualifying them as starting points for lead generation campaigns.

The Veterinary Anti-Parasitic Selamectin Is a Novel Inhibitor of the Mycobacterium tuberculosis DprE1 Enzyme

Avermectins are macrocyclic lactones with anthelmintic activity. Recently, they were found to be effective against Mycobacterium tuberculosis, which accounts for one third of the worldwide deaths from antimicrobial resistance. However, their anti-mycobacterial mode of action remains to be elucidated. The activity of selamectin was determined against a panel of M. tuberculosis mutants. Two strains carrying mutations in DprE1, the decaprenylphosphoryl-β-D-ribose oxidase involved in the synthesis of mycobacterial arabinogalactan, were more susceptible to selamectin. Biochemical assays against the Mycobacterium smegmatis DprE1 protein confirmed this finding, and docking studies predicted a binding site in a loop that included Leu275. Sequence alignment revealed variants in this position among mycobacterial species, with the size and hydrophobicity of the residue correlating with their MIC values; M. smegmatis DprE1 variants carrying these point mutations validated the docking predictions. However, the correlation was not confirmed when M. smegmatis mutant strains were constructed and MIC phenotypic assays performed. Likewise, metabolic labeling of selamectin-treated M. smegmatis and M. tuberculosis cells with ¹⁴C-labeled acetate did not reveal the expected lipid profile associated with DprE1 inhibition. Together, our results confirm the in vitro interactions of selamectin and DprE1 but suggest that selamectin could be a multi-target anti-mycobacterial compound.