Indoleamides are active against drug-resistant Mycobacterium tuberculosis

Abstract

Responsible for nearly two million deaths each year, the infectious disease tuberculosis remains a serious global health challenge. The emergence of multidrug- and extensively drug-resistant strains of Mycobacterium tuberculosis confounds control efforts, and new drugs with novel molecular targets are desperately needed. Here we describe lead compounds, the indoleamides, with potent activity against both drug-susceptible and drug-resistant strains of M. tuberculosis by targeting the mycolic acid transporter MmpL3. We identify a single mutation in mmpL3 which confers high resistance to the indoleamide class while remaining susceptible to currently used first- and second-line tuberculosis drugs, indicating a lack of cross-resistance. Importantly, an indoleamide derivative exhibits dose-dependent anti-mycobacterial activity when orally administered to M. tuberculosis-infected mice. The bioavailability of the indoleamides, combined with their ability to kill tubercle bacilli, indicates great potential for translational developments of this structure class for the treatment of drug-resistant tuberculosis.

Novel Insights into the Mechanism of Inhibition of MmpL3, a Target of Multiple Pharmacophores in Mycobacterium tuberculosis

“…A number of structurally diverse hydrophobic inhibitors have been reported in the last 2 years to target the essential TMM transporter MmpL3 (7,(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)21). Various explanations have been advanced for this apparent bias, including the fact that MmpL3 may represent a particularly vulnerable and druggable target and/or one in which spontaneous resistance-conferring mutations may be easier to achieve (12).…”

“…Surprisingly, in the last 2 years, the whole-cell-based screening of compound libraries against M. tuberculosis in culture coupled to the whole-genome sequencing of spontaneous resistant mutants identified a variety of pharmacophores that apparently shared the same mode of action as SQ109. These inhibitors include the 1,5-diarylpyrrole derivative BM212 and analogs (10,11), the benzimidazole C215 (12), tetrahydropyrazolo [1,5-a]pyrimidine-3-carboxamides (THPPs) (13,14), N-benzyl-6=,7=-dihydrospiro[piperidine-4,4=-thieno [3,2-c]pyrans (13), indolecarboxamides (15)(16)(17)(18), and adamantyl ureas (AUs) (19) (Fig. 1).…”

Therapeutic Potential of the Mycobacterium tuberculosis Mycolic Acid Transporter, MmpL3

“…The identification and characterization of MmpL3 inhibitors have thus far rested on the whole-genome sequencing of spontaneous resistant mutants and the metabolic labeling with [1,2-14 C]acetate of inhibitor-treated cells to monitor the transfer of mycolic acids to their cell envelope acceptors (5)(6)(7)(8)(9)(10)(11)(12)(13)(14)17). Because the development and further optimization of MmpL3 inhibitors would greatly benefit from less cumbersome approaches, and because of the technical difficulty of developing an in vitro transport assay for this protein, we next sought to determine whether the M. tuberculosis mc 2 6206 MmpL3-DUC knockdown could be used in the development of a target-based whole-cell screening assay.…”

“…To date, whole-cell screening strategies are the ones that have led to the identification of the greatest number of novel inhibitors of potential therapeutic interest (2)(3)(4). Intriguingly, in the last 4 years, the screening of compound libraries against M. tuberculosis in culture followed by the whole-genome sequencing of spontaneous resistant mutants has identified multiple small molecules, including the TB drug candidate SQ109, as inhibitors of the mycolic acid transporter, MmpL3 (5)(6)(7)(8)(9)(10)(11)(12)(13)(14). MmpL3 is an integral inner membrane transporter of the resistance, nodulation, and division (RND) superfamily, involved in the export of mycolic acids under the form of trehalose monomycolate (TMM) to the periplasmic space, where this glycolipid can then serve as a mycolic acid donor in the building of the mycobacterial outer membrane, otherwise known as the mycomembrane (5,15,16).…”

Recent Progress on the Development of Novel Antitubercular Agents from Whole-Cell Screening Hits

“…Generation of resistant mutants against their indolecarboxamide analogues followed by whole geneome sequencing of the mutants suggested Mmpl3 was the target of this scaffold ( Figure 13). 29 Novartis recently reported their medicinal chemistry studies starting from the HTS hit 62, and also described the in vivo PK pro le and mouse ef cacy of the optimized compounds. 30 Their efforts primarily focused on modi cation of the indole and cycloalkyl moieties of 62.…”