Identification of novel mutations associated with clofazimine resistance in Mycobacterium tuberculosis : Table 1.

Available chemotherapeutic options are very limited against Mycobacterium abscessus, which imparts a particular challenge in the treatment of cystic fibrosis (CF) patients infected with this rapidly growing mycobacterium. New drugs are urgently needed against this emerging pathogen, but the discovery of active chemotypes has not been performed intensively. Interestingly, however, the repurposing of thiacetazone (TAC), a drug once used to treat tuberculosis, has increased following the deciphering of its mechanism of action and the detection of significantly more potent analogues. We therefore report studies performed on a library of 38 TAC-related derivatives previously evaluated for their antitubercular activity. Several compounds, including D6, D15, and D17, were found to exhibit potent activity in vitro against M. abscessus, Mycobacterium massiliense, and Mycobacterium bolletii clinical isolates from CF and non-CF patients. Similar to TAC in Mycobacterium tuberculosis, the three analogues act as prodrugs in M. abscessus, requiring bioactivation by the EthA enzyme, MAB_0985. Importantly, mutations in the transcriptional TetR repressor MAB_4384, with concomitant upregulation of the divergently oriented adjacent genes encoding an MmpS5/MmpL5 efflux pump system, accounted for high cross-resistance levels among all three compounds. Overall, this study uncovered a new mechanism of drug resistance in M. abscessus and demonstrated that simple structural optimization of the TAC scaffold can lead to the development of new drug candidates against M. abscessus infections.

Section: Discussionsupporting

confidence: 70%

Section: Discussionmentioning

confidence: 99%

Resistance to Thiacetazone Derivatives Active against Mycobacterium abscessus Involves Mutations in the MmpL5 Transcriptional Repressor MAB_4384

Halloum

Viljoen

Khanna

et al. 2017

“…Zhang et al (29) recently reported in vitro selection of a pepQ mutant in M. tuberculosis with clofazimine. However, they did not report the results of direct susceptibility testing with clofazimine or bedaquiline or confirm the causative role of pepQ mutation in clofazimine resistance.…”

Section: Discussionmentioning

confidence: 99%

Mutations in pepQ Confer Low-Level Resistance to Bedaquiline and Clofazimine in Mycobacterium tuberculosis

Almeida

Ioerger

Tyagi

et al. 2016

169

142

fThe novel ATP synthase inhibitor bedaquiline recently received accelerated approval for treatment of multidrug-resistant tuberculosis and is currently being studied as a component of novel treatment-shortening regimens for drug-susceptible and multidrug-resistant tuberculosis. In a limited number of bedaquiline-treated patients reported to date, >4-fold upward shifts in bedaquiline MIC during treatment have been attributed to non-target-based mutations in Rv0678 that putatively increase bedaquiline efflux through the MmpS5-MmpL5 pump. These mutations also confer low-level clofazimine resistance, presumably by a similar mechanism. Here, we describe a new non-target-based determinant of low-level bedaquiline and clofazimine cross-resistance in Mycobacterium tuberculosis: loss-of-function mutations in pepQ (Rv2535c), which corresponds to a putative Xaa-Pro aminopeptidase. pepQ mutants were selected in mice by treatment with clinically relevant doses of bedaquiline, with or without clofazimine, and were shown to have bedaquiline and clofazimine MICs 4 times higher than those for the parental H37Rv strain. Coincubation with efflux inhibitors verapamil and reserpine lowered bedaquiline MICs against both mutant and parent strains to a level below the MIC against H37Rv in the absence of efflux pump inhibitors. However, quantitative PCR (qPCR) revealed no significant differences in expression of Rv0678, mmpS5, or mmpL5 between mutant and parent strains. Complementation of a pepQ mutant with the wild-type gene restored susceptibility, indicating that loss of PepQ function is sufficient for reduced susceptibility both in vitro and in mice. Although the mechanism by which mutations in pepQ confer bedaquiline and clofazimine cross-resistance remains unclear, these results may have clinical implications and warrant further evaluation of clinical isolates with reduced susceptibility to either drug for mutations in this gene. Multidrug-resistant tuberculosis (MDR-TB) is a major threat to global control of tuberculosis (TB). When multidrug resistance is not diagnosed, patients respond poorly to standardized first-line regimens and additional resistance may develop. When MDR-TB is diagnosed, current second-line regimens require prolonged treatment durations and are less effective, more toxic, and far more expensive than first-line therapy (1).The diarylquinoline drug bedaquiline (B) received accelerated approval from the U.S. Food and Drug Administration as part of combination therapy for MDR-TB when other alternatives are not available (2). It is now being studied as a component of novel short-course regimens for MDR as well as drug-susceptible TB (ClinicalTrials.gov identifiers NCT02333799, NCT02193776, NCT02589782, NCT02409290, and NCT02454205 [https://clinicaltrials.gov/]). For new drugs such as bedaquiline, it is essential to define and catalog the mechanisms conferring bacterial resistance in order to design appropriate diagnostic tests (including rapid molecular tests), to better manage the treatment of patients who fail ...

“…Recently, mutations in Rv0678, which encodes the MarR-like transcriptional regulator of the MmpS5-MmpL5 efflux system, were shown to cause cross-resistance between clofazimine and bedaquiline in vitro (9,10). Indeed, mutations in Rv0678 were the major mechanism of clofazimine resistance among isolates selected with clofazimine in vitro (9,11). During clinical trials of bedaquiline, isolates with reduced susceptibility to bedaquiline were shown to have Rv0678 mutations and cross-resistance to clofazimine (10,12).…”

mentioning

confidence: 99%

Primary Clofazimine and Bedaquiline Resistance among Isolates from Patients with Multidrug-Resistant Tuberculosis

Wang

et al. 2017

119

116

Clofazimine has been repurposed for the treatment of tuberculosis, especially for multidrug-resistant tuberculosis (MDR-TB). To test the susceptibility to clofazimine of Mycobacterium tuberculosis clinical isolates, MICs of clofazimine were determined using the microplate alamarBlue assay (MABA) method for 80 drugresistant isolates and 10 drug-susceptible isolates for comparison. For five clofazimineresistant strains isolated from previously treated pre-extensively drug-resistant TB (pre-XDR-TB) and XDR-TB patients without prior exposure to clofazimine or bedaquiline, clofazimine MICs were Ն1.2 g/ml. Four isolates with cross-resistance to bedaquiline had Rv0678 mutations. The other isolate with no resistance to bedaquiline had an Rv1979c mutation. This study adds to a recent study showing that 6.3% of MDR-TB patients without prior clofazimine or bedaquiline exposure harbored isolates with Rv0678 mutations, which raises concern that preexisting resistance to these drugs may be associated with prior TB treatment. Furthermore, we propose a tentative breakpoint of 1.2 g/ml for clofazimine resistance using the MABA method. Morewidespread surveillance and individualized testing for clofazimine and bedaquiline resistance, together with assessment of their clinical usage, especially among previously treated and MDR-TB patients, are warranted.