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Pharmacokinetics and safety of TBAJ-587, a novel antimycobacterial diarylquinoline, in healthy participants.

TBAJ-587 is a second-generation diarylquinoline with greater antimycobacterial activity and a potentially better safety profile than the first-generation bedaquiline. It is currently under development for the treatment of drug-susceptible and drug-resistant tuberculosis. A first-in-human trial of TBAJ-587, including single and multiple ascending oral doses and a dedicated food-effect cohort, was conducted in 92 healthy adults. Plasma exposures of TBAJ-587 were generally linear for AUCtau and slightly subproportional for Cmax, with the major circulating active metabolite, M3, remaining low relative to the parent. A high-fat meal increased the mean Cmax and AUClast 3.46- and 2.26-fold, respectively. TBAJ-587 accumulated with multiple dosing over the 28-day period, with mean accumulation ratios across the three tested doses ranging from 1.69 to 2.32 for Cmax and from 2.74 to 3.73 for AUCtau. However, steady-state conditions were not yet reached on day 28. Mean terminal half-lives after 28-day dosing of TBAJ-587 ranged from approximately 80 to 111 days. There were no deaths or serious adverse events, and TBAJ-587 was generally safe and well tolerated at single doses of 25-800 mg under fasting conditions and multiple doses of 50-200 mg once daily for 28 days after a standard breakfast. In addition, no dose- or time-dependent effects were noted for any of the other safety and tolerability parameters, including no clinically significant effects on the QTc interval. These results support further investigation of TBAJ-587 for the treatment of tuberculosis.CLINICAL TRIALSThis study is registered with ClinicalTrials.gov as NCT04890535.

Humans

Genomic and structural insights into the atpB L173I substitution: modulation of the F₀ rotor architecture in Mycobacterium tuberculosis ATP synthase and altered Bedaquiline binding dynamics.

The F₀F₁ ATP synthase of Mycobacterium tuberculosis (M. tuberculosis) is an essential membrane-embedded rotary motor responsible for ATP synthesis and maintenance of the proton motive force in bacteria. The transmembrane F₀ domain comprises the c-subunit (atpE) and the a-subunit (atpB). Their coordinated interactions are needed for proton translocation and torque generation. Bedaquiline (BDQ), FDA-approved diarylquinoline for the treatment of multidrug-resistant tuberculosis (MDR-TB), targets the F₀ motor by binding at the a-c interface and inhibiting rotary catalysis. To the best of our knowledge, this study represents the first attempt to analyze the effects of mutations in the atpB protein on its structural stability in the F₀ domain, thereby highlighting the novelty of this work. In this study, we integrated Indian whole-genome sequencing (WGS) datasets (PRJNA37907) with long-timescale (1000 ns) membrane-embedded molecular dynamics (MD) simulations. Among 57 atpB mutations identified from WGS analysis, L173I was selected for structural and MD analysis. L173I is located at the atpB-atpE interface near the BDQ-binding region, despite V177L and S184A showing higher prevalence. Comparative MD simulations encompassed four systems: wild-type apo, wild-type with BDQ, L173I apo, and L173I with BDQ. Structural interrogation revealed that the L173I substitution induces subtle destabilization of the global fold of the atpB-atpE complex relative to the apo state, while more critically attenuating inter-subunit contacts between the a-subunit and the c-ring. These perturbations provide a mechanistic rationale for reduced BDQ susceptibility, arising from altered interfacial dynamics rather than complete abrogation of drug binding. This integrative genomic-structural framework advances our understanding of ATP synthase-mediated resistance in M. tuberculosis.

Diarylquinolines

No phenotypic resistance observed for most group-3 and -4 variants in Mycobacterium tuberculosis genes related to bedaquiline, clofazimine, delamanid, and pretomanid in a Central and West African context.

The interpretation of genetic variants' association (or not) with phenotypic resistance to newly introduced and repurposed antituberculosis drugs remains challenging, as many mutations detected by whole-genome sequencing (WGS) are classified as of uncertain significance (group 3) or not associated with resistance-interim (group 4) by the World Health Organization (WHO) mutation catalog v2. We evaluated the phenotypic impact of such variants on minimum inhibitory concentrations (MICs) for bedaquiline (BDQ), clofazimine (CFZ), delamanid (DLM), and pretomanid (PA) in Mycobacterium tuberculosis complex isolates from the multi-country DIAMA cohort in sub-Saharan Africa (SSA), which recruited RR/RS-TB patients naïve to these drugs. Among 1,475 isolates with available WGS data, 163 variants met eligibility criteria; due to viable strain unavailability, 89 isolates carrying 29 unique BDQ/CFZ-related and 60 unique DLM/PA-related variants were tested for MIC determination using broth microdilution. Additional structural modeling was performed to explore potential effects of amino-acid substitutions on protein stability. Among BDQ/CFZ-related variants, MICs above the critical concentrations (CCs) were consistently associated with mmpR5 variants, whereas variants in atpE, pepQ, and Rv1979c were not. DLM/PA variants (ddn, fbiA-D, and fgd1) were frequently detected as non-fixed populations, yet rarely yielding MIC values above the CC. Predicted structural destabilization showed no consistent association with MIC values or variant fixation status. Under the conditions tested, phenotypic resistance was not detected for most group 3 and 4 variants detected by WGS. Our data provide evidence from SSA to support improved interpretation of resistance-associated mutations for new and repurposed antituberculosis drugs.IMPORTANCEWhole-genome sequencing increasingly detects Mycobacterium tuberculosis complex mutations classified by the World Health Organization (WHO) mutation catalog v2 as group 3 variants of uncertain significance or group 4 variants not associated with resistance-interim, limiting reliable prediction of resistance to new and repurposed antituberculosis drugs. By generating minimum inhibitory concentration (MIC) data for such variants identified in a multi-country sub-Saharan African cohort, this study provides phenotypic evidence to support future refinement and expansion of the WHO mutation catalog v2. Notably, mmpR5 variants associated with elevated bedaquiline/clofazimine MICs were identified in eight isolates, suggesting that some patients in this cohort may have harbored pre-existing resistance-associated variants yet remained potentially eligible for bedaquiline-containing regimens. These findings contribute to improving the interpretation of genomic resistance data and strengthening surveillance of resistance to bedaquiline, clofazimine, delamanid, and pretomanid.

Mycobacterium tuberculosis