In vitro killing dynamics of the diarylquinolone TBAJ-587 and its main metabolites against Mycobacterium tuberculosis

Ramón García, Santiago
TUBERCULOSIS 2022 - EMBO Workshop on Tuberculosis 2022 - From innovation to intervention
Participation type: 
Other authors: 
D. Aguilar Ayala, M. Eveque, M.S. Rabodoarivelo, A. Leding, A. Picó Marco, N. Willand, S. Serbina, U. S. H. Simonsson, A. Lucía Quintana, S. Ramón García
Paris, France. Sep 12-16 2022

The first-in-class diarylquinoline bedaquiline was recently added to WHO essential medicines list for drug-resistant tuberculosis (TB). Improved efficacy of bedaquiline may be possible, beyond current doses, but reported adverse effects limit evaluation of higher exposures. TBAJ- 587 is a next-generation diarylquinoline with anti-Mtb activity and better properties than bedaquiline in terms of safety and efficacy in animal models. Its dose optimization for new combinatorial regimens is currently under evaluation within the ERA4TB consortium.
The in vitro antibacterial activity of TBAJ-587 and its metabolites M2, M3, and M12 (structurally similar to its parent compound) were evaluated against Mycobacterium tuberculosis H37Rv under conditions with differing carbon sources found in the granuloma, including standard in vitro conditions (dextrose), cholesterol, long-chain fatty acids, butyrate, acetate, and pyruvate. First, minimum inhibitory concentrations (MIC) were determined by the resazurin microtiter assay. Then, 28-days dose-response time-kill assays (TKA) were performed to obtain both pharmacodynamic (PD) (Log10 CFU/mL) and pharmacokinetic (PK) parameters (concentration of the drug at every time-point of the kill kinetic) in standard and two lipid conditions. TKA drug concentrations were measured by LC-MSMS.
The MIC of TBAJ-587 and its main metabolites was conserved between the different carbon sources with average MIC90 values of MIC587= 0.031-0.062 μg/mL; MIC587 (M2)= 0.4-1.6 μg/mL; MIC587 (M3)= 0.062-0.125 μg/mL; and MIC587 (M12)= 2.2-9 μg/mL. In TKA, all four compounds showed bactericidal activities at ≥5xMIC, and bacteriostatic activities at 1xMIC and 2xMIC with regrowth by day 28. Patterns of activity were independent of the carbon source used in the assay. Drug concentrations in all media suffer a drastic drop of up to 90% by day 1, probably due to unspecific binding to the plastic ware, similar to observed for bedaquiline. The remaining drug was stable during the full length of the experiment.
This in vitro study applies a multimodal approach and links for the first time the activity of a compound (PD) to its effective concentration (PK) at every time point. Our data suggest that the actual in vitro activity of TBAJ-587 might have been underestimated.
This work has received support from the Innovative Medicines Initiatives 2 Joint Undertaking (grant No 853989).