Abstract
BackgroundThere is a need for better tools to evaluate new or repurposed TB drugs. The whole blood bactericidal activity (WBA) assay has been advocated for this purpose. We investigated whether transcriptional responses in the WBA assay resemble TB responses in vivo, and whether the approach might additionally reveal mechanisms of action.Results1422 of 1798 (79%) of differentially expressed genes in WBA incubated with the standard combination of rifampicin, isoniazid, pyrazinamide and ethambutol were also expressed in sputum (P < 0.0001) obtained from patients taking the same combination of drugs; these comprised well-established treatment-response genes. Gene expression profiles in WBA incubated with the standard drugs individually, or with moxifloxacin or faropenem (with amoxicillin and clavulanic acid) clustered by individual drug exposure. Distinct pathways were detected for individual drugs, although only with isoniazid did these relate to known mechanisms of drug action.ConclusionsSubstantial agreement between whole blood cultures and sputum and the ability to differentiate individual drugs suggest that transcriptomics may add value to the whole blood assay for evaluating new TB drugs.
Highlights
There is a need for better tools to evaluate new or repurposed TB drugs
There was evidence of strong bactericidal activity in the whole blood assay with isoniazid, rifampicin, and moxifloxacin tested individually and with isoniazid, rifampicin, pyrazinamide and ethambutol tested in combination (− 1.62, − 2.74, − 1.92 and 3.49 Δlog colonies forming units (CFU) respectively), whereas pyrazinamide, ethambutol and faropenem used individually had no substantive evidence of bactericidal activity over the 72-h incubation period (Supplementary Figure 1)
In the whole blood assays set-up for gene expression analysis, microarray signals were obtained from all experimental conditions and no sample outliers were detected after RNA normalization
Summary
There is a need for better tools to evaluate new or repurposed TB drugs. The whole blood bactericidal activity (WBA) assay has been advocated for this purpose. We investigated whether transcriptional responses in the WBA assay resemble TB responses in vivo, and whether the approach might reveal mechanisms of action. It is an ex vivo model that measures the bactericidal activity of one or more drugs combined with host immune responses. This has been applied to testing a variety of established and novel antibacterial drugs and, more recently, putative host-directed therapies [8,9,10,11,12,13,14,15]. The objectives of this study were to determine if Mtb transcriptome responses in the WBA model could reflect
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