BEYOND BURDEN: NEW TOOLS FOR TUBERCULOSIS ANTIBIOTICREGIMEN DESIGN

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Project Summary A key priority for combatting the global tuberculosis (TB) epidemic is shortening the length of treatment required to reliably cure TB. A critical impediment to drug and regimen development is the lack of metrics of effective treatment response for use in drug discovery and pre-clinical development. Two factors considered crucial to shortening treatment are the capacity of a drug to penetrate and accumulate in lung lesions and the inherent activity of a drug against residual drug-tolerant Mycobacterium tuberculosis (Mtb) populations that survive initial drug killing. This proposal focuses on the inherent treatment-shortening activity of drugs, independent of PK. Unfortunately, the bacteriological basis of why existing TB drugs and regimens vary in treatment-shortening activity remains unclear. This project evaluates the basis of drug treatment-shortening activity in TB, focusing particularly on the role of overall bacterial activity and replication during treatment. Conventionally, drugs are assessed based on the degree to which they lower Mtb burden. Our alternative approach evaluates how drugs affect fundamental bacterial cellular processes. Specifically, we developed an assay that quantifies how drugs affect ongoing ribosomal RNA synthesis called RS ratio. We found TB drugs and regimens that shorten treatment profoundly suppress rRNA synthesis; whereas drugs with high bactericidal activity but low treatment-shortening activity allow surviving Mtb populations to sustain rRNA synthesis. The RS ratio is already transforming drug development pipelines and clinical trials, but the physiological basis for the predictive power of the RS ratio needs to be fully elucidated. Since the rate of rRNA synthesis is fundamentally correlated with replication rate, we hypothesize that Mtb replication during treatment is an important unrecognized factor in treatment-shortening. Aim 1 will elucidate the effect of diverse drugs on replication while validating the RS ratio as a measure of Mtb replication and establishing a series of confirmatory molecular assays. Aim 2 will test the paradigm in vivo by evaluating pairwise combinations selected based on their potency on inhibiting Mtb replication. Collectively, our innovations are moving beyond crude measures of bacterial burden to a new era in which drugs and regimens are evaluated based on nuanced multifaceted molecular testing of their impact on fundamental physiologic processes of the pathogen.