A Macrophage Infection Model to Predict Drug Efficacy AgainstMycobacterium Tuberculosis

Abstract

In the last 40 years, only a single new antituberculosis drug was FDA approved. New tools that improve the drug development process will be essential to accelerate the development of next-generation antituberculosis drugs. The drug development process seems to be hampered by the inefficient transition of initially promising hits to candidate compounds that are effective in vivo. In this study, we introduce an inexpensive, rapid, and BSL-2 compatible infection model using macrophage-passaged Mycobacterium tuberculosis (Mtb) that forms densely packed Mtb/macrophage aggregate structures suitable for drug efficacy testing. Susceptibility to antituberculosis drugs determined with this Mtb/macrophage aggregate model differed from commonly used in vitro broth-grown single-cell Mtb cultures. Importantly, altered drug susceptibility correlated well with the reported ability of the respective drugs to generate high tissue and cerebrospinal fluid concentrations relative to their serum concentrations, which seems to be the best predictors of in vivo efficacy. Production of these Mtb/macrophage aggregates could be easily scaled up to support throughput efforts. Overall, its simplicity and scalability should make this Mtb/macrophage aggregate model a valuable addition to the currently available Mtb drug discovery tools.

Hit Generation in TB Drug Discovery: From Genome to Granuloma

“…Moreover, the granuloma is a good predictor of a drug’s in vivo efficacy. 226 However, it is important to be mindful that in vivo Mtb does not only reside inside the cellular granuloma. For example, extracellular Mtb is found in the caseum of the necrotic granuloma, and infection may be found outside the lung.…”

Mycobacterium tuberculosis exploits the PPM1A signaling pathway to block host macrophage apoptosis

“…Kinome analysis provided us with a basic understanding of the protein-protein interaction network governed by PPM1A and allowed us to identify pharmacologically addressable targets to bring proof of principle that therapeutic restoration of the ability of macrophages to undergo apoptosis in response to Mtb infection can be achieved. Beyond this, we demonstrate that selective killing of Mtb -infected macrophages increased the efficacy of the first-line anti-tuberculosis drug rifampicin, which has been reported to be less effective against intracellular Mtb 26 27 due to inefficient penetration into cells 28 29 . As such, a “release and kill” strategy to deprive the replicative niche of Mtb by inducing Mtb -infected macrophage cell death would be a means to more efficiently expose the bacteria to already existing Mtb drugs, thereby shortening the currently long treatment times.…”

“…Apoptosis of infected macrophages stimulates the antibacterial response 5 and plays a significant role in promoting adaptive immunity 3 . Alternatively, given reports that several key TB drugs such as rifampicin 26 27 , streptomycin, and fluoroquinolones have decreased efficacy against intracellular Mtb likely due to penetration properties 29 , induction of apoptosis may also improve the ability of existing antimicrobial chemotherapy against Mtb .…”

“…Beyond this, drug-induced selective killing of Mtb -infected macrophages could likely increase the efficacy of existing anti- Mtb drugs as they gain better access to the bacteria. This approach would be particularly useful as adjunctive TB therapy since the commonly used anti- Mtb drugs rifampicin 26 27 , streptomycin, and fluoroquinolones having decreased efficacy against intracellular Mtb likely due to penetration properties 29 . Indeed, in a process we term “release and kill”, our results show that anisomycin induced killing of Mtb -infected macrophages removes the protective niche of the bacteria and increases the efficacy of rifampicin to kill Mtb at concentrations that are normally inactive against intracellular Mtb .…”

Drug permeation and metabolism in Mycobacterium tuberculosis: Prioritising local exposure as essential criterion in new TB drug development

“…Using a combination of New Zealand White rabbits, imaging mass spectrometry, three first-line anti-TB drugs (INH, RIF, and PZA), and the fluoroquinolone MXF, the group demonstrated that drug plasma concentration was indeed a poor proxy for drug concentration in TB lesions (8). The lack of data on how this might translate into humans combined with the absence of cellular protein binding data were acknowledged as weaknesses by the authors; nevertheless, this work prompted a growing appreciation of the need to include permeation studies in their drug development pipeline (16,129,130). …”