Advancing host-directed therapy for tuberculosis

Preliminary preclinical and observational studies suggest the potential utility of metformin as an adjunctive, host-directed agent for treatment of tuberculosis (TB). In this study, we sought to investigate the bactericidal and sterilizing activities of human-like exposures of metformin when given in combination with the firstline regimen against chronic tuberculosis in BALB/c mice. Mice receiving metformin adjunctive therapy had similar lung bacillary burdens with control mice during treatment, and the proportion of mice with microbiological relapse was similar between the two groups.KEYWORDS Mycobacterium tuberculosis, metformin, standard first-line regimen, BALB/c, bactericidal, sterilizing, host-directed therapy, relapse, cure, Denver regimen H ost-directed therapy (HDT) may offer expanded therapeutic options for improving tuberculosis (TB) treatment (1-5). Metformin (MetF), an AMP-activated protein kinase (AMPK)-activating drug for type 2 diabetes (DM), was reported to inhibit intracellular growth of mycobacteria by inducing reactive oxygen species and to enhance the efficacy of conventional anti-TB drugs in mouse models of acute and chronic TB; its use was associated with decreased TB severity and improved clinical outcomes in a retrospective analysis of 220 patients with DM and TB (6). In another retrospective study, Srujitha et al. showed that MetF use was associated with a 3.9-fold reduction in TB incidence among patients with DM (7). Based on these findings, we hypothesized that MetF adjunctive therapy would enhance the bactericidal and sterilizing activities of the standard first-line treatment (8, 9) against chronic TB infection in mice and shorten the duration of curative treatment as assessed by microbiological relapse.All animal-related procedures were approved by the Johns Hopkins University (JHU) School of Medicine Animal Care and Use Committee. A total of 170 female BALB/c mice aged 4 to 6 weeks (Charles River Labs, Wilmington, MA) were aerosol infected with Mycobacterium tuberculosis H37Rv (JHU) using the inhalation exposure system (GlasCol, Terre Haute, IN) calibrated to deliver ϳ10 2 CFU per mouse lung in two consecutive runs. After aerosol infection, the mice were randomized into the two treatment groups. Six weeks postinfection, the mice were treated daily (5 days/week) via esophageal cannulation with human-equivalent doses of rifampin (10 mg/kg), isoniazid (10 mg/kg), pyrazinamide (150 mg/kg), and ethambutol (100 mg/kg) (RHZE) with or without MetF (250 mg/kg) for up to 6 months (2, 10, 11). For the first 2 months of treatment, the mice received RHZE and, for the remaining 4 months, only rifampin and isoniazid (RH) to mirror the first-line regimen in humans. The rifampin dose preceded that of the other drugs by at least 1 h to prevent pharmacokinetic antagonism (12, 13). The dose of MetF (6) and is estimated (14) to be equivalent to 25 mg/kg in humans (15), which is well tolerated (15, 16). Groups of 5 mice were sacrificed on the day after infection, on the day of treatment initi...

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confidence: 99%

Metformin Adjunctive Therapy Does Not Improve the Sterilizing Activity of the First-Line Antitubercular Regimen in Mice

Dutta

Pinn

Karakousis

2017

“…Recently, there has been significant interest in host-directed therapy to treat TB (71). Although BCG vaccination does not enhance the bactericidal activity of chemotherapy in the murine model (72), a DNA vaccine expressing heat shock protein 65 has been shown to synergize with conventional antitubercular drugs, further reducing the bacterial burden in the lungs of M. tuberculosis-infected mice or nonhuman primates (72,73).…”

Section: Discussionmentioning

confidence: 99%

Stringent Response Factors PPX1 and PPK2 Play an Important Role in Mycobacterium tuberculosis Metabolism, Biofilm Formation, and Sensitivity to Isoniazid In Vivo

Chuang

Dutta

Hung

et al. 2016

g Mycobacterium tuberculosis remains a global health threat largely due to the lengthy duration of curative antibiotic treatment, contributing to medical nonadherence and the emergence of drug resistance. This prolonged therapy is likely due to the presence of M. tuberculosis persisters, which exhibit antibiotic tolerance. Inorganic polyphosphate [poly(P)] is a key regulatory molecule in the M. tuberculosis stringent response mediating antibiotic tolerance. The polyphosphate kinase PPK1 is responsible for poly(P) synthesis in M. tuberculosis, while the exopolyphosphatases PPX1 and PPX2 and the GTP synthase PPK2 are responsible for poly(P) hydrolysis. In the present study, we show by liquid chromatography-tandem mass spectrometry that poly(P)-accumulating M. tuberculosis mutant strains deficient in ppx1 or ppk2 had significantly lower intracellular levels of glycerol-3-phosphate (G3P) and 1-deoxy-xylulose-5-phosphate. Real-time PCR revealed decreased expression of genes in the G3P synthesis pathway in each mutant. The ppx1-deficient mutant also showed a significant accumulation of metabolites in the tricarboxylic acid cycle, as well as altered arginine and NADH metabolism. Each poly(P)-accumulating strain showed defective biofilm formation, while deficiency of ppk2 was associated with increased sensitivity to plumbagin and meropenem and deficiency of ppx1 led to enhanced susceptibility to clofazimine. A DNA vaccine expressing ppx1 and ppk2, together with two other members of the M. tuberculosis stringent response, M. tuberculosis rel and sigE, did not show protective activity against aerosol challenge with M. tuberculosis, but vaccine-induced immunity enhanced the killing activity of isoniazid in a murine model of chronic tuberculosis. In summary, poly(P)-regulating factors of the M. tuberculosis stringent response play an important role in M. tuberculosis metabolism, biofilm formation, and antibiotic sensitivity in vivo.

“…In recent years, increased focus has been placed on characterizing host mechanisms/pathways exploited by bacteria during pathogenesis. Drugs able to block these pathways represent novel therapeutic options and also reduce the likelihood of the development of resistance, unlike antibiotics (5)(6)(7). Some recent studies utilized such drug-repurposing approaches to identify both novel bactericidal and host-directed drugs as potential therapeutics against pathogens, such as Ebola virus, Borrelia burgdorferi, Coxiella burnetii, and Legionella pneumophila (5,(8)(9)(10).…”

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confidence: 99%

New Role for FDA-Approved Drugs in Combating Antibiotic-Resistant Bacteria

Andersson

Fitts

Kirtley

et al. 2016

h Antibiotic resistance in medically relevant bacterial pathogens, coupled with a paucity of novel antimicrobial discoveries, represents a pressing global crisis. Traditional drug discovery is an inefficient and costly process; however, systematic screening of Food and Drug Administration (FDA)-approved therapeutics for other indications in humans offers a rapid alternative approach. In this study, we screened a library of 780 FDA-approved drugs to identify molecules that rendered RAW 264.7 murine macrophages resistant to cytotoxicity induced by the highly virulent Yersinia pestis CO92 strain. Of these compounds, we identified 94 not classified as antibiotics as being effective at preventing Y. pestis-induced cytotoxicity. A total of 17 prioritized drugs, based on efficacy in in vitro screens, were chosen for further evaluation in a murine model of pneumonic plague to delineate if in vitro efficacy could be translated in vivo. Three drugs, doxapram (DXP), amoxapine (AXPN), and trifluoperazine (TFP), increased animal survivability despite not exhibiting any direct bacteriostatic or bactericidal effect on Y. pestis and having no modulating effect on crucial Y. pestis virulence factors. These findings suggested that DXP, AXPN, and TFP may modulate host cell pathways necessary for disease pathogenesis. Finally, to further assess the broad applicability of drugs identified from in vitro screens, the therapeutic potential of TFP, the most efficacious drug in vivo, was evaluated in murine models of Salmonella enterica serovar Typhimurium and Clostridium difficile infections. In both models, TFP treatment resulted in increased survivability of infected animals. Taken together, these results demonstrate the broad applicability and potential use of nonantibiotic FDA-approved drugs to combat respiratory and gastrointestinal bacterial pathogens.