Sterilizing Activity of Novel TMC207- and PA-824-Containing Regimens in a Murine Model of Tuberculosis

Abstract

To truly transform the landscape of tuberculosis treatment, novel regimens containing at least 2 new drugs are needed to simplify the treatment of both drug-susceptible and drug-resistant forms of tuberculosis. As part of an ongoing effort to evaluate novel drug combinations for treatment-shortening potential in a murine model, we performed two long-term, relapse-based experiments. In the first experiment, TMC207 plus pyrazinamide, alone or in combination with any third drug, proved superior to the first-line regimen including rifampin, pyrazinamide, and isoniazid. On the basis of CFU counts at 1 month, clofazimine proved to be the best third drug combined with TMC207 and pyrazinamide, whereas the addition of PA-824 was modestly antagonistic. Relapse results were inconclusive due to the low rate of relapse in all test groups. In the second experiment evaluating 3-drug combinations composed of TMC207, pyrazinamide, PA-824, moxifloxacin, and rifapentine, TMC207 plus pyrazinamide plus either rifapentine or moxifloxacin was the most effective, curing 100% and 67% of the mice treated, respectively, in 2 months of treatment. Four months of the first-line regimen did not cure any mice, whereas the combination of TMC207, PA-824, and moxifloxacin cured 50% of the mice treated. The results reveal new building blocks for novel regimens with the potential to shorten the duration of treatment for both drug-susceptible and drug-resistant tuberculosis, including the combination of TMC207, pyrazinamide, PA-824, and a potent fluoroquinolone.New drugs with potent activity against Mycobacterium tuberculosis are needed to shorten the duration of treatment for tuberculosis (TB) and facilitate the global implementation of directly observed therapy (25). Several new drugs in clinical development have demonstrated the potential to shorten TB treatment in animal models (13,20,23,24,29,35) and even clinical trials (6,9,30). To truly transform the TB treatment landscape, novel regimens containing 2 or more new drugs are needed to simplify the treatment of drug-susceptible and multidrug-resistant (MDR) or extensively drug-resistant (XDR) TB alike. Therefore, a new paradigm is needed in which new regimens, rather than new drugs, become the focus of both preclinical and clinical development programs (31).The Global Alliance for TB Drug Development (TB Alliance) recently launched a phase II study of the extended (to 2 weeks) early bactericidal activity of the novel regimen of PA-824, pyrazinamide (PZA), and moxifloxacin (MXF), a combination, which contains neither rifampin (RIF) nor isoniazid (INH) yet was superior to the current first-line regimen of RIF-PZA-INH in mice (23). While the drugs in this regimen should be active against the majority of MDR-TB isolates, PZA and MXF are unlikely to be active against XDR TB. Moreover, both PZA resistance and fluoroquinolone resistance are on the rise in MDR TB patients (1, 9, 10, 21). Replacement of one or both of these agents with a new drug with a novel mechanism of action may lead to short-course...

Contribution of Moxifloxacin or Levofloxacin in Second-Line Regimens with or without Continuation of Pyrazinamide in Murine Tuberculosis

“…On the other hand, continuing Z in the face of resistance may not provide any treatment-shortening benefit while increasing the risk of intolerance and/or toxicity, as observed with fluoroquinolone-Z combinations used to treat latent TB infection among MDR-TB contacts (46)(47)(48)(49). Given the favorable interactions between Z and new TB drugs in development and rising concerns over Z resistance among MDR-TB isolates, improved susceptibility testing methods for Z, including genotypic resistance testing, will continue to require attention in the future (50)(51)(52)(53).…”

The epidemiology, pathogenesis, transmission, diagnosis, and management of multidrug-resistant, extensively drug-resistant, and incurable tuberculosis

“…In preclinical testing, bedaquiline plus pyrazinamide had better sterilising activity than rifampicin, pyrazinamide, and isoniazid. 362 Bedaquiline displays notable synergy with pyrazinamide. 362 Spontaneous mutations conferring resistance to bedaquiline occur in approximately 1 in 10⁷ or 10⁸ bacteria (similar to rifampicin).…”

“…362 Bedaquiline displays notable synergy with pyrazinamide. 362 Spontaneous mutations conferring resistance to bedaquiline occur in approximately 1 in 10⁷ or 10⁸ bacteria (similar to rifampicin). 363 High-level resistance to bedaquiline results from mutations in the ATP synthase binding site, but such mutants have yet to be observed in clinical isolates.…”

Assessment of Clofazimine Activity in a Second-Line Regimen for Tuberculosis in Mice

“…The appropriate dilutions of the homogenates were plated on 7H11 agar enriched with 10% oleic acid-albumin-dextrose-catalase and rendered selective by supplementation with cycloheximide (10 mg/ml), carbenicillin (50 mg/ml), polymyxin B (25 mg/ml), and trimethoprim (20 mg/ml) to prevent contamination with minimal impact on M. tuberculosis growth (17). To detect and limit the consequences of clofazimine carryover, lung homogenates from the clofazimine-treated mice were plated in duplicate on 7H11 selective agar with and without 0.4% (weight/volume) activated charcoal, as Tasneen and colleagues have demonstrated that supplementation of the agar with this percentage of charcoal is effective in adsorbing clofazimine and minimizing carryover of the drug (18). For assessing relapse after treatment cessation in mice that received clofazimine, the lung homogenate was inoculated onto plain and charcoal-containing 7H11 agar plates.…”