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This study extends earlier reports regarding the in vitro and in vivo efficacies of the nitroimidazopyran PA-824 against Mycobacterium tuberculosis . PA-824 was tested in vitro against a broad panel of multidrug-resistant clinical isolates and was found to be highly active against all isolates (MIC < 1 μg/ml). The activity of PA-824 against M. tuberculosis was also assessed grown under conditions of oxygen depletion. PA-824 showed significant activity at 2, 10, and 50 μg/ml, similar to that of metronidazole, in a dose-dependent manner. In a short-course mouse infection model, the efficacy of PA-824 at 50, 100, and 300 mg/kg of body weight formulated in methylcellulose or cyclodextrin/lecithin after nine oral treatments was compared with those of isoniazid, rifampin, and moxifloxacin. PA-824 at 100 mg/kg in cyclodextrin/lecithin was as active as moxifloxacin at 100 mg/kg and isoniazid at 25 mg/kg and was slightly more active than rifampin at 20 mg/kg. Long-term treatment with PA-824 at 100 mg/kg in cyclodextrin/lecithin reduced the bacterial load below 500 CFU in the lungs and spleen. No significant differences in activity between PA-824 and the other single drug treatments tested (isoniazid at 25 mg/kg, rifampin at 10 mg/kg, gatifloxacin at 100 mg/kg, and moxifloxacin at 100 mg/kg) could be observed. In summary, its good activity in in vivo models, as well as its activity against multidrug-resistant M. tuberculosis and against M. tuberculosis isolates in a potentially latent state, makes PA-824 an attractive drug candidate for the therapy of tuberculosis. These data indicate that there is significant potential for effective oral delivery of PA-824 for the treatment of tuberculosis.

This study describes an in vivo model for evaluating the sterilizing activity of compounds against persisting Mycobacterium tuberculosis . The initial treatment with isoniazid and rifampin in granulocyte-macrophage colony-stimulating factor gene-disrupted mice reduced the number of bacteria more than 99% within 3 weeks. A subsequent treatment with individual drugs was performed to assess their activity on the 1% of remaining bacilli and disease relapse.

A novel subclass of quinolones, 2-pyridones, showed potent activity against Mycobacterium tuberculosis , with KRQ-10018 being an early lead. KRQ-10018 showed better activity in vitro against M. tuberculosis versus moxifloxacin. In vivo efficacy of KRQ-10018 at 300 mg/kg of body weight was similar to that of isoniazid at 25 mg/kg, but showed less activity than moxifloxacin at 300 mg/kg.

The assessment of physiochemical and pharmacological properties at early stages of drug discovery can accelerate the conversion of hits and leads into candidates for further development. A strategy for streamlined evaluation of compounds against Mycobacterium tuberculosis in the early preclinical stage is presented in this report. As a primary assay to rapidly select experimental compounds with sufficient in vitro activity, the growth inhibition microtiter plate assay was devised as an alternative to current methods. This microdilution plate assay is a liquid culture method based on spectrophotometric readings of the bacillary growth. The performance of this method was compared to the performance of two established susceptibility methods using clinical available tuberculosis (TB) drugs. Data generated from all three assays were similar for all of the tested compounds. A second simple bioassay was devised to assess the oral bioavailability of compounds prior to extensive in vivo efficacy testing. The bioassay estimates drug concentrations in collected serum samples by a microdilution MIC plate method using M. tuberculosis . In the same assay, the MIC of the compound is also determined in the presence of 10% mouse serum as an indication of protein binding. The method was validated using different clinically available TB drugs, and results are discussed in this report. With these methodological advances, screening of compounds against tuberculosis in the preclinical phase will be rapid, can be adapted to semi-high-throughput screening, and will add relevant physicochemical and basic pharmacological criteria to the decision process of drug discovery.