Contribution of Oxazolidinones to the Efficacy of Novel Regimens Containing Bedaquiline and Pretomanid in a Mouse Model of Tuberculosis.

New regimens based on two or more novel agents are sought to shorten or simplify treatment of tuberculosis (TB). Pretomanid (PMD) is a nitroimidazole in phase 3 trials that has significant bactericidal activity alone and in combination with bedaquiline (BDQ) and/or pyrazinamide (PZA). We previously showed that the novel combination of BDQ+PMD plus the oxazolidinone sutezolid (SZD) had sterilizing activity superior to that of the first-line regimen in a murine model of TB. The present experiments compared the activity of different oxazolidinones in combination with BDQ+PMD with or without PZA in the same model. The 3-drug regimen of BDQ+PMD plus linezolid (LZD) had sterilizing activity approaching that of BDQ+PMD+SZD and superior to that of the first-line regimen. The addition of PZA further enhanced activity. Reducing the duration of LZD to 1 month did not significantly affect the activity of the regimen. Halving the LZD dose or replacing LZD with RWJ-416457 modestly reduced activity over the first month but not after 2 months. AZD5847 and tedizolid also increased the bactericidal activity of BDQ+PMD, but they were less effective than the other oxazolidinones. These results provide optimism for safe, short-course oral regimens for drug-resistant TB that may also be superior to the current first-line regimen for drug-susceptible TB.

Contribution of the nitroimidazoles PA-824 and TBA-354 to the activity of novel regimens in murine models of tuberculosis.

New regimens based on two or more novel agents are sought in order to shorten or simplify the treatment of both drug-susceptible and drug-resistant forms of tuberculosis. PA-824 is a nitroimidazo-oxazine now in phase II trials and has shown significant early bactericidal activity alone and in combination with the newly approved agent bedaquiline or with pyrazinamide with or without moxifloxacin. While the development of PA-824 continues, a potential next-generation derivative, TBA-354, has been discovered to have in vitro potency superior to that of PA-824 and greater metabolic stability than that of the other nitroimidazole derivative in clinical development, delamanid. In the present study, we compared the activities of PA-824 and TBA-354 as monotherapies in murine models of the initial intensive and continuation phases of treatment, as well as in combination with bedaquiline plus pyrazinamide, sutezolid, and/or clofazimine. The monotherapy studies demonstrated that TBA-354 is 5 to 10 times more potent than PA-824, but selected mutants are cross-resistant to PA-824 and delamanid. The combination studies revealed that TBA-354 is 2 to 4 times more potent than PA-824 when combined with bedaquiline, and when administered at a dose equivalent to that of PA-824, TBA-354 demonstrated superior sterilizing efficacy. Perhaps most importantly, the addition of either nitroimidazole significantly improved the sterilizing activities of bedaquiline and sutezolid, with or without pyrazinamide, confirming the value of each agent in this potentially universally active short-course regimen.

Potent rifamycin-sparing regimen cures guinea pig tuberculosis as rapidly as the standard regimen.

Strategies involving new drug combinations, as well as new uses of existing drugs, are urgently needed to reduce the time required to cure patients with drug-sensitive or multidrug-resistant (MDR) tuberculosis (TB). We compared the sterilizing activity of the standard first-line antitubercular regimen, rifampin-isoniazid-pyrazinamide (RHZ), with that of the novel regimen PA-824-moxifloxacin-pyrazinamide (PaMZ), which is currently being studied in clinical trials (NCT01498419), in the guinea pig model of chronic TB infection, in which animals develop necrotic granulomas histologically resembling their human counterparts. Guinea pigs were aerosol infected with ~2 log10 bacilli of wild-type Mycobacterium tuberculosis H37Rv, and antibiotic treatment was initiated 6 weeks after infection. Separate groups of animals received RHZ, PaMZ, or single or two-drug components of the latter regimen administered at human-equivalent doses 5 days/week for a total of 8 weeks. Relapse rates were assessed 3 months after discontinuation of treatment to determine the sterilizing activity of each combination regimen. PaMZ given at human-equivalent doses was safe and well tolerated for the entire treatment period and rendered guinea pig lungs culture negative more rapidly than RHZ did. After 1 month of treatment, 80% and 50% of animals in the RHZ and PaMZ groups, respectively, had lung culture-positive relapse. Both combination regimens prevented microbiological relapse when administered for a total of 2 months. Our data support the use of PaMZ as a novel isoniazid- and rifamycin-sparing regimen suitable for treatment of both drug-sensitive TB and MDR-TB.

Dose-ranging comparison of rifampin and rifapentine in two pathologically distinct murine models of tuberculosis.

In previous experiments, replacing the 10-mg/kg of body weight daily dose of rifampin with 7.5 to 10 mg/kg of rifapentine in combinations containing isoniazid and pyrazinamide reduced the duration of treatment needed to cure tuberculosis in BALB/c mice by approximately 50% due to rifapentine's more potent activity and greater drug exposures obtained. In the present study, we performed dose-ranging comparisons of the bactericidal and sterilizing activities of rifampin and rifapentine, alone and in combination with isoniazid and pyrazinamide with or without ethambutol, in BALB/c mice and in C3HeB/FeJ mice, which develop necrotic lung granulomas after infection with Mycobacterium tuberculosis. Each rifamycin demonstrated a significant increase in sterilizing activity with increasing dose. Rifapentine was roughly 4 times more potent in both mouse strains. These results reinforce the rationale for ongoing clinical trials to ascertain the highest well-tolerated doses of rifampin and rifapentine. This study also provides an important benchmark for the efficacy of the first-line regimen in C3HeB/FeJ mice, a strain in which the lung lesions observed after M. tuberculosis infection may better represent the pathology of human tuberculosis.

Rifapentine is not more active than rifampin against chronic tuberculosis in guinea pigs.

Rifamycins are key sterilizing drugs in the current treatment of active tuberculosis (TB). Daily dosing of rifapentine (P), a potent rifamycin with high intracellular accumulation, in place of rifampin (R) in the standard antitubercular regimen significantly shortens the duration of treatment needed to prevent relapse in a murine model of active TB. We undertook the current study to compare directly the activities of human-equivalent doses of P and R in a guinea pig model of chronic TB, in which bacilli are predominantly extracellular within human-like necrotic granulomas. Hartley strain guinea pigs were aerosol infected with ~200 bacilli of Mycobacterium tuberculosis H37Rv, and treatment given 5 days/week was initiated 6 weeks later. R at 100 mg/kg of body weight and P at 100 mg/kg were given orally alone or in combination with isoniazid (H) at 60 mg/kg and pyrazinamide (Z) at 300 mg/kg. Culture-positive relapse was assessed in subgroups of guinea pigs after completion of 1 and 2 months of treatment. Human-equivalent doses of R and P showed equivalent bactericidal activity when used alone and in combination therapy. In guinea pigs treated with rifampin, isoniazid, and pyrazinamide (RHZ) or PHZ, microbiological relapse occurred in the lungs of 8/10 animals treated for 1 month and in 0/10 animals treated for 2 months. Substitution of P for R in the standard antitubercular regimen did not shorten the time to cure in this guinea pig model of chronic TB. Data from ongoing clinical trials comparing the activity of these two drugs are awaited to determine the relevance of the guinea pig TB model in preclinical drug screening.

Sterilizing activities of novel combinations lacking first- and second-line drugs in a murine model of tuberculosis.

Novel oral regimens composed of new drugs with potent activity against Mycobacterium tuberculosis and no cross-resistance with existing agents are needed to shorten and simplify treatment for both drug-susceptible and drug-resistant tuberculosis. As part of a continuing 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, several 3- and 4-drug combinations containing new agents currently in phase 2/3 trials (TMC207 [bedaquiline], PA-824 and PNU-100480 [sutezolid], and/or clofazimine) proved superior to the first-line regimen of rifampin, pyrazinamide, and isoniazid. TMC207 plus PNU-100480 was the most effective drug pair. In the second experiment, in which 3- and 4-drug combinations composed of TMC207 and pyrazinamide plus rifapentine, clofazimine, PNU-100480, or both rifapentine and clofazimine were evaluated, the rank order of drugs improving the sterilizing activity of TMC207 and pyrazinamide was as follows: rifapentine plus clofazimine ≥ clofazimine ≥ rifapentine > PNU-100480. The results revealed potential new building blocks for universally active short-course regimens for drug-resistant tuberculosis. The inclusion of pyrazinamide against susceptible isolates may shorten the duration of treatment further.

Sterilizing activity of novel TMC207- and PA-824-containing regimens in a murine model of tuberculosis.

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.

Activity of the fluoroquinolone DC-159a in the initial and continuation phases of treatment of murine tuberculosis.

DC-159a is a new fluoroquinolone with more potent in vitro activity than available fluoroquinolones against both drug-susceptible and fluoroquinolone-resistant Mycobacterium tuberculosis. Here, we report that DC-159a displays pharmacokinetics similar to those of moxifloxacin yet is more active than moxifloxacin during both the initial and continuation phases of treatment in a murine model. These results warrant further preclinical evaluation of DC-159a in selected drug combinations against drug-susceptible and fluoroquinolone-resistant tuberculosis.

A Novel indole compound that inhibits Pseudomonas aeruginosa growth by targeting MreB is a substrate for MexAB-OprM.

Drug efflux systems contribute to the intrinsic resistance of Pseudomonas aeruginosa to many antibiotics and biocides and hamper research focused on the discovery and development of new antimicrobial agents targeted against this important opportunistic pathogen. Using a P. aeruginosa PAO1 derivative bearing deletions of opmH, encoding an outer membrane channel for efflux substrates, and four efflux pumps belonging to the resistance nodulation/cell division class including mexAB-oprM, we identified a small-molecule indole-class compound (CBR-4830) that is inhibitory to growth of this efflux-compromised strain. Genetic studies established MexAB-OprM as the principal pump for CBR-4830 and revealed MreB, a prokaryotic actin homolog, as the proximal cellular target of CBR-4830. Additional studies establish MreB as an essential protein in P. aeruginosa, and efflux-compromised strains treated with CBR-4830 transition to coccoid shape, consistent with MreB inhibition or depletion. Resistance genetics further suggest that CBR-4830 interacts with the putative ATP-binding pocket in MreB and demonstrate significant cross-resistance with A22, a structurally unrelated compound that has been shown to promote rapid dispersion of MreB filaments in vivo. Interestingly, however, ATP-dependent polymerization of purified recombinant P. aeruginosa MreB is blocked in vitro in a dose-dependent manner by CBR-4830 but not by A22. Neither compound exhibits significant inhibitory activity against mutant forms of MreB protein that bear mutations identified in CBR-4830-resistant strains. Finally, employing the strains and reagents prepared and characterized during the course of these studies, we have begun to investigate the ability of analogues of CBR-4830 to inhibit the growth of both efflux-proficient and efflux-compromised P. aeruginosa through specific inhibition of MreB function.

Molecular validation of LpxC as an antibacterial drug target in Pseudomonas aeruginosa.

LpxC [UDP-3-O-(R-3-hydroxymyristoyl)-GlcNAc deacetylase] is a metalloamidase that catalyzes the first committed step in the biosynthesis of the lipid A component of lipopolysaccharide. A previous study (H. R. Onishi, B. A. Pelak, L. S. Gerckens, L. L. Silver, F. M. Kahan, M. H. Chen, A. A. Patchett, S. M. Galloway, S. A. Hyland, M. S. Anderson, and C. R. H. Raetz, Science 274:980-982, 1996) identified a series of synthetic LpxC-inhibitory molecules that were bactericidal for Escherichia coli. These molecules did not inhibit the growth of Pseudomonas aeruginosa and were therefore not developed further as antibacterial drugs. The inactivity of the LpxC inhibitors for P. aeruginosa raised the possibility that LpxC activity might not be essential for all gram-negative bacteria. By placing the lpxC gene of P. aeruginosa under tight control of an arabinose-inducible promoter, we demonstrated the essentiality of LpxC activity for P. aeruginosa. It was found that compound L-161,240, the most potent inhibitor from the previous study, was active against a P. aeruginosa construct in which the endogenous lpxC gene was inactivated and in which LpxC activity was supplied by the lpxC gene from E. coli. Conversely, an E. coli construct in which growth was dependent on the P. aeruginosa lpxC gene was resistant to the compound. The differential activities of L-161,240 against the two bacterial species are thus the result primarily of greater potency toward the E. coli enzyme rather than of differences in the intrinsic resistance of the bacteria toward antibacterial compounds due to permeability or efflux. These data validate P. aeruginosa LpxC as a target for novel antibiotic drugs and should help direct the design of inhibitors against clinically important gram-negative bacteria.