Contribution of the Nitroimidazoles PA-824 and TBA-354 to the Activity of Novel Regimens in Murine Models of Tuberculosis

Abstract

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.

Physiology, Biochemistry, and Applications of F420- and Fo-Dependent Redox Reactions

“…Delamanid (OPC-67683; approved for multidrug-resistant TB [MDR-TB]) (446), pretomanid (PA-824; phase III clinical trials) (33), and the next-generation TBA-354 (phase I clinical trials) (447,448) are recently developed nitroimidazole prodrugs that are activated by hydride transfer from F 420 H 2 (Fig. 20).…”

Visualization of the Charcoal Agar Resazurin Assay for Semi-quantitative, Medium-throughput Enumeration of Mycobacteria

“…CARA predictions should be rigorously evaluated using a standard CFU assay. The addition of 0.4% activated charcoal to Petri plates for CFU analysis may help improve correlation to CARA data, and may result in more accurate CFU counts, the magnitude of the correction generally being proportional to the compound's potency 21,22 . In a CFU assay, in addition to serial dilutions that often range up to 10 6 -fold, the agar plate typically dilutes molecules by an additional ~800-fold (10 μl onto 8 ml in a tri-style Petri plate).…”

“…The majority of tuberculosis drugs and clinical candidates bind activated charcoal rapidly and completely, with the exception of the aminoglycoside streptomycin 7 . Inclusion of activated charcoal in agar plates for CFU assays prevented bacterial growth inhibition, or bacterial kill, by carried-over TMC207 and PA-824 7,21,22 . Thus, by virtue of incorporating activated charcoal in the bacteriologic agar, the CARA is not dependent on serial dilutions of cells and test agent.…”

“…In buffer solutions in vitro, activated charcoal rapidly sequesters most of the standard drugs used to treat tuberculosis 7 . Activated charcoal in CARA microplates binds compounds that may carry over from an assay microplate, and this feature of the CARA eliminates the requirement to serially dilute assay well contents prior to enumeration 7,21,22 . The number of mycobacterial microcolonies on the agar surface of CARA microplates is estimated by the addition of resazurin, a blue dye, whose reduced form, resorufin, is a pink molecule whose fluorescence is measured by a spectrophotometry 23 .…”

Treatment Outcomes of Adolescents With Drug-Resistant Tuberculosis in Resource-Constrained Settings

“…Recently, there has been considerable progress in drug development. At present, several promising new or repurposed anti-TB drugs are in clinical trials (8): bedaquiline (TMC207), an inhibitor of Mycobacterium tuberculosis ATP synthase; delamanid (OPC-67683) and other nitroimidazoles (PA-824 and TBA-354) that inhibit mycolic acid synthesis; sutezolid (PNU-100480), a new oxazolidinone; faropenem, an orally bioavailable β-lactam antibiotic; and other new anti-TB agents (7,9,10). Besides individual compounds, new combinations of drugs are being tested in several human clinical trials (7,8).…”