In Vitro and In Vivo Activities of Three Oxazolidinones against Nonreplicating Mycobacterium tuberculosis

Abstract

cOxazolidinones represent a new class of antituberculosis drugs that exert their function by inhibiting protein synthesis. Here, we compared the activities of three oxazolidinones, linezolid, PNU-100480, and AZD5847, against latent tuberculosis using a simple model employing the streptomycin-starved Mycobacterium tuberculosis strain 18b. The in vitro drug susceptibility results showed that the three oxazolidinones had a bacteriostatic effect against actively growing bacilli but potent bactericidal activity against nonreplicating cells. In the murine model of latent infection with M. tuberculosis 18b, the efficacy of the three compounds varied greatly. Indeed, AZD5847 or its prodrug exhibited no activity or only modest activity, respectively, after 2 months of treatment, whereas both linezolid and PNU-100480 were effective against latent bacilli in mice and showed promising outcomes in combination therapy with rifampin. Moreover, the potency of PNU-100480 was significantly greater than that of linezolid, making it an attractive drug candidate in the development of new combination therapies for latent tuberculosis. Despite the availability of effective chemotherapy, tuberculosis (TB) is still a major global health problem, and Ͼ8.6 million cases of active disease and 1.4 million deaths were reported in 2012 (1). Moreover, approximately one-third of the world's population is latently infected with Mycobacterium tuberculosis and at risk of reactivation (1). The slow growth and dormancy of M. tuberculosis contribute to the chronic nature of the infection, and effective treatment of active disease requires lengthy multidrug regimens. This situation is now worsened by the increasing emergence of multidrug-resistant (MDR), extensively drug-resistant (XDR), and even totally drug-resistant M. tuberculosis strains (1), thus underscoring the urgent need for new molecules with potent activity against latent M. tuberculosis and no cross-resistance with existing therapeutic agents.Oxazolidinones are one of the only three new classes of antibiotics that have been approved by the Food and Drug Administration (FDA) in the last 35 years (2). Oxazolidinones inhibit bacterial protein synthesis via competitive binding to the 23S rRNA in the catalytic site of the bacterial 50S ribosomes (3, 4). Linezolid (LZD), the first oxazolidinone that entered clinical use, exhibits bacteriostatic activity against M. tuberculosis with an MIC of less than 1 g/ml (5) and has been used against MDR/XDR TB cases (4, 6, 7). However, long-term administration of LZD may cause severe side effects such as anemia, thrombocytopenia, and peripheral neuropathy (8). PNU-100480 (sutezolid; PNU) is an oxazolidinone analogue that has been reported to have an improved safety profile compared to LZD (2). PNU has an MIC similar to that of LZD for M. tuberculosis in vitro but has more potent bactericidal activity in ex vivo whole-blood cultures and in a murine model of TB (9-11). In mice, addition of PNU not only enhanced the bactericidal activity during the initial ph...

Mode of Action of Clofazimine and Combination Therapy with Benzothiazinones against Mycobacterium tuberculosis

“…In addition, the residual metabolism of dormant M. tuberculosis presumably requires some de novo RNA and protein synthesis for survival during this phase or for reactivation (24). Given the sensitivity of nonreplicating bacteria to inhibitors of these processes (14,25), combining PBTZ169 and other drugs active against nonreplicating bacilli, such as BDQ, CZM, oxazolidinones, or pyrazinamide, offers an attractive foundation for a new TB regimen. In the present study, the combination of PBTZ169 and CZM was extremely potent in a murine model of chronic TB, and similar results are to be expected with the newer riminophenazines.…”

Early Bactericidal Activity of AZD5847 in Patients with Pulmonary Tuberculosis

“…The drug has also been shown to have activity in murine models of TB (9). AZD5847 has an MIC of 1.0 g/ml against both drug-susceptible and drugresistant strains of M. tuberculosis (10).…”

“…AZD5847 has an MIC of 1.0 g/ml against both drug-susceptible and drugresistant strains of M. tuberculosis (10). AZD5847 is orally bioavailable, with bioavailability increasing after food intake; is 80% protein bound; has a half-life of 7 to 11 h in healthy human subjects; and is excreted in the feces (9). In vitro studies have shown the drug to have killing kinetics against M. tuberculosis superior to those of linezolid and to have additive activity when used in combination with other anti-TB drugs (9).…”

“…AZD5847 is orally bioavailable, with bioavailability increasing after food intake; is 80% protein bound; has a half-life of 7 to 11 h in healthy human subjects; and is excreted in the feces (9). In vitro studies have shown the drug to have killing kinetics against M. tuberculosis superior to those of linezolid and to have additive activity when used in combination with other anti-TB drugs (9). The drug has a carboxylic acid metabolite that is also active against M. tuberculosis.…”

Bioluminescence for Assessing Drug Potency against Nonreplicating Mycobacterium tuberculosis

“…The streptomycin (STR)-dependent M. tuberculosis strain 18b has been extensively validated in our laboratory as a simple but robust model for testing drug potency against nonreplicating bacilli in vitro and in vivo (4)(5)(6). We demonstrated an absence of growth upon STR removal, an extremely stable STR-dependent phenotype, good agreement between in vitro and in vivo drug efficacy studies, consistency with previously developed models of nonreplicating persistence, and, finally, suitability for highthroughput screening (HTS).…”