Objectives In this study, we sought to compare the sterilizing activity of human-equivalent doses of the ‘Denver regimen’ against acute tuberculosis (TB) infection in the standard mouse model and in ...the guinea pig. Methods Pharmacokinetic studies in guinea pigs were used to establish human-equivalent doses for rifampicin, isoniazid and pyrazinamide. Guinea pigs and mice were aerosol-infected with Mycobacterium tuberculosis CDC1551 and treatment was started 2 weeks later with rifampicin/isoniazid/pyrazinamide for up to 6 months. For the first 2 weeks of therapy, the dosing frequency was 5 days/week, and for the remaining period, twice weekly. Treatment was discontinued in groups of 30 mice and 10 guinea pigs at 5 months and at 6 months, and these animals were held for a further 3 months in order to assess relapse rates. Results Guinea pig lungs became culture-negative after 3 months of predominantly twice-weekly treatment and relapse rates were 0% (0/10) both after 5 months and after 6 months of treatment. In contrast, all mice remained culture-positive despite 6 months of the same treatment, and 93% (28/30) and 69% (20/29) of mice relapsed after treatment for 5 and 6 months, respectively. Conclusions Treatment with rifampicin/isoniazid/pyrazinamide administered at human-equivalent doses is much more potent against acute TB infection in guinea pigs than in mice. Our findings have important implications for the use of alternative animal models in testing novel TB drug regimens and for modelling M. tuberculosis persistence.
Mycobacterium xenopi is a common agent of non-tuberculous mycobacterial lung diseases in Europe. However, an optimal treatment regimen for M. xenopi infection has not yet been established. ...Appropriate in vitro and in vivo model systems are needed for characterization of the activity of potential drugs and drug combinations against M. xenopi.
We utilized three experimental platforms to analyse the anti-M. xenopi activity of single and combination drug regimens. First, we determined the bacteriostatic and bactericidal activities of drugs alone and in combination in vitro. Second, we used serum from treated mice to evaluate drug activities ex vivo. Third, we analysed M. xenopi growth in four strains of mice (BALB/c, C57BL/6, beige and athymic nude) and developed a mouse model of chemotherapy for this infection.
Two-drug combinations of ethambutol with rifampicin, rifapentine or moxifloxacin, and of clarithromycin with moxifloxacin were bactericidal in vitro, and the combination of ethambutol and rifampicin with either clarithromycin or moxifloxacin showed significant bactericidal activity ex vivo. Nude mice were the most susceptible strain to M. xenopi infection, and in this model amikacin-containing regimens were the most effective against M. xenopi. No difference in activity was found between regimens containing clarithromycin and moxifloxacin in vivo.
The ethambutol/rifampicin combination with clarithromycin or moxifloxacin had significant bactericidal activity against M. xenopi. The nude mouse, being highly susceptible to M. xenopi, can be utilized for in vivo chemotherapy studies for this infection.
Daily rifapentine plus isoniazid-pyrazinamide in mice infected with Mycobacterium tuberculosis produces cure in 3 months. Whether cure corresponds to latent infection contained by host immunity or ...true tissue sterilization is unknown.
To determine the length of treatment with rifapentine-isoniazid-pyrazinamide or rifampin-isoniazid-pyrazinamide needed to prevent relapse in immune-deficient mice.
Aerosol-infected BALB/c and nude mice were treated 5 days per week with either 2 months of the rifapentine-based regimen followed by rifapentine-isoniazid up to 12 months or the same regimen with rifampin instead of rifapentine. Cultures of lung homogenates were performed during the first 3 months and then every 3 months. Relapse rates were assessed after 3, 6, 9, and 12 months of treatment in BALB/c (± 1 mo of cortisone) and nude mice.
All rifapentine-treated mice were lung culture-negative at 3 months but 13% of BALB/c that received cortisone and 73% of nude mice relapsed. After 6, 9, and 12 months of treatment no mouse relapsed. Rifampin-treated BALB/c mice remained culture positive at 3 months. All were culture negative at 6, 9, and 12 months. None, including those receiving cortisone, relapsed. Rifampin-treated nude mice harbored more than 4 log(10) lung cfu at Month 2 and approximately 6 log(10) cfu with isoniazid resistance at Month 3. A supplementary experiment demonstrated that 7 days a week treatment did not prevent isoniazid resistance, whereas addition of ethambutol did.
In nude mice, sterilization of tuberculosis is obtained with rifapentine-containing treatment, whereas failure with development of isoniazid resistance is obtained with rifampin-containing treatment.
The objective of this review is to report evidence about the efficacy and potential of currently licensed drugs and new molecules beyond pre-clinical development for improving the chemotherapy of ...tuberculosis (TB). Rifapentine, a rifamycin with low minimum inhibitory concentration, long half-life and potent sterilizing activity in mice did not confirm its potential in a recent short-term clinical trial and is being extensively re-evaluated. Moxifloxacin, a fluoroquinolone, improved the activity of the standard drug regimen when substituted for ethambutol (EMB). It is being studied to shorten the duration of treatment for fully drug-susceptible TB (Remox study). Clofazimine, a fat-soluble dye with experimental activity against TB, but used only for leprosy in the last 50 years, requires further study because it has been included in a successful short 9-month combined drug regimen for the treatment of multidrug-resistant TB. The diarylquinoline TMC207 is the most promising among the new TB drugs because of its experimental and clinical rate of culture conversion. Also exciting, 200 mg daily doses in humans of the nitroimidazo-oxazine PA-824 and the nitro-dihydro-imidazooxazole OPC-67683 were safe and induced a bactericidal effect of respectively 0.098 ± 0.072 log(10) and 0.040 ± 0.056 log(10) per day. The new oxazolidinones PNU-100480 and AZD-5847 might be at least as active as linezolid and much less toxic. SQ109 is an EMB analogue that does not have cross-resistance with EMB and might have synergistic activity in combined regimens. Benzothiazinones and dinitrobenzamides show exciting in vitro anti-microbial activity and deserve careful attention.
Evaluation of: Diacon AH, Dawson R, Von Groote-Bidlingmaier F et al. Randomized dose-ranging study of the 14-day early bactericidal activity of bedaquiline (TMC207) in patients with sputum microscopy ...smear-positive pulmonary tuberculosis. Antimicrob. Agents Chemother. 57(5), 2199-2203 (2013). During the past decade considerable efforts have been made to develop and register new anti-TB drugs, making them available for patients in need. Bedaquiline (BDQ), approved by the US FDA in December 2012, is the first new anti-TB drug available for treatment of this disease since rifampicin became available in 1967. BDQ has the peculiarity of being a drug with a very long half-life and potent antimicrobial activity that becomes noticeable only after the first 4 days of treatment. Consequently, Diacon et al. have conducted a 14-day dose-ranging study aimed at assessing the early bactericidal activity of BDQ in TB patients who received loading doses of the drug during the first 2 days of treatment. The loading doses partially overcame the delayed antimicrobial activity only in patients treated daily with as much as 400 mg.
It has been hypothesized that the virulence of lab-passaged Mycobacterium tuberculosis and recombinant M. tuberculosis mutants might be reduced due to multiple in vitro passages, and that virulence ...might be augmented by passage of these strains through mice before quantitative virulence testing in the mouse or guinea pig aerosol models.
By testing three M. tuberculosis H37Rv samples, one deletion mutant, and one recent clinical isolate for survival by the quantitative organ CFU counting method in mouse or guinea pig aerosol or intravenous infection models, we could discern no increase in bacterial fitness as a result of passaging of M. tuberculosis strains in mice prior to quantitative virulence testing in two animal models. Surface lipid expression as assessed by neutral red staining and thin-layer chromatography for PDIM analysis also failed to identify virulence correlates.
These results indicate that animal passaging of M. tuberculosis strains prior to quantitative virulence testing in mouse or guinea pig models does not enhance or restore potency to strains that may have lost virulence due to in vitro passaging. It is critical to verify virulence of parental strains before genetic manipulations are undertaken and comparisons are made.
Objectives
It is widely believed that persistent Mycobacterium tuberculosis inhabits necrotic lung granulomas in humans and that the microenvironmental conditions encountered therein render the ...bacilli phenotypically tolerant to antibiotics, accounting for the long duration required for successful treatment of tuberculosis (TB). To validate this belief, we directly compared the activity of rifampicin/isoniazid/pyrazinamide (RHZ) against chronic TB infection in guinea pigs, which exhibit caseous granulomas histologically resembling human caseous foci, and in mice, which lack necrotic granulomas.
Methods
Guinea pigs and mice were aerosol-infected with M. tuberculosis CDC1551 and twice weekly treatment with RHZ was started 4 weeks later. Culture-positive relapse was assessed in subgroups of guinea pigs after 3 months and 4 months of treatment.
Results
All guinea pig lungs exhibited histological evidence of granulomas with central caseation, while mouse lungs exhibited cellular lesions at the initiation of antibiotic treatment. Guinea pig lungs became culture-negative after 2 months of RHZ given twice weekly at human-equivalent doses. Relapse rates in guinea pigs were 0% (0/10) both after 3 months and 4 months of treatment. In contrast, all mouse lungs remained culture-positive after 4 months of equivalent RHZ exposures.
Conclusions
Caseous necrosis does not reduce the sterilizing activity of the standard antituberculosis regimen of RHZ. Our findings have important implications for the use of alternative animal models in testing novel TB drug regimens and for modelling M. tuberculosis persistence.
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