Improving treatment outcome assessment in a mouse tuberculosis model.

Preclinical treatment outcome evaluation of tuberculosis (TB) occurs primarily in mice. Current designs compare relapse rates of different regimens at selected time points, but lack information about the correlation between treatment length and treatment outcome, which is required to efficiently estimate a regimens' treatment-shortening potential. Therefore we developed a new approach. BALB/c mice were infected with a Mycobacterium tuberculosis Beijing genotype strain and were treated with rifapentine-pyrazinamide-isoniazid-ethambutol (RpZHE), rifampicin-pyrazinamide-moxifloxacin-ethambutol (RZME) or rifampicin-pyrazinamide-moxifloxacin-isoniazid (RZMH). Treatment outcome was assessed in n = 3 mice after 9 different treatment lengths between 2-6 months. Next, we created a mathematical model that best fitted the observational data and used this for inter-regimen comparison. The observed data were best described by a sigmoidal Emax model in favor over linear or conventional Emax models. Estimating regimen-specific parameters showed significantly higher curative potentials for RZME and RpZHE compared to RZMH. In conclusion, we provide a new design for treatment outcome evaluation in a mouse TB model, which (i) provides accurate tools for assessment of the relationship between treatment length and predicted cure, (ii) allows for efficient comparison between regimens and (iii) adheres to the reduction and refinement principles of laboratory animal use.

Assessment of Bactericidal Drug Activity and Treatment Outcome in a Mouse Tuberculosis Model Using a Clinical Beijing Strain.

Mycobacterium tuberculosis Beijing strains are associated with lower treatment success rates in tuberculosis (TB) patients. In contrast, laboratory strains such as H37Rv are often used in preclinical tuberculosis models. Therefore, we explored the impact of using a clinical Beijing strain on treatment outcome in our mouse tuberculosis model. Additionally, the predictive value of bactericidal activity on treatment outcome was assessed. BALB/c mice were infected with a Beijing strain and treated with one of 10 different combinations of conventional anti-TB drugs. Bactericidal activity was assessed by determining reductions in mycobacterial load after 7, 14, and 28 days and after 2, 3, and 6 months of treatment. Treatment outcome was evaluated after a 6-month treatment course and was based on lung culture status 3 months posttreatment. None of the anti-TB drug regimens tested could achieve 100% treatment success. Treatment outcome depended critically on rifampin. Four non-rifampin-containing regimens showed 0% treatment success compared to success rates between 81 and 95% for six rifampin-containing regimens. Bactericidal activity was predictive only for treatment outcome after 3 months of treatment. Our data advocate the use of multiple mycobacterial strains, including a Beijing strain, to increase the translational value of mouse TB models evaluating treatment outcome. Additionally, our findings support the notion that bactericidal activity in the first 2 months of treatment, as measured in clinical phase IIa/b trials, has limited predictive value for tuberculosis treatment outcome, thus emphasizing the need for better parameters to guide future phase IIII trials.