Comparative Studies Evaluating Mouse Models Used for Efficacy Testing of Experimental Drugs against Mycobacterium tuberculosis

Abstract

Methodologies for preclinical animal model testing of drugs against Mycobacterium tuberculosis vary from laboratory to laboratory; however, it is unknown if these variations result in different outcomes. Thus, a series of head-to-head comparisons of drug regimens in three commonly used mouse models (intravenous, a low-dose aerosol, and a high-dose aerosol infection model) and in two strains of mice are reported here. Treatment with standard tuberculosis (TB) drugs resulted in similar efficacies in two mouse species after a low-dose aerosol infection. When comparing the three different infection models, the efficacies in mice of rifampin and pyrazinamide were similar when administered with either isoniazid or moxifloxacin. Relapse studies revealed that the standard drug regimen showed a significantly higher relapse rate than the moxifloxacin-containing regimen. In fact, 4 months of the moxifloxacin-containing combination regimen showed similar relapse rates as 6 months of the standard regimen. The intravenous model showed slower bactericidal killing kinetics with the combination regimens tested and a higher relapse of infection than either aerosol infection models. All three models showed similar outcomes for in vivo efficacy and relapse of infection for the drug combinations tested, regardless of the mouse infection model used. Efficacy data for the drug combinations used also showed similar results, regardless of the formulation used for rifampin or timing of the drugs administered in combination. In all three infection models, the dual combination of rifampin and pyrazinamide was less sterilizing than the standard three-drug regimen, and therefore the results do not support the previously reported antagonism between standard TB agents.For the first time in many years, there is a portfolio of promising new compounds at every level of tuberculosis (TB) drug discovery and development (4; www.tballiance.org). However, careful selection of new drug candidates is imperative, and efficient screening models for new drugs, including pertinent animal models, need to be further developed and studied. Preclinical testing in animals of newly discovered agents alone, and in combination with new and old agents, prior to being tested in humans is a crucial but lengthy process. These drug regimens include agents that provide bactericidal activities against rapidly growing bacilli, but they especially aim to include those that possess potent sterilizing activities and hence prevent relapse (8). The most commonly used animal species in TB drug development is the mouse, mainly because of economical and practical reasons, but also because of the limited requirement of compound (26).Various mouse Mycobacterium tuberculosis infection models are utilized by both industry and academia, and they differ in the route of infection with M. tuberculosis, inoculum and strain of M. tuberculosis, strain of mice, timing of the start of treatment after infection, the length of treatment, etc. A model where therapy is started immediately after in...

Importance of Confirming Data on the In Vivo Efficacy of Novel Antibacterial Drug Regimens against Various Strains of Mycobacterium tuberculosis

“…Six-to eight-week-old female BALB/c mice were exposed to a high-dose aerosol infection in a GlasCol aerosol chamber with the virulent M. tuberculosis strains in the Colorado State University animal biosafety level 3 laboratories (ABSL-3), as previously described (9). A highdose aerosol infection is defined here as an inoculum that will result in all animals succumbing to disease within 1 month after infection.…”

“…A sequence of in vitro assays followed by in vivo testing in validated animal models to assess the activity against M. tuberculosis, the pharmacology, and the toxicity is generally used for advancing compounds in a preclinical stage (31,41). Generally, these preclinical studies are performed with historic laboratory-adapted M. tuberculosis strains such as H37Rv (ATCC 25618 and 27294) (22,29) or Erdman (ATCC 35801) (9). M. tuberculosis is a member of the M. tuberculosis complex, and genetic diversity has recently been linked to clinical, pathogenic, and immunologic heterogeneity in disease progression and outcomes (5,12,30).…”

“…Methods for preclinical animal model testing of drugs against M. tuberculosis vary from laboratory to laboratory; however, it was unknown until recently whether these variations can result in different outcomes. Our earlier work demonstrated that certain experimental variables in preclinical evaluations (such as the mouse strain, route of infection, drug formulations for rifampin, and dosing schedule) did not necessarily affect the result of mouse bactericidal efficacy trials for the TB drug combinations evaluated (9). By performing these head-to-head mouse studies, we were still unable to resolve the discrepancy seen among laboratories regarding the reported antagonism between the standard drugs isoniazid (H), rifampin (R), and pyrazinamide (Z), which has been observed in some (1,37,38) but not all (9,20) laboratories.…”

“…Our earlier work demonstrated that certain experimental variables in preclinical evaluations (such as the mouse strain, route of infection, drug formulations for rifampin, and dosing schedule) did not necessarily affect the result of mouse bactericidal efficacy trials for the TB drug combinations evaluated (9). By performing these head-to-head mouse studies, we were still unable to resolve the discrepancy seen among laboratories regarding the reported antagonism between the standard drugs isoniazid (H), rifampin (R), and pyrazinamide (Z), which has been observed in some (1,37,38) but not all (9,20) laboratories. In our published head-to-head studies, the combination HRZ was significantly more effective than RZ dual therapy in all three mouse models evaluated (9), and we did not observe antagonism of H in the HRZ combination in the three infection models evaluated.…”

Mouse Model for Efficacy Testing of Antituberculosis Agents via Intrapulmonary Delivery

“…At the start of therapy, on day 24 postinfection, 6 mice were sacrificed to determine the bacterial load in the lungs. The bacterial load was determined using serial dilutions of homogenized organs that were plated on 7H11 agar plates as previously described (2). The bacterial load in each animal was expressed as the log 10 numbers of CFU.…”