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

Abstract

In preclinical testing of antituberculosis drugs, laboratory-adapted strains of Mycobacterium tuberculosis are usually used both for in vitro and in vivo studies. However, it is unknown whether the heterogeneity of M. tuberculosis stocks used by various laboratories can result in different outcomes in tests of antituberculosis drug regimens in animal infection models. In head-to-head studies, we investigated whether bactericidal efficacy results in BALB/c mice infected by inhalation with the laboratory-adapted strains H37Rv and Erdman differ from each other and from those obtained with clinical tuberculosis strains. Treatment of mice consisted of dual and triple drug combinations of isoniazid (H), rifampin (R), and pyrazinamide (Z). The results showed that not all strains gave the same in vivo efficacy results for the drug combinations tested. Moreover, the ranking of HRZ and RZ efficacy results was not the same for the two H37Rv strains evaluated. The magnitude of this strain difference also varied between experiments, emphasizing the risk of drawing firm conclusions for human trials based on single animal studies. The results also confirmed that the antagonism seen within the standard HRZ regimen by some investigators appears to be an M. tuberculosis strainspecific phenomenon. In conclusion, the specific identity of M. tuberculosis strain used was found to be an important variable that can change the apparent outcome of in vivo efficacy studies in mice. We highly recommend confirmation of efficacy results in late preclinical testing against a different M. tuberculosis strain than the one used in the initial mouse efficacy study, thereby increasing confidence to advance potent drug regimens to clinical trials.

Consequences of Noncompliance for Therapy Efficacy and Emergence of Resistance in Murine Tuberculosis Caused by the Beijing Genotype of Mycobacterium tuberculosis

“…The results revealed that for the Beijing genotype bacteria, a much higher dosage of rifampin was required to achieve 100% killing, and two out of five Beijing strains exhibited a remarkably high frequency of mutations conferring rifampin resistance (7). These data underline the importance of the use of different M. tuberculosis strains in preclinical experimental studies using animal models, as stated by de Groote et al (3). They recommend the use of different M. tuberculosis strains in the confirmation of treatment efficacy results of novel drugs in the translational phase in order to strengthen the likelihood of success of novel drug regimens that advance into clinical trials (3).…”

Sterilizing Activities of Novel Combinations Lacking First- and Second-Line Drugs in a Murine Model of Tuberculosis

“…Efforts to confirm these promising results in a second animal model and against a second strain of M. tuberculosis are warranted (9). The second model could include another mouse strain (e.g., C3HeB/ FeJ mice), guinea pigs, or larger species, which all exhibit more human-like pathology (2,7,15), or the intravenous inoculation mouse model, which is known to produce more conservative estimates of treatment durations needed to prevent relapse (8,10).…”

Importance of the Genetic Diversity within the Mycobacterium tuberculosis Complex for the Development of Novel Antibiotics and Diagnostic Tests of Drug Resistance

“…To control for this factor in a systematic manner, well-characterized reference collections encompassing representatives of all major MTBC genotypes and species must be tested in vitro and in vivo, given that even the differences among the various stocks of the H37Rv laboratory strains can be significant (38,89). The identity of the clinical isolates in these collections should be confirmed using multiple deletions or single-nucleotide polymorphisms rather than traditional techniques to avoid the pitfalls of homoplasy (1, 36, 52, 62, 84, 109, 135, 142).…”