Bedaquiline and Pyrazinamide Treatment Responses Are Affected by Pulmonary Lesion Heterogeneity in Mycobacterium tuberculosis Infected C3HeB/FeJ Mice

Abstract

BALB/c and Swiss mice are routinely used to validate the effectiveness of tuberculosis drug regimens, although these mouse strains fail to develop human-like pulmonary granulomas exhibiting caseous necrosis. Microenvironmental conditions within human granulomas may negatively impact drug efficacy, and this may not be reflected in non-necrotizing lesions found within conventional mouse models. The C3HeB/FeJ mouse model has been increasingly utilized as it develops hypoxic, caseous necrotic granulomas which may more closely mimic the pathophysiological conditions found within human pulmonary granulomas. Here, we examined the treatment response of BALB/c and C3HeB/FeJ mice to bedaquiline (BDQ) and pyrazinamide (PZA) administered singly and in combination. BALB/c mice consistently displayed a highly uniform treatment response to both drugs, while C3HeB/FeJ mice displayed a bimodal response composed of responsive and less-responsive mice. Plasma pharmacokinetic analysis of dissected lesions from BALB/c and C3HeB/FeJ mice revealed that PZA penetrated lesion types from both mouse strains with similar efficiency. However, the pH of the necrotic caseum of C3HeB/FeJ granulomas was determined to be 7.5, which is in the range where PZA is essentially ineffective under standard laboratory in vitro growth conditions. BDQ preferentially accumulated within the highly cellular regions in the lungs of both mouse strains, although it was present at reduced but still biologically relevant concentrations within the central caseum when dosed at 25 mg/kg. The differential treatment response which resulted from the heterogeneous pulmonary pathology in the C3HeB/FeJ mouse model revealed several factors which may impact treatment efficacy, and could be further evaluated in clinical trials.

Prediction of Drug Penetration in Tuberculosis Lesions

“…9–11 We have previously shown, by MALDI mass spectrometry imaging (MSI) and the conventional quantitation of drugs in TB lesions, that different drugs display very distinct partitioning into the cellular and caseous regions of granulomas and cavities. 2,13,17 Because necrotic material or caseum is entirely acellular and thus devoid of a vascular supply and active transport, only the free drug fraction can penetrate this matrix via passive diffusion. We hypothesized that factors influencing passive diffusion into caseum would include intrinsic physicochemical properties and the extent of binding to caseum macromolecules.…”

Pyrazinamide Resistance Is Caused by Two Distinct Mechanisms: Prevention of Coenzyme A Depletion and Loss of Virulence Factor Synthesis

“…25 Finally, old reports from the 1930s 26,27 were confirmed, showing that the necrotic core of TB lesions is not acidic. 28–30 …”

Contribution of pretomanid to novel regimens containing bedaquiline with either linezolid or moxifloxacin and pyrazinamide in murine models of tuberculosis

“…To further examine the contribution of PMD to BPaMZ, we used the emerging C3HeB/FeJ mouse model to better mimic the pathophysiological conditions found within caseating human lung lesions (e.g., hypoxia, more neutral pH) (18–20, 22, 24, 27). Prior observations have indicated reduced diffusion of BDQ into the caseous regions of necrotic lung lesions relative to the bordering cellular regions and reduced activity of PZA in caseum with near-neutral pH in this strain (23, 24). On the other hand, PMD appears to diffuse well through caseum and is active under hypoxic conditions (10, 28), so should lend important bactericidal activity in caseous lesions.…”