Determination of [11C]rifampin pharmacokinetics within Mycobacterium tuberculosis-infected mice by using dynamic positron emission tomography bioimaging

Abstract

Information about intralesional pharmacokinetics (PK) and spatial distribution of tuberculosis (TB) drugs is limited and has not been used to optimize dosing recommendations for new or existing drugs. While new techniques can detect drugs and their metabolites within TB granulomas, they are invasive, rely on accurate resection of tissues, and do not capture dynamic drug distribution in the tissues of interest. In this study, we assessed the in situ distribution of (11)C-labeled rifampin in live, Mycobacterium tuberculosis-infected mice that develop necrotic lesions akin to human disease. Dynamic positron emission tomography (PET) imaging was performed over 60 min after injection of [(11)C]rifampin as a microdose, standardized uptake values (SUV) were calculated, and noncompartmental analysis was used to estimate PK parameters in compartments of interest. [(11)C]rifampin was rapidly distributed to all parts of the body and quickly localized to the liver. Areas under the concentration-time curve for the first 60 min (AUC0-60) in infected and uninfected mice were similar for liver, blood, and brain compartments (P > 0.53) and were uniformly low in brain (10 to 20% of blood values). However, lower concentrations were noted in necrotic lung tissues of infected mice than in healthy lungs (P = 0.03). Ex vivo two-dimensional matrix-assisted laser desorption ionization (MALDI) imaging confirmed restricted penetration of rifampin into necrotic lung lesions. Noninvasive bioimaging can be used to assess the distribution of drugs into compartments of interest, with potential applications for TB drug regimen development.

FIG 1

Postmortem histology demonstrating necrotic pulmonary granulomas. Lung tissues obtained from mice 10 weeks after infection with Mycobacterium tuberculosis are shown. (A and B) Hematoxylin and eosin staining shows necrotic TB granulomas (arrows). Panel B is a high-power view of the inset in panel A. (C) Masson's trichrome staining demonstrates collagen staining (blue, arrow) surrounding the granuloma. (D to F) High-power views of the inset in panel B show cellular infiltrate with foamy macrophages (hematoxylin and eosin) (D), acid-fast bacilli (E), and reticulin staining (F) at the edge of the granuloma (red, arrow).

FIG 2

Pulmonary [¹¹C]rifampin PET/CT imaging. (A) Three-dimensional CT reconstruction of a representative mouse is shown. The yellow line marks the location of transverse PET/CT images in panels B and C. (B) Transverse images from a representative mouse 10 weeks after infection with Mycobacterium tuberculosis demonstrate a much lower [¹¹C]rifampin PET signal (purple) in the areas of consolidation seen on CT (gray areas, outlined) than in uninfected areas. (C) More-uniform [¹¹C]rifampin PET signal is noted in the lung of an uninfected mouse. PET signal is also noted in the heart (H).

FIG 3

Postmortem localization of rifampin in infected lung sections by MALDI mass spectrometry imaging. Lungs from Mycobacterium tuberculosis-infected mice were processed for two-dimensional MALDI imaging 1 h after administration of 10 mg/kg of rifampin intravenously. Hematoxylin and eosin staining (A) and the corresponding two-dimensional heat map (high, red/yellow; low, blue/green) with relative rifampin signal ([M-H]⁻, m/z 821.399) imaged by MALDI mass spectrometry imaging (B) from a representative Mycobacterium tuberculosis-infected mouse are shown. Necrotic (solid line), pneumonic (dotted line), and uninvolved (dashed line) lung tissues are outlined in panel A. Limited penetration of rifampin into the necrotic caseum (arrowheads) is observed (B), with little signal from the drug noted in the center of the large necrotic lesions.

FIG 4

Dynamic [¹¹C]rifampin PET imaging in live animals. Standardized uptake values (SUV) for liver (A), blood (B), brain (C), and lung (D) compartments in Mycobacterium tuberculosis-infected (red) and uninfected (black) mice are shown. After a single intravenous dose, [¹¹C]rifampin rapidly localizes to the liver (A). No differences are noted in the tissue concentrations of [¹¹C]rifampin between infected and uninfected animals in the liver (A), blood (B), and brain (C) compartments. However, tissue concentrations were lower in infected than in uninfected lung tissues (D). Data are represented as medians and interquartile ranges. Five animals were used for each group.