Current antibiotic dosing recommendations and breakpoints for drug susceptibility are based on plasma concentrations and historic measures of efficacy, without specific information at the infection sites. Since inappropriate antibiotic concentrations in target tissues can lead to treatment failure, selection of resistant organisms, or toxicity, several studies and the U.S. Food and Drug Administration (FDA) support measuring drug concentrations in infected tissues. However, current tools to detect tissue drug levels are invasive (require tissue resection), which is difficult in humans and generally limited to a single time point even in animals. Our overarching hypothesis is that multiple, heterogeneous pathological states, e.g. cavitation, pneumonia, and necrotic lesions in pulmonary tuberculosis (TB), occur simultaneously in the same patient. Moreover, these lesions can also have distinct bacterial burdens and antibiotic exposures, which also change with disease progression and antibiotic treatment. Cavitation is a key pathological feature of human TB and a well- recognized risk factor for transmission of infection, relapse, and emergence of drug resistance after treatment. While cavitary walls have high bacterial burden (107-109), they are poorly vascularized with thick fibrous capsules. Therefore, while adequately high antibiotic levels are need to effectively kill bacteria in cavities, using PET bioimaging in patients with pulmonary TB, we have demonstrated that rifampin exposure is paradoxically the lowest in cavitary walls. Bedaquiline, a bromine-containing diarylquinoline, was recently approved for the treatment of multi-drug resistant (MDR) tuberculosis (TB). However, bedaquiline distribution into infected tissues (e.g. granulomas and cavitary lesions) has not been studied extensively whilst preliminary preclinical studies have reported variability in the treatment response in mice with caseous necrotic granulomas. While highly effective in treating MDR- TB, bedaquiline can also cause cardiac events (QT-interval prolongation) leading to safety warnings by regulatory agencies. Therefore, there is a need for noninvasive methods to measure the biodistribution of bedaquiline in infected tissues (e.g. cavities) and other target organs to inform appropriate dosing and develop effective, antibiotic treatments with minimal toxicities. The overall goals of this project are to leverage our expertise in animal models of TB and in vivo PET, a clinically translatable technology. We will develop efficient radiolabeling methods for 76Br-bedaquiline. Using Mycobacterium tuberculosis infections as a model for heterogeneous necrotic-lesions in multiple-compartments, quantitative 76Br-bedaquiline PET in live animals and post-mortem high-resolution / sensitivity autoradiography (<10 m resolution, sub-nanogram sensitivity) will be utilized in animal models of cavitary TB to provide detailed biodistribution and temporal kinetics of intralesional bedaquiline exposures in multiple-compartments. This proposal fulfills an important research gap in TB drug development and aligned with the NIAID Strategic Plan for TB Research.
The overall goals of this project are to utilize in vivo bioimaging to understand the biodistribution of bedaquline, a new antibiotic with novel mode of action active against multi-drug resistant mycobacterial infections, in animal models of cavitary TB.
