Experimental Animal Models of TB: Chemotherapeutics and Imaging

National Institute Of Allergy And Infectious Diseases

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Abstract

This project encompasses approaches to understand how current anti-tubercular chemotherapy works using the most modern technologies and to develop new and improved therapies and therapeutic approaches. Individual projects within this framework are (1) developing structural and functional imaging techniques using PET/CT for use in live, M. tuberculosis (Mtb) infected animals, (2) development of advanced animal models for predicting drug efficacy under conditions that exactly mimic those experienced by TB patients, (3) understanding the activity of various drugs in animal models of tuberculosis therapy, (4) correlating responses seen in animal models with the pathology and response to therapy observed in human TB, and (5) developing techniques for assessing drug distribution, penetration, and pharmacokinetics in vivo. In 2022 and continuing into 2023 we used mice to examine MTB lesions and the function of their neutrophils in relationship to the activity of the anti-TB drug pyrazinamide. In addition, we continued to study the effect of disabling the production of certain secondary metabolites in MTB mutants and found possible effects in host infection control and survival. Most of our PET/CT studies have used 18F-2-fluoro-2-deoxyglucose (FDG) to image the metabolism of the eukaryotic cells in TB lesions in our animal models of tuberculosis. Yet, we would prefer a small molecule that could be used to label Mtb in vivo endogenously as a PET radiotracer. For several years we have focused employing Mtb antigen 85 enzymes that are expressed on the exterior of Mtb cell walls to incorporate exogenous-provided 18F 2-deoxy trehalose (FDT) as either the mono- or dimycolate in or near the cell wall. Use of FDT in the imaging of Mtb in non-human primates, allows the specific imaging of TB-associated lesions and to monitor the effects of treatment in marmosets. In 2023, we and partners began producing the enzymes necessary to finalize FDT characterization including the pharmacokinetics of the probe in NHPs needed to move it toward the clinic. In the past we explored if the marmoset model accurately reflects the response to treatment by providing standard TB treatment HRZE (RIF, INH, PZA, and EMB) to infected symptomatic marmosets and demonstrated that marmosets show similar treatment results as humans. As with the HRZE regimen, during 2022 and finishing up in 2023 we have investigated the combination DBO of Delamanid (D), BDQ (B), and an DprE2 inhibitor OPC-167832 (O) in marmosets in single, double and the triple drug combination. Each individual agent was highly effective promoting survival, reducing pathology, inflammation, and bacterial burdens in the lung and extrapulmonary organs. The 3-drug combination DBO is significantly better than the individual agents and two drug combinations in reducing bacterial burden and organ culture positivity rates. These data have been provided to the stakeholders to share with the FDA. The analysis of the PET/CT derived pathology measures are ongoing, at present, no difference in these measures distinguish DBO from HRZE. We continued to use the mouse, marmoset and rabbit infection models to evaluate classes of antibiotics from our partners in the Gates Foundation's TB Drug Accelerator and other academic partners including diarylquinolines, quinolines, imidazopyridines, nitroimidazoles, among others. These classes of antibiotics are being explored as composing new regimens for treatment of MTB and understanding the specific contribution of each one to activity including consideration of spatial distribution and the kinetics of accumulation in lesions to avoid temporal and spatial black holes of monotherapy. With each new drug candidate, we test for suitable pharmacokinetics, tolerability with longer term dosing (2 weeks to 2 months), in vivo efficacy, and also the candidates penetration into granulomas and cavities to correlate the information with any observed efficacy. We found that the myxobacterial antibiotic myxovalargin was not tolerable in MTB-infected mice although the compound was highly active against MTB, suggesting that while inhibiting translation initiation by occluding the ribosome exit was a viable target, the compound scaffold needed improvement (PMID 36603206). Also in 2023 we specifically examined Bedaquiline (BDQ) and 2 newer diarylquinolines TBAJ876 and TBAJ587, that target the MTB adenosine triphosphate (ATP) synthase enzyme in MTB infected rabbits and found that the new drug candidates had more rapid penetration and faster wash-out periods than BDQ and that one achieved high enough penetration into the center of larger (3-5 cm) lesions to exceed the concentration necessary to kill at least 90% of resident MTB. Both exhibited superior bactericidal activity against caseum resident bacteria than BDQ and were more active in regimens as substitutes for BDQ (PMID 37017524).