Diagnosis and treatment of tuberculosis: one potential solution, PA-824

Monday, October 24, 2011 — Poster Session I
Noon – 2:00 p.m.	Natcher Conference Center	NIAID	BIOCHEM/CHEM-20

* FARE Award Winner

Authors

• T Mukherjee
• M Gurumurthy
• G Marriner
• S Cellitti
• R Singh
• A Nayyar
• I Choi
• E Dayao
• D Schimel
• D Weiner
• Y Lee
• B Geierstanger
• U Manjunatha
• H Boshoff
• L Via
• C Barry

Abstract

PA-824 is a nitroimidazole-oxazine pro-drug (currently in Phase II clinical trials for tuberculosis treatment) is activated by the deazaflavin dependent nitroreductase (Ddn) encoded by Rv3547 using F420 as the cofactor. The key active metabolite generated from the nitroimidazole group is nitrous acid which disproportionate to form nitric oxide and other reactive nitrogen species whose formation correlates with the cidal activity of M. tuberculosis (MTb). The X-ray crystal structure for the Ddn enzyme from MTb as well as its active homolog from Norcardia farcinica was solved at less than 2 Å resolutions with or without bound cofactor. Molecular docking in combination with structure activity relationship studies analyzing enzyme kinetics of Ddn identified a number of residues which might constitute the binding pocket of PA-824, which were corroborated by enzymatic analysis of the corresponding site directed mutants. Elaboration of the catalytic mechanism, which involves a novel multistep mechanism consisting of both enzymatic and non-enzymatic transformations, has paved the path towards developing analogs with increased cidal activity. The (18F) PA-824 analog has been synthesized for PET imaging studies in MTb-infected and naïve rabbits. The radiotracer appears to concentrate in the granuloma in the rabbit lung (2-3-fold signal increase compared to normal lung tissue).

back to top