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Comparative bioactivation of the novel anti‐tuberculosis agent PA‐824 in Mycobacteria and a subcellular fraction of human liver
Author(s) -
Dogra M,
Palmer BD,
Bashiri G,
Tingle MD,
Shinde SS,
Anderson RF,
O'Toole R,
Baker EN,
Denny WA,
Helsby NA
Publication year - 2011
Publication title -
british journal of pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.432
H-Index - 211
eISSN - 1476-5381
pISSN - 0007-1188
DOI - 10.1111/j.1476-5381.2010.01040.x
Subject(s) - mycobacterium smegmatis , metabolite , nitroreductase , mycobacterium tuberculosis , prodrug , chemistry , biochemistry , tuberculosis , medicine , pathology
BACKGROUND AND PURPOSE PA‐824 is a 2‐nitroimidazooxazine prodrug currently in Phase II clinical trial for tuberculosis therapy. It is bioactivated by a deazaflavin (F 420 )‐dependent nitroreductase (Ddn) isolated from Mycobacterium tuberculosis to form a des‐nitro metabolite. This releases toxic reactive nitrogen species which may be responsible for its anti‐mycobacterial activity. There are no published reports of mammalian enzymes bioactivating this prodrug. We have investigated the metabolism of PA‐824 following incubation with a subcellular fraction of human liver, in comparison with purified Ddn, M. tuberculosis and Mycobacterium smegmatis. EXPERIMENTAL APPROACH PA‐824 (250 µM) was incubated with the 9000× g supernatant (S9) of human liver homogenates, purified Ddn, M. tuberculosis and M. smegmatis for metabolite identification by liquid chromatography mass spectrometry analysis. KEY RESULTS PA‐824 was metabolized to seven products by Ddn and M. tuberculosis, with the major metabolite being the des‐nitro product. Six of these products, but not the des‐nitro metabolite, were also detected in M. smegmatis . In contrast, only four of these metabolites were observed in human liver S9; M3, a reduction product previously proposed as an intermediate in the Ddn‐catalyzed des‐nitrification and radiolytic reduction of PA‐824; two unidentified metabolites, M1 and M4, which were products of M3; and a haem‐catalyzed product of imidazole ring hydration (M2). CONCLUSIONS AND IMPLICATIONS PA‐824 was metabolized by des‐nitrification in Ddn and M. tuberculosis, but this does not occur in human liver S9 and M. smegmatis . Thus, PA‐824 was selectively bioactivated in M. tuberculosis and there was no evidence for ‘cross‐activation’ by human enzymes.