Figure 2. Schematic representation of the respiratory of The chain M. tuberculosis. components are Ndh/NdhA type II NADH:(mena)quinone oxidoreductase (two isoforms), ETF – electron transferring flavoprotein (transfer of reducing equivalents from fatty acid – β-oxidation into the Q-pool), nuo protonmotive NADH dehydrogenase (Complex I), cytochrome bcc bcc – – complex (note that there is no evidence for soluble cytochrome c in this organism), aa3 – cytochrome oxidase, postulated to form a supercomplex with An alternative terminal bcc bcc. oxidase pathway is utilised in under conditions of low oxygen tension, M. tuberculosis containing quinol oxidase (cytochrome fumarate reductase (FRD) and nitrate reductase (nar) bd), components. and correspond to the positive and negative sides of the respiratory membrane P n with respect to proton translocation. Proton movements are indicative only, and do not represent H+/e- ratios for the respective complexes. Respiratory-chain inhibition-induced death represents a fundamental shift from traditional drug design that have until recently relied on drugs that selectively target the replication machinery of Mtb. 9, 23-28 Anti-tubercular drugs developed to target the respiratory pathways should therefore have the potential to have sterilizing activity against current MDR and XDR Mtb strains. Identification of hit compounds was achieved through a HTS screen of approximately 11,000 compounds that were predicted to possess activity against the Ndh enzyme. Ndh was chosen for the HTS due to the critical role as an important dehydrogenase during growth and pathogenicity9, 17 and due to its tractability for heterologous expression in and HTS29. E.coli The enzyme has been observed to be sensitive to phenothiazine-based inhibitors such as trifluoperazine and thioridazine9. These inhibitors have been shown by a number of different laboratories to have sterilizing activity against replicating and slow growing MDR Mtb (grown
Figure 2. Schematic representation of the respiratory of M. tuberculosis. The chain components are Ndh/NdhA – type II NADH:(mena)quinone oxidoreductase (two isoforms), ETF – electron transferring flavoprotein (transfer of reducing equivalents from fatty acid β-oxidation into the Q-pool), nuo – protonmotive NADH dehydrogenase (Complex I), bcc – cytochrome bcc complex (note that there is no evidence for soluble cytochrome c in this organism), aa3 – cytochrome bcc oxidase, postulated to form a supercomplex with bcc. An alternative terminal oxidase pathway is utilised in M. tuberculosis under conditions of low oxygen tension, containing quinol oxidase (cytochrome bd), fumarate reductase (FRD) and nitrate reductase (nar) components. P and n correspond to the positive and negative sides of the respiratory membrane with respect to proton translocation. Proton movements are indicative only, and do not represent H+/e- ratios for the respective complexes. Respiratory-chain inhibition-induced death represents a fundamental shift from traditional drug design that have until recently relied on drugs that selectively target the replication machinery of Mtb. 9, 23-28 Anti-tubercular drugs developed to target the respiratory pathways should therefore have the potential to have sterilizing activity against current MDR and XDR Mtb strains. Identification of hit compounds was achieved through a HTS screen of approximately 11,000 compounds that were predicted to possess activity against the Ndh enzyme. Ndh was chosen for the HTS due to the critical role as an important dehydrogenase during growth and pathogenicity9, 17 and due to its tractability for heterologous expression in E.coli and HTS29. The enzyme has been observed to be sensitive to phenothiazine-based inhibitors such as trifluoperazine and thioridazine9. These inhibitors have been shown by a number of different laboratories to have sterilizing activity against replicating and slow growing MDR Mtb (grown