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Open Access Research article

Bactericidal activity of PA-824 against Mycobacterium tuberculosis under anaerobic conditions and computational analysis of its novel analogues against mutant Ddn receptor

Sulochana Somasundaram1, Ramaian Santhaseela Anand2, Perumal Venkatesan3 and Chinnambedu N Paramasivan4*

Author Affiliations

1 Department of Biotechnology, Sri Venkateswara College of Engineering, Sriperumbudur, India

2 Centre for Biotechnology, Anna University, Chennai, India

3 National Institute for Research in Tuberculosis, Chennai, India

4 Foundation for Innovative New Diagnostics, Flat No. 6-14 (excluding No. 7), 9th floor, Vijaya Building, 17-Barakhamba Road, New Delhi 110 001, India

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BMC Microbiology 2013, 13:218  doi:10.1186/1471-2180-13-218

Published: 1 October 2013

Abstract

Background

The resurgence of multi-drug resistant tuberculosis (MDR-TB) and HIV associated tuberculosis (TB) are of serious global concern. To contain this situation, new anti-tuberculosis drugs and reduced treatment regimens are imperative. Recently, a nitroimidazole, PA-824, has been shown to be active against both replicating and non-replicating bacteria. It is activated by the enzyme Deazaflavin-dependent nitroreductase (Ddn) present in Mycobacterium tuberculosis which catalyzes the reduction of PA-824, resulting in the release of lethal reactive nitrogen species (RNS) within the bacteria. In this context, PA-824 was analyzed for its activity against latent tuberculosis under anaerobic conditions and compared with rifampicin (RIF) and pyrazinamide (PZA). Recent mutagenesis studies have identified A76E mutation which affects the above mentioned catalysis and leads to PA-824 resistance. Hence, novel analogues which could cope up with their binding to mutant Ddn receptor were also identified through this study.

Results

PA-824 at an optimum concentration of 12.5 μg/ml showed enhanced bactericidal activity, resulting in 0 CFU/ml growth when compared to RIF and PZA at normal pH and anaerobic condition. Further docking studies revealed that a combinatorial structure of PA-824 conjugated with moxifloxacin (ligand 8) has the highest binding affinity with the wild type and mutant Ddn receptor.

Conclusions

PA-824 has been demonstrated to have better activity under anaerobic condition at 12.5 μg/ml, indicating an optimized dose that is required for overcoming the detoxifying mechanisms of M. tuberculosis and inducing its death. Further, the development of resistance through A76E mutation could be overcome through the in silico evolved ligand 8.

Keywords:
Bactericidal activity; Mycobacterium tuberculosis; Anaerobic activity; Docking; Ddn; PA-824