Activity of 5-chloro-pyrazinamide in mice infected with Mycobacterium tuberculosis or Mycobacterium bovis
Zahoor Ahmad1, Sandeep Tyagi2, Austin Minkowski2, Deepak Almeida2, Eric L Nuermberger2, Kaitlin M Peck3, John T Welch3, Anthony D Baughn4, Williams R Jacobs4, Jr3, Jacques H Grosset5
1 Center for Tuberculosis Research, Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA; *Present address: Indian Institute of Integrative Medicine, Sanat Nagar, Srinagar, Kashmir, India
2 Center for Tuberculosis Research, Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA
3 Department of Chemistry, University at Albany, SUNY, Albany, New York, USA
4 Howard Hughes Medical Institute, Department of Microbiology & Immunology, Albert Einstein College of Medicine, Bronx, New York, USA
Jacques H Grosset
Department of Medicine, Johns Hopkins University School of Medicine, 1550 Orleans Street, Baltimore, MD 21231, USA
Source of Support: None, Conflict of Interest: None
Background & objectives: Pyrazinamide is an essential component of first line anti-tuberculosis regimen as well as most of the second line regimens. This drug has a unique sterilizing activity against Mycobacterium tuberculosis. Its unique role in tuberculosis treatment has lead to the search and development of its structural analogues. One such analogue is 5-chloro-pyrazinamide (5-Cl-PZA) that has been tested under in vitro conditions against M. tuberculosis. The present study was designed with an aim to assess the activity of 5-Cl-PZA, alone and in combination with first-line drugs, against murine tuberculosis.
Methods: The minimum inhibitory concentration (MIC) of 5-Cl-PZA in Middlebrook 7H9 broth (neutral pH) and the inhibitory titre of serum from mice that received a 300 mg/kg oral dose of 5-Cl-PZA 30 min before cardiac puncture were determined. To test the tolerability of orally administered 5-Cl-PZA, uninfected mice received doses up to 300 mg/kg for 2 wk. Four weeks after low-dose aerosol infection either with M. tuberculosis or M. bovis, mice were treated 5 days/wk with 5-Cl-PZA, at doses ranging from 37.5 to 150 mg/kg, either alone or in combination with isoniazid and rifampicin. Antimicrobial activity was assessed by colony-forming unit counts in lungs after 4 and 8 wk of treatment.
Results: The MIC of 5-Cl-PZA against M. tuberculosis was between 12.5 and 25 μg/ml and the serum inhibitory titre was 1:4. Under the same experimental conditions, the MIC of pyrazinamide was >100 μg/ml and mouse serum had no inhibitory activity after a 300 mg/kg dose; 5-Cl-PZA was well tolerated in uninfected and infected mice up to 300 and 150 mg/kg, respectively. While PZA alone and in combination exhibited its usual antimicrobial activity in mice infected with M. tuberculosis and no activity in mice infected with M. bovis, 5-Cl-PZA exhibited antimicrobial activity neither in mice infected with M. tuberculosis nor in mice infected with M. bovis.
Interpretation & conclusion: Our findings showed that 5-Cl-PZA at doses up to 150 mg/kg was not active in chronic murine TB model. Further studies need to be done to understand the mechanism and mode of inactivation in murine model of tuberculosis.