Mechanisms of Pyrazinamide Action and Resistance

Pyrazinamide (PZA) is a unique antituberculosis (antiTB) drug that plays a key role in shortening TB therapy. PZA kills nonreplicating persisters that other TB drugs fail to kill, which makes it an essential drug for inclusion in any drug combinations for treating drug-susceptible and drug-resistant TB such as multidrug-resistant TB. PZA acts differently from common antibiotics by inhibiting multiple targets such as energy production, trans-translation, and perhaps pantothenate/coenzyme A required for persister survival. Resistance to PZA is mostly caused bymutations in the pncA gene encoding pyrazinamidase,which is involved in conversion of the prodrug PZA to the active form pyrazinoic acid. Mutations in the drug target ribosomal protein S1 (RpsA) are also found in some PZA-resistant strains. The recent finding that panD mutations are found in some PZA-resistant strains without pncA or rpsA mutations may suggest a third PZA resistance gene and a potential new target of PZA. Current phenotype-based PZA susceptibility testing is not reliable due to false resistance; sequencing of the pncA gene represents a more rapid, cost-effective, and reliable molecular test for PZA susceptibility testing and should be used for guiding improved treatment of multidrug-resistant and extensively multidrug-resistant TB. Finally, the story of PZA has important implications for not only TB therapy but also chemotherapy in general. PZA serves as a model prototype persister drug and hopefully a “tipping point” that inspires new efforts at developing a new type of antibiotic or drug that targets nonreplicating persisters for improved treatment of not only TB but also other persistent bacterial infections. THE HISTORY: THE UNUSUAL DISCOVERY AND THE ROLLER COASTER OF PZA Pyrazinamide (PZA), a nicotinamide analogue (Fig. 1), was first chemically synthesized in 1936 (1), but its antituberculosis (anti-TB) potential was not recognized until 1952 (2). Its discovery as a TB drug was based on a serendipitous observation that nicotinamide had certain activity against mycobacteria in animal models (3). Subsequent synthesis of nicotinamide analogs and direct testing in the mouse model of TB infection without in vitro testing led to the identification of PZA as an active agent (4, 5). Before the 1970s, PZA was mainly used as a second-line TB drug for the treatment of drugresistant TB or in treatment of relapsed TB because of the hepatic toxicity caused by a higher PZA dosage (3.0 g daily) and longer treatment used in earlier clinical studies. However, largely encouraged by the impressive mouse studies by McDermott and colleagues that demonstrated high sterilizing activity of PZA in combination with isoniazid (INH) (6), the British Medical Research Council conducted clinical trials in East Africa with lower PZA doses (1.5 to 2.0 g daily), which are not significantly hepatotoxic. PZA was found to be almost as effective as rifampin (RIF) as a sterilizing drug, as judged by more frequent sputum conversion at 2 months and by the relapse rates. Subsequent clinical studies showed that the effects of RIF and PZA were synergistic. Received: 1 August 2013, Accepted: 27 August 2013, Published: 18 July 2014 Editors: Graham F. Hatfull, University of Pittsburgh, Pittsburgh, PA, and William R. Jacobs, Jr., Howard Hughes Medical Institute, Albert Einstein College of Medicine, Bronx, NY Citation: Zhang Y, Shi W, Zhang W, Mitchison D. 2014. Mechanisms of pyrazinamide action and resistance, Microbiol Spectrum 2(4):