Dissecting the role of host enzyme PARP1 in tuberculosis infection and therapy

Johns Hopkins University, Baltimore MD

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Abstract

Project Summary Tuberculosis (TB), a devastating pulmonary disease caused by the bacillus Mycobacterium tuberculosis (Mtb), is a global public health thread that results in over 10 million new cases and nearly 2 million deaths a year. Even though most cases can be cured by standard TB therapy, increasing drug-resistance calls for the development of new and improved treatment options. Since most individuals are able to contain Mtb infection without developing TB, a better understanding of the immune response to Mtb may identify targets for host-directed therapies that could improve the treatment of TB. Pyrazinamide (PZA) has been a fundamental component of standard TB therapy for decades but its mechanism of action remains poorly defined. In contrast to other TB drugs, PZA has host-directed as well as antimicrobial activity and stunts pro-inflammatory cytokine responses to Mtb in a pattern that suggests suppression of the NF-?B signaling pathway. However, a mammalian target of PZA has not yet been identified. I recently demonstrated that PZA inhibits the host enzyme Poly(ADP-ribose) Polymerase-1 (PARP-1), a key immune regulator required for tumor necrosis factor alpha (TNF-?) production and NF-?B target gene expression. Although the role of PARP-1 in TB infection has not yet been determined, PARP-1 is potently activated by conditions induced in Mtb infection and thus may be an important driver of TB immune responses and pathogenesis. Therefore, PARP-1 inhibition may be the mechanism behind PZA?s immunomodulatory activity and a potential host-directed intervention that may improve the treatment of TB. In this study, I propose to validate PARP-1 as a key host target of PZA and evaluate PARP-1 inhibition in TB therapy. I will first systematically characterize the role of PARP-1 in a mouse model of TB infection by comparing the susceptibility, disease progression and immune responses to Mtb in wild type (WT) and PARP-1 knock-out (PARP-1-/-) mice. Next, I will analyze PARP-1 inhibition as a potential mechanism of PZA by correlating PARP-1 activity with the effects of PZA in macrophage and mouse models of TB infection. Lastly, I will evaluate the efficacy of talazoparib, a potent PARP-1/2 inhibitor already in Phase 3 clinical development, as a novel host-directed adjunct therapy to standard TB therapy. Results from the proposed study will validate PARP-1 as a key host target of the TB drug PZA and determine if PARP-1 inhibition presents a viable but unexplored strategy to improving the treatment of TB. A better understanding of PARP-1 and PZA in Mtb infection promises new insight into the mechanisms involved in pathogenesis and disease control and could lead to new therapies for the treatment of drug-susceptible as well as drug-resistant strains of Mtb.