Inhibition of host Lactate dehydrogenase A by a small-molecule limits Mycobacterium tuberculosis growth and potentiates bactericidal activity of isoniazid

Lactate dehydrogenase A (LDHA) mediates interconversion of pyruvate and lactate. Increased lactate turnover is shared by malignant and immune cells. Hypoxic lung granuloma in Mycobacterium tuberculosis-infected animals present elevated levels of Ldha and lactate. Such alteration in metabolic milieu could influence the outcome of interactions between M. tuberculosis and its infected immune cells. Given the central role of LDHA for tumorigenicity, targeting lactate metabolism is a promising approach for cancer therapy. Here, we sought to determine the importance of LDHA for Tuberculosis (TB) disease progression and its potential as a host-directed therapeutic target. To this end, we administered FX11, a small-molecule NADH-competitive LDHA inhibitor, to M. tuberculosis infected C57BL/6J mice and Nos2-/- mice with hypoxic necrotizing lung TB lesions mimicking human pathology more closely. FX11 did not inhibit M. tuberculosis growth in aerobic/hypoxic liquid culture, but modestly reduced the pulmonary bacterial burden in C57BL/6J mice. Intriguingly, FX11 administration limited M. tuberculosis replication and onset of necrotic lesions in Nos2-/- mice. In this model, Isoniazid (INH) monotherapy has been known to exhibit biphasic killing kinetics owing to the probable selection of an INH-tolerant subpopulation. This adverse effect was corrected by adjunct FX11 treatment and augmented the INH-derived bactericidal effect against M. tuberculosis. Our findings therefore support LDHA as a potential target for host-directed adjunctive TB therapy and encourage further investigations into the underlying mechanism.\n\nIMPORTANCETuberculosis (TB) continues to be a global health threat of critical dimension. Standard TB drug treatment is prolonged and cumbersome. Inappropriate treatment or non-compliance results in emergence of drug-resistant Mycobacterium tuberculosis strains (MDR-TB) that render current treatment options ineffective. Targeting the host immune system as adjunct therapy to augment bacterial clearance is attractive as it is also expected to be effective against MDR-TB. Here, we provide evidence that pharmaceutical blockade of host lactate dehydrogenase A (LDHA) by a small-molecule limits M. tuberculosis growth and reduces pathology. Notably, LDHA inhibition potentiates the effect of Isoniazid, a first-line anti-TB drug. Hence, its implications of our findings for short-term TB treatment are profound. In sum, our findings establish murine LDHA as a potential target for host-directed TB therapy.