Pharmacological modulation of the autophagy pathway enhances Mtb killing

Mycobacterium tuberculosis (Mtb) is the causative agent for tuberculosis which remains a serious health concern globally. The emergence of multi-drug resistant strains and the failure of BCG vaccine to control the epidemic highlight the need to achieve a better understanding of the host immune response and develop new therapies. Autophagy has been identified as an important element in both innate and adaptive immunity against tuberculosis. However Mtb employs an array of immune modulators to invade and thrive in macrophages including by inhibiting autophagosome fusion with lysosomes. Our aim is to identify novel modulators of the autophagy pathway. To do this we have screened a number of FDA approved autophagy-enhancing drugs to reverse the Mtb-induced block of autophagic flux and boost host immune responses. Murine BMDMs expressing EGFP-LC3 were infected with H37Ra and treated with or without autophagy-enhancing drugs. The number of GFP-LC3-positive puncta per cell was quantified by high content analysis to assess autophagic induction and flux, thereby identifying compounds capable of overcoming the Mtb-induced block in autophagy. We identified three compounds, Sorafenib, Valproic Acid and Carbamazepine, which promote autophagic flux in Mtb-infected cells. Human MDMs were infected with H37Ra and treated with or without these drugs to determine their ability to promote intracellular killing of Mtb and boost the innate immune response. Our data show that Sorafenib, Valproic Acid and Carbamazepine are capable of overcoming the Mtb-induced block in autophagy and reducing bacterial burden in MDMs. This work highlights the potential for autophagy-enhancing drugs as adjunctive treatment for tuberculosis.