Eradication of intracellular Francisella tularensis in THP-1 human macrophages with a novel autophagy inducing agent

Our results show that AR-12 induces autophagy in THP-1 macrophages, as indicated by increased autophagosome formation, and potently inhibits the intracellular survival of F. tularensis (type A strain, Schu S4) and F. novicida in macrophages in association with increased bacterial co-localization with autophagosomes. The effect of AR-12 on intracellular F. novicida was fully reversed in the presence of the autophagy inhibitor, 3-methyl adenine or the lysosome inhibitor, chloroquine. Intracellular F. novicida were not susceptible to the inhibitory activity of AR-12 added at 12 h post-infection in THP-1 macrophages, and this lack of susceptibility was independent of the intracellular location of bacteria.Together, AR-12 represents a proof-of-principle that intracellular F. tularensis can be eradicated by small-molecule agents that target innate immunity.Macroautophagy (called autophagy hereafter) is a cellular response of eukaryotic cells to a number of deleterious stimuli including nutrient deprivation, organelle damage and accumulation of unfolded proteins [1]. In addition, evidence indicates that autophagy also aids in controlling infection by certain microorganisms, including viruses, bacteria and parasites [2]. Indeed, the induction of autophagy by amino acid starvation, interferons or pharmacological agents has been shown to decrease the survival of various intracellular bacteria, including Mycobacterium tuberculosis, Group A Streptococcus pyrogenes and Salmonella typhimurium [3-5]. Thus, the induction of autophagy may represent a viable therapeutic approach for the treatment of infections caused by intracellular bacteria that is worthy of further investigation.Francisella tularensis is a Gram negative, facultative coccobacillus that causes the zoonotic disease, tularemia [6,7]. Depending on the route of infection, F. tularensis can lead to different forms of tularemia. Inhalation of bacteria causes the most severe form of the disease, pneumonic tularemia, which