IspH inhibitors kill Gram-negative bacteria and mobilize immune clearance

Isoprenoids are vital to all organisms in supporting core functions of life, like respiration and membrane stability.(1) IspH, an enzyme in the methyl erythritol phosphate pathway of isoprenoid synthesis, is essential to gram-negative bacteria, mycobacteria and apicomplexans.(2,3) The IspH substrate, HMBPP, is not produced in humans and other metazoans and activates cytotoxic Vγ9Vδ2 T-cells in humans and primates at extremely low concentrations.(4-6) We describe novel IspH inhibitors and through structure-guided analog design, refine their potency to nanomolar levels. We have modified these into prodrugs for delivery into bacteria and report that they kill clinical isolates of several multidrug resistant bacterial species such as Acinetobacter, Pseudomonas, Klebsiella, Enterobacter, Vibrio, Shigella, Salmonella, Yersinia, Mycobacterium and Bacillus, while being relatively non-toxic to mammalian cells. Proteomic analysis reveals that bacteria treated with prodrugs resemble those with conditional IspH knockdown. Notably, these prodrugs also cause expansion and activation of human Vγ9Vδ2 T-cells in a humanized mouse model of bacterial infection. These IspH prodrugs synergize direct antibiotic killing with a simultaneous rapid immune response by cytotoxic γδ T-cells, which may limit the rise of antibiotic resistant bacterial populations.