IspD inhibitor’s, as a new solution against Bacillus anthracis. – MENAX

The Ebola epidemic in West Africa, and more recently Zika virus, have highlighted our vulnerability to outbreaks of infection disease. In the current geopolitical context, terrorist and bioterrorism threats grow. These bioterrorist attacks can be performed with bacteria, viruses or toxins. Among these agents, Bacillus anthracis (responsible for anthrax) is one of the most dangerous. Current treatment against this microorganism involves the administration of an antibiotic, such as penicillin, doxycycline or ciprofloxaxin. However, the emergence of strains resistant to current antibiotics, coupled with the low numbers of new bactericidal molecules introduced into the market in recent years reprsent a real public health problem. It is therefore an urgent need to develop new antibiotics with new modes of action, especially to counter the bacterial strains that can be used in attacks.

A promising target for the development of new antimicrobial agents is the biosynthesis of isoprenoids. This family of molecules, relatively broad and diverse, is vital for all living organisms. Isoprenoids and their precursors are synthesized by two pathways: the mevalonate (MVA) pathway and the methylerythritol phosphate (MEP) pathway. Most bacteria, including several pathogens (Bacillus anthracis, Mycobacterium tuberculosis or Mycobacterium leprae) have exclusively the MEP pathway, while mammals possess only the MVA pathway. This metabolic difference can be exploited to develop inhibitors that should have reduced side-effects in patients.

This project consists in designing inhibitors of IspD, the third enzyme of the MEP pathway. IspD catalyzes the formation of 4-diphosphocytidyl-2-C-methyl-D-erythritol (CDP -ME) and inorganic diphosphate (PPi) from MEP and cytidine triphosphate (CTP). We will use two IspD enzymes, one from Escherichia coli and the other from Bacillus anthracis. A fragment based approach will be used to develop new inhibitors of IspD. This technique relies on the identification of fragments (small molecules <300Da) that bind to a biological target. The binding of these fragments to the target is ascertained using biophysical methods (surface plasmon resonance (SPR), isothermal titration calorimetry (ITC), mass spectrometry, X-ray crystallography or NMR) that should be sensitive enough to detect weak affinities (in the mM range). From the obtained data, we will identify the binding sites and binding modes of the fragments. After selection, the most effective fragments will be optimized using molecular modeling. Molecules based on these fragments will be synthesized in order to increase their affinity and their specificity with the aim of obtaining a potent inhibitor.