NADK: a new bacterial target for the development of antibiotics – NADKiller

Multidrug resistance is a major public health problem requiring urgent development of new antibiotics and thus identification of new bacterial targets, as pointed out by the World Health Organization again this year. The core of the consortium involved in this project has initiated a decade ago the characterization of such a new target: the nicotinamide adenine dinucleotide kinase (NADK). This enzyme is essential in all bacteria tested so far including many pathogens in which antibiotic resistance spreads such as Staphylococcus aureus, Pseudomonas aeruginosa, etc. However, there is still no drug on the market targeting a NADK. The genes encoding the NADKs have remained unknown until 2000, and this may explain the limited knowledge gathered around this unique enzyme despite its central role in most metabolisms.
We were able to connect this enzyme family to three other distantly related enzymes, and pointed out their very particular sequence and global architecture compare to all other known kinases. Since then, we have solved the structure of the NADK from a human pathogen, Listeria monocytogenes. Further structural and functional characterization led us to decipher its original enzymatic mechanism, to identify the first inhibitory hit and to design the first inhibitor active on bacterial cell culture. More recently, using a structure-based approach, we have designed a new lead compound showing increased activity against NADKs in the low micromolar range (unpublished). Importantly, this compound is strongly active in a staphylococcal infection model in mice.
Our main objectives are to:
1) validate that our lead compound targets the NADK and define its mode of action
2) evaluate its in vitro and in vivo activity against various life threatening pathogens listed by the WHO as priority for R&D of new antibiotics
3) develop compounds with enhanced in vivo activity and/or better pharmacokinetic properties.
To achieve these goals, our consortium includes five teams with complementary expertises that will allow monitoring of the antibacterial activity against clinical isolates (including antibiotic-resistant ones), as well as the activity in cellular and animal infection models. State-of-the-art time-resolved enzymology will precise the mechanism of action of the inhibitor and identify the rate-limiting step to be targeted by the next generation of compounds. These new approaches will add on structural biology to guide medicinal chemistry. We have already improved by almost three orders of magnitude the potency of our compounds (from a mM hit to a low µM lead) and we are now looking for a ten-fold improvement. Extending activity testing on various bacteria in vitro and in vivo will allow evaluating better our lead compound alone, but also in synergy with other anti-infectious drugs. Such studies shall also highlight the appearance of resistance, an important issue for further development of antibiotics.
In conclusion, this project should bring novel insights into the activity of an original lead compound showing promising antibiotic activity in mice. It will also bring novel knowledge on its putative targets (including NADK) and guide the design and synthesis of better compounds.