New intervention strategy for tuberculosis: blocking multiple essential targets

Project description

Mycobacterium tuberculosis is the causative agent of tuberculosis (TB), a disease responsible for almost 1.5 million deaths per year. In recent years, different classes of drug resistant strains have emerged, making the discovery of novel tuberculostatic drugs a major priority. A major disadvantage of most existing and new TB compounds is that they target a single molecule, which significantly increases the chance of resistance development. 

Aim

In this project, we have focused on type VII secretion (T7S) systems as promising new drug targets. T7S systems are used by M. tuberculosis to secrete proteins across the outer membrane. Interestingly, the tubercle bacillus produces several different T7S systems, three of which are essential for viability or virulence. To target T7S systems, we have developed a whole cell-based secretion activity assay. Using this assay we succeeded to identify five new classes of small molecules that inhibit the secretion, while T7S-independent proteins were still produced. We used hit-to-lead optimization to identify compounds that work in the micromolar range. Importantly, we have identified compounds that show activity in infected host cells and in infected animals. We are now pursuing the best compounds to produce a lead compound.

(Expected) results

As part of an international consortium we focused on inhibitors of the ESX-5 system, whereas our partners worked on the other ESX systems. We developed an assay based a highly active lipase that is also an ESX-5 substrate. In close collaboration with the EPFL (Lausanne) we screened a library of 32,000 compounds. A second assay was used to exclude lipase inhibitors and immunoblot assays were used to confirm ESX-5 inhibition. As predicted, most of our hit compounds blocked growth of the tubercle bacillus. After toxicity testing on different eukaryotic cells, dose-response analysis and chemical analysis, we have now five classes of hit compounds that are all novel, drug-like compounds active at the micromolar range (1-10 μM). All these compounds were resynthesized and also up to 50 different version were produced. Importantly, these compounds were also shown to be active in vivo, as they blocked growth of fish tuberculosis bacteria in a zebrafish larvae infection model. As expected, these compounds did not block the growth of other bacteria, they are specific for the tubercle bacillus and closely related species. One of the identified compounds also inhibited ESX-1 secretion, which is in line with our goal of “one drug – multiple targets”. Blocking two important targets at the same time is known to significantly reduce resistance development.