Structure-based drug discovery against M. tuberculosis MptpB: a novel strategy

Tuberculosis is one of the oldest and most persistent bacterial infectious diseases that affect humans. Despite significant advances to control the spread of tuberculosis with the introduction of vaccines and antibiotics, one third of the human population is still infected. The recent resurgence of the disease, together with the development of drug resistance, is threatening to expand into a future epidemic. New therapeutic approaches are then urgently needed to fight the pathogens. A main bottleneck in the development of drugs is that generally resources and expertise are concentrated in the private sector. In addition companies are highly reluctant to allocate serious investments in poor people s diseases that would certainly compromise their return benefits. We have characterised the activity profile of a protein known to be a virulence factor for tuberculosis causing bacteria and we propose to develop a new drug candidate against this target to treat tuberculosis. We have already identified compounds, which are potent inhibitors of this protein. To take our ambitions further, we must now develop some of the leads we have identified and be able to test them with in vivo mouse models. This will only be possible in a non-profit academic environment at this stage. To do that, we will analyse the molecular interactions of the inhibitors and substrates with the target protein by X-ray crystallography and computer simulations. The information obtained from the structural analysis will be used to design and synthesise new compounds with more specific and selective properties. These new compounds will then be tested for activity against the protein and in cell assays and mouse models to select the best drug candidate for future clinical trials.

Tuberculosis, one the oldest human infectious disease known, still poses a serious threat to all nations. Tuberculosis incidence and mortality continues to grow worldwide triggered by new viral infections like HIV. The long and complex current treatments discourage compliance from patients and have resulted in multi-drug resistant strains further promoting persistence of the disease. Clearly, new approaches and therapeutical treatments are urgently needed to tackle the increasing spread of the infection, by reducing drug resistance, time of treatment and to be compatible with anti-retroviral therapies. For this, new targets need to be identified and inhibitory compounds explored as suitable drugs anti-tuberculosis. We propose to do that using a novel target, the MptpB phosphatase, a virulence factor from M. tuberculosis. We have recently discovered a new phosphoinositide phosphatase activity for this protein, which is an important factor for the survival of mycobacteria in infected macrophages. Following our biochemical characterisation and the identification of essential catalytic residues, we tested the effect of specific phosphatase inhibitors against MptpB. We found potent inhibitors of this enzyme, which are active in mycobacteria-infected macrophages. MptpB is a unique gene in mycobacterium with no human orthologue, suggesting that it is a potential good candidate for selective drug targeting against tuberculosis. We believe that inhibition of MptpB would potentially trigger the innate immune response in infected patients accelerating the treatment and reducing drug resistance.
Our aim is to develop a drug candidate by optimising the lead compounds we identified. For this, we need to understand the mechanism of inhibition of the compounds and define the molecular determinants for ligand binding to MptpB. We propose a structure-based drug discovery programme that will involve X-ray crystallographic analysis of MptpB in complex with substrates and inhibitors, computer docking simulations, compound synthesis of new specific inhibitors, and integrated with toxicity and activity essays in in vitro cell cultures and in mouse models. The expected outcome of this multidisciplinary programme of work will be new anti-tuberculosis drug candidate for further clinical studies.