PLASMOPUR

Plasmodium falciparum causes the most lethal form of malaria which leads to more than 600,000 deaths worldwide annually, and which remains a major health threat in tropical and subtropical countries with an increasing expansion due to global warming. Indeed, approximately 215 million people in the world are infected by malaria, which has a massive impact on human health being the world’s second biggest killer after tuberculosis. Despite intense efforts, there is currently no approved vaccine against malaria or any other human parasite, and the treatment has become complicated by the emergence of drug resistant parasites, necessitating the development of new drugs. Metabolic pathways that are vital for parasite survival display ideal drug targets. The purine salvage pathway is essential for Plasmodium, hence enzymes of this pathway possess a high druggability index. The objective of the project is to conduct structure-function-activity relationship studies focusing on three selected P. falciparum enzymes: inosine monophosphate dehydrogenase (IMPDH), guanosine monophosphate synthetase (GMPS) and IMP specific nucleotidase (ISN1). All are involved in the purine nucleotide metabolism. IMPDH catalyzes the first step of GMP (guanosine monophosphate) synthesis wherein IMP (inosine monophosphate) is converted to XMP (xanthine monophosphate). Thereafter, GMPS catalyzes the conversion of XMP to GMP in a reaction coordinated across two catalytic pockets and coupled by substrate channeling. ISN1, a novel purine nucleotidase, is present only in certain parasitic protozoa and all fungi. We recently determined the first three-dimensional structure of a member of this family which is essential for nucleotide pool regulation, and which converts IMP to inosine which in turn is converted to hypoxanthine. A full structural and enzymatic characterization of enzyme targets involved in unexplored parasitic pathways is still a prerequisite for multi-target rational drug design aiming at minimizing or circumventing resistance. Crystal structures of the various ligand complexed states of the enzymes studied within this research program will allow contributing to the understanding of substrate recognition and enzymatic catalysis. Together with results from biochemical, biophysical and enzyme kinetic studies, they will form the essential basis for the understanding of catalytic mechanisms and for the design and synthesis of novel inhibitors. These latter will be evaluated for their inhibitory effect on the enzymes and on parasite growth in culture. In this context, substrate analogues (such as mononucleotides) acting as competitive inhibitors will represent an attractive strategy for the development of highly potent anti-malaria drugs. The main objective of the project is to contribute to design ligand molecules via a structure/function/activity based rational drug design approach. The consortium includes three academic partners. Two are based in France (MMSB-CNRS/University of Lyon I and IBMM-CNRS/UM/ENSCM) with strong expertise on the biochemical and structural aspects of the studied protein targets and in the chemical synthesis of substrate analogues as e.g. non-cleavable 5’-mononucleotide mimics, respectively. The third partner is based in India (JNCASR, Bangalore) and brings in not only essential expertise in molecular biology and kinetics of enzymes from purine metabolism but also on parasitology with facilities for inhibitor screening in vitro on P. falciparum in culture and in vivo using P. berghei infected mice models. The consortium possesses the entire infrastructure needed for the studies. This project opens up very promising and innovative perspectives for the treatment of malaria, not only in terms of development of therapeutic candidates, which may also provide valuable information in the fight against other pathogenic strains, but also by its contribution to the understanding of the functioning of these very fundamental enzymes.