Malaria is a global infectious disease with devastating human impact. The high prevalence of resistance towards existing drugs necessitates development of new drug therapies. De novo pyrimidine biosynthesis is an essential and non-redundant pathway in the malarial parasite, but not in mammals, and the fourth enzyme in this pathway, dihydroorotate dehydrogenase (DHODH), offers host-parasite differences at its active site. A high-throughput screen of a small-molecule library identified a number of good inhibitors of malarial DHODH. The most promising hit, GR34, is a potent and selective inhibitor of Plasmodium falciparum DHODH (IC50 = 38 nM) and demonstrates similar potent activity against parasites in whole cell assays, while having no effect on a cultured mammalian cell line. The molecule is synthesized at low cost in 3 steps. Preliminary pharmacokinetic studies have demonstrated that GR34 is orally bioavailable in rats and metabolic studies confirm that the GR34 scaffold should be pharmaceutically acceptable. The compound is well tolerated in both mice and rats with no current evidence of limiting toxicity. The next goal is to design and deliver a clinical development candidate with improved inhibitory activity against DHODH. The initial focus will be to optimize the GR34 lead compound with respect to its in vivo biological activity profile and pharmaceutical developmental properties (ADME, toxicity). A combination of structural biology and medicinal chemistry will help determine which parts of the lead molecule can be improved without loosing desirable properties. We will also prioritize DHODH inhibitors based on lack of cross-resistance with existing drugs, and with low propensity to acquire drug resistance de novo. The project will also advance a backup candidate from the lead development series and explore other chemically attractive alternative scaffolds derived from the initial HTS. The proposed work plan encompasses an integrated and multi-disciplinary approach, bringing together the expertise of the three laboratories: Biochemistry and structural biology will be performed at the University of Texas Southwestern Medical Center (Phillips lab);Medicinal chemistry and malaria biology will be performed at the University of Washington in Seattle (Rathod lab);and ADME lead optimization and preclinical development progression will be performed at Monash University (Charman lab). MMV has a well-established target product profile for drug development candidates for malaria, and these criteria will inform the work plan to develop DHODH inhibitors as novel anti-malarials. Once a compound has been nominated, MMV will fund and manage the GLP preclinical development program and First in Human (FIH) Phase 1 clinical trials as part of its internally funded clinical development program.
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