Drug-like molecules with activity against Trypanosoma brucei are urgently required as potential therapeutics for the treatment of African sleeping sickness. Starting from known inhibitors of other glycosyltransferases, we have developed the first small molecular inhibitors of dolicholphosphate mannose synthase (DPMS), a mannosyltransferase critically involved in glycoconjugate biosynthesis in T. brucei. We show that these DPMS inhibitors prevent the biosynthesis of glycosylphosphatidylinositol (GPI) anchors, and possess trypanocidal activity against live trypanosomes. KeywordsAfrican sleeping sickness; Trypanosoma; Dolicholphosphate mannose synthase; Enzyme inhibitors African sleeping sickness, also known as Human African Trypanosomiasis (HAT), is an infectious disease caused by the protozoan parasite Trypanosoma brucei (T. brucei). The parasite is transmitted by the bite of an infected tsetse fly, multiplies within the bloodstream of the mammalian host, and eventually invades the central nervous system. If untreated, HAT is invariably lethal. Despite becoming close to eradication by the late 1960s, 1 the disease has made a dramatic re-emergence within the last half century, with prevalence in parts of Africa now as high as they were in the 1920s. In 2002 alone, around 48,000 deaths were reported. 2 The WHO presently records around 17,500 new cases per year, 3 with a cumulative rate of 50,000-70,000 cases 3 and potentially over 60 million people at risk. 2 The situation is further exacerbated by the growing resistance to established drug treatments for HAT, which have long been considered unsatisfactory. 2 Serious side effects kill between 4% and 10% of patients who receive the arsenical melarsoprol, 4 introduced in 1949, and the drug fails to cure between 10% and 30% of patients. 5 The only relatively modern anti-HAT drug, the ornithine decarboxylase inhibitor eflornithine, is expensive, difficult to administer, and only effective against T. brucei gambiense. 6 Thus, HAT has been described as one of the most neglected diseases of mankind, 7 and novel therapeutic approaches to HAT are urgently needed. GPI anchor biosynthesis in T. brucei involves three mannosyltransferases (MTs) on the luminal face of the endoplasmic reticulum, which catalyze the assembly of the trimannoside core structure (Fig. 1). 20,21 All three of these MTs use dolicholphosphate mannose (Dol-PMan) as their donor substrate, whose biosynthesis from dolicholphosphate (Dol-P) and the sugar-nucleotide GDP-mannose (GDP-Man) is catalyzed by another mannosyltransferase, dolicholphosphate mannose synthase (DPMS). All T. brucei VSG variants also contain at least one N-glycan, which requires another four Dol-P-Man-dependant mannosyltransferases for the formation of its lipid-linked oligosaccharide precursor. [22][23][24] Consequently, T. brucei is doubly dependant upon Dol-P-Man for the synthesis of mature, N-glycosylated and GPIanchored VSGs, and this double dependency makes DPMS an excellent target for inhibition of VSG biosynthesis. Recently...

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