Flagellar cAMP signaling controls trypanosome progression through host tissues.

The unicellular parasite Trypanosoma brucei is transmitted between mammals by tsetse flies. Following the discovery that flagellar phosphodiesterase PDEB1 is required for trypanosomes to move in response to signals in vitro (social motility), we investigated its role in tsetse flies. Here we show that PDEB1 knockout parasites exhibit subtle changes in movement, reminiscent of bacterial chemotaxis mutants. Infecting flies with the knockout, followed by live confocal microscopy of fluorescent parasites within dual-labelled insect tissues, shows that PDEB1 is important for traversal of the peritrophic matrix, which separates the midgut lumen from the ectoperitrophic space. Without PDEB1, parasites are trapped in the lumen and cannot progress through the cycle. This demonstrates that the peritrophic matrix is a barrier that must be actively overcome and that the parasite's flagellar cAMP signaling pathway facilitates this. Migration may depend on perception of chemotactic cues, which could stem from co-infecting parasites and/or the insect host.

Substituted 2-phenylimidazopyridines: a new class of drug leads for human African trypanosomiasis.

A phenotypic screen of a compound library for antiparasitic activity on Trypanosoma brucei, the causative agent of human African trypanosomiasis, led to the identification of substituted 2-(3-aminophenyl)oxazolopyridines as a starting point for hit-to-lead medicinal chemistry. A total of 110 analogues were prepared, which led to the identification of 64, a substituted 2-(3-aminophenyl)imidazopyridine. This compound showed antiparasitic activity in vitro with an EC50 of 2 nM and displayed reasonable druglike properties when tested in a number of in vitro assays. The compound was orally bioavailable and displayed good plasma and brain exposure in mice. Compound 64 cured mice infected with Trypanosoma brucei when dosed orally down to 2.5 mg/kg. Given its potent antiparasitic properties and its ease of synthesis, compound 64 represents a new lead for the development of drugs to treat human African trypanosomiasis.

Synthesis and antiprotozoal activities of benzyl phenyl ether diamidine derivatives.

Sixty-two cationic benzyl phenyl ether derivatives (36 amidines and 26 prodrugs) were prepared and assayed for activities in vitro and in vivo against Trypanosoma brucei rhodesiense (STIB900), and in vitro against Plasmodium falciparum (K1) and Leishmania donovani axenic amastigotes. 3-Amidinobenzyl 4-amidino-2-iodo-6-methoxyphenyl ether dihydrochloride (55, IC50 = 3.0 nM) and seven other compounds exhibited IC50 values below 10 nM against T. b. rhodesiense in vitro. The 2-bromo-4,4'-diamidino analogue 19 (IC50 = 4.0 nM) and 12 other analogues were more potent than pentamidine (IC50 = 46 nM) against P. falciparum. The 3',4-diamidino-2,6-diiodo analogue 49 (IC50 = 1.4 µM) and two other compounds were more effective than pentamidine (IC50 = 1.8 µM) against L. donovani. A prodrug, 3',4-bis(N″-methoxy)amidino-2-bromo derivative 38, was the most efficacious against trypanosome infected mice, attaining 4/4 cures in four daily 25 mg/kg oral doses, and the 2-chloro-4,4'-diamidine 18 cured 3/4 mice in four daily 5 mg/kg intraperitoneal doses.