Lisa M. Sturk, Ph.D.

Dissertation research performed under the direction of Richard R. Tidwell

ABSTRACT
    Human African trypanosomiasis (HAT) is a complex parasitic disease caused by Trypanosoma brucei subspecies. The current epidemic of human African trypanosomiasis places nearly 60 million people in sub-Saharan Africa at risk for developing this life threatening infection. New treatments are desperately needed for cerebral (late) stage trypanosomiasis. DB75, a pentamidine analog, has potent anti-trypanosomal activity but does not exhibit significant oral bioavailability. An N-methoxyamidine prodrug (DB289) was designed to improve oral availability of DB75. Despite excellent activity against early-stage sleeping sickness, oral DB289 exhibited limited efficacy in mouse models of late stage disease. Uninfected mice were utilized to assess single-dose pharmacokinetics of intravenous DB75, oral DB289 and intravenous DB289. Following intravenous administration, DB75 was detectable in brain extracts but was sequestered within cells lining the blood-brain and blood-cerebrospinal fluid barriers. Brain tissue of mice treated with oral DB289 exhibited diffuse fluorescence within the brain parenchyma, suggesting that the prodrug was not trapped within blood-brain barrier cells. A near five-fold increase in brain levels of DB289 combined with parenchymal localization of compound fluorescence after intravenous administration suggest that the unaltered prodrug penetrates the blood-brain barrier and may be subject to in situ biotransformation.  DB844 (N-methoxy-6-{5-[4-( N -methoxyamidino)phenyl]-furan-2-yl}-nicotinamidine, an aza analog of DB289, was recently synthesized. Results demonstrate that oral DB844 is 20-fold more potent in the STIB 900 Trypanosoma brucei rhodesiense acute mouse model. Moreover, oral DB844 cured mice chronically infected with T. b. brucei , the first prodrug of aromatic diamidines to completely cure the CNS model. Pharmacokinetic analysis of revealed that DB844 has excellent oral absorption, with peak plasma concentrations reached within 15 min after dosing. Oral DB844 produced high concentrations of prodrug and active diamidine in mouse brain. DB820 formed from oral DB844, however, was distributed throughout brain parenchyma. Enhanced plasma and brain pharmacokinetic properties of DB844 may contribute to its improved oral potency in both acute and chronic models of trypanosomiasis. Considering the resulted obtained in these investigations, DB844 should be considered a new lead candidate drug for treating first and second stage trypanosomiasis and should thus be evaluated for potency and toxicity in advanced animal models.