u-50488 and Trypanosomiasis--African

Screening of the Sigma-Aldrich Library of Pharmacologically Active Compounds (LOPAC) against cultured Trypanosoma brucei, the causative agent of African sleeping sickness, resulted in the identification of a number of compounds with selective antiproliferative activity over mammalian cells. These included (+)-(1R,2R)-U50488, a weak opioid agonist with an EC(50) value of 59 nM as determined in our T. brucei in vitro assay reported previously. This paper describes the modification of key structural elements of U50488 to investigate structure-activity relationships (SAR) and to optimise the antiproliferative activity and pharmacokinetic properties of this compound.

Topics: 3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer; Antiprotozoal Agents; Humans; Models, Molecular; Narcotic Antagonists; Receptors, Opioid; Structure-Activity Relationship; Trypanosoma brucei brucei; Trypanosomiasis, African

A resazurin-based cell viability assay was developed for phenotypic screening of the LOPAC 1280 'library of pharmacologically active compounds' against bloodstream forms of Trypanosoma brucei in vitro identifying 33 compounds with EC(50) values <1 μM. Counter-screening vs. normal diploid human fibroblasts (MRC5 cells) was used to rank these hits for selectivity, with the most potent (<70 nM) and selective (>700-fold) compounds being suramin and pentamidine. These are well-known antitrypanosomal drugs which demonstrate the robustness of the resazurin cell viability assay. The most selective novel inhibitor was (+)-trans-(1R,2R)-U50,488 having an EC(50) value of 60 nM against T. brucei and 270-fold selectivity over human fibroblasts. Interestingly, (-)-U50,488, a known CNS-active κ-opioid receptor agonist and other structurally related compounds were >70-fold less active or inactive, as were several μ- and κ-opioid antagonists. Although (+)-U50,488 was well tolerated by the oral route and displayed good pharmaceutical properties, including high brain penetration, the compound was not curative in the mouse model of infection. Nonetheless, the divergence of antinociceptive and antitrypanosomal activity represents a promising start point for further exploratory chemistry. Bioinformatic studies did not reveal any obvious candidate opioid receptors and the target of this cytostatic compound is unknown. Among the other potent, but less selective screening hits were compound classes with activity against protein kinases, topoisomerases, tubulin, as well as DNA and energy metabolism.

Topics: 3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer; Animals; Antiprotozoal Agents; Cells, Cultured; Drug Discovery; Fibroblasts; Humans; Ligands; Mice; Parasitic Sensitivity Tests; Receptors, Opioid, kappa; Structure-Activity Relationship; Trypanosoma brucei brucei; Trypanosomiasis, African