Structure-activity relationships of synthetic cordycepin analogues as experimental therapeutics for African trypanosomiasis.

Novel methods for treatment of African trypanosomiasis, caused by infection with Trypanosoma brucei are needed. Cordycepin (3'-deoxyadenosine, 1a) is a powerful trypanocidal compound in vitro but is ineffective in vivo because of rapid metabolic degradation by adenosine deaminase (ADA). We elucidated the structural moieties of cordycepin required for trypanocidal activity and designed analogues that retained trypanotoxicity while gaining resistance to ADA-mediated metabolism. 2-Fluorocordycepin (2-fluoro-3'-deoxyadenosine, 1b) was identified as a selective, potent, and ADA-resistant trypanocidal compound that cured T. brucei infection in mice. Compound 1b is transported through the high affinity TbAT1/P2 adenosine transporter and is a substrate of T. b. brucei adenosine kinase. 1b has good preclinical properties suitable for an oral drug, albeit a relatively short plasma half-life. We present a rapid and efficient synthesis of 2-halogenated cordycepins, also useful synthons for the development of additional novel C2-substituted 3'-deoxyadenosine analogues to be evaluated in development of experimental therapeutics.

Ebsulfur is a benzisothiazolone cytocidal inhibitor targeting the trypanothione reductase of Trypanosoma brucei.

Trypanosoma brucei is the causing agent of African trypanosomiasis. These parasites possess a unique thiol redox system required for DNA synthesis and defense against oxidative stress. It includes trypanothione and trypanothione reductase (TryR) instead of the thioredoxin and glutaredoxin systems of mammalian hosts. Here, we show that the benzisothiazolone compound ebsulfur (EbS), a sulfur analogue of ebselen, is a potent inhibitor of T. brucei growth with a favorable selectivity index over mammalian cells. EbS inhibited the TryR activity and decreased non-protein thiol levels in cultured parasites. The inhibition of TryR by EbS was irreversible and NADPH-dependent. EbS formed a complex with TryR and caused oxidation and inactivation of the enzyme. EbS was more toxic for T. brucei than for Trypanosoma cruzi, probably due to lower levels of TryR and trypanothione in T. brucei. Furthermore, inhibition of TryR produced high intracellular reactive oxygen species. Hydrogen peroxide, known to be constitutively high in T. brucei, enhanced the EbS inhibition of TryR. The elevation of reactive oxygen species production in parasites caused by EbS induced a programmed cell death. Soluble EbS analogues were synthesized and cured T. brucei brucei infection in mice when used together with nifurtimox. Altogether, EbS and EbS analogues disrupt the trypanothione system, hampering the defense against oxidative stress. Thus, EbS is a promising lead for development of drugs against African trypanosomiasis.

In vitro and in vivo activities of 2-aminopyrazines and 2-aminopyridines in experimental models of human African trypanosomiasis.

New drugs for the treatment of human African trypanosomiasis are urgently needed. A number of 2-aminopyrazines/2-aminopyridines were identified as promising leads following a focused screen of 5,500 compounds for Trypanosoma brucei subsp. brucei viability. Described compounds are trypanotoxic in the submicromolar range and show comparably low cytotoxicity on representative mammalian cell lines. Specifically, 6-([6-fluoro-3,4-dihydro-2H-1-benzopyran-4-yl)]oxy)-N-(piperidin-4-yl)pyrazin-2-amine (CBK201352) is trypanotoxic for T. brucei subsp. brucei, T. brucei subsp. gambiense, and T. brucei subsp. rhodesiense and is nontoxic to mammalian cell lines, and in vitro preclinical assays predict promising pharmacokinetic parameters. Mice inoculated intraperitoneally (i.p.) with 25 mg/kg CBK201352 twice daily for 10 days, starting on the day of infection with T. brucei subsp. brucei, show complete clearance of parasites for more than 90 days. Thus, CBK201352 and related analogs are promising leads for the development of novel treatments for human African trypanosomiasis.

Regulatory role of 5-HT and muscarinic receptor antagonists on the migrating myoelectric complex in rats.

The 5-HT(3) and 5-HT(4) receptor antagonists alosetron and piboserod, and the muscarinic receptor antagonists PNU-171990A (2-(diisopropylamino)ethyl 1-phenylcyclopentanecarboxylate, hydrochloride) and PNU-174708A (2-(diisopropylamino)ethyl 1-phenylcyclohexanecarboxylate) were studied by electromyography, defining the migrating myoelectric complex (MMC) after i.v. administration in conscious rats. Alosetron prolonged the MMC cycle length from 16.6 to maximally 30.4 min at the dose 0.5 mg kg(-1). Piboserod promptly abolished MMC pattern and prolonged cycle length from 16.5 to >60 min at 0.5 mg kg(-1). PNU-171990A and PNU-174708A had no effect on basal cycle length up to a dose of 20 mg kg(-1). In controls, saline did not change the MMC pattern, while L-hyoscyamine at the same dose, 20 mg kg(-1), prolonged cycle length from 17.6 to 29.0 min. None of the drugs affected duration or propagation velocity of phase III of MMC. Blockade of 5-HT(4) receptors seems to exert a powerful inhibitory effect on motility, 5-HT(3) receptor blockade is less efficient and muscarinic receptor blockade has low efficacy.