Biomedical subjects
Publications and source records attributed to Reto Brun.
Potential inhibitors of the Trypanosoma cruzi dUTP nucleotidohydrolase were docked into the enzyme using the program FlexX. Compounds that docked selectively were then selected and synthesized using solid phase methodology, giving rise to a novel library of amino acid uracil acetamide compounds which were evaluated for enzyme inhibition and anti-parasitic activity.
Only three drugs are available for the treatment of East African trypanosomiasis. Patients suffer from painful application, severe side effects and increasing resistance against these drugs. Malaria tropica kills more than 2 million people every year mainly due to growing drug resistance. 4-Dialkylaminobicyclo[2.2.2]octan-2-ols and some of their esters have shown activity against both the causative organisms, Trypanosoma brucei rhodesiense and Plasmodium falciparum. Ethers and new esters with markedly higher lipophilicity were prepared in three-step procedures from acyclic synthons. The new compounds were screened for their antiprotozoal activities against T. b. rhodesiense (STIB 900) and P. falciparum K1 (resistant to chloroquine and pyrimethamine), and for their cytotoxicity with L-6 cells by means of in vitro microplate assays. The results were compared to those of the parent compounds indicating that higher lipophilicity increases the antiprotozoal activities. The pivalate 10a showed the highest antitrypanosomal activity. The 4-chlorobenzoate 9b exhibited good antiplasmodial activity and low cytotoxicity. The most active antiplasmodial agent was the benzhydryl ether 13c which was nearly as active as chloroquine against sensitive strains.
Plasmodium vivax is an important human pathogen causing malaria in more temperate climates of the world. Similar to Plasmodium falciparum, the causative agent for malaria tropica, drug resistance is beginning to emerge for this parasite species and this hampers adequate treatment of infection. We have used a short-term ex vivo drug assay to monitor activity of OZ277 (RBx-11160), a fully synthetic anti-malarial peroxide, and the diamidine DB75 against P. vivax. For both compounds as well as the anti-malarial reference compounds artesunate, artemether, and chloroquine, the in vitro IC(50) values were determined in one-cycle hypoxanthine incorporation assays. Results from such assays were found to be very similar compared to IC(50) values obtained from one-cycle P. falciparum hypoxanthine assays. We demonstrate the anti-parasite activity of OZ277 and the reference compounds to be faster than that of DB75. These data warrant clinical testing of OZ277 against P. vivax malaria and support recent data on clinical activity against P. vivax for DB75.
African trypanosomes, Trypanosoma brucei rhodesiense (TBR) and Trypanosoma brucei gambiense (TBG), affect hundreds of thousands of lives in tropical regions of the world. The toxicity of the diamidine pentamidine, an effective drug against TBG, necessitates the design of better drugs. An orally effective prodrug of the diamidine, furamidine (DB75), presently scheduled for phase III clinical trials, has excellent activity against TBG with toxicity lower than that of pentamidine. As part of an effort to develop additional and improved diamidines against African trypanosomes, CoMFA and CoMSIA 3D QSAR analyses have been conducted with furamidine and a set of 25 other structurally related compounds. Two different alignment strategies, based on a putative kinetoplast DNA minor groove target, were used. Due to conserved electrostatic properties across the compounds, models that used only steric and electronic properties did not perform well in predicting biological results. An extended CoMSIA model with additional descriptors for hydrophobic, donor, and acceptor properties had good predictive ability with a q2=0.699, r2=0.974, SEE, standard error of estimate=0.1, and F=120.04. The results have been used as a guide to design compounds that, potentially, have better activity against African trypanosomes.
Baibutoside (5), a new cycloartane-type triterpene glycoside, has been isolated from the roots of Astragalus baibutensis along with four known glycosides, acetylastragaloside I (1), and astragalosides I, II, and IV (2-4, resp.). The structure elucidation of the compounds were achieved by a combination of one- and two-dimensional NMR techniques (DQF-COSY, HSQC, HMBC, and ROESY), and mass spectrometry (ESI-MS), where all the compounds were shown to have cycloastragenol (=(20R,24S)-3beta,6alpha,16beta,25-tetrahydroxy-20,24-epoxy-9,19-cyclolanostane) as aglycone. All compounds were tested for in vitro antiprotozoal activity. Compounds 1-4 displayed notable activity vs. Trypanosoma brucei rhodesiense, with acetylastragaloside I (1) being the most potent (IC50 9.5 microg/ml). Acetylastragaloside I (1) was also lethal to T. cruzi (IC50 5.0 microg/ml), and it is the first cycloartane-type triterpene with remarkable trypanocidal activity against both T. brucei rhodesiense and T. cruzi. However, it exhibits some cytotoxicity on mammalian cells.
Primin (=2-methoxy-6-pentylcyclohexa-2,5-diene-1,4-dione), a natural benzoquinone synthesized in our laboratory, was investigated for its in vitro antiprotozoal, antimycobacterial, and cytotoxic potential. Primin showed very potent activity against Trypanosoma brucei rhodesiense (IC50 0.144 microM) and Leishmania donovani (IC50 0.711 microM), and revealed low cytotoxicity (IC50 15.4 microM) on mammalian cells. Only moderate inhibitory activity was observed against Mycobacterium tuberculosis, Trypanosoma cruzi, and Plasmodium falciparum. When tested for in vivo efficacy in a Trypanosoma b. brucei rodent model, primin failed to cure the infection at 20 mg/kg given intraperitoneally. Primin was too toxic in vivo at a higher concentration (30 mg/kg, injected i.p. route) in mice infected with L. donovani. Taken together, primin can serve as a lead compound for the rational design of more potent and less toxic antiprotozoal agents.
PURPOSE OF REVIEW: To review recent literature on human African trypanosomiasis, focussing on genome sequencing, diagnosis and drug discovery, and typing of trypanosomes. RECENT FINDINGS: The most important recent development has been the completion of the Trypanosoma brucei genome which will greatly facilitate the discovery of new drug targets and genetic markers. Correct staging of the disease is of key importance for treatment. The analysis of sleep patterns is a promising new method to this end and has advanced enough to begin thorough clinical trials. In terms of novel drug candidates, dicationic molecules show the most promise with one oral diamidine in phase 3 clinical trials. New targets and classes of molecules which show in vitro trypanocidal activity are also described. Two new methods - MGE-PCR and microsatellites - allow analyses without parasite cultivation, eliminating a major impediment to efficient sampling for population studies. The finding that several wild animal species harbour T. b. gambiense, and that parasite transmission is efficient even from very low parasitaemias, sheds a new light on the importance of animal reservoirs. SUMMARY: The use of T. brucei as model system for molecular and cell biology is regularly producing new technologies exploitable for diagnosis and new drugs. Drug discovery and development experience a revival through new public-private partnerships and initiatives. The challenge remains to translate this progress into improvements for affected people in disease endemic areas.
We examined the effects of praziquantel and the artemisinins on adult Echinostoma caproni. In vitro, both praziquantel and the artemisinins exhibited exposure-response relationships. In vivo, worm burden reductions of 100% were achieved with single oral doses of praziquantel, artesunate, and artemether at 50, 700, and 1,100 mg/kg of body weight, respectively.
Trypanosomiasis and leishmaniasis are important parasitic diseases affecting millions of people in Africa, Asia, and South America. In a previous study, we identified several flavonoid glycosides as antiprotozoal principles from a Turkish plant. Here we surveyed a large set of flavonoid aglycones and glycosides, as well as a panel of other related compounds of phenolic and phenylpropanoid nature, for their in vitro activities against Trypanosoma brucei rhodesiense, Trypanosoma cruzi, and Leishmania donovani. The cytotoxicities of more than 100 compounds for mammalian L6 cells were also assessed and compared to their antiparasitic activities. Several compounds were investigated in vivo for their antileishmanial and antitrypanosomal efficacies in mouse models. Overall, the best in vitro trypanocidal activity for T. brucei rhodesiense was exerted by 7,8-dihydroxyflavone (50% inhibitory concentration [IC50], 68 ng/ml), followed by 3-hydroxyflavone, rhamnetin, and 7,8,3',4'-tetrahydroxyflavone (IC50s, 0.5 microg/ml) and catechol (IC50, 0.8 microg/ml). The activity against T. cruzi was moderate, and only chrysin dimethylether and 3-hydroxydaidzein had IC50s less than 5.0 microg/ml. The majority of the metabolites tested possessed remarkable leishmanicidal potential. Fisetin, 3-hydroxyflavone, luteolin, and quercetin were the most potent, giving IC50s of 0.6, 0.7, 0.8, and 1.0 microg/ml, respectively. 7,8-Dihydroxyflavone and quercetin appeared to ameliorate parasitic infections in mouse models. Generally, the test compounds lacked cytotoxicity in vitro and in vivo. By screening a large number of flavonoids and analogues, we were able to establish some general trends with respect to the structure-activity relationship, but it was not possible to draw clear and detailed quantitative structure-activity relationships for any of the bioactivities by two different approaches. However, our results can help in directing the rational design of 7,8-dihydroxyflavone and quercetin derivatives as potent and effective antiprotozoal agents.
We previously showed that over-expression of Trypanosoma brucei MRPA, a member of the multidrug resistance protein family in T. brucei, reproducibly resulted in resistance to the anti-trypanosomal drug melarsoprol in vitro. MRPA is predicted to mediate efflux of melarsoprol as a conjugate with trypanothione, a glutathione-spermidine conjugate which is the major small thiol in trypanosomes. Here, we show that depletion of MRPA by RNA interference resulted in moderate hypersensitivity to both melarsoprol and melarsen oxide. Over-expression of MRPA alone is not sufficient to cause melarsoprol resistance in vivo, although it is sufficient in vitro. This discrepancy is not an effect of drug metabolism since over-expression of MRPA alone conferred resistance to melarsoprol and its principle metabolite, melarsen oxide, in vitro. Over-expression of MRPA was not detected in four melarsoprol-resistant trypanosome isolates from sleeping sickness patients.
PURPOSE: New 2-azabicyclo[3.2.2]nonanes were prepared from antiprotozoal bicyclo[2.2.2]octan-2-ones to investigate the influence of the replacement of the rigid bicyclo-octane structure by the more flexible bicyclo-nonane system on the antiplasmodial and antitrypanosomal activity. METHODS: The 2-azabicyclo[3.2.2]nonanes were synthesized via a one-step procedure from bicyclo[2.2.2]octan-2-ones and tested for their activities against Trypanosoma b. rhodesiense and Plasmodium falciparum K1 (resistant to chloroquine and pyrimethamine) using in vitro microplate assays. RESULTS: 2-azabicyclo[3.2.2]non-5-ylamines exhibit higher antiprotozoal activities than 4-aminobicyclo[2.2.2]octanes, 4-aminobicycl [2.2.2]octan-2-ones and 4-amino-2-azabicyclo[3.2.2]nonan-3-ones. (7, 8-Diphenyl-2-azabicyclo[3.2.2]non-5-yl)-dimethylamine shows enhanced anti-trypanosomal (IC50 = 0.60 microM) and remarkable antiplasmodial (IC50 = 0.28 microM) activity. However, the in vivo activity of this compound against Plasmodium berghei in mice is moderate. CONCLUSIONS: Due to their promising in vitro antiprotozoal activity and their low cytotoxicity, 2-azabicyclo[3.2.2]nonanes should serve as lead compounds for further modifications.
The rapid increase of resistance to drugs commonly used in the treatment of tropical diseases such as malaria and African sleeping sickness calls for the prompt development of new safe and efficacious drugs. The pathogenic protozoan parasites lack the capability of synthesising purines de novo and they take up preformed purines from their host through various transmembrane transporters. Adenosine derivatives constitute a class of potential therapeutics due to their selective internalisation by these transporters. Automated solid-phase synthesis can speed up the process of lead finding and we pursued the solid-phase synthesis of di- and trisubstituted 5'-carboxamidoadenosine derivatives by using a safety-catch approach. While efforts with Kenner's sulfonamide linker remained fruitless, successful application of the hydrazide safety-catch linker allowed the construction of two representative combinatorial libraries. Their antiprotozoal evaluation identified two compounds with promising activity: N(6)-benzyl-5'-N-phenylcarboxamidoadenosine with an IC(50) value of 0.91 microM against Trypanosoma brucei rhodesiense and N(6)-diphenylethyl-5'-phenylcarboxamidoadenosine with an IC(50) value of 1.8 microM against chloroquine resistant Plasmodium falciparum.
Analogues of the natural antibiotic thiolactomycin (TLM), an inhibitor of the condensing reactions of type II fatty acid synthase, were synthesized and evaluated for their ability to inhibit the growth of the malaria parasite Plasmodium falciparum. Alkylation of the C4 hydroxyl group led to the most significant increase in growth inhibition (over a 100-fold increase in activity compared to TLM). To investigate the mode of action, the P. falciparum KASIII enzyme was produced for inhibitor assay. A number of TLM derivatives were identified that showed improved inhibition of this enzyme compared to TLM. Structure-activity relationships for enzyme inhibition were identified for some series of TLM analogues, and these also showed weak correlation with inhibition of parasite growth, but this did not hold for other series. On the basis of the lack of a clear correlation between inhibition of pfKASIII activity and parasite growth, we conclude that pfKASIII is not the primary target of TLM analogues. Some of the analogues also inhibited the growth of the parasitic protozoa Trypanosoma cruzi, T. brucei, and Leishmania donovani.
This paper describes a structure-activity study to identify novel, small-molecule inhibitors of the enzyme deoxyuridine 5'-triphosphate nucleotidohydrolase (dUTPase) from parasitic protozoa. The successful synthesis of a variety of analogues of dUMP is described in which the substituents are introduced at the 3'- and 5'-positions, together with variation in the heteroatom at the 5'-position. The compounds were assayed against recombinant Plasmodium falciparum and Leishmania major enzymes and the human enzyme to give a measure of selectivity. The compounds were also tested in vitro against the intact parasites P. falciparum and L. donovani. A number of potent and selective inhibitors of the P. falciparum dUTPase that show drug-like properties and represent good leads for future development were identified. The best inhibitors included the compounds 5'-tritylamino-2',5'-dideoxyuridine (2j) (Ki = 0.2 microM) and 5'-O-triphenylsilyl-2',3'-didehydro-2',3'-dideoxyuridine (5h) (Ki = 1.3 microM), with selectivity greater than 200-fold compared to the human enzyme. Structural features important for antiplasmodial activity were determined. The correlation observed between the inhibition of the enzyme and the inhibition of the parasite growth in vitro demonstrates that the P. falciparum dUTPase constitutes a valid and attractive novel target for the development of much-needed new antimalarial drugs.
The parasites that give rise to human African trypanosomiasis (HAT) are auxotrophs for various nutrients from the human host, including purines. They have specialist nucleoside transporters to import these metabolites. In addition to uptake of purine nucleobases and purine nucleosides, one of these transporters, the P2 transporter, can carry melamine derivatives; these derivatives are not substrates for the corresponding mammalian transporters. In this paper, we report the coupling of the melamine moiety to selected nitro heterocycles with the aim of selectively delivering these compounds to the parasites. Some compounds prepared have similar in vitro trypanocidal activities as melarsoprol, the principal drug used against late-stage HAT, with 50% growth inhibitory concentrations in the submicromolar range. Selected compounds were also evaluated in vivo in rodent models infected with Trypanosoma brucei brucei and T. brucei rhodesiense and showed pronounced activity and in two cases were curative without overt signs of toxicity. Compounds were also tested against other trypanosomatid pathogens, Leishmania donovani and Trypanosoma cruzi, and significant activity in vitro was noted for T. cruzi against which various nitro heterocycles are already registered for use.
Dicationic guanidine, N-alkylguanidine, and reversed amidine derivatives of fused ring systems have been synthesized from their corresponding bis-amines. DNA binding studies suggest that the diguanidines and the N-alkyl diguanidines fluorenes bind in the minor groove in a manner similar to that of the previously reported dicationic carbazole derivatives. The diguanidines and the N-alkyl diguanidines showed promising in vitro activity against both Trypanosoma brucei rhodesiense and Plasmodium falciparum. Promising in vivo biological results were obtained for the dicationic N-isopropylguanidino-9H-fluorene, giving 4/4 cures of the treated animals in the STIB900 animal model for African trypanosomiasis. The N-methyl analogue showed high activity as well. In addition, with the goal of enhancing the oral bioavailability, two novel classes of potential guanidine prodrugs were prepared. The N-alkoxyguanidine derivatives were not effective as prodrugs. In contrast, a number of the carbamates showed promising activity. The value of the carbamate prodrugs was clearly demonstrated by the results, which gave 4/4 cures on oral administration in the STIB900 mouse model.
A series of near-linear biphenyl benzimidazole diamidines 5a-h were synthesized from their respective diamidoximes (4a-h), through the bis-O-acetoxyamidoxime, followed by hydrogenation in glacial acetic acid/ethanol in the presence of Pd-C. Compounds 4a-h were obtained in three steps, starting with the Suzuki coupling reaction of the appropriate haloarylcarbonitriles 1a-g or 4-bromo-2-fluorobenzaldehyde with 4-formylphenylboronic acid or 4-cyanophenylboronic acid to form the anticipated 4-formylbiphenyl carbonitrile analogues 2a-h. Subsequent condensation of the formyl derivatives 2a-h with 3,4-diaminobenzonitrile in the presence of sodium bisulfite or 1,4-benzoquinone gave the desired dinitriles 3a-h, the precursors for 4a-h. All the diamidines showed strong DNA affinities, as judged by high Delta Tm values with poly(dA.dT)2) The compounds were quite active in vitro versus Trypanosoma brucei rhodesiense, giving IC50 values ranging from 3 to 37 nM. These compounds were even more active versus Plasmodium falciparum, exhibiting IC50 values ranging from 0.5 to 23 nM. The compounds showed moderate to good activity in vivo in the STIB900 model for acute African trypanosomiasis. The most active compounds 5b and e gave 3/4 cures on an IP dosage of 20 mg/kg.
This paper describes the discovery of synthetic 1,2,4-trioxolane antimalarials and how we established a workable structure-activity relationship in the context of physicochemical, biopharmaceutical, and toxicological profiling. An achiral dispiro-1,2,4-trioxolane (3) in which the trioxolane is flanked by a spiroadamantane and spirocyclohexane was rapidly identified as a lead compound. Nonperoxidic 1,3-dioxolane isosteres of 3 were inactive as were trioxolanes without the spiroadamantane. The trioxolanes were substantially less effective in a standard oral suspension formulation compared to a solubilizing formulation and were more active when administered subcutaneously than orally, both of which suggest substantial biopharmaceutical liabilities. Nonetheless, despite their limited oral bioavailability, the more lipophilic trioxolanes generally had better oral activity than their more polar counterparts. In pharmacokinetic experiments, four trioxolanes had high plasma clearance values, suggesting a potential metabolic instability. The toxicological profiles of two trioxolanes were comparable to that of artesunate.