Lauren Rattray

Anti-malarial efficacy of pyronaridine and artesunate in combination in vitro and in vivo

Pyronaridine is a Mannich base anti-malarial with demonstrated efficacy against drug resistant Plasmodium falciparum, P. vivax, P. ovale and P. malariae. However, resistance to pyronaridine can develop quickly when it is used alone but can be considerably delayed when it is administered with artesunate in rodent malaria models. The aim of this study was to evaluate the efficacy of pyronaridine in combination with artesunate against P. falciparum in vitro and in rodent malaria models in vivo to support its clinical application. Pyronaridine showed consistently high levels of in vitro activity against a panel of six P. falciparum drug-sensitive and resistant strains (Geometric Mean IC50=2.24 nM, 95% CI=1.20-3.27). In vitro interactions between pyronaridine and artesunate showed a slight antagonistic trend, but in vivo compared to pyronaridine and artesunate administered alone, the 3:1 ratio of the combination, reduced the ED90 of artesunate by approximately 15.6-fold in a pyronaridine-resistant P. berghei line and by approximately 200-fold in an artesunate-resistant line of P. berghei. Complete cure rates were achieved with doses of the combination above or equal to 8 mg/kg per day against P. chabaudi AS. These results indicate that the combination had an enhanced effect over monotherapy and lower daily doses of artesunate could be used to obtain a curative effect. The data suggest that the combination of pyronaridine and artesunate should have potential in areas of multi-drug resistant malaria.

New Azasterols against Trypanosoma brucei: Role of 24-Sterol Methyltransferase in Inhibitor Action

ABSTRACT A series of azasterol derivatives, designed as potential inhibitors of the Δ24-sterol methyltransferase enzyme (24-SMT), were synthesized and evaluated for their activities against parasitic protozoa. Values in the nanomolar range were obtained for 50% effective dose against the Trypanosoma brucei subsp. rhodesiense bloodstream form cultured in vitro. In order to investigate the mode of action, Trypanosoma brucei subsp. brucei 24-SMT was cloned and overexpressed and compounds were assayed for inhibitory activity. None of the inhibitors tested appeared to be active against the enzyme. Sterol composition analysis showed that only cholestane type sterols are present in membranes of bloodstream forms while ergosterol is a major component of procyclic sterol extracts. Interestingly, Northern blot analysis showed the presence of 24-SMT mRNA in both the procyclic and the bloodstream forms of the parasite, although levels of mRNA were threefold lower in the latter. Likewise, Western blot analysis and activity determinations evidenced the existence of active enzyme in both forms of the parasite. We conclude that the designed compounds act at sites other than 24-SMT in Trypanosoma brucei.

Antiprotozoal activity of drimane and coloratane sesquiterpenes towards Trypanosoma brucei rhodesiense and Plasmodium falciparum in vitro.

The extracts and 12 sesquiterpenes obtained from the East African medicinal plant Warburgia ugandensis Sprague (Canellaceae) were assessed for their antiplasmodial activity against the chloroquine‐sensitive (3D7) and chloroquine‐resistant (K1) strains of Plasmodium falciparum and antitrypanosomal activity against Trypanosoma brucei rhodesiense. The dichloromethane extract displayed strong antiplasmodial and antitrypanosomal activities with IC50 values of 8.10 and 1.10 µg/mL against K1 strain of the malaria parasite and STlB900 strain of T. b. rhodesiense, respectively. Among the compounds evaluated for inhibition of trypomastigotes, both drimane and coloratane sesquiterpenes possessing aldehyde groups at positions 8 and 9 were found to show most antitrypanosomal activity with IC50 values in the range 0.56–6.4 µM. The antiplasmodial assays also revealed that the six coloratane and six drimane sesquiterpenes isolated from this extract exhibited significant antitrypanosomal activity with IC50 values ranged from 0.45 to ?114 µM. Among the compounds tested against the malarial parasite P. falciparum 11?‐hydroxymuzigadiolide (3) was most active with an IC50 value of 6.40 µM. Copyright

Antiparasitic activities of acridone alkaloids from Swinglea glutinosa (Bl.) Merr.

Onze alcaloides acridonicos isolados de Swinglea glutinosa (Bl.) Merr. foram avaliados para suas atividades in vitro contra linhagens de Plasmodium falciparum sensiveis a cloroquina 3D7, Trypanosoma brucei rhodesiense STIB9000 e Leishmania donovani L82. Ensaios com celulas KB foram tambem executados com o objetivo de se determinar o grau de toxicidade das substâncias ativas contra os parasitas. Nove dos compostos apresentaram IC 50 entre 0,3 e 11,6 µM contra P. falciparum. Em contraste, um pequeno numero de compostos mostrou atividade significativa contra T. brucei rhodesiense e nenhum apresentou atividade contra L. donovani. Entre os alcaloides tres tiveram IC 50 < 1,0 µM contra P. falciparum, enquanto que contra T. b. rhodesiense cinco mostraram IC 50 < 10 µM. A caracterizacao dos alcaloides, 1,3,5-triidroxi-4-metoxi-10-metil-2,8bis(3-metilbut-2-enil)acridin-9(10H)-ona (1), 2,3-diidro-4,9-diidroxi-2-(2-hidroxipropan-2-il)11-metoxi-10-metilfuro[3,2-b]acridin-5(10H)-ona (2) e 3,4-diidro-3,5,8-triidroxi-6-metoxi-2,2,7trimetil-2H-pirano[2,3-a]acridin-12(7H)-ona (3), e aqui discutida. Discute-se tambem a relacao estrutura-atividade para todos os compostos ensaiados. O isolamento e dados espectrais para os alcaloides 1-3 estao sendo aqui descritos pela primeira vez, embora em trabalho anterior tenham sido relatadas as suas atividades citotoxicas. Eleven acridone alkaloids isolated from Swinglea glutinosa (Bl.) Merr. were examined for in vitro activity against chloroquine-sensitive Plasmodium falciparum 3D7, Trypanosoma brucei rhodesiense STIB900 and Leishmania donovani L82. An assay with KB cells was developed in order to compare in vitro toxicity of alkaloids with the selective action on the parasites. Nine of the compounds had IC 50 values ranging from 0.3 to 11.6 µM against P. falciparum. In contrast, a small number of compounds showed significant activity against T. brucei rhodesiense and none had activity against L. donovani. Among the alkaloids three had IC 50 < 1.0 µM against P. falciparum, whereas against T. b. rhodesiense five had IC 50 < 10 µM. The characterization of the acridone alkaloids, 1,3,5-trihydroxy-4-methoxy-10-methyl-2,8-bis(3-methylbut-2-enyl)acridin-9(10H)-one (1), 2,3-dihydro-4,9-dihydroxy-2-(2-hydroxypropan-2-yl)-11-methoxy-10-methylfuro[3,2-b] acridin-5(10H)-one (2) and 3,4-dihydro-3,5,8-trihydroxy-6-methoxy-2,2,7-trimethyl-2Hpyrano[2,3-a]acridin-12(7H)-one (3), is discussed, as well as the structure-activity relationship of all compounds assayed. Isolation and spectral data of alkaloids 1-3 are described for the first time although their citotoxicities to cancer cells have been described before.

Preparation of N-Sulfonyl- and N-Carbonyl-11-Azaartemisinins with Greatly Enhanced Thermal Stabilities: in vitro Antimalarial Activities

As the clinically used artemisinins do not withstand the thermal stress testing required to evaluate shelf life for storage in tropical countries where malaria is prevalent, there is a need to develop thermally more robust artemisinin derivatives. Herein we describe the attachment of electron‐withdrawing arene‐ and alkanesulfonyl and ‐carbonyl groups to the nitrogen atom of the readily accessible Ziffer 11‐azaartemisinin to provide the corresponding N‐sulfonyl‐ and ‐carbonylazaartemisinins. Two acylurea analogues were also prepared by treatment of the 11‐azaartemisinin with arylisocyanates. Several of the N‐sulfonylazaartemisinins have melting points above 200 °C and possess substantially greater thermal stabilities than the artemisinins in current clinical use, with the antimalarial activities of several of the arylsulfonyl derivatives being similar to that of artesunate against the drug‐sensitive 3D7 clone of the NF54 isolate and the multidrug‐resistant K1 strain of P. falciparum. The compounds possess relatively low cytotoxicities. The carbonyl derivatives are less crystalline than the N‐sulfonyl derivatives, but are generally more active as antimalarials. The N‐nitroarylcarbonyl and arylurea derivatives possess sub‐ng ml−1 activities. Although several of the azaartemisinins possess log P values below 3.5, the compounds have poor aqueous solubility (<1 mg L−1 at pH 7). The greatly enhanced thermal stability of our artemisinins suggests that strategic incorporation of electron‐withdrawing polar groups into both new artemisinin derivatives and totally synthetic trioxanes or trioxolanes may assist in the generation of practical new antimalarial drugs which will be stable to storage conditions in the field, while retaining favorable physicochemical properties.

Anti-African trypanocidal and antimalarial activity of natural flavonoids, dibenzoylmethanes and synthetic analogues.

Objectives The known anti‐protozoal activity of flavonoids has stimulated the testing of other derivatives from natural and synthetic sources.