RESUMO
Atovaquone-proguanil (Malarone®) is used for malaria prophylaxis and treatment. While the cytochrome bc1-inhibitor atovaquone has potent activity, proguanil's action is attributed to its cyclization-metabolite, cycloguanil. Evidence suggests that proguanil has limited intrinsic activity, associated with mitochondrial-function. Here we demonstrate that proguanil, and cyclization-blocked analogue tBuPG, have potent, but slow-acting, in vitro anti-plasmodial activity. Activity is folate-metabolism and isoprenoid biosynthesis-independent. In yeast dihydroorotate dehydrogenase-expressing parasites, proguanil and tBuPG slow-action remains, while bc1-inhibitor activity switches from comparatively fast to slow-acting. Like proguanil, tBuPG has activity against P. berghei liver-stage parasites. Both analogues act synergistically with bc1-inhibitors against blood-stages in vitro, however cycloguanil antagonizes activity. Together, these data suggest that proguanil is a potent slow-acting anti-plasmodial agent, that bc1 is essential to parasite survival independent of dihydroorotate dehydrogenase-activity, that Malarone® is a triple-drug combination that includes antagonistic partners and that a cyclization-blocked proguanil may be a superior combination partner for bc1-inhibitors in vivo.
Assuntos
Antimaláricos/farmacologia , Atovaquona/farmacologia , Inibidores Enzimáticos/farmacologia , Plasmodium berghei/efeitos dos fármacos , Plasmodium falciparum/efeitos dos fármacos , Proguanil/análogos & derivados , Animais , Anopheles , Antimaláricos/química , Atovaquona/química , Ciclização/efeitos dos fármacos , Di-Hidro-Orotato Desidrogenase , Relação Dose-Resposta a Droga , Combinação de Medicamentos , Complexo III da Cadeia de Transporte de Elétrons/antagonistas & inibidores , Complexo III da Cadeia de Transporte de Elétrons/metabolismo , Inibidores Enzimáticos/química , Eritrócitos/efeitos dos fármacos , Eritrócitos/parasitologia , Ácido Fólico/metabolismo , Células Hep G2 , Humanos , Concentração Inibidora 50 , Fígado/efeitos dos fármacos , Fígado/parasitologia , Oxirredutases atuantes sobre Doadores de Grupo CH-CH/metabolismo , Plasmodium berghei/crescimento & desenvolvimento , Plasmodium berghei/metabolismo , Plasmodium falciparum/crescimento & desenvolvimento , Plasmodium falciparum/metabolismo , Proguanil/química , Proguanil/farmacologia , Esporozoítos/efeitos dos fármacos , Esporozoítos/crescimento & desenvolvimento , Esporozoítos/metabolismo , Terpenos/metabolismo , Triazinas/química , Triazinas/farmacologiaRESUMO
Nuclear hormone receptors, such as the ecdysone receptor, often display a large amount of induced fit to ligands. The size and shape of the binding pocket in the EcR subunit changes markedly on ligand binding, making modelling methods such as docking extremely challenging. It is, however, possible to generate excellent 3D QSAR models for a given type of ligand, suggesting that the receptor adopts a relatively restricted number of binding site configurations or 'attractors'. We describe the synthesis, in vitro binding and selected in vivo toxicity data for gamma-methylene gamma-lactams, a new class of high-affinity ligands for ecdysone receptors from Bovicola ovis (Phthiraptera) and Lucilia cuprina (Diptera). The results of a 3D QSAR study of the binding of methylene lactams to recombinant ecdysone receptor protein suggest that this class of ligands is indeed recognised by a single conformation of the EcR binding pocket.
