Antimalarial Activities of (Z)-2-(Nitroheteroarylmethylene)-3(2H)-Benzofuranone Derivatives: In Vitro and In Vivo Assessment and β-Hematin Formation Inhibition Activity.

A series of (Z)-2-(nitroheteroarylmethylene)-3(2H)-benzofuranones possessing nitroheteroaryl groups of nitroimidazole, nitrofuran, and nitrothiophene moieties was screened for antiplasmodium activity against a drug-sensitive strain (3D7 strain) and a multidrug-resistant (chloroquine [CQ] and pyrimethamine) strain (K1 strain) of Plasmodium falciparum. 5-Nitroimidazole and 4-nitroimidazole analogs were highly selective and active against resistant parasites, while 5-nitrofuran and 5-nitrothiophene derivatives were more potent against the 3D7 strain than against the K1 strain. Among the synthetic analogues, (Z)-6-chloro-2-(1-methyl-5-nitroimidazol-2-ylmethylene)-3(2H)-benzofuranone (compound 5h) exhibited the highest activity (50% inhibitory concentration [IC50], 0.654 nM) against the K1 strain and (Z)-7-methoxy-2-(5-nitrothiophen-2-ylmethylene)-3(2H)-benzofuranone (10g) showed the highest activity (IC50, 0.28 μM) against the 3D7 strain in comparison with the activities of CQ (IC50s of 3.13 and 206.3 nM against 3D7 and K1 strains, respectively). The more active compounds, with IC50s lower than 5 μg/ml (∼20 μM), were further studied for their cytotoxicity responses using KB cells. From these studies, 5-nitroimidazole, 4-nitroimidazole, and 5-nitrofuran analogues were shown to be cytotoxic against KB cells, while 5-nitrothiophene analogues were shown to have the least cytotoxic effects. To gain some insight into their potential contributing mechanisms of action, three derivatives, 10e, 10g, and 10h (from the nitrothiophene subgroup, possessing 6-methoxy, 7-methoxy, and 6,7-dimethoxy substituents, respectively, on their benzofuranone moieties), showing the least toxicity and highest selectivity indices were assessed for their β-hematin formation inhibition activity. Compound 10g demonstrated the highest inhibition activity (IC50, 10.78 μM) in comparison with that of CQ (IC50, 2.63 μM) as the reference drug. Finally, these three analogues (10e, 10g, and 10h) were further evaluated for their in vivo activities against the Plasmodium berghei/albino mouse model (Peter's test). The tested analogues were shown to be active, reducing the percentages of erythrocytes that contained parasites by 53.4, 48.8, and 32.4%, respectively.