Acute toxicity tests of antiplasmodial N-alkyl and N-benzyl-1,10-phenanthroline derivatives in Swiss mice.

Five new derivatives of N-alkyl and N-benzyl-1,10-phenanthroline had been shown to inhibit growth in vitro of Plasmodium falciparum FCR3 and in vivo of P. berghei. Acute toxicity tests demonstrated that some of those compounds had wide therapeutic indices. Safety tests of five N-alkyl and N-benzyl-1,10-phenanthroline derivatives were conducted in five groups of Swiss mice by a single intraperitoneal injection with various amounts of the test compounds, with chloroquine as comparison. Signs of toxic effects were observed during 24 hours and observations were continued for 14 days on the surviving mice. Mice were weighed before and after the test period. There were immediate behavioral changes among mice in the high dose group including restlessness, tremor, convulsion and eventually death, which was postulated to be due to the test compounds acting on the nervous system. There was no dose-dependent histopathological changes in the internal organs. Histopathological changes, such as congestion, degeneration and necrosis, were not found. There are no significant differences in mean weight gain among the groups of mice treated with the different compounds and controls. These results indicated that those new N-alkyl and N-benzyl-1,10-phenanthroline antiplasmodial compounds were toxic at high dose, but at non-toxic doses had no effect on weight gain and no histopathological effects on the appearance of internal organs.

Additive in vitro antiplasmodial effect of N-alkyl and N-benzyl-1,10-phenanthroline derivatives and cysteine protease inhibitor e64.

Potential new targets for antimalarial chemotherapy include parasite proteases, which are required for several cellular functions during the Plasmodium falciparum life cycle. Four new derivatives of N-alkyl and N-benzyl-1,10-phenanthroline have been synthesized. Those are (1)-N-methyl-1,10-phenanthrolinium sulfate, (1)-N-ethyl-1,10-phenanthrolinium sulfate, (1)-N-benzyl-1,10-phenanthrolinium chloride, and (1)-N-benzyl-1,10-phenanthrolinium iodide. Those compounds had potential antiplasmodial activity with IC(50) values from 260.42 to 465.38 nM. Cysteine proteinase inhibitor E64 was used to investigate the mechanism of action of N-alkyl and N-benzyl-1,10-phenanthroline derivatives. A modified fixed-ratio isobologram method was used to study the in vitro interactions between the new compounds with either E64 or chloroquine. The interaction between N-alkyl and N-benzyl-1,10-phenanthroline derivatives and E64 was additive as well as their interactions with chloroquine were also additive. Antimalarial mechanism of chloroquine is mainly on the inhibition of hemozoin formation. As the interaction of chloroquine and E64 was additive, the results indicated that these new compounds had a mechanism of action by inhibiting Plasmodium proteases.

In vitro antiplasmodial activity and cytotoxicity of newly synthesized N-alkyl and N-benzyl-1,10-phenanthroline derivatives.

A previous study showed that the 1,10-phenanthroline skeleton was active in vitro against chloroquine-resistant and sensitive strains of Plasmodium falciparum. Based on this skeleton, 8 derivatives of N-alkyl and N-benzyl-1,10-phenanthrolines have been synthesized. This study was conducted to evaluate the in vitro antiplasmodial activity and cytotoxicity of these compounds. The in vitro antiplasmodial activity was tested on two strains of P. falciparum, FCR-3 chloroquine-resistant and D10 chloroquine-sensitive strains, while their cytotoxicity was tested on the Vero cell line. The parasite and cell growth were estimated by hypoxantine-[2,8-3H] uptake after 24- and 72-hour incubation with each compound tested. The control parasite or cell free from any compounds was referred to as having 100% growth. For this radioactive method, the IC50 value showing concentration inhibiting 50% of the parasite growth was determined by probit analysis. The results showed that the highest antiplasmodial activity was observed with (1)-N-benzyl-1,10-phenanthrolinium iodide with the IC50 0.18-0.45 microM, and the IC50 of the compound on Vero cells ranged from 2,582.30 to 7,057.71 microM. The cytotoxic/ antiplasmodial ratio indicates that this compound has high selectivity (10,993 +/- 330.79-38,965 +/- 6,888.27).