Abstract In antimalarial research there are no standard procedures to determine the toxicity of a drug candidate. Among the alternatives available, in vitro cytotoxicity assays are the most widely used to predict toxic effects of future therapeutic products. They have the advantage over the in vivo assays, in that they offer the possibility to restrain the number of experimental variables. The objective of the present study was to compare in vitro cytotoxic methods by testing various compounds currently used to treat malaria against different cell lines. Neutral red (NR) uptake and methylthiazoletetrazolium (MTT) colorimetric in vitro assays were used to determine preliminary toxicity of commercially available antimalarial drugs against tumor and non-tumor cells lines. Toxicity through brine shrimp lethality bioassay and hemolytic activity were also evaluated. Significant differences were observed in the tests measured by NR uptake. The tumor cell lines TOV-21G and HepG2 and non-tumor WI-26VA4 cells showed relatively uniform toxicity results, with TOV-21G being the most sensitive cell tested, presenting the lowest concentration to cause death to 50% of viable cells (CC50) values. The results of this study support the use of TOV-21G, HepG2 and WI-26VA4 cells lines as the choice for cytotoxicity tests to evaluate potential bioactive compounds.

This work reports the in vitro activity against Plasmodium falciparumblood forms (W2 clone, chloroquine-resistant) of tamoxifen-based compounds and their ferrocenyl (ferrocifens) and ruthenocenyl (ruthenocifens) derivatives, as well as their cytotoxicity against HepG2 human hepatoma cells. Surprisingly with these series, results indicate that the biological activity of ruthenocifens is better than that of ferrocifens and other tamoxifen-like compounds. The synthesis of a new metal-based compound is also described. It was shown, for the first time, that ruthenocifens are good antiplasmodial prototypes. Further studies will be conducted aiming at a better understanding of their mechanism of action and at obtaining new compounds with better therapeutic profile.

Infusions of Aspidosperma nitidum (Apocynaceae) wood bark are used to treat fever and malaria in the Amazon Region. Several species of this family are known to possess indole alkaloids and other classes of secondary metabolites, whereas terpenoids, an inositol and the indole alkaloids harmane-3 acid and braznitidumine have been described in A. nitidum . In the present study, extracts from the wood bark, leaves and branches of this species were prepared for assays against malaria parasites and cytotoxicity testing using human hepatoma and normal monkey kidney cells. The wood bark extracts were active against Plasmodium falciparum and showed a low cytotoxicity in vitro, whereas the leaf and branch extracts and the pure alkaloid braznitidumine were inactive. A crude methanol extract was subjected to acid-base fractionation aimed at obtaining alkaloid-rich fractions, which were active at low concentrations against P. falciparum and in mice infected with and sensitive Plasmodium berghei parasites. Our data validate the antimalarial usefulness of A. nitidum wood bark, a remedy that can most likely help to control malaria. However, the molecules responsible for this antimalarial activity have not yet been identified. Considering their high selectivity index, the alkaloid-rich fractions from the plant bark might be useful in the development of new antimalarials.