Interactions between antiplasmodial 3,6-diamino-1'-dimethyl-9-anilinoacridine and hematin and concanamycin A.

Antiplasmodial 9-anilinoacridine derivatives exert their effects either by inhibiting DNA topoisomerase (topo) II or by interfering with heme crystallization within the parasite acidic food vacuole. Previous studies have shown that analogs of 9-anilinoacridine containing 3,6-diamino substitutions (in the acridine ring) inhibit Plasmodium falciparum DNA topo II in situ, whereas those with a 3,6-diCl substitution act by inhibiting beta-hematin formation, a property also seen with 3,6-diamino-1'-dimethyl-9-anilinoacridine (DDAA). To understand this seemingly anomalous property of DDAA, studies of its interaction with hematin and localization within the parasite food vacuole were undertaken. A weak interaction with hematin was demonstrated spectroscopically. Antagonism of DDAA inhibition of Plasmodium falciparum growth in culture by concanamycin A, a macrolide antibiotic inhibitor of vacuolar H(+)-ATPase derived from Streptomyces sp, was equivocal.

Plasmepsin II inhibitory activity of alkoxylated and hydroxylated chalcones.

Sixteen antimalarial alkoxylated and hydroxylated chalcones were tested for their ability to inhibit recombinant plasmepsin II in vitro. The best inhibitory compounds had either a chloro or dimethylamino group at the 4-position of phenyl ring A in the chalcone template. Combination of the chalcones with chloroquine showed additivity or mild antagonism of Plasmodium falciparum K1 growth in culture.

Antimalarial activity of concanamycin A alone and in combination with pyronaridine.

Concanamycin A, a macrolide antibiotic inhibitor of vacuolar H+-ATPase derived from Streptomyces sp, inhibited Plasmodium falciparum K1 growth in culture with an IC500 value of 0.2 nM. It exhibited an additive effect when tested together with the antimalarial pyronaridine.

Effects of water-soluble antioxidants and MAPKK/MEK inhibitor on curcumin-induced apoptosis in HL-60 human leukemic cells.

Curcumin is the main biologically active phytochemical compound in turmeric. It has been shown to have anticarcinogenic activity. The aims of the study were to identify the mechanism of apoptosis of HL-60 human promyelocytic leukemic cells induced by curcumin and to determine the effects of water-soluble antioxidants, ascorbic acid, Trolox (a water-soluble form of vitamin E), glutathione (GSH) and N-acetylcysteine (NAC) on this process. HL-60 cells were incubated with curcumin for 24 h and apoptotic cells were quantitated by flow cytometry following staining with annexin V-FITC and propidium iodide. Curcumin-treated HL-60 cells produced reactive oxygen species as detected by the dichlorofluorescein fluorescent assay. Apoptosis occurred via the mitochondria pathway as curcumin reduced mitochondrial membrane potential in a dose-dependent manner. In the presence of 10 microM curcumin, vitamin C (56 nM-5.6 microM) inhibited apoptosis of HL-60 cells; GSH at low concentration (1 microM) reduced apoptosis but had no effect at higher concentrations (10, 100 microM); and Trolox and NAC at 10 and 100 microM, respectively, enhanced apoptosis, but this effect was abolished at higher concentration (1 mM) of NAC. MAPKK/MEK inhibitor PD98059, enhanced curcumin-induced HL-60 apoptotic cell death.

Cyquant cell proliferation assay as a fluorescence-based method for in vitro screening of antimalarial activity.

The appearance of drug resistant parasites and the absence of an effective vaccine have resulted in the need for new effective antimalarial drugs. Consequently, a convenient method for in vitro screening of large numbers of antimalarial drug candidates has become apparent. The CyQUANT cell proliferation assay is a highly sensitive fluorescence-based method for quantitation of cell number by measuring the strong fluorescence produced when green GR dye binds to nucleic acids. We have applied the CyQUANT assay method to evaluate the growth of Plasmodium falciparum D6 strain in culture. The GR-nucleic acid fluorescence linearly correlated with percent parasitemia at both 0.75 or 1 percent hematocrit with the same correlation coefficient of r2 = 0.99. The sensitivity of P. falciparum D6 strain to chloroquine and to 3,6-bis-omega-diethylaminoamyloxyxanthone, a novel antimalarial, determined by the CyQUANT assay were comparable to those obtained by the traditional [3H]-ethanolamine assay: IC50 value of chloroquine was 54 nM and 51 nM by the CyQUANT and [3H]-ethanolamine assay, respectively; IC50 value for 3,6-bis-omega-diethylaminoamyloxyxanthone was 254 nM and 223 nM by the CyQUANT and [3H]-ethanolamine assay, respectively. This procedure requires no radioisotope, uses simple equipment, and is an easy and convenient procedure, with no washing and harvesting steps. Moreover, all procedures can be set up continuously and thus, the CyQUANT assay is suitable in automatic high through-put drug screening of antimalarial drugs.