In vitro activity of iron-binding compounds against Senegalese isolates of Plasmodium falciparum.

OBJECTIVES: The in vitro activities of FR160, a synthetic catecholate siderophore, and two iron-binding agents, desferrioxamine and doxycycline, were evaluated against Plasmodium falciparum isolates. Correlations between these compounds and standard antimalarial drugs (chloroquine, quinine, amodiaquine, pyronaridine, artemether, artesunate, atovaquone, cycloguanil and pyrimethamine) were assessed to determine any degree of cross-resistance. METHODS: Between October 1997 and February 1998, and September and November 1998, 189 P. falciparum isolates were obtained in Dielmo and Ndiop (Dakar). Their susceptibilities were assessed using an isotopic, microwell format, drug susceptibility test. RESULTS: The 137 inhibitory concentrations (IC(50)) values of FR160 ranged from 0.1 to 10 microM and the geometric mean IC(50) was 1.48 microM (95% CI = 1.29-1.68 microM). The geometric mean IC(50) of doxycycline for 121 isolates was 18.9 microM (95% CI = 16.8-21.3 microM) and that of desferrioxamine for 73 isolates was 20.7 microM (95% CI = 17.3-24.8 microM). FR160 was significantly less active against the chloroquine-resistant isolates (P < 0.0001). The mean IC(50)s of doxycycline were significantly higher for the chloroquine-susceptible isolates than for the resistant parasites (P = 0.0447). There was a weak correlation between the responses to FR160, desferrioxamine or doxycycline and those to the other antimalarial compounds (r(2) < 0.22). CONCLUSIONS: The activities of FR160 and desferrioxamine, determined for P. falciparum clones, were confirmed against 137 isolates. The coefficients of determination between the responses to FR160, doxycycline or desferrioxamine and those to all the antimalarial drugs tested are too weak to suggest cross-resistance. FR160 could be a rationale partner to use in combination with doxycycline.

Iron chelators as antimalarial agents: in vitro activity of dicatecholate against Plasmodium falciparum.

The present study was undertaken to explore the antimalarial effect of a series of dicatecholate iron chelators. They may be made more or less lipophilic by increasing or reducing the length of the R substituent on the nitrogen. In vitro activity against the W2 and 3D7 clones of Plasmodium falciparum, toxicity on Vero cells and toxicity on uninfected erythrocytes by measure of the released haemoglobin were assessed for each compound. These findings were compared with the ability of iron(III), iron(II) and ferritin to reverse the inhibitory effect of catecholates. This study shows that increased lipid solubility of catecholate iron chelators does not lead to improved antimalarial activity. However, their activity is well correlated with their interaction with iron and with their toxicity against Vero cells. This study demonstrates a potent antimalarial effect of FR160 (R = C9H19) on five different strains of P. falciparum in vitro. FR160 inhibited parasite growth with an IC50 between 0.8 and 1.5 micro M. The effects of FR160 on mammalian cells were minimal compared with those obtained with malaria parasites. FR160 acted on parasites at considerably higher rates than desferrioxamine, and at all stages of parasite growth. The drug was more effective at the late trophozoite and young schizont stages, although FR160 affected rings and schizonts as well. Ascorbic acid, a free radical scavenger, reduced the activities of FR160 and artesunate. FR160 might induce formation of free radicals, which could explain why FR160 antagonized the effects of artesunate and dihydroartemisinin.

Synthesis and in vitro antibacterial activity of catechol-spiramycin conjugates.

The first synthesis of siderophore conjugates of two macrolide antibiotics, spiramycin 1 and neospiramycin 2, which are unable to penetrate the outer membrane of gram-negative bacteria are described. These novel conjugates were prepared by regioselective acylation of a hydroxyl function of 1 and 2 with a dihydroxybenzoic Fe(III) complexing ligand linked via a carboxyl group containing spacer to the macrolide antibiotics. The preliminary biological evaluation of these novel conjugates under standard and iron depleted conditions has shown that their antibacterial activity was comparable to that of spiramycin 1 and neospiramycin 2.

Evaluation of growth promotion and inhibition from mycobactins and nonmycobacterial siderophores (Desferrioxamine and FR160) in Mycobacterium aurum.

Heterologous mycobactins and the synthetic FR160 [N4-nonyl,N1,N8-bis(2,3-dihydroxybenzoyl) spermidine hydrobromide (C3 0H4 6N3, O6 Br)] promoted growth in Mycobacterium aurum in low concentrations. They were otherwise highly inhibitory, as opposed to homologous mycobactin, which was strictly growth promoting. Desferrioxamine B (Desferal) had no significant effect on growth.

Siderophore activity of chemically synthesized dihydroxybenzoyl derivatives of spermidines and cystamide.

Chemically synthesized dihydroxybenzoyl derivatives of spermidine and cystamide containing two-, three- and four-bidentates with the hydroxyl groups in 2,3 or 3,4 position were examined in cross-feeding tests using Gram-negative siderophore indicator strains carrying different iron-related markers, and two Mycobacterium spp. The catecholates were unable to feed tonB mutants of E. coli and S. typhimurium as well as the fepA, fiu, cir mutant of E. coli, pointing to a tonB- and fepA, cir, fiu-dependent transport. Bis(2,3-dihydroxybenzoyl)derivatives promoted Salmonella spp, E. coli, K. pneumoniae and P. aeruginosa strains significantly better than did 3,4-dihydroxybenzoyl derivatives. N4-substituted spermidines acted more effectively than non-substituted derivatives. Bis(2,3-dihydroxybenzoyl) cystamide was superior to the other catecholates tested in growth promotion of Gram-negative bacteria. The two four-bidentates and the tri-bidentate reacted to K. pneumoniae in an inhibitory mode. The position of the hydroxyl groups did not significantly influence the growth promotion of M. smegmatis and M. fortiutum in the cases of substituted spermidines and of cystamides.

Incorporation of fatty acids into cuticular hydrocarbons of male and female Drosophila melanogaster.

The biosynthesis of cuticular hydrocarbons was investigated in male and female Drosophila melanogaster (Canton-S strain), especially in those with a pheromonal role i.e. male 7-tricosene and female 7, 11- heptacosadiene. The incorporation of radioactivity was followed after topical application of (14)C-labelled myristic, palmitic and stearic acid and (3)H-labelled cis-vaccenic acid on one to ten day old flies. The incorporation levels into unsaturated hydrocarbons are similar in both sexes, depending markedly on the chain length of the saturated precursor, with a maximum level from myristic acid. Cis-vaccenic acid leads only to unsaturated compounds. With this precursor, there is an enhanced incorporation into female monoenes and dienes, maximum in two to three day old females. The total fatty acid composition shows the highest abundance of fatty acids with 16 carbon atoms and the presence of a major position for double bond, Delta9. Moreover, cis-vaccenic acid and 17-tetracosenoic acid are identified by GC-MS analysis. These data support an elongation-decarboxylation mechanism for the biosynthesis of D. melanogaster cuticular hydrocarbons. Its early steps for male monoenes and female monoenes and dienes might involve a Delta9 desaturase transforming palmitic acid into palmitoleic acid which would then be elongated into vaccenic acid, an important common precursor for all pheromones.

In vitro activities of novel catecholate siderophores against Plasmodium falciparum.

The activities of novel iron chelators, alone and in combination with chloroquine, quinine, or artemether, were evaluated in vitro against susceptible and resistant clones of Plasmodium falciparum with a semimicroassay system. N4-nonyl,N1,N8-bis(2,3-dihydroxybenzoyl) spermidine hydrobromide (compound 7) demonstrated the highest level of activity: 170 nM against a chloroquine-susceptible clone and 1 microM against a chloroquine-resistant clone (50% inhibitory concentrations). Compounds 6, 8, and 10 showed antimalarial activity with 50% inhibitory concentrations of about 1 microM. Compound 7 had no effect on the activities of chloroquine, quinine, and artemether against either clone, and compound 8 did not enhance the schizontocidal action of either chloroquine or quinine against the chloroquine-resistant clone. The incubation of compound 7 with FeCI3 suppressed or decreased the in vitro antimalarial activity of compound 7, while no effect was observed with incubation of compound 7 with CuSO4 and ZnSO4. These results suggest that iron deprivation may be the main mechanism of action of compound 7 against the malarial parasites. Chelator compounds 7 and 8 primarily affected trophozoite stages, probably by influencing the activity of ribonucleotide reductase, and thus inhibiting DNA synthesis.

Desferrioxamine-dependent iron transport in Erwinia amylovora CFBP1430: cloning of the gene encoding the ferrioxamine receptor FoxR.

Iron deprivation of Erwinia amylovora CFBP1430, a species causing fire blight on Pomoïdeae, was shown to induce the production of siderophores of the desferrioxamine (dfo) family and two outer membrane polypeptides with apparent molecular weight of about 70 and 80 kDa, respectively. Cyclic dfo E was characterized as the major metabolite. Phage MudIIpR13 insertional mutagenesis and screening on CAS-agar medium yielded three dfo non-producing and one overproducing clones. These clones failed to grow in the presence of the Fe(III) chelator EDDHA and were determined further as dfo and ferrioxamine transport negative mutants, respectively. The transport mutant which appeared to lack the 70 kDa polypeptide in the outer membrane allowed the purification of dfo E. Growth under iron limitation of dfo negative mutants was stimulated with ferrioxamine E and B but not with other ferrisiderophores tested. The host DNA sequence flanking the left terminal part of the MudIIpR13 prophage responsible for the transport mutation was cloned and used to probe a parental gene library by DNA-DNA hybridization. Two recombinant cosmids restoring the transport mutation to normal were identified. Both cosmids also conferred the ability to utilize ferrioxamine B and E as iron sources on a FhuE- mutant of Escherichia coli. This correlated with the production of an additional polypeptide of 70 kDa in the outer membrane of E. coli transconjugants, thus confirming that this protein serves the ferrioxamine receptor function (FoxR) in E. amylovora.

Sex pheromones of rice moth,Corcyra cephalonica Stainton : I. Identification of male pheromone.

Behavioral observations of the rice moth (Corcyra cephalonica, Pyralidae, Galleriinae) in the laboratory have shown that a male wing-gland pheromone induces attraction of female moths. This pheromone was identified as a blend of (E,E) and (Z,E)-farnesal. Wing-gland extracts or synthetic compounds were shown to be attractive to females by inducing walking.

Effect of cinnamoyl putrescines on in vitro cell multiplication and differentiation of tobacco explants.

Hydroxycinnamoyl putrescines promote the cell multiplication of leaf discs of a tobacco mutant, RMB7, cultivatedin vitro on the Murashige and Skoog medium. This mutant never accumulates these molecules during its development and does not enter in floweirng. Maximal effect is obtained at 2.5·10(-4)M. The same molecules inhibit bud formation ofNicotiana tabacum var. Xanthi nc, at 5·10(-5) M but promote callus formation. From 10(-4) M to 5·10(-3) M they strongly inhibit cell multiplication and bud formation without toxic effect. Their possible role in plant metabolism is discussed.