2D-quantitative structure-activity relationships model using PLS method for anti-malarial activities of anti-haemozoin compounds.

BACKGROUND: Emergence of cross-resistance to current anti-malarial drugs has led to an urgent need for identification of potential compounds with novel modes of action and anti-malarial activity against the resistant strains. One of the most promising therapeutic targets of anti-malarial agents related to food vacuole of malaria parasite is haemozoin, a product formed by the parasite through haemoglobin degradation. METHODS: With this in mind, this study developed two-dimensional-quantitative structure-activity relationships (QSAR) models of a series of 21 haemozoin inhibitors to explore the useful physicochemical parameters of the active compounds for estimation of anti-malarial activities. The 2D-QSAR model with good statistical quality using partial least square method was generated after removing the outliers. RESULTS: Five two-dimensional descriptors of the training set were selected: atom count (a_ICM); adjacency and distance matrix descriptor (GCUT_SLOGP_2: the third GCUT descriptor using atomic contribution to logP); average total charge sum (h_pavgQ) in pKa prediction (pH = 7); a very low negative partial charge, including aromatic carbons which have a heteroatom-substitution in "ortho" position (PEOE_VSA-0) and molecular descriptor (rsynth: estimating the synthesizability of molecules as the fraction of heavy atoms that can be traced back to starting material fragments resulting from retrosynthetic rules), respectively. The model suggests that the anti-malarial activity of haemozoin inhibitors increases with molecules that have higher average total charge sum in pKa prediction (pH = 7). QSAR model also highlights that the descriptor using atomic contribution to logP or the distance matrix descriptor (GCUT_SLOGP_2), and structural component of the molecules, including topological descriptors does make for better anti-malarial activity. CONCLUSIONS: The model is capable of predicting the anti-malarial activities of anti-haemozoin compounds. In addition, the selected molecular descriptors in this QSAR model are helpful in designing more efficient compounds against the P. falciparum 3D7A strain.

Antimalarial Benzimidazole Derivatives Incorporating Phenolic Mannich Base Side Chains Inhibit Microtubule and Hemozoin Formation: Structure-Activity Relationship and In Vivo Oral Efficacy Studies.

A novel series of antimalarial benzimidazole derivatives incorporating phenolic Mannich base side chains at the C2 position, which possess dual asexual blood and sexual stage activities, is presented. Structure-activity relationship studies revealed that the 1-benzylbenzimidazole analogues possessed submicromolar asexual blood and sexual stage activities in contrast to the 1H-benzimidazole analogues, which were only active against asexual blood stage (ABS) parasites. Further, the former demonstrated microtubule inhibitory activity in ABS parasites but more significantly in stage II/III gametocytes. In addition to being bona fide inhibitors of hemozoin formation, the 1H-benzimidazole analogues also showed inhibitory effects on microtubules. In vivo efficacy studies in Plasmodium berghei-infected mice revealed that the frontrunner compound 41 exhibited high efficacy (98% reduction in parasitemia) when dosed orally at 4 × 50 mg/kg. Generally, the compounds were noncytotoxic to mammalian cells.

Highly Sensitive and Rapid Characterization of the Development of Synchronized Blood Stage Malaria Parasites Via Magneto-Optical Hemozoin Quantification.

The rotating-crystal magneto-optical diagnostic (RMOD) technique was developed as a sensitive and rapid platform for malaria diagnosis. Herein, we report a detailed in vivo assessment of the synchronized Plasmodium vinckei lentum strain blood-stage infections by the RMOD method and comparing the results to the unsynchronized Plasmodium yoelii 17X-NL (non-lethal) infections. Furthermore, we assess the hemozoin production and clearance dynamics in chloroquine-treated compared to untreated self-resolving infections by RMOD. The findings of the study suggest that the RMOD signal is directly proportional to the hemozoin content and closely follows the actual parasitemia level. The lack of long-term accumulation of hemozoin in peripheral blood implies a dynamic equilibrium between the hemozoin production rate of the parasites and the immune system's clearing mechanism. Using parasites with synchronous blood stage cycle, which resemble human malaria parasite infections with Plasmodium falciparum and Plasmodium vivax, we are demonstrating that the RMOD detects both hemozoin production and clearance rates with high sensitivity and temporal resolution. Thus, RMOD technique offers a quantitative tool to follow the maturation of the malaria parasites even on sub-cycle timescales.

VPO1 Modulates Vascular Smooth Muscle Cell Phenotypic Switch by Activating Extracellular Signal-regulated Kinase 1/2 (ERK 1/2) in Abdominal Aortic Aneurysms.

Background Hydrogen peroxide (H2O2) is a critical molecular signal in the development of abdominal aortic aneurysm ( AAA ) formation. Vascular peroxidase 1 ( VPO 1) catalyzes the production of hypochlorous acid ( HOC l) from H2O2 and significantly enhances oxidative stress. The switch from a contractile phenotype to a synthetic one in vascular smooth muscle cells ( VSMC s) is driven by reactive oxygen species and is recognized as an early and important event in AAA formation. This study aims to determine if VPO 1 plays a critical role in the development of AAA by regulating VSMC phenotypic switch. Methods and Results VPO 1 is upregulated in human and elastase-induced mouse aneurysmal tissues compared with healthy control tissues. Additionally, KLF 4, a nuclear transcriptional factor, is upregulated in aneurysmatic tissues along with a concomitant downregulation of differentiated smooth muscle cell markers and an increase of synthetic phenotypic markers, indicating VSMC phenotypic switch in these diseased tissues. In cultured VSMC s from rat abdominal aorta, H2O2 treatment significantly increases VPO 1 expression and HOC l levels as well as VSMC phenotypic switch. In support of these findings, depletion of VPO 1 significantly attenuates the effects of H2O2 and HOC l treatment. Furthermore, HOC l treatment promotes VSMC phenotypic switch and ERK 1/2 phosphorylation. Pretreatment with U0126 (a specific inhibitor of ERK 1/2) significantly attenuates HOC l-induced VSMC phenotypic switch. Conclusions Our results demonstrate that VPO 1 modulates VSMC phenotypic switch through the H2O2/ VPO 1/ HOC l/ ERK 1/2 signaling pathway and plays a key role in the development of AAA . Our findings also implicate VPO 1 as a novel signaling node that mediates VSMC phenotypic switch and plays a key role in the development of AAA . Clinical Trial Registration URL : www.chictr.org.cn . Unique identifier: Chi CTR 1800016922.

High-Content Screening of the Medicines for Malaria Venture Pathogen Box for Plasmodium falciparum Digestive Vacuole-Disrupting Molecules Reveals Valuable Starting Points for Drug Discovery.

Plasmodium falciparum infections leading to malaria have severe clinical manifestations and high mortality rates. Chloroquine (CQ), a former mainstay of malaria chemotherapy, has been rendered ineffective due to the emergence of widespread resistance. Recent studies, however, have unveiled a novel mode of action in which low-micromolar levels of CQ permeabilized the parasite's digestive vacuole (DV) membrane, leading to calcium efflux, mitochondrial depolarization, and DNA degradation. These phenotypes implicate the DV as an alternative target of CQ and suggest that DV disruption is an attractive target for exploitation by DV-disruptive antimalarials. In the current study, high-content screening of the Medicines for Malaria Venture (MMV) Pathogen Box (2015) was performed to select compounds which disrupt the DV membrane, as measured by the leakage of intravacuolar Ca2+ using the calcium probe Fluo-4 AM. The hits were further characterized by hemozoin biocrystallization inhibition assays and dose-response half-maximal (50%) inhibitory concentration (IC50) assays across resistant and sensitive strains. Three hits, MMV676380, MMV085071, and MMV687812, were shown to demonstrate a lack of CQ cross-resistance in parasite strains and field isolates. Through systematic analyses, MMV085071 emerged as the top hit due to its rapid parasiticidal effect, low-nanomolar IC50, and good efficacy in triggering DV disruption, mitochondrial degradation, and DNA fragmentation in P. falciparum These programmed cell death (PCD)-like phenotypes following permeabilization of the DV suggests that these compounds kill the parasite by a PCD-like mechanism. From the drug development perspective, MMV085071, which was identified to be a potent DV disruptor, offers a promising starting point for subsequent hit-to-lead generation and optimization through structure-activity relationships.

Inhibition of Plasmodium falciparum cysteine proteases by the sugarcane cystatin CaneCPI-4.

Malaria is a disease caused by Plasmodium parasites that affects hundreds of millions of people. Plasmodium proteases are involved in invasion, erythrocyte egress and degradation of host proteins. Falcipains are well-studied cysteine peptidases located in P. falciparum food vacuoles that participate in hemoglobin degradation. Cystatins are natural cysteine protease inhibitors that are implicated in a wide range of regulatory processes. Here, we report that a cystatin from sugarcane, CaneCPI-4, is selectively internalized into P. falciparum infected erythrocytes and is not processed by the parasite proteolytic machinery. Furthermore, we demonstrated the inhibition of P. falciparum cysteine proteases by CaneCPI-4, suggesting that it can exert inhibitory functions inside the parasites. The inhibition of the proteolytic activity of parasite cells is specific to this cystatin, as the addition of an anti-CaneCPI-4 antibody completely abolished the inhibition. We extended the studies to recombinant falcipain-2 and falcipain-3 and demonstrated that CaneCPI-4 strongly inhibits these enzymes, with IC50 values of 12nM and 42nM, respectively. We also demonstrated that CaneCPI-4 decreased the hemozoin formation in the parasites, affecting the parasitemia. Taken together, this study identified a natural molecule as a potential antimalarial that specifically targets falcipains and also contributes to a better understanding of macromolecule acquisition by Plasmodium falciparum infected RBCs.

Evaluation of antiplasmodial properties of a cyanobacterium, Spirulina platensis and its mechanism of action.

The rapid emergence of antimalarial drug resistance necessitates a continual effort on novel drug discovery. A cyanobacterium, Spirulina platensis, is a potential antimalarial agent that has been widely consumed as food supplement in the form of crude extract. It is known to possess antiviral, antibacterial and antifungi activities. This study examined the antimalarial activities of several Spirulina formulas against Plasmodium falciparum 3D7, in vitro. The tested Spirulina formulas included commercially available capsule, crude extract and alkaloid fraction. Results showed that all tested formula possessed antimalarial activities with the Spirulina capsule exhibited the highest activities (IC50 = 2.16 µg/mL). Light and electron microscopies revealed interference of the Spirulina with the parasite hemozoin formation. In conclusion, all tested Spirulina formulas and fraction exhibited moderate to high antimalarial activities.

Investigation of antimalarial activity, cytotoxicity and action mechanism of piperazine derivatives of betulinic acid.

OBJECTIVES: To semisynthesise piperazine derivatives of betulinic acid to evaluate antimalarial activity, cytotoxicity and action mechanism. METHODS: The new derivatives were evaluated against the CQ-sensitive Plasmodium falciparum 3D7 strain by flow cytometry (FC) using YOYO-1 as stain. Cytotoxicity of 4a and 4b was performed with HEK293T cells for 24 and 48 h by MTT assay. The capability of compound 4a to modulate Ca(2+) in the trophozoite stage was investigated. The trophozoites were stained with Fluo4-AM and analysed by spectrofluorimetry. Effect on mitochondrial membrane potential (ΔΨm) was tested for 4a by FC with DiOC6 (3) as stain. For ß-haematin assay, 4a was incubated for 24 h with reagents such as haemin, and the fluorescence was measured by FlexStation at an absorbance of 405 nm. RESULTS: Antimalarial activity of 4a and 4b was IC50 = 1 and 4 µm, respectively. Compound 4a displayed cytotoxicity with IC50 = 69 and 29 µm for 24 and 48 h, respectively, and 4b was not cytotoxic at the tested concentrations. Addition of 4a leads to an increase in cytosolic Ca(2+) . We have measured ΔΨm after treating parasites with the compound. Data on Figure 4a show that mitochondria were not affected. The action mechanism for 4a, inhibition of ß-haematin formation (17%), was lower than CQ treatment (83%; IC50 = 3 mm). CONCLUSION: Compound 4a showed excellent antimalarial activity, and its action mechanism is involved in Ca(2+) pathway(s).

Active site analysis of yeast flavohemoglobin based on its structure with a small ligand or econazole.

UNLABELLED: Flavohemoglobins (flavoHbs) serve various microorganisms as the major protective enzymes against NO˙-mediated toxicity. FlavoHbs dominantly function as an NO˙ dioxygenase (O2+ NO→ NO3 -), the required electron being shuttled from NAD(P)H via FAD to the heme iron. The X-ray structures of the flavoHb from Saccharomyces cerevisae presented in complex with an unknown small ligand (Yhb) and with econazole (Yhb(E) ) at 2.1 and 3.0 Å resolutions, respectively, reveal a high architectural accordance between prokaryotic and eukaryotic family members. The active site is characterized by a proximal heme side with a strictly conserved histidine, glutamate and tyrosine triad and a highly variable distal heme side with helix shifts up to 10 Å mainly dependent on the presence/absence and size of the bound ligand. In yeast flavoHb, the small heme iron ligand adjusts a catalytically productive active site geometry that reliably suggests the NO and O(2) binding site. O(2) is activated by its ligation to an electron-rich heme iron and a hydrogen bond to Tyr29 and Gln53. High active site similarities between eukaryotic Yhb and bacterial single-domain globins argue for identical biochemical reactions. Binding of the bulky econazole implies a large-scale induced-fit process concerning, in particular, an outwards shift of helices B and E to increase the active site pocket. Yeast Yhb and Ralstonia eutropha flavoHb both structurally studied in complex with econazole indicate conformational differences between the inhibitors and the polypeptide primarily caused by stable binding of a phospholipid to the latter and by distinct loop D structures. DATABASE: Structural data and final coordinates of Yhb and Yhb-econazole are available in the Protein Data Bank under the accession numbers 4G1V and 4G1B.

In vitro antimalarial activity of ICL670: a further proof of the correlation between inhibition of ß-hematin formation and of peroxidative degradation of hemin.

Iron chelators such as deferiprone, deferoxamine (DFO) and ICL670 (deferasirox) have previously been shown to display in vitro and/or in vivo antimalarial activities. To gain further insight in their antimalarial mechanism of action, their activities on inhibition of ß-hematin formation and on both peroxidative and glutathione (GSH)-mediated degradation of hemin were investigated. Neither deferiprone nor DFO were able to inhibit ß-hematin formation while ICL670 activity nearly matched that of chloroquine (CQ). Peroxidative degradation of hemin was also only strongly inhibited by both CQ and ICL670, the latter being significantly more efficient at pH 5.2. All iron chelators displayed minor, if any, inhibitory activity on GSH-mediated degradation of hemin. Discrepancies in the results obtained for the three iron chelators show that iron chelation is not the main driving force behind interference with heme degradation. Deferiprone, DFO and ICL670 share little structural community but both ICL670 and antimalarial ursolic acid derivatives (previously shown to block ß-hematin formation and the peroxidative degradation of hemin) have hydrophobic groups and hydroxyphenyl moieties. These similarities in structures and activities further back up a possible two-step mechanism of action previously proposed for ursolic acid derivatives (Mullié et al., 2010) implying (1) stacking of an hydrophobic structure to hemin and (2) additive protection of hemin ferric iron from H(2)O(2) by hydroxyphenyl groups through steric hindrance and/or trapping of oxygen reactive species in the direct neighborhood of ferric iron. These peculiar antimalarial mechanisms of action for ICL670 warrant further investigations and development.

Hydrogen sulfide and hemeproteins: knowledge and mysteries.

Historically, hydrogen sulfide (H(2)S) has been regarded as a poisonous gas, with a wide spectrum of toxic effects. However, like ·NO and CO, H(2)S is now referred to as a signaling gas involved in numerous physiological processes. The list of reports highlighting the physiological effects of H(2)S is rapidly expanding and several drug candidates are now being developed. As with ·NO and CO, not a single H(2)S target responsible for all the biological effects has been found till now. Nevertheless, it has been suggested that H(2)S can bind to hemeproteins, inducing different responses that can mediate its effects. For instance, the interaction of H(2)S with cytochrome c oxidase has been associated with the activation of the ATP-sensitive potassium channels, regulating muscle relaxation. Inhibition of cytochrome c oxidase by H(2)S has also been related to inducing a hibernation-like state. Although H(2)S might induce these effects by interacting with hemeproteins, the mechanisms underlying these interactions are obscure. Therefore, in this review we discuss the current state of knowledge about the interaction of H(2)S with vertebrate and invertebrate hemeproteins and postulate a generalized mechanism. Our goal is to stimulate further research aimed at evaluating plausible mechanisms that explain H(2)S reactivity with hemeproteins.

Inhibitory effect of ursolic acid derivatives on hydrogen peroxide- and glutathione-mediated degradation of hemin: a possible additional mechanism of action for antimalarial activity.

Compounds obtained by the condensation of ursolic acid (UA) with 1,4-bis(3-aminopropyl)piperazines have previously been shown as cytocidal to Plasmodium falciparum strains. Preliminary results indicated that the inhibition of beta-hematin formation (one of the possible mechanisms of action of antimalarial drugs) was achieved by a few of these molecules with varying efficiencies. To gain further insight in the antimalarial action of UA derivatives, we report here the results of additional pathways that may explain their in vitro cytocidal activity such as inhibition of hemin degradation by H(2)O(2) or glutathione (GSH). H(2)O(2)-mediated hemin degradation was drastically reduced by hydroxybenzyl-substituted UA derivatives while UA and intermediate compounds displayed weaker inhibitory actions. The results of GSH-mediated hemin degradation inhibition did not parallel those of H(2)O(2) degradation as hydroxybenzyl-substituted UA only proved to be a weak inhibitor. As H(2)O(2) interaction with the iron moiety of hemin is the first step towards its degradation, we assume that the interaction of our products with the ferric ion in the hemin structure is of upmost importance in inhibiting its peroxidative degradation. A two-step mechanism of action implying (1) stacking of the acetylursolic acid structure to hemin and (2) additive protection of hemin ferric iron from H(2)O(2) by hydroxyphenyl groups through steric hindrance and/or trapping of oxygen reactive species in the direct neighborhood of ferric iron can be put forward. For GSH degradation pathway, grafting of UA structure with a piperazine structure gave the best inhibition, pleading for the implication of this latter moiety in the inhibitory process.

Steric decompression of picket-strapped porphyrins for the synthesis of side-differentiated chelates.

A general method to synthesize various alphabeta alphabeta bis-strapped porphyrins, with a different functionalization on each side of the macrocycle, is described. The resulting new chelates may find applications as analogues of heme protein active sites, bifunctional chelates, or specific bis-chelating molecules with potential medical utility.

Plasmodium falciparum: effect of Solanum nudum steroids on thiol contents and beta-hematin formation in parasitized erythrocytes.

We studied the effects on total thiols glutathione (GSH) and cysteine contents in Plasmodium falciparum in vitro when treated with four steroid derivatives and a sapogenin (Diosgenone) extracted from Solanum nudum. We also determined their capacity to inhibit beta-hematin formation. We showed that SN-1 (16alpha-acetoxy-26-hydroxycholest-4-ene-3,22-dione) increased total glutathione and cysteine concentrations while SN-4 (26-O-beta-d-glucopyranosyloxy-16alpha-acetoxycholest-4-ene-3,22-dione) decreased the concentration of both thiols. Acetylation in C16 was crucial for the effect of SN-1 while type furostanol and terminal glucosidation were necessary for the inhibitory properties of SN-4. The combination of steroids and buthionine sulfoximine, a specific inhibitor of a step-limiting enzyme in GSH synthesis, did not modify the glutathione contents. Finally, we found that SN-1 inhibited more than 80% of beta-hematin formation at 5.0mM, while the other steroids did not show any effect.

Haemozoin: from melatonin pigment to drug target, diagnostic tool, and immune modulator.

Plasmodium spp produce a pigment (haemozoin) to detoxify the free haem that is generated by haemoglobin degradation. Haemozoin was originally thought to be an inert waste byproduct of the parasite. However, recent research has led to the recognition that haemozoin is possibly of great importance in various aspects of malaria. Haemozoin is the target of many antimalarial drugs, and the unravelling of the exact modes of action may allow the design of novel antimalarial compounds. The detection of haemozoin in erythrocytes or leucocytes facilitates the diagnosis of malaria. The number of haemozoin-containing monocytes and granulocytes has been shown to correlate well with disease severity and may hold the potential for becoming a novel, automated laboratory marker in the assessment of patients. Finally, haemozoin has a substantial effect on the immune system. Further research is needed to clarify these aspects, many of which are important in clinical practice.

Extracellular lipid droplets promote hemozoin crystallization in the gut of the blood fluke Schistosoma mansoni.

Hemozoin (Hz) is a heme crystal produced upon hemoglobin digestion as the main mechanism of heme disposal in several hematophagous organisms. Here, we show that, in the helminth Schistosoma mansoni, Hz formation occurs in extracellular lipid droplets (LDs). Transmission electron microscopy of adult worms revealed the presence of numerous electron-lucent round structures similar to LDs in gut lumen, where multicrystalline Hz assemblies were found associated to their surfaces. Female regurgitates promoted Hz formation in vitro in reactions partially inhibited by boiling. Fractionation of regurgitates showed that Hz crystallization activity was essentially concentrated on lower density fractions, which have small amounts of pre-formed Hz crystals, suggesting that hydrophilic-hydrophobic interfaces, and not Hz itself, play a key catalytic role in Hz formation in S. mansoni. Thus, these data demonstrate that LDs present in the gut lumen of S. mansoni support Hz formation possibly by allowing association of heme to the lipid-water interface of these structures.

Crystal nucleation, growth, and morphology of the synthetic malaria pigment beta-hematin and the effect thereon by quinoline additives: the malaria pigment as a target of various antimalarial drugs.

The morphology of micrometer-sized beta-hematin crystals (synthetic malaria pigment) was determined by TEM images and diffraction, and by grazing incidence synchrotron X-ray diffraction at the air-water interface. The needle-like crystals are bounded by sharp {100} and {010} side faces, and capped by {011} and, to a lesser extent, by {001} end faces, in agreement with hemozoin (malaria pigment) crystals. The beta-hematin crystals grown in the presence of 10% chloroquine or quinine took appreciably longer to precipitate and tended to be symmetrically tapered toward both ends of the needle, due to stereoselective additive binding to {001} or {011} ledges. Evidence, but marginal, is presented that additives reduce crystal mosaic domain size along the needle axis, based on X-ray powder diffraction data. Coherent grazing exit X-ray diffraction suggests that the mosaic domains are smaller and less structurally stable than in pure crystals. IR-ATR and Raman spectra indicate molecular based differences due to a modification of surface and bulk propionic acid groups, following additive binding and a molecular rearrangement in the environment of the bulk sites poisoned by occluded quinoline. These results provided incentive to examine computationally whether hemozoin may be a target of antimalarial drugs diethylamino-alkoxyxanthones and artemisinin. A variation in activity of the former as a function of the alkoxy chain length is correlated with computed binding energy to {001} and {011} faces of beta-hematin. A model is proposed for artemisinin activity involving hemozoin nucleation inhibition via artemisinin-beta-hematin adducts bound to the principal crystal faces. Regarding nucleation of hemozoin inside the digestive vacuole of the malaria parasite, nucleation via the vacuole's membranous surface is proposed, based on a reported hemozoin alignment. As a test, a dibehenoyl-phosphatidylcholine monolayer transferred onto OTS-Si wafer nucleated far more beta-hematin crystals, albeit randomly oriented, than a reference OTS-Si.

Heme inhibits the DNA binding properties of the cytoplasmic heme binding protein of Shigella dysenteriae (ShuS).

Heme uptake and utilization by pathogenic bacteria are critical for virulence and disease, since heme and heme proteins are a major source of iron within the host. Although the role of outer membrane heme receptors in this process has been extensively characterized at the genetic and biochemical level, the role of the cytoplasmic heme binding proteins is not yet clear. The Shigella dysenteriae cytoplasmic heme binding protein, ShuS, has previously been shown to promote utilization of heme as an iron source at low to moderate heme concentrations and to protect against heme toxicity at high heme concentrations. Herein, we provide evidence that ShuS of S. dysenteriae sequesters DNA non-sequence-specifically with a binding affinity of 3.6 microM as determined by fluorescence anisotropy studies. The ability to bind DNA was observed to be restricted to the apoprotein only. The molecular mass of the apo-ShuS-DNA complex was estimated to be approximately 700 kDa by size exclusion chromatography. Atomic force microscopy (AFM) revealed that apo-ShuS forms aggregates in the presence of DNA and provides a scaffolding matrix from which DNA is observed to loop outward. The AFM images of apo-ShuS-DNA complexes were strikingly similar to the AFM images of the stress-induced Escherichia coli protein, Dps, when complexed with DNA; however, unlike the Dps protein, ShuS failed to protect DNA against oxidative stress in vitro and in vivo. Since free heme can generate reactive oxygen species which are damaging to cellular DNA, the ability of ShuS to physically sequester DNA may provide a molecular basis for its role in preventing toxicity associated with high heme concentrations.

Current status and progresses made in malaria chemotherapy.

Malaria is the most important parasitic disease worldwide, affecting more than 500 million people and causing close to 1 million deaths per annum. This serious fact is mainly attributable to the emergence of drug resistant strains of Plasmodium falciparum. The advances made in malaria chemotherapy based on unique aspects of the biochemistry and physiology of the responsible agents for this disease, parasites of Plasmodium genus, are covered in this review. Increasing resistance to conventional antimalarial drugs constitutes the main drawback for the persistence of this disease. In the present article, a comprehensive analysis of selected molecular targets is depicted in terms of their potential utility as chemotherapeutic agents. Our review focuses on different and important molecular targets for drug design that include proteases that hydrolyze hemoglobin, protein farnesyltransferase, heme detoxification pathway, polyamine pathways, dihydrofolate reductase, artemisinin-based combination therapies (ACTs), etc. Therefore, rational approaches to control malaria targeting metabolic pathways of malaria parasites which are essential for parasites survival are presented.

Plasmodium berghei: in vitro and in vivo activity of dequalinium.

Bisquinoline compounds have exhibited remarkable activity in vitro and in vivo against Plasmodium parasites by inhibition of heme detoxification. We have tested the ability of dequalinium 1,1'-(1,10-decanediyl)bis(4-amino-2-methylquinoline), a known antimicrobial agent, to inhibit beta-hematin synthesis using a non-emzymatic colorimetric assay and globin proteolysis by electrophoretic analysis (SDS-PAGE-15%). Dequalinium was able to inhibit both processes in vitro with close correlation to a murine malaria model, reducing parasitemia levels, prolonging the survival time post-infection and curing 40% of infected mice using a combination therapy with a loading dose of chloroquine. These results confirm that dequalinium is a promising lead for antimalarial drug development.