Polyamine transport in parasites: a potential target for new antiparasitic drug development

Targeting Trypanothione Metabolism in Trypanosomatids

Infectious diseases caused by trypanosomatids, including African trypanosomiasis (sleeping sickness), Chagas disease, and different forms of leishmaniasis, are Neglected Tropical Diseases affecting millions of people worldwide, mainly in vulnerable territories of tropical and subtropical areas. In general, current treatments against these diseases are old-fashioned, showing adverse effects and loss of efficacy due to misuse or overuse, thus leading to the emergence of resistance. For these reasons, searching for new antitrypanosomatid drugs has become an urgent necessity, and different metabolic pathways have been studied as potential drug targets against these parasites. Considering that trypanosomatids possess a unique redox pathway based on the trypanothione molecule absent in the mammalian host, the key enzymes involved in trypanothione metabolism, trypanothione reductase and trypanothione synthetase, have been studied in detail as druggable targets. In this review, we summarize some of the recent findings on the molecules inhibiting these two essential enzymes for Trypanosoma and Leishmania viability.

Polyamine Metabolism for Drug Intervention in Trypanosomatids

Neglected tropical diseases transmitted by trypanosomatids include three major human scourges that globally affect the world's poorest people: African trypanosomiasis or sleeping sickness, American trypanosomiasis or Chagas disease and different types of leishmaniasis. Different metabolic pathways have been targeted to find antitrypanosomatid drugs, including polyamine metabolism. Since their discovery, the naturally occurring polyamines, putrescine, spermidine and spermine, have been considered important metabolites involved in cell growth. With a complex metabolism involving biosynthesis, catabolism and interconversion, the synthesis of putrescine and spermidine was targeted by thousands of compounds in an effort to produce cell growth blockade in tumor and infectious processes with limited success. However, the discovery of eflornithine (DFMO) as a curative drug against sleeping sickness encouraged researchers to develop new molecules against these diseases. Polyamine synthesis inhibitors have also provided insight into the peculiarities of this pathway between the host and the parasite, and also among different trypanosomatid species, thus allowing the search for new specific chemical entities aimed to treat these diseases and leading to the investigation of target-based scaffolds. The main molecular targets include the enzymes involved in polyamine biosynthesis (ornithine decarboxylase, S-adenosylmethionine decarboxylase and spermidine synthase), enzymes participating in their uptake from the environment, and the enzymes involved in the redox balance of the parasite. In this review, we summarize the research behind polyamine-based treatments, the current trends, and the main challenges in this field.

Molecular-level strategic goals and repressors in Leishmaniasis - Integrated data to accelerate target-based heterocyclic scaffolds

Leishmaniasis is a complex of neglected tropical diseases caused by various species of leishmanial parasites that primarily affect the world's poorest people. A limited number of standard medications are available for this disease that has been used for several decades, these drugs have many drawbacks such as resistance, higher cost, and patient compliance, making it difficult to reach the poor. The search for novel chemical entities to treat leishmaniasis has led to target-based scaffold research. Among several identified potential molecular targets, enzymes involved in the purine salvage pathway include polyamine biosynthetic process, such as arginase, ornithine decarboxylase, S-adenosylmethionine decarboxylase, spermidine synthase, trypanothione reductase as well as enzymes in the DNA cell cycle, such as DNA topoisomerases I and II plays vital role in the life cycle survival of leishmanial parasite. This review mainly focuses on various heterocyclic scaffolds, and their specific inhibitory targets against leishmaniasis, particularly those from the polyamine biosynthesis pathway and DNA topoisomerases with estimated activity studies of various heterocyclic analogs in terms of their IC₅₀ or EC₅₀ value, reported molecular docking analysis from available published literatures.

Further Investigations of Nitroheterocyclic Compounds as Potential Antikinetoplastid Drug Candidates

Due to the lack of specific vaccines, management of the trypanosomatid-caused neglected tropical diseases (sleeping sickness, Chagas disease and leishmaniasis) relies exclusively on pharmacological treatments. Current drugs against them are scarce, old and exhibit disadvantages, such as adverse effects, parenteral administration, chemical instability and high costs which are often unaffordable for endemic low-income countries. Discoveries of new pharmacological entities for the treatment of these diseases are scarce, since most of the big pharmaceutical companies find this market unattractive. In order to fill the pipeline of compounds and replace existing ones, highly translatable drug screening platforms have been developed in the last two decades. Thousands of molecules have been tested, including nitroheterocyclic compounds, such as benznidazole and nifurtimox, which had already provided potent and effective effects against Chagas disease. More recently, fexinidazole has been added as a new drug against African trypanosomiasis. Despite the success of nitroheterocycles, they had been discarded from drug discovery campaigns due to their mutagenic potential, but now they represent a promising source of inspiration for oral drugs that can replace those currently on the market. The examples provided by the trypanocidal activity of fexinidazole and the promising efficacy of the derivative DNDi-0690 against leishmaniasis seem to open a new window of opportunity for these compounds that were discovered in the 1960s. In this review, we show the current uses of nitroheterocycles and the novel derived molecules that are being synthesized against these neglected diseases.

Polyamines in cancer: integrating organismal metabolism and antitumour immunity

The natural mammalian polyamines putrescine, spermidine and spermine are essential for both normal and neoplastic cell function and replication. Dysregulation of metabolism of polyamines and their requirements is common in many cancers. Both clinical and experimental depletion of polyamines have demonstrated their metabolism to be a rational target for therapy; however, the mechanisms through which polyamines can establish a tumour-permissive microenvironment are only now emerging. Recent data indicate that polyamines can play a major role in regulating the antitumour immune response, thus likely contributing to the existence of immunologically 'cold' tumours that do not respond to immune checkpoint blockade. Additionally, the interplay between the microbiota and associated tissues creates a tumour microenvironment in which polyamine metabolism, content and function can all be dramatically altered on the basis of microbiota composition, dietary polyamine availability and tissue response to its surrounding microenvironment. The goal of this Perspective is to introduce the reader to the many ways in which polyamines, polyamine metabolism, the microbiota and the diet interconnect to establish a tumour microenvironment that facilitates the initiation and progression of cancer. It also details ways in which polyamine metabolism and function can be successfully targeted for therapeutic benefit, including specifically enhancing the antitumour immune response.

Unique thiol metabolism in trypanosomatids: Redox homeostasis and drug resistance

Trypanosomatids are mainly responsible for heterogeneous parasitic diseases: Leishmaniasis, Sleeping sickness, and Chagas disease and control of these diseases implicates serious challenges due to the emergence of drug resistance. Redox-active biomolecules are the endogenous substances in organisms, which play important role in the regulation of redox homeostasis. The redox-active substances like glutathione, trypanothione, cysteine, cysteine persulfides, etc., and other inorganic intermediates (hydrogen peroxide, nitric oxide) are very useful as defence mechanism. In the present review, the suitability of trypanothione and other essential thiol molecules of trypanosomatids as drug targets are described in Leishmania and Trypanosoma. We have explored the role of tryparedoxin, tryparedoxin peroxidase, ascorbate peroxidase, superoxide dismutase, and glutaredoxins in the anti-oxidant mechanism and drug resistance. Up-regulation of some proteins in trypanothione metabolism helps the parasites in survival against drug pressure (sodium stibogluconate, Amphotericin B, etc.) and oxidative stress. These molecules accept electrons from the reduced trypanothione and donate their electrons to other proteins, and these proteins reduce toxic molecules, neutralize reactive oxygen, or nitrogen species; and help parasites to cope with oxidative stress. Thus, a better understanding of the role of these molecules in drug resistance and redox homeostasis will help to target metabolic pathway proteins to combat Leishmaniasis and trypanosomiases.

Tetraazamacrocyclic derivatives and their metal complexes as antileishmanial leads

A total of 44 bis-aryl-monocyclic polyamines, monoaryl-monocyclic polyamines and their transition metal complexes were prepared, chemically characterized, and screened in vitro against the Leishmania donovani promastigotes, axenic amastigotes and intracellular amastigotes in THP1 cells. The IC50 and/or IC90 values showed that 10 compounds were similarly active at about 2-fold less potent than known drug pentamidine against promastigotes. The most potent compound had an IC50 of 2.82 μM (compared to 2.93 μM for pentamidine). Nine compounds were 1.1-13.6-fold more potent than pentamidine against axenic amastigotes, the most potent one being about 2-fold less potent than amphotericin B. Fourteen compounds were about 2-10 fold more potent than pentamidine, the most potent one is about 2-fold less potent than amphotericin B against intracellular amastigotes in THP1 cells. The 2 most promising compounds (FeL7Cl2 and MnL7Cl2), with strong activity against both promastigotes and amastigotes and no observable toxicity against the THP1 cells are the Fe2+- and Mn2+- complexes of a dibenzyl cyclen derivative. Only 2 of the 44 compounds showed observable cytotoxicity against THP1 cells. Tetraazamacrocyclic monocyclic polyamines represent a new class of antileishmanial lead structures that warrant follow up studies.

Synthesis of three dissymmetrical pentaamines via bisaminals of linear tetraamines

Bisaminals of linear tetraamines were selectively N-monofunctionalised with acrylonitrile in a Michael-type addition giving rise, after reduction, to three open-chain dissymmetrical pentaamines, bearing a new aminopropyl group on one terminal nitrogen atom.

Arginine and Polyamines Fate in Leishmania Infection

Leishmania is a protozoan parasite that alternates its life cycle between the sand fly and the mammalian host macrophages, involving several environmental changes. The parasite responds to these changes by promoting a rapid metabolic adaptation through cellular signaling modifications that lead to transcriptional and post-transcriptional gene expression regulation and morphological modifications. Molecular approaches such as gene expression regulation, next-generation sequencing (NGS), microRNA (miRNA) expression profiling, in cell Western blot analyses and enzymatic activity profiling, have been used to characterize the infection of murine BALB/c and C57BL/6 macrophages, as well as the human monocytic cell-lineage THP-1, with Leishmania amazonensis wild type (La-WT) or arginase knockout (La-arg^-). These models are being used to elucidate physiological roles of arginine and polyamines pathways and the importance of arginase for the establishment of the infection. In this review, we will describe the main aspects of Leishmania-host interaction, focusing on the arginine and polyamines pathways and pointing to possible targets to be used for prognosis and/or in the control of the infection. The parasite enzymes, arginase and nitric oxide synthase-like, have essential roles in the parasite survival and in the maintenance of infection. On the other hand, in mammalian macrophages, defense mechanisms are activated inducing alterations in the mRNA, miRNA and enzymatic profiles that lead to the control of infection. Furthermore, the genetic background of both parasite and host are also important to define the fate of infection.

Spermidine-mediated poly(lactic-co-glycolic acid) nanoparticles containing fluorofenidone for the treatment of idiopathic pulmonary fibrosis

Idiopathic pulmonary fibrosis is a progressive, fatal lung disease with poor survival. The advances made in deciphering this disease have led to the approval of different antifibrotic molecules, such as pirfenidone and nintedanib. An increasing number of studies with particles (liposomes, nanoparticles [NPs], microspheres, nanopolymersomes, and nanoliposomes) modified with different functional groups have demonstrated improvement in lung-targeted drug delivery. In the present study, we prepared, characterized, and evaluated spermidine (Spd)-modified poly(lactic-co-glycolic acid) (PLGA) NPs as carriers for fluorofenidone (AKF) to improve the antifibrotic efficacy of this drug in the lung. Spd-AKF-PLGA NPs were prepared and functionalized by modified solvent evaporation with Spd and polyethylene glycol (PEG)-PLGA groups. The size of Spd-AKF-PLGA NPs was 172.5±4.3 nm. AKF release from NPs was shown to fit the Higuchi model. A549 cellular uptake of an Spd-coumarin (Cou)-6-PLGA NP group was found to be almost twice as high as that of the Cou-6-PLGA NP group. Free Spd and difluoromethylornithine (DFMO) were preincubated in A549 cells to prove uptake of Spd-Cou-6-PLGA NPs via a polyamine-transport system. As a result, the uptake of Spd-Cou-6-PLGA NPs significantly decreased with increased Spd concentrations in incubation. At higher Spd concentrations of 50 and 500 µM, uptake of Spd-Cou-6-PLGA NPs reduced 0.34- and 0.49-fold from that without Spd pretreatment. After pretreatment with DFMO for 36 hours, cellular uptake of Spd-Cou-6-PLGA NPs reached 1.26-fold compared to the untreated DFMO group. In a biodistribution study, the drug-targeting index of Spd-AKF-PLGA NPs in the lung was 3.62- and 4.66-fold that of AKF-PLGA NPs and AKF solution, respectively. This suggested that Spd-AKF-PLGA NPs accumulated effectively in the lung. Lung-histopathology changes and collagen deposition were observed by H&E staining and Masson staining in an efficacy study. In the Spd-AKF-PLGA NP group, damage was further improved compared to the AKF-PLGA NP group and AKF-solution group. The results indicated that Spd-AKF-PLGA NPs are able to be effective nanocarriers for anti-pulmonary fibrosis therapy.

Computer-Aided Drug Discovery from Marine Compounds: Identification of the Three-Dimensional Structural Features Responsible for Antimalarial Activity

An integrated computational approach, based on molecular dynamics/mechanics, semi-empirical, and DFT calculations as well as dynamic docking studies, has been employed to gain insight into the mechanism of action of new antimalarial agents characterized by the scaffold of the marine compounds plakortin and aplidinone. The results of this approach show that these molecules, after interaction with Fe(II), likely coming from the heme molecule, give rise to the formation of radical species, that should represent the toxic intermediates responsible for subsequent reactions leading to plasmodium death. The three-dimensional structural requirements necessary for the activity of these new classes of antimalarial agents have been identified and discussed throughout the chapter.

Oligopeptidase B and B2: comparative modelling and virtual screening as searching tools for new antileishmanial compounds

Leishmaniasis are diseases caused by parasites of the genus Leishmania and transmitted to humans by the bite of infected insects of the subfamily Phlebotominae. Current drug therapy shows high toxicity and severe adverse effects. Recently, two oligopeptidases (OPBs) were identified in Leishmania amazonensis, namely oligopeptidase B (OPB) and oligopeptidase B2 (OPB2). These OPBs could be ideal targets, since both enzymes are expressed in all parasite lifecycle and were not identified in human. This work aimed to identify possible dual inhibitors of OPB and OPB2 from L. amazonensis. The three-dimensional structures of both enzymes were built by comparative modelling and used to perform a virtual screening of ZINC database by DOCK Blaster server. It is the first time that OPB models from L. amazonensis are used to virtual screening approach. Four hundred compounds were identified as possible inhibitors to each enzyme. The top scored compounds were submitted to refinement by AutoDock program. The best results suggest that compounds interact with important residues, as Tyr490, Glu612 and Arg655 (OPB numbers). The identified compounds showed better results than antipain and drugs currently used against leishmaniasis when ADMET in silico were performed. These compounds could be explored in order to find dual inhibitors of OPB and OPB2 from L. amazonensis.

Plasmodium AdoMetDC/ODC bifunctional enzyme is essential for male sexual stage development and mosquito transmission

Polyamines are positively-charged organic molecules that are important for cellular growth and division. Polyamines and their synthesizing enzymes are particularly abundant in rapidly proliferating eukaryotic cells such as parasitic protozoa and cancer cells. Polyamine biosynthesis inhibitors, such as Elfornithine, are now being considered for cancer prevention and have been used effectively against Trypanosoma brucei. Inhibitors of polyamine biosynthesis have caused growth arrest of Plasmodium falciparum blood stages in vitro, but in P. berghei only partial inhibition has been observed. While polyamine biosynthesis enzymes are characterized and conserved in Plasmodium spp., little is known on the biological roles of these enzymes inside malaria parasite hosts. The bifunctional polyamine biosynthesis enzyme S-adenosyl methionine decarboxylase/ornithine decarboxylase (AdoMetDC/ODC) was targeted for deletion in P. yoelii. Deletion of AdoMetDC/ODC significantly reduced blood stage parasitemia but Anopheles transmission was completely blocked. We showed that male gametocytogenesis and male gamete exflagellation were abolished and consequently no ookinetes or oocyst sporozoites could be generated from adometdc/odc(–) parasites. Supplementation of putrescine and spermidine did not rescue the defective phenotypes of male gametocytes and gametes of the knockout parasites. These results highlight the crucial role of polyamine homeostasis in the development and functions of Plasmodium erythrocytic stages in the blood and in the mosquito vector and validate polyamine biosynthesis pathway enzymes as drug targeting candidates for malaria parasite transmission blocking.

Summary: We provide the first genetic evidence for the crucial roles of de novo polyamine biosynthesis in the development of Plasmodium male sexual stages and in the transmission of malaria parasite to mosquito.

Stage-dependent expression and up-regulation of trypanothione synthetase in amphotericin B resistant Leishmania donovani

Kinetoplastids differ from other organisms in their ability to conjugate glutathione and spermidine to form trypanothione which is involved in maintaining redox homeostasis and removal of toxic metabolites. It is also involved in drug resistance, antioxidant mechanism, and defense against cellular oxidants. Trypanothione synthetase (TryS) of thiol metabolic pathway is the sole enzyme responsible for the biosynthesis of trypanothione in Leishmania donovani. In this study, TryS gene of L. donovani (LdTryS) was cloned, expressed, and fusion protein purified with affinity column chromatography. The purified protein showed optimum enzymatic activity at pH 8.0–8.5. The TryS amino acids sequences alignment showed that all amino acids involved in catalytic and ligands binding of L. major are conserved in L. donovani. Subcellular localization using digitonin fractionation and immunoblot analysis showed that LdTryS is localized in the cytoplasm. Furthermore, RT-PCR coupled with immunoblot analysis showed that LdTryS is overexpressed in Amp B resistant and stationary phase promastigotes (∼2.0-folds) than in sensitive strain and logarithmic phase, respectively, which suggests its involvement in Amp B resistance. Also, H₂O₂ treatment upto 150 µM for 8 hrs leads to 2-fold increased expression of LdTryS probably to cope up with oxidative stress generated by H₂O₂. Therefore, this study demonstrates stage- and Amp B sensitivity-dependent expression of LdTryS in L. donovani and involvement of TryS during oxidative stress to help the parasites survival.

Involvement of polyamine binding protein D (PotD) of Synechocystis sp. PCC 6803 in spermidine uptake and excretion

The in vivo function of polyamine binding protein D (PotD) in Synechocystis sp. PCC 6803 for the transport of spermidine was investigated using Synechocystis mutant disrupted in potD gene. The growth rate of potD mutant was similar to that of wild-type when grown in BG11 medium. However, the mutant exhibited severely reduced growth compared to the wild-type when BG11 medium was supplemented with 0.5 mM spermidine. The mutant accumulated a higher spermidine level than the wild-type when grown in the medium with or without spermidine. Transport experiments revealed that the mutant had a reduction in both the uptake and the excretion of spermidine. Moreover, [(14)C]spermidine-loaded wild-type and mutant cells showed a decrease of [(14)C]spermidine excretion when the assay medium contained exogenous spermidine. These data suggest that PotD is involved in both the uptake and the excretion of spermidine in Synechocystis cells.

Natural product based leads to fight against leishmaniasis

The growing incidence of parasitic resistance against generic pentavalent antimonials, specifically for visceral disease in Indian subcontinent, is a serious issue in Leishmania control. Notwithstanding the two treatment alternatives, that is amphotericin B and miltefosine are being effectively used but their high cost and therapeutic complications limit their use in endemic areas. In the absence of a vaccine candidate, identification, and characterization of novel drugs and targets is a major requirement of leishmanial research. This review describes current drug regimens, putative drug targets, numerous natural products that have shown promising antileishmanial activity alongwith some key issues and strategies for future research to control leishmaniasis worldwide.

Determination of polyamines in human plasma by high-performance liquid chromatography coupled with Q-TOF mass spectrometry

A high-performance liquid chromatography coupled with Q-time of flight mass spectrometry (HPLC/Q-TOF MS) method was developed and validated for the determination of 1, 3-diaminopropane, putrescine, cadaverine, spermidine and spermine in human plasma. The plasma samples were first pretreated by 10% HClO(4) and then derived by benzoyl chloride with 1, 6-diaminohexane as internal standard. The derived polyamines were separated on a C(18) column using a gradient program. The detection was performed on a Q-TOF MS by positive ionization mode. Calibration curve for each polyamine was obtained in the concentration range of 0.4 ~ 200.0 ng • ml(-1), with limit of detection of 0.02 ~ 0.1 ng • ml(-1). The intra- and inter-day RSD for all polyamines were 2.5-14.0% and 2.9 ~ 13.4%, respectively. The method was applied to determine the polyamines in human plasma from cancer patients and healthy volunteers. Results showed that the mean levels of polyamines in the plasma of cancer patients were higher than that of healthy volunteers, which suggested that the plasma polyamines could be employed as cancer diagnostic indicators in clinical testing.

Erythrocyte membranes convert monomeric ferriprotoporphyrin IX to β-hematin in acidic environment at malarial fever temperature

Hemozoin production makes it possible for intraerythrocytic malaria parasites to digest massive quantities of hemoglobin but still avoid potential ferriprotoporphyrin IX (FP) toxicity, which they cannot decompose further. Some antimalarial drugs, such as chloroquine, work by inhibiting this production, forcing the parasite to starve to death. As part of the efforts to identify possible biological mechanisms of FP polymerization, we have used normal human erythrocyte membranes as a model, to promote β-hematin (β-h) synthesis. Hemin in 35% aqueous dimethyl sulfoxide (DMSO) was reacted with isolated erythrocyte membranes and incubated overnight in sodium acetate buffer, pH 4.8, at 41°C. Infrared spectroscopy and electron microscopy showed that β-h was produced. Hemin in 10% was less effective as the substrate than when it was in 35% DMSO. A high malarial temperature seemed to be necessary, because FP polymerization was less at 37°C than at 41°C. Production was partially inhibited by chloroquine. These observations are of interest because other investigators have reported that membrane lipids mediated FP polymerization, but whole membranes were ineffective. On the other hand, our hypothesis is that the transport vesicles (TV) in malaria parasites could provide the receptor for FP and the lipids that promote hemozoin formation. Erythrocyte membranes may not be directly involved, but Plasmodium species transport hemoglobin in membrane-bound TV into food vacuoles, where hemoglobin catabolism is completed and hemozoin crystals are stored.

Leishmaniasis: current status of available drugs and new potential drug targets

The control of Leishmania infection relies primarily on chemotherapy till date. Resistance to pentavalent antimonials, which have been the recommended drugs to treat cutaneous and visceral leishmaniasis, is now widespread in Indian subcontinents. New drug formulations like amphotericin B, its lipid formulations, and miltefosine have shown great efficacy to treat leishmaniasis but their high cost and therapeutic complications limit their usefulness. In addition, irregular and inappropriate uses of these second line drugs in endemic regions like state of Bihar, India threaten resistance development in the parasite. In context to the limited drug options and unavailability of either preventive or prophylactic candidates, there is a pressing need to develop true antileishmanial drugs to reduce the disease burden of this debilitating endemic disease. Notwithstanding significant progress of leishmanial research during last few decades, identification and characterization of novel drugs and drug targets are far from satisfactory. This review will initially describe current drug regimens and later will provide an overview on few important biochemical and enzymatic machineries that could be utilized as putative drug targets for generation of true antileishmanial drugs.

Therapeutic potential of adenosine analogues and conjugates

This review summarizes current knowledge of adenosine analogues and conjugates with promising therapeutic properties. Adenosine is a signaling molecule that triggers numerous physiological responses. It acts through the adenosine receptors (ARs), belonging to the family of G-protein-coupled receptors and widely distributed throughout the body. Moreover, adenosine is involved in key biochemical processes as a part of ATP, the universal energy currency. Thus, compounds that are analogues of adenosine and its conjugates have been extensively studied as potential therapeutics. Many inhibitors of ARs are in clinical trials as promising agents in treatment of inflammation, type 2 diabetes, arrhythmia and as vasodilators used in the myocardial perfusion imaging (MPI) stress test. Furthermore, adenosine analogues revealed high efficacy as enzyme inhibitors, tested for antitrypanosomal action and as bivalent ligands and adenosine-oligoarginine conjugates as inhibitors of protein kinases.

Trimethoxy-chalcone derivatives inhibit growth of Leishmania braziliensis: synthesis, biological evaluation, molecular modeling and structure-activity relationship (SAR)

In this work we described the synthesis, the antileishmanial activity and the molecular modeling and structure-activity relationship (SAR) evaluations of a series of chalcone derivatives. Among these compounds, the methoxychalcones 2h, 2i, 2j, 2k and 2l showed significant antileishmanial activity (IC(50)<10 μM). Interestingly 2i (IC(50)=2.7 μM), 2j (IC(50)=3.9 μM) and 2k (IC(50)=4.6 μM) derivatives presented better antileishmanial activity than the control drug pentamidine (IC(50)=6.0 μM). Our SAR study showed the importance of methoxy di-ortho substitution at phenyl ring A and the relationship between the frontier orbital HOMO coefficients distribution of these molecules and their activity. The most active compounds 2h, 2i, 2j, 2k, and 2l fulfilled the Lipinski rule-of-five which theoretically is important for good drug absorption and permeation through biological membranes. The potential profile of 2j (IC(50)=3.9 μM and CC(50)=216 μM) pointed this chalcone derivative as a hit compound to be further explored in antileishmanial drug design.

Metabolism of N-alkylated spermine analogues by polyamine and spermine oxidases

N-alkylated polyamine analogues have potential as anticancer and antiparasitic drugs. However, their metabolism in the host has remained incompletely defined thus potentially limiting their utility. Here, we have studied the degradation of three different spermine analogues N,N'-bis-(3-ethylaminopropyl)butane-1,4-diamine (DESPM), N-(3-benzyl-aminopropyl)-N'-(3-ethylaminopropyl)butane-1,4-diamine (BnEtSPM) and N,N'-bis-(3-benzylaminopropyl)butane-1,4-diamine (DBSPM) and related mono-alkylated derivatives as substrates of recombinant human polyamine oxidase (APAO) and spermine oxidase (SMO). APAO and SMO metabolized DESPM to EtSPD [K(m(APAO)) = 10 microM, k(cat(APAO)) = 1.1 s(-1) and K(m(SMO)) = 28 microM, k(cat(SMO)) = 0.8 s(-1), respectively], metabolized BnEtSPM to EtSPD [K(m(APAO)) = 0.9 microM, k(cat(APAO)) = 1.1 s(-1) and K(m(SMO)) = 51 microM, k(cat(SMO)) = 0.4 s(-1), respectively], and metabolized DBSPM to BnSPD [K(m(APAO)) = 5.4 microM, k(cat(APAO)) = 2.0 s(-1) and K(m(SMO)) = 33 microM, k(cat(SMO)) = 0.3 s(-1), respectively]. Interestingly, mono-alkylated spermine derivatives were metabolized by APAO and SMO to SPD [EtSPM K(m(APAO)) = 16 microM, k(cat(APAO)) = 1.5 s(-1); K(m(SMO)) = 25 microM, k(cat(SMO)) = 8.2 s(-1); BnSPM K(m(APAO) )= 6.0 microM, k(cat(APAO)) = 2.8 s(-1); K(m(SMO)) = 19 muM, k(cat(SMO)) = 0.8 s(-1), respectively]. Surprisingly, EtSPD [K(m(APAO)) = 37 microM, k(cat(APAO)) = 0.1 s(-1); K(m(SMO)) = 48 microM, k(cat(SMO)) = 0.05 s(-1)] and BnSPD [K(m(APAO)) = 2.5 microM, k(cat(APAO)) = 3.5 s(-1); K(m(SMO)) = 60 microM, k(cat(SMO)) = 0.54 s(-1)] were metabolized to SPD by both the oxidases. Furthermore, we studied the degradation of DESPM, BnEtSPM or DBSPM in the DU145 prostate carcinoma cell line. The same major metabolites EtSPD and/or BnSPD were detected both in the culture medium and intracellularly after 48 h of culture. Moreover, EtSPM and BnSPM were detected from cell samples. Present data shows that inducible SMO parallel with APAO could play an important role in polyamine based drug action, i.e. degradation of parent drug and its metabolites, having significant impact on efficiency of these drugs, and hence for the development of novel N-alkylated polyamine analogues.

Antiprotozoal activity of 1-phenethyl-4-aminopiperidine derivatives

A series of 44 4-aminopiperidine derivatives was screened in vitro against four protozoan parasites (Trypanosoma brucei rhodesiense, Trypanosoma cruzi, Leishmania donovani, and Plasmodium falciparum). This screening identified 29 molecules selectively active against bloodstream-form T. b. rhodesiense trypomastigotes, with 50% inhibitory concentrations (IC50) ranging from 0.12 to 10 microM, and 33 compounds active against the chloroquine- and pyrimethamine-resistant K1 strain of P. falciparum (IC50 range, 0.17 to 5 microM). In addition, seven compounds displayed activity against intracellular T. cruzi amastigotes in the same range as the reference drug benznidazole (IC50, 1.97 microM) but were also cytotoxic to L-6 cells, showing little selectivity for T. cruzi. None of the molecules tested showed interesting antileishmanial activity against axenic amastigotes of L. donovani. To our knowledge, this is the first report of the antitrypanosomal activity of molecules bearing the 4-aminopiperidine skeleton.

Therapeutic evaluation of polyamine analogue drug candidates against Enterocytozoon bieneusi in a SCID mouse model

Enterocytozoon bieneusi is the most common cause of chronic diarrhea in individuals with human immunodeficiency virus infection or AIDS, and there is no effective therapy. The inhibitory activities of polyamine analogues (PG-11157, PG-11158, and PG-11302) against E. bieneusi infection were evaluated in SCID mice preconditioned with anti-gamma interferon monoclonal antibody intraperitoneally (i.p.). Mice were challenged orally with 10(4) E. bieneusi spores, and groups of mice were treated orally or i.p. 14 days later for 7 days. The inhibitory activities of the drugs against infection were determined by enumerating the E. bieneusi spores in feces three times a week by an immunofluorescence assay. Immunohistochemistry staining confirmed the infection within enterocytes. Oral administration of the analogues PG-11157 (at 150 or 75 mg/kg of body weight/day) and PG-11302 (at 250 mg/kg/day) had significant inhibitory activity (96.2 to 99.6%) that was slightly better than that of fumagillin (1 mg/kg/day; 93.7%). The inhibitory activity with i.p. injection was significant only with PG-11302 at 20 mg/kg/day. While the treatments considerably reduced the levels of spore excretion, neither polyamine analogues nor fumagillin was able to completely eliminate E. bieneusi, as excretion reappeared within 7 days after the end of treatment. Drug toxicity was apparent during treatment, but it disappeared at the end of treatment. These results warrant further examination of the analogues PG-11157 and PG-11302.

Co-inhibition of Plasmodium falciparum S-adenosylmethionine decarboxylase/ornithine decarboxylase reveals perturbation-specific compensatory mechanisms by transcriptome, proteome, and metabolome analyses

Polyamines are ubiquitous components of all living cells, and their depletion usually causes cytostasis, a strategy employed for treatment of West African trypanosomiasis. To evaluate polyamine depletion as an anti-malarial strategy, cytostasis caused by the co-inhibition of S-adenosylmethionine decarboxylase/ornithine decarboxylase in Plasmodium falciparum was studied with a comprehensive transcriptome, proteome, and metabolome investigation. Highly synchronized cultures were sampled just before and during cytostasis, and a novel zero time point definition was used to enable interpretation of results in lieu of the developmentally regulated control of gene expression in P. falciparum. Transcriptome analysis revealed the occurrence of a generalized transcriptional arrest just prior to the growth arrest due to polyamine depletion. However, the abundance of 538 transcripts was differentially affected and included three perturbation-specific compensatory transcriptional responses as follows: the increased abundance of the transcripts for lysine decarboxylase and ornithine aminotransferase and the decreased abundance of that for S-adenosylmethionine synthetase. Moreover, the latter two compensatory mechanisms were confirmed on both protein and metabolite levels confirming their biological relevance. In contrast with previous reports, the results provide evidence that P. falciparum responds to alleviate the detrimental effects of polyamine depletion via regulation of its transcriptome and subsequently the proteome and metabolome.

The design of guanidinium-rich transporters and their internalization mechanisms

The ability of a drug or probe to cross a biological barrier has historically been viewed to be a function of its intrinsic physical properties. This view has largely restricted drug design and selection to agents within a narrow log P range. Molecular transporters offer a strategy to circumvent these restrictions. In the case of guanidinium-rich transporters (GRTs), a typically highly water-soluble conjugate is found to readily pass through the non-polar membrane of a cell and for some across tissue barriers. This activity opens a field of opportunities for the use of GRTs to enable delivery of polar and non-polar drugs or probes as well as to enhance uptake of those of intermediate polarity. The field of transporter enabled or enhanced uptake has grown dramatically in the last decade. Some GRT drug conjugates have been advanced into clinical trials. This review will provide an overview of recent work pertinent to the design and mechanism of uptake of GRTs.

Living in a phagolysosome; metabolism of Leishmania amastigotes

Leishmania amastigotes primarily proliferate within macrophages in the mammalian host. Genome-based metabolic reconstructions, combined with biochemical, reverse genetic and mRNA or protein profiling studies are providing new insights into the metabolism of this intracellular stage. We propose that the complex nutritional requirements of amastigotes have contributed to the tropism of these parasites for the amino acid-rich phagolysosome of macrophages. Amastigote metabolism in this compartment is robust because many metabolic mutants are capable of either growing normally or persisting long term in susceptible animals. New approaches for measuring amastigote metabolism in vivo are discussed.

Real-time analysis of uptake and bioactivatable cleavage of luciferin-transporter conjugates in transgenic reporter mice

Many therapeutic leads fail to advance clinically because of bioavailability, selectivity, and formulation problems. Molecular transporters can be used to address these problems. Molecular transporter conjugates of otherwise poorly soluble or poorly bioavailable drugs or probes exhibit excellent solubility in water and biological fluids and at the same time an enhanced ability to enter tissues and cells and with modification to do so selectively. For many conjugates, however, it is necessary to release the drug/probe cargo from the transporter after uptake to achieve activity. Here, we describe an imaging method that provides quantification of transporter conjugate uptake and cargo release in real-time in animal models. This method uses transgenic (luciferase) reporter mice and whole-body imaging, allowing noninvasive quantification of transporter conjugate uptake and probe (luciferin) release in real time. This process effectively emulates drug-conjugate delivery, drug release, and drug turnover by an intracellular target, providing a facile method to evaluate comparative uptake of new transporters and efficacy and selectivity of linker release as required for fundamental studies and therapeutic applications.

Design, synthesis, and antitumor activity of bile acid–polyamine–nucleoside conjugates

A series of bile acid-polyamine amides conjugated with 3'-azido-3'-deoxythymidine (AZT) as potential antitumor prodrugs in the form of phosphoramidates were synthesized in good yields and their antitumor activities were assayed against two human cancer cells in vitro: cervix cancer HeLa cells and renal cancer 7860 cells. The improved antitumor activity probably derived from the enhanced delivery efficiency of AZT due to bile acid-polyamine conjugates.

Effect of polyamines and synthetic polyamine-analogues on the expression of antizyme (AtoC) and its regulatory genes

Background

In bacteria, the biosynthesis of polyamines is modulated at the level of transcription as well as post-translationally. Antizyme (Az) has long been identified as a non-competitive protein inhibitor of polyamine biosynthesis in E. coli. Az was also revealed to be the product of the atoC gene. AtoC is the response regulator of the AtoS-AtoC two-component system and it functions as the positive transcriptional regulator of the atoDAEB operon genes, encoding enzymes involved in short chain fatty acid metabolism. The antizyme is referred to as AtoC/Az, to indicate its dual function as both a transcriptional and post-translational regulator.

Results

The roles of polyamines on the transcription of atoS and atoC genes as well as that of atoDAEB(ato) operon were studied. Polyamine-mediated induction was tested both in atoSC positive and negative E. coli backgrounds by using β-galactosidase reporter constructs carrying the appropriate promoters patoDAEB, patoS, patoC. In addition, a selection of synthetic polyamine analogues have been synthesized and tested for their effectiveness in inducing the expression of atoC/Az, the product of which plays a pivotal role in the feedback inhibition of putrescine biosynthesis and the transcriptional regulation of the ato operon. The effects of these compounds were also determined on the ato operon expression. The polyamine analogues were also tested for their effect on the activity of ornithine decarboxylase (ODC), the key enzyme of polyamine biosynthesis and on the growth of polyamine-deficient E. coli.

Conclusion

Polyamines, which have been reported to induce the protein levels of AtoC/Az in E. coli, act at the transcriptional level, since they cause activation of the atoC transcription. In addition, a series of polyamine analogues were studied on the transcription of atoC gene and ODC activity.

Current therapeutics, their problems, and sulfur-containing-amino-acid metabolism as a novel target against infections by "amitochondriate" protozoan parasites

The "amitochondriate" protozoan parasites of humans Entamoeba histolytica, Giardia intestinalis, and Trichomonas vaginalis share many biochemical features, e.g., energy and amino acid metabolism, a spectrum of drugs for their treatment, and the occurrence of drug resistance. These parasites possess metabolic pathways that are divergent from those of their mammalian hosts and are often considered to be good targets for drug development. Sulfur-containing-amino-acid metabolism represents one such divergent metabolic pathway, namely, the cysteine biosynthetic pathway and methionine gamma-lyase-mediated catabolism of sulfur-containing amino acids, which are present in T. vaginalis and E. histolytica but absent in G. intestinalis. These pathways are potentially exploitable for development of drugs against amoebiasis and trichomoniasis. For instance, L-trifluoromethionine, which is catalyzed by methionine gamma-lyase and produces a toxic product, is effective against T. vaginalis and E. histolytica parasites in vitro and in vivo and may represent a good lead compound. In this review, we summarize the biology of these microaerophilic parasites, their clinical manifestation and epidemiology of disease, chemotherapeutics, the modes of action of representative drugs, and problems related to these drugs, including drug resistance. We further discuss our approach to exploit unique sulfur-containing-amino-acid metabolism, focusing on development of drugs against E. histolytica.

Leishmania donovani polyamine biosynthetic enzyme overproducers as tools to investigate the mode of action of cytotoxic polyamine analogs

A number of anticancer and antiparasitic drugs are postulated to target the polyamine biosynthetic pathway and polyamine function, but the exact mode of action of these compounds is still being elucidated. To establish whether polyamine analogs specifically target enzymes of the polyamine pathway, a model was developed using strains of the protozoan parasite Leishmania donovani that overproduce each of the polyamine biosynthetic enzymes. Promastigotes overexpressing episomal constructs encoding ornithine decarboxylase (ODC), S-adenosylmethionine decarboxylase (ADOMETDC), or spermidine synthase (SPDSYN) revealed robust overproduction of the corresponding polyamine biosynthetic enzyme. Polyamine pools, however, were either unchanged or only marginally affected, implying that regulatory mechanisms must exist. The ODC, ADOMETDC, and SPDSYN overproducer strains exhibited a high level of resistance to difluoromethylornithine, 5'-{[(Z)-4-amino-2-butenyl]methylamino}-5'-deoxyadenosine, and n-butylamine, respectively, confirming previous observations that these agents specifically target polyamine enzymes. Conversely, augmented levels of polyamine biosynthetic enzymes did not affect the sensitivity of L. donovani promastigotes to pentamidine, berenil, and mitoguazone, drugs that were postulated to target the polyamine pathway, implying alternative and/or additional targets for these agents. The sensitivities of wild-type and overproducing parasites to a variety of polyamine analogs were also tested. The polyamine enzyme-overproducing lines offer a rapid cell-based screen for assessing whether synthetic polyamine analogs exert their mechanism of action predominantly on the polyamine biosynthetic pathway in L. donovani. Furthermore, the drug resistance engendered by the amplification of target genes and the overproduction of the encoded protein offers a general strategy for evaluating and developing therapeutic agents that target specific proteins in Leishmania.