Design and Synthesis of Novel Amino and Acetamidoaurones with Antimicrobial Activities.

The development of new and effective antimicrobial compounds is urgent due to the emergence of resistant bacteria. Natural plant flavonoids are known to be effective molecules, but their activity and selectivity have to be increased. Based on previous aurone potency, we designed new aurone derivatives bearing acetamido and amino groups at the position 5 of the A ring and managing various monosubstitutions at the B ring. A series of 31 new aurone derivatives were first evaluated for their antimicrobial activity with five derivatives being the most active (compounds 10, 12, 15, 16, and 20). The evaluation of their cytotoxicity on human cells and of their therapeutic index (TI) showed that compounds 10 and 20 had the highest TI. Finally, screening against a large panel of pathogens confirmed that compounds 10 and 20 possess large spectrum antimicrobial activity, including on bioweapon BSL3 strains, with MIC values as low as 0.78 µM. These results demonstrate that 5-acetamidoaurones are far more active and safer compared with 5-aminoaurones, and that benzyloxy and isopropyl substitutions at the B ring are the most promising strategy in the exploration of new antimicrobial aurones.

Promising antibacterial efficacy of arenicin peptides against the emerging opportunistic pathogen Mycobacterium abscessus.

BACKGROUND: Mycobacterium abscessus, a fast-growing non-tuberculous mycobacterium, is an emerging opportunistic pathogen responsible for chronic bronchopulmonary infections in people with respiratory diseases such as cystic fibrosis (CF). Due to its intrinsic polyresistance to a wide range of antibiotics, most treatments for M. abscessus pulmonary infections are poorly effective. In this context, antimicrobial peptides (AMPs) active against bacterial strains and less prompt to cause resistance, represent a good alternative to conventional antibiotics. Herein, we evaluated the effect of three arenicin isoforms, possessing two or four Cysteines involved in one (Ar-1, Ar-2) or two disulfide bonds (Ar-3), on the in vitro growth of M. abscessus. METHODS: The respective disulfide-free AMPs, were built by replacing the Cysteines with alpha-amino-n-butyric acid (Abu) residue. We evaluated the efficiency of the eight arenicin derivatives through their antimicrobial activity against M. abscessus strains, their cytotoxicity towards human cell lines, and their hemolytic activity on human erythrocytes. The mechanism of action of the Ar-1 peptide was further investigated through membrane permeabilization assay, electron microscopy, lipid insertion assay via surface pressure measurement, and the induction of resistance assay. RESULTS: Our results demonstrated that Ar-1 was the safest peptide with no toxicity towards human cells and no hemolytic activity, and the most active against M. abscessus growth. Ar-1 acts by insertion into mycobacterial lipids, resulting in a rapid membranolytic effect that kills M. abscessus without induction of resistance. CONCLUSION: Overall, the present study emphasized Ar-1 as a potential new alternative to conventional antibiotics in the treatment of CF-associated bacterial infection related to M. abscessus.

Evaluation of the Efficiency of Random and Diblock Methacrylate-Based Amphiphilic Cationic Polymers against Major Bacterial Pathogens Associated with Cystic Fibrosis.

Cystic fibrosis (CF) is associated with repeated lung bacterial infection, mainly by Pseudomonas aeruginosa, Staphylococcus aureus, and Mycobacterium abscessus, all known to be or becoming resistant to several antibiotics, often leading to therapeutic failure and death. In this context, antimicrobial peptides and antimicrobial polymers active against resistant strains and less prompt to cause resistance, appear as a good alternative to conventional antibiotics. In the present study, methacrylate-based copolymers obtained by radical chemistry were evaluated against CF-associated bacterial strains. Results showed that the type (Random versus Diblock) and the size of the copolymers affected their antibacterial activity and toxicity. Among the different copolymers tested, four (i.e., Random10200, Random15000, Random23900, and Diblock9500) were identified as the most active and the safest molecules and were further investigated. Data showed that they inserted into bacterial lipids, leading to a rapid membranolytic effect and killing of the bacterial. In relation with their fast bactericidal action and conversely to conventional antibiotics, those copolymers did not induce a resistance and remained active against antibiotic-resistant strains. Finally, the selected copolymers possessed a preventive effect on biofilm formation, although not exhibiting disruptive activity. Overall, the present study demonstrates that methacrylate-based copolymers are an interesting alternative to conventional antibiotics in the treatment of CF-associated bacterial infection.

Cell death in Leishmania.

Leishmaniases still represent a global scourge and new therapeutic tools are necessary to replace the current expensive, difficult to administer treatments that induce numerous adverse effects and for which resistance is increasingly worrying. In this context, the particularly original organization of the Leishmania parasite in comparison to higher eukaryotes is a great advantage. It allows for the development of new, very specific, and thus non-cytotoxic treatments. Among these originalities, Leishmania cell death can be cited. Despite a classic pattern of apoptosis, key mammalian apoptotic proteins are not present in Leishmania, such as caspases, cell death receptors, and anti-apoptotic molecules. Recent studies have helped to develop a better understanding of parasite cell death, identifying new proteins or even new apoptotic pathways. This review provides an overview of the current knowledge on Leishmania cell death, describing its physiological roles and its phenotype, and discusses the involvement of various proteins: endonuclease G, metacaspase, aquaporin Li-BH3AQP, calpains, cysteine proteinase C, LmjHYD36 and Lmj.22.0600. From these data, potential apoptotic pathways are suggested. This review also offers tools to identify new Leishmania cell death effectors. Lastly, different approaches to use this knowledge for the development of new therapeutic tools are suggested: either inhibition of Leishmania cell death or activation of cell death for instance by treating cells with proteins or peptides involved in parasite death fused to a cell permeant peptide or encapsulated into a lipidic vector to target intra-macrophagic Leishmania cells.

TITLE: La mort cellulaire chez Leishmania. ABSTRACT: Alors que les leishmanioses représentent toujours un fléau mondial, de nouveaux outils thérapeutiques sont nécessaires pour remplacer les traitements actuels qui sont chers, difficiles à administrer, qui induisent de nombreux effets secondaires et pour lesquels la résistance est de plus en plus inquiétante. Pour cela, l'organisation très originale du parasite Leishmania par rapport aux eucaryotes supérieurs est un grand avantage. En effet, cela permet le développement de nouveaux traitements très spécifiques et donc non cytotoxiques. Parmi ces originalités, la mort cellulaire de Leishmania peut être citée. Malgré un aspect classique d'apoptose, les protéines apoptotiques clefs des mammifères ne sont pas présentes chez Leishmania, telles que les caspases, les récepteurs de mort et les molécules anti-apoptotiques. Des études récentes ont participé à une meilleure compréhension de la mort cellulaire du parasite, identifiant de nouvelles protéines ou même de nouvelles voies apoptotiques. Cette revue fait le point sur l'état actuel des connaissances sur la mort cellulaire de Leishmania, décrivant ses rôles physiologiques et son phénotype et discutant l'implication de différentes protéines : endonucléase G, métacaspase, aquaporine Li-BH3AQP, calpaïnes, cystéine protéinase C, LmjHYD36 et Lmj.22.0600. À partir de ces données, différentes voies apoptotiques potentielles sont suggérées. Cette revue fournit également des outils pour identifier de nouveaux effecteurs de la mort cellulaire de Leishmania. Pour finir, différentes approches pour utiliser ces connaissances pour le développement de nouveaux outils thérapeutiques sont suggérées : soit inhibition de la mort cellulaire de Leishmania, soit activation de celle-ci par exemple en traitant les cellules avec des protéines/peptides impliqués dans la mort du parasite fusionnés à un peptide pénétrant dans les cellules ou encapsulés dans un vecteur lipidique pour cibler les cellules de Leishmania intra-macrophagiques.

A novel hydrolase with a pro-death activity from the protozoan parasite Leishmania major.

Apoptosis is a cell death process generally described as involving a cascade of caspase activation, death receptors and/or pro- and antiapoptotic molecules from the BcL-2 family. But about 20 years ago, a caspase-independent apoptotic pathway has been described. Regarding this pathway, we can learn a lot from Leishmania parasites. Indeed, these parasitic protozoa enter, in response to different stimuli, in a form of cell death phenotypically similar to mammalian apoptosis but without involving caspases or death receptors. So far, only two proteins have been clearly identified as being involved in Leishmania-regulated cell death: the metacaspase and the endonuclease G. We report here the identification of a new protein modeled as a potential hydrolase, highly conserved among Leishmania species and absent in the very close parasite Trypanosoma brucei. This protein is involved in L. major-regulated cell death induced by curcumin, miltefosine and pentamidine, after gene overexpression and/or protein translocation to the nucleus. The identification of proteins involved in Leishmania-regulated cell death will provide a better understanding of nonconventional apoptotic pathways in higher eukaryotes. It will also allow the development of new therapeutic tools via the identification of new specific targets.

A potential acetyltransferase involved in Leishmania major metacaspase-dependent cell death.

BACKGROUND: Currently, there is no satisfactory treatment for leishmaniases, owing to the cost, mode of administration, side effects and to the increasing emergence of drug resistance. As a consequence, the proteins involved in Leishmania apoptosis seem a target of choice for the development of new therapeutic tools against these neglected tropical diseases. Indeed, Leishmania cell death, while phenotypically similar to mammalian apoptosis, is very peculiar, involving no homologue of the key mammalian apoptotic proteins such as caspases and death receptors. Furthermore, very few proteins involved in Leishmania apoptosis have been identified. RESULTS: We identified a protein involved in Leishmania apoptosis from a library of genes overexpressed during Leishmania differentiation during which autophagy occurs. Indeed, the gene was overexpressed when L. major cell death was induced by curcumin or miltefosine. Furthermore, its overexpression increased L. major curcumin- and miltefosine-induced apoptosis. This gene, named LmjF.22.0600, whose expression is dependent on the expression of the metacaspase, another apoptotic protein, encodes a putative acetyltransferase. CONCLUSIONS: This new protein, identified as being involved in Leishmania apoptosis, will contribute to a better understanding of Leishmania death, which is needed owing to the absence of a satisfactory treatment against leishmaniases. It will also allow a better understanding of the original apoptotic pathways of eukaryotes in general, while evidence of the existence of such pathways is accumulating.

(De)glutamylation and cell death in Leishmania parasites.

Trypanosomatids are flagellated protozoan parasites that are very unusual in terms of cytoskeleton organization but also in terms of cell death. Most of the Trypanosomatid cytoskeleton consists of microtubules, forming different substructures including a subpellicular corset. Oddly, the actin network appears structurally and functionally different from other eukaryotic actins. And Trypanosomatids have an apoptotic phenotype under cell death conditions, but the pathways involved are devoid of key mammal proteins such as caspases or death receptors, and the triggers involved in apoptotic induction remain unknown. In this article, we have studied the role of the post-translational modifications, deglutamylation and polyglutamylation, in Leishmania. We have shown that Leishmania apoptosis was linked to polyglutamylation and hypothesized that the cell survival process autophagy was linked to deglutamylation. A balance seems to be established between polyglutamylation and deglutamylation, with imbalance inducing microtubule or other protein modifications characterizing either cell death if polyglutamylation was prioritized, or the cell survival process of autophagy if deglutamylation was prioritized. This emphasizes the role of post-translational modifications in cell biology, inducing cell death or cell survival of infectious agents.

Nongenotoxic 3-Nitroimidazo[1,2-a]pyridines Are NTR1 Substrates That Display Potent in Vitro Antileishmanial Activity.

Twenty nine original 3-nitroimidazo[1,2-a]pyridine derivatives, bearing a phenylthio (or benzylthio) moiety at position 8 of the scaffold, were synthesized. In vitro evaluation highlighted compound 5 as an antiparasitic hit molecule displaying low cytotoxicity for the human HepG2 cell line (CC50 > 100 µM) alongside good antileishmanial activities (IC50 = 1-2.1 µM) against L. donovani, L. infantum, and L. major; and good antitrypanosomal activities (IC50 = 1.3-2.2 µM) against T. brucei brucei and T. cruzi, in comparison to several reference drugs such as miltefosine, fexinidazole, eflornithine, and benznidazole (IC50 = 0.6 to 13.3 µM). Molecule 5, presenting a low reduction potential (E° = -0.63 V), was shown to be selectively bioactivated by the L. donovani type 1 nitroreductase (NTR1). Importantly, molecule 5 was neither mutagenic (negative Ames test), nor genotoxic (negative comet assay), in contrast to many other nitroaromatics. Molecule 5 showed poor microsomal stability; however, its main metabolite (sulfoxide) remained both active and nonmutagenic, making 5 a good candidate for further in vivo studies.

Temporal analysis of the autophagic and apoptotic phenotypes in Leishmania parasites.

The leishmaniases are worldwide neglected tropical diseases caused by parasitic protozoa of the Leishmania genus. Different stimuli induce Leishmania cell death, but the proteins involved remain poorly understood. Furthermore, confusion often appears between cell death and the cell survival process autophagy, whose phenotype is not clearly defined. In this article, we present a comprehensive and temporal analysis of the cellular events occurring during miltefosine-induced cell death and autophagy in L. major. We also provide a list of features in order to clearly identify apoptotic cells, autophagic cells and to distinguish both processes. Furthermore, we demonstrate that autophagy is followed by apoptosis in the absence of nutrients. Finally, we show that cells treated with the generic kinase inhibitor staurosporine express apoptotic as well as autophagic markers and therefore cannot be used as an apoptosis inducer in Leishmania. These descriptions lead to a better recognition and understanding of apoptosis and autophagy, enabling their targeting in the development of new anti-leishmanial drugs. These researches also make it possible to better understand these processes in general, through the study of an ancestral eukaryote.

Calcein+/PI- as an early apoptotic feature in Leishmania.

Although leishmaniases are responsible for high morbidity and mortality all over the world, no really satisfying treatment exists. Furthermore, the corresponding parasite Leishmania undergoes a very characteristic form of programmed cell death. Indeed, different stimuli can induce morphological and biochemical apoptotic-like features. However, the key proteins involved in mammal apoptosis, such as caspases and death receptors, are not encoded in the genome of this parasite. Currently, little is known about Leishmania apoptosis, notably owing to the lack of specific tools for programmed cell death analysis in these parasites. Furthermore, there is a need for a better understanding of Leishmania programmed cell death in order (i) to better understand the role of apoptosis in unicellular organisms, (ii) to better understand apoptosis in general through the study of an ancestral eukaryote, and (iii) to identify new therapeutic targets against leishmaniases. To advance understanding of apoptosis in Leishmania, in this study we developed a new tool based on the quantification of calcein and propidium iodide by flow cytometry. This double labeling can be employed to distinguish early apoptosis, late apoptosis and necrosis in Leishmania live cells with a very simple and rapid assay. This paper should, therefore, be of interest for people working on Leishmania and related parasites.

Characterisation of polyglutamylases in trypanosomatids.

Microtubules are subject to post-translational modifications, which are thought to have crucial roles in the function of complex microtubule-based organelles. Among these, polyglutamylation was relatively recently discovered, and was related to centrosome stability, axonemal maintenance and mobility, and neurite outgrowth. In trypanosomatids, parasitic protozoa where microtubules constitute the essential component of the cytoskeleton, the function of polyglutamylated microtubules is unknown. Here, in order to better understand the role of this conserved but highly divergent post-translational modification, we characterised glutamylation and putative polyglutamylases in these parasites. We showed that microtubules are intensely glutamylated in all stages of the cell cycle, including interphase. Moreover, a cell cycle-dependent gradient of glutamylation was observed along the cell anteroposterior axis, which might be related to active growth of the microtubule 'corset' during the cell cycle. We also identified two putative polyglutamylase proteins (among seven analysed here) which appeared to be clearly and directly involved in microtubule polyglutamylation in in vitro activity assays. Paradoxically, in view of the importance of tubulins and of their extensive glutamylation in these organisms, RNA interference-based knockdown of all these proteins had no effect on cell growth, suggesting either functional redundancy or, more likely, subtle roles such as function modulation or interaction with protein partners.

Targeting the human parasite Leishmania donovani: discovery of a new promising anti-infectious pharmacophore in 3-nitroimidazo[1,2-a]pyridine series.

We report herein the discovery of antileishmanial molecules based on the imidazo[1,2-a]pyridine ring. In vitro screenings of imidazopyridines belonging to our chemical library, toward the promastigotes stage of Leishmania donovani, J774A.1 murine and HepG2 human cells, permitted to identify three selective hit-compounds (12, 20 and 28). New derivatives were then synthesized to allow structure-activity and -toxicity relationships analyses, enabling to characterize a lead-compound (44) displaying both a high potency (IC50=1.8 µM) and a good selectivity index, in comparison with three antileishmanial reference drug-compounds (amphotericin B, miltefosine and pentamidine). Moreover, lead-compound 44 also exhibits good in vitro activity against the intracellular amastigote stage of L. donovani. Thus, the 6-halo-3-nitro-2-(phenylsulfonylmethyl)imidazo[1,2-a]pyridine scaffold appears as a new promising selective antileishmanial pharmacophore, especially when substituted at position 8 by a bromine atom.

A new, rapid and sensitive bioluminescence assay for drug screening on Leishmania.

We validated a new method, based on luciferine/luciferase bioluminescence, for drug screening on promastigotes of different Leishmania species. Results obtained with this new, rapid, reproducible, and reliable method are in good accordance with results obtained by the conventional MTT assay. This bioluminescence assay has a lower detection limit.

Discovery of a new antileishmanial hit in 8-nitroquinoline series.

A series of nitrated 2-substituted-quinolines was synthesized and evaluated in vitro toward Leishmania donovani promastigotes. In parallel, the in vitro cytotoxicity of these molecules was assessed on the murine J774 and human HepG2 cell lines. Thus, a very promising antileishmanial hit molecule was identified (compound 21), displaying an IC(50) value of 6.6 µM and CC(50) values ≥ 100 µM, conferring quite good selectivity index to this molecule, in comparison with 3 drug-compounds of reference (amphotericin B, miltefosine and pentamidine). Compound 21 also appears as an efficient in vitro antileishmanial molecule against both Leishmania infantum promastigotes and the intracellular L. donovani amastigotes (respective IC(50) = 7.6 and 6.5 µM). Moreover, hit quinoline 21 does not show neither significant antiplasmodial nor antitoxoplasmic in vitro activity and though, presents a selective antileishmanial activity. Finally, a structure-activity relationships study enabled to define precisely the antileishmanial pharmacophore based on this nitroquinoline scaffold: 2-hydroxy-8-nitroquinoline.

Microtubule-severing proteins are involved in flagellar length control and mitosis in Trypanosomatids.

Microtubules are key players in the biology of Trypanosomatid parasites, not only as classical components of the mitotic spindle, microtubule-organizing centres and flagellum but also as the essential constituent of the cytoskeleton. Their length dynamics are regulated by, among others, microtubule-severing proteins. Four and six genes encoding microtubule-severing proteins can be found bioinformatically in the Leishmania major and Trypanosoma brucei genome respectively. We investigated all these proteins in these organisms, which include the katanin, katanin-like, spastin and fidgetin, and looked at their subcellular localization as well as their putative function by examining 'loss-of-function' phenotypes. The katanin-like KAT60b was found implicated in flagellar length reduction, but not in its size increase, while the katanin p80 subunit appeared clearly involved in cytokinesis. Fidgetin and spastin homologues were both localized in the nucleus: the first as a discrete and variable number of dots during most of the cell cycle, redistributing to the spindle and midbody during mitosis; the second concentrated as < or = 5 perinucleolar punctuations, similar to the electron-dense plaques identified in T. brucei, which were assimilated to kinetochores. This first study of microtubule-severing proteins in 'divergent' eukaryotes gives further insight into the multiple functions of these proteins identified in the hitherto studied models.