Molecular basis for fungal selectivity of novel antimitotic compounds

Development of Novel and Efficient Processes for the Synthesis of 5-Amino and 5-Iminoimidazo[1,2-a]imidazoles via Three-Component Reaction Catalyzed by Zirconium(IV) Chloride

General and efficient approaches for the synthesis of new 5-amino and 5-iminoimidazo[1,2-a]imidazoles were developed through a three-component reaction of 1-unsubstituted 2-aminoimidazoles with various aldehydes and isocyanides mediated by zirconium(IV) chloride. The protocols were established considering the reactivity of the starting substrate, which varies depending on the presence of a substituent on the 2-aminoimidazole moiety. A library of new N-fused ring systems with wide structural diversification, novel synthetic, and potential pharmacological interest was obtained in moderate to good yields.

New Application of Neomycin B-Bisbenzimidazole Hybrids as Antifungal Agents

Alkylated aminoglycosides and bisbenzimidazoles have previously been shown to individually display antifungal activity. Herein, we explore for the first time the antifungal activity (in liquid cultures and in biofilms) of ten alkylated aminoglycosides covalently linked to either mono- or bisbenzimidazoles. We also investigate their toxicity against mammalian cells, their hemolytic activity, and their potential mechanism(s) of action (inhibition of fungal ergosterol biosynthetic pathway and/or reactive oxygen species (ROS) production). Overall, many of our hybrids exhibited broad-spectrum antifungal activity. We also found them to be less cytotoxic to mammalian cells and less hemolytic than the FDA-approved antifungal agents amphotericin B and voriconazole, respectively. Finally, we show with our best derivative (8) that the mechanism of action of our compounds is not the inhibition of ergosterol biosynthesis, but that it involves ROS production in yeast cells.

Effective killing of the human pathogen Candida albicans by a specific inhibitor of non-essential mitotic kinesin Kip1p

Kinesins from the bipolar (Kinesin-5) family are conserved in eukaryotic organisms and play critical roles during the earliest stages of mitosis to mediate spindle pole body separation and formation of a bipolar mitotic spindle. To date, genes encoding bipolar kinesins have been reported to be essential in all organisms studied. We report the characterization of CaKip1p, the sole member of this family in the human pathogenic yeast Candida albicans. C. albicans Kip1p appears to localize to the mitotic spindle and loss of CaKip1p function interferes with normal progression through mitosis. Inducible excision of CaKIP1 revealed phenotypes unique to C. albicans, including viable homozygous Cakip1 mutants and an aberrant spindle morphology in which multiple spindle poles accumulate in close proximity to each other. Expression of the C. albicans Kip1 motor domain in Escherichia coli produced a protein with microtubule-stimulated ATPase activity that was inhibited by an aminobenzothiazole (ABT) compound in an ATP-competitive fashion. This inhibition results in ‘rigor-like’, tight association with microtubules in vitro. Upon treatment of C. albicans cells with the ABT compound, cells were killed, and terminal phenotype analysis revealed an aberrant spindle morphology similar to that induced by loss of the CaKIP1 gene. The ABT compound discovered is the first example of a fungal spindle inhibitor targeted to a mitotic kinesin. Our results also show that the non-essential nature and implementation of the bipolar motor in C. albicans differs from that seen in other organisms, and suggest that inhibitors of a non-essential mitotic kinesin may offer promise as cidal agents for antifungal drug discovery.

Current state of three-dimensional characterisation of antifungal targets and its use for molecular modelling in drug design

The alarming rise in life-threatening systemic fungal infections due to the emergence of drug-resistant fungal strains had produced an increased demand for new antimycotics, especially those targeting novel antifungal structures. Drug discovery has developed from screening natural products and chemical synthesis to a modern approach, namely structure-based drug design. Whilst many antifungal agents currently in use were discovered more than 30 years ago, characterisation of various drug targets has only been achieved recently, contributing immensely to understanding the structure-activity relationships of antifungals and their targets. Three-dimensional characterisation has become a well established tool for modern antifungal drug research and should play an important role in investigations for new antifungal agents.

Giardia lamblia: Evaluation of the in vitro effects of nocodazole and colchicine on trophozoites

Giardia lamblia is the most commonly detected parasite in the intestinal tract of humans and other mammals causing giardiasis. Giardia presents several cytoskeletal structures with microtubules as major components such as the ventral adhesive disk, eight flagella axonemes, the median body and funis. Many drugs have already been tested as antigiardial agents, such as albendazole and mebendazole, which act by specifically inhibiting tubulin polymerization and hence microtubule assembly. In the present work, we used the microtubule inhibitors nocodazole and colchicine in order to investigate their direct and indirect effects on Giardia ultrastructure and attachment to the glass surface, respectively. Axenically grown G. lamblia trophozoites were treated with nocodazole or colchicine for different time intervals and analyzed by light and electron microscopy. It was observed that trophozoites became completely misshapen, detached from the glass surface and failed to complete cell division. The main alterations observed included disc fragmentation, presence of large vacuoles, and appearance of electrondense deposits made of tubulin. The cytokinesis was blocked, but not the karyokinesis, and membrane blebs were observed. These findings show that Giardia behavior and cytoskeleton are clearly affected by the commonly used microtubule targetting agents colchicine and nozodazole.

Identification of phenolics for control of Aspergillus flavus using Saccharomyces cerevisiae in a model target-gene bioassay

The yeast Saccharomyces cerevisiae was used in a high-throughput bioassay to identify phenolic agents for control of the aflatoxigenic fungus Aspergillus flavus. Veratraldehyde, 1, cinnamic acid, 5, and the respective benzoic acid derivatives vanillin, 2, vanillic acid, 3, and vanillylacetone, 4, and cinnamic acid derivatives o-coumaric acid, 6, m-coumaric acid, 7, and p-coumaric acid, 8, showed significant antifungal activities (from highest to lowest, 2, 5 > 1 > 6, 7 > 4 > 3, 8) in the yeast system, with caffeic acid, 9, having little to no effect. Antifungal activity levels against A. flavus were similar. This similarity in antifungal activity demonstrated the usefulness of the S. cerevisiae bioassay for screening antifungal compounds. Assays using deletion mutants of yeast identified signal transduction and antioxidative stress response genes important to fungal tolerance. Targeting the antioxidative stress response system with certain compounds (e.g., 4) in combination with strobilurin fungicides had a synergistic effect against both fungi.