Discovery of Entamoeba histolytica hexokinase 1 inhibitors through homology modeling and virtual screening

Dynamic Association of ESCRT-II Proteins with ESCRT-I and ESCRT-III Complexes during Phagocytosis of Entamoeba histolytica

By their active movement and voraux phagocytosis, the trophozoites of Entamoeba histolytica constitute an excellent system to investigate the dynamics of the Endosomal Sorting Complex Required for Transport (ESCRT) protein interactions through phagocytosis. Here, we studied the proteins forming the E. histolytica ESCRT-II complex and their relationship with other phagocytosis-involved molecules. Bioinformatics analysis predicted that EhVps22, EhVps25, and EhVps36 are E. histolytica bona fide orthologues of the ESCRT-II protein families. Recombinant proteins and specific antibodies revealed that ESCRT-II proteins interact with each other, with other ESCRT proteins, and phagocytosis-involved molecules, such as the adhesin (EhADH). Laser confocal microscopy, pull-down assays, and mass spectrometry analysis disclosed that during phagocytosis, ESCRT-II accompanies the red blood cells (RBCs) from their attachment to the trophozoites until their arrival to multivesicular bodies (MVBs), changing their interactive patterns according to the time and place of the process. Knocked-down trophozoites in the Ehvps25 gene presented a 50% lower rate of phagocytosis than the controls and lower efficiency to adhere RBCs. In conclusion, ESCRT-II interacts with other molecules during prey contact and conduction throughout the phagocytic channel and trophozoites membranous system. ESCRT-II proteins are members of the protein chain during vesicle trafficking and are fundamental for the continuity and efficiency of phagocytosis.

Bioactive Aurones, Indanones, and Other Hemiindigoid Scaffolds: Medicinal Chemistry and Photopharmacology Perspectives

Hemiindigoids comprise a range of natural and synthetic scaffolds that share the same aromatic hydrocarbon backbone as well as promising biological and optical properties. The encouraging therapeutic potential of these scaffolds has been unraveled by many studies over the past years and uncovered representants with inspiring pharmacophoric features such as the acetylcholinesterase inhibitor donezepil and the tubulin polymerization inhibitor indanocine. In this review, we summarize the last advances in the medicinal potential of hemiindigoids, with a special attention to molecular design, structure-activity relationship, ligand-target interactions, and mechanistic explanations covering their effects. As their strong fluorogenic potential and photoswitch behavior recently started to be highlighted and explored in biology, giving rise to the development of novel fluorescent probes and photopharmacological agents, we also discuss these properties in a medicinal chemistry perspective.

Unlocking the Potential of HK2 in Cancer Metabolism and Therapeutics

Glycolysis is a tightly regulated process in which several enzymes, such as Hexokinases (HKs), play crucial roles. Cancer cells are characterized by specific expression levels of several isoenzymes in different metabolic pathways and these features offer possibilities for therapeutic interventions. Overexpression of HKs (mostly of the HK2 isoform) have been consistently reported in numerous types of cancer. Moreover, deletion of HK2 has been shown to decrease cancer cell proliferation without explicit side effects in animal models, which suggests that targeting HK2 is a viable strategy for cancer therapy. HK2 inhibition causes a substantial decrease of glycolysis that affects multiple pathways of central metabolism and also destabilizes the mitochondrial outer membrane, ultimately enhancing cell death. Although glycolysis inhibition has met limited success, partly due to low selectivity for specific isoforms and excessive side effects of the reported HK inhibitors, there is ample ground for progress. The current review is focused on HK2 inhibition, envisaging the development of potent and selective anticancer agents. The information on function, expression, and activity of HKs is presented, along with their structures, known inhibitors, and reported effects of HK2 ablation/inhibition. The structural features of the different isozymes are discussed, aiming to stimulate a more rational approach to the design of selective HK2 inhibitors with appropriate drug-like properties. Particular attention is dedicated to a structural and sequence comparison of the structurally similar HK1 and HK2 isoforms, aiming to unveil differences that could be explored therapeutically. Finally, several additional catalytic- and non-catalytic roles on different pathways and diseases, recently attributed to HK2, are reviewed and their implications briefly discussed.

In Vitro Testing of Potential Entamoeba histolytica Pyruvate Phosphate Dikinase Inhibitors

Adverse effects and resistance to metronidazole have motivated the search for new antiamoebic agents against Entamoeba histolytica. Control of amoeba growth may be achieved by inhibiting the function of the glycolytic enzyme and pyruvate phosphate dikinase (PPDK). In this study, we screened 10 compounds using an in vitro PPDK enzyme assay. These compounds were selected from a virtual screening of compounds in the National Cancer Institute database. The antiamoebic activity of the selected compounds was also evaluated by determining minimal inhibitory concentrations (MICs) and IC₅₀ values using the nitro-blue tetrazolium reduction assay. Seven of the 10 compounds showed inhibitory activities against the adenosine triphosphate (ATP)/inorganic phosphate binding site of the ATP-grasp domain. Two compounds, NSC349156 (pancratistatin) and NSC228137 (7-ethoxy-4-[4-methylphenyl] sulfonyl-3-oxido-2, 1, 3-benzoxadiazol-3-ium), exhibited inhibitory effects on the growth of E. histolytica trophozoites with MIC values of 25 and 50 μM, and IC₅₀ values of 14 and 20.7 μM, respectively.

Activity, stability and folding analysis of the chitinase from Entamoeba histolytica

Human amebiasis, caused by the parasitic protozoan Entamoeba histolytica, remains as a significant public health issue in developing countries. The life cycle of the parasite compromises two main stages, trophozoite and cyst, linked by two major events: encystation and excystation. Interestingly, the cyst stage has a chitin wall that helps the parasite to withstand harsh environmental conditions. Since the amebic chitinase, EhCHT1, has been recognized as a key player in both encystation and excystation, it is plausible to consider that specific inhibition could arrest the life cycle of the parasite and, thus, stop the infection. However, to selectively target EhCHT1 it is important to recognize its unique biochemical features to have the ability to control its cellular function. Hence, to gain further insights into the structure-function relationship, we conducted an experimental approach to examine the effects of pH, temperature, and denaturant concentration on the enzymatic activity and protein stability. Additionally, dependence on in vivo oxidative folding was further studied using a bacterial model. Our results attest the potential of EhCHT1 as a target for the design and development of new or improved anti-amebic therapeutics. Likewise, the potential of the oxidoreductase EhPDI, involved in oxidative folding of amebic proteins, was also confirmed.

Noninvasive intestinal amebiasis: Entamoeba histolytica colonization without invasion

PURPOSE OF REVIEW

Entamoeba histolytica infection remains a major cause of morbidity and mortality worldwide. Although research with the organism began in the late nineteenth century, our understanding of the natural history of the infection remains incomplete and is heavily based on expert opinion. Most persons infected with E. histolytica are carriers with the organism colonizing the large intestine. Host defense mechanisms that prevent invasive diseases are poorly understood. A timely review could lead to renewed interest.

RECENT FINDINGS

We herein review 2012 and 2013 publications related to the epidemiology, diagnosis, management and potential mechanisms that enable noninvasive E. histolytica colonization without invasion.

SUMMARY

There are several publications that advance our knowledge in the first three categories listed above, but studies of mechanisms for noninvasive E. histolytica colonization are glaringly few.

Inhibition and biochemical characterization of methicillin-resistant Staphylococcus aureus shikimate dehydrogenase: an in silico and kinetic study

Methicillin-resistant Staphylococcus auerus (MRSA) strains are having a major impact worldwide, and due to their resistance to all β-lactams, an urgent need for new drugs is emerging. In this regard, the shikimate pathway is considered to be one of the metabolic features of bacteria and is absent in humans. Therefore enzymes involved in this route, such as shikimate dehydrogenase (SDH), are considered excellent targets for discovery of novel antibacterial drugs. In this study, the SDH from MRSA (SaSDH) was characterized. The results showed that the enzyme is a monomer with a molecular weight of 29 kDa, an optimum temperature of 65 °C, and a maximal pH range of 9–11 for its activity. Kinetic studies revealed that SDH showed Michaelis-Menten kinetics toward both substrates (shikimate and NADP⁺). Initial velocity analysis suggested that SaSDH catalysis followed a sequential random mechanism. Additionally, a tridimensional model of SaSDH was obtained by homology modeling and validated. Through virtual screening three inhibitors of SaSDH were found (compounds 238, 766 and 894) and their inhibition constants and mechanism were obtained. Flexible docking studies revealed that these molecules make interactions with catalytic residues. The data of this study could serve as starting point in the search of new chemotherapeutic agents against MRSA.