Screening for Small Molecule Modulators of Trypanosoma brucei Hsp70 Chaperone Activity Based upon Alcyonarian Coral-Derived Natural Products

Structure-Activity Study on Substituted, Core-Extended, and Dyad Naphthalene Diimide G-Quadruplex Ligands Leading to Potent Antitrypanosomal Agents

Several G-quadruplex nucleic acid (G4s) ligands have been developed seeking target selectivity in the past decade. Naphthalene diimide (NDI)-based compounds are particularly promising due to their biological activity and red-fluorescence emission. Previously, we demonstrated the existence of G4s in the promoter region of parasite genomes, assessing the effectiveness of NDI-derivatives against them. Here, we explored the biological activity of a small library of G4-DNA ligands, exploiting the NDI pharmacophore, against both Trypanosoma brucei and Leishmania major parasites. Biophysical and biological assays were conducted. Among the various families analyzed, core-extended NDIs exhibited the most promising results concerning the selectivity and antiparasitic effects. NDI 16 emerged as the most potent, with an IC50 of 0.011 nM against T. brucei and remarkable selectivity vs MRC-5 cells (3454-fold). Fascinating, 16 is 480-fold more potent than the standard drug pentamidine (IC50 = 5.3 nM). Cellular uptake and parasite localization were verified by exploiting core-extended NDI red-fluorescent emission.

Tackling Sleeping Sickness: Current and Promising Therapeutics and Treatment Strategies

Human African trypanosomiasis is a neglected tropical disease caused by the extracellular protozoan parasite Trypanosoma brucei, and targeted for eradication by 2030. The COVID-19 pandemic contributed to the lengthening of the proposed time frame for eliminating human African trypanosomiasis as control programs were interrupted. Armed with extensive antigenic variation and the depletion of the B cell population during an infectious cycle, attempts to develop a vaccine have remained unachievable. With the absence of a vaccine, control of the disease has relied heavily on intensive screening measures and the use of drugs. The chemotherapeutics previously available for disease management were plagued by issues such as toxicity, resistance, and difficulty in administration. The approval of the latest and first oral drug, fexinidazole, is a major chemotherapeutic achievement for the treatment of human African trypanosomiasis in the past few decades. Timely and accurate diagnosis is essential for effective treatment, while poor compliance and resistance remain outstanding challenges. Drug discovery is on-going, and herein we review the recent advances in anti-trypanosomal drug discovery, including novel potential drug targets. The numerous challenges associated with disease eradication will also be addressed.

Three-component microwave-assisted synthesis of 3,5-disubstituted pyrazolo[3,4-d]pyrimidin-4-ones

A practical three-component method for the synthesis of pyrazolo[3,4-d]pyrimidin-4-ones was developed. The reaction was performed in a one-pot manner under controlled microwave irradiation using easily accessible methyl 5-aminopyrazole-4-carboxylates, trimethyl orthoformate, and primary amines. Under the optimized conditions, challenging substrates, such as N-1 unsubstituted 5-aminopyrazole-4-carboxylates with another substituted amino group in position 3, reacted selectively affording 5-substituted 3-arylamino-1,5-dihydro-4H-pyrazolo[3,4-d]pyrimidin-4-ones. The reaction tolerated a range of primary amines, including anilines. The advantages of the developed protocol include short reaction time, pot- and step-economy, and convenient chromatography-free product isolation. The structural features of representative products were explored by X-ray crystallography.

Marine natural products

Covering: 2020This review covers the literature published in 2020 for marine natural products (MNPs), with 757 citations (747 for the period January to December 2020) referring to compounds isolated from marine microorganisms and phytoplankton, green, brown and red algae, sponges, cnidarians, bryozoans, molluscs, tunicates, echinoderms, mangroves and other intertidal plants and microorganisms. The emphasis is on new compounds (1407 in 420 papers for 2020), together with the relevant biological activities, source organisms and country of origin. Pertinent reviews, biosynthetic studies, first syntheses, and syntheses that led to the revision of structures or stereochemistries, have been included. A meta analysis of bioactivity data relating to new MNPs reported over the last five years is also presented.

Characterization of an Atypical Trypanosoma brucei Hsp70 Demonstrates Its Cytosolic-Nuclear Localization and Modulation by Quercetin and Methylene Blue

Trypanosoma brucei (Tb) harbours twelve Hsp70 chaperones. Of these, four are predicted to reside in the parasite cytosol. TbHsp70.c is predicted to be cytosolic and upregulated upon heat stress and is an ATPase that exhibits holdase chaperone function. Cytosol-localized Tbj2 stimulates the ATPase activity of TbHsp70.c. In the current study, immunofluorescence confirmed that TbHsp70.c is both a cytosolic and a nuclear protein. Furthermore, in silico analysis was used to elucidate an atypical linker and hydrophobic pocket. Tellingly, TbHsp70.c lacks the EEVD and GGMP motifs, both of which are implicated in substrate selectivity and co-chaperone binding in canonical Hsp70s. Far western analysis revealed that TbSTi1 interacts directly with TbHsp70 and TbHsp70.4, but does not bind TbHsp70.c. We further investigated the effect of quercetin and methylene blue on the Tbj2-driven ATPase activity of TbHsp70.c. We established that quercetin inhibited, whilst methylene blue enhanced, the Tbj2-stimulated ATPase activity of TbHsp70.c. Furthermore, these inhibitors were lethal to parasites. Lastly, we used molecular docking to show that quercetin and methylene blue may bind the nucleotide binding pocket of TbHsp70.c. Our findings suggest that small molecule inhibitors that target TbHsp70.c could be developed to serve as possible drug candidates against T. brucei.

Design, synthesis, antitrypanosomal activity, DNA/RNA binding and in vitro ADME profiling of novel imidazoline-substituted 2-arylbenzimidazoles

Novel imidazoline benzimidazole derivatives containing diversely substituted phenoxy moieties were synthesized with the aim of evaluating their antitrypanosomal activity, DNA/RNA binding affinity and in vitro ADME properties. The presence of the diethylaminoethyl subunit in 18a-18c led to enhanced antitrypanosomal potency, particularly for 18a and 18c, which contain unsubstituted and methoxy-substituted phenoxy moieties. They were found to be > 2-fold more potent against African trypanosomes than nifurtimox. Fluorescence and CD spectroscopy, thermal denaturation assays and computational analysis indicated a preference of 18a-18c toward AT-rich DNA and their minor groove binding mode. Replacement of the amidine group with less basic and ionisable nitrogen-containing moieties failed to improve membrane permeability of the investigated compounds. Due to structural diversification, the compounds displayed a range of physico-chemical features resulting in variable in vitro ADME properties, leaving space for further optimization of the biological profiles.