Design, synthesis and biological evaluation of new aryl thiosemicarbazone as antichagasic candidates

Discovery of Novel Inhibitors of Cruzain Cysteine Protease of Trypanosoma cruzi

Chagas disease (CD) is a parasitic disease endemic in several developing countries. According to the World Health Organization, approximately 6-8 million people worldwide are inflicted by CD. The scarcity of new drugs, mainly for the chronic phase, is the main reason for treatment limitation in CD. Therefore, there is an urgent need to discover new targets for which new therapeutical agents could be developed. Cruzain cysteine protease (CCP) is a promising alternative because this enzyme exhibits pleiotropic effects by acting as a virulence factor, modulating host immune cells, and interacting with host cells. This systematic review was conducted to discover new compounds that act as cruzain inhibitors, and their effects in vitro were studied through enzymatic assays and molecular docking. Additionally, the advances and perspectives of these inhibitors are discussed. These findings are expected to contribute to medicinal chemistry in view of the design of new, safe, and efficacious inhibitors against Trypanosoma cruzi CCP detected in the last decade (2013-2022) to provide scaffolds for further optimization, aiming toward the discovery of new drugs.

Experimental and Computational Study of Aryl-thiosemicarbazones Inhibiting Cruzain Reveals Reversible Inhibition and a Stepwise Mechanism

Trypanosoma cruzi is a parasite that infects about 6-7 million people worldwide, mostly in Latin America, causing Chagas disease. Cruzain, the main cysteine protease of T. cruzi, is a validated target for developing drug candidates for Chagas disease. Thiosemicarbazones are one of the most relevant warheads used in covalent inhibitors targeting cruzain. Despite its relevance, the mechanism of inhibition of cruzain by thiosemicarbazones is unknown. Here, we combined experiments and simulations to unveil the covalent inhibition mechanism of cruzain by a thiosemicarbazone-based inhibitor (compound 1). Additionally, we studied a semicarbazone (compound 2), which is structurally similar to compound 1 but does not inhibit cruzain. Assays confirmed the reversibility of inhibition by compound 1 and suggested a two-step mechanism of inhibition. The K_i was estimated to be 36.3 μM and K_i* to be 11.5 μM, suggesting the pre-covalent complex to be relevant for inhibition. Molecular dynamics simulations of compounds 1 and 2 with cruzain were used to propose putative binding modes for the ligands. One-dimensional (1D) quantum mechanics/molecular mechanics (QM/MM) potential of mean force (PMF) and gas-phase energies showed that the attack of Cys25-S^- on the C═S or C═O bond yields a more stable intermediate than the attack on the C═N bond of the thiosemicarbazone/semicarbazone. Two-dimensional (2D) QM/MM PMF revealed a putative reaction mechanism for compound 1, involving the proton transfer to the ligand, followed by the Cys25-S^- attack at C═S. The ΔG and energy barrier were estimated to be -1.4 and 11.7 kcal/mol, respectively. Overall, our results shed light on the inhibition mechanism of cruzain by thiosemicarbazones.

Thiosemicarbazone derivatives: Evaluation as cruzipain inhibitors and molecular modeling study of complexes with cruzain

The development of cruzipain inhibitors represents one of the most attractive challenges in the search for drugs for the treatment of Chagas disease. A recombinant form of this enzyme, cruzain, has been crystallized with numerous inhibitors, excluding thiosemicarbazones. These compounds have been established as potent inhibitors of cruzain, although there is very little data in the literature of thiosemicarbazones tested on cruzipain. In this work, we present the results of the evaluation of eleven thiosemicarbazones on cruzipain, isolated from T. cruzi epimastigotes, six of them previously evaluated on cruzain. For these latter, we studied through computational methods, the mode of interaction with the active site of cruzain and the contribution of geometric parameters to the possible mechanism of action involved in the observed inhibition. Finally, from some geometric parameters analyzed on modeled TSC-cruzain complexes, a semi-quantitative relationship was established that could explain the inhibitory activity of thiosemicarbazones on cruzipain, the enzyme actually present in the parasite.

The biological activities of butyrylcholinesterase inhibitors

Acetylcholinesterase (AChE) inhibitor is the first choice for the treatment of Alzheimer's disease (AD), but it has some defects, such as dose limitation and unsatisfactory long-term treatment effect. Recent studies have shown that butyrylcholinesterase (BuChE) inhibitors or double acetyl and butyryl cholinesterase inhibitors have better curative effects on AD, and the side effects are lower than those of specific AChE inhibitors. Dual target cholinesterase inhibitors have become a new hotspot in the research of anti-AD drugs. Herein, the synthesis and bioactivities of BuChE inhibitors were reviewed.

Monosubstituted Acetophenone Thiosemicarbazones as Potent Inhibitors of Tyrosinase: Synthesis, Inhibitory Studies, and Molecular Docking

A set of 12 monosubstituted acetophenone thiosemicarbazone derivatives (TSCs) were synthesized and their inhibitory properties toward tyrosinase activity were tested. Moreover, their ability to inhibit melanogenesis in the B16F10 murine melanoma cell line was studied. In order to investigate the nature of interactions between the enzyme and the inhibitors, molecular docking to the active site was performed. TSCs 5, 6, 8, and 9 revealed a half maximal inhibitory concentration (IC₅₀) below 1 µM. Compound 6 turned out to be the most potent tyrosinase inhibitor. All investigated compounds showed reversible inhibition of competitive or mixed type. The para-substituted TSCs had higher affinity for the enzyme as compared to their ortho- and meta-analogues. All investigated compounds inhibited melanin production in B16F10 cells at the micromolar level. Molecular docking showed that the sulfur atom of the thiourea moiety penetrates the active site and interacts with copper ions. The above outcomes might be helpful in the design of new tyrosinase inhibitors in the food and cosmetic industries.

Dual Parasiticidal Activities of Phthalimides: Synthesis and Biological Profile against Trypanosoma cruzi and Plasmodium falciparum

Chagas disease and malaria are two neglected tropical diseases (NTDs) that prevail in tropical and subtropical regions in 149 countries. Chagas is also present in Europe, the US and Australia due to immigration of asymptomatic infected individuals. In the absence of an effective vaccine, the control of both diseases relies on chemotherapy. However, the emergence of parasite drug resistance is rendering currently available drugs obsolete. Hence, it is crucial to develop new molecules. Phthalimides, thiosemicarbazones, and 1,3-thiazoles have been used as scaffolds to obtain antiplasmodial and anti-Trypanosoma cruzi agents. Herein we present the synthesis of 24 phthalimido-thiosemicarbazones (3 a-x) and 14 phthalimido-thiazoles (4 a-n) and the corresponding biological activity against T. cruzi, Plasmodium falciparum, and cytotoxicity against mammalian cell lines. Some of these compounds showed potent inhibition of T. cruzi at low cytotoxic concentrations in RAW 264.7 cells. The most active compounds, 3 t (IC₅₀ =3.60 μM), 3 h (IC₅₀ =3.75 μM), and 4 j (IC₅₀ =4.48 μM), were more active than the control drug benznidazole (IC₅₀ =14.6 μM). Overall, the phthalimido-thiosemicarbazone derivatives were more potent than phthalimido-thiazole derivatives against T. cruzi. Flow cytometry assay data showed that compound 4 j was able to induce necrosis and apoptosis in trypomastigotes. Analysis by scanning electron microscopy showed that T. cruzi trypomastigote cells treated with compounds 3 h, 3 t, and 4 j at IC₅₀ concentrations promoted changes in the shape, flagella, and surface of the parasite body similar to those observed in benznidazole-treated cells. The compounds with the highest antimalarial activity were the phthalimido-thiazoles 4 l (IC₅₀ =1.2 μM), 4 m (IC₅₀ =1.7 μM), and 4 n (IC₅₀ =2.4 μM). Together, these data revealed that phthalimido derivatives possess a dual antiparasitic profile with potential effects against T. cruzi and lead-like characteristics.

Thiazole, thio and semicarbazone derivatives against tropical infective diseases: Chagas disease, human African trypanosomiasis (HAT), leishmaniasis, and malaria

Thiazole, thiosemicarbazone and semicarbazone moieties are privileged scaffolds (acting as primary pharmacophores) in many compounds that are useful to treat several diseases, mainly tropical infectious diseases. In this review article, we critically analyzed the contribution of these scaffolds to medicinal chemistry in the last five years, focusing on tropical infectious diseases, such as Chagas disease, human African trypanosomiasis (HAT), leishmaniasis, and malaria. We also present perspectives for their use in drug design in order to contribute to the development of new drugs.

Aryl thiosemicarbazones for the treatment of trypanosomatidic infections

Basing on a library of thiadiazole derivatives showing anti-trypanosomatidic activity, we have considered the thiadiazoles opened forms and reaction intermediates, thiosemicarbazones, as compounds of interest for phenotypic screening against Trypanosoma brucei (Tb), intracellular amastigote form of Leishmania infantum (Li) and Trypanosoma cruzi (Tc). Similar compounds have already shown interesting activity against the same organisms. The compounds were particularly effective against T. brucei and T. cruzi. Among the 28 synthesized compounds, the best one was (E)-2-(4-((3.4-dichlorobenzyl)oxy)benzylidene) hydrazinecarbothioamide (A14) yielding a comparable anti-parasitic activity against the three parasitic species (TbEC₅₀ = 2.31 μM, LiEC₅₀ = 6.14 μM, TcEC₅₀ = 1.31 μM) and a Selectivity Index higher than 10 with respect to human macrophages, therefore showing a pan-anti-trypanosomatidic activity. (E)-2-((3'.4'-dimethoxy-[1.1'-biphenyl]-3-yl)methyle ne) hydrazinecarbothioamide (A12) and (E)-2-(4-((3.4-dichlorobenzyl)oxy)benzylidene)hydrazine carbothioamide (A14) were able to potentiate the anti-parasitic activity of methotrexate (MTX) when evaluated in combination against T. brucei, yielding a 6-fold and 4-fold respectively Dose Reduction Index for MTX. The toxicity profile against four human cell lines and a panel of in vitro early-toxicity assays (comprising hERG, Aurora B, five cytochrome P450 isoforms and mitochondrial toxicity) demonstrated the low toxicity for the thosemicarbazones class in comparison with known drugs. The results confirmed thiosemicarbazones as a suitable chemical scaffold with potential for the development of properly decorated new anti-parasitic drugs.

Facile high-yield synthesis of unsymmetric end-off compartmental double Schiff-base ligands: easy access to mononuclear precursor and unsymmetric dinuclear complexes

Novel approach to unsymmetric end-off compartmental ligands with a selective high-yield synthesis and access to unsymmetric dinuclear complexes.

Novel Non-Peptide Inhibitors against SmCL1 of Schistosoma mansoni: In Silico Elucidation, Implications and Evaluation via Knowledge Based Drug Discovery

Schistosomiasis is a major endemic disease known for excessive mortality and morbidity in developing countries. Because praziquantel is the only drug available for its treatment, the risk of drug resistance emphasizes the need to discover new drugs for this disease. Cathepsin SmCL1 is the critical target for drug design due to its essential role in the digestion of host proteins for growth and development of Schistosoma mansoni. Inhibiting the function of SmCL1 could control the wide spread of infections caused by S. mansoni in humans. With this objective, a homology modeling approach was used to obtain theoretical three-dimensional (3D) structure of SmCL1. In order to find the potential inhibitors of SmCL1, a plethora of in silico techniques were employed to screen non-peptide inhibitors against SmCL1 via structure-based drug discovery protocol. Receiver operating characteristic (ROC) curve analysis and molecular dynamics (MD) simulation were performed on the results of docked protein-ligand complexes to identify top ranking molecules against the modelled 3D structure of SmCL1. MD simulation results suggest the phytochemical Simalikalactone-D as a potential lead against SmCL1, whose pharmacophore model may be useful for future screening of potential drug molecules. To conclude, this is the first report to discuss the virtual screening of non-peptide inhibitors against SmCL1 of S. mansoni, with significant therapeutic potential. Results presented herein provide a valuable contribution to identify the significant leads and further derivatize them to suitable drug candidates for antischistosomal therapy.

Phenolic thio- and selenosemicarbazones as multi-target drugs

A series of isosteric phenolic thio- and selenosemicarbazones have been obtained by condensation of naturally-occurring phenolic aldehydes and thio(seleno)semicarbazides. Title compounds were designed as potential multi-target drugs, and a series of structure-activity relationships could be established upon their in vitro assays: antioxidant activity, α-glucosidase inhibition and antiproliferative activity against six human tumor cell lines: A549 (non-small cell lung), HBL-100 (breast), HeLa (cervix), SW1573 (non-small cell lung), T-47D (breast) and WiDr (colon). For the antiradical activity, selenium atom and 2 or 3 phenolic hydroxyl groups proved to be essential motifs; remarkably, the compound with the most potent activity, with a trihydroxyphenyl scaffold (EC50 = 4.87 ± 1.57 μM) was found to be stronger than natural hydroxytyrosol, a potent antioxidant present in olive oil (EC50 = 13.80 ± 1.41 μM). Furthermore, one of the thiosemicarbazones was found to be a strong non-competitive inhibitor of α-glucosidase (Ki = 9.6 ± 1.6 μM), with an 8-fold increase in activity compared to acarbose (Ki = 77.9 ± 11.4 μM), marketed for the treatment of type-2 diabetes. Most of the synthesized compounds also exhibited relevant antiproliferative activities; in particular, seleno derivatives showed GI50 values lower than 6.0 μM for all the tested cell lines; N-naphthyl mono- and dihydroxylated derivatives behaved as more potent antiproliferative agents than 5-fluorouracil or cisplatin.