In Silico Identification and In Vitro Evaluation of Natural Inhibitors of Leishmania major Pteridine Reductase I

Phytochemical investigation of Chrysanthellum americanum Vatke and its constituents- a targeted approach for the treatment of leishmaniasis

The present study is focused on the isolation and identification of new therapeutic candidates from Chrysanthellum americanum Vatke., and their efficacy against pteridine reductase-1 (PTR1), a valid chemotherapeutic target in the Leishmania parasite. Henceforth, a new compound, chrysanamerine (1), along with 7 known compounds, polyacetylene 2, and flavonoids 3-8, were isolated from C. americanum. Their structures were determined by chemical and spectroscopic analyses and compared with the reported spectroscopic data. All compounds were evaluated for their anti-leishmanial activity against PTR1 via biochemical mechanism-based assay. The in vitro results showed five potential hits including a new compound, chrysanamerine (1), and four known compounds against the PTR1 enzyme. Among them, compound 1 showed a potent enzyme inhibition with an IC50 of 31.02 ± 2.36 μM, whereas a moderate inhibition was observed in cases of compounds 5 and 6 (IC50 = 59.86 ± 3.32, and 45.32 ± 3.5 μM, respectively). Whereas, compounds 3 and 8 showed mild inhibition (IC50 = 72.12 ± 1.12, and 97.18 ± 1.23 μM, respectively) against PTR1, compared with trimethoprim (positive control) (IC50 = 21.07 ± 1.6 μM). Moreover, the results were further validated via molecular docking and molecular dynamics (MD) simulations. Compound 1 showed a strong affinity to the binding site with a docking score of -11.83, along with the formation of a stable protein-ligand complex over the trajectory of 100 ns. Besides, compounds 1-8 were found to be non-cytotoxic on BJ (human fibroblast) cells.

Sophoraflavanone G: A review of the phytochemistry and pharmacology

Bioactive compounds derived from natural sources have long been investigated for the prevention and treatment of human diseases. Sophoraflavanone G (SFG), a lavandulyl flavanone naturally occurring in several Sophora plant species, belongs to the group of prenylated flavonoids that have garnered significant interest in contemporary research. The natural molecule exhibits a wide range of pharmacological properties and shows remarkable efficacy. Its ability to effectively suppress a range of malignant tumor cells, such as leukemia, breast cancer, and lung cancer, is attributed to its multi-target, multi-pathway, and multi-faceted mechanisms of action. Simultaneously, it can also alleviate various inflammatory diseases by mediating inflammatory mediators and molecular pathways. Furthermore, it has the capability to combat antibiotic resistance, exhibit synergistic antibacterial properties with diverse antibiotics, and prevent and treat various agricultural pests. Theoretically, it can bring benefits to human health and has potential value as a drug. Nevertheless, the drawbacks of poor water solubility and inadequate targeting cannot be overlooked. To comprehensively assess the current research on SFG, leverage its structural advantages and pharmacological activity, overcome its low bioavailability limitations, expedite its progression into a novel therapeutic drug, and better serve the clinic, this article presents a overall retrospect of the current research status of SFG. The discussion includes an analysis of the structural characteristics, physicochemical properties, bioavailability, pharmacological activities, and structure-activity relationships of SFG, with the goal of offering valuable insights and guidance for future research endeavors in this field.

In Silico and In Vitro Search for Dual Inhibitors of the Trypanosoma brucei and Leishmania major Pteridine Reductase 1 and Dihydrofolate Reductase

The parasites Trypanosoma brucei (Tb) and Leishmania major (Lm) cause the tropical diseases sleeping sickness, nagana, and cutaneous leishmaniasis. Every year, millions of humans, as well as animals, living in tropical to subtropical climates fall victim to these illnesses' health threats. The parasites' frequent drug resistance and widely spread natural reservoirs heavily impede disease prevention and treatment. Due to pteridine auxotrophy, trypanosomatid parasites have developed a peculiar enzyme system consisting of dihydrofolate reductase-thymidylate synthase (DHFR-TS) and pteridine reductase 1 (PTR1) to support cell survival. Extending our previous studies, we conducted a comparative study of the T. brucei (TbDHFR, TbPTR1) and L. major (LmDHFR, LmPTR1) enzymes to identify lead structures with a dual inhibitory effect. A pharmacophore-based in silico screening of three natural product databases (approximately 4880 compounds) was performed to preselect possible inhibitors. Building on the in silico results, the inhibitory potential of promising compounds was verified in vitro against the recombinant DHFR and PTR1 of both parasites using spectrophotometric enzyme assays. Twelve compounds were identified as dual inhibitors against the Tb enzymes (0.2 μM < IC50 < 85.1 μM) and ten against the respective Lm enzymes (0.6 μM < IC50 < 84.5 μM). These highly promising results may represent the starting point for the future development of new leads and drugs utilizing the trypanosomatid pteridine metabolism as a target.

Incorporation of Perillyl Alcohol into Lipid-Based Nanocarriers Enhances the Antiproliferative Activity in Malignant Glioma Cells

Perillyl alcohol (PA), a naturally existing monocyclic terpene related to limonene, is characterized by its poor aqueous solubility and very limited bioavailability. Its potential anti-cancer activity against malignant glioma has been reported. The aim was to develop PA-loaded lipid-based nanocarriers (LNCs), and to investigate their anti-cancer activity against two different brain cell lines. Non-medicated and PA-loaded LNCs were prepared and characterized. The mechanism of cytotoxic activity of PA was conducted using a molecular docking technique. The cell viabilities against A172 and ANGM-CSS cells were evaluated. The results revealed that the average particle size of the prepared LNCs ranged from 248.67 ± 12.42 to 1124.21 ± 12.77 nm, the polydispersity index was 0.418 ± 0.043-0.509 ± 0.064, while the zeta potential ranged from -36.91 ± 1.31 to -15.20 ± 0.96 mV. The molecular docking studies demonstrated that the drug had binding activity to human farnesyltransferase. Following exposure of the two glioblastoma cell lines to the PA-loaded nanoformulations, MTS assays were carried out, and the data showed a far lower half-maximal inhibitory concentration in both cell lines when compared to pure drug and non-medicated nanocarriers. These results indicate the potential in vitro antiproliferative activity of PA-loaded LNCs. Therefore, the prepared PA-loaded nanocarriers could be used to enhance drug delivery across the blood-brain barrier (BBB) in order to treat brain cancer, especially when formulated in a suitable dosage form. The size, surface charge, and lipid composition of the LNCs make them promising for drug delivery across the BBB. Detailed pharmacokinetic and pharmacodynamic assessments, including the evaluation of BBB penetration, are necessary to better understand the compound's distribution and effects within the brain.

Unveiling the Efficacy of Sesquiterpenes from Marine Sponge Dactylospongia elegans in Inhibiting Dihydrofolate Reductase Using Docking and Molecular Dynamic Studies

Dihydrofolate reductase (DHFR) is a crucial enzyme that maintains the levels of 5,6,7,8-tetrahydrofolate (THF) required for the biological synthesis of the building blocks of DNA, RNA, and proteins. Over-activation of DHFR results in the progression of multiple pathological conditions such as cancer, bacterial infection, and inflammation. Therefore, DHFR inhibition plays a major role in treating these illnesses. Sesquiterpenes of various types are prime metabolites derived from the marine sponge Dactylospongia elegans and have demonstrated antitumor, anti-inflammation, and antibacterial capacities. Here, we investigated the in silico potential inhibitory effects of 87 D. elegans metabolites on DHFR and predicted their ADMET properties. Compounds were prepared computationally for molecular docking into the selected crystal structure of DHFR (PDB: 1KMV). The docking scores of metabolites 34, 28, and 44 were the highest among this series (gscore values of -12.431, -11.502, and -10.62 kcal/mol, respectively), even above the co-crystallized inhibitor SRI-9662 score (-10.432 kcal/mol). The binding affinity and protein stability of these top three scored compounds were further estimated using molecular dynamic simulation. Compounds 34, 28, and 44 revealed high binding affinity to the enzyme and could be possible leads for DHFR inhibitors; however, further in vitro and in vivo investigations are required to validate their potential.

Anti-trypanosomatid structure-based drug design - lessons learned from targeting the folate pathway

INTRODUCTION

Trypanosomatidic parasitic infections of humans and animals caused by Trypanosoma brucei, Trypanosoma cruzi, and Leishmania species pose a significant health and economic burden in developing countries. There are few effective and accessible treatments for these diseases, and the existing therapies suffer from problems such as parasite resistance and side effects. Structure-based drug design (SBDD) is one of the strategies that has been applied to discover new compounds targeting trypanosomatid-borne diseases.

AREAS COVERED

We review the current literature (mostly over the last 5 years, searched in PubMed database on Nov 11^th 2021) on the application of structure-based drug design approaches to identify new anti-trypanosomatidic compounds that interfere with a validated target biochemical pathway, the trypanosomatid folate pathway.

EXPERT OPINION

The application of structure-based drug design approaches to perturb the trypanosomatid folate pathway has successfully provided many new inhibitors with good selectivity profiles, most of which are natural products or their derivatives or have scaffolds of known drugs. However, the inhibitory effect against the target protein(s) often does not translate to anti-parasitic activity. Further progress is hampered by our incomplete understanding of parasite biology and biochemistry, which is necessary to complement SBDD in a multiparameter optimization approach to discovering selective anti-parasitic drugs.

Metabolic Pathways of Leishmania Parasite: Source of Pertinent Drug Targets and Potent Drug Candidates

Leishmaniasis is a tropical disease caused by a protozoan parasite Leishmania that is transmitted via infected female sandflies. At present, leishmaniasis treatment mainly counts on chemotherapy. The currently available drugs against leishmaniasis are costly, toxic, with multiple side effects, and limitations in the administration route. The rapid emergence of drug resistance has severely reduced the potency of anti-leishmanial drugs. As a result, there is a pressing need for the development of novel anti-leishmanial drugs with high potency, low cost, acceptable toxicity, and good pharmacokinetics features. Due to the availability of preclinical data, drug repurposing is a valuable approach for speeding up the development of effective anti-leishmanial through pointing to new drug targets in less time, having low costs and risk. Metabolic pathways of this parasite play a crucial role in the growth and proliferation of Leishmania species during the various stages of their life cycle. Based on available genomics/proteomics information, known pathways-based (sterol biosynthetic pathway, purine salvage pathway, glycolysis, GPI biosynthesis, hypusine, polyamine biosynthesis) Leishmania-specific proteins could be targeted with known drugs that were used in other diseases, resulting in finding new promising anti-leishmanial therapeutics. The present review discusses various metabolic pathways of the Leishmania parasite and some drug candidates targeting these pathways effectively that could be potent drugs against leishmaniasis in the future.

Sesquiterpene Lactones with Dual Inhibitory Activity against the Trypanosoma brucei Pteridine Reductase 1 and Dihydrofolate Reductase

The parasite Trypanosoma brucei (T. brucei) is responsible for human African trypanosomiasis (HAT) and the cattle disease "Nagana" which to this day cause severe medical and socio-economic issues for the affected areas in Africa. So far, most of the available treatment options are accompanied by harmful side effects and are constantly challenged by newly emerging drug resistances. Since trypanosomatids are auxotrophic for folate, their pteridine metabolism provides a promising target for an innovative chemotherapeutic treatment. They are equipped with a unique corresponding enzyme system consisting of the bifunctional dihydrofolate reductase-thymidylate synthase (TbDHFR-TS) and the pteridine reductase 1 (TbPTR1). Previously, gene knockout experiments with PTR1 null mutants have underlined the importance of these enzymes for parasite survival. In a search for new chemical entities with a dual inhibitory activity against the TbPTR1 and TbDHFR, a multi-step in silico procedure was employed to pre-select promising candidates against the targeted enzymes from a natural product database. Among others, the sesquiterpene lactones (STLs) cynaropicrin and cnicin were identified as in silico hits. Consequently, an in-house database of 118 STLs was submitted to an in silico screening yielding 29 further virtual hits. Ten STLs were subsequently tested against the target enzymes in vitro in a spectrophotometric inhibition assay. Five compounds displayed an inhibition over 50% against TbPTR1 as well as three compounds against TbDHFR. Cynaropicrin turned out to be the most interesting hit since it inhibited both TbPTR1 and TbDHFR, reaching IC50 values of 12.4 µM and 7.1 µM, respectively.

Novel coumarin-isatin hybrids as potent antileishmanial agents: Synthesis, in silico and in vitro evaluations

Leishmaniasis being one of the six major tropical diseases that affects nearly 0.7-1.3 million people annually, has so far limited and high toxic therapeutic options. Herein, we report the synthesis, in silico, and in vitro evaluations of novel coumarin-incorporated isatin hydrazones (Spf-1 - Spf-10) as highly potent and safe antileishmanial agents. Molecular docking was initially carried out to decipher the binding confirmation of lead molecules towards the active cavity of the target protein (Leishmanolysin gp63) of Leishmania tropica. Among all the docked compounds, only Spf-6, Spf-8, and Spf-10 showed high binding affinities due to a pattern of strong conventional hydrogen bonds and hydrophobic π-interactions. The molecular dynamics simulations showed the stable pattern of such bonding and structure-based confirmation with a time scale of 50 ns towards the top compound (Spf-10) and protein. These analyses affirmed the high stability of the system. Three out of ten compounds evaluated for their antileishmanial activity against Leishmania tropica promastigotes and amastigotes were found to be active at micromolar concentrations (IC₅₀ range 0.1-4.13 μmol/L), and most importantly, they were also found to be highly biocompatible when screened for their toxicity in human erythrocytes.

Targeting pteridine reductase 1 and dihydrofolate reductase: the old is a new trend for leishmaniasis drug discovery

Leishmaniasis is one of the major neglected tropical diseases in the world and it is considered endemic in 88 countries. This disease is transmitted by a Leishmania spp. infected sandfly and it may lead to cutaneous or systemic manifestations. The preconized treatment has low efficacy and there are cases of resistance to some drugs. Therefore, the search for new efficient molecular targets that can lead to the preparation of new drugs must be pursued. This review aims to evaluate both Leishmania enzymes PTR1 and DHFR-TS as potential drug targets, highlight their inhibitors and to discuss critically the use of chemoinformatics to elucidate interactions and propose new molecules against these enzymes.

LeishInDB: A web-accessible resource for small molecule inhibitors against Leishmania sp

Despite the availability of drugs to treat Leishmaniasis, various other factors including drug resistance and adverse side effects encourage the researchers to search for new strategies and alternatives for treating Leishmaniasis. Repurposing and devising combination therapy with the existing small molecules would serve as an alternative strategy to address the issue, especially the drug resistance. Hence, here we report LeishInDB, a web-accessible resource of small molecule inhibitors having a varying degree of activity towards Leishmania sp. The database includes searchable information of >7000 small molecules collected from >600 literature. The comprehensive information of inhibitors mainly include the activity details (IC50, EC50, Ki, binding energy etc., if any); information on species and form of Leishmania the inhibitor is active against; and the details about their protein target (actively linked to TriTrypDB). In addition, chemical properties including the log P-value, number of rotatable bonds, number of hydrogen bond donors and acceptors, molecular weight, 2D/3D structural information etc., were also included. Toxicity prediction for each molecule was performed using admetSAR and their corresponding results were available to perform the filtered search. In addition, facility to perform sub-structure search, facility to perform the dynamic search on various fields, and facility to download all the structure of molecules that match the search criteria were also included. We believe that the scope of LeishInDB allows the researchers to utilize the available information for repurposing the inhibitors as well as for the investigation of new therapeutics. Database URL:http://leishindb.biomedinformri.com/.

In-Vitro Activity of Silybin and Related Flavonolignans against Leishmania infantum and L. donovani

Flavonolignans from the seeds of the milk thistle (Silybum marianum) have been extensively used in folk medicine for centuries. Confirmation of their properties as hepatoprotective, antioxidant and anticancer has been obtained using standardized extracts and purified flavonolignans. Information on their potential effect on Leishmania is very scarce. We have investigated the effect of silymarin, silybin and related flavonolignans on the multiplication of promastigotes in vitro and ex vivo on intracellular amastigotes of L. infantum (Li) and L. donovani (Ld), causative agents of human and canine visceral leishmaniasis (VL). In addition, the potential synergistic effect of the most active molecule and well-established antileishmanial drugs against promastigotes was explored. Dehydroisosilybin A elicited the highest inhibition against Ld and Li promastigotes with an approximate IC₅₀ of 90.23 µM. This molecule showed a moderate synergism with amphotericin B (AmB) but not with Sb^III or paromomycin, although it was ineffective against amastigotes. Antileishmanial activity on intracellular amastigotes of the two diastereoisomers of dehydrosilybin (10 µM) was comparable to that elicited by 0.1 µM AmB. Antiproliferative activity and safety of flavonolignans suggest the interest of exploring their potential value in combination therapy against VL.