Natural Products: Key Prototypes to Drug Discovery Against Neglected Diseases Caused by Trypanosomatids

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.

Inhibitors Targeting Multiple Janus Kinases From Zanthoxylum simulans Mediate Inhibition and Apoptosis Against Gastric Cancer Cells via the Estrogen Pathway

Janus kinases (JAKs) play a key role in subtly regulating proliferation, apoptosis, and differentiation of cancer cells, and their inhibitors are actively sought as new drug leads. By developing JAKs based affinity ultrafiltration method coupled with LC/Q-TOF-MS in order to discover selective JAKs inhibitors from total quaternary alkaloids (QAs) from Zanthoxylum simulans, peak 19 (Berberine) and peak 21 (Chelerythrine) were revealed to exhibit notable selectivity on JAK1, JAK2, and JAK3 over Tyk2. In addition, Chelerythrine showed stronger inhibitory activity than the positive control (Cerdulatinib) on gastric cancer cells (AGS), while Berberine, with weaker inhibition. Chelerythrine and Berberine also showed obvious inhibition on human hepatocyte cells (LO2). Furthermore, molecular docking analysis revealed their discrepancies due to different interaction bonds and characteristic residues. Quaternary N was proposed as the functional group to enhance the selectivity of JAK1, and some specific moieties towards Asp1021, Leu855, and Leu828 were suggested to increase the selectivity for JAK1, JAK2, and JAK3, respectively. As the most potential inhibitor of JAKs from QAs, Chelerythrine exhibited distinct suppression of adhesion, migration, invasion, and stimulating apoptosis of AGS cells, which was consistent with the significant down-regulation of estrogen receptors (ER-α36, ER-α66, and ER-β1) and Src expression. In conclusion, an efficient screening approach was developed to identify Berberine and Chelerythrine as potential selective candidates from Zanthoxylum simulans with significant anti-proliferative activity against gastric carcinoma. As we know, it was the first report to propose an estrogen signal pathway for Chelerythrine in anti-gastric cancer cells (AGS) study. The results supported Chelerythrine inhibitory effects on AGS by not only direct inhibiting JAKs but also down-regulating the estrogen pathway.

Identification of Kaurane-Type Diterpenes as Inhibitors of Leishmania Pteridine Reductase I

The current treatments against Leishmania parasites present high toxicity and multiple side effects, which makes the control and elimination of leishmaniasis challenging. Natural products constitute an interesting and diverse chemical space for the identification of new antileishmanial drugs. To identify new drug options, an in-house database of 360 kauranes (tetracyclic diterpenes) was generated, and a combined ligand- and structure-based virtual screening (VS) approach was performed to select potential inhibitors of Leishmania major (Lm) pteridine reductase I (PTR1). The best-ranked kauranes were employed to verify the validity of the VS approach through LmPTR1 enzyme inhibition assay. The half-maximal inhibitory concentration (IC₅₀) values of selected bioactive compounds were examined using the random forest (RF) model (i.e., 2β-hydroxy-menth-6-en-5β-yl ent-kaurenoate (135) and 3α-cinnamoyloxy-ent-kaur-16-en-19-oic acid (302)) were below 10 μM. A compound similar to 302, 3α-p-coumaroyloxy-ent-kaur-16-en-19-oic acid (302a), was also synthesized and showed the highest activity against LmPTR1. Finally, molecular docking calculations and molecular dynamics simulations were performed for the VS-selected, most-active kauranes within the active sites of PTR1 hybrid models, generated from three Leishmania species that are known to cause cutaneous leishmaniasis in the new world (i.e., L. braziliensis, L. panamensis, and L. amazonensis) to explore the targeting potential of these kauranes to other species-dependent variants of this enzyme.

Coumarin-1,2,3-triazole Hybrid Molecules: An Emerging Scaffold for Combating Drug Resistance

Undoubtedly, antibiotics have saved billions of lives, but lack of novel antibiotics, development of resistance mechanisms in almost all clinical isolates of bacteria, and recurrent infections caused by persistent bacteria hamper the successful treatment of the infections. Due to the widespread emergence of resistance, even the new families of anti-microbial agents have a short life expectancy. Drugs acting on a single target often lead to drug resistance and are associated with various side effects. For overcoming this problem, either multidrug therapy, or a single drug acting on multiple targets may be used. The latter is called 'hybrid molecules,' which are formed by clubbing two biologically active pharmacophores together, with or without an appropriate linker. In this rapidly evolving era, the development of natural product-based hybrid molecules may be a super-alternative to multidrug therapy, for combating drug resistance caused by various bacterial and fungal strains. Coumarins (benzopyran-2-one) are one of the earliest reported plant secondary metabolites having a clinically proven diverse range of pharmacological properties. On the other hand, 1,2,3-triazole is a common pharmacophore in many drugs responsible for polar interactions, improving the solubility and binding affinity to biomolecular targets. In this review, we discuss recent advances in Coumarin-1,2,3-triazole hybrids as potential anti-bacterial agents, aiming to provide a useful platform for the exploration of new leads with a broader spectrum, more effectiveness and less toxicity with multiple modes of action for the development of cost-effective and safer drugs in the future.

Microorganisms as a Potential Source of Molecules to Control Trypanosomatid Diseases

Trypanosomatids are the causative agents of leishmaniasis and trypanosomiasis, which affect about 20 million people in the world’s poorest countries, leading to 95,000 deaths per year. They are often associated with malnutrition, weak immune systems, low quality housing, and population migration. They are generally recognized as neglected tropical diseases. New drugs against these parasitic protozoa are urgently needed to counteract drug resistance, toxicity, and the high cost of commercially available drugs. Microbial bioprospecting for new molecules may play a crucial role in developing a new generation of antiparasitic drugs. This article reviews the current state of the available literature on chemically defined metabolites of microbial origin that have demonstrated antitrypanosomatid activity. In this review, bacterial and fungal metabolites are presented; they originate from a range of microorganisms, including cyanobacteria, heterotrophic bacteria, and filamentous fungi. We hope to provide a useful overview for future research to identify hits that may become the lead compounds needed to accelerate the discovery of new drugs against trypanosomatids.

In vitro, in vivo and in silico Antihyperglycemic Activity of Some Semi-synthetic Phytol Derivatives

BACKGROUND

Due to the prevalence of type-2 diabetes across the globe, there is unmet need to explore new molecular targets for the development of cost-effective and safer antihyperglycemic agents.

OBJECTIVE

Structural modification of phytol and evaluation of in vitro, in vivo and in silico antihyperglycemic activity of derivatives establishing the preliminary structure activity relationship (SAR).

METHODS

The semi-synthetic derivatives of phytol were prepared following previously described methods. The antihyperglycemic potential was measured in vitro in terms of increase in 2-deoxyglucose (2-DG) uptake by L-6 rat skeletal muscle cells as well as in vivo in sucrose-loaded (SLM) and streptozotocin (STZ)-induced diabetic rat models. The blood glucose profile was measured at 30, 60, 90, 120, 180, 240, 300 and 1440 min post administration of sucrose in rats. The in silico docking was performed on peroxisome proliferator-activated receptor gamma (PPARγ) as anti-diabetic target along with absorption, distribution, metabolism, excretion and toxicity (ADMET) studies.

RESULTS

Nine semi-synthetic ester derivatives: acetyl (1), lauroyl (2), palmitoyl (3), pivaloyl (4), trans-crotonyl (5), benzoyl (6), m-anisoyl (7), 3,4,5-trimethoxy benzoyl (8) cinnamoyl (9) along with bromo derivative (10) of phytol were prepared. The derivatives 9, 8 and 2 caused 4.5, 3.2 and 2.7 times more in vitro uptake of 2-DG respectively than rosiglitazone (ROSI). The derivatives showed significant improvement on oral glucose tolerance both in SLM (29.6-21%) as well as STZ-induced diabetic (30.8-19.0%) rats. The in silico ADMET, docking studies showed non-toxicity and high binding affinity with PPARγ.

CONCLUSION

The potent antihyperglycemic activity with favorable pharmacokinetics supports phytol derivatives as suitable antidiabetic lead.

Evaluation of the antitrypanosoma activity and SAR study of novel LINS03 derivatives

Chagas' disease is a parasitic infection caused by Trypanosoma cruzi that is still treated by old and toxic drugs. In the search for novel alternatives, natural sources are an important source for new drug prototypes against T. cruzi to further structural exploitation. A set of natural-based compounds (LINS03) was designed, showing promising antitrypanosoma activity and low cytotoxicity to host cells. In this paper, nine novel LINS03 derivatives were evaluated against T. cruzi trypomastigotes and amastigotes. The selectivity was assessed through cytotoxicity assays using NCTC mammalian cells and calculating the CC₅₀/IC₅₀ ratio. The results showed that compounds 2d and 4c are noteworthy, due their high activity against amastigotes (IC₅₀ 13.9 and 5.8 µM) and low cytotoxicity (CC₅₀ 107.7 µM and >200 µM, respectively). These compounds did not showed alteration on plasma membrane permeability in a Sytox green model. SAR analysis suggested an ideal balance between hydrosolubility and lipophilicity is necessary to improve the activity, and that insertion of a meta-substituent is detrimental to the activity of the amine derivatives but not to the neutral derivatives, suggesting different mechanisms of actions. The results presented herein are valuable for designing novel compounds with improved activity and selectivity to be applied in future studies.

Chemical Composition, Antimicrobial and Antiparasitic Screening of the Essential Oil from Phania matricarioides (Spreng.) Griseb

Essential oils (EOs) have gained increasing attention due to their pharmacological effectiveness, and they also constitute some of the most popular natural products. In this study, we present the chemical characterization of the EO from Phania matricarioides and the in vitro activity/selectivity against a wide panel of bacteria, fungi and parasitic protozoa. Forty-five compounds were identified in the studied EO, of which lavandulyl acetate (40.1%) and thymyl isobutyrate (13.9%) were the major components. The EO did not inhibit bacterial or fungal growth at the maximum concentration tested (64 µg/mL), although it displayed activity on all evaluated protozoa (IC₅₀ values ranging from 2.2 to 56.6 µg/mL). In parallel, the EO demonstrated a noteworthy cytotoxic activity against peritoneal macrophages (CC₅₀ values of 28.0 µg/mL). The most sensitive microorganism was Trypanosoma cruzi, which had a superior activity (IC₅₀ = 2.2 µg/mL) and selectivity (SI = 13) in respect to other parasitic protozoa and the reference drug (p < 0.05). Further in vivo studies are needed to evaluate the potential use of this EO and the main compounds as antitrypanosomal agents. To our knowledge, this is the first report of chemical characterization and antimicrobial assessment of the EO from P. matricarioides.

Active Natural Product Scaffolds against Trypanosomatid Parasites: A Review

Neglected tropical diseases caused by trypanosomatid parasites are a continuing and escalating problem, which devastate the less economically developed cultures in countries in which they are endemic by impairing both human and animal health. Current drugs for these diseases are regarded as out-of-date and expensive, with unacceptable side-effects and mounting parasite resistance, meaning there is an urgent need for new therapeutics. Natural products have long been a source of potent, structurally diverse bioactive molecules. Herein are reviewed natural products with reported trypanocidal activity, which have been clustered based on core structural similarities, to aid the future discovery of new trypanocidal core motifs with potential routes to synthetically accessible natural product cores suggested.