Synthesis and antitumour activity of arctigenin amino acid ester derivatives against H22 hepatocellular carcinoma

A systematic review on botany, ethnopharmacology, quality control, phytochemistry, pharmacology and toxicity of Arctium lappa L. fruit

ETHNOPHARMACOLOGICAL RELEVANCE

Arctium lappa L., is a biennial plant that grows around the Eurasia. Many parts of Arctium lappa L. (roots, leaves and fruits, etc.) are medically used in different countries. Arctium lappa L. fruit, also called Arctii Fructus, is traditionally applied to dispel wind-heat, ventilate lung to promote eruption, remove toxicity substance and relieve sore throat.

THE AIM OF THE REVIEW

The review aims to integrate the botany, ethnopharmacology, quality control, phytochemistry, pharmacology, derivatives and toxicity information of Arctii Fructus, so as to facilitate future research and explore the potential of Arctii Fructus as an agent for treating diseases.

MATERIALS AND METHODS

Related knowledge about Arctii Fructus were acquired from Science Direct, GeenMedical, PubMed, China National Knowledge Infrastructure (CNKI), Web of Science, Pharmacopoeia of the People's Republic of China, Doctoral and Master's thesis, ancient books, etc. RESULTS: Arctii Fructus as an herb used for medicine and food was pervasively distributed and applicated around the world. It was traditionally used to treat anemopyretic cold, dyspnea and cough, sore throat, etc. To date, more than 200 compounds have been isolated and identified from Arctii Fructus. It contained lignans, phenolic acids and fatty acids, terpenoids, volatile oils and others. Lignans, especially arctigenin and arctiin, had the extensive pharmacological effects such as anti-cancer, antiviral, anti-inflammatory activities. The ester derivatives of arctigenin had the anti-cancer, anti-Alzheimer's disease and immunity enhancing effects. Although Arctii Fructus extract had no toxicity, arctigenin was toxic at a certain dose. The alleviating effects of Arctii Fructus on chronic inflammation and ageing have been demonstrated by clinical studies.

CONCLUSION

Arctii Fructus is regarded as a worthy herb with many chemical components and various pharmacological effects. Several traditional applications have been supported by modern pharmacological research. However, their action mechanisms need to be further studied. Although many chemical components were isolated from Arctii Fructus, the current research mainly focused on lignans, especially arctiin and arctigenin. Therefore, it is very important to deeply clarify the pharmacological activities and action mechanism of the compounds and make full medicinal use of the resources of Arctii Fructus.

Arctigenin: pharmacology, total synthesis, and progress in structure modification

Arctium lappa L. is a prevalent medicinal herb and a health supplement that is commonly used in Asia. Over the last few decades, the bioactive component arctigenin has attracted the attention of researchers because of its anti-inflammatory, antioxidant, immunomodulatory, multiple sclerosis fighting, antitumor, and anti-leukemia properties. After summarising the research and literature on arctigenin, this study outlines the current status of research on pharmacological activity, total synthesis, and structural modification of arctigenin. The purpose of this study is to assist academics in obtaining a more comprehensive understanding of the research progress on arctigenin and to provide constructive suggestions for further investigation of this useful molecule.

Amino-Acid-Conjugated Natural Compounds: Aims, Designs and Results

Protein is one of the essential macronutrients required by all living things. The breakdown of protein produces monomers known as amino acids. The concept of conjugating natural compounds with amino acids for therapeutic applications emerged from the fact that amino acids are important building blocks of life and are abundantly available; thus, a greater shift can result in structural modification, since amino acids contain a variety of sidechains. This review discusses the data available on amino acid–natural compound conjugates that were reported with respect to their backgrounds, the synthetic approach and their bioactivity. Several amino acid–natural compound conjugates have shown enhanced pharmacokinetic characteristics, including absorption and distribution properties, reduced toxicity and increased physiological effects. This approach could offer a potentially effective system of drug discovery that can enable the development of pharmacologically active and pharmacokinetically acceptable molecules.

Arctigenin, an anti-tumor agent; a cutting-edge topic and up-to-the-minute approach in cancer treatment

Today, herbal-derived compounds are being increasingly studied in cancer treatment. Over the past decade, Arctigenin has been introduced as a bioactive dibenzylbutyrolactone lignan which is found in Chinese herbal medicines. In addition to anti-microbial, anti-inflammatory, immune-modulatory functions, Arctigenin has attracted growing attention due to its anti-tumor capabilities. It has been shown that Arctigenin can induce apoptosis and necrosis and abolish drug resistance in tumor cells by inducing apoptotic signaling pathways, caspases, cell cycle arrest, and the modulating proteasome. Moreover, Arctigenin mediates other anti-tumor functions through several mechanisms. It has been demonstrated that Arctigenin can act as an anti-inflammatory compound to inhibit inflammation in the tumor microenvironment. It also downregulates factors involved in tumor metastasis and angiogenesis, such as matrix metalloproteinases, N-cadherin, TGF-β, and VEGF. Additionally, Arctigenin, through modulation of MAPK signaling pathways and stress-related proteins, is able to abolish tumor cell growth in nutrient-deprived conditions. Due to the limited solubility of Arctigenin in water, it is suggested that modification of this compound through amino acid esterification can improve its pharmacogenetic properties. Collectively, it is hoped that using Arctigenin or its derivates might introduce new chemotherapeutic approaches in future treatment.

Application of Amino Acids in the Structural Modification of Natural Products: A Review

Natural products and their derivatives are important sources for drug discovery; however, they usually have poor solubility and low activity and require structural modification. Amino acids are highly soluble in water and have a wide range of activities. The introduction of amino acids into natural products is expected to improve the performance of these products and minimize their adverse effects. Therefore, this review summarizes the application of amino acids in the structural modification of natural products and provides a theoretical basis for the structural modification of natural products in the future. The articles were divided into six types based on the backbone structures of the natural products, and the related applications of amino acids in the structural modification of natural products were discussed in detail.

Design and synthesis of diosgenin derivatives as apoptosis inducers through mitochondria-related pathways

Diosgenin (DSG) has attracted attention recently as a potential anticancer therapeutic agent due to its profound antitumor activity. To better utilize DSG as an antitumor compound, two series of DSG-amino acid ester derivatives (3a-3g and 7a-7g) were designed and synthesized, and their cytotoxic activities against six human cancer cell lines (K562, T24, MNK45, HepG2, A549, and MCF-7) were evaluated. The results obtained showed that a majority of derivatives exhibited cytotoxic activities against these six human tumor cells. Structure-activity relationship analysis revealed that the introduction of l-tryptophan to the C-3 position of DSG and the C-26 position of derivative 5 was the preferred option for these compounds to display significant cytotoxic activities. Among them, compound 7g exhibited significant cytotoxicity against the K562 cell line (IC₅₀ = 4.41 μM) and was 6.8-fold more potent than diosgenin (IC₅₀ = 30.04 μM). Further cellular mechanism studies in K562 cells elucidated that compound 7g triggered mitochondrial-related apoptosis by increasing the generation of intracellular reactive oxygen species (ROS) and decreasing mitochondrial membrane potential (MMP), which was associated with upregulation of the gene and protein expression levels of Bax, downregulation of the gene and protein expression levels of Bcl-2 and activation of the caspase cascade. The above results suggested that compound 7g might be considered a promising scaffold for further modification of more potent anticancer agents.

Discovery of stereospecific cytotoxicity of (8R,8'R)-trans-arctigenin against insect cells and structure-activity relationship on aromatic ring

One of the arctigenin stereoisomers, (8R,8'R)-trans-form 1, showed stereospecific cytotoxicity against insect cells, Sf9 and NIAS-AeAl-2 cells. By the comparison with other stereoisomers, the most importance of the 8'R stereochemistry for the higher activities was clarified. On the other hand, the wider range of activity level among stereoisomers against cancer cells, HL-60, was not observed. The structure-activity relationship research using derivatives bearing (8R,8'R)-trans-form was performed to show the same level of activities of 3-iodo, 4-iodo, and 3,4-methylenedioxy derivatives 28, 29, and 36 as (8R,8'R)-trans-arctigenin 1. In the examination of thiono derivatives, 4-iodo thiono and 3,4-methylenedioxy thiono derivatives 66, 67 showed similar level of activities to that of (8R,8'R)-trans-arctigenin 1. The expression of ribosomal 28S rRNA gene of Sf9 cells was increased by (8R,8'R)-trans-arctigenin 1, whereas a degradation of DNA was not observed.

Recent Advances in Molecular Mechanisms of the NKG2D Pathway in Hepatocellular Carcinoma

Hepatocellular carcinoma is a common malignant tumor with high mortality. Its malignant proliferation, invasion, and metastasis are closely related to the cellular immune function of the patients. NKG2D is a key activated and type II membrane protein molecule expressed on the surface of almost all NK cells. The human NKG2D gene is 270 kb long, located at 12p12.3-p13.1, and contains 10 exons and 9 introns. The three-dimensional structure of the NKG2D monomeric protein contains two alpha-helices, two beta-lamellae, and four disulfide bonds, and its' signal of activation is transmitted mainly by the adaptor protein (DAP). NKG2D ligands, including MICA, MICB, and ULBPs, can be widely expressed in hepatoma cells. After a combination of NKG2D and DAP10 in the form of homologous two polymers, the YxxM motif in the cytoplasm is phosphorylated and then signaling pathways are also gradually activated, such as PI3K, PLCγ2, JNK-cJunN, and others. Activated NK cells can enhance the sensitivity to hepatoma cells and specifically dissolve by releasing a variety of cytokines (TNF-α and IFN-γ), perforin, and high expression of FasL, CD16, and TRAIL. NK cells may specifically bind to the over-expressed MICA, MICB, and ULBPs of hepatocellular carcinoma cells through the surface activating receptor NKG2D, which can help to accurately identify hepatoma, play a critical role in anti-hepatoma via the pathway of cytotoxic effects, and obviously delay the poor progress of hepatocellular carcinoma.

Upregulation of p53 through induction of MDM2 degradation: Amino acid prodrugs of anthraquinone analogs

Previously, we reported a class of MDM2-MDM4 dimerization inhibitors that upregulate p53 and showed potent anticancer activity in animal models. However, water solubility hinders their further development. Herein we describe our effort to develop a prodrug approach that overcomes the solubility problem. The prodrug of BW-AQ-238, a potent anthraquinone analog, was made by esterification of the hydroxyl group with various natural amino acids. Cytotoxicity of these compounds toward Hela and EU-1 cells, their aqueous solubility, and the release kinetics of these prodrugs in buffer and in the presence of hydrolytic enzymes were studied. The results demonstrate that the amino acid prodrug approach significantly improved the water solubility while maintaining the potency of the parent drug.

Design, Synthesis and Biological Evaluation of Diosgenin-Amino Acid Derivatives with Dual Functions of Neuroprotection and Angiogenesis

Diosgenin, a natural product with steroidal structure, has a wide range of clinical applications in China. It also shows great potential in the treatment of blood clots and nerve damage. To enhance the bioavailability as well as efficacy of diosgenin, eighteen diosgenin-amino acid derivatives were designed and synthesized. The neuroprotective effects of these compounds were evaluated by SH-SY5Y cell line and the biosafety was evaluated by H9c2 cell line. The results displayed that part of the derivatives' activities (EC₅₀ < 20 μM) were higher than positive control edaravone (EC₅₀ = 21.60 ± 3.04 μM), among which, DG-15 (EC₅₀ = 6.86 ± 0.69 μM) exhibited the best neuroprotection. Meanwhile, biosafety evaluation showed that DG-15 had no cytotoxicity on H9c2 cell lines. Interestingly, combined neuroprotective and cytotoxic results, part of the derivatives without their protecting group were superior to compounds with protecting group. Subsequently, Giemsa staining and DAPI (4',6-diamidino-2-phenylindole) staining indicated that DG-15 had a protective effect on damaged SH-SY5Y cells by reducing apoptosis. Moreover, DG-15 showed a higher role in promoting angiogenesis at high concentrations (4 mg/mL) on the chorioallantoic membrane model. This finding displayed that DG-15 had dual functions of neuroprotection and angiogenesis, which provided further insight into designing agent for the application in treatment of ischemic stroke.

Synthesis and cytotoxic activity of 7,4’-O-modified genistein amino acid derivatives

Fifteen 7,4’- O-modified genistein amino acid derivatives are synthesized through nucleophilic substitution and hydrolysis, followed by condensation with diverse amino acid esters. The antiproliferative activity of all the synthesized compounds is evaluated against three cancer cell lines (MGC-803, HeLa, HCT-116) and one normal cell line (HUVEC) using 5-fluorouracil (5-Fu) as the positive control. The results show that methyl [2-({5-hydroxy-3-[4-(2-{[3-(4-hydroxyphenyl)-1-methoxy-1-oxopropan-2-yl]amino}-2-oxoethoxy)phenyl]-4-oxo-4 H-chromen-7-yl}oxy)acetyl] tyrosinate exhibits significant antiproliferative activity against the MGC-803 cell line with an IC50 value of 8.52 µM, and its inhibitory effects on HeLa and HCT-116 cancer cells are stronger than that of the positive control drug 5-Fu.

3'-Desmethylarctigenin induces G2/M cell cycle arrest and apoptosis through reactive oxygen species generation in hepatocarcinoma cells

Previous studies have shown that arctigenin is a promising chemopreventive or therapeutic agent against various cancers. However, less is known about anticancer activity of 3'-desmethylarctigenin (3'-DMAG), which is a biotransformed product from arctigenin or arctin. In this study, we compared the anticancer activity of 3'-DMAG with its parent compound arctigenin and demonstrated that 3'-DMAG exerted a more potent inhibitory effect on HepG2 cells than arctigenin. Mechanistically, reactive oxygen species generation played an apical role in 3'-DMAG-induced G2/M cell cycle arrest and apoptosis in HepG2 cells. Furthermore, the Chk2-Cdc25c-Cdc2-cyclin B1 cascade was found to contribute to the cell cycle arrest, whereas the activation of mitochondrial pathway was involved in the cell apoptosis by 3'-DMAG. Additionally, a mouse xenograft hepatocellular carcinoma model was used to evaluate the antitumor effect of 3'-DMAG in vivo, and the results indicated that 3'-DMAG treatment significantly inhibited tumor growth without apparent toxicity. Taken together, 3'-DMAG is highly effective against liver cancer both in vitro and in vivo. The findings of the present study suggest that this compound deserves to be further investigated for its potential anticancer activity.

Oleanolic Acid-amino Acids Derivatives: Design, Synthesis, and Hepatoprotective Evaluation In Vitro and In Vivo

Activated hepatic stellate cells (HSCs) are the main extracellular matrix (ECM)-producing cells in the injured liver and the key mediators of liver fibrosis; they also promote the progression of hepatocellular carcinoma (HCC). In the acidic extracellular microenvironment of HCC, HSCs are activated to promote the migration of HCC cells. It is worth attempting to alter the weak acidic microenvironment to promote activated HSC apoptosis to treat liver fibrosis and liver cancer. In the present study, a series of novel OA-amino acids analogues were designed and synthesized to introduce different amino acids in the 3-hydroxyl of OA using the ester condensation reaction to enhance hydrophilicity, alkalinity, and biological activity. We found that OA-lysine derivative (3g) could improve the hydrophilic of OA and induce HSCs apoptosis via inducing MMP depolarization and increasing intracellular Ca2+ levels. Additionally, 3g displayed a better hepatoprotective effect than OA (20 mg/kg, intragastric administration) against the acute liver injury induced by carbon tetrachloride (CCl₄) in mice. The results suggested that basic amino acids (lysine) could effectively enhance OA's hydrophilicity, alkalinity, and hepatoprotective activity in vitro and in vivo, which might be likely associated with increasing bioavailability and altering an extracellular weak acidic microenvironment with further verification. Therefore, the OA-lysine derivative (3g) has the potential to be developed as an agent with hepatoprotective activity.