Synthesis and selective anticancer activity of steroidal glycoconjugates

Diosgenyl glucosamine conjugates increase pro-apoptotic and selective activities in cancer cell lines

BACKGROUND INFORMATION

Antiproliferative and apoptotic activities have been attributed to the phytosteroid diosgenin ((25R)-spirost-5-en-3β-ol; 1). It is known that combining glucose with two rhamnoses (the chacotrioside framework) linked to diosgenin increases its apoptotic activity. However, the effects of diosgenin glucosamine glycosides on different cancer cell types and cell death have not been entirely explored.

RESULTS

This study reports the antiproliferative, cytotoxic, and apoptotic activities of diosgenin and its glycosylated derivative ((25R)-spirost-5-en-3β-yl β-D-glucopyranoside; 2). It also explores the effects of two diosgenin glucosamine derivates, diosgenin 2-acetamido-2-deoxy-β-D-glucopyranoside (3), and diosgenin 2-amino-2-deoxy-β-D-glucopyranoside hydrochloride (4), on different cancer cell lines. We found that all the compounds affected proliferative activity with minimal toxicity. In addition, all cancer cell lines showed morphological and biochemical characteristics corresponding to an apoptotic process. Apoptotic cell death was higher in all cell lines treated with compounds 2, 3 and 4 than in those treated with diosgenin. Moreover, compounds 3 and 4 induced apoptosis better than compounds 1 and 2. These results suggest that combining glucosamine with modified glucosamine attached to diosgenin has a greater apoptotic effect than diosgenin or its glycosylated derivative (compound 2). Furthermore, diosgenin and the abovementioned glycosides had a selective effect on tumour cells since the proliferative capacity of human lymphocytes, keratinocytes (HaCaT) and epithelial cells (CCD841) was not significantly affected.

CONCLUSIONS

Altogether, these results demonstrate that diosgenin glucosamine compounds exert an antiproliferative effect on cancer cell lines and induce apoptotic effects more efficiently than diosgenin alone without affecting non-tumour cells.

SIGNIFICANCE

This study evidences the pro-apoptotic and selective activities of diosgenyl glucosamine compounds in cancer cell lines.

Anticancer Activity of Diosgenin and Its Molecular Mechanism

Diosgenin, a steroidal sapogenin, obtained from Trigonella foenum-graecum, Dioscorea, and Rhizoma polgonati, has shown high potential and interest in the treatment of various cancers such as oral squamous cell carcinoma, laryngeal cancer, esophageal cancer, liver cancer, gastric cancer, lung cancer, cervical cancer, prostate cancer, glioma, and leukemia. This article aims to provide an overview of the in vivo, in vitro, and clinical studies reporting the diosgenin's anticancer effects. Preclinical studies have shown promising effects of diosgenin on inhibiting tumor cell proliferation and growth, promoting apoptosis, inducing differentiation and autophagy, inhibiting tumor cell metastasis and invasion, blocking cell cycle, regulating immunity and improving gut microbiome. Clinical investigations have revealed clinical dosage and safety property of diosgenin. Furthermore, in order to improve the biological activity and bioavailability of diosgenin, this review focuses on the development of diosgenin nano drug carriers, combined drugs and the diosgenin derivatives. However, further designed trials are needed to unravel the diosgenin's deficiencies in clinical application.

Hecogenin and its derivates: A pharmacology review

Despite the several uses of drugs from natural compounds in the pharmaceutical industry, new molecules have been discovered and associated with pharmacological activities over the years. Hecogenin, a steroidal saponin, has been the subject of several studies due to reports of pharmacological activities. This study combines the articles published to date that show the pharmacological activity and the mechanism of action of hecogenin, its acetate, and its derivates. This compilation shows that the compounds can act in different pathologies that affect many systems of the human body. They showed pharmacological properties in inflammation, mediating cytokines, cells, and environment. Also, it participated in tumoral processes by pathways like PPGARγ, ERK½, and MMP-2 and showed antimicrobial effects against organisms like Candida and Aedes aegypti's larvae. This review indicates that continuing studies with these molecules are essential once they have the potential to be a future drug.

Design, Synthesis, and Antifungal Activities of Hymexazol Glycosides Based on a Biomimetic Strategy

Hymexazol (HYM) is irreplaceable for treating soil-borne diseases due to its high efficiency and low cost, as a broad-spectrum fungicide. However, when HYM is absorbed by plants, it is rapidly converted into two glycoside metabolites, and the antifungal activities of these glycosides are inferior to that of HYM. Therefore, in this study, to maintain strong antifungal activity in vitro and in vivo, HYM was glycosylated with amino sugars that have diverse biological activities to simulate plant glycosylation. The antifungal experiment proved that glycoside 15 has the highest antifungal activity, and N-acetyl glucosamine and HYM had obvious synergistic effects. According to the structure-activity relationship studies, glycoside 15 had greater numbers of active electron-rich regions and front-line orbital electrons due to the introduction of N-acetyl glucosamine. Moreover, glycoside 15 can significantly promote plant growth and induce an increase in plant defense enzyme activity. Additionally, compared to HYM, the results of electron microscopy and proteomics revealed that glycoside 15 has a unique antifungal mechanism. The promising antifungal activity and interactions with plants mean that glycoside 15 is a potential green fungicide candidate. Furthermore, this research conducted an interesting exploration of the agricultural applications of amino sugars.

Developments in the Antitumor Activity, Mechanisms of Action, Structural Modifications, and Structure-Activity Relationships of Steroidal Saponins

Steroidal saponins, a class of natural products formed by the combination of spirosteranes with sugars, are widely distributed in plants and have various biological activities, such as anti-tumor, anti-inflammatory, anti-bacterial, anti-Alzheimer's, anti-oxidation, etc. Particularly, extensive researches on the antitumor property of steroidal saponins have been received. Steroidal sapogenins, the aglycones of steroidal saponins, also have attracted much attention due to a vast range of pharmacological activities similar to steroidal saponins. In the past few years, structural modifications on the aglycones and sugar chains of steroidal saponins have been carried out and some achievements have been made. In this mini-review, the antitumor activity, action mechanisms, and structural modifications along with the structure-activity relationships of steroidal saponins and their derivatives are summarized.

Synthesis and biological in vitro evaluation of the effect of hydroxyimino steroidal derivatives on breast cancer cells

Breast cancer is the most common cause of cancer death in women, according to Global Cancer Observatory. This fact forces scientists to continue in the search for effective treatments against this aggressive type of cancer. Breast cancer frequently metastasizes to other organs, most often the bones, lungs, and liver. Breast cancer is normally associated with estrogen and progestogen levels and can be hormone or non-hormone dependent. In current experiments herein reported, some hydroxyimino spirostan derivatives showed great potential against MCF-7 breast cancer, a Luminal-A cancer. On the other hand, a set of synthesized 6-hydroxyimino-22-oxocholestane compounds had excellent activity against the MDA-MB-231 breast cancer cell line. The synthesis of hydroxyamino derivatives from spirostan and 22-oxocholestane compounds was improved. The hydroxyimino compounds enhanced the bioactivity when compared with their parent carbonyl skeletons.

Synthesis, Modification and Biological Activity of Diosgenyl β-d-Glycosaminosides: An Overview

Saponins are a structurally diverse class of natural glycosides that possess a broad spectrum of biological activities. They are composed of hydrophilic carbohydrate moiety and hydrophobic triterpenoid or steroid aglycon. Naturally occurring diosgenyl glycosides are the most abundant steroid saponins, and many of them exhibit various pharmacological properties. Herein, we present an overview of semisynthetic saponins syntheses-diosgenyl β-d-glycosaminosides (d-gluco and d-galacto). These glycosides possess a 2-amino group, which creates great possibilities for further modifications. A wide group of glycosyl donors, different N-protecting groups and various reaction conditions used for their synthesis are presented. In addition, this paper demonstrates the possibilities of chemical modifications of diosgenyl β-d-glycosaminosides, associated with functionalisation of the amino group. These provide N-acyl, N-alkyl, N,N-dialkyl, N-cinnamoyl, 2-ureido and 2-thiosemicarbazonyl derivatives of diosgenyl β-d-glycosaminosides, for which the results of biological activity tests (antifungal, antibacterial, anti-cancer and hemolytic) are presented.

Apoptotic, necrotic, and antiproliferative activity of diosgenin and diosgenin glycosides on cervical cancer cells

(25R)-spirost-5-en-3β-ol, also known as diosgenin (DSG), exerts antiproliferative activity on diverse cell lines, induces apoptosis, and acts as a chemopreventative agent. However, the relationship between DSG glycosides and apoptotic, necrotic, and antiproliferative activity remains unclear. It is in this regard that we report the antiproliferative, necrotic, and apoptotic activities of DSG and its glycoside derivatives: (25R)-spirost-5-en-3β-yl O-β-D-glucopyranoside (3GD), (25R)-spirost-5-en-3β-yl O-α-L-rhamnopyranosyl-(1 → 4)-β-D-glucopyranoside (3GRD); and (25R)-spirost-5-en-3β-yl O-α-L-rhamnopyranosyl-(1 → 2)-O-[α-L-rhamnopyranosyl-(1 → 4)]-β-D-glucopyranoside), also known as dioscin (DSC), in in vitro assays of cervical HeLa and CaSki cancer cells. The results demonstrated that DSG glycosidic derivatives preserved their antiproliferative activity. However, in both cancer cell lines, 3GD and 3GRD were less potent than DSG, while DSC was more potent than DSG. With respect to necrotic activity, all tested compounds showed no or low activity on the two cervical cancer cell lines. Regarding apoptosis, the results showed that DSG glycosides were better apoptosis-inducers than DSG, suggesting that glucose and rhamnose residues play a central role in enhancing the apoptotic activity of DSG. Finally, DSG and its glycosidic derivatives were shown to affect the proliferative potential of lymphocytes (non-tumour cells) to a lesser extent than cancer cells, suggesting that these compounds have selective action. In conclusion, the results indicate that DSG and its glycosidic derivatives are promising anticancer compounds since they are compounds with low necrotic activity and selective action.

Gold mediated sp3αC-H functionalization of steroidal diglycoside and their anti-cancer evaluation

C(sp³)-H alkylation at α-position of methyl-keto group on D-ring of Steroidal diglycoside (SG) with (i) C=N of Schiff base imines to form amine derivatives and (ii) C=C of acrylate Michael acceptors to form Markovnikov ester products using AuCl₃/NHC as pre-catalyst and Ag(I) salts as co-catalyst was described. The original form of SG (1) and its derivatives (3b-f & 5a-d) were screened for in vitro anti-cancer activity specifically on two breast cancer cell lines (i.e. MCF-7, MDA-MB-231) and deduced the structure-activity-relationship with the support of molecular docking studies. Among these compounds 3b, 3f, 5b & 5d have shown more potent anticancer activity than standard drug cisplatin with considerable IC50 values.

N-Aminoacyl and N-hydroxyacyl derivatives of diosgenyl 2-amino-2-deoxy-β-d-glucopyranoside: Synthesis, antimicrobial and hemolytic activities

Diosgenyl 2-amino-2-deoxy-β-d-glucopyranoside is a semisynthetic saponin with antimicrobial and antitumor activities. To search for more effective analogues, N-aminoacyl and N-hydroxyacyl derivatives of this saponin were synthesized conventionally and with microwave assistance, and tested against the human pathogenic fungi and Gram-positive and Gram-negative bacteria. None of the tested compounds exhibit activity against Gram-negative bacteria. Almost all of the synthesized N-aminoacyl saponins exhibit antifungal activity and act effectively against Gram-positive bacteria, some better than the parent compound. The best acting saponins are the same size and possess sarcosine or l- or d-alanine attached to the parent glucosaminoside. Shorter and longer aminoacyl residues are less advantageous. d-Alanine derivative is the most effective against Gram positive bacteria. Structure-activity relationship (SAR) analysis indicates that the free α-amino group in aminoacyl residue is necessary for antimicrobial activities of the tested saponins. (N-Acetyl)aminoacyl and N-hydroxyacyl analogs are inactive. Measurements of the hemolytic activities demonstrate that the best acting saponins are not toxic towards human red blood cells.

Diversified synthesis and α-selective glycosylation of 3-amino-2,3,6-trideoxy sugars

Quick access to various unnatural 3-amino-2,3,6-trideoxy sugars was achieved by sequential functionalization of a glycal intermediate. This strategy and the further glycosylation method allowed the efficient late-stage modification of bioactive natural products and drugs.

Diosgenyl 2-amino-2-deoxy-β-D-galactopyranoside: synthesis, derivatives and antimicrobial activity

The synthesis of diosgenyl 2-amino-2-deoxy-β-D-galactopyranoside is presented for the first time. This synthetic saponin was transformed into its hydrochloride as well as N-acyl, 2-ureido, N-alkyl, and N,N-dialkyl derivatives. Antifungal and antibacterial studies show that some of the obtained compounds are active against Gram-positive bacteria and Candida type fungi.

BCL3 exerts an oncogenic function by regulating STAT3 in human cervical cancer

Aberrant expression of oncogenes and/or tumor suppressors play a fundamental effect on the pathogenesis and tumorigenicity of cervical cancer (CC). B-cell CLL/lymphoma 3 (BCL3) was previously found to be a putative proto-oncogene in human cancers and regulated signal transducer and activator of transcription 3 (STAT3), a critical oncogene, in CC cell line. However, its expression status, clinical significance and biological functions in CC remain largely unclear. The expressions of BCL3 and STAT3 in CC specimens were determined by immunohistochemistry. MTT, colony formation assays and flow cytometry analysis were carried out to test proliferation and cell cycle of CC cells. Here, the levels of BCL3 were overexpressed in CC compared to adjacent cervical tissues. Furthermore, high levels of BCL3 protein were confirmed by immunoblotting in CC cells as compared with normal cervical epithelial cells. The positive expression of BCL3 was correlated with adverse prognostic features and reduced survival rate. In addition, BCL3 regulated STAT3 abundance in CC cells. STAT3 was found to be upregulated and positively correlated with BCL3 expression in CC specimens. BCL3 overexpression resulted in prominent increased proliferation and cell cycle progression in Hela cells. By contrast, inhibition of BCL3 in CaSki cells remarkably suppressed proliferative ability and cell cycle progression. In vivo studies showed that knockdown of BCL3 inhibited tumor growth of CC in mice xenograft model. Notably, we confirmed that STAT3 mediated the oncogenic roles of BCL3 in CC. In conclusion, we suggest that BCL3 serves as an oncogene in CC by modulating proliferation and cell cycle progression, and its oncogenic effect is mediated by its downstream target gene, STAT3.

Effect of Hecogenin on DNA instability

Hecogenin is a sapogenin found in Agave species in high quantities and is responsible for the many therapeutic effects of these medicinal plants. In addition, this compound is also widely used in the pharmaceutical industry as a precursor for the synthesis of steroidal hormones and anti-inflammatory drugs. Despite Hecogenin being widely used, little is known about its toxicological properties. Therefore, the present study aimed to investigate the cytotoxic, genotoxic and mutagenic effects of Hecogenin on HepG2 cells. Cytotoxicity was analyzed using the MTT test. Then, genotoxic and mutagenic potentials were assessed by comet assay and cytokinesis-block micronucleus assay, respectively. Cytotoxic effect was observed only when cells were exposed to concentrations of Hecogenin equal or higher than 100 μM. Although a lower concentration of Hecogenin caused DNA damage, a reduction on nuclear mutagenic markers in HepG2 cells was observed. The results indicated that Hecogenin treatment generated DNA damage, but in fact it would be repaired, avoiding dissemination of the damage throughout the cell division. Further studies need to be performed to confirm the observed protective effect of Hecogenin against genomic instability.

Evaluation of antimicrobial activity of glycinate and carbonate derivatives of cholesterol: Synthesis and characterization

A series of glycinate and carbonate derivatives of cholesterol (4a–t) were synthesized, characterized and assessed for their in vitro antimicrobial activity. Our results revealed that the compounds exerted inhibitory activities against gram-negative bacteria and fungi.

N-Alkyl derivatives of diosgenyl 2-amino-2-deoxy-β-D-glucopyranoside; synthesis and antimicrobial activity

Diosgenyl 2-amino-2-deoxy-β-D-glucopyranoside is a synthetic saponin exhibiting attractive pharmacological properties. Different pathways tested by us to obtain this glycoside are summarized here. Moreover, the synthesis of N-alkyl and N,N-dialkyl derivatives of the glucopyranoside is presented. Evaluation of antibacterial and antifungal activities of these derivatives indicates that they have no inhibitory activity against Gram-negative bacteria, whereas many of the tested N-alkyl saponins were found to inhibit the growth of Gram-positive bacteria and human pathogenic fungi.

Synthesis and biological evaluation of novel sarsasapogenin derivatives as potential anti-tumor agents

Based on the fact that timosaponin A-III (TA-III) exhibits potent cytotoxic effects and has been considered as a potential anti-tumor agent, a range of novel sarsasapogenin derivatives 1, 2a-2g, 3, 4, 5, 6a-6g have been synthesized by a simple and facile synthetic route. The in vitro cytotoxic activity of these synthetic compounds has been evaluated against ten human cancer cell lines. The pharmacological results showed that most of the sarsasapogenin derivatives displayed excellent selective cytotoxicity toward the cancer cell lines. An amino group at C-3 or C-26 position of the sapogenin had a profound influence on the cytotoxic activity. In particular, compound 6c exhibited significantly inhibitory activity against A375-S2 (IC50=0.56μM) and HT1080 (IC50=0.72μM) cells. However, introducing a bromo or morpholinyl substituent at the C-3 and C-26 position of the sapogenin generally rendered it inactive against the human cancer cell lines. This research provides a theoretical reference for the exploration of new anti-tumor drugs.

Synthesis of novel anticancer agents through opening of spiroacetal ring of diosgenin

Diosgenin has been modified to furostane derivatives after opening the F-spiroacetal ring. The aldehyde group at C26 in derivative 8 was unexpectedly transformed to the ketone 9. The structure of ketone 9 was confirmed by spectroscopy and finally by X-ray crystallography. Five of the diosgenin derivatives showed significant anticancer activity against human cancer cell lines. The most potent molecule of this series i.e. compound 7, inhibited cellular growth by arresting the population at G0/G1 phase of cell division cycle. Cells undergo apoptosis after exposure to the derivative 7 which was evident by increase in sub G0 population in cell cycle analysis. Docking experiments showed caspase-3 and caspase-9 as possible molecular targets for these compounds. This was further validated by cleavage of PARP, a caspase target in apoptotic pathway. Compound 7 was found non-toxic up to 1000mg/kg dose in acute oral toxicity in Swiss albino mice.

Current status on development of steroids as anticancer agents

Steroids are important biodynamic agents. Their affinities for various nuclear receptors have been an interesting feature to utilize them for drug development particularly for receptor mediated diseases. Steroid biochemistry and its crucial role in human physiology, has attained importance among the researchers. Recent years have seen an extensive focus on modification of steroids. The rational modifications of perhydrocyclopentanophenanthrene nucleus of steroids have yielded several important anticancer lead molecules. Exemestane, SR16157, fulvestrant and 2-methoxyestradiol are some of the successful leads emerged on steroidal pharmacophores. The present review is an update on some of the steroidal leads obtained during past 25 years. Various steroid based enzyme inhibitors, antiestrogens, cytotoxic conjugates and steroidal cytotoxic molecules of natural as well as synthetic origin have been highlighted. This article is part of a Special Issue entitled "Synthesis and biological testing of steroid derivatives as inhibitors".