Enzymatic synthesis of phenolic acid glucosyl esters to test activities on cholangiocarcinoma cells

While glycoside hydrolase family 1 (GH1) enzymes mostly catalyze hydrolysis reactions, rice Os9BGlu31 preferentially catalyzes transglycosylation to transfer a glucosyl moiety to another aglycone moiety to form a new glycosylated compound through a retaining mechanism. In this study, Os9BGlu31 was used to synthesize eight phenolic acid glucosyl esters, which were evaluated for activities in cholangiocarcinoma cells. The transglycosylation products of Os9BGlu31 wild type and its mutant variants were detected, produced on a milligram scale, and purified, and their structures were characterized by NMR spectroscopy. The transglycosylation products were evaluated by antioxidant and anti-proliferative assays, followed by an anti-migration assay for the selected phenolic acid glucosyl ester. Os9BGlu31 mutants produced higher yield and activity than wild-type enzymes on phenolic acids to produce phenolic acid glucosyl esters. Among these, gallic acid glucosyl ester (β-glucogallin) had the highest antioxidant activity and anti-proliferative activity in cholangiocarcinoma cells. It also inhibited the migration of cholangiocarcinoma cells. Our study demonstrated that rice Os9BGlu31 transglucosidase is a promising enzyme for glycosylation of bioactive compounds in one-step reactions and provides evidence that β-glucogallin inhibits cell proliferation and migration of cholangiocarcinoma cells. KEY POINTS: • Os9BGlu31 transglucosidases produced phenolic acid glucosyl esters for bioactivity testing. • Phenolic acid glucosyl esters were tested for cytotoxicity in cholangiocarcinoma cells. • β-Glucogallin displayed the highest inhibition of cholangiocarcinoma cell growth.

Semi-synthesis of phenolic-amides and their cytotoxicity against THP-1, HeLa, HepG2 and MCF-7 cell lines

In the present study, we derivatized several hydroxycinnamic and hydroxybenzoic acids to phenolic amides (PAMs) via one step BOP mediated amide coupling reactions. Fifteen PAMs were synthesized in >40% yields and were screened for their cytotoxic activities against four cancer cell lines: THP-1 (leukaemia), HeLa (cervical), HepG2 (liver), and MCF-7 (breast), in comparison to 5-flurouracil (5-FU). Four amides showed IC50 ranging from 5 to 55 µM against all four cell lines. In contrast, tetradecyl-gallic-amide (13) affected only THP-1 leukaemia cells with IC50 of 3.08 µM. The activities of these compounds support the promise of phenolic amides as anticancer agents.

Synthesis and mammalian cell compatibility of light-released glycan precursors for controlled metabolic engineering

Sugar additions to biomolecules, or glycans, are some of the most abundant biomolecule modifications in biology because they enable cells to adapt to changing nutrient and stress conditions. An unmet challenge for the field of glycobiology is the study of glycan biosynthetic pathways with chemical control, especially in live cell settings. The objective of this study was to create biocompatible glycan precursors with controlled release properties. Here, we report eleven "caged" sugar probes that release glycan biosynthetic precursor molecules upon light exposure. The specific sugar pathways we target with our probes regulate the addition of the N-acetyl sugars GlcNAc, GalNAc, and sialic acid onto biomolecules in cells, each of which has the potential to alter glycan processes involved in cell morphology, signaling, and behavior. We hypothesized that our glycan precursor probes would remain biologically inert until light-initiated decaging conditions were met, avoiding biological activities including metabolism and cytotoxicity. The photocaged analogs of GlcNAc, GalNAc, and ManNAc (sialic acid precursor) sugars, which we call "photo-sugars," were released within minutes of light exposure at their optimal wavelengths. During the course of the study, we characterized the cell compatibility of these sugars under their respective decaging conditions, and found highly cell compatible GlcNAc, GalNAc, and ManNAc photocaged precursors. Release of GlcNAc-1-phosphate precursors led to altered ATP levels in cells, demonstrating preliminary metabolic engineering. We envision these probes as useful additions to the chemical glycobiology field that will enable spatiotemporal control over glycosylation pathways in living mammalian cells.

Unravelling the Immune Modulatory Effect of Indian Spices to Impede the Transmission of COVID-19: A Promising Approach

Months after WHO declared COVID-19 as a Global Public Health Emergency of International Concern, it does not seem to be flattening the curve as we are still devoid of an effective treatment modality and vaccination is in the first phase in many countries. Amid such uncertainty, being immune is the best strategy to defend against corona attacks. As the whole world is referring back to immune-boosting traditional remedies, interest is rekindled in the Indian system of Medicine, which is gifted with an abundance of herbal medicines as well as remedies. Among them, spices (root, rhizome, seed, fruit, leaf, bud, and flower of various plants used to add taste and flavors to food) are bestowed with immense medicinal potential. A plethora of clinical as well as preclinical studies reported the effectiveness of various spices for various ailments. The potential immune-boosting properties together with their excellent safety profiles are making spices the current choice of phytoresearch as well as the immune-boosting home remedies during these sceptical times. The present review critically evaluates the immune impact of various Indian spices and their potential to tackle the novel coronavirus, with comments on the safety and toxicity aspects of spices.

Total synthesis of ceramides and β-O-glucosylceramides via intramolecular fatty acyl group migration

Fatty acyl group utilized as both protection and migratory group for the synthesis of ceramides and glucosylceramides.

Chemoenzymatic and Protecting-Group-Free Synthesis of 1,4-Substituted 1,2,3-Triazole-α-d-glucosides with Potent Inhibitory Activity toward Lysosomal α-Glucosidase

α-Glucosyl triazoles have rarely been tested as α-glucosidase inhibitors, partly due to inefficient synthesis of their precursor α-d-glucosylazide (αGA1). Glycosynthase enzymes, made by nucleophile mutations of retaining β-glucosidases, produce αGA1 in chemical rescue experiments. Thermoanaerobacterium xylanolyticus glucosyl hydrolase 116 β-glucosidase (TxGH116) E441G nucleophile mutant catalyzed synthesis of αGA1 from sodium azide and pNP-β-d-glucoside (pNPGlc) or cellobiose in aqueous medium at 45 °C. The pNPGlc and azide reaction product was purified by Sephadex LH-20 column chromatography to yield 280 mg of pure αGA1 (68% yield). αGA1 was successfully conjugated with alkynes attached to different functional groups, including aryl, ether, amine, amide, ester, alcohol, and flavone via copper-catalyzed azide-alkyne cycloaddition (CuAAC) click chemistry reactions. These reactions afforded the 1,4-substituted 1,2,3-triazole-α-d-glucoside derivatives AGT2-14 without protection and deprotection. Several of these glucosyl triazoles exhibited strong inhibition of human lysosomal α-glucosidase, with IC50 values for AGT4 and AGT14 more than 60-fold lower than that of the commercial α-glucosidase inhibitor acarbose.

Cogent role of flavonoids as key orchestrators of chemoprevention of hepatocellular carcinoma: A review

Chemopreventive approaches with food-derived phytochemicals are progressively rising as a significant aspect of tumor management and control. Herein, we have showcased the major phytoconstituents belonging to the group of flavanoid, as anti-cancer agents used for the treatment and prevention of hepatocellular carcinoma (HCC). Sorafenib is the sole drug used for the treatment of advanced HCC, but its clinical application is limited because of its severe adverse effects and drug resistance. Diet-based chemoprevention seems to be the way forward for this disease of malignant nature. As HCC is derived from a chronic inflammatory milieu, the regular incorporation of bioactive phytochemicals in the diet will confer protection and prevent progression to hepatocarcinogenesis. Many preclinical studies proved that the health benefits of flavonoids confer cytotoxic potential against various types of cancers including hepatocellular carcinoma. As flavonoids with excellent safety profile are abundantly present in common vegetables and fruits, they can be better utilized for chemoprevention and chemosensitization in such chronic condition. This review highlights the plausible role of the eight most promising flavonoids (Curcumin, Kaempferol, Resveratrol, Quercetin, Silibinin, Baicalein, Galangin and Luteolin) as key orchestrators of chemoprevention in hepatocellular carcinoma with preclinical and clinical evidence. An attempt to address the challenges in its clinical translation is also included. This review also provides an insight into the close association of HCC and metabolic disorders which may further decipher the chemopreventive effect of dietary bioactive from a proof of concept to extensive clinical translation. PRACTICAL APPLICATIONS: According to GLOBOCAN 2020 database, it is estimated that 905,677 new cases of liver cancer and approximately 830,180 deaths related to that. The cancer incidence and mortality are almost similar as it is diagnosed at an advanced stage in patients where systemic drug therapy is the sole approach. Due to the emergence of multidrug resistance and drug-related toxicities, most of the patient can not adhere to the therapy regimen. Flavonoids are known to be a potential anticancer agent with an excellent safety profile. These are found to be effective preclinically against hepatocellular carcinoma through modulation of numerous pathways in hepatocarcinogenesis. But, the bioavailability issue, lack of well designed-validated clinical evidence, the possibility of food-drug interaction etc limit its clinical utility. The research inputs mainly to overcome pharmacokinetic issues along with suitable validation of efficacy and toxicity will be a critical point for establishing flavonoids as an effective, safe, affordable therapeutics.

Glucose conjugated aza-BODIPY for enhanced photodynamic cancer therapy

Compared with normal cells, cancer cells usually exhibit an increase in glucose uptake as part of the Warburg effect. To take advantage of this hallmark of cancer, glucose transporters could be a good candidate for cancer targeting. Herein, we report novel glycoconjugate aza-BODIPY dyes (AZB-Glc and AZB-Glc-I) that contain two glucose moieties conjugated to near-infrared dyes via the azide-alkyne cycloaddition reaction. As anticipated, a higher level of AZB-Glc uptake was observed in breast cancer cells that overexpressed glucose transporters (GLUTs), especially GLUT-1, including the triple-negative breast cancer cell line (MDA-MB-231) and human breast adenocarcinoma cell line (MCF-7), compared to that of normal cells (human fetal lung fibroblasts, HFL1). The cellular uptake of AZB-Glc was in a dose- and time-dependent manner and also depended on GLUT, as evidenced by the decreased uptake of AZB-Glc in the presence of d-glucose or a glucose metabolism suppressor, combretastatin. In addition, light triggered cell death was also investigated through photodynamic therapy (PDT), since near-infrared (NIR) light is known to penetrate deeper tissue than light of shorter wavelengths. AZB-Glc-I, the analog of AZB-Glc containing iodine for enhanced singlet oxygen production upon NIR irradiation, was used for all treatment assays. AZB-Glc-I showed significant NIR light-induced cytotoxicity in cancer cells (IC₅₀ = 1.4-1.6 μM under 1 min irradiation), which was about 20-times lower than that in normal cells (IC₅₀ = 32 μM) under the same conditions, with negligible dark toxicity (IC₅₀ > 100 μM) in all cell lines. Moreover, the singlet oxygen was detected inside the cancer cells after exposure to light in the presence of AZB-Glc-I. Therefore, our glucose conjugated systems proved to efficiently target cancer cells for enhanced photodynamic cancer therapy.

Author Correction: Evaluation of uttroside B, a saponin from Solanum nigrum Linn, as a promising chemotherapeutic agent against hepatocellular carcinoma

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Gram scale production of 1-azido-β-d-glucose via enzyme catalysis for the synthesis of 1,2,3-triazole-glucosides

The production of analytical amounts of azido sugars is used as a means of verifying catalytic acid/base mutations of retaining glycosidase, but application of this process to preparative synthesis has not been reported. The catalytic acid/base mutant of Thermoanaerobacterium xylanolyticus GH116 β-glucosidase, TxGH116D593A, catalyzed the gram scale production of 1-azido-β-d-glucose (1) from p-nitropheyl-β-d-glucopyranoside (pNPGlc) and azide via a transglucosylation reaction. Overnight reaction of the enzyme with pNPGlc and NaN₃ in aqueous MES buffer (pH 5.5) at 55 °C produced 1 (3.27 g), which was isolated as a white foamy solid in 96% yield. This 1 was successfully utilized for the synthesis of fifteen 1,2,3-triazole-β-d-glucosyl derivatives (2–16) containing a variety of functional groups, via click chemistry.

The retaining β-glucosidase acid/base mutant TxGH116D593A catalyzed the production of 1-azido-β-d-glucose for synthesis of 15 1,2,3-triazole β-glucosyl derivatives.

Evaluation of uttroside B, a saponin from Solanum nigrum Linn, as a promising chemotherapeutic agent against hepatocellular carcinoma

We report, for the first time, the remarkable efficacy of uttroside B, a potent saponin from Solanum nigrum Linn, against liver cancer. The compound has been isolated and characterized from the leaves of Solanum nigrum Linn, a plant widely used in traditional medicine and is a rich resource of several anticancer molecules. Uttroside B, that comprises of β-D-glucopyranosyl unit at C-26 of the furostanol and β-lycotetraosyl unit at C-3, is ten times more cytotoxic to the liver cancer cell line, HepG2 (IC50: 0.5 μM) than sorafenib (IC50: 5.8 μM), the only FDA-approved drug for liver cancer. Moreover, it induces cytotoxicity in all liver cancer cell lines, irrespective of their HBV status, while being non-toxic to normal immortalized hepatocytes. It induces apoptosis in HepG2 cells by down-regulating mainly the activation of MAPK and mTOR pathways. The drastic reduction in HepG2-xenograft tumor size achieved by uttroside B in NOD-SCID mice and substantiation of its biological safety through both acute and chronic toxicity studies in Swiss albino mice warrants clinical validation of the molecule against hepatic cancer, for which, the chemotherapeutic armamentarium currently has limited weapons.

Kaempferide, the most active among the four flavonoids isolated and characterized from Chromolaena odorata, induces apoptosis in cervical cancer cells while being pharmacologically safe

We report the isolation and characterization of four compounds from a cytotoxic fraction F-17, isolated from the DCM extract of C. odorata by bioactivity guided fractionation.

Cytotoxicity studies of semi-synthetic derivatives of theveside derived from the aqueous extract of leaves of 'suicide tree' Cerbera odollam

We report the isolation of two known iridoid glucosides theviridoside (1) and theveside (2) from the aqueous extract of leaves of Cerbera odollam and semi-synthetic derivatisation of theveside prepared in a single step under protection group-free conditions. Derivatives 2a-j were evaluated for cytotoxicity towards five human cancer cell lines of different origins, namely SKBR3 (breast), HeLa (cervical), A375 (skin), HepG2 (liver) and HCT-116 (colon), and IC50 values were determined. Derivatives 2b and 2h exhibited moderate cytotoxicity against HCT-116 and A375 cell lines, respectively.