Solid Lipid Nanoparticles Encapsulating a Benzoxanthene Derivative in a Model of the Human Blood-Brain Barrier: Modulation of Angiogenic Parameters and Inflammation in Vascular Endothelial Growth Factor-Stimulated Angiogenesis

Lignans, a class of secondary metabolites found in plants, along with their derivatives, exhibit diverse pharmacological activities, including antioxidant, antimicrobial, anti-inflammatory, and antiangiogenic ones. Angiogenesis, the formation of new blood vessels from pre-existing ones, is a crucial process for cancer growth and development. Several studies have elucidated the synergistic relationship between angiogenesis and inflammation in various inflammatory diseases, highlighting a correlation between inflammation and vascular endothelial growth factor (VEGF)-induced angiogenesis. Thus, the identification of novel molecules capable of modulating VEGF effects presents promising prospects for developing therapies aimed at stabilizing, reversing, or even arresting disease progression. Lignans often suffer from low aqueous solubility and, for their use, encapsulation in a delivery system is needed. In this research, a bioinspired benzoxantene has been encapsulated in solid lipid nanoparticles that have been characterized for their pharmacotechnical properties and their thermotropic behavior. The effects of these encapsulated nanoparticles on angiogenic parameters and inflammation in VEGF-induced angiogenesis were evaluated using human brain microvascular endothelial cells (HBMECs) as a human blood-brain barrier model.

Benzo[k,l]xanthene Lignan-Loaded Solid Lipid Nanoparticles for Topical Application: A Preliminary Study

Skin is the first human barrier that is daily exposed to a broad spectrum of physical and chemical agents, which can increase reactive oxygen species (ROS) and lead to the formation of topical disorders. Antioxidant molecules, such as benzo[k,l]xanthene lignans (BXL), are ideal candidates to eliminate or minimize the effects of ROS. Herein, we aimed to formulate BXL-loaded solid lipid nanoparticles (SLN-BXL) to improve the bioavailability and interaction with the skin, and also to investigate the protective impact against intracellular ROS generation in HFF-1 in comparison with the drug-free situation. SLN-BXL were formulated using the PIT/ultrasonication method, and then were subjected to physicochemical characterizations, i.e., average size, zeta potential (ZP), polydispersity index (PDI), encapsulation efficiency (%EE), thermotropic behavior, and interaction with a biomembrane model. The results show a mean size around 200 nm, PDI of 0.2, and zeta potential of about -28 mV, with values almost unchanged over a period of three months, while the EE% is ≈70%. Moreover, SLN-BXL are able to deeply interact with the biomembrane model, and to achieve a double-action release in mildly hydrophobic matrices; the results of the in vitro experiments confirm that SLN-BXL are cell-safe and capable of attenuating the IL-2-induced high ROS levels. In conclusion, based on our findings, the formulation can be proposed as a candidate for a preventive remedy against skin disorders induced by increased levels of ROS.

Characterization and Interaction with Biomembrane Model of Benzo[k,l]xanthene Lignan Loaded Solid Lipid Nanoparticles

Benzo[k,l]xanthene lignans are a group of rare natural products belonging to the class of polyphenols with promising biological activities and are studied as potential chemotherapeutic agents. The lipophilic character of a xanthene core makes these molecules difficult to be used in an aqueous medium, limiting their employment in studies for pharmaceutical applications. To overcome this problem, a drug-delivery system which is able to improve the stability and bioavailability of the compound can be used. In this study, a bioactive benzoxanthene lignan (BXL) has been included in SLN. Unloaded and BXL-loaded SLN have been prepared using the Phase Inversion Temperature method and characterized in terms of size, zeta potential, entrapment efficiency and stability. Differential scanning calorimetry was used to evaluate the thermotropic behavior and ability of SLN to act as carriers for BXL. A biomembrane model, represented by multilamellar vesicles, was used to simulate the interaction of the SLN with the cellular membrane. Unloaded and loaded SLN were incubated with the MLV, and their interactions were evaluated through variations in their calorimetric curves. The results obtained suggest that SLN could be used as a delivery system for BXL.

Asymmetric synthesis of 9-alkyl tetrahydroxanthenones via tandem asymmetric Michael/cyclization promoted by chiral phosphoric acid

A tandem asymmetric Michael-addition/cyclization of cyclic 1,3-dicarbonyl compounds to β,γ-unsaturated α-ketoesters catalyzed by chiral phosphoric acid is presented. This protocol provides a facile approach for the construction of enantioenriched 9-alkyl tetrahydroxanthenones, an ubiquitous framework found in a number of natural products and pharmaceutical molecules, in high yields with good to high enantioselectivities.

Xanthenes in Medicinal Chemistry - Synthetic strategies and biological activities

BACKGROUND

Xanthenes are a special class of oxygen-incorporating tricyclic compounds. Structurally related to xanthones, the presence of different substituents in position 9 strongly influences their physical and chemical properties, as well as their biological applications. This review explores the synthetic methodologies developed to obtain 9H-xanthene, 9-hydroxyxanthene and xanthene-9-carboxylic acid, as well as respective derivatives, from simple starting materials or through modification of related structures. Azaxanthenes, bioisosteres of xanthenes, are also explored. Efficiency, safety, ecological impact and applicability of the described synthetic methodologies are discussed. Synthesis of multi-functionalized derivatives with drug-likeness properties are also reported and their activities explored. Synthetic methodologies for obtaining (aza)xanthenes from simple building blocks are available, and electrochemical and/or metal free procedures recently developed arise as greener and efficient methodologies. Nonetheless, the synthesis of xanthenes through the modification of the carbonyl in position 9 of xanthones represents the most straightforward procedure to easily obtain a variety of (aza)xanthenes. (Aza)xanthene derivatives displayed biological activity as neuroprotector, antitumor, antimicrobial, among others, proving the versatility of this nucleus for different biological applications. However, in some cases their chemical structures suggest a lack of pharmacokinetic properties being associated with safety concerns, which should be overcome if intended for clinical evaluation.

A Rare Natural Benzo[k,l]xanthene as a Turn-Off Fluorescent Sensor for Cu2+ Ion

Rapid and efficient analyses of copper ions are crucial to providing key information for Cu²⁺ in living cells because of their biological importance. In this study, we reported one new turn-off fluorescent sensor for Cu²⁺ with a benzo[k,l]xanthene core, which served as an efficient cation sensor for copper ion over a wide range of other cations (Na⁺, K⁺, Ag⁺, Hg²⁺, Cd²⁺, Co²⁺, Ni²⁺, Zn²⁺, Mg²⁺, and Fe³⁺) owing to the catechol group in the aromatic core. The sensor showed selectivity for Cu²⁺ over other ions; the logK_β for Cu²⁺ binding to compound 1 had a value of 13.265. In the presence of Cu²⁺, sensor 1 provided significant fluorescence decrement; Co²⁺, and Ni²⁺ caused a fluorescence decrement when employed at a higher concentration than Cu²⁺, while Na⁺, K⁺, Hg²⁺, Cd²⁺, Zn²⁺, and Mg²⁺ metal ions produced only minor changes in fluorescence intensity. Fluorescence experiments demonstrate that compound 1 may have an application as a fluorescent probe for detecting Cu²⁺ with a limit of detection of 0.574 µM.

Synthesis, DNA/RNA-interaction and biological activity of benzo[k,l]xanthene lignans

Interactions of two newly synthesized and six previously reported benzoxanthene lignans (BXLs), analogues of rare natural products, with DNA/RNA, G-quadruplex and HSA were evaluated by a set of spectrophotometric methods. Presence/absence of methoxy and hydroxy groups on the benzoxanthene core and minor modifications at C-1/C-2 side pendants - presence/absence of phenyl ring and presence/absence of methoxy and hydroxy groups on phenyl ring - influenced the fluorescence changes and the binding strength to double-stranded (ds-) and G-quadruplex structures. In general, compounds without phenyl ring showed stronger fluorescence changes upon binding than phenyl-substituted BXLs. On the other hand, BXLs with an unsubstituted phenyl ring showed the best stabilization effects of G-quadruplex. Circular dichroism spectroscopy results suggest mixed binding mode, groove binding and partial intercalation, to ds-DNA/RNA and end-stacking to top or bottom G-tetrads as the main binding modes of BXLs to those targets. All compounds exhibited micromolar binding affinities toward HSA and an increased protein thermal stability. Moderate to strong antiradical scavenging activity was observed for all BXLs with hydroxy groups at C-6, C-9 and C-10 positions of the benzoxanthene core, except for derivative bearing methoxy groups at these positions. BXLs with unsubstituted or low-substituted phenyl ring and one derivative without phenyl ring showed strong growth inhibition of Gram-positive Staphylococcus aureus. All compounds showed moderate to strong tumor cell growth-inhibitory activity and cytotoxicity.

Structure-Bioactivity Relationship Study of Xanthene Derivatives: A Brief Review

Over the last decades, several heterocyclic derivatives compounds have been synthesized or extracted from natural resources and have been tested for their pharmaceutical activities. Xanthene is one of these heterocyclic derivatives. These compounds consist of an oxygen-containing central heterocyclic structure with two more cyclic structures fused to the central cyclic compound. It has been shown that xanthane derivatives are bioactive compounds with diverse activities such as anti-bacterial, anti-fungal, anti-cancer, and anti-inflammatory as well as therapeutic effects on diabetes and Alzheimer. The anti-cancer activity of such compounds has been one of the main research fields in pharmaceutical chemistry. Due to this diverse biological activity, xanthene core derivatives are still an attractive research field for both academia and industry. This review addresses the current finding on the biological activities of xanthene derivatives and discussed in detail some aspects of their structure-activity relationship (SAR).

Garcinol and Related Polyisoprenylated Benzophenones as Topoisomerase II Inhibitors: Biochemical and Molecular Modeling Studies

Garcinol, a polyisoprenylated benzophenone isolated from Garcinia genus, has been reported to inhibit eukaryotic topoisomerase I and topoisomerase II at concentrations comparable to that of etoposide (∼25-100 μM). With the aim to clarify the underlying molecular mechanisms by which garcinol inhibits human topoisomerase IIα and topoisomerase IIβ, biochemical assays along with molecular docking and molecular dynamics studies were carried out on garcinol and six congeners. The biochemical results revealed that garcinol derivatives appear to act as catalytic inhibitors of topoisomerase II and to inhibit ATP hydrolysis by topoisomerase II via some form of mixed inhibition. The computational investigation identified the structural elements responsible for binding to the biological target and also provided information for the eventual design of more selective and potent analogues. Collectively, our data suggest that garcinol-type agents may bind to the DNA binding surface and/or ATP domain of type II topoisomerases to antagonize function.

Novel benzoxanthene lignans that favorably modulate lipid mediator biosynthesis: A promising pharmacological strategy for anti-inflammatory therapy

Lipid mediators (LM) encompass pro-inflammatory prostaglandins (PG) and leukotrienes (LT) but also specialized pro-resolving mediators (SPM) which display pivotal bioactivities in health and disease. Pharmacological intervention with inflammatory disorders such as osteoarthritis and rheumatoid arthritis commonly employs anti-inflammatory drugs that can suppress PG and LT formation, which however, possess limited effectiveness and side effects. Here, we report on the discovery and characterization of the two novel benzoxanthene lignans 1 and 2 that modulate select LM biosynthetic enzymes enabling the switch from pro-inflammatory LT to SPM biosynthesis as potential pharmacological strategy to intervene with inflammation. In cell-free assays, compound 1 and 2 inhibit microsomal prostaglandin E₂ synthase-1 and leukotriene C₄ synthase (IC₅₀ ∼ 0.6-3.4 µM) and potently interfere with 5-lipoxygenase (5-LOX), the key enzyme in LT biosynthesis (IC₅₀ = 0.04 and 0.09 µM). In human neutrophils, monocytes and M1 and M2 macrophages, compound 1 and 2 efficiently suppress LT biosynthesis (IC₅₀ < 1 µM), accompanied by elevation of 15-LOX-derived LM including SPM. In zymosan-induced murine peritonitis, compound 1 and 2 ameliorated self-limited inflammation along with suppression of early LT formation and elevation of subsequent SPM biosynthesis in vivo. Together, these novel benzoxanthene lignans promote the LM class switch from pro-inflammatory towards pro-resolving LM to terminate inflammation, suggesting their suitability as novel leads for pharmacotherapy of arthritis and related inflammatory disorders.

Bioinspired benzoxanthene lignans as a new class of antimycotic agents: synthesis and Candida spp. growth inhibition

In this work we synthetized the bioinspired benzoxanthene lignans (BXLs) 3, 14-22, and the phenazine derivative 23 as potential antimycotic agents. MICs and MFCs against Candida strains were determined. In a preliminary screening, compounds 3, 15, 20, 21, 22 were substantially inactive. Compounds 14 and 17 showed antifungal activity, being able to inhibit the growth of the majority of Candida strains with MIC values in the range 4.6-19.2 µM (14) and 26.0-104.3 µM (17); for three strains, the MICs were lower than those obtained using the antimycotic drug fluconazole. The three BXLs 18, 19 and 23 showed some MIC values lower than that of fluconazole; 18 was also active against two non-albicans Candida strains resistant to fluconazole. Phenazine 23, although active only against one strain (MIC = 1.3 µM), was one order of magnitude more potent than fluconazole. All the BXLs were fungicidal.

Dihydrobenzofuran Neolignanamides: Laccase-Mediated Biomimetic Synthesis and Antiproliferative Activity

The biomimetic synthesis of a small library of dihydrobenzofuran neolignanamides (the natural trans-grossamide (4) and the related compounds 21-28) has been carried out through an eco-friendly oxidative coupling reaction mediated by Trametes versicolor laccase. These products, after complete spectroscopic characterization, were evaluated for their antiproliferative activity against Caco-2 (colon carcinoma), MCF-7 (mammary adenocarcinoma), and PC-3 (prostate cancer) human cells, using an MTT bioassay. The racemic neolignamides (±)-21 and (±)-27, in being the most lipophilic in the series, were potently active, with GI50 values comparable to or even lower than that of the positive control 5-FU. The racemates were resolved through chiral HPLC, and the pure enantiomers were subjected to ECD measurements to establish their absolute configurations at C-2 and C-3. All enantiomers showed potent antiproliferative activity, with, in particular, a GI50 value of 1.1 μM obtained for (2R,3R)-21. The effect of (±)-21 on the Caco-2 cell cycle was evaluated by flow cytometry, and it was demonstrated that (±)-21 exerts its antiproliferative activity by inducing cell cycle arrest and apoptosis.

Copper catalyzed coupling of protecting group free and sterically hindered 2-bromobenzyl tertiary alcohols with phenols and anilines: facile synthesis of xanthenes and dihydroacridines

Protecting group free and sterically hindered tertiary alcohols used in coupling reaction. Two-step process with a single column chromatography. Synthesis of interesting xanthenes and dihydroacridines.

Bio-inspired benzo[k,l]xanthene lignans: synthesis, DNA-interaction and antiproliferative properties

In this work twelve benzo[k,l]xanthene lignans were synthesized by biomimetic, Mn-mediated oxidative coupling of caffeic esters and amides. These compounds, bearing different flexible pendants at position C1/C2 of the aromatic core, interact with DNA in a dual mode, as confirmed by DF-STD NMR analysis and molecular docking: the planar core acts as a base pair intercalant, whereas the flexible pendants act as minor groove binders. Their antiproliferative activity was evaluated on a panel of six tumor cell lines: HT-29, Caco-2, HCT-116 (human colon carcinoma), H226, A549 (human lung carcinoma), and SH-SY5Y (human neuroblastoma). All compounds under study, except 29, resulted in activity against one or more cell lines, and the markedly lipophilic esters 13 and 28 showed the highest activity. Compound 13 was more active than the anticancer drug 5-fluorouracil (5-FU) towards HCT-116 (colon, GI50 = 3.16 μM) and H226 (lung, GI50 = 4.33 μM) cell lines.

Effects of a Ferulate-Derived Dihydrobenzofuran Neolignan on Angiogenesis, Steroidogenesis, and Redox Status in a Swine Cell Model

In the ongoing search for new therapeutic compounds, lignans and neolignans, which are widely distributed in plants, deserve special attention because of their interactions with several biological targets. Searching for potential antiangiogenic agents related to natural lignans/neolignans, we were attracted by a previously studied synthetic dihydrobenzofuran neolignan. We synthesized the compound by means of an eco-friendly, enzyme-mediated biomimetic coupling of the methyl ester of ferulic acid, and the present study was aimed to deeply investigate its effect in angiogenesis bioassays validated in our laboratory. In addition, a previously well-defined granulosa cell model was employed to evaluate the effect of dihydrobenzofuran neolignan on cell viability, steroidogenesis, and redox status. Present data support the antiangiogenic effect of this neolignan. Moreover, we demonstrate that, at least at the highest concentrations tested, dihydrobenzofuran neolignan affects granulosa cell viability and steroidogenesis. In addition, the compound inhibits generation of free radicals and stimulates scavenger enzyme activities. The present data, which are a further deepening of the evaluation of the biological activities of the dihydrobenzofuran lignan in well-defined cell models, are of interest and worthy of special attention.

Phenethyl caffeate benzoxanthene lignan is a derivative of caffeic acid phenethyl ester that induces bystander autophagy in WiDr cells

We recently reported that Phenethyl caffeate benzoxanthene lignan (PCBL), a semisynthetic compound derived from Caffeic Acid Phenethyl Ester (CAPE), induces DNA damage and apoptosis in tumor cells. In this study, we further investigated whether PCBL induces autophagy in WiDr cells. We also analyzed the pathways regulating autophagy and the role of autophagy in PCBL-induced cell death. Our acridine orange staining and LC3 II expression results suggest that PCBL induces autophagosomes in WiDr cells. The levels of LC3 II expression we observed after co-treatment of PCBL with bafilomycin A1 and the reductions in p62 expression we observed after PCBL treatment in WiDr cells demonstrate increased autophagic flux, a reliable indicator of autophagic induction. The increased Beclin 1 expression in PCBL-treated cells and the incapacity of PCBL to induce LC3 II in 3-methyladenine (3-MA)-treated cells we observed suggests that PCBL-induced autophagy is class III PI3-kinase dependent. PCBL did not alter phosphorylation of the mTOR substrate p70 S6 kinase, indicating that PCBL-induced autophagy was not mTOR regulated. Two autophagy related proteins, Atg5 and Atg12, also remained uninduced during PCBL treatment. The increased caspase activity and expression levels of LC3 II and p62 we observed in response to PCBL treatment in primary glioma cells demonstrates that PCBL-induced apoptosis and autophagy were not cell line specific. Pharmacological inhibition of autophagy did not alter the antitumor efficacy of PCBL in WiDr cells. This attests to the bystander nature of PCBL-induced autophagy (in terms of cell death). In toto, these data suggest that PCBL induces a class III kinase dependent, but mTOR independent, bystander mode of autophagy in WiDr cells.

Picea mariana bark: a new source of trans-resveratrol and other bioactive polyphenols

The ethyl acetate soluble fraction obtained from the hot water extract of Picea mariana bark (BS-EAc(f)) has been demonstrated to have anti-inflammatory and antioxidant properties. Thus, in the current study, we isolated and characterised major compounds of this fraction by HPLC, NMR and MS analyses. On the whole, 28 compounds were identified, among which were five neolignans, seven lignans, trans-resveratrol, three phenolic acids and four flavonoids. To the best of our knowledge, 2,3-dihydro-3-(4-hydroxy-3-methoxyphenyl)-2-(hydroxymethyl)-(2S,3S)-1,4-benzodioxin-6-propanol, threo and erythro 3-methoxy-8,4'-oxyneolignan-3',4,7,9,9'-pentol, pallasiin, (±) epi-taxifolin, homovanillyl alcohol, orcinol and 2-[4-(3-hydroxypropyl)-2-methoxyphenoxy]-1,3-propanediol are reported for the first time in the Picea genus. P. mariana dry bark contains at least 104μgg(-1)dw of trans-resveratrol and it could be therefore considered as a new accessible source of this molecule. This study provides novel information about the identity of major compounds present in BS-EAc(f), which is essential for the understanding of the anti-inflammatory and nutraceutical potential of this extract.

Antiradical and antioxidant activities of new bio-antioxidants

Antioxidants could be promising agents for management of oxidative stress-related diseases. New biologically active compounds, belonging to a rare class of natural lignans with antiangiogenic, antitumoral and DNA intercalating properties, have been recently synthesized. These compounds are benzo[kl]xanthene lignans (1,2) and dihydrobenzofuran neolignans (3,4). The radical scavenging and chain-breaking antioxidant activities of compounds 1-4 were studied by applying different methods: radical scavenging activity by DPPH rapid test, chain-breaking antioxidant activity and quantum chemical calculations. All studied compounds were found to be active as DPPH scavengers but reaction time with DPPH and compounds' concentrations influenced deeply the evaluation. The highest values of radical scavenging activity (%RSAmax) and largest rate constants for reaction with DPPH were obtained for compounds 2 and 3. Comparison of %RSAmax with that of standard antioxidants DL-α-tocopherol (TOH), caffeic acid (CA) and butylated hydroxyl toluene (BHT) give the following new order of %RSA max: TOH (61.1%) > CA (58.6%) > 3 (36.3%) > 2 (28.1%) > 4 (6.7%) > 1 (3.6%) = BHT (3.6%). Chain-breaking antioxidant activities of individual compounds (0.1-1.0 mM) and of their equimolar binary mixtures (0.1 mM) with TOH were determined from the kinetic curves of lipid autoxidation at 80 °C. On the basis of a comparable kinetic analysis with standard antioxidants a new order of the antioxidant efficiency (i.e., protection factor, PF) of compounds 1-4 were obtained: 2 (7.2) ≥ TOH (7.0) ≥ CA (6.7) > 1 (3.1) > 3 (2.2) > ferulic acid FA (1.5) > 4 (0.6); and of the antioxidant reactivity (i.e. inhibition degree, ID): 2 (44.0) >> TOH (18.7) >> CA (9.3) >> 1 (8.4) > 3 (2.8) > FA (1.0) > 4 (0.9). The important role of the catecholic structure in these compounds, which is responsible for the high chain-breaking antioxidant activity, is discussed and a reaction mechanism is proposed. Higher oxidation stability of the lipid substrate was found in the presence of equimolar binary mixtures 2 + TOH, 3 + TOH and 4 + TOH. However, an actual synergism was only obtained for the binary mixtures with compounds 3 and 4. The geometries of compounds and all possible phenoxyl radicals were optimized using density functional theory. For description of the scavenging activity bond dissociation enthalpies (BDE), HOMO energies and spin densities were employed. The best correlation between theoretical and experimental data was obtained for compound 2, with the highest activity, and for compound 4 with the lowest activity. The BDE is the most important theoretical descriptor, which correlates with the experimentally obtained antioxidant activity of the studied benzo[kl]xanthene lignans and dihydrobenzofuran neolignans.

Strategies for the Synthesis of 2,3-Dihydrobenzofurans

This article gives an overview of synthetic approaches to the 2,3-dihydrobenzofuran ring system with an emphasis on recently developed methods. The synthetic approaches are classified according to the key bond(s) formed during the construction of the dihydrobenzofuran skeleton, and approaches of relevance to the synthesis of natural products are highlighted.