Evaluation of Dual 5-Lipoxygenase/Microsomal Prostaglandin E2 Synthase-1 Inhibitory Effect of Natural and Synthetic Acronychia-Type Isoprenylated Acetophenones

Total synthesis/semi-synthesis of natural isopentenyl flavonoids with inhibitory activity on NLRP3 inflammasome

Inflammation is the body's defense response to stimuli. When the homeostatic balance is disturbed, disease may result. Flavonoids have clear anti-inflammatory effects and the isopentenyl group significantly enhances the pharmacological activity of flavonoids. Therefore, isopentenyl flavonoids have the potential to serve as lead compounds for the development of anti-inflammatory drugs. Throughout this research, eight natural compounds were synthesized, including 5,7-dihydroxy-4'-methoxy-8-prenylflavonoid (1), 4'-O-Methylatalantoflavone (2), Kushenol W (3) and Racemoflavone (5), which were totally synthesized for the first time. Additionally, three flavonols: Licoflavonol (6), 3,5,7,3',4'-pentahydroxy-6-prenylflavonol (7) and Macarangin (8), can be one-step synthesized by direct C-isopentenylation. In the process, an economical and efficient C-isopentenylation method was also simultaneously explored that could facilitate the efficient synthesis of natural products. These compounds were evaluated for their potential anti-inflammatory activities via the NLRP3 signaling pathway. Notably, Macarangin (8) manifested the most potent inhibitory effect. The SAR (Structure-Activity Relationships) also showed the introduction of the isopentenyl group was determined to enhance these effects, whereas simple flavonoid frameworks or cyclization of isopentenyl groups all diminished anti-inflammatory activity.

Lipoxygenase Inhibitors as Cancer Chemopreventives: Discovery, Recent Developments and Future Perspectives

BACKGROUND

Leukotrienes (LTs) constitute a bioactive group of Polyunsaturated Fatty Acid (PUFA) metabolites molded by the enzymatic activity of lipoxygenase (LO) and have a pivotal role in inflammation and allergy. Evidence is accumulating both by in vitro cell culture experiments and animal tumor model studies in support of the direct involvement of aberrant metabolism of arachidonic acid (ACD) in the development of several types of human cancers such as lung, prostate, pancreatic and colorectal malignancies. Several independent experimental data suggest a correlation between tumoral cells viability and LO gene expression, especially, 5-lipoxygenase (5-LO). Overexpressed 5-LO cells live longer, proliferate faster, invade more effectively through extracellular matrix destruction and activate the anti-apoptotic signaling mechanisms more intensively compared to the normal counterparts. Thus, some groups of lipoxygenase inhibitors may be effective as promising chemopreventive agents.

METHODS

A structured search of bibliographic databases for peer-reviewed research literature regarding the role of LO in the pathogenesis of cancer was performed. The characteristics of screened papers were summarized and the latest advances focused on the discovery of new LO inhibitors as anticancer agents were discussed.

RESULTS

More than 180 papers were included and summarized in this review; the majority was about the newly designed and synthesized 5-LO inhibitors as anti-inflammatory and anticancer agents. The enzyme's structure, 5-LO pathway, 5-LO inhibitors structure-activity relationships as well as the correlation between these drugs and a number of most prevalent human cancers were described. In most cases, it has been emphasized that dual cyclooxygenase-2/5-lipoxygenase (COX-2/5-LO) or dual 5-lipoxygenase/microsomal prostaglandin E synthase-1 (5-LO/mPGES-1) inhibitors possess considerable inhibitory activities against their target enzymes as well as potent antiproliferative effects. Several papers disclosing 5-lipoxygenase activating protein (FLAP) antagonists as a new group of 5-LO activity regulators are also subject to this review. Also, the potential of 12-lipoxygenase (12- LO) and 15-lipoxygenase (15-LO) inhibitors as chemopreventive agents was outlined to expand the scope of new anticancer agents discovery. Some peptides and peptidomimetics with anti-LT activities were described as well. In addition, the cytotoxic effects of lipoxygenase inhibitors and their adverse effects were discussed and some novel series of natural-product-derived inhibitors of LO was also discussed in this review.

CONCLUSION

This review gives insights into the novel lipoxygenase inhibitors with anticancer activity as well as the different molecular pharmacological strategies to inhibit the enzyme effectively. The findings confirm that certain groups of LO inhibitors could act as promising chemopreventive agents.

The Anti-Inflammatory and Antimicrobial Potential of Selected Ethnomedicinal Plants from Sri Lanka

Traditional folk medicine in Sri Lanka is mostly based on plants and plant-derived products, however, many of these medicinal plant species are scientifically unexplored. Here, we evaluated the anti-inflammatory and antimicrobial potency of 28 different extracts prepared from seven popular medicinal plant species employed in Sri Lanka. The extracts were subjected to cell-based and cell-free assays of 5-lipoxygenase (5-LO), microsomal prostaglandin E₂ synthase (mPGES)-1, and nitric oxide (NO) scavenging activity. Moreover, antibacterial and disinfectant activities were assessed. Characterization of secondary metabolites was achieved by gas chromatography coupled to mass spectrometric (GC-MS) analysis. n-Hexane- and dichloromethane-based extracts of Garcinia cambogia efficiently suppressed 5-LO activity in human neutrophils (IC₅₀ = 0.92 and 1.39 µg/mL), and potently inhibited isolated human 5-LO (IC₅₀ = 0.15 and 0.16 µg/mL) and mPGES-1 (IC₅₀ = 0.29 and 0.49 µg/mL). Lipophilic extracts of Pothos scandens displayed potent inhibition of mPGES-1 only. A methanolic extract of Ophiorrhiza mungos caused significant NO scavenging activity. The lipophilic extracts of G. cambogia exhibited prominent antibacterial and disinfectant activities, and GC-MS analysis revealed the presence of fatty acids, sesquiterpenes and other types of secondary metabolites. Together, our results suggest the prospective utilization of G.cambogia as disinfective agent with potent anti-inflammatory properties.

Prenylated Acetophloroglucinol Dimers from Acronychia trifoliolata: Structure Elucidation and Total Synthesis

The isolation of 12 secondary metabolites, including seven new acetophenone monomers, from the 50% CH3OH/CH2Cl2 extract (N089419-L/6) of Acronychia trifoliolata was reported previously. In the present work, three new prenylated acetophenone dimers (1-3) and five known dimers (4-8) were isolated, and their structures were elucidated by using various NMR spectroscopic techniques and HRMS. Among the new dimers, an unprecedented 4-isobutyl-3-isopropyltetrahydro-2H-pyran ring was observed in the structure of 1. This study is the first to report the formation of a 2H-pyran ring between two prenylated acetophloroglucinols. Only four related dimers have been reported before, and they were formylated phloroglucinol dimers from the family Eucalypteae. Compounds 2 and 3 are acrovestone-like dimers, and the structure of 3 was confirmed by total synthesis. The evaluation of the antiproliferative activity of isolated and synthesized acrovestone-like dimers indicated that a double bond in the prenyl-like moiety as found in the more active compounds might be important for mediating activity, while the pendant isobutyl group seems to be less important.

Synthesis and Anti-inflammatory Evaluation of ( R)-, ( S)-, and (±)-Sanjuanolide Isolated from Dalea frutescens

The known chalcone (±)-sanjuanolide (1) can be isolated from Dalea frutescens. This study presents a convergent strategy for the first total synthesis of ( R)-, ( S)-, and (±)-sanjuanolide (1). The key step for synthesizing ( R)- and ( S)-1 was a Corey-Bakshi-Shibata enantioselective carbonyl reduction to construct the C-2″ configuration. ( R)-1 efficiently inhibited the lipopolysaccharides (LPS)-induced expression of tumor necrosis factor alpha (TNF-α) and interleukin-6 (IL-6), while ( S)-1 produced no significant anti-inflammatory effect. ( R)-1 also effectively inhibited the mRNA expression of several inflammatory cytokines after the LPS challenge in vitro. The synthesis and biological properties of these compounds have confirmed ( R)-sanjuanolide and (±)-sanjuanolide as promising new leads for developing anti-inflammatory agents.

Isolation and identification of new prenylated acetophenone derivatives from Acronychia oligophlebia

Three new prenylated acetophenone derivatives, acronyculatin P (1), acronyculatin Q (2), and acronyculatin R (3) were isolated from the leaves of Acronychia oligophlebia. Their structures were identified by extensive analyses of spectroscopic data (IR, UV, ESI-HRMS, 1D and 2D NMR) and comparison with the literatures. In addition, the cytotoxic activity against MCF-7 cells of the compounds were evaluated by the MTT assay and the IC₅₀ values were 56.8, 40.4 and 69.1 μM, respectively.

Acrofolione A and B, acetophenone dimers from Acronychia pendunculata, induce an apoptotic effect on human NALM-6 pre-B cell leukaemia cells

OBJECTIVES

We investigated the apoptotic activities of acrofolione A (1) and B (2) isolated from Acronychia pedunculata against a human pre-B cell leukaemia cell line (NALM-6) to explore the apoptosis-related signalling molecules targeted by 1 and 2.

METHODS

The apoptosis effects of 1 and 2 in NALM-6 cells were investigated by TUNEL staining, annexin V, mitochondria membrane potential and caspase 3/7 activity. We carried out a protein array to explore the signalling molecules involved in apoptosis comprehensively.

KEY FINDINGS

Acrofolione A (1) suppressed the growth of NALM-6, K562 and HPB-ALL cells (IC₅₀ 16.7 ± 1.9, 17.9 ± 0.3 and 10.1 ± 0.2 μm, respectively) more effectively than acrofolione B (2). Both compounds time-dependently increased the number of NALM-6 cells with abnormal nuclei, and increased the number of annexin V-positive cells and decreased the mitochondrial membrane potential of NALM-6 cells. Acrofolione A (1) markedly elevated caspase 3/7 activity and increased the number of TUNEL-positive cells. Cells treated with either compound showed enhanced expression of cleaved PARP and cleaved caspase 3 and 7, and reduced survivin protein levels.

CONCLUSIONS

Acrofolione A (1) and B (2) may be useful in the treatment of various types of leukaemia.

Natural products as inhibitors of prostaglandin E2 and pro-inflammatory 5-lipoxygenase-derived lipid mediator biosynthesis

Non-steroidal anti-inflammatory drugs (NSAIDs) inhibit prostanoid formation and represent prevalent therapeutics for treatment of inflammatory disorders. However, NSAIDs are afflicted with severe side effects, which might be circumvented by more selective suppression of pro-inflammatory eicosanoid biosynthesis. This concept led to dual inhibitors of microsomal prostaglandin E₂ synthase (mPGES)-1 and 5-lipoxygenase that are crucial enzymes in the biosynthesis of pro-inflammatory prostaglandin E₂ and leukotrienes. The potential of their dual inhibition in light of superior efficacy and safety is discussed. Focus is placed on natural products, for which direct inhibition of mPGES-1 and leukotriene biosynthesis has been confirmed.