Discovery of Michael reaction acceptors from the leaves of Ailanthus altissima by a modified tactic.

Structural characteristics-guided investigation of Ailanthus altissima (Mill.) Swingle resulted in the isolation and identification of seven undescribed potential Michael reaction acceptors (1-7). Ailanlactone A (1) possesses an unusual 1,7-epoxy-11,12-seco quassinoid core. Ailanterpene B (6) was a rare guaianolide-type sesquiterpene with a 5/6/6/6-fused skeleton. Their structures were determined through extensive analysis of physiochemical and spectroscopic data, quantum chemical calculations, and single crystal X-ray crystallographic technology using Cu Kα radiation. The cytotoxic activities of isolates on HepG2 and Hep3B cells were evaluated in vitro. Encouragingly, ailanaltiolide K (4) showed significant cytotoxicity against Hep3B cells with IC50 values of 1.41 ± 0.21 µM, whose covalent binding mode was uncovered in silico.

Chemical constituents from the twigs and leaves of Picrasma quassioides.

Two new compounds, including a norsesquiterpenoid, annuionone H (1), and a quassinoid, picraqualide G (2), along with eleven known compounds (3-13), were isolated from the twigs and leaves of Picrasma quassioides. Comprehensive spectroscopic analyses and NMR calculation with DP4+ analysis were used to identify their structures. Moreover, of all these compounds, compound 4 showed a week inhibition rate in the anti-inflammatory screening results against mouse macrophage J774A.1 cell.

Quassinoids from Eurycoma longifolia and their bone formation evaluation in zebrafish, C3H10 cells and silico.

Phytochemicals with bone formation potential in traditional medicines captured more and more attentions due to their advantages to bone loss and fewer side effects. As a famous aphrodisiac phytomedicine, Eurycoma longifolia (EL) has acquired general recognition in improving male sexual health, and thus been considered as traditional medicine for the treatment of androgen-deficient osteoporosis. Although the aqueous extract of EL had been proved to be beneficial to bone loss, the active constituents and the mechanisms underlying the effects are still obscure. The current study performed a chemical investigation on the roots of EL, which resulted in the isolation and identification of ten quassinoids (EL-1-EL-10), and then conducted their osteogenic activity evaluations in vivo zebrafish model with or without dexamethasone (Dex) and in vitro C3H10 cell model. The result displayed that most tested concentrations of EL-1-EL-5 could significantly increase the mineralization areas and integrated optical densities (IODs) of skull in both zebrafish model. The majority tested concentrations of EL-1-EL-5 could also improve the mRNA expression of early osteogenic associated genes ALPL, Runx2a, Sp7 in zebrafish model without Dex, but only a few could accelerate the mRNA expression of late osteogenic associated genes OCN. These results suggested the ability of EL-1-EL-5 to increase bone formation mainly by accelerating osteogenic differentiation at the early stage. The structure-based virtual screening based on the pharmacophores in ePharmaLib, as well as the molecular docking study, implied that the effects of the quassinoids (EL-1-EL-5) on the enhancement of bone formation might be related with improving the content and the activity of androgen through binding with CYP19A, SHBG and AKR1C2, and activating bone metabolism-related ANDR target genes and signal pathways by combining with ANDR directly. Although the assumptions are in silico model-based and further in vitro and in vivo validations are still necessary, we provided a new perspective to explore the potential of EL to be used as an alternative treatment for not only androgen-deficient osteoporosis, but also estrogen-deficient bone loss, by combining with SHBG.

Recent syntheses and biological profiling of quassinoids.

Quassinoid natural products have gained considerable recognition for their diverse biological properties and their synthetically challenging, highly oxygenated polycyclic structures. Herein, we discuss strategies and tactics in the total synthesis of quassinoids that have been evolving over the past 15 years. Additionally, recent structure-activity relationships and potential biological mechanisms of actions are briefly summarized.

A New C22-Quassinoid with Anti-Pancreatic Adenocarcinoma Activity from Seeds of Brucea javanica.

An undescribed C22-quassinoid named sergeolide A (1) and fifteen known quassinoids (2-16) were obtained from the seeds of Brucea javanica (Simaroubaceae). All chemical structures were established based on spectroscopic data and X-ray diffraction analysis. Sergeolide A (1) is the first example of a naturally occurring C22-quassinoid bearing a butenolide group fused the A ring of the bruceolide skeleton from Brucea genus. And this is the first report of the NMR data for desmethyl-bruceines B (2) and C (3) and the crystal structure for bruceolide (11). In addition, all isolates were evaluated for their anti-pancreatic adenocarcinoma activity by measuring the growth inhibitory of the MIA PaCa-2 cell lines. Consequently, compounds 1, 7-10, and 12-16 exhibited potent anti-pancreatic cancer activity in vitro (IC50 =0.054∼0.357 µM).

Bruceine A protects against diabetic kidney disease via inhibiting galectin-1.

Bruceine A is a natural quassinoid compound extracted from the fruit of the Traditional Chinese Medicine Brucea javanica (L.) Merr. that has various types of various biological activities. However, whether the compound has a protective effect on diabetic kidney disease remains unknown. Galectin-1 is actively involved in a variety of chronic inflammation-relevant human diseases including diabetic kidney disease. Here, we identified Bruceine A as a kidney protective molecule against a model of diabetic kidney disease in db/db mice with potent anti-inflammatory activity both in vitro and in vivo. Mechanistically, by selectively binding to the conserved carbohydrate-recognition domain of galectin-1 and disrupting the interaction between galectin-1 and the receptor for activated protein C kinase 1, Bruceine A was found to inhibit galectin-1-mediated inflammatory signal transduction under high glucose stress in rat mesangial HBZY-1 cells. Thus, our findings reveal Bruceine A as an unidentified galectin-1 inhibitor affording significant protection against diabetic kidney disease and may provide novel pharmacological therapeutics for the disease.

Enhanced ROS-Boosted Phototherapy against Pancreatic Cancer via Nrf2-Mediated Stress-Defense Pathway Suppression and Ferroptosis Induction.

In situ oxygen generation is the most common strategy to boost reactive oxygen species (ROS) for enhancing the efficacy of phototherapy in cancer, including photodynamic therapy (PDT) and photothermal therapy (PTT). However, hyperoxidation or hyperthermia often triggers stress-defense pathways and promotes tumor cell survival, thus severely limiting the therapeutic efficacy. To overcome the tumor hypoxia and thermal resistance existing in phototherapy, we constructed a self-synergistic nanoplatform for tumors by incorporating brusatol, a nuclear factor erythroid 2-related factor (Nrf2) inhibitor, into the silica nanonetwork. It was then sequentially decorated with MnO2 and the photosensitizer chlorin e6 (Ce6) and then coated with poly(ethylene glycol)-folate (PEG-FA)-functionalized polydopamine (PDA) (designated as brusatol/silica@MnO2/Ce6@PDA-PEG-FA). As an oxygen generator, MnO2 can promote ROS production, which not only directly enhances Ce6-mediated PDT but also strengthens PDA-mediated PTT by attacking heat shock proteins (HSPs). Particularly, brusatol could efficiently inhibit the activation of Nrf2 defense pathway under hyperoxidation and hyperthermia and cause glutathione peroxidase 4 (GPX4) and ferritin heavy chain (FTH) inactivation, thereby inducing ferroptosis and ultimately enhancing the phototherapeutic effects. By exploiting these features, brusatol/silica@MnO2/Ce6@PDA-PEG-FA exhibited excellent antitumor efficacy with enhanced PDT and PTT both in in vitro and in vivo studies. Overall, our work highlights a promising strategy against hypoxia- and hyperthermia-associated resistance in phototherapy via suppressing stress-defense system and inducing ferroptosis.

Ailanthone suppresses the activity of human colorectal cancer cells through the STAT3 signaling pathway.

Ailanthone (AIL) is a major quassinoid extracted from the Chinese medicinal herb, Ailanthus altissima, which has been reported to exert anti­proliferative effects on various cancer cells. The present study aimed to investigate the antitumor effects of AIL on HCT116 and SW620 colon cancer cells, and to analyze the underlying molecular mechanisms. CCK­8 assay was used to detect cell viability. Furthermore, colony formation and Transwell assays, and flow cytometry were used to examine the effects of AIL on cell proliferation, apoptosis and migration. Finally, the expression levels of cell cycle control proteins, and caspase and Bcl­2 family­related proteins involved in the regulation of apoptosis, as well as those of cell migration­ and pathway­related proteins were examined using western blot analysis. Reverse transcription­quantitative PCR was used to quantitatively analyze the changes in the JAK and STAT3 gene levels in each group. The in vitro cell function tests revealed that AIL inhibited the proliferation and migration, and induced the apoptosis and cell cycle arrest of HCT116 and SW620 cells. It was further found exerted these effects via the JAK/STAT3 signaling pathway, as well as through caspase and Bcl­2 family proteins. On the whole, the present study demonstrates that AIL suppresses the activity of colon cancer cells via the STAT3 pathway.

Brusatol inhibits laryngeal cancer cell proliferation and metastasis via abrogating JAK2/STAT3 signaling mediated epithelial-mesenchymal transition.

AIMS: This study aimed at investigating the role of Brusatol (BR) on human laryngeal squamous carcinoma cell (Hep-2) to study its underlying mechanism through in vitro and in vivo approaches. MATERIALS AND METHOD: In the present research, we employed various cell-based assays, such as cell proliferation, apoptosis, cell cycle assessment, migration and invasion assays were used to examine the anti-tumor effect of BR on Hep-2 cells. Immunohistochemistry (IHC), qRT-PCR and Western blotting were performed to study the underlying molecular mechanisms. To validate our in vitro findings we used a subcutaneous tumor-bearing model of Balb/c mice with Hep-2 cells of laryngeal carcinoma (LC) to study the inhibitory effect of BR on Hep-2 cells in vivo. KEY FINDINGS: The results indicated that BR markedly inhibited the viability, migration and invasion capacity of Hep-2 cells, with no significant toxic effect on normal Human bronchial epithelial cell line (BEAS-2B). Also, BR induced cellular apoptosis by blocking the cells in S phase to suppress cell proliferation. Immunohistochemistry results revealed that BR inhibited the protein expression levels of epithelial-mesenchymal transition (EMT)-related markers. Mechanistically, western blotting results exhibited that BR could suppress the protein expression of both JAK2/STAT3 and their phosphorylation levels. Our in vivo experiments further validated the anti-tumor effect of BR on Hep-2 cells in vitro, where BR suppressed the growth of xenograft laryngeal tumor without apparent toxicity. SIGNIFICANCE: The present study highlights the anti-LC effect of BR by possibly abrogating JAK2/STAT3 signaling mediated EMT process. BR may be a promising therapeutic candidate for the treatment of LC.

Quassinoids with Inhibitory Activities against Plant Fungal Pathogens from Picrasma javanica.

A bioactivity-guided study on the leaves of Picrasma javanica led to the isolation of 19 quassinoids, including 13 new compounds. The structures of the new compounds were elucidated by a combination of spectroscopic data analysis, X-ray crystallography studies, and electronic circular dichroism (ECD) data interpretation. Compounds 1-7 are rare examples of quassinoids with a keto carbonyl group at C-12. The biological activities of 11 of the more abundant isolates were evaluated against five phytopathogenic fungi in vitro, and several of them including 6 and 15 showed moderate inhibitory effects that were comparative to those of the positive control, carbendazim. In addition, the preliminary structure-activity relationships (SARs) of these quassinoids were also investigated.

Two Novel Quassinoid Glycosides with Antiviral Activity from the Samara of Ailanthus altissima.

Phytochemistry investigations on Ailanthus altissima (Mill.) Swingle, a Simaroubaceae plant that is recognized as a traditional herbal medicine, have afforded various natural products, among which C20 quassinoid is the most attractive for their significant and diverse pharmacological and biological activities. Our continuous study has led to the isolation of two novel quassinoid glycosides, named chuglycosides J and K, together with fourteen known lignans from the samara of A. altissima. The new structures were elucidated based on comprehensive spectra data analysis. All of the compounds were evaluated for their anti-tobacco mosaic virus activity, among which chuglycosides J and K exhibited inhibitory effects against the virus multiplication with half maximal inhibitory concentration (IC50) values of 56.21 ± 1.86 and 137.74 ± 3.57 µM, respectively.

Molecular mechanisms and systemic targeting of NRF2 dysregulation in cancer.

NF-E2-related factor 2 (NRF2) is a master regulator of redox homeostasis and provides cellular protection against oxidants and electrophiles by inducing the expression of a wide array of phase II cytoprotective genes. Until now, a number of NRF2 activators have been developed for treatment of chronic diseases and some are under evaluation in the clinical studies. On the other hand, accumulating evidence indicates that NRF2 confers chemoresistance and radioresistance, and its expression is correlated with poor prognosis in cancer patients. Studies in the last decade demonstrate that diverse mechanisms such as somatic mutations, accumulation of KEAP1 binding proteins, transcriptional dysregulation, oncogene activation, and accumulation of reactive metabolites contribute to NRF2 activation in cancer. In the present review, we illustrate the molecular mechanisms governing the function of NRF2 and explain how they are hijacked in cancer. We also provide some examples of NRF2 inhibitors together with a brief explanation of their mechanisms of action.

Unprecedented Quassinoids from Eurycoma longifolia: Biogenetic Evidence and Antifeedant Effects.

Six new quassinoids (1-6) were isolated from the roots of Eurycoma longifolia, and their structures with absolute configurations were determined unambiguously by spectroscopic analyses and single-crystal X-ray crystallographic experiments. Compounds 1 and 2 are the first members of a new class of quassinoids with an unusual C26 carbon skeleton. Compound 6 features a C20 cage-like scaffold with an unprecedented densely functionalized 2,5-dioxatricyclo[5.2.2.04,8]undecane core. The discovery of the two C26 quassinoids 1 and 2 has provided firm evidence for the better understanding the biogenetic process from C30 triterpenoid precursors to quassinoids. Compound 5 exhibited significant antifeedant activity on the diamondback moth (DBM) larvae and excellent systemic absorption and accumulated properties in Brassica chinensis.

Bruceine D elevates Nrf2 activation to restrain Parkinson's disease in mice through suppressing oxidative stress and inflammatory response.

Parkinson's disease (PD) is neurodegenerative disease, featured by a loss of dopaminergic neurons in the substantia nigra pars compacta (SNpc), characteristic motor symptoms and cognitive impairment. Development of effective therapeutic drugs for PD is necessary. In this study, we investigated the potential of Bruceine D (BD) during PD progression. After establishment of PD mouse models, we found that BD markedly improved the motor function of mice and alleviated chemically induced dopaminergic neuron loss of tyrosine hydroxylase (TH) in the SNpc area. BD treatments markedly repressed the neuroinflammation in SNpc by restricting nuclear factor κB (NF-κB) activation, accompanied with the reduced activity of astrocytes and microglial. BD also improved the antioxidant system in MPTP-challenged mice, as proved by the up-regulated superoxide dismutase (SOD) and glutathione (GSH), and down-regulated malondialdehyde (MDA) in SNpc and striatum (STR). The anti-oxidant effects of BD were regulated by the activation of nuclear factor E2-related factor 2 (Nrf2) signaling, contributing to the expression of Nrf2 down-streaming signals such as heme oxygenase-1 (HO-1), NAD(P)H: quinone oxidoreductase 1 (NQO1) and glutathione cysteine ligase modulatory subunit (GCLM). In MPP+-challenged mouse neurons, BD exhibited cytoprotective effects by improving the Nrf2-meditated antioxidant system and abolished the MPP+-triggered inflammatory response through hindering the activation of the NF-κB signal. The pharmacokinetic parameters and organ distribution findings demonstrated that BD showed a brain tissue targeting function. Moreover, both in vivo and in vitro analysis indicated that BD had few side effects. Collectively, results here demonstrated that BD was effective for the inhibition of dopaminergic neuronal loss and PD progression by activating Nrf2 without toxicity.

Quassilactones A and B, structural characterization of a new class of norquassinoids from Brucea javanica.

Two novel norquassinoids possessing a unique ketal skeleton, designated quassilactones A (1) and B (2), were isolated from the fruits of Brucea javanica (Simaroubaceae). Their structures were established by extensive NMR and HR-ESI-MS spectroscopic analysis. The absolute configuration of 1 was determined through single-crystal X-ray crystallography, and that of 2 was assigned by comparing the calculated electronic and experimental circular dichroism with compound 1. In addition, their cytotoxic activities against three human cancer cell lines and their antimicrobial activities were evaluated.

Three new quassinoids isolated from the wood of Picrasma javanica and their anti-Vpr activities.

Three new quassinoids, javanicinols A and B (1 and 2) and 4-keto-(16S)-methoxyjavanicin B (3), together with three known quassinoids (4-6) were isolated from the chloroform-soluble fraction of the methanol extract of the Picrasma javanica wood. The structures of 1-3 were determined by spectroscopic analyses, including 1D and 2D NMR, HRESIMS, and CD. The anti-HIV-1 viral protein R (Vpr) assay revealed that 1 and 2 exhibited potent anti-Vpr activities at 1.25 µM. Furthermore, the assay also revealed the potent anti-Vpr activities of (16R)-methoxyjavanicin B (7) and (16S)-methoxyjavanicin B (8), which were previously isolated from the Picrasma javanica wood.

Nifedipine inhibits oxidative stress and ameliorates osteoarthritis by activating the nuclear factor erythroid-2-related factor 2 pathway.

Nifedipine is a voltage-gated calcium channel inhibitor widely used in the treatment of hypertension. Nifedipine has been reported to have antioxidant and anti-apoptotic effects and promotes cell proliferation. However, the effects of nifedipine on oxidative stress and apoptosis in osteoarthritic (OA) chondrocytes are still unclear. In this study, we sought to investigate whether nifedipine alleviates oxidative stress and apoptosis in OA through nuclear factor erythroid-2-related factor 2 (Nrf2) activation. The cytotoxicity of nifedipine against human chondrocytes was detected using a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) kit, whereas mRNA and protein expression levels were measured using reverse transcription-polymerase chain reaction (RT-PCR) and Western blotting, respectively. The oxidative stress level was analyzed by measuring reactive oxygen species (ROS), glutathione peroxidase (GSH-px), catalase (CAT) and superoxide dismutase (SOD) activities. The role of Nrf2 in the effect of nifedipine on OA was analyzed using an Nrf2 inhibitor brusatol (BR). The result showed that nifedipine inhibited the expression of matrix metalloprotein(MMP)-13, interleukin (IL)-1ß, IL-6, tumor necrosis factor (TNF)-α, cyclooxygenase (COX)-2, inducible nitric oxide (NO) synthase (iNOS), and prostaglandin E2 (PGE2), as well as reduced ROS production in human OA chondrocytes, which was partially reversed by BR. Nifedipine prevented cartilage degeneration and contributed to the expression of Nrf-2 in chondrocytes. These results indicate that nifedipine inhibited inflammation and oxidative stress in chondrocytes via activation of Nrf-2/HO-1 signaling.

Quassinoids with Insecticidal Activity against Diaphorina citri Kuwayama and Neuroprotective Activities from Picrasma quassioides.

Six new quassinoids, named kumulactone F (1), kumulactone G (2), kumulactone H (4), kumulactone I (5), kumulactone J (6), and kumulactone K (7), a pair of undescribed epimers α- and ß-nigakihemiacetal G (3), 15 known quassinoids (8-22), and a mixture of the known compounds α- and ß-neoquassin (23) were separated from the dried stems of the medical plants Picrasma quassioides. The chemical structures of all of the new compounds were established by spectroscopic data analyses (HR-ESI-MS, 1D and 2D NMR spectroscopy, and electronic circular dichroism (ECD)). Biologically, compounds 9 and 21 showed toxicity toward the Asian citrus psyllid Diaphorina citri Kuwayama with potent activity even equal to that of the positive control (Abamectin), compound 11 exhibited an excellent neuroprotective effect against SH-SY5Y cells which were pretreated by H2O2 with potent activity equal to that of the positive control (Trolox), and none of them showed cytotoxic activity toward the HeLa or A549 cell lines (IC50 > 100 µM).

A novel recombinant javanicin with dual antifungal and anti-proliferative activities.

Resistance to common drugs by microorganisms and cancers has become a major issue in modern healthcare, increasing the number of deaths worldwide. Novel therapeutic agents with a higher efficiency and less side effects for the treatment of certain diseases are urgently needed. Plant defensins have an integral role in a hosts' immune system and are attractive candidates for combatting drug-resistant microorganisms. Interestingly, some of these defensins also showed great potential due to their cytotoxic activity toward cancer cells. In this study, a defensin encoding gene was isolated from five legume seeds using 3' rapid amplification of cDNA ends (3' RACE) with degenerate primers and cDNA cloning strategies. Bioinformatic tools were used for in silico identification and the characterization of new sequences. To study the functional characteristics of these unique defensins, the gene encoded for Sesbania javanica defensin, designated as javanicin, was cloned into pTXB-1 plasmid and expressed in the Escherichia coli Origami 2 (DE3) strain. Under optimized conditions, a 34-kDa javanicin-intein fusion protein was expressed and approximately 2.5-3.5 mg/L of soluble recombinant javanicin was successfully extracted with over 90% purity. Recombinant javanicin displayed antifungal properties against human pathogenic fungi, including resistant strains, as well as cytotoxic activities toward the human breast cancer cell lines, MCF-7 & MDA-MB-231. Recombinant javanicin holds great promise as a novel therapeutic agent for further medical applications.

Relationship between Structural Characteristics and Plant Sources along with Pharmacology Research of Quassinoids.

Quassinoids, one kind of triterpenoids with multiple bioactivities such as anti-cancer, anti-malarial, anti-oxidative, anti-microbial, anti-diabetic, anti-viral, and anti-inflammatory effects, have drawn much attention in recent years. Between 2004 and 2018, the structural characteristics and plant sources of 190 quassinoids were reported. Herein, the structure-activity relationships (SARs) of quassinoids along with the anti-cancer mechanisms of four representative quassinoids, eurycomanone, bruceine D, dehydrobruceine B, and brusatol are discussed. This review might be useful for further research and development of quassinoids.