Brusatol-mediated induction of leukemic cell differentiation and G(1) arrest is associated with down-regulation of c-myc

Plant-derived inducers in tumor differentiation therapy:A systematic review

BACKGROUND

Differentiation therapy, a highly regarded treatment method in tumor research, aims to induce tumor cells to differentiate back to normal cells, deviating from the malignant pathway and returning to a benign state. Its development relies on the continuous discovery of efficient and low-toxic differentiation inducers, including plant-derived active components that offer significant biological utilization and therapeutic potential. For this reason, the exploration of plant-derived inducers, particularly in their application in differentiation therapy, holds great promise in advancing cancer treatment strategies toward more effective and safer alternatives.

PURPOSE

This paper aims to provide a valuable reference for researchers seeking to identify natural, efficient, and low-toxic differentiation inducers from plants and highlights a promising research direction for the application of differentiation therapy in malignant tumor treatment.

METHODS

For the collection of pertinent information, an extensive search was conducted across diverse literature and electronic databases, including PubMed, ScienceDirect, Wiley, ACS, CNKI, Springer, Taylor & Francis, Web of Science, Google Scholar, and Baidu Scholar. This comprehensive approach aimed to retrieve and include all relevant literature from 1985 to 2023. Primary keywords such as "Natural medicinal plant," "Differentiation therapy," and "Differentiation inducer" were utilized, supplemented by secondary search terms including "Cancer," "Tumor," "Herbal medicine," "Induced differentiation," and "Cancer treatment."

RESULTS

This study systematically evaluated the application of plant-derived inducers in tumor-induced differentiation therapy. Through extensive literature review, specific plant components with confirmed differentiation-inducing properties were identified. Furthermore, potential molecular mechanisms underlying this process were outlined, shedding light on the future development of differentiation therapy in cancer treatment.

CONCLUSION

Plant-derived active components exhibit substantial biological utility and therapeutic potential. Delving deeper into the research on these components as differentiation inducers holds promise for the selection of novel cancer drugs and the unveiling of novel pathways for cancer treatment. These results emphasize the importance of continued exploration and in-depth research into natural, efficient, and low-toxic differentiation inducers from plants, which could significantly advance cancer treatment strategies. Moreover, the highlighted research direction underscores the relevance of differentiation therapy in the context of malignant tumor treatment, indicating its potential as a safer and more effective alternative in cancer therapy.

KLF4 suppresses anticancer effects of brusatol via transcriptional upregulating NCK2 expression in melanoma

Brusatol (Bru), a main extract from traditional Chinese medicine Brucea javanica, has been reported to exist antitumor effect in many tumors including melanoma. However, the underlying mechanism in its anti-melanoma effect still need further exploration. Here, we reported that the protein expression of KLF4 in melanoma cells were significantly downregulated in response to brusatol treatment. Overexpression of KLF4 suppressed brusatol-induced melanoma cell apoptosis; while knockdown of KLF4 enhanced antitumor effects of brusatol on melanoma cells not only in vitro but also in vivo. Further studies on the mechanism revealed that KLF4 bound to the promoter of NCK2 directly and facilitated NCK2 transcription, which suppressed the antitumor effect of brusatol on melanoma. Furthermore, our findings showed that miR-150-3p was dramatically upregulated under brusatol treatment which resulted in the downregulation of KLF4. Our results suggested that the miR-150-3p/KLF4/NCK2 axis might play an important role in the antitumour effects of brusatol in melanoma.

A review of Brucea javanica: metabolites, pharmacology and clinical application

This review examines advances in the metabolites, pharmacological research, and therapeutic applications of the medicinal fruit of Brucea javanica (L.) Merr. Brucea javanica (BJ) is derived from the fruit of the Brucea javanica (L.) Merr. There are nearly 200 metabolites present in BJ, and due to the diversity of its metabolites, BJ has a wide range of pharmacological effects. The traditional pharmacological effects of BJ include anti-dysentery, anti-malaria, etc. The research investigating the contemporary pharmacological impacts of BJ mainly focuses on its anti-tumor properties. In the article, the strong monomeric metabolites among these pharmacological effects were preliminarily screened. Regarding the pharmacological mechanism of action, current research has initially explored BJ's pharmacological agent and molecular signaling pathways. However, a comprehensive system has yet to be established. BJ preparations have been utilized in clinical settings and have demonstrated effectiveness. Nevertheless, clinical research is primarily limited to observational studies, and there is a need for higher-quality research evidence to support its clinical application. There are still many difficulties and obstacles in studying BJ. However, it is indisputable that BJ is a botanical drugs with significant potential for application, and it is expected to have broader global usage.

Cytotoxicity of isolated compounds from Picrasma crenata (Vell.) Engl. in animal tumor cell (HTC)

The study aim was to evaluate the cytotoxic activity, using the MTT test [3-(4,5-Dimethilthiazol-2-yl)-2,5-diphenil tetrazolium bromide], from the crude extract of Picrasma crenata (Pau Tenente) and its isolated compounds, quassin and parain, in culture of rat liver tumor cells (HTC). The test was carried out exposing the cells for 24, 48 and 72 hours to concentrations of 5, 10, 50, 100, 200, 300, 400, 500 and 1000 μg of crude extract of Pau Tenente/mL of culture medium and 1, 5, 10, 15, 20, 40, 60, 80 and 100 μg of quassin or parain compounds/mL of culture medium. The absorbances averages results obtained showed that the crude extract did not present cytotoxicity for the HTC cells in all the concentrations and evaluated times. For quassin, the concentrations of 80 and 100 μg/mL were cytotoxic, after 72 hours of treatment. For parain, the concentrations of 1, 5, 20, 40, 60, 80 and 100 µg/mL, in 72 hours, were cytotoxic, revealing a new activity for this compound. Thus, the results demonstrate a first indication of the cytotoxic activity of compounds quassin and parain, adding an important social and economic value to them, and may have application in future research and in pharmaceutical industry.

Brusatol: A potential sensitizing agent for cancer therapy from Brucea javanica

Cancer is currently the most important problem endangering human health. As antitumor drugs have always been the most common methods for treating cancers, searching for new antitumor agents is of great significance. Brusatol, a quassinoid from the seeds of Brucea javanica, exhibits a potent tumor-suppressing effect with improved disease outcome. Studies have shown that brusatol not only shows potential tumor inhibition through multiple pharmacological effects, such as promoting apoptosis and inhibiting metastasis but also exhibits significant synergistic antitumor effects in combination with chemotherapeutic agents and overcoming chemical resistance in a wide range of cancer types. In this paper, the antitumor effects and mechanisms of brusatol were reviewed to provide evidence that brusatol has the exact antitumor efficacy of chemotherapeutic agents and show the potential of brusatol to be developed as a promising antitumor drug.

Natural Products as Cancer Chemo Preventive Agents: Where We Stand

This work briefly reviews cancer chemoprevention. This is a very challenging field, as products with a high level of toxicity such as chemotherapeutic agents may be proposed and accepted only under life-threatening conditions. Cancer chemoprevention is otherwise limited to completely safe substances, preferably having neither toxic nor side effects, administered in relatively low amounts. Phases of clinical trials, therapeutic end-points, and biomarkers of chemoprevention are difficult to be defined. The clinical trials needed to prove the efficacy of chemopreventive agents must be very long and extremely widespread to achieve significance, with many variables difficult to control, and therefore subjected to many confounding factors. This makes them almost impossible. It is, therefore, no surprise, if the progress of chemoprevention has been so far very limited. There are only a few examples of direct use of chemopreventive agents, under investigation, but with anything but established protocols, in addition to indirect uses such as general supplementation with antioxidant, anti-inflammatory, and immune-supportive agents. Cancer chemoprevention remains a potentially very rewarding approach, certainly worth further study, but extremely difficult to pursue, in need of different methodological approaches to producing valuable chemopreventive compounds of clear dosages and benefits.

Phenolic constituents with anti-inflammatory and cytotoxic activities from the rhizomes of Iris domestica

Four undescribed flavonoid glucosides (iridins B-C, tectoridin A and ampelopsinin A); one undescribed phenolic glucoside (diplostephioside B); one undescribed phenolic compound (phenanthrenetriol A); and seventeen known compounds were isolated from the rhizomes of Iris domestica. The chemical structures of the undescribed compounds were established by spectroscopic/spectrometric data interpretation using HRESIMS, NMR, and ECD. Tectoridin A, nigricin A and naringenin exhibited anti-inflammatory activities with inhibition rates of 53.71%, 57.68% and 88.71%, respectively, against the NF-κB signaling pathway at a concentration of 10 μM. 4'-O-methylnyasol (10 μM) exhibited 84.91% antiproliferative activity against the K562 human leukemia cell line with an IC₅₀ value of 4.20 μM.

Role of caspase-3-cleaved/activated PAK2 in brusatol-triggered apoptosis of human lung cancer A549 cells

Brusatol, a major quassinoid extract of Bruceae fructus, is an important bioactive component with antineoplastic capacity. Several beneficial pharmacological and biological properties of brusatol have been uncovered to date, including anti-inflammatory, anticolitis, antimalarial, and anticancer activities. To confer anticancer benefits, brusatol is reported to effectively inhibit the Nrf2-mediated antioxidant response and trigger apoptotic signaling. In this study, we investigated the regulatory mechanisms underlying apoptotic processes in brusatol-treated A549 cells in detail. Our experiments showed that brusatol induces cell death through intracellular ROS-triggered mitochondria-dependent apoptotic events and does not involve necrosis. Mechanistically, p21-activated protein kinase 2 (PAK2) was cleaved by caspase-3 to generate an activated p34 fragment involved in brusatol-induced apoptosis of A549 cells. Notably, PAK2 knockdown led to downregulation of caspase-3-mediated PAK2 activity, in turn, effectively attenuating brusatol-induced apoptosis, highlighting a crucial role of caspase-3-activated PAK2 in this process. Moreover, knockdown of PAK2 resulted in significant inhibition of c-Jun N-terminal kinase (JNK) activity in brusatol-treated A549 cells, clearly suggesting that JNK serves as a downstream substrate of caspase-3-cleaved/activated PAK2 in the apoptotic cascade. SP600125, a specific JNK inhibitor, significantly suppressed brusatol-induced JNK activity but only partially prevented apoptosis, implying that JNK serves as only one of a number of substrates for PAK2 in the brusatol-triggered apoptotic cascade. Based on the collective results, we propose a signaling cascade model for brusatol-induced apoptosis in human A549 cells involving ROS, caspases, PAK2, and JNK.

Antitumor Effect of Brusatol in Acute Lymphoblastic Leukemia Models Is Triggered by Reactive Oxygen Species Accumulation

Acute lymphoblastic leukemia (ALL) is one of the most common hematological malignancies at pediatric ages and is characterized by different chromosomal rearrangements and genetic abnormalities involved in the differentiation and proliferation of lymphoid precursor cells. Brusatol is a quassinoid plant extract extensively studied due to its antineoplastic effect through global protein synthesis and nuclear factor erythroid 2-related factor-2 (NRF2) signaling inhibition. NRF2 is the main regulator of cellular antioxidant response and reactive oxygen species (ROS), which plays an important role in oxidative stress regulation. This study aimed to evaluate the effect of brusatol in in vitro models of ALL. KOPN-8 (B-ALL), CEM (T-ALL), and MOLT-4 (T-ALL) cell lines were incubated with increasing concentrations of brusatol, and the metabolic activity was evaluated using the resazurin assay. Flow cytometry was used to evaluate cell death, cell cycle, mitochondrial membrane potential (Δψmit), and to measure ROS and reduced glutathione (GSH) levels. Our results show that brusatol promoted a decrease in metabolic activity in ALL cell lines in a time-, dose-, and cell-line-dependent manner. Brusatol induced a cytostatic effect by cell cycle arrest in G0/G1 in all cell lines; however, cell death mediated by apoptosis was only observed in T-ALL cells. Brusatol leads to an oxidative stress imbalance by the increase in ROS levels, namely, superoxide anion. Redox imbalance and cellular apoptosis induced by brusatol are highly modulated by mitochondria disruption as a decrease in mitochondrial membrane potential is detected. These data suggest that brusatol might represent a new therapeutic approach for acute lymphoblastic leukemia, particularly for ALL T-cell lineage.

Jiyuan oridonin A induces differentiation of acute myeloid leukemia cells including leukemic stem-like cells

Acute myeloid leukemia (AML) is an aggressive form of hematological neoplasia characterized by failure of myeloid differentiation. AML is a leading cause of death from leukemia. Cytarabine chemotherapy resistance is a major source of refractory/relapsed AML. A major obstacle to the successful treatment of AML results from residual disease maintained by leukemic stem cells (LSCs), which are mostly resistant to conventional chemotherapy. Here, we determined the effect of a natural compound, Jiyuan oridonin A (JOA), on the differentiation blockade in the M2 subtype [particularly t (8;21)] of AML cells, M3 subtype of AML cells (APL cells), and leukemic stem-like cells both in vitro and in vivo. We found that JOA induced cell differentiation and suppressed the colony formation capacity in various AML cell lines (Kasumi-1, KG-1, MUTZ-8, NB4, and HL-60) without eliciting apoptosis. The mechanism of JOA-induced cell differentiation depends on the specificity of cell type. JOA mediated the differentiation of Kasumi-1 cells by activating the hematopoietic cell lineage signaling pathway, while inhibition of c-MYC was involved in the JOA-induced differentiation of NB4 cells. Moreover, JOA was identified to target leukemic stem-like cells by induced cell differentiation in vivo. These findings demonstrated that JOA could inhibit the proliferation of M2 and M3 subtypes of AML cells and leukemic stem-like cells by overcoming the differentiation blockade, which may offer a novel therapeutic strategy for AML to overcome relapse and drug resistance in patients with AML. Our findings highlight the possibility of using compounds like JOA as a promising differentiation-induced agent for the treatment of AML.

Combining empirical knowledge, in silico molecular docking and ADMET profiling to identify therapeutic phytochemicals from Brucea antidysentrica for acute myeloid leukemia

Acute myeloid leukemia (AML) is one of the deadly cancers. Chemotherapy is the first-line treatment and the only curative intervention is stem cell transplantation which are intolerable for aged and comorbid patients. Therefore, finding complementary treatment is still an active research area. For this, empirical knowledge driven search for therapeutic agents have been carried out by long and arduous wet lab processes. Nonetheless, currently there is an accumulated bioinformatics data about natural products that enabled the use of efficient and cost effective in silico methods to find drug candidates. In this work, therefore, we set out to computationally investigate the phytochemicals from Brucea antidysentrica to identify therapeutic phytochemicals for AML. We performed in silico molecular docking of compounds against AML receptors IDH2, MCL1, FLT3 and BCL2. Phytochemicals were docked to AML receptors at the same site where small molecule drugs were bound and their binding affinities were examined. In addition, random compounds from PubChem were docked with AML targets and their docking score was compared with that of phytochemicals using statistical analysis. Then, non-covalent interactions between phytochemicals and receptors were identified and visualized using discovery studio and Protein-Ligand Interaction Profiler web tool (PLIP). From the statistical analysis, most of the phytochemicals exhibited significantly lower (p-value ≤ 0.05) binding energies compared with random compounds. Using cutoff binding energy of less than or equal to one standard deviation from the mean of the phytochemicals’ binding energies for each receptor, 12 phytochemicals showed considerable binding affinity. Especially, hydnocarpin (-8.9 kcal/mol) and yadanzioside P (-9.4 kcal/mol) exhibited lower binding energy than approved drugs AMG176 (-8.6 kcal/mol) and gilteritinib (-9.1 kcal/mol) to receptors MCL1 and FLT3 respectively, indicating their potential to be lead molecules. In addition, most of the phytochemicals possessed acceptable drug-likeness and absorption, distribution, metabolism, excretion, and toxicity (ADMET) properties. Based on the binding affinities as exhibited by the molecular docking studies supported by the statistical analysis, 12 phytochemicals from Brucea antidysentrica (1,11-dimethoxycanthin-6-one, 1-methoxycanthin-6-one, 2-methoxycanthin-6-one, beta-carboline-1-propionic acid, bruceanol A, bruceanol D, bruceanol F, bruceantarin, bruceantin, canthin-6-one, hydnocarpin, and yadanzioside P) can be considered as candidate compounds to prevent and manage AML. However, the phytochemicals should be further studied using in vivo & in vitro experiments on AML models. Therefore, this study concludes that combination of empirical knowledge, in silico molecular docking and ADMET profiling is useful to find natural product-based drug candidates. This technique can be applied to other natural products with known empirical efficacy.

Potential cancer treatment effects of brusatol or eriodictyol combined with 5-fluorouracil (5-FU) in colorectal cancer cell

Colorectal cancer is among the most frequently diagnosed cancers in patients today. In the treatment of this disease, combination or multicomponent therapy has been identified as a potential method to improve patient response and delay side effects. The aim of this study was to determine the effects on cell viability of commercial Bru and Erio used together with the anticancer drug 5-FU in the human colorectal cancer (CRC) cell line (HT-29 cell line) for the first time, as far as can be determined from available literature at this time. Additionally, the research seeks to study any potential effects on apoptosis. For this purpose, the effects of independent and combined treatments of the aforementioned agents on cell viability were investigated through the MTT experiment. Apoptotic effects were determined by Annexin V/PI and real-time PCR methods. In addition, a cell cycle analysis was used to determine the distribution of cells in the cycle. Data from experiments for 48 h showed that Bru, alone or in combination with 5-FU, is capable of causing an increase in the percentage of apoptotic cells in HT-29 cells compared to those of Erio alone or in combination with 5-FU. A significant increase in the level of bax and caspase-3 apoptotic genes was also detected in combinations of IC₅₀ concentrations of Bru and 5-FU. These findings suggest that unlike Erio, Bru alone or in combination with 5-FU may be useful for increasing the effects of 5-FU used in the treatment of CRC and to provide data on alternative treatment approaches.

A Review on Mechanistic Insight of Plant Derived Anticancer Bioactive Phytocompounds and Their Structure Activity Relationship

Cancer is a disorder that rigorously affects the human population worldwide. There is a steady demand for new remedies to both treat and prevent this life-threatening sickness due to toxicities, drug resistance and therapeutic failures in current conventional therapies. Researchers around the world are drawing their attention towards compounds of natural origin. For decades, human beings have been using the flora of the world as a source of cancer chemotherapeutic agents. Currently, clinically approved anticancer compounds are vincristine, vinblastine, taxanes, and podophyllotoxin, all of which come from natural sources. With the triumph of these compounds that have been developed into staple drug products for most cancer therapies, new technologies are now appearing to search for novel biomolecules with anticancer activities. Ellipticine, camptothecin, combretastatin, curcumin, homoharringtonine and others are plant derived bioactive phytocompounds with potential anticancer properties. Researchers have improved the field further through the use of advanced analytical chemistry and computational tools of analysis. The investigation of new strategies for administration such as nanotechnology may enable the development of the phytocompounds as drug products. These technologies have enhanced the anticancer potential of plant-derived drugs with the aim of site-directed drug delivery, enhanced bioavailability, and reduced toxicity. This review discusses mechanistic insights into anticancer compounds of natural origins and their structural activity relationships that make them targets for anticancer treatments.

Revisiting therapeutic strategies for ovarian cancer by focusing on redox homeostasis

Recent advances in molecular genetics have expanded our understanding of ovarian cancer. High levels of reactive oxygen species (ROS) and upregulation of antioxidant genes are common characteristic features of human cancers. This review reconsiders novel therapeutic strategies for ovarian cancer by focusing on redox homeostasis. A literature search was performed for preclinical and clinical studies published between January 1998 and October 2021 in the PubMed database using a combination of specific terms. ROS serves a central role in tumor suppression and progression by inducing DNA damage and mutations, genomic instability, and aberrant anti- and pro-tumorigenic signaling. Cancer cells increase their antioxidant capacity to neutralize the extra ROS. Additionally, antioxidants, such as CD44 variant isoform 9 (CD44v9) and nuclear factor erythroid 2-related factor 2 (Nrf2), mediate redox homeostasis in ovarian cancer. Furthermore, studies conducted on different cancer types revealed the dual role of antioxidants in tumor progression and inhibition. However, in animal models, genetic loss of antioxidant capacity in the host cannot block cancer initiation and progression. Host-derived antioxidant systems are essential to suppress carcinogenesis, suggesting that antioxidants serve a pivotal role in suppressing cancer development. By contrast, antioxidant activation in cancer cells confers aggressive phenotypes. Antioxidant inhibitors can promote cancer cell death by enhancing ROS levels. Concurrent inhibition of CD44v9 and Nrf2 may trigger apoptosis induction, potentiate chemosensitivity and enhance antitumor activities through the ROS-activated p38/p21 pathway. Antioxidants may have tumor-promoting and -suppressive functions. Therefore, an improved understanding of the role of antioxidants in redox homeostasis and developing antioxidant-specific inhibitors is necessary for treating ovarian cancer.

Brusatol has therapeutic efficacy in non-small cell lung cancer by targeting Skp1 to inhibit cancer growth and metastasis

Skp1-Cul1-F-box protein (SCF) ubiquitin E3 ligases play important roles in cancer development and serve as a promising therapeutic target in cancer therapy. Brusatol (Bru), a known Nrf2 inhibitor, holds promise for treating a wide range of tumors; however, the direct targets of Bru and its anticancer mode of action remain unclear. In our study, 793 Bru-binding candidate proteins were identified by using a biotin-brusatol conjugate (Bio-Bru) followed by streptavidin-affinity pull down-based mass spectrometry. We found that Bru can directly bind to Skp1 and disrupt the interactions of Skp1 with the F-box protein Skp2, leading to the inhibition of the Skp2-SCF E3 ligase. Bru inhibited both proliferation and migration via promoting the accumulation of the substrates p27 and E-cadherin; Skp1 overexpression attenuated while Skp1 knockdown enhanced these effects of Bru in non-small cell lung cancer (NSCLC) cells. Moreover, Bru binding to Skp1 also inhibited the β-TRCP-SCF E3 ligase. In both subcutaneous and orthotopic NSCLC xenografts, Bru significantly inhibited the growth and metastasis of NSCLC through targeting SCF complex and upregulating p27 and E-cadherin protein levels. These data demonstrate that Bru is a Skp1-targeting agent that may have therapeutic potentials in lung cancer.

Synthesis and Encapsulation of Ajuga parviflora Extract with Zeolitic Imidazolate Framework-8 and Their Therapeutic Action against G+ and G- Drug-Resistant Bacteria

Infectious diseases caused by bacteria have become a public health issue. Antibiotic therapy for infectious disorders, as well as antibiotic overuse, has resulted in antibiotic-resistant bacterial strains. Zeolitic imidazolate framework-8 (ZIF-8) possesses a wide surface area, high porosity, variable functionality, and potential drug carriers. We have established a clear method for making a nanoscale APE@ZIF-8 nanocomposite agent with outstanding antibacterial activity against methicillin-resistant Staphylococcus aureus (MRSA) and cephalosporin-carbapenem-resistant Escherichia coli (CCREC). We present a unique approach for encapsulating molecules ofAjuga parviflora extract (APE) with ZIF-8. APE@ZIF-8 has a positive charge. By electrostatic contact with the negatively charged bacterial surface of S. aureus and E. coli, APE@ZIF-8 NPs produce reactive oxygen species (ROS) that damage bacterial cell organelles. As a result, the APE@ZIF-8 nanocomposite offers limitless application potential in the treatment of infectious disorders caused by drug-resistant gram-positive and gram-negative bacteria.

A Concise Enantioselective Approach to Quassinoids

A synthetic approach to quassinoids is described. The route to the tetracyclic core relies on an efficient and selective annulation between two unsaturated carbonyl components that is initiated by catalytic hydrogen atom transfer from an iron hydride to an alkene. Application of this strategy allows for enantioselective synthesis of quassin, which is prepared in 14 steps from commercially available starting material.

Brusatol Inhibits Proliferation and Invasion of Glioblastoma by Down-Regulating the Expression of ECM1

Brusatol (Bru), a Chinese herbal extract, has a variety of anti-tumor effects. However, little is known regarding its role and underlying mechanism in glioblastoma cells. Here, we found that Bru could inhibit the proliferation of glioblastoma cells in vivo and in vitro. Besides, it also had an inhibitory effect on human primary glioblastoma cells. RNA-seq analysis indicated that Bru possibly achieved these effects through inhibiting the expression of extracellular matrix protein 1 (ECM1). Down-regulating the expression of ECM1 via transfecting siRNA could weaken the proliferation and invasion of glioblastoma cells and promote the inhibitory effect of Bru treatment. Lentivirus-mediated overexpression of ECM1 could effectively reverse this weakening effect. Our findings indicated that Bru could inhibit the proliferation and invasion of glioblastoma cells by suppressing the expression of ECM1, and Bru might be a novel effective anticancer drug for glioblastoma cells.

Inhibition of Nrf2-mediated glucose metabolism by brusatol synergistically sensitizes acute myeloid leukemia to Ara-C

Chemotherapy resistance remains to be the primary barrier to acute myeloid leukemia (AML) treatment failure. Nuclear factor-erythroid 2-related factor 2 (Nrf2) has been well established as a truly pleiotropic transcription factor. Inhibition of Nrf2 function increases the sensitivity of various chemotherapeutics and overcomes chemoresistance effectively. Brusatol (Bru) has been reported to decrease Nrf2 protein expression specifically by ubiquitin degradation of Nrf2. However, it remains elusive whether combination of Brusatol and Cytarabine (Ara-C) elicits a synergistic antitumor effect in AML. Our results demonstrated that combination of Ara-C and Brusatol synergistically exerted remarkable pro-apoptosis effect in HL-60 and THP-1 cells. Mechanistically, synergistic anti-tumor effect of Ara-C/Brusatol in AML cells is mediated by attenuating Nrf2 expression. To our surprise, Nrf2 inhibition by Brusatol causes downregulation of the expression of glycolysis-related proteins and decreased glucose consumption and lactate production, whereas the level of ROS production was unaffected. The activation of Nrf2 by Sulforaphane (SFP) could reverse the chemotherapeutic effect and changes of glycolysis of concomitant of Ara-C with Brusatol in AML cell lines. Additionally, Ara-C/Brusatol co-treatment decreased Glucose-6-phosphate dehydrogenase (G6PD) protein expression and increased the sensitivity of Ara-C. Moreover, the mouse xenograft in vivo experiment confirmed that combining Ara-C with Brusatol exerted stronger antileukemia than Ara-C alone. The efficacy, together with the mechanistic observations, reveals the potential of simultaneously giving these two drugs and provides a rational basis for targeting glucose catabolism in future clinical therapeutic approach.

Brusatol Inhibits Tumor Growth and Increases the Efficacy of Cabergoline against Pituitary Adenomas

Cabergoline (CAB) is the first choice for treatment of prolactinoma and the most common subtype of pituitary adenoma. However, drug resistance and lack of effectiveness in other pituitary tumor types remain clinical challenges to this treatment. Brusatol (BT) is known to inhibit cell growth and promote apoptosis in a variety of cancer cells. In our present studies, we investigate the effects of BT on pituitary tumor cell proliferation in vitro and in vivo. BT treatment resulted in an increase in Annexin V-expressing cells and promoted the expression of apoptosis-related proteins in rat and human pituitary tumor cells. Investigation of the mechanism underlying this effect revealed that BT increased the production of reactive oxygen species (ROS) and inhibited the phosphorylation of 4EBP1 and S6K1. Furthermore, treatment with a combination of BT and CAB resulted in greater antitumor effects than either treatment alone in nude mice and pituitary tumor cells. Collectively, our results suggest that the BT-induced ROS accumulation and inhibition of mTORC1 signaling pathway leads to inhibition of tumor growth. Combined use of CAB and BT may increase the clinical effectiveness of treatment for human pituitary adenomas.

Natural products as drugs and tools for influencing core processes of eukaryotic mRNA translation

Eukaryotic protein synthesis is the highly conserved, complex mechanism of translating genetic information into proteins. Although this process is essential for cellular homoeostasis, dysregulations are associated with cellular malfunctions and diseases including cancer and diabetes. In the challenging and ongoing search for adequate treatment possibilities, natural products represent excellent research tools and drug leads for new interactions with the translational machinery and for influencing mRNA translation. In this review, bacterial-, marine- and plant-derived natural compounds that interact with different steps of mRNA translation, comprising ribosomal assembly, translation initiation and elongation, are highlighted. Thereby, the exact binding and interacting partners are unveiled in order to accurately understand the mode of action of each natural product. The pharmacological relevance of these compounds is furthermore assessed by evaluating the observed biological activities in the light of translational inhibition and by enlightening potential obstacles and undesired side-effects, e.g. in clinical trials. As many of the natural products presented here possess the potential to serve as drug leads for synthetic derivatives, structural motifs, which are indispensable for both mode of action and biological activities, are discussed. Evaluating the natural products emphasises the strong diversity of their points of attack. Especially the fact that selected binding partners can be set in direct relation to different diseases emphasises the indispensability of natural products in the field of drug development. Discovery of new, unique and unusual interacting partners again renders them promising tools for future research in the field of eukaryotic mRNA translation.

Development of Potential Antitumor Agents from the Scaffolds of Plant-Derived Terpenoid Lactones

Naturally occurring terpenoid lactones and their synthetic derivatives have attracted increasing interest for their promising antitumor activity and potential utilization in the discovery and design of new antitumor agents. In the present perspective article, selected plant-derived five-membered γ-lactones and six-membered δ-lactones that occur with terpenoid scaffolds are reviewed, with their structures, cancer cell line cytotoxicity and in vivo antitumor activity, structure-activity relationships, mechanism of action, and the potential for developing cancer chemotherapeutic agents discussed in each case. The compounds presented include artemisinin (ART, 1), parthenolide (PTL, 2), thapsigargin (TPG, 3), andrographolide (AGL, 4), ginkgolide B (GKL B, 5), jolkinolide B (JKL B, 6), nagilactone E (NGL E, 7), triptolide (TPL, 8), bruceantin (BRC, 9), dichapetalin A (DCT A, 10), and limonin (LMN, 11), and their naturally occurring analogues and synthetic derivatives. It is hoped that this contribution will be supportive of the future development of additional efficacious anticancer agents derived from natural products.

Brusatol: A potential anti-tumor quassinoid from Brucea javanica

Brusatol, a triterpene lactone compound mainly from Brucea javanica, sensitizes a broad spectrum of cancer cells. It is known as a specific inhibitor of nuclear factor-erythroid 2-related factor 2 (Nrf2) pathway. In this review, we provide a comprehensive overview on the antitumor effect and molecular mechanisms of brusatol in vitro and in vivo. This review also covers pharmacokinetics studies, modification of dosages forms of brusatol. Increasing evidences have validated the value of brusatol as a chemotherapeutic agent in cancers, which may contribute to drug development and clinical application.

Quassinoid analogs with enhanced efficacy for treatment of hematologic malignancies target the PI3Kγ isoform

Development of novel PI3K inhibitors is an important strategy to overcome their resistance and poor tolerability in clinical trials. The quassinoid family member Brusatol shows specific inhibitory activity against hematologic malignancies. However, the mechanism of its anti-cancer activity is unknown. We investigated the anti-cancer activity of Brusatol on multiple hematologic malignancies derived cell lines. The results demonstrated that the PI3Kγ isoform was identified as a direct target of Brusatol, and inhibition was dramatically reduced on cells with lower PI3Kγ levels. Novel synthetic analogs were also developed and tested in vitro and in vivo. They shared comparable or superior potency in their ability to inhibit malignant hematologic cell lines, and in a xenograft transplant mouse model. One unique analog had minimal toxicity to normal human cells and in a mouse model. These new analogs have enhanced potential for development as a new class of PI3K inhibitors for treatment of hematologic malignancies.

Pei et al. demonstrate that PI3Kγ isoform is a direct target of Brusatol, a natural compound with inhibitory activity against hematologic malignancies. They further develop several Brusatol analogs with superior in vitro and in vivo anti-cancer activity.

Small molecular Nrf2 inhibitors as chemosensitizers for cancer therapy

The basic leucine zipper transcription factor Nrf2 is the primary regulator of cellular oxidative stress. Activation of Nrf2 is regarded as a potential preventive and therapeutic strategy. However, aberrant hyperactivation of Nrf2 is found in a variety of cancers and promotes cancer progression and metastasis. Moreover, constitutive activation of Nrf2 confers cancer cells resistance to chemo- and radio-therapy. Thus, inhibiting Nrf2 could be a new therapeutic strategy for cancer. With the aim of accelerating the discovery and development of novel Nrf2 inhibitors, we summarize the biological and pathological functions of Nrf2 in cancer. Furthermore, the recent studies of small molecular Nrf2 inhibitors and potential Nrf2 inhibitory mechanisms are also summarized in this review.

Brusatol, an NRF2 inhibitor for future cancer therapeutic

Background

Natural products from herbal medicines have long been investigated for their potentials as cancer therapeutics. Besides the development of several herbal medicine-derived anti-cancer agents, such as paclitaxel, vincristine and podophyllotoxin, many recent laboratory findings demonstrated that brusatol, a quassinoid from the seeds of Brucea sumatrana, exhibits potent tumor suppressing effect with improved disease outcome. Our recent finding further demonstrated that brusatol synergizes with the intrinsic metabolic burden in cancer cells.

Main body

Here, we summarized the recent investigations of brusatol as an experimental therapeutic for human malignancies, such as leukemia, lung cancer, pancreatic cancer and brain tumor. We also discussed the molecular target brusatol, with a focus on the Nuclear factor erythroid 2-related factor 2 (NRF2)-guided gene transcription, as well as glutathione de novo synthesis. Further, we discussed the challenges and future applications of brusatol for cancer therapy.

Conclusion

In conclusion, we believe increasing evidences have shown the value of brusatol as a novel strategy for cancer treatment, which may indicate future drug development and clinical translation.

The protein synthesis inhibitor brusatol normalizes high-fat diet-induced glucose intolerance in male C57BL/6 mice: role of translation factor eIF5A hypusination

The naturally occurring quassinoid compound brusatol improves the survival of insulin-producing cells when exposed to the proinflammatory cytokines IL-1β and IFN-γ in vitro. The aim of the present study was to investigate whether brusatol also promotes beneficial effects in mice fed a high-fat diet (HFD), and if so, to study the mechanisms by which brusatol acts. In vivo, we observed that the impaired glucose tolerance of HFD-fed male C57BL/6 mice was counteracted by a 2 wk treatment with brusatol. Brusatol treatment improved both β-cell function and peripheral insulin sensitivity of HFD-fed mice. In vitro, brusatol inhibited β-cell total protein and proinsulin biosynthesis, with an ED50 of ∼40 nM. In line with this, brusatol blocked cytokine-induced iNOS protein expression via inhibition of iNOS mRNA translation. Brusatol may have affected protein synthesis, at least in part, via inhibition of eukaryotic initiation factor 5A (eIF5A) hypusination, as eIF5A spermidine association and hypusination in RIN-5AH cells was reduced in a dose- and time-dependent manner. The eIF5A hypusination inhibitor GC7 promoted a similar effect. Both brusatol and GC7 protected rat RIN-5AH cells against cytokine-induced cell death. Brusatol reduced eIF5A hypusination and cytokine-induced cell death in EndoC-βH1 cells as well. Finally, hypusinated eIF5A was reduced in vivo by brusatol in islet endocrine and endothelial islet cells of mice fed an HFD. The results of the present study suggest that brusatol improves glucose intolerance in mice fed an HFD, possibly by inhibiting protein biosynthesis and eIF5A hypusination.-Turpaev, K., Krizhanovskii, C., Wang, X., Sargsyan, E., Bergsten, P., Welsh, N. The protein synthesis inhibitor brusatol normalizes high-fat diet-induced glucose intolerance in male C57BL/6 mice: role of translation factor eIF5A hypusination.

UVA Irradiation Enhances Brusatol-Mediated Inhibition of Melanoma Growth by Downregulation of the Nrf2-Mediated Antioxidant Response

Brusatol (BR) is a potent inhibitor of Nrf2, a transcription factor that is highly expressed in cancer tissues and confers chemoresistance. UVA-generated reactive oxygen species (ROS) can damage both normal and cancer cells and may be of potential use in phototherapy. In order to provide an alternative method to treat the aggressive melanoma, we sought to investigate whether low-dose UVA with BR is more effective in eliminating melanoma cells than the respective single treatments. We found that BR combined with UVA led to inhibition of A375 melanoma cell proliferation by cell cycle arrest in the G1 phase and triggers cell apoptosis. Furthermore, inhibition of Nrf2 expression attenuated colony formation and tumor development from A375 cells in heterotopic mouse models. In addition, cotreatment of UVA and BR partially suppressed Nrf2 and its downstream target genes such as HO-1 along with the PI3K/AKT pathway. We propose that cotreatment increased ROS-induced cell cycle arrest and cellular apoptosis and inhibits melanoma growth by regulating the AKT-Nrf2 pathway in A375 cells which offers a possible therapeutic intervention strategy for the treatment of human melanoma.

Synergistic antitumor effect of brusatol combined with cisplatin on colorectal cancer cells

Colorectal cancer (CRC) is a common and life-threatening type of malignant cancer, which is associated with a high mortality rate. Cisplatin (CDDP) is a commonly used chemotherapy drug with significant side effects. Brusatol (BR) is one of the principal chemical compounds isolated from the Chinese herb Bruceae Fructus, which has been reported to markedly inhibit the proliferation of numerous cancer cell lines. The present study aimed to investigate the possible synergistic anticancer effects of CDDP combined with BR on CT-26 cells, and to evaluate the underlying mechanisms of action. The growth inhibitory effects of BR, CDDP, and BR and CDDP cotreatment on CT-26 cells were assessed by MTT assay. Cell apoptosis were determined by flow cytometry and western blot analysis. The results indicated that compared with single-agent treatment, cotreatment of CT-26 cells with CDDP and BR synergistically inhibited cell proliferation and increased cellular apoptosis. Furthermore, treatment of CT-26 cells with CDDP and BR resulted in a marked increase in the release of cytosolic cytochrome c, decreased expression of procaspase-3 and procaspase-9, and upregulation of the B-cell lymphoma 2 (Bcl-2)-associated X protein/Bcl-2 ratio compared with treatment with BR or CDDP alone. These results strongly suggested that the combination of CDDP and BR was able to produce a synergistic antitumor effect in CRC cells, thus providing a solid foundation for further development of this combination regimen into an effective therapeutic method for CRC.

Nrf2 inhibition affects cell cycle progression during early mouse embryo development

Brusatol, a quassinoid isolated from the fruit of Bruceajavanica, has recently been shown to inhibit nuclear factor erythroid 2-related factor 2 (Nrf2) via Keap1-dependent ubiquitination and proteasomal degradation or protein synthesis. Nrf2 is a transcription factor that regulates the cellular defense response. Most studies have focused on the effects of Nrf2 in tumor development. Here, the critical roles of Nrf2 in mouse early embryonic development were investigated. We found that brusatol treatment at the zygotic stage prevented the early embryo development. Most embryos stayed at the two-cell stage after 5 days of culture (P < 0.05). This effect was associated with the cell cycle arrest, as the mRNA level of CDK1 and cyclin B decreased at the two-cell stage after brusatol treatment. The embryo development potency was partially rescued by the injection of Nrf2 CRISPR activation plasmid. Thus, brusatol inhibited early embryo development by affecting Nrf2-related cell cycle transition from G₂ to M phase that is dependent on cyclin B-CDK1 complex.

Brusatol-Mediated Inhibition of c-Myc Increases HIF-1α Degradation and Causes Cell Death in Colorectal Cancer under Hypoxia

HIF-1 (hypoxia-inducible factor-1) regulates the expression of ~100 genes involved in angiogenesis, metastasis, tumor growth, chemoresistance and radioresistance, underscoring the growing interest in targeting HIF-1 for cancer control. In the present study, we investigated the molecular mechanisms underlying brusatol-induced HIF-1α degradation and cell death in colorectal cancer under hypoxia (0.5% O₂). Under hypoxia, pretreatment of cancer cells with brusatol increased HIF-1α degradation and cancer cell death in a dose-dependent manner. This effect was mediated by activation of prolyl hydroxylases (PHDs), as evidenced by the block of brusatol-induced HIF-1α degradation and cancer cell death by both pharmacological inhibition and siRNA-mediated knockdown of PHDs. In addition, a ferrous iron chelator (2,2'-bypyridyl) blocked brusatol-induced degradation of HIF-1α and cancer cell death in hypoxia by inhibiting PHD activation. We further found that brusatol inhibited c-Myc expression, and showed that overexpression of c-Myc prevented brusatol-induced degradation of HIF-1α and cancer cell death by increasing mitochondrial ROS production and subsequent ROS-mediated transition of ferrous iron to ferric iron. Consistent with these results, treatment of tumor-bearing mice with brusatol significantly suppressed tumor growth by promoting PHD-mediated HIF-1α degradation. Collectively, our results suggest that brusatol-mediated inhibition of c-Myc/ROS signaling pathway increases HIF-1α degradation by promoting PHD activity and induces cell death in colorectal cancer under hypoxia

Determination of brusatol in plasma and tissues by LC-MS method and its application to a pharmacokinetic and distribution study in mice

OBJECTIVES

The quassinoid brusatol, which can be isolated from Brucea javanica (L.) Merr., becomes popularly studied because of its anti-tumor activity. In order to further investigate brusatol and extend its applications, a sensitive analytical method for determination of brusatol in biological samples is essential. However, few methods had been reported until now. In this study, a highly sensitive and reproducible LC-MS method for simultaneous quantification of brusatol in mouse plasma and tissues was developed and validated.

METHOD

Plasma samples and tissue homogenate were extracted with diethyl ether after addition of the internal standard solution(IS). The supernatant was blown to dryness with nitrogen and residual was reconstituted with 100μl of methanol. The separation was performed on an Intersil ODS-3 column and gradient elution was conducted with the mobile phase of water and methanol (0-5min 47:53, 5-5.5min 47:53-10:90, 5.5-9min 10:90, posttime 4min 47:53) at a flow rate of 0.8mL/min. Quantification was performed in the selected ion monitoring (SIM) mode at m/z 543.2 for brusatol and 220.0 for IS (ornidazole). The method was validated by analyzing quality control plasma and tissue homogenate samples, and was applied to analyze samples obtained from mice after injections of brusatol via the tail vein.

RESULTS

With ornidazole as the internal standard, calibration curve of the method ranged from 10 to 320ng/ml for plasma and 10-240ng/ml for tissues. Recovery rate of brusatol from plasma and tissues were between 71.09%-94.91%. Relative standard deviation (RSD) for inter- and intra-day precision was less than 15%, and the accuracy was between 96.1%-111.8%. The pharmacokinetics and distribution study of brusatol in mice after three single doses via the tail vein were carried out based on this method. The concentration of brusatol in plasma decreased rapidly and a more than 10 fold concentration of brusatol was found as compared to that in other tissues.

CONCLUSIONS

This is the first reported LC-MS method for detecting brusatol in tissues and can accurately determine the concentrations of these compounds in plasma and different tissues. Further research on the metabolism of brusatol in vivo is still needed.

Java brucea and Chinese herbal medicine for the treatment of cholesterol granuloma in the suprasellar and sellar regions: A case report and literature review

RATIONALE

A cholesterol granuloma (CG) is usually found in the middle ear, papilla, orbits, petrous apex, and choroid plexus, but is highly uncommon in the skull. In spite of benign clinicopathological lesions, bone erosion can be seen occasionally in the patient with CG. The optimal treatment strategy is radical surgery, but complete excision is usually impossible due to anatomical restrictions and a risk of injury to the key structures located nearby. Here, we report a patient with CGs in the suprasellar and sellar regions who was successfully treated with Java brucea and Chinese herbal medicine.

PATIENT CONCERNS

A 31-year-old man presenting with progressive decreased vision in both eyes was analyzed.

DIAGNOSES

A skull magnetic resonance imaging (MRI) scan showed a low-density tumor in the uprasellar and sellar regions and histopathological examination revealed a CG.

INTERVENTIONS

The patient was referred the surgery and radiotherapy. In the meantime, brucea soft capsules and herbal medicine combined were administered to him.

OUTCOMES

The related clinical symptoms and signs resolved significantly after several months, as his therapy progressed. The patient showed no sign of recurrence during the treatment period. Furthermore, he was still alive and disease-free at 37 months of follow-up visit.

LESSONS

Overall, brucea soft capsules and a Chinese herbal formula treatment combined could be beneficial in improving the patient's quality of life with CG in the skull.

Bruceantin inhibits multiple myeloma cancer stem cell proliferation

Multiple myeloma (MM) continues to claim the lives of a majority of patients. MM cancer stem cells (CSCs) have been demonstrated to sustain tumor growth. Due to their ability to self-renew and to express detoxifying enzymes and efflux transporters, MM-CSCs are rendered highly resistant to conventional therapies. Therefore, managing MM-CSCs characteristics could have profound clinical implications. Bruceantin (BCT) is a natural product previously demonstrated to inhibit the growth of MM in RPMI 8226 cells-inoculated mouse xenograft models, and to cause regression in already established tumors. The objectives of the present study were to test the inhibitory effects of BCT on MM-CSCs growth derived from a human primary tumor, and to explore a mechanism of action underlying these effects. BCT exhibited potent antiproliferative activity in MM-CSCs starting at 25 nM. BCT induced cell cycle arrest, cell death and apoptosis in MM-CSCs as well as inhibited cell migration and angiogenesis in vitro. Using a qPCR screen, it was found that the gene expression of a number of Notch pathway members was altered. Pretreatment of MM-CSCs with the γ-secretase inhibitor RO4929097, a Notch pathway inhibitor, reversed BCT-induced effects on MM-CSCs proliferation. In this study, BCT was shown to be an effective agent in controlling the proliferation, viability and migration of MM-CSCs as well as angiogenesis in vitro. The effect on MM-CSCs proliferation may be mediated by the Notch pathway. These results warrant further investigation of BCT in a broader set of human-derived MM-CSCs and with in vivo models representative of MM.

Research of Brucea javanica against cancer

Brucea javanica, a Chinese herbal medicine, combined with conventional anticancer modalities, has been widely used for treatment of various cancers. Based on researches over the last decades, authors briefly summarized its active constituents, molecular mechanisms and clinical application for cancer treatment.

Determination of a potential antitumor quassinoid in rat plasma by UPLC-MS/MS and its application in a pharmacokinetic study

A sensitive UPLC-MS/MS method was developed and validated for the determination of brusatol in rat plasma. Chromatographic separation was carried out on a C18 column using methanol and 10mM ammonium acetate containing 0.1% (v/v) formic acid (55:45, v/v). The lower limit of quantification (LLOQ) was 1.0 ng/mL for brusatol in plasma. The intra- and inter-day precision for the analyte ranged from 3.2% to 9.2% and 1.3% to 7.8%, and the accuracy was between 97.3% and 108.5%. The method was successfully applied in a pharmacokinetic study of brusatol following intravenous injection (0.5, 1.0, and 2.0mg/kg) of brusatol.

Apoptosis induction of dehydrobruceine B on two kinds of human lung cancer cell lines through mitochondrial-dependent pathway

BACKGROUND

Brucea javanica is an effective traditional medicine listed in Chinese Pharmacopoeia. In China, the seed oil of B. javanica has long been used as commercially available drug for the treatment of tumor in clinic. Dehydrobruceine B (DHB) is a quassinoid isolated from B. javanica.

PURPOSE

The aim of the present study is to investigate the apoptotic effects induced by DHB in human lung cancer A549 and NCI-H292 cells. The involvement of a mitochondria-mediated intrinsic pathway in the pro-apoptotic action of DHB was also investigated.

MATERIAL AND METHODS

Cell viability was determined by MTT assay. Cell cycle and apoptosis were assessed by flow cytometry analysis. Mitochondrial membrane potential (MMP) was examined through JC-1 staining. The protein translocation in cells was examined by immunostaining. The expression levels of proteins which are closely related to mitochondria-mediated apoptosis pathway were measured by immunoblot analysis.

RESULTS

Treatment with DHB decreased cell viability, induced apoptosis and blocked cell cycle at S phase. DHB-induced apoptosis was found to be mediated through mitochondrial intrinsic pathway, evidenced by the loss of MMP, the release of cytochrome c into cytosol, and the cleavage of caspase-9, caspase-3 and poly (ADP-ribose) polymerase (PARP).

CONCLUSION

DHB triggers apoptosis in A549 and NCI-H292 cells via mitochondrial pathway, making it a promising candidate as a therapeutic agent for lung carcinoma.

Natural Products as a Vital Source for the Discovery of Cancer Chemotherapeutic and Chemopreventive Agents

Throughout history, natural products have played a dominant role in the treatment of human ailments. For example, the legendary discovery of penicillin transformed global existence. Presently, natural products comprise a large portion of current-day pharmaceutical agents, most notably in the area of cancer therapy. Examples include Taxol, vinblastine, and camptothecin. These structurally unique agents function by novel mechanisms of action; isolation from natural sources is the only plausible method that could have led to their discovery. In addition to terrestrial plants as sources for starting materials, the marine environment (e.g., ecteinascidin 743, halichondrin B, and dolastatins), microbes (e.g., bleomycin, doxorubicin, and staurosporin), and slime molds (e.g., epothilone B) have yielded remarkable cancer chemotherapeutic agents. Irrespective of these advances, cancer remains a leading cause of death worldwide. Undoubtedly, the prevention of human cancer is highly preferable to treatment. Cancer chemoprevention, the use of vaccines or pharmaceutical agents to inhibit, retard, or reverse the process of carcinogenesis, is another important approach for easing this formidable public health burden. Similar to cancer chemotherapeutic agents, natural products play an important role in this field. There are many examples, including dietary phytochemicals such as sulforaphane and phenethyl isothiocyanate (cruciferous vegetables) and resveratrol (grapes and grape products). Overall, natural product research is a powerful approach for discovering biologically active compounds with unique structures and mechanisms of action. Given the unfathomable diversity of nature, it is reasonable to suggest that chemical leads can be generated that are capable of interacting with most or possibly all therapeutic targets.

Activation of p53 by sodium selenite switched human leukemia NB4 cells from autophagy to apoptosis

It was revealed by our previous research that sodium selenite repressed autophagy accompanied by the induction of apoptosis in human leukemia NB4 cells. The inhibition of autophagy exerted a facilitative effect on apoptosis. In the present study, we further explored the mechanisms underlying the switch from autophagy to apoptosis and elucidated p53 played a key role. Selenite induced phosphorylation of p53 at the vital site Ser15 via p38MAPK and ERK. Subsequently p53 dissociated with its inhibitory protein mouse double minute 2 (MDM2). Meanwhile, the nucleolar protein B23 transferred from the nucleolus to the nucleoplasm and associated with MDM2, probably stabilizing p53. The active p53 participated in the decrease of autophagic protein Beclin-1 and LC-3, as well as activation of apoptosis-related caspases. Furthermore, in p53 mutant U937 leukemia cells, selenite could not elicit such a switch from autophagy to apoptosis, laying emphasis on the crucial role p53 played in this process.

Brusatol inhibits the response of cultured beta-cells to pro-inflammatory cytokines in vitro

Brusatol is a natural terpenoid that is capable of inducing a variety of biological effects. We presently report that this substance dramatically improves beta-cell survival when exposed to pro-inflammatory cytokines (IL-1β and IFNγ) in vitro. This was observed in insulin producing rat (RIN-5AH), mouse (βTC6) and human (EndoC-βH1) beta-cell lines. Brusatol prevented beta-cell oxidative stress in response to cytokines and counteracted induction of iNOS on the protein level. Brusatol, however, block neither the cytokine-induced increase of iNOS mRNA, nor NF-κB activation, suggesting that inhibition of iNOS protein expression relies on posttranscriptional mechanism. This indicates that brusatol acts via a novel protective pathway, which may represent a more promising way of improving beta-cell function and survival.

Involvement of autophagy inhibition in Brucea javanica oil emulsion-induced colon cancer cell death

Brucea javanica oil emulsion (BJOE), the petroleum ether extract of B. javanica emulsified by phospholipid, is widely used in China as an anticancer agent. The extracts from B. javanica induce cancer cell death by various mechanisms; however, it is not known whether these mechanisms involve autophagy, which is an important process in cancer development and treatment. Thus, the current study aimed to investigate whether BJOE modulates autophagy in HCT116 human colon cancer cells and whether modulation of autophagy is an anticancer mechanism of BJOE. Immunoblotting was employed to analyze the protein expression levels of microtubule-associated protein light-chain 3 (LC3), a specific protein marker of autophagy, in HCT116 cancer cells following exposure to BJOE. The apoptosis rate of the HCT116 cancer cells was detected by performing an Annexin V-fluorescein isothiocyanate/propidium iodide assay. According to the effect of BJOE administration on autophagy in the HCT116 cancer cells (induction or suppression), a functionally opposite agent (autophagy suppressor or inducer) was applied to counteract this effect, and the apoptosis rate of the cancer cells was detected again. The role of autophagy (pro-survival or pro-death) was demonstrated by comparing the rates of apoptotic cancer cells prior to and following the counteraction. The results revealed that BJOE suppressed the protein expression levels of LC3, including the LC3-I and LC3-II forms, and induced apoptosis in the HCT116 cancer cells with a high level of basal LC3. The apoptosis-inducing activity of BJOE was significantly attenuated when autophagy was induced by the administration of trehalose, an autophagy inducer. The data indicates that autophagy inhibition is involved in BJOE-induced cancer cell death, and that this inhibition may be a potential anticancer mechanism of BJOE.

Brusatol isolated from Brucea javanica (L.) Merr. induces apoptotic death of insect cell lines

Brucea javanica (L.) Merr. is a medicine plant distributed widely throughout Asia where its bitter fruits have been used traditionally in medicine for treating various ailments and controlling some pests. In recent years, concerns over the potential impact of synthetic pesticides on human health and environment have now become more pressing to develop environmentally friendly pesticides. In this paper, brusatol, a quassinoid, was isolated from the fruit of B. javanica, and identified using X-ray crystallographic analysis. Results showed that brusatol has potent contact toxicity (LD50, 2.91 μg/larva, 72 h) and anfieedant activity (AFC50, 17.4 mg/L, 48 h) against the third-instar larvae of Spodoptera exigua. Brusatol demonstrated cytotoxic effects to the tested insect cell lines, IOZCAS-Spex-II and Sf21, in a time- and dose-dependent manner. After brusatol treatment, apoptotic cell death with the DNA fragmentation, activation of caspase-3 and release of cytochrome c was preliminarily observed in both IOZCAS-Spex-II and Sf21. These results indicated the existence of apoptotic death with the mitochondrial-dependent pathway induced by brusatol in Sf21 and IOZCAS-Spex-II cell lines. Our studies will provide important knowledge to understand mechanisms of action of brusatol and to develop brusatol and its derivatives as insecticides.

Anti-angiogenic quassinoid-rich fraction from Eurycoma longifolia modulates endothelial cell function

Targeting angiogenesis could be an excellent strategy to combat angiogenesis-dependent pathophysiological conditions such as cancer, rheumatoid arthritis, obesity, systemic lupus erythematosus, psoriasis, proliferative retinopathy and atherosclerosis. Recently a number of clinical investigations are being undertaken to assess the potential therapeutic application of various anti-angiogenic agents. Many of these angiogenesis inhibitors are directed against the functions of endothelial cells, which are considered as the building blocks of blood vessels. Similarly, roots of a traditional medicinal plant, Eurycoma longifolia, can be used as an alternative treatment to prevent and treat the angiogenesis-related diseases. In the present study, antiangiogenic potential of partially purified quassinoid-rich fraction (TAF273) of E. longifolia root extract was evaluated using ex vivo and in vivo angiogenesis models and the anti-angiogenic efficacy of TAF273 was investigated in human umbilical vein endothelial cells (HUVEC). TAF273 caused significant suppression in sprouting of microvessels in rat aorta with IC50 11.5μg/ml. TAF273 (50μg/ml) showed remarkable inhibition (63.13%) of neovascularization in chorioallantoic membrane of chick embryo. Tumor histology also revealed marked reduction in extent of vascularization. In vitro, TAF273 significantly inhibited the major angiogenesis steps such as proliferation, migration and differentiation of HUVECs. Phytochemical analysis revealed high content of quassinoids in TAF273. Specially, HPLC characterization showed that TAF273 is enriched with eurycomanone, 13α(21)-epoxyeurycomanone and eurycomanol. These results demonstrated that the antiangiogenic activity of TAF273 may be due to its inhibitory effect on endothelial cell proliferation, differentiation and migration which could be attributed to the high content of quassinoids in E. longifolia.

Involvement of intrinsic mitochondrial pathway in neosergeolide-induced apoptosis of human HL-60 leukemia cells: the role of mitochondrial permeability transition pore and DNA damage

CONTEXT

Quassinoids are biologically active secondary metabolites found exclusively in the Simaroubaceae family of plants. These compounds generally present important biological properties, including cytotoxic and antitumor properties.

OBJECTIVE

In the present study, the cytotoxic effects of neosergeolide, a quassinoid isolated from Picrolemma sprucei Hook. f., were evaluated in human promyelocytic leukemia cells (HL-60).

MATERIALS AND METHODS

Cytotoxicity and antiproliferative effects were evaluated by the MTT assay, May-Grünwald-Giemsa's staining, BrdU incorporation test, and flow cytometry procedures. The comet assay and micronuclei analysis were applied to determine the genotoxic and mutagenic potential of neosergeolide.

RESULTS

After 24 h exposure, neosergeolide strongly inhibited cancer cell proliferation (IC₅₀ 0.1 µM), and its activity seemed to be selective to tumor cells because it had no antiproliferative effect on human peripheral blood mononuclear cells (PBMC) at tested concentrations. Apoptosis was induced at submicromolar concentrations (0.05, 0.1, and 0.2 µM) as evidenced by morphological changes, mitochondrial depolarization, phosphatidylserine externalization, caspases activation, and internucleosomal DNA fragmentation. Additionally, neosergeolide effects were prevented by cyclosporine A (CsA), an inhibitor of the mitochondrial permeability transition (MPT) pore, which reinforced the participation of intrinsic pathways in the apoptotic process induced by this natural quassinoid. Direct DNA damage was further confirmed by comet assay and cytokinesis-block micronucleus test.

DISCUSSION AND CONCLUSION

The present study provided experimental evidence to support the underlying mechanism of action involved in the neosergeolide-mediated apoptosis. In addition, no antiproliferative effect or DNA damage effect of neosergeolide was evident in PBMC, highlighting its therapeutic potential.

Brusatol enhances the efficacy of chemotherapy by inhibiting the Nrf2-mediated defense mechanism

The major obstacle in cancer treatment is the resistance of cancer cells to therapies. Nrf2 is a transcription factor that regulates a cellular defense response and is ubiquitously expressed at low basal levels in normal tissues due to Keap1-dependent ubiquitination and proteasomal degradation. Recently, Nrf2 has emerged as an important contributor to chemoresistance. High constitutive expression of Nrf2 was found in many types of cancers, creating an environment conducive for cancer cell survival. Here, we report the identification of brusatol as a unique inhibitor of the Nrf2 pathway that sensitizes a broad spectrum of cancer cells and A549 xenografts to cisplatin and other chemotherapeutic drugs. Mechanistically, brusatol selectively reduces the protein level of Nrf2 through enhanced ubiquitination and degradation of Nrf2. Consequently, expression of Nrf2-downstream genes is reduced and the Nrf2-dependent protective response is suppressed. In A549 xenografts, brusatol and cisplatin cotreatment induced apoptosis, reduced cell proliferation, and inhibited tumor growth more substantially when compared with cisplatin treatment alone. Additionally, A549-K xenografts, in which Nrf2 is expressed at very low levels due to ectopic expression of Keap1, do not respond to brusatol treatment, demonstrating that brusatol-mediated sensitization to cisplatin is Nrf2 dependent. Moreover, a decrease in drug detoxification and impairment in drug removal may be the primary mechanisms by which brusatol enhances the efficacy of chemotherapeutic drugs. Taken together, these results clearly demonstrate the effectiveness of using brusatol to combat chemoresistance and suggest that brusatol can be developed into an adjuvant chemotherapeutic drug.