Securinine, a myeloid differentiation agent with therapeutic potential for AML

Securinine inhibits the tumor growth of human bladder cancer cells by suppressing Wnt/β-catenin signaling pathway and activating p38 and JNK signaling pathways

Bladder cancer (BC) is the most common malignant tumor in urinary system. Although chemotherapy is one of the most important adjuvant treatments for BC, drug resistance, non-specific toxicity and severe side effects are the major obstacles to BC chemotherapy. Natural products have always been a leading resource of antitumor drug discovery, with the advantages of excellent effectiveness, low toxicity, multi-targeting potency and easy availability. In this study, we evaluated the potential anti-tumor effect of securinine (SEC), a natural alkaloid from Securinega suffruticosa, on BC cells in vitro and in vivo, and delineated the underlying mechanism. We found that SEC inhibited the proliferation, migration and invasion, induced the apoptosis of BC cells in vitro, and retarded the xenograft tumor growth of BC cell in vivo. Notably, SEC had a promising safety profile because it presented no or low toxicity on normal cells and mice. Mechanistically, SEC inactivated Wnt/β-catenin signaling pathway while activated p38 and JNK signaling pathway. Moreover, β-catenin overexpression, the p38 inhibitor SB203580 and the JNK inhibitor SP600125 both mitigated the inhibitory effect of SEC on BC cells. Furthermore, we demonstrated a synergistic inhibitory effect of SEC and gemcitabine (GEM) on BC cells in vitro and in vivo. Taken together, our findings suggest that SEC may exert anti-BC cell effect at least through the activation of p38 and JNK signaling pathways, and the inhibition of Wnt/β-catenin signaling pathway. More meaningfully, the findings indicate that GEM-induced BC cell killing can be enhanced by combining with SEC.

Naringenin prevents non-alcoholic steatohepatitis by modulating the host metabolome and intestinal microbiome in MCD diet-fed mice

Non-alcoholic steatohepatitis (NASH) is a severe inflammatory phase of the non-alcoholic fatty liver disease (NAFLD) spectrum and can progress to advanced stages of NAFLD if left untreated. This study uses multi-omics data to elucidate the underlying mechanism of naringenin's reported benefit in alleviating (NASH). Male mice were fed a NASH-inducing (methionine-choline-deficient) MCD diet with or without naringenin supplementation for 6 weeks. Naringenin prevented NASH-induced histopathological liver damage and reversed the abnormal levels of hepatic triglyceride (TG)/total cholesterol (TC), serum TG/TC, serum alanine aminotransferase/aspartate transaminase, and hepatic malondialdehyde and glutathione. Importantly, naringenin intervention significantly modulated the relative abundance of gut microbiota and the host metabolomic profile. We detected more than 700 metabolites in the serum and found that the gut genus levels of Anaeroplasma and the [Eubacterium] nodatum group were closely associated with xanthine, 2-picoline, and securinine, respectively. Tuzzerella alterations showed the highest number of associations with host endogenous metabolites such as FAHFA (8:0/10:0), FFA (20:2), carnitine C8:1, tridecanedioic acid, securinine, acetylvaline, DL-O-tyrosine, and Phe-Asn. This study indicates that the interplay between host serum metabolites and gut microbiota may contribute to the therapeutic effect of naringenin against NASH.

Phytochemicals and bioactive compounds effective against acute myeloid leukemia: A systematic review

This systematic review identified various bioactive compounds which have the potential to serve as novel drugs or leads against acute myeloid leukemia. Acute myeloid leukemia (AML) is a heterogeneous hematopoietic malignancy that arises from the dysregulation of cell differentiation, proliferation, and cell death. The risk factors associated with the onset of AML include long-term exposure to radiation and chemicals such as benzene, smoking, genetic disorders, blood disorders, advancement in age, and others. Although novel strategies to manage AML, including a refinement of the conventional chemotherapy regimens, hypomethylating agents, and molecular targeted drugs, have been developed in recent years, resistance and relapse remain the main clinical problems. In this study, three databases, PubMed/MEDLINE, ScienceDirect, and Google Scholar, were systematically searched to identify various bioactive compounds with antileukemic properties. A total of 518 articles were identified, out of which 59 were viewed as eligible for the current report. From the data extracted, over 60 bioactive compounds were identified and divided into five major groups: flavonoids, alkaloids, organosulfur compounds, terpenes, and terpenoids, and other known and emerging bioactive compounds. The mechanism of actions of the analyzed individual bioactive molecules differs remarkably and includes disrupting chromatin structure, upregulating the synthesis of certain DNA repair proteins, inducing cell cycle arrest and apoptosis, and inhibiting/regulating Hsp90 activities, DNA methyltransferase 1, and histone deacetylase 1.

Synthesis, biological activity and mechanism of action of novel allosecurinine derivatives as potential antitumor agents

Cancer with low survival rates is the second main cause of death among all diseases in the world and consequently, effective antineoplastic agents are urgently needed. Allosecurinine is a plant-derived indolicidine securinega alkaloid shown bioactivity. The object of this study is to investigate synthetic allosecurinine derivatives with considerable anticancer capacity against nine human cancer cell lines as well as mechanism of action. We synthesized twenty-three novel allosecurinine derivatives and evaluated their antitumor activity against nine cancer cell lines for 72 h by MTT and CCK8 assays. FCM was applied to analyze the apoptosis, mitochondrial membrane potential, DNA content, ROS production, CD11b expression. Western blot was selected to analyze the protein expression. Structure-activity relationships were established and potential anticancer lead BA-3 which induced differentiation of leukemia cells towards granulocytosis at low concentration and apoptosis at high concentration was identified. Mechanism studies showed that mitochondrial pathway mediated apoptosis within cancer cells with cell cycle blocking was induced by BA-3. In addition, western blot assays revealed that BA-3 induced expression of the proapoptotic factor Bax, p21 and reduced the levels of antiapoptotic protein such as Bcl-2, XIAP, YAP1, PARP, STAT3, p-STAT3, and c-Myc. Collectively, BA-3 was a lead compound for oncotherapy at least in part, through the STAT3 pathway. These results were an important step in further studies on allosecurinine-based antitumor agent development.

Potential anticancer activities of securinine and its molecular targets

BACKGROUND

Securinine is an alkaloid identified from the roots and leaves of the shrub Flueggea suffruticosa (Pall.) Baill. The molecular structure of securinine consists of four rings, including three chiral centers. It has been suggested that securinine can be chemically synthesized from tyrosine and lysine. Securinine has long been used to treat central nervous system diseases. In recent years, more and more evidence shows that securinine also has anticancer activity, which has not been systematically discussed and analyzed.

PURPOSE

This study aims to propose an overall framework to describe the molecular targets of securinine in different signal pathways, and discuss the current status and prospects of each pathway, so as to provide a theoretical basis for the development securinine as an effective anticancer drug.

METHODS

The research databases on the anticancer activity of securinine from PubMed, Scopus, Web of Science and ScienceDirect to 2021 were systematically searched. This paper follows the Preferred Reporting Items and Meta-Analysis guidelines.

RESULTS

Securinine has the ability to kill a variety of human cancer cells, including, leukemia as well as prostate, cervical, breast, lung, and colon cancer cells. It can regulate the signal pathways of phosphatidylinositol-3-kinase/protein kinase B/mammalian target of rapamycin, Wnt and Janus kinase-signal transducer and activator of transcription, promote cancer cell apoptosis and autophagy, and inhibit cancer cell metastasis. Securinine also has the activity of inducing leukemia cell differentiation.

CONCLUSION

Although there has been some experimental evidence indicating the anticancer effect of securinine and its possible pharmacology, in order to design more effective anticancer drugs, it is necessary to study the synergy of intracellular signaling pathways. More in vivo experiments and even clinical studies are needed, and the synergy between securinine and other drugs is also worth studying.

Anti-leukemic principle(s) from Momordica charantia seeds induce differentiation of HL-60 cells through ERK/MAPK signalling pathway

Myeloid leukemia is one of the major causes of deaths among elderly with very poor prognosis. Due to the adverse effects of existing chemotherapeutic agents, plant-derived components are being screened for their anti-leukemic potential. Momordica charantia (bitter gourd) possesses a variety of therapeutic activities. We have earlier demonstrated anti-leukemic activity of acetone extract of M. charantia seeds. The present study reports purification of differentiation inducing principle(s) from further fractionated seed extract (hexane fraction of the acetone extract, Mc2-Ac-hex) using HL-60 cells. Out of the 5 peak fractions (P1-P5) obtained from normal phase HPLC of the Mc2-Ac-hex, only peak fraction 3 (P3) induced differentiation of HL-60 cells as evident from an increase in NBT-positive cells and increased expression of cell surface marker CD11b. The P3 differentiated the HL-60 cells to granulocytic lineage, established by increased CD15 (granulocytic cell surface marker) expression in the treated cells. Further, possible molecular mechanism and the signalling pathway involved in the differentiation of HL-60 cells were also investigated. Use of specific signalling pathway inhibitors in the differentiation study, and proteome array analysis of the treated cells collectively revealed the involvement the of ERK/MAPK mediated pathway. Partial characterization of the P3 by GC-MS analysis revealed the presence of dibutyl phthalate, and derivatives of 2,5-dihydrofuran to be the highest among the 5 identified compounds. This study thus demonstrated that purified differentiation-inducing principle(s) from M. charantia seed extract induce HL-60 cells to granulocytic lineage through ERK/MAPK signalling pathway.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10616-022-00547-x.

Nonenzymatic Reactions in Natural Product Formation

Biosynthetic mechanisms of natural products primarily depend on systems of protein catalysts. However, within the field of biosynthesis, there are cases in which the inherent chemical reactivity of metabolic intermediates and substrates evades the involvement of enzymes. These reactions are difficult to characterize based on their reactivity and occlusion within the milieu of the cellular environment. As we continue to build a strong foundation for how microbes and higher organisms produce natural products, therein lies a need for understanding how protein independent or nonenzymatic biosynthetic steps can occur. We have classified such reactions into four categories: intramolecular, multicomponent, tailoring, and light-induced reactions. Intramolecular reactions is one of the most well studied in the context of biomimetic synthesis, consisting of cyclizations and cycloadditions due to the innate reactivity of the intermediates. There are two subclasses that make up multicomponent reactions, one being homologous multicomponent reactions which results in dimeric and pseudodimeric natural products, and the other being heterologous multicomponent reactions, where two or more precursors from independent biosynthetic pathways undergo a variety of reactions to produce the mature natural product. The third type of reaction discussed are tailoring reactions, where postmodifications occur on the natural products after the biosynthetic machinery is completed. The last category consists of light-induced reactions involving ecologically relevant UV light rather than high intensity UV irradiation that is traditionally used in synthetic chemistry. This review will cover recent nonenzymatic biosynthetic mechanisms and include sources for those reviewed previously.

Research Progress of Natural Small-Molecule Compounds Related to Tumor Differentiation

Tumor differentiation is a therapeutic strategy aimed at reactivating the endogenous differentiation program of cancer cells and inducing cancer cells to mature and differentiate into other types of cells. It has been found that a variety of natural small-molecule drugs can induce tumor cell differentiation both in vitro and in vivo. Relevant molecules involved in the differentiation process may be potential therapeutic targets for tumor cells. Compared with synthetic drugs, natural small-molecule antitumor compounds have the characteristics of wide sources, structural diversity and low toxicity. In addition, natural drugs with structural modification and transformation have relatively concentrated targets and enhanced efficacy. Therefore, using natural small-molecule compounds to induce malignant cell differentiation represents a more targeted and potential low-toxicity means of tumor treatment. In this review, we focus on natural small-molecule compounds that induce differentiation of myeloid leukemia cells, osteoblasts and other malignant cells into functional cells by regulating signaling pathways and the expression of specific genes. We provide a reference for the subsequent development of natural small molecules for antitumor applications and promote the development of differentiation therapy.

Securinine induces mitotic block in cancer cells by binding to tubulin and inhibiting microtubule assembly: A possible mechanistic basis for its anticancer activity

AIM

Analysis of the anticancer and antimitotic activity of the plant derived alkaloid securinine along with its effect on the organization of cellular microtubules as well as its binding with purified goat brain tubulin in-vitro.

MATERIALS AND METHODS

The cytotoxicity of securinine on different cell lines was conducted using SRB assay. The effect of securinine on the cellular microtubules was analyzed using immunofluorescence microscopy. The binding of securinine on purified goat brain tubulin was evaluated using fluorescent spectroscopy.

KEY FINDINGS

Securinine effectively prevented the proliferation of cervical, breast and lung cancer cells with an IC₅₀ of 6, 10 and 11 μM respectively and induced minimal toxicity in HEK cell line. Securinine at concentrations higher than IC₅₀ induced significant depolymerization in interphase and mitotic microtubules and it suppressed the reassembly of cold depolymerized spindle microtubules in HeLa cells. In the wound healing assay, securinine effectively suppressed the migration of HeLa cells to close the wound. Securinine bound to tubulin with a Kd of 9.7 μM and inhibited the assembly of tubulin into microtubules. The treatment with securinine induced a mitochondrial dependent ROS response in HeLa cells which enhanced the cytotoxic effect of securinine. The result from gene expression studies indicates that securinine induced apoptosis in MCF-7 cells through p53 dependent pathway.

SIGNIFICANCE

Considering the strong anticancer and anti-metastatic property and low toxicity in non-malignant cell lines, we suggest that securinine can be used as a chemotherapeutic drug either alone or in combination with other known anticancer molecules.

Hsa-circ_0003420 induces apoptosis in acute myeloid leukemia stem cells and impairs stem cell properties

OBJECTIVE

To explore the effect of circular RNA-0003420 (circ_0003420) in acute myeloid leukemia (AML) relapse and leukemia stem cells (LSCs) properties.

MATERIALS AND METHODS

TRIzol reagent was used to extract total RNA from AML tissues or cells. Cell viability was assessed by Cell Counting Kit-8 and EdU staining assays. Cell apoptosis was determined by flow cytometry.

RESULTS

Compared with normal hematopoietic stem cells, circular RNA hsa-circ_0003420 expression was considerably decreased in non-m3 AML stem cells. Furthermore, the lack of hsa-circ_0003420 is correlated with poor clinical results and impaired therapeutic effects in AML. Overexpression of hsa-circ_0003420 via transfection caused LSC death and inhibited the characteristics of leukemia tumor stem cells, including expression of Homeobox B4 (HOXB4), MYB, and aldehyde dehydrogenase 1 family member A1 (ALDH1A1) axis. Furthermore, hsa-circ_0003420 targets the mRNA of insulin-like growth factor 2 mRNA-binding protein 1 (IGF2BP1) and hsa-circ_0003420 expression markedly repressed IGF2BP1 levels in LSCs. Restoration of IGF2BP1 eliminated the effect of hsa-circ_0003420 on the replication, apoptosis, and LSC phenotype of KG-1a cells.

DISCUSSION AND CONCLUSIONS

Up-regulation of hsa-circ_0003420 expression in LSCs caused redox disorder, inflammation and apoptosis, suggesting that this protein could be used as a target for the treatment AML.

Thioredoxin reductase is a major regulator of metabolism in leukemia cells

Despite the fact that AML is the most common acute leukemia in adults, patient outcomes are poor necessitating the development of novel therapies. We identified that inhibition of Thioredoxin Reductase (TrxR) is a promising strategy for AML and report a highly potent and specific inhibitor of TrxR, S-250. Both pharmacologic and genetic inhibition of TrxR impairs the growth of human AML in mouse models. We found that TrxR inhibition leads to a rapid and marked impairment of metabolism in leukemic cells subsequently leading to cell death. TrxR was found to be a major and direct regulator of metabolism in AML cells through impacts on both glycolysis and the TCA cycle. Studies revealed that TrxR directly regulates GAPDH leading to a disruption of glycolysis and an increase in flux through the pentose phosphate pathway (PPP). The combined inhibition of TrxR and the PPP led to enhanced leukemia growth inhibition. Overall, TrxR abrogation, particularly with S-250, was identified as a promising strategy to disrupt AML metabolism.

Securinine Induces Differentiation of Human Promyelocytic Leukemic HL-60 Cells through JNK-Mediated Signaling Pathway

Acute myeloid leukemia is characterized by abnormal differentiation of hematopoietic stem cells, leading to the accumulation of immature myeloid cells. Differentiation therapy has been a successful treatment option for acute promyelocytic leukemia but suffers from adverse effects. Therefore, search for novel differentiation-inducing agents with minimal side effects is desirable. Securinine, a naturally-occurring alkaloid, induces differentiation in various leukemic cells and apoptosis in other types of cancers. However, the underlying molecular mechanism(s) remain elusive. Our study aimed to elucidate the possible molecular mechanism(s) and signaling events involved in securinine-induced differentiation of HL-60 cells. Securinine inhibited proliferation in a time- and dose-dependent manner and triggered differentiation. A higher CD14+ population indicated maturation toward monocytic lineage. Securinine caused cell cycle arrest at the G0/G1 phase and enhanced ROS generation. Quantitative gene expression analysis showed significant down-regulation of C/EBP-α, C/EBP-ε, GAΤΑ, and c-myc and up-regulation of the PU.1 gene. The expression of distinct protein kinases Lyn, Chk-2, Yes, FAK, c-Jun, and JNK were enhanced. Use of specific inhibitors of crucial intracellular signaling proteins indicated that JNK and ERK blockade resulted in a significant decline in differentiation. These data thus confirm that securinine induces differentiation through the activation of the JNK-ERK signaling pathway in HL-60 cells.

Unique indolizidine alkaloid securinine is a promising scaffold for the development of neuroprotective and antitumor drugs

Alkaloids, secondary plant metabolites, are used in traditional medicine in many countries to treat various pathological conditions. Securinine, a unique indolizidine alkaloid combining four cycles, “6-azobicyclo[3.2.1]octane” as a key structure fused with α,β-unsaturated-γ-lactone and piperidine ring, has a broad spectrum of actions including anti-inflammatory, antibacterial, neuroprotective and antitumor, and has been previously used in medical practice. It has several reactive centers, which are double bonds at positions 12–13 and 14–15, and this is a challenging scaffold for the synthesis of biologically active compounds. In this review, works on the production of modified securinine derivatives and their biological activity are addressed. Both monovalent and bivalent derivatives that are most promising in our opinion, and have potential for further research, are considered.

Derivatives of unique indolizidine alkaloid securinine used for neuroprotection and as antitumor agents.

Biologically active indolizidine alkaloids

Indolizidine alkaloids are chemical constituents isolated from various marine and terrestrial plants and animals, including but not limited to trees, fungi, ants, and frogs, with a myriad of important biological activities. In this review, we discuss the biological activity and pharmacological effects of indolizidine alkaloids and offer new avenues toward the discovery of new and better drugs based on these naturally occurring compounds.

Satureja hortensis induces cell death and inhibited cell cycle progression in K562 myelogenous and Jurkat T cell leukemia cell lines

Several plants of Satureja genus have shown anti-tumor activity. We investigated the antileukemia effects of different fractions of Satureja hortensis (Summer savory). The growth inhibitory effect of S. hortensis fractions on K562 and Jurkat leukemia cells were determined by MTT assay. The most effective fractions were analyzed by flow cytometry and colorimetric assay for apoptosis induction and cell cycle changes. Various fractions from S. hortensis showed growth inhibitory effects on leukemia cells, among them two hexane and dichloromethane fractions with IC₅₀ values of 32.1-47.8 μg/ml (K562) and 44.3-45.7 μg/ml (Jurkat) were the most effective. According to annexin V staining, both of these fractions significantly induced apoptosis at 50μg/ml in K562 (hexane; 73.06 ± 5.11% and dichloromethane; 96.14 ± 2.33%) and Jurkat cells (hexane; 78.85 ± 11.9% and dichloromethane; 94.05 ± 2.47%) 48 h after treatment. They increased cell accumulation in sub-G1 phase (>50%, p < .001) and decreased number of cells in G0-G1, S and G2M phases. The fractions significantly increased the caspase-3 activity in both cell lines (≈2.5-3.5 fold of untreated cells). Hexane and dichloromethane fractions of S. hortensis had the capacity to induce death and change the cell cycle distribution in leukemia cells; therefore they might be good candidates for more studies in regard to their possible therapeutic usefulness in leukemia.

Flueggeacosines A-C, Dimeric Securinine-Type Alkaloid Analogues with Neuronal Differentiation Activity from Flueggea suffruticosa

Flueggeacosines A-C (1-3), three dimeric securinine-type alkaloid analogues with unprecedented skeletons, were isolated from Flueggea suffruticosa. Compounds 1 and 2 are the first examples of C-3-C-15' connected dimeric securinine-type alkaloids. Compound 3 is an unprecedented heterodimer of securinine-type and benzoquinolizidine alkaloids. Biosynthetic pathways for 1-3 were proposed on the basis of the coexisting alkaloid monomers as the precursors. Compound 2 exhibited significant activity in promoting neuronal differentiation of Neuro-2a cells.

ZNF521 sustains the differentiation block in MLL-rearranged acute myeloid leukemia

Zinc finger protein 521 (ZNF521) is a multiple zinc finger transcription factor and a strong candidate as regulator of hematopoietic stem cell homeostasis. Recently, independent gene expression profile studies have evidenced a positive correlation between ZNF521 mRNA overexpression and MLL-rearranged acute myeloid leukemia (AML), leaving open the question on the role of ZNF521 in this subtype of leukemia. In this study, we sought to analyze the effect of ZNF521 depletion on MLL-rearranged AML cell lines and MLL-AF9 xenograft primary cells. Knockdown of ZNF521 with short-hairpin RNA (shRNA) led to decreased leukemia proliferation, reduced colony formation and caused cell cycle arrest in MLL-rearranged AML cell lines. Importantly, we showed that loss of ZNF521 substantially caused differentiation of both MLL-rearranged cell lines and primary cells. Moreover, gene profile analysis in ZNF521-silenced THP-1 cells revealed a loss of MLL-AF9-directed leukemic signature and an increase of the differentiation program. Finally, we determined that both MLL-AF9 and MLL-ENL fusion proteins directly interacted with ZNF521 promoter activating its transcription. In conclusion, our findings identify ZNF521 as a critical effector of MLL fusion proteins in blocking myeloid differentiation and highlight ZNF521 as a potential therapeutic target for this subtype of leukemia.

Secreted frizzled-related protein 1 (SFRP1) gene methylation changes in the human lung adenocarcinoma cells treated with L-securinine

Lung cancer remains the leading cause of cancer-related death worldwide. It is important to explore the biomarkers of diagnosis and prognosis in lung cancer. To evaluate the cytotoxicity of L-securinine and the expression and methylation of secreted frizzled-related proteins (SFRPs) genes in the human lung adenocarcinoma cells, cell counting kit-8 (CCK-8) assay was used to assess the proliferation of lung adenocarcinoma cells treated with L-securinine. Quantitative real-time PCR (qRT-PCR) and bisulfite sequencing PCR were used to detect the expression and the DNA methylation of SFRPs genes, respectively. L-securinine inhibited the proliferation of lung adenocarcinoma cells and induced the upregulation of SFRP1 gene expression and the methylation changes at CpG sites in the SFRP1 promoter region. L-securinine was a potential agent in the treatment of lung cancer by upregulation of SFRP1 gene expression and changing the SFRP1 gene methylation.

L-securinine inhibits the proliferation of A549 lung cancer cells and promotes DKK1 promoter methylation

L-securinine is a natural product extracted and isolated from the leaf of dried Securinega suffruticosa. The aim of the present study was to explore the effects of L-securinine on proliferation, and the methylation profile of the dickkopf-related protein 1 (DKK1) gene in human lung cancer cells and fibroblasts. L-securinine was extracted, isolated and the structure was identified. The cytotoxicity of L-securinine in A549 cells was evaluated by Cell Counting Kit-8 assays. The expression and DNA methylation profile of DKK genes was analyzed by reverse transcription-quantitative polymerase chain reaction and bisulfite sequencing polymerase chain reaction, respectively. L-securinine inhibited the proliferation of lung cancer cells; the half-maximal inhibitory concentration values were 8.92, 4.73 and 3.81 µg/ml, at 24, 36 and 48 h post-treatment, respectively. DKK1, 2 and 3 expression was significantly increased in A549 cells compared with HLF-a cells. L-securinine induced the downregulation of DKK1 in A549 cells in a dose-dependent manner and induced methylation changes at CpG sites in the DKK1 promoter region. L-securinine may be a potential anticancer drug that mediates its effects by altering DKK1 gene methylation.

Canthin-6-one induces cell death, cell cycle arrest and differentiation in human myeloid leukemia cells

BACKGROUND

Canthin-6-one is a natural product isolated from various plant genera and from fungi with potential antitumor activity. In the present study, we evaluate the antitumor effects of canthin-6-one in human myeloid leukemia lineages.

METHODS

Kasumi-1 lineage was used as a model for acute myeloid leukemia. Cells were treated with canthin-6-one and cell death, cell cycle and differentiation were evaluated in both total cells (Lin⁺) and leukemia stem cell population (CD34⁺CD38^-Lin^-/low).

RESULTS

Among the human lineages tested, Kasumi-1 was the most sensitive to canthin-6-one. Canthin-6-one induced cell death with apoptotic (caspase activation, decrease of mitochondrial potential) and necrotic (lysosomal permeabilization, double labeling of annexin V/propidium iodide) characteristics. Moreover, canthin-6-one induced cell cycle arrest at G₀/G₁ (7μM) and G₂ (45μM) evidenced by DNA content, BrdU incorporation and cyclin B1/histone 3 quantification. Canthin-6-one also promoted differentiation of Kasumi-1, evidenced by an increase in the expression of myeloid markers (CD11b and CD15) and the transcription factor PU.1. Furthermore, a reduction of the leukemic stem cell population and clonogenic capability of stem cells were observed.

CONCLUSIONS

These results show that canthin-6-one can affect Kasumi-1 cells by promoting cell death, cell cycle arrest and cell differentiation depending on concentration used.

GENERAL SIGNIFICANCE

Canthin-6-one presents an interesting cytotoxic activity against leukemic cells and represents a promising scaffold for the development of molecules for anti-leukemic applications, especially by its anti-leukemic stem cell activity.

Securinine enhances SMN2 exon 7 inclusion in spinal muscular atrophy cells

Spinal muscular atrophy (SMA) is an autosomal recessive disease characterized by the degeneration of motor neurons in the spinal cord, leading to muscular atrophy. SMA is caused by deletions or mutations in the survival motor neuron gene (SMN1) on chromosome 5q13. A second copy of the SMN gene (SMN2) also exists on chromosome 5, and both genes can produce functional protein. However, due to alternative splicing of the exon 7, the majority of SMN protein produced by SMN2 is truncated and unable to compensate for the loss of SMN1. Increasing full-length SMN protein production by promoting the exon 7 inclusion in SMN2 mRNA or increasing SMN2 gene transcription could be a therapeutic approach for SMA. In this study, we screened for the compounds that enhance SMN2 exon 7 inclusion by using SMN2 minigene-luciferase reporter system. We found that securinine can increase luciferase activity, indicating that securinine promoted SMN2 exon 7 inclusion. In addition, securinine increased full-length SMN2 mRNA and SMN protein expression in SMA patient-derived lymphoid cell lines. To investigate the mechanism of securinine effect on SMN2 splicing, we compared the protein levels of relevant splicing factors between securinine-treated and untreated cells. We found that securinine downregulated hnRNP A1 and Sam68 and upregulated Tra2-β1 expression. However, securinine, unlike HDAC inhibitors, did not enhance tra2-β1 gene transcription, indicating a post-transcriptional mechanism for Tra2-β1 upregulation. Furthermore, we treated SMA-like mice with securinine by i.p. injection and found that securinine treatment increased SMN2 exon 7 inclusion and SMN protein expression in the brain and spinal cord. According to our results, securinine might have the potential to become a therapeutic drug for SMA disease.

Securinine from Phyllanthus glaucus Induces Cell Cycle Arrest and Apoptosis in Human Cervical Cancer HeLa Cells

Background

The Securinega-type alkaloids occur in plants belonging to Euphorbiaceae family. One of the most widely distributed alkaloid of this group is securinine, which was identified next to allosecurinine in Phyllanthus glaucus (leafflower). Recently, some Securinega-type alkaloids have paid attention to its antiproliferative potency towards different cancer cells. However, the cytotoxic properties of allosecurinine have not yet been evaluated.

Methods

The cytotoxicity of the extract, alkaloid fraction obtained from P. glaucus, isolated securinine and allosecurinine against HeLa cells was evaluated by real-time xCELLigence system and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. Apoptosis was detected by annexin V and 7-amino-actinomycin (7-AAD) staining and confirmed with fluorescent Hoechst 33342 dye. The assessment of mitochondrial membrane potential (MMP), reactive oxygen species (ROS) generation, the level of extracellular signal-regulated protein kinases 1 and 2 (ERK1/2), caspase-3/7 activity and cell cycle analysis were measured by flow cytometry. The enzymatic activity of caspase-9 was assessed by a luminometric assay. The expression of apoptosis associated genes was analyzed by real-time PCR.

Results

The experimental data revealed that securinine and the alkaloid fraction were significantly potent on HeLa cells growth inhibition with IC₅₀ values of 7.02 ± 0.52 μg/ml (32.3 μM) and 25.46 ± 1.79 μg/ml, respectively. The activity of allosecurinine and Phyllanthus extract were much lower. Furthermore, our study showed that the most active securinine induced apoptosis in a dose-dependent manner in the tested cells, increased the percentage of ROS positive cells and depolarized cells as well as stimulated the activity of ERK1/2, caspase-9 and -3/7. Securinine also induced cell cycle arrest in S phase. Real-time PCR analysis showed high expression of TNFRSF genes in the cells stimulated with securinine.

Conclusions

Securinine induces apoptosis and activates cell cycle checkpoints in HeLa cells which is associated with oxidative stress. The results indicate that the mitochondrial pathway is involved in the programmed cell death.

Synthesis and Antiproliferative and Metabolic Evaluations of Novel Securinine Derivatives

New securinine analogues have been prepared by semisynthesis. Two series were developed using either Suzuki or Sonogashira cross coupling reactions. The in vitro cytotoxicity of the compounds was assayed against HCT-116 colon cancer cells. The most potent derivatives showed promising growth inhibition on four tumoral cell lines giving a valuable insight on the structure-activity relationship (SAR) of securinine. Moreover, high antiproliferative effect against A-375 (melanoma) was observed with IC50 up to 60 nM.

GSK-3 Inhibition Sensitizes Acute Myeloid Leukemia Cells to 1,25D-Mediated Differentiation

1,25-dihydroxyvitamin D3 (1,25D), the biologically active form of vitamin D, is widely considered a promising therapy for acute myeloid leukemia (AML) based on its ability to drive differentiation of leukemic cells. However, clinical trials have been disappointing in part to dose-limiting hypercalcemia. Here we show how inhibiting glycogen synthase kinase 3 (GSK3) can improve the differentiation response of AML cells to 1,25D-mediated differentiation. GSK3 inhibition in AML cells enhanced the differentiating effects of low concentrations of 1,25D. In addition, GSK3 inhibition augmented the ability of 1,25D to induce irreversible growth inhibition and slow the progression of AML in mouse models. Mechanistic studies revealed that GSK3 inhibition led to the hyperphosphorylation of the vitamin D receptor (VDR), enabling an interaction between VDR and the coactivator, SRC-3 (NCOA3), thereby increasing transcriptional activity. We also found that activation of JNK-mediated pathways in response to GSK3 inhibition contributed to the potentiation of 1,25D-induced differentiation. Taken together, our findings offer a preclinical rationale to explore the repositioning of GSK3 inhibitors to enhance differentiation-based therapy for AML treatment. Cancer Res; 76(9); 2743-53. ©2016 AACR.

Synthesis and biological evaluation of new securinine analogues as potential anticancer agents

A series of new securinine analogues was prepared by Heck reaction from readily accessible securinine and commercially available iodoarenes. The in vitro cytotoxicity of the prepared compounds was assayed against a panel of four cancer cell lines: A375, A549, HCT-116 and HL-60 showing promising growth inhibition with excellent IC50 values in the nanomolar range. The plasmatic stability of the most potent analogue was also investigated demonstrating that they might serve as valuable leads for the development of anticancer drugs.

The interplay of autophagy and β-Catenin signaling regulates differentiation in acute myeloid leukemia

The major feature of leukemic cells is an arrest of differentiation accompanied by highly active proliferation. In many subtypes of acute myeloid leukemia, these features are mediated by the aberrant Wnt/β-Catenin pathway. In our study, we established the lectin LecB as inducer of the differentiation of the acute myeloid leukemia cell line THP-1 and used it for the investigation of the involved processes. During differentiation, functional autophagy and low β-Catenin levels were essential. Corresponding to this, a high β-Catenin level stabilized proliferation and inhibited autophagy, resulting in low differentiation ability. Initiated by LecB, β-Catenin was degraded, autophagy became active and differentiation took place within hours. Remarkably, the reduction of β-Catenin sensitized THP-1 cells to the autophagy-stimulating mTOR inhibitors. As downmodulation of E-Cadherin was sufficient to significantly reduce LecB-mediated differentiation, we propose E-Cadherin as a crucial interaction partner in this signaling pathway. Upon LecB treatment, E-Cadherin colocalized with β-Catenin and thereby prevented the induction of β-Catenin target protein expression and proliferation. That way, our study provides for the first time a link between E-Cadherin, the aberrant Wnt/β-Catenin signaling, autophagy and differentiation in acute myeloid leukemia. Importantly, LecB was a valuable tool to elucidate the underlying molecular mechanisms of acute myeloid leukemia pathogenesis and may help to identify novel therapy approaches.

Natural compounds and pharmaceuticals reprogram leukemia cell differentiation pathways

In addition to apoptosis resistance and cell proliferation capacities, the undifferentiated state also characterizes most cancer cells, especially leukemia cells. Cell differentiation is a multifaceted process that depends on complex regulatory networks that involve transcriptional, post-transcriptional and epigenetic regulation of gene expression. The time- and spatially-dependent expression of lineage-specific genes and genes that control cell growth and cell death is implicated in the process of maturation. The induction of cancer cell differentiation is considered an alternative approach to elicit cell death and proliferation arrest. Differentiation therapy has mainly been developed to treat acute myeloid leukemia, notably with all-trans retinoic acid (ATRA). Numerous molecules from diverse natural or synthetic origins are effective alone or in association with ATRA in both in vitro and in vivo experiments. During the last two decades, pharmaceuticals and natural compounds with various chemical structures, including alkaloids, flavonoids and polyphenols, were identified as potential differentiating agents of hematopoietic pathways and osteogenesis.

Chiroptical study and absolute configuration of securinine oxidation products

Time-dependant density functional theory-electronic circular dichroism spectra prediction was carried out to study the absolute configuration of phyllanthidine-type derivatives 5 and 6, derived from securinine (1) and its enantiomer virosecurinine (2), respectively. This method demonstrated to be very reliable in this alkaloid series. Thus, 5 and 6 shared the same stereochemistry as their parent precursors, confirming the retentive nature of the oxidation sequence. In addition, this study highlighted the key role of the methylene bridge (BC ring) in the chiroptical activity of these compounds. These results fully clarified the stereochemical relationships between the phyllanthidine and the securinine subgroups.

Cytotoxic effects of stem bark extracts and pure compounds from Margaritaria discoidea on human ovarian cancer cell lines

Margaritaria discoidea (Baill.) G. L. Webster (Euphorbiaceae) is a well-known medicinal plant in Africa used for the treatment of various diseases. So far, no cytotoxic effects of plant extracts on cancer cell lines have been reported.

AIM OF THE STUDY

To evaluate the cytotoxicity against human ovarian cancer cells of extracts of M. discoidea and characterize the major bioactive compounds.

METHODS

Both organic and aqueous extracts of this plant were obtained by maceration. The sulforhodamine B cell proliferation assay was used for evaluation of their cytotoxic activities and the potential bioactive compounds were characterized by gas chromatography-mass spectrometry.

RESULTS

The organic extract of M. discoidea showed stronger cytotoxicity than the aqueous extract with IC50 values of 14.4±3.0, 14.2±1.2 and 34.7±0.5µg/ml on OVCAR-8, A2780 and cisplatin-resistant A2780cis ovarian cancer cells, respectively. The organic extract was further subjected to bioassay-guided fractionation by partitioning with n-hexane, ethyl acetate, and n-butanol in water. The ethyl acetate fraction was the most potent on the three ovarian cancer cell lines. A GC-MS analysis of trimethylsilyl derivatives of this fraction indicated the presence of phenolic compounds such as gallic acid and the alkaloid securinine. The IC50 values of these two compounds were determined to be in the range of 3-16µM, which indicated that they could contribute to the cytotoxic activity of the extract of M. discoidea.

CONCLUSIONS

This study has evaluated the cytotoxicity of stem bark extracts of M. discoidea against ovarian cancer cells and provided a basis of further development of this plant for the treatment of ovarian cancer.

Production of therapeutically relevant indolizidine alkaloids in Securinega suffruticosa in vitro shoots maintained in liquid culture systems

Microshoot cultures of the Chinese medicinal plant Securinega suffruticosa (Pall.) Rehd. were established and evaluated for the presence of therapeutically relevant indolizidine alkaloids securinine (S) and allosecurinine (AS). The cultures were maintained in shake flasks (SFs) and a bubble column bioreactor (BCB) using the modified Murashige's shoot multiplication medium supplemented with 1.0 mg l(-1) benzyladenine (BA), 3.0 mg l(-1) 2-isopentenyladenine (2iP), and 0.3 mg l(-1) 1-naphthaleneacetic acid (NAA). The influence of light and medium supplementation strategies with biosynthesis precursor (lysine (LY)) and nutrient formulations (casein hydrolysate (CH) and coconut water (CW)) on biomass growth and alkaloid production were investigated. SF cultures grown in the presence of light yielded up to 6.02 mg g(-1) dry weight (DW) S and 3.70 mg g(-1) DW AS, corresponding to the respective productivities of 98.39 and 60.21 mg l(-1). Among feeding experiments, CW supplementation proved most effective for SF-grown shoots, increasing biomass yield and AS productivity by 52 and 44 %, respectively. Maximum concentrations of securinine (3.25 mg g(-1) DW) and allosecurinine (3.41 mg g(-1) DW) in BCB cultures were achieved in the case of 1.0 g l(-1) LY supplementation. These values corresponded to the productivities of 42.64 and 44.47 mg per bioreactor, respectively.

Retinoic acid synergizes ATO-mediated cytotoxicity by precluding Nrf2 activity in AML cells

Background:

Standard therapy for acute promyelocytic leukaemia (APL) includes retinoic acid (all-trans retinoic acid (ATRA)), which promotes differentiation of promyelocytic blasts. Although co-administration of arsenic trioxide (ATO) with ATRA has emerged as an effective option to treat APL, the molecular basis of this effect remains unclear.

Methods:

Four leukaemia cancer human models (HL60, THP-1, NBR4 and NBR4-R2 cells) were treated either with ATO alone or ATO plus ATRA. Cancer cell survival was monitored by trypan blue exclusion and DEVDase activity assays. Gene and protein expression changes were assessed by RT-PCR and western blot.

Results:

ATO induced an antioxidant response characterised by Nrf2 nuclear translocation and enhanced transcription of downstream target genes (that is, HO-1, NQO1, GCLM, ferritin). In cells exposed to ATO plus ATRA, the Nrf2 nuclear translocation was prevented and cytotoxicity was enhanced. HO-1 overexpression reversed partially the cytotoxicity by ATRA-ATO in HL60 cells. The inhibitory effects of ATRA on ATO-mediated responses were not observed in either the ATRA-resistant NB4-R2 cells or in NB4 cells pre-incubated with the RARα antagonist Ro-41-52-53.

Conclusions:

The augmented cytotoxicity observed in leukaemia cells following combined ATO-ATRA treatment is likely due to inhibition of Nrf2 activity, thus explaining the efficacy of combined ATO-ATRA treatment in the APL therapy.

Development and validation of LC-MS/MS method for quantitative determination of (-)-securinine in mouse plasma

(-)-Securinine (SE) is a major alkaloid found in plant Securinega suffruticosa, which has a wide range of pharmacological activities including anticancer, anti-parasitic and central nervous system stimulating effects, etc. To aid the pharmacological study of SE, we developed an LC-MS/MS method for quantitative determination of SE in mouse plasma. In this method, plasma samples were first prepared with salting-out assisted liquid-liquid extraction using cold acetonitrile (-20°C) and 2.00 M ammonium acetate. Separation of SE and the internal standard (IS) from sample matrix was achieved on a Gemini Nx C18 column using 40% acetonitrile and 60% 10.0mM ammonium acetate at a flow rate of 0.200 mL min(-1). Quantification of SE was accomplished with positive electrospray ionization tandem mass spectrometry using mass transitions m/z 218.1→84.1 for SE, and m/z 204.1→70.2 for the IS. This method has a lower limit of quantitation (LLOQ) of 0.600 ng mL(-1) and a linear calibration range up to 600 ng mL(-1) in mouse plasma. The intra- and inter-run accuracy (%RE) and precision (%CV) were ≤ ± 6% and 6%, respectively. The IS normalized matrix factors from six lots of plasma matrices ranged 0.92-1.07, and the recoveries of plasma SE were 99-109%. The validated method has been applied to the measurement of SE in plasma samples of a mouse study.

Nitric oxide mediates selective degeneration of hypothalamic orexin neurons through dysfunction of protein disulfide isomerase

We addressed the role of nitric oxide (NO) in orexin neuron degeneration that has been observed under various pathological conditions. Administration of an NO donor NOC18 (50 nmol) into the third ventricle of mice resulted in a significant decrease of orexin-immunoreactive (-IR) neurons, in contrast to a modest change in melanin-concentrating hormone-IR neurons. In addition, NOC18 promoted formation of orexin-A-IR aggregates within orexin neurons. An endoplasmic reticulum stress inducer tunicamycin replicated the effect of NOC18 with regard to decrease of orexin-IR neurons and formation of aggregates. We also found that NOC18 caused an increase in S-nitrosation of protein disulfide isomerase (PDI) and a decrease in PDI activity in hypothalamic tissues. Moreover, PDI inhibitors, such as cystamine and securinine, caused a selective decrease of orexin neurons and promoted formation of orexin-A-IR aggregates. Aggregate formation in orexin-IR neurons was also induced by local injection of small interfering RNA targeting PDI. Interestingly, sleep deprivation for 7 consecutive days induced a selective decrease of orexin-IR neurons, which was preceded by aggregate formation in orexin-IR neurons and an increase in S-nitrosated PDI in the hypothalamus. Activity of neuronal NO synthase (nNOS)-positive neurons in the lateral hypothalamus as assessed by c-Fos expression was elevated in response to sleep deprivation. Finally, sleep deprivation-induced decrease of orexin-IR neurons, formation of aggregates, and S-nitrosation of PDI were not observed in nNOS knock-out mice. These results indicate that nNOS-derived NO may mediate specific pathological events in orexin neurons, including neuropeptide misfolding via S-nitrosation and inactivation of PDI.

Citrate induces apoptosis of the acute monocytic leukemia U937 cell line through regulation of HIF-1α signaling

The present study aimed to investigate the anti-tumor effect of citrate on acute monocytic leukemia (AML) and its mechanisms. The apoptosis of the AML cell line, U937, was assessed by MTT and Hoechst staining, the expression of Bcl-2, caspases-3 and -9, hypoxia-inducible factor 1α (HIF‑1α) and its target gene GLUT-1, were assayed by western blotting and the role of HIF‑1α was evaluated through siRNA. The results showed that citrate inhibits the expression of Bcl-2, while it induces the activation of caspases-3 and -9. In addition, citrate induces U937 apoptosis in a dose- and time-dependent manner by regulating the expression of HIF‑1α and its downstream target GLUT-1. The results suggest that citrate performs an anti-acute monocytic leukemia action by targeting HIF‑1α signaling and may be a promising clinical approach.

GSK3 is a regulator of RAR-mediated differentiation

Acute myeloid leukemia (AML) is the most common form of leukemia in adults. Unfortunately, the standard therapeutic agents used for this disease have high toxicities and poor efficacy. The one exception to these poor outcomes is the use of the retinoid, all-trans retinoic acid (ATRA), for a rare subtype of AML (APL). The use of the differentiation agent, ATRA, in combination with low-dose chemotherapy leads to the long-term survival and presumed cure of 75-85% of patients. Unfortunately ATRA has not been clinically useful for other subtypes of AML. Though many non-APL leukemic cells respond to ATRA, they require significantly higher concentrations of ATRA for effective differentiation. Here we show that the combination of ATRA with glycogen synthase kinase 3 (GSK3) inhibition significantly enhances ATRA-mediated AML differentiation and growth inhibition. These studies have revealed that ATRA's receptor, the retinoic acid receptor (RAR), is a novel target of GSK3 phosphorylation and that GSK3 can impact the expression and transcriptional activity of the RAR. Overall, our studies suggest the clinical potential of ATRA and GSK3 inhibition for AML and provide a mechanistic framework to explain the promising activity of this combination regimen.