Activation of polyamine catabolic enzymes involved in diverse responses against epibrassinolide-induced apoptosis in LNCaP and DU145 prostate cancer cell lines

Polyamine Catabolism Revisited: Acetylpolyamine Oxidase Plays a Minor Role due to Low Expression

Biogenic polyamines are ubiquitous compounds. Dysregulation of their metabolism is associated with the development of various pathologies, including cancer, hyperproliferative diseases, and infections. The canonical pathway of polyamine catabolism includes acetylation of spermine and spermidine and subsequent acetylpolyamine oxidase (PAOX)-mediated oxidation of acetylpolyamines (back-conversion) or their direct efflux from the cell. PAOX is considered to catalyze a non-rate-limiting catabolic step. Here, we show that PAOX transcription levels are extremely low in various tumor- and non-tumor cell lines and, in most cases, do not change in response to altered polyamine metabolism. Its enzymatic activity is undetectable in the majority of cell lines except for neuroblastoma and low passage glioblastoma cell lines. Treatment of A549 cells with N1,N11-diethylnorspermine leads to PAOX induction, but its contribution to polyamine catabolism remains moderate. We also describe two alternative enzyme isoforms and show that isoform 4 has diminished oxidase activity and isoform 2 is inactive. PAOX overexpression correlates with the resistance of cancer cells to genotoxic antitumor drugs, indicating that PAOX may be a useful therapeutic target. Finally, PAOX is dispensable for the replication of various viruses. These data suggest that a decrease in polyamine levels is achieved predominantly by the secretion of acetylated spermine and spermidine rather than by back-conversion.

Interkingdom Hormonal Regulations between Plants and Animals Provide New Insight into Food Safety

Food safety has become an attractive topic among consumers. Raw material production for food is also a focus of social attention. As hormones are widely used in agriculture and human disease control, consumers' concerns about the safety of hormone agents have never disappeared. The present review focuses on the interkingdom regulations of exogenous animal hormones in plants and phytohormones in animals, including physiology and stress resistance. We summarize these interactions to give the public, researchers, and policymakers some guidance and suggestions. Accumulated evidence demonstrates comprehensive hormonal regulation across plants and animals. Animal hormones, interacting with phytohormones, help regulate plant development and enhance environmental resistance. Correspondingly, phytohormones may also cause damage to the reproductive and urinary systems of animals. Notably, the disease-resistant role of phytohormones is revealed against neurodegenerative diseases, cardiovascular disease, cancer, and diabetes. These resistances derive from the control for abnormal cell cycle, energy balance, and activity of enzymes. Further exploration of these cross-kingdom mechanisms would surely be of greater benefit to human health and agriculture development.

Cancer and brassinosteroids: Mechanisms of action, SAR and future perspectives

Brassinosteroids are plant hormones whose main function is to stimulate plant growth. However, they have been studied for their biological applications in humans. Brassinosteroid compounds have displayed an important role in the study of cancer pathology and show potential for developing novel anticancer drugs. In this review we describe the relationship of brassinosteroids with cancer with focus on the last decade, the mechanisms of cytotoxic activity described to date, and a structure-activity relationship based on the available information.

Polyamine homeostasis-based strategies for cancer: The role of combination regimens

Spermine, spermidine and putrescine polyamines are naturally occurring ubiquitous positively charged amines and are essential metabolites for biological functions in our life. These compounds play a crucial role in many cell processes, including cellular proliferation, growth, and differentiation. Intracellular levels of polyamines depend on their biosynthesis, transport and degradation. Polyamine levels are high in cancer cells, which leads to the promotion of tumor growth, invasion and metastasis. Targeting polyamine metabolism as an anticancer strategy is considerably rational. Due to compensatory mechanisms, a single strategy does not achieve satisfactory clinical effects when using a single agent. Combination regimens are more clinically promising for cancer chemoprevention because they work synergistically with causing little or no adverse effects due to each individual agent being used at lower doses. Moreover, bioactive substances have advantages over single chemical agents because they can affect multiple targets. In this review, we discuss anticancer strategies targeting polyamine metabolism and describe how combination treatments and effective natural active ingredients are promising therapies. The existing research suggests that polyamine metabolic enzymes are important therapeutic targets and that combination therapies can be more effective than monotherapies based on polyamine depletion.

Epibrassinolide activates AKT to trigger autophagy with polyamine metabolism in SW480 and DLD-1 colon cancer cell lines

Epibrassinolide (EBR), a plant-derived polyhydroxylated derivative of 5α-cholestane, structurally shows similarities to animal steroid hormones. According to the present study, EBR treatment triggered a significant stress response via activating ER stress, autophagy, and apoptosis in cancer cells. EBR could also increase Akt phosphorylation in vitro. While the activation of Akt resulted in cellular metabolic activation in normal cells to proceed with cell survival, a rapid stress response was induced in cancer cells to reduce survival. Therefore, Akt as a mediator of cellular survival and death decision pathways is a crucial target in cancer cells. In this study, we determined that EBR induces stress responses through activating Akt, which reduced the mTOR complex I (mTORC1) activation in SW480 and DLD-1 colon cancer cells. As a consequence, EBR triggered macroautophagy and led to lipidation of LC3 most efficiently in SW480 cells. The cotreatment of spermidine (Spd) with EBR increased lipidation of LC3 synergistically in both cell lines. We also found that EBR promoted polyamine catabolism in SW480 cells. The retention of polyamine biosynthesis was remarkable following EBR treatment. We suggested that EBR-mediated Akt activation might determine the downstream cellular stress responses to induce autophagy related to polyamines.

Reduction of oxidative stress and ornithine decarboxylase expression in a human prostate cancer cell line PC-3 by a combined treatment with α-tocopherol and naringenin

Differentiation of a human aggressive PC-3 cancer cell line was obtained, in a previous investigation, by the synergic effect of α-tocopherol (α-TOC) and naringenin (NG). This combined treatment induced apoptosis and subsequent reduction of the PC-3 cell proliferation and invasion, by a pro-differentiating action. Since one of the peculiar characteristics of NG and α-TOC is their strong antioxidant activity, this study aimed to investigate their potential effect on the activity of the main enzymes involved in the antioxidant mechanism in prostate cancer cells. NG and α-TOC administered singularly or combined in the PC-3 cell line, affected the activity of several enzymes biomarkers of the cellular antioxidant activity, as well as the concentration of total glutathione (GSH + GSSG) and thiobarbituric acid reactive substances (TBARS). The combined treatment increased the TBARS levels and superoxide dismutase (SOD) activity, while decreased the glutathione S-transferase (GST), glutathione reductase (GR), and glyoxalase I (GI) activities. The results obtained indicate that a combined treatment with these natural compounds mitigated the oxidative stress in the human PC-3 cell line. In addition, a significant reduction of both ornithine decarboxylase (ODC) expression and intracellular levels of polyamines, both well-known positive regulators of cell proliferation, accompanied the reduction of oxidative stress observed in the combined α-TOC and NG treatment. Considering the established role of polyamines in cell differentiation, the synergism with NG makes α-TOC a potential drug for further study on the differentiation therapy in prostate cancer patients.

Epibrassinolide-induced autophagy occurs in an Atg5-independent manner due to endoplasmic stress induction in MEF cells

Epibrassinolide (EBR), a polyhydroxysteroid belongs to plant growth regulator family, brassinosteroids and has been shown to have a similar chemical structure to mammalian steroid hormones. Our findings indicated that EBR could trigger apoptosis in cancer cells via induction of endoplasmic reticulum (ER) stress, caused by protein folding disturbance in the ER. Normal cells exhibited a remarkable resistance to EBR treatment and avoid from apoptotic cell death. The unfolded protein response clears un/misfolded proteins and restore ER functions. When stress is chronic, cells tend to die due to improper cellular functions. To understand the effect of EBR in non-malign cells, mouse embryonic fibroblast (MEF) cells were investigated in detail for ER stress biomarkers, autophagy, and polyamine metabolism in this study. Evolutionary conserved autophagy mechanism is a crucial cellular process to clean damaged organelles and protein aggregates through lysosome under the control of autophagy-related genes (ATGs). Cells tend to activate autophagy to promote cell survival under stress conditions. Polyamines are polycationic molecules playing a role in the homeostasis of important cellular events such as cell survival, growth, and, proliferation. The administration of PAs has been markedly extended the lifespan of various organisms via inducing autophagy and inhibiting oxidative stress. Our data indicated that ER stress is induced following EBR treatment in MEF cells as well as MEF Atg5^-/- cells. In addition, autophagy is activated following EBR treatment by targeting PI3K/Akt/mTOR in wildtype (wt) cells. However, EBR-induced autophagy targets ULK1 in MEF cells lacking Atg5 expression. Besides, EBR treatment depleted the PA pool in MEF cells through the alterations of metabolic enzymes. The administration of Spd with EBR further increased autophagic vacuole formation. In conclusion, EBR is an anticancer drug candidate with selective cytotoxicity for cancer cells, in addition the induction of autophagy and PA metabolism are critical for responses of normal cells against EBR.

Therapeutic Potential of Brassinosteroids in Biomedical and Clinical Research

Steroids are a pivotal class of hormones with a key role in growth modulation and signal transduction in multicellular organisms. Synthetic steroids are widely used to cure large array of viral, fungal, bacterial, and cancerous infections. Brassinosteroids (BRs) are a natural collection of phytosterols, which have structural similarity with animal steroids. BRs are dispersed universally throughout the plant kingdom. These plant steroids are well known to modulate a plethora of physiological responses in plants leading to improvement in quality as well as yield of food crops. Moreover, they have been found to play imperative role in stress-fortification against various stresses in plants. Over a decade, BRs have conquered worldwide interest due to their diverse biological activities in animal systems. Recent studies have indicated anticancerous, antiangiogenic, antiviral, antigenotoxic, antifungal, and antibacterial bioactivities of BRs in the animal test systems. BRs inhibit replication of viruses and induce cytotoxic effects on cancerous cell lines. Keeping in view the biological activities of BRs, this review is an attempt to update the information about prospects of BRs in biomedical and clinical application.

Molecular mechanisms of plant steroids and study of their interaction with nuclear receptors in prostate cancer cells

Plant hormone brassinosteroids (BRs) have multiple important functions in plants. They have also been found to exhibit anti-tumor, anti-angiogenic and anti-proliferative activity. The experimental part of this article describes the effects of BR biosynthetic precursors on prostate cancer cells. The experiments were performed with LNCaP and DU-145 prostate cancer cell lines. These were cultivated and treated with tested BRs in different concentrations and time intervals. The tested compounds were found to affect cell viability, nuclear receptor expression, cell cycle and apoptosis in the tumor cells. IC₅₀ concentrations were determined based on MTT test and the two most active compounds (cathasterone and 6-oxocampestanol) were used in the next experiments. Cathasterone was the most effective of all tested compounds and effectively inhibited integrity of cell spheres. It was found that both BRs had no significant effect on the cell cycle in LNCaP at IC₅₀ concentration, while in DU-145 a significant block in G₀/G₁ phase after the BR treatment was observed. The effect of BRs on the nuclear steroid receptors was manifested by changes in their expression and localization. BRs demonstrated their significant effect on prostate cancer cells and the compounds have potential used in anticancer drug research and cancer treatment.

The investigation of structure-activity relationship of polyamine-targeted synthetic compounds from different chemical groups

The polyamine (PA) metabolism is involved in cell proliferation and differentiation. Increased cellular PA levels are observed in different types of cancers. Products of PA oxidation induce apoptosis in cancer cells. These observations open a perspective to exploit the enzymes of PA catabolism as a target for anticancer drug design. The substances capable to enhance PA oxidation may become potential anticancer agents. The goal of our study was to explore how the mode of ligand binding with a PA catabolic enzyme is associated with its stimulatory or inhibitory effect upon PA oxidation. Murine N1-acetylpolyamine oxidase (5LFO) crystalline structure was used for molecular docking with ligands of various chemical structures. In vitro experiments were carried out to evaluate the action of the tested compounds upon PA oxidative deamination in a cell-free test system from rat liver. Two amino acid residues (Aps211 and Tyr204) in the structure of 5LFO were found to be significant for binding with the tested compounds. 19 out of 51 screened compounds were activators and 17 were inhibitors of oxidative deamination of PA. Taken together, these results enabled to construct a recognition model with characteristic descriptors depicting activators and inhibitors. The general tendency indicated that a strong interaction with Asp211 or Tyr204 was rather typical for activators. The understanding of how the structure determines the binding mode of compounds with PA catabolic enzyme may help in explanation of their structure-activity relationship and thus promote structure-based drug design.

Steroids-specific target library for steroids target prediction

Steroids exist universally and play critical roles in various biological processes. Identifying potential targets of steroids is of great significance in studying their physiological and biochemical activities, the side effects and for drug repurposing. Herein, aiming at more precise steroids targets prediction, a steroids-specific target library integrating 3325 PDB or homology modeling structures categorized into 196 proteins was built by considering chemical similarity from DrugBank and biological processes from KEGG. The main properties of this library include: (1) It was manually prepared and checked to eliminate mistakes. (2) The library enriched the possible steroids targets and could decrease the false positives of structure-based target screening for steroids. (3) The ranking by protein name instead of PDB ID could make the screening more efficiency and precise. (4) Protein flexibility was taken into account partially by the different active conformations through the structural redundancy of each category of protein, which leads to more accurate prediction. The case studies of glycocholic acid and 24-epibrassinolide proved its powerful predictive accuracy. In summary, our strategy to build the steroids-specific protein library for steroids target prediction is a promising approach and it provides a novel idea for the target prediction of small molecules.

Curcumin inhibits autocrine growth hormone-mediated invasion and metastasis by targeting NF-κB signaling and polyamine metabolism in breast cancer cells

Curcumin is assumed to be a plant-derived therapeutic drug that triggers apoptotic cell death in vitro and in vivo by affecting different molecular targets such as NF-κB. Phase I/II trial of curcumin alone or with chemotherapeutic drugs has been accomplished in pancreatic, colon, prostate and breast cancer cases. Recently, autocrine growth hormone (GH) signaling-induced cell growth, metastasis and drug resistance have been demonstrated in breast cancer. In this study, our aim was to investigate the potential therapeutic effect of curcumin by evaluating the molecular machinery of curcumin-triggered apoptotic cell death via focusing on NF-κB signaling and polyamine (PA) metabolism in autocrine GH-expressing MCF-7, MDA-MB-453 and MDA-MB-231 breast cancer cells. For this purpose, a pcDNA3.1 (+) vector with a GH gene insert was transfected by a liposomal agent in all breast cancer cells and then selection was conducted in neomycin (G418) included media. Autocrine GH-induced curcumin resistance was overcome in a dose-dependent manner and curcumin inhibited cell proliferation, invasion-metastasis and phosphorylation of p65 (Ser536), and thereby partly prevented its DNA binding activity in breast cancer cells. Moreover, curcumin induced caspase-mediated apoptotic cell death by activating the PA catabolic enzyme expressions, which led to generation of toxic by-products such as H₂O₂ in MCF-7, MDA-MB-453 and MDA-MB-231 GH+ breast cancer cells. In addition, transient silencing of SSAT prevented curcumin-induced cell viability loss and apoptotic cell death in each breast cancer cells. In conclusion, curcumin could overcome the GH-mediated resistant phenotype via modulating cell survival, death-related signaling routes and activating PA catabolic pathway.

Design, synthesis and biological activities of new brassinosteroid analogues with a phenyl group in the side chain

We have prepared and studied a series of new brassinosteroid derivatives with a p-substituted phenyl group in the side chain. To obtain the best comparison between molecular docking and biological activities both types of brassinosteroids were synthesized; 6-ketones, 10 examples, and B-lactones, 8 examples. The phenyl group was introduced into the steroid skeleton by Horner-Wadsworth-Emmons. The docking studies were carried out using AutoDock Vina 1.05. Plant biological activities were established using different brassinosteroid bioassays in comparison with natural brassinosteroids. Differences in the production of the plant hormone ethylene were also observed in etiolated pea seedlings after treatment with new brassinosteroids. The most active compounds were lactone 8f and 6-oxo derivatives 8c and 9c, their biological activities were comparable or even better than naturally occurring brassinolide. Finally the cytotoxicity of the new derivatives was studied using human normal and cancer cell lines.

Polyamines: therapeutic perspectives in oxidative stress and inflammatory diseases

Polyamines are naturally occurring aliphatic compounds, particularly essential elements for biological functions. These compounds play a central role in regulating molecular pathways which are responsible for cellular proliferation, growth, and differentiation. Importantly, excessive polyamine catabolism can lead to a prominent source of oxidative stress which increases inflammatory response and thought to be involved in several diseases including stroke, renal failure, neurological disease, liver disease, and even cancer. Moreover, polyamine supplementation increases life span in model organisms and may encounter oxidative stress via exerting its potential anti-oxidant and anti-inflammatory properties. The revealed literature indicates that an emerging role of polyamine biosynthetic pathway could be a novel target for drug development against inflammatory diseases. In this review, we expand the knowledge on the metabolism of polyamines, and its anti-oxidant and anti-inflammatory activities which might have future implications against inflammatory diseases in humans and animals.

Calreticulin is a fine tuning molecule in epibrassinolide-induced apoptosis through activating endoplasmic reticulum stress in colon cancer cells

Epibrassinolide (EBR), a member of brassinostreoids plant hormones with cell proliferation promoting role in plants, is a natural polyhydroxysteroid with structural similarity to steroid hormones of vertebrates. EBR has antiproliferative and apoptosis-inducing effect in various cancer cells. Although EBR has been shown to affect survival and mitochondria-mediated apoptosis pathways in a p53-independent manner, the exact molecular targets of EBR are still under investigation. Our recent SILAC (Stable Isotope Labeling by Amino Acids in Cell Culture) data showed that the most significantly altered protein after EBR treatment was calreticulin (CALR). CALR, a chaperone localized in endoplasmic reticulum (ER) lumen, plays role in protein folding and buffering Ca²⁺ ions. The alteration of CALR may cause ER stress and unfolded protein response correspondingly the induction of apoptosis. Unfolded proteins are conducted to 26S proteasomal degradation following ubiquitination. Our study revealed that EBR treatment caused ER stress and UPR by altering CALR expression causing caspase-dependent apoptosis in HCT 116, HT29, DLD-1, and SW480 colon cancer cells. Furthermore, 48 h EBR treatment did not caused UPR in Fetal Human Colon cells (FHC) and Mouse Embryonic Fibroblast cells (MEF). In addition our findings showed that HCT 116 colon cancer cells lacking Bax and Puma expression still undergo UPR and related apoptosis. CALR silencing and rapamycin co-treatment prevented EBR-induced UPR and apoptosis, whereas 26S proteasome inhibition further increased the effect of EBR in colon cancer cells. All these findings showed that EBR is an ER stress and apoptotic inducer in colon cancer cells without affecting non-malignant cells.

Flow-cytometric analysis of reactive oxygen species in cancer cells under treatment with brassinosteroids

To explore the underlying mechanism of cancer cell growth inhibition by brassinosteroids (BS), reactive oxygen species (ROS) generation under treatment with 28-homocastasterone and its synthetic derivatives (22S,23S)-28-homocastasterone was measured in A549 human lung adenocarcinoma cells. BS induced ROS generation in A549 cells and their growth in a time and dose-dependent manner. The maximal effect was observed for (22S,23S)-28-homocastasterone which at 30μM concentration showed a 6-fold increase of ROS generation in comparison with the control.

SILAC-Based Mass Spectrometry Analysis Reveals That Epibrassinolide Induces Apoptosis via Activating Endoplasmic Reticulum Stress in Prostate Cancer Cells

Epibrassinolide (EBR) is a polyhydroxylated sterol derivative and biologically active compound of the brassinosteroids. In addition to well-described roles in plant growth, EBR induces apoptosis in the LNCaP prostate cancer cells expressing functional androgen receptor (AR). Therefore, it is suggested that EBR might have an inhibitory potential on androgen receptor signaling pathway. However, the mechanism by which EBR exerts its effects on LNCaP is poorly understood. To address this gap in knowledge, we used an unbiased global proteomics approach, i.e., stable-isotope labeling by amino acids in cell culture (SILAC). In total, 964 unique proteins were identified, 160 of which were differentially expressed after 12 h of EBR treatment. The quantification of the differentially expressed proteins revealed that the expression of the unfolded protein response (UPR) chaperone protein, calreticulin (CALR), was dramatically downregulated. The decrease in CALR expression was also validated by immunoblotting. Because our data revealed the involvement of the UPR in response to EBR exposure, we evaluated the expression of the other UPR proteins. We demonstrated that EBR treatment downregulated calnexin and upregulated BiP and IRE1α expression levels and induced CHOP translocation from the cytoplasm to nucleus. The translocation of CHOP was associated with caspase-9 and caspase-3 activation after a 12 h EBR treatment. Co-treatment of EBR with rapamycin, an upstream mTOR pathway inhibitor, prevented EBR-induced cell viability loss and PARP cleavage in LNCaP prostate cancer cells, suggesting that EBR could induce ER stress in these cells. In addition, we observed similar results in DU145 cells with nonfunctional androgen receptor. When proteasomal degradation of proteins was blocked by MG132 co-treatment, EBR treatment further induced PARP cleavage relative to drug treatment alone. EBR also induced Ca²⁺ sequestration, which confirmed the alteration of the ER pathway due to drug treatment. Therefore, we suggest that EBR promotes ER stress and induces apoptosis.

Steroid plant hormones: effects outside plant kingdom

Brassinosteroids (BS) are the first group of steroid-hormonal compounds isolated from and acting in plants. Among numerous physiological effects of BS growth stimulation and adaptogenic activities are especially remarkable. In this review, we provide evidence that BS possess similar types of activity also beyond plant kingdom at concentrations comparable with those for plants. This finding allows looking at steroids from a new point of view: how common are the mechanisms of steroid bioregulation in different types of organisms from protozoa to higher animals.