Anticancer activities of pterostilbene-isothiocyanate conjugate in breast cancer cells: involvement of PPARγ

Pterostilbene-isothiocyanate reduces miR-21 level by impeding Dicer-mediated processing of pre-miR-21 in 5-fluorouracil and tamoxifen-resistant human breast cancer cell lines

Converging evidences identifies that microRNA-21 (miR-21) is responsible for drug resistance in breast cancer. This study aims to evaluate the miR-21-modulatory potential of a hybrid compound, pterostilbene-isothiocyanate (PTER-ITC), in tamoxifen-resistant MCF-7 (TR/MCF-7) and 5-fluorouracil-resistant MDA-MB 231 (5-FUR/MDA-MB 231) breast cancer cell lines, established by repeated exposure to gradually increasing the concentrations of tamoxifen and 5-fluorouracil, respectively. The outcome of this study shows that PTER-ITC effectively reduced the TR/MCF-7 (IC50: 37.21 µM) and 5-FUR/MDA-MB 231 (IC50: 47.00 µM) cell survival by inducing apoptosis, inhibiting cell migration, colony and spheroid formations in TR/MCF-7 cells, and invasiveness of 5-FUR/MDA-MB 231 cells. Most importantly, PTER-ITC significantly reduced the miR-21 expressions in these resistant cell lines. Moreover, the downstream tumor suppressor target gene of miR-21 such as PTEN, PDCD4, TIMP3, TPM1, and Fas L were upregulated after PTER-ITC treatment, as observed from transcriptional (RT-qPCR) and translational (immunoblotting) data. In silico and miR-immunoprecipitation (miR-IP) results showed reduced Dicer binding to pre-miR-21, after PTER-ITC treatment, indicating inhibition of miR-21 biogenesis. Collectively, the significance of this study is indicated by preliminary evidence for miR-21-modulatory effects of PTER-ITC that highlights the potential of this hybrid compound as an miR-21-targeting therapeutic agent.

Pterostilbene-isothiocyanate impedes RANK/TRAF6 interaction to inhibit osteoclastogenesis, promoting osteogenesis in vitro and alleviating glucocorticoid induced osteoporosis in rats

Prolonged glucocorticoid treatment often leads to glucocorticoid-induced osteoporosis (GIOP), a common iatrogenic complication. This study has explored the anti-osteoporotic potential of semi-synthetic compound, pterostilbene isothiocyanate (PTER-ITC) in GIOP rat model and bone formation potential in vitro. Dysregulated bone-remodelling leads to osteoporosis. PTER-ITC has shown anti-osteoclastogenic activity in vitro. However, its molecular target remains unidentified, which has been explored in this study through in silico and experimental approaches. Alizarin Red S and von-Kossa staining, and alkaline phosphatase (ALP) activity showed the osteogenic differentiation potential of PTER-ITC in pre-osteoblastic mouse MC3T3-E1 and human hFOB 1.19 cells, further, confirmed through the expressions of osteogenic markers at transcriptional (RT-qPCR) and translational (immunoblotting) levels. The anti-osteoclastogenic property of PTER-ITC was confirmed through inhibition of actin ring formation in mouse RAW 264.7 and human THP-1 macrophagic cells. Molecular docking and molecular dynamic simulation showed that PTER-ITC inhibited the crucial osteoclastogenic RANK/TRAF6 interaction, which was further confirmed biochemically through co-immunoprecipitation assay. Osteoporotic bone architecture [validated through scanning electron microscopy (SEM), X-ray radiography, and micro-computed tomography (µ-CT)], physiology (confirmed through compression testing, Young's modulus and stress versus strain output) and histology (verified through hematoxylin-eosin, Alizarin Red S, von-Kossa and Masson-trichrome staining) of PTER-ITC-treated GIOP female Wistar rats were assuaged. Osteoporotic amelioration through PTER-ITC treatment was further substantiated through serum biomarkers, like, parathyroid hormone (PTH), ALP, calcium (Ca²⁺), Procollagen type I N-terminal propeptide (P1NP), and 25-hydroxy vitamin D. In conclusion, this study identifies the molecular target of PTER-ITC in impeding osteoclastogenesis and facilitating osteogenesis to ameliorate osteoporosis.

Pterostilbene-isothiocyanate inhibits breast cancer metastasis by selectively blocking IKK-β/NEMO interaction in cancer cells

Metastasis, the main cause of breast cancer-associated fatalities, relies on many regular pathways involved in normal cell physiology and metabolism, thus, making it challenging to identify disease-specific therapeutic target(s). Chemically synthesized anti-metastatic agents are preferred for their fast and robust actions. However, these agents have adverse side effects, thus, increasingly favouring the identification of phytocompounds as suitable alternatives. Resveratrol and pterostilbene have long been established as potent anti-cancer agents. Earlier studies from our laboratory documented the anti-cancer activities associated with pterostilbene-isothiocyanate (PTER-ITC), a derivative of pterostilbene. The current study focuses on evaluating the anti-metastatic property of PTER-ITC and the underlying mechanism, by employing in silico, in vitro, and in vivo approaches. The significant anti-metastatic activity of PTER-ITC was observed in vitro against breast cancer metastatic cell line (MDA-MB-231) and in vivo in the 4T1 cell-induced metastatic mice model. Epithelial-mesenchymal transition (EMT), a hallmark of metastasis regulated by the transcription factors, Snail1 and Twist, was found to be reverted in vitro by PTER-ITC treatment. PTER-ITC blocked the activation of NF-κB/p65 and its concomitant nuclear translocation, resulting in the transcriptional repression of its target genes, Snail1 and Twist. PTER-ITC prevented the formation of IKK complex, central to NF-κB activation, by binding to the NEMO-binding domain (NBD) of IKK-β and inhibiting its interaction with NEMO (NF-κB essential modulator). According to our observations, PTER-ITC attenuated NF-κB activation selectively in cancerous cells. In conclusion, this study demonstrated that PTER-ITC is a potent anti-metastatic agent capable of targeting physiologically important pathways in a cancer-specific manner.

In Vitro Anticancer Effects of Stilbene Derivatives: Mechanistic Studies on HeLa and MCF-7 Cells

BACKGROUND AND OBJECTIVE

The growing prevalence of cancer and the resulting chemoresistance exert a huge burden on healthcare systems and impose a great challenge to public health around the world. In efforts to develop new chemotherapeutic agents for cancer treatment, a class of heterocyclic compounds i.e. triazine-based molecules were investigated as anticancer agents.

MATERIALS AND METHODS

New triazine hybrids of stilbene were synthesized and evaluated as anticancer agents for cervical (HeLa) and breast (MCF-7) carcinoma cells. The compound (7e), sodium (E)-6,6'-(ethene-1,2- diyl)bis(3-((4-chloro-6-((3-luorophenyl)amino)-1,3,5-triazin-2-yl)amino)benzenesulfonate) was found to be most potent among synthesized derivatives and was explored further for detailed mechanistic studies.

RESULTS

In a set comprised of twelve derivatives, compound 7e, sodium (E)-6,6'-(ethene-1,2-diyl)bis(3-((4- chloro-6-((3-luorophenyl)amino)-1,3,5-triazin-2-yl)amino)benzenesulfonate) was found most potent inhibitor for HeLa and MCF-7 cells.

DISCUSSION

The present study has revealed that compound 7e may activate mitochondrial pathway of apoptosis in HeLa and MCF-7 cells which was assessed by DNA binding studies, estimation of the release of Lactate Dehydrogenase (LDH), fluorescence imaging, production of Reactive Oxygen Species (ROS) in cancer cells, analysis of cell cycle by flow cytometry, change in Mitochondrial Membrane Potential (MMP) and activation of caspase-9 and caspase-3.

CONCLUSION

Compound 7e may serve as a lead in designing new anticancer compounds based on stilbene scaffold.

Suicide gene therapy-mediated purine nucleoside phosphorylase/fludarabine system for in vitro breast cancer model with emphasis on evaluation of vascular endothelial growth factor promoter efficacy

In this study, a suicide gene therapy approach was optimized by a non-viral polyplex system based on pEGFP-N1 vector harboring purine nucleoside phosphorylase gene conducted by vascular endothelial growth factor promoter for an in vitro breast cancer model (4T1 cell line). The VEGF promoter and purine nucleoside phosphorylase gene were cloned into the vector from the source of 4T1 and E. coli genomic DNA, respectively. A gene construct was developed by replacing VEGF promoter instead of CMV promoter in pEGFP-N1vector. PNP gene was integrated in to the multiple cloning site of the obtained vector. On the other hand, a construct from pEGFP-N1 harboring PNP gene under the control of the original CMV promoter was developed. The transfection method using cationic polymer was optimized based on N/P ratio, cell cytotoxicity, polyplex size, zeta potential and the green fluorescent protein (GFP) expression by fluorescent microscopy and flowcytometry. Also, the effect of hypoxia condition induced by 0.5 mM H₂O₂ on the promoter efficiency was investigated. The results showed that the performed gene delivery system is capable of the gene transfection to more than 30% of the cancer cells with both VEGF-PNP-pEGFP-N1 and PNP-pEGFP-N1 plasmids. The hypoxia condition did not show a significant effect on the VEGF promoter. But, it revealed that bystander effect can improve the efficacy of this system and reduce drug IC50 to 2 and fourfold for plasmids VEGF-PNP-pEGFP-N1 and PNP-pEGFP-N1, respectively. These results showed that the bystander effect could almost compensate the low efficiency of non-viral gene delivery systems. We suggest that the tumor-specific gene expression system mediated by the VEGF promoter can be especially useful in the present model of breast cancer gene therapy.

The Role of PPARγ Ligands in Breast Cancer: From Basic Research to Clinical Studies

Peroxisome proliferator-activated receptor gamma (PPARγ), belonging to the nuclear receptor superfamily, is a ligand-dependent transcription factor involved in a variety of pathophysiological conditions such as inflammation, metabolic disorders, cardiovascular disease, and cancers. In this latter context, PPARγ is expressed in many tumors including breast cancer, and its function upon binding of ligands has been linked to the tumor development, progression, and metastasis. Over the last decade, much research has focused on the potential of natural agonists for PPARγ including fatty acids and prostanoids that act as weak ligands compared to the strong and synthetic PPARγ agonists such as thiazolidinedione drugs. Both natural and synthetic compounds have been implicated in the negative regulation of breast cancer growth and progression. The aim of the present review is to summarize the role of PPARγ activation in breast cancer focusing on the underlying cellular and molecular mechanisms involved in the regulation of cell proliferation, cell cycle, and cell death, in the modulation of motility and invasion as well as in the cross-talk with other different signaling pathways. Besides, we also provide an overview of the in vivo breast cancer models and clinical studies. The therapeutic effects of natural and synthetic PPARγ ligands, as antineoplastic agents, represent a fascinating and clinically a potential translatable area of research with regards to the battle against cancer.

PPAR Ligands Containing Stilbene Scaffold

Peroxisome proliferator-activated receptors (PPARs) are transcriptional factors which belong to the ligand-activated nuclear receptor superfamily. They are ubiquitously expressed throughout the body. So far, three major subtypes have been identified, PPARα, PPARβ/δ and PPARγ. They are crucial for lipid and glucose metabolism and are also involved in the regulation of several types of tumors, inflammation, cardiovascular diseases and infertility. The importance of these transcription factors in physiology and pathophysiology has been largely investigated. Synthetic PPAR ligands are widely used in the treatment of dyslipidemia (e.g. fibrates - PPARα activators) or in diabetes mellitus (e.g. thiazolidinediones - PPARγ agonists) while a new generation of dual agonists reveals hypolipemic, hypotensive, antiatherogenic, anti-inflammatory and anticoagulant action. Many natural ligands, including polyphenolic compounds, influence the expression of these receptors. They have several health-promoting properties, including antioxidant, anti-inflammatory, and antineoplastic activities. Resveratrol, a stilbene polyphenol, is a biological active modulator of several signaling proteins, including PPARs. Given the enormous pharmacological potential of resveratrol, stilbene-based medicinal chemistry had a rapid increase covering various areas of research. The present review discusses ligands of PPARs that contain stilbene scaffold and summarises the different types of compounds on the basis of chemical structure.

Pterostilbene, a natural phenolic compound, synergizes the antineoplastic effects of megestrol acetate in endometrial cancer

Endometrial cancer is the most common gynecologic cancer in the United States and its incidence and mortality has been rising over the past decade. Few treatment options are available for patients with advanced and recurring endometrial cancers. Novel therapies, which are frequently toxic, are difficult to establish in this patient population which tends to be older and plagued by comorbidities such as diabetes mellitus and hypertension. Therefore, novel, non-toxic therapies are urgently needed. Megestrol acetate is a frequently used drug in endometrial cancer patients. However, its response rate is only 20–30%. To enhance the activity of megestrol acetate in endometrial cancer patients, we explored the potential of combining natural supplements with megestrol acetate and found that the addition of the natural phenolic compound, pterostilbene, to megestrol acetate resulted in a synergistic inhibition of cancer cell growth in vitro and an enhanced reduction of tumor growth in a xenograft mouse model. In addition, dual treatment led to attenuation of signaling pathways, as well as cell cycle and survival pathways. Our results demonstrated for the first time that the anti-tumor activity of megestrol acetate can be enhanced by combining with pterostilbene, providing an insight into the potential application of pterostilbene and megestrol acetate combination for the treatment of endometrial cancer.

Synthesis of Saccharumoside-B analogue with potential of antiproliferative and pro-apoptotic activities

A new series of phenolic glycoside esters, saccharumoside-B and its analogs (9b-9n, 10) have been synthesized by the Koenigs-Knorr reaction. Antiproliferative activities of the compounds (9b-9n, 10) were evaluated on various cancer cell lines including, MCF-7 breast, HL-60 leukemia, MIA PaCa-2 pancreatic, DU145 prostate, HeLa cervical and CaCo-2 colon, as well as normal human MCF10A mammary epithelial and human peripheral blood mononuclear cells (PBMC) by MTT assay. Compounds (9b-9n, 10) exhibited considerable antiproliferative effects against cancer cells with IC₅₀ range of 4.43 ± 0.35 to 49.63 ± 3.59 µM, but they are less cytotoxic on normal cells (IC₅₀ > 100 µM). Among all the compounds, 9f showed substantial antiproliferative activity against MCF-7 and HL-60 cells with IC₅₀ of 6.13 ± 0.64 and 4.43 ± 0.35, respectively. Further mechanistic studies of 9f were carried out on MCF-7 and HL-60 cell lines. 9f caused arrest of cell cycle of MCF-7 and HL-60 cells at G0/G1 phase. Apoptotic population elevation, mitochondrial membrane potential loss, increase of cytosolic cytochrome c and Bax levels, decrease of Bcl-2 levels and enhanced caspases-9 and -3 activities were observed in 9f-treated MCF-7 and HL-60 cells. These results demonstrate anticancer and apoptosis-inducing potentials of 9f in MCF-7 and HL-60 cells via intrinsic pathway.

Pterostilbene carboxaldehyde thiosemicarbazone, a resveratrol derivative inhibits 17β-Estradiol induced cell migration and proliferation in HUVECs

Angiogenesis plays important roles in tumor growth and metastasis, thus development of a novel angiogenesis inhibitor is essential for the improvement of therapeutics against cancer. Thrombospondins-1 (TSP-1) is a potent endogenous inhibitor of angiogenesis that acts through direct effects on endothelial cell migration, proliferation, survival, and activating apoptotic pathways. TSP-1 has been shown to disrupt estrogen-induced endothelial cell proliferation and migration. Here we investigated the potential of pterostilbene carboxaldehyde thiosemicarbazone (PTERC-T), a novel resveratrol (RESV) derivative, to inhibit angiogenesis induced by female sex steroids, particularly 17β-Estradiol (E2), on Human umbilical vein endothelial cells (HUVECs) and to elucidate the involvement of TSP-1 in PTERC-T action. Our results showed that PTERC-T significantly inhibited 17β-E2-stimulated proliferation of HUVECs and induced apoptosis as determined by annexin V/propidium iodide staining and cleaved caspase-3 expression. Furthermore, PTERC-T also inhibited endothelial cell migration, and invasion in chick chorioallantoic membrane (CAM) assay. In contrast, RESV failed to inhibit 17β-E2 induced HUVECs proliferation and invasion at similar dose. PTERC-T was also found to increase TSP-1 protein expression levels in a dose-dependent manner which, however, was counteracted by co-incubation with p38MAPK or JNK inhibitors, suggesting involvement of these pathways in PTERC-T action. These results suggest that the inhibitory effect of PTERC-T on 17β-E2 induced angiogenesis is associated, at least in part, with its induction of endothelial cell apoptosis and inhibition of cell migration through targeting TSP-1. Thus, PTERC-T could be considered as a potential lead compound for developing a class of new drugs targeting angiogenesis-related diseases.

Resveratrol for breast cancer prevention and therapy: Preclinical evidence and molecular mechanisms

Globally, breast cancer is the most frequently diagnosed cancer among women. The major unresolved problems with metastatic breast cancer is recurrence after receiving objective response to chemotherapy, drug-induced side effects of first line chemotherapy and delayed response to second line of treatment. Unfortunately, very few options are available as third line treatment. It is clear that under such circumstances there is an urgent need for new and effective drugs. Phytochemicals are among the most promising chemopreventive treatment options for the management of cancer. Resveratrol (3,5,4'-trihydroxy-trans-stilbene), a non-flavonoid polyphenol present in several dietary sources, including grapes, berries, soy beans, pomegranate and peanuts, has been shown to possess a wide range of health benefits through its effect on a plethora of molecular targets.The present review encompasses the role of resveratrol and its natural/synthetic analogue in the light of their efficacy against tumor cell proliferation, metastasis, epigenetic alterations and for induction of apoptosis as well as sensitization toward chemotherapeutic drugs in various in vitro and in vivo models of breast cancer. The roles of resveratrol as a phytoestrogen, an aromatase inhibitor and in stem cell therapy as well as adjuvent treatment are also discussed. This review explores the full potential of resveratrol in breast cancer prevention and treatment with current limitations, challenges and future directions of research.

A pterostilbene derivative suppresses osteoclastogenesis by regulating RANKL-mediated NFκB and MAPK signaling in RAW264.7 cells

BACKGROUND

A dysfunctional osteoclast activity is often the cause of bone destructive diseases, such as osteoporosis, periodontitis, erosive arthritis, and cancer. The NFκB ligand (RANKL) has been identified as a major mediator of bone resorption. Agents that suppress RANKL signaling have the potential to inhibit bone resorption or osteoclastogenesis. The present study aimed to determine the effect of a pterostilbene derivative (PTERC-T) for suppressing RANKL or tumor cells-induced osteoclastogenesis in RAW264.7 murine macrophages.

METHODS

Cytotoxicity was measured by MTT assay and inhibitory effect on osteoclastogenesis was analyzed by counting the number of tartrate-resistant acid phosphatase (TRAP)-positive multinucleated cells and measuring the expression levels of the osteoclast-specific genes. The reactive oxygen species (ROS) generation was detected by FACS. Further, signaling pathways were analyzed by immunofluorescence and immunoblot analyses.

RESULTS

PTERC-T suppressed the differentiation of monocytes to osteoclasts in a dose and time-dependent manner. The expression of osteoclast marker genes like TRAP, cathepsin K (CTSK), matrix metalloproteinase 9 (MMP9) and transcription factors c-Fos, and nuclear factor of activated T cells cytoplasmic 1 (NFATc1) were also diminished by PTERC-T. PTERC-T scavenged intracellular ROS generation within osteoclast precursors during RANKL-stimulated osteoclastogenesis. Mechanistically, PTERC-T abrogated the phosphorylation of MAPKs (ERK and JNK) and inhibited RANKL-induced activation of NFκB by suppressing IκBα phosphorylation and preventing NFκB/p65 nuclear translocation.

CONCLUSIONS

This study thus identifies PTERC-T as an inhibitor of osteoclast formation and provides evidence for its role in preventing osteoporosis and other bone related disorders. However, further studies are needed to establish its efficacy in vivo.

Aryl Hydrocarbon Receptor Ligand 5F 203 Induces Oxidative Stress That Triggers DNA Damage in Human Breast Cancer Cells

Breast tumors often show profound sensitivity to exogenous oxidative stress. Investigational agent 2-(4-amino-3-methylphenyl)-5-fluorobenzothiazole (5F 203) induces aryl hydrocarbon receptor (AhR)-mediated DNA damage in certain breast cancer cells. Since AhR agonists often elevate intracellular oxidative stress, we hypothesize that 5F 203 increases reactive oxygen species (ROS) to induce DNA damage, which thwarts breast cancer cell growth. We found that 5F 203 induced single-strand break formation. 5F 203 enhanced oxidative DNA damage that was specific to breast cancer cells sensitive to its cytotoxic actions, as it did not increase oxidative DNA damage or ROS formation in nontumorigenic MCF-10A breast epithelial cells. In contrast, AhR agonist and procarcinogen benzo[a]pyrene and its metabolite, 1,6-benzo[a]pyrene quinone, induced oxidative DNA damage and ROS formation, respectively, in MCF-10A cells. In sensitive breast cancer cells, 5F 203 activated ROS-responsive kinases: c-Jun-N-terminal kinase (JNK) and p38 mitogen activated protein kinase (p38). AhR antagonists (alpha-naphthoflavone, CH223191) or antioxidants (N-acetyl-l-cysteine, EUK-134) attenuated 5F 203-mediated JNK and p38 activation, depending on the cell type. Pharmacological inhibition of AhR, JNK, or p38 attenuated 5F 203-mediated increases in intracellular ROS, apoptosis, and single-strand break formation. 5F 203 induced the expression of cytoglobin, an oxidative stress-responsive gene and a putative tumor suppressor, which was diminished with AhR, JNK, or p38 inhibition. Additionally, 5F 203-mediated increases in ROS production and cytoglobin were suppressed in AHR100 cells (AhR ligand-unresponsive MCF-7 breast cancer cells). Our data demonstrate 5F 203 induces ROS-mediated DNA damage at least in part via AhR, JNK, or p38 activation and modulates the expression of oxidative stress-responsive genes such as cytoglobin to confer its anticancer action.