Regulation of cell cycle and RNA transcription genes identified by microarray analysis of PC-3 human prostate cancer cells treated with luteolin

Elucidating molecular and cellular targets and the antiprostate cancer potentials of promising phytochemicals: a review

Prostate cancer (PCa) has become the major health problem and the leading causes of cancer mortality among men. PCa often progresses from an early androgen-dependent form of cancer to a late (metastatic) androgen-independent cancer, for which no effective treatment options are available. Current therapies target testosterone depletion, androgen axis inhibition, androgen receptor (AR) downregulation and regulation PSA expression. These conventional treatment options, however, are intense and pose severe side effects. From the past few years, plant-derived compounds or phytochemicals have attracted much attention by the researchers worldwide for their promising approach in inhibiting the development and growth of cancer. This review emphasizes mechanistic role of promising phytochemicals on PCa. This review imparts to score anticancer efficacy of promising phyto-agents luteolin, fisetin, coumestrol and hesperidin with focus on the mechanistic action in management and treatment of PCa. These phytocompounds were also selected for their best binding affinity with the ARs on the basis of molecular docking studies.

Research Progress with Luteolin as an Anti-Tumor Agent

In this review, we outline the new expertise and research progress with luteolin as an antitumor agent, and clarify the related results from the aspects of tumor proliferation, apoptosis, invasion, metastasis, sensitivity to radiotherapy and chemotherapy, angiogenesis, and immunotherapy. In recent years, with the development of medical technology, the early detection rate of tumors has increased significantly. However, the number of cancer patients remains high. Therefore, a new and reasonably effective tumor therapeutic drug is urgently demanded. Luteolin, a flavonoid and widespread in nature, attracts more and more attention due to its universal biological utility, especially in the study of antitumor activity. This article reviews the work published in the past 20 years on the role and mechanism of luteolin as an antitumor agent, showing that this compound has a variety of effects for antitumor treatment by acting on different cytokines. Although clinical studies have not yet been widely carried out, a series of basic studies have confirmed that luteolin is a reasonably effective antineoplastic agent or anticancer adjuvant. Besides, derivatives of luteolin have good application prospects.

Phytochemicals in Inhibition of Prostate Cancer: Evidence from Molecular Mechanisms Studies

Prostate cancer is one of the leading causes of death for men worldwide. The development of resistance, toxicity, and side effects of conventional therapies have made prostate cancer treatment become more intensive and aggressive. Many phytochemicals isolated from plants have shown to be tumor cytotoxic. In vitro laboratory studies have revealed that natural compounds can affect cancer cell proliferation by modulating many crucial cellular signaling pathways frequently dysregulated in prostate cancer. A multitude of natural compounds have been found to induce cell cycle arrest, promote apoptosis, inhibit cancer cell growth, and suppress angiogenesis. In addition, combinatorial use of natural compounds with hormone and/or chemotherapeutic drugs seems to be a promising strategy to enhance the therapeutic effect in a less toxic manner, as suggested by pre-clinical studies. In this context, we systematically reviewed the currently available literature of naturally occurring compounds isolated from vegetables, fruits, teas, and herbs, with their relevant mechanisms of action in prostate cancer. As there is increasing data on how phytochemicals interfere with diverse molecular pathways in prostate cancer, this review discusses and emphasizes the implicated molecular pathways of cell proliferation, cell cycle control, apoptosis, and autophagy as important processes that control tumor angiogenesis, invasion, and metastasis. In conclusion, the elucidation of the natural compounds' chemical structure-based anti-cancer mechanisms will facilitate drug development and the optimization of drug combinations. Phytochemicals, as anti-cancer agents in the treatment of prostate cancer, can have significant health benefits for humans.

Role of Flavonoids as Epigenetic Modulators in Cancer Prevention and Therapy

Epigenetic regulation involves reversible changes in histones and DNA modifications that can be inherited without any changes in the DNA sequence. Dysregulation of normal epigenetic processes can lead to aberrant gene expression as observed in many diseases, notably cancer. Recent insights into the mechanisms of DNA methylation, histone modifications, and non-coding RNAs involved in altered gene expression profiles of tumor cells have caused a paradigm shift in the diagnostic and therapeutic approaches towards cancer. There has been a surge in search for compounds that could modulate the altered epigenetic landscape of tumor cells, and to exploit their therapeutic potential against cancers. Flavonoids are naturally occurring phenol compounds which are abundantly found among phytochemicals and have potentials to modulate epigenetic processes. Knowledge of the precise flavonoid-mediated epigenetic alterations is needed for the development of epigenetics drugs and combinatorial therapeutic approaches against cancers. This review is aimed to comprehensively explore the epigenetic modulations of flavonoids and their anti-tumor activities.

Remodeling the Epigenetic Landscape of Cancer-Application Potential of Flavonoids in the Prevention and Treatment of Cancer

Epigenetics, including DNA methylation, histone modification, and noncoding RNA regulation, are physiological regulatory changes that affect gene expression without modifying the DNA sequence. Although epigenetic disorders are considered a sign of cell carcinogenesis and malignant events that affect tumor progression and drug resistance, in view of the reversible nature of epigenetic modifications, clinicians believe that associated mechanisms can be a key target for cancer prevention and treatment. In contrast, epidemiological and preclinical studies indicated that the epigenome is constantly reprogrammed by intake of natural organic compounds and the environment, suggesting the possibility of utilizing natural compounds to influence epigenetics in cancer therapy. Flavonoids, although not synthesized in the human body, can be consumed daily and are common in medicinal plants, vegetables, fruits, and tea. Recently, numerous reports provided evidence for the regulation of cancer epigenetics by flavonoids. Considering their origin in natural and food sources, few side effects, and remarkable biological activity, the epigenetic antitumor effects of flavonoids warrant further investigation. In this article, we summarized and analyzed the multi-dimensional epigenetic effects of all 6 subtypes of flavonoids (including flavonols, flavones, isoflavones, flavanones, flavanols, and anthocyanidin) in different cancer types. Additionally, our report also provides new insights and a promising direction for future research and development of flavonoids in tumor prevention and treatment via epigenetic modification, in order to realize their potential as cancer therapeutic agents.

Luteolin attenuates Wnt signaling via upregulation of FZD6 to suppress prostate cancer stemness revealed by comparative proteomics

The mechanisms underlying luteolin-induced inhibition of prostate cancer (PCa) stemness have remained elusive. Here, we report that luteolin suppresses PCa stemness through Wnt signaling by upregulation of FZD6 (frizzled class receptor 6). Luteolin inhibits PCa cell proliferation, migration, self-renewal as well as the expression of prostate cancer stem cell markers in vitro. Through iTRAQ-based quantitative proteomics study, we identified 208 differentially expressed proteins in luteolin-treated PC-3 cells. Subsequent mechanistic analysis revealed that luteolin inhibits Wnt signaling by transcriptional upregulation of FZD6, and thereby suppressing the stemness of PCa cells. Furthermore, we identified FZD6 as a tumor suppressor that can abolish PCa stemness. In summary, our findings demonstrate that suppression of Wnt signaling by upregulation of FZD6 is a mechanism underlying luteolin-induced inhibition of PCa stemness. Our work suggests a new therapeutic strategy against human prostate cancer caused by aberrant activation of Wnt signaling.

Inhibition of ANO1 by luteolin and its cytotoxicity in human prostate cancer PC-3 cells

Anoctamin 1 (ANO1), a calcium-activated chloride channel, is highly amplified in prostate cancer, the most common form of cancer and leading causes of cancer death in men, and downregulation of ANO1 expression or its functional activity is known to inhibit cell proliferation, migration and invasion in prostate cancer cells. Here, we performed a cell-based screening for the identification of ANO1 inhibitors as potential anticancer therapeutic agents for prostate cancer. Screening of ~300 selected bioactive natural products revealed that luteolin is a novel potent inhibitor of ANO1. Electrophysiological studies indicated that luteolin potently inhibited ANO1 chloride channel activity in a dose-dependent manner with an IC₅₀ value of 9.8 μM and luteolin did not alter intracellular calcium signaling in PC-3 prostate cancer cells. Luteolin inhibited cell proliferation and migration of PC-3 cells expressing high levels of ANO1 more potently than that of ANO1-deficient PC-3 cells. Notably, luteolin not only inhibited ANO1 channel activity, but also strongly decreased protein expression levels of ANO1. Our results suggest that downregulation of ANO1 by luteolin is a potential mechanism for the anticancer effect of luteolin.

Capturing drug responses by quantitative promoter activity profiling

Quantitative analysis of cellular responses to drugs is of major interest in pharmaceutical research. Microarray technologies have been widely used for monitoring genome-wide expression changes. However, this approach has several limitations in terms of coverage of targeted RNAs, sensitivity, and quantitativeness, which are crucial for accurate monitoring of cellular responses. In this article, we report an application of genome-wide and quantitative profiling of cellular responses to drugs. We monitored promoter activities in MCF-7 cells by Cap Analysis of Gene Expression using a single-molecule sequencer. We identified a distinct set of promoters affected even by subtle inhibition of the Ras-ERK and phosphatidylinositol-3-kinase-Akt signal-transduction pathways. Furthermore, we succeeded in explaining the majority of promoter responses to inhibition of the upstream epidermal growth factor receptor kinase quantitatively based on the promoter profiles upon inhibition of the two individual downstream signaling pathways. Our results demonstrate unexplored utility of highly quantitative promoter activity profiling in drug research.

Luteolin sensitises drug-resistant human breast cancer cells to tamoxifen via the inhibition of cyclin E2 expression

Luteolin is a flavonoid that has been identified in many plant tissues and exhibits chemopreventive or chemosensitising properties against human breast cancer. However, the oncogenic molecules in human breast cancer cells that are inhibited by luteolin treatment have not been identified. This study found that the level of cyclin E2 (CCNE2) mRNA was higher in tumour cells (4.89-fold, (∗)P=0.005) than in normal paired tissue samples as assessed using real-time reverse-transcriptase polymerase chain reaction (RT-PCR) analysis (n=257). Further, relatively high levels of CCNE2 protein expression were detected in tamoxifen-resistant (TAM-R) MCF-7 cells. These results showed that the level of CCNE2 protein expression was specifically inhibited in luteolin-treated (5μM) TAM-R cells, either in the presence or absence of 4-OH-TAM (100nM). Combined treatment with 4-OH-TAM and luteolin synergistically sensitised the TAM-R cells to 4-OH-TAM. The results of this study suggest that luteolin can be used as a chemosensitiser to target the expression level of CCNE2 and that it could be a novel strategy to overcome TAM resistance in breast cancer patients.

Effects of Auraptene on IGF-1 Stimulated Cell Cycle Progression in the Human Breast Cancer Cell Line, MCF-7

Auraptene is being investigated for its chemopreventive effects in many models of cancer including skin, colon, prostate, and breast. Many mechanisms of action including anti-inflammatory, antiproliferative, and antiapoptotic effects are being suggested for the chemopreventive properties of auraptene. We have previously shown in the N-methylnitrosourea induced mammary carcinogenesis model that dietary auraptene (500 ppm) significantly delayed tumor latency. The delay in time to tumor corresponded with a significant reduction in cyclin D1 protein expression in the tumors. Since cyclin D1 is a major regulator of cell cycle, we further studied the effects of auraptene on cell cycle and the genes related to cell cycle in MCF-7 cells. Here we show that auraptene significantly inhibited IGF-1 stimulated S phase of cell cycle in MCF-7 cells and significantly changed the transcription of many genes involved in cell cycle.

Multiple Sites of Type II Site Ligand (Luteolin and BMHPC) Regulation of Gene Expression in PC-3 Cells

Type II [(3)H]estradiol binding site ligands including luteolin (a naturally occurring bioflavonoid) and synthetic compounds such as 2,6-bis((3-methoxy-4-hydroxyphenyl)methylene)cyclohexanone (BMHPC) inhibit normal and malignant prostate cell (PC-3, LNCaP, DU-145) proliferation in vitro and in vivo. Type II sites represent a binding domain on histone H4 possibly involved in an epigenetic mechanism for controlling gene transcription. Treatment of PC-3 human prostate cancer cells with luteolin or BMHPC modulated the expression of a number of genes in the epidermal growth factor receptor signaling pathway (EGFRSP) and cell cycle pathway (CCP). Pronounced stimulation (400-2000% of control) of c-FOS and p21 RNA expression was observed, suggesting that these were primary sites of action. Both compounds also caused irreversible G2/M arrest (p<0.001). siRNA's for c-FOS or p21 reduced the RNA expression of their respective targets by 85-95%, with minimal effects on cell proliferation. Furthermore, neither siRNA alone (single knockdown), or in combination (double knockdown), blocked luteolin or BMHPC inhibition of PC-3 cell proliferation. Thus, although c-FOS and p21 are known to modulate the expression of genes in the ESGRSP (EGFR, SOS, GRB2, JNK1, MKK4, RasGAP) and CCP (CCNA2, CCNE2, CDC25A, CDKN1A, CDKN1B, p27, PLK1) involved in the regulation of cell proliferation by luteolin and BMHPC, the c-FOS and p21 siRNA knockdown studies reported here suggest that c-FOS and p21 may be secondary bystanders in the overall response to these ligands in the regulation of PC-3 cell proliferation.

Apigenin induces DNA damage through the PKCδ-dependent activation of ATM and H2AX causing down-regulation of genes involved in cell cycle control and DNA repair

Apigenin, an abundant plant flavonoid, exhibits anti-proliferative and anti-carcinogenic activities through mechanisms yet not fully defined. In the present study, we show that the treatment of leukemia cells with apigenin resulted in the induction of DNA damage preceding the activation of the apoptotic program. Apigenin-induced DNA damage was mediated by p38 and protein kinase C-delta (PKCδ), yet was independent of reactive oxygen species or caspase activity. Treatment of monocytic leukemia cells with apigenin induced the phosphorylation of the ataxia-telangiectasia mutated (ATM) kinase and histone H2AX, two key regulators of the DNA damage response, without affecting the ataxia-telangiectasia mutated and Rad-3-related (ATR) kinase. Silencing and pharmacological inhibition of PKCδ abrogated ATM and H2AX phosphorylation, whereas inhibition of p38 reduced H2AX phosphorylation independently of ATM. We established that apigenin delayed cell cycle progression at G1/S and increased the number of apoptotic cells. In addition, genome-wide mRNA analyses showed that apigenin-induced DNA damage led to down-regulation of genes involved in cell-cycle control and DNA repair. Taken together, the present results show that the PKCδ-dependent activation of ATM and H2AX define the signaling networks responsible for the regulation of DNA damage promoting genome-wide mRNA alterations that result in cell cycle arrest, hence contributing to the anti-carcinogenic activities of this flavonoid.

Luteolin Regulation of Estrogen Signaling and Cell Cycle Pathway Genes in MCF-7 Human Breast Cancer Cells

cRNA microarray and real-time PCR (qPCR) studies identified a number of Estrogen Signaling Pathway (ESP) genes (GTF2H2, NCOR1, TAF9, NRAS, NRIP1, POLR2A, DDX5, NCOA3) and Cell Cycle Pathway genes (CCNA2, PCNA, CDKN1A, CCND1, PLK1) in MCF-7 breast cancer cells that are regulated by the bioflavonoid luteolin. Chromatin immunoprecipitation (ChIP) studies revealed that luteolin modified histone H4 acetylation at the PLK-1 promoter suggesting that this bioflavonoid controls gene transcription via an epigenetic mechanism involving histone H4 acetylation. These findings are consistent with the anti-estrogenic and anti-proliferative properties of luteolin in normal and malignant cells.

Luteolin and gefitinib regulation of EGF signaling pathway and cell cycle pathway genes in PC-3 human prostate cancer cells

cRNA microarray and real-time PCR (qPCR) studies from our lab identified five Cell Cycle Pathway (CCP) genes (CCNA2, CCNE2, CDC25A, CDKN1B, and PLK-1) as targets for luteolin in PC-3 prostate cancer cells [Shoulars et al., J. Steroid Biochem. Mol. Biol. 118 (2010) 41-50]. In this paper, Ingenuity Pathway Analysis of the microarray data identified 7 luteolin-regulated genes (EGFR, c-Fos, SOS, GRB2, JNK1, MKK4 and RasGAP) in the Epidermal Growth Factor Signaling Pathway (EGFSP) potentially involved in luteolin regulation of CCP genes and cell proliferation. To address these possibilities, we compared the response profiles (RNA and protein) of these EGFSP and CCP genes to luteolin and gefitinib by real-time PCR (qPCR) and Western blot analyses. Luteolin and gefitinib are known antagonists of EGFR-associated tyrosine protein kinase. Thus, the response profiles of EGFR regulated EGFSP or CCP genes should be very similar if genes in both pathways are controlled through this common mechanism of action. Treatment of PC-3 cell with luteolin for 24h caused a 4-fold stimulation of c-Fos gene expression, significant inhibition (p<0.001) of the CCP genes and G2/M arrest. Treatment of PC-3 cells with gefitinib also inhibited most of the CCP genes in a fashion similar to that of luteolin, however, the EGFR antagonist inhibited c-Fos gene expression, stimulated CDKN1B (p27) and arrested the cells in G0/G1. Thus, although the response patterns of most of the CCP genes to luteolin or gefitinib were similar, the effects of the two compounds on EGFSP gene expression and cell cycle arrest were clearly different. Combination studies revealed that the response of EGFSP genes to luteolin was not affected by gefitinib, even though the two compounds were additive with respect to their abilities to inhibit CCNA2, CCNE2, CDC25A and PCNA. These findings suggest that luteolin and gefitinib regulate CCP gene expression through a common mechanism involving EGFR-associated tyrosine kinase. Conversely, luteolin regulates PC-3 cell proliferation through an EGFR-tyrosine kinase independent mechanism(s), likely involving the epigenetic control of gene EGFSP gene expression through histone H4 binding interactions resulting in the upregulation of c-Fos and p21 gene expression.