Anti-hepatoma cells function of luteolin through inducing apoptosis and cell cycle arrest

Antioxidative and Anticancer Potential of Luteolin: A Comprehensive Approach Against Wide Range of Human Malignancies

Luteolin is widely distributed phytochemical, a flavonoid, in kingdom plantae. Luteolin with potential antioxidant activity prevent ROS-induced damages and reduce oxidative stress which is mainly responsible in pathogenesis of many diseases. Several chemo preventive activities and therapeutic benefits are associated with luteolin. Luteolin prevents cancer via modulation of numerous pathways, that is, by inactivating proteins; such as procaspase-9, CDC2 and cyclin B or upregulation of caspase-9 and caspase-3, cytochrome C, cyclin A, CDK2, and APAF-1, in turn inducing cell cycle arrest as well as apoptosis. It also enhances phosphorylation of p53 and expression level of p53-targeted downstream gene. By Increasing BAX protein expression; decreasing VEGF and Bcl-2 expression it can initiate cell cycle arrest and apoptosis. Luteolin can stimulate mitochondrial-modulated functions to cause cellular death. It can also reduce expression levels of p-Akt, p-EGFR, p-Erk1/2, and p-STAT3. Luteolin plays positive role against cardiovascular disorders by improving cardiac function, decreasing the release of inflammatory cytokines and cardiac enzymes, prevention of cardiac fibrosis and hypertrophy; enhances level of CTGF, TGFβ1, ANP, Nox2, Nox4 gene expressions. Meanwhile suppresses TGFβ1 expression and phosphorylation of JNK. Luteolin helps fight diabetes via inhibition of alpha-glucosidase and ChE activity. It can reduce activity levels of catalase, superoxide dismutase, and GS4. It can improve blood glucose, insulin, HOMA-IR, and HbA1c levels. This review is an attempt to elaborate molecular targets of luteolin and its role in modulating irregularities in cellular pathways to overcome severe outcomes during diseases including cancer, cardiovascular disorders, diabetes, obesity, inflammation, Alzheimer's disease, Parkinson's disease, hepatic disorders, renal disorders, brain injury, and asthma. As luteolin has enormous therapeutic benefits, it could be a potential candidate in future drug development strategies.

Vulnerability of Antioxidant Drug Therapies on Targeting the Nrf2-Trp53-Jdp2 Axis in Controlling Tumorigenesis

Control of oxidation/antioxidation homeostasis is important for cellular protective functions, and disruption of the antioxidation balance by exogenous and endogenous ligands can lead to profound pathological consequences of cancerous commitment within cells. Although cancers are sensitive to antioxidation drugs, these drugs are sometimes associated with problems including tumor resistance or dose-limiting toxicity in host animals and patients. These problems are often caused by the imbalance between the levels of oxidative stress-induced reactive oxygen species (ROS) and the redox efficacy of antioxidants. Increased ROS levels, because of abnormal function, including metabolic abnormality and signaling aberrations, can promote tumorigenesis and the progression of malignancy, which are generated by genome mutations and activation of proto-oncogene signaling. This hypothesis is supported by various experiments showing that the balance of oxidative stress and redox control is important for cancer therapy. Although many antioxidant drugs exhibit therapeutic potential, there is a heterogeneity of antioxidation functions, including cell growth, cell survival, invasion abilities, and tumor formation, as well as the expression of marker genes including tumor suppressor proteins, cell cycle regulators, nuclear factor erythroid 2-related factor 2, and Jun dimerization protein 2; their effectiveness in cancer remains unproven. Here, we summarize the rationale for the use of antioxidative drugs in preclinical and clinical antioxidant therapy of cancer, and recent advances in this area using cancer cells and their organoids, including the targeting of ROS homeostasis.

Combination of transcriptomic and proteomic approaches helps unravel the mechanisms of luteolin in inducing liver cancer cell death via targeting AKT1 and SRC

Introduction

Luteolin, a natural compound commonly used in traditional Chinese medicine, shows clinical potential as an anti-liver cancer agent. The mechanisms underlying the anti-liver cancer effect of luteolin are limited versus those reported for other cancers. Accordingly, this study was conducted to bridge the existing knowledge gap.

Methods

Transcriptomic and proteomic analyses of the response of the hepatocellular carcinoma cell line HuH-7 to luteolin were conducted, and a possible pathway was elucidated using confocal laser scanning microscopy (CLSM), flow cytometry, western blotting, qRT-PCR and bio-layer interferometry assay to systematically explore the possible mechanisms underlying the inhibition of the proliferation of liver cancer cells by luteolin.

Results and Discussion

Results showed that luteolin significantly inhibited HuH-7 cell proliferation. Transcriptomic and proteomic analyses collectively revealed that luteolin could promote cell cycle arrest and apoptosis in HuH-7 cells through transcription factors p53, nuclear factor kappa B (NF-κB), FOXO, ATF2, and TCF/LEF via AKT1, as well as the KEAP-NRF and SRC-STAT3 pathways. Furthermore, AKT1 and SRC were identified as the 2 targets of luteolin. Nuclear translocation of transcription factors p53 and NF-κB were affected by luteolin administration. Additionally, AKT1 activity affected normal metabolism in HuH-7 cells and resulted in the accumulation of reactive oxygen species, which activated MOMP and further promoted apoptosis. Our results systematically elucidate the mechanism of luteolin in inhibiting the proliferation of liver cancer cells, mainly through cell cycle arrest and apoptosis via targeting AKT1 and SRC.

Luteolin: A promising modulator of apoptosis and survival signaling in liver cancer

Due to the increasing incidence of cancer and the difficulties in determining the safety profile of existing therapeutic approaches, cancer research has recently become heavily involved in the search for new therapeutic approaches. The therapeutic significance of natural substances, especially flavonoids, against the onset and progression of cancer has been emphasized in traditional food-based medicine. Interestingly, the flavone luteolin possesses biological effects that have been linked to its anti-inflammatory, antioxidant, and anticancer effects. Luteolin interacts with several downstream chemicals and signaling pathways, including those involved in apoptosis, autophagy, cell cycle progression, and angiogenesis, to exert its anticancer effects on various cancerous cells. A complete understanding of both intrinsic and extrinsic apoptotic pathways, autophagy, and, most critically, the nanodelivery of luteolin in liver cancer is provided in the current review.

Targeting epidermal growth factor receptor and its downstream signaling pathways by natural products: A mechanistic insight

The epidermal growth factor receptor (EGFR) is a transmembrane receptor tyrosine kinase (RTK) that maintains normal tissues and cell signaling pathways. EGFR is overactivated and overexpressed in many malignancies, including breast, lung, pancreatic, and kidney. Further, the EGFR gene mutations and protein overexpression activate downstream signaling pathways in cancerous cells, stimulating the growth, survival, resistance to apoptosis, and progression of tumors. Anti-EGFR therapy is the potential approach for treating malignancies and has demonstrated clinical success in treating specific cancers. The recent report suggests most of the clinically used EGFR tyrosine kinase inhibitors developed resistance to the cancer cells. This perspective provides a brief overview of EGFR and its implications in cancer. We have summarized natural products-derived anticancer compounds with the mechanistic basis of tumor inhibition via the EGFR pathway. We propose that developing natural lead molecules into new anticancer agents has a bright future after clinical investigation.

Phytochemicals as Potential Lead Molecules against Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is the most prevalent form of liver cancer, accounting for 85-90% of liver cancer cases and is a leading cause of cancer-related mortality worldwide. The major risk factors for HCC include hepatitis C and B viral infections, along with chronic liver diseases, such as cirrhosis, fibrosis, and non-alcoholic steatohepatitis associated with metabolic syndrome. Despite the advancements in modern medicine, there is a continuous rise in the annual global incidence rate of HCC, and it is estimated to reach >1 million cases by 2025. Emerging research in phytomedicine and chemotherapy has established the anti-cancer potential of phytochemicals, owing to their diverse biological activities. In this review, we report the major phytochemicals that have been explored in combating hepatocellular carcinoma and possess great potential to be used as an alternative or in conjunction with the existing HCC treatment modalities. An overview of the pre-clinical observations, mechanism of action and molecular targets of some of these phytochemicals is also incorporated.

Luteolin as a potential hepatoprotective drug: Molecular mechanisms and treatment strategies

Luteolin is a flavonoid widely present in various traditional Chinese medicines. In recent years, luteolin has received more attention due to its impressive liver protective effect, such as metabolic associated fatty liver disease, hepatic fibrosis and hepatoma. This article summarizes the pharmacological effects, pharmacokinetic characteristics, and toxicity of luteolin against liver diseases, and provides prospect. The results indicate that luteolin improves liver lesions through various mechanisms, including inhibiting inflammatory factors, reducing oxidative stress, regulating lipid balance, slowing down excessive aggregation of extracellular matrix, inducing apoptosis and autophagy of liver cancer cells. Pharmacokinetics research manifested that due to metabolic effects, the bioavailability of luteolin is relatively low. It is worth noting that appropriate modification, new delivery systems, and derivatives can enhance its bioavailability. Although many studies have shown that the toxicity of luteolin is minimal, strict toxicity experiments are still needed to evaluate its safety and promote its reasonable development. In addition, this study also discussed the clinical applications related to luteolin, indicating that it is a key component of commonly used liver protective drugs in clinical practice. In view of its excellent pharmacological effects, luteolin is expected to become a potential drug for the treatment of various liver diseases.

Therapeutic Potential of Luteolin on Cancer

Cancer is a global concern, as the rate of incidence is increasing each year. The challenges related to the current chemotherapy drugs, such as the concerns related to toxicity, turn to cancer therapeutic research to discover alternative therapy strategies that are less toxic to normal cells. Among those studies, the use of flavonoids—natural compounds produced by plants as secondary metabolites for cancer therapy—has been a hot topic in cancer treatment. Luteolin, a flavonoid that has been present in many fruits, vegetables, and herbs, has been identified to exhibit numerous biological activities, including anti-inflammatory, antidiabetic, and anticancer properties. The anticancer property of Luteolin has been extensively researched in many cancer types and has been related to its ability to inhibit tumor growth by targeting cellular processes such as apoptosis, angiogenesis, migration, and cell cycle progression. It achieves this by interacting with various signaling pathways and proteins. In the current review, the molecular targets of Luteolin as it exerts its anticancer properties, the combination therapy that includes Luteolin with other flavonoids or chemotherapeutic drugs, and the nanodelivery strategies for Luteolin are described for several cancer types.

Targeting regulated cell death with plant natural compounds for cancer therapy: A revisited review of apoptosis, autophagy-dependent cell death, and necroptosis

Regulated cell death (RCD) refers to programmed cell death regulated by various protein molecules, such as apoptosis, autophagy-dependent cell death, and necroptosis. Accumulating evidence has recently revealed that RCD subroutines have several links to many types of human cancer; therefore, targeting RCD with pharmacological small-molecule compounds would be a promising therapeutic strategy. Moreover, plant natural compounds, small-molecule compounds synthesized from plant sources, and their derivatives have been widely reported to regulate different RCD subroutines to improve potential cancer therapy. Thus, in this review, we focus on updating the intricate mechanisms of apoptosis, autophagy-dependent cell death, and necroptosis in cancer. Moreover, we further discuss several representative plant natural compounds and their derivatives that regulate the above-mentioned three subroutines of RCD, and their potential as candidate small-molecule drugs for the future cancer treatment.

Crosstalk between xanthine oxidase (XO) inhibiting and cancer chemotherapeutic properties of comestible flavonoids- a comprehensive update

Gout is an inflammatory disease caused by metabolic disorder or genetic inheritance. People throughout the world are strongly dependent on ethnomedicine for the treatment of gout and some receive satisfactory curative treatment. The natural remedies as well as established drugs derived from natural sources or synthetically made exert their action by mechanisms that are closely associated with anticancer treatment mechanisms regarding inhibition of xanthine oxidase, feedback inhibition of de novo purine synthesis, depolymerization and disappearance of microtubule, inhibition of NF-ĸB activation, induction of TRAIL, promotion of apoptosis, and caspase activation and proteasome inhibition. Some anti-gout and anticancer novel compounds interact with same receptors for their action, e.g., colchicine and colchicine analogues. Dietary flavonoids, i.e., chrysin, kaempferol, quercetin, fisetin, pelargonidin, apigenin, luteolin, myricetin, isorhamnetin, phloretinetc etc. have comparable IC₅₀ values with established anti-gout drug and effective against both cancer and gout. Moreover, a noticeable number of newer anticancer compounds have already been isolated from plants that have been using by local traditional healers and herbal practitioners to treat gout. Therefore, the anti-gout plants might have greater potentiality to become selective candidates for screening of newer anticancer leads.

Therapeutic Effects of Crocin Alone or in Combination with Sorafenib against Hepatocellular Carcinoma: In Vivo & In Vitro Insights

This study investigated the therapeutic effects of the phytochemical crocin alone or in combination with sorafenib both in rats chemically induced with hepatocellular carcinoma (HCC) and in human liver cancer cell line (HepG2). Male rats were randomly divided into five groups, namely, control group, HCC induced group, and groups treated with sorafenib, crocin or both crocin and sorafenib. HCC was induced in rats with a single intraperitoneal injection of diethylnitrosamine (DEN), then 2-acetylaminofluorene (2-AAF). The HCC-induced rats showed a significant decrease in body weight compared to animals treated with either or both examined drugs. Serum inflammatory markers (C-reactive protein (CRP); interleukin-6 (IL-6); lactate dehydrogenase (LDH), and oxidative stress markers were significantly increased in the HCC group and were restored upon treatment with either or both of therapeutic molecules. Morphologically, the HCC-induced rats manifested most histopathological features of liver cancer. Treatment with either or both of crocin and sorafenib successfully restored normal liver architecture. The expression of key genes involved in carcinogenesis (TNFα, p53, VEGF and NF-κB) was highly augmented upon HCC induction and was attenuated post-treatment with either or both examined drugs. Treatment with both crocin and sorafenib improved the histopathological and inflammation parameters as compared to single treatments. The in vivo anti-cancer effects of crocin and/or sorafenib were supported by their respective cytotoxicity on HepG2 cells. Crocin and sorafenib displayed an anti-tumor synergetic effect on HepG2 cells. The present findings demonstrated that a treatment regimen with crocin and sorafenib reduced liver toxicity, impeded HCC development, and improved the liver functions.

In Vitro Validation of Network Pharmacology Predictions: Ginsenoside Rg3 Inhibits Hepatocellular Carcinoma Cell Proliferation via SIRT2

To elucidate the molecular mechanisms underlying the therapeutic activity of ginsenoside Rg3 (Gs-Rg3) in the context of hepatocellular carcinoma (HCC). Methods Relevant databases were searched to identify protein targets that were both dysregulated and implicated in HCC, as well as targeted by Gs-Rg3. Generation of a protein-protein interaction network facilitated the selection of connected nodes for the construction of a shared disease- and drug-target interaction network model, and topological analysis identified the most highly connected nodes. Targets were annotated with their associated Gene Ontology terms, followed by Kyoto Encyclopedia of Genes and Genomes biological pathway enrichment analysis. In vitro experiments using 2 hours CC cell lines (Bel-7402 and HCCLM3) were performed to investigate the impact of Gs-Rg3 on cell proliferation, viability, cell cycle, cyclin D1 and sirtuin 2 (SIRT2) levels, and global cellular histone acetylation (specifically H3K18ac and H4K16ac). Results Network pharmacology suggested that Gs-Rg3 synergistically targets multiple proteins and pathways relevant to HCC pathogenesis, including those involved in cell cycle and proliferation. In vitro experiments confirmed that Gs-Rg3 dose-dependently inhibits cell proliferation and viability; induces G1 phase cell cycle arrest; decreases cyclin D1, cyclin-dependent kinase 2 (CDK2), and SIRT2 levels; and enhances global H3K18ac and H4K16ac. Conclusions Hypotheses derived from the network analysis were confirmed in vitro. Gs-Rg3 induces G1 phase cell cycle arrest, concomitant with decreased cyclin D1 and CDK2 levels, suggesting a possible mechanism for inhibiting proliferation. In addition, Gs-Rg3 decreases SIRT2 levels, concomitant with enhanced global H3K18ac and H4K16ac. These findings provide a theoretical basis and a support for further preclinical study of the safety and antineoplastic molecular mechanisms of Gs-Rg3, with the goal of eventual clinical translation.

Perspectives on the Clinical Development of NRF2-Targeting Drugs

The transcription factor NRF2 (nuclear factor erythroid 2-related factor 2) triggers homeostatic responses against a plethora of environmental or endogenous deviations in redox metabolism, inflammation, proteostasis, etc. Therefore, pharmacological activation of NRF2 is a promising therapeutic strategy for several chronic diseases that are underlined by low-grade oxidative inflammation and dysregulation of redox metabolism, such as neurodegenerative, cardiovascular, and metabolic diseases. While NRF2 activation is useful in inhibiting carcinogenesis, its inhibition is needed in constituted tumors where NRF2 provides a survival advantage in the challenging tumor niche. This review describes the electrophilic and non-electrophilic NRF2 activators with clinical projection in various chronic diseases. We also analyze the status of NRF2 inhibitors, which are for the moment in a proof-of-concept stage. Advanced in silico screening and medicinal chemistry are expected to provide new or repurposing small molecules with increased potential for fostering the development of targeted NRF2 modulators. The nuclear factor erythroid 2 (NFE2)-related factor 2 (NRF2) is rapidly degraded by proteasomes under a basal condition in a Keap1-dependent manner. ROS oxidatively modifies Keap1 to release NRF2 and allow its nuclear translocation. Here it binds to the antioxidant response element to regulate gene transcription. An alternative mechanism controlling NRF2 stability is glycogen synthase kinase 3 (GSK-3)-induced phosphorylation. Indicated in blue are NRF2-activating and NRF2-inhibiting drugs.

Luteolin inhibits melanoma growth in vitro and in vivo via regulating ECM and oncogenic pathways but not ROS

Luteolin inhibited growth of several cancer cells in vitro in previous studies, with limited in vivo studies, and no comprehensive understanding of molecular mechanisms at genomics level. This study identified luteolin as an effective agent to inhibit melanoma cell growth in vitro and in vivo. Molecular studies and genomic profiling were used to identify the mechanism of action of luteolin in melanoma cells. As a ROS (reactive oxygen species) scavenger, luteolin unexpectedly induced ROS; but co-treatment with antioxidants NAC or mito-TEMPO did not rescue cell growth inhibition, although the levels of ROS levels were reduced. Next, we profiled luteolin-induced differentially expressed genes (DEGs) in 4 melanoma cell lines using RNA-Seq, and performed pathway analysis using a combination of bioinformatics software including PharmetRx which was especially effective in discovering pharmacological pathways for potential drugs. Our results show that luteolin induces changes in three main aspects: the cell-cell interacting pathway (extracellular matrix, ECM), the oncogenic pathway and the immune response signaling pathway. Based on these results, we further validated that luteolin was especially effective in inhibiting cell proliferation when cells were seeded at low density, concomitantly with down-regulation of fibronectin accumulation. In conclusion, through extensive DEG profiling in a total of 4 melanoma cell lines, we found that luteolin-mediated growth inhibition in melanoma cells was perhaps not through ROS induction, but likely through simultaneously acting on multiple pathways including the ECM (extracellular matrix) pathway, the oncogenic signaling and the immune response pathways. Further investigations on the mechanisms of this promising compound are warranted and likely result in application to cancer patients as its safety pharmacology has been validated in autism patients.

Can luteolin be a therapeutic molecule for both colon cancer and diabetes?

Diabetes and colon cancer are the leading cause of mortality worldwide. According to World Health Organization, the number of patients with diabetes and cancer is going to be elevated by 50% in 2020. However, several flavonoids have been known to be useful in reducing the chance of cancer/diabetes but the hunt of a single biomolecule that can act as therapeutic and preventive molecules for future epidemic continues. In this review, we aim to perform an illustration of all researches done that target molecular signaling using luteolin in cancer/diabetes and predicted target protein using PharmMapper. The search confirms that luteolin can be a remedial molecule for both cancer and diabetes via acting on variety of signaling pathway. Furthermore, we also intend to illustrate/compare the predicted and verified molecular modes of action of luteolin. Fluorescence in situ hybridization analysis confirms the expression of CCND1 in colon cancer while immunofluorescence analysis confirms the CDK4 in diabetes. Finally, an effort has been made to map docking of marker protein-luteolin at a particular site using docking software. This review gives a holistic overview about luteolin as a therapeutic molecule for cancer/diabetes via acting on multiple signaling cascade such as p53, Wnt, eNOS, iNOS, SOD and MMP9, with especial emphasis on the cyclin-CDK pathway. Altogether, the review concludes that luteolin can be a molecule for the therapy of both cancer and diabetes by acting on broad signaling pathway.

Traditional Chinese medicine combined with hepatic targeted drug delivery systems: A new strategy for the treatment of liver diseases

Liver diseases are clinically common and present a substantial public health issue. Many of the currently available drugs for the treatment of liver diseases suffer from limitations that include low hepatic distribution, lack of target effects, poor in vivo stability and adverse effects on other organs. Consequently, conventional treatment of hepatic diseases is ineffective. TCM is commonly used in the treatment of liver diseases worldwide, particularly in China, and has advantages over conventional therapy. HTDDS can be designed to enhance clinical efficacy in the treatment of liver diseases. We have conducted an extensive review of 335 studies reported since 1964. These included about 166 references involving the treatment of liver diseases with TCM (covering active components of TCM, single TCM and Chinese medicine formulas), 169 reports on HTDDS and background studies on liver-related diseases. Here we review the long history of TCM in the treatment of liver diseases.We have also reviewed the status of studies on active components of TCM using nanotechnology-based targeted delivery systems to provide support for further research and development of TCM-based targeted preparations for the treatment of liver disease.

Luteolin, a flavonoid, as an anticancer agent: A review

Many food-derived phytochemicals and their derivatives represent a cornucopia of new anti-cancer compounds. Luteolin (3,4,5,7-tetrahydroxy flavone) is a flavonoid found in different plants such as vegetables, medicinal herbs, and fruits. It acts as an anticancer agent against various types of human malignancies such as lung, breast, glioblastoma, prostate, colon, and pancreatic cancers. It also blocks cancer development in vitro and in vivo by inhibition of proliferation of tumor cells, protection from carcinogenic stimuli, and activation of cell cycle arrest, and by inducing apoptosis through different signaling pathways. Luteolin can additionally reverse epithelial-mesenchymal transition (EMT) through a mechanism that involves cytoskeleton shrinkage, induction of the epithelial biomarker E-cadherin expression, and by down-regulation of the mesenchymal biomarkers N-cadherin, snail, and vimentin. Furthermore, luteolin increases levels of intracellular reactive oxygen species (ROS) by activation of lethal endoplasmic reticulum stress response and mitochondrial dysfunction in glioblastoma cells, and by activation of ER stress-associated proteins expressions, including phosphorylation of eIF2α, PERK, CHOP, ATF4, and cleaved-caspase 12. Accordingly, the present review article summarizes the progress of recent research on luteolin against several human cancers.

Luteolin inhibits cell cycle progression and induces apoptosis of breast cancer cells through downregulation of human telomerase reverse transcriptase

Luteolin is a flavonoid, which has been extensively investigated due to its antitumor effects; however, the underlying mechanisms of its action remain largely unknown. The present study aimed to investigate the role of luteolin in breast cancer (BC), and explored how luteolin suppresses the growth and induces the apoptosis of BC cells. The MTS assay was used to determine the anticancer activity of luteolin. Colony formation and Transwell assays were performed to evaluate the effects of luteolin on cell growth and invasion. Cell cycle progression and apoptosis were analyzed by flow cytometry. In addition, western blotting was performed to analyze cellular apoptosis and signaling pathways elicited by luteolin. The present study revealed that the proliferation of the BC cell line MDA-MB-231 was effectively suppressed by luteolin in a dose-dependent manner. Additionally, luteolin was revealed to increase apoptotic rates in BC cells. Dose-dependent cell cycle arrest in S phase was observed following treatment with luteolin in MDA-MB-231 cells. Mechanistically, luteolin reduced telomerase levels in a dose-dependent manner. Additionally, luteolin inhibited phosphorylation of the nuclear factor-κB inhibitor α and its target gene c-Myc, to suppress human telomerase reverse transcriptase (hTERT) expression, which encodes the catalytic subunit of telomerase. Collectively, the results of the present study indicated that luteolin may inhibit BC cell growth by targeting hTERT, suggesting that the mechanism of hTERT regulation by luteolin may justify further study regarding its potential as a therapeutic target for BC treatment.

Borneol and Luteolin from Chrysanthemum morifolium Regulate Ubiquitin Signal Degradation

Targeting the two degradation systems, ubiquitin proteasome pathway and ubiquitin signal autophagy lysosome system, plays an important function in cancer prevention. Borneol is called an "upper guiding drug". Luteolin has demonstrated anticancer activity. The fact that borneol regulates luteolin can be sufficient to serve as an alternative strategy. Borneol activates luteolin to inhibit E1 and 20S activity (IC₅₀ = 118.8 ± 15.7 μM) and perturb the 26S proteasome structure in vitro. Borneol regulates luteolin to inhibit 26S activity (IC₅₀ = 157 ± 19 μM), induces apoptosis (LC₅₀ = 134 ± 4 μM), and causes pre-G1 and G0/G1 arrest in HepG2 cells. Borneol regulates luteolin to induce ubiquitin signal autophagic degradation, resulting in induction of E1, reduction of USP47, and accumulation of p62 in HepG2 reporter cells. Interestingly, luteolin decreased Ub conjugates, while borneol increased the accumulation of Ub conjugates in HepG2 reporter cells. E1, p62, and ubiquitin levels were downregulated in borneol-treated HepG2 reporter cells at 24 h. These observations suggest a potential autophagic inhibitor of borneol that may guide luteolin in the ubiquitin proteasome pathway and the ubiquitin signal autophagic degradation.

Targeting the SET and RING-associated (SRA) domain of ubiquitin-like, PHD and ring finger-containing 1 (UHRF1) for anti-cancer drug development

Ubiquitin-like containing PHD Ring Finger 1 (UHRF1) is a multi-domain protein with a methyl-DNA binding SRA (SET and RING-associated) domain, required for maintenance DNA methylation mediated by DNMT1. Primarily expressed in proliferating cells, UHRF1 is a cell-cycle regulated protein that is required for S phase entry. Furthermore, UHRF1 participates in transcriptional gene regulation by connecting DNA methylation to histone modifications. Upregulation of UHRF1 may serve as a biomarker for a variety of cancers; including breast, gastric, prostate, lung and colorectal carcinoma. To this end, overexpression of UHRF1 promotes cancer metastasis by triggering aberrant patterns of DNA methylation, and subsequently, silencing tumor suppressor genes. Various small molecule effectors of UHRF1 have been reported in the literature, although the mechanism of action may not be fully characterized. Small molecules that potentially bind to the SRA domain may affect the ability of UHRF1 to bind hemimethylated DNA; thereby reducing aberrant DNA methylation. Therefore, in a subset of cancers, small molecule UHRF1 inhibitors may restore normal gene expression and serve as useful anti-cancer therapeutics.

Luteolin induces myelodysplastic syndrome‑derived cell apoptosis via the p53‑dependent mitochondrial signaling pathway mediated by reactive oxygen species

Luteolin, a common dietary flavonoid, induces the apoptosis of cells in several types of cancer. However, its role in myelodysplastic syndrome (MDS) and the potential underlying mechanisms remain to be elucidated. To evaluate the potential benefit and underlying mechanisms of luteolin in MDS cells, the viability of SKM‑1 cells and primary bone marrow (PBM) mononuclear cells from patients with intermediate‑ or high‑risk MDS were assessed using a Cell Counting Kit‑8 assay. The apoptotic features of cell morphology were assessed using Wright‑Giemsa staining, DNA fragmentation was analyzed by agarose gel electrophoresis, and the extent of apoptosis was quantified by flow cytometry (FCM). Reactive oxygen species (ROS) were measured by FCM with 2,7‑dichlorodihydrofluorescein diacetate staining and mitochondrial membrane potential (ΔΨm) was determined using 5,5',6,6'‑tetrachloro‑1,1',3,3'‑tetraethylbenzimidazolylcarbocyanine iodide staining. Caspase activity was detected using a fluorometric protease assay. Furthermore, the effects of luteolin on the expression of apoptosis‑related proteins were analyzed using western blot analysis. The resulting data revealed that luteolin significantly inhibited the proliferation of SKM‑1 cells in vitro, and its half maximal inhibitory concentration was 139.41 µM at 24 h and 23.95 µM at 72 h. Luteolin also markedly inhibited the proliferation of mononuclear cells from patients with intermediate‑ or high‑risk MDS. Luteolin suppressed cell proliferation, mainly as a result of the induction of apoptosis, as demonstrated by typical apoptotic morphological features, the ladder pattern of genomic DNA fragmentation, and the results of FCM using Annexin V‑FITC/PI double staining. It was also found that short‑term exposure of SKM‑1 cells to luteolin led to a marked increase in the accumulation of ROS. The increased intracellular level of ROS appeared to induce the activation of p53 and elevate the B‑cell lymphoma 2 (Bcl‑2)‑associated X protein/Bcl‑2 ratio, which modulates ΔΨm and triggers the release of cytochrome c, and may increase the activities of apoptotic protease activating factor 1, caspase‑3, ‑8 and ‑9 to further trigger the destruction of structural and specific proteins and thereby cell apoptosis. Notably, the inhibition of ROS generation by the antioxidant N‑acetyl‑L‑cysteine significantly attenuated the luteolin‑induced loss of ΔΨm and activities of caspase‑3, ‑8 and ‑9. These data suggested that luteolin exerts its pro‑apoptotic action partly through the p53‑dependent mitochondrial signaling pathway mediated by intracellular ROS, which provides a promising therapeutic candidate for patients with MDS.

Selective Cytotoxicity of Luteolin and Kaempferol on Cancerous Hepatocytes Obtained from Rat Model of Hepatocellular Carcinoma: Involvement of ROS-Mediated Mitochondrial Targeting

To evaluate the cytotoxicity effects of luteolin (LUT) and kaempferol (KAE) via reactive oxygen species (ROS) mediated mitochondrial targeting on hepatocytes obtained from the liver of hepatocellular carcinoma (HCC) rats. In this study, HCC induced by diethylnitrosamine (DEN) and 2-acetylaminofluorene (2-AAF). In the following, rat liver hepatocytes and mitochondria were isolated and tested for every eventual apoptotic and anti-HCC effects of LUT and KAE. The results of MTT assay showed that LUT and KAE were able to induce selective cytotoxicity in hepatocytes of HCC group in a dose- and time-dependent manner. Treatment of mitochondria from hepatocytes of HCC group with LUT and KAE were accompanied by loss of mitochondrial membrane potential (MMP) and mitochondrial swelling and release of cytochrome c (P < 0.001) via reactive oxygen species (ROS) generation before cytotoxicity ensued. LUT and KAE also increased activation of caspase-3 (P < 0.001 and P < 0.01, respectively). Flow-cytometry analysis indicated that the mode of cell death induced by these flavonoids were mostly apoptosis. Importantly, LUT and KAE were nontoxic for healthy hepatocytes and mitochondria. Therefore, we suggest that LUT and KAE are a good candidate for the complementary therapeutic agent against HCC.

Luteolin induces apoptosis in vitro through suppressing the MAPK and PI3K signaling pathways in gastric cancer

Luteolin, an active component of traditional Chinese medicine, exhibits potential for anti-tumor proliferation; however, the molecular events occurring in such process and the signal transduction pathways involved are currently unknown. Our group previously reported that luteolin inhibited proliferation and induced apoptosis in the gastric cancer cell line BGC-823. The aim of the present study was to investigate the mechanism by which the mitogen-activated protein kinase (MAPK) and phosphatidylinositol-4,5-bisphosphate 3-kinase (PI3K) signaling pathways regulate the apoptosis in vitro of BGC-823 cells following treatment with luteolin. It was observed that luteolin induced apoptosis through the intrinsic pathway by increasing the levels of caspase-3, caspase-9 and cytochrome c, and the ratio of B-cell lymphoma (Bcl)-2 associated X protein (Bax) to Bcl-2. Luteolin suppressed the phosphorylation of extracellular signal-regulated kinase in the MAPK signaling pathway, as well as suppressing the phosphorylation of AKT, PI3K and mechanistic target of rapamycin in the PI3K signaling pathway. In addition, luteolin combined with LY294002 markedly increased the Bax/Bcl-2 ratio, while when combined with U0126, luteolin had less effects on the Bax/Bcl-2 ratio compared with luteolin treatment alone, suggesting that both the MAPK and PI3K signaling pathways are involved in the apoptosis induced by luteolin. Furthermore, luteolin attenuated the MAPK and PI3K signaling pathways by increasing the expression of specific dual-specificity phosphatases and decreasing the expression of chemokine (C-X-C motif) ligand 16 at the messenger RNA level, respectively. Taken together, the present results demonstrate that luteolin is a potential chemotherapeutic agent against gastric cancer by exerting a dual inhibition on the MAPK and PI3K signaling pathways.

Assessing the anticancer effects associated with food products and/or nutraceuticals using in vitro and in vivo preclinical development-related pharmacological tests

This review is part of a special issue entitled "Role of dietary pattern, foods, nutrients and nutraceuticals in supporting cancer prevention and treatment" and describes a pharmacological strategy to determine the potential contribution of food-related components as anticancer agents against established cancer. Therefore, this review does not relate to chemoprevention, which is analysed in several other reviews in the current special issue, but rather focuses on the following: i) the biological events that currently represent barriers against the treatment of certain types of cancers, primarily metastatic cancers; ii) the in vitro and in vivo pharmacological pre-clinical tests that can be used to analyse the potential anticancer effects of food-related components; and iii) several examples of food-related components with anticancer effects. This review does not represent a catalogue-based listing of food-related components with more or less anticancer activity. By contrast, this review proposes an original pharmacological strategy that researchers can use to analyse the potential anticancer activity of any food-related component-e.g., by considering the crucial characteristics of cancer biological aggressiveness. This review also highlights that cancer patients undergoing chemotherapy should restrict the use of "food complements" without supervision by a medical nutritionist. By contrast, an equilibrated diet that includes the food-related components listed herein would be beneficial for cancer patients who are not undergoing chemotherapy.

Application of luteolin nanomicelles anti-glioma effect with improvement in vitro and in vivo

Glioblastoma multiforme (GBM) is one of the most common and malignant tumor. Luteolin, a polyphenolic compound, has been proposed to have anti-tumor activity against various cancers. However, the greatest obstacle in the administration of luteolin is its hydrophobicity as well as the low oral bioavailability. In this study, we formulated luteolin-loaded MPEG-PCL (Luteolin/MPEG-PCL) micelles aiming to improve its solubility in aqueous solution and investigate the anti-tumor effect on glioma in vitro and in vivo. The spherical Luteolin/MPEG-PCL micelles were completely dispersible in normal saline and could release luteolin in a sustained manner in vitro. We demonstrated that Luteolin/MPEG-PCL micelles had stronger cytotoxicity and induced a higher percentage of apoptosis in C6 and U87 cells than free luteolin in vitro. The immunohistochemical study revealed that Luteolin/MPEG-PCL micelles induced more glioma cell apoptosis than free luteolin and inhibited neovascularization in tumor tissues. The Pro-caspase9 and Bcl-2 down-regulation and cleaved-caspase9 and Bax up-regulation suggested that luteolin induced apoptosis via the mitochondrial pathway in vitro. What is more, we found the drug could cumulated much more in the nano-drug group than free drug group through imaging in vivo. In conclusion, the Luteolin/MPEG-PCL micelles have the potential clinical application in glioma chemotherapy.

Molecular targets of luteolin in cancer

Many food-derived phytochemical compounds and their derivatives represent a cornucopia of new anticancer compounds. Despite extensive study of luteolin, the literature has no information on the exact mechanisms or molecular targets through which it deters cancer progression. This review discusses existing data on luteolin's anticancer activities and then offers possible explanations for and molecular targets of its cancer-preventive action. Luteolin prevents tumor development largely by inactivating several signals and transcription pathways essential for cancer cells. This review also offers insights into the molecular mechanisms and targets through which luteolin either prevents cancer or mediates cancer cell death.

Enhanced anticancer activity in vitro and in vivo of luteolin incorporated into long-circulating micelles based on DSPE-PEG2000 and TPGS

OBJECTIVES

This study aimed to evaluate enhanced anticancer activity in vitro and in vivo of luteolin-loaded long-circulating micelles (DTLLMs) formulated.

METHODS

DTLLM was the luteolin formulation prepared with 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-methoxy-poly (ethylene glycol 2000) (DSPE-PEG2000 ) and d-α-tocopheryl polyethylene glycol succinate (TPGS) in this study. We performed a systematic comparative evaluation of the antiproliferative effect, cellular uptake, antitumour efficacy and in vivo tumour targeting of these micelles using non-small cell lung cancer (NSCLC) A549 cells.

KEY FINDINGS

Results showed that the obtained micelles have a mean particle size of around 42.34 nm, and the size of micelles was narrowly distributed. With the improved cellular uptake, DTLLM displayed a more potent antiproliferative action on A549 cell lines than luteolin; half-maximal inhibitory concentration (IC50 ) was 7.29 vs 19.14 μg/ml, respectively. The antitumour efficacy test in nude mice showed that DTLLM exhibited significantly higher antitumour activity against NSCLC with lesser toxic effects on normal tissues. The imaging study for in vivo targeting demonstrated that the long-circulating micelles formulation achieved targeted drug delivery and make drug release slow to prolong the circulating time.

CONCLUSION

DTLLM might be a potential antitumour formulation.

Chemical Library Screening and Structure-Function Relationship Studies Identify Bisacodyl as a Potent and Selective Cytotoxic Agent Towards Quiescent Human Glioblastoma Tumor Stem-Like Cells

Cancer stem-like cells reside in hypoxic and slightly acidic tumor niches. Such microenvironments favor more aggressive undifferentiated phenotypes and a slow growing "quiescent state" which preserves them from chemotherapeutic agents that essentially target proliferating cells. Our objective was to identify compounds active on glioblastoma stem-like cells, including under conditions that mimick those found in vivo within this most severe and incurable form of brain malignancy. We screened the Prestwick Library to identify cytotoxic compounds towards glioblastoma stem-like cells, either in a proliferating state or in more slow-growing "quiescent" phenotype resulting from non-renewal of the culture medium in vitro. Compound effects were assessed by ATP-level determination using a cell-based assay. Twenty active molecules belonging to different pharmacological classes have thus been identified. Among those, the stimulant laxative drug bisacodyl was the sole to inhibit in a potent and specific manner the survival of quiescent glioblastoma stem-like cells. Subsequent structure-function relationship studies led to identification of 4,4'-dihydroxydiphenyl-2-pyridyl-methane (DDPM), the deacetylated form of bisacodyl, as the pharmacophore. To our knowledge, bisacodyl is currently the only known compound targeting glioblastoma cancer stem-like cells in their quiescent, more resistant state. Due to its known non-toxicity in humans, bisacodyl appears as a new potential anti-tumor agent that may, in association with classical chemotherapeutic compounds, participate in tumor eradication.

Evasion of anti-growth signaling: A key step in tumorigenesis and potential target for treatment and prophylaxis by natural compounds

The evasion of anti-growth signaling is an important characteristic of cancer cells. In order to continue to proliferate, cancer cells must somehow uncouple themselves from the many signals that exist to slow down cell growth. Here, we define the anti-growth signaling process, and review several important pathways involved in growth signaling: p53, phosphatase and tensin homolog (PTEN), retinoblastoma protein (Rb), Hippo, growth differentiation factor 15 (GDF15), AT-rich interactive domain 1A (ARID1A), Notch, insulin-like growth factor (IGF), and Krüppel-like factor 5 (KLF5) pathways. Aberrations in these processes in cancer cells involve mutations and thus the suppression of genes that prevent growth, as well as mutation and activation of genes involved in driving cell growth. Using these pathways as examples, we prioritize molecular targets that might be leveraged to promote anti-growth signaling in cancer cells. Interestingly, naturally occurring phytochemicals found in human diets (either singly or as mixtures) may promote anti-growth signaling, and do so without the potentially adverse effects associated with synthetic chemicals. We review examples of naturally occurring phytochemicals that may be applied to prevent cancer by antagonizing growth signaling, and propose one phytochemical for each pathway. These are: epigallocatechin-3-gallate (EGCG) for the Rb pathway, luteolin for p53, curcumin for PTEN, porphyrins for Hippo, genistein for GDF15, resveratrol for ARID1A, withaferin A for Notch and diguelin for the IGF1-receptor pathway. The coordination of anti-growth signaling and natural compound studies will provide insight into the future application of these compounds in the clinical setting.

Radiosensitization to X-ray radiation by telomerase inhibitor MST-312 in human hepatoma HepG2 cells

AIMS

Previous studies in malignant cells have shown that irradiation-induced upregulation of telomerase activity, not only protected damaged telomeres, but also contributed to DNA damage repair by chromosomal healing and increased resistance to irradiation. The purpose of the present study was to investigate the radiosensitizing effect of telomerase inhibitor MST-312 and the corresponding mechanism in the human hepatoma cell line HepG2.

MAIN METHODS

Cell proliferation, telomerase activity, cell cycle distribution, DNA damage and repair, expression of p53, mitochondrial membrane potential, and cell apoptosis were measured with the MTT assay, real-time fluorescent quantitative PCR, flow cytometry, immunofluorescence, western blots, JC-1 staining, and Hoechst 33258 staining, respectively.

KEY FINDINGS

MST-312 effectively inhibited telomerase activity and showed relative weak toxicity to HepG2 cells at 4 μM. Compared with irradiation alone, 4 μM MST-312 pretreatment, followed by X-ray treatment, significantly reduced clonogenic potential. Aggravated DNA damage and increased sub-G1 cell fractions were observed. Further investigation found that homologous recombination (HR) repair protein Rad51 foci nuclear formation was blocked, and expression of p53 was elevated. These led to the collapse of mitochondrial membrane potential, and enhanced the apoptotic rate.

SIGNIFICANCE

These data demonstrated that disturbances of telomerase function could enhance the radiosensitivity of HepG2 cells to X-ray irradiation by impairing HR repair processes. In addition, telomerase inhibitor MST-312 may be useful as an adjuvant treatment in combination with irradiation.