The dietary flavonoid apigenin blocks phorbol 12-myristate 13-acetate-induced COX-2 transcriptional activity in breast cell lines

Pyrazoles have a multifaceted anti-inflammatory effect targeting prostaglandin E2, cyclooxygenases and leukocytes' oxidative burst

Elevated levels of prostaglandin E2 have been implicated in the pathophysiology of various diseases. Anti-inflammatory drugs that act through the inhibition of cyclooxygenase enzymatic activity, thereby leading to the suppression of prostaglandin E2, are often associated with several side effects due to their non-specific inhibition of cyclooxygenase enzymes. Consequently, the targeted suppression of prostaglandin E2 production with innovative molecules and/or mechanisms emerges as a compelling therapeutic strategy for the treatment of inflammatory-related diseases. Therefore, in this study, a systematic analysis of 28 pyrazole derivatives was conducted to explore their potential mechanisms for reducing prostaglandin E2 levels. In this context, the evaluation of these derivatives extended to examining their capacity to reduce prostaglandin E2in vitro in human whole blood, inhibit cyclooxygenase-1 and cyclooxygenase-2 enzymes, modulate cyclooxygenase -2 expression, and suppress oxidative burst in human leukocytes. The results enabled the establishment of significant structure-activity relationships, elucidating key determinants for their activities. In particular, the 4-styryl group on the pyrazole moiety and the presence of chloro substitutions were identified as key determinants. Pyrazole 8 demonstrated the capacity to reduce prostaglandin E2 levels by downregulating cyclooxygenase-2 expression, and pyrazole-1,2,3-triazole 18 emerged as a dual-acting agent, inhibiting human leukocytes' oxidative burst and cyclooxygenase-2 activity. Furthermore, pyrazole 26 demonstrated effective reduction of prostaglandin E2 levels through selective cyclooxygenase-1 inhibition. These results underscore the multifaceted anti-inflammatory potential of pyrazoles, providing new insights into the substitutions and structural frameworks that are beneficial for the studied activity.

Therapeutic Influence on Important Targets Associated with Chronic Inflammation and Oxidative Stress in Cancer Treatment

Simple Summary

There is no doubt that the need for new effective methods of cancer treatment remains challenging, as cancer is the second cause of death based on the number of cases in the world. In this review, we investigated the role of one of the leading determinants in the development and progression of various types of cancer—oxidative stress and inflammation, as well as clinical and experimental data from the studies of promising drugs of natural origin, such as flavonoids, that target these stages of oncogenesis. This can all help in the expansion and systematization of the existing knowledge regarding the fight against cancer, the facilitation of the development of effective anti-cancer drugs, and the progression of research in this field, in order to improve the treatment of these disorders.

Abstract

Chronic inflammation and oxidative stress are the interconnected pathological processes, which lead to cancer initiation and progression. The growing level of oxidative and inflammatory damage was shown to increase cancer severity and contribute to tumor spread. The overproduction of reactive oxygen species (ROS), which is associated with the reduced capacity of the endogenous cell defense mechanisms and/or metabolic imbalance, is the main contributor to oxidative stress. An abnormal level of ROS was defined as a predisposing factor for the cell transformation that could trigger pro-oncogenic signaling pathways, induce changes in gene expression, and facilitate accumulation of mutations, DNA damage, and genomic instability. Additionally, the activation of transcription factors caused by a prolonged oxidative stress, including NF-κB, p53, HIF1α, etc., leads to the expression of several genes responsible for inflammation. The resulting hyperactivation of inflammatory mediators, including TNFα, TGF-β, interleukins, and prostaglandins can contribute to the development of neoplasia. Pro-inflammatory cytokines were shown to trigger adaptive reactions and the acquisition of resistance by tumor cells to apoptosis, while promoting proliferation, invasion, and angiogenesis. Moreover, the chronic inflammatory response leads to the excessive production of free radicals, which further aggravate the initiated reactions. This review summarizes the recent data and progress in the discovery of mechanisms that associate oxidative stress and chronic inflammation with cancer onset and metastasis. In addition, the review provides insights for the development of therapeutic approaches and the discovery of natural substances that will be able to simultaneously inhibit several key oncological and inflammation-related targets.

Rationalizing the therapeutic potential of apigenin against cancer

BACKGROUND

Despite the remarkable advances made in the diagnosis and treatment of cancer during the past couple of decades, it remains the second largest cause of mortality in the world, killing approximately 9.6 million people annually. The major challenges in the treatment of the advanced stage of this disease are the development of chemoresistance, severe adverse effects of the drugs, and high treatment cost. Therefore, the development of drugs that are safe, efficacious, and cost-effective remains a 'Holy Grail' in cancer research. However, the research over the past four decades shed light on the cancer-preventive and therapeutic potential of natural products and their underlying mechanism of action. Apigenin is one such compound, which is known to be safe and has significant potential in the prevention and therapy of this disease.

AIM

To assess the literature available on the potential of apigenin and its analogs in modulating the key molecular targets leading to the prevention and treatment of different types of cancer.

METHOD

A comprehensive literature search has been carried out on PubMed for obtaining information related to the sources and analogs, chemistry and biosynthesis, physicochemical properties, biological activities, bioavailability and toxicity of apigenin.

KEY FINDINGS

The literature search resulted in many in vitro, in vivo and a few cohort studies that evidenced the effectiveness of apigenin and its analogs in modulating important molecular targets and signaling pathways such as PI3K/AKT/mTOR, JAK/STAT, NF-κB, MAPK/ERK, Wnt/β-catenin, etc., which play a crucial role in the development and progression of cancer. In addition, apigenin was also shown to inhibit chemoresistance and radioresistance and make cancer cells sensitive to these agents. Reports have further revealed the safety of the compound and the adaptation of nanotechnological approaches for improving its bioavailability.

SIGNIFICANCE

Hence, the present review recapitulates the properties of apigenin and its pharmacological activities against different types of cancer, which warrant further investigation in clinical settings.

Apigenin as an anticancer agent

Apigenin is an edible plant-derived flavonoid that has been reported as an anticancer agent in several experimental and biological studies. It exhibits cell growth arrest and apoptosis in different types of tumors such as breast, lung, liver, skin, blood, colon, prostate, pancreatic, cervical, oral, and stomach, by modulating several signaling pathways. Apigenin induces apoptosis by the activation of extrinsic caspase-dependent pathway by upregulating the mRNA expressions of caspase-3, caspase-8, and TNF-α. It induces intrinsic apoptosis pathway as evidenced by the induction of cytochrome c, Bax, and caspase-3, while caspase-8, TNF-α, and B-cell lymphoma 2 levels remained unchanged in human prostate cancer PC-3 cells. Apigenin treatment leads to significant downregulation of matrix metallopeptidases-2, -9, Snail, and Slug, suppressing invasion. The expressions of NF-κB p105/p50, PI3K, Akt, and the phosphorylation of p-Akt decreases after treatment with apigenin. However, apigenin-mediated treatment significantly reduces pluripotency marker Oct3/4 protein expression which might be associated with the downregulation of PI3K/Akt/NF-κB signaling.

Resveratrol induces sumoylated COX-2-dependent anti-proliferation in human prostate cancer LNCaP cells

Cyclooxygenase (COX)-2 has been implicated in cancer development. However, resveratrol-induced nuclear accumulation of COX-2 enhances p53-dependent anti-proliferation in different types of cancers. Treatment with resveratrol leads to phosphorylation and nuclear translocation of mitogen-activated protein kinase (ERK1/2), and accumulation of nuclear COX-2 to complex with pERK1/2 and p53. The consequence is Ser-15 phosphorylation of p53 (pSer15-p53), and induction of anti-proliferation in cancer cells. We investigated the mechanisms by which resveratrol-inducible COX-2 facilitates p53-dependent anti-proliferation in prostate cancer LNCaP cells. Resveratrol treatment caused nuclear accumulation and complexing of ERK1/2, pSer15-p53 and COX-2 which was activated ERK1/2-dependent. Knockdown of SUMO-1 by shRNA also reduced nuclear accumulation of COX-2. Inhibition of nuclear accumulation by the COX-2 specific inhibitor, NS-398, inhibited co-localization of nuclear COX-2 and SUMO-1. Similar results were observed in the PD98059-treated cells. Finally, inhibition of SUMO-1 expression also reduced resveratrol-induced expression of pro-apoptotic genes but increased the expression of proliferative genes. In summary, these results demonstrate that inducible COX-2 associates with phosphorylated ERK1/2 to induce the phosphorylation of Ser-15 in p53 and then complexes with p53 and SUMO-1 which binds to p53-responsive pro-apoptotic genes to enhance their expression. The inhibition of COX-2 expression and activity significantly blocks the pro-apoptotic effect of resveratrol.

Amplexicaule A exerts anti-tumor effects by inducing apoptosis in human breast cancer

Chemotherapy is the main treatment for patients with breast cancer metastases, but natural alternatives have been receiving attention for their potential as novel anti-tumor reagents. Amplexicaule A (APA) is a flavonoid glucoside isolated from rhizomes of Polygonum amplexicaule D. Don var. sinense Forb (PADF). We found that APA has anti-tumor effects in a breast cancer xenograft mouse model and induces apoptosis in breast cancer cell lines. APA increased levels of cleaved caspase-3,-8,-9 and PARP, which resulted from suppression of MCL-1 and BCL-2 expression in the cells. APA also inactivated the Akt/mTOR pathway in breast cancer cells. Thus, APA exerts a strong anti-tumor effect on breast cancer cells, most likely through induction of apoptosis. Our study is the first to identify this novel anti-tumor compound and provides a new strategy for isolation and separation of single compounds from herbs.

Targeting arachidonic acid pathway by natural products for cancer prevention and therapy

Arachidonic acid (AA) pathway, a metabolic process, plays a key role in carcinogenesis. Hence, AA pathway metabolic enzymes phospholipase A₂s (PLA₂s), cyclooxygenases (COXs) and lipoxygenases (LOXs) and their metabolic products, such as prostaglandins and leukotrienes, have been considered novel preventive and therapeutic targets in cancer. Bioactive natural products are a good source for development of novel cancer preventive and therapeutic drugs, which have been widely used in clinical practice due to their safety profiles. AA pathway inhibitory natural products have been developed as chemopreventive and therapeutic agents against several cancers. Curcumin, resveratrol, apigenin, anthocyans, berberine, ellagic acid, eugenol, fisetin, ursolic acid, [6]-gingerol, guggulsteone, lycopene and genistein are well known cancer chemopreventive agents which act by targeting multiple pathways, including COX-2. Nordihydroguaiaretic acid and baicalein can be chemopreventive molecules against various cancers by inhibiting LOXs. Several PLA₂s inhibitory natural products have been identified with chemopreventive and therapeutic potentials against various cancers. In this review, we critically discuss the possible utility of natural products as preventive and therapeutic agents against various oncologic diseases, including prostate, pancreatic, lung, skin, gastric, oral, blood, head and neck, colorectal, liver, cervical and breast cancers, by targeting AA pathway. Further, the current status of clinical studies evaluating AA pathway inhibitory natural products in cancer is reviewed. In addition, various emerging issues, including bioavailability, toxicity and explorability of combination therapy, for the development of AA pathway inhibitory natural products as chemopreventive and therapeutic agents against human malignancy are also discussed.

Systems-Pharmacology Dissection of Traditional Chinese Medicine Compound Saffron Formula Reveals Multi-scale Treatment Strategy for Cardiovascular Diseases

Cardiovascular diseases (CVDs) have been regarding as “the world’s first killer” of human beings in recent years owing to the striking morbidity and mortality, the involved molecular mechanisms are extremely complex and remain unclear. Traditional Chinese medicine (TCM) adheres to the aim of combating complex diseases from an integrative and holistic point of view, which has shown effectiveness in CVDs therapy. However, system-level understanding of such a mechanism of multi-scale treatment strategy for CVDs is still difficult. Here, we developed a system pharmacology approach with the purpose of revealing the underlying molecular mechanisms exemplified by a famous compound saffron formula (CSF) in treating CVDs. First, by systems ADME analysis combined with drug targeting process, 103 potential active components and their corresponding 219 direct targets were retrieved and some key interactions were further experimentally validated. Based on this, the network relationships among active components, targets and diseases were further built to uncover the pharmacological actions of the drug. Finally, a “CVDs pathway” consisted of several regulatory modules was incorporated to dissect the therapeutic effects of CSF in different pathological features-relevant biological processes. All this demonstrates CSF has multi-scale curative activity in regulating CVD-related biological processes, which provides a new potential way for modern medicine in the treatment of complex diseases.

Poly-γ-glutamic acid induces apoptosis via reduction of COX-2 expression in TPA-induced HT-29 human colorectal cancer cells

Poly-γ-glutamic acid (PGA) is one of the bioactive compounds found in cheonggukjang, a fast-fermented soybean paste widely utilized in Korean cooking. PGA is reported to have a number of beneficial health effects, and interestingly, it has been identified as a possible anti-cancer compound through its ability to promote apoptosis in cancer cells, although the precise molecular mechanisms remain unclear. Our findings demonstrate that PGA inhibits the pro-proliferative functions of the phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA), a known chemical carcinogen in HT-29 human colorectal cancer cells. This inhibition was accompanied by hallmark apoptotic phenotypes, including DNA fragmentation and the cleavage of poly (ADP-ribose) polymerase (PARP) and caspase 3. In addition, PGA treatment reduced the expression of genes known to be overexpressed in colorectal cancer cells, including cyclooxygenase 2 (COX-2) and inducible nitric oxide synthase (iNOS). Lastly, PGA promoted activation of 5' adenosine monophosphate-activated protein (AMPK) in HT-29 cells. Taken together, our results suggest that PGA treatment enhances apoptosis in colorectal cancer cells, in part by modulating the activity of the COX-2 and AMPK signaling pathways. These anti-cancer functions of PGA make it a promising compound for future study.

Post-column mobile phase adjustment: a strategy to eliminate the contradiction between liquid chromatography and mass spectrometry in the determination of flavonoids in rat plasma

Flavonoids are a group of important naturally occurring polyphenolic compounds with a wide range of biological effects. In this study, a sensitive liquid chromatography tandem mass spectrometry method was developed to simultaneously determine multiple active flavonoids, including quercetin (Que), kaempferol (Kae), apigenin (Api), isorhamnetin (Iso), luteolin (Lut), and naringenin (Nar), in rat plasma. To achieve a satisfied peak shape and LC separation, formic acid with the concentration between 0.05 and 0.2%, or in some case 5%, was generally used to acidify the LC mobile phase in reported studies. Here we found that even 0.05% formic acid could lead to strong mass signal suppression, and the absence of formic acid could reverse the signal suppression but cause serious peak tailing. There is an irreconcilable contradiction between liquid chromatography (LC) and mass spectrometry (MS). In order to simultaneously satisfy LC and MS, LC mobile phase with 0.00075% formic acid and post column mobile phase adjustment with 0.0677% ammonium solution in isopropanol were applied. Compared with the conventional method with mobile phase containing 0.05% formic acid, the mass signal response of Que, Kae, Api, Iso, Lut, Nar, and Oka increased 26.2, 18.6, 13.6, 23.5, 17.5, 15.6 and 15.4 fold, respectively. In addition, the post column mobile phase addition exhibited the better peak shape for the reduction of analytes longitudinal diffusion. The method has been fully validated according to FDA guidelines within the linear range between 0.328 ng mL⁻¹ and 168 ng mL⁻¹, and successfully applied to a pilot pharmacokinetic study of rats after administering 5.43 g kg⁻¹ Pollen of Brassica campestris.

The flavonoid apigenin improves glucose tolerance through inhibition of microRNA maturation in miRNA103 transgenic mice

Polyphenols are representative bioactive substances with diverse biological effects. Here, we show that apigenin, a flavonoid, has suppressive effects on microRNA (miRNA) function. The effects were mediated by impaired maturation of a subset of miRNAs, probably through inhibition of the phosphorylation of TRBP, a component of miRNA-generating complexes via impaired mitogen-activated protein kinase (MAPK) Erk activation. While glucose intolerance was observed in miRNA103 (miR103)-overexpressing transgenic mice, administration of apigenin improved this pathogenic status likely through suppression of matured miR103 expression levels. These results suggest that apigenin may have favorable effects on the pathogenic status induced by overexpression of miRNA103, whose maturation is mediated by phosphorylated TRBP.

Flavones induce neutrophil apoptosis by down-regulation of Mcl-1 via a proteasomal-dependent pathway

Neutrophil apoptosis and subsequent nonphlogistic clearance by surrounding phagocytes are key to the successful resolution of neutrophilic inflammation, with dysregulated apoptosis reported in multiple human inflammatory diseases. Enhancing neutrophil apoptosis has proresolution and anti-inflammatory effects in preclinical models of inflammation. Here we investigate the ability of the flavones apigenin, luteolin, and wogonin to induce neutrophil apoptosis in vitro and resolve neutrophilic inflammation in vivo. Human neutrophil apoptosis was assessed morphologically and by flow cytometry following incubation with apigenin, luteolin, and wogonin. All three flavones induced time- and concentration-dependent neutrophil apoptosis (apigenin, EC₅₀=12.2 μM; luteolin, EC₅₀=14.6 μM; and wogonin, EC₅₀=28.9 μM). Induction of apoptosis was caspase dependent, as it was blocked by the broad-spectrum caspase inhibitor Q-VD-OPh and was associated with both caspase-3 and caspase-9 activation. Flavone-induced apoptosis was preceded by down-regulation of the prosurvival protein Mcl-1, with proteasomal inhibition preventing flavone-induced Mcl-1 down-regulation and apoptosis. The flavones abrogated the survival effects of mediators that prolong neutrophil life span, including lipoteichoic acid, peptidoglycan, dexamethasone, and granulocyte-macrophage colony stimulating factor, by driving apoptosis. Furthermore, wogonin enhanced resolution of established neutrophilic inflammation in a zebrafish model of sterile tissue injury. Wogonin-induced resolution was dependent on apoptosis in vivo as it was blocked by caspase inhibition. Our data show that the flavones induce neutrophil apoptosis and have potential as neutrophil apoptosis-inducing anti-inflammatory, proresolution agents.—Lucas, C. D., Allen, K. C., Dorward, D. A., Hoodless, L. J., Melrose, L. A., Marwick, J. A., Tucker, C. S., Haslett, C., Duffin, R., Rossi, A. G. Flavones induce neutrophil apoptosis by down-regulation of Mcl-1 via a proteasomal-dependent pathway.

Apigenin-induced suicidal erythrocyte death

Apigenin, a flavone in fruits and vegetables, stimulates apoptosis and thus counteracts cancerogenesis. Erythrocytes may similarly undergo suicidal cell death or eryptosis, characterized by cell shrinkage and phosphatidylserine exposure at the cell surface. Triggers of eryptosis include increase of cytosolic Ca(2+) activity ([Ca(2+)](i)), ceramide formation and ATP depletion. The present study explored the effect of apigenin on eryptosis. [Ca(2+)](i) was estimated from Fluo3-fluorescence, cell volume from forward scatter, phosphatidylserine exposure from annexin V binding, hemolysis from hemoglobin release, ceramide utilizing antibodies, and cytosolic ATP with luciferin-luciferase. A 48 h exposure to apigenin significantly increased [Ca(2+)](i) (≥ 1 μM), increased ceramide formation (15 μM), decreased ATP concentration (15 μM), decreased forward scatter (≥ 1 μM), and increased annexin V binding (≥ 5 μM) but did not significantly modify hemolysis. The effect of 15 μM apigenin on annexin V binding was blunted by Ca(2+) removal. The present observations reveal novel effects of apigenin, i.e. stimulation of Ca(2+) entry, ceramide formation and ATP depletion in erythrocytes with subsequent triggering of suicidal erythrocyte death, paralleled by cell shrinkage and phosphatidylserine exposure.

Preventive effect of phytoglycoprotein (38 kDa) on expression of alpha-fetoprotein and matrix metalloproteinase-9 in diethylnitrosamine-treated ICR mice

Metastasis is one of the major causes of cancer-associated mortality. Aberrant expression of matrix metalloproteinase-9 (MMP-9) has been implicated in the metastasis of various cancer cells. The aim of this study was to investigate the inhibitory effect of a glycoprotein (38 kDa) isolated from Styrax japonica Siebold et al Zuccarini (SJSZ) on metastasis of hepatocellular carcinoma (HCC) in diethylnitrosamine (DEN)-treated imprinting control region (ICR) mice. To study the chemopreventive effect of SJSZ glycoprotein on the metastasis of HCC, ICR mice were injected intraperitoneally with DEN (75 mg/kg) for 11 weeks. Subsequently, we evaluated nitric oxide (NO), alpha-fetoprotein (AFP), activator protein (AP)-1, cyclooxygenase (COX)-2, inducible nitric oxide synthase (iNOS), matrix metalloproteinase (MMP)-9, and interleukin (IL)-6 using biochemical reaction, immunoblot analysis, and reverse-transcription polymerase chain reaction. Here, the results showed that SJSZ glycoprotein (10 mg/kg body weight) reduced the production of NO in DEN (75 mg/kg)-treated ICR mice. Also, it suppressed the activity of AFP, AP-1 (c-Jun and c-Fos), COX-2, iNOS, and MMP-9. Taken together, SJSZ glycoprotein inhibits the activity of MMP-9 as a metastasis factor.

Flavonoids targeting of IκB phosphorylation abrogates carcinogen-induced MMP-9 and COX-2 expression in human brain endothelial cells

Brain endothelial cells play an essential role as structural and functional components of the blood–brain barrier (BBB). Increased BBB breakdown and brain injury are associated with neuroinflammation and are thought to trigger mechanisms involving matrix metalloproteinase upregulation. Emerging evidence also indicates that cyclooxygenase (COX) inhibition limits BBB disruption, but the mechanisms linking metalloproteinase to COX remain unknown. In this study, we sought to investigate the nuclear factor-kappa B (NF-κB) signaling pathway, a common pathway in both the regulation of matrix metalloproteinase-9 (MMP-9) and COX-2 expression, and the inhibitory properties of several chemopreventive flavonoids. Human brain microvascular endothelial cells were treated with a combination of phorbol 12-myristate 13-acetate (PMA), a carcinogen documented to increase MMP-9 and COX-2 through NF-κB, and several naturally occurring flavonoids. Among the molecules tested, we found that fisetin, apigenin, and luteolin specifically and dose-dependently antagonized PMA-induced COX-2 and MMP-9 gene and protein expressions as assessed by qRT-PCR, immunoblotting, and zymography respectively. We further demonstrate that flavonoids impact on IκK-mediated phosphorylation activity as demonstrated by the inhibition of PMA-induced IκB phosphorylation levels. Our results suggest that BBB disruption during neuroinflammation could be pharmacologically reduced by a specific class of flavonoids acting as NF-κB signal transduction inhibitors.