Peroxisome-proliferator-activated receptor alpha agonists inhibit cyclo-oxygenase 2 and vascular endothelial growth factor transcriptional activation in human colorectal carcinoma cells via inhibition of activator protein-1

Interference of alpha-alkyl-substituted pirinixic acid derivatives with neutrophil functions and signalling pathways

Pirinixic acid (Wy-14,643) is an agonist of the peroxisome proliferator-activated receptor (PPAR) subtype alpha exhibiting beneficial effects in various inflammation-related processes in a slow, long-termed fashion. We recently showed that alpha-substituted pirinixic acid derivatives are agonists of PPAR alpha and act as dual inhibitors of 5-lipoxygenase (5-LO, EC 1.13.11.34) and the microsomal prostaglandin E(2) synthase-1 (EC 5.3.99.3). Here, we explored short-term effects of alpha-substituted pirinixic acid derivatives on typical neutrophil functions evoked by the agonist N-formyl-methionyl-leucyl-phenylalanine (fMLP) including leukotriene formation, generation of reactive oxygen species, and release of human leukocyte elastase (EC 3.4.21.37), and we investigated the modulation of related signalling pathways. Pirinixic acid derivatives that are substituted with alkyl residues in alpha-position of the carboxylic group and with a 6-aminoquinoline residue at the pyrimidine moiety cause inhibition of leukotriene formation, reactive oxygen species formation, and leukocyte elastase release in response to fMLP. In parallel, Ca(2+) mobilisation and the phosphorylation (activation) of p38 mitogen-activated protein kinase was significantly reduced, whereas phosphorylation of the extracellular signal-regulated kinase-2 was unaffected. Pirinixic acid itself was not or only marginally active in all these assays. Conclusively, targeted structural modification of pirinixic acid leads to bioactive compounds that display immediate anti-inflammatory properties in human neutrophils with potential therapeutic value.

Prostacyclin-induced peroxisome proliferator-activated receptor-alpha translocation attenuates NF-kappaB and TNF-alpha activation after renal ischemia-reperfusion injury

Prostacyclin and peroxisome proliferator-activated receptors (PPAR) protect against ischemia-reperfusion (I/R) injury by the induction of an anti-inflammatory pathway. In this study, we examined the prostacyclin-enhanced protective effect of PPARalpha in I/R-induced kidney injury. PPAR-alpha reduced the NF-kappaB-induced overexpression of TNF-alpha and apoptosis in cultured kidney cells. In a murine model, pretreating wild-type (WT) mice with a PPAR-alpha activator, docosahexaenoic acid (DHA), significantly reduced I/R-induced renal dysfunction (lowered serum creatinine and urea nitrogen levels), apoptotic responses (decreased apoptotic cell number and caspase-3, -8 activation), and NF-kappaB activation. By comparison, I/R-induced injury was exacerbated in PPAR-alpha knockout mice. This indicated that PPAR-alpha attenuated renal I/R injury via NF-kappaB-induced TNF-alpha overexpression. Overexpression of prostacyclin using an adenovirus could also induce PPAR-alpha translocation from the cytosol into the nucleus to inhibit caspase-3 activation. This prostacyclin/PPAR-alpha pathway attenuated TNF-alpha promoter activity by binding to NF-kappaB. Using a cAMP inhibitor (CAY10441) and a prostacyclin receptor antibody, we also found that there was another prostacyclin/IP receptor/cAMP pathway that could inhibit TNF-alpha production. Taken together, our results demonstrate for the first time that prostacyclin induces the translocation of PPAR-alpha from the cytosol into the nucleus and attenuates NF-kappaB-induced TNF-alpha activation following renal I/R injury. Treatments that can augment prostacyclin, PPAR-alpha, or the associated signaling pathways may ameliorate conditions associated with renal I/R injury.

PPARs Mediate Lipid Signaling in Inflammation and Cancer

Lipid mediators can trigger physiological responses by activating nuclear hormone receptors, such as the peroxisome proliferator-activated receptors (PPARs). PPARs, in turn, control the expression of networks of genes encoding proteins involved in all aspects of lipid metabolism. In addition, PPARs are tumor growth modifiers, via the regulation of cancer cell apoptosis, proliferation, and differentiation, and through their action on the tumor cell environment, namely, angiogenesis, inflammation, and immune cell functions. Epidemiological studies have established that tumor progression may be exacerbated by chronic inflammation. Here, we describe the production of the lipids that act as activators of PPARs, and we review the roles of these receptors in inflammation and cancer. Finally, we consider emerging strategies for therapeutic intervention.

The Role of PPARs in the Endothelium: Implications for Cancer Therapy

The growth and metastasis of cancers intimately involve the vasculature and in particular the endothelial cell layer. Tumours require new blood vessel formation via angiogenesis to support growth. In addition, inflammation, coagulation, and platelet activation are common signals in the growth and metastasis of tumour cells. The endothelium plays a central role in the homeostatic control of inflammatory cell recruitment, regulating platelet activation and coagulation pathways. PPARalpha, -beta/delta, and -gamma are all expressed in endothelial cells. This review will discuss the roles of PPARs in endothelial cells in relation to angiogenesis, inflammation, coagulation, and platelet control pathways. In particular, we will discuss the recent evidence that supports the hypothesis that PPARalpha and PPARgamma are antiangiogenic receptors, while PPARbeta/delta is proangiogenic.

Upregulation of Activator Protein-4 in Human Colorectal Cancer With Metastasis

The aim of this study is to investigate the expression of AP-4, VEGF, and MMP-9 genes in human colorectal cancer. The expression pattern of activator protein-4 in 160 colorectal cancer compared with 32 colorectal adenomas and 32 normal colorectal tissues is demonstrated by tissue microarray-immunohistochemistry and real-time reverse transcriptase—polymerase chain reaction. Apoptosis status using terminal deoxynucleotidyl transferase—mediated dUTP nick-end labeling by comparing activator protein-4 positive versus activator protein-4 negative colorectal cancer is also assessed. The messenger RNA levels of vascular endothelial growth factor and matrix metalloproteinase-9 expression in activator protein-4 positive and negative colorectal cancer were measured using real-time reverse transcriptase— polymerase chain reaction. The activator protein-4 expression in normal colorectal tissue, adenoma, and adenocarcinoma were 4 of 32, 8 of 32, and 78 of 160, respectively. It is shown that the activator protein-4 expression was significantly correlated with the progression of colorectal cancer ( P < .01) and differentiation and lymph node metastasis ( P < .01). Our results also presented that the activator protein-4 expression was associated with the expression of matrix metalloproteinase-9 and vascular endothelial growth factor in the advanced colorectal cancer.

Novel and potent inhibitors of 5-lipoxygenase product synthesis based on the structure of pirinixic acid

A novel class of potent 5-lipoxygenase (5-LO) product synthesis inhibitors based on the structure of pirinixic acid (4-chloro-6-(2,3-xylidino)-2-pyrimidinylthioacetic acid, compound 1) is presented. Systematic profiling of 1, i.e., esterification of the carboxylic acid, alpha-substitution, and replacement of the o-dimethylaniline by 6-aminoquinoline, leads to potent suppressors of 5-LO product formation in activated polymorphonuclear leukocytes, exemplified by ethyl 2-[4-chloro-6-(quinoline-6-ylamino)-pyrimidin-2-ylsulfanyl]octane-1-carboxylate (6d, IC50 = 0.6 microM). These derivatives may possess potential for intervention with inflammatory and allergic diseases.

Keratinocyte-derived vascular endothelial growth factor biosynthesis represents a pleiotropic side effect of peroxisome proliferator-activated receptor-gamma agonist troglitazone but not rosiglitazone and involves activation of p38 mitogen-activated protein kinase: implications for diabetes-impaired skin repair

The peroxisome proliferator-activated receptors (PPARs) represent pharmacological target molecules to improve insulin resistance in type 2 diabetes mellitus. Here we assessed a functional connection between pharmacological activation of PPAR and vascular endothelial growth factor (VEGF) expression in keratinocytes and during diabetes-impaired acute skin repair in obese/obese (ob/ob) mice. PPARbeta/delta agonist 4-[3-[4-acetyl-3-hydroxy-2-propylphenoxy)propoxy]phenoxy]acetic acid (L165,041) and PPARgamma agonists ciglitazone and troglitazone, but not rosiglitazone, potently induced VEGF mRNA and protein expression from cultured keratinocytes. Inhibitor studies revealed a strong functional dependence of troglitazone- and L165,041-induced VEGF expression on p38 and p42/44 mitogen-activated protein kinase (MAPK) activation in keratinocytes. Rosiglitazone also induced activation of p38 MAPK but failed to mediate the activation of p42/44 MAPK in the cells. Functional ablation of PPARbeta/delta and PPARgamma from keratinocytes by small interfering RNA did not abrogate L165,041- and troglitazone-induced VEGF biosynthesis and suggested VEGF induction as a pleiotropic, PPAR-independent effect of both drugs in the cells. In accordance with the in vitro situation, we found activated p38 MAPK in wound keratinocytes from acute wounds of rosiglitazone- and troglitazone-treated diabetic obese/obese mice, whereas keratinocyte-specific VEGF protein signals were only prominent upon troglitazone treatment. In summary, our data from cell culture and wound healing experiments suggested p38 MAPK activation as a side effect of thiazolidinediones; however, only troglitazone, but not rosiglitazone, seemed to translate p38 MAPK activation into a PPARgamma-independent induction of VEGF from keratinocytes.

1,1-Bis(3'-indolyl)-1-(p-biphenyl)methane inhibits basal-like breast cancer growth in athymic nude mice

Introduction

1,1-Bis (3'-indolyl)-1-(p-biphenyl) methane (CDIM9) has been identified as a new peroxisome proliferator-activated receptor (PPAR)-γ agonist that exhibits both receptor dependent and independent antitumor activities. CDIM9 has not previously been studied with respect to its effects against basal-like breast cancer. Our goal in the present study was to investigate the anti-basal-like breast tumor activity of CDIM9 in vitro and in vivo.

Methods

The effects of CDIM9 on cell protein and DNA syntheses were determined in basal-like breast cancer MDA-MB231 and BT549 cells in vitro. Maximum tolerated dose and dose-limited toxicity were determined in BalB/c mice, and antitumor growth activities were assessed in MDA-MB231 basal-like breast tumor xenografts in athymic nude mice.

Results

CDIM9 exhibited selective cell cytotoxicity and anti-proliferation effects on basal-like breast cancer lines. In MDA-MB231 cell, CDIM9 induced caveolin-1 and p27 expression, which was significantly downregulated by co-treatment with the PPAR-γ antagonist GW9662. Nonsteroidal anti-inflammatory drug-activated gene-1 and activating transcription factor-3 were upregulated by CDIM9 through a PPAR-γ independent pathway. CDIM9 (40 mg/kg daily, intraperitoneally, for 35 days) inhibited the growth of subcutaneous MDA-MB231 tumor xenografts by 87%, and produced a corresponding decrease in proliferation index. Nearly half of the treated mice (46%) had complete durable remissions, confirmed by histology. The growth of an established tumor was inhibited by CDIM9 treatment (64 mg/kg daily, intraperitoneally, for 10 days), with a mean tumor growth inhibition of 67% as compared with controls. CDIM9 induced increases in tumor caveolin-1 and p27 in vivo, which may contribute to its antitumor activity in basal-like breast cancer.

Conclusion

CDIM9 showed potent antiproliferative effects on basal-like breast cancer cell in tissue culture and dramatic growth inhibition in animal models at safe doses. These findings justify further development of this drug for treatment of basal-like breast cancer.

PPARalpha agonist fenofibrate suppresses tumor growth through direct and indirect angiogenesis inhibition

Angiogenesis and inflammation are central processes through which the tumor microenvironment influences tumor growth. We have demonstrated recently that peroxisome proliferator-activated receptor (PPAR)alpha deficiency in the host leads to overt inflammation that suppresses angiogenesis via excess production of thrombospondin (TSP)-1 and prevents tumor growth. Hence, we speculated that pharmacologic activation of PPARalpha would promote tumor growth. Surprisingly, the PPARalpha agonist fenofibrate potently suppressed primary tumor growth in mice. This effect was not mediated by cancer-cell-autonomous antiproliferative mechanisms but by the inhibition of angiogenesis and inflammation in the host tissue. Although PPARalpha-deficient tumors were still susceptible to fenofibrate, absence of PPARalpha in the host animal abrogated the potent antitumor effect of fenofibrate. In addition, fenofibrate suppressed endothelial cell proliferation and VEGF production, increased TSP-1 and endostatin, and inhibited corneal neovascularization. Thus, both genetic abrogation of PPARalpha as well as its activation by ligands cause tumor suppression via overlapping antiangiogenic pathways. These findings reveal the potential utility of the well tolerated PPARalpha agonists beyond their use as lipid-lowering drugs in anticancer therapy. Our results provide a mechanistic rationale for evaluating the clinical benefits of PPARalpha agonists in cancer treatment, alone and in combination with other therapies.

UDN glycoprotein inhibits activator protein-1 and matrix metalloproteinase-9 via blocking of oxygen radicals in HT-29 cells

The present study was performed to investigate the anti-inflammatory potential of a 116-kDa glycoprotein isolated from Ulmus davidiana Nakai (UDN glycoprotein) in lipopolysaccaride (LPS)-treated cancerous human colon epithelial cells (HT-29 cells). UDN glycoprotein inhibited the production of intracellular superoxide anion (O (2) (.-) ), hydrogen peroxides (H(2)O(2)), and nitric oxide (NO), whereas normalized the activity of anti-oxidant enzymes [superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPX)], accompanying the inhibition of manganese-superoxide dismutases (Mn-SOD) activity in LPS-treated HT-29 cells. In addition, UDN glycoprotein blocked the DNA binding activity of activator protein-1 (AP-1) through suppression of c-Jun and c-Fos activities, respectively. We also evaluated the anti-inflammatory potential of UDN glycoprotein based on the activity of the pro-inflammatory signal mediators [inducible nitric oxide synthase (iNOS), cyclooxygenase-2 (COX-2), and matrix metalloproteinases-9 (MMP-9)]. The results showed that UDN glycoprotein (200 mug/ml) has an inhibitory effect on the activation of iNOS, COX-2, and MMP-9 proteins in the LPS-treated HT-29 cells. From these results, we suggest that UDN glycoprotein is one of the potential anti-inflammatory agents that blocks LPS-mediated inflammatory signal pathway in HT-29 cells. Here, we speculate that UDN glycoprotein could be used as an antioxidative agent for inflammatory gastrointestinal cancers.

The activator protein-1 transcription factor in respiratory epithelium carcinogenesis

Respiratory epithelium cancers are the leading cause of cancer-related death worldwide. The multistep natural history of carcinogenesis can be considered as a gradual accumulation of genetic and epigenetic aberrations, resulting in the deregulation of cellular homeostasis. Growing evidence suggests that cross-talk between membrane and nuclear receptor signaling pathways along with the activator protein-1 (AP-1) cascade and its cofactor network represent a pivotal molecular circuitry participating directly or indirectly in respiratory epithelium carcinogenesis. The crucial role of AP-1 transcription factor renders it an appealing target of future nuclear-directed anticancer therapeutic and chemoprevention approaches. In the present review, we will summarize the current knowledge regarding the implication of AP-1 proteins in respiratory epithelium carcinogenesis, highlight the ongoing research, and consider the future perspectives of their potential therapeutic interest.

Activation of PPARα lowers synthesis and concentration of cholesterol by reduction of nuclear SREBP-2

To elucidate the mechanisms underlying the cholesterol lowering effects of PPARalpha agonists we investigated key regulators of cholesterol synthesis and uptake in rats and in the rat hepatoma cell line Fao after treatment with the PPARalpha agonists clofibrate and WY 14,643, respectively. In rat liver as well as in Fao cells, PPARalpha activation led to a decrease of transcriptionally active nuclear SREBP-2. mRNA concentrations of the key regulators of SREBP processing, Insig-1 in rat liver and Insig-1 and Insig-2a in Fao cells, were increased upon PPARalpha activation. Thus we suggest, that the observed reduction of the amount of nuclear SREBP-2 was due to an inhibition of the processing of the precursor protein. Both, in rat liver and in Fao cells, mRNA concentrations of the SREBP-2 target genes HMG-CoA reductase (EC1.1.1.34) and LDL receptor were reduced after treatment with the PPARalpha agonists. Furthermore, treatment of Fao cells with WY 14,643 reduced cholesterol synthesis. As a result, the amount of total cholesterol in liver, plasma and lipoproteins of clofibrate treated rats and in WY 14,643 treated Fao cells was decreased compared to control animals and cells, respectively. In conclusion, we could show a novel link between PPARalpha and cholesterol metabolism by demonstrating that PPARalpha activation lowers cholesterol concentration by reducing the abundance of nuclear SREBP-2.

Crosstalk between peroxisome proliferator-activated receptor delta and VEGF stimulates cancer progression

Peroxisome proliferator-activated receptor (PPAR) delta is a member of the nuclear hormone receptor superfamily. PPARdelta may ameliorate metabolic diseases such as obesity and diabetes. However, PPARdelta's role in colorectal carcinogenesis remains controversial. Here, we present genetic and pharmacologic evidence demonstrating that deletion of PPARdelta decreases intestinal adenoma growth in Apc(Min/+) mice and inhibits tumor-promoting effects of a PPARdelta agonist GW501516. More importantly, we found that activation of PPARdelta up-regulated VEGF in colon carcinoma cells. VEGF directly promotes colon tumor epithelial cell survival through activation of PI3K-Akt signaling. These results not only highlight concerns about the use of PPARdelta agonists for treatment of metabolic disorders in patients who are at high risk for colorectal cancer, but also support the rationale for developing PPARdelta antagonists for prevention and/or treatment of cancer.

Molecular mechanism of cyclooxygenase-2 inhibitor in regulating proliferation of colon cancer cells through modulating PPAR signal transduction pathway

AIM: To investigate the role of selective cyclooxygenase-2 (COX-2) inhibitor NS398 on the proliferation and apoptosis of colorectal cancer cells, and reveal the COX-2-independent mechanism.

METHODS: Reverse transcription-polymerase chain reaction (RT-PCR) was performed on human colon cancer cell line SW480 to examine COX-2 mRNA expression. Then, NS-398 (a selective COX-2 inhibitor) was added into culture media, and MTT assay was used to examine the proliferation of the cells; Western blot analysis was performed to detect the expression of peroxisome proliferators-activated receptor (PPAR); Flow cytometry was applied to analyze the cell cycle and apoptosis.

RESULTS: The expression of COX-2 mRNA was not detected in colon cancer SW480 cells. NS-398 inhibited the cell proliferation and induced apoptosis in colon cancer cell lines. Seventy-two hours after the treatment of NS398 (75 mmol/L), the proliferative level of SW480 cells was decreased; the rate of the cells at G₁ stage was increased from 31.2% to 40.6%, while the rate of those at S stage was decreased from 52.8% to 41.2%. The expression of PPARa, PPARd, PPARg, cyclin D1 and Bcl-xl were decreased along with the prolonging of NS398 treated time.

CONCLUSION: The selective COX-2 inhibitor NS-398 can inhibit the proliferation while induce the apoptosis of colon cancer cell lines through COX-2-independent pathway.