Prognostic and functional significance of thromboxane synthase gene overexpression in invasive bladder cancer

Investigation of Novel Urinary Biomarkers in Hepatocellular Carcinoma Risk in a Predominantly African American Population: A Case-Control Study

Introduction

African Americans are at increased risk of hepatocellular carcinoma (HCC) compared to other racial and ethnic groups. We investigated the associations of four urinary biomarkers of prostaglandin E2 (PGE-M), prostacyclin (PGI-M), and thromboxane (11dTxB2) synthesis and the ratio of PGI-M to 11dTXB2 with HCC risk in a cohort of predominantly African American populations.

Methods

We conducted a nested case-control study (50 cases; 43 with HCC, 151 controls) in the Southern Community Cohort Study (SCCS), a large prospective cohort study including over 80,000 study participants, of whom two-thirds are African Americans. Urine samples were collected at enrollment and subsequently analyzed to assess biomarker levels. Multivariable regression models adjusted for age, race, sex, BMI, smoking status, NSAID use, education level, income, and alcohol consumption were used to assess the relationship between the biomarker and HCC risk.

Results

Only 11dTxB2 (OR = 11.50; 95% CI [2.34-56.47] for highest tertile vs. lowest tertile, p = 0.004) and the PGI-M/11dTXB2 ratio of the second quartile (0.25-0.49) (OR = 5.16; 95% CI [1.44-18.47]; p = 0.01) were significantly associated with increased risk of liver cancer.

Conclusion

11dTXB2 and PGI-M/11dTXB2 ratio may be urinary markers of HCC risk, particularly among African Americans, and future prospective studies are needed to evaluate this finding further and to develop accessible methods.

The Role and Regulation of Thromboxane A2 Signaling in Cancer-Trojan Horses and Misdirection

Over the last two decades, there has been an increasing awareness of the role of eicosanoids in the development and progression of several types of cancer, including breast, prostate, lung, and colorectal cancers. Several processes involved in cancer development, such as cell growth, migration, and angiogenesis, are regulated by the arachidonic acid derivative thromboxane A₂ (TXA₂). Higher levels of circulating TXA₂ are observed in patients with multiple cancers, and this is accompanied by overexpression of TXA₂ synthase (TBXAS1, TXA₂S) and/or TXA₂ receptors (TBXA2R, TP). Overexpression of TXA₂S or TP in tumor cells is generally associated with poor prognosis, reduced survival, and metastatic disease. However, the role of TXA₂ signaling in the stroma during oncogenesis has been underappreciated. TXA₂ signaling regulates the tumor microenvironment by modulating angiogenic potential, tumor ECM stiffness, and host immune response. Moreover, the by-products of TXA₂S are highly mutagenic and oncogenic, adding to the overall phenotype where TXA₂ synthesis promotes tumor formation at various levels. The stability of synthetic enzymes and receptors in this pathway in most cancers (with few mutations reported) suggests that TXA₂ signaling is a viable target for adjunct therapy in various tumors to reduce immune evasion, primary tumor growth, and metastasis.

Aspirin and cancer: biological mechanisms and clinical outcomes

Evidence on aspirin and cancer comes from two main sources: (1) the effect of aspirin upon biological mechanisms in cancer, and (2) clinical studies of patients with cancer, some of whom take aspirin. A series of systematic literature searches identified published reports relevant to these two sources. The effects of aspirin upon biological mechanisms involved in cancer initiation and growth appear to generate reasonable expectations of effects upon the progress and mortality of cancer. Clinical evidence on aspirin appears overall to be favourable to the use of aspirin, but evidence from randomized trials is limited, and inconsistent. The main body of evidence comes from meta-analyses of observational studies of patients with a wide range of cancers, about 25% of whom were taking aspirin. Heterogeneity is large but, overall, aspirin is associated with increases in survival and reductions in metastatic spread and vascular complications of different cancers. It is important that evaluations of aspirin used as an adjunct cancer treatment are based upon all the available relevant evidence, and there appears to be a marked harmony between the effects of aspirin upon biological mechanisms and upon the clinical progress of cancer.

Mechanisms and biomarkers of cancer-associated thrombosis

Cancer-associated thrombosis is a leading cause of non-cancer death in cancer patients and is comprised of both arterial and venous thromboembolism (VTE). There are multiple risk factors for developing VTE, including cancer type, stage, treatment, and other medical comorbidities, which suggests that the etiology of thrombosis is multifactorial. While cancer-associated thrombosis can be treated with anticoagulation, benefits of therapy must be balanced with the increased bleeding risks seen in patients with cancer. Although risk models exist for primary and recurrent VTE, additional predictors are needed to improve model performance and discrimination of high-risk patients. This review will outline the diverse mechanisms driving thrombosis in cancer patients, as well as provide an overview of biomarkers studied in thrombosis risk and important considerations when selecting candidate biomarkers.

Novel Aspects of Extracellular Vesicles as Mediators of Cancer-Associated Thrombosis

The establishment of prothrombotic states during cancer progression is well reported but the precise mechanisms underlying this process remain elusive. A number of studies have implicated the presence of the clotting initiator protein, tissue factor (TF), in circulating tumor-derived extracellular vesicles (EVs) with thrombotic manifestations in certain cancer types. Tumor cells, as well as tumor-derived EVs, may activate and promote platelet aggregation by TF-dependent and independent pathways. Cancer cells and their secreted EVs may also facilitate the formation of neutrophil extracellular traps (NETs), which may contribute to thrombus development. Alternatively, the presence of polyphosphate (polyP) in tumor-derived EVs may promote thrombosis through a TF-independent route. We conclude that the contribution of EVs to cancer coagulopathy is quite complex, in which one or more mechanisms may take place in a certain cancer type. In this context, strategies that could attenuate the crosstalk between the proposed pro-hemostatic routes could potentially reduce cancer-associated thrombosis.

Impacts of Cancer on Platelet Production, Activation and Education and Mechanisms of Cancer-Associated Thrombosis

Platelets are small anucleate cells that are traditionally described as the major effectors of hemostasis and thrombosis. However, increasing evidence indicates that platelets play several roles in the progression of malignancies and in cancer-associated thrombosis. A notable cross-communication exists between platelets and cancer cells. On one hand, cancer can “educate” platelets, influencing their RNA profiles, the numbers of circulating platelets and their activation states. On the other hand, tumor-educated platelets contain a plethora of active biomolecules, including platelet-specific and circulating ingested biomolecules, that are released upon platelet activation and participate in the progression of malignancy. The numerous mechanisms by which the primary tumor induces the production, activation and aggregation of platelets (also known as tumor cell induced platelet aggregation, or TCIPA) are directly related to the pro-thrombotic state of cancer patients. Moreover, the activation of platelets is critical for tumor growth and successful metastatic outbreak. The development or use of existing drugs targeting the activation of platelets, adhesive proteins responsible for cancer cell-platelet interactions and platelet agonists should be used to reduce cancer-associated thrombosis and tumor progression.

Eicosanoids and cancer

Eicosanoids are 20-carbon bioactive lipids derived from the metabolism of polyunsaturated fatty acids, which can modulate various biological processes including cell proliferation, adhesion and migration, angiogenesis, vascular permeability and inflammatory responses. In recent years, studies have shown the importance of eicosanoids in the control of physiological and pathological processes associated with several diseases, including cancer. The polyunsaturated fatty acid predominantly metabolized to generate 2-series eicosanoids is arachidonic acid, which is the major n-6 polyunsaturated fatty acid found in animal fat and in the occidental diet. The three main pathways responsible for metabolizing arachidonic acid and other polyunsaturated fatty acids to generate eicosanoids are the cyclooxygenase, lipoxygenase and P450 epoxygenase pathways. Inflammation plays a decisive role in various stages of tumor development including initiation, promotion, invasion and metastasis. This review will focus on studies that have investigated the role of prostanoids and lipoxygenase-derived eicosanoids in the development and progression of different tumors, highlighting the findings that may provide insights into how these eicosanoids can influence cell proliferation, cell migration and the inflammatory process. A better understanding of the complex role played by eicosanoids in both tumor cells and the tumor microenvironment may provide new markers for diagnostic and prognostic purposes and identify new therapeutic strategies in cancer treatment.

Thromboxane A2 receptor (TBXA2R) is a potent survival factor for triple negative breast cancers (TNBCs)

Triple Negative Breast Cancer (TNBC) is defined by the lack of ERα, PR expression and HER2 overexpression and is the breast cancer subtype with the poorest clinical outcomes. Our aim was to identify genes driving TNBC proliferation and/or survival which could represent novel therapeutic targets.

We performed microarray profiling of primary TNBCs and generated differential genelists based on clinical outcomes following the chemotherapy regimen FEC (5-Fluorouracil/Epirubicin/Cyclophosphamide -‘good’ outcome no relapse > 3 years; ‘poor’ outcome relapse < 3 years). Elevated expression of thromboxane A2 receptor (TBXA2R) was observed in ‘good’ outcome TNBCs. TBXA2R expression was higher specifically in TNBC cell lines and TBXA2R knockdowns consistently showed dramatic cell killing in TNBC cells. TBXA2R mRNA and promoter activities were up-regulated following BRCA1 knockdown, with c-Myc being required for BRCA1-mediated transcriptional repression.

We demonstrated that TBXA2R enhanced TNBC cell migration, invasion and activated Rho signalling, phenotypes which could be reversed using Rho-associated Kinase (ROCK) inhibitors. TBXA2R also protected TNBC cells from DNA damage by negatively regulating reactive oxygen species levels. In summary, TBXA2R is a novel breast cancer-associated gene required for the survival and migratory behaviour of a subset of TNBCs and could provide opportunities to develop novel, more effective treatments.

Endometriosis-Derived Stromal Cells Secrete Thrombin and Thromboxane A2, Inducing Platelet Activation

Platelets have been recently revealed to play important roles in the development of endometriosis. However, it is unclear whether endometriotic lesions can secrete any platelet inducers outside the menstruation window. Hence, this study was undertaken to see whether endometriosis-derived stromal cells secrete platelet activators and cause platelet activation. We employed in vitro experimentation using primary ectopic endometrial stromal cells (EESCs) and platelets from healthy male volunteers and evaluated the extent of platelet aggregation by aggregometer and the platelet activation rate by flow cytometry using supernatants harvested from EESCs of different cell densities. We also measured the concentration of thromboxane B2 (TXB2), a metabolite of thromboxane A2 (TXA2), and thrombin activity in supernatants harvested from EESCs of different densities and evaluated the extent of platelet aggregation after treatment of EESCs with hirudin, Ozagrel, and apyrase. Finally, the concentration of TXB2, thrombin, and transforming growth factor β1 (TGF-β1) in platelets cocultured with different densities of EESCs is measured by enzyme-linked immunosorbent assay. We found that EESCs secrete thrombin and TXA2 and induce platelet activation and aggregation in a density-dependent fashion. Treatment of platelets with EESCs resulted in increased concentration of TXB2, thrombin, and TGF-β1 in a density-dependent manner. Treatment of EESCs with hirudin and Ozagrel, but not apyrase, resulted in significant suppression of platelet aggregation. Thus, given recently reported effects of activated platelets on the cell behaviors of EESCs and endometriotic lesions in general, our findings establish that endometriotic lesions and platelets engage active cross-talks in the development of endometriosis, highlighting the importance of lesion microenvironment in endometriosis.

Downregulation of TBXAS1 in an iron-induced malignant mesothelioma model

Malignant mesothelioma is an aggressive and therapy-resistant neoplasm arising from mesothelial cells. Evidence suggests that the major pathology associated with asbestos-induced mesothelioma is local iron overload. In the present study, we induced iron-induced mesothelioma in rats based on previous reports. Ten Wistar rats were given ferric saccharate and nitrilotriacetate i.p. for 5 days a week. Five of the ten rats exhibited widespread mesotheliomas in the peritoneum and tunica vaginalis. The tumor cells showed positive immunostaining for calretinin, wilms tumor-1, podoplanin and the oxidative DNA marker 8-hydroxy-2′-deoxyguanosine. In three of the five rats with mesothelioma, array-based comparative genomic hybridization analysis identified a common chromosomal deletion mapped to the chromosomal 4q31 locus, which encompasses the TBXAS1 gene. Downregulation of the TBXAS1 gene was confirmed using quantitative PCR. TBXAS1 gene expression was also reduced in three of four human malignant pleural mesothelioma cell lines compared with normal bronchial epithelial cells. Immunohistochemistry revealed that TBXAS1 expression was weakly positive and positive in five and three out of eight human malignant mesothelioma samples, respectively. In conclusion, TBXAS1 gene expression was downregulated in rats with iron-induced mesothelioma. The relationship between iron overload and TBXAS1 downregulation should be pursued further.

Regulation of the tumor suppressor FOXO3 by the thromboxane-A2 receptors in urothelial cancer

The transcription factor FOXO3 is a well-established tumor suppressor whose activity, stability, and localization are regulated by phosphorylation and acetylation. Previous data by our laboratory demonstrated amplified thromboxane-A₂ signaling was associated with poor prognoses in bladder cancer patients and overexpression of the thromboxane-A₂ isoform-β receptor (TPβ), but not TPα, induced malignant transformation of immortalized bladder cells in vivo. Here, we describe a mechanism of TP mediated modulation of FOXO3 activity and localization by phosphorylation and deacetylation in a bladder cancer cell model. In vitro gain and loss of function studies performed in non-transformed cell lines, UROsta and SV-HUC, revealed knockdown of FOXO3 expression by shRNA increased cell migration and invasion, while exogenously overexpressing TPβ raised basal phosphorylated (p)FOXO3-S294 levels. Conversely, overexpression of ERK-resistant, mutant FOXO3 reduced increases in UMUC3 cell migration and invasion, including that mediated by TP agonist (U46619). Additionally, stimulation of UMUC3 cells with U46619 increased pFOXO3-S294 expression, which could be attenuated by treatment with a TP antagonist (PTXA₂) or ERK inhibitor (U0126). Initially U46619 caused nuclear accumulation of pFOXO3-S294; however, prolonged stimulation increased FOXO3 cytoplasmic localization. U46619 stimulation decreased overall FOXO3 transcriptional activity, but was associated with increased expression of its pro-survival target, manganese superoxide dismutase. The data also shows that TP stimulation increased the expression of the histone deacetylase, SIRT1, and corresponded with decreased acetylated-FOXO3. Collectively, the data suggest a role for TP signaling in the regulation of FOXO3 activity, mediated in part through phosphorylation and deacetylation.

Functional analysis of human thromboxane synthase polymorphic variants

BACKGROUND

Thromboxane A synthase (TXAS) metabolizes the cyclooxygenase product prostaglandin (PG) H2 into thromboxane H2 (TXA2), a potent inducer of blood vessel constriction and platelet aggregation. Nonsynonymous polymorphisms in the TXAS gene have the potential to alter TXAS activity and affect TXA2 generation.

OBJECTIVES

The aim of this study was to assess the functional effects of genetic variants in the TXAS protein, including K258E, L357V, Q417E, E450K, and T451N.

METHODS

Wild-type TXAS and the variant proteins were expressed in a bacterial system and purified by affinity and hydroxyapatite chromatography. The two characteristic catalytic activities of TXAS were assayed in each of the purified recombinant proteins: isomerization of PGH2 to TXA2 and fragmentation of PGH2 to 12-hydroxyheptadecatrienoic acid and malondialdehyde.

RESULTS

All of the variants showed both isomerization and fragmentation activities. The Km values of the variants ranged from 27 to 52 µmol/l PGH2 (wild-type value: 32 μmol/l PGH2); the Vmax values of the variants ranged from 18 to 40 U/mg (wild-type value: 41 U/mg). The kinetic differences were largest for the L357V variant, whose Vmax/Km ratio was just 27% of the wild-type value.

CONCLUSION

The increased Km and decreased Vmax values observed with L357V suggest that this variant may generate less TXA2 at the low levels of PGH2 expected in vivo, raising the possibility of attenuated signaling through the thromboxane pathway.

Epigenetic deregulation of the COX pathway in cancer

Inflammation is a major cause of cancer and may condition its progression. The deregulation of the cyclooxygenase (COX) pathway is implicated in several pathophysiological processes, including inflammation and cancer. Although, its targeting with nonsteroidal antiinflammatory drugs (NSAIDs) and COX-2 selective inhibitors has been investigated for years with promising results at both preventive and therapeutic levels, undesirable side effects and the limited understanding of the regulation and functionalities of the COX pathway compromise a more extensive application of these drugs. Epigenetics is bringing additional levels of complexity to the understanding of basic biological and pathological processes. The deregulation of signaling and biosynthetic pathways by epigenetic mechanisms may account for new molecular targets in cancer therapeutics. Genes of the COX pathway are seldom mutated in neoplastic cells, but a large proportion of them show aberrant expression in different types of cancer. A growing body of evidence indicates that epigenetic alterations play a critical role in the deregulation of the genes of the COX pathway. This review summarizes the current knowledge on the contribution of epigenetic processes to the deregulation of the COX pathway in cancer, getting insights into how these alterations may be relevant for the clinical management of patients.

The thromboxane synthase and receptor signaling pathway in cancer: an emerging paradigm in cancer progression and metastasis

Thromboxane A(2) (TXA(2)) is a biologically active metabolite of arachidonic acid formed by the action of the terminal synthase, thromboxane A(2) synthase (TXA(2)S), on prostaglandin endoperoxide (PGH(2)). TXA(2) is responsible for multiple biological processes through its cell surface receptor, the T-prostanoid (TP) receptor. Thromboxane A(2) synthase and TP are the two necessary components for the functioning of this potent bioactive lipid. Thromboxane A(2) is widely implicated in a range of cardiovascular diseases, owing to its acute and chronic effects in promoting platelet aggregation, vasoconstriction, and proliferation. In recent years, additional functional roles for both TXA(2)S and TP in cancer progression have been indicated. Increased cyclooxygenase (COX)-2 expression has been described in a variety of human cancers, which has focused attention on TXA(2) as a downstream metabolite of the COX-2-derived PGH(2). Several studies suggest potential involvement of TXA(2)S and TP in tumor progression, especially tumor cell proliferation, migration, and invasion that are key steps in cancer progression. In addition, the regulation of neovascularization by TP has been identified as a potent source of control during oncogenesis. There have been several recent reviews of TXA(2)S and TP but thus far none have discussed its role in cancer progression and metastasis in depth. This review will focus on some of the more recent findings and advances with a significant emphasis on understanding the functional role of TXA(2)S and TP in cancer progression and metastasis.

Thromboxane A₂ receptor signaling facilitates tumor colonization through P-selectin-mediated interaction of tumor cells with platelets and endothelial cells

Thromboxane A(2) (TXA(2) ) is a prostanoid formed by thromboxane synthase using the cyclooxygenase product, prostaglandin H(2), as the substrate. TXA(2) was shown to enhance tumor metastasis, but the underlying mechanism remains unclear. B16F1 melanoma cells were intravenously injected into TXA(2) receptor (TP) knockout mice (TP(-/-) ) and wild-type littermates (WT). TP(-/-) showed a reduction in B16F1 lung colonization and mortality rate, which were associated with a decreased number of platelets. Platelet activation as assessed by P-selectin expression was suppressed in TP(-/-) . A selective P-selectin neutralizing antibody decreased the lung colonization in WT mice, but not in TP(-/-) . The expression of P-selectin glycoprotein ligand-1 in B16F1 and HUVEC were enhanced by treatment with U46619, a thromboxane analog. The plasma levels of vascular endothelial growth factor (VEGF) and stromal-derived factor (SDF)-1 were lower in TP(-/-) . In TP(-/-) , the mobilization of progenitor cells expressing CXCR4(+) VEGFR1(+) from bone marrow and the recruitment of those cells to lung tissues were suppressed. These results suggest that TP signaling plays a critical role in tumor colonization through P-selectin-mediated interactions between platelets-tumor cells and tumor cells-endothelial cells through the TP signaling-dependent production of VEGF and SDF-1, which might be involved in the mobilization of VEGFR1(+) CXCR4(+) cells. Blockade of TP signaling might be useful in the treatment of tumor metastasis.

Upregulation of thromboxane synthase mediates visfatin-induced interleukin-8 expression and angiogenic activity in endothelial cells

Thromboxane synthase (TXAS) is an enzyme that catalyzes the synthesis of thromboxane A(2) (TXA(2)). Overexpression of TXAS is associated with a variety of vascular diseases. Recently, we reported that visfatin, a novel adipokine, exhibits angiogenic actions. In this study, we showed that visfatin increased mRNA and protein levels of TXAS and stimulated TXA(2) biosynthesis in vascular endothelial cells. In addition, visfatin induced the expression and secretion of interleukin-8 (IL-8), which is blocked by a TXAS inhibitor and by the transfection of siRNA specific for TXAS. Furthermore, the inhibition of TXAS activity and blockade of the IL-8 receptor attenuated visfatin-induced endothelial angiogenesis. Together, these results showed that visfatin promoted IL-8 production by upregulation of TXAS, leading to angiogenic activation in endothelial cells.

Urinary thromboxane B2 and thromboxane receptors in bladder cancer: opportunity for detection and monitoring

We have previously found increased expression of thromboxane synthase (TXAS) and thromboxane receptor (TP) beta isoform in the tissues of patients with bladder cancer. Studies in cell lines and mice have indicated a potential significant role of the thromboxane signaling pathway in the pathogenesis of human bladder cancer. This study was designed to determine if the changes observed in the tissues of patients with bladder cancer were mirrored by changes in the urine of these patients. We found increased levels of thromboxane B(2) (TXB(2)) the major metabolite of TXAS and increased levels of the TPβ receptor. These results raised the possibility that patients with bladder cancer may be followed for progression or remission of their disease by quantitation of these substances in their urine.

COX-derived prostanoid pathways in gastrointestinal cancer development and progression: novel targets for prevention and intervention

Arachidonic acid metabolism through cyclooxygenase (COX) pathways leads to the generation of biologically active eicosanoids. Eicosanoid expression levels vary during development and progression of gastrointestinal (GI) malignancies. COX-2 is the major COX-isoform responsible for G.I. cancer development/progression. COX-2 expression increases during progression from a normal to cancerous state. Evidence from observational studies has demonstrated that chronic NSAID use reduces the risk of cancer development, while both incidence and risk of death due to G.I. cancers were significantly reduced by daily aspirin intake. A number of randomized controlled trials (APC trial, Prevention of Sporadic Adenomatous Polyps trial, APPROVe trial) have also shown a significant protective effect in patients receiving selective COX-2 inhibitors. However, chronic use of selective COX-2 inhibitors at high doses was associated with increased cardiovascular risk, while NSAIDs have also been associated with increased risk. More recently, downstream effectors of COX-signaling have been investigated in cancer development/progression. PGE(2), which binds to both EP and PPAR receptors, is the major prostanoid implicated in the carcinogenesis of G.I. cancers. The role of TXA(2) in G.I. cancers has also been examined, although further studies are required to uncover its role in carcinogenesis. Other prostanoids investigated include PGD(2) and its metabolite 15d-PGJ2, PGF(1α) and PGI(2). Targeting these prostanoids in G.I. cancers has the promise of avoiding cardiovascular toxicity associated with chronic selective COX-2 inhibition, while maintaining anti-tumor reactivity. A progressive sequence from normal to pre-malignant to a malignant state has been identified in G.I. cancers. In this review, we will discuss the role of the COX-derived prostanoids in G.I. cancer development and progression. Targeting these downstream prostanoids for chemoprevention and/or treatment of G.I. cancers will also be discussed. Finally, we will highlight the latest pre-clinical technologies as well as avenues for future investigation in this highly topical research field.

Examination of thromboxane synthase as a prognostic factor and therapeutic target in non-small cell lung cancer

Background

Thromboxane synthase (TXS) metabolises prostaglandin H2 into thromboxanes, which are biologically active on cancer cells. TXS over-expression has been reported in a range of cancers, and associated with a poor prognosis. TXS inhibition induces cell death in-vitro, providing a rationale for therapeutic intervention. We aimed to determine the expression profile of TXS in NSCLC and if it is prognostic and/or a survival factor in the disease.

Methods

TXS expression was examined in human NSCLC and matched controls by western analysis and IHC. TXS metabolite (TXB₂) levels were measured by EIA. A 204-patient NSCLC TMA was stained for COX-2 and downstream TXS expression. TXS tissue expression was correlated with clinical parameters, including overall survival. Cell proliferation/survival and invasion was examined in NSCLC cells following both selective TXS inhibition and stable TXS over-expression.

Results

TXS was over-expressed in human NSCLC samples, relative to matched normal controls. TXS and TXB₂ levels were increased in protein (p < 0.05) and plasma (p < 0.01) NSCLC samples respectively. TXS tissue expression was higher in adenocarcinoma (p < 0.001) and female patients (p < 0.05). No significant correlation with patient survival was observed. Selective TXS inhibition significantly reduced tumour cell growth and increased apoptosis, while TXS over-expression stimulated cell proliferation and invasiveness, and was protective against apoptosis.

Conclusion

TXS is over-expressed in NSCLC, particularly in the adenocarcinoma subtype. Inhibition of this enzyme inhibits proliferation and induces apoptosis. Targeting thromboxane synthase alone, or in combination with conventional chemotherapy is a potential therapeutic strategy for NSCLC.

Expression of genes related to apoptosis, cell cycle and signaling pathways are independent of TP53 status in urinary bladder cancer cells

Urinary bladder cancer is the fourth most common malignancy in the Western world. Transitional cell carcinoma (TCC) is the most common subtype, accounting for about 90% of all bladder cancers. The TP53 gene plays an essential role in the regulation of the cell cycle and apoptosis and therefore contributes to cellular transformation and malignancy; however, little is known about the differential gene expression patterns in human tumors that present with the wild-type or mutated TP53 gene. Therefore, because gene profiling can provide new insights into the molecular biology of bladder cancer, the present study aimed to compare the molecular profiles of bladder cancer cell lines with different TP53 alleles, including the wild type (RT4) and two mutants (5637, with mutations in codons 280 and 72; and T24, a TP53 allele encoding an in-frame deletion of tyrosine 126). Unsupervised hierarchical clustering and gene networks were constructed based on data generated by cDNA microarrays using mRNA from the three cell lines. Differentially expressed genes related to the cell cycle, cell division, cell death, and cell proliferation were observed in the three cell lines. However, the cDNA microarray data did not cluster cell lines based on their TP53 allele. The gene profiles of the RT4 cells were more similar to those of T24 than to those of the 5637 cells. While the deregulation of both the cell cycle and the apoptotic pathways was particularly related to TCC, these alterations were not associated with the TP53 status.

Inhibition of thromboxane synthase activity improves glioblastoma response to alkylation chemotherapy

Thromboxane synthase (TXSA), an enzyme of the arachidonic acid metabolism, is upregulated in human glial tumors and is involved in glioma progression. Here, we analyzed the in vitro and in vivo effects of pharmacological inhibition of TXSA activity on human glioblastoma cells. Furegrelate, a specific inhibitor of TXSA, significantly inhibited tumor growth in an orthotopic glioblastoma model by inducing proapoptotic, antiproliferative, and antiangiogenic effects. Inhibition of TXSA induced a proapoptotic disposition of glioma cells and increased the sensitivity to the chemotherapeutic agent 1,3-bis(2-chloroethyl)-1-nitrosourea, significantly prolonging the survival time of intracerebral glioma-bearing mice. Our data demonstrate that the targeted inhibition of TXSA activity improves the efficiency of conventional alkylation chemotherapy in vivo. Our study supports the role of TXSA activity for the progression of malignant glioma and the potential utility of its therapeutic modulation for glioma treatment.

Thromboxane A2 receptor-mediated epidermal growth factor receptor transactivation: involvement of PKC-delta and PKC-epsilon in the shedding of epidermal growth factor receptor ligands

We examined thromboxane A(2) receptor (TP)-mediated transactivation of epidermal growth factor receptor (EGFR) through the shedding of EGFR ligands. A TP agonist U46619 caused the phosphorylation of EGFR in 1321N1 human astrocytoma cells, which was inhibited by an EGFR selective inhibitor AG1478 and by a disintegrin and metalloproteinase (ADAM) inhibitor TAPI-2, indicating TP stimulation caused the EGFR transactivation through the EGFR ligand shedding. Since 1321N1 cells expressed heparin-binding EGF (HB-EGF) mRNA, the mechanism of TP-mediated EGFR transactivation was examined in HEK293 cells expressing alkaline phosphatase-conjugated HB-EGF and TP. U46619 caused the shedding of HB-EGF in a time- and concentration-dependent manner. The TP-mediated shedding was inhibited by a furin inhibitor CMK, TAP-2, dominant-negative G alpha(q), a G(q/11) inhibitor YM254890, and also by a non-selective PKC inhibitor GF109203X and PKC down-regulation, but not by a conventional PKC inhibitor Gö6976. Furthermore, siRNAs of PKC-delta and PKC-epsilon inhibited U46619-induced HB-EGF shedding. Although BAPTA/AM had no effect on U46619-induced shedding of HB-EGF, EGTA inhibited it. These results suggest that TP-mediated EGFR transactivation is partially caused by shedding of HB-EGF, which involves furin and ADAM via novel types of PKCs (PKC-delta and PKC-epsilon) through G alpha(q/11) proteins in an extracellular Ca(2+)-dependent manner.

Alternative splicing of G protein-coupled receptors: physiology and pathophysiology

The G protein-coupled receptors (GPCRs) are a superfamily of transmembrane receptors that have a broad distribution and can collectively recognise a diverse array of ligands. Activation or inhibition of GPCR signalling can affect many (patho)physiological processes, and consequently they are a major target for existing and emerging drug therapies. A common observation has been that the pharmacological, signalling and regulatory properties of GPCRs can differ in a cell- and tissue-specific manner. Such "phenotypic" diversity might be attributable to post-translational modifications and/or association of GPCRs with accessory proteins, however, post-transcriptional mechanisms are also likely to contribute. Although approximately 50% of GPCR genes are intronless, those that possess introns can undergo alternative splicing, generating GPCR subtype isoforms that may differ in their pharmacological, signalling and regulatory properties. In this review we shall highlight recent research into GPCR splice variation and discuss the potential consequences this might have for GPCR function in health and disease.

Activation of thromboxane A(2) receptors induces orphan nuclear receptor Nurr1 expression and stimulates cell proliferation in human lung cancer cells

Previous studies implicate that activation of thromboxane A(2) receptor (TP) induced cell proliferation and transformation in several cell lines. We report here that the activation of TP by its agonist, [1S-[1alpha, 2alpha (Z), 3beta (1E, 3S*), 4alpha]]-7-[3-[3-hydroxy-4-(4-iodophenoxy)-1-butenyl]-7-oxabicyclo [2.2.1] hept-2-yl]-5-heptenoic acid (I-BOP), induced Nurr1 expression and stimulated proliferation of human lung cancer cells. Nurr1, an orphan nuclear receptor in the nuclear receptor subfamily 4A subfamily, has been implicated in cell proliferation, differentiation and apoptosis. I-BOP markedly induced Nurr1 messenger RNA and protein levels as compared with other subfamily members, Nur77 and Nor-1. The signaling pathways of I-BOP-induced Nurr1 expression were examined by using various inhibitors of signaling molecules. The induction of Nurr1 expression by I-BOP appeared to be mediated through protein kinase A (PKA)/cAMP response element binding (CREB), protein kinase C and mitogen-activated protein kinase/extracellular signal-regulated kinase pathways and not related to epidermal growth factor receptor and prostaglandin E(2) pathways. Transcriptional activation of Nurr1 gene by I-BOP was further investigated at the promoter level in H157 cells. 5'-Deletion analysis, site-directed mutagenesis and luciferase reporter assay demonstrated that Nurr1 expression was induced by I-BOP in a PKA/CREB-dependent manner. Further studies have revealed that Nurr1 may mediate cyclin D1 expression and I-BOP-induced cell proliferation in H157 cells since small interfering RNA of Nurr1 blocked I-BOP-induced cyclin D1 expression and cell proliferation and also decreased cell growth rate. These results provide strong evidence that Nurr1 plays a significant role in cell proliferation and may mediate TP agonist-induced proliferation in lung cancer cells.

Eicosanoids in tumor progression and metastasis

Eicosanoids and the enzymes responsible for their generation in living systems are involved in the mediation of multiple physiological and pathophysiological responses. These bioactive metabolites are part of complex cascades that initiate and perpetuate several disease processes such as atherosclerosis, arthritis, neurodegenerative conditions, and cancer. The intricate role played by each of these metabolites in the initiation, progression, and metastasis of solid tumors has been a subject of intense research in the scientific community. This review summarizes some of the key aspects of eicasonoids and the associated enzymes, and the pathways they mediate in promoting tumor progression and metastasis.

Novel role of thromboxane receptors beta isoform in bladder cancer pathogenesis

These studies were undertaken to determine the potential role of thromboxane receptors (TP) in bladder cancer. The data reported herein show that expression of the TP-beta receptor protein is increased in tissue obtained from patients with bladder cancer and associated with a significantly poorer prognosis (P < 0.005). Bladder cancer cell lines express the TP-beta isoform, unlike immortalized nontransformed urothelial cells (SV-HUC) that express only the TP-alpha isoform. TP-beta receptor expression, but not TP-alpha, promoted cell proliferation, migration, and invasion in vitro, and also resulted in malignant transformation of SV-HUC cells in vivo. Agonist-mediated phosphorylation of extracellular signal-regulated kinase and FAK was dependent on the expression of TP-beta. Furthermore, TP-beta mediated multiple biological effects by signaling through either G-protein alpha subunit 12 or beta-arrestin 2. Treatment of mice with the TP receptor antagonist GR32191, alone or in combination with cisplatin, significantly delayed tumor onset and prolonged survival of mice transplanted with TCC-SUP bladder cancer cells compared with vehicle or cisplatin alone. These results support the model that the TP-beta receptor isoform plays a unique role in bladder cancer progression and its expression may have predictive value and provide a novel therapeutic target.

Activation of extracellular signal-regulated kinase by 12-hydroxyheptadecatrienoic acid in prostate cancer PC3 cells

Both 12-hydroxyheptadecatrienoic acid (12-HHT) and thromboxane A2 (TXA2) are products derived from prostaglandin H2 (PGH2) catalyzed by thromboxane synthase. Whether or not they exhibit similar actions remains to be determined. While TXA2-induced activation of extracellular signal-regulated kinases (ERKs) has been extensively studied, 12-HHT-induced activation of ERKs has not been explored. We reported for the first time that 12-HHT induced activation of ERKs in human prostate cancer cell line, PC3. We also compared the mechanisms of 12-HHT- and I-BOP-, a TXA2 mimetic, mediated ERK activation in PC3 cells. The activation of ERKs induced by either agent was shown to involve protein kinase C (PKC)-, protein kinase A (PKA)-, Src kinase and phosphoinositide-3 kinase (PI-3K)-dependent mechanisms in addition to the transactivation of the EGF receptor (EGFR) and the involvement of matrix metalloproteinases (MMPs) based on the sensitivity of the activation to their respective inhibitors. JNK/SAPK and p38 MAPK pathways were responsive to I-BOP but not to 12-HHT stimulation. Both 12-HHT- and I-BOP-induced activations of ERKs were also examined in other human prostate cancer cells, human lung cancer cells, and human lung fibroblast. I-BOP appeared to induce activation of ERKs in most cell lines, whereas 12-HHT induced activation of ERKs only in lung fibroblast in addition to PC3 cells. It appears that TPs are more generally expressed and the potential 12-HHT receptor (s) is expressed in limited specific cell types. Our results suggest that increased expression of thromboxane synthase as seen in prostate tumor may stimulate tumorigenesis as a consequence of concurrent increased synthesis of two fatty acids capable of activating ERKs.

Rofecoxib and cardiovascular adverse events in adjuvant treatment of colorectal cancer

BACKGROUND

Selective cyclooxygenase inhibitors may retard the progression of cancer, but they have enhanced thrombotic potential. We report on cardiovascular adverse events in patients receiving rofecoxib to reduce rates of recurrence of colorectal cancer.

METHODS

All serious adverse events that were cardiovascular thrombotic events were reviewed in 2434 patients with stage II or III colorectal cancer participating in a randomized, placebo-controlled trial of rofecoxib, 25 mg daily, started after potentially curative tumor resection and chemotherapy or radiotherapy as indicated. The trial was terminated prematurely owing to worldwide withdrawal of rofecoxib. To examine possible persistent risks, we examined cardiovascular thrombotic events reported up to 24 months after the trial was closed.

RESULTS

The median duration of active treatment was 7.4 months. The 1167 patients receiving rofecoxib and the 1160 patients receiving placebo were well matched, with a median follow-up period of 33.0 months (interquartile range, 27.6 to 40.1) and 33.4 months (27.7 to 40.4), respectively. Of the 23 confirmed cardiovascular thrombotic events, 16 occurred in the rofecoxib group during or within 14 days after the treatment period, with an estimated relative risk of 2.66 (from the Cox proportional-hazards model; 95% confidence interval [CI], 1.03 to 6.86; P=0.04). Analysis of the Antiplatelet Trialists' Collaboration end point (the combined incidence of death from cardiovascular, hemorrhagic, and unknown causes; of nonfatal myocardial infarction; and of nonfatal ischemic and hemorrhagic stroke) gave an unadjusted relative risk of 1.60 (95% CI, 0.57 to 4.51; P=0.37). Fourteen more cardiovascular thrombotic events, six in the rofecoxib group, were reported within the 2 years after trial closure, with an overall unadjusted relative risk of 1.50 (95% CI, 0.76 to 2.94; P=0.24). Four patients in the rofecoxib group and two in the placebo group died from thrombotic causes during or within 14 days after the treatment period, and during the follow-up period, one patient in the rofecoxib group and five patients in the placebo group died from cardiovascular causes.

CONCLUSIONS

Rofecoxib therapy was associated with an increased frequency of adverse cardiovascular events among patients with a median study treatment of 7.4 months' duration. (Current Controlled Trials number, ISRCTN98278138 [controlled-trials.com].).

Inhibition of thromboxane synthase activity modulates bladder cancer cell responses to chemotherapeutic agents

Recently, we reported prognostic significance of thromboxane synthase (TXAS) gene expression in invasive bladder cancer. The positive correlation between elevated TXAS expression and shorter patient survival supports a potential role for TXAS-regulated pathways in tumor metastases. In this study, using immunohistochemical analysis, we found an increased expression of TXAS protein in bladder cancer. Treatment of T24 and transitional cell carcinoma TCC-SUP bladder cancer cells with the TXAS inhibitors furegrelate or ozagrel induced an apoptotic effect measured as an increase in caspase-3 activation and cell death, and decreased survivin expression. Pharmacological inhibition of TXAS using the TXAS inhibitor furegrelate increased sensitivity to the chemotherapeutic agents cisplatin and paclitaxel. Molecular inhibition of TXAS expression by siRNA significantly decreased cell growth and migration. In concordance with the pharmacological data, siRNA-mediated reduction of TXAS expression increased sensitivity to cisplatin and paclitaxel in T24 and TCC-SUP cells. In summary, the data support a role for the thromboxane A(2) pathway in the pathogenesis of bladder cancer and the potential utility of modulation of this signaling pathway for cancer chemotherapy.

Activation of thromboxane receptor alpha induces expression of cyclooxygenase-2 through multiple signaling pathways in A549 human lung adenocarcinoma cells

Human lung adenocarcinoma A549 cells stably transfected with TPalpha (A549-TPalpha) were used to study agonist I-BOP-induced expression of cyclooxygenase-2 (COX-2) and the related mechanisms of induced expression. I-BOP, a TP agonist, induced a time- and dose-dependent expression of COX-2 in A549-TPalpha cells. The signaling pathways of I-BOP-induced COX-2 expression were elucidated by using various inhibitors of the signaling molecules. The effects of these inhibitors were assessed at protein level, enzyme activity and promoter activity of COX-2. Within MAPK family, both ERK and p38 MAPK but not JNK/SAPK pathways were involved in the induction. Other pathways such as JAK/Stat3 pathway and beta-catenin/TCF/LEF pathway also participated in the induction. The activation of key signaling molecules, ERK, p38 MAPK, CREB and NF-kappaB, involved in the COX-2 transcription was further studied at the phosphorylation step. Activation of ERK and p38 MAPK appeared to be mediated primarily by transactivation of EGFR, whereas activation of CREB and NF-kappaB was mediated by PKA, PKC and ERK. The role of CREB and NF-kappaB in I-BOP-induced COX-2 expression was further explored at the promoter level. Studies on promoter fragments and mutation of responsive motifs indicated that CRE and NF-kappaB sites are critical for the COX-2 induction. Distal NF-kappaB site is essential for the basal induction of the COX-2 transcription, whereas CRE and proximal NF-kappaB sites are important for the induced transcription. These results indicate that I-BOP-induced COX-2 expression through multiple signaling pathways.

Oncogene coexpression in mesenchymal neoplasia correlates with EGF transcription

Epidermal growth factor (EGF) is a potent mitogenic factor for cells of mesodermal and ectodermal origin, and its over-expression is associated with a variety of cancers. We asked whether oncogene coexpression occurs in mesenchymal neoplasms, if coexpression correlates with EGF transcription, and whether coexpression can be attributed to the EGF-induced overexpression of oncogenes. We quantified the mRNA concentrations of EGF and 14 oncogenes in 42 primary sarcomas, 31 benign tumors, and 10 skeletal muscle controls, and compared mRNA concentrations and gene pair correlations in EGF positive (EGF+) tumors to transcript concentrations and correlations in EGF negative (EGF-) tumors. Transcripts were detected by real time reverse transcription-polymerase chain reaction. Pearson's correlation coefficients identified gene associations, and gene synchrony associated with EGF expression was evaluated using chi square. Transcript concentrations in tumors were compared graphically and with t tests. Gene correlations predominated in EGF+ benign tumors and in EGF- primary sarcomas. The dichotomy in oncogene coexpression evident in benign and malignant tumors could not be attributed to statistical differences in mRNA content between EGF+ and EGF- tumors. EGF may enhance, or may indicate the presence of, oncogene coexpression in benign mesenchymal lesions, but counters gene synchronization in sarcomas.

Evaluation of original dual thromboxane A2 modulators as antiangiogenic agents

Angiogenesis is a promising target for the therapy of several diseases including cancer. This study was undertaken to characterize the antiangiogenic properties of a series of original dual thromboxane A(2) (TXA(2)) inhibitors derived from torasemide, a marketed loop diuretic with TXA(2) antagonistic properties, by evaluating their effects on human endothelial cell migration, adhesion, and viability in vitro, as well as in the ex vivo rat aortic ring assay. All drugs tested exhibited a marked affinity toward human platelet TXA(2) receptor, significantly prevented platelet aggregation induced by U-46,619, a stable TXA(2) receptor agonist, and inhibited platelet TXA(2) synthase without affecting cyclooxygenase (COX)-1 or COX-2 enzymatic activities. These dual TXA(2) inhibitors dose dependently inhibited endothelial cell migration in chemotaxis assays using vascular endothelial growth factor (VEGF) as a chemoattractant but failed to affect cell adhesion and viability. The highest rates of cell migration inhibition were obtained with original compounds BM-567 and BM-573 (50.3 and 59.4% inhibition, respectively) when used at the final concentration of 10 microM. In addition, pretreatment of endothelial cells with these two drugs significantly prevented U-46,619-induced intracellular Ca(2+) pool mobilization, thus suggesting a mechanistic link between inhibition of the TXA(2) pathway and reduced endothelial cell migration. Treatment of rat aortic explants with U-46,619 (9,11-dideoxy-9,11-methanoepoxy-prostaglandin F(2)) significantly enhanced vessel sprouting whereas aortic rings treated with some of the compounds, including BM-567 (N-n-pentyl-N'-[2-(cyclohexylamino)-5-nitrobenzenesulfonyl]urea) and BM-573 (N-tert-butyl-N'-[5-nitro-2-p-toluylaminobenzenesulfonyl]urea), showed a significant decrease in vessel sprouting, which was not reversed by the addition of VEGF. These data suggest that our original dual TXA(2) inhibitors bear antiangiogenic properties, mainly by inhibiting endothelial cell migration.

Upregulation of thromboxane synthase in human colorectal carcinoma and the cancer cell proliferation by thromboxane A2

Tumor growth of colorectal cancers accompanies upregulation of cyclooxygenase-2, which catalyzes a conversion step from arachidonic acid to prostaglandin H(2) (PGH(2)). Here, we compared the expression levels of thromboxane synthase (TXS), which catalyzes the conversion of PGH(2) to thromboxane A(2) (TXA(2)), between human colorectal cancer tissue and its accompanying normal mucosa. It was found that TXS protein was consistently upregulated in the cancer tissues from different patients. TXS was also highly expressed in human colonic cancer cell lines. Depletion of TXS protein by the antisense oligonucleotide inhibited proliferation of the cancer cells. This inhibition was rescued by the direct addition of a stable analogue of TXA(2). The present results suggest that overexpression of TXS and subsequent excess production of TXA(2) in the cancer cells may be involved in the tumor growth of human colorectum.