Clinical significance of prostacyclin and thromboxane in cancer of the female breast and genital tract

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.

Prostanoid receptor antagonists: development strategies and therapeutic applications

Identification of the primary products of cyclo-oxygenase (COX)/prostaglandin synthase(s), which occurred between 1958 and 1976, was followed by a classification system for prostanoid receptors (DP, EP(1), EP(2) ...) based mainly on the pharmacological actions of natural and synthetic agonists and a few antagonists. The design of potent selective antagonists was rapid for certain prostanoid receptors (EP(1), TP), slow for others (FP, IP) and has yet to be achieved in certain cases (EP(2)). While some antagonists are structurally related to the natural agonist, most recent compounds are 'non-prostanoid' (often acyl-sulphonamides) and have emerged from high-throughput screening of compound libraries, made possible by the development of (functional) assays involving single recombinant prostanoid receptors. Selective antagonists have been crucial to defining the roles of PGD(2) (acting on DP(1) and DP(2) receptors) and PGE(2) (on EP(1) and EP(4) receptors) in various inflammatory conditions; there are clear opportunities for therapeutic intervention. The vast endeavour on TP (thromboxane) antagonists is considered in relation to their limited pharmaceutical success in the cardiovascular area. Correspondingly, the clinical utility of IP (prostacyclin) antagonists is assessed in relation to the cloud hanging over the long-term safety of selective COX-2 inhibitors. Aspirin apart, COX inhibitors broadly suppress all prostanoid pathways, while high selectivity has been a major goal in receptor antagonist development; more targeted therapy may require an intermediate position with defined antagonist selectivity profiles. This review is intended to provide overviews of each antagonist class (including prostamide antagonists), covering major development strategies and current and potential clinical usage.

Increased thromboxane B2 levels are associated with lipid peroxidation and Bcl-2 expression in human lung carcinoma

There is little information regarding simultaneous investigations of thromboxane A(2) (TXA(2)) lipid peroxidation and Bcl-2, three cancer-related agents, and analyses of their relationships in lung cancer. The present study was to study thromboxane B(2) (TXB(2)), a stable metabolite of TXA(2), lipid peroxidation and Bcl-2 expression in 52 non-small cell lung carcinoma (NSCLC) tissue samples. The level of thiobarbituric acid reactive substances (TBARS), an index for lipid peroxidation was significantly increased in the lung tumor tissues, compared with non-tumor tissues. TXB(2) was much higher in the tumor tissues than non-tumor tissues. Interestingly, the concentration of TXB(2) in samples from those who smoked was higher than that from those who did not smoke. The expression of Bcl-2 was significantly elevated in the tumor tissues, compared to the non-tumor tissues. There was also a positive correlation between TXB(2) and TBARS in tumor tissues; advanced stage cancers had higher levels of TXB(2). This finding supports the idea that TXB(2) may have a role in promoting tumor growth. In conclusion, our study demonstrates that the production of TXB(2) is increased in lung tumor tissues and that such an increase can result in lipid peroxidation which may be met by an elevation in Bcl-2 expression.

Platelet-Mimicry of Cancer Cells: Epiphenomenon with Clinical Significance

Stem cell mimicry of cancer cells has been known for a long time and is considered to be responsible for ectopic gene expressions. The stem cell characteristics of tumor cells are shown to be involved in epithelial-mesenchymal transition and in the phenomenon of vascular mimicry. Certain cancer types acquire a geno-phenotype closely resembling the platelets and express several megakaryocytic genes (adhesion receptors alpha IIb beta 3, thrombin receptor and PECAM/CD 31 and/or platelet-type 12-LOX) able to activate the coagulation cascade or the platelets themselves. Here we define these potentials as platelet mimicry of cancer cells typical of pancreatic, breast, prostate, colorectal and urogenital cancers and melanoma. Data all support that platelet mimicry of certain cancer types is an important factor in their hematogenous dissemination and provides an attractive therapeutic target. Besides the long-available preclinical data, clinical trials have only recently provided evidence that targeting platelet mimicry of cancers is an efficient way to prevent tumor progression. The systematic discovery of the markers of platelet mimicry in various cancer types and their molecular targeting may provide new supportive therapeutic modalities for the management of the progressing disease.

Development of a screening assay for the in vitro evaluation of thromboxane A2 synthase inhibitors

Inhibitors of thromboxane A2 (TxA2) synthase are regarded as potentially useful agents in the treatment of cardiovascular diseases and in the prevention of tumour cell metastases. We report here a novel in vitro assay for the evaluation of TxA2 synthase inhibitors. For the determination of inhibitory activity, malondialdehyde (MDA) formation by TxA2 synthase in whole blood was utilized. After reaction with thiobarbituric acid MDA was quantified spectrofluorimetrically. The blank value was obtained by incubation with a selective TxA2 synthase inhibitor. For the screening of compounds the simple MDA assay represents an alternative to the rather expensive and time consuming radioimmunoassay, HPLC and TLC methods. Only for compounds which have been shown to be good inhibitors in the MDA assay should a radioimmunoassay for selective inhibition of TxA2 synthase be performed.

Thromboxane A2 analogue U 46619 enhances tumour cell proliferation in HeLa cells via specific receptors which are apparently distinct from TXA2 receptors on human platelets

In this study, we have demonstrated for the first time by using U 46619, a stable analogue of thromboxane A2 (TXA2), that TXA2 exerts a cell proliferative effect on HeLa cells which is mediated by specific TXA2 receptors, inasmuch as the cell proliferation could be dose-dependently suppressed by TXA2 receptor antagonist BM 13177. The investigation of the phospholipase C pathway by U 46619 and prostaglandin H2 (PGH2) in the presence and absence of BM 13177 in cells with or without pertussis toxin pretreatment, as well as radioligand receptor binding studies, revealed that, in contrast to TXA2 receptors on human platelets, where TXA2 and PGH2 share the same receptor binding sites, HeLa cells possess distinct receptors for TXA2 and PGH2.