Inhibition of thromboxane synthase induces lung cancer cell death via increasing the nuclear p27

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.

Tobacco carcinogen NNK-induced lung cancer animal models and associated carcinogenic mechanisms

Tobacco usage is a major risk factor in the development, progression, and outcomes for lung cancer. Of the carcinogens associated with lung cancer, tobacco-specific nitrosamines 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) is among the most potent ones. The oncogenic mechanisms of NNK are not entirely understood, hindering the development of effective strategies for preventing and treating smoking-associated lung cancers. Here, we introduce the NNK-induced lung cancer animal models in different species and its potential mechanisms. Finally, we summarize several chemopreventive agents developed from these animal models.

Sorafenib inhibits proliferation and invasion of human hepatocellular carcinoma cells via up-regulation of p53 and suppressing FoxM1

AIM

Forkhead box M1 (FoxM1) is a transcription factor that plays important roles in the pathogenesis and progression of human cancers, including hepatocellular carcinoma (HCC). The aim of this study was to examine the involvement of FoxM1 in the anti-cancer action of sorafenib, a multikinase inhibitor, in human HCC cells.

METHODS

HCC cell lines HepG2 and HuH-7 were tested. Cell viability was examined using MTT assay and cell invasion was determined with Transwell migration assay. The relevant mRNA expression was determined with RT-PCR, and the proteins were detected using Western blotting and immunofluorescence assays. RNA interference was used to modify the expression of p53 and FoxM1. HuH-7 cell line xenograft mice were used for in vivo study, which were treated with sorafenib (40 mg/kg, po) daily for 3 weeks.

RESULTS

Sorafenib (2-20 μmol/L) inhibited the proliferation of the cells in dose- and time-dependent manners with an IC50 value of nearly 6 μmol/L at 48 h. Sorafenib (6 μmol/L) markedly suppressed the cell invasion. Furthermore, sorafenib (2-6 μmol/L) dose-dependently decreased the expression of FoxM1, MMP-2, and Ki-67, and up-regulated that of p53 in the cells. Silencing p53 abolished the decrease of FoxM1 and increase of p53 in sorafenib-treated cells. Silencing FoxM1 significantly reduced the expression of MMP-2 and Ki-67, and enhanced the anti-proliferation action of sorafenib in the cells, whereas overexpression of FoxM1 increased the expression of MMP-2 and Ki-67, and abrogated the anti-proliferation action of sorafenib. In the xenograft mice, sorafenib administration decreased the tumor growth by 40%, and markedly increased the expression of p53, and decreased the expression of FoxM1, MMP-2, and Ki-67 in tumor tissues.

CONCLUSION

Sorafenib inhibits HCC proliferation and invasion by inhibiting MMP-2 and Ki-67 expression due to up-regulation of P53 and suppressing FoxM1.

Anti-tumor activities of lipids and lipid analogues and their development as potential anticancer drugs

Lipids have the potential for development as anticancer agents. Endogenous membrane lipids, such as ceramides and certain saturated fatty acids, have been found to modulate the viability of tumor cells. In addition, many tumors over-express cyclooxygenase, lipoxygenase or cytochrome P450 enzymes that mediate the biotransformation of ω-6 polyunsaturated fatty acids (PUFAs) to potent eicosanoid regulators of tumor cell proliferation and cell death. In contrast, several analogous products from the biotransformation of ω-3 PUFAs impair particular tumorigenic pathways. For example, the ω-3 17,18-epoxide of eicosapentaenoic acid activates anti-proliferative and proapoptotic signaling cascades in tumor cells and the lipoxygenase-derived resolvins are effective inhibitors of inflammatory pathways that may drive tumor expansion. However, the development of potential anti-cancer drugs based on these molecules is complex, with in vivo stability a major issue. Nevertheless, recent successes with the antitumor alkyl phospholipids, which are synthetic analogues of naturally-occurring membrane phospholipid esters, have provided the impetus for development of further molecules. The alkyl phospholipids have been tested against a range of cancers and show considerable activity against skin cancers and certain leukemias. Very recently, it has been shown that combination strategies, in which alkyl phospholipids are used in conjunction with established anticancer agents, are promising new therapeutic approaches. In future, the evaluation of new lipid-based molecules in single-agent and combination treatments may also be assessed. This could provide a range of important treatment options in the management of advanced and metastatic cancer.

Human thromboxane synthase: comparative modeling and docking evaluation with the competitive inhibitors Dazoxiben and Ozagrel

Thromboxane synthase (TXAS) is a P450 epoxygenase that synthesizes thromboxane A2 (TXA2), a potent mediator of platelet aggregation, vasoconstriction and bronchoconstriction. This enzyme plays an important role in several human diseases, including myocardial infarction, stroke, septic shock, asthma and cancer. Despite of the increasing interest on developing TXAS inhibitors, the structure and activity of TXAS are still not totally elucidated. In this study, we used a comparative molecular modeling approach to construct a reliable model of TXAS and analyze its interactions with Dazoxiben and Ozagrel, two competitive inhibitors. Our results were compatible with experimental published data, showing feasible cation-π interaction between the iron atom of the heme group of TXAS and the basic nitrogen atom of the imidazolyl group of those inhibitors. In the absence of the experimental structure of thromboxane synthase, this freely available model may be useful for designing new antiplatelet drugs for diseases related with TXA2.

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.

3,3'-Diindolylmethane enhances taxotere-induced growth inhibition of breast cancer cells through downregulation of FoxM1

Emerging evidence suggests that the transcription factor Forkhead Box M1 (FoxM1) is associated with aggressive human carcinomas, including breast cancer. Because elevated expression of FoxM1 has been observed in human breast cancers, FoxM1 has attracted much attention in recent years as a potential target for the prevention and/or therapeutic intervention in breast cancer. However, no information is currently available regarding how downregulation of FoxM1 could be achieved for breast cancer prevention and therapy. Here, we report for the first time that 3,3'-diindolylmethane (DIM), a nontoxic dietary chemopreventive agent could effectively downregulate FoxM1 in various breast cancer cell lines. Using gene transfection, real-time reverse transcription-PCR, Western blotting, invasion and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assays, we found that DIM could enhance Taxotere-induced growth inhibition of breast cancer cells, and decreased invasive capacity of breast cancer cells was observed after either treatment alone or the combination. These effects were associated with downregulation of FoxM1. We also found that knock down of FoxM1 expression by small interfering RNA (siRNA) transfection increased DIM-induced cell growth inhibition, whereas over-expression of FoxM1 by cDNA transfection attenuated DIM-induced cell growth inhibition, suggesting the mechanistic role of FoxM1. Most importantly, the combination treatment significantly inhibited tumor growth in severe combined immunodeficiency (SCID) mice, and the results were correlated with the downregulation of FoxM1 in tumor remnants. We conclude that inactivation of FoxM1 and its target genes by DIM could enhance the therapeutic efficacy of Taxotere in breast cancer, which could be a useful strategy for the prevention and/or treatment of breast cancer.

Cigarette smoking, cyclooxygenase-2 pathway and cancer

Cigarette smoking is a major cause of mortality and morbidity worldwide. Cyclooxygenase (COX) and its derived prostanoids, mainly including prostaglandin E2 (PGE2), thromboxane A2 (TxA2) and prostacyclin (PGI2), have well-known roles in cardiovascular disease and cancer, both of which are associated with cigarette smoking. This article is focused on the role of COX-2 pathway in smoke-related pathologies and cancer. Cigarette smoke exposure can induce COX-2 expression and activity, increase PGE2 and TxA2 release, and lead to an imbalance in PGI2 and TxA2 production in favor of the latter. It exerts pro-inflammatory effects in a PGE2-dependent manner, which contributes to carcinogenesis and tumor progression. TxA2 mediates other diverse biologic effects of cigarette smoking, such as platelet activation, cell contraction and angiogenesis, which may facilitate tumor growth and metastasis in smokers. Among cigarette smoke components, nicotine and its derived nitrosamines 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) are the most potent carcinogens. COX-2 and PGE2 have been shown to play a pivotal role in many cancers associated with cigarette smoking, including cancers of lung, gastric and bladder, while the information for the role of TxA2 and PGI2 in smoke-associated cancers is limited. Recent findings from our group have revealed how NNK influences the TxA2 to promote the tumor growth. Better understanding in the above areas may help to generate new therapeutic protocols or to optimize the existing treatment strategy.

4-Methylnitrosamino-1-3-pyridyl-1-butanone (NNK) promotes lung cancer cell survival by stimulating thromboxane A2 and its receptor

The role of thromboxane A(2) (TxA(2)) in smoking-associated lung cancer is poorly understood. This study was conducted to study the role of TxA(2) in smoking carcinogen 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK)-promoted cell survival and growth in human lung cancer cells. We found that NNK increased TxA(2) synthase (TxAS) expression and thromboxane B(2) (TxB(2)) generation in cultured lung cancer cells, the result of which was supported by the increased level of TxAS in lung cancer tissues of smokers. Both TxAS-specific inhibitor furegrelate and TxA(2) receptor antagonist SQ29548 completely blocked NNK-mediated cell survival and growth via inducting apoptosis. TxA(2) receptor agonist U46619 reconstituted a near-full survival and growth response to NNK when TxAS was inhibited, affirming the role of TxA(2) receptor in NNK-mediated cell survival and growth. Suppression of cyclic adenosine monophosphate response element binding protein (CREB) activity by its small interference RNA blocked the effect of NNK. Phosphatidylinositol 3-kinase (PI3K)/Akt and extracellular signal-regulated kinase (ERK) also had a positive role. Altogether, our results have revealed that NNK stimulates TxA(2) synthesis and activates its receptor in lung cancer cells. The increased TxA(2) may then activate CREB through PI3K/Akt and extracellular ERK pathways, thereby contributing to the NNK-promoted survival and growth of lung cancer cells.