The cytochrome P450 arachidonic acid epoxygenase metabolites, the epoxyeicosatrienoic acids (EETs) are powerful, nonregioselective, stimulators of cell proliferation. In this study we compared the ability of the four EETs (5,6-, 8,9-, 11,12-, and 14,15-EETs) to regulate endothelial cell proliferation in vitro and angiogenesis in vivo and determined the molecular mechanism by which EETs control these events. Inhibition of the epoxygenase blocked serum-induced endothelial cell proliferation, and exogenously added EETs rescued cell proliferation from epoxygenase inhibition. Studies with selective ERK, p38 MAPK, or PI3K inhibitors revealed that whereas activation of p38 MAPK is required for the proliferative responses to 8,9-and 11,12-EET, activation of PI3K is necessary for the cell proliferation induced by 5,6-and 14,15-EET. Among the four EETs, only 5,6-and 8,9-EET are capable of promoting endothelial cell migration and the formation of capillary-like structures, events that are dependent on EET-mediated activation of ERK and PI3K. Using subcutaneous sponge models, we showed that 5,6-and 8,9-EET are pro-angiogenic in mice and that their neo-vascularization effects are enhanced by the co-administration of an inhibitor of EET enzymatic hydration, presumably because of reduced EET metabolism and inactivation. These studies identify 5,6-and 8,9-EET as powerful and selective angiogenic lipids, provide a functional link between the EET proliferative chemotactic properties and their angiogenic activity, and suggest a physiological role for them in angiogenesis and de novo vascularization.

Cytochromes P450 of the CYP2C and CYP4A gene subfamilies metabolize arachidonic acid to 5,6-, 8,9-, 11,12-, and 14,15-epoxyeicosatrienoic acids (EETs) and to 19-and 20-hydroxyeicosatetraenoic acids (HETEs), respectively. Abundant functional studies indicate that EETs and HETEs display powerful and often opposing biological activities as mediators of ion channel activity and regulators of vascular tone and systemic blood pressures. Incubation of 8,9-, 11,12-, and 14,15-EETs with microsomal and purified forms of rat CYP4A isoforms led to rapid NADPH-dependent metabolism to the corresponding 19-and 20-hydroxylated EETs. Comparisons of reaction rates and catalytic efficiency with those of arachidonic and lauric acids showed that EETs are one of the best endogenous substrates so far described for rat CYP4A isoforms. CYP4A1 exhibited a preference for 8,9-EET, whereas CYP4A2, CYP4A3, and CYP4A8 preferred 11,12-EET. In general, the closer the oxido ring is to the carboxylic acid functionality, the higher the rate of EET metabolism and the lower the regiospecificity for the EET -carbon. Analysis of cis-parinaric acid displacement from the ligand-binding domain of the human peroxisome proliferator-activated receptor-␣ showed that -hydroxylated 14,15-EET bound to this receptor with high affinity (K i ‫؍‬ 3 ؎ 1 nM). Moreover, at 1 M, the -alcohol of 14,15-EET or a 1:4 mixture of the -alcohols of 8,9-and 11,12-EETs activated human and mouse peroxisome proliferator-activated receptor-␣ in transient transfection assays, suggesting a role for them as endogenous ligands for these orphan nuclear receptors.Cytochromes P450 of the CYP4A gene subfamily are structurally and functionally conserved fatty-acid hydroxylases that are expressed in most mammalian tissues, including rat and human kidney and liver (1-7). These enzymes are selective for the /-1-hydroxylation of saturated and unsaturated fatty acids (1-7) and lack known roles in drug metabolism. The expression of some CYP4A isoforms is under the control of the peroxisome proliferator-activated receptor-␣ (PPAR␣) 1 (8 -13) and regulated by a variety of physiological and pathophysiological stimuli, including dietary fatty acids, hormones, diabetes, and starvation (9 -13). Interest in the molecular and functional properties of these enzymes has been stimulated by the demonstration of their role in the /-1-hydroxylation of arachidonic acid (AA) (4 -7) and the powerful biological activities of 19-and 20-hydroxyeicosatetraenoic acids (HETEs) as modulators of renal ion fluxes and vasoactivity (14 -18). Based on biochemical and functional correlates of CYP4A renal expression, 20-HETE biosynthesis, and the onset of systemic high blood pressure in the SHR/WKY rat model of spontaneous hypertension, a pro-hypertensive role for 20-HETE and CYP4A isoforms was proposed (14).The cytochrome P450 AA epoxygenase catalyzes the in vivo regio-and enantioselective metabolism of AA to epoxyeicosatrienoic acids (EETs) (16). Studies with microsomal and/or purified cytochrome P450 preparations showed tha...

Cytosine deaminase (EC 3.5.4.1), a non-mammalian enzyme, catalyzes the deamination of cytosine and 5-fluorocytosine to form uracil and 5-fluorouracil, respectively. Eukaryotic cells have been genetically modified with a bacterial cytosine deaminase gene to express a functional enzyme. When the genetically modified cells are combined with 5-fluorocytosine, it creates a potent negative selection system, which may have important applications in cancer gene therapy. In this paper, we introduce a novel positive selection method based upon the expression of the cytosine deaminase gene. This method utilizes inhibitors in the pyrimidine de novo synthesis pathway to create a condition in which cells are dependent on the conversion of pyrimidine supplements to uracil by cytosine deaminase. Thus, only cells expressing the cytosine deaminase gene can be rescued in a positive selection medium.

Cytochrome P450 BM-3 catalyzes the high turnover regio-and stereoselective metabolism of arachidonic and eicosapentaenoic acids. To map structural determinants of productive active site fatty acid binding, we mutated two amino acid residues, arginine 47 and phenylalanine 87, which flank the surface and heme ends of the enzyme's substrate access channel, respectively.Replacement of arginine 47 with glutamic acid resulted in a catalytically inactive mutant. Replacement of arginine 47 with alanine yielded a protein with reduced substrate binding affinity and arachidonate sp 3 carbon hydroxylation activity (72% of control wild type). On the other hand, arachidonic and eicosapentaenoic acid epoxidation was significantly enhanced (154 and 137%, of control wild type, respectively). As with wild type, the alanine 47 mutant generated (18R)-hydroxyeicosatetraenoic, (14S,15R)-epoxyeicosatrienoic, and (17S,18R)-epoxyeicosatetraenoic acids nearly enantiomerically pure.Replacement of phenylalanine 87 with valine converted cytochrome P450 BM-3 into a regio-and stereoselective arachidonic acid epoxygenase ((14S,15R)-epoxyeicosatrienoic acid, 99% of total products). Conversely, metabolism of eicosapentaenoic acid by the valine 87 mutant yielded a mixture of (14S,15R)-and (17S,18R)-epoxyeicosatetraenoic acids (26 and 69% of total, 94 and 96% optical purity, respectively). Finally, replacement of phenylalanine 87 with tyrosine yielded an inactive protein.We propose that: (a) fatty acid oxidation by P450 BM-3 is incompatible with the presence of residues with negatively charged side chains at the surface opening of the substrate access channel or a polar aromatic side chain in the vicinity of the heme iron; (b) the high turnover regio-and stereoselective metabolism of arachidonic and eicosapentaenoic acids involves charge-dependent anchoring of the fatty acids at the mouth of the access channel by arginine 47, as well as steric gating of the heme-bound oxidant by phenylalanine 87; and (c) substrate binding coordinates, as opposed to oxygen chemistries, are the determining factors responsible for reaction rates, product chemistry, and, thus, catalytic outcome.

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Cyclooxygenase (COX) and its prostanoid metabolites have been implicated in the control of cell survival; however, their role as mitogens remains undefined. To better understand the role of prostanoids on cell growth, we used mouse colon adenocarcinoma (CT26) cells to investigate the role of prostaglandin E 2 (PGE 2 ) in cell proliferation. CT26 cells express both COX1 and COX2 and metabolize arachidonic acid to PGE 2. Treatment with indomethacin, or COXselective inhibitors, prevents PGE 2 biosynthesis and CT26 cell proliferation. The anti-proliferative effects of COX inhibition are rescued specifically by treatment with PGE 2 or the EP4 receptor-selective agonist PGE 1 -OH via phosphatidylinositol 3-kinase/extracellular signal-regulated kinase (ERK) activation, thus providing a functional link between PGE 2 -induced cell proliferation and EP4-mediated ERK signaling. Indomethacin or COX2 inhibitors, but not COX1 inhibitors, reduced the size and number of CT26-derived tumors in vivo. These inhibitory effects are paralleled by marked declines in the levels of tumor PGE 2 , suggesting that their anti-tumor effects are directly associated with the inhibition of COX2 enzymatic activity. The described anti-tumor effects of indomethacin are evident whether it is administered at the time of, or 7 days after, tumor cell injection, suggesting that it has tumor preventive and therapeutic actions. Furthermore, the observation that indomethacin increases the survival rates of tumor-bearing mice, even after withdrawal of the drug, indicates that its effects are long lasting and that it may be potentially useful for the prevention and the clinical management of human cancers.The identification of cyclooxygenase (COX) 1 as the target for non-steroidal anti-inflammatory drugs (NSAIDs) led to new understandings of its pathophysiological role and of the mechanisms of action of these drugs (1, 2). The discovery of COX2, an isoform that, although catalytically identical to COX1, shows inducible tissue-selective expression, suggested physiological and pathophysiological roles for the constitutively expressed (COX1) and inducible (COX2) isoforms, respectively (1-4). Studies showing a correlation between NSAIDs and decreased colon cancer incidence, and the demonstration of up-regulated COX2 expression in colon carcinoma, suggested a role for COX2 in the pathophysiology of colon cancer and created new paradigms for the study of the role of prostanoids in cancer (1-3). Nevertheless, despite extensive supporting evidence, direct links between the anti-tumor effects of NSAIDs and COX inhibition are yet to be established (4 -9). The potential for non-COX-dependent anti-tumor effects of NSAIDs (6 -9), as well as limited evidence available identifying a specific prostanoid(s) as the mediator responsible for the anti-tumor effects of the COX inhibitors (5), raised questions regarding the mechanism of action of NSAIDs and of the role of arachidonic acid, prostanoids, and COXs in human cancer (4 -9).During studies of arachidonic acid metabolism ...

Non-small cell lung cancer (NSCLC) not amenable to surgical resection has a high mortality rate, due to the ineffectiveness and toxicity of chemotherapy. Thus, there remains an urgent need of efficacious drugs that can combat this disease. In this study, we show that targeting the formation of pro-angiogenic epoxyeicosatrienoic acids (EETs) by the cytochrome P450 arachidonic acid epoxygenases (Cyp2c) represents a new and safe mechanism to treat NSCLC growth and progression. In the transgenic murine K-Ras model and human orthotopic models of NSCLC, we found that Cyp2c44 could be downregulated by activating the transcription factor PPARα with the ligands bezafibrate and Wyeth-14,643. Notably, both treatments reduced primary and metastatic NSCLC growth, tumor angiogenesis, endothelial Cyp2c44 expression and circulating EET levels. These beneficial effects were independent of the time of administration, whether before or after the onset of primary NSCLC, and they persisted after drug withdrawal, suggesting the benefits were durable. Our findings suggest that strategies to downregulate Cyp2c expression and/or its enzymatic activity may provide a safer and effective strategy to treat NSCLC. Moreover, as bezafibrate is a well-tolerated clinically approved drug used for managing lipidemia, our findings provide an immediate cue for clinical studies to evaluate the utility of PPARα ligands as safe agents for the treatment of lung cancer in humans.

Arachidonic acid is an essential constituent of cell membranes that is esterified to the sn-2-position of glycerophospholipids and is released from selected lipid pools by phospholipase cleavage. The released arachidonic acid can be metabolized by three enzymatic pathways: the cyclooxygenase pathway forming prostaglandins and thromboxanes, the lipoxygenase pathway generating leukotrienes and lipoxins, and the cytochrome P450 (cP450) pathway producing epoxyeicosatrienoic acids and hydroxyeicosatetraenoic acids. The present study describes a novel group of cP450 epoxygenase-dependent metabolites of arachidonic acid, termed 2-epoxyeicosatrienoylglycerols (2-EG), including two regioisomers, 2-(11,12-epoxyeicosatrienoyl)glycerol (2-11,12-EG) and 2-(14,15-epoxyeicosatrienoyl)-glycerol (2-14,15-EG), which are both produced in the kidney and spleen, whereas 2-11,12-EG is also detected in the brain. Both 2-11,12-EG and 2-14,15-EG activated the two cannabinoid (CB) receptor subtypes, CB1 and CB2, with high affinity and elicited biological responses in cultured cells expressing CB receptors and in intact animals. In contrast, the parental arachidonic acid and epoxyeicosatrienoic acids failed to activate CB1 or CB2 receptors. Thus, these cP450 epoxygenasedependent metabolites are a novel class of endogenously produced, biologically active lipid mediators with the characteristics of endocannabinoids. This is the first evidence of a cytochrome P450-dependent arachidonate metabolite that can activate G-protein-coupled cell membrane receptors and suggests a functional link between the cytochrome P450 enzyme system and the endocannabinoid system. When cells are stimulated by relevant growth factors or hormones, the essential constituent of cell membrane, arachidonic acid, is hydrolyzed from the sn-2-position of selected glycerophospholipids by activated phospholipases (1). We and others (2-4) have previously documented that metabolism of the released arachidonic acid by the cytochrome P450 enzyme system (cP450) 2 produces biologically active lipid mediators, epoxyeicosatrienoic acids (EETs) and hydroxyeicosatetraenoic acids. Subsequent studies revealed that EETs can serve as intracellular second messengers (5, 6), activate Ca 2ϩ signaling (7), and promote cell proliferation (8, 9). EETs also act as endothelium-derived hyperpolarizing factors by opening Ca 2ϩ -activated K ϩ channels (10, 11) and play an anti-inflammatory role by inhibiting NF-B-mediated vascular cell adhesion molecule 1 expression (12). Recent studies indicate that EETs are downstream effectors of anandamide that activate TRPV4 (13). Since cP450 arachidonate metabolites have been demonstrated to play important roles in regulating salt and fluid balance, vascular tone, systemic blood pressure, and local blood supply in vital organs such as the brain, heart, and kidney, the cP450-dependent metabolic pathway has emerged as a potential target for treatment of hypertension and ischemic organ damage (14 -17).Cell surface receptors that mediate the biological effects of...