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Query: UMLS:C0027651 (tumor)
 685,946 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We have shown, in a preliminary report, that macrophages can induce strand breaks in the DNA of co-cultured tumor cells (Chong et al., 1988). The present study is designed to determine if oxygen-centered species generated by the cell-free enzyme-substrate combination of hypoxanthine and xanthine oxidase can induce similar lesions and to identify the specific mediator(s). We report that co-incubation of murine mammary tumor cell lines with hypoxanthine and xanthine oxidase leads to the induction of DNA-strand breaks as determined by fluorescence analysis of DNA unwinding (FADU) assay or alkaline elution techniques. This damage is preventable by catalase which removes hydrogen peroxide but no protection is provided by agents to remove or prevent the formation of superoxide anion (superoxide dismutase), or hydroxyl radical (mannitol or the iron chelator o-phenanthroline). Likewise, cyclooxygenase or lipoxygenase inhibitors of arachidonate metabolism (indomethacin, nordihydroguaiaretic acid, caffeic acid) or bromophenacyl bromide do not alter the degree of DNA scission. Treatment with higher doses of oxygen species leads to significant toxicity as determined by evaluation of cell growth potential or colony-forming ability. Again, toxicity is prevented only by the presence of catalase. Tumor cells are able to rejoin strand breaks at lower, less toxic doses. When comparing different tumor cell subpopulations at various stages of progression, i.e., metastatic vs. nonmetastatic, for sensitivity to hydrogen peroxide-induced strand breakage, we found that at lower concentrations (less than 5 microM) metastatic populations are sensitive whereas nonmetastatic populations exhibit no significant breakage. At higher concentrations of hydrogen peroxide, all lines were sensitive, suggesting that a lower threshold of sensitivity may exist for more progressed tumor cell lines.
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PMID:Reactive oxygen-mediated damage to murine mammary tumor cells. 255 50

The effects of inhibitors of arachidonic acid metabolism and antioxidants on the rat liver tumor promotion activity of phenobarbital (PB) were assessed using the enzyme-altered focus as the end-point lesion. Fischer 344 male rats were initiated with N-nitrosodiethylamine (200 mg/kg) and then divided into five groups placed on basal diet, diet containing 0.05% PB, diet containing 0.05% PB plus 0.75%, 1% or 1.5% levels of various inhibitors of arachidonic acid metabolism or antioxidants, or diet containing 1% or 1.5% inhibitors or antioxidants alone for 10 weeks, and then killed. p-Bromophenacyl bromide, an inhibitor of phospholipase A2, significantly inhibited the promotion activity of PB at dose levels of 0.75% and 1.5%, reaching plateau at 0.75%. Both quercetin, an inhibitor of lipoxygenase, and morin, a dual inhibitor of lipoxygenase-cyclooxygenase, significantly reduced the promotion activity of PB at the 1.5% but not 0.75% dose levels. Moreover, acetylsalicylic acid, an inhibitor of cyclooxygenase dose-dependently inhibited the promotion activity of PB. Among the antioxidants investigated, vitamin E did not affect, but n-propyl gallate and ethoxyquin exerted a dose-dependent inhibition of PB promotion. These results are strongly suggestive of an involvement of phospholipase A2, lipoxygenase and cyclooxygenase arachidonic acid metabolic pathways in the mechanisms underlying PB enhancement of hepatocarcinogenesis.
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PMID:Possible involvement of arachidonic acid metabolism in phenobarbital promotion of hepatocarcinogenesis. 257 27

The mechanism of human interleukin (IL)-1 beta-mediated cytolysis was studied in a human melanoma cell line, A375.6. Purified recombinant human IL-1 beta produced 50% cytocidal activity at 50 pg/ml. A variety of compounds were tested for their ability to interfere with A375.6 lysis. Compounds were added simultaneously with IL-1 beta (100 pg/ml), and tumor cytolysis was measured after 72 hr of culture by release of 125I from DNA of A375.6 cells labeled with [125I]-dUrd. A variety of anti-inflammatory/immunosuppressive agents (including auranofin, chloroquine, cyclosporin A, d-penicillamine) and several cyclooxygenase/lipoxygenase inhibitors (AA-861, BW755c, and indomethacin) lacked protective activity. Similarly, phospholipase inhibitors (mepacrine and 4-bromophenacyl bromide), putrescine, inhibitors of lysosomal activity (chloroquine and NH4Cl), calcium channel blockers (nifedipine and verapamil), calmodulin inhibitors (W-7 and calmidazolium), and inhibitors of ADP ribosylation (nicotinamide and 3-aminobenzamide) were inactive. In contrast, corticosteroids (dexamethasone, hydrocortisone, and paramethasone acetate), tilorone, and protein kinase C inhibitors (1-[5-isoquinolinyl-sulfonyl]-2-methylpiperazine and staurosporine) significantly inhibited IL-1 beta-mediated A375.6 cytolysis. These compounds also interfered with tumor necrosis factor-mediated lysis of A375.6, suggesting common mechanisms of tumor cytotoxicity by these monokines. This model may be useful for delineating intracellular biochemical events integral to IL-1 action.
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PMID:Potent inhibition of interleukin 1 beta-mediated human melanoma (A375.6) lysis by corticosteroids, staurosporine, and tilorone. 262 25

A 12-lipoxygenase metabolite of arachidonic acid, 12(S)-hydroxyeicosatetraenoic acid (12[S]-HETE), which is produced by platelets and tumor cells, was tested for its ability to induce retraction of endothelial cell monolayers. The induction of endothelial cell retraction is a critical step in tumor cell metastasis. Endothelial cells demonstrated reversible retraction in response to 12(S)-HETE, but did not respond to the stereoisomer 12(R)-HETE or to unrelated 5-lipoxygenase (i.e., 5[S]-HETE) or 15-lipoxygenase (i.e., 15[S]-HETE) metabolites. Endothelial cells did not demonstrate loss of viability in response to 12(S)-HETE. The induction of retraction was both dose and time dependent. Scanning electron microscopy confirmed that 12(S)-HETE induced endothelial cell retraction and revealed collapsed filopodia on their surface, the appearance of spaces between endothelial cells and the underlying subendothelial matrix, in addition to large gaps between adjacent endothelial cells. Tumor cell adhesion to endothelial cell monolayers was enhanced 1 h after pretreatment of monolayers with 12(S)-HETE but not after pretreatment with other lipoxygenase metabolites. Tumor cell adhesion to endothelial cell monolayers 36 h after pretreatment with 12(S)-HETE was not different from adhesion to untreated monolayers. Therefore we suggest that 12(S)-HETE generated during tumor cell-platelet-endothelial cell interactions may induce reversible endothelial cell retraction, allowing tumor cell access to the subendothelial matrix, which is a critical step in their eventual extravasation from the microvasculature during hematogenous metastasis.
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PMID:Enhanced tumor cell adhesion to the subendothelial matrix resulting from 12(S)-HETE-induced endothelial cell retraction. 267

We have shown previously that macrophages are mutagenic to bacteria (A. M. Fulton et al., Cancer Res., 44: 4308-4311, 1984) and can induce the appearance of drug-resistant variants of murine mammary tumor cells (K. Yamashina et al., Cancer Res., 46: 2396-2401, 1986). The present study asks whether inflammatory macrophages can induce lesions in the DNA of cocultured tumor cells and seeks to determine the mediators of this damage. We quantitated the induction of DNA strand breaks using the technique of fluorometric analysis of DNA unwinding. We report that inflammatory macrophages coincubated with a mammary tumor cell line for 60 min at a 1:1 ratio result in significant numbers of strand breaks in the tumor cell DNA. The degree of damage is equivalent to 300 to 1200 rads of gamma-irradiation. Resident (unstimulated) peritoneal macrophages also induce tumor cell DNA strand breaks. However, inhibitor studies reveal quantitative and qualitative differences in strand breaks induced by inflammatory (elicited) versus resident peritoneal macrophages. Resident macrophages require a longer induction period (60 min) before significant breaks are detected, but induce more breaks than do elicited macrophages, which require only a 5-min coincubation period to induce significant damage. The enzyme catalase, which removes H2O2, protects tumor cells from both macrophage effector populations as does the prostaglandin synthase inhibitor, indomethacin. The superoxide anion scavenger, superoxide dismutase, and the lipoxygenase inhibitor, nordihydroguaiaretic acid, are protective against resident macrophage effects only. The metal chelator, o-phenanthroline, provides limited protection for elicited macrophages but induces total DNA breakage in the presence of resident macrophages. Taken together, our data indicate that the degree of strand breakage is greater for the macrophage population with high arachidonate metabolism and low oxidative metabolism (resident macrophages) and less for the macrophage population with high oxidative and low arachidonate metabolism (MVE-2 elicited macrophages). Inhibitor studies implicate both metabolites of reactive oxygen and arachidonate as mediators of this tumor cell DNA damage, with the relevant mediator dependent upon the particular macrophage population under study.
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PMID:Macrophage-mediated induction of DNA strand breaks in target tumor cells. 281 15

The participation of lysosomal enzymes, hydroxyl radicals, and mitochondrial respiration in the cytocidal effect of TNF on tumor cells was investigated. The cytotoxicity of TNF on L-M cells was clearly reduced by lysosomotropic agents, DMSO (hydroxyl radical scavenger), NDGA (lipoxygenase inhibitor), and sodium azide (mitochondrial respiration inhibitor). The results suggest that lysosomal enzyme and hydroxyl radicals play an important triggering role in the destruction of tumor cells by TNF, and that the process of destruction might require ATP.
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PMID:Cytocidal mechanism of TNF: effects of lysosomal enzyme and hydroxyl radical inhibitors on cytotoxicity. 283 28

It is increasingly recognized that macrophages play a crucial role in the development of chronic inflammatory states such as alcoholic liver disease. These cells can metabolize free arachidonic acid in the absence of a discernible trigger. The present study was undertaken to examine the short-term effects of ethanol on the generation of these exogenous arachidonate-derived extracellular mediators. Ethanol caused a dose-dependent decrease in the production of both cyclooxygenase and lipoxygenase metabolites. Similar effects were observed on the esterification of exogenous arachidonate into cellular lipids. To characterize further the effects of ethanol on exogenous arachidonic acid metabolism, we studied the short-term responses displayed by macrophages challenged with another soluble stimulus; the tumor-promoting agent phorbol myristate acetate. We observed an inhibition by ethanol of the superoxide anion response triggered by phorbol myristate acetate similar to that observed for exogenous arachidonate oxygenation. Our results show that ethanol can inhibit these soluble stimuli-elicited responses, possibly through its disorganizing effect on plasma membrane.
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PMID:The interaction of ethanol and exogenous arachidonic acid in the generation of extracellular messengers by mouse peritoneal macrophages. 283 91

Indomethacin enhanced macrophage cytostasis against MOPC-315 tumor cells in vitro. The effect of indomethacin was inhibited by prostaglandin E2 and by the lipoxygenase inhibitor nordihydroguaiaretic acid. Prostaglandin E2 and nordihydroguaiaretic acid also inhibited indomethacin stimulation of macrophage thymidine incorporation. Indomethacin inhibited macrophage prostaglandin E2 formation and stimulated leukotriene B4 synthesis. Nordihydroguaiaretic acid inhibited leukotriene B4 production. Our data indicate that eicosanoids play a role in regulating macrophage cytostasis.
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PMID:Indomethacin stimulation of macrophage cytostasis against MOPC-315 tumor cells is inhibited by both prostaglandin E2 and nordihydroguaiaretic acid, a lipoxygenase inhibitor. 284 83

Exposure of isolated SENCAR mouse epidermal cells to the tumor promoter 12-0-tetradecanoylphorbol-13-acetate (TPA) in vitro resulted in the production of oxidant species detected as chemiluminescence. This oxidant response can be inhibited by superoxide dismutase and copper complexes but not catalase or scavengers of hydroxyl radical or singlet oxygen, suggesting that the oxidant is superoxide anion. Inhibitors of various parts of the arachidonate cascade affect the TPA-induced oxidant response in a manner that corresponds to their effects on in vivo tumor promotion experiments. Agents that inhibit lipoxygenase activity, i.e. nordihydroguaiaretic acid, benoxaprofen, but not agents that are cyclooxygenase inhibitors, i.e. indomethacin, are effective in suppressing the oxidant response to TPA. Phospholipase C but not phospholipase A2 or D produced an oxidant response kinetically similar to that elicited by TPA. The inhibitors of TPA-induced oxidants inhibited the phospholipase C response to the same extent, suggesting that TPA and phospholipase C may produce an oxidant species through a common mechanism, via phospholipid turnover-protein kinase C activation. The relevance of oxidant production to the tumor promotion process is suggested by the ability of exogenous xanthine/xanthine oxidase, a superoxide anion-generating system, to induce ornithine decarboxylase, a characteristic of TPA-treated cells. In addition, oxidant production is significantly lower in cells from the TPA-promotion resistant C57BL/6J mouse. These studies provide further support for a role for reactive oxygens in the tumor promotion process.
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PMID:Reactive oxygen in the tumor promotion stage of skin carcinogenesis. 284 22

The metabolism of 1-14C arachidonic acid (AA) by arterial wall in patients with renal cell carcinoma and in control patients undergoing nephrectomy was investigated by a high pressure liquid chromatography (HPLC) system. No differences in 1-14C AA uptake and in the total amount of metabolites were found between the two groups, whereas the amounts of cyclooxygenase and lipoxygenase pathway (COP and LOP) metabolites produced by patients with renal cell carcinoma were significantly lower and, respectively, higher than those produced by the control group. The COP/LOP ratio was 7.2 +/- 5.5 in the control group in comparison to 1.9 +/- 0.5 in renal cell carcinoma patients. The decrease in COP metabolites was due to a markedly reduced synthesis of prostacyclin (PGI2), with no changes in thromboxane B2 (TxB2), prostaglandin F2 alpha (PGF2 alpha) and prostaglandin E2 (PGE2) production. The changes in PGI2 and 12-hydroxy-eicosatetraenoic acid (12-HETE) (metabolite of LOP) vascular production were not related to tumor dimension. The decrease in PGI2 synthesis may represent a factor favoring metastasis and thrombosis in neoplastic patients.
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PMID:Altered 1-14C arachidonic acid metabolism in arterial wall from patients with renal cell carcinoma. 293 33


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