leukotriene-b4 and Melanoma

Topics: Allergens; Animals; Antineoplastic Agents; Boronic Acids; Bortezomib; Cattle; Female; Glycogen Storage Disease Type II; Human papillomavirus 16; Human papillomavirus 18; Humans; Hypersensitivity; Immunotherapy; Leukotriene B4; Melanoma; Milk; Milk Proteins; Papillomavirus Infections; Pyrazines; Receptors, Leukotriene B4; Skin Neoplasms; Tumor Escape; Uterine Cervical Neoplasms; Viral Vaccines

Chronic inflammation has long been associated with neoplastic progression. Our group had recently shown that the addition of a large number of apoptotic tumor cells to the tumor microenvironment induces a potent acute inflammatory reaction capable of promoting melanoma growth; however, primarily necrotizing cells do not cause such a reaction. Here, we show that potent inflammatory agents, such as lipopolysaccharide (LPS) and carrageenan, also promote growth of subtumorigenic doses of melanoma cells, having no effect on melanoma proliferation in vitro. Inhibition of 5-lipoxygenase (5-LOX) seems to have a pivotal role in this model because caffeic acid and MK886, a FLAP (5-LOX-activating protein) inhibitor, partially hindered tumor growth induced by apoptotic cells or LPS. Other enzymes of the arachidonic acid pathway, cyclooxygenase-1 and cyclooxygenase-2, seem to have no participation in this tumor promoter effect, as the inhibitor of both enzymes (indomethacin) did not alter melanoma growth. Leukotriene B4 (LTB4), the main product of the 5-LOX pathway, was able to induce growth of subtumorigenic inocula of melanoma cells, and a LTB4 receptor antagonist inhibited acute inflammation-associated tumor growth. Addition to the tumor inflammatory microenvironment of eicosapentaenoic acid, an omega3-polyunsaturated fatty acid with anti-inflammatory properties, or leukotriene B5, an eicosapentaenoic acid-derived leukotriene, significantly inhibited tumor development. These results give new insights to the mechanisms through which inflammation may contribute to tumor progression and suggest that LOX has an important role in tumor progression associated with an inflammatory state in the presence of apoptosis, which may be a consideration for apoptosis-inducing treatments, such as chemotherapy and radiotherapy.

Topics: Animals; Apoptosis; Arachidonate 5-Lipoxygenase; Carrageenan; Cell Growth Processes; Cell Line, Tumor; Disease Progression; Eicosapentaenoic Acid; Histocytochemistry; Indomethacin; Inflammation; Leukotriene B4; Lipopolysaccharides; Lipoxygenase Inhibitors; Melanoma; Mice; Prostaglandin-Endoperoxide Synthases

We examined the synthesis of leukotrienes (LTs) in human melanoma cells in order to assess the function of LTs in human melanocytes. LTA4 hydrolase, which catalyzes the conversion of LTA4 to LTB4, was detected in the supernatant of cultured human melanoma (MeWo) cells and melanoma cells obtained from patients. Immunoblotting analysis using an antihuman LTA4 hydrolase antibody showed LTA4 hydrolase to be a 70-kDa protein in both MeWo and melanoma cells. Considerable activity of LTC4 synthase, which catalyzes the conversion of LTA4 to LTC4, was detected in the microsomal fraction of both MeWo and melanoma cells. The HPLC profile of the LTC4 synthase reaction products revealed that LTC4 was the main product. LTD4 was not detected under these conditions, indicating that the microsomal fraction of human melanoma cells lacks the membrane-bound gamma-glutamyl transferase that converts LTC4 to LTD4. LTC4 synthase activity was inhibited by the addition of MK-886, and was not altered by treatment with N-ethylmaleimide or 1-chloro-2,4-dinitrobenzene. These results indicate that the enzyme responsible for the conversion of LTA4 to LTC4 in human melanoma cells is LTC4 synthase rather than a nonspecific or microsomal glutathione-S-transferase. These results also suggest that human melanoma cells can generate LTB4 and LTC4 from LTA4, and that this process is catalyzed by two enzymes: LTA4 hydrolase and LTC4 synthase.

Topics: Dinitrochlorobenzene; Enzyme Inhibitors; Epoxide Hydrolases; Ethylmaleimide; Glutathione Transferase; Humans; Indoles; Leukotriene A4; Leukotriene B4; Leukotriene C4; Leukotriene D4; Melanoma; Microsomes; Tumor Cells, Cultured

Modulation of cytoplasmic Ca++ concentration is a mechanism common to signal transduction pathways regulating many cellular phenomena, including the interactions of tumors with the hemostatic system. We have investigated the pro-aggregating and pro-coagulant activities of human tumor cell lines cultured in vitro and the ability of different platelet agonists to induce Ca++ transients in these cells. Cells of a malignant mesothelioma line activated platelets by a thrombin-dependent mechanism; on the contrary, HeLa cells, derived from a uterine cervical cancer, possessed ADP-dependent pro-aggregating activity, and DND-IA melanoma cells did not stimulate platelet aggregation. All cell lines showed a tissue-factor-like procoagulant property, more pronounced in mesothelioma cells. Furthermore, ADP was able to induce a transient increase in cytoplasmic Ca++ concentration in tumor cells from all lines; collagen showed this effect in mesothelioma cells and in HeLa cells, and thrombin was effective only in mesothelioma cells. PAF never induced Ca++ fluxes in any of the cell lines investigated. Finally, the calcium-channel blocker verapamil inhibited agonist-induced Ca++ transients in tumor cells and in vitro tumor-cell growth. These data may help to identify new possible mechanisms of the 2-way interaction of tumors with the hemostatic system.

Topics: Adenosine Diphosphate; Adult; Blood Coagulation; Blood Platelets; Calcium; Cell Communication; Cell Division; Collagen; HeLa Cells; Humans; Intracellular Fluid; Leukotriene B4; Melanoma; Mesothelioma; Platelet Activating Factor; Platelet Activation; Platelet Aggregation; Platelet-Derived Growth Factor; Thrombin; Thromboxane B2; Tumor Cells, Cultured; Verapamil