thromboxane-b2 and Cell-Transformation--Neoplastic

The induced synthesis of bioactive prostanoids downstream of cyclooxygenase-2 (COX-2) and prostaglandin H(2) (PGH(2)) exerts a critical event in colorectal carcinogenesis. Here we demonstrate that APC(Min/+) mice with genetic deletion of microsomal prostaglandin E synthase-1 (mPGES-1), which catalyses the terminal conversion of PGH(2) into PGE(2), surprisingly develop more and generally larger intestinal tumors than do mPGES-1 wild type littermates (mean number of tumors/intestine 80 vs. 38, p<0.0005, mean tumor diameter 1.64 vs. 1.12 mm, p<0.0005). No deviation regarding the expression of other PGE(2) related enzymes (COX-1, COX-2, mPGES-2, cPGES, and 15-PGDH) or receptors (EP1-4) was obvious among the mPGES-1 deficient mice. PGE(2) levels were suppressed in tumors of mPGES-1 deficient animals, but the concentrations of other PGH(2) derived prostanoids were generally enhanced, being most prominent for TxA(2) and PGD(2). Thus, we hypothesise that a redirected synthesis towards other lipid mediators might (over)compensate for loss of mPGES-1/PGE(2) during intestinal tumorigenesis. Nevertheless, our results question the suitability for mPGES-1 targeting therapy in the treatment or prevention of colorectal cancer.

Topics: 6-Ketoprostaglandin F1 alpha; Animals; Cell Transformation, Neoplastic; Colorectal Neoplasms; Dinoprostone; Female; Gene Deletion; Intramolecular Oxidoreductases; Male; Mice; Mice, Mutant Strains; Prostaglandin-E Synthases; RNA, Messenger; Thromboxane B2

In these studies, we performed experiments designed to elucidate the role that arachidonic acid metabolism plays in oncogenic transformation in vitro. The levels of TxB2 and 6-keto-PGF1 alpha were elevated in cells treated with X-rays. A significant increase in the levels of these eicosanoids was observed following irradiation. Treatment of cells with the anticarcinogenic protease inhibitors, Bowman-Birk Inhibitor (BBI) and N-tosyl-L-phenylalanine chloromethyl ketone (TPCK), significantly reduced the levels of TxB2 and 6-keto-PGF1 alpha present. Indomethacin treatment significantly reduced the levels of TxB2 and 6-keto-PGF1 alpha to < 10% of those present in untreated or irradiated cells. We also report that addition of lipoxygenase or minoxidil [a selective inhibitor of prostacyclin (PGl2) synthetase] led to a highly significant decrease in transformation. In addition, minoxidil treatment resulted in a significant reduction in the levels of 6-keto-PGF1 alpha in irradiated cells. Our results suggest the hypothesis that the relative levels of 6-keto-PGF1 alpha are important in radiation induced transformation.

Topics: 6-Ketoprostaglandin F1 alpha; Animals; Arachidonic Acids; Cell Line; Cell Transformation, Neoplastic; Indomethacin; Mice; Mice, Inbred C3H; Minoxidil; Models, Biological; Protease Inhibitors; Thromboxane B2; Tosylphenylalanyl Chloromethyl Ketone; Trypsin Inhibitor, Bowman-Birk Soybean; X-Rays

The U937 monocytic cell line and its differentiated macrophage-like form have been well characterized, illustrating many similarities with their analogous in vivo cells. We examined the release of thromboxane B2 (TXB2) from undifferentiated and differentiated cells after stimulation with opsonized zymosan and investigated whether the release of this mediator could be modified by isoprenaline. After stimulation, the U937 cells released TXB2 in a dose-dependent manner, with the release greater from the differentiated cells. The TXB2 released was inhibited by flurbiprofen (> 10(-8) M; P < .01) and isoprenaline (> 10(-6) M; P < .01), and the inhibition was reversed by propranolol (10(-6) M; P < .02). Thus, it is clear that undifferentiated and differentiated U937 cells release TXB2, which can be inhibited by beta 2-adrenoceptor stimulation. These findings illustrate an important functional difference between the in vivo macrophages and differentiated U937 cells because beta 2-adrenoceptor stimulation does not inhibit mediator release from macrophages.

Topics: Cell Transformation, Neoplastic; Dose-Response Relationship, Drug; Flurbiprofen; Humans; Isoproterenol; Leukemia, Monocytic, Acute; Macrophages; Opsonin Proteins; Propranolol; Receptors, Adrenergic, beta; Thromboxane B2; Tumor Cells, Cultured; Urinary Bladder Neoplasms; Zymosan

In a previous study we found a correlation between metastatic potential and platelet aggregating activity in sublines of a benzopyrene-induced murine fibrosarcoma ( mFS6 ); the purpose of the present work was to elucidate the role of thromboxane biosynthesis by platelets and/or by neoplastic cells in the activation of platelets in this system. The cells of the more malignant subline induced higher aggregation and TxB2 production than those of the non metastasizing one. The supernatants of aggregating cell suspensions contained very few TxB2; furthermore, preincubation of platelets with ASA or Apyrase resulted in inhibition of aggregation and TxB2 production, while preincubation of the cells was ineffective; these results suggest the platelet origin of the measured TxB2 and indicate that platelet-derived ADP plays an important role in their activation, while the production of ADP by the cells does not seem to be relevant in this model. The involvement of platelet prostaglandin biosynthesis pathway in neoplastic cell induced platelet activation could play an important role in the development of platelet-dependent tumour metastasis.

Topics: Animals; Apyrase; Aspirin; Blood Platelets; Cell Line; Cell Transformation, Neoplastic; Fibrosarcoma; Humans; Mice; Platelet Aggregation; Thromboxane B2; Thromboxanes