No abstract

Activating internal tandem duplication (ITD) insertions in the juxtamembrane domain of the FLT3 tyrosine kinase are found in about one fourth of patients with acute myeloid leukemia and have been shown to be an independent negative prognostic factor for survival. We show that sorafenib (BAY 43-9006, Nexavar) potently inhibits FLT3 enzymatic and signaling activities. In HEK293 cells stably transfected with FLT3-WT or FLT3-ITD, sorafenib blocked basal and ligand dependent FLT3-mediated tyrosine autophosphorylation as well as extracellular signal-regulated kinase1/2 and Stat5 phosphorylation. In leukemia cell lines MV4-11 and EOL-1, sorafenib treatment resulted in decreased cell proliferation and inhibition of FLT3 signaling. The growth of the FLT3-independent RS4-11 cell line was only weakly inhibited by sorafenib. Cell cycle arrest and induction of apoptosis were observed upon treatment with sorafenib in MV4-11 and EOL-1 cells. The antitumor efficacy of sorafenib was evaluated against the MV4-11 leukemia grown subcutaneously in NCr nu/nu mice. Doses of 3 and 10 mg/kg administered orally for 14 days resulted in six and nine out of 10 animals with complete responses, respectively. The demonstration that sorafenib exhibits potent target inhibition and efficacy in FLT3-driven models suggests that this compound may have a therapeutic benefit for patients with FLT3-driven leukemias.

Two groups of six adults with persistent asthma, who were identical clinically, received 0.1 or 4 g of purified eicosapentaenoic acid ethyl ester (EPA) daily for 8 weeks. Both doses increased significantly the generation of leukotriene B5 (LTB5) from EPA by polymorphonuclear (PMN) and mononuclear leukocytes, while only the high dose decreased leukocyte arachidonic acid (AA) and the generation of LTB4 and prostaglandin E2 from AA. Only the high dose led to inhibition of PMN leukocyte chemotaxis to multiple stimuli by a mean of 57-70% (P less than 0.01), without altering monocyte chemotaxis, the production of platelet-activating factor by mononuclear leukocytes, or the IgE-dependent release of histamine from basophils. Both doses of EPA increased the responses of T lymphocytes to phytohemagglutinin by a mean of 73% or more (P less than 0.01) without modifying the numbers of helper and suppressor T lymphocytes. EPA affects the functions of several types of leukocytes critical to inflammation and immunity.

No abstract

Leukotrienes are a unique class of potent humoral and cellular mediators that are generated by the specific lipoxygenation and subsequent enzymatic conversions of arachidonic acid in basophils, mastocytoma cells, polymorphonuclear leukocytes (PMN) and mononuclear leukocytes, and human lung tissue (1-6). The structural characteristics shared by the leukotriene mediators include three conjugated double bonds, a 5-hydroxy group, and either a 6-sulfido-cysteine(yl) or 12-hydroxy group. 5-hydroxy-6-sulfido-glutathionyl-eicosa-7,9,11,14-tetraenoic acid (leukotriene (34 [or LT(34], where the subscript 4 indicates the total number of double bonds) and 5-hydroxy-6-sulfido-cysteinyl-glycine-7,9,11,14-tetraenoic acid (LTD4), which are the principal active constituents of the slow-reacting substance of anaphylaxis (termed SRS-A), constrict pulmonary airways with a potency up to 20,000 times greater than that of histamine and alter the tone and permeability of the microvasculature (7). 5(S),12(R)-di-hydroxy-eicosa-6,8,10(trans/trans/cis),14(cis)-tetraenoic acid, which is designated LTB4 (6), is chemotactic and chemokinetic for human and rat PMN and, to a lesser extent, mononuclear leukocytes (8-10). The maximal human neutrophil chemotactic response elicited by LTB4 is similar in magnitude to those evoked by synthetic formyl-methionyl peptides or fragments of the fifth component of human complement, and the neutrophil chemotactic potency of LTB4 is far greater than that of the mono-hydroxy-eicosatetraenoic acids (HETE) derived from arachidonic acid, whereas neither LT(34 nor platelet-derived tri-HETE exhibit leukocyte chemotactic activity (8). The results of our study indicate that the conformation of the hydroxylgroups and the geometry of the double bonds in the conjugated triene are the critical structural determinants of the potency of LTB4 as a neutrophil chemotactic factor. Materials and MethodsPreparation and Purification of Lipoxygenase Products of Arachidonic Acid. Neutrophils that had been isolated from venous blood of normal subjects were incubated for 30 rain at 37°(2 at a concentration of 5 × 10 7 neutrophils/ml in Hanks' balanced salt solution containing 0.02 M Tris-HCll (pH 8), 10/LM indomethacin, 5/zM calcium ionophore A23187, and 0.5 mg/ml of arachidonic acid. The HETE were extracted and resolved from both the residual arachidonic acid and more polar products by silicic acid column chromatography (6,8). LTB4 and 5-HETE