No abstract

Active suppression of tumor-specific T lymphocytes can limit the immune-mediated destruction of cancer cells. Of the various strategies used by tumors to counteract immune attacks, myeloid suppressors recruited by growing cancers are particularly efficient, often resulting in the induction of systemic T lymphocyte dysfunction. We have previously shown that the mechanism by which myeloid cells from tumor-bearing hosts block immune defense strategies involves two enzymes that metabolize L-arginine: arginase and nitric oxide (NO) synthase. NO-releasing aspirin is a classic aspirin molecule covalently linked to a NO donor group. NO aspirin does not possess direct antitumor activity. However, by interfering with the inhibitory enzymatic activities of myeloid cells, orally administered NO aspirin normalized the immune status of tumorbearing hosts, increased the number and function of tumorantigen-specific T lymphocytes, and enhanced the preventive and therapeutic effectiveness of the antitumor immunity elicited by cancer vaccination. Because cancer vaccines and NO aspirin are currently being investigated in independent phase I͞II clinical trials, these findings offer a rationale to combine these treatments in subjects with advanced neoplastic diseases.arginase ͉ immunosuppression ͉ myeloid cells ͉ nitric oxide ͉ immunotherapy I dentifying effective treatments for cancer is a clinical priority.Despite the plethora of evidence in preclinical models, the most advanced immunotherapy, either active or passive, has had limited success in human clinical trials (1). Basis for this conclusion appears to involve at least in part the progressive accumulation of myeloid cells, which exert a powerful inhibitory activity on antitumor lymphocytes as a function of tumor growth. In tumor-bearing hosts, for example, tumor progression is often associated with altered hematopoiesis, which leads to the accumulation of myeloid cells at the tumor site and in blood, secondary lymphoid organs, and bone marrow (2-4).Mouse myeloid cells express the CD11b and Gr-1 markers, have a mixed mature-immature myeloid phenotype, and are responsible for the induction of tumor-specific and nonspecific T cell dysfunctions, which are frequently observed not only in transplantable tumors but also in tumors spontaneously arising with transgenic expression of tissue-restricted oncogenes (2, 5). These cells have been termed myeloid suppressor cells (MSCs) and arise from bone marrow and other hematopoietic organs exposed to systemically released factors acting on myelomonocytic precursors (reviewed in refs. 2, 3, and 6). Moreover, MSCs are the final effectors of a circuit that negatively affects tumor immunity and that requires participation of natural killer T cells. Cytotoxic T lymphocyte (CTL)-mediated tumor immunosurveillance was recently shown to be down-regulated by TGF-␤ released by CD11b ϩ ͞Gr-1 ϩ cells, an event driven by cytokine IL-13 release from CD1d-restricted natural killer T cells (7). This circuit is activated very early in tumor progression and ...

Nonsteroidal anti-inflammatory drugs are among the most commonly used prescription and over-the-counter medications, but they often produce significant gastrointestinal ulceration and bleeding, particularly in elderly patients and patients with certain co-morbidities. Novel anti-inflammatory drugs are seldom tested in animal models that mimic the high risk human users, leading to an underestimate of the true toxicity of the drugs. In the present study we examined the effects of two novel NSAIDs and two commonly used NSAIDs in models in which mucosal defence was expected to be impaired. Naproxen, celecoxib, ATB-346 (a hydrogen sulfide- and naproxen-releasing compound) and NCX 429 (a nitric oxide- and naproxen-releasing compound) were evaluated in healthy, arthritic, obese, and hypertensive rats and in rats of advanced age (19 months) and rats co-administered low-dose aspirin and/or omeprazole. In all models except hypertension, greater gastric and/or intestinal damage was observed when naproxen was administered in these models than in healthy rats. Celecoxib-induced damage was significantly increased when co-administered with low-dose aspirin and/or omeprazole. In contrast, ATB-346 and NCX 429, when tested at doses that were as effective as naproxen and celecoxib in reducing inflammation and inhibiting cyclooxygenase activity, did not produce significant gastric or intestinal damage in any of the models. These results demonstrate that animal models of human co-morbidities display the same increased susceptibility to NSAID-induced gastrointestinal damage as observed in humans. Moreover, two novel NSAIDs that release mediators of mucosal defence (hydrogen sulfide and nitric oxide) do not induce significant gastrointestinal damage in these models of impaired mucosal defence.

Cyclooxygenases are involved in the metabolism of arachidonic acid to prostaglandins (PGs) and thromboxane (TX) A 2 (6). In vascular biology, the two major products of COX are TXA 2 , which is mainly formed by the constitutive form of COX, COX-1 in activated platelets, and prostacyclin or PGI 2 , which is mainly produced in vascular cells by COX-1 and the inducible form of COX, COX-2 (7, 8). TXA 2 participates in platelet aggregation and vascular contraction, whereas PGI 2 acts as an antiaggregant for platelets and a vasodilator. PGI 2 plays an important role in vascular physiology as illustrated by the therapeutic effect of stable analogs of PGI 2 such as iloprost (9). Platelets from patients suffering from hypercholesterolemia are characterized by hypersensitivity to various aggregating agents. Notarbartolo et al. (10) have shown that simvastatin decreased platelet aggregation in hypercholesterolemic subjects and supported a decrease in the thromboxane platelet production, although the underlying mechanism of the statin effect on platelet function remains unclear.In this study, we demonstrated in human aortic smooth muscle cells (hASMC) that two different statins, mevastatin and lovastatin, increased COX-2 expression and PGI 2 formation. We further demonstrated using selective inhibitors of geranylgeranyltransferases and modulators of Rho GTPases that geranylgeranylated proteins such as Rho seem to be responsible for COX-2 down-regulation, which is prevented by statins.

Polymorphonuclear leukocytes (PMNL) possess relatively large amounts of 5-lipoxygenase, the enzyme catalyzing the sequential conversion of arachidonic acid to 5-hydroperoxyeicosatetraenoic acid (5-HPETE) and LTA 4 (9). Upon cell activation, significant amounts of LTB 4 and its -oxidized metabolites 20-hydroxy-and 20-carboxy-LTB 4 are released into the extracellular milieu together with nonenzymatic breakdown products of LTA 4 , namely ⌬ 6 -trans-LTB 4 isomers and 5,6-dihydroxyeicosatetraenoic acids (5,6-diHETEs) (10 -12). Recent studies in complex organ systems (13-18) showed that perfusion of PMNL in the isolated lung or heart of the rabbit only caused a significant increase in the production of cysteinyl leukotrienes when PMNL were activated during the perfusion process. These data suggest that transcellular biosynthesis of cysteinyl leukotrienes might indeed be of physiopathological relevance when tight cell-cell interactions occur, such as during adhesion and diapedesis of PMNL through the microvascular endothelium of a functioning organ system.In light of these observations it was of interest to assess the relative amount of LTA 4 released from PMNL and therefore available for transcellular biosynthesis of cysteinyl leukotrienes, with respect to total LTA 4 synthesized. The release of LTA 4 into the extracellular milieu would remove this intermediate from intracellular LTA 4 hydrolase that catalyzes conversion of LTA 4 into LTB 4 . Intracellular LTB 4 can be further metabolized by a specific cytochrome P-450 to 20-hydroxy-LTB 4 and 20-carboxy-LTB 4 (19). The extracellular (released) LTA 4 will react with water with a half-life lower than 30 s (20) to yield the nonenzymatic products, ⌬ 6 -trans-LTB 4 , ⌬ 6 -trans-12-epi-LTB 4 , and 5,6-dihydroxyeicosatetraenoic acid isomers. But PMNL are able to take up exogenously added LTA 4 (21) and metabolize it into LTB 4 , thus reducing the fraction of released LTA 4 that is actually available for transcellular metabolism (or nonenzymatic hydrolysis).In the present study experiments were designed to test the effect of dilution on the quantitative profile of LTA 4 metabolites produced after challenge with the Ca 2ϩ ionophore A23187. The hypothesis that in diluted cell preparations LTA 4 would have less chance of being reabsorbed and metabolized by vicinal PMNL has been tested. In a previous study, Cluzel et al. (22) showed that the use of diluted cell suspensions provided important information concerning the amount of platelet activating factor and LTB 4 released by PMNL. Using a similar approach, we provide evidence that significant transcellular * The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.§ To whom correspondence should be addressed. Tel.: 39-2-20488312; Fax 39-2-29404961. 1 The abbreviations used are: 5-LO, 5-lipoxygenase; PMNL, polymorphonuclear leukocytes; LTA, leukotriene A; RP-HP...