No abstract

No abstract

When rabbit peritoneal neutrophils were treated with glucocorticoids, their chemotactic response to stimulation by the chemoattractant fMet-Leu-Phe was markedly reduced. Preincubation of cells with glucocorticoids also decreased phospholipase A2 (phosphatide 2-acylhydrolase, EC 3.1.1.4) activity in situ as measured by the release of [l-14C- Glucocorticoids exhibit a variety of biological effects, such as enzyme induction and anti-inflammatory actions (1, 2). The steroids act as a consequence of their binding to cytoplasmic receptors, followed by the translocation of the ligand-receptor complex into the nucleus, which, in turn, affects the transcription of various RNA species (3). The anti-inflammatory action of glucocorticoids is expressed in their ability to inhibit both chemotaxis and release of lysosomal enzymes in phagocytic cells (4-6). Recently, it has been demonstrated that chemotactic peptides enhance the release of arachidonic acid, a product of phospholipase A2 (phosphatide 2-acylhydrolase, EC 3.1.1.4), in rabbit neutrophils (7). Steroids possibly exert their anti-inflammatory action by preventing the release of arachidonic acid from phospholipids and its conversion to prostaglandins (8). These observations prompted a search for a steroid-induced inhibitor of phospholipase A2 in neutrophils. Here, we report the existence of a protein in rabbit neutrophils that inhibits phospholipase A2 and whose synthesis is induced by glucocorticoids.METHODS AND MATERIALS Assay of Phospholipase A2 Activities in Situ and in Vitro. Rabbit peritoneal neutrophils were obtained as described (7) and treated with various glucocorticoids in RPMI 1640 medium (GIBCO) for 16 hr at 37°C under a humid atmosphere of 95% 02/5% CO2. Phospholipase A2 activity was measured by the release of ["4C]arachidonic acid from the cellular lipids, mainly phospholipids, with a slight modification of the method described (7). Bovine serum albumin (1%) was included in Gey's balanced salt solution buffered with 10 mM Hepes, pH 7.4 (modified Gey's buffer). The cells (8-11 X 106 cells per ml) were preincubated in a total volume of 5 ml with 1.25 ,uCi of [1-'4C]arachidonic acid (55.5 mCi/mmol) at 370C for 1 hr (1 Ci = 3.7 X 1010 becquerels). The cells were washed twice with 5 ml of modified Gey's buffer and resuspended in 5 ml of the same buffer. For arachidonic acid release, the cells were stimulated with 10 nM fMet-Leu-Phe for 10 min at 370C (7). 16 hr. After three washings with 0.84% NaCl solution buffered with 10 mM sodium phosphate buffer, pH 7.4, the cells (8 X 106 cells) were lysed in 3 ml of distilled water. After centrifugation, at 27,000 X g for 50 min, the precipitates were solubilized with 0.5 ml of 2% Nonidet P40. Samples (0.5 ml) of 2533The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U. S. C. §1734 solely to indicate this fact.

The ErbB receptors and their cognate ligands that belong to the epidermal growth factor (EGF) family of peptides are involved in the pathogenesis of different types of carcinomas. In fact, the ErbB receptors and the EGF-like growth factors are frequently expressed in human tumors. These proteins form a complex system that regulates the proliferation and the survival of cancer cells. Therefore, ErbB receptors and their ligands might represent suitable targets for novel therapeutic approaches in human carcinomas. In this regard, different target-based agents that are directed against the ErbB receptors have been developed in the past two decades. One of these compounds, the humanized anti-ErbB-2 monoclonal antibody trastuzumab has been approved for the treatment of patients with metastatic breast cancer. The anti-EGF receptor (EGFR) antibody C225, as well as EGFR tyrosine kinase inhibitors ZD1839 and OSI-774 are currently in phase III clinical development. Several other ErbB tyrosine kinase inhibitors are in phase I/II studies. These compounds have generally been shown to have an acceptable toxicity profile and promising anti-tumor activity in heavily pretreated patients. The mechanisms of action of these compounds, as well as the potential therapeutic strategies to improve their efficacy are discussed in this review with particular regard to the combinations of anti-ErbB agents with cytotoxic drugs, or combinations of different ErbB-targeting agents.

No abstract