6-(bromomethylene)tetrahydro-3-(1-naphthaleneyl)-2h-pyran-2-one and Ovarian-Neoplasms

We and others have shown that calcium-independent phospholipase A(2) (iPLA(2)) is involved in epithelial ovarian cancer (EOC). Hence, we propose that iPLA(2) is a potential effective and novel target for EOC. We tested this concept and found that bromoenol lactone (BEL), a selective inhibitor of iPLA(2), significantly inhibited EOC metastatic tumor growth in mouse xenograft models using human SKOV3 and HEY ovarian cancer cells. Moreover, the combination of BEL with paclitaxel (PTX), one of the most commonly used therapeutic agents in EOC, almost completely blocked tumor development in the xenograft mouse model. BEL showed no detectable cytotoxic effects in mice. Another iPLA(2) inhibitor, FKGK11, also inhibited tumor development in the xenograft mouse model, supporting that the major target of action was iPLA(2). The additional effects of BEL with PTX in vivo likely stem from their distinct cellular effects. BEL and FKGK11 reduced adhesion, migration, and invasion of EOC cells in vitro; the reduced ability to adhere, migrate, and invade seems to increase the vulnerability of tumor cells to PTX. These results provide an important basis for the development of new treatment modalities for EOC.

Topics: Animals; Antineoplastic Agents, Phytogenic; Antineoplastic Combined Chemotherapy Protocols; Cell Adhesion; Cell Line, Tumor; Cell Movement; Cell Proliferation; Female; Fluorocarbons; Group IV Phospholipases A2; Humans; Immunoenzyme Techniques; Ketones; Mice; Mice, Inbred NOD; Mice, SCID; Naphthalenes; Ovarian Neoplasms; Paclitaxel; Phosphodiesterase Inhibitors; Pyrones

PLA2 (phospholipase A2) enzymes play critical roles in membrane phospholipid homoeostasis and in generation of lysophospholipid growth factors. In the present study, we show that the activity of the cytosolic iPLA2 (calcium-independent PLA2), but not that of the calcium-dependent cPLA2 (cytosolic PLA2), is required for growth-factor-independent, autonomous replication of ovarian carcinoma cells. Blocking iPLA2 activity with the pharmacological inhibitor BEL (bromoenol lactone) induces cell cycle arrest in S- and G2/M-phases independently of the status of the p53 tumour suppressor. Inhibition of iPLA2 activity also leads to modest increases in apoptosis of ovarian cancer cells. The S- and G2/M-phase accumulation is accompanied by increased levels of the cell cycle regulators cyclins B and E. Interestingly, the S-phase arrest is released by supplementing the growth factors LPA (lysophosphatidic acid) or EGF (epidermal growth factor). However, inhibition of iPLA2 activity with BEL remains effective in repressing growth-factor- or serum-stimulated proliferation of ovarian cancer cells through G2/M-phase arrest. Down-regulation of iPLA2b expression with lentivirus-mediated RNA interference inhibited cell proliferation in culture and tumorigenicity of ovarian cancer cell lines in nude mice. These results indicate an essential role for iPLA2 in cell cycle progression and tumorigenesis of ovarian carcinoma cells.

Topics: Animals; Apoptosis; Blotting, Western; Calcium; Cell Division; Cell Proliferation; Cyclins; Cytosol; Epidermal Growth Factor; Female; G2 Phase; Group VI Phospholipases A2; Humans; Lysophospholipids; Mice; Mice, Inbred BALB C; Mice, Nude; Naphthalenes; Ovarian Neoplasms; Phospholipases A; Phospholipases A2; Pyrones; RNA, Small Interfering; S Phase; Tumor Cells, Cultured

Lysophosphatidic acid (LPA) is both a potential marker and a therapeutic target for ovarian cancer. It is critical to identify the sources of elevated LPA levels in ascites and blood of patients with ovarian cancer. We show here that human peritoneal mesothelial cells constitutively produce LPA, which accounts for a significant portion of the chemotactic activity of the conditioned medium from peritoneal mesothelial cells to ovarian cancer cells. Both production of LPA by peritoneal mesothelial cells and the chemotactic activity in the conditioned medium can be blocked by HELSS [an inhibitor of the calcium-independent phospholipase A(2) (iPLA(2))] and AACOCF(3) [an inhibitor of both cytosolic PLA(2) (cPLA(2)) and iPLA(2)]. Moreover, cell-based enzymatic activity assays for PLA(2) indicate that peritoneal mesothelial cells have strong constitutive PLA(2) activity. Receptors for LPA, LPA(2), and LPA(3) are involved in the conditioned medium-induced chemotactic activity. Invasion of ovarian cancer cells into peritoneal mesothelial cells has also been analyzed and shown to require PLA(2), LPA receptors, and the mitogen-activated protein/extracellular signal-regulated kinase kinase/extracellular signal-regulated kinase signaling pathway. Thus, we show here, for the first time, that human peritoneal mesothelial cells constitutively produce bioactive lipid signaling molecules, such as LPA, via iPLA(2) and/or cPLA(2) activities. Conditioned medium from peritoneal mesothelial cells stimulate migration, adhesion, and invasion of ovarian cancer cells, and may play similar roles in vivo.

Topics: Arachidonic Acids; Cell Adhesion; Cell Line, Tumor; Cell Movement; Collagen Type I; Culture Media, Conditioned; Cytosol; Epithelium; Extracellular Signal-Regulated MAP Kinases; Female; Group VI Phospholipases A2; Humans; Isoenzymes; Lysophospholipids; Naphthalenes; Ovarian Neoplasms; Peritoneal Cavity; Peritoneum; Phosphodiesterase Inhibitors; Phospholipases A; Proto-Oncogene Proteins c-akt; Pyrones