Lipid generation and signaling in ovarian cancer

Diacylglycerol Kinase Alpha in Radiation-Induced Fibrosis: Potential as a Predictive Marker or Therapeutic Target

Radiotherapy is an efficient tool in cancer treatment, but it brings along the risk of side effects such as fibrosis in the irradiated healthy tissue thus limiting tumor control and impairing quality of life of cancer survivors. Knowledge on radiation-related fibrosis risk and therapeutic options is still limited and requires further research. Recent studies demonstrated that epigenetic regulation of diacylglycerol kinase alpha (DGKA) is associated with radiation-induced fibrosis. However, the specific mechanisms are still unknown. In this review, we scrutinized the role of DGKA in the radiation response and in further cellular functions to show the potential of DGKA as a predictive marker or a novel target in fibrosis treatment. DGKA was reported to participate in immune response, lipid signaling, exosome production, and migration as well as cell proliferation, all processes which are suggested to be critical steps in fibrogenesis. Most of these functions are based on the conversion of diacylglycerol (DAG) to phosphatidic acid (PA) at plasma membranes, but DGKA might have also other, yet not well-known functions in the nucleus. Current evidence summarized here underlines that DGKA activation may play a central role in fibrosis formation post-irradiation and shows a potential of direct DGKA inhibitors or epigenetic modulators to attenuate pro-fibrotic reactions, thus providing novel therapeutic choices.

Elevated and secreted phospholipase A₂ activities as new potential therapeutic targets in human epithelial ovarian cancer

Ascites in epithelial ovarian cancer (EOC) promotes tumor development by mechanisms that are incompletely understood. Lysophosphatidic acid (LPA), a major tumor-promoting factor in EOC ascites, is an enzymatic product of autotaxin (ATX) and phospholipase A(2) (PLA(2))enzymes. The contribution of PLA(2) activities to ovarian tumorigenesis was investigated. The quantitative measurement of PLA(2) activities in ascites and tissues, as well as assay conditions selective for PLA(2) subtypes, were optimized and validated. PLA(2) activities correlated with tumor-promoting activates in cell-based and in vivo assays. High activities consistent with both cytosolic and calcium-independent PLA(2) were found in human EOC ascites for the first time. Elevated PLA(2) and ATX activities were also observed in EOC compared to benign tumors and normal tissues. Cell-free and vesicle-free (S4) human EOC ascites potently promoted proliferation, migration, and invasion of human EOC cells in a PLA(2)-dependent manner. LPA mediated a significant part of the cell-stimulating effects of ascites. S4 ascites stimulated tumorigenesis/metastasis in vivo, and methyl arachidonyl fluorophosphonate was highly effective in inhibiting EOC metastasis in mouse xenograft models. PLA(2) activity was found in conditioned media from both EOC cells and macrophages. Collectively, our work implies that PLA(2) activity is a potential marker and therapeutic target in EOC.

Diverse mechanisms for activation of Wnt signalling in the ovarian tumour microenvironment

Wnt signalling pathways have been shown to play key roles in both normal development and tumorigenesis. Progression of many human cancers is associated with defined mutations in Wnt pathway components that result in dysregulated β-catenin-mediated gene transcription. Although Wnt pathway mutations are rare in epithelial ovarian cancer (with the exception of the endometrioid histotype), accumulating evidence supports a role for Wnt signalling in ovarian tumorigenesis in the absence of genetic mutations. The present review summarizes evidence in support of activated Wnt signalling in ovarian tumours and discusses alternative mechanisms for Wnt pathway activation in the ovarian tumour microenvironment.

Combination therapy of an inhibitor of group VIA phospholipase A2 with paclitaxel is highly effective in blocking ovarian cancer development

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.