Gingkolide may prevent ovarian cancer through the platelet activating factor receptor (PAFR) pathway.

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In our previous epidemiologic and in vitro cancer cell studies, we identified Ginkgo Biloba as a potential chemo-preventive agent for non-mucinous types of ovarian cancer and found that its components, Gingkolide A and B, decrease ovarian cancer cell proliferation. Seeking a further basis for biological action, we found that Ginkgolide B is a well-known natural inhibitor of Platelet-Activating Factor (PAF)−a potent proinflammatory phospholipid. PAF and its receptor (PAFR) enhance the expression of oncogenes and increase the growth of several tumor cell lines. In this study, our goal was to define the biological relevance of PAF and PAF Receptor (PAFR) in ovarian cancer and confirm its potential as a target for prevention or treatment. By Quantitative Real Time-PCR (qRT-PCR) and Western blot, we evaluated mRNA and protein expression levelsof PAFR in 21 ovarian cell lines established in our lab. Normal ovarian epithelial cells had extremely low expression (<300-600 times) compared to the ovarian carcinoma cell lines. A high PAFR-expressive cell line, OVCA 429, and low expressive-cell lines, HOSE and RMUG-L, were treated with PAF (1pM-1µM). PAF significantly increased the proliferation of OVCA 429 between 40-80% after 72 hours of incubation, which was reversed by the administration of Gingkolide B. Gingkolide B did not affect the growthof HOSE and RMUG-L, which lack PAFR, indicating the specificityof the observed effect. Additionally, we performed a tissue array-based immunohistochemical staining in a total of 242 samples for PAFR protein expression. Comparing benigns to other histological types, the overall ANOVA was F=44.7, p<0.0001. Of note, PAFR staining intensity was generally stronger in clear cell carcinomas, strong in high grade serous, intermediate in endometrioid and weak in borderline serous carcinomas. There was not a significant difference between benigns and mucinous cancers, were staining was barely detectable. This differential protein expression pattern was tightly correlated to the gene expression pattern observed in ovarian cancer tissue specimens by qRT-PCR. The present data revealed that PAFR, to which Gingkolide B is a natural inhibitor, is over expressed in certain ovarian cancer cell lines and in the different histological types of ovarian cancer tissue, except in mucinous types compared to normals and benigns. Additionally high PAFR expressive cells respond to PAF by increasing their proliferation and the natural compound Gingkolide B inhibits this effect. This data provides a basis for further study of the role of PAF and PAFR in ovarian cancer and Gingkolide B as a potential chemo preventive or therapeutic agent for ovarian cancer.