Potential of Pharmaceutical Intervention in Platelets and Cancer Positive Feedback Loop

Significance High platelet counts and advanced stage of ovarian cancer go hand‐in‐hand in promoting each other in a feed‐forward loop that results in blood coagulation and chemotherapy resistance. This results in a high incidence of death due to thrombosis in ovarian cancer patients, and especially in patients with the ovarian clear cell carcinoma histologic type. Objective and Hypothesis We sought to develop an experimental model of the positive interactions between platelets and cancer cells and test the hypothesis that interference with platelet clotting will inhibit this interaction. Approach The effects of platelets on spheroid formation by cancer or healthy epithelial cells were evaluated using a magnetic 3D cancer spheroids assay. The ES2 and MESOV cell lines, which represent clear cell carcinoma and high grade serous histologies, respectively were used for the ovarian cancer cells. Primary human fallopian tube secretory epithelial cell cultures were used to represent healthy cells. The spheroids were imaged and measured using the Optronix GelCount colony counter and evaluated using metabolic viability (MTT) and protein concentration (SRB) assays. The shear‐free platelet aggregation assay was performed in the presence of healthy or cancer cells or their conditioned media. Furthermore, we evaluated possible interruption of this feed‐forward loop using antiplatelet agents: aspirin—a cyclooxygenase (COX)‐1 and ‐2 inhibitor, celecoxib—a selective COX‐2 inhibitor, clopidogrel—an ADP binding inhibitor, dipyridamole—an ADP uptake inhibitor, eptifibatide—a platelet's GP IIb/IIIa inhibitor, and prostacyclin—a platelet aggregation inhibitor. Results Incubation of platelets with cancer spheroids as they are forming decreased the size and density of the spheres in less than 15 minutes of exposure. The MTT assay indicated that condensed spheres were just as live and viable as the spheres that formed in the absence of platelets. Incubation of cancer cells or cancer cells’ conditioned media with platelets caused clumping of platelets in a cancer cells number‐dependent manner. Healthy cells’ conditioned media did not cause platelets aggregation. Pre‐treating platelets with up to a 1 mM of aspirin, clopidogrel, dipyridamole, and prostacyclin did not prevent cancer cell‐induced aggregation, unlike celecoxib, which prevented aggregation at high concentrations, and eptifibatide, which was able to prevent aggregation at low concentrations as 0.1 µM. Conclusions The positive interaction between platelets and cancer cells can be mimicked in co‐culture conditions. This interaction appears to involve platelets GPIIb/IIIa binding.