Canine Cancer Cells Activate Platelets via the Platelet P2Y12 Receptor

In addition to their well-known functions in haemostasis, anucleated platelets have a critical role in cancer biology. Many human and non-human cancer types can directly interact with and activate platelets, promoting cancer malignancy and progression. Although naturally occurring canine neoplastic diseases mimic the biologically complex conditions of human cancers more closely than laboratory-bred mice, studies evaluating the relationship between cancer cells and platelets in dogs are scarce, and the effects of tumour cells on platelets in these animals are unknown. To evaluate whether cancer cells could activate canine platelets, we assessed the response of platelet-rich plasma to cultured canine cancer cells using light transmittance aggregometry. Similar to human and murine cancer cell research, we demonstrated that both canine osteosarcoma and mammary carcinoma cells activated canine platelets in vitro, resulting in platelet aggregation. The degree of aggregation was most pronounced at a cancer cell to platelet ratio of 1:200 for most cell lines. Mechanistic studies revealed that the platelet adenosine diphosphate (ADP) receptor P2Y12 is essential for canine platelet aggregation induced by canine cancer. ADP receptor blockage on platelets inhibited >50% of cancer cell-induced maximum platelet aggregation in all cell lines evaluated. As in other species, our results suggest that canine cancers may activate canine platelets in vivo. This mechanism is likely relevant for the biology and progression of cancer in the dog.