Platelet-derived microparticles increase the interaction of colorectal cancer cells with the endothelium to promote metastatic events.

backgroundThe major challenge in colorectal cancer (CRC) therapy involves the formation of distant metastases, which represent the primary cause of treatment failure and patient death. To undergo metastasis, cancer cells of an invasive phenotype must intravasate and extravasate the blood or lymphatic vessels to reach distant sites. Platelet-derived microparticles (PMP) are considered important factors in various diseases, including CRC. Here, we examined the influence of PMP on the intravasation and extravasation abilities of CRC cells and established associations with these PMP to metastatic events in vivo.

methodsFluorescence microscopy was used to investigate the effects of PMP on CRC cell adhesion to the endothelial (HMEC-1) monolayer, endothelial integrity and CRC cell transendothelial migration. Quantitative real-time PCR and flow cytometry were used to assess endothelial gap junction and tight junction protein expression. For the in vivo experiments we performed intrasplenic injections of CRC cell lines with different molecular characteristics into immunodeficient mice, followed by the intravenous administration of multiple human PMP. The presence of metastases and inflammation in the liver was confirmed via histopathological examinations. Immunohistochemical analyses of human CD41 in metastatic lesions were performed to detect human PMP. Platelet surface activation markers and the plasma concentrations of inflammatory cytokines were evaluated via flow cytometry. The plasma levels of metalloproteases (MMPs) 2 and 9 were measured via ELISA.

resultsOur study revealed that PMP enhanced CRC cell adhesion to endothelial cells and transendothelial migration. PMP injections increased the number of metastases in the liver and the concentrations of total MMP-2 and human MMP-9 in the plasma of mice injected with selected CRC cell lines. PMP were observed to be present at the margins of metastatic lesions and endothelial capillaries. PMP injections also increased the level of platelet receptors, which determine blood platelet activation and reactivity.

conclusionsOur in vitro findings suggest that PMP can promote CRC cell adhesion to endothelial cells, which contributes to cancer cell extravasation. PMP can also disrupt the integrity of endothelial cell junctions and enhance the transendothelial migration of CRC cells. PMP demonstrate a supportive role in metastatic events via the upregulation of plasma levels of metalloproteases.