Fibrin Clot Shields Formation in the Tumor Microenvironment, Induced By Cancer Cells' Hypercoagubility, Serves As Scaffolds for Invasion and Protection Against Anticancer Treatments

Introduction: Neoangogenesis, vascular mimicry and highly permeable blood vessels expose cancer cells to coagulation factors from plasma. The expression of Tissue Factor (TF) by cancer cells leads to local hypercoagubility in the tumor microenvironment. We aimed to study the ability of cancer cells to induce fibrin formation in the tumor microenvironment, and the role of fibrin in cancer cells' physiology.

Materials and methods: Highly procoagulant pancreatic cancer cells (BXPC3), highly procoagulant and invasive breast cancer cells (MDA-MB231), weakly procoagulant and non-invasive breast cancer cells (MCF7) were cultured in the presence of of normal human platelet-poor plasma (PPP) diluted 10% in RPMI-1640 media (PPP-media). Structural characteristics of fibrin clot were analyzed using Scanning Electron Microscopy. Fibrinolytic activities were studied by quantifying tissue-type plasminogen activator (t-PA) and D-Dimer concentrations. Cancer cells' invasion was observed using Laser Scanning Confocal Microscopy. The efficacity of paclitaxel (PTX) and 4-hydroxytamoxifen (4OHTam), at their IC50 concentrations, on cancer cells viability in the absence and presence of fibrin clot shields was assessed.

Results: Culture of cancer cells in the presence of PPP-media led to the formation of Fibrin Clot Shields (FCS) in a “bird's nest-like” architecture. MDA-MB231 cells led to the formation of the most dense FCS with finest fibers, smallest pores and highest number of intersections, as contrast to MCF7 cells. The structure of FCS formed by BXPC3 are intermediated. Adding 1 pM of TF to the culture media of MCF7 led to FCS with similar structures to those of BXPC3 cells. MCF7 cells do not possess fibrinolytic activity as contrast to the other two cell lines. All of the three cancer cell lines showed invasion ability in the presence of FCS. The presence of FCS also abrogated the efficacity of PTX and 4OHTam in inducing cell death.

Conclusions: The procoagulant fingerprint of cancer cells leads to the formation of FCS in the microenvironment. We showed for the first time a clear image of the architecture of FCS formed by cancer cells. FCS serve as scaffolds for cell invasion and protection against anticancer treatments such as PTX and 4OHTam. These results suggested FCS as a new mechanism for resistance to treatments and a potential new target to improve treatments' efficacity.

No relevant conflicts of interest to declare.