<p>Thrombosis is a common complication of chemotherapy for breast cancer patients. However, the specific mechanisms by which chemotherapy agents modulate these hemostatic pathways are not well understood. In this thesis, we investigated the mechanism(s) by which chemotherapy agents can upregulate procoagulant pathways (tissue factor (TF), phosphatidylserine exposure, and cell-free DNA (CFDNA) release) and impair the protein C (PC) anticoagulant pathway. We examined the effects of chemotherapy agents doxorubicin, epirubicin and the cyclophosphamide metabolite acrolein on cell surface procoagulant activity. We found that treatment of endothelial cells with the chemotherapy drugs increased phosphatidylserine exposure and TF activity on treated endothelial cells, blood monocytes and/or smooth muscle cells. This corresponded to an increase in thrombin generation on chemotherapy-treated cells exposed to recalcified, defibrinated plasma. We also found that found that doxorubicin and epirubicin can increase CFDNA release from breast cancer chemotherapy patients and healthy mice, which corresponds to an increase in thrombin-antithrombin levels. Treatment of venous whole blood and isolated neutrophils with doxorubicin and epirubicin increased CFDNA release. We found that exposure of recalcified plasma to CFDNA isolated from epirubicin-treated whole blood increased thrombin generation by activating the contact pathway. We investigated the effects of chemotherapy on the PC anticoagulant pathway. We found that acrolein decreased EPCR while increasing thrombomodulin expression on treated endothelial cells. A corresponding decrease in activated PC generation was measured on acrolein-treated endothelial cells exposed to recalcified, defibrinated plasma. Healthy mice treated with acrolein and cyclophosphamide increased PC antigen levels, but no measurable increase in plasma APC levels. Breast cancer chemotherapy drugs elevate thrombin generation by activating coagulation through the TF and contact pathways, and by promoting phosphatidylserine exposure, as well as by impairing PC activation EPCR expression. These studies provide insight into the mechanisms of breast cancer chemotherapy-induced hypercoagulation.</p> / Doctor of Philosophy (Medical Science)

A mathematical model of blood coagulation under defined flow conditions, initiated and modulated by spatially discrete regions of surface bound tissue factor (TF) and thrombomodulin (TM), respectively, is presented. The model incorporates fluid phase and surface-associated reactions of the extrinsic, intrinsic, and common pathways, as well as three inhibitory pathways. The spatially heterogeneous model is formulated by finite element method, and an effective prothrombotic zone, which quantifies the spatial propagation of thrombin generation is defined. Characteristic features of coagulation are simulated under physiologic conditions, and the behavior of the system in response to perturbations in TF and TM surface densities, TF site dimensions, and wall shear rate is explored. The major findings of these studies include: (i) The model system responds in an 'all-or-none', threshold-like manner to changes in model parameters. (ii) It was found that prothrombotic effects may extend significantly beyond the dimensions of the spatially discrete site of TF expression in both axial and radial directions. (iii) The relationship between the length of the effective prothrombotic zone and the interval distance between tandem sites of TF expression dictate the net response of the system. Additive prothrombotic effects of sub-clinical lesions as well as suppressive antithrombotic effects of intervening TM-containing regions were observed. Secondly, the computational model is applied to calculate an individualized, systems-based metric of clotting potential for 210 pre-menopausal women in the Leiden Thrombophilia Study (LETS). The simulated variable was found to be a highly predictive parameter for deep venous thrombosis risk.