Distinct Roles Of Antithrombin-Dependent Antithrombotic Agents (Lovenox, Fondaparinux) and Direct Anti-Xa Anti-Coagulant (Apixaban) On The Inhibition Of Thrombin Generation Induced By Human Pancreatic (BXPC3) and Human Breast (MCF7) Cells

Introduction The optimization of the antithrombotic treatment with LMWH (enoxaparin), direct and indirect anti-Xa ( Apixaban, fondaparinux), in patients with adenocarcinoma of the pancreas, or human breast carcinoma is a challenging issue. The understanding of their mechanism of action in cancer-induced hypercoagulability might provide evidence for treatment optimization. To this aim, we studied the influence of pancreas adenocarcinoma cells (BXPC3), or human breast carcinoma cells (MCF7) on the antithrombotic activity of enoxaparin, fondaparinux and apixaban. Materials and Methods Cells were cultured and adhered in 96-well plates (50cells/µl). Thrombin generation (TG) of normal platelet poor plasma spiked with clinically relevant concentrations of enoxaparin, fondaparinux and apixaban which was added in wells carrying cancer cells was assessed with the Calibrated Automated Thrombogram assay. In the control experiment TG was triggered using PPP-Reagent 5 pM TF. The lag-time of thrombin generation, the maximum concentration of thrombin (Peak), and the mean rate index (MRI) of the propagation phase of thrombin generation were analysed [MRI=Peak/(ttPeak-lag-time)]. The IC50 of the studied compounds were calculated by extrapolation from the concentration-response curve, and compared. Results All studied antithrombotic agents inhibited in a concentration dependent manner the thrombin generation. The three studied agents significantly inhibited TG at plasma concentrations usually achieved at doses for thromboprophylaxis. However the presence of cancer cells and their type was determinant for the antithrombotic potency of the studied drugs. Comparison on the basis of IC50 showed that the presence of either BXPC3 or MCF7 cells did not significantly modify the antithrombotic potency of enoxaparin as compared to the control experiment. In contrast the inhibitory effect of fondaparinux and apixaban on thrombin generation was partially reversed when TG was triggered by BXPC3 since the IC50 were significantly increased as compared to the control experiment. The presence of MCF7 cells did not significantly modify the antithrombotic activity of apixaban and fondaparinux. Conclusions The LMWH enoxaparin and the specific FXa inhibitors apixaban and fondaparinux demonstrate potent inhibitory capacity on thrombin generation triggered by cancer cells. The type of cancer cells is determinant for the antithrombotic efficiency of the specific factor Xa inhibitors independently of their mechanism of action (i.e. antithrombin dependent or independent inhibition of FXa). In contrast the type of cancer cells does not significantly influence the potency of enoxaparin. This is probably due to the presence of the trace amounts of anti-IIa activity. The present study stresses out that the impact of the type of cancer cells on the antithrombotic activity of the specific Xa inhibitors should not be neglected. These data have to be taken into consideration for the design of dose-finding studies of the direct orally active FXa inhibitors in patients with different histological types of cancer. Disclosures: No relevant conflicts of interest to declare.