HDAC Inhibitor CS014 Attenuates Thrombosis Alone and in Combination with Rivaroxaban without Increased Risk of Bleeding

Introduction: Targeting the human platelet for prevention of occlusive thrombotic events remains an active area of research due to the high incidence of myocardial infarction and stroke due to platelet-rich thrombotic clots. While, many patients taking FXa anticoagulant therapy require further inhibition of thrombosis, dual therapy including anticoagulant plus antiplatelet drugs result in an increased risk for bleeding. The current study sought to determine if a histone deacetylase (HDAC) inhibitor, either alone or in combination with the FXa inhibitor rivaroxaban, is able to effectively inhibit platelet and fibrin formation at the site of vascular injury without causing a significant increase in the bleeding risk in mice.

Methods and Results: Thrombosis and bleeding models in the mouse were assessed in the presence of the HDAC inhibitors valproic acid (VPA) or the newly developed HDAC inhibitor, CS014. Both CS014 and VPA significantly, dose-dependently inhibit platelet accumulation and fibrin formation at the site of a vascular injury using the laser-induced cremaster thrombosis assay model. Further, to determine if CS014 has the potential to be used in conditions where an anticoagulant is already on board, mice were dosed for 5 days with rivaroxaban alone or in combination with CS014 and were assessed for prevention of laser-induced thrombosis in the cremaster arteriole. Both rivaroxaban and CS014 alone cause significant attenuation of clot formation. To determine if the combination results in an increased risk for bleeding, blood from mice treated with CS014 or rivaroxaban alone, or in combination was assessed for coagulation activity and clot strength using thromboelestography (TEG). Rivaroxaban was found to significantly delay onset of clotting in TEG whereas CS014 did not show any delay in coagulation or clotting with TEG. In combination CS014 was not observed to cause any additional delay in clotting time or decrease in maximal clot strength compared to rivaroxaban alone. Finally, a tail vein bleeding assay was conducted to determine if CS014 alone or in combination with rivaroxaban result in an increased risk for bleeding. Neither CS014 alone, rivaroxaban alone, or the combination of CS014 plus rivaroxaban resulted in increased bleeding time in the resected tail experiment.

Conclusions: The data presented here suggests that while CS014 and rivaroxaban are each effective antithrombotic agents, they work well together to minimize clot formation without altering coagulation or clotting compared to rivaroxaban alone. Hence, CS014 has the potential to enrich the toolbox of anticoagulant therapies in patients with a high risk of thrombotic events.