Tyrosine Kinases and Thrombosis

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Project Summary Tyrosine kinase inhibitors (TKIs) are important therapeutic agents to treat various cancers. However, any agent has a tradeoff between efficacy and on or off target deleterious effects. This notion became evident in the treatment of chronic myelogenous leukemia (CML) when a potent and broadly inhibitory tyrosine kinase inhibitor, ponatinib (Iclusig, Ariad Pharmaceuticals, now Takeda) was recognized to have a 31% incidence of cardiovascular (CV) events of which 21% overall were significant adverse events (SAEs). In a Phase II trial (PACE) at 4 yrs. the incidence of arterial occlusive events was 26% (myocardial infarction 14%, stroke 11%, and limb ischemia 11% - some patients have more than 1 organ event). Ponatinib (poni) is one of 5 TKIs approved for the treatment of CML We have created a murine model to examine the effects of TKIs on blood coagulation, vascular, and platelet function. In aged mice treated with the various TKIs under steady-state conditions, ponatinib, unlike imatinib, demonstrated an increased risk of arterial and venous thrombosis. Poni treatment leads to decreased arterial occlusion times, larger venous clots and generates hyperactive platelets - features that contribute to heightened thrombosis. Our laboratory has identified key mechanisms underlying the prothrombotic phenotype of poni. First, poni-treated mice have increased vessel wall reactive oxygen species (ROS), apoptosis, and inflammatory vascular lymphocyte infiltrates that expresses coagulation factors V and VIII. Second, platelets from poni-treated mice are hyperactive to in response to collagen. Additionally, we have determined that pioglitazone (pio), a PPAR agonist, when given with poni normalizes the vessel wall inflammation and platelet hyperactivity to correct murine thrombosis risk The overall hypothesis of this application is that poni-associated thrombosis results from immune cell vascular inflammation expressing prothrombotic genes and altered platelet signaling resulting in platelet hyperreactivity. Poni treatment has identified a novel mechanism of prothrombotic vascular dysfunction by which vascular infiltrating lymphocytes express coagulation enzymes FV and FVIII potentially to contribute to thrombosis. At therapeutic dosing in man, poni inhibits p-LynY507, a negative regulator of activated GPVI, in both unstimulated and activated platelets with little effect on p-LynY396 and p-SykY352, suggesting that these platelets may be more reactive. In fact, poni-treated mice have platelets that react to lower concentrations of CRP. These defects are genetically and functionally corrected by pio’s genomic and non-genomic PPAR agonism. The specific aims of the proposal are as follows: The specific aims of the proposal are as follows: 1) Determine the mechanism of ponatinib- and other TKI- induced vascular inflammation 2) Identify the mechanisms of poni-induced platelet hyperactivation. These studies will determine the mechanisms of poni and other TKI effects on vessel wall and platelets that lead to cardiovascular events. They present a pre-clinical model for poni-associated thrombosis and correction with pio, a PPAR agonist. Last, they will serve as a paradigm for CVD assessment for TKIs in general.