Disrupting the platelet internal membrane via PI3KC2α inhibition impairs thrombosis independently of canonical platelet activation

Arterial thrombosis causes heart attacks and most strokes and is the most common cause of death in the world. Platelets are the cells that form arterial thrombi, and antiplatelet drugs are the mainstay of heart attack and stroke prevention. Yet, current drugs have limited efficacy, preventing fewer than 25% of lethal cardiovascular events without clinically relevant effects on bleeding. The key limitation on the ability of all current drugs to impair thrombosis without causing bleeding is that they block global platelet activation, thereby indiscriminately preventing platelet function in hemostasis and thrombosis. Here, we identify an approach with the potential to overcome this limitation by preventing platelet function independently of canonical platelet activation and in a manner that appears specifically relevant in the setting of thrombosis. Genetic or pharmacological targeting of the class II phosphoinositide 3-kinase (PI3KC2α) dilates the internal membrane reserve of platelets but does not affect activation-dependent platelet function in standard tests. Despite this, inhibition of PI3KC2α is potently antithrombotic in human blood ex vivo and mice in vivo and does not affect hemostasis. Mechanistic studies reveal this antithrombotic effect to be the result of impaired platelet adhesion driven by pronounced hemodynamic shear stress gradients. These findings demonstrate an important role for PI3KC2α in regulating platelet structure and function via a membrane-dependent mechanism and suggest that drugs targeting the platelet internal membrane may be a suitable approach for antithrombotic therapies with an improved therapeutic window.

BSCI-16. HEMODYNAMIC SHEAR STRESS SELECTS A SUBPOPULATION OF LUNG ADENOCARCINOMA CELLS WITH HIGHER METASTATIC CAPACITY

Patients with primary cancers often develop delayed brain metastases. One of the most common cancer types and sources of brain metastasis is lung cancer. For metastasis from lung cancer the 3-year survival is < 5%. Cancer cells in circulation are responsible for metastatic spread. The mechanical microenvironment plays an important role in cancer cells behavior. When cancer cells reach the bloodstream they are exposed to hemodynamic shear stress. It has been shown that most of the circulating tumor cells die once they reach the bloodstream, but the biology of the survival cells is poorly understood. We designed a microfluidics system that simulated the mechanical stress in the human circulating system such as turbulence, change in pressure (0.4-15dyn/cm2) and flow rate (1.06–106.1mm/s). Lung adenocarcinoma cells (A549) were put into circulation and collected after 72 hours. It was found that, 1.4±0.3% of the cells survived, and viability was evaluated by LDH and calcein. CD133, SOX2, and NANOG were downregulated and EMT genes were upregulated in the circulating cancer cells (CCCs) compared with cells in static-suspension or 2D. After re-seeding in 2D, CCCs overexpressed CD133. Female athymic nude rats (6-8weeks,n=16) received intracardiac injections of CCCs or 2D cells (GFP-LUC lentivirus traduced). Bioluminescence imaging was performed every week; the survival in of the CCCs group was lower than the 2D group. One-way ANOVA test was used to analyze survival and gene expression. Survival data was plotted on a Kaplan-Meier curve and compared using the Mantel-Cox logrank test, p=< 0.05. We have isolated a cellular subpopulation of lung adenocarcinoma with high resistance to hemodynamic shear stress that shows a higher metastatic capacity and genetic plasticity compared with cells growing in suspension or 2D. Targeting these cells would potentially allow us to develop personalized treatments to help to stop metastatic spread and improve actual therapeutical strategies.