Anionic phospholipid membranes (aPL)

Anionic phospholipid membranes, characterized by the exposure of negatively charged lipids like phosphatidylserine (PS) on the outer cell surface, serve as essential scaffolds for the assembly of the blood coagulation cascade. In resting platelets and healthy cells, these phospholipids are actively sequestered in the inner leaflet of the plasma membrane; however, upon activation or apoptosis, they are externalized via scramblase enzymes such as TMEM16F (1.3.1, 1.5.2). This exposure creates a procoagulant surface that facilitates the binding of vitamin K-dependent clotting factors, dramatically accelerating thrombin generation by several orders of magnitude (1.5.5). In the context of oncology, externalized PS on tumor cells and tumor-derived microvesicles acts as a 'global' immunosuppressive signal that inhibits the activity of T cells and macrophages, promoting tumor growth and metastasis (1.2.3). Consequently, these membranes have emerged as significant therapeutic targets for both antithrombotic agents and cancer immunotherapies. Drugs such as bavituximab and Annexin V derivatives are designed to bind and mask these anionic sites, thereby preventing pathological thrombosis or restoring anti-tumor immune responses (1.2.1, 1.2.5).

Other names

Procoagulant phospholipidsPhosphatidylserine-exposing membranesNegatively charged phospholipid membranesExternalized phosphatidylserineAnionic phospholipid membranes on activated platelets and other cells

Drugs targeting anionic phospholipid membranes primarily function by binding to and masking externalized phosphatidylserine (PS) or phosphatidylethanolamine (PE). In the context of thrombosis, this masking prevents the assembly of the tenase and prothrombinase complexes on the cell surface, thereby inhibiting the explosive generation of thrombin and subsequent fibrin formation (1.3.1, 1.5.5). In oncology, PS-targeting agents block the immunosuppressive signaling pathways initiated when PS binds to receptors on macrophages and T cells, effectively 're-arming' the immune system to attack the tumor (1.2.3, 1.2.5). Additionally, these membranes serve as docking sites for the targeted delivery of cytotoxic or thrombolytic payloads using PS-binding proteins or antibodies as carriers (1.2.4, 1.4.2).