Polyphosphate is a novel modulator of coagulation and inflammation and is a therapeutic target

While the basic outline of the enzymes and reactions that make up the traditional blood coagulation cascade has been understood for many years, appreciation of the complexity of these interactions has greatly increased in recent times. This has resulted in unofficial “revisions” of the coagulation cascade to include new amplification pathways and interactions between the standard coagulation cascade enzymes as well as novel and extensive connections between the immune system and the coagulation cascade. One exciting new area of research in hemostasis and thrombosis focuses on how inorganic polyphosphate (polyP) can mediate many of these novel amplification steps and many of the connections between coagulation and inflammation. Additionally, the multiple procoagulant and proinflammatory roles for polyP discovered in both mice and humans suggest that it may be an attractive therapeutic target for disorders of coagulation and inflammation. \n \nThe discovery that polyP is stored in platelet dense granules and is secreted during platelet activation has resulted in a recent burst of interest in the role of this ancient molecule in human biology; however, many standard biochemical techniques are not amenable to working with an inorganic polymer like polyP. To increase our ability to visualize polyP accumulation under both physiological and pathological conditions such as inflammation or thrombosis, I first developed a method for visualizing polyP based upon using a recombinant polyP binding protein as a modified “primary antibody” to specifically label polyP using immunofluorescent staining in cells and tissues. These techniques continue to provide us with more information about the role of polyP in normal human physiology and under pathological conditions like inflammation and thrombosis. \n \nIn order to determine if we could target polyP-mediated pathology as an effective method of treatment for inflammation and thrombosis, I have also developed a method of testing polyP inhibitors from high-throughput in vitro screening all the way to in vivo mouse models. First generation polyP inhibitors based on polycationic substances such as polyethylenimine, polyamidoamine (PAMAM) dendrimers and polymyxin B, while attenuating thrombosis, all had significant toxicity in vivo, likely due to the presence of multiple primary amines responsible for their polyP binding ability. In collaboration with the Kizhakkedathu lab at the University of British Columbia in Vancouver, Canada, I next examined a novel class of non-toxic polycationic compounds, initially designed as Universal Heparin Reversal Agents (UHRAs). I first worked with them to help evaluate the UHRA compounds in clinically relevant mouse models showing that the UHRA compounds can effectively reverse the bleeding side effects associated with a wide variety of heparins currently in clinical use. Next, they worked with me to screen the entire UHRA library for potential polyP inhibitors that shared the non-toxic nature of the UHRA compounds developed to reverse heparin anticoagulation. Several UHRA compounds strongly inhibited polyP procoagulant activity in vitro and four were selected for further examination in mouse models of thrombosis and hemostasis. Compounds UHRA 9 and UHRA 10 significantly reduced arterial thrombosis in mice. In mouse tail bleeding tests, administration of UHRA 9 or UHRA 10 was associated with significantly less bleeding compared to therapeutically equivalent doses of heparin. Furthermore, in collaboration with the Esmon Laboratory at the Oklahoma Medical Research Foundation, I have begun to characterize the polyP binding abilities of a family of anti-polyP antibodies discovered in an autoimmune strain of mice. PolyP inhibitors like the UHRA compounds or anti-polyP antibodies offer a new platform for developing novel antithrombotic and anti-inflammatory agents that target anionic polymers like polyP with reduced toxicity and bleeding side effects compared to conventional anticoagulant therapeutics.

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