Abstract: Novel polypeptides or derivatives comprising the factor VIIIa binding site on factor IXa are disclosed. The novel polypeptides or derivatives have anti-coagulation activity. Nucleic acids encoding those polypeptides are also disclosed. Methods for identifying an agent having anti-coagulation activity are also disclosed. These methods comprise determining whether the agent displaces the polypeptide or derivative from its factor VIIIa binding site. The agent identified in these methods is also useful in methods for treating a patient to prevent thrombosis. The treatment methods comprise administration of the agent to the patient. Additional methods are also disclosed for treating a patient to prevent thrombosis, comprising treating the patient with a polypeptide or derivative comprising the factor VIIIa binding site on factor IXa. Methods of preventing coagulation in a blood sample are also disclosed, comprising adding the polypeptides or derivatives described above to the blood sample.

Abstract: Novel agents that inhibit the interaction of factor VIIIa with factor IXa in newly discovered regions of interaction, Region 2 and Region 3, are disclosed. The novel polypeptides or derivatives of polypeptides prevent activation of factor X and have anti-coagulation activity. The agents include polypeptides or polypeptide derivatives that are homologous to factor VIIIa or factor IXa in Region 2 and/or Region 3, as well as agents that are not homologous, such as antibodies Region 2 or Region 3. Pharmaceutical compositions comprising the agents are also disclosed. Methods of treatment are also disclosed, comprising the step of determining whether the compound displaces the interaction of the above agent from factor VIII or factor IX. Methods for preventing coagulation in a blood sample are also disclosed. These methods comprise adding the above agent to the sample.

Abstract: Novel polypeptides or derivatives comprising the factor VIIIa binding site on factor IXa are disclosed. The novel polypeptides or derivatives have anti-coagulation activity. Nucleic acids encoding those polypeptides are also disclosed. Methods for identifying an agent having anti-coagulation activity are also disclosed. These methods comprise determining whether the agent displaces the polypeptide or derivative from its factor VIIIa binding site. The agent identified in these methods is also useful in methods for treating a patient to prevent thrombosis. The treatment methods comprise administration of the agent to the patient. Additional methods are also disclosed for treating a patient to prevent thrombosis, comprising treating the patient with a polypeptide or derivative comprising the factor VIIIa binding site on factor IXa. Methods of preventing coagulation in a blood sample are also disclosed, comprising adding the polypeptides or derivatives described above to the blood sample.