Reports from 2007 meeting of ASH.

Reports from 2007 meeting of ASH

ATLANTA u At this year's annual meeting of the American Society for Hematology (Washington), the distinction of having an abstract selected for the scientific plenary session went to Amgen (Thousand Oaks, California).

The company presented the results of two Phase III studies and an extension study on its AMG-531 for the bleeding disorder idiopathic thrombocytopenic purpura and Phase III data from splenectomized patients were presented in the plenary session. Thrombocytopenia, or low platelet count, can be the consequence of a number of disease states u or their treatments, such as chemotherapy. In the autoimmune condition idiopathic thrombocytopenic purpura, the primary problem is that platelets are coated with autoantibodies and destroyed by the immune system, but there are also fewer platelets than normal being produced in the first place.

AMG-531 works by increasing both the production of platelets and their circulation time in the blood; the drug is a combination of a peptide sequence that stimulates the TPO receptor, leading to increased platelet production, and an antibody that prevents the peptide from being degraded. The peptide sequence of AMG-531 has no homology to endogenous thrombopoietin, making it less likely that patients will develop antibodies to it; indeed, only one patient developed such antibodies, and they disappeared after discontinuing the drug.

Amgen reported results from two separate studies, with patients whose spleen had or had not been removed. In both studies, patients received weekly doses of AMG-531 for 24 weeks. Platelet levels were monitored throughout the study and for 12 weeks afterward. The overall response rate was nearly 80% for splenectomized and nearly 90% for non-splenectomized patients.

All patients taking AMG-531 were able to either eliminate or reduce concurrent medications. Bleeding occurred at the same rate in treatment and control groups, prompting one speaker to wonder during the question-and-ansswer session whether the platelets were functional. But presenter James Bussel said that bleeding was euqivalent "because we don't let patients bleed" u instead, patients receive so-called rescue medication when their platelet counts fall to dangerously low levels.

The company also presented interim data from a long-term extension study that has followed some patients for over two years. Though a few patients sustained the increase in platelet levels when they are no longer taking the drug, this is not the norm; presenting data from the ...