THROMBOPOIETIN CLONED IN MAJOR BREAKTHROUGH

Researchers at ZymoGenetics, a subsidiary of Novo Nordisk A/S, with the collaboration of scientists at the University of Washington, have successfully isolated and cloned thrombopoietin, an elusive hormone that stimulates platelet production and has long been sought as a potential therapy for thrombocytopenia. Meantime, Genentech has reported that it has also achieved this objective. Both sets of research are reported in the current issue of the journal Nature (June 16).

Thrombopoietin joins the family of known cytokines, which includes erythropoietin, granulocyte colony stimulating factor and granulocyte macrophage colony stimulating factor amongst others. It has been considered almost the "holy grail" of cytokine research, mainly because thrombocytopenia is a serious problem in patients receiving radiotherapy or chemotherapy for cancer, and as yet no effective agent is available to treat it. Patients currently receive platelet transfusions, which can be subject to attack by the recipient's immune system.

Potent Action ZymoGenetics notes that its cloned TPO increased platelet levels in laboratory mice by more than 400%, a much higher increase than has been achieved with any other platelet-stimulating compound. To date, studies of other compounds under development for thrombocytopenia, including interleukin-3, interleukin-6, interleukin-11 and Pixykine (a compound which combines IL-3 and GM-CSF) have revealed increases in platelet levels of between 30% and 70%. Genentech said that its TPO clone had achieved a similar level of platelet stimulation in animals.