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The biology of thrombopoietin and thrombopoietin receptor agonists

Authors
  • Kuter, David J.1, 2
  • 1 Harvard Medical School, Boston, MA, USA , Boston (United States)
  • 2 Yawkey 7858, Massachusetts General Hospital, Hematology Division, 55 Fruit Street, Boston, MA, 02114, USA , Boston (United States)
Type
Published Article
Journal
International Journal of Hematology
Publisher
Springer-Verlag
Publication Date
Jul 03, 2013
Volume
98
Issue
1
Pages
10–23
Identifiers
DOI: 10.1007/s12185-013-1382-0
Source
Springer Nature
Keywords
License
Yellow

Abstract

Thrombopoietin (TPO) is the major physiological regulator of platelet production. TPO binds the TPO receptor, activates JAK and STAT pathways, thus stimulating megakaryocyte growth and platelet production. There is no “sensor” of the platelet count; rather TPO is produced in the liver at a constant rate and cleared by TPO receptors on platelets. TPO levels are inversely proportional to the rate of platelet production. Early recombinant TPO molecules were potent stimulators of platelet production and increased platelets in patients with immune thrombocytopenia, chemotherapy-induced thrombocytopenia, myelodysplastic syndromes and platelet apheresis donors. Neutralizing antibodies formed against one recombinant protein and ended their development. A second generation of TPO receptor agonists, romiplostim and eltrombopag, has been developed. Romiplostim is an IgG heavy chain into which four TPO agonist peptides have been inserted. Eltrombopag is an oral small molecule. These activate the TPO receptor by different mechanisms to increase megakaryocyte growth and platelet production. After administration of either to healthy volunteers, there is a delay of 5 days before the platelet count rises and subsequently reaches a peak after 12–14 days. Both have been highly effective in treating ITP and hepatitis C thrombocytopenia. Studies in a wide variety of other thrombocytopenic conditions are underway.

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