title: Dose-response effects of pegylated human megakaryocyte growth and development factor on platelet production and function in nonhuman primates.
abstract: Thrombopoietin (TPO) is the physiologic Mpl-ligand regulating platelet production. Pegylated human recombinant megakaryocyte growth and development factor (PEG-rHuMGDF), a truncated polypeptide Mpl-ligand derivitized with poly-(ethylene glycol), induces megakaryocyte endoreduplication and proliferation in vitro and in vivo. In the present study, the dose-response effects of PEG-rHuMGDF on pharmacokinetics, megakaryocytopoiesis, platelet production, and platelet function were characterized for dosing 0.05, 0.10, 0.50, or 2.5 micrograms/kg/d in 22 baboons for 28 days. Daily subcutaneous injections of PEG-rHuMGDF produced linear log-dose responses in (1) steady-state trough plasma levels of PEG-HuMGDF (P < 10(-3)); (2) marrow megakaryocyte volume (P < 10(-3)), ploidy (P < 10(-4)), and number (P < .01); and (3) peripheral platelet concentrations (P < 10(-4)) and platelet mass turnover (P < 10(-3)). Platelet morphology, life span, and recovery were normal, and peripheral leukocyte, neutrophil, and erythrocyte counts were not significantly affected by PEG-rHuMGDF (P > .1 in all cases). PEG-rHuMGDF at 0.5 micrograms/kg/d produced similar blood concentrations of Mpl-ligand and platelets as 10 times the dose of rHu-MGDF (5.0 micrograms/kg/d), reflecting the extended plasma half-life achieved through pegylation. Whereas PEG-rHuMGDF did not induce platelet aggregation in vitro, platelet aggregatory responsiveness induced by thrombin receptor agonist peptide (TRAP1-6) and collagen was transiently enhanced ex vivo during the initial few days of PEG-rHuMGDF administration. However, adenosine diphosphate (ADP)-induced platelet aggregation was not enhanced ex vivo by PEG-rHuMGDF therapy. 111In-platelet deposition on segments of homologous endarterectomized aorta (EA) and vascular graft (VG) interposed in arteriovenous femoral shunts increased in direct proportion to the circulating platelet concentration (P < 10(-4) for both EA and VG); 125l-fibrin accumulation was not affected by PEG-rHuMGDF-induced increases in peripheral platelet counts. Changes in platelet production and function produced by PEG-rHuMGDF returned to baseline within 2 weeks after discontinuing treatment. Thus, in nonhuman primates, PEG-rHuMGDF increases platelet production in a linear log-dose-dependent manner by stimulating megakaryocyte endoreduplication and new megakaryocyte formation from marrow hematopoietic progenitors. These findings suggest that appropriate dosing of PEG-rHuMGDF therapy during periods of chemotherapy-induced marrow suppression may maintain hemostatic concentrations of peripheral platelets without increasing the risk of thrombosis.
authors.affiliation: Division of Hematology and Oncology, Yerkes Regional Primate Research Center, Emory University School of Medicine, Atlanta, GA 30322, USA.
authors.forename: L A
authors.initials: LA
authors.lastname: Harker
authors.forename: U M
authors.initials: UM
authors.lastname: Marzec
authors.forename: P
authors.initials: P
authors.lastname: Hunt
authors.forename: A B
authors.initials: AB
authors.lastname: Kelly
authors.forename: A
authors.initials: A
authors.lastname: Tomer
authors.forename: E
authors.initials: E
authors.lastname: Cheung
authors.forename: S R
authors.initials: SR
authors.lastname: Hanson
authors.forename: R B
authors.initials: RB
authors.lastname: Stead
mesh_terms: D000244:Adenosine Diphosphate / Q000494:pharmacology; D000818:Animals; D001166:Arteriovenous Shunt, Surgical; D001792:Blood Platelets / Q000166:cytology*; D001807:Blood Vessel Prosthesis; D003094:Collagen / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004691:Endarterectomy; D006410:Hematopoiesis / Q000187:drug effects; D006801:Humans; D007279:Injections, Subcutaneous; D008297:Male; D008533:Megakaryocytes / Q000187:drug effects*; D009363:Neoplasm Proteins; D010215:Papio; D010446:Peptide Fragments / Q000494:pharmacology; D010974:Platelet Aggregation / Q000187:drug effects; D010976:Platelet Count / Q000187:drug effects; D011092:Polyethylene Glycols / Q000494:pharmacology*; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D018121:Receptors, Cytokine; D053628:Receptors, Thrombopoietin; D011993:Recombinant Fusion Proteins / Q000494:pharmacology; D011994:Recombinant Proteins; D013926:Thrombopoietin / Q000008:administration & dosage / Q000494:pharmacology*
chemical_list: D009363:Neoplasm Proteins; D010446:Peptide Fragments; D011518:Proto-Oncogene Proteins; D018121:Receptors, Cytokine; D053628:Receptors, Thrombopoietin; D011993:Recombinant Fusion Proteins; D011994:Recombinant Proteins; C103117:polyethylene glycol-recombinant human megakaryocyte growth and development factor; C082835:thrombin receptor peptide (42-47); C082218:MPL protein, human; D011092:Polyethylene Glycols; D000244:Adenosine Diphosphate; D003094:Collagen; D013926:Thrombopoietin