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Dose-response effects of pegylated human megakaryocyte growth and development factor on platelet production and
L A Harker1, U M Marzec, P Hunt
1Division of Hematology and Oncology, Yerkes Regional Primate Research Center, Emory University School of Medicine, Atlanta, GA 30322, USA.
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.
Insights
Pegylated human recombinant megakaryocyte growth and development factor (PEG-rHuMGDF) effectively boosts platelet production in baboons. This thrombopoietin analog stimulates megakaryocyte growth and increases platelet counts without adverse effects on other blood cells.
Area of Science:
- Hematology
- Pharmacology
- Biotechnology
Background:
- Thrombopoietin (TPO) is crucial for regulating platelet production.
- Pegylated human recombinant megakaryocyte growth and development factor (PEG-rHuMGDF) is a modified TPO analog designed to enhance megakaryocyte proliferation and platelet generation.
Purpose of the Study:
- To evaluate the dose-response effects of PEG-rHuMGDF on pharmacokinetics, megakaryocytopoiesis, platelet production, and platelet function in baboons.
- To assess the safety and efficacy of PEG-rHuMGDF in a non-human primate model.
Main Methods:
- Administered daily subcutaneous injections of PEG-rHuMGDF at doses of 0.05, 0.10, 0.50, or 2.5 micrograms/kg/d to 22 baboons for 28 days.
- Monitored plasma levels, bone marrow megakakaryocyte parameters (volume, ploidy, number), peripheral platelet counts, and platelet function (aggregation, deposition).
Main Results:
- Demonstrated linear log-dose responses in plasma PEG-rHuMGDF levels, bone marrow megakaryocyte parameters, and peripheral platelet concentrations.
- Observed normal platelet morphology, lifespan, and recovery, with no significant impact on leukocyte, neutrophil, or erythrocyte counts.
- Noted transient enhancement of platelet aggregation induced by TRAP1-6 and collagen, but not by ADP; platelet deposition on vascular surfaces increased proportionally to platelet count.
Conclusions:
- PEG-rHuMGDF effectively increases platelet production in a dose-dependent manner by stimulating megakaryocyte proliferation and differentiation.
- The extended half-life of PEG-rHuMGDF allows for lower dosing compared to non-pegylated forms.
- Findings suggest PEG-rHuMGDF may be a valuable therapeutic agent for maintaining platelet counts during chemotherapy-induced thrombocytopenia without increasing thrombosis risk.