Harker L A, Marzec U M, Hunt P, Kelly A B, Tomer A, Cheung E, Hanson S R, Stead R B
Division of Hematology and Oncology, Yerkes Regional Primate Research Center, Emory University School of Medicine, Atlanta, GA 30322, USA.
Blood. 1996 Jul 15;88(2):511-21.
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.
血小板生成素（TPO）是调节血小板生成的生理性Mpl配体。聚乙二醇化人重组巨核细胞生长和发育因子（PEG-rHuMGDF）是一种用聚乙二醇衍生化的截短多肽Mpl配体，可在体内外诱导巨核细胞内复制和增殖。在本研究中，对22只狒狒连续28天给予0.05、0.10、0.50或2.5微克/千克/天的PEG-rHuMGDF，以表征其对药代动力学、巨核细胞生成、血小板生成和血小板功能的剂量反应效应。每日皮下注射PEG-rHuMGDF在以下方面产生线性对数剂量反应：（1）PEG-HuMGDF的稳态谷血浆水平（P < 10^(-3)）；（2）骨髓巨核细胞体积（P < 10^(-3)）、倍性（P < 10^(-4)）和数量（P < 0.01）；（3）外周血小板浓度（P < 10^(-4)）和血小板质量周转率（P < 10^(-3)）。血小板形态、寿命和恢复正常，外周白细胞、中性粒细胞和红细胞计数未受PEG-rHuMGDF的显著影响（所有情况下P > 0.1）。0.5微克/千克/天的PEG-rHuMGDF产生的Mpl配体和血小板血药浓度与rHu-MGDF剂量（5.0微克/千克/天）的10倍相似，反映了聚乙二醇化实现的延长血浆半衰期。虽然PEG-rHuMGDF在体外不诱导血小板聚集，但在PEG-rHuMGDF给药的最初几天内，凝血酶受体激动肽（TRAP1-6）和胶原诱导的血小板聚集反应性在体内短暂增强。然而，PEG-rHuMGDF治疗并未在体内增强二磷酸腺苷（ADP）诱导的血小板聚集。插入股动静脉分流中的同源动脉内膜切除主动脉（EA）段和血管移植物（VG）上的111In-血小板沉积与循环血小板浓度成正比增加（EA和VG均为P < 10^(-4)）；125I-纤维蛋白积累不受PEG-rHuMGDF诱导的外周血小板计数增加的影响。停止治疗后2周内，PEG-rHuMGDF引起的血小板生成和功能变化恢复至基线水平。因此，在非人灵长类动物中，PEG-rHuMGDF通过刺激巨核细胞内复制和骨髓造血祖细胞形成新的巨核细胞，以线性对数剂量依赖性方式增加血小板生成。这些发现表明，在化疗诱导的骨髓抑制期，适当剂量的PEG-rHuMGDF治疗可维持外周血小板的止血浓度，而不增加血栓形成风险。
