In vitro Effects of Recombinant Human Megakaryocyte Growth and Development Factor on Primary Human Tumour Colony Growth

Megakaryocyte growth and development factor (MGDF) is a novel cytokine that binds to the c-mpl receptor and stimulates megakaryocyte development in vitro and in vivo. This report describes the ability of recombinant human (r-Hu) MGDF to affect megakaryocytopoiesis in normal nonhuman primates. r-HuMGDF was administered subcutaneously to normal, male rhesus monkeys once per day for 10 consecutive days at dosages of 2.5, 25, or 250 micrograms/kg of body weight. Bone marrow and peripheral blood were assayed for clonogenic activity and peripheral blood counts were monitored. Circulating platelet counts increased significantly (P < .05) for all doses within 6 days of r-HuMGDF administration and reached maximal levels between day 12 and day 14 postcytokine administration. The 2.5, 25.0, and 250.0 micrograms/kg/d doses elicited peak mean platelet counts that were 592%, 670%, and 449% of baseline, respectively. Bone marrow-derived clonogenic data showed significant increases in the concentration of megakaryocyte (MEG)- colony-forming unit (CFU) and granulocyte-erythroid-macrophage- megakaryocyte (GEMM)-CFU, whereas that of granulocyte-macrophage (GM)- CFU and burst-forming unit-erythroid (BFU-e) remained unchanged during the administration of r-HuMGDF. These data show that r-HuMGDF is a potent stimulator of thrombocytopoiesis in the normal nonhuman primate.

Download Full-text

Platelets Exposed to Elevated Levels of Endogenous Thrombopoietin In Vivo Have a Reduced Response to Megakaryocyte Growth and Development Factor In Vitro

Thrombosis and Haemostasis ◽

10.1055/s-0037-1612918 ◽

2001 ◽

Vol 85 (01) ◽

pp. 152-159 ◽

Cited By ~ 5

Author(s):

Uichi Nishiyama ◽

Haruhiko Morita ◽

Yoshifumi Torii ◽

Tomoaki Kuwaki ◽

Eiko Shimizu ◽

...

Keyword(s):

Growth And Development ◽

Platelet Reactivity ◽

Biochemical Properties ◽

Human Platelets ◽

Janus Kinase ◽

Intravenous Injections ◽

Development Factor ◽

Lower Reactivity

SummaryThrombopoietin (TPO), or megakaryocyte growth and development factor (MGDF), has been shown to potentiate the sensitivity of normal human platelets to various agonists in vitro. The present study investigated the functional and biochemical properties of platelets from mice rendered thrombocytopenic by sublethal irradiation with regard to the reactivity to recombinant murine MGDF (rmMGDF) in vitro. During the course of reversible thrombocytopenia following irradiation, platelets from irradiated mice which had lower platelet counts and reciprocally higher plasma TPO levels showed lower reactivity to rmMGDF in agonist-induced platelet aggregation. Intravenous injections of recombinant soluble murine c-Mpl (sMpl), which has the ability to capture TPO, after irradiation restored the reactivity of platelets at the platelet nadir to rmMGDF. On the other hand, platelets prepared from normal mice 3 h after a single intravenous injection of pegylated rmMGDF did not respond to rmMGDF. There was a marked decrease in c-Mpl and Janus kinase 2 (JAK2) in platelets from irradiated mice at the platelet nadir. Similar results were observed with platelets from mice administered pegylated rmMGDF. JAK2 was only moderately decreased, however, in platelets from mice given sMpl after irradiation. These results indicate that exposure of platelets to increased endogenous TPO levels in vivo in thrombocytopenic mice leads to a reduction in the platelet reactivity to rmMGDF in vitro. Further, these results suggest that the c-Mpl-mediated signaling pathway, which is essential for the priming effect of rmMGDF, is defective in thrombocytopenic murine platelets.

Download Full-text

Pegylated megakaryocyte growth and development factor abrogates the lethal thrombocytopenia associated with carboplatin and irradiation in mice

Blood ◽

10.1182/blood.v86.12.4486.bloodjournal86124486 ◽

1995 ◽

Vol 86 (12) ◽

pp. 4486-4492 ◽

Cited By ~ 132

Author(s):

MM Hokom ◽

D Lacey ◽

OB Kinstler ◽

E Choi ◽

S Kaufman ◽

...

Keyword(s):

Growth And Development ◽

Granulocyte Colony Stimulating Factor ◽

Potent Inducer ◽

Development Factor ◽

Internal Bleeding ◽

Life Threatening ◽

Stimulating Factor ◽

Sublethal Irradiation

Megakaryocyte growth and development factor (MGDF) is a potent inducer of megakaryopoiesis in vitro and thrombopoiesis in vivo. The effects of MGDF appear to be lineage-selective, making this cytokine an ideal candidate for use in alleviating clinically relevant thrombocytopenias. This report describes a murine model of life-threatening thrombocytopenia that results from the combination treatment of carboplatin and sublethal irradiation. Mortality of this regimen is 94% and is associated with widespread internal bleeding. The daily administration of pegylated recombinant human MGDF (PEG-rMGDF) significantly reduced mortality (to < 15%) and ameliorated the depth and duration of thrombocytopenia. The severity of leucopenia and anemia was also reduced, although it was not clear whether these effects were direct. Platelets generated in response to PEG-rMGDF were morphologically indistinguishable from normal platelets. PEG-rMGDF administered in combination with murine granulocyte colony-stimulating factor completely prevented mortality and further reduced leukopenia and thrombocytopenia. These data support the concept that PEG-rMGDF may be useful to treat iatrogenic thrombocytopenias.

Download Full-text