Hematopoietic growth factors in pediatrics

G-CSF induces stabilization of ETS protein Fli-1 during myeloid cell development

Granulocyte colony-stimulating factor (G-CSF) is a growth factor that regulates the production and function of neutrophils. G-CSF has been used to treat neutropenia in neonates, pediatric cancer patients, and patients undergoing stem cell transplantation. The regulation of transcription factors mediating G-CSF activity has not been well characterized. The goal of this study was to examine the regulation of the ETS binding protein, Friend leukemia integration site 1 (Fli-1), in myeloid cells treated with G-CSF. Fli-1 has oncogenic properties in humans and mice, and plays a role in vascular and hematopoietic cell development. We previously reported that Fli-1 and the serum response factor bind at adjacent sites within the serum response element-1 of the early growth response gene-1 promoter in the murine myeloid leukemic cell line, NFS60. We also identified that Fli-1 DNA binding increased in G-CSF-treated cells compared with untreated cells. To determine whether the change in binding activity is due to increased Fli-1 transcription or protein stability, we examined endogenous Fli-1 expression in G-CSF-treated or -untreated NFS60 cells. Our results demonstrated that levels of Fli-1 protein, but not RNA, were higher in extracts from cells treated with G-CSF. The increase in Fli-1 protein was also dependent on protein synthesis. Finally, we showed that the half-life of Fli-1 is prolonged in G-CSF-treated cells compared with control-treated cells. These results suggest that G-CSF induces stabilization of Fli-1 protein in myeloid cells, thus proposing a novel mechanism by which hematopoietic growth factors regulate transcription factors.

Administration of recombinant human granulocyte-macrophage colony-stimulating factor to children undergoing allogeneic marrow transplantation: a prospective, randomized, double-masked, placebo-controlled trial

Granulocyte-macrophage colony-stimulating factor (GM-CSF) was administered to 40 pediatric patients undergoing partially matched related, or closely matched unrelated, allogeneic marrow transplants. This trial was set up in a prospective, randomized, double-masked, placebo-controlled manner to establish if the administration of GM-CSF to such patients enhanced neutrophil recovery in this allogeneic transplant setting. The GM-CSF group had a significantly shorter time to neutrophil recovery to > 500 x 10(9) cells/L (15 days) than the placebo group (p = 0.0036). In addition, the GM-CSF group had a significantly shorter neutrophil recovery time to > 1,000 x 10(9) cells/L (18 days) than the placebo group (p = 0.0053). The primary objective of this study was met by showing that GM-CSF enhanced neutrophil recovery in this allogeneic setting. However, within the study group of patients, there was no effect of GM-CSF on the incidence or severity of graft-vs.-host disease (GvHD), one of the secondary end-points of the study. With regard to the other secondary end-points, there was no effect of GM-CSF on marrow cellularity, duration of systemic antibiotics given for real infections or as prophylaxis to prevent infections, risk of significant infections (as defined by systemic culture of virus, fungus, or bacteria), and duration or cost of hospitalization, platelet recovery, and nutritional support. With the secondary end-points, it will be necessary to study larger numbers of pediatric patients to identify differences that are small in this study group. In conclusion, GM-CSF can be safely administered to children with few, if any, significant side-effects. Additional work remains to facilitate earlier discharge of patients and decreased antibiotic usage, to offset the cost of using a neutrophil growth factor.