Defibrotide in combination with granulocyte colony-stimulating factor significantly enhances the mobilization of primitive and committed peripheral blood progenitor cells in mice

Defibrotide is a polydeoxyribonucleotide, which significantly reduces the expression of adhesion molecules on endothelial cells. We investigated the activity of Defibrotide alone or in combination with recombinant human granulocyte colony-stimulating factor (rhG-CSF) to mobilize peripheral blood progenitor cells (PBPCs) in BALB/c mice. A 5-day treatment with Defibrotide alone (1-15 mg/mouse/day) had no effect on WBC counts, frequencies and absolute numbers of total circulating colony-forming cells (CFCs), i.e., granulocyte-macrophage colony-forming units, erythroid burst-forming units, and multilineage colony-forming units. As compared with mock-injected mice, administration of rhG-CSF alone (5 micro g/mouse/day) for 5 days significantly (Por = 0.0001) increased WBC counts, CFC frequencies, and CFC absolute numbers by 2-, 13-, and 27-fold, respectively. As compared with control mice, the combined administration of Defibrotide (15 mg/mouse/day) and rhG-CSF significantly (Por = 0.0001) increased WBC counts, frequencies and absolute numbers of CFCs by 4-, 38-, and 119-fold, respectively. As compared with rhG-CSF alone, administration of Defibrotide plus rhG-CSF resulted in a significant increase (Por = 0.001) of the frequency of circulating long-term culture-initiating cells. In addition, transplantation of 2 x 10(5) rhG-CSF- or Defibrotide/rhG-CSF-mobilized mononuclear cells rescued 43% and 71% of recipient mice, respectively. Experiments of CFC homing performed in lethally irradiated or nonirradiated recipients showed that marrow homing of transplanted PBPCs was reduced by 3-fold in Defibrotide-treated animals as compared with mock-injected mice (Por = 0.001), suggesting that the mobilizing effect of Defibrotide might be because of an effect on PBPC trafficking. In conclusion, our data demonstrate that Defibrotide synergizes with rhG-CSF and significantly increases the mobilization of a broad spectrum of PBPCs, including primitive and committed progenitor cells. These data might have relevant implications for autologous and allogeneic anticancer therapy in humans.