Effects of amifostine on the proliferation and differentiation of megakaryocytic progenitor cells

Protective Effect of the c-mpl Agonist Romiplostim on Megakaryocytopoiesis of Human CD34+ Hematopoietic Progenitor Cells Exposed to Ionizing Radiation

A thrombopoiesis-stimulating protein, the myeloproliferative leukemia virus protooncogene (Mpl) ligand romiplostim (RP), is currently approved as a therapeutic agent for idiopathic thrombocytopenic purpura in many countries. Although the action of the initial MPL ligand thrombopoietin (TPO) on human megakaryocytic regeneration from irradiated human hematopoietic stem cells has been examined, there are few reports on the action of RP. In the present study, freshly prepared nonirradiated and 2-Gy X-irradiated human CD34 positive (CD34⁺) cells from placental umbilical cord blood were cultured with a combination of RP and various cytokines. As a result, the effect of RP on cell proliferation of nonirradiated CD34⁺ cells was found to be comparable to that of TPO. However, the stimulating activity of RP on megakaryocytic progenitor-derived colony formation was markedly lower compared with TPO. Regarding the action of RP with various cytokines, the present results showed that a combination of RP with interleukin-3 (IL-3) or IL-3 plus stem cell factor (SCF) showed a high regenerative effect on cell proliferation, megakaryopoiesis, thrombopoiesis, and megakaryocyte colony formation from X-irradiated CD34⁺ cells. The present study showed that human recombinant RP has potential effects on human megakaryocytic regeneration from X-irradiated human CD34⁺ cells and synergistically acts with IL-3 and IL-3 plus SCF, just as observed with TPO.

The effect of amifostine on differentiation of the human megakaryoblastic Dami cell line

Amifostine is a cytoprotective drug that was initially used to control and treat nuclear radiation injury and is currently used to provide organ protection in cancer patients receiving chemotherapy. Clinical studies have also found that amifostine has some efficacy in the treatment of cytopenia caused by conditions such as myelodysplastic syndrome and immune thrombocytopenia, both of which involve megakaryocyte maturation defects. We hypothesized that amifostine induced the differentiation of megakaryocytes and investigated this by exposing the human Dami megakaryocyte leukemia cell line to amifostine (1 mmol/L). After 12 days of amifostine exposure, optical microscopy showed that the proportion of Dami cells with diameters >20 μm had increased to 24.63%. Transmission electron microscopy identified the development of a platelet demarcation membrane system, while flow cytometry detected increased CD41a expression and decreased CD33 expression on the Dami cell surface. Ploidy analysis found that the number of polyploid cells with >4N DNA content increased to 27.96%. We did not detect any elevation in the mRNA or protein levels of megakaryocytic differentiation-associated transcription factors GATA-binding factor 1 (GATA-1) and nuclear factor, erythroid 2 (NF-E2), but nuclear import assay revealed an increased nuclear translocation of these proteins. These findings indicate that amifostine induced the differentiation of Dami cells into mature megakaryocytes via a mechanism involving increased nuclear translocation of the transcription factors, NF-E2 and GATA-1.

Inhibition of HIF-1alpha by the anticancer drug TAS106 enhances X-ray-induced apoptosis in vitro and in vivo

In a previous study, we showed that a novel anticancer drug, 1-(3-C-ethynyl-β-D-ribo-pentofuranosyl)cytosine (TAS106, ECyd) increased the antitumour efficacy of X-irradiation. However, its effects on hypoxic cells in tumours remain unclarified. Here, we show that TAS106 enhances the induction of apoptosis in X-irradiated human gastric adenocarcinoma MKN45 and MKN28 cells under hypoxia in vitro. At the same time, the accumulation of HIF-1α observed under hypoxia was shown to be decreased to the level of normoxia in the presence of 0.1 μM TAS106. To study the function of HIF-1α protein in apoptosis of hypoxic cells, we employed an HIF-1α reductive approach using its specific antisense oligodeoxynucleotide. The reduction of HIF-1α gene expression dramatically enhanced X-ray-induced apoptosis in hypoxic cells. In in vivo experiments in which MKN45 cells were transplanted into severe combined immunodeficient (SCID) mice, TAS106 (0.5 mg kg⁻¹) suppressed HIF-1α expression and subsequently reduced the area of the hypoxic region in the tumour and enhanced the induction of apoptosis in the hypoxic region when combined with 2 Gy of X-irradiation. These results suggest the possibility that TAS106 acts as a potent radiosensitiser through the inhibition of HIF-1α expression and can be a useful agent against radiotherapy-resistant hypoxic cells in solid tumours.

Maternal and neonatal factors associated with the high yield of mononuclear low-density/CD34+ cells from placental/umbilical cord blood

Placental/umbilical cord blood (CB) contains nucleated cells and hematopoietic stem/progenitor cells (CD34(+) cells). However it is difficult to predict the number of nucleated/CD34(+) cells in each CB before cell processing. Despite many previous studies from institutes affiliated with CB banks in metropolitan areas, little information is available regarding the characteristics of CB units from other medical facilities. The purpose of the present study was to analyze the maternal/neonatal factors on the yield of cells in CB units. A total of 176 CB units were obtained from single-birth and normal vaginal deliveries. Mononuclear low-density (LD) cells were separated using Ficoll-Paque within 24 hrs after CB collection and then processed for the purification of CD34(+) cells. A multiple linear regression analysis was performed to assess the correlations between the yield of cells and maternal/neonatal factors including maternal age, gravid status, duration of labor, gestational age, neonatal height and weight, cord length, and meconium in the amniotic fluid. The total LD cells per CB unit had a weak positive correlation with the maternal age of primigravidae. The total LD cells per CB unit from the primigravidae aged > or = 25 were significantly higher than those from the primigravidae aged < or = 24. The total CD34(+) cells per CB unit from the 1-gravidae were significantly higher than those from the 2-gravidae and 3-gravidae, respectively among all donors. These results indicate that the CB units from the primigravidae aged > or = 25 are more likely to contain higher yield of LD/CD34(+) cells.

Purvalanol A Enhances Cell Killing by Inhibiting Up-Regulation of CDC2 Kinase Activity in Tumor Cells Irradiated with High Doses of X Rays

To clarify the relationship between CDC2 kinase activity and radiation-induced apoptosis, we examined whether the cyclin-dependent kinase (CDK) inhibitor purvalanol A enhanced radiation-induced apoptosis in gastric tumor cells. MKN45 cells exposed to 20 Gy of X rays increased the CDC2 kinase activity and the expression of regulatory proteins (phospho-CDC2 and cyclin B1) of the G2/M phase, followed by activation of the G2/M checkpoint, whereas the treatment of X-irradiated MKN45 cells with 20 microM purvalanol A suppressed the increase in the CDC2 kinase activity and expression of the G2/M-phase regulatory proteins and reduced the fraction of the cells in the G2/M phase in the cell cycle. Furthermore, this treatment resulted in not only a significant increase in radiation-induced apoptosis but also the loss of clonogenicity in both MKN45 (p53-wild) and MKN28 (p53-mutated) cells. The expression of anti-apoptosis proteins, inhibitor of apoptosis protein (IAP) family members (survivin and XIAP) and BCL2 family members (Bcl-X(L) and Bcl-2), in purvalanol A-treated cells with and without X rays was significantly lower than for cells exposed to X rays alone. These results suggest that the inhibition of radiation-induced CDC2 kinase activity by purvalanol A induces apoptosis through the enhancement of active fragments of caspase 3.