Growth factors in human cancer.
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Biomedical subjects
Publications and source records attributed to J Gabrilove.
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Basic fibroblast growth factor (bFGF) is a potent mitogen for human bone marrow stromal cells. Normally, large numbers of human bone marrow stromal cells are difficult to obtain. However, nanogram/ml concentrations of bFGF stimulate the growth of passaged bone marrow stromal cells both in media formulated for optimal growth of stromal cells and in a simple mixture of RPMI-1640 and 10% fetal calf serum facilitating the successive expansion of stromal cells through multiple passages. bFGF also greatly accelerates the formation of a primary stromal cell layer following inoculation of newly harvested bone marrow cells into dishes. In the presence of bFGF, the stromal cells attain high densities, lose their contact inhibition and grow in multilayered sheets. Heparin greatly potentiates the stimulatory effect of low concentrations of bFGF. The effects of bFGF are fully reversible: cells cultured in the presence of this factor for multiple passages revert to normal growth rates following trypsinization and subculture. A short (4 h) exposure of the cells to bFGF elicits profound growth stimulation. This supports the hypothesis that this factor binds to glycosaminoglycans in the cell matrix which act as a storage reservoir for this cytokine.
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One of the most exciting recent developments in cancer-related research has been the discovery and understanding of colony-stimulating factors. There is now a general optimism that these factors will be used in the treatment of a variety of solid tumors, lymphomas, and leukemias, as well as in the treatment of patients who are immunocompromised or undergoing bone marrow transplantation. We have gathered a distinguished panel of experts to discuss the current status of this rapidly moving field.
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Experiments were conducted to isolate and characterize the gene and gene product of a human hematopoietic colony-stimulating factor with pluripotent biological activities. This factor has the ability to induce differentiation of a murine myelomonocytic leukemia cell line WEHI-3B(D+) and cells from patients with newly diagnosed acute nonlymphocytic leukemia (ANLL). A complementary DNA copy of the gene encoding a pluripotent human granulocyte colony-stimulating factor (hG-CSF) was cloned and expressed in Escherichia coli. The recombinant form of hG-CSF is capable of supporting neutrophil proliferation in a CFU-GM assay. In addition, recombinant hG-CSF can support early erythroid colonies and mixed colony formation. Competitive binding studies done with 125I-labeled hG-CSF and cell samples from two patients with newly diagnosed human leukemias as well as WEHI-3B(D+) cells showed that one of the human leukemias (ANLL, classified as M4) and the WEHI-3B(D+) cells have receptors for hG-CSF. Furthermore, the murine WEHI-3B(D+) cells and human leukemic cells classified as M2, M3, and M4 were induced by recombinant hG-CSF to undergo terminal differentiation to macrophages and granulocytes. The secreted form of the protein produced by the bladder carcinoma cell line 5637 was found to be O-glycosylated and to have a molecular weight of 19,600.
The human promyelocytic leukemia cell line HL-60 and monoblastic leukemia cell line U937 undergo differentiation when induced by lymphokine and cytokine preparations. Growth inhibition, acquisition of immunoglobulin Fc receptors, increased expression of monocyte-related surface antigens, and an increase in lysosomal enzyme contents accompany maturation induced by gamma-interferon and other cytokine factors tested. Additionally, increased receptors for chemotactic peptide (fMLPR), increased hydrogen peroxide release in response to phorbol myristic acetate stimulation, and the release of prostaglandins (PGE2 and 6-keto-PGF1a) follow exposure to lymphokine and cell line sources of myeloid colony-stimulating activity (CSA). Gamma-Interferon (gamma-IFN) induced fMLPR in HL-60 (only at 1000 units/ml) but not in U937. Additionally, gamma-IFN did not induce prostaglandin release in either cell line. These myeloid colony-stimulating activity-associated differentiation-inducing factors were obtained from the human hepatoma++ cell line SK-Hep and bladder carcinoma cell line 5637, which were free of interferon activity. The 2-day phytohemagglutinin-induced lymphokine contained no detectable CSA and was a good source of differentiation activity. A simple, rapid assay for a new human CSA with pluripotent hematopoietic stimulating activity (pluripoietin) is described based on stimulation of [3H]glucosamine incorporation. Cell line conditioned media containing pluripoietin, purified pluripoietin, and gamma-IFN are active in this assay. These myeloid leukemia cell line differentiation factors are thus different from interferon and conventional CSA. These results suggest that endogenous human cytokines may have a role in the differentiation of leukemic as well as normal myeloid cells.
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Murine post-endotoxin sera contain high levels of myeloid colony-stimulating factor(s) (GM-CSF) and factors capable of inducing terminal granulocyte and macrophage differentiation of the murine myelomonocytic leukemic cell line WEHI-3. The combination of C. parvum and endotoxin induced a serum activity capable of inducing tumor necrosis and inhibiting leukemic colony formation in vitro. This factor (TNF) could be separated from the differentiation-inducing factor (GM-DF) and from CSF. In conjunction with a Phase I trial of highly purified endotoxin in patients with advanced malignancy, we monitored human post-endotoxin sera for CSF and GM-DF. Induction of GM-DF occurred maximally at 2-6 h and was associated with increased serum levels of CSF active against the patient's own bone marrow. Following repeated injections of escalating doses of endotoxin, persistent levels of GM-DF were detected both pre-endotoxin and 24 h post-endotoxin treatment. The ability to induce repeatedly a serum protein with potent capacity to promote terminal differentiation of myelomonocytic leukemic cells suggests a possible therapeutic role in human myeloid leukemias.