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Objective: Notch signaling plays a role in regulating the self-renewal and differentiation of hematopoietic progenitors. Since acute myeloblastic leukemia (AML) originates from dysregulated hematopoietic progenitors, the Notch system may be involved in the abnormal growth. We previously reported that AML cells express Notch proteins. In this study, we examined the effects of recombinant human Notch ligand proteins, Jagged1 and Delta1, on the growth and differentiation of primary AML cells., Materials and Methods: AML cells separated from blood from 12 patients were cultured in wells coated with Jagged1, Delta1, or control IgG. The short-term growth was evaluated using a colorimetric assay. The self-renewal capacity was evaluated by the clonogenic cells recovered, which were obtained via a colony assay involving cells cultured with the ligands or control IgG. Differentiation was evaluated by the morphology of the cultured cells and flow cytometric analysis., Results: The ligand stimulation caused three types of response in the short-term growth of the primary AML cells, namely, promotion, suppression, or no significant effect. The self-renewal capacity was suppressed or not significantly affected by the ligands, even in cells showing short-term growth promotion. The ligand stimulation altered blast cells into macrophage-like cells from their morphology and increased the expression of differentiation markers such as CD13 or CD14 in some samples., Conclusions: The Notch ligands had diverse effects on the short-term growth of primary AML cells. The ligands did not promote the self-renewal capacity of any of the cells examined and instead tended to induce differentiation under the conditions used.

We studied the effects of vesnarinone, a quinolinone derivative used clinically for the treatment of chronic congestive heart failure, on the leukemic blast progenitors in acute myelogenous leukemia (AML) patients and on the normal hematopoietic precursors, colony-forming unit in culture (CFU-C), and colony-forming unit erythroid (CFU-E). Leukemic blast progenitors made blast colonies in the presence of granulocyte-colony stimulating factor (G-CSF), granulocyte-macrophage CSF (GM-CSF), or interleukin-3 (IL-3). Blast colony-formation was suppressed by vesnarinone in a dose-responsive manner regardless of growth factor added. Vesnarinone suppressed the primary (PE1) and secondary (PE2) colony-formation of leukemic blast progenitors in six AML patients tested. The suppression by vesnarinone did not significantly differ between PE1 and PE2. This finding suggests that vesnarinone exerts an almost equivalent effects on the terminal divisions and the self-renewal of leukemic blast progenitors. Furthermore, this drug suppressed the growth of clonogenic cells of five AML cell lines, OCI/AML1a, OCI/AML2, OCI/AML3, OCI/AML5, and OCI/AML6. Normal hematopoietic precursors CFU-C and CFU-E were also suppressed by vesnarinone, although vesnarinone was less toxic to normal hematopoietic than to leukemic blast progenitors. The possible usefulness of vesnarinone as a new approach to the treatment of AML patients is discussed.

The effect of basic and acidic fibroblast growth factors on leukemic blast progenitors was studied in 14 patients with acute myelogenous leukemia and in one patient with chronic myelocytic leukemia in myeloid crisis. bFGF and aFGF stimulated blast-colony formation by leukemic blast progenitors cultured in methylcellulose in two patients. In the other 13 patients, no significant effect of either FGF on blast-colony formation was noted. The combination of bFGF or a FGF and G-CSF, GM-CSF, interleukin-3, or stem cell factor (SCF) had a synergistic effect on blast-colony formation in three patients. In the other patients, however, synergism between FGF and CSF was not detected. In fact, bFGF was found to suppress the stimulation of blast-colony formation due to GM-CSF in one of 10 patients and that due to SCF in four of eight patients. aFGF suppressed the stimulation of blast-colony formation due to GM-CSF in two of 11 patients and that due to SCF in four of eight patients. The results show that bFGF and aFGF do not directly play a major role in leukemic hematopoiesis but that they may modulate the cytokine network affecting leukemic cell growth.

For the optimal growth of clonogenic cells in acute myeloblastic leukemia (AML), several cytokines such as tumor necrosis factor alpha (TNF-alpha), interleukin-1 (IL-1) and IL-6 are required in addition to colony-stimulating factor (CSF), which may be produced by blast cells themselves. In the present study, we addressed the potential role of endogenous production of TNF-alpha and/or IL-1 in the in vitro growth of AML clonogenic cells supported by IL-3. Addition of a specific neutralizing antibody against TNF-alpha (anti-TNF-alpha) to the culture significantly reduced the growth-stimulating effect of IL-3 on the cells in 11 of 14 patients. Simultaneous addition of anti-IL-1 alpha and anti-IL-1 beta also partly affected the growth, although to a much lesser extent when compared to the effect observed with anti-TNF-alpha. In 3 patients, the growth-stimulating effect of IL-3 was completely abrogated by anti-TNF-alpha or a combination of all three antibodies. Constitutive TNF-alpha transcript was observed in 5 patients and TNF-alpha protein was present in culture supernatant. Following in vitro culture, a transient but profound increase in c-fos, c-jun, TNF-alpha and IL-1 beta mRNA levels was observed. Anti-TNF-alpha inhibited the accumulation of TNF-alpha transcript, suggesting that membrane-integrated TNF-alpha may be partly responsible for the induction of TNF-alpha mRNA. It seems likely that the accumulation of these genes occurs through a protein kinase C-independent signaling pathway.

The in vitro growth activities and drug sensitivities of leukemic blast progenitors were compared among the subgroups of acute myelocytic leukemia (AML) classified according to the French-American-British (FAB) cooperative group. Leukemic cells separated from the peripheral bloods of AML patients were cultured in methylcellulose media, and the plating efficiencies of primary colonies (PE1) and secondary colonies after replating (PE2) were determined. PE1 and PE2 have been considered to reflect the capacities of terminal divisions and self-renewal of leukemic blast progenitors, respectively. PE1 and PE2 were variable among AML patients; these findings suggest that AML is a heterogeneous disease in terms of the proliferative activities of leukemic cells. No significant correlation was noted between PE1 or PE2 and the AML subtype. The sensitivities to cytosine arabinoside (Ara-C) of leukemic blast progenitors were studied in methylcellulose and suspension cultures. Ara-C sensitivity was not significantly correlated with the AML subtype, either. In contrast, there was statistically significant correlation between PE2 and the remission outcome of the patients, whereas PE1 was not significantly associated with the clinical outcome. The results in the present study indicate that the proliferative activity, especially self-renewal capacity, of leukemic blast progenitors is highly predictive of the prognosis of AML patients but is not significantly correlated with the AML subtype classified by the blast morphology.

We tested the effect of interleukin 1 (IL-1) on the growth of leukemic blast progenitors from patients with acute myeloblastic leukemia (AML). A purified blast cell fraction depleted of both T cells and phagocytic cells was tested at different cell densities. Addition of 1 ng/ml of IL-1 alpha alone enhanced blast colony formation in 10 of 13 cases tested, and the enhancement was prominent when plated cell densities were lowered. The conditioned media (CM) from AML patients contained varied levels of IL-1 activity, and following depletion of phagocytic cells, the levels decreased markedly in all cases tested. Addition of either antiserum against IL-1 alpha or IL-1 beta reduced the IL-1 activity in CM, suggesting that AML blasts produce both IL-1 alpha and IL-1 beta. Addition of IL-1 alpha or IL-1 beta antiserum inhibited blast colony formation in a dose-dependent manner, and a combination of both antisera showed the most marked inhibition. However, the augmentation of blast colony formation was almost completely inhibited by addition of anti-granulocyte-macrophage colony-stimulating factor (GM-CSF) serum in all three cases tested. IL-1 is also devoid of this activity when tested in the presence of a combination of granulocyte CSF (G-CSF), GM-CSF, and interleukin 3 (IL-3) at an optimal concentration. These results suggest that blast cells could produce and secrete CSF(s) and/or IL-1, and that the growth-enhancing effect of IL-1 on AML blasts is indirect, via production of CSFs by leukemic cells.