Functional significance of induction of differentiation in human myeloid leukaemic blasts by 1,25-dihydroxyvitamin D3 and GM-CSF

Inhibitory control of TGF-beta1 on the activation of Rap1, CD11b, and transendothelial migration of leukocytes

Beta2-integrins are a family of dimeric adhesion molecules expressed on leukocytes. Their capacity to bind ligand is regulated by their state of activation. CD11b, an alphaMbeta2 integrin, is implicated in a number of physiological and pathological events such as inflammation, thrombosis, or atherosclerosis. The GTPase Rap1 is essential for its activation and could therefore play a strategic role in the regulation of leukocyte functioning. Because low levels of circulating TGF-beta have been linked with severe atherosclerosis, we have assessed the role of this cytokine in the regulation of Rap1 and CD11b activation in differentiated U937 cells and in human peripheral blood monocytes. TGF-beta1 caused a significant reduction in the expression of CD11b but not in the expression of other integrins tested. More importantly, TGF-beta1 greatly reduced the capacity of PMA or chemokines to activate CD11b and Rap1, a phenomenon paralleled by a loss of the Epac transcript and a reduction in 8-pCPT-2'-O-Me-cAMP-mediated activation of Rap1. This inhibition diminished the capacity of monocytes to migrate across a monolayer of endothelial cells. The inhibitory effect of TGF-beta1 on Rap1 activity may exert a general protective influence against aberrant transendothelial migration, thereby holding inflammatory responses in check.

Enhancement by other compounds of the anti-cancer activity of vitamin D(3) and its analogs

Differentiation therapy holds promise as an alternative to cytotoxic drug therapy of cancer. Among compounds under scrutiny for this purpose is the physiologically active form of vitamin D(3), 1,25-dihydroxyvitamin D(3), and its chemically modified derivatives. However, the propensity of vitamin D(3) and its analogs to increase the levels of serum calcium has so far precluded their use in cancer patients except for limited clinical trials. This article summarizes the range of compounds that have been shown to increase the differentiation-inducing and antiproliferative activities of vitamin D(3) and its analogs, and discusses the possible mechanistic basis for this synergy in several selected combinations. The agents discussed include those that have differentiation-inducing activity of their own that is increased by combination with vitamin D(3) or analogs, such as retinoids or transforming growth factor-beta and plant-derived compounds and antioxidants, such as curcumin and carnosic acid. Among other compounds discussed here are dexamethasone, nonsteroidal anti-inflammatory drugs, and inhibitors of cytochrome P450 enzymes, for example, ketoconazole. Thus, recent data illustrate that there are extensive, but largely unexplored, opportunities to develop combinatorial, differentiation-based approaches to chemoprevention and chemotherapy of human cancer.

Gene expression profile of Vitamin D3 treated HL60 cells shows an incomplete molecular phenotypic conversion to monocytes

By high density oligonucleotide microarrays we have studied the expression profile of proliferating and VD treated HL60 cells and the molecular phenotype of VD monocytes and that of CD14+ peripheral monocytes has been compared. The results indicate that important changes in functional categories of the differentially expressed genes underlie the differentiation transition from myeloblasts to monocytes. This differential gene expression pattern leads to an increased expression of mRNAs involved in surface and external activities since many of the VD induced genes belong to ligand binding, receptors, cell surface antigens, defense/immunity and adhesion molecules functional categories. The results also indicate that the molecular phenotypes of monocytes and VD induced cells diverge for a small but significant set of defense related genes. Particularly, class II MHC genes are not expressed in these cells. Furthermore, the high levels of expression of these genes induced by serum treatment of monocytes are decreased by VD.

Generation of phagocytic MAK and MAC-DC for therapeutic use: characterization and in vitro functional properties

Phagocytic cells with macrophage or dendritic cell phenotype, able to capture and ingest tumor cells, were derived in large numbers from peripheral blood mononuclear cells using two different activation procedures. Peripheral blood mononuclear cells were stimulated in nonadherent conditions in the presence of human AB serum with either granulocyte-macrophage colony-stimulating factor and dihydroxy-vitamin D3 for 7 days and with interferon-gamma for the last 18 hours to obtain activated macrophages (MAK) or with granulocyte-macrophage colony-stimulating factor and interleukin-13 for 7 days (with fresh interleukin-13 added on day 4) to obtain macrophage-dendritic cells (MAC-DC). A strong ability of MAC-DC to phagocytose yeasts was observed, in contrast to a low-intermediate phagocytosis capacity by MAK. Both CD14+ FCgammaR+ (FcgammaRI/CD64, FcgammaRII/CD32, FcgammaRIII/CD16) MAK and CD1a+/CD86+, CD14- MAC-DC were able to phagocytose whole tumor cells. However, only MAK phagocytosis was enhanced by FcgammaR engagement. MAK but not MAC-DC could lyse tumor cell in antibody-dependent cell cytotoxicity assays, via FcgammaRI. Thus, MAK as well as MAC-DC may represent valuable tools for different in vivo therapy strategies that do or do not include the use of monoclonal antibodies.

Leukemia cell differentiation: cellular and molecular interactions of retinoids and vitamin D

1. The conventional approach to treatment of acute myeloid leukemia has been the use of chemotherapy, which although being cytotoxic to malignant clones, is also cytodestructive to normal cells. In addition, some leukemia cells develop resistance to chemotherapy and are therefore difficult to eradicate. 2. Differentiation therapy, whereby immature cells are induced to attain a mature phenotype by differentiation agents, has provided an alternative strategy in the treatment of hyperproliferative disorders. This has been highlighted by the use of all-trans retinoic acid (ATRA) in the treatment of acute promyelocytic leukemia (APL). 3. Another differentiation agent, 1,25-dihydroxyvitamin D3 (1,25(OH)2D3), directs monocytic maturation of normal and leukemic cells. Cellular studies have revealed that combinations of vitamin D derivatives and retinoids such as ATRA and 9-cis retinoic acid (9-cis RA) exhibit cooperative effects on differentiation in established leukemia cell lines such as HL-60, U937, and NB4. Furthermore, vitamin D compounds, although not able to induce apoptosis when used alone, potentiate apoptosis induced by 9-cis RA in HL-60 cells and differentially regulate the expression of the apoptosis-related gene products bcl-2 and bax. The molecular mechanisms involved in regulating differentiation and apoptosis by these agents are mediated through the interactions of the nuclear receptors for vitamin D (VDR), ATRA (RAR), and 9-cis RA (RXR), which are able to form homo- or heterodimeric complexes and transcriptionally activate or repress target gene expression. 4. There is evidence to suggest that nitric oxide may also play a role in leukemic cell differentiation and that 1,25(OH)2D3 may influence endogenous nitric oxide production either by directly increasing tumor necrosis factor-alpha (TNF-alpha) or through a secondary mediator such as the C-type lectin CD23.

Effects of hyperthermia and granulocyte-macrophage colony-stimulating factor on the differentiation of human leukemic cell line U937

We have studied the effects of granulocyte-macrophage colony-stimulating factor (GM-CSF) and hyperthermia individually and in combination on the cell growth and differentiation of human monoblastic leukemia cell line U937. Several criteria were used to evaluate the differentiation of these cells, including the reduction in the plating efficiency and cell growth, the ability to phagocytize latex particles, the reduction of nitro blue tetrazolium (NBT), and development of surface antigenic markers. Hyperthermia alone was able to inhibit cell proliferation, reduce cell viability, and induce differentiation. In the range of 41-43 degrees C, the major effect of hyperthermia was cell differentiation induction as judged by above criteria. On average, hyperthermia induced differentiation in 32% of cells. GM-CSF was able to induce differentiation in 37% of U937 cells as judged by similar criteria. The combined treatment with GM-CSF and hyperthermia resulted in the differentiation of 60% of U937 cells. The extent of differentiation obtained is comparable or better than other combinatorial treatments using various cytokines or cytokines and chemical reagents reported before.

Overgrowth of a leukemic culture by a minor CD34+ population

We have investigated the differentiation potential of blast cells in a case of acute myeloid leukemia which comprised a majority CD34- population and a minor (2%) CD34+ fraction. Blasts were cultured for 2 weeks in a combination of cytokines--c-Kit ligand, interleukin 3 and granulocyte macrophage colony-stimulating factor (SIGm mix)--together with all-trans retinoic acid or 1alpha ,25-dihydroxy vitamin D3. Maturation of blasts was assessed by morphology on Romanowsky-stained slides, changes in surface CD markers and clonogenic culture. After 7 days of culture of unseparated blasts in SIGm, most maturation was monocytic, but with retinoic acid 63% of blasts had matured into granulocytes. Vitamin D3 enhanced monocytic differentiation, with 60% of cells becoming monocytic. The percentage of CD14 and CD15 positive cells decreased over 7 days in SIGm (from 62% to 17% and from 76% to 39% for CD14 and CD15, respectively). CD14+ cell numbers were maintained, or recovered, in cultures supplemented with vitamin D3 (59% at day 7), and CD15+ cell numbers, too, remained unchanged in the presence of retinoic acid (67%) or vitamin D3 (66%). Aberrant markers CD7 and CD56 declined under any conditions. When separated, both the CD34- and CD34+ fractions showed similar changes in morphology and surface maturation markers, suggesting that these two populations may be closely related. However, only a few CD34+ cells expressed the aberrant markers present on the majority blast population. The CD34- population declined in culture while the CD34+ fraction rapidly expanded. This probably reflects the difference in progenitor content; high numbers of colony-forming cells were concentrated in the CD34+ subpopulation. We conclude that both CD34- and CD34+ populations can differentiate but only the CD34+ fraction proliferates. Primitive clonogenic CD34+ cells from this patient may generate occasional aberrant CD34+ blasts which could then differentiate into the accumulating aberrant CD34- blast population.

Modulation of Idarubicin-Induced Apoptosis in Human Acute Myeloid Leukemia Blasts by All-Trans Retinoic Acid, 1,25(OH)2 Vitamin D3, and Granulocyte-Macrophage Colony-Stimulating Factor

The relationship between differentiation of human myeloid cells and apoptosis remains unclear. Recent studies have shown that terminal differentiation need not necessarily lead to the apoptotic demise of myeloid cells, while other studies have shown that induction of differentiation is associated with increased resistance to apoptosis-inducing agents, such as chemotherapy and γ-irradiation. Such results are pertinent to the treatment of acute myeloid leukemia (AML) and myelodysplastic syndrome, where differentiating agents and hemopoietic growth factors are being combined with chemotherapy to enhance response and limit toxicity. To elucidate the factors governing apoptosis in human AML blasts, we have studied the cytotoxic effect of idarubicin on HL60, U937 and KG1 cells, after incubation with all-trans retinoic acid (ATRA), 1,25(OH)2 D3, and granulocyte-macrophage colony-stimulating factor (GM-CSF ). We show that prior incubation of human myeloid leukemic cells with ATRA or 1,25(OH)2 D3 induced resistance to idarubicin-induced apoptosis, which was modulated by coincubation with GM-CSF. The altered chemosensitivity of cells depended on the degree of G0/G1 cell-cycle arrest induced by incubation with ATRA, 1,25(OH)2 D3, and GM-CSF and was independent of differentiation status or Bcl-2 oncoprotein expression. These findings suggest that cell-cycle arrest in human leukemic cells can be induced by exogenous agents and may promote drug resistance. Determining the mechanisms by which cell-cycle arrest is induced may permit understanding of the processes by which the cells escape cytotoxic drug-mediated apoptosis.

Modulation of Idarubicin-Induced Apoptosis in Human Acute Myeloid Leukemia Blasts by All-Trans Retinoic Acid, 1,25(OH)2 Vitamin D3, and Granulocyte-Macrophage Colony-Stimulating Factor

The relationship between differentiation of human myeloid cells and apoptosis remains unclear. Recent studies have shown that terminal differentiation need not necessarily lead to the apoptotic demise of myeloid cells, while other studies have shown that induction of differentiation is associated with increased resistance to apoptosis-inducing agents, such as chemotherapy and γ-irradiation. Such results are pertinent to the treatment of acute myeloid leukemia (AML) and myelodysplastic syndrome, where differentiating agents and hemopoietic growth factors are being combined with chemotherapy to enhance response and limit toxicity. To elucidate the factors governing apoptosis in human AML blasts, we have studied the cytotoxic effect of idarubicin on HL60, U937 and KG1 cells, after incubation with all-trans retinoic acid (ATRA), 1,25(OH)2 D3, and granulocyte-macrophage colony-stimulating factor (GM-CSF ). We show that prior incubation of human myeloid leukemic cells with ATRA or 1,25(OH)2 D3 induced resistance to idarubicin-induced apoptosis, which was modulated by coincubation with GM-CSF. The altered chemosensitivity of cells depended on the degree of G0/G1 cell-cycle arrest induced by incubation with ATRA, 1,25(OH)2 D3, and GM-CSF and was independent of differentiation status or Bcl-2 oncoprotein expression. These findings suggest that cell-cycle arrest in human leukemic cells can be induced by exogenous agents and may promote drug resistance. Determining the mechanisms by which cell-cycle arrest is induced may permit understanding of the processes by which the cells escape cytotoxic drug-mediated apoptosis.

Effect of GM-CSF, 1, 25-Dihydroxycholecalciferol (Vit.D) and All-Trans-Retinoic Acid (ATRA) on the Proliferation and Differentiation of MDS-Bone Marrow (BM)-Cells In Vitro

Myelodysplastic syndromes (MDS) are a heterogenous group of stem cell disorders characterized by an impaired differentiation of the pluripotent stem cell resulting in dysplastic changes of all three hemopoietic lineages. We studied the effect of vitamin D (Vit.D) or all-trans retinoic acid (ATRA; 10(-6) and 10(-8)M) in combination with GM-CSF on the proliferation and differentiation of mononuclear bone marrow-cells (MNC) of 48 MDS-patients as compared to 9 normal bone marrow (BM)-controls in a special colony assay: 30,000 MNC were cultured in agar plugs for 7 days (d) and the resulting colonies immunophenotyped in situ by a panel of monoclonal antibodies. In 14 of 48 cultured MDS-BM-samples hemopoietic clones could be grown which expressed myelomonocytic antigens (CD14 (21%*), CD15 (35%*)) as well as blast antigens (CD20 (9%*), CD34 (10%*), Glycophorin A (Glyco A, 18%*)) whereas all normal BM-colonies were negative for blast markers. Vit.D or ATRA in combination with GM-CSF could not induce an (immunologically measurable) increased differentiation (5 higher percentage of differentiated clones) as compared to GM-CSF alone. We conclude that Vit.D and ATRA have no sufficient differentiation effect on MDS-cells. Our colony assay in combination with immunophenotyping enables an in vitro measurement of differentiation and proliferation in MDS. We suggest the use of this technique to measure effects of therapy in the course of the disease.

Granulocyte-macrophage colony-stimulating factor down-regulates CD14 expression on monocytes

CD14 is a differentiation-stage-linked glycosyl-phophatidyl-inositol-linked glycoprotein on human peripheral blood monocytes and tissue macrophages, which functions as a receptor for lipopolysaccharide. Here, the effects of granulocyte macrophage colony-stimulating factor (GM-CSF1 a cytokine with proliferation- and differentiation-inducing properties on myeloid lineage cells, were studied on CD14 expression by peripheral blood cells. GM-CSF down-regulated the membrane expression of CD14 on monocytes while it up-regulated expression on neutrophils. GM-CSF also decreased the spontaneous release of CD14 in monocyte culture supernatants. Down-regulation of CD14 expression and release was accompanied by a decrease in the mRNA transcript for CD14, suggesting that it most likely reflects an effect on the transcriptional level. The functional significance of this phenomenon, and its potential relation to the terminal differentiation of monocytes, are discussed.

Expression of cell surface antigens during the differentiation of HL-60 cells induced by 1,25-dihydroxyvitamin D3, retinoic acid and DMSO

HL-60 cells were induced to differentiate by 1,25-dihydroxyvitamin D3, retinoic acid or DMSO. In order to investigate to which extent this maturation mimics the in vivo monocytic or myeloid differentiation, we compared induced HL-60 cells with peripheral blood monocytes and granulocytes by using a panel of mAbs directed against myeloid cell surface antigens. Upon exposure to 1,25-(OH)2D3, HL-60 cells acquired a differentiation phenotype close to that of mature monocytes. The changes in myeloid cell surface antigens induced by retinoic acid or DMSO paralleled the expression pattern of these molecules in normal granulopoiesis, although maturation was not achieved and partially defective.

Neopterin release by myeloid leukaemic cells can be synergistically augmented by 1,25-dihydroxyvitamin D3 in combination with gamma interferon or granulocyte-macrophage colony stimulating factor

Neopterin is a pteridine molecule released by immune activated monocytes. Monocytic maturation may be induced in acute myeloid leukaemia (AML) blasts and the U937 leukaemic cell line by 1,25-dihydroxyvitamin D3 [1,25(OH)2D3], an effect which is augmented by both gamma interferon (IFN) or granulocyte-macrophage colony stimulating factor (GM-CSF). We have demonstrated that, while 1,25(OH)2D3 and GM-CSF alone have little effect, both IFN and GM-CSF act synergistically with 1,25(OH)2D3 to increase neopterin secretion in the U937 cell line. Neopterin secretion was associated with, but not necessarily dependent on, the degree of phenotypic differentiation achieved by cells. Neopterin secretion was also synergistically enhanced in AML blasts by the action of 1,25(OH)2D3 in combination with IFN but not GM-CSF; secretion was enhanced in AML blasts without concomitant evidence of phenotypic maturation. We have shown that the monocytoid cell line U937, under appropriate conditions, may secrete neopterin in response to stimulatory agents other than IFN. In addition, the distinct difference in the pattern of response to the combination of 1,25(OH)2D3 with GM-CSF compared with that of 1,25(OH)2D3 plus IFN suggests that the augmentation of 1,25(OH)2D3 effect by IFN and GM-CSF is mediated by separate mechanisms.