Enhanced mitogenic responsiveness to granulocyte-macrophage colony-stimulating factor in HL-60 promyelocytic leukemia cells upon induction of differentiation

Treatment of HL-60 leukemia cells with the inducers of differentiation dimethyl sulfoxide (DMSO) and 6-thioguanine (TG) reduces the proliferative capacity of the cells. DMSO acted in a serum-independent manner and reversibly inhibited competence to enter S phase after 24 h of treatment. Purified human granulocyte-macrophage colony-stimulating factor (GM-CSF) but not human CSF-1, restored S phase competence and growth of DMSO-treated cells over a 7-day period. GM-CSF had no effect on the saturation density of control cells, even under conditions of reduced growth. Furthermore, GM-CSF antagonized the growth inhibitory actions of TG associated with cytodifferentiation but not those associated solely with TG cytotoxicity. The number of high affinity, cell surface GM-CSF receptors doubled after treatment of HL-60 cells with DMSO for 24 h and reached a maximum 4- to 5-fold increase within 72 h of exposure. The Kd of GM-CSF binding, 240 pM, was comparable to the concentration required to elicit a mitogenic response in DMSO-treated cells. An HL-60 variant that had been selected for resistance to TG-induced growth inhibition and differentiation (R. E. Gallagher et al., Cancer Res., 44: 2642-2653, 1984) was found to have less than 20% of the cell surface GM-CSF receptors when compared to either wild type cells, or a variant line selected for resistance to TG cytotoxicity. These studies demonstrate that HL-60 cells undergoing differentiation simultaneously lose autonomous growth properties and acquire cell surface growth factor receptors and mitogenic responsiveness.     

Granulocyte colony-stimulating factor receptors on human acute leukemia: biphenotypic leukemic cells possess granulocyte colony-stimulating factor receptors.

Granulocyte colony-stimulating factor (G-CSF) receptors on the gated leukemic blast cells from newly diagnosed patients with acute leukemia or crisis of chronic myelogenous leukemia were investigated using flow cytometric detection. Surface marker analysis and cytochemical studies were conducted simultaneously to characterize the blast cells. Among 24 leukemia cases examined, G-CSF receptor-positive blast cells were detected in all 11 cases of acute myeloblastic leukemia even though the percentage range of positive cells was widely variable. On the other hand, they were not detected on the blast cells from patients with peroxidase-negative acute lymphoblastic leukemia with no myeloid surface antigens. However, G-CSF receptors were demonstrated in significant amounts on blast cells from 5 of 8 cases of peroxidase-negative acute leukemia expressing both myeloid and lymphoid surface antigens (biphenotypic leukemia). The percentage of blast cells positive for G-CSF receptors was significantly smaller in biphenotypic cases [33 +/- 14% (SD)] than in acute myeloblastic leukemia cases [65 +/- 22%] (P less than 0.01). The percentage expression of CD13 antigen by blast cells was significantly related to their percentage positivity for G-CSF receptors (rs = 0.50, P less than 0.05). These findings indicate that the distribution of flow cytometrically detectable G-CSF receptors on leukemic cells possessing myeloid characteristics may be related to the maturation process.     

Diphtheria toxin fused to granulocyte-macrophage colony-stimulating factor and Ara-C exert synergistic toxicity against human AML HL-60 cells.

Human granulocyte-macrophage colony-stimulating factor fused to truncated diphtheria toxin (DT388-GM-CSF) sensitized wild-type and Bcl2-overexpressing HL60 human leukemia cells to intoxication by Ara-C based on proliferation and clonogenic assays. The toxin/drug combination showed dramatic synergistic toxicity with combination indices of < 0.1. Synergy was not seen with two other protein synthesis inhibiting drugs--ricin and cycloheximide nor with GMCSF alone. No changes in Ara-C incorporation into cellular DNA or cell cycle occupancy were seen. As compared to exposure to DT388-GM-CSF or Ara-C alone, co-treatment produced significant increases in cytosolic accumulation of cytochrome c, a higher percentage of cells with loss of mitochondrial membrane potential and an increase in reactive oxygen species and morphologic changes of apoptosis, and a greater induction of poly(ADP-ribose) polymerase (PARP) and DNA fragmentation factor 45 (DFF45) cleavage activities of caspase 3. Co-treatment did not significantly alter Bcl2, Bcl-xL, Bax or Fas receptor (FasR), but modestly increased Fas ligand (FasL) protein. These finding suggest that co-treatment with DT388-GM-CSF may lead to a lowered apoptotic threshold and clonogenic survival of human AML blasts due to Ara-C. These observations also suggest that clinical trials of combination therapy may be warranted in patients with AML.     

Granulocyte colony-stimulating factor, granulocyte-macrophage colony-stimulating factor and macrophage colony-stimulating factor in the treatment of acute myeloid leukemia and acute lymphoblastic leukemia

The role of G-CSF, GM-CSF and M-CSF in the treatment of AML and ALL was reviewed. These CSFs significantly accelerate the neutrophil recovery after intensive chemotherapy, and reduce febrile neutropenia and documented infections. There is no clear evidence that CSFs accelerate early regrowth of AML cells at the doses and schedules presently used clinically except one study. Patients who have received CSFs tend to have a higher CR rate, which does not seem to be translated into definite survival benefit. There has been no prospective randomized study showing any beneficial priming effect of CSFs on AML cells with better clinical outcomes.     

Granulocyte colony-stimulating factor and granulocyte-macrophage colony-stimulating factor promote malignant growth of cells from head and neck squamous cell carcinomas in vivo

Granulocyte colony-stimulating factor (G-CSF) and granulocyte-macrophage colony-stimulating factor (GM-CSF) are used to ameliorate cancer therapy-induced neutropenia and mucositis. Yet, first data in head and neck squamous cell carcinoma (HNSCC) indicate an impaired long-term prognosis on G-CSF treatment, and previous studies showed a contribution of both factors to the progression of human epithelial tumors. Therefore, we investigate the role of G-CSF and GM-CSF in progression of tumor cells from human HNSCC. Both factors stimulated proliferation and migration of tumor cell lines established from patient tumors expressing G-CSF and GM-CSF and/or their receptors. Blockade of G-CSF and GM-CSF inhibited tumor cell invasion in a three-dimensional organotypic culture model. The contribution of both factors to tumor malignancy was further confirmed in nude mouse transplants in vivo. Invasive and malignant growth yielding a similar tumor phenotype as the original patient tumor was exclusively observed in G-CSF- and GM-CSF-expressing tumors and was associated with enhanced and persistent angiogenesis and enhanced inflammatory cell recruitment. Although factor-negative tumors grew somewhat faster, they were characterized by lack of invasion, reduced and transient angiogenesis, and large necrotic areas. These data provide evidence for a progression-promoting effect of G-CSF and GM-CSF in human HNSCC and suggest further detailed evaluation of their use in the therapy of these tumors.     

Induction of differentiation in HL-60 cells by retinoic acid and lymphocyte-derived differentiation-inducing factor but not by recombinant G-CSF and GM-CSF

Various concentrations of retinoic acid (RA, 10⁻⁹ to 10⁻⁷ M), lymphocyte-derived differentiation-inducing factor (DIF, 10–30%), and recombinant human G-CSF (100–4000 U/ml) and GM-CSF (100–4000 U/ml) were used to induce the differentiation of the HL-60 promyelocytic leukemia cells. Retinoic acid at a concentration of 10⁻⁷M could significantly inhibit the growth of HL-60 cells both in suspension and in soft agar cultures, and induced these cells to differentiate into mature granulocytes capable of reducing nitro-blue tetrazolium and ingesting latex beads. Thirty per cent (v/v) DIF was also an effective inducer of HL-60 cell differentiation, but it triggered the cells to mature into monocytes rather than granulocytes. In contrast, rG-CSF and rGM-CSF had no growth inhibitory effect on HL-60 cells either in suspension or in agar cultures at all concentrations tested, nor could these factors induce HL-60 cells to acquire the more mature granulocytic or monocytic phenotypes. Furthermore, rG-CSF/rGM-CSF had no differentiation-enhancing effect when added to RA-containing HL-60 cultures. These results argue against the efficacy of using CSFs for the treatment of myelocytic leukemia based on the principle of differentiation induction.     

The role of granulocyte-macrophage colony-stimulating factor in induction of monocytic differentiation of HL-60 cells: synergistic interaction with 1 alpha, 25-dihydroxyvitamin D3 and interferon-gamma in inducing interleukin-1 beta.

1 alpha, 25-Dihydroxyvitamin D3 (D3) (100 nM) and interferon-gamma (IFN-gamma) (100 U/ml) cooperatively inhibited the proliferation of HL-60 cells, and synergistically induced their monocytic differentiation. The growth-promoting effect of granulocyte-macrophage colony-stimulating factor (GM-CSF) (10 ng/ml) was inhibited appreciably by D3 and slightly by IFN-gamma. Despite the clear difference in their effects on growth of HL-60 cells, both IFN-gamma and GM-CSF in combination with D3 induced cell cycle changes, decreasing the number of cells in the S phase and increasing their percentage in the G1/0 phase. GM-CSF alone had no effect on differentiation, but enhanced differentiation induced by D3 distinctly though to a limited extent, and also enhanced monocytic differentiation, including morphological changes of HL-60 cells in the presence of D3 and IFN-gamma. GM-CSF as well as D3 and IFN-gamma induced interleukin-1 beta (IL-1 beta) production by the HL-60 cells, clearly indicating their importance in differentiation of these cells. IFN-gamma and GM-CSF had mutually potentiating effects and induced maximum IL-1 beta production in response to lipopolysaccharide (LPS) in the presence of D3. Thus despite its growth-promoting effect, GM-CSF is a potential inducer of monocytic differentiation of human myeloid leukemia cells, because in cooperation with IFN-gamma it induced monocyte-macrophage differentiation of HL-60 cells in the presence of D3.     

Lack of correlation between induction of chemotactic peptide receptors and stimulus-induced actin polymerization in HL-60 cells treated with dibutyryl cyclic adenosine monophosphate or retinoic acid

We used the promyelocytic leukemic cell line HL-60 to explore the molecular mechanisms regulating stimulus-induced actin polymerization in myeloid cells. HL-60 cells express very few chemotactic peptide receptors in their undifferentiated state and fail to undergo actin polymerization when stimulated with the chemotactic peptide N-formyl-methionyl-leucyl-phenylalanine (FMLP). However, when the cells were induced to differentiate with dibutyryl cyclic AMP (dbcAMP) or retinoic acid, they acquired the ability to undergo actin polymerization on stimulation with FMLP or phorbol myristate acetate. Kinetic experiments revealed that in the first 48 h of retinoic acid treatment there was no increase in the chemotactic peptide receptors on HL-60 cells, but the cells were capable of undergoing actin polymerization on stimulation with FMLP. Similarly, treatment with dbcAMP showed no increase in chemotactic peptide receptors until 24 h but stimulus-induced actin polymerization was demonstrable as early as 4 h after the treatment. In addition, with dbcAMP-treated cells the magnitude of stimulus-induced actin polymerization showed large variation depending on the duration of exposure to the drug. Dual-label studies using propidium iodide to measure DNA content and NBD-phallacidin to measure the F-actin content revealed that these variations were not related to the stages of cell cycle. Cells in all stages of the cell cycle responded to stimulus-induced actin polymerization, but the magnitude of the response appeared to be more in cells in G2/M phase. The observations reported here indicate that the small number of chemotactic peptide receptors present on HL-60 cells are adequate to mount an actin polymerization response, provided the required intracellular mechanisms exist. Differentiation-inducing agents, therefore, must cause changes within the cell, such as induction of actin-binding proteins, to cause actin polymerization following FMLP stimulation. The HL-60 system serves as a useful model for studying the molecular mechanisms regulating stimulus-induced actin polymerization in human neutrophils.     

Granulocyte, granulocyte-macrophage, and macrophage colony-stimulating factors can stimulate the invasive capacity of human lung cancer cells.

We and other researchers have previously found that colony-stimulating factors (CSFs), which generally include granulocyte colony-stimulating factor (G-CSF), granulocyte-macrophage colony-stimulating factor (GM-CSF) and macrophage colony-stimulating factor (M-CSF), promote invasion by lung cancer cells. In the present study, we studied the effects of these CSFs on gelatinase production, urokinase plasminogen activator (uPA) production and their activity in human lung cancer cells. Gelatin zymographs of conditioned media derived from human lung adenocarcinoma cell lines revealed two major bands of gelatinase activity at 68 and 92 kDa, which were characterized as matrix metalloproteinase (MMP)-2 and MMP-9 respectively. Treatment with CSFs increased the 68- and 92-kDa activity and converted some of a 92-kDa proenzyme to an 82-kDa enzyme that was consistent with an active form of the MMP-9. Plasminogen activator zymographs of the conditioned media from the cancer cells showed that CSF treatment resulted in an increase in a 48-55 kDa plasminogen-dependent gelatinolytic activity that was characterized as human uPA. The conditioned medium from the cancer cells treated with CSFs stimulated the conversion of plasminogen to plasmin, providing a direct demonstration of the ability of enhanced uPA to increase plasmin-dependent proteolysis. The enhanced invasive behaviour of the cancer cells stimulated by CSFs was well correlated with the increase in MMPs and uPA activities. These data suggest that the enhanced production of extracellular matrix-degrading proteinases by the cancer cells in response to CSF treatment may represent a biochemical mechanism which promotes the invasive behaviour of the cancer cells.     

三羟基苯甲酸诱导HL-60细胞凋亡的实验性研究

目的 观察3,4,5-三羟基苯甲酸对HL-60细胞的增殖抑制及诱导其凋亡的作用。方法 MTT法检测3.125、6.25、12.5、25、50、100μg/mL TBA对HL-60细胞生长的抑制作用,吖啶橙荧光染色、流式细胞仪检测细胞凋亡;结果 TBA显著抑制HL-60细胞的增殖,其作用呈剂量依赖性。18.7μg/mL TBA作用HL-60细胞48小时后AO染色,荧光显微镜下可见细胞出现体积缩小,核碎裂、染色质凝集等凋亡形态改变,HL-60细胞凋亡率为(28.24±5.24)%、与对照组(2.53±0.56)%比较差异有显著性意义(P＜0.05)。结论 TBA可能通过诱导HL-60细胞凋亡抑制其生长。     

Reversible effects of retinoic acid on glycosaminoglycan synthesis during differentiation of HL-60 leukemia cells

Glycosaminoglycans (GAGs) play an important role in cell-cell and cell-substratum interactions, and undergo specific changes during neutrophil development. Previous studies (Luikart, S.D., Maniglia, C. A., and Sartorelli, A. C. Cancer Res., 44: 2907-2912, 1984) have shown that both dimethyl sulfoxide and 4-beta-phorbol-12-beta-myristate-13-alpha-acetate decreased GAG production by a hypoxanthine-guanine phosphoribosyl transferase-deficient clone of HL-60 promyelocytic leukemia cells prior to the appearance of a mature myeloid or monocytoid phenotype. To expand these investigations further, GAGs were analyzed by cetylpyridinium chloride precipitation and DEAE-Sephacel ion-exchange chromatography after labeling of parental HL-60 cultures with [35S]sulfate and D-[3H]glucosamine for 6 h, following treatment with 1 microM all-trans retinoic acid (RA). Chondroitin sulfate represented the major GAG species produced, although endo-beta-galactosidase-sensitive undersulfated macromolecules which possibly might be keratan sulfate, were also identified. GAG production decreased over a time period of 144 h in culture. RA treatment reduced the amount of radiolabeled cell-associated GAGs by 50% after 48, 96, and 144 h of exposure. In contrast, commitment to myelocytic maturation of the majority (i.e., approximately 60%) of the cells occurred between 72 and 96 h of RA treatment. Concurrently with the appearance of mature granulocytic cells, two-thirds of the radiolabeled GAGs were recovered from the medium, compared to one-third in untreated cultures, a phenomenon that resulted in an overall alteration in the distribution of GAGs. When RA was removed by washing after either 48 h (i.e., precommitment to differentiation) or 96 h (i.e., postcommitment to differentiation), a 1.5- to 3.5-fold increase in GAG production was noted 48 h later; this increase was unrelated to the medium change or to alterations in cell cycle distribution. The amounts of endo-beta-galactosidase-sensitive macromolecules were unaltered. Thus, although 1 microM RA inhibited the synthesis of chondroitin sulfate by HL-60 leukemia cells, this inhibition was reversible by removal of the drug and appeared to be unrelated to the commitment to myelocytic maturation.     

Synergistic induction of the differentiation of WEHI-3B D+ myelomonocytic leukemia cells by retinoic acid and granulocyte colony-stimulating factor.

Retinoic acid (RA) has been shown to be an inducer of the terminal differentiation of several leukemia cell lines in vitro and in clinical trials to produce a high percentage of remissions in patients with acute promyelocytic leukemia. In an effort to increase the therapeutic efficacy of RA, we have measured the capacity of granulocyte colony-stimulating factor (G-CSF) to enhance the differentiation inducing activity of RA in WEHI-3B D+ monomyelocytic leukemia cells. Combinations of G-CSF and RA produced a supra-additive increase in the percentage of WEHI-3B D+ cells reducing nitro blue tetrazolium and expressing Mac-1 (CD11b) antigen on the cell surface, two markers of the mature state. In the presence of 50 ng/ml of G-CSF, which produced only 12% differentiation when used alone, 0.5 microM RA induced the same degree of cellular differentiation as the optimum concentration of RA (i.e. 7 microM) employed alone. The supra-additive differentiation produced by this combination was prevented by the presence of G-CSF monoclonal antibody in the culture medium, resulting in a degree of maturation comparable to that produced by the retinoid alone. When cells were sequentially exposed to G-CSF followed by RA, a much higher level of differentiation was obtained than when the order was reversed, suggesting that WEHI-3B D+ cells were primed to enter a differentiation pathway by G-CSF. The supra-additive terminal differentiation exhibited by the mixture of G-CSF and RA suggests that these agents should be evaluated for the therapeutic efficacy of the combination in patients with acute non-lymphocytic leukemia.     

全反式维甲酸对HL-60细胞hTERT基因表达和端粒酶活性的影响

目的 探讨全反式维甲(ATRA)诱导HL-60细胞分化过程中人类端粒酶逆转录酶(hTERT)蛋白表达和端粒酶活性的改变。 方法 应用间接免疫荧光标记法通过流式细胞仪检测hTERT蛋白含量的变化;采用多聚酶链反应-酶联免疫反应(PCR-ELISA)方法检测ATRA处理HL-60细胞前后端粒酶活性的改变,用碘化丙锭染色经流式细胞仪检测细胞周期变化。 结果 1μmol/L ATRA作用HL-60细胞24、48、72h,hTERT蛋白平均荧光强度分别为61.87±4.36、37.47±2.85、33.45±2.37,与空白对照组相比,具有显著性差异,P<0.05。1μmol/L ATRA作用48h后,HL-60细胞的端粒酶活性即出现下降,作用72h,端粒酶的活性明显受到抑制。 结论 在HL-60细胞分化过程中,ATRA能抑制HL60细胞的hTERT基因的表达和端粒酶活性。     

Human granulocyte-macrophage colony-stimulating factor is a growth factor active on human ovarian cancer cells.

Human granulocyte-macrophage colony-stimulating factor (GM-CSF) is a regulatory glycoprotein that stimulates the production of granulocytes and macrophages from committed hematopoietic progenitor cells both in vitro and in vivo. In this report, we show that recombinant human GM-CSF enhances colony formation by nonhematopoietic human ovarian cancer cell lines, IGROV-1, A2774, ME-180, Pa-1 and A2780. GM-CSF also enhanced the colony formation by cells obtained from fresh ascites of a patient with ovarian mucinous cystadenocarcinoma and a patient with serous papillary ovarian carcinoma. Our observations were made with GM-CSF concentrations between 0.1 to 1 ng/ml; these concentrations are equivalent to the dosages generally used for bone marrow recovery after chemotherapy.     

Effect of protein kinase inhibitors on the proliferation of leukemic cells stimulated by granulocyte colony-stimulating factor, granulocyte-macrophage colony-stimulating factor or interleukin-3.

The effects of the inhibitor for protein kinase A or C, or tyrosine kinase (H-8, staurosporine, or genistein, respectively) on the proliferation of leukemic and normal bone marrow cells stimulated by granulocyte colony-stimulating factor (G-CSF), granulocyte-macrophage colony-stimulating factor (GM-CSF), or interleukin-3 (IL-3) were studied using the MTT assay. These inhibitors suppressed the proliferation of leukemic and normal bone marrow cells in a dose-dependent manner. Although the suppressive effect of each inhibitor on cell proliferation was varied in each instance, the effects were almost similar whichever CSF was added. A significant difference was not recognized between leukemic and normal bone marrow cells in terms of sensitivity to these inhibitors. The data indicate that protein kinase inhibitors have an inhibitory effect on leukemic and normal hematopoietic cell proliferation and that further studies are required to determine if this effect is due to the inhibition of protein kinases acting as the second messenger of CSFs.     

Granulocytic differentiation induced by retinoic acid in HL-60 cells is associated with changes in adenylate cyclase activity

The effect of all-trans Retinoic Acid (RA) on the activity of membrane bound adenylate cyclase (AC) of human malignant cell lines (HL-60 and U-937) was studied. Granulocytic terminal differentiation of the HL-60 cells was correlated to an increase of AC activity and to a potentiation of guanosine 5' triphosphate (GTP) inhibitory effects on the enzyme activity. No direct in vitro effect of RA on HL-60 membranes was found. Monocytic terminal differentiation obtained on 1 B-D arabinofuranosyl cytosine (Ara-C) treated HL-60 cells, or on RA treated U-937 cells, did not modify AC activity. The results here reported suggest relations between the modification of GTP binding protein activity and RA induced granulocytic differentiation of malignant cells.     

全反式维甲酸和佛波酯对HL-60细胞表面N-糖链结构的影响

目的：研究肿瘤细胞分化时细胞膜上糖链结构的改变。方法：通过蛋白酶消化提取细胞表面＾３Ｈ标记Ｎ－糖链,结合外切糖苷酶处理,经序列凝纱亲和层析分析ＨＬ－６０细胞诱导分化后细胞表面Ｎ－糖链结构。结果：全反式维甲（ＡＴＲＡ）和佛波醇－１２豆莞酰－１３－乙酸酯（ＰＭＡ）均引起ＨＬ－６０细胞二天线复杂型和高甘露糖型糖链升高,多天线复杂型糖链减少。但对平分型β－Ｎ－乙酰氨基葡萄糖（ＧｌｃＮＡｃ）糖基的影响却相反     

Granulocyte colony-stimulating factor potentiates differentiation induction by all-trans retinoic acid and arsenic trioxide and enhances arsenic uptake in the acute promyelocytic leukemia cell line HT93A

The effects of arsenic trioxide (ATO), all-trans retinoic acid (ATRA) and granulocyte colony-stimulating factor (G-CSF), alone or in combination, were investigated by focusing on differentiation, growth inhibition and arsenic uptake in the acute promyelocytic leukemia (APL) cell line HT93A. ATO induced differentiation at low concentrations (0.125?μM) and apoptosis at high concentrations (1-2?μM). Furthermore, ATRA induced greater differentiation than ATO. No synergistic effect of ATRA and ATO was found on differentiation. G-CSF promoted differentiation-inducing activities of both ATO and ATRA. The combination of ATRA and G-CSF showed maximum differentiation and ATO addition was not beneficial. Addition of 1?μM ATRA and/or 50?ng/ml G-CSF to ATO did not affect apoptosis compared to ATO treatment alone. ATRA induced expression of aquaporin-9 (AQP9), a transmembrane transporter recognized as a major pathway of arsenic uptake, in a time- and dose-dependent manner. However, treatment with 1?μM ATRA decreased arsenic uptake by 43.7% compared to control subject. Although G-CSF addition did not enhance AQP9 expression in the cells, the reduced arsenic uptake was recovered to the same level as that in controls. ATRA decreased cell viability and addition of 50?ng/ml G-CSF to ATRA significantly increased the number of viable cells compared with that in ATRA alone treated cells. G-CSF not only promotes differentiation-inducing activities of both ATRA and ATO, but also makes APL cells vulnerable to increased arsenic uptake. These observations provide new insights into combination therapy using these three agents for the treatment of APL.     

Quantitative morphological aspects of granulocytic differentiation induced in HL-60 cells by dimethylsulfoxide and retinoic acid

HL-60 cells differentiate to mature granulocytes when cultured with DMSO or retinoic acid. These two drugs can induce different expression of phenotypic or functional properties in these cells. The morphological characteristics of the differentiation sequences elicited by these two drugs have been therefore evaluated by a quantitative cytological analysis technique using a SAMBA 200 cell image processor. The maturation sequences induced by DMSO or retinoic acid differed mainly in nuclear geometry and cytoplasmic granules expression. Multivariate statistical analyses of data reveal that DMSO and retinoic acid elicited granulocytic maturation through two separate morphological pathways which can be individualized as early as 24 hr after differentiation induction. Image processing may therefore offer an interesting tool for studying new drugs with differentiation potential in chemotherapy.     

Characterization of two novel retinoic acid-resistant cell lines derived from HL-60 cells following long-term culture with all-trans-retinoic acid.

Either all-trans-retinoic acid (RA) or vitamin D3 (VD) induces differentiation of the myeloid leukemia cell line HL-60. RA is available for the treatment of acute promyeloleukemia, although the development of resistance to the agent is a serious problem for differentiation-inducing therapy. To approach the mechanisms of resistance to RA, we developed two novel cell lines, HL-60-R2 and R9, which were subcloned after exposure to increasing concentrations of RA. The growth rate of HL-60-R2 cells was significantly increased by RA treatment, whereas the growth rate of HL-60-R9 was not affected. RA induces apoptosis in the parental HL-60 cells. The number of apoptotic cells, however, was not increased and nitroblue tetrazolium (NBT) reduction was not altered by 1 microM RA in either of the cloned cell lines. Treatment with VD induced monocytic differentiation and increased the expression of CD11b in HL-60 and HL-60-R9 cells, but not in HL-60-R2 cells. Flow cytometric and G-banding analysis demonstrated that R2 cells were near-triploid. The sequencing analysis revealed a deletion of three nucleotides in the sequence of the RAR alpha gene in HL-60-R9 cells, resulting in deletion of codon 286. No mutation was found in HL-60-R2 cells. Taken together, these data indicate that the resistance to RA is caused by the mutation in RAR alpha of HL-60-R9, but by other factor(s), which also affect the VD-response pathways, in HL-60-R2. The abnormal response to VD may be associated with the abnormal ploidy of the R2 cells.