Lipoteichoic acid derived from Enterococcus faecalis modulates the functional characteristics of both normal peripheral blood leukocytes and native human acute myelogenous leukemia blasts

OBJECTIVES: Several case reports have described complete hematological remissions for patients with otherwise untreated acute myelogenous leukemia (AML) who receive hematopoietic growth factor therapy during complicating bacterial infections. This may be caused by indirect cytokine effects, but direct effects of infecting agents on the malignant cells are also possible because bacterial molecules can bind to specific receptors expressed by normal and malignant leukocytes. Lipoteichoic acid (LTA) is a cell wall component of gram-positive bacteria, and it can activate normal immunocompetent cells through binding to specific cell membrane receptors. METHODS: We investigated effects of LTA derived from Enterococcus faecalis on in vitro cultured (i) normal peripheral blood mononuclear cells (PBMC); (ii) remaining T cells derived from patients with hematologic malignancies and chemotherapy-induced leukopenia; and (iii) native human AML cells. RESULTS: Increased interleukin 1beta (IL1beta) and IL8 release by in vitro cultured normal PBMC was observed after stimulation with LTA at concentrations > or =5 microg/mL; these levels were lower than for lipopolysaccharide (LPS)-stimulated cells and LTA antagonized LPS-induced cytokine release by normal PBMC. In most cases LTA did not alter T-cell proliferation for patients with chemotherapy-induced leukopenia. The LTA effects on AML blasts were investigated for 62 consecutive patients. LTA altered either cytokine (granulocyte-macrophage colony-stimulating factor + stem cell factor + IL3)-dependent proliferation or the release of IL1beta/IL8 for 23 patients; the effects were divergent but increased proliferation/cytokine levels were most commonly observed. CONCLUSION: The LTA derived from E. faecalis can modulate the functional characteristics of normal leukocytes and native human AML blasts.     

Effects of acute myelogenous leukemia blasts on platelet release of soluble P-selectin and platelet-derived growth factor

Complex interactions occur between platelets and normal as well as leukemic myeloid cells. In vitro co-culture of platelets and acute myelogenous leukemia (AML) blasts with allogeneic platelets enhances blast proliferation and constitutive cytokine secretion. In the present study the effects of AML blasts on the platelet release of soluble mediators are characterized. Normal platelets released soluble (s) P-selectin and platelet-derived growth factor (PDGF), both when cultured alone and in the presence of AML blasts, and for certain patients the presence of AML blasts increased the platelet release of these mediators.Addition of exogenous interleukin (IL) 10 to platelet-AML blast cultures further increased platelet release of PDGF and sP-selectin. For certain patients decreased AML blast cytokine secretion was observed when PDGF-specific antibodies were added to cultures with blasts plus platelets, these results indicate that platelet release of PDGF is a molecular mechanism for the enhancement of AML blast cytokine secretion. We conclude that complex functional alterations are induced both in AML blasts and normal allogeneic platelets during in vitro co-culture of leukemia cells and platelets.     

Flt3-mediated signaling in human acute myelogenous leukemia (AML) blasts: a functional characterization of Flt3-ligand effects in AML cell populations with and without genetic Flt3 abnormalities

BACKGROUND AND OBJECTIVES: Intracellular signaling initiated via Flt3 seems important in both leukemogenesis and chemosensitivity in acute myelogenous leukemia (AML). Flt3 is activated by binding of its natural Flt3-ligand (Flt3-L), but Flt3 genes with internal tandem duplications (Flt3-ITD) or Asp(D)-835 point mutations encode molecules with constitutive activation. The aim of this study was to compare functional effects of exogenous Flt3-L on AML blast populations with and without genetic Flt3 abnormalities. DESIGN AND METHODS: Native AML blasts were derived from 64 consecutive patients with high blast counts in peripheral blood, and in vitro models were used to characterize the Flt3-L effects. RESULTS: The Flt3 protein levels showed a similar wide variation between AML blast populations with and without genetic Flt3 abnormalities. Flt3-L was an autocrine growth factor only for 2 patients. Flt3-ITD+ AML cells had lower responsiveness to exogenous cytokines than cell populations without Flt3 abnormalities, but exogenous Flt3-L increased blast proliferation both for patients without Flt3 abnormalities and patients with Flt3-ITD as well as D835 mutations. This enhancement was observed even in the presence of other exogenous cytokines and included clonogenic AML progenitors. Flt3-L inhibited proliferation only for 1 patient, but had divergent effects on AML blast cytokine release. Flt3-L affected AML blast differentiation (inhibition of erythroid colonies, increased neutrophil granulation) only in a minority of patients, whereas it had an anti-apoptotic effect for a larger subset of patients. INTERPRETATION AND CONCLUSIONS: Intracellular signaling initiated by Flt3 ligation modulates the functional phenotype for native human AML blasts both with and without genetic Flt3 abnormalities.     

Serum leptin level in acute myeloid leukemia patients

Leptin is a regulator of fat metabolism that is synthesized in adipocytes and released into circulation. The serum levels of leptin are, therefore, correlated with body fat mass and show a wide variation in healthy individuals. Leptin may have an additional indirect effect on leukemic hematopoesis. We investigated serum leptin levels with enzyme-linked immunosorbent assays in 14 acute myeloblastic leukemia (AML) patients before and after chemotherapy and compared the results with that of the levels determined 14 healthy controls. We found no significant difference between leptin levels before and after chemotherapy and control group. Therefore, serum leptin level should not be used as a diagnostic marker in acute leukemia patients. However, the possibility of regional leptin production by leukemia blasts in bone marrow stroma creates a high local concentration of leptin within bone marrow microenvironment and systemic leptin level in combination with local leptin production may affect leukemic hematopoesis.     

In vitro effects of insulin-like growth factor-1 (IGF-1) on proliferation and constitutive cytokine secretion by acute myelogenous leukemia blasts

The effects of insulin-like growth factor 1 (IGF-1) on autonomous proliferation, cytokine-dependent proliferation and constitutive cytokine secretion by acute myelogenous leukemia (AML) blasts were investigated using serum-free in vitro conditions. IGF-1 enhanced AML blast proliferation independent of the presence of other exogenous cytokines only for 2 of 21 patients, but for 10 additional patients IGF-1 altered blast proliferation in the presence of certain exogenous cytokines or cytokine combinations. IGF-1 had minor effects on AML blast cytokine secretion only for a subset of the patients (decreased levels for 1 patient, increased levels for 7 patients). Our in vitro observations indicate that IGF-1 can modulate AML blast proliferation and/or cytokine secretion for a subset of patients.     

Platelet-derived growth factor (PDGF) in human acute myelogenous leukemia: PDGF receptor expression, endogenous PDGF release and responsiveness to exogenous PDGF isoforms by in vitro cultured acute myelogenous leukemia blasts

We investigated effects of Platelet-derived growth factor (PDGF) and Platelet factor 4 (PF-4) on the functional characteristics of native, human acute myelogenous leukemia (AML) blasts. AML blast expression of the PDGF-receptor alpha-chain was detected for a subset of patients (45%), whereas PDGF-receptor beta-chain expression was detected for most patients (90%). Constitutive AML blast release of the PDGF-AB isoform (the major form also derived from normal platelets) was detected for 43% of patients, whereas PDGF-BB release was not detected for any patient. The PDGF isoforms AA, AB and BB had dose-dependent and divergent effects on spontaneous and cytokine-dependent AML blast proliferation, whereas for constitutive cytokine secretion (IL-1beta, IL-6, TNF-alpha) inhibitory effects were rare and all three isoforms usually had no effect or enhanced the constitutive secretion. The PDGF effects were caused by a direct effect on the AML blasts and were not dependent on the presence of serum. The PDGF effects could also be detected after in vitro culture of AML cells in the presence of IL-4+granulocyte-macrophage colony stimulating factor. PF-4 had divergent effects on proliferation and cytokine secretion by native AML blasts. Our results suggest that exogenous (e.g. platelet-secreted) PDGF and PF-4 can function as regulators of leukemic hematopoiesis and possibly also modulate the function of residual AML cells in peripheral blood stem cell grafts. On the other hand, endogenous release of PDGF-AB by native blasts may modulate the function of normal cells in the bone marrow microenvironment (e.g. bone marrow stromal cells).     

Platelet-derived growth factor (PDGF) in human acute myelogenous leukemia: PDGF receptor expression, endogenous PDGF release and responsiveness to exogenous PDGF isoforms by in vitro cultured acute myelogenous leukemia blasts

We investigated effects of Platelet-derived growth factor (PDGF) and Platelet factor 4 (PF-4) on the functional characteristics of native, human acute myelogenous leukemia (AML) blasts. AML blast expression of the PDGF-receptor alpha-chain was detected for a subset of patients (45%), whereas PDGF-receptor beta-chain expression was detected for most patients (90%). Constitutive AML blast release of the PDGF-AB isoform (the major form also derived from normal platelets) was detected for 43% of patients, whereas PDGF-BB release was not detected for any patient. The PDGF isoforms AA, AB and BB had dose-dependent and divergent effects on spontaneous and cytokine-dependent AML blast proliferation, whereas for constitutive cytokine secretion (IL-1beta, IL-6, TNF-alpha) inhibitory effects were rare and all three isoforms usually had no effect or enhanced the constitutive secretion. The PDGF effects were caused by a direct effect on the AML blasts and were not dependent on the presence of serum. The PDGF effects could also be detected after in vitro culture of AML cells in the presence of IL-4+ granulocyte-macrophage colony stimulating factor. PF-4 had divergent effects on proliferation and cytokine secretion by native AML blasts. Our results suggest that exogenous (e.g. platelet-secreted) PDGF and PF-4 can function as regulators of leukemic hematopoiesis and possibly also modulate the function of residual AML cells in peripheral blood stem cell grafts. On the other hand, endogenous release of PDGF-AB by native blasts may modulate the function of normal cells in the bone marrow microenvironment (e.g. bone marrow stromal cells).     

Effects of normal platelets on proliferation and constitutive cytokine secretion by human acute myelogenous leukaemia blasts

The effects of soluble E-selectin, P-selectin and normal platelets on acute myelogenous leukaemia (AM L) blasts were investigated in vitro. We investigated effects on spontaneous and cytokine-dependent blast proliferation, and constitutive blast secretion of different cytokines. The presence of normal platelets during in vitro culture caused a dose-dependent increase in both spontaneous and cytokine-dependent AML blast proliferation. Addition of platelets also increased constitutive blast secretion of Interleukin 1beta (IL1beta ), IL6, GM-CSF and TNFalpha, whereas platelets had no effect on the release of IL1 receptor antagonist. The effects of platelets on constitutive cytokine secretion were also detected when platelets and AML blasts were cultured in different chambers separated by a permeable membrane, and a further enhancement was achieved when blasts and platelets were cultured together. Soluble P-selectin had no effect on constitutive AML blast cytokine secretion or the platelet-induced enhancement of the secretion. However, both soluble E- and P-selectin altered AML blast proliferation for a minority of patients. We conclude that normal platelets can modulate the function of human AML blasts in vitro.     

Effects of normal platelets on proliferation and constitutive cytokine secretion by human acute myelogenous leukaemia blasts

The effects of soluble E-selectin, P-selectin and normal platelets on acute myelogenous leukaemia (AM L) blasts were investigated in vitro . We investigated effects on spontaneous and cytokine-dependent blast proliferation, and constitutive blast secretion of different cytokines. The presence of normal platelets during in vitro culture caused a dose-dependent increase in both spontaneous and cytokine-dependent AML blast proliferation. Addition of platelets also increased constitutive blast secretion of Interleukin 1 beta (IL1 beta ), IL6, GM-CSF and TNF alpha , whereas platelets had no effect on the release of IL1 receptor antagonist. The effects of platelets on constitutive cytokine secretion were also detected when platelets and AML blasts were cultured in different chambers separated by a permeable membrane, and a further enhancement was achieved when blasts and platelets were cultured together. Soluble P-selectin had no effect on constitutive AML blast cytokine secretion or the platelet-induced enhancement of the secretion. However, both soluble E- and P-selectin altered AML blast proliferation for a minority of patients. We conclude that normal platelets can modulate the function of human AML blasts in vitro .     

Effects of angiogenic regulators on in vitro proliferation and cytokine secretion by native human acute myelogenous leukemia blasts

Angiogenesis seems to be important in the pathogenesis of acute myelogenous leukemia (AML). The endothelial cell proliferation and microvessel formation are regulated by a wide range of soluble mediators, including angiogenin, angiopoietin-2, basic fibroblast growth factors, vascular endothelial growth factor (VEGF), VEGF-D, angiostatin and endostatin. In the present study, it has been investigated whether these mediators have an additional direct effect on the proliferation and cytokine release by native human AML blasts. AML cells derived from a large group of consecutive patients were investigated. All these mediators could alter the proliferation and cytokine release [interleukin (IL) 1beta, IL6, IL8, tumor necrosis factor alpha] for a minority of patients. Alteration of spontaneous proliferation by at least one mediator was detected in five of 38 patients; whereas, altered cytokine (Flt3-ligand, granulocyte-macrophage colony-stimulating factor, stem cell factor)-dependant proliferation was observed for 10 patients. Growth enhancement was most frequently observed, whereas growth inhibition was uncommon. The effects on AML blast proliferation were often dependant on or were modulated by the presence of the three hematopoietic growth factors. Based on the present results, it is concluded that angioregulatory mediators have additional growth-enhancing effects directly on the AML blasts for certain patients. However, based on the results from this investigation and previous studies it is suggested that their major contribution to the pathogenesis of AML is through their effects on regulation of bone marrow angiogenesis, and future studies of these mediators in AML should probably focus on these effects.     

Granulocyte colony-stimulating factor enhances the in vitro cytotoxicity of gemtuzumab ozogamicin against acute myeloid leukemia cell lines and primary blast cells

OBJECTIVE: To evaluate the effects of granulocyte colony-stimulating factor (G-CSF) on the in vitro sensitivity of acute myeloid leukemia (AML) cell lines and primary AML blast cells to gemtuzumab ozogamicin (GO). MATERIALS AND METHODS: AML cell lines and primary blasts from 10 patients with AML were first incubated for 72 hours in the presence of G-CSF (5 or 100 ng/mL) and then exposed to increasing concentrations of GO (1-1,000 ng/mL) for an additional 72 hours. RESULTS: Pretreatment with G-CSF translated into significant enhancement of GO-induced cytotoxicity in the GO-sensitive HL-60 and NB-4 cells. Conversely, the response of GO-insensitive KG-1a, TF-1, and K562 cells was unaffected by in vitro priming with G-CSF. In vitro exposure to G-CSF augmented GO-induced apoptosis in 7 of 10 primary AML samples and rendered blast cells from three refractory patients sensitive to killing effect of GO. The G-CSF-induced increase of the cytocidal activity of GO was independent of effects on the cell cycle and on the expression levels of CD33 antigen. Of potential interest, G-CSF induced dose-dependent inhibition of P-glycoprotein (P-gp/ABCB1) function in the GO-sensitive HL-60 and NB-4 cells and in blasts from three patients with AML that we tested. CONCLUSION: Collectively, our findings point to G-CSF as a potential sensitizing agent that can be exploited therapeutically to improve the clinical efficacy of GO.     

The angioregulatory phenotype of native human acute myelogenous leukemia cells: influence of karyotype,Flt3 abnormalities and differentiation status

INTRODUCTION: The cytogenetic abnormalities and the response to induction therapy have been regarded as the most important prognostic parameters in acute myelogenous leukemia (AML) patients. Recent studies have demonstrated that internal tandem duplications and specific D-835 point mutations of the Flt3 gene, as well as the angioregulatory phenotype represent additional adverse prognostic factors. The aim of the study was to investigate possible associations between genetic abnormalities, differentiation status and angioregulatory phenotype in native human AML blasts. METHOD: Native AML blasts derived from consecutive patients were cultured in vitro and concentrations of angioregulatory molecules determined in the supernatants. RESULTS: Most patients released at least two different angioregulatory mediators. Pro-angiogenic interleukin 8 (IL8) was released at relatively high levels for most patients, many of these patients showed additional release of pro-angiogenic vascular endothelial growth factor (VEGF) and hepatocyte growth factor (HGF). High release of anti-angiogenic IL12 was associated with high release of pro-angiogenic IL8 and VEGF. Furthermore, patients with D-835 mutations showed increased IL12 release, whereas patients with normal karyotype had decreased HGF release. Myelomonocytic differentiation was associated with IL18 release and CD34 expression with low IL12 release. CONCLUSION: Our results suggest that native human AML blasts have a pro-angiogenic phenotype. Although the investigated genetic abnormalities are associated with variation in the in vitro release of angioregulators, these differences are relatively small and do not quantitatively involve the most important IL8 release. It therefore seems unlikely that this phenotypic variation can explain the prognostic impact of the genetic abnormalities.     

Comparison of in vivo and in vitro effects of granulocyte-macrophage colony-stimulating factor (GM-CSF) in patients with acute myeloid leukemia.

We studied the in vitro effects of granulocyte-macrophage colony-stimulating factor (GM-CSF) in 13 patients with acute myeloid leukemia (AML) and one patient with refractory anemia with excess of blasts in transformation using the AML blast (AML colony-forming units, AML-CFU) and mixed (granulocyte erythrocyte macrophage megakaryocyte colony-forming units, CFU-GEMM) colony culture assays. In parallel, these patients received GM-CSF s.c. at 125 micrograms/m2/day, or in escalated doses starting with 10 micrograms/m2/day for a week or until circulating blast counts reached 50 x 10(9)/liter, in an effort to sensitize leukemic blasts to cell-cycle-specific agents. Results of in vivo GM-CSF treatment were correlated with those of in vitro assays. In 9 of 12 patients (75%), GM-CSF treatment increased peripheral blood blast counts (in vivo effect). GM-CSF also stimulated in vitro AML blast colony proliferation in these nine patients and increased the S+G2M phases of the cell cycle in five out of five of these patients' samples. Two of three patients in whom an in vivo response could not be demonstrated also failed to have a detectable in vitro response. These observations suggest that the AML blast colony culture assay may be useful in predicting the response of AML to cytokine therapy. Finally, GM-CSF stimulated granulocyte-macrophage (granulocyte-macrophage colony-forming units, CFU-GM) and erythroid (erythroid burst-forming units, BFU-E) colony proliferation in 14 and 11 patients, respectively, including the 3 individuals who demonstrated no clinical effect on blast counts. It is, therefore, possible that GM-CSF may be used to stimulate proliferation of progenitors that differentiate into mature granulocyte, monocyte-macrophage, and erythroid cells.     

Circulating thrombopoietin as an in vivo growth factor for blast cells in acute myeloid leukemia

Thrombopoietin (TPO), the major growth factor for cells of the megakaryocytic lineage, is removed from circulation by binding to c-mpl receptors present on platelets and megakaryocytes. We studied patients with acute lymphoblastic leukemia (ALL) or acute myeloblastic leukemia (AML) and used TPO-induced c-fos protein up-regulation as a marker of c-mpl functionality and observed that c-mpl-presenting blast cells were present in 62% (37 of 60) of patients with ALL but that c-mpl was nonfunctional in 0 of 28 patients and that they were present in 56% (22 of 39) of patients with AML and were functional in 43% (12 of 28). Adequate increases in serum TPO level in response to thrombocytopenia were seen in patients with ALL and with c-mpl-deficient (c-mpl-) AML. In contrast, in patients with c-mpl-proficient (c-mpl+) AML, TPO levels were found to be inappropriately low but increased to expected values during induction chemotherapy as blasts disappeared. In vitro significant TPO-associated blast cell proliferation or decreased apoptosis was observed only in patients with c-mpl+ AML compared with ALL or c-mpl- AML and was highly correlated with low in vivo TPO levels (P < .001). These data suggest that, in patients with AML, inadequate TPO levels are secondary to TPO clearing by functional c-mpl receptor myeloid blast cells and that TPO may serve as an in vivo myeloid leukemic growth factor in a significant number of patients.     

Effects of purified human native granulocyte colony-stimulating factor (G-CSF) on proliferation of blast progenitors in acute myeloblastic leukemia

Blast progenitors in acute myeloblastic leukemia (AML) grow in methylcellulose and suspension cultures. Blast colony formation in methylcellulose culture reflects the terminal divisions of blast progenitors, while secondary colony formation, by replating in methylcellulose and recovering clonogenic cells in suspension culture, reflects the self-renewal of blast progenitors. To analyze the regulatory mechanisms of the proliferation of leukemic blast progenitors, the effects of highly purified native granulocyte colony-stimulating factor (G-CSF) obtained from human squamous cell carcinoma line (CHU-2) on blast progenitors in AML patients were studied in methylcellulose and suspension cultures. Purified G-CSF stimulated the growth of blast progenitors in both culture systems, although sensitivity to G-CSF varied from patient to patient. No obvious maturation of leukemic blasts was noted in suspension culture in the presence of G-CSF. The data suggest that a normal hemopoietic regulator may play a role in the growth of blast progenitors in AML patients.     

Coculture of native human acute myelogenous leukemia blasts with fibroblasts and osteoblasts results in an increase of vascular endothelial growth factor levels

Abstract:  Objectives : Angiogenesis seems important in the development of acute myelogenous leukemia (AML). Proangiogenic vascular endothelial growth factor (VEGF) is constitutively secreted by the AML blasts for a subset of patients, but it can also be released by non-leukemic bone marrow cells. Methods : VEGF levels were determined after coculture of native human AML blasts with fibroblast lines, osteoblastic sarcoma cell lines, normal bone marrow stromal cells and normal osteoblasts. Cultures were prepared with leukemic and non-leukemic cells separated by a semipermeable membrane or in direct contact. Results : The non-leukemic cells usually showed higher spontaneous VEGF release than AML cell populations. Coculture of AML blasts with HFL1 fibroblasts caused a supra-additive increase of VEGF levels when the cell populations were cultured separately, and the increase was also observed when cells were cultured in direct contact. An increase was also observed when AML blasts were cultured with osteoblastic sarcoma cells, normal bone marrow stromal cells and normal osteoblasts. Coculture had divergent effects on VEGF mRNA levels both for leukemic and non-leukemic cells, but increased mRNA levels were commonly observed especially for the non-leukemic cells. Cytokine inhibition experiments suggest that IL1 is important for the VEGF-increasing crosstalk, whereas the mechanisms are probably heterogeneous for coculture with osteoblasts. Conclusion : The bi-directional crosstalk via local cytokine networks between AML blasts and non-leukemic cells results in increased local VEGF levels, an observation suggesting that VEGF-targeting antiangiogenic therapy should be considered as a general therapeutic strategy in AML.     

The effect of granulocyte-macrophage colony-stimulating factor on undifferentiated and mature acute myelogenous leukemia blast progenitors.

Granulocyte-macrophage colony-stimulating factor (GM-CSF) has been used recently to recruit undifferentiated acute myelogenous leukemia (AML) blasts into the S-phase of the cell cycle and increase the fraction of cells killed by cell cycle-specific drugs. Using three AML blast colony assays combined with a suspension culture (delta assay), we determined the in vitro effect of GM-CSF on mature and undifferentiated AML blast progenitors obtained from bone marrow aspirates of six AML patients. GM-CSF stimulated AML blast colony proliferation at a concentration of 5 ng/ml in the methylcellulose and the agar clonogenic assays in six of six AML marrow samples. However, in the delta assay, which selects for immature AML progenitors, GM-CSF did not affect AML blast colony-forming cells in five of six AML marrow samples at concentrations ranging from 5 to 300 ng/ml. Our data imply that GM-CSF stimulates mature but not undifferentiated AML blast progenitors. It is therefore possible that GM-CSF may not be beneficial as a recruiting agent in most AML patients.     

Cytotoxic effects of dacarbazine in patients with acute myelogenous leukemia: a pilot study.

BACKGROUND AND METHODS. Preclinical studies performed in our laboratory showed that mouse leukemias become highly immunogenic following in vivo treatment with Decarbazine. This observation led to a successful immunochemotherapy protocol in mice using Dacarbazine plus cytoreductive chemotherapy. Therefore an in vivo and in vitro pilot study was conducted in patients (pts) with resistant or relapsed acute myelogenous leukemia (AML). The DNA-repair enzyme O6-alkylguanine-DNA-alkyl-transferase (OGAT) and the in vitro chemosensitivity to Temozolomide, a Dacarbazine derivative, were evaluated in leukemic blasts. RESULTS. Nine pts received Dacarbazine (0.4-0.8 g/sqm/day) on days 0, 1 and 2. On day 7, noticeable blast reduction occurred in 4 pts: pt 1 was in partial remission on day 21, pt 6 still showed bone marrow leukemia, pt 8 died of sepsis on day 8, pt 9 is still in aplasia on day 25. Low OGAT levels and consistent sensitivity to Temozolomide in vitro were found in the blasts of pts responsive to Dacarbazine. Subsequently, pts 1-7 underwent Ara-C (1g/sqm/day) plus Mitoxantrone (6mg/sqm/day) treatment for 6 days. Four pts entered complete remission after 27-45 days of aplasia. Failures were due to hypoplastic death, absolute drug resistance, or hypoplasia followed by blast cell regrowth. CONCLUSIONS. These data point out that Dacarbazine can induce a marked reduction of blast cells as well as severe myelotoxicity in leukemic patients.     

Biological effects of recombinant human granulocyte colony-stimulating factor in patients with untreated acute myeloid leukemia

Hematopoietic growth factors are being administered to patients with acute myeloid leukemia (AML) both to shorten the duration of chemotherapy-induced neutropenia and in an attempt to increase cytotoxicity of cell cycle-specific agents. However, limited information is available concerning the effects of growth factors in AML patients. To examine the in vivo effects of recombinant human granulocyte colony-stimulating factor (G-CSF) on AML cells, laboratory studies were performed before and after a 72-hour intravenous infusion of G-CSF (10 micrograms/kg/d) administered to 28 untreated AML patients. Twenty-seven patients (96%) showed increases in at least one of the following parameters after G-CSF: blood blasts, bone marrow (BM) blasts, leukemia cells in S phase or interphase cells with leukemia- specific markers shown by fluorescence in situ hybridization. The median paired change in absolute blast count was +2.7 x 10(9)/L (P = .0001) after G-CSF, as compared with 0.0 during the 72 hours before initiation of G-CSF. The median percentage of BM leukemia cells in S phase increased from 6.0% to 10.7% after G-CSF (median change, %5.9%; P = .009). Interphase BM cells with trisomy 8 or monosomy 7 increased in 6 of 6 patients with these abnormalities (P = .02) with a median percent increase of 47%. Blood neutrophil counts also increased during G-CSF (median paired change, +2.8 x 10(9)/L; P < .0001). Trisomy 8 or monosomy 7 was shown by fluorescence in situ hybridization in post-G- CSF blood neutrophils from 4 of 6 patients but was also present in neutrophils before G-CSF. We conclude that the percentage of leukemia cells in S phase increases and that leukemia cell populations undergo expansion during short-term administration of G-CSF in almost all AML patients.